Science.gov

Sample records for dilute magnetic semiconductor

  1. XAFS in dilute magnetic semiconductors.

    PubMed

    Sun, Zhihu; Yan, Wensheng; Yao, Tao; Liu, Qinghua; Xie, Yi; Wei, Shiqiang

    2013-10-14

    X-Ray absorption fine structure (XAFS) spectroscopy has experienced a rapid development in the last four decades and has proved to be a powerful structure characterization technique in the study of local environments in condensed matter. In this article, we first introduce the XAFS basic principles including theory, data analysis and experiment in some detail. Then we attempt to make a review on the applications of XAFS to the study of atomic and electronic structure in dilute magnetic semiconductor (DMS) systems. The power of XAFS in characterizing this interesting material system, such as determining the occupation sites and distribution of the dopants, detecting the presence of metal clusters or secondary phases, as well as identifying the defect types and dopant valence, will be illuminated by selected examples. This review should be of interest both to newcomers in the DMS field and to an interdisciplinary community of researchers working in synthesis, characterization and utilization of DMS materials. PMID:23884341

  2. Diluted magnetic semiconductor nanowires exhibiting magnetoresistance

    DOEpatents

    Yang, Peidong; Choi, Heonjin; Lee, Sangkwon; He, Rongrui; Zhang, Yanfeng; Kuykendal, Tevye; Pauzauskie, Peter

    2011-08-23

    A method for is disclosed for fabricating diluted magnetic semiconductor (DMS) nanowires by providing a catalyst-coated substrate and subjecting at least a portion of the substrate to a semiconductor, and dopant via chloride-based vapor transport to synthesize the nanowires. Using this novel chloride-based chemical vapor transport process, single crystalline diluted magnetic semiconductor nanowires Ga.sub.1-xMn.sub.xN (x=0.07) were synthesized. The nanowires, which have diameters of .about.10 nm to 100 nm and lengths of up to tens of micrometers, show ferromagnetism with Curie temperature above room temperature, and magnetoresistance up to 250 Kelvin.

  3. Spin dynamics in paramagnetic diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Phan, Van-Nham; Tran, Minh-Tien

    2015-10-01

    Microscopic properties of low-energy spin dynamics in diluted magnetic semiconductor are addressed in a framework of the Kondo lattice model including random distribution of magnetic dopants. Based on the fluctuation-dissipation theorem, we derive an explicit dependence of the spin diffusion coefficient on the single-particle Green function which is directly evaluated by dynamical mean-field theory. In the paramagnetic state, the magnetic scattering has been manifested to suppress spin diffusion. In agreement with other ferromagnet systems, we also point out that the spin diffusion in diluted magnetic semiconductors at small carrier concentration displays a monotonic 1 /T -like temperature dependence. By investigating the spin diffusion coefficient on a wide range of the model parameters, the obtained results have provided a significant scenario to understand the spin dynamics in the paramagnetic diluted magnetic semiconductors.

  4. Phase Transition of Diluted Magnetic Semiconductor

    NASA Astrophysics Data System (ADS)

    Li, M. K.; Lee, S. J.; Yuldashev, S. U.; Ihm, G.; Kang, T. W.

    2011-12-01

    Three types of phase transitions in diluted magnetic semiconductor, first-order, second-order and mixed-order, are found in theory. Especially the mixed type transition shows two steps transition and novel specific heat property. Specific heat properties disclose a possible meta ferromagnetic phase confirmed by the experimental qualitative result.

  5. Diluted magnetic III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Munekata, H.; Ohno, H.; von Molnar, S.; Segmüller, Armin; Chang, L. L.; Esaki, L.

    1989-10-01

    A new diluted magnetic III-V semiconductor of In1-xMnxAs (x<=0.18) has been produced by molecular-beam epitaxy. Films grown at 300 °C are predominantly ferromagnetic and their properties suggest the presence of MnAs clusters. Films grown 200 °C, however, are predominantly paramagnetic, and the lattice constant decreases with increasing Mn composition; both are indicative of the formation of a homogeneous alloy. These films have n-type conductivity and reduced band gaps.

  6. Disorder Problem In Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Nelson, Ryky; Ekuma, Chinedu; Terletska, Hanna; Sudhindra, Vidhyadhiraja; Moreno, Juana; Jarrell, Mark

    2015-03-01

    Motivated by experimental studies addressing the role of impurity disorder in diluted magnetic semiconductors (DMS), we investigate the effects of disorder using a simple tight-binding Hamiltonian with random impurity potential and spin-fermion exchange which is self-consistently solved using the typical medium theory. Adopting the typical density of states (TDoS) as the order parameter, we find that the TDoS vanishes below a critical concentration of the impurity, which indicates an Anderson localization transition in the system. Our results qualitatively explain why at concentrations lower than a critical value DMS are insulating and paramagnetic, while at larger concentrations are ferromagnetic. We also compare several simple models to explore the interplay between ferromagnetic order and disorder induced insulating behavior, and the role of the spin-orbit interaction on this competition. We apply our findings to (Ga,Mn)As and (Ga,Mn)N to compare and contrast their phase diagrams.

  7. Diluted magnetic semiconductor superlattices and heterostructures

    NASA Astrophysics Data System (ADS)

    Datta, S.; Furdyna, J. K.; Gunshor, R. L.

    Diluted magnetic semiconductors (DMS) are mixed semiconducting crystals whose lattice is made up in part of substitutional magnetic ions. Cd 1-xMn xTe and Hg 1-xMn xTe are examples of such materials. Their structural and band parameters can be "tuned" by composition over a wide range. They can thus be exploited in situations completely similar to those involving Ga 1-xAl xAs. Using molecular beam epitaxy, we have grown Cd 1-xMn xTe superlattices with alternating Mn content, having up to 150 layers, with layer thickness ranging from 50 to 100 Å. The superlattice structure is clearly revealed by transmission electron microscopy and by zone-folding of the phonon spectrum observed in Raman scattering. Photoluminescence observed on Cd 1-xMn xTe superlattices is several orders of magnitude greater than that from a Cd 1-xMn xTe film with uniform Mn content, or from bulk Cd 1-xMn xTe specimens. The presence of localized magnetic moments in DMS results in a strong exchange interaction between these moments and band electrons. This in turn leads to gigantic Zeeman splittings of impurity states, exciton levels, Landau levels, and the bands themselves. Zeeman splittings as large as 20 meV (which in non-magnetic semiconductors would require unrealistic megagauss fields) are easily achieved in DMS in fields of several kilogauss. Since the magnitude of this exchange-induced splitting in DMS can be comparable to the binding energies and to the minigaps encountered in multiple quantum wells, DMS superlattices hold promise of a host of novel effects of both fundamental and applied interest.

  8. EDITORIAL: Focus on Dilute Magnetic Semiconductors FOCUS ON DILUTE MAGNETIC SEMICONDUCTORS

    NASA Astrophysics Data System (ADS)

    Chambers, Scott A.; Gallagher, Bryan

    2008-05-01

    This focus issue of New Journal of Physics is devoted to the materials science of dilute magnetic semiconductors (DMS). A DMS is traditionally defined as a diamagnetic semiconductor doped with a few to several atomic per cent of some transition metal with unpaired d electrons. Several kinds of dopant-dopant interactions can in principle couple the dopant spins leading to a ferromagnetic ground state in a dilute magnetic system. These include superexchange, which occurs principally in oxides and only between dopants with one intervening oxygen, and double exchange, in which dopants of different formal charges exchange an electron. In both of these mechanisms, the ferromagnetic alignment is not critically dependent on free carriers in the host semiconductor because exchange occurs via bonds. A third mechanism, discovered in the last few years, involves electrons associated with lattice defects that can apparently couple dopant spins. This mechanism is not well understood. Finally, the most desirable mechanism is carrier-mediated exchange interaction in which the dopant spins are coupled by itinerant electrons or holes in the host semiconductor. This mechanism introduces a fundamental link between magnetic and electrical transport properties and offers the possibility of new spintronic functionalities. In particular electrical gate control of ferromagnetism and the use of spin polarized currents to carry signals for analog and digital applications. The spin light emitting diode is a prototypical device of this kind that has been extensively used to characterize the extent of spin polarization in the active light emitting semiconductor heterostructure. The prototypical carrier mediated ferromagnetic DMS is Mn-doped GaAs. This and closely related narrow gap III-V materials have been very extensively studied. Their properties are generally quite well understood and they have led to important insights into fundamental properties of ferromagnetic systems with strong spin

  9. Current density and state density in diluted magnetic semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Pérez Merchancano, S. T.; Paredes Gutiérrez, H.; Zuñiga, J. A.

    2016-02-01

    We study in this paper the spin-polarized current density components in diluted magnetic semiconductor tunnelling diodes with different sample geometries. We calculate the resonant JxV and the density of states. The differential conductance curves are analyzed as functions of the applied voltage and the magnetic potential strength induced by the magnetic ions.

  10. Magnetization steps and bound magnetic polarons in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    McCabe, Gao Hua

    1997-09-01

    Magnetization measurements and computer simulations were used to address several current problems in the area of the Diluted Magnetic Semiconductors (DMS). The method of Magnetization Steps (MSTs) was used to study Jahn-Teller Distortions in Zn1-xCrxTe, and exchange constants in Pb1-xEuxSe and Pb1- xEuxTe. Bound magnetic polarons in Cu2MnxZn1-xSnS4 were studied by conventional magnetometry. Jahn-Teller Distortions in cubic Zn1- xCrxTe were studied using MSTs. Possible Jahn- Teller Distortions in this material are along the three equivalent /langle 100/rangle axes. Energy states for the three distortion directions are equivalent at H = 0, but are different for finite H. The main issue is whether the populations of three possible distortions will vary with field, or remain frozen at their values in zero- field. The data showed that the populations of the distortions changed significantly. The dominant antiferomagnetic exchange constants J between Eu2+ ions in IV-VI Pb1- xEuxSe and Pb1-xEuxTe were determined using the MST method. Measurements were made at 0.6 K in fields up to 150 kOe. Supplementary data by our collaborators were taken at much lower temperatures. Simulations of various MSTs (from isolated Eu2+ ions, pairs of ions, and triplets) were performed to fit the experimental data. Because J is determined from the MSTs for pairs, the effects of other anisotropies and exchange interactions on these MSTs were considered. They were found to bring little change to the values of J. The exchange constants were J/kB = -0/24 ± 0.03 K for Ph 1-xEu xSe amd os J/KB = -0.264 ± 0.018 K for Ph1-xEuxTe. The dominant AF exchange constants were identified as J1, between nearest-neighbors, by comparing the experimental magnetization curves to the theoretical simulations using the single J model. The dominant antiferromagnetic exchange constants J between Eu2+ ions in IV-VI Pb1- xEuxSe and Pb1-xEuxTe were determined using the MST method. Measurements were made at 0.6 K in

  11. Uniform Doping in Quantum-Dots-Based Dilute Magnetic Semiconductor.

    PubMed

    Saha, Avijit; Shetty, Amitha; Pavan, A R; Chattopadhyay, Soma; Shibata, Tomohiro; Viswanatha, Ranjani

    2016-07-01

    Effective manipulation of magnetic spin within a semiconductor leading to a search for ferromagnets with semiconducting properties has evolved into an important field of dilute magnetic semiconductors (DMS). Although a lot of research is focused on understanding the still controversial origin of magnetism, efforts are also underway to develop new materials with higher magnetic temperatures for spintronics applications. However, so far, efforts toward quantum-dots(QDs)-based DMS materials are plagued with problems of phase separation, leading to nonuniform distribution of dopant ions. In this work, we have developed a strategy to synthesize highly crystalline, single-domain DMS system starting from a small magnetic core and allowing it to diffuse uniformly inside a thick CdS semiconductor matrix and achieve DMS QDs. X-ray absorption fine structure (XAFS) spectroscopy and energy-dispersive X-ray spectroscopy-scanning transmission electron microscopy (STEM-EDX) indicates the homogeneous distribution of magnetic impurities inside the semiconductor QDs leading to superior magnetic property. Further, the versatility of this technique was demonstrated by obtaining ultra large particles (∼60 nm) with uniform doping concentration as well as demonstrating the high quality magnetic response. PMID:27295453

  12. Magnetism in dilute iron doped YN semiconductors

    NASA Astrophysics Data System (ADS)

    Sharma, Ramesh; Dwievdi, Shalini; Sharma, Yamini

    2016-05-01

    The full potential linearized augmented plane-wave (FP-LAPW) scheme of computation is used to explore the electronic and magnetic properties of Fe doped into YN. Band structure calculations show that YN is a semicon ductor with a narrow indirect band gap of 0.08 eV along D-X direction. Optical properties such as reflectivity, absorption coefficient are reported and are discussed on the basis of corresponding electronic structure. Spin polarized results indicate that the ground state of Y1-xFexN (x=0.06, 0.12, 0.25) is ferromagnetic with a high moment on Fe-atom and zero moment on Y and N atoms, except in the case of 25 % doping. A discussion of the transport properties of YN and Y1-xFexN is given in order to get insights of the Fe substitution effects.

  13. Scanning Hall probe microscopy of a diluted magnetic semiconductor

    SciTech Connect

    Kweon, Seongsoo; Samarth, Nitin; Lozanne, Alex de

    2009-05-01

    We have measured the micromagnetic properties of a diluted magnetic semiconductor as a function of temperature and applied field with a scanning Hall probe microscope built in our laboratory. The design philosophy for this microscope and some details are described. The samples analyzed in this work are Ga{sub 0.94}Mn{sub 0.06}As films grown by molecular beam epitaxy. We find that the magnetic domains are 2-4 mum wide and fairly stable with temperature. Magnetic clusters are observed above T{sub C}, which we ascribe to MnAs defects too small and sparse to be detected by a superconducting quantum interference device magnetometer.

  14. Novel diluted magnetic semiconductor materials based on zinc oxide

    NASA Astrophysics Data System (ADS)

    Chakraborti, Deepayan

    The primary aim of this work was to develop a ZnO based diluted magnetic semiconductor (DMS) materials system which displays ferromagnetism above room temperature and to understand the origin of long-range ferromagnetic ordering in these systems. Recent developments in the field of spintronics (spin based electronics) have led to an extensive search for materials in which semiconducting properties can be integrated with magnetic properties to realize the objective of successful fabrication of spin-based devices. For these devices we require a high efficiency of spin current injection at room temperature. Diluted magnetic semiconductors (DMS) can serve this role, but they should not only display room temperature ferromagnetism (RTFM) but also be capable of generating spin polarized carriers. Transition metal doped ZnO has proved to be a potential candidate as a DMS showing RTFM. The origin of ferromagnetic ordering in ZnO is still under debate. However, the presence of magnetic secondary phases, composition fluctuations and nanoclusters could also explain the observation of ferromagnetism in the DMS samples. This encouraged us to investigate Cu-doped(+ spin in the 2+ valence state) ZnO system as a probable candidate exhibiting RTFM because neither metallic Cu nor its oxides (Cu2O or CuO) are ferromagnetic. The role of defects and free carriers on the ferromagnetic ordering of Cu-doped ZnO thin films was studied to ascertain the origin of ferromagnetism in this system. A novel non-equilibrium Pulsed Laser Deposition technique has been used to grow high quality epitaxial thin films of Cu:ZnO and (Co,Cu):ZnO on c-plane Sapphire by domain matching epitxay. Both the systems showed ferromagnetic ordering above 300K but Cu ions showed a much stronger ferromagnetic ordering than Co, especially at low concentrations (1-2%) of Cu where we realized near 100% polarization. But, the incorporation of Cu resulted in a 2-order of magnitude rise in the resistivity from 10-1 to 101

  15. Spin-dependent shot noise in diluted magnetic semiconductor/semiconductor heterostructures with a nonmagnetic barrier

    NASA Astrophysics Data System (ADS)

    Wu, Shuang; Guo, Yong

    2014-05-01

    We investigate quantum size effect on the spin-dependent shot noise in the diluted magnetic semiconductor (DMS)/semiconductor heterostructure with a nonmagnetic semiconductor (NMS) barrier in the presence of external magnetic and electric fields. The results demonstrate that the NMS barrier plays a quite different role from the DMS layer in the electron transport process. It is found that spin-down shot noise shows relatively regular oscillations as the width of DMS layer increases, while the spin-up shot noise deceases monotonically. However, as the width of NMS layer increases, the spin-down shot noise displays irregular oscillations at first and then decreases while the spin-up shot noise decreases at a quite different rate. The results indicate that the shot noise can be used as a sensitive probe in detecting material type and its size.

  16. Diluted magnetic semiconductor effects in Mn-implanted silicon carbide

    SciTech Connect

    Komarov, A. V.; Ryabchenko, S. M.; Los, A. V.; Romanenko, S. M.

    2011-04-15

    Light transmission and Faraday rotation spectra measured at the temperature of 2 K were compared for silicon carbide single crystals of 4H polytype (4H-SiC), implanted with 3.8 x 10{sup 16} cm{sup -2} of Mn ions at the beam energy of 190 keV, and a control 4H-SiC single crystal sample, which was not implanted. Mn ion implantation led to the creation of a Mn-doped surface layer with the average Mn concentration of 10{sup 21} cm{sup -3} and a thickness of approximately 0.2 {mu}m. Transmission of light through the implanted crystal changed only slightly in comparison with the control sample, which however, corresponded to a relatively strong attenuation in the implanted layer. This was interpreted as a result of scattering, which emerges in the surface layer due to optical nonuniformities, created by the high energy ion irradiation. The presence of a thin Mn-ion-containing surface layer led, despite its small thickness, to noticeable changes in the sample Faraday rotation spectra. The estimated values of the Verdet constant for this layer were about three orders of magnitude larger and of opposite sign compared to the Verdet constant values of the undoped sample. Magnetic field dependencies of the Faraday rotation contribution from the implanted layer were found to be saturating functions, which points to a proportionality of the Faraday rotation to the magnetization of the paramagnetic Mn ion subsystem. Based on these findings we conclude that the Mn-implanted SiC layer exhibits magneto-optical properties typical of a diluted magnetic semiconductor. At the same time, no ferromagnetic ordering was observed in the studied (Si, Mn)C sample.

  17. Growth, structure, and optical characterization of diluted magnetic semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Cooley, Benjamin Joseph

    Nanowires combining the usually disparate areas of semiconductors and magnetism are of contemporary relevance within the context of semiconductor spintronics. This is a relatively new field of research that seeks to exploit electron spin within electronic and opto-electronic semiconductor devices. While much of the effort within semiconductor spintronics has been directed toward fundamental studies and applications of 3D, 2D and 0D systems, there has been little work to date on 1D systems. The distinctive change in the electronic density of states with changing dimensionality provides a strong motivation for developing and exploring semiconductor nanowires in which one might be able to probe and control spin-dependent phenomena within a 1D or quasi-1D environment. This thesis explores the crystal growth, structural properties and magneto-optical behavior of quasi-1D semiconductor nanowires in which we incorporate magnetism through two approaches: first, by synthesizing nanowires of the diluted magnetic semiconductor (Zn,Mn)Se, wherein the d-shell electrons of substitutional Mn ions interact with the band states of the ZnSe host lattice via sp--d exchange; second, by making hybrid core-shell nanostructures wherein a metallic ferromagnetic shell (MnAs) is epitaxially deposited on a semiconductor nanowire (GaAs). After an introductory overview of past work in the field and a description of the experimental techniques relevant to the thesis, we discuss our experimental results. The first set of experiments focuses on ZnSe and (Zn,Mn)Se nanowires grown in a single stage. The nanowires were grown on Si and GaAs substrates with a thin layer of gold evaporated onto them, which were then annealed before growth so that the gold formed nanoscale droplets. The growth yields samples covered in random arrays of nanowires growing out an an angle to the substrate, with an undergrowth of crooked nanowires and other small structures. The long thin nanowires vary in diameter, down to

  18. Spin selector based on periodic diluted-magnetic-semiconductor/nonmagnetic-barrier superlattices

    SciTech Connect

    Yang, Ping-Fan; Guo, Yong; Zhu, Rui

    2015-07-15

    We propose a spin selector based on periodic diluted-magnetic-semiconductor/nonmagnetic-barrier (DMS/NB) superlattices subjected to an external magnetic field. We find that the periodic DMS/NB superlattices can achieve 100% spin filtering over a dramatically broader range of incident energies than the diluted-magnetic-semiconductor/semiconductor (DMS/S) case studied previously. And the positions and widths of spin-filtering bands can be manipulated effectively by adjusting the geometric parameters of the system or the strength of external magnetic field. Such a compelling filtering feature stems from the introduction of nonmagnetic barrier and the spin-dependent giant Zeeman effect induced by the external magnetic field. We also find that the external electric field can exert a significant influence on the spin-polarized transport through the DMS/NB superlattices.

  19. Spin-dependent tunneling time in periodic diluted-magnetic-semiconductor/nonmagnetic-barrier superlattices

    NASA Astrophysics Data System (ADS)

    Yang, Ping-Fan; Guo, Yong

    2016-02-01

    We investigate the tunneling time (dwell time) in periodic diluted-magnetic-semiconductor/nonmagnetic-barrier (DMS/NB) superlattices subjected to an external magnetic field. It is found that spin-dependent resonant bands form in the spectra of dwell time, which can be effectively manipulated by not only the external magnetic field but also the geometric parameters of the system. Moreover, an intuitive semiclassical delay is defined to illustrate the behavior of the dwell time, and the former one is shown to be the result of "smoothing out" the latter one. We also find that the dwell time in diluted-magnetic-semiconductor/semiconductor superlattices behaves surprisingly different from the DMS/NB case, especially for spin-down electrons.

  20. Tuning magnetic disorder in diluted magnetic semiconductors using high fields to 89 Tesla

    SciTech Connect

    Crooker, Scott A; Samarth, Nitin

    2008-01-01

    We describe recent and ongoing studies at the National High Magnetic Field Laboratory at Los Alamos using the new '100 Tesla Multi-Shot Magnet', which is presently delivering fields up to {approx}89 T during its commissioning. We discuss the first experiments performed in this magnet system, wherein the linewidth of low-temperature photoluminescence spectra was used to directly reveal the degree of magnetic alloy disorder 'seen' by excitons in single Zn{sub 0.80}Cd{sub 0.22}Mn{sub 0.08}Se quantum wells. The magnetic potential landscape in II-VI diluted magnetic semiconductors (DMS) is typically smoothed when the embedded Mn{sup 2+} spins align in an applied field. However, an important (but heretofore untested) prediction of current models of compositional disorder is that magnetic alloy fluctuations in many DMS compounds should increase again in very large magnetic fields approaching 100 T. We observed precisely this increase above {approx}70 T, in agreement with a simple model of magnetic alloy disorder.

  1. Exploration of oxide-based diluted magnetic semiconductors toward transparent spintronics

    NASA Astrophysics Data System (ADS)

    Fukumura, T.; Yamada, Y.; Toyosaki, H.; Hasegawa, T.; Koinuma, H.; Kawasaki, M.

    2004-02-01

    A review is given for the recent progress of research in the field of oxide-based diluted magnetic semiconductor (DMS), which was triggered by combinatorial discovery of transparent ferromagnet. The possible advantages of oxide semiconductor as a host of DMS are described in comparison with conventional compound semiconductors. Limits and problems for identifying novel ferromagnetic DMS are described in view of recent reports in this field. Several characterization techniques are proposed in order to eliminate unidentified ferromagnetism of oxide-based DMS unidentified ferromagnetic oxide (UFO). Perspectives and possible devices are also given.

  2. Influence of cation choice on magnetic behavior of III-N dilute magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Frazier, Rachel Marian

    With the increasing interest in spintronics, many attempts have been made at incorporating spin-based functionality into existing semiconductor technology. One approach, utilizing dilute magnetic semiconductors (DMS) formed via introduction of transition metal ions into III-Nitride hosts, would allow for integration of spin based phenomena into current wide bandgap device technology. To accomplish such device structures, it is necessary to achieve single phase transition metal doped GaN and AlN which exhibit room temperature magnetic behavior. Ion implantation is an effective survey method for introduction of various transition metals into AlN. In ion implanted AlN, the Co and Cr doped films showed hysteresis at 300K while the Mn doped material did not. However, it is not a technique which will allow for the development of advanced spin based devices. Such devices will require epitaxial methods of the sort currently used for synthesis of III-Nitride optoelectronics. One such technique, Gas Source Molecular Beam Epitaxy (GSMBE), has been used to synthesize AlN films doped with Cr and Mn. Room temperature ferromagnetism has been observed for AlMnN and AlCrN grown by GSMBE. In both cases, the magnetic signal was found to depend on the flux of the dopant. The magnetization of the AlCrN was found to be an order of magnitude greater than in the AlMnN. The temperature dependent magnetic behavior of AlCrN was also superior to AlMnN; however, the AlCrN was not resistant to thermal degradation. An all-semiconductor tunneling magnetoresistive device (TMR) was grown with GaMnN as a spin injector and AlMnN as a spin filter. The resistance of the device should change with applied magnetic field depending on the magnetization of the injector and filter. However, due to the impurity bands found in the AlMnN, the resistance was found to change very little with magnetic field. To overcome such obstacles as found in the transition metal doped AlN, another dopant must be used. One

  3. Nonequilibrium spin transport through a diluted magnetic semiconductor quantum dot system with noncollinear magnetization

    SciTech Connect

    Ma, Minjie; Jalil, Mansoor Bin Abdul; Tan, Seng Gee

    2013-03-15

    The spin-dependent transport through a diluted magnetic semiconductor quantum dot (QD) which is coupled via magnetic tunnel junctions to two ferromagnetic leads is studied theoretically. A noncollinear system is considered, where the QD is magnetized at an arbitrary angle with respect to the leads' magnetization. The tunneling current is calculated in the coherent regime via the Keldysh nonequilibrium Green's function (NEGF) formalism, incorporating the electron-electron interaction in the QD. We provide the first analytical solution for the Green's function of the noncollinear DMS quantum dot system, solved via the equation of motion method under Hartree-Fock approximation. The transport characteristics (charge and spin currents, and tunnel magnetoresistance (TMR)) are evaluated for different voltage regimes. The interplay between spin-dependent tunneling and single-charge effects results in three distinct voltage regimes in the spin and charge current characteristics. The voltage range in which the QD is singly occupied corresponds to the maximum spin current and greatest sensitivity of the spin current to the QD magnetization orientation. The QD device also shows transport features suitable for sensor applications, i.e., a large charge current coupled with a high TMR ratio. - Highlights: Black-Right-Pointing-Pointer The spin polarized transport through a diluted magnetic quantum dot is studied. Black-Right-Pointing-Pointer The model is based on the Green's function and the equation of motion method. Black-Right-Pointing-Pointer The charge and spin currents and tunnel magnetoresistance (TMR) are investigated. Black-Right-Pointing-Pointer The system is suitable for current-induced spin-transfer torque application. Black-Right-Pointing-Pointer A large tunneling current and a high TMR are possible for sensor application.

  4. Organic analogues of diluted magnetic semiconductors: bridging quantum chemistry to condensed matter physics

    NASA Astrophysics Data System (ADS)

    Furis, Madalina; Rawat, Naveen; Cherian, Judy G.; Wetherby, Anthony; Waterman, Rory; McGill, Stephen

    2015-09-01

    The selective coupling between polarized photons and electronic states in materials enables polarization-resolved spectroscopy studies of exchange interactions, spin dynamics, and collective magnetic behavior of conduction electrons in semiconductors. Here we report on Magnetic Circular Dichroism (MCD) studies of magnetic properties of electrons in crystalline thin films of small molecule organic semiconductors. Specifically, the focus was on the magnetic exchange interaction properties of d-shell ions (Cu2+, Co2+ and Mn2+) metal phthalocyanine (Pc) thin films that one may think of as organic analogues of diluted magnetic semiconductors (DMS). These films were deposited in-house using a recently developed pen-writing method that results in crystalline films with macroscopic long range ordering and improved electronic properties, ideally suited for spectroscopy techniques. Our experiments reveal that, in analogy to DMS, the extended π-orbitals of the Pc molecule mediate the spin exchange between highly localized d-like unpaired spins. We established that exchange mechanisms involve different electronic states in each species and/or hybridization between d-like orbitals and certain delocalized π-orbitals. Unprecedented 25T MCD and PL conducted in the unique 25T Split Florida HELIX magnet at the National High Magnetic Field Laboratory (NHMFL) will prove useful in probing these exchange interactions.

  5. Successive spin polarizations underlying a new magnetic coupling contribution in diluted magnetic semiconductors.

    PubMed

    Andriotis, Antonis N; Fthenakis, Zacharias G; Menon, Madhu

    2015-02-11

    We propose a new type of magnetic coupling (MC) that is found in diluted magnetic semiconductors (DMSs). The origin of this is found to be the result of charge transfer processes followed by successive spin polarizations (SSPs) along successive cation-anion segments which include the impurities. The basic process underlying the SSP-based MC (SSP-MC) is the sharing of a single spin orbital by two neighboring impurities. As such, it can be considered as a localized double exchange as it is not mediated by free carriers. SSP-MC can be either ferromagnetic (SSP-FMC) or antiferromagnetic (SSP-AFMC) and, as demonstrated here, the SSP-FMC can be significantly enhanced via codoping; it can act in competition with superexchange and/or double and/or p-d exchange interactions. While the SSP-MC is not directly related to the magnitude of the magnetic moments of the impurities, it depends strongly on the energy difference of the host and impurity d-band centers, the difference of their electronegativities and rather weakly on the coupling interactions between them as well as between the cations and their mediating anions. The validity of the proposed SSP-MC as a new type of magnetic coupling is demonstrated by ab initio results for DMSs, namely ZnO, GaN, GaP, TiO2 and MoS2 monodoped (with Co, Cu and Mn) and codoped (with Co-Cu-Co and Mn-Cu-Mn). PMID:25614683

  6. Successive spin polarizations underlying a new magnetic coupling contribution in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Andriotis, Antonis N.; Fthenakis, Zacharias G.; Menon, Madhu

    2015-02-01

    We propose a new type of magnetic coupling (MC) that is found in diluted magnetic semiconductors (DMSs). The origin of this is found to be the result of charge transfer processes followed by successive spin polarizations (SSPs) along successive cation-anion segments which include the impurities. The basic process underlying the SSP-based MC (SSP-MC) is the sharing of a single spin orbital by two neighboring impurities. As such, it can be considered as a localized double exchange as it is not mediated by free carriers. SSP-MC can be either ferromagnetic (SSP-FMC) or antiferromagnetic (SSP-AFMC) and, as demonstrated here, the SSP-FMC can be significantly enhanced via codoping; it can act in competition with superexchange and/or double and/or p-d exchange interactions. While the SSP-MC is not directly related to the magnitude of the magnetic moments of the impurities, it depends strongly on the energy difference of the host and impurity d-band centers, the difference of their electronegativities and rather weakly on the coupling interactions between them as well as between the cations and their mediating anions. The validity of the proposed SSP-MC as a new type of magnetic coupling is demonstrated by ab initio results for DMSs, namely ZnO, GaN, GaP, TiO2 and MoS2 monodoped (with Co, Cu and Mn) and codoped (with Co-Cu-Co and Mn-Cu-Mn).

  7. A computational study on magnetic effects of Zn1-x Crx O type diluted magnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Duru, İzzet Paruğ; Değer, Caner; Kalaycı, Taner; Arucu, Muhammet

    2015-12-01

    Diluted magnetic semiconductors (DMS) have been intensely investigated both experimentally and theoretically in recent years. In spite of large body of studies to have a better understanding on working principles of devices based on DMS materials and taking a detailed control during fabrication process, nature of the system remains largely unknown. It is proposed that dominant contribution to DMS Hamiltonian is originated from ferromagnetic interaction between antiferromagnetic Cr+3 and its nearest neighbors rather than long-range interactions which commonly reported. In the light of experimental data obtained from literature, we simulated Zn1-x Crx O wurtzite thin film based on Metropolis algorithm and Markov Chain Monte Carlo (MC-MC) method as realistic as possible. We found that the soft ferromagnetic behaviour of Zn1-x Crx O thin film emerges by increasing doping ratios up to 15% (x=0.15), then it gradually vanishes above 15% (x=0.15) at room temperature. Results obtained here was found to be highly consistent with experimental studies.

  8. Ferromagnetism in Dilute Magnetic Semiconductors through Defect Engineering: Li-Doped ZnO

    NASA Astrophysics Data System (ADS)

    Yi, J. B.; Lim, C. C.; Xing, G. Z.; Fan, H. M.; van, L. H.; Huang, S. L.; Yang, K. S.; Huang, X. L.; Qin, X. B.; Wang, B. Y.; Wu, T.; Wang, L.; Zhang, H. T.; Gao, X. Y.; Liu, T.; Wee, A. T. S.; Feng, Y. P.; Ding, J.

    2010-04-01

    We demonstrate, both theoretically and experimentally, that cation vacancy can be the origin of ferromagnetism in intrinsic dilute magnetic semiconductors. The vacancies can be controlled to tune the ferromagnetism. Using Li-doped ZnO as an example, we found that while Li itself is nonmagnetic, it generates holes in ZnO, and its presence reduces the formation energy of Zn vacancy, and thereby stabilizes the zinc vacancy. Room temperature ferromagnetism with p type conduction was observed in pulsed laser deposited ZnO:Li films with certain doping concentration and oxygen partial pressure.

  9. Ferromagnetism in dilute magnetic semiconductors through defect engineering: Li-doped ZnO.

    PubMed

    Yi, J B; Lim, C C; Xing, G Z; Fan, H M; Van, L H; Huang, S L; Yang, K S; Huang, X L; Qin, X B; Wang, B Y; Wu, T; Wang, L; Zhang, H T; Gao, X Y; Liu, T; Wee, A T S; Feng, Y P; Ding, J

    2010-04-01

    We demonstrate, both theoretically and experimentally, that cation vacancy can be the origin of ferromagnetism in intrinsic dilute magnetic semiconductors. The vacancies can be controlled to tune the ferromagnetism. Using Li-doped ZnO as an example, we found that while Li itself is nonmagnetic, it generates holes in ZnO, and its presence reduces the formation energy of Zn vacancy, and thereby stabilizes the zinc vacancy. Room temperature ferromagnetism with p type conduction was observed in pulsed laser deposited ZnO:Li films with certain doping concentration and oxygen partial pressure. PMID:20481907

  10. Domain walls in the (Ga,Mn)as diluted magnetic semiconductor.

    PubMed

    Sugawara, Akira; Kasai, H; Tonomura, A; Brown, P D; Campion, R P; Edmonds, K W; Gallagher, B L; Zemen, J; Jungwirth, T

    2008-02-01

    We report experimental and theoretical studies of magnetic domain walls in an in-plane magnetized (Ga,Mn)As dilute moment ferromagnetic semiconductor. Our high-resolution electron holography technique provides direct images of domain wall magnetization profiles. The experiments are interpreted based on microscopic calculations of the micromagnetic parameters and Landau-Lifshitz-Gilbert simulations. We find that the competition of uniaxial and biaxial magnetocrystalline anisotropies in the film is directly reflected in orientation dependent wall widths, ranging from approximately 40 to 120 nm. The domain walls are of the Néel type and evolve from near-90 degrees walls at low temperatures to large angle [11[over ]0]-oriented walls and small angle [110]-oriented walls at higher temperatures. PMID:18352324

  11. Quest for high-Curie temperature MnxGe1-x diluted magnetic semiconductors for room-temperature spintronics applications

    NASA Astrophysics Data System (ADS)

    Nie, Tianxiao; Tang, Jianshi; Wang, Kang L.

    2015-09-01

    In this paper, we report the non-equilibrium growth of various Mn-doped Ge dilute magnetic semiconductor nanostructures using molecular-beam epitaxy, including quantum dots, nanodisks and nanowires. Their detailed structural and magnetic properties are characterized. By comparing the results with those in MnxGe1-x thin films, it is affirmed that the use of nanostructures helps eliminate crystalline defects and meanwhile enhance the carrier-mediate ferromagnetism from substantial quantum confinements. Our systematic studies provide a promising platform to build nonvolatile spinFET and other novel spintronic devices based upon dilute magnetic semiconductor nanostructures.

  12. On the theory of domain structure in ferromagnetic phase of diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Stephanovich, V. A.

    2006-09-01

    We present a comprehensive analysis of domain structure formation in ferromagnetic phase of diluted magnetic semiconductors (DMS) of p-type. Our analysis is carried out on the base of effective magnetic free energy of DMS calculated by us earlier [Yu.G. Semenov, V.A. Stephanovich, Phys. Rev. B 67 (2003) 195203]. This free energy, substituting DMS (a disordered magnet) by effective ordered substance, permits to apply the standard phenomenological approach to domain structure calculation. Using coupled system of Maxwell equations with those obtained by minimization of above free energy functional, we show the existence of critical ratio ν of concentration of charge carriers and magnetic ions such that sample critical thickness L (such that at Lν the sample is monodomain. This feature makes DMS different from conventional ordered magnets as it gives a possibility to control the sample critical thickness and emerging domain structure period by variation of ν. As concentration of magnetic impurities grows, ν→∞ restoring conventional behavior of ordered magnets. Above facts have been revealed by examination of the temperature of transition to inhomogeneous magnetic state (stripe domain structure) in a slab of finite thickness L of p-type DMS. Our theory can be easily generalized for arbitrary temperature and DMS shape.

  13. Preparation of dilute magnetic semiconductor films by metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Nouhi, Akbar (Inventor); Stirn, Richard J. (Inventor)

    1990-01-01

    A method for preparation of a dilute magnetic semiconductor (DMS) film is provided, wherein a Group II metal source, a Group VI metal source and a transition metal magnetic ion source are pyrolyzed in the reactor of a metalorganic chemical vapor deposition (MOCVD) system by contact with a heated substrate. As an example, the preparation of films of Cd.sub.1-x Mn.sub.x Te, wherein 0.ltoreq..times..ltoreq.0.7, on suitable substrates (e.g., GaAs) is described. As a source of manganese, tricarbonyl (methylcyclopentadienyl) maganese (TCPMn) is employed. To prevent TCPMn condensation during the introduction thereof int the reactor, the gas lines, valves and reactor tubes are heated. A thin-film solar cell of n-i-p structure, wherein the i-type layer comprises a DMS, is also described; the i-type layer is suitably prepared by MOCVD.

  14. Developing Spectroscopic Ellipsometry to Study II-Vi and Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Kim, Young-Dong

    We have constructed a rotating analyzer spectroscopic ellipsometer (RAE) to study effects of magnetic and nonmagnetic doping on the E_1 and E _1 + Delta_1 band gap energies in ZnSe-based II-VI semiconductors. To remove the natural surface oxide overlayer which distorts the intrinsic dielectric response of the sample, a chemical etching technique using dilute NH_4OH solution was developed. The successful removal of the oxide overlayer on ZnSe was confirmed via the XPS technique. For diluted magnetic semiconductors (DMS), we found that the E_1 and E _1 + Delta_1 band gap energies increase with x for Zn_{1-x}Fe _{x}Se and Zn_ {1-x}Co_{x}Se, and decrease with x for Zn_{1-x} Mn_{x}Se. An sp -d direct exchange interaction model which explained the Gamma-point band gap energy of Zn _{1-x}Mn_ {x}Se was applied. The calculated band gap energies at the L-point are only consistent with Zn _{1-x}Mn_ {x}Se data. We showed that an sp-d hybridization model, which includes the location of the energy levels of the magnetic impurity d-levels can account for the concentration dependence of E_1 and E _1 + Delta_1 band gap energies of all three materials. For Zn_{x}Cd _{1-x}Se systems, all spectral features of CdSe were identified as E_0, E_0 + Delta_0, E_1, E_1 + Delta_1, E_2, and E _sp{0}{'} threshold energies from band structure calculations using a nonlocal empirical pseudopotential method. Many-body effect has to be included in the calculation of the dielectric function of CdSe to obtain good agreement with the measured spectrum. Concentration dependent spin-orbit splitting band gap Delta _1(x) is well explained by the statistical fluctuation of the alloy composition.

  15. Magnetic Interactions in the Diluted Magnetic Semiconductor Mn_xGe_1-x

    NASA Astrophysics Data System (ADS)

    Erwin, Steven C.; Hellberg, C. Stephen

    2001-03-01

    Much current debate has focused on the origins of ferromagnetism in III-V magnetic semiconductors. Less attention has been paid to magnetically doped Group-IV semiconductors, although they have been predicted to have Curie temperatures of the same order [1]. We use density-functional theoretical (DFT) methods to study the electronic structure and magnetic interactions in Mn_xGe_1-x, the first such elemental magnetic semiconductor to be realized experimentally [2]. We use ordered supercells to simulate 6% Mn concentration, and calculate total energies within DFT for a variety of positional and magnetic arrangements of Mn at fixed concentration. We then fit these energies to a Heisenberg model to extract the spin coupling constants. The result is a strong but very short-ranged antiferromagnetic interaction between Mn atoms, and a weaker but longer-ranged ferromagnetic interaction. The ferromagnetic interaction dominates at all Mn-Mn distances beyond nearest neighbor. [1] T. Dietl et al., Science 287, 1019 (2000). [2] Y.D. Park, J. Mattson, A. Hanbicki, and B. Jonker (unpublished).

  16. Solubility control in dilute magnetic semiconductors by using the co-doping method

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori; Fujii, Hitoshi; Bergqvist, Lars; Dederichs, Peter H.; Katayama-Yoshida, Hiroshi

    2009-03-01

    To overcome low solubility limit of magnetic impurities in dilute magnetic semiconductors (DMS) and realize room temperature ferromagnetism, we propose a co-doping method to increase solubility of magnetic impurities in DMS [1]. We calculate electronic structure of (Ga, Mn)As, (Ga, Mn)N, (Ga, Cr)N and (Zn, Cr)Te with interstitial impurities, such as Li, Na and Cu, from first-principles by using the Korringa-Kohn- Rostoker coherent potential approximation (KKR-CPA) method. From the total energy results, it is shown that the mixing energy of magnetic impurity becomes negative and the solubility of magnetic impurities is strongly enhanced under the existence of interstitials [1]. In general, the co-dopants compensate hole carriers, thus the system becomes paramagnetic. However, owing to the large diffusivity of these interstitial impurities, we can anneal out the co-dopants after the crystal growth to recover the ferromagnetism. As an example, kinetic Monte Carlo simulations for the diffusion of interstitial co-dopants in DMS will be shown. [1] K. Sato et al., Jpn. J. Appl. Phys. 46 L1120 (2007)

  17. Stabilization of Ferromagnetic States by Electron Doping in ZnO-Based Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2001-03-01

    In order to investigate functionality of ZnO as a diluted magnetic semiconductor (DMS), we had studied the magnetism in ZnO doped with 3d transition metal atoms (TM) and showed that it was also a candidate for a new functional magnetic material [1]. In this paper, we develop our previous work and give detailed materials design with ZnO-based DMS based on ab initio calculations. The electronic structure of a TM-doped ZnO was calculated within the local density approximation by the Korringa-Kohn-Rostoker method combined with the coherent potential approximation. Total energies of Zn_1-xTM^\\uparrow_xO and Zn_1-xTM^\\uparrow_x/2TM^downarrow_x/2O, where up and down arrows mean the directions of respective atomic magnetic moments, were compared and appearance of the ferromagnetism was discussed. Effects of carrier doping to these systems were also considered. It was found that their magnetic states were controllable by changing the carrier density. In particular, ferromagnetic states were stabilized by electron doping in the case of Fe, Co or Ni doped ZnO. From the point of practical applications, it is favorable feature to realize high Curie temperature ferromagnet, because n-type ZnO is easily available. [1] K. Sato and H. Katayama-Yoshida, Jpn. J. Appl. Phys. 39 (2000) L555.

  18. Novel photoinduced phase transitions in transition metal oxides and diluted magnetic semiconductors

    PubMed Central

    2012-01-01

    Some transition metal oxides have frustrated electronic states under multiphase competition due to strongly correlated d electrons with spin, charge, and orbital degrees of freedom and exhibit drastic responses to external stimuli such as optical excitation. Here, we present photoemission studies on Pr0.55(Ca1 − ySry)0.45MnO3 (y = 0.25), SrTiO3, and Ti1 − xCoxO2 (x = 0.05, 0.10) under laser illumination and discuss electronic structural changes induced by optical excitation in these strongly correlated oxides. We discuss the novel photoinduced phase transitions in these transition metal oxides and diluted magnetic semiconductors on the basis of polaronic pictures such as orbital, ferromagnetic, and ferroelectric polarons. PMID:23092248

  19. Materials design of dilute magnetic semiconductors based on the control of spinodal decomposition

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori

    2010-03-01

    Recently, spinodal decomposition phenomena attract much attention in the fabrication of dilute magnetic semiconductors (DMS). Many experimental results indicate that the magnetic properties of DMS are strongly affected by the occurrence of spinodal decomposition [1], thus people are now interested in controlling the magnetic properties of DMS by tuning the spinodal decomposition. In this talk, I will discuss spinodal decomposition in DMS based on the first-principles calculation. The electronic structure of DMS is calculated by using the Korringa-Kohn-Rostoker coherent potential approximation method. Based on the calculated mixing energy I will discuss phase diagrams of DMS systems and their chemical trends. By using the calculated chemical pair interactions between magnetic impurities in DMS, the self-organization of nano-structures in DMS of the nano-structures are simulated by using the Monte Carlo method. The simulation results indicate that we can control super-paramagnetic blocking temperature by optimizing the size of the nano-structures by changing the crystal growth condition [2]. Next, I will propose co-doping method to control solubility limit of magnetic impurities in DMS. From the total energy calculations, it is shown that the solubility of magnetic impurities is strongly enhanced under the existence of interstitial donors [2]. However, due to the compensation of holes by the co-dopants, the ferromagnetism is suppressed. Based on the kinetic Monte Carlo simulations, we propose low temperature annealing method to remove interstitial co-dopants for recovering the ferromagnetism. By combining the co-doping and the low temperature annealing, we can fabricate DMS with high concentration of magnetic impurities which should show high-Tc. This work is based on the collaboration with H. Fujii, L. Bergqvist, P. H. Dederichs and H. Katayama-Yoshida.[4pt] [1] A. Bonanni, Semicond. Sci. Technol. 22 (2007) R41.[0pt] [2] K. Sato et al., Rev. Mod. Phys. Phys

  20. Carriers-mediated ferromagnetic enhancement in Al-doped ZnMnO dilute magnetic semiconductors

    SciTech Connect

    Saleem, Murtaza; Siddiqi, Saadat A.; Atiq, Shahid; Anwar, M. Sabieh; Hussain, Irshad; Alam, Shahzad

    2011-11-15

    Nano-crystalline Zn{sub 0.95-x}Mn{sub 0.05}Al{sub x}O (x = 0, 0.05, 0.10) dilute magnetic semiconductors (DMS) were synthesized by sol-gel derived auto-combustion. X-ray diffraction (XRD) analysis shows that the samples have pure wurtzite structure typical of ZnO without the formation of secondary phases or impurity. Crystallite sizes were approximated by Scherrer formula while surface morphology and grain sizes were measured by field emission scanning electron microscopy. Incorporation of Mn and Al into the ZnO structure was confirmed by energy-dispersive X-ray analysis. Temperature dependent electrical resistivity measurements showed a decreasing trend with the doping of Al in ZnMnO, which is attributable to the enhancement of free carriers. Vibrating sample magnetometer studies confirmed the presence of ferromagnetic behavior at room temperature. The results indicate that Al doping results in significant variation in the concentration of free carriers and correspondingly the carrier-mediated magnetization and room temperature ferromagnetic behavior, showing promise for practical applications. We attribute the enhanced saturation magnetization and electrical conductivity to the exchange interaction mediated by free electrons.

  1. Electric field control of room temperature ferromagnetism in III-N dilute magnetic semiconductor films

    NASA Astrophysics Data System (ADS)

    Nepal, N.; Luen, M. Oliver; Zavada, J. M.; Bedair, S. M.; Frajtag, P.; El-Masry, N. A.

    2009-03-01

    We report on the electrical field control of ferromagnetism (FM) at room temperature in III-N dilute magnetic semiconductor (DMS) films. A GaMnN layer was grown on top of an n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. This FM in GaMnN can be controlled by depletion of the holes in the GaMnN/p-GaN/n-GaN multilayer structures. We have demonstrated the dependence of the FM on the thickness of the p-GaN in this heterostructure and on the applied bias to the GaN p-n junction. The Ms was measured by an alternating gradient magnetometer (AGM) and a strong correlation between the hole concentration near the GaMnN/p-GaN interface and the magnetic properties of the DMS was observed. At room temperature an anomalous Hall effect was measured for zero bias and an ordinary Hall effect for reverse bias in a fully depleted p-GaN layer. This is in close agreement with the AGM measurement results.

  2. Unraveling the nature of carrier-mediated ferromagnetism in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Bouzerar, Georges; Bouzerar, Richard

    2015-10-01

    After more than a decade of intensive research in the field of diluted magnetic semiconductors (DMS), the nature and origin of ferromagnetism, especially in III-V compounds, is still controversial. Many questions and open issues are under intensive debates. Why after so many years of investigations, Mn-doped GaAs remains the candidate with the highest Curie temperature among the broad family of III-V materials doped with transition metal (TM) impurities? How can one understand that these temperatures are almost two orders of magnitude larger than that of hole-doped (Zn,Mn)Te or (Cd,Mn)Se? Is there any intrinsic limitation or is there any hope to reach room-temperature ferromagnetism in the dilute regime? How can one explain the proximity of (Ga,Mn)As to the metal-insulator transition and the change from Ruderman-Kittel-Kasuya-Yosida (RKKY) couplings in II-VI compounds to double-exchange type in (Ga,Mn)N? In spite of the great success of density functional theory-based studies to provide accurately the critical temperatures in various compounds, till very lately a theory that provides a coherent picture and understanding of the underlying physics was still missing. Recently, within a minimal model, it has been possible to show that among the physical parameters, the key one is the position of the TM acceptor level. By tuning the value of that parameter, one is able to explain quantitatively both magnetic and transport properties in a broad family of DMS. We will see that this minimal model explains in particular the RKKY nature of the exchange in (Zn,Mn)Te/(Cd,Mn)Te and the double exchange type in (Ga,Mn)N and simultaneously the reason why (Ga,Mn)As exhibits the highest critical temperature among both II-VI and III-V DMS's. xml:lang="fr"

  3. Study of the new diluted magnetic semiconductors based on the doping of iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Feng, Shan; Li, Linxian; Wang, Shaolei; Li, Yuke

    Diluted magnetic semiconductors(DMSs) have attracted increasing attention because of their potential applications in spintronics. Recently, a series of new bulk DMS materialswere synthesized by doping in the 122 and 1111 phases of iron-based superconductors(Fe-SC), which sheds light on the DMS research[3]. In this report, we have synthesized two systems of 1111 phases of DMSs based on Fe-SC materials (La1-xSrx) (Ag0.925 Mn0.075) SO(x =0, 0.025, 0.05, 0.075 and 0.1) and (Y1-xSrx) (Cu0.925 Mn0.075) SO (x =0, 0.025, 0.05,0.075 and 0.1) by solid state method. The structure and electrical, magnetic and optical properties have been investigated by means of XRD, 4KCCS, MPMS, PL, UV-Vis and Raman technique, respectively. Some interesting phenomena are found (Such as the Curie temperature Tc and band-gap energy Eg change regularly with the dopants additon). The results are helpful to clarify the intrinsic mechanism of the DMSs, and will provide new insights on the fabrication and application of devices based on these materials. This work was supported by the National Science Foundation of China (Grant No 61376094). Li Zhang would like to acknowledge a scholarship Granted by China Scholarship Council (CSC-201408330028)

  4. Preparation of dilute magnetic semiconductor films by metalorganic chemical vapor deposition

    NASA Technical Reports Server (NTRS)

    Nouhi, Akbar (Inventor); Stirn, Richard J. (Inventor)

    1988-01-01

    A method for preparation of a dilute magnetic semiconductor (DMS) film is provided, in which a Group II metal source, a Group VI metal source and a transition metal magnetic ion source are pyrolyzed in the reactor of a metalorganic chemical vapor deposition (MOCVD) system by contact with a heated substrate. As an example, the preparation of films of Cd(sub 1-x)Mn(sub x)Te, in which 0 is less than or equal to x less than or equal to 0.7, on suitable substrates (e.g., GaAs) is described. As a source of manganese, tricarbonyl (methylcyclopentadienyl) manganese (TCPMn) is employed. To prevent TCPMn condensation during its introduction into the reactor, the gas lines, valves and reactor tubes are heated. A thin-film solar cell of n-i-p structure, in which the i-type layer comprises a DMS, is also described; the i-type layer is suitably prepared by MOCVD.

  5. Study of the new diluted magnetic semiconductors based on the doping of iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Feng, Shan; Li, Linxian; Wang, Shaolei; Lu, Bin; Li, Yuke

    2015-03-01

    Diluted magnetic semiconductors(DMSs) have attracted increasing attention because of their potential applications in spintronics. Recently, a series of new bulk DMS materialswere synthesized by doping in the 122 and 1111 phases of iron-based superconductors(Fe-SC), which sheds light on the DMS research. In this report, we have synthesized two systems of 1111 phases of DMSs based on Fe-SC materials (La1 - xSrx) (Ag0.925 Mn0.075)SO(x=0, 0.025, 0.05, 0.075 and 0.1) and (Y1 - xSrx) (Cu0.925 Mn0.075) SO (x=0, 0.025, 0.05,0.075 and 0.1) by solid state method. The structure and electrical, magnetic and optical properties have been investigated by means of XRD, 4KCCS, MPMS, PL, UV-Vis and Raman technique, respectively. Some interesting phenomena are found (Such as the Curie temperature Tc and band-gap energy Eg change regularly with the dopants additon). The results are helpful to clarify the intrinsic mechanism of the DMSs, and will provide new insights on the fabrication and application of devices based on these materials. This work was supported by the National Science Foundation of China (Grant No. 61376094). Li Zhang would like to acknowledge a scholarship granted by China Scholarship Council (CSC-201408330028).

  6. Generation of diluted magnetic semiconductor nanostructures by pulsed laser ablation in liquid

    NASA Astrophysics Data System (ADS)

    Savchuk, Ol. A.; Savchuk, A. I.; Stolyarchuk, I. D.; Tkachuk, P. M.; Garasym, V. I.

    2015-11-01

    Results of study of two members of diluted magnetic semiconductor (DMS) family, namely Cd1-xMnxTe and Zn1-xMnxO, which are in form of micro- and nanoparticles generated by pulsed laser ablation in liquid medium (PLAL), have been presented. The structural analysis using X-ray diffraction (XRD) of nanocrystals indicated that Mn has entered the AIIBVI lattice without changing the crystal structure and systematically substituted the A2+ ions in the lattice. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. The scanning electron microscopy (SEM) clearly illustrates flower-like particles of Zn1-xMnxO, which consist of nanosheets and nanoleaves with average thickness about (5-8) nm. Obviously, these nanoobjects are responsible for the observed blue shift of the absorption edge in DMS nanostructures. In magneto-optical Faraday rotation spectra of both Cd1-xMnxTe and Zn1-xMnxO nanostructures there were exhibited peculiarities associated with s,p-d spin exchange interactions and confinement effect. It was observed almost linear dependence of the Faraday rotation as function of magnetic field strength for nanoparticles in contrast to the dependence with saturation in bulk case.

  7. (GaMn)As: GaAs-based III?V diluted magnetic semiconductors grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Hayashi, T.; Tanaka, M.; Nishinaga, T.; Shimada, H.; Tsuchiya, H.; Otuka, Y.

    1997-05-01

    We have grown novel III-V diluted magnetic semiconductors, (Ga 1 - xMn x)As, on GaAs substrates by low-temperature molecular beam epitaxy using strong nonequilibrium growth conditions. When the Mn concentration x is relatively low (≲0.08), homogeneous alloy semiconductors, GaMnAs, are grown with zincblende structure and slightly larger lattice constants than that of GaAs, whereas inhomogeneous structures with zincblende GaMnAs (or GaAs) plus hexagonal MnAs are formed when x is relatively high. Magnetization measurements indicate that the homogeneous GaMnAs films have ferromagnetic ordering at low temperature.

  8. Design of dilute magnetic semiconductors with room temperature ferromagnetism by controlling spinodal decompostion

    NASA Astrophysics Data System (ADS)

    Sato, Kazunori

    2008-03-01

    Owing to the recent development of the first-principles method for calculating magnetic properties of dilute magnetic semiconductors (DMS), it has been recognized that the magnetic percolation effect is disastrous to the high temperature ferromagnetism in DMS in particular for low concentrations [1]. The exchange interactions calculated from first-principles are strong for nearest neighbors, but those interactions are short ranged and can not play an important role for realizing high- TC because the solubility of magnetic impurities into DMS is too low to achieve magnetic percolation. To overcome this difficulty and realize room temperature ferromagnetism, we focus on the spinodal decomposition in DMS, and suggest that by controlling the spinodal decomposition high blocking temperature can be realized leading to ferromagnetic behaviour at high temperature [2]. We calculate electronic structure of DMS from first-principles by using the Korringa- Kohn-Rostoker coherent potential approximation (KKR-CPA) method. Then, chemical pair interactions and magnetic exchange interactions between magnetic are calculated. We use the Monte Carlo techniques to simulate spinodal decomposition of DMS and to estimate the magnetic properties of them [3]. The computer simulations for the magnetization process of the decomposition phases indicate that we can control super-paramagnetic blocking temperature by optimizing the size of the clusters by changing the crystal growth condition. This simulation suggests the material design of high blocking temperature DMS by controlling the spinodal decomposition [2].As another approach for realizing high-Tc DMS we propose co-doping method to increase solubility limit of transition metal impurities in DMS [4]. This work is based on the collaboration with H. Katayama-Yoshida and T. Fukushima. [1] L. Bergqvist et al, Phys. Rev. Lett. 93, 137202 (2004), K. Sato et al., Phys. Rev. B 70, 201202 (2004) [2] K. Sato et al., Jpn. J. Appl. Phys. 46, L682

  9. Ab initio description of the diluted magnetic semiconductor Ga1-xMnxAs: Ferromagnetism, electronic structure, and optical response

    NASA Astrophysics Data System (ADS)

    Craco, L.; Laad, M. S.; Müller-Hartmann, E.

    2003-12-01

    Motivated by a study of various experiments describing the electronic and magnetic properties of the diluted magnetic semiconductor Ga1-xMnxAs, we investigate its physical response in detail using a combination of first-principles band structure with methods based on dynamical mean field theory to incorporate strong, dynamical correlations, and intrinsic as well as extrinsic disorder in one single theoretical picture. We show how ferromagnetism is driven by double exchange (DE), in agreement with very recent observations, along with a good quantitative description of the details of the electronic structure, as probed by scanning tunneling microscopy and optical conductivity. Our results show how ferromagnetism can be driven by DE even in diluted magnetic semiconductors with small carrier concentration.

  10. Extended coherence length of spatially oscillating electron-spin polarization in dilute-magnetic-semiconductor quantum wells

    SciTech Connect

    Tsuchiya, Takuma

    2013-12-04

    We have investigated the possibility that the coherence length of spatially oscillating electron-spin polarization is improved in dilute magnetic semiconductors. In usual nonmagnetic quantum wells, the spin polarization of the electrons injected from a ferromagnetic source electrode oscillates spatially because of the spin precession due to spin-orbit effective magnetic fields, i.e., the Rashba and Dresselhaus fields. However, the polarization is damped within an oscillation period by the D’yakonov-Perel’ spin relaxation. In paramagnetic dilute magnetic semiconductors, impurity spin polarization is induced under the electron-spin polarization, and this impurity polarization influences the electron-spin precession and possibly improves the spatial electron-spin coherence. The validity of this effect is demonstrated by a numerical simulation for a CdMnTe quantum well.

  11. Crossover from impurity to valence band in diluted magnetic semiconductors: Role of Coulomb attraction by acceptors

    SciTech Connect

    Popescu, Florentin; Sen, Cengiz; Dagotto, Elbio R; Moreo, Adriana

    2007-01-01

    The crossover between an impurity band (IB) and a valence band (VB) regime as a function of the magnetic impurity concentration in a model for diluted magnetic semiconductors (DMSs) is studied systematically by taking into consideration the Coulomb attraction between the carriers and the magnetic impurities. The density of states and the ferromagnetic transition temperature of a spin-fermion model applied to DMSs are evaluated using dynamical mean-field theory and Monte Carlo (MC) calculations. It is shown that the addition of a square-well-like attractive potential can generate an IB at small enough Mn doping x for values of the p-d exchange J that are not strong enough to generate one by themselves. We observe that the IB merges with the VB when x>=xc where xc is a function of J and the Coulomb strength V. Using MC simulations, we demonstrate that the range of the Coulomb attraction plays an important role. While the on-site attraction, which has been used in previous numerical simulations, effectively renormalizes J for all values of x, an unphysical result, a nearest-neighbor range attraction renormalizes J only at very low dopings, i.e., until the bound holes wave functions start to overlap. Thus, our results indicate that the Coulomb attraction can be neglected to study Mn-doped GaSb, GaAs, and GaP in the relevant doping regimes, but it should be included in the case of Mn-doped GaN, which is expected to be in the IB regime.

  12. An X-ray standing wave study of the diluted magnetic semiconductor Ga(Mn)As

    NASA Astrophysics Data System (ADS)

    Nemsak, Slavomir; Kuo, Cheng-Tai; Schlueter, Christoph; Gehlmann, Mathias; Lin, Shih-Chieh; Doering, Sven; Eschbach, Markus; Mlynczak, Ewa; Plucinski, Lukasz; Borek, Stephan; Minar, Jan; Ohno, Hideo; Lee, Tien-Lin; Schneider, Claus M.; Fadley, Charles S.

    We have combined the recently developed techniques of soft x-ray standing-wave angle-resolved photoemission (SW-ARPES) [Gray et al., EPL 104, 17004 (2013)] and hard x-ray ARPES (HARPES) [Gray et al., Nature Mat. 11, 957 (2012)] so as to be able to use single-crystal Bragg reflection to create the SW [Thiess et al., Sol. St. Comm. 150, 553 (2010)], thus permitting the first measurements of momentum- and element- resolved bulk electronic structure. The strengths of the SW-HARPES method are demonstrated using the dilute magnetic semiconductor Ga(1 - x)MnxAs. A strong SW is generated by Bragg reflection of ca. 3 keV x-rays from the (111) planes of both undoped GaAs and Mn-doped thin films with x=0.05. Due to the uneven occupancy of (111) planes by either Ga(Mn) or As atoms, the element-specific band structure can be obtained with a help of the SW modulation in core levels. Apart from the site specific decomposition of the electronic structure, the SW measurements also confirmed a substitutional presence of Mn atoms at the Ga sites. This technique should be applicable to a broad range of complex materials.

  13. Magnetism and Transport in the Group-IV Dilute Magnetic Semiconductor Germanium(1-x) Manganese(x)

    NASA Astrophysics Data System (ADS)

    Dolph, Melissa Ann Commisso

    Dilute magnetic semiconductors (DMS) have gained interest over the past decade because of their potential applications in spintronics. DMS systems exhibit carriermediated ferromagnetism, a property which enables electric-field control over the magnetization. In this thesis, the DMS Ge1-xMn x was studied. Germanium (Ge) is a desirable semiconductor because of its high hole mobility and its compatibility with silicon. Manganese (Mn) was chosen for its exhibition of indirect ferromagnetic coupling. These properties are deemed necessary for the realization of a magnetic quantum-dot based device such as a magnetic spin switch. Ion implantation of Mn into Ge-on-insulator and molecular beam expitaxy (MBE) were two methods utilized to synthesize the studied Ge1-x Mnx thin films. Several of the Ge1-xMn x films were treated with rapid thermal annealing (RTA) or pulsed laser melting (PLM) in an attempt to improve the crystallinity and make more of the Mn ferromagnetically active. Of all the Ge1-xMn x systems studied, those that exhibited correlated magnetic and magneto-transport properties were those with hole concentrations on the order of 1019 --1020 holes/cm3. Although these systems exhibited robust magneto-transport properties, electric-field biasing proved ineffective at modulating the carrier concentration and ultimately the magnetization as monitored by the ordinary and anomalous Hall effects and the resistivity. The inefficiency of the electric gating was attributed to localized trap states which reside in the energy band gap of the defect-plagued Ge semiconductor. If crystallinity is a prerequisite for gatability, PLM may prove useful as it was found to restore the single crystal structure damaged during Mn implantation. However, PLM resulted in an undesirable segregation of Mn toward the surface of the film (as observed by secondary ion mass spectrometry (SIMS)); a decrease in the saturation magnetization after PLM was attributed to this segregation. The information

  14. Optical properties of diluted magnetic semiconductor Cu:ZnS quantum dots

    NASA Astrophysics Data System (ADS)

    Imam, N. G.; Bakr Mohamed, Mohamed

    2014-09-01

    Herein quantum dots (QDs) of diluted magnetic semiconductor Cu:ZnS have been synthesized via a simple chemical synthesis method. A single phase solid solution is formed up to x = 0.1 which confirmed by using X-ray diffraction. Crystal structure and microstructure analyses were performed by Rietveld refinement. Photoluminescence (PL) emission spectra were recorded for pure and Cu doped ZnS QDs excited at 268 and 228 nm respectively. PL emission and excitation spectra were investigated in different wavelength regions within the range of 200-900 nm. PL results in the range of 220-300 nm emission band reveals that the band gap of pure ZnS QDs is about 4.43 eV which greater than that of bulk ZnS (3.7 eV). The band gap of Cu:ZnS QDs is tunable with Cu content (x) as well as the crystalline size, and it is peaked around 4.47 eV. PL emission in the range of 350-650 nm exhibits a green fluorescence band peaking around 552 nm for pure ZnS QDs, which confirms the characteristic feature of Zn2+ as luminescent centers in the lattice, while blue emission bands peaked around 471 nm for Cu:ZnS QDs that is attributed to the transition of electrons from conduction band of ZnS to the Cu impurity level. The blue shift of the absorption peak directly reflects the effect of quantum confinement. The PL results have been supported by X-ray phase analysis, high-resolution electron microscopy (HRTEM and SEM), compositional evaluation (EDX) and magnetic measurements (VSM).

  15. Comparison of Magnetic Property of Cu-, Al-, and Li-DOPED ZnO Dilute Magnetic Semiconductor Thin Films

    NASA Astrophysics Data System (ADS)

    van, L. H.; Ding, J.; Hong, M. H.; Fan, Z. C.; Wang, L.

    The properties of Cu-, Al-, and Li-doped ZnO dilute magnetic semiconductor (DMS) have been analyzed and compared. Zincite with wurtzite structures have been synthesized successfully on SiO2 (101) and SiO2 (110) substrates in both the Cu-ZnO and Li-ZnO DMS. The highly textured ZnO (002) peaks were able to form in the Cu-ZnO system at 400°C. However, it formed at even much lower temperature in the Li-ZnO system, that is only 25°C. ZnO (002) peaks in both systems were formed without any impurity phases. However, no crystalline structure is synthesized in the Al-ZnO system. The thin films formed are amorphous. The structural and related magnetic properties of the films were analyzed by XRD, AFM, and VSM. The films were found to be at their highest magnetism at the value of 3.1 emu/cm3 for Co-ZnO and 2.5 emu/cm3 for Li-ZnO, synthesized at 400°C, and under 1 × 10-4 Torr oxygen partial pressure.

  16. Large positive magnetoresistance effects in the dilute magnetic semiconductor (Zn,Mn)Se in the regime of electron hopping

    SciTech Connect

    Jansson, F. Wiemer, M.; Gebhard, F.; Baranovskii, S. D.; Nenashev, A. V.; Petznick, S.; Klar, P. J.; Hetterich, M.

    2014-08-28

    Magnetoresistance in dilute magnetic semiconductors is studied in the hopping transport regime. Measurements performed on Cl-doped Zn{sub 1–x}Mn{sub x}Se with x < 8% are compared with simulation results obtained by a hopping transport model. The energy levels of the Cl donors are affected by the magnetization of Mn atoms in their vicinity via the s-d exchange interaction. Compositional disorder, in particular, the random distribution of magnetic atoms, leads to a magnetic-field induced broadening of the donor energy distribution. As the energy distribution broadens, the electron transport is hindered and a large positive contribution to the magnetoresistance arises. This broadening of the donor energy distribution is largely sufficient to account for the experimentally observed magnetoresistance effects in n-type (Zn,Mn)Se with donor concentrations below the metal–insulator transition.

  17. Magnetic, structural and optical properties of Mn-based and Cr-based diluted magnetic semiconductors and alloys

    NASA Astrophysics Data System (ADS)

    Alsaad, A.

    2009-03-01

    We have implemented supercell approach by using local spin density functional theory for Mn-doped GaN, Mn-doped ScN and the linear muffin-tin orbital method to predict the structural and magnetic properties of these novel diluted magnetic semiconductors and their GaxMn1-xN and ScxMn1-xN alloys. The global energy minimum of MnN is obtained for zinc-blende structure. If the compound is compressed by 6 % the energy minimum corresponds to the NaCl structure in disagreement with the experimentally observed a slightly tetragonally distorted rocksalt structure, known as ? phase. The rocksalt structure of CrN at about 8 % lattice expansion becomes stable in the ferromagnetic (FM) state and has a global minimum energy at a lattice constant of 3.9 å. We have observed an isostructural phase transition for ScxMn1-xN alloys from zince-blende phase to hexagonal phase that occurs at a hydrostatic pressure of 17.5 GPa. Moreover, the structural and optical properties of single crystal CrN/ScN superlattices and Cr1-xScxN alloys are studied in details. We report an isostructural phase transition from wurtzite (w-CrN) to hexagonal (h-ScN) at a hydrostatic pressure of 21 GPa. We have also used first-principles methods to study the electronic, optical and magnetic properties of MnN and MnAs compounds in the hypothetical cubic zinc-blende phase, a phase in which the two MnN and MnAs binaries have the same local environment as that they have in GaMnN and GaMnAs alloys. We show that MnN exhibits antiferromagnetic (AFM) ground state and MnAs adopts ferromagnetic (FM) ground state.

  18. Structural and magnetic properties of Co + implanted n-GaN dilute magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Husnain, G.; Tao, Fa; Yao, Shu-De

    2010-05-01

    The n-type GaN epilayer was grown on sapphire prepared by metal organic chemical vapour deposition and subsequently Co + ions implanted. The properties of Co + ions implanted GaN epilayer were investigated by structural and magnetic measurements. The results of Rutherford backscattering spectrometry and channeling illustrate that an excellent crystalline quality ( χmin=1.3%) of as-grown GaN. After the implantation of 150 keV Co + ions with dose 3×10 16 cm -2 into GaN and subsequently annealed at 700, 800 and 900 °C, no secondary phase or metal related-peaks were detected by typical XRD. In addition high-resolution X-ray diffraction (HRXRD) was performed to study structural related properties. The magnetization curves were obtained by SQUID and AGM measurements, a well-defined hysteresis loop was observed even at 300 K. The temperature dependence of magnetization was taken in FC and ZFC conditions showed the highest Curie temperature ( TC) ∼370 K recorded for Co + implanted GaN.

  19. Defects induced magnetization in B-doped ZnFeO dilute magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Saleem, Murtaza; Sabieh Anwar, M.; Mahmood, Asif; Atiq, Shahid; Ramay, Shahid M.; Siddiqi, Saadat A.

    2015-05-01

    Zn0.95-xFe0.05BxO (x=0, 0.05) nano-particles have been synthesized using a modified chemically derived citrate gel method. X-ray diffraction analysis demonstrates the wurtzite type hexagonal structure belonging to P63mc space group without the presence of any secondary phase in both compositions. The Diffraction analysis shows that Fe2+ and B3+ ions have replaced some of the Zn2+ ions while some occupy un-detectable interstitial and inter-granular positions inside the structure. Scanning electron micrographs obtained using scanning electron microscopy show typical smaller size of particles in B-doped composition. Temperature dependent electrical resistivity analysis shows the semiconducting characteristics of the compositions and that doping of Fe and B up to 10 at% does not change the electrical behavior of the host material. Magnetic measurements display room temperature ferromagnetism in both compositions with enhanced magnetization in B-doped composition associated with defect induced magnetic mechanism belonging to intrinsically augmented interstitial and inter-granular effects.

  20. Dilute magnetic semiconductors based on wide bandgap SiO 2 with and without transition metal elements

    NASA Astrophysics Data System (ADS)

    Dinh, Van An; Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2005-10-01

    Material designs based on the first principle calculations of electronic structures are proposed for α-quartz SiO 2-based dilute magnetic semiconductors. The incorporation of transition metals (TMs) into Si sites and of the non-TM atoms into O sites are treated for various concentrations. At temperatures higher than room temperature, most of the TM-doped SiO 2 have no magnetism, yet Si 1- xMn xO 2 might achieve the ferromagnetism. The substitution of O by non-TM atoms as C or N also induces the magnetism in the host. However, while the N's substitution induces the ferromagnetism, C's substitution causes an anti-ferromagnetic behavior in the host material SiO 2.

  1. The origin of ferromagnetic interaction between bound magnetic polarons in diluted magnetic semiconductors: A minimal model

    NASA Astrophysics Data System (ADS)

    Bednarski, Henryk

    2014-01-01

    We present a detailed analysis of the role of various interaction mechanisms contributing to the bound magnetic polaron (BMP) molecule Hamiltonian with the purpose of gaining an insight into the origin of the ferromagnetic interaction between BMPs. Explicitly, it appears that the BMP molecule Hamiltonian without interatomic direct exchange interaction does not lead to appearance of the parallel alignment of polaronic clouds in the lowest energy state even for large magnitudes of the polaronic exchange fields (up to ~65 meV in Cd0.95Mn0.05Se). Also, it appears that for the range of moderate values of polaronic exchange fields (16-25 meV in Cd0.95Mn0.05Se), the regular Hubbard BMP pair Hamiltonian must be supplemented with the direct interatomic (Heisenberg) exchange interaction to form a minimal model Hamiltonian of BMP molecule with the parallel alignment of the polaronic clouds in the lowest energy state.

  2. A sensitive and label-free photoelectrochemical aptasensor using Co-doped ZnO diluted magnetic semiconductor nanoparticles.

    PubMed

    Li, Hongbo; Qiao, Yunfei; Li, Jing; Fang, Hailin; Fan, Dahe; Wang, Wei

    2016-03-15

    Co-doped ZnO diluted magnetic semiconductor as a novel photoelectric beacon was first constructed for photoelectrochemical (PEC) aptasensor of acetamiprid. The fabricated PEC sensing is based on the specific binding of acetamiprid and its aptamer, which induces the decreasement of enhanced photocurrent produced by the electron donor of quercetin. Co(2+) doping has a beneficial effect in extending the band width of light absorption of ZnO into the visible region and to promote the separation of the photoinduced carriers due to the sp-d exchange interactions existing between the band electrons and the localized d electrons of Co(2+). The fabricated aptasensor was linear with the concentration of acetamiprid in the range of 0.5-800 nmolL(-1) with the detection limit of 0.18 nmolL(-1). The presence of same concentration of other conventional pesticides did not interfere in the detection of acetamiprid and the recovery is between 96.2% and 103.7%. This novel PEC aptasensor has good performances with high sensitivity, good selectivity, low cost and portable features. The strategy of Co-doped ZnO diluted magnetic semiconductor paves a new way to improve the performances of PEC aptasensor. PMID:26436325

  3. Structural, optical, magnetic and photocatalytic properties of Co doped CuS diluted magnetic semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Sreelekha, N.; Subramanyam, K.; Amaranatha Reddy, D.; Murali, G.; Ramu, S.; Rahul Varma, K.; Vijayalakshmi, R. P.

    2016-08-01

    Pristine and Co doped covellite CuS nanoparticles were synthesized in aqueous solution by facile chemical co-precipitation method with Ethylene Diamine Tetra Acetic Acid (EDTA) as a stabilizing agent. EDAX measurements confirmed the presence of Co in the CuS host lattice. Hexagonal crystal structure of pure and Co doped CuS nanoparticles were authenticated by XRD patterns. TEM images indicated that sphere-shape of nanoparticles through a size ranging from 5 to 8 nm. The optical absorption edge moved to higher energies with increase in Co concentration as indicated by UV-vis spectroscopy. Magnetic measurements revealed that bare CuS sample show sign of diamagnetic character where as in Co doped nanoparticles augmentation of room temperature ferromagnetism was observed with increasing doping precursor concentrations. Photocatalytic performance of the pure and Co doped CuS nanoparticles were assessed by evaluating the degradation rate of rhodamine B solution under sun light irradiation. The 5% Co doped CuS nanoparticles provide evidence for high-quality photocatalytic activity.

  4. Structural stability at high pressure, electronic, and magnetic properties of BaFZnAs: A new candidate of host material of diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Bi-Juan, Chen; Zheng, Deng; Xian-Cheng, Wang; Shao-Min, Feng; Zhen, Yuan; Si-Jia, Zhang; Qing-Qing, Liu; Chang-Qing, Jin

    2016-07-01

    The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized. Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measurements demonstrate that the structure of BaFZnAs is stable under pressure up to 17.5 GPa at room temperature. The resistivity and the magnetic susceptibility data show that BaFZnAs is a non-magnetic semiconductor. BaFZnAs is recommended as a candidate of the host material of diluted magnetic semiconductor. Project supported by the National Natural Science Foundation of China and Project of Ministry of Science and Technology of China.

  5. First principles study of Fe in diamond: A diamond-based half metallic dilute magnetic semiconductor

    SciTech Connect

    Benecha, E. M.; Lombardi, E. B.

    2013-12-14

    Half-metallic ferromagnetic ordering in semiconductors, essential in the emerging field of spintronics for injection and transport of highly spin polarised currents, has up to now been considered mainly in III–V and II–VI materials. However, low Curie temperatures have limited implementation in room temperature device applications. We report ab initio Density Functional Theory calculations on the properties of Fe in diamond, considering the effects of lattice site, charge state, and Fermi level position. We show that the lattice sites and induced magnetic moments of Fe in diamond depend strongly on the Fermi level position and type of diamond co-doping, with Fe being energetically most favorable at the substitutional site in p-type and intrinsic diamond, while it is most stable at a divacancy site in n-type diamond. Fe induces spin polarized bands in the band gap, with strong hybridization between Fe-3d and C-2s,2p bands. We further consider Fe-Fe spin interactions in diamond and show that substitutional Fe{sup +1} in p-type diamond exhibits a half-metallic character, with a magnetic moment of 1.0 μ{sub B} per Fe atom and a large ferromagnetic stabilization energy of 33 meV, an order of magnitude larger than in other semiconductors, with correspondingly high Curie temperatures. These results, combined with diamond's unique properties, demonstrate that Fe doped p-type diamond is likely to be a highly suitable candidate material for spintronics applications.

  6. Development of transition-metal doped copper oxide and zinc oxide dilute magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Ivill, Mathew P.

    The field of spintronics has recently attracted much attention because of its potential to provide new functionalities and enhanced performance in conventional electronic devices. Oxide materials provide a convenient platform to study the spin-based functionality in host semiconducting material. Recent theoretical treatments predict that wide band-gap semiconductors, including ZnO, can exhibit high temperature ferromagnetic ordering when doped with transition metals. This work focused on the possibility of using wide band-gap oxide semiconductors as potential spintronic materials. The structure, magnetic, and electronic transport properties of transition-metal doped ZnO and Cu 2O were investigated. Mn and Co were used as transition metal dopants. Thin films of these materials were fabricated using pulsed laser deposition (PLD). The Mn solubility in Cu2O was found to be small and the precipitation of Mn-oxides was favored at high growth temperatures. Phase pure Mn-doped Cu2O samples were found to be non-magnetic. Samples were p-type with carrier concentrations on the order of 1014-10 16 cm-3. The effects of carrier concentration on the magnetic properties of Mn-doped ZnO were studied using Sn and P as electronic codopants. Sn acts as an n-type dopant providing extra electrons to the ZnO. P acts as a p-type dopant that supplies excess holes to compensate the native electron concentration in ZnO. The electron concentration was decreased using P, but the films remained n-type. An inverse correlation was found between the ferromagnetism and the electron concentration; the ferromagnetic coupling between Mn spins increased with decreasing electron concentration. The nature of ferromagnetism in Co-doped ZnO was also investigated. Ferromagnetism was found in films deposited at 400°C in vacuum, while films deposited in oxygen or at higher temperatures were non-magnetic. Films deposited under vacuum had rather high electron concentrations and were presumably doped with

  7. Magnetopolaron effect in diluted semimagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Tarasov, Georgiy G.; Mazur, Yuri I.; Rakitin, Andrey S.; Lavoric, S. R.; Tomm, Jens W.; Hoerstel, W.

    1997-08-01

    Phonon-assisted self-trapping of free carrier is considered in diluted semimagnetics. It is shown that the binding energy of free magnetic polaron can be substantially larger when the 'spin-phonon' coupling is taken into account. For the particular case of 'soft' lattice dynamics the region of stability for hole-induced polaron can be promoted to the temperature of tenths of degrees and magnetic field of a few Tesla. The possible hybridized excitations with the partition of free magnetic polaron are discussed in semimagnetic semiconductors.

  8. Wave Function Mixing and g-Factors in Narrow Gap Ferromagnetic III-V Dilute Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Sun, Y.; Sanders, G. D.; Stanton, C. J.

    2002-03-01

    We present a theory for wave-function mixing and g-factors in ferromagnetic p-doped narrow gap In_1-xMn_xAs dilute magnetic semiconductor alloys in an ultrahigh external magnetic field, B. We generalize an 8 band Pidgeon-Brown model to include (i) the wavevector, k, dependence of the electronic states along B, (ii) s-d and p-d exchange interactions with localized Mn d-electrons, and (iii) finite magnetic moment in the ferromagnetic state. The complex valence band structure at finite k plays an important role in the cyclotron resonance spectra. We look at the band-mixing and spin-dependence of the wave functions as a function of the wavevector, magnetic field (0-100T), temperature (4 K to 290 K), and Mn concentration (0 to 12 %). From this, we can extract magnetic field dependent g-factors. The sensitivity of the band mixing and g-factors to the s-d and p-d exchange interactions is also investigated. Finally, we look at the effect of band-mixing on optical properties such as the polarization dependence of the absorption and luminescence.

  9. Graphene activating room-temperature ferromagnetic exchange in cobalt-doped ZnO dilute magnetic semiconductor quantum dots.

    PubMed

    Sun, Zhihu; Yang, Xiaoyu; Wang, Chao; Yao, Tao; Cai, Liang; Yan, Wensheng; Jiang, Yong; Hu, Fengchun; He, Jingfu; Pan, Zhiyun; Liu, Qinghua; Wei, Shiqiang

    2014-10-28

    Control over the magnetic interactions in dilute magnetic semiconductor quantum dots (DMSQDs) is a key issue to future development of nanometer-sized integrated "spintronic" devices. However, manipulating the magnetic coupling between impurity ions in DMSQDs remains a great challenge because of the intrinsic quantum confinement effects and self-purification of the quantum dots. Here, we propose a hybrid structure to achieve room-temperature ferromagnetic interactions in DMSQDs, via engineering the density and nature of the energy states at the Fermi level. This idea has been applied to Co-doped ZnO DMSQDs where the growth of a reduced graphene oxide shell around the Zn(0.98)Co(0.02)O core turns the magnetic interactions from paramagnetic to ferromagnetic at room temperature, due to the hybridization of 2p(z) orbitals of graphene and 3d obitals of Co(2+)-oxygen-vacancy complexes. This design may open up a kind of possibility for manipulating the magnetism of doped oxide nanostructures. PMID:25222885

  10. ZnMnO diluted magnetic semiconductor nanoparticles: Synthesis by laser ablation in liquids, optical and magneto-optical properties

    NASA Astrophysics Data System (ADS)

    Savchuk, A. I.; Perrone, A.; Lorusso, A.; Stolyarchuk, I. D.; Savchuk, O. A.; Shporta, O. A.

    2014-05-01

    Nanoparticles of ZnO and Zn1-xMnxO were synthesized by pulsed laser ablation in liquid medium (PLAL). Metal zinc target was used for preparing of pure ZnO nanostructures and Zn1-xMnxO ceramic plates served for preparing of ternary nanoparticles. As synthesized nanomaterials are characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy analysis (EDS), atomic force microscopy (AFM), UV-vis absorption, photoluminescence and Faraday rotation spectroscopy. SEM images showed a well-defined flower-like nanostructures. Absorption edge of Zn0.95Mn0.05O nanoparticles in colloid solution exhibits blue shift due to confinement effect. The observed photoluminescence peaks are attributed to the band-edge transitions and vacancies or defects. The Faraday rotation as a function of photon energy demonstrates behavior typical for diluted magnetic semiconductors (DMSs) in paramagnetic state.

  11. Chemical trend of exchange coupling in diluted magnetic II-VI semiconductors: Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Chanier, T.; Virot, F.; Hayn, R.

    2009-05-01

    We have calculated the chemical trend of magnetic exchange parameters ( Jdd , Nα , and Nβ ) of Zn-based II-VI semiconductors ZnA ( A=O , S, Se, and Te) doped with Co or Mn. We show that a proper treatment of electron correlations by the local spin-density approximation (LSDA)+U method leads to good agreement between experimental and theoretical values of the nearest-neighbor exchange coupling Jdd between localized 3d spins in contrast to the LSDA method. The exchange couplings between localized spins and doped electrons in the conduction band Nα are in good agreement with experiment as well. But the values for Nβ (coupling to doped holes in the valence band) indicate a crossover from weak coupling (for A=Te and Se) to strong coupling (for A=O ) and a localized hole state in ZnO:Mn. This hole localization explains the apparent discrepancy between photoemission and magneto-optical data for ZnO:Mn.

  12. Growth and magnetic properties of IV-VI diluted magnetic semiconductor Ge{sub 1-x}Cr{sub x}Te

    SciTech Connect

    Fukuma, Y.; Taya, T.; Miyawaki, S.; Irisa, T.; Asada, H.; Koyanagi, T.

    2006-04-15

    IV-VI diluted magnetic semiconductor Ge{sub 1-x}Cr{sub x}Te films were grown on BaF{sub 2} substrates by molecular-beam epitaxy. The Ge{sub 1-x}Cr{sub x}Te film up to x=0.103 is single phase as determined by reflection high-energy electron diffraction and x-ray diffraction measurements. The optical band gap decreases with increasing Cr composition. Ferromagnetic order of the Ge{sub 1-x}Cr{sub x}Te films is characterized by direct magnetization and anomalous Hall effect measurements.

  13. Cd{sub 0.9375}Mn{sub 0.0625}S diluted magnetic semiconductor: A DFT study

    SciTech Connect

    Rani, Anita; Kaur, Kulwinder; Kumar, Ranjan

    2015-08-28

    We studied the spin polarized electronic band structures and magnetic properties of the diluted magnetic semiconductor Cd{sub 1-x}Mn{sub x}S in Zinc Blende phase (B3) with 0.0625 Mn by using ab initio method. The calculations were performed by using Density Functional Theory as implemented in the Spanish Initiative for Electronic Simulations with Thousands of Atoms code using local density approximation (LDA). Calculated electronic band structures and magnetic properties of Cd{sub 1-x}Mn{sub x}S are discussed in terms of contribution of Mn 3d{sup 5} 4s{sup 2}, Cd 4d{sup 10} 5s{sup 2}, S 3s{sup 2} 3p{sup 4} orbitals. The total magnetic moment is found to be 5.00 µb for Cd{sub 1−x}Mn{sub x}S at x=0.0625. This value indicate that Mn atom adds no hole carrier to the perfect CdS crystal. We found that Mn doped systems are ferromagnetic. Calculated results are in good agreement with previous studies.

  14. Materials and device design with III-V and II-VI compound-based diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Katayama-Yoshida, Hiroshi; Sato, Kazunori

    2002-03-01

    Since the discovery of the carrier induced ferromagnetism in (In, Mn)As and (Ga, Mn)As, diluted magnetic semiconductors (DMS) have been of much interest from the industrial viewpoint because of their potentiality as a new functional material (spintronics). In this paper, the magnetism in DMS is investigated based on the first principles calculations, and materials and device design with the DMS is proposed toward the spintronics. The electronic structure is calculated by the Korringa-Kohn-Rostoker method combined with the coherent potential approximation based on the local spin density approximation. We calculate the electronic structure of ferromagnetic and spin-glass DMS, and total energy difference between them is calculated to estimate whether the ferromagnetic state is stable or not. It is shown that V-, Cr- and Mn-doped III-V compounds, V- and Cr-doped II-VI compounds and Fe-, Co- and Ni-doped ZnO are promising candidates for a high-Curie temperature ferromagnet. A chemical trend in the ferromagnetism is well understood based on the double exchange mechanism [1]. Based upon this material design, some prototypes of the spintronics devices, such as a spin-FET, a photo-induced-magnetic memory and a coherent-spin-infection device, are proposed. [1] K. Sato and H. Katayama-Yoshida, Jpn. J. Appl. Phys. 39 (2000) L555, 40 (2001) L334, L485 and L651.

  15. Sub-picosecond time-resolved carrier, phonon, and spin dynamics in Cd(Mn)Te diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Wang, D.; Sobolewski, Roman; Mycielski, A.

    2005-08-01

    We present here our research on time-resolved carrier, phonon, and spin dynamics in the diluted-magnetic semiconductor Cd1-xMnxTe [Cd(Mn)Te] system. Our test samples were the high-quality single crystals with the Mn doping concentrations ranging from 9% to 12%, grown by a modified Bridgeman method. Femtosecond optical pump-probe spectroscopy experiments allowed us to study time-resolved dynamics of both the excited carriers and coherent acoustic phonons. Using pump photons with the energy just exceeding the Cd(Mn)Te energy gap, we observed the bleaching effect as excited carriers occupied essentially all available states at the bottom of the conduction band. With the increase of the pump photon energy, the normalized differential reflectivity (ΔR/R) signal changed sign to positive, being dominated by the electron-phonon relaxation process. All our ΔR/R traces, on the delay-time scale well above 100 ps, exhibited very regular oscillations, which were identified, as the signature of coherent acoustic phonons, generated by an electronic and thermal stress introduced at the sample surface by the pump photons. We have also excited our samples with sub-picosecond magnetic transients, generated by a low-temperature-grown GaAs photoconductive switch, and observed the sub-picosecond magneto-optic (Faraday) effect (Mn-ion spin dynamics). The sub-picosecond Faraday response makes this semimagnetic semiconductor an excellent candidate for practical applications in magneto-optics, such as in time-resolved magneto-optical sampling and imaging techniques, or in ultrafast magneto-optical transducers and modulators. In addition, Cd(Mn)Te is a very promising material for ultrafast spintronic and magnetic memory-type devices.

  16. Magnetic mechanism investigations on K and Mn co-doped diluted magnetic semiconductor (Sr,K)(Zn,Mn)2As2

    NASA Astrophysics Data System (ADS)

    Yang, Jun-Tao; Luo, Shi-Jun; Xiong, Yong-Chen

    2016-06-01

    On the basic of the first-principles calculations with strong-correlated correction, the electronic structures and magnetic properties of a II-II-V based diluted magnetic semiconductor (Sr,K)(Zn,Mn)2As2 are investigated within Perdew-Burke-Ernzerhof generalized gradient approximation. With local spins doped via isovalent (Zn2+, Mn2+) substitutions, Sr(Zn,Mn)2As2 system prefers antiferromagnetic ground state, caused by Mn-Mn superexchange interactions. Via off-stoichiometry (Sr2+, K+) substitutions, holes are introduced into (Sr,K)(Zn,Mn)2As2 system, resulting in the ferromagnetic spin responses for local moments, except for the most nearest neighboring Mn-Mn pair. The ferromagnetism of this diluted magnetic semiconductor originates from the competition between the direct anti-ferromagnetic superexchange interaction and the indirect ferromagnetic coupling mediated by Zener's p - d exchange interaction. Our calculations show that Zener's p - d exchange interaction depends on the location of K dopants. From the investigation on the magnetic properties of Mn clusters, it is found that the reduction of the measured Mn saturation moments is caused by the counteraction of the local moments of the most nearest neighboring Mn-Mn pair.

  17. Effect of oxygen vacancy on half metallicity in Ni-doped CeO{sub 2} diluted magnetic semiconductor

    SciTech Connect

    Saini, Hardev S. Saini, G. S. S.; Singh, Mukhtiyar; Kashyap, Manish K.

    2015-05-15

    The electronic and magnetic properties of Ni-doped CeO{sub 2} diluted amgentic semiconductor (DMS) including the effect of oxygen vacancy (V{sub o}) with doping concentration, x = 0.125 have been calculated using FPLAPW method based on Density Functional Theory (DFT) as implemented in WIEN2k. In the present supercell approach, the XC potential was constructed using GGA+U formalism in which Coulomb correction is applied to standard GGA functional within the parameterization of Perdew-Burke-Ernzerhof (PBE). We have found that the ground state properties of bulk CeO{sub 2} compound have been modified significantly due to the substitution of Ni-dopant at the cation (Ce) site with/without V{sub O} and realized that the ferromagnetism in CeO{sub 2} remarkably depends on the V{sub o} concentrations. The presence of V{sub o}, in Ni-doped CeO{sub 2}, can leads to strong ferromagnetic coupling between the nearest neighboring Ni-ions and induces a HMF in this compound. Such ferromagnetic exchange coupling is mainly attributed to spin splitting of Ni-d states, via electrons trapped in V{sub o}. The HMF characteristics of Ni-doped CeO{sub 2} including V{sub o} makes it an ideal material for spintronic devices.

  18. Magnetic properties of the layered III-VI diluted magnetic semiconductor Ga1-xFexTe

    NASA Astrophysics Data System (ADS)

    Pekarek, T. M.; Edwards, P. S.; Olejniczak, T. L.; Lampropoulos, C.; Miotkowski, I.; Ramdas, A. K.

    2016-05-01

    Magnetic properties of single crystalline Ga1-xFexTe (x = 0.05) have been measured. GaTe and related layered III-VI semiconductors exhibit a rich collection of important properties for THz generation and detection. The magnetization versus field for an x = 0.05 sample deviates from the linear response seen previously in Ga1-xMnxSe and Ga1-xMnxS and reaches a maximum of 0.68 emu/g at 2 K in 7 T. The magnetization of Ga1-xFexTe saturates rapidly even at room temperature where the magnetization reaches 50% of saturation in a field of only 0.2 T. In 0.1 T at temperatures between 50 and 400 K, the magnetization drops to a roughly constant 0.22 emu/g. In 0 T, the magnetization drops to zero with no hysteresis present. The data is consistent with Van-Vleck paramagnetism combined with a pronounced crystalline anisotropy, which is similar to that observed for Ga1-xFexSe. Neither the broad thermal hysteresis observed from 100-300 K in In1-xMnxSe nor the spin-glass behavior observed around 10.9 K in Ga1-xMnxS are observed in Ga1-xFexTe. Single crystal x-ray diffraction data yield a rhombohedral space group bearing hexagonal axes, namely R3c. The unit cell dimensions were a = 5.01 Å, b = 5.01 Å, and c = 17.02 Å, with α = 90°, β = 90°, and γ = 120° giving a unit cell volume of 369 Å3.

  19. Resonant inelastic scattering in dilute magnetic semiconductors by x-ray fluorescence spectroscopy

    SciTech Connect

    Lawniczak-Jablonska, K. |; Jia, J.J.; Underwood, J.H.

    1997-04-01

    As modern, technologically important materials have become more complex, element specific techniques have become invaluable in studying the electronic structure of individual components from the system. Soft x-ray fluorescence (SXF) and absorption (SXA) spectroscopies provide a unique means of measuring element and angular momentum density of electron states, respectively, for the valence and conducting bands in complex materials. X-ray absorption and the decay through x-ray emission are generally assumed to be two independent one-photon processes. Recent studies, however have demonstrated that SXF excited near the absorption threshold generate an array of spectral features that depend on nature of materials, particularly on the localization of excited states in s and d-band solids and that these two processes can no be longer treated as independent. Resonant SXF offers thus the new way to study the dynamics of the distribution of electronic valence states in the presence of a hole which is bound to the electron low lying in the conduction band. This process can simulate the interaction between hole-electron pair in wide gap semiconductors. Therefore such studies can help in understanding of transport and optics phenomena in the wide gap semiconductors. The authors report the result of Mn and S L-resonant emission in Zn{sub 1{minus}x}Mn{sub x}S (with x=0.2 and 0.3) and MnS as the energy of exciting radiation is tuned across the Mn and S L{sub 3,2} absorption edge, along with the resonant excited spectra from elemental Mn as a reference.

  20. Carrier-impurity spin transfer dynamics in paramagnetic II-VI diluted magnetic semiconductors in the presence of a wave-vector-dependent magnetic field

    NASA Astrophysics Data System (ADS)

    Cygorek, M.; Tamborenea, P. I.; Axt, V. M.

    2016-05-01

    Quantum kinetic equations of motion for carrier and impurity spins in paramagnetic II-VI diluted magnetic semiconductors in a k -dependent effective magnetic field are derived, where the carrier-impurity correlations are taken into account. In the Markov limit, rates for the electron-impurity spin transfer can be derived for electron spins parallel and perpendicular to the impurity spins corresponding to measurable decay rates in Kerr experiments in Faraday and Voigt geometry. Our rigorous microscopic quantum kinetic treatment automatically accounts for the fact that, in an individual spin flip-flop scattering process, a spin flip of an electron is necessarily accompanied by a flop of an impurity spin in the opposite direction and the corresponding change of the impurity Zeeman energy influences the final energy of the electron after the scattering event. This shift in the electron energies after a spin flip-flop scattering process, which usually has been overlooked in the literature, turns out to be especially important in the case of extremely diluted magnetic semiconductors in an external magnetic field. As a specific example for a k -dependent effective magnetic field the effects of a Rashba field on the dynamics of the carrier-impurity correlations in a Hg1 -x -yCdyMnxTe quantum well are described. It is found that, although accounting for the Rashba interaction in the dynamics of the correlations leads to a modified k -space dynamics, the time evolution of the total carrier spin is not significantly influenced. Furthermore, a connection between the present theory and the description of collective carrier-impurity precession modes is presented.

  1. Investigation of transport and magnetic properties of SiC/Cu diluted magnetic semiconductor nano-multilayer films

    NASA Astrophysics Data System (ADS)

    Sun, Ning; Li, Chunjing; Fu, Yuting; Li, Yanghua; Bu, Dechong; An, Yukai; Liu, Jiwen

    2016-09-01

    The SiC/Cu nano-multilayer films were deposited on Si substrates using radio frequency and direct current alternative sputtering technique. In this paper, the transport and magnetic properties of the films were investigated. XRR shows the SiC/Cu periodical structures of the films. XRD confirms that the 3C-SiC crystal structure is formed in the films without heating substrates. The XPS indicates that the Cu atoms substitute for Si sites of the SiC lattice and exist in a mixed valance state of Cu+ and Cu2+. The best fitting for the plots of ln ρ versus T-1/4 using the combination of the Mott and the band gap VRH models suggests that the carriers in the films are strongly localized. The films have a typical semiconductor characteristic and an obvious room temperature ferromagnetism which should arise from the bond magnetic polarons. The maximum values of saturation magnetization and carrier concentration are up to 15.2 emu/cm3 and 1.86E + 22/cm3 respectively.

  2. Raman Scattering Studies in Dilute Magnetic Semiconductor Zn(1-x)Co(x)O

    NASA Technical Reports Server (NTRS)

    Samanta, K.; Bhattacharya, P.; Katiyar, R. S.; Iwamoto, W.; Pagiluso, P. G.; Rettori, C.

    2006-01-01

    Raman spectra of ZnO and Co substituted Zn1-xCoxO (ZCO) were carried out using the Raman microprobe system with an p.,+ ion laser source of 514.5 nm wavelength. The shift towards the lower frequency side of the nonpolar E210w mode and the broadening due to Co substitution in ZnO were analyzed using the phonon confinement model. The magnetic measurements showed ferromagnetic behavior with the maximum saturation magnetization (1.2micron Beta/ErCo) for 10% Co substitution, which decreased wi th at further increase in Co concentrations. The intensities of E1(LO) at 584 cm-1 and multiphonon modes at 540 cm-1 were increased with an increase in Co substitution. The additional Raman modes in ceramic targets of ZCO spectra for higher concentration of Co substitution (x=15%-20%) were identified to be due to the spinel ZnCo2O4 secondary phase.

  3. Moment enhancement in dilute magnetic semiconductors: MnxSi1-x with x = 0.1%

    SciTech Connect

    Shaughnessy, M; Fong, C Y; Snow, R; Liu, K; Pask, J E; Yang, L H

    2009-03-12

    The experimentally determined magnetic moments/Mn, M, in Mn{sub x}Si{sub 1-x} are considered, with particular attention to the case with 5.0 {micro}{sub B}/Mn, obtained for x = 0.1%. The existing theoretical M values for neutral Mn range from 2.83 to 3.78 {micro}B/Mn. To understand the observed M = 5.0 {micro}{sub B}/Mn, we investigated Mn{sub x}Si{sub 1-x} for a series of Mn concentrations and defect configurations using a first-principles density functional method. We find a structure in which the moment is enhanced. It has 5.0 {micro}B/Mn, the Mn at a substitutional site, and a Si at a second-neighbor interstitial site in a large unit cell. Subsequent analysis shows that the observed large moment can be understood as a consequence of the weakened d-p hybridization resulting from the introduction of the second-neighbor interstitial Si and substantial isolation of the Mn-second-neighbor Si complex at such concentrations.

  4. μSR investigation of a new diluted magnetic semiconductor Li(Zn,Mn,Cu)As with Mn and Cu codoping at the same Zn sites

    NASA Astrophysics Data System (ADS)

    Guo, S. L.; Zhao, Y.; Man, H. Y.; Ding, C.; Gong, X.; Zhi, G. X.; Fu, L. C.; Gu, Y. L.; Frandsen, B. A.; Liu, L.; Cheung, S. C.; Munsie, T. J.; Wilson, M. N.; Cai, Y. P.; Luke, G. M.; Uemura, Y. J.; Ning, F. L.

    2016-09-01

    We report the successful synthesis and characterization of a new type I–II–V bulk form diluted magnetic semiconductor (DMS) Li(Zn,Mn,Cu)As, in which charge and spin doping are decoupled via (Cu,Zn) and (Mn,Zn) substitution at the same Zn sites. Ferromagnetic transition temperature up to  ∼33 K has been observed with a coercive field  ∼40 Oe for the 12.5% doping level. μSR measurements confirmed that the magnetic volume fraction reaches nearly 100% at 2 K, and the mechanism responsible for the ferromagnetic interaction in this system is the same as other bulk form DMSs.

  5. Dilute Magnetic Semiconductor and Half-Metal Behaviors in 3d Transition-Metal Doped Black and Blue Phosphorenes: A First-Principles Study.

    PubMed

    Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

    2016-12-01

    We present first-principles density-functional calculations for the structural, electronic, and magnetic properties of substitutional 3d transition metal (TM) impurities in two-dimensional black and blue phosphorenes. We find that the magnetic properties of such substitutional impurities can be understood in terms of a simple model based on the Hund's rule. The TM-doped black phosphorenes with Ti, V, Cr, Mn, Fe, and Ni impurities show dilute magnetic semiconductor (DMS) properties while those with Sc and Co impurities show nonmagnetic properties. On the other hand, the TM-doped blue phosphorenes with V, Cr, Mn, and Fe impurities show DMS properties, with Ni impurity showing half-metal properties, whereas Sc- and Co-doped systems show nonmagnetic properties. We identify two different regimes depending on the occupation of the hybridized electronic states of TM and phosphorous atoms: (i) bonding states are completely empty or filled for Sc- and Co-doped black and blue phosphorenes, leading to nonmagnetic; (ii) non-bonding d states are partially occupied for Ti-, V-, Cr-, Mn-, Fe- and Ni-doped black and blue phosphorenes, giving rise to large and localized spin moments. These results provide a new route for the potential applications of dilute magnetic semiconductor and half-metal in spintronic devices by employing black and blue phosphorenes. PACS numbers: 73.22.-f, 75.50.Pp, 75.75. + a. PMID:26858159

  6. Dilute Magnetic Semiconductor and Half-Metal Behaviors in 3 d Transition-Metal Doped Black and Blue Phosphorenes: A First-Principles Study

    NASA Astrophysics Data System (ADS)

    Yu, Weiyang; Zhu, Zhili; Niu, Chun-Yao; Li, Chong; Cho, Jun-Hyung; Jia, Yu

    2016-02-01

    We present first-principles density-functional calculations for the structural, electronic, and magnetic properties of substitutional 3 d transition metal (TM) impurities in two-dimensional black and blue phosphorenes. We find that the magnetic properties of such substitutional impurities can be understood in terms of a simple model based on the Hund's rule. The TM-doped black phosphorenes with Ti, V, Cr, Mn, Fe, and Ni impurities show dilute magnetic semiconductor (DMS) properties while those with Sc and Co impurities show nonmagnetic properties. On the other hand, the TM-doped blue phosphorenes with V, Cr, Mn, and Fe impurities show DMS properties, with Ni impurity showing half-metal properties, whereas Sc- and Co-doped systems show nonmagnetic properties. We identify two different regimes depending on the occupation of the hybridized electronic states of TM and phosphorous atoms: (i) bonding states are completely empty or filled for Sc- and Co-doped black and blue phosphorenes, leading to nonmagnetic; (ii) non-bonding d states are partially occupied for Ti-, V-, Cr-, Mn-, Fe- and Ni-doped black and blue phosphorenes, giving rise to large and localized spin moments. These results provide a new route for the potential applications of dilute magnetic semiconductor and half-metal in spintronic devices by employing black and blue phosphorenes. PACS numbers: 73.22.-f, 75.50.Pp, 75.75. + a

  7. Synthesis and characterization of three-dimensional transition metal ions doped zinc oxide based dilute magnetic semiconductor thin films

    NASA Astrophysics Data System (ADS)

    Samanta, Kousik

    Dilute magnetic semiconductors (DMS), especially 3d-transition metal (TM) doped ZnO based DMS materials are the most promising candidates for optoelectronics and spintronics applications; e.g. in spin light emitting diode (SLED), spin transistors, and spin field effect transistors (SFET), etc. In the present dissertation, thin films of Zn1-xTMxO (TM = Co2+, Cu2+, and Mn2+) were grown on (0001) oriented Al2O3 substrates by pulsed laser deposition (PLD) technique. The films were highly c-axis oriented, nearly single crystalline, and defects free for a limited concentration of the dilution of transition metal ions. In particular, we have obtained single crystalline phases of Zn1-xTMxO thin films for up to 10, 3, and 5 stoichiometric percentages of Co2+, Cu2+, and Mn2+ respectively. Raman micro-probe system was used to understand the structural and lattice dynamical properties at different physical conditions. The confinement of optical phonons in the disorder lattice was explained by alloy potential fluctuation (APF) using a spatial correlation (SC) model. The detailed analysis of the optical phonon behavior in disorder lattice confirmed the substitution of the transition metal ions in Zn 2+ site of the ZnO host lattice. The secondary phases of ZnCo 2O4, CuO, and ZnMn2O4 were detected in higher Co, Cu, and Mn doped ZnO thin films respectively; where as, XRD did not detect these secondary phases in the same samples. Room temperature ferromagnetism was observed in Co2+ and Cu2+ ions doped ZnO thin films with maximum saturation magnetization (Ms) of 1.0 and 0.76 muB respectively. The origin of the observed ferromagnetism in Zn1-xCoxO thin films was tested by the controlled introduction of shallow donors (Al) in Zn0.9-x Co0.1O:Alx (x = 0.005 and 0.01) thin films. The saturation magnetization for the 10% Co-doped ZnO (1.0 muB /Co) at 300K reduced (˜0.25 muB/Co) due to Al doping. The observed ferromagnetism and the reduction due to Al doping can be explained by the Bound

  8. Magneto-optical properties in diluted magnetic semiconductors Cd 0.65-yMn 0.35Ni yTe single crystals

    NASA Astrophysics Data System (ADS)

    Hwang, Y. H.; Kim, H. K.; Cho, S.; Um, Y. H.; Park, H. Y.

    2007-03-01

    We investigated the magneto-optical properties of diluted magnetic semiconductor Cd 0.65-yMn 0.35Ni yTe single crystals grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of y<0.06. The fundamental enegy gap was increased and the lattice constant was decreased showing inverse relationship with the band gap energy with increasing Ni contents. The Verdet constant increased with increasing y, which is consistent with behavior of the magnetization. The Faraday rotation in Cd 0.65-yMn 0.35Ni yTe crystals was increased as Ni contents was increased, which is due to the increasing of magnetization with Ni contents.

  9. La(Zn1‑2xMnxCux)AsO: A 1111-type diluted magnetic semiconductor with manganese and copper codoping at Zn sites

    NASA Astrophysics Data System (ADS)

    Guo, Shengli; Zhao, Yao; Gong, Xin; Man, Huiyuan; Ding, Cui; Zhi, Guoxiang; Fu, Licheng; Gu, Yilun; Wang, Hangdong; Chen, Bin; Guo, Yang; Ning, F. L.

    2016-06-01

    We report the successful synthesis and characterization of a new layered diluted magnetic semiconductor (DMS) La(Zn,Mn,Cu)AsO which is isostructural to Fe-based “1111” superconductor. Mn and Cu are codoped into the same Zn sites to provide local moments and carriers, respectively. A ferromagnetic transition with the highest T C of ∼ 8 K has been observed for x = 0.150 from magnetization measurements. Iso-thermal magnetization plots show that the compound has a coercive field, ∼ 500 Oe, much smaller than that in (La,Ba)(Zn,Mn)AsO. The resistivity of all samples display semiconducting behavior with the doping level up to 15%.

  10. Microstructures, magnetic and electric properties of diluted magnetic semiconductors InTe{sub 1−x} Fe{sub x} (Co{sub x})

    SciTech Connect

    El-Sayed, Karimat; Sedeek, K.; Heiba, Z.K.; Hantour, H.H.

    2013-06-01

    Highlights: ► The prepared InTe{sub 0.9}Fe{sub 0.1} was found to be ferromagnetic at room temperature and can be characterized as diluted magnetic semiconductors. ► The presence of staking faults, various types of defects, strained lattice, grain boundaries and the impurity of minor non-magnetic phase were suggested to participate in high temperature ferromagnetism. - Abstract: InTe compound doped by 10% of Fe or Co respectively was synthesized. X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), vibrating sample magnetometer (VSM) and Kiethley electrometer were used for characterizing the prepared samples. XRD show the presence of InTe{sub 0.9}Fe{sub 0.1} or InTe{sub 0.9}Co{sub 0.1} together with minor In{sub 4}Te{sub 3} phase. InTe{sub 0.9}Fe{sub 0.1} is ferromagnetic with high Curie and high blocking temperature, while InTe{sub 0.9}Co{sub 0.1} is antiferromagnetic with two high Neels temperatures. σRT of InTe{sub 0.9}Fe{sub 0.1} and InTe{sub 0.9}Co{sub 0.1} are greater than those of InTe. The higher conductivity is due to the higher carrier's density obtained from the interaction of the sp-d orbitals, of the electric and magnetic system. The presence of In{sub 4}Te{sub 3} minor phase and different kinds of defects are taking major roles in the formation of high Tc ferromagnetism and antiferromagnetism.

  11. Structural, optical, and magnetic properties of Cu- and Ni-codoped CdO dilute magnetic nanocrystalline semiconductor: effect of hydrogen post-treatment

    NASA Astrophysics Data System (ADS)

    Dakhel, A. A.; Bououdina, M.

    2015-06-01

    Cadmium oxide codoped with Cu and Ni ions powders was synthesised by thermal co-decomposition of a mixture of cadmium, copper, and nickel acetylacetonates. The mass ratio of Cu/Cd was fixed, while the Ni/Cd mass ratio was varied systematically. The purpose of the present study is to prepare powders having room-temperature ferromagnetic (RT-FM) properties. X-ray fluorescence (XRF) and X-ray diffraction (XRD) confirm the purity and the formation of single nanocrystalline structure of the as-prepared powders. The energy bandgap of the as-prepared powders was found to vary slightly and then increases by 3.96-38.02 % after post-H2-treatment. Magnetic measurements reveal that all as-prepared doped CdO powders gained partial (RT-FM) properties. Furthermore, the created RT-FM is dependent on the Ni% doping level. After annealing under H2 gas, a strong enhancement of RT-FM was observed, especially for 1.2 % Ni-doping-level powder where the whole powder became ferromagnetic with coercivity, remanence, and saturation magnetisation of 249.2 Oe, 4.52 memu/g, and 14.57 memu/g, respectively, representing an increase by ~241.3, 1062, and 1700 %, respectively, in comparison with the as-prepared sample. Thus, it was proved, for the first time, the possibility of producing of codoped CdO with RT-FM, where the magnetic characteristics can be tailored by doping and post-treatment under H2 atmosphere, thus a new potential candidate for dilute magnetic semiconductor (DMS).

  12. - and Photo-Modulation Studies of Semiconductors: I. Diluted Magnetic Semiconductors. I. Gallium-Arsenide - - Arsenide, Zinc-Selenide and Cadmium - Manganese - Telluride Heterostructures.

    NASA Astrophysics Data System (ADS)

    Lee, Yung-Rai

    1987-09-01

    The reflectivity and transmission spectra of the diluted magnetic semiconductors (DMS) were investigated using piezo- and photo-modulation techniques. The spectra for Cd_{rm 1-x}Mn _{rm x}Te and Zn _{rm 1-x}Mn _{rm x}Te show a characteristic exciton A of the zinc blende DMS. The energy E _{A}, linear in x, is given by 1.595 + 1.592x (eV) for Cd_{rm 1-x}Mn_{rm x} Te and 2.376 + 0.820x (eV) for Zn_ {rm 1-x}Mn_{ rm x}Te at liquid helium temperature, yielding E _{A} = 3.187(3.196) eV for the "hypothetical" zinc blende MnTe. For the wurtizite DMS's, such as Cd_{rm 1-x} Mn_{rm x}Se, signatures characteristic of the crystal field split valence band--the A and the B exciton--are observed for electric vector {rm (vec{E}) } perpendicular and parallel to the c -axis, respectively. For x <=q 0.35, Zn _{rm 1-x}Mn _{rm x}Se has the zinc blende structure; correspondingly only one exciton feature appears in the spectrum. For x > 0.35, two exciton features are observed consistent with the wurtzite structure of Zn_{rm 1-x}Mn _{rm x}Se for higher x. A signature with a sign opposite to that of free exciton is observed at ~ 2.2 eV for Cd _{rm 1-x}Mn _{rm x}Te and Cd _{rm 1-x}Mn_ {rm x}Se for x > 0.4 and for all x in Zn_{rm 1 -x}Mn_{rm x} Te and Zn_{rm 1-x} Mn_{rm x}Se. The feature, identified with a Mn^{2+} internal transition, shows no x dependence. In addition, we have observed signatures associated with imperfections in the crystals. In the magnetoreflectivity measurements, the Mn^{2+} transition fails to show any observable Zeeman shift or splitting when examined in magnetic fields up to 15.58 T. In contrast, the free exciton exhibits huge Zeeman splittings, a consequence of the large Mn^{2+}-band electron exchange interaction. These observations favor the assignment of ^6 A_1(^6 S) to ^4 T _1(^4 G) to the 2.2 eV Mn ^{2+} transition where the levels are associated with the crystal-field-split 3 d ^5 manifold of Mn^{2+ }. We have also applied the piezo- and photo

  13. Structural, electrical and magnetic properties of (Fe, Co) co-doped SnO2 diluted magnetic semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Mehraj, Sumaira; Ansari, M. Shahnawaze; Alimuddin

    2015-01-01

    Nanostructures (NSs) of basic composition Sn1-xFex/2Cox/2O2 with x=0.00, 0.04, 0.06, 0.08 and 0.1 were synthesized by citrate-gel route and characterized to understand their structural, electrical and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase rutile type tetragonal structure. The crystallite sizes calculated by using Williamson Hall were found to decrease with increasing doping level. In addition to the fundamental Raman peaks of rutile SnO2, the other three weak Raman peaks at about 505, 537 and 688 cm-1 were also observed. Field emission scanning electron microscopy studies showed the emergence of structural transformation. Electric properties such as dc electrical resistivity as a function of temperature and ac conductivity as a function of frequency were also studied. The variation of dielectric properties with frequency reveals that the dispersion is due to Maxwell-Wagner type of interfacial polarization in general. Hysteresis loops were clearly observed in M-H curves of Fe and Co co-doped SnO2 NSs. However, pure SnO2 nanoparticles (NPs) showed paramagnetic behaviour which vanished at higher values of magnetic field. The grain and grain boundary contribution in the conduction process is estimated through complex impedance plot fitted with non-linear least square (NLLS) approach which shows that the role of grain boundaries increases rapidly as compared to the grain volume with the increase of Fe and Co ions in to system.

  14. IV-VI diluted magnetic semiconductor Ge{sub 1-x}Mn{sub x}Te epilayer grown by molecular beam epitaxy

    SciTech Connect

    Fukuma, Y.; Goto, K.; Senba, S.; Miyawaki, S.; Asada, H.; Koyanagi, T.; Sato, H.

    2008-03-01

    Growth of the IV-VI diluted magnetic semiconductor Ge{sub 1-x}Mn{sub x}Te by molecular beam epitaxy is reported. The epitaxial growth of Ge{sub 1-x}Mn{sub x}Te (x=0.13) on BaF{sub 2} (111) with a GeTe buffer layer is confirmed by x-ray diffraction and reflection high-energy electron diffraction. The ferromagnetic order is clearly established by the magnetization and magnetotransport measurements. The Curie temperature of 100 K is obtained for the hole concentration of 7.86x10{sup 20} cm{sup -3}. The existence of the strong p-d exchange which gives rise to the ferromagnetic order is revealed by the hard x-ray photoemission measurements.

  15. μSR investigation of a new diluted magnetic semiconductor Li(Zn,Mn,Cu)As with Mn and Cu codoping at the same Zn sites.

    PubMed

    Guo, S L; Zhao, Y; Man, H Y; Ding, C; Gong, X; Zhi, G X; Fu, L C; Gu, Y L; Frandsen, B A; Liu, L; Cheung, S C; Munsie, T J; Wilson, M N; Cai, Y P; Luke, G M; Uemura, Y J; Ning, F L

    2016-09-14

    We report the successful synthesis and characterization of a new type I-II-V bulk form diluted magnetic semiconductor (DMS) Li(Zn,Mn,Cu)As, in which charge and spin doping are decoupled via (Cu,Zn) and (Mn,Zn) substitution at the same Zn sites. Ferromagnetic transition temperature up to  ∼33 K has been observed with a coercive field  ∼40 Oe for the 12.5% doping level. μSR measurements confirmed that the magnetic volume fraction reaches nearly 100% at 2 K, and the mechanism responsible for the ferromagnetic interaction in this system is the same as other bulk form DMSs. PMID:27401041

  16. K and Mn co-doped BaCd2As2: A hexagonal structured bulk diluted magnetic semiconductor with large magnetoresistance

    NASA Astrophysics Data System (ADS)

    Yang, Xiaojun; Li, Yuke; Zhang, Pan; Jiang, Hao; Luo, Yongkang; Chen, Qian; Feng, Chunmu; Cao, Chao; Dai, Jianhui; Tao, Qian; Cao, Guanghan; Xu, Zhu-An

    2013-12-01

    A bulk diluted magnetic semiconductor was found in the K and Mn co-doped BaCd2As2 system. Different from recently reported tetragonal ThCr2Si2-structured II-II-V based (Ba,K)(Zn,Mn)2As2, the Ba1-yKyCd2-xMnxAs2 system has a hexagonal CaAl2Si2-type structure with the Cd2As2 layer forming a honeycomb-like network. The Mn concentration reaches up to x ˜ 0.4. Magnetization measurements show that the samples undergo ferromagnetic transitions with Curie temperature up to 16 K. With low coercive field of less than 10 Oe and large magnetoresistance of about -70%, the hexagonal structured Ba1-yKyCd2-xMnxAs2 can be served as a promising candidate for spin manipulations.

  17. Influence of Fe doping on the structural, optical and magnetic properties of ZnS diluted magnetic semiconductor

    NASA Astrophysics Data System (ADS)

    Saikia, D.; Raland, RD.; Borah, J. P.

    2016-09-01

    Fe doped ZnS nanoparticles with different concentrations of Fe, synthesized by microwave assisted co-precipitation method have been reported. The incorporation of Fe2+ and Fe3+ ions into ZnS lattice are confirmed by X-ray diffraction (XRD) and Electron Paramagnetic resonance (EPR) study. XRD and High Resolution Transmission electron Microscope (HRTEM) results confirm the phase purity of the samples and indicate a reduction of the particle size with increase in Fe concentration. EDAX analysis confirms the presence of Zn, S and Fe in the samples. A yellow-orange emission peak is observed in Photoluminescence (PL) spectra which exhibits the Characteristic 4T2 (4G)-6A1 (6S) transition of Fe3+ ion. The room temperature magnetic studies as analyzed from M-H curves were investigated from vibrating samples magnetometer (VSM) which shows a weak ferro and superparamagnetic like behavior in 1% and 3% Fe-doped ZnS nanocrystals, whereas; at 10% Fe-doping concentrations, antiferromagnetism behavior is achieved. The ZFC-FC measurement reveals that the blocking temperature of the nanoparticle is above the room temperature.

  18. Enhancement of two photon absorption with Ni doping in the dilute magnetic semiconductor ZnO crystalline nanorods

    SciTech Connect

    Rana, Amit Kumar; Kumar, Yogendra; Arjunan, M.S.; Sen, Somaditya; Shirage, Parasharam M. E-mail: paras.shirage@gmail.com; J, Aneesh; Adarsh, K. V.

    2015-12-07

    In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient (β) increases by as much as 14 times, i.e., 7.6 ± 0.4 to 112 ± 6 cm/GW, when the Ni doping is increased from 0% to 10%. The substantial enhancement in β is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UV-Vis and photoluminescence spectroscopies, continuously redshift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.

  19. Enhancement of two photon absorption with Ni doping in the dilute magnetic semiconductor ZnO crystalline nanorods

    NASA Astrophysics Data System (ADS)

    Rana, Amit Kumar; J, Aneesh; Kumar, Yogendra; M. S, Arjunan; Adarsh, K. V.; Sen, Somaditya; Shirage, Parasharam M.

    2015-12-01

    In this letter, we have investigated the third-order optical nonlinearities of high-quality Ni doped ZnO nanorods crystallized in wurtzite lattice, prepared by the wet chemical method. In our experiments, we found that the two photon absorption coefficient (β) increases by as much as 14 times, i.e., 7.6 ± 0.4 to 112 ± 6 cm/GW, when the Ni doping is increased from 0% to 10%. The substantial enhancement in β is discussed in terms of the bandgap scaling and Ni doping. Furthermore, we also show that the optical bandgap measured by UV-Vis and photoluminescence spectroscopies, continuously redshift with increasing Ni doping concentration. We envision that the strong nonlinear optical properties together with their dilute magnetic effects, they form an important class of materials for potential applications in magneto-optical and integrated optical chips.

  20. Electronic and magnetic properties of a new 2D diluted magnetic semiconductor La1 - x Ba x Zn1 - x Mn x AsO from Ab initio calculations

    NASA Astrophysics Data System (ADS)

    Bannikov, V. V.; Ivanovskii, A. L.

    2013-12-01

    Very recently, on the example of hole- and spin-doped semiconductor LaZnAsO, quite an unexpected area of potential applications of quasi-two-dimensional 1111-like phases was proposed (C. Ding et al., Phys. Rev. B 88, 041102R (2013)) as a promising platform for searching for new diluted magnetic semiconductors (DMSs). In this work, by means of the ab initio calculations, we have examined in detail the electronic and magnetic properties of LaZnAsO alloyed with Ba and Mn. Our results demonstrate that Ba or Mn doping transforms the parent non-magnetic semiconductor LaZnAsO into a non-magnetic metal or a magnetic semiconductor, respectively. On the other hand, the joint effect of these dopants (i.e., co-doping Ba + Mn) leads to transition of La0.89Ba0.11Zn0.89Mn0.11AsO into the state of magnetic metal, which is formed by alternately stacked semiconducting non-magnetic blocks [La0.89Ba0.11O] and metallic-like magnetic blocks [Zn0.89Mn0.11As].

  1. (La1-xBax)(Zn1-xMnx)AsO: A two-dimensional 1111-type diluted magnetic semiconductor in bulk form

    NASA Astrophysics Data System (ADS)

    Ding, Cui; Man, Huiyuan; Qin, Chuan; Lu, Jicai; Sun, Yunlei; Wang, Quan; Yu, Biqiong; Feng, Chunmu; Goko, T.; Arguello, C. J.; Liu, L.; Frandsen, B. A.; Uemura, Y. J.; Wang, Hangdong; Luetkens, H.; Morenzoni, E.; Han, W.; Jin, C. Q.; Munsie, T.; Williams, T. J.; D'Ortenzio, R. M.; Medina, T.; Luke, G. M.; Imai, T.; Ning, F. L.

    2013-07-01

    We report the synthesis and characterization of a bulk diluted magnetic semiconductor (La1-xBax)(Zn1-xMnx)AsO (0 ⩽ x ⩽ 0.2) with a layered crystal structure identical to that of the 1111-type FeAs superconductors. No ferromagnetic order occurs with (Zn,Mn) substitution in the parent compound LaZnAsO without charge doping. Together with carrier doping via (La,Ba) substitution, a small amount of Mn substituting for Zn results in ferromagnetic order with TC up to ˜40 K, although the system remains semiconducting. Muon spin relaxation measurements confirm the development of ferromagnetic order in the entire volume, with the relationship between the internal field and TC consistent with the trend found in (Ga,Mn)As and the 111-type Li(Zn,Mn)As and the 122-type (Ba,K)(Zn,Mn)2As2 systems.

  2. Pressure effect on the magnetism of the diluted magnetic semiconductor (B a1 -xKx ) (Zn1-yM ny ) 2A s2 with independent spin and charge doping

    NASA Astrophysics Data System (ADS)

    Sun, F.; Li, N. N.; Chen, B. J.; Jia, Y. T.; Zhang, L. J.; Li, W. M.; Zhao, G. Q.; Xing, L. Y.; Fabbris, G.; Wang, Y. G.; Deng, Z.; Uemura, Y. J.; Mao, H. K.; Haskel, D.; Yang, W. G.; Jin, C. Q.

    2016-06-01

    We used x-ray magnetic circular dichroism (XMCD) to probe the ferromagnetic properties of As p -symmetric (4 p ) states in the recently synthesized diluted magnetic semiconductor (B a1 -xKx) (Zn1-yM ny) 2A s2 system under ambient- and high-pressure conditions. The As K -edge XMCD signal scales with the sample magnetization (dominated by Mn) and scales with the ferromagnetic ordering temperature T c , and hence it is representative of the bulk magnetization. The XMCD intensity gradually decreases upon compression and vanishes at around 25 GPa, indicating quenching of ferromagnetism at this pressure. Transport measurements show a concomitant increase in conductivity with pressure, leading to a nearly metallic state at about the same pressure where magnetic order collapses. High-pressure x-ray diffraction shows an absence of structural transitions to 40 GPa. The results indicate that the mobility of doped holes, probed by both transport and x-ray absorption spectroscopy (4 p band broadening), is intimately connected with the mechanism of magnetic ordering in this class of compounds and that its control using external pressure provides an alternative route for tuning the magnetic properties in diluted magnetic semiconductor materials.

  3. Microstructural and Optical properties of transition metal (Cu) doped ZnO diluted magnetic semiconductor nano thin films fabricated by sol gel method

    NASA Astrophysics Data System (ADS)

    Ozturk, Ozgur; Asikuzun, Elif; Tasci, A. Tolga; Arda, Lutfi; Demirozu Senol, Sevim; Celik, Sukru; Terzioglu, Cabir

    Undoped and Cu (Copper) doped ZnO (Zn1-xCuxO) semiconductor thin films were produced by using sol-gel method. Cu was doped 1%, 2%, 3%, 4% and 5% ratio. Methanol and monoethanolamine (MEA) were used as solvent and stabilizer. In this study, the effect of Cu doping was investigated on microstructural and optical properties of ZnO DMS thin films. XRD, SEM, AFM and UV-VIS spectrometer measurements were performed for the microstructural and optical characterization. XRD, SEM and AFM results were showed that all of Cu doped ZnO based thin films have a hexagonal structure. The grain size of Cu doped ZnO thin films and morphology of surface were changed with increasing Cu doping. The optical transmittance of transition metal (Cu) doped ZnO thin films were decreased with doping. Keywords:Diluted Magnetic Semiconductor (DMS), Thin Film, Cu-doping, Bandgap Energy, ZnO. This research has been supported by the Kastamonu University Scientific Research Projects Coordination Department under the Grant No. KU-BAP-05/2015-12 and the Scientific and Technological Research Council of Turkey (TUBITAK) Project No. 114F259.

  4. Weak ferromagnetism and temperature dependent dielectric properties of Zn{sub 0.9}Ni{sub 0.1}O diluted magnetic semiconductor

    SciTech Connect

    Ahmed, Raju; Moslehuddin, A.S.M.; Mahmood, Zahid Hasan; Hossain, A.K.M. Akther

    2015-03-15

    Highlights: • Single phase wurtzite structure was confirmed from XRD analysis. • Weak ferromagnetic behaviour at room temperature. • Pure semiconducting properties confirmed from temperature dependent conductivity. • Smaller dielectric properties at higher frequency. • Possible potential application in high frequency spintronic devices. - Abstract: In this study the room temperature ferromagnetic behaviour and dielectric properties of ZnO based diluted magnetic semiconductor (DMS) have been investigated using nominal chemical composition Zn{sub 0.9}Ni{sub 0.1}O. The X-ray diffraction analysis confirmed formation of single phase hexagonal wurtzite structure. An increase in grain size with increasing sintering temperature was observed from scanning electron microscopy. Field dependent DC magnetization values indicated dominant paramagnetic ordering along with a slight ferromagnetic behaviour at room temperature. Frequency dependent complex initial permeability showed some positive values around 12 at room temperature. In dielectric measurement, an increasing trend of complex permittivity, loss tangent and ac conductivity with increasing temperature were observed. The temperature dependent dispersion curves of dielectric properties revealed clear relaxation at higher temperature. Frequency dependent ac conductivity was found to increase with frequency whereas complex permittivity and loss tangent showed an opposite trend.

  5. Generalized gradient calculations of magneto-electronic properties for diluted magnetic semiconductors ZnMnS and ZnMnSe

    NASA Astrophysics Data System (ADS)

    Méçabih, S.; Benguerine, K.; Benosman, N.; Abbar, B.; Bouhafs, B.

    2008-10-01

    Using the first-principles method, we investigate the electronic and magnetic properties of the diluted magnetic semiconductors Zn 1-xMn xS and Zn 1-xMn xSe with 25% of Mn. The calculations are performed by a developed full-potential augmented plane wave plus local orbitals (FP-L/APW+lo) method within the spin density functional theory. As exchange-correlation potential we used the new generalized gradient approximation GGA form. Structural properties are determined from the total energy calculations. We show that the cohesive energy of ZnMnS and ZnMnSe exceeds that of the parent elements ZnS and ZnSe. We discuss the electronic structures, total and partial densities of states and local moments. We have calculated the Mn 3d spin-exchange splitting energies Δ x( d), which reflect the effective potential of the majority and the minority spin. From the charge spin densities calculations, we study the nature of the bonding and the effect of the Mn 3d states on these densities. Furthermore, we found that p-d hybridization reduces the local moment of Mn from its free space value of 5.0 μB.

  6. Characterization of n-GaN dilute magnetic semiconductors by cobalt ions implantation at high-fluence

    NASA Astrophysics Data System (ADS)

    Husnain, G.; Shu-De, Yao; Ahmad, Ishaq; Rafique, H. M.; Mahmood, Arshad

    2012-03-01

    In this study, we present the structural and magnetic characteristics of cobalt ions implantation at a high-fluence (5×1016 cm-2) into n-GaN epilayer of thickness about 1.6 μm. The n-GaN was grown on sapphire by metal organic chemical vapor deposition (MOCVD). Rutherford backscattering channeling was used for the structural study. After implantation, samples were annealed at 700, 800 and 900 °C by rapid thermal annealing in ambient N2. XRD measurements did not show any secondary phase or metal related-peaks. High resolution X-ray diffraction (HRXRD) was performed as well to characterize structures. Well-defined hysteresis loops were observed at 5 K and room temperature using alternating gradient magnetometer AGM and Superconducting Quantum Interference Device (SQUID) magnetometer. Temperature-dependent magnetization indicated magnetic moment at the lowest temperatures and retained magnetization up to 380 K for cobalt-ion-implanted samples.

  7. Rutile-type Co doped SnO2 diluted magnetic semiconductor nanoparticles: Structural, dielectric and ferromagnetic behavior

    NASA Astrophysics Data System (ADS)

    Mehraj, Sumaira; Shahnawaze Ansari, M.; Alimuddin

    2013-12-01

    Nanoparticles of basic composition Sn1-xCoxO2 (x=0.00, 0.01, 0.03, 0.05 and 0.1) were synthesized through the citrate-gel method and were characterized for structural properties using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). XRD analysis of the powder samples sintered at 500 °C for 12 h showed single phase rutile type tetragonal structure and the crystallite size decreased as the cobalt content was increased. FT-IR spectrum displayed various bands that came due to fundamental overtones and combination of O-H, Sn-O and Sn-O-Sn entities. The effect of Co doping on the electrical and magnetic properties was studied using dielectric spectroscopy and vibrating sample magnetometer (VSM) at room temperature. The dielectric parameters (ε, tan δ and σac) show their maximum value for 10% Co doping. The dielectric loss shows anomalous behavior with frequency where it exhibits the Debye relaxation. The variation of dielectric properties and ac conductivity with frequency reveals that the dispersion is due to the Maxwell-Wagner type of interfacial polarization in general and hopping of charge between Sn2+ and Sn4+ as well as between Co2+ and Co3+ ions. The complex impedance analysis was used to separate the grain and grain boundary contributions in the system which shows that the conduction process in grown nanoparticles takes place predominantly through grain boundary volume. Hysteresis loops were observed clearly in M-H curves from 0.01 to 0.1% Co doped SnO2 samples. The saturation magnetization of the doped samples increased slightly with increase of Co concentration. However pure SnO2 displayed paramagnetism which vanished at higher values of magnetic field.

  8. Enhanced Room Temperature Ferromagnetism by Fe Doping in Zn0.96Cu0.04O Diluted Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Muthukumaran, S.; Ashokkumar, M.

    2016-02-01

    Zn0.96- x Cu0.04Fe x O (0 ≤ x ≤ 0.04) nanoparticles synthesized via the sol-gel technique had a hexagonal wurtzite ZnO structure without any Fe/Cu-related secondary phases. The crystallite size was reduced from Fe = 0% (23 nm) to Fe = 4% (16 nm) due to the suppression of grain surface growth by foreign impurities. Doping of higher Fe concentrations into Zn-Cu-O suppressed the ultra-violet (UV) emission band and balanced the defect-related visible emissions. The decrease of the UV and green emission intensity ratio ( I UV/ I green) and the UV and blue emission intensity ratio ( I UV/ I blue) in photoluminescence spectra implied an increase of defect states with the increase of Fe concentrations. All the samples showed clear room temperature ferromagnetism. The saturation magnetization was increased by Fe co-doping which was attributed to the interaction between Fe-Fe ions. X-ray photoelectron spectra confirmed the absence of secondary phases like Fe3O4.

  9. Electronic structure and magnetism in some transition metal nitrides: Manganese-doped scandium nitride, dilute magnetic semiconductor and chromium nitride, Mott insulator

    NASA Astrophysics Data System (ADS)

    Herwadkar, Aditi A.

    The thesis presented here deal with calculations of electronic and magnetic properties of transition metal based materials. Electronic structure of Mn-doped ScN: a possible new magnetic semiconductor. We performed fully relaxed full-potential linear muffin-tin orbital method calculations of Mn-doped ScN using a supercell approach. We found that a t2g like defect level exists in the gap and gives rise to a magnetic moment between 2 an 3 muB. Calculations for 64 atom cells with two Mn in 1st-4th neighbor positions indicated a preference for ferromagnetic coupling. By mapping the energy differences on a Heisenberg Hamiltonian and assuming interactions with distant atoms except those in the adjacent unit cells are zero, we extracted the exchange interactions, which were found to be rather large and indicate a Curie temperature above room temperature even for only 3% Mn. Calculations of the miscibility indicated only 1% equilibrium miscibility at typical growth temperatures. However, non-equilibrium growth techniques have shown that in practice mixed alloys up to 26% Mn can be grown. We also studied the effect of n-type doping. Unexpectedly, Mn defects in the negative charge state still have an even larger magnetic moment with an increase in the eg state contribution. Subsequently, we carried out further calculations of the exchange interactions using non-collinear magnetic configurations in which the spin is slowly rotated. It was found that the previous calculations overestimate the J 0 = sumi J0i, i.e. the sum of all interactions connected to a given site, by about 30%. Further studies using the Liechtenstein linear response approach show that the latter is a sum over many long range interactions extending significantly beyond the range of the cells we had used. In this approach the long range interactions are obtained by Fourier transform of the Jij (k) for a mesh of k-points in the supercell. The nearest neighbor interactions are found to be an order of magnitude

  10. Characteristic Behavior of ESR Linewidth in Cr-doped PbTe-based Diluted Magnetic Semiconductors in the Vicinity of Ferromagnetic Ordering Transition

    NASA Astrophysics Data System (ADS)

    Zvereva, E.; Savelieva, O.; Ibragimov, S.; Slyn'ko, E.; Slyn'ko, V.

    2011-12-01

    Here we report on magnetization (T = 1.8-400 K, B≤7 T) and X-band ESR study (f = 9.1-9.6 GHz, T = 90-450 K) for Pb1-yCryTe ferromagnetic semiconductor and two new PbTe-based semiconductors Pb1-x-ySnxCryTe and Pb1-x-yMgxCryTe in the vicinity of the transition to ferromagnetic state. It was found that these semiconductors demonstrate ferromagnetism at temperatures higher than room temperature. The Curie temperature TC varies in a wide range (150-390 K) depending on the matrix composition and chromium content. In the paramagnetic phase the ESR spectra show a single asymmetrical line of Dysonian shape due to skin effect, typical of conducting materials. Regardless of matrix composition the effective g-factor tends to the saturation value g = 2.08±0.02 and the linewidth is ΔB≈0.08 T at the highest temperature limit. Upon approaching TC from above g-factor slowly increases, while the linewidth falls approximately two times and passes through the minimum at T*≈1.2TC. In the vicinity of TC the ESR parameters show distinct anomalies, which were associated with presence of strong magnetic fluctuation at an onset of FM ordering.

  11. Atomically thin dilute magnetism in Co-doped phosphorene

    NASA Astrophysics Data System (ADS)

    Seixas, L.; Carvalho, A.; Castro Neto, A. H.

    2015-04-01

    Two-dimensional dilute magnetic semiconductors can provide fundamental insights into the very nature of magnetic order and their manipulation through electron and hole doping. Besides the fundamental interest, due to the possibility of control of charge density, they can be extremely important in spintronics applications such as spin valve and spin-based transistors. In this paper, we studied a two-dimensional dilute magnetic semiconductor consisting of a phosphorene monolayer doped with cobalt atoms in substitutional and interstitial defects. We show that these defects can be stabilized and are electrically active. Furthermore, by including holes or electrons by a potential gate, the exchange interaction and magnetic order can be engineered, and may even induce a ferromagnetic-to-antiferromagnetic phase transition in p -doped phosphorene. At a Co concentration of 2.7%, we estimate a Curie temperature of TCMF A=466 K in the mean-field approximation.

  12. Electronic and magnetic properties of a new diluted magnetic semiconductor Li(Zn,TM)As (TM:V, Cr, Mn, Fe, Co and Ni)

    NASA Astrophysics Data System (ADS)

    Tao, H. L.; Lin, L.; Zhang, Z. H.; He, M.; Song, B.

    2016-07-01

    First-principles calculations were performed to study electronic structures and magnetic properties of transition metal (TM) doped LiZnAs system. V, Mn, Fe and Co doped LiZnAs preferred anti-ferromagnetic states while no magnetisms were found for Cr and Ni-doped LiZnAs system. In contrast, V/Li, Cr/Li, Mn/Li, Fe/Li and Co/Li codoped LiZnAs preferred ferromagnetic couplings between the TM atoms other than the anti-ferromagnetic states. Thus off-stoichiometry of Li is very essential for the preparation of ferromagnetic LiZnAs materials. For Ni/Li-codoped LiZnAs, anti-ferromagnetic is more stable, which is resulted from the through-bond spin polarization mechanism.

  13. Theory of carrier mediated ferromagnetism in dilute magnetic oxides

    SciTech Connect

    Calderon, M.J. Das Sarma, S.

    2007-11-15

    We analyze the origin of ferromagnetism as a result of carrier mediation in diluted magnetic oxide semiconductors in the light of the experimental evidence reported in the literature. We propose that a combination of percolation of magnetic polarons at lower temperature and Ruderman-Kittel-Kasuya-Yosida ferromagnetism at higher temperature may be the reason for the very high critical temperatures measured (up to {approx}700 K)

  14. Structural, optical and magnetic properties of Zn 1- xCo xO dilute magnetic semiconductors thin films by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Yang, Shanying; Man, B. Y.; Liu, M.; Chen, C. S.; Gao, X. G.; Wang, C. C.; Hu, B.

    2010-09-01

    We fabricated Zn 1- xCo xO ( x=0.05) thin films on sapphire (0 0 0 1) substrates by the pulsed laser deposition (PLD) method at various temperatures in an oxygen-deficient ambient. X-ray diffraction (XRD) spectra, UV-vis transmittance spectra, X-ray photoelectron spectroscopy and photoluminescence (PL) were used for charecterization. All samples possessed the wurtzite structure with the preferential c-axis orientation; PL located at about 418, 450 and 471 nm was observed; Co 2+ ions incorporated into the ZnO lattice with substitution for Zn 2+ ions, oxygen vacancies, oxygen antisites and Zn interstitials existed in the as-samples. Results of magnetic property of the films investigated by an alternating gradient magnetometer (AGM) indicated that all samples take on room temperature ferromagnetism. It suggested that the ferromagnetism originated from the Co 2+-Co 2+ exchange interaction related to oxygen vacancies, oxygen antisites and Zn interstitials.

  15. (Ba1-xKx)(Cu2-xMnx)Se2: A copper-based bulk form diluted magnetic semiconductor with orthorhombic BaCu2S2-type structure

    NASA Astrophysics Data System (ADS)

    Guo, Shengli; Man, Huiyuan; Gong, Xin; Ding, Cui; Zhao, Yao; Chen, Bin; Guo, Yang; Wang, Hangdong; Ning, F. L.

    2016-02-01

    A new copper-based bulk form diluted magnetic semiconductor (DMS) (Ba1-xKx)(Cu2-xMnx)Se2 (x=0.075, 0.10, 0.125, and 0.15) with TC ∼18 K has been synthesized. K substitution for Ba introduces hole-type carriers, while Mn substitution for Cu provides local spins. Different from previous reported DMSs, this material crystallizes into orthorhombic BaCu2S2-type crystal structure. No ferromagnetism is observed when only doping Mn, and clear ferromagnetic transition and hysteresis loop have been observed as K and Mn are codoped into the parent compound BaCu2Se2.

  16. The synthesis and characterization of 1111-type diluted magnetic semiconductors (La1-xSrx)(Zn1-xTMx)AsO (TM = Mn, Fe, Co)

    NASA Astrophysics Data System (ADS)

    Lu, Jicai; Man, Huiyuan; Ding, Cui; Wang, Quan; Yu, Biqiong; Guo, Shengli; Wang, Hangdong; Chen, Bin; Han, Wei; Jin, Changqing; Uemura, Yasutomo J.; Ning, Fanlong

    2013-09-01

    The doping effect of Sr and transition metals Mn, Fe, Co into the direct-gap semiconductor LaZnAsO has been investigated. Our results indicate that the single phase ZrCuSiAs-type tetragonal crystal structure is preserved in (La1-xSrx)(Zn1-xTMx)AsO (TM = Mn, Fe, Co) with the doping level up to x = 0.1 . While the system remains semiconducting, doping with Sr and Mn results in ferromagnetic order with T_C\\sim30\\ \\text{K} , and doping with Sr and Fe results in a spin-glass-like state below {\\sim}6\\ \\text{K} with a saturation moment of ˜0.02 μB/Fe, an order of magnitude smaller than the ˜0.4 μB/Mn of Sr- and Mn-doped samples. The same type of magnetic state is observed neither for (Zn,Fe) substitution without carrier doping, nor for Sr- and Co-doped specimens.

  17. Elimination of charge carrier trapping in diluted semiconductors

    NASA Astrophysics Data System (ADS)

    Abbaszadeh, D.; Kunz, A.; Wetzelaer, G. A. H.; Michels, J. J.; Crăciun, N. I.; Koynov, K.; Lieberwirth, I.; Blom, P. W. M.

    2016-06-01

    In 1962, Mark and Helfrich demonstrated that the current in a semiconductor containing traps is reduced by N/Ntr, with N the amount of transport sites, Nt the amount of traps and r a number that depends on the trap energy distribution. For r > 1, the possibility opens that trapping effects can be nearly eliminated when N and Nt are simultaneously reduced. Solution-processed conjugated polymers are an excellent model system to test this hypothesis, because they can be easily diluted by blending them with a high-bandgap semiconductor. We demonstrate that in conjugated polymer blends with 10% active semiconductor and 90% high-bandgap host, the typical strong electron trapping can be effectively eliminated. As a result we were able to fabricate polymer light-emitting diodes with balanced electron and hole transport and reduced non-radiative trap-assisted recombination, leading to a doubling of their efficiency at nearly ten times lower material costs.

  18. Structural and Optical properties of Er doped ZnO diluted magnetic semiconductor nano thin films produced by sol gel method

    NASA Astrophysics Data System (ADS)

    Tasci, A. Tolga; Ozturk, Ozgur; Asikuzun, Elif; Arda, Lutfi; Celik, Sukru; Terzioglu, Cabir

    Undoped and Er doped ZnO (Zn1-xErxO) transparent semiconductor thin films were coated using sol-gel method on non-alkali glass. Erbium was doped 1%, 2%, 3%, 4% and 5% ratio. Methanol and monoethanolamine were used as solvent and stabilizer. In this study, the effect of Er doping was examined on the structural and optical properties of ZnO DMS thin films. XRD, SEM and UV-VIS-NIR spectrometer measurements were performed for the structural and optical characterization. XRD results showed that, all of Er doped ZnO thin films have a hexagonal structure. The optical transmittance of rare earth element (Er) doped ZnO thin films were increased. The Er doped ZnO thin films showed high transparency (>84) in the visible region (400-700 nm). This research has been supported by the Kastamonu University Scientific Research Projects Coordination Department under the Grant No. KUBAP-03/2013-41 and the Scientific and Technological Research Council of Turkey (TUBITAK) Project No. 114F259.

  19. Coherent magnetic semiconductor nanodot arrays

    PubMed Central

    2011-01-01

    In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors. Up to now, lack of reliable methods to obtain high-quality MnGe nanostructures with a desired shape and a good controllability has been a barrier to make these materials practically applicable for spintronic devices. Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility. Magnetotransport experiments reveal that the nanodot arrays possess giant magneto-resistance associated with geometrical effects. The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation. PMID:21711627

  20. First-principles study on half-metallic ferromagnetism in the diluted magnetic semiconductor (DMS) Al1-xMnxP compounds

    NASA Astrophysics Data System (ADS)

    Kervan, Selçuk; Kervan, Nazmiye

    2015-05-01

    We report the half-metallic properties of the Mn-doped AlP compounds using the full-potential linearized augmented plane wave (FPLAPW) method within the generalized gradient approximation (GGA) embedded in WIEN2k code. Geometry optimization for the Al1-xMnxP compounds was carried out for the different Mn concentrations x=0.0, 0.0625, 0.125 and 0.25 using supercell. The calculated band structure and density of states show that the half-metallic ferromagnetism is stable for the x=0.0625, 0.125 and 0.25 with a total magnetization of 4 μB/f.u. The total magnetic moment is mainly due to Mn-d states occurring around the Fermi level. The half-metallic band gaps are 1.70, 1.52 and 1.68 eV for x=0.0625, 0.125 and 0.25, respectively. We also performed GGA with the Hubbard correction (GGA+U) to minimize self-interaction errors.

  1. Sol-gel derived Zn1-xFexS diluted magnetic semiconductor thin films: Compositional dependent room or above room temperature ferromagnetism

    NASA Astrophysics Data System (ADS)

    Goktas, A.

    2015-06-01

    Zn1-xFexS (where x = 0.00, 0.01, 0.03, 0.05, 0.1 and 0.2) thin films were synthesized by sol-gel method. To investigate the origin of room or above room temperature ferromagnetism in these films several tools such as XRD, SEM, XPS, UV-Vis spectrophotometer and SQUİD magnetometer were used. The XRD studies showed that the phase singularity of ZnS zinc blende (hexagonal) structure. The SEM images indicated the homogeneous film surface with no cracking and increased particle size with increasing Fe-doping ratio except for 1 at.% Fe dopant. The presence of Zn, Fe, S, Si and O atoms in the films was observed in EDS spectrum. The XPS studies confirmed that the existence of Fe3+ ions in host ZnS thin films. In the UV-Vis measurements the band gap energy corresponding to the absorption edge was estimated to be approximately in the range of 3.59-2.08 eV, depending on the Fe doping level. The magnetization measurements revealed that the films had paramagnetic or ferromagnetic order depending on Fe doping ratio at 5, 100, 200, 300 and 350 K. The observed room or above room temperature ferromagnetism can be attributed to the strong p-d exchange interaction between Fe3+ d and anion (S2-) p orbitals as well as impurities.

  2. Fermi surfaces and p -d hybridization in the diluted magnetic semiconductor Ba1 -xKx(Zn1-yMny) 2As2 studied by soft x-ray angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Suzuki, H.; Zhao, G. Q.; Zhao, K.; Chen, B. J.; Horio, M.; Koshiishi, K.; Xu, J.; Kobayashi, M.; Minohara, M.; Sakai, E.; Horiba, K.; Kumigashira, H.; Gu, Bo; Maekawa, S.; Uemura, Y. J.; Jin, C. Q.; Fujimori, A.

    2015-12-01

    The electronic structure of the new diluted magnetic semiconductor Ba1-xKx(Zn1-yMny )2As2 (x =0.30 , y =0.15 ) in single crystal form has been investigated by angle-resolved photoemission spectroscopy (ARPES). Measurements with soft x rays clarify the host valence-band electronic structure primarily composed of the As 4 p states. Two hole pockets around the Γ point, a hole corrugated cylinder surrounding the Γ and Z points, and an electron pocket around the Z point are observed, and explain the metallic transport of Ba1-xKx(Zn1-yMny )2As2 . This is contrasted with Ga1-xMnxAs (GaMnAs), where it is located above the As 4 p valence-band maximum (VBM) and no Fermi surfaces have been clearly identified. Resonance soft x-ray ARPES measurements reveal a nondispersive (Kondo-resonance-like) Mn 3 d impurity band near the Fermi level, as in the case of GaMnAs. However, the impurity band is located well below the VBM, unlike the impurity band in GaMnAs, which is located around and above the VBM. We conclude that, while the strong hybridization between the Mn 3 d and the As 4 p orbitals plays an important role in creating the impurity band and inducing high temperature ferromagnetism in both systems, the metallic transport may predominantly occur in the host valence band in Ba1-xKx(Zn1-yMny )2As2 and in the impurity band in GaMnAs.

  3. Detecting excitation and magnetization of individual dopants in a semiconductor.

    PubMed

    Khajetoorians, Alexander A; Chilian, Bruno; Wiebe, Jens; Schuwalow, Sergej; Lechermann, Frank; Wiesendanger, Roland

    2010-10-28

    An individual magnetic atom doped into a semiconductor is a promising building block for bottom-up spintronic devices and quantum logic gates. Moreover, it provides a perfect model system for the atomic-scale investigation of fundamental effects such as magnetism in dilute magnetic semiconductors. However, dopants in semiconductors so far have not been studied by magnetically sensitive techniques with atomic resolution that correlate the atomic structure with the dopant's magnetism. Here we show electrical excitation and read-out of a spin associated with a single magnetic dopant in a semiconductor host. We use spin-resolved scanning tunnelling spectroscopy to measure the spin excitations and the magnetization curve of individual iron surface-dopants embedded within a two-dimensional electron gas confined to an indium antimonide (110) surface. The dopants act like isolated quantum spins the states of which are governed by a substantial magnetic anisotropy that forces the spin to lie in the surface plane. This result is corroborated by our first principles calculations. The demonstrated methodology opens new routes for the investigation of sample systems that are more widely studied in the field of spintronics-that is, Mn in GaAs (ref. 5), magnetic ions in semiconductor quantum dots, nitrogen-vacancy centres in diamond and phosphorus spins in silicon. PMID:20981095

  4. Photoemission and magnetic circular dichroism studies of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Fujimori, Atsushi

    2005-03-01

    Recently, a series of novel ferromagnetic semiconductors have been synthesized using MBE and related techniques and have attracted much attention because of unknown mechanisms of carrier-induced ferromagnetism and potential applications as "spin electronics" devices. Some new materials show ferromagnetism even well above room temperature. Photoemission spectroscopy has been used to study the d orbitals of the dilute transition-metal atoms, mostly Mn, and their hybridization with the host band states [1]. Soft x-ray absorption spectroscopy (XAS) and magnetic circular dichroism (MCD) at the transition-metal 2p-3d absorption edges are useful techniques to study the valence and spin states of the transition-metal atoms. Furthermore, since MCD has different sensitivities to the ferromagnetic and paramagnetic components at different temperatures and magnetic fileds, if the sample is a mixture of ferromagnetic and non-ferromagnetic transition- metal atoms, it can be used to separate the two components and to study their electronic structures. In this talk, results are presented for the prototypical diluted ferromagnetic semiconductor Ga1-xMnxAs [2] and the room-temperature ferromagnets Zn1-xCoxO and Ti1-xCoxO2.I acknowledge collaboration with Y. Ishida, J.-I. Hwang, M. Kobayashi, Y. Takeda, Y. Saitoh, J. Okamoto, T. Okane, Y. Muramatsu, K. Mamiya, T. Koide, A. Tanaka, M. Tanaka, Hayashi, S. Ohya, T. Kondo, H. Munekata, H. Saeki, H. Tabata, T. Kawai, Y. Matsumoto, H. Koinuma, T. Fukumura and M. Kawasaki. This work was supported by a Grant-in-Aid for Scientific Research in Priority Area "Semiconductor nano-spintronics" (14076209) from MEXT, Japan.1. J. Okabayashi et al., Phys. Rev. B 64, 125304 (2001).2. A. Fujimori et al., J. Electron Spectrosc. Relat. Phenom., in press.

  5. Zero-field optical manipulation of magnetic ions in semiconductors.

    PubMed

    Myers, R C; Mikkelsen, M H; Tang, J-M; Gossard, A C; Flatté, M E; Awschalom, D D

    2008-03-01

    Controlling and monitoring individual spins is desirable for building spin-based devices, as well as implementing quantum information processing schemes. As with trapped ions in cold gases, magnetic ions trapped on a semiconductor lattice have uniform properties and relatively long spin lifetimes. Furthermore, diluted magnetic moments in semiconductors can be strongly coupled to the surrounding host, permitting optical or electrical spin manipulation. Here we describe the zero-field optical manipulation of a few hundred manganese ions in a single gallium arsenide quantum well. Optically created mobile electron spins dynamically generate an energy splitting of the ion spins and enable magnetic moment orientation solely by changing either photon helicity or energy. These polarized manganese spins precess in a transverse field, enabling measurements of the spin lifetimes. As the magnetic ion concentration is reduced and the manganese spin lifetime increases, coherent optical control and readout of single manganese spins in gallium arsenide should be possible. PMID:18278049

  6. Polaronic trapping in magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Raebiger, Hannes

    2012-02-01

    GaN doped with iron is an interesting candidate material for magnetic semiconductors, as p-d coupling between the localized Fe-d and extended N-p hole states is expected to facilitate long-range ferromagnetic alignment of the Fe spins [1]. This picture of extended states in GaN:Fe, however, falls apart due to a polaronic localization of the hole carriers nearby the Fe impurities. To elucidate the carrier localization in GaN:Fe and related iron doped III-V semiconductors, I present a systematic study using self-interaction corrected density-functional calculations [2]. These calculations predict three distinct scenarios. (i) Some systems do sustain extended host-like hole states, (ii) some exhibit polaronic trapping, (iii) and some exhibit carrier trapping at Fe-d orbitals. These behaviors are described in detail to give an insight as to how to distinguish them experimentally. I thank T. Fujita, C. Echeverria-Arrondo, and A. Ayuela for their collaboration.[4pt] [1] T. Dietl et al, Science, 287, 1019 (2000).[0pt] [2] S. Lany and A. Zunger, Phys. Rev. B, 80, 085202 (2009).

  7. Simulations of the magnetization and magnetoviscosity of dilute magnetic fluids

    NASA Astrophysics Data System (ADS)

    Sanchez Toro, Jorge Hernan

    In this work was studied the rotational Brownian motion of magnetic spherical and tri-axial ellipsoidal particles suspended in a Newtonian fluid, in the dilute suspension limit, under applied shear and magnetic fields by Brownian dynamics simulation to determine the magnetization and magnetoviscosity of the suspension. The algorithm describing the change in the magnetization and magnetoviscosity of the suspension was derived from the stochastic angular momentum equation using the fluctuation-dissipation theorem and a quaternion formulation of orientation space. Results are presented for the response of dilute suspensions of magnetic nanoparticles to constant and transient magnetic fields with and without simple shear flow fields. Simulation results are in agreement with the Langevin function for equilibrium magnetization and with single-exponential relaxation from equilibrium at small fields using Perrin's effective relaxation time. Dynamic susceptibilities for ellipsoidal particles of different aspect ratios were obtained from the response to oscillating magnetic fields of different frequencies and described by Debye's model for the complex susceptibility using Perrin's effective relaxation time. Suspensions of ellipsoidal particles show a significant effect of aspect ratio on the intrinsic magnetoviscosity of the suspension, and this effect is more pronounced as the aspect ratio becomes more extreme. The use of an effective rotational diffusion coefficient Dr,eff collapses the normalized intrinsic magnetoviscosity of all suspensions to a master curve as a function of Peclet number and the Langevin parameter alpha = (mu0muH)/(kBT), up to a critical value of alpha for which the results for suspensions of spherical particles deviate from those of suspensions of ellipsoids. This discrepancy is attributed to the action of the shear-torque on the ellipsoidal particles, which tends to orient the particles in the direction of maximum deformation of the simple shear flow

  8. Lieb-Mattis ferrimagnetism in magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Kuzian, R. O.; Richter, J.; Kuz'min, M. D.; Hayn, R.

    2016-06-01

    We show the possibility of long-range ferrimagnetic ordering with a saturation magnetization of ˜1 μB per spin for arbitrarily low concentration of magnetic impurities in semiconductors, provided that the impurities form a superstructure satisfying the conditions of the Lieb-Mattis theorem. Explicit examples of such superstructures are given for the wurtzite lattice, and the temperature of ferrimagnetic transition is estimated from a high-temperature expansion. Exact diagonalization studies show that small fragments of the structure exhibit enhanced magnetic response and isotropic superparamagnetism at low temperatures. A quantum transition in a high magnetic field is considered and similar superstructures in cubic semiconductors are discussed as well.

  9. Magnetic Properties of Diluted Fcc System Nickel

    NASA Astrophysics Data System (ADS)

    Feng, Zhen

    Starting from Ni and Mg nitrates, about 20 samples of Ni_{rm p}Mg _{rm 1-p}O (0.06 <=q p <=q 0.86) were prepared and X-ray diffraction studies showed the samples to have the NaCl structure with the lattice constant fitting the equation a(p) = 4.2115 - 0.0340p A. Temperature dependent dc magnetic susceptibility (chi ) studies of the samples were carried out between 1.8K and 600K using a SQUID magnetometer and the Neel temperature T_{rm N} were determined from the peak in partial(chiT)/ partialT. The variation of t = T _{rm N}(p)/T _{rm N}(1) versus p is compared with that in Co_{rm p}Mg _{rm 1-p}O. For both systems, the variations for p > 0.31 are found to fit the predicted values for a simple cubic Heisenberg antiferromagnet and a theoretical basis for this anomalous results is advanced. The experimental percolation threshold p_{rm c} = 0.15 +/- 0.01. For p_ {rm c} <=q p <=q 0.33, chi below T_{rm N} shows irreversible behavior for the zero-field-cooled and field -cooled cases, suggestive of spin-glass-like behavior, also observed in other diluted fcc antiferromagnets such as Co_{rm p}Mg _{rm 1-p}O and Eu _{rm p}Sr_ {rm 1-p}Te. It is suggested that the differences in the t vs p variations for p < 0.33 in Ni_{rm p} Mg_{rm 1-p}O, Co_{rm p}Mg _{rm 1-p}O and Eu _{rm p}Sr_ {rm 1-p}Te may be related to the differences in the ratio of the next-nearest-neighbor to nearest-neighbor exchange constants in these systems. A higher order correction to Curie-Weiss law was applied for sample with 0.19 <=q p <=q 0.59 which explains why 1/ chi curve versus T bends downward with decreasing temperatures. For the sample Ni_{0.33} Mg_{0.67}O, the magnetization M versus magnetic field H (0 to 0.2T) are measured with temperature ranging from 5.2K to 13.4K at intervals of 0.2K. The magnitude of the non-linear susceptibility, a_3, is determined from the M versus H data at different temperatures. The divergence of a _3 around 9.4 +/- 0.6K indicates spin-glass behavior in this system.

  10. Diluted II-VI oxide semiconductors with multiple band gaps.

    PubMed

    Yu, K M; Walukiewicz, W; Wu, J; Shan, W; Beeman, J W; Scarpulla, M A; Dubon, O D; Becla, P

    2003-12-12

    We report the realization of a new mult-band-gap semiconductor. Zn(1-y)Mn(y)OxTe1-x alloys have been synthesized using the combination of oxygen ion implantation and pulsed laser melting. Incorporation of small quantities of isovalent oxygen leads to the formation of a narrow, oxygen-derived band of extended states located within the band gap of the Zn(1-y)Mn(y)Te host. When only 1.3% of Te atoms are replaced with oxygen in a Zn0.88Mn0.12Te crystal the resulting band structure consists of two direct band gaps with interband transitions at approximately 1.77 and 2.7 eV. This remarkable modification of the band structure is well described by the band anticrossing model. With multiple band gaps that fall within the solar energy spectrum, Zn(1-y)Mn(y)OxTe1-x is a material perfectly satisfying the conditions for single-junction photovoltaics with the potential for power conversion efficiencies surpassing 50%. PMID:14683137

  11. (Magnetic properties of doped semiconductors)

    SciTech Connect

    Not Available

    1990-01-01

    Research continued on the transport behavior of doped semiconductors on both sides of the metal-insulator transition, and the approach to the transition from both the insulating and the metallic side. Work is described on magneto resistance of a series of metallic Si:B samples and CdSe. (CBS)

  12. Magnetization and Hysteresis of Dilute Magnetic-Oxide Nanoparticles

    NASA Astrophysics Data System (ADS)

    Skomski, Ralph; Balamurugan, B.; Sellmyer, D. J.

    2014-03-01

    Real-structure imperfections in dilute magnetic oxides tend to create small concentrations of local magnetic moments that are coupled by fairly long-range exchange interactions, mediated by p-electrons. The robustness of these interactions is caused by the strong overlap of the p orbitals, as contrasted to the much weaker interatomic exchange involving iron-series 3d electrons. The net exchange between defect moments can be positive or negative, which gives rise to spin structures with very small net moments. Similarly, the moments exhibit magnetocrystalline anisotropy, reinforced by electron hopping to and from 3d states and generally undergoing some random-anuisotropy averaging. Since the coercivity scales as 2K1/M and M is small, this creates pronounced and -- in thin films -- strongly anisotropic hysteresis loops. In finite systems with N moments, both K1 and M are reduced by a factor of order N1/2 due to random anisotropy and moment compensation, respectively, so that that typical coercivities are comparable to bulk magnets. Thermal activation readily randomizes the net moment of small oxide particles, so that the moment is easier to measure in compacted or aggregated particle ensembles. This research is supported by DOE (BES).

  13. Diluted Ising Magnet on the Bethe Lattice

    NASA Astrophysics Data System (ADS)

    Semkin, S. V.; Smagin, V. P.

    2016-04-01

    A solution is obtained for the Ising model on the Bethe lattice comprising a mixture of magnetic and nonmagnetic atoms in a thermodynamic equilibrium. The concentration and temperature dependences of spontaneous magnetization, the Curie temperature, and the percolation threshold are found together with the pair correlation functions of three types that characterize the arrangement of impurity atoms and the correlation of magnetic moments. It is demonstrated that the system with mobile impurities in the thermodynamic equilibrium can be brought closer to the system with frozen impurities by adjusting the parameters of interatomic interaction.

  14. Magnetic relaxation of diluted and self-assembled cobalt nanocrystals

    NASA Astrophysics Data System (ADS)

    Zhang, X. X.; Wen, G. H.; Xiao, Gang; Sun, Shouheng

    2003-04-01

    We have studied the magnetic relaxation of monodispersed 4 nm cubic ɛ-cobalt nanocrystals in both randomly oriented and pre-aligned assemblies. The blocking temperature TB, for the closely packed Co nanocrystal assemblies, is 30% higher than that of the highly diluted and well-dispersed Co nanocrystal-organic composites. This increase is attributed to the strong magnetic dipole interaction induced from the close packing of the nanocrystals. It is found that the frequency-dependent susceptibility data, obtained from the diluted samples, can be fitted to the half-circle Argand Diagrams, indicating a single barrier (or very narrow energy distribution) of the nanocrystals. This agrees well with the physical observation from TEM that the nanocrystals are monodispersed. The long time magnetic relaxation measurements reveal that energy barrier distribution in a pre-aligned nanocrystal assembly is significantly different from that in a randomly oriented one.

  15. Semiconductor Crystal Growth in Static and Rotating Magnetic fields

    NASA Technical Reports Server (NTRS)

    Volz, Martin

    2004-01-01

    Magnetic fields have been applied during the growth of bulk semiconductor crystals to control the convective flow behavior of the melt. A static magnetic field established Lorentz forces which tend to reduce the convective intensity in the melt. At sufficiently high magnetic field strengths, a boundary layer is established ahead of the solid-liquid interface where mass transport is dominated by diffusion. This can have a significant effect on segregation behavior and can eliminate striations in grown crystals resulting from convective instabilities. Experiments on dilute (Ge:Ga) and solid solution (Ge-Si) semiconductor systems show a transition from a completely mixed convective state to a diffusion-controlled state between 0 and 5 Tesla. In HgCdTe, radial segregation approached the diffusion limited regime and the curvature of the solid-liquid interface was reduced by a factor of 3 during growth in magnetic fields in excess of 0.5 Tesla. Convection can also be controlled during growth at reduced gravitational levels. However, the direction of the residual steady-state acceleration vector can compromise this effect if it cannot be controlled. A magnetic field in reduced gravity can suppress disturbances caused by residual transverse accelerations and by random non-steady accelerations. Indeed, a joint program between NASA and the NHMFL resulted in the construction of a prototype spaceflight magnet for crystal growth applications. An alternative to the suppression of convection by static magnetic fields and reduced gravity is the imposition of controlled steady flow generated by rotating magnetic fields (RMF)'s. The potential benefits of an RMF include homogenization of the melt temperature and concentration distribution, and control of the solid-liquid interface shape. Adjusting the strength and frequency of the applied magnetic field allows tailoring of the resultant flow field. A limitation of RMF's is that they introduce deleterious instabilities above a

  16. Raman Scattering in the Magnetized Semiconductor Plasma

    NASA Astrophysics Data System (ADS)

    Jankauskas, Zigmantas; Kvedaras, Vygaudas; Balevičius, Saulius

    2005-04-01

    Radio frequency (RF) magnetoplasmic waves known as helicons will propagate in solid-state plasmas when a strong magnetic field is applied. In our device the helicons were excited by RFs (the range 100-2000 MHz) much higher than the helicon generation frequency (the main peak at 20 MHz). The excitation of helicons in this case may be described by the effect similar to the Combination Scattering (Raman effect) when a part of the high RF wave energy that passes through the active material is absorbed and re-emitted by the magnetized solid-state plasma. It is expedient to call this experimental device a Helicon Maser (HRM) and the higher frequency e/m field - a pumping field. In full analogy with the usual Raman maser (or laser) the magnetized semiconductor sample plays the role of active material and the connecting cable - the role of high quality external resonator.

  17. Raman Scattering in the Magnetized Semiconductor Plasma

    NASA Astrophysics Data System (ADS)

    Jankauskas, Zigmantas; Kvedaras, Vygaudas; Balevičius, Saulius

    Radio frequency (RF) magnetoplasmic waves known as helicons will propagate in solid-state plasmas when a strong magnetic field is applied. In our device the helicons were excited by RFs (the range 100-2000 MHz) much higher than the helicon generation frequency (the main peak at 20 MHz). The excitation of helicons in this case may be described by the effect similar to the Combination Scattering (Raman effect) when a part of the high RF wave energy that passes through the active material is absorbed and re-emitted by the magnetized solid-state plasma. It is expedient to call this experimental device a Helicon Maser (HRM) and the higher frequency e/m field - a pumping field. In full analogy with the usual Raman maser (or laser) the magnetized semiconductor sample plays the role of active material and the connecting cable - the role of high quality external resonator.

  18. Growth and Properties of the Dilute Bismide Semiconductor GaAs1-xBix a Complementary Alloy to the Dilute Nitrides

    SciTech Connect

    Tiedje, T.; Young, E. C.; Mascarenhas, A.

    2008-01-01

    In this review we describe the growth and properties of the dilute bismide semiconductor alloy GaAs{sub 1-x}Bi{sub x} and show how its properties are in certain respects complementary to the dilute nitride alloy, GaN{sub y}As{sub 1-y}. Like the dilute nitrides the dilute bismides show a giant band gap bowing effect in which a small concentration of the alloying element has a disproportionate effect on the band gap, however in the case of the bismide the band gap reduction is associated with an increase in the energy of the valence band maximum (VBM) rather than a reduction in the energy of the conduction band minimum (CBM). Under standard GaAs growth conditions Bi acts as a surfactant with associated improvements in surface quality. In order to incorporate Bi, growth temperatures below 400 C are used with As{sub 2}/Ga flux ratios close to unity. The electron mobility of GaAs is only weakly affected by Bi alloying, in contrast to the dilute nitrides where the electron mobility decreases rapidly with N alloying. Bi alloying also produces a giant bowing effect in the spin orbit splitting in the valence band. Strong room temperature photoluminescence is observed. Prospects for future device applications of this new compound semiconductor alloy are discussed.

  19. Tunable exchange bias in dilute magnetic alloys - chiral spin glasses

    NASA Astrophysics Data System (ADS)

    Hudl, Matthias; Mathieu, Roland; Nordblad, Per

    2016-01-01

    A unidirectional anisotropy appears in field cooled samples of dilute magnetic alloys at temperatures well below the cusp temperature of the zero field cooled magnetization curve. Magnetization measurements on a Cu(13.5 at% Mn) sample show that this anisotropy is essentially temperature independent and acts on a temperature dependent excess magnetization, ΔM. The anisotropy can be partially or fully transferred from being locked to the direction of the cooling field at lower fields to becoming locked to the direction of ΔM at larger fields, thus instead appearing as a uniaxial anisotropy. This introduces a deceiving division of the anisotropy into a superposition of a unidirectional and a uniaxial part. This two faced nature of the anisotropy has been empirically scrutinized and concluded to originate from one and the same exchange mechanism: the Dzyaloshinsky-Moriya interaction.

  20. Three-dimensional Heisenberg critical behavior in the highly disordered dilute ferromagnetic semiconductor (Ga,Mn)As

    NASA Astrophysics Data System (ADS)

    Wang, M.; Marshall, R. A.; Edmonds, K. W.; Rushforth, A. W.; Campion, R. P.; Gallagher, B. L.

    2016-05-01

    We present detailed studies of critical behavior in the strongly site-disordered dilute ferromagnetic semiconductor (Ga,Mn)As. (Ga,Mn)As has a low saturation magnetization and relatively strong magnetocrystalline anisotropy. This combination of properties inhibits domain formation, thus removing a principal experimental difficulty in determining the critical coefficients β and γ . We find that there are still a large number of problems to overcome in terms of measurement procedures and methods of analysis. In particular, the combined effects of disorder and inhomogeneity limit the accessible critical region. However, we find that accurate and reproducible values of the critical exponents β and γ can be obtained from Kouvel-Fisher plots of remanent magnetization and magnetic susceptibility for our (Ga,Mn)As samples. The values of β and γ obtained are consistent with those of the three-dimensional Heisenberg class, despite the very strong disorder present in this system, and they are inconsistent with mean field behavior. Log-log plots of M (H ) data for our samples are consistent with the three-dimensional Heisenberg value of the critical exponent δ , but accurate values of δ could not be obtained for our samples from these plots. We also find that accurate values of the critical exponent α could not be obtained by fitting to the measured temperature derivative of resistivity for our samples. We find that modified Arrott plots and scaling plots are not a practical way to determine the universality class or critical exponents, though they are found to be in better agreement with three-dimensional Heisenberg values than mean field values. Below the critical temperature range, we find that the magnetization shows power-law behavior down to a reduced temperature of t ˜0.5 , with a critical exponent β ˜0.4 , a value appreciably lower than the mean field value of β =0.5 . At lower temperatures, Bloch 3/2 law behavior is observed due to magnons.

  1. Angular dependent study on spin transport in magnetic semiconductor heterostructures with Dresselhaus spin-orbit interaction

    NASA Astrophysics Data System (ADS)

    Mirzanian, S. M.; Shokri, A. A.; Mikaili Agah, K.; Elahi, S. M.

    2015-09-01

    We investigate theoretically the effects of Dresselhaus spin-orbit coupling (DSOC) on the spin-dependent current and shot noise through II-VI diluted magnetic semiconductor/nonmagnetic semiconductor (DMS/NMS) barrier structures. The calculation of transmission probability is based on an effective mass quantum-mechanical approach in the presence of an external magnetic field applied along the growth direction of the junction and also applied voltage. We also study the dependence of spin-dependent properties on external magnetic field and relative angle between the magnetizations of two DMS layers in CdTe/CdMnTe heterostructures by including the DSOC effect. The results show that the DSOC has great different influence on transport properties of electrons with spin up and spin down in the considered system and this aspect may be utilized in designing new spintronics devices.

  2. Optical investigation of effective permeability of dilute magnetic dielectrics with magnetic field

    NASA Astrophysics Data System (ADS)

    Banerjee, Ananya; Sarkar, A.

    2016-05-01

    The prime objective of this paper is to investigate the magnetic nature of dilute magnetic dielectrics (DMD) under variation of external magnetic field. The said variation is studied over developed nano-sized Gadolinium Oxide as a DMD system. The observed experimental field variation of the effective magnetic permeability is analyzed results of optical experiment. The experiment records the variation of Brewster angle of incident polarized LASER beam from the surface of developed DMD specimen with applied out of plane external magnetic field. The effective refractive index and hence relative magnetic permeability were estimated following electro-magnetic theory. The overall results obtained and agreement between theory and experiment are good.

  3. Investigation of III-V magnetic semiconductor thin films and heterojunction devices

    NASA Astrophysics Data System (ADS)

    Rangaraju, Nikhil

    Magnetic field control of semiconductor device properties is of great interest for novel electronics because it offers a way to control the spin degree of freedom of charge carriers. One way to achieve this control is the use of dilute magnetic semiconductor as an active element in semiconductor devices. In this work, the relationship between the magnetic and electronic properties of magnetic bipolar heterojunction devices is examined. InMnAs/n-type heterojunctions were fabricated using metalorganic vapor phase epitaxy. The capacitace of these devices was measured at room temperature as a function of magnetic field. The capacitance of these junction increases with magnetic field by up to 1.25% at 0.5 T. The change in capacitance suggests that there is spin splitting in the material. The magnetotransport properties of InMnAs/InAs heterojunction diode were measured as a function of magnetic field from 0 to 18 T and at various temperatures. These devices exhibit excellent rectifying properties at room temperature and zero magnetic field. When a magnetic field is applied, the junctions show resistive behavior, which dominates at high magnetic fields. The magnetoresistance of these diodes was measured as a function of current. The magnetoresistance for 15 mA through the device is 2600% at 18 T. The magnetoresistance of this device is attributed to efficient spin-polarized carrier transport. The conductance behavior of InMnAs diodes in high magnetic fields is analyzed to explain the spin selective transport. The change in current through the device at a constant voltage increases linearly with magnetic field for low magnetic fields and saturates at high magnetic field. The measured field dependence of the current change is attributed to the existence of a paramagnetic component, which determines the degree of spin polarization of the junction current. This work indicates that highly spin-polarized magnetic semiconductor heterojunction devices that operate at room

  4. Multifractality in dilute magnetorheological fluids under an oscillating magnetic field.

    PubMed

    Moctezuma, R E; Arauz-Lara, J L; Donado, F

    2014-12-01

    A study of the multifractal characteristics of the structure formed by magnetic particles in a dilute magnetorheological fluid is presented. A quasi-two-dimensional magnetorheological fluid sample is simultaneously subjected to a static magnetic field and a sinusoidal magnetic field transverse to each other. We analyzed the singularity spectrum f(α) and the generalized dimension D(q) of the whole structure to characterize the distribution of the aggregates under several conditions of particle concentration, magnetic field intensities, and liquid viscosity. We also obtained the fractal dimension D(g), calculated from the radius of gyration of the chains, to describe the internal distribution of the particles. We present a thermodynamic interpretation of the multifractal analysis, and based on this, we discussed the characteristics of the structure formed by the particles and its relation with previous studies of the average chain length. We have found that this method is useful to quantitatively describe the structure of magnetorheological fluids, especially in systems with high particle concentration where the aggregates are more complex than simple chains or columns. PMID:25615089

  5. Optimal doping control of magnetic semiconductors via subsurfactant epitaxy

    SciTech Connect

    Zeng, Changgan; Zhang, Zhenyu; van Benthem, Klaus; Chisholm, Matthew F; Weitering, Harm H

    2008-02-01

    Dilute magnetic semiconductors (DMS) with high ferromagnetic ordering temperatures (T{sub c}) have vast potential for advancing spin-based electronics or 'spintronics'. To date, achieving high-T{sub c} DMS typically required doping levels of order 5%. Such high doping levels inevitably compromise the structural homogeneity and carrier mobility of the DMS. Here, we establish 'subsurfactant epitaxy' as a novel kinetic pathway for synthesizing Mn-doped germanium with T{sub c} much higher than room temperature, at dramatically reduced doping levels. This is accomplished by optimal control of the diffusion kinetics of the dopant atoms near the growth front in two separate deposition steps. The first involves a submonolayer dose of Mn on Ge(100) at low temperature, which populates subsurface interstitial sites with Mn while suppressing lateral Mn diffusion and clustering. The second step involves epitaxial growth of Ge at elevated temperature, taking advantage of the strong floating ability of the interstitial Mn dopants towards the newly defined subsurface sites at the growth front. Most remarkably, the Mn dopants trapped inside the film are uniformly distributed at substitutional sites, and the resulting film exhibits ferromagnetism above 400 K at the nominal doping level of only 0.2%.

  6. Integrated semiconductor-magnetic random access memory system

    NASA Technical Reports Server (NTRS)

    Katti, Romney R. (Inventor); Blaes, Brent R. (Inventor)

    2001-01-01

    The present disclosure describes a non-volatile magnetic random access memory (RAM) system having a semiconductor control circuit and a magnetic array element. The integrated magnetic RAM system uses CMOS control circuit to read and write data magnetoresistively. The system provides a fast access, non-volatile, radiation hard, high density RAM for high speed computing.

  7. Spin-spin relaxation in magnetically dilute crystals

    NASA Astrophysics Data System (ADS)

    Dzheparov, F. S.; Lvov, D. V.; Veretennikov, M. A.

    2015-01-01

    Magnetic resonance is examined in paramagnetic systems with a small concentration of spins. The free induction signal (FIS) and resonance line shape function (LSF) are calculated. The theory is based on the introduction of an auxiliary system where one spin does not have a flip-flop interaction with the surroundings. The FIS is calculated for this spin using the Anderson-Weiss-Kubo theory and its memory function is used to construct the memory of the main system. The needed numerical coefficients are obtained from expansions of the FIS in terms of the concentration. Here the polarization transport in magnetically dilute systems is taken into account for the first time. This is shown to lead to significant slowing down of the decay in the FIS for times longer than the phase relaxation time. Existing experimental data are compared with theoretical models. Satisfactory agreement is obtained for the description of the central part of the LSF after an additional experimentally observed broadening is introduced in the theory. Data on the amplitude and position of the sideband peaks from the different experiments are not in good agreement with one another or with the theory.

  8. Magnetic birefringence studies of dilute purple membrane suspensions.

    PubMed Central

    Lewis, B A; Rosenblatt, C; Griffin, R G; Courtemanche, J; Herzfeld, J

    1985-01-01

    We have observed the magnetically induced orientation of purple membrane suspensions by measuring the birefringence as a function of concentration and temperature at fields up to 10.5 Tesla (T). At these fields, the orientation approaches saturation even in dilute solutions; therefore, the birefringence data, together with an estimate of the membrane size distribution obtained from electron microscopy, permits one to determine the diamagnetic susceptibility anisotropy. We find delta chi mole = 1.2 +/- 0.3 X 10(-3) erg G-2mol-1 of bacteriorhodopsin. If delta chi were due only to the oriented peptide bonds of the transmembrane alpha helices, this experimental value would indicate that delta K, the anisotropy per mole of peptide bonds, is considerably larger than previously suggested. On the other hand, the large value for delta chi mole of bacteriorhodopsin can also be explained by a net orientation of the aromatic amino acid side chains of bacteriorhodopsin with their planes perpendicular to the membrane surface. In addition, the present data analysis demonstrates the critical dependence of the calculated delta chi value on the values for the membrane size distribution. PMID:3978196

  9. Colossal positive magnetoresistance in a doped nearly magnetic semiconductor

    SciTech Connect

    Hu, R.; Thomas, K.; Lee, Y.; Vogt, T.; Choi, E.; Mitrovic, V.; Hermann, R.; Grandjean, F.; Canfield, P.; Kim, J.; Goldman, A.; Petrovic, C.

    2008-02-27

    We report on a positive colossal magnetoresistance (MR) induced by metallization of FeSb{sub 2}, a nearly magnetic or 'Kondo' semiconductor with 3d ions. We discuss the contribution of orbital MR and quantum interference to the enhanced magnetic field response of electrical resistivity.

  10. Photo-induced Magnetism and Spintronics in Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Yoo, Jung Woo

    2009-03-01

    Recent years have witnessed growing attention on manipulating spins in organic species. One of the interesting phenomena in organic-based magnets is controlling magnetic properties by optical stimulus, a property not exhibited in metallurgical magnets. Three classes of known phenomena and mechanism will be discussed: i) manipulation of number of spins by optically induced charge transfer in cyano-bimetallic complexes [1], ii) optical control of exchange coupling in Mn(TCNE)2 compound [2], iii) light-induced change of magnetic anisotropy in the magnetic semiconductor V(TCNE)x [3]. The second part of this talk will be devoted to ongoing research on transferring spin polarized carriers through organic semiconductors. Recently, there have been lively activities as well as controversies on the application of organic semiconductors for transporting spin information. However, the understanding of spin injection and transport in organic semiconductors is still limited. We will address detailed mechanisms for spin injection and transport in organic semiconductor film of our rubrene (C42H28)-based spin valve and potential applications of organic-based spintronics. [4pt] [1] O. Sato, T. Iyoda, A. Fujishima, and K. Hashimoto, Science 272, 704 (1996).[0pt] [2] D. A. Pejakovic', C. Kitamura, J. S. Miller, and A. J. Epstein, Phys. Rev. Lett. 88, 057202 (2002).[0pt] [3] J. W. Yoo et al., Phys. Rev. Lett. 97, 247205 (2006); 99, 157205 (2007).

  11. Spin injection into semiconductors

    NASA Astrophysics Data System (ADS)

    Oestreich, M.; Hübner, J.; Hägele, D.; Klar, P. J.; Heimbrodt, W.; Rühle, W. W.; Ashenford, D. E.; Lunn, B.

    1999-03-01

    The injection of spin-polarized electrons is presently one of the major challenges in semiconductor spin electronics. We propose and demonstrate a most efficient spin injection using diluted magnetic semiconductors as spin aligners. Time-resolved photoluminescence with a Cd0.98Mn0.02Te/CdTe structure proves the feasibility of the spin-alignment mechanism.

  12. Ultrafast Control of Magnetism in Ferromagnetic Semiconductors via Photoexcited Transient Carriers

    SciTech Connect

    Cotoros, Ingrid A.

    2008-12-01

    The field of spintronics offers perspectives for seamless integration of coupled and inter-tunable electrical and magnetic properties in a single device. For integration of the spin degree of freedom with current electronic technology, new semiconductors are needed that show electrically-tunable magnetic properties at room temperature and above. Dilute magnetic semiconductors derived from III-V compounds, like GaMnAs and InMnAs, show coupled and tunable magnetic, transport, and optical properties, due to the fact that their ferromagnetism is hole-mediated. These unconventional materials are ideal systems for manipulating the magnetic order by changing the carrier polarization, population density, and energy band distribution of the complementary subsystem of holes. This is the main theme we cover in this thesis. In particular, we develop a unique setup by use of ultraviolet pump, near-infrared probe femtosecond laser pulses, that allows for magneto-optical Kerr effect (MOKE) spectroscopy experiments. We photo-excite transient carriers in our samples, and measure the induced transient magnetization dynamics. One set of experiments performed allowed us to observe for the first time enhancement of the ferromagnetic order in GaMnAs, on an ultrafast time scale of hundreds of picoseconds. The corresponding transient increase of Curie temperature (Tc, the temperature above which a ferromagnetic material loses its permanent magnetism) of about 1 K for our experimental conditions is a very promising result for potential spintronics applications, especially since it is seconded by observation of an ultrafast ferromagnetic to paramagnetic phase transition above Tc. In a different set of experiments, we "write" the magnetization in a particular orientation in the sample plane. Using an ultrafast scheme, we alter the distribution of holes in the system and detect signatures of the particular memory state in the subsequent magnetization dynamics, with unprecedented hundreds of

  13. Optical absorption in semiconductor nanorings under electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Zhang, Tong-Yi; Cao, Jun-Cheng; Zhao, Wei

    2005-01-01

    The optical absorption in semiconductor nanorings under a lateral DC field and a perpendicular magnetic field is numerically simulated by coherent wave approach. The exciton dominated optical absorption is compared with the free-carrier interband absorption to demonstrate the key role of Coulomb interaction between electron and hole. The influence of the lateral DC field and the perpendicular magnetic field on the optical absorption are discussed in detail. It shows that the lateral DC field can significantly enhance the Aharonov-Bohm effect of the neutral excitons in semiconductor nanorings.

  14. Magnetoresistance near the ferromagnetic-paramagnetic phase transition in magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Brodowska, B.; Kuryliszyn-Kudelska, I.; Wojtowicz, T.; Arciszewska, M.; Dobrowolski, W.; Slynko, E. I.; Slynko, V. E.; Liu, X.; Furdyna, J. K.

    2008-07-01

    Magnetic and transport properties of ferromagnetic semiconductors (FMSs) near the ferromagnetic-paramagnetic phase transition were studied in two classes of FMSs: in the III-V-based In1-xMnxSb and Ga1-xMnxAs epitaxial films and in IV-VI-based Sn1-xMnxTe and Sn1-x-yMnxEryTe alloys in bulk crystal form. Magnetoresistance data for both FMS classes are in excellent agreement with the theory of Majumdar and Littlewood, indicating that near the Curie temperature, magnetic fluctuations play a key role as scattering centers. These results also show that the Majumdar-Littlewood model can be applied to magnetically very dilute systems.

  15. Pulsed laser ablation of preferentially orientated ZnO:Co diluted magnetic semiconducting thin films on Si substrates

    NASA Astrophysics Data System (ADS)

    Zhang, Y. B.; Liu, Q.; Sritharan, T.; Gan, C. L.; Li, S.

    2006-07-01

    ZnO:Co thin films with room-temperature ferromagnetism have been synthesized on (001) Si substrates by pulsed laser deposition using a Zn0.95Co0.05O ceramic target. Single-phase wurtzite thin films with (002) preferential orientation were grown at 450°C in vacuum. There is no indication of Co nanocluster formation. However, copious edge dislocations appear to have formed during the film growth. A saturation magnetization of 1.04μB/Co and a coercivity of 25Oe were obtained at room temperature. In addition to O vacancies, the Zn interstitial induced by edge dislocations may also contribute to the ferromagnetic properties in this oxide-diluted magnetic semiconductor.

  16. Ba(Zn1-2xMnxCux)2As2: A Bulk Form Diluted Ferromagnetic Semiconductor with Mn and Cu Codoping at Zn Sites

    NASA Astrophysics Data System (ADS)

    Man, Huiyuan; Guo, Shengli; Sui, Yu; Guo, Yang; Chen, Bin; Wang, Hangdong; Ding, Cui; Ning, F. L.

    2015-10-01

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor Ba(Zn1-2xMnxCux)2As2 with the crystal structure identical to that of “122” family iron based superconductors and the antiferromagnet BaMn2As2. No ferromagnetic order occurs with (Zn, Mn) or (Zn, Cu) substitution in the parent compound BaZn2As2. Only when Zn is substituted by both Mn and Cu simultaneously, can the system undergo a ferromagnetic transition below TC ~ 70 K, followed by a magnetic glassy transition at Tf  ~ 35 K. AC susceptibility measurements for Ba(Zn0.75Mn0.125Cu0.125)2As2 reveal that Tf strongly depends on the applied frequency with and a DC magnetic field dependence of , demonstrating that a spin glass transition takes place at Tf. As large as -53% negative magnetoresistance has been observed in Ba(Zn1-2xMnxCux)2As2, enabling its possible application in memory devices.

  17. Ba(Zn1−2xMnxCux)2As2: A Bulk Form Diluted Ferromagnetic Semiconductor with Mn and Cu Codoping at Zn Sites

    PubMed Central

    Man, Huiyuan; Guo, Shengli; Sui, Yu; Guo, Yang; Chen, Bin; Wang, Hangdong; Ding, Cui; Ning, F.L.

    2015-01-01

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor Ba(Zn1−2xMnxCux)2As2 with the crystal structure identical to that of “122” family iron based superconductors and the antiferromagnet BaMn2As2. No ferromagnetic order occurs with (Zn, Mn) or (Zn, Cu) substitution in the parent compound BaZn2As2. Only when Zn is substituted by both Mn and Cu simultaneously, can the system undergo a ferromagnetic transition below TC ~ 70 K, followed by a magnetic glassy transition at Tf  ~ 35 K. AC susceptibility measurements for Ba(Zn0.75Mn0.125Cu0.125)2As2 reveal that Tf strongly depends on the applied frequency with and a DC magnetic field dependence of , demonstrating that a spin glass transition takes place at Tf. As large as −53% negative magnetoresistance has been observed in Ba(Zn1−2xMnxCux)2As2, enabling its possible application in memory devices. PMID:26492957

  18. Magnetic Damping of Solid Solution Semiconductor Alloys

    NASA Technical Reports Server (NTRS)

    Szofran, Frank R.; Benz, K. W.; Croell, Arne; Dold, Peter; Cobb, Sharon D.; Volz, Martin P.; Motakef, Shariar

    1999-01-01

    The objective of this study is to: (1) experimentally test the validity of the modeling predictions applicable to the magnetic damping of convective flows in electrically conductive melts as this applies to the bulk growth of solid solution semiconducting materials; and (2) assess the effectiveness of steady magnetic fields in reducing the fluid flows occurring in these materials during processing. To achieve the objectives of this investigation, we are carrying out a comprehensive program in the Bridgman and floating-zone configurations using the solid solution alloy system Ge-Si. This alloy system has been studied extensively in environments that have not simultaneously included both low gravity and an applied magnetic field. Also, all compositions have a high electrical conductivity, and the materials parameters permit reasonable growth rates. An important supporting investigation is determining the role, if any, that thermoelectromagnetic convection (TEMC) plays during growth of these materials in a magnetic field. TEMC has significant implications for the deployment of a Magnetic Damping Furnace in space. This effect will be especially important in solid solutions where the growth interface is, in general, neither isothermal nor isoconcentrational. It could be important in single melting point materials, also, if faceting takes place producing a non-isothermal interface. In conclusion, magnetic fields up to 5 Tesla are sufficient to eliminate time-dependent convection in silicon floating zones and possibly Bridgman growth of Ge-Si alloys. In both cases, steady convection appears to be more significant for mass transport than diffusion, even at 5 Tesla in the geometries used here. These results are corroborated in both growth configurations by calculations.

  19. Spin transport in strained non-magnetic zinc blende semiconductors

    NASA Astrophysics Data System (ADS)

    Moehlmann, Benjamin James

    The problem of spin manipulation via the spin-orbit interaction in nonmagnetic semiconductors in the absence of magnetic fields is investigated in this work. We begin with a review of the literature on spin dynamics in semiconductors, then discuss the semi-empirical k·p method of calculating direct-gap semiconductor properties, which we use to estimate material parameters significant for manipulation of spin even in the absence of a magnetic field. The total effective magnetic fields and precession lengths are calculated for a variety of quantum well orientations, and a class of devices are proposed that will allow for all-electric arbitrary manipulation of spin orientations. The strain- and momentum-dependent spin splitting coefficient C3 has been calculated using a fourteen band Kane k·p model for a variety of III-V semiconductors as well as ZnSe and CdSe. It is observed that the spin-splitting parameters C 3 and gamma, corresponding to the strain-induced spin-orbit interaction and Dresselhaus coefficient, are sensitive to the value of the inter-band spin-orbit coupling Delta- between the p valence and p second conduction band in all cases. The value of Delta- has therefore been recalculated in these materials using a tight-binding model and modern experimental values of the valence and second conduction band spin-orbit splittings. The total effective magnetic field and precession length of spins in strained quantum wells in the (001), (110), and (111) planes are derived with consideration for all known effective magnetic fields except those due to interface effects in non- common-atom heterostructures (native inversion asymmetry). The orientation of the k-linear Dresselhaus field and the strain-dependent fields vary strongly with the growth axis of the quantum well. The precession length in the (110) and (001) cases can achieve infinite anisotropy, while the precession length of (111) quantum wells is always isotropic. We find that the electronic spin rotation

  20. (Ca,Na)(Zn,Mn){sub 2}As{sub 2}: A new spin and charge doping decoupled diluted ferromagnetic semiconductor

    SciTech Connect

    Zhao, K.; Chen, B. J.; Deng, Z.; Zhao, G. Q.; Zhu, J. L.; Liu, Q. Q.; Wang, X. C.; Han, W.; Frandsen, B.; Liu, L.; Cheung, S.; Uemura, Y. J.; Ning, F. L.; Munsie, T. J. S.; Medina, T.; Luke, G. M.; Carlo, J. P.; Munevar, J.; Zhang, G. M.; Jin, C. Q.

    2014-10-28

    Here, we report the successful synthesis of a spin- and charge-decoupled diluted magnetic semiconductor (DMS) (Ca,Na)(Zn,Mn){sub 2}As{sub 2}, crystallizing into the hexagonal CaAl{sub 2}Si{sub 2} structure. The compound shows a ferromagnetic transition with a Curie temperature up to 33 K with 10% Na doping, which gives rise to carrier density of n{sub p} ∼ 10{sup 20 }cm{sup −3}. The new DMS is a soft magnetic material with H{sub C} < 400 Oe. The anomalous Hall effect is observed below the ferromagnetic ordering temperature. With increasing Mn doping, ferromagnetic order is accompanied by an interaction between the local spin and mobile charge, giving rise to a minimum in resistivity at low temperatures and localizing the conduction electrons. The system provides an ideal platform for studying the interaction of the local spins and conduction electrons.

  1. Wide-Gap Magnetic Semiconductors and Their Nanostructures

    NASA Astrophysics Data System (ADS)

    Furdyna, Jacek K.

    2000-03-01

    Although the field of wide-gap magnetic semiconductors (particularly those involving II-VI semiconductor alloys with Mn) has been active for two decades, a number of new advances have recently emerged, that illustrate the effect of spin-based effects on the electrtonic properties of wide-gap systems generally. We will discuss four of these advances. First, it has recently been shown in ZnSe/CdSe quantum dot (QD) systems containing Mn (either in the quantum dot interior, or in the surrounding matrix) that the photoluminescence intensity emitted by the dots can be amplified (by orders of magnitude) by applying an external magnetic field. This effect can be understood by the very efficient coupling of the QD excitonic emission with the well-known spin-flip transitions taking place within the Mn ions. As an interesting byproduct, it has been demonstrated that Mn act in this system as a nucleating agent for the QDs, resulting in dots that are more uniform and more homogeneous. Second, neutron diffraction experiments on wide-gap ZnTe/MnTe superlattices have shown that the magnetic coupling between the magnetic layers can be contolled by the introduction of deep levels via doping, again pointing to the connection of spin and electronic subsystems. Understanding inter-layer coupling betweem spin-polarized layers is of key importance for "spintronic" applications, and superlattices such as those just mentioned thus constitute a convenient laboratory for investigating these interactions. Third -- again in the context of "spintronics" -- we shall present the various schemes which are used to achieve ferromagnetic order in wide-gap II-VI magnetic semiconductors, and will compare these advances to the concurrent emergence of ferromagnetism in III-V semiconductors alloyed with Mn. And finally, we will discuss magnetic band-edge tuning in magnetic semiconductors as a tool for measuring band offsets, and -- by using ZnSe/ZnBeMnSe heterostructures -- will apply this method to

  2. Nanoscale Tailoring of the Polarization Properties of Dilute-Nitride Semiconductors via H-Assisted Strain Engineering

    NASA Astrophysics Data System (ADS)

    Felici, Marco; Birindelli, Simone; Trotta, Rinaldo; Francardi, Marco; Gerardino, Annamaria; Notargiacomo, Andrea; Rubini, Silvia; Martelli, Faustino; Capizzi, Mario; Polimeni, Antonio

    2014-12-01

    In dilute-nitride semiconductors, the possibility to selectively passivate N atoms by spatially controlled hydrogen irradiation allows for tailoring the effective N concentration of the host—and, therefore, its electronic and structural properties—with a precision of a few nanometers. In the present work, this technique is applied to the realization of ordered arrays of GaAs1 -xNx/GaAs1 -xNx∶H wires oriented at different angles with respect to the crystallographic axes of the material. The creation of a strongly anisotropic strain field in the plane of the sample, due to the lattice expansion of the fully hydrogenated regions surrounding the GaAs1 -xNx wires, is directly responsible for the peculiar polarization properties observed for the wire emission. Temperature-dependent polarization-resolved microphotoluminescence measurements, indeed, reveal a nontrivial dependence of the degree of linear polarization on the wire orientation, with maxima for wires parallel to the [110] and [1 1 ¯ 0 ] directions and a pronounced minimum for wires oriented along the [100] axis. In addition, the polarization direction is found to be precisely perpendicular to the wire when the latter is oriented along high-symmetry crystal directions, whereas significant deviations from a perfect orthogonality are measured for all other wire orientations. These findings, which are well reproduced by a theoretical model based on finite-element calculations of the strain profile of our GaAs1 -xNx/GaAs1 -xNx∶H heterostructures, demonstrate our ability to control the polarization properties of dilute-nitride micro- and nanostructures via H-assisted strain engineering. This additional degree of freedom may prove very useful in the design and optimization of innovative photonic structures relying on the integration of dilute-nitride-based light emitters with photonic crystal microcavities.

  3. Magnetic effect on hopping rate of electrons in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Zhao, Junqing; Wang, Ting; Zhang, Meisheng; Zhang, Ningyu; Pang, Yantao; Li, Luyan; Ji, Yanju; Zhuang, Shidong; Mao, Jinhua; Wang, Huilin

    2013-10-01

    Considering effects of molecular vibration (ω0), hyperfine interaction (J), spin energy split, spin flip, and spin entanglement (η) of electron with nucleus on the hopping rate of electrons in organic semiconductors, we establish a model to calculate organic magnetoresistance (OMAR) within magnetic field B of 1 T. The results show that the effect of spin energy split is minimal, ω0 influences the gradient of OMAR to B in high field, J influences the OMAR in low field, the spin flip shows impact mainly in low field, η affects OMAR throughout the considered magnetic field and turns the high-field OMAR from positive to negative value.

  4. Simulation of the magnetization dynamics of diluted ferrofluids in medical applications.

    PubMed

    Rogge, Henrik; Erbe, Marlitt; Buzug, Thorsten M; Lüdtke-Buzug, Kerstin

    2013-12-01

    Ferrofluids, which are stable, colloidal suspensions of single-domain magnetic nanoparticles, have a large impact on medical technologies like magnetic particle imaging (MPI), magnetic resonance imaging (MRI) and hyperthermia. Here, computer simulations promise to improve our understanding of the versatile magnetization dynamics of diluted ferrofluids. A detailed algorithmic introduction into the simulation of diluted ferrofluids will be presented. The algorithm is based on Langevin equations and resolves the internal and the external rotation of the magnetic moment of the nanoparticles, i.e., the Néel and Brown diffusion. The derived set of stochastic differential equations are solved by a combination of an Euler and a Heun integrator and tested with respect to Boltzmann statistics. PMID:24163220

  5. Magnetic instability in a dilute circular rarefaction wave

    SciTech Connect

    Dieckmann, M. E.; Sarri, G.; Borghesi, M.

    2012-12-15

    The growth of magnetic fields in the density gradient of a rarefaction wave has been observed in simulations and in laboratory experiments. The thermal anisotropy of the electrons, which gives rise to the magnetic instability, is maintained by the ambipolar electric field. This simple mechanism could be important for the magnetic field amplification in astrophysical jets or in the interstellar medium ahead of supernova remnant shocks. The acceleration of protons and the generation of a magnetic field by the rarefaction wave, which is fed by an expanding circular plasma cloud, is examined here in form of a 2D particle-in-cell simulation. The core of the plasma cloud is modeled by immobile charges, and the mobile protons form a small ring close to the cloud's surface. The number density of mobile protons is thus less than that of the electrons. The protons of the rarefaction wave are accelerated to 1/10 of the electron thermal speed, and the acceleration results in a thermal anisotropy of the electron distribution in the entire plasma cloud. The instability in the rarefaction wave is outrun by a TM wave, which grows in the dense core distribution, and its magnetic field expands into the rarefaction wave. This expansion drives a secondary TE wave.

  6. Analytical study of acoustically perturbed Brillouin active magnetized semiconductor plasma

    SciTech Connect

    Shukla, Arun; Jat, K. L.

    2015-07-31

    An analytical study of acoustically perturbed Brillouin active magnetized semiconductor plasma has been reported. In the present analytical investigation, the lattice displacement, acousto-optical polarization, susceptibility, acousto-optical gain constant arising due to the induced nonlinear current density and acousto-optical process are deduced in an acoustically perturbed Brillouin active magnetized semiconductor plasma using the hydrodynamical model of plasma and coupled mode scheme. The influence of wave number and magnetic field has been explored. The analysis has been applied to centrosymmetric crystal. Numerical estimates are made for n-type InSb crystal duly irradiated by a frequency doubled 10.6 µm CO{sub 2} laser. It is found that lattice displacement, susceptibility and acousto-optical gain increase linearly with incident wave number and applied dc magnetic field, while decrease with scattering angle. The gain also increases with electric amplitude of incident laser beam. Results are found to be well in agreement with available literature.

  7. Static Magnetic Fields in Semiconductor Floating-Zone Growth

    NASA Technical Reports Server (NTRS)

    Croll, Arne; Benz, K. W.

    1999-01-01

    Heat and mass transfer in semiconductor float-zone processing are strongly influenced by convective flows in the zone, originating from sources such as buoyancy convection, thermocapillary (Marangoni) convection, differential rotation, or radio frequency heating. Because semiconductor melts are conducting, flows can be damped by the use of static magnetic fields to influence the interface shape and the segregation of dopants and impurities. An important objective is often the suppression of time-dependent flows and the ensuing dopant striations. In RF-heated Si-FZ - crystals, fields up to O.STesla show some flattening of the interface curvature and a reduction of striation amplitudes. In radiation-heated (small-scale) SI-FZ crystals, fields of 0.2 - 0.5 Tesla already suppress the majority of the dopant striations. The uniformity of the radial segregation is often compromised by using a magnetic field, due to the directional nature of the damping. Transverse fields lead to an asymmetric interface shape and thus require crystal rotation (resulting in rotational dopant striations) to achieve a radially symmetric interface, whereas axial fields introduce a coring effect. A complete suppression of dopant striations and a reduction of the coring to insignificant values, combined with a shift of the axial segregation profile towards a more diffusion-limited case, are possible with axial static fields in excess of 1 Tesla. Strong static magnetic fields, however, can also lead to the appearance of thermoelectromagnetic convection, caused by the interaction of thermoelectric currents with the magnetic field.

  8. The synthesis and characterization of 1 1 1 1 type diluted ferromagnetic semiconductor (La(1-x)Ca(x))(Zn(1-x) Mn(x))AsO.

    PubMed

    Ding, Cui; Guo, Shengli; Zhao, Yao; Man, Huiyuan; Fu, Licheng; Gu, Yilun; Wang, Zhouyang; Liu, L; Frandsen, B A; Cheung, S; Uemura, Y J; Goko, T; Luetkens, H; Morenzoni, E; Zhao, Yang; Ning, F L

    2016-01-20

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor, (La(1-x)Ca(x))(Zn(1-y) Mn(y))AsO, with a layered crystal structure isostructural to that of the 1 1 1 1 type Fe-based high-temperature superconductor LaFeAsO and the antiferromagnetic LaMnAsO. With Ca and Mn codoping into LaZnAsO, the ferromagnetic ordering occurs below the Curie temperature T(c) ∼30 K. Taking advantage of the decoupled charge and spin doping, we investigate the influence of carrier concentration on the ferromagnetic ordering state. For a fixed Mn concentration of 10%, T(c) increases from 24 K to 30 K when the Ca concentration increases from 5% to 10%. Further increase of Ca concentration reduces both the coercive field and saturation moment. Muon spin relaxation measurements confirm the ferromagnetically ordered state, and clearly demonstrate that La(1-x)Ca(x))(Zn(1-y) Mn(y))AsO shares a common mechanism for the ferromagnetic exchange interaction with (Ga,Mn)As. Neutron scattering measurements show no structural transition in (La(0.90)Ca(0.10))(Zn(0.90)Mn(0.10)) AsO below 300 K. PMID:26679223

  9. The synthesis and characterization of 1 1 1 1 type diluted ferromagnetic semiconductor (La1-x Ca x )(Zn1-x Mn x )AsO

    NASA Astrophysics Data System (ADS)

    Ding, Cui; Guo, Shengli; Zhao, Yao; Man, Huiyuan; Fu, Licheng; Gu, Yilun; Wang, Zhouyang; Liu, L.; Frandsen, B. A.; Cheung, S.; Uemura, Y. J.; Goko, T.; Luetkens, H.; Morenzoni, E.; Zhao, Yang; Ning, F. L.

    2016-01-01

    We report the synthesis and characterization of a bulk form diluted magnetic semiconductor, (La1-x Ca x )(Zn1-y Mn y )AsO, with a layered crystal structure isostructural to that of the 1 1 1 1 type Fe-based high-temperature superconductor LaFeAsO and the antiferromagnetic LaMnAsO. With Ca and Mn codoping into LaZnAsO, the ferromagnetic ordering occurs below the Curie temperature {{T}\\text{C}}   ˜30 K. Taking advantage of the decoupled charge and spin doping, we investigate the influence of carrier concentration on the ferromagnetic ordering state. For a fixed Mn concentration of 10%, {{T}\\text{C}} increases from 24 K to 30 K when the Ca concentration increases from 5% to 10%. Further increase of Ca concentration reduces both the coercive field and saturation moment. Muon spin relaxation measurements confirm the ferromagnetically ordered state, and clearly demonstrate that (La1-x Ca x )(Zn1-y Mn y )AsO shares a common mechanism for the ferromagnetic exchange interaction with (Ga,Mn)As. Neutron scattering measurements show no structural transition in (La0.90Ca0.10)(Zn0.90Mn0.10)AsO below 300 K.

  10. Peltier heat of a small polaron in a magnetic semiconductor

    SciTech Connect

    Liu, N.H.; Emin, D.

    1985-04-15

    For the first time the heat transported with a small polaron in both antiferromagnetic and ferromagnetic semiconductors is calculated. This heat, the Peltier heat, ..pi.., is obtained from the change of the entropy of the total system upon introduction of a charge carrier. We explicitly consider both the intrasite and intersite exchange interactions between a small polaron and the interacting spins of a spin-1/2 magnet. There are two competing magnetic contributions to the Peltier heat. First, adding the carrier increases the spin entropy of the system. This provides a positive contribution to ..pi... Second, the exchange between the carrier and the sites about it enhances the exchange binding between these sites. This reduces the energetically allowable spin configurations and provides a negative contribution to ..pi... At extremely high temperatures when kT exceeds the intrasite exchange energy, the first effect dominates. Then ..pi.. is simply augmented by kT ln 2. However, well below the magnetic transition temperature the second effect dominates. In the experimentally accessible range between these limits both effects are comparable and sizable. The net magnetic contribution to the Peltier heat rises with temperature. Thus, a carrier's interactions with its magnetic environment produces a significant and distinctive contribution to its Peltier heat.

  11. Peltier heat of a small polaron in a magnetic semiconductor

    SciTech Connect

    Liu, N.L.H.; Emin, D.

    1984-01-01

    The heat transported with a small polaron in both antiferromagnetic and ferromagnetic semiconductors is calculated. This heat, the Peltier heat, ..pi.., is obtained from the change of the entropy of the total system upon introduction of a charge carrier. We explicitly consider both the intrasite and intersite exchange interactions between a small polaron and the interacting spins of a spin-1/2 magnet. There are two competing magnetic contributions to the Peltier heat. First, adding the carrier increases the spin entropy of the system. This provides a positive contribution to ..pi... Second, the exchange between the carrier and the sites about it enhances the exchange binding between these sites. This reduces the energetically allowable spin configurations and provides a negative contribution to ..pi... At extremely high temperature when kT exceeds the intrasite exchange energy, the first effect dominates. Then ..pi.. is simply augmented by kTln2. However, well below the magnetic transition temperature the second effect dominates. In the experimentally accessible range between these limits both effects are comparable and sizable. The net magnetic contribution to the Peltier heat rises with temperature. Thus, a carrier's interactions with its magnetic environment produces a significant and distinctive contribution to its Peltier heat.

  12. Correlation of nanoscale structure with electronic and magnetic properties in semiconductor materials

    NASA Astrophysics Data System (ADS)

    He, Li

    The goal of this research is to correlate individual nanostructures with their electronic and magnetic properties. Three classes of semiconductor materials and nanostructures were investigated: nanowires, dilute magnetic semiconductors, and quantum dots. First, we fabricated electrical contact to free-standing nanowires using focused ion beam (FIB)-induced deposition and achieved ohmic contact between GaP nanowires and FIB-deposited Pt. Ion irradiation was found to change the nanowire resistance, presumably through the generation of electrical active defects. Based on the finding that ion beam induces deposition outside the direct impact area, a new fabrication method for nanowire core-shell structures was developed by creating an annular direct deposition pattern around the nanowire. We also developed a new nanowire transmission electron microscopy (TEM) sample preparation method that enabled the free-standing nanowires to be individually studied in the TEM. Distribution of Pt and Si elements in the deposited layers was confirmed by x-ray energy dispersive spectroscopy and electron energy filtered imaging (elemental mapping). The indirect deposition mechanism is attributed to the interaction of secondary electrons generated from the primary ion impact area with the deposition precursor absorbed at the nanowire surface. The calculated secondary electron flux distribution matched well with the variation of deposition thickness along the nanowire length and with the pattern radius. The second part of this work employed Mn implantation in Ge with subsequent rapid thermal annealing or TEM in-situ annealing to study the correlation between structure and magnetic properties in Ge:Mn magnetic semiconductor materials. Implantation at 75°C with dual Mn doses (2.4x10 15/cm2 at 170 keV, followed by 5.6x10 15/cm2 at 60 keV) produced an amorphous Ge film containing Mn-rich clusters. Its magnetic properties indicated dispersion of ferromagnetic regions in a non-magnetic matrix

  13. Dynamics of Coulomb correlations in semiconductors in high magnetic fields

    SciTech Connect

    Fromer, Neil Alan

    2002-05-01

    Current theories have been successful in explaining many nonlinear optical experiments in undoped semiconductors. However, these theories require a ground state which is assumed to be uncorrelated. Strongly correlated systems of current interest, such as a two dimensional electron gas in a high magnetic field, cannot be explained in this manner because the correlations in the ground state and the low energy collective excitations cause a breakdown of the conventional techniques. We perform ultrafast time-resolved four-wave mixing on $n$-modulation doped quantum wells, which contain a quasi-two dimensional electron gas, in a large magnetic field, when only a single Landau level is excited and also when two levels are excited together. We find evidence for memory effects and as strong coupling between the Landau levels induced by the electron gas. We compare our results with simulations based on a new microscopic approach capable of treating the collective effects and correlations of the doped electrons, and find a good qualitative agreement. By looking at the individual contributions to the model, we determine that the unusual correlation effects seen in the experiments are caused by the scattering of photo-excited electron-hole pairs with the electron gas, leading to new excited states which are not present in undoped semiconductors, and also by exciton-exciton interactions mediated by the long-lived collective excitations of the electron gas, inter-Landau level magnetoplasmons.

  14. Magnetic Field Suppression of Flow in Semiconductor Melt

    NASA Technical Reports Server (NTRS)

    Fedoseyev, A. I.; Kansa, E. J.; Marin, C.; Volz, M. P.; Ostrogorsky, A. G.

    2000-01-01

    One of the most promising approaches for the reduction of convection during the crystal growth of conductive melts (semiconductor crystals) is the application of magnetic fields. Current technology allows the experimentation with very intense static fields (up to 80 KGauss) for which nearly convection free results are expected from simple scaling analysis in stabilized systems (vertical Bridgman method with axial magnetic field). However, controversial experimental results were obtained. The computational methods are, therefore, a fundamental tool in the understanding of the phenomena accounting during the solidification of semiconductor materials. Moreover, effects like the bending of the isomagnetic lines, different aspect ratios and misalignments between the direction of the gravity and magnetic field vectors can not be analyzed with analytical methods. The earliest numerical results showed controversial conclusions and are not able to explain the experimental results. Although the generated flows are extremely low, the computational task is a complicated because of the thin boundary layers. That is one of the reasons for the discrepancy in the results that numerical studies reported. Modeling of these magnetically damped crystal growth experiments requires advanced numerical methods. We used, for comparison, three different approaches to obtain the solution of the problem of thermal convection flows: (1) Spectral method in spectral superelement implementation, (2) Finite element method with regularization for boundary layers, (3) Multiquadric method, a novel method with global radial basis functions, that is proven to have exponential convergence. The results obtained by these three methods are presented for a wide region of Rayleigh and Hartman numbers. Comparison and discussion of accuracy, efficiency, reliability and agreement with experimental results will be presented as well.

  15. Polydispersity effects on the magnetization of diluted ferrofluids: a lognormal analysis

    NASA Astrophysics Data System (ADS)

    Wang, Xu-Fei; Shi, Li-Qun

    2010-10-01

    Based on a lognormal particle size distribution, this paper makes a model analysis on the polydispersity effects on the magnetization behaviour of diluted ferrofluids. Using a modified Langevin relationship for the lognormal dispersion, it first performs reduced calculations without material parameters. From the results, it is extrapolated that for the ferrofluid of lognormal polydispersion, in comparison with the corresponding monodispersion, the saturation magnetization is enhanced higher by the particle size distribution. It also indicates that in an equivalent magnetic field, the lognormally polydispersed ferrofluid is magnetically saturated faster than the corresponding monodispersion. Along the theoretical extrapolations, the polydispersity effects are evaluated for a typical ferrofluid of magnetite, with a dispersity of σ = 0.20. The results indicate that the lognormal polydispersity leads to a slight increase of the saturation magnetization, but a noticeable increase of the speed to reach the saturation value in an equivalent magnetic field.

  16. Random site dilution properties of frustrated magnets on a hierarchical lattice.

    PubMed

    Fortin, Jean-Yves

    2013-07-24

    We present a method to analyze the magnetic properties of frustrated Ising spin models on specific hierarchical lattices with random dilution. Disorder is induced by dilution and geometrical frustration rather than randomness in the internal couplings of the original Hamiltonian. The two-dimensional model presented here possesses a macroscopic entropy at zero temperature in the large size limit, very close to the Pauling estimate for spin-ice on the pyrochlore lattice, and a crossover towards a paramagnetic phase. The disorder due to dilution is taken into account by considering a replicated version of the recursion equations between partition functions at different lattice sizes. An analysis to first order in replica number allows a systematic reorganization of the disorder configurations, leading to a recurrence scheme. This method is numerically implemented to evaluate thermodynamical quantities such as specific heat and susceptibility in an external field. PMID:23807800

  17. Magnetic anisotropy control in Ga1-x Mnx As magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Stagraczyński, S.; Jasiukiewicz, C.; Dugaev, V. K.; Berakdar, J.

    2016-08-01

    Using the six-band Kane model of the electron energy spectrum in the valence band of GaMnAs magnetic semiconductor we investigate the dependence of the crystalline magnetic anisotropy on the magnitude of magnetization and on the doping with holes. Our main focus is on the difference between two possible models related to the constraint on the total hole number or on the chemical potential. Our results show that the theoretical results for magnetic anisotropy can change dramatically with the use of different constraints.

  18. Magnetite and magnetite/silver core/shell nanoparticles with diluted magnet-like behavior

    SciTech Connect

    Garza-Navarro, Marco; Gonzalez, Virgilio; Ortiz, Ubaldo; De la Rosa, Elder

    2010-01-15

    In the present work is reported the use of the biopolymer chitosan as template for the preparation of magnetite and magnetite/silver core/shell nanoparticles systems, following a two step procedure of magnetite nanoparticles in situ precipitation and subsequent silver ions reduction. The crystalline and morphological characteristics of both magnetite and magnetite/silver core/shell nanoparticles systems were analyzed by high resolution transmission electron microscopy (HRTEM) and nanobeam diffraction patterns (NBD). The results of these studies corroborate the core/shell morphology and the crystalline structure of the magnetite core and the silver shell. Moreover, magnetization temperature dependent, M(T), measurements show an unusual diluted magnetic behavior attributed to the dilution of the magnetic ordering in the magnetite and magnetite/silver core/shell nanoparticles systems. - Graphical abstract: Biopolymer chitosan was used as stabilization media to synthesize both magnetite and magnetite/silver core/shell nanoparticles. Results of HRTEM and NBD patterns confirm core/shell morphology of the obtained nanoparticles. It was found that the composites show diluted magnet-like behavior.

  19. Comparison of ferromagnetism in n- and p-type magnetic semiconductor thin films of ZnCoO

    NASA Astrophysics Data System (ADS)

    Lee, Y. H.; Lee, J. C.; Min, J. F.; Su, C. W.

    2011-07-01

    Both n- and p-type diluted magnetic semiconductor ZnCoO are made by magnetron co-sputtering with, respectively, dopants of Al and dual dopants of Al and N. The two sputtering targets are compound ZnCoO with 5% weight of Co and pure metal Al. Sputtering gases for n- and p-type films are pure Ar and N 2, respectively. These films are magnetic at room temperature and possess free electron- and hole-concentration of 5.34×10 20 and 5.27×10 13 cm -3. Only the n-type film exhibits anomalous Hall-effect signals. Magnetic properties of these two types of films are compared and discussed based on measurements of microstructure and magneto-transport properties.

  20. Recent progress in magnetic iron oxide-semiconductor composite nanomaterials as promising photocatalysts

    NASA Astrophysics Data System (ADS)

    Wu, Wei; Changzhong Jiang, Affc; Roy, Vellaisamy A. L.

    2014-11-01

    Photocatalytic degradation of toxic organic pollutants is a challenging tasks in ecological and environmental protection. Recent research shows that the magnetic iron oxide-semiconductor composite photocatalytic system can effectively break through the bottleneck of single-component semiconductor oxides with low activity under visible light and the challenging recycling of the photocatalyst from the final products. With high reactivity in visible light, magnetic iron oxide-semiconductors can be exploited as an important magnetic recovery photocatalyst (MRP) with a bright future. On this regard, various composite structures, the charge-transfer mechanism and outstanding properties of magnetic iron oxide-semiconductor composite nanomaterials are sketched. The latest synthesis methods and recent progress in the photocatalytic applications of magnetic iron oxide-semiconductor composite nanomaterials are reviewed. The problems and challenges still need to be resolved and development strategies are discussed.

  1. Magnetic moment formation at a dilute 140Ce impurity in RCo2 compounds

    NASA Astrophysics Data System (ADS)

    de Oliveira, A. L.; Chaves, C. M.; de Oliveira, N. A.; Troper, A.

    2010-05-01

    A great deal of experimental work using perturbed angular correlation has succeed in measuring hyperfine fields in Ce diluted in metallic systems, thus allowing the determination of the local impurity moment at low temperatures. Motivated by such experimental work on C140e placed on a R site of the rare earth (R =Gd,Tb,Dy,Ho,Er) in RCo2, we theoretically discuss, within a simple model, the local magnetic moments and, thereby, calculate the magnetic hyperfine fields. The results are in good agreement with the experimental data. For the sake of comparison we recall our previous results on Ta d-impurity embedded in the same hosts.

  2. Transverse gradient diffusion in a polydisperse dilute suspension of magnetic spheres during sedimentation.

    PubMed

    Cunha, F R; Couto, H L G

    2008-05-21

    In this work we investigate the pair interaction of magnetic particles in a dilute polydisperse sedimenting suspension. The suspension is composed of magnetic spherical forms of different radii and densities immersed in a Newtonian fluid, settling due to the gravity. When in close contact, the particles may exert on each other a magnetic force due to a permanent magnetization. We restrict our attention to dispersions of micromagnetic composite with negligible Brownian motion. The calculations of the relative particle trajectories are based on direct computations of the hydrodynamic interactions among rigid spheres in the regime of low particle Reynolds number. Depending on the relative importance of the interparticle forces and gravity, the collisions may result in aggregation or simply in a breaking of the particle relative trajectory time reversibility. After summing over all possible encounters, the transverse self-diffusion and down-gradient diffusion coefficients that describe the cross-flow migration of the particles are calculated. Our calculation shows first evidence and the significance of the diffusion process arising from magnetic interactions in dilute non-Brownian suspensions. PMID:21694258

  3. Engineering Gilbert damping by dilute Gd doping in soft magnetic Fe thin films

    SciTech Connect

    Zhang, W. Jiang, S.; Sun, L.; Wang, Y. K.; Zhai, Y.; Wong, P. K. J.; Wang, K.; Jong, M. P. de; Wiel, W. G. van der; Laan, G. van der

    2014-05-07

    By analyzing the ferromagnetic resonance linewidth, we show that the Gilbert damping constant in soft magnetic Fe thin films can be enhanced by ∼6 times with Gd doping of up to 20%. At the same time, the magnetic easy axis remains in the film plane while the coercivity is strongly reduced after Gd inclusion. X-ray magnetic circular dichroism measurements reveal a strong increase in the orbital-to-spin moment ratio of Fe with increasing Gd concentration, in full agreement with the increase in the Gilbert damping obtained for these thin films. Combined with x-ray diffraction and vibrating sample magnetometry, the results demonstrate that the FeGd thin films with dilute Gd doping of up to 20% are promising candidates for spin-transfer-torque applications in soft magnetic devices, in which an enhanced damping is required.

  4. Tunable exchange bias in dilute magnetic alloys – chiral spin glasses

    PubMed Central

    Hudl, Matthias; Mathieu, Roland; Nordblad, Per

    2016-01-01

    A unidirectional anisotropy appears in field cooled samples of dilute magnetic alloys at temperatures well below the cusp temperature of the zero field cooled magnetization curve. Magnetization measurements on a Cu(13.5 at% Mn) sample show that this anisotropy is essentially temperature independent and acts on a temperature dependent excess magnetization, ΔM. The anisotropy can be partially or fully transferred from being locked to the direction of the cooling field at lower fields to becoming locked to the direction of ΔM at larger fields, thus instead appearing as a uniaxial anisotropy. This introduces a deceiving division of the anisotropy into a superposition of a unidirectional and a uniaxial part. This two faced nature of the anisotropy has been empirically scrutinized and concluded to originate from one and the same exchange mechanism: the Dzyaloshinsky-Moriya interaction. PMID:26817418

  5. Dispersion regions overlapping for bulk and surface polaritons in a magnetic-semiconductor superlattice

    NASA Astrophysics Data System (ADS)

    Fesenko, Volodymyr I.; Fedorin, Illia V.; Tuz, Vladimir R.

    2016-05-01

    Extraordinary dispersion features of both bulk and surface polaritons in a finely-stratified magnetic-semiconductor structure which is under an action of an external static magnetic field in the Voigt geometry are discussed in this letter. It is shown that the conditions for total overlapping dispersion regions of simultaneous existence of bulk and surface polaritons can be reached providing a conscious choice of the constitutive parameters and material fractions for both magnetic and semiconductor subsystems.

  6. Magnetoviscosity of dilute suspensions of magnetic ellipsoids obtained through rotational Brownian dynamics simulations.

    PubMed

    Sánchez, J H; Rinaldi, C

    2009-03-15

    The magnetic field dependent viscosity (magnetoviscosity) of dilute suspensions of magnetic tri-axial ellipsoidal particles suspended in a Newtonian fluid and under applied shear and magnetic fields was studied numerically. Brownian dynamics simulations were performed to compute the intrinsic magnetoviscosity of the suspension. Results are presented for the response of dilute suspensions of ellipsoidal particles to constant magnetic and shear flow fields. Suspensions of ellipsoidal particles show a significant effect of aspect ratio on the intrinsic magnetoviscosity of the suspension, and this effect is more pronounced as the aspect ratio becomes more extreme. The use of an effective rotational diffusion coefficient D(r,eff) collapses the normalized intrinsic magnetoviscosity of all suspensions to a master curve as a function of Péclet number with the Langevin parameter alpha=(mu(0)muH)/(k(B)T) as parameter, up to a critical value of alpha for which the results for suspensions of spherical particles deviate from those of suspensions of ellipsoids. This discrepancy is attributed to the action of the shear-torque on the ellipsoidal particles, which tends to orient these particles in the direction of maximum deformation of the simple shear flow, and which does not act on spherical particles. PMID:19100560

  7. Spin-polarized semiconductor induced by magnetic impurities in graphene

    NASA Astrophysics Data System (ADS)

    Daghofer, Maria

    2011-03-01

    Magnetic impurities adsorbed on graphene sheets are coupled antiferromangetically via the itinerant electrons in the graphene. We study this interaction and its impact on the electrons' spectral density by use of unbiased Monte-Carlo simulations. The antiferromagnetic order breaks the symmetry between the sublattices, and a gap for the itinerant electrons opens. Our simulations show that the itinerant states below and above the gap are not dispersionless states trapped by the impurities, but are instead mobile states with a large dispersion. We compare various scenarios for the impurity distribution and find that random doping produces a standard semiconductor. If, on the other hand, all or most of the impurities are localized in the same sublattice, the spin degeneracy is lifted and the conduction band becomes spin-polarized. We also discuss the properties of edge states at edges or magnetic domain boundaries. M.~Daghofer, N.~Zheng, A.~Moreo; Phys.~Rev.~B 82, 121405(R) (2010) Supported by the DFG under the Emmy-Noether Program, and the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. DOE.

  8. Spin-density-wave magnetism in dilute copper-manganese alloys

    SciTech Connect

    Lamelas, F.J.; Werner, S.A.; Shapiro, S.M.; Mydosh, J.A.

    1995-02-01

    Elastic neutron-scattering measurements on two samples of Cu alloyed with 1.3% Mn and 0.55% Mn show that the spin-density-wave (SDW) features found in more concentrated alloys persist in the limit of very dilute alloys. These features consist of temperature-dependent incommensurate peaks in magnetic neutron scattering, with positions and strengths which are fully consistent with those in the concentrated alloys. The implications of these measurements are twofold. First, it is clear from this data that SDW magnetic ordering occurs across the entire range of CuMn alloys which have typically been interpreted as spin glasses. Second, the more fundamental significance of this work is the suggestion via extrapolation that a peak in the magnetic susceptibility x(q) occurs in pure copper, at a value of q given by the Fermi-surface diameter 2k{sub F}.

  9. Magnetization dynamics, rheology, and an effective description of ferromagnetic units in dilute suspension.

    PubMed

    Ilg, Patrick; Kröger, Martin

    2002-08-01

    The rheological properties of a dilute suspension of ellipsoidal ferromagnetic particles in the presence of a magnetic field are studied on the basis of a kinetic model, where the flow and magnetic external fields couple in qualitatively different ways to the orientational behavior of the suspension. In the uniaxial phase the stress tensor is found to be of the same form as in the Ericksen-Leslie theory for nematic liquid crystals in the steady state. Expressions for a complete set of viscosity coefficients in terms of orientational order parameters are worked out. In the low Péclet number regime, the viscosity coefficients are given as explicit functions of the magnetic field and a particle shape factor, where the shape factor may equally represent a nonspherical unit (agglomerate, chain) composed of spherical particles. Effects due to possible flow-induced breakup of units are not covered in this work. Further, by considering the magnetization as the only relevant variable, a magnetization equation within an effective field approach is derived from the kinetic equation and compared to existing magnetization equations. The alignment angle of the magnetization and the first and second normal stress coefficient are studied for the special case of plane Couette flow. The assumptions employed are tested against a Brownian dynamics simulation of the full kinetic model, and a few comparisons with experimental data are made. PMID:12241181

  10. Thermoelectric power of small polarons in magnetic semiconductors

    SciTech Connect

    Liu, N.H.; Emin, D.

    1984-09-15

    The thermoelectric power (Seebeck coefficient) ..cap alpha.. of a small polaron in both ferromagnetic and antiferromagnetic semiconductors and insulators is calculated for the first time. In particular, we obtain the contribution to the Seebeck coefficient arising from exchange interactions between the severely localized carrier (i.e., small polaron) of charge q and the spins of the host lattice. In essence, we study the heat transported along with a carrier. This heat, the Peltier heat, Pi, is related to the Seebeck coefficient by the Kelvin relation: Pi = qT..cap alpha.., where T is the temperature. The heat per carrier is simply the product of the temperature and the change of the entropy of the system when a small polaron is added to it. The magnetic contribution to the Seebeck coefficient is therefore directly related to the change of the magnetic entropy of the system upon introduction of a charge carrier. We explicitly treat the intrasite and intersite exchange interactions between a small polaron and the spins of a spin-1/2 system. These magnetic interactions produce two competing contributions to the Seebeck coefficient. First, adding the carrier tends to provide extra spin freedom (e.g., spin up or spin down of the carrier). This effect augments the entropy of the system, thereby producing a positive contribution to the Peltier heat. Second, however, the additional exchange between the carrier and the sites about it enhances the exchange binding among these sites. This generally reduces the energetically allowable spin configurations. The concomitant reduction of the system's entropy provides a negative contribution to the Peltier heat. At the highest of temperatures, when kT exceeds the intrasite exchange energy, the first effect dominates. Then, the Peltier heat is simply augmented by kT ln2.

  11. On the self-organization of magnetic field and highly diluted matter in astrophysics

    NASA Astrophysics Data System (ADS)

    Berdichevsky, D. B.

    2015-12-01

    It is explored the self organization of matter and field in regions beyond our common reach on the surface of our planet and its atmospheric surroundings. This state of matter, which most basic property, the freezing in the magnetic field, see e.g., Chew et al, 1956, has proved to exist in the regions where robotic observations in the near and far space perform detailed observations of magnetic fields, and extreme dilute plasma (commonly about 1000 to 0.1 or less ionized particles per cubic cm). We present and discuss here simple hypotheses on the nature of what could be this state of magnetized matter which in the electron distribution shows a shape which often can successfully be described with a kappa distribution when inside a strongly magnetized transient, of the magnetic cloud kind, see e.g., Nieves Chinchilla and Figueroa-Viñas, 2008. This work is in many ways an extension of Alfven work on magnetized space plasmas, Alven, 1942. Chew, G.F., M.L., Goldberger, and F.E. Low, 1956, the Royal Soc. London, section Math & Phys Sc., 236, pp. 112. Nieves-Chinchilla, T., and A., Figueroa-Viñas, 2008, J. Geophys. Res., 113, A02105. Alfvén, H (1942). "Existence of electromagnetic-hydrodynamic waves". Nature 150: 405.. doi:10.1038/150405d0

  12. How to Magnetically Generate Flows in Dead-Ends with Dilute Suspensions of Iron Particles

    NASA Astrophysics Data System (ADS)

    Bonnecaze, Roger; Clements, Michael

    2015-11-01

    Dilute suspensions of iron particles in the presence of a magnetic field can create flows in dead-ends of pores, channels and even blocked arteries to help dissolve clots. Observations show that added iron particles in a rotating magnetic field form rotating rods along the wall of the blocked channel, creating a convective flow. We present a proposed mechanism for this magnetically driven flow in the form of coupled particle-scale and channel-scale flow models. At the particle-scale, particles chain up to lengths balancing magnetic and hydrodynamic forces on the resulting rods. The weak gradient of the magnetic field causes the rods to accumulate on one side of the channel. The rods rotate due to the rotating magnetic field, provided the field strength is high enough, which creates a localized body couple in the flow that drives a macroscopic convective flow in the channel. Coupled transport equations for the particles and the suspension as a whole are presented. The model equations are solved asymptotically and numerically and compared to experimental observations. Design rules for implementation of this technique are presented to optimize the flow.

  13. Controlled aggregation of magnetic ions in a semiconductor: an experimental demonstration.

    PubMed

    Bonanni, A; Navarro-Quezada, A; Li, Tian; Wegscheider, M; Matĕj, Z; Holý, V; Lechner, R T; Bauer, G; Rovezzi, M; D'Acapito, F; Kiecana, M; Sawicki, M; Dietl, T

    2008-09-26

    The control on the distribution of magnetic ions into a semiconducting host is crucial for the functionality of magnetically doped semiconductors. Through a structural analysis at the nanoscale, we give experimental evidence that the aggregation of Fe ions in (Ga,Fe)N and consequently the magnetic response of the material are affected by the growth rate and doping with shallow impurities. PMID:18851460

  14. Converting a topologically trivial superconductor into a chiral topological superconductor via diluted magnetic doping

    NASA Astrophysics Data System (ADS)

    Qin, Wei; Xiao, Di; Chang, Kai; Shen, Shun-Qing; Zhang, Zhenyu

    We employ two complementary theoretical approaches to explore the feasibility of altering the topological properties of two-dimensional Rashba spin-orbit coupled superconductors by proper introduction of magnetic disorders. First, using the self-consistent Born approximation, we show that a topologically trivial superconductor can be driven into a chiral topological superconductor upon diluted doping of isolated magnetic disorders, which gradually narrow, close, and reopen the quasi-particle gap of the paired electrons in a nontrivial manner. Such a topological phase transition is further characterized by the change in the corresponding topological invariant. The central predictions made here are then confirmed using the complementary numerical approach by solving the Bogoliubov-de Gennes equations self-consistently within a tight-binding model. We also discuss the validity of the present model studies in connection with existing experimental findings. Collectively, the present study offers appealing new schemes for potential experimental realization of topological superconductors. Supported by NSF of China.

  15. Enhancement of magnetization damping coefficient of permalloy thin films with dilute Nd dopants

    NASA Astrophysics Data System (ADS)

    Luo, C.; Feng, Z.; Fu, Y.; Zhang, W.; Wong, P. K. J.; Kou, Z. X.; Zhai, Y.; Ding, H. F.; Farle, M.; Du, J.; Zhai, H. R.

    2014-05-01

    For spintronics application, which requires fast field switching, it is important to have a kind of soft magnetic material with large damping coefficient. Here, we present the studies of the Nd dopant-level-dependent damping coefficient of Ndx-Py(1-x) thin films (30 nm) in a dilute region utilizing ferromagnetic resonance (FMR). With the Nd content increasing, the film structure was found to be changing from polycrystalline to amorphous when the Nd content is around 3.4%. Meanwhile, the magnetization decreases linearly. Interestingly, we find that along the easy axis, both low coercivity and high hysteresis squareness are simultaneously maintained in the system; i.e., the magnetic softness has been well kept. By theoretical fitting of the angular dependence of the FMR field, the first- and second-order magnetic anisotropy constants, K1 and K2, and the Lande g factor are obtained and discussed quantitatively. The measurements of angular and frequency dependence of the ferromagnetic resonance linewidth, as well as the theoretical fitting by considering the contributions of Gilbert damping, two-magnon scattering, and inhomogeneous broadening, show that the damping coefficient α increases rapidly (about 25-fold) as the Nd content increases to 11.6%, which is mainly due to the enhanced spin-orbit coupling by the Nd additives, supported by x-ray magnetic circular dichroism measurements.

  16. Mössbauer and vibrational DOS studies of diluted magnetic tin oxides and nano iron oxides

    NASA Astrophysics Data System (ADS)

    Nomura, K.; Rykov, A. I.; Navarro, A. M. Mudarra; Torres, C. E. Rodriguez; Errico, L. A.; Barrero, C. A.; Yoda, Y.

    2013-04-01

    The magnetic properties and Mössbauer results for SnO2 doped with 57Fe are reviewed, and the values of isomer shift and quadrupole splitting are compared with the results obtained by ab initio calculations. It is concluded that the exchange interactions between oxygen defects and magnetic atoms are responsible for long range magnetic interactions of dilute Fe ions dispersed in SnO2. Fe atom precipitated clusters may be formed in highly Fe doped SnO2 samples by annealing at relatively high temperatures for several hours. The reduction of the particle size to nano-scale dimensions induces magnetization, which can be associated with oxygen defects. We have measured the nuclear inelastic scattering (NIS) spectra of Fe oxides, and 57Fe and (Co or Mn) doped SnO2 synthesized mainly by sol-gel methods and we have derived the vibration density of states (VDOS). The local phonons are sensitive to the presence of precipitated clusters.

  17. Mössbauer and vibrational DOS studies of diluted magnetic tin oxides and nano iron oxides

    NASA Astrophysics Data System (ADS)

    Nomura, K.; Rykov, A. I.; Navarro, A. M. Mudarra; Torres, C. E. Rodriguez; Errico, L. A.; Barrero, C. A.; Yoda, Y.

    2014-01-01

    The magnetic properties and Mössbauer results for SnO2 doped with 57Fe are reviewed, and the values of isomer shift and quadrupole splitting are compared with the results obtained by ab initio calculations. It is concluded that the exchange interactions between oxygen defects and magnetic atoms are responsible for long range magnetic interactions of dilute Fe ions dispersed in SnO2. Fe atom precipitated clusters may be formed in highly Fe doped SnO2 samples by annealing at relatively high temperatures for several hours. The reduction of the particle size to nano-scale dimensions induces magnetization, which can be associated with oxygen defects. We have measured the nuclear inelastic scattering (NIS) spectra of Fe oxides, and 57Fe and (Co or Mn) doped SnO2 synthesized mainly by sol-gel methods and we have derived the vibration density of states (VDOS). The local phonons are sensitive to the presence of precipitated clusters.

  18. Electronic structure and magnetic properties of dilute U impurities in metals

    NASA Astrophysics Data System (ADS)

    Mohanta, S. K.; Cottenier, S.; Mishra, S. N.

    2016-05-01

    The electronic structure and magnetic moment of dilute U impurity in metallic hosts have been calculated from first principles. The calculations have been performed within local density approximation of the density functional theory using Augmented plane wave+local orbital (APW+lo) technique, taking account of spin-orbit coupling and Coulomb correlation through LDA+U approach. We present here our results for the local density of states, magnetic moment and hyperfine field calculated for an isolated U impurity embedded in hosts with sp-, d- and f-type conduction electrons. The results of our systematic study provide a comprehensive insight on the pressure dependence of 5f local magnetism in metallic systems. The unpolarized local density of states (LDOS), analyzed within the frame work of Stoner model suggest the occurrence of local moment for U in sp-elements, noble metals and f-block hosts like La, Ce, Lu and Th. In contrast, U is predicted to be nonmagnetic in most transition metal hosts except in Sc, Ti, Y, Zr, and Hf consistent with the results obtained from spin polarized calculation. The spin and orbital magnetic moments of U computed within the frame of LDA+U formalism show a scaling behavior with lattice compression. We have also computed the spin and orbital hyperfine fields and a detail analysis has been carried out. The host dependent trends for the magnetic moment, hyperfine field and 5f occupation reflect pressure induced change of electronic structure with U valency changing from 3+ to 4+ under lattice compression. In addition, we have made a detailed analysis of the impurity induced host spin polarization suggesting qualitatively different roles of f-band electrons on moment stability. The results presented in this work would be helpful towards understanding magnetism and spin fluctuation in U based alloys.

  19. Specific Heat of the Dilute Ising Magnet LiHoxY1-xF4

    NASA Astrophysics Data System (ADS)

    Quilliam, J. A.; Mugford, C. G. A.; Gomez, A.; Kycia, S. W.; Kycia, J. B.

    2007-01-01

    We present specific heat data on three samples of the dilute Ising magnet LiHoxY1-xF4 with x=0.018, 0.045, and 0.080. Previous measurements of the ac susceptibility of an x=0.045 sample showed the Ho3+ moments to remain dynamic down to very low temperatures, and the specific heat was found to have unusually sharp features. In contrast, our measurements do not exhibit these sharp features in the specific heat and instead show a broad feature, for all three samples studied, which is qualitatively consistent with a spin glass state. Integrating C/T, however, reveals an increase in residual entropy with lower Ho concentration, consistent with recent Monte Carlo simulations showing a lack of spin glass transition for low x.

  20. Relaxation and coherent oscillations in the spin dynamics of II-VI diluted magnetic quantum wells

    NASA Astrophysics Data System (ADS)

    Ungar, F.; Cygorek, M.; Tamborenea, P. I.; Axt, V. M.

    2015-10-01

    We study theoretically the ultrafast spin dynamics of II-VI diluted magnetic quantum wells in the presence of spin-orbit interaction. We extend a recent study where it was shown that the spin-orbit interaction and the exchange sd coupling in bulk and quantum wells can compete resulting in qualitatively new dynamics when they act simultaneously. We concentrate on Hg1-x-yMnxCdyTe quantum wells, which have a highly tunable Rashba spin-orbit coupling. Our calculations use a recently developed formalism which incorporates electronic correlations originating from the exchange sd-coupling. We find that the dependence of electronic spin oscillations on the excess energy changes qualitatively depending on whether or not the spin-orbit interaction dominates or is of comparable strength with the sd interaction.

  1. Magnetic hysteresis curve influenced by power-semiconductor characteristics in pulse-width-modulation inverter

    NASA Astrophysics Data System (ADS)

    Fujisaki, Keisuke; Liu, Sungju

    2014-05-01

    The influence of power semiconductor characteristic in Pulse-width-modulation (PWM) inverter on the magnetic hysteresis curve in silicon steel is discussed through the measured magnetic hysteresis curves. The magnetic hysteresis curve of PWM inverter-fed silicon steel has a lot of minor loops as closed loops and open loops, which make an influence on the iron loss. Two shapes of minor loops are found to be caused by the voltage shifts and they are derived from the on-voltage of the semiconductors in PWM inverter circuit. Therefore, it is concluded that the power-semiconductor characteristic in PWM inverter makes an influence on the magnetic hysteresis curve in silicon steel.

  2. Bistable Magnetism and Potential for Voltage-Induced Spin Crossover in Dilute Magnetic Ferroelectrics.

    PubMed

    Weston, L; Cui, X Y; Ringer, S P; Stampfl, C

    2015-06-19

    A first-principles investigation into the magnetic ferroelectric PbTi(1-x)Co(x)O(3) has revealed a bi-stable magnetic system with strong spin-lattice coupling. The local distortions induced by the low-spin to high-spin crossover are ferroelectric in nature, and are characterized by the displacement of the dopant ion with respect to the surrounding O(6) octahedral cage. We demonstrate how this spin-lattice effect could mediate magnetoelectric coupling and possible electric field induced spin-crossover, indicating a promising route to voltage manipulation of isolated spins in a solid-state system. PMID:26197012

  3. Semiconductor-halfmetal-metal transition and magnetism of bilayer graphene nanoribbons/hexagonal boron nitride heterostructure

    NASA Astrophysics Data System (ADS)

    Ilyasov, V. V.; Meshi, B. C.; Nguyen, V. C.; Ershov, I. V.; Nguyen, D. C.

    2014-12-01

    The paper presents the results of ab initio study of electronic structure modulation and edge magnetism in the antiferromagnetic (AF) bilayer zigzag graphene nanoribbons (AF-BZGNR)/hexagonal boron nitride (h-BN(0001)) semiconductor heterostructure induced with transverse external electric field (Eext) and nanomechanical compression (extension), performed within the framework of the density functional theory using Grimme's DFT(PBE)-D2 scheme. For the first time we established critical values of Eext and interlayer distance in the bilayer for the BZGNR/h-BN(0001) heterostructure providing for semiconductor-halfmetal-metal phase transition for one of the electron spin configurations. We discovered the effect of preserved local magnetic moment (0.3μB) of edge carbon atoms of the lower (buffer) graphene nanoribbon during nanomechanical uniaxial compression (or extension) of the BZGNR/h-BN(0001) semiconductor heterostructure. It has been demonstrated that magnetic properties of the AF-BZGNR/h-BN(0001) semiconductor heterostructure can be controlled using Eext. In particular, the local magnetic moment of edge carbon atoms decreases by 10% at a critical value of the positive potential. We have established that local magnetic moments and band gaps can be altered in a wide range using nanomechanical uniaxial compression and Eext, thus making the AF-BZGNR/h-BN(0001) semiconductor heterostructure potentially promising for nanosensors, spin filters, and spintronics applications.

  4. Electron correlations in semiconductors: Bulk cohesive properties and magnetic-field-induced Wigner crystal at heterojunctions

    SciTech Connect

    Louie, S.G.; Zhu, X.

    1992-08-01

    A correlated wavefunction variational quantum Monte Carlo approach to the studies of electron exchange and correlation effects in semiconductors is presented. Applications discussed include the cohesive and structural properties of bulk semiconductors, and the magnetic-field-induced Wigner electron crystal in two dimensions. Landau level mixing is shown to be important in determining the transition between the quantum Hall liquid and the Wigner crystal states in the regime of relevant experimental parameters.

  5. Regularities in temperature, magnetic field and pressure effect on the resistive properties of magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Polyakov, P. I.; Kucherenko, S. S.

    2002-08-01

    The influence of hydrostatic pressure, magnetic field and temperature on resistivity behaviour of bulk and film samples La 0.9Mn 1.1O 3 and La 0.56Ca 0.24Mn 1.2O 3 at action of magnetic field and temperature has been analysed. It is established that the maximum of magnetoresistive and the revealed baroresistive, magnetobaroresistive effects coincide at the same temperature Tpp. This temperature is equal to the "metal-semiconductor" phase transition temperature Tms. "Cooling" and "heating" effects of pressure and magnetic field have been revealed. A mutual correspondence of T- P- H (6.2 K, 1 kbar, 2.7 kOe) influence on polycrystalline sample La 0.9Mn 1.1O 3 resistivity has been determined. The linear change of Tms( P) and Tms( H) in La 0.9Mn 1.1O 3, La 0.56Ca 0.24Mn 1.2O 3 resistivity have been found. An importance of the regularities of elastic-deforming correspondence of T- H- P influence on magnetic, resistivity properties, phase transitions and effects was elucidated and explained. An alternating influence of T- H- P and its role in resistivity has been pointed. A correlation between structural, elastic and resistive properties is specified.

  6. Magnetic dilution and domain selection in the X Y pyrochlore antiferromagnet Er2Ti2O7

    NASA Astrophysics Data System (ADS)

    Gaudet, J.; Hallas, A. M.; Maharaj, D. D.; Buhariwalla, C. R. C.; Kermarrec, E.; Butch, N. P.; Munsie, T. J. S.; Dabkowska, H. A.; Luke, G. M.; Gaulin, B. D.

    2016-08-01

    Below TN=1.1 K, the X Y pyrochlore Er2Ti2O7 orders into a k =0 noncollinear, antiferromagnetic structure referred to as the ψ2 state. The magnetic order in Er2Ti2O7 is known to obey conventional three-dimensional (3D) percolation in the presence of magnetic dilution, and in that sense is robust to disorder. Recently, however, two theoretical studies have predicted that the ψ2 structure should be unstable to the formation of a related ψ3 magnetic structure in the presence of magnetic vacancies. To investigate these theories, we have carried out systematic elastic and inelastic neutron scattering studies of three single crystals of Er2 -xYxTi2O7 with x =0 (pure), 0.2 (10 %Y ) and 0.4 (20 % Y ), where magnetic Er3 + is substituted by nonmagnetic Y3 +. We find that the ψ2 ground state of pure Er2Ti2O7 is significantly affected by magnetic dilution. The characteristic domain selection associated with the ψ2 state, and the corresponding energy gap separating ψ2 from ψ3, vanish for Y3 + substitutions between 10 % Y and 20 % Y , far removed from the three-dimensional percolation threshold of ˜60 % Y . The resulting ground state for Er2Ti2O7 with magnetic dilutions from 20 % Y up to the percolation threshold is naturally interpreted as a frozen mosaic of ψ2 and ψ3 domains.

  7. Specific Heat of the Dilute Ising Magnet LiHoxY1-xF4

    NASA Astrophysics Data System (ADS)

    Quilliam, Jeffrey; Mugford, Chas; Lettress, Lauren; Kycia, Jan

    2007-03-01

    We will present specific heat results on the dilute dipolar-coupled Ising magnet LiHoxY1-xF4. This material was previously observed to change from a spin glass to an unusual ``anti-glass'' state at a Ho concentration of x˜0.045. This state showed dynamics that are very different from those of a spin glass and also exhibited sharp features in its specific heat at around 100 and 300 mK. In contrast, our measurements of the heat capacity do not reproduce these sharp features and instead find broad curves for three concentrations (1.8%, 4.5% and 8.0%). Integrating C/T reveals a residual entropy S0 which is 0 for 8.0% Ho but increases with lower concentration (to 0.31R at 1.8% Ho). This provides some evidence for a change to a different magnetic ground state below 8.0% Ho and is qualitatively consistent with Monte Carlo simulations. AC susceptibility measurements probing the dynamics of this system are currently being performed and results will be presented. S. Ghosh et al., Science 296, 2195 (2002) S. Ghosh et al., Nature 425, 48 (2003). J. Snider and C. C. Yu, Phys. Rev. B 72, 214203 (2005).

  8. First-principles approach to spin-orbit coupling in dilute magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Theurich, G.; Hill, N. A.

    2002-09-01

    We describe the implementation of a spin-polarized fully relativistic plane wave pseudopotential density functional method. Using the method, we compare the calculated electronic band structures of hypothetical ferromagnetic zinc blende structure MnAs and MnSe within the scalar-relativistic and fully relativistic pseudopotential approximations. We extract the conduction band and valence band exchange constants and extrapolate to the low concentration limit following a simple mean field approximation. Finally we investigate how strongly the exchange constants are affected by the spin-orbit term and provide a computational justification for extracting these constants from scalar-relativistic calculations.

  9. Sub-surface characterization and three dimensional profiling of semiconductors by magnetic resonance force microscopy

    SciTech Connect

    Hammel, P.C.; Moore, G.; Roukes, M.; Zhenyong Zhang

    1996-10-01

    This is the final report of a two-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project successfully developed a magnetic resonance force microscope (MRFM) instrument to mechanically detect magnetic resonance signals. This technique provides an intrinsically subsurface, chemical-species-specific probe of structure, constituent density and other properties of materials. As in conventional magnetic resonance imaging (MRI), an applied magnetic field gradient selects a well defined volume of the sample for study. However mechanical detection allows much greater sensitivity, and this in turn allows the reduction of the size of the minimum resolvable volume. This requires building an instrument designed to achieve nanometer-scale resolution at buried semiconductor interfaces. High-resolution, three-dimensional depth profiling of semiconductors is critical in the development and fabrication of semiconductor devices. Currently, there is no capability for direct, high-resolution observation and characterization of dopant density, and other critical features of semiconductors. The successful development of MRFM in conjunction with modifications to improve resolution will enable for the first time detailed structural and electronic studies in doped semiconductors and multilayered nanoelectronic devices, greatly accelerating the current pace of research and development.

  10. Room temperature magnetism and metal to semiconducting transition in dilute Fe doped Sb1-xSex semiconducting alloy thin films

    NASA Astrophysics Data System (ADS)

    Agrawal, Naveen; Sarkar, Mitesh; Chawda, Mukesh; Ganesan, V.; Bodas, Dhananjay

    2015-02-01

    The magnetism was observed in very dilute Fe doped alloy thin film Fe0.008Sb1-xSex, for x = 0.01 to 0.10. These thin films were grown on silicon substrate using thermal evaporation technique. Structural, electrical, optical, charge carrier concentration measurement, surface morphology and magnetic properties were observed using glancing incidence x-ray diffraction (GIXRD), four probe resistivity, photoluminescence, Hall measurement, atomic force microscopy (AFM) and magnetic force microscopy (MFM) techniques, respectively. No peaks of iron were seen in GIXRD. The resistivity results show that activation energy increases with increase in selenium (Se) concentration. The Arrhenius plot reveals metallic behavior below room temperature. The low temperature conduction is explained by variable range-hopping mechanism, which fits very well in the temperature range 150-300 K. The decrease in density of states has been observed with increasing selenium concentration (x = 0.01 to 0.10). There is a metal-to-semiconductor phase transition observed above room temperature. This transition temperature is Se concentration dependent. The particle size distribution ˜47-61 nm is evaluated using AFM images. These thin films exhibit ferromagnetic interactions at room temperature.

  11. Photoexcitation-induced magnetism in arrays of semiconductor nanoparticles with a strong excitonic oscillator strength

    NASA Astrophysics Data System (ADS)

    Yannopapas, V.; Vitanov, N. V.

    2006-11-01

    A type of magnetic metamaterial which exhibits strong magnetic activity within and below the optical region is presented. The metamaterial consists of semiconductor nanoparticles such as CuCl or Cu2O particles. The magnetic activity is attributed to the strong oscillator strength stemming from the exciton absorption line. The magnetic permeability of the proposed metamaterial is calculated from the extended Maxwell-Garnett theory, and its validity is compared against ab initio layer multiple-scattering calculations. The proposed structure is a low-loss, subwavelength, isotropic magnetic metamaterial, and its response is robust against stacking and point disorder.

  12. Magneto-optical studies of magnetic and non-magnetic narrow-gap semiconductors

    NASA Astrophysics Data System (ADS)

    Khodaparast, Giti

    2005-03-01

    In light of the growing interest in spin-related phenomena and devices, there is now renewed interest in the science and engineering of narrow gap semiconductors. Narrow gap semiconductors (NGS) offer many unique features such as small effective masses, high intrinsic mobilities, large effective g- factors, and large spin-orbit coupling effects. This talk will discuss our recent magneto-optical studies on InSb quantum wells (QWs) and InMnAs ferromagnetic heterostructures. In InSb QWs, we observe spin-resolved cyclotron resonance (CR) caused by the non- parabolicity in conduction band and electron spin resonance in symmetric and asymmetric confinement potentials. The asymmetric wells exhibit a strong deviation in behavior from the symmetric wells at low magnetic fields with far more spin splitting than expected from the bulk g-factor of InSb. In InMnAs/GaSb we observe light and heavy hole CR peaks which demonstrate the existence of delocalized p-like carriers. In addition, In order to increase our understanding of the dynamics of carriers and spins, we performed time resolved measurements such as time- resolved CR spectroscopy on undoped InSb QWs and time-resolved magneto-optical Kerr effect on InMnAs/GaSb. Our results are important for understanding the electronic and magnetic states in NGS. This work was performed in collaboration with M. B. Santos and R. E. Doezema at the Univ. of Oklahoma, J. Wang and J. Kono at Rice Univ., H. Munekata at Tokyo Institute of Technology, C. J. Stanton at the Univ. of Florida, and Y. H. Matsuda and N. Miura at the Univ. of Tokyo.

  13. Hydrogenated Graphene Nanoflakes: Semiconductor to Half-Metal Transition and Remarkable Large Magnetism

    SciTech Connect

    Zhou, Yungang; Wang, Zhiguo; Yang, Ping; Sun, Xin; Zu, Xiaotao; Gao, Fei

    2012-03-08

    The electronic and magnetic properties of graphene nanoflakes (GNFs) can be tuned by patterned adsorption of hydrogen. Controlling the H coverage from bare GNFs to half hydrogenated and then to fully hydrogenated GNFs, the transformation of small-gap semiconductor {yields} half-metal {yields} wide-gap semiconductor occurs, accompanied by a magnetic {yields} magnetic {yields} nonmagnetic transfer and a nonmagnetic {yields} magnetic {yields} nonmagnetic transfer for triangular and hexagonal nanoflakes, respectively. The half hydrogenated GNFs, associated with strong spin polarization around the Fermi level, exhibit the unexpected large spin moment that is scaled squarely with the size of flakes. The induced spin magnetizations of these nanoflakes align parallel and lead to a substantial collective character, enabling the half hydrogenated GNFs to be spin-filtering flakes. These hydrogenation-dependent behaviors are then used to realize an attractive approach to engineer the transport properties, which provides a new route to facilitate the design of tunable spin devices.

  14. Magnetic anisotropy induced by crystal distortion in Ge{sub 1−x}Mn{sub x}Te/PbTe//KCl (001) ferromagnetic semiconductor layers

    SciTech Connect

    Knoff, W. Łusakowski, A.; Domagała, J. Z.; Minikayev, R.; Taliashvili, B.; Łusakowska, E.; Pieniążek, A.; Szczerbakow, A.; Story, T.

    2015-09-21

    Ferromagnetic resonance (FMR) study of magnetic anisotropy is presented for thin layers of IV-VI diluted magnetic semiconductor Ge{sub 1−x}Mn{sub x}Te with x = 0.14 grown by molecular beam epitaxy on KCl (001) substrate with a thin PbTe buffer. Analysis of the angular dependence of the FMR resonant field reveals that an easy magnetization axis is located near to the normal to the layer plane and is controlled by two crystal distortions present in these rhombohedral Ge{sub 1−x}Mn{sub x}Te layers: the ferroelectric distortion with the relative shift of cation and anion sub-lattices along the [111] crystal direction and the biaxial in-plane, compressive strain due to thermal mismatch.

  15. Conductivity and magnetic properties of TmSe and TmS: Comparison to the dilute cases

    NASA Astrophysics Data System (ADS)

    Holtzberg, F.; Flouquet, J.; Haen, P.; Lapierre, F.; Lassailly, Y.; Vettier, C.

    1985-04-01

    Magnetization, neutron diffraction, and resistivity measurements performed on the compounds TmSe and TmS are compared to those on the dilute alloys (Tm,Y)Se and (Tm,Y)S. In the paramagnetic regime, major differences exist between a regular array of Tm ions (TmSe and TmS) and the dilute systems. Localization (TmSe) or magnetic correlations (TmS) appear clearly in the conductivity behavior or in the dependence of the static susceptibility. A low content of Y atoms in TmSe has a drastic effect on the conductivity and on the magnetic order. We will discuss the connection between the degeneracy of the ground state with the opening of a gap.

  16. Origin and enhancement of spin polarized current in diluted magnetic oxides by oxygen vacancies

    NASA Astrophysics Data System (ADS)

    Chou, Hsiung; Yang, Kung-Shang; Tsao, Yao-Chung; Dwivedi, G. D.; Lin, Cheng-Pang; Sun, Shih-Jye; Lin, L. K.; Lee, S. F.

    2016-04-01

    Spin polarized current (SPC) is a crucial characteristic of diluted magnetic oxides due to the potential application of oxides in spintronic devices. However, most research has been focused on ferromagnetic properties rather than polarization of electric current, because direct measurements are difficult and the origin of SPC has yet to be fully understood. The method to increase the SPC percentage is beyond practical consideration at present. To address this problem, we focus on the role of oxygen vacancies (VO) on SPC, which are controlled by growing the Co-doped ZnO thin-films at room temperature in a reducing atmosphere [Ar + (1%-30%)H2]. We found that the conductivity increases with an increase of VO via two independent channels: the variable range hopping (VRH) within localized states and the itinerant transport in the conduction band. The point contact Andreev reflection measurements at 4.2 K, where the electric conduction is governed only by the VRH mechanism, prove that the current flowing in the VRH hopping channel is SPC. The percentage of SPC increases with the introduction of VO and increase in its concentration. The transport measurement shows that by manipulating VO, one can control the percentage of VRH hopping conduction such that it can even dominate room temperature conduction. The highest achieved SPC ratio at room temperature was 80%.

  17. Magnetic Field Applications in Semiconductor Crystal Growth and Metallurgy

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin; Ramachandran, Narayanan; Grugel, Richard; Curreri, Peter A. (Technical Monitor)

    2002-01-01

    The Traveling Magnetic Field (TMF) technique, recently proposed to control meridional flow in electrically conducting melts, is reviewed. In particular, the natural convection damping capability of this technique has been numerically demonstrated with the implication of significantly improving crystal quality. Advantages of the traveling magnetic field, in comparison to the more mature rotating magnetic field method, are discussed. Finally, results of experiments with mixing metallic alloys in long ampoules using TMF is presented

  18. Magnetic coupling in ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers

    NASA Astrophysics Data System (ADS)

    Wang, M.; Wadley, P.; Campion, R. P.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L.; Charlton, T. R.; Kinane, C. J.; Langridge, S.

    2015-08-01

    We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields.

  19. Magnetic coupling in ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers

    SciTech Connect

    Wang, M.; Wadley, P.; Campion, R. P.; Rushforth, A. W.; Edmonds, K. W.; Gallagher, B. L.; Charlton, T. R.; Kinane, C. J.; Langridge, S.

    2015-08-07

    We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields.

  20. Theoretical and experimental investigations of superconductivity. Amorphous semiconductors, superconductivity and magnetism

    NASA Technical Reports Server (NTRS)

    Cohen, M. H.

    1973-01-01

    The research activities from 1 March 1963 to 28 February 1973 are summarized. Major lectures are listed along with publications on superconductivity, superfluidity, electronic structures and Fermi surfaces of metals, optical spectra of solids, electronic structure of insulators and semiconductors, theory of magnetic metals, physics of surfaces, structures of metals, and molecular physics.

  1. Parametric distortion of the optical absorption edge of a magnetic semiconductor by a strong laser field

    SciTech Connect

    Nunes, O.A.C.

    1985-09-15

    The influence of a strong laser field on the optical absorption edge of a direct-gap magnetic semiconductor is considered. It is shown that as the strong laser intensity increases the absorption coefficient is modified so as to give rise to an absorption tail below the free-field forbidden gap. An application is made for the case of the EuO.

  2. Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

    SciTech Connect

    Sachleben, J. R.

    1993-09-01

    Semiconductor nanocrystals, small biomolecules, and {sup 13}C enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution {sup 1}H and {sup 13}C liquid state spectra of thiophenol ligands on the nanocrystal surfaces. The surface coverage by thiophenol was found to be low, being 5.6 and 26% for nanocrystal radii of 11.8 and 19.2 {angstrom}. Internal motion is estimated to be slow with a correlation time > 10{sup {minus}8} s{sup {minus}1}. The surface thiophenol ligands react to form a dithiophenol when the nanocrystals were subjected to O{sub 2} and ultraviolet. A method for measuring {sup 14}N-{sup 1}H J-couplings is demonstrated on pyridine and the peptide oxytocin; selective 2D T{sub 1} and T{sub 2} experiments are presented for measuring relaxation times in crowded spectra with overlapping peaks in 1D, but relaxation effects interfere. Possibility of carbon-carbon cross relaxation in {sup 13}C enriched solids is demonstrated by experiments on zinc acetate and L-alanine.

  3. Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

    NASA Astrophysics Data System (ADS)

    Sachleben, J. R.

    1993-09-01

    Semiconductor nanocrystals, small biomolecules, and C-13 enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution H-1 and C-13 liquid state spectra of thiophenol ligands on the nanocrystal surfaces. The surface coverage by thiophenol was found to be low, being 5.6 and 26% for nanocrystal radii of 11.8 and 19.2 angstrom. Internal motion is estimated to be slow with a correlation time greater than 10(exp -8) s(exp -1). The surface thiophenol ligands react to form a dithiophenol when the nanocrystals were subjected to O2 and ultraviolet. A method for measuring (N-14)-(H-1) J-couplings is demonstrated on pyridine and the peptide oxytocin; selective 2D T(sub 1) and T(sub 2) experiments are presented for measuring relaxation times in crowded spectra with overlapping peaks in 1D, but relaxation effects interfere. Possibility of carbon-carbon cross relaxation in C-13 enriched solids is demonstrated by experiments on zinc acetate and L-alanine.

  4. Electronic structure and exchange interactions in diluted semimagnetic semiconductors (Zn,Co)Se and (Zn,Mn)Se

    NASA Astrophysics Data System (ADS)

    Mašek, J.

    1991-05-01

    A comparative study of the electronic structure of (Zn,Co)Se and (Zn,Mn)Se is done by using a tight-binding version of the coherent potential approximation. The densities of states, relevant for a photoemission experiment, are calculated for a magnetically disordered phase. The exchange constant Jpd is obtained from the splitting of the valence band top in the ferromagnetic phase of the mixed crystal; Jdd is estimated from the energy of a spin reversal. We explain the large exchange constant in the Co-based systems as a result of efficient hybridization of the d-states with the valence band.

  5. Technique for magnetic susceptibility determination in the highly doped semiconductors by electron spin resonance

    SciTech Connect

    Veinger, A. I.; Zabrodskii, A. G.; Tisnek, T. V.; Goloshchapov, S. I.; Semenikhin, P. V.

    2014-08-20

    A method for determining the magnetic susceptibility in the highly doped semiconductors is considered. It is suitable for the semiconductors near the metal - insulator transition when the conductivity changes very quickly with the temperature and the resonance line form distorts. A procedure that is based on double integration of the positive part of the derivative of the absorption line having a Dyson shape and takes into account the depth of the skin layer is described. Analysis is made for the example of arsenic-doped germanium samples at a rather high concentration corresponding to the insulator-metal phase transition.

  6. Strongly correlated systems: Magnetic measurements of magnesium diboride and group IV magnetic semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Guchhait, Samaresh

    Nuclear Magnetic Resonance Force Microscopy (NMRFM) is a unique quantum microscopy technique, which combines the three-dimensional imaging capabilities of magnetic resonance imaging (MRI) with the high sensitivity and resolution of atomic force microscopy (AFM). It has potential applications in many different fields. This novel scanning probe instrument holds potential for atomic-scale resolution. MgB2 is a classic example of two-band superconductor. However, the behavior of these two bands below the superconducting transition temperature is not well understood yet. Also, the anisotropic relaxation times of single crystal MgB2 have not been measured because it is not yet possible to grow large enough MgB2 single crystals for conventional NMR. Using our homemade NMRFM probe, we have set out to measure the relaxation times of micron size MgB2 single crystals to answer several questions relating to the anisotropy, multiband behavior, and coherence effects in this unusual superconductor. The goal of a second project is to study the effects of doping on the critical current of MgB2 superconducting wires. Ti-sheathed MgB 2 wires doped with nanosize crystalline-SiC up to a concentration of 15 wt% SiC have been fabricated, and the effects of the SiC doping on the critical current density (Jc) and other superconducting properties studied. In contrast with the previously reported results, our measurements show that SiC doping decreases Jc over almost the whole field range from 0 to 7.3 tesla at all temperatures. Furthermore, it is found that the degradation of Jc becomes stronger at higher SiC doping levels. Our results indicate that these negative effects on Jc could be attributed to the absence of significant effective pinning centers (mainly Mg2Si) due to the high chemical stability of the crystalline-SiC particles. The principle goal of a third project, the study of magnetic semiconductors, is to investigate magnetic properties of Mn-implanted GeC thin films. 20 ke

  7. Study on the oxygen vacancy redistribution and the mechanism of electrical manipulation of ferromagnetism in diluted magnetic oxides

    SciTech Connect

    Ren, Shuxia; Dong, Jingyu; Chen, Wei Zhang, Liyong; Guo, Jiajun; Zhang, Li; Zhao, Jing; Zhao, Xu

    2015-12-21

    Electrical manipulation of room temperature ferromagnetism (RTFM) has been observed in several kinds of transition metal doped diluted magnetic oxide films. We demonstrate using X-ray photoelectron spectroscopy that the redistribution of the oxygen vacancies in a film under an electric field plays a crucial role in the enhancement of the RTFM. Based on a detailed analysis of the X-ray photoelectron spectroscopy data for the oxygen vacancy distribution in different resistive states, a unified mechanism has been proposed. This work points out a new direction for improving the magnetic properties of these materials by controlling oxygen vacancies in the interior of the films.

  8. Spin noise explores local magnetic fields in a semiconductor

    NASA Astrophysics Data System (ADS)

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-02-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates.

  9. Spin noise explores local magnetic fields in a semiconductor

    PubMed Central

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-01-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new – magnetometric – potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates. PMID:26882994

  10. Spin noise explores local magnetic fields in a semiconductor.

    PubMed

    Ryzhov, Ivan I; Kozlov, Gleb G; Smirnov, Dmitrii S; Glazov, Mikhail M; Efimov, Yurii P; Eliseev, Sergei A; Lovtcius, Viacheslav A; Petrov, Vladimir V; Kavokin, Kirill V; Kavokin, Alexey V; Zapasskii, Valerii S

    2016-01-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new - magnetometric - potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This "optical field" is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates. PMID:26882994

  11. Magnetic Properties of Randomly Diluted Antiferromagnetic System: COBALT(P)MAGNESIUM(1-P)OXYGEN.

    NASA Astrophysics Data System (ADS)

    Kannan, Raman

    In this work, the effect of randomly diluting CoO (a fcc antiferromagnet with Neel temperature T _{rm N} = 289 K) with MgO has been investigated using temperature dependent dc magnetic susceptibility measurements. About twenty samples of Co _{rm p}Mg _{rm 1-p}O with p = 0.10, 0.13, 0.17, 0.22, 0.23, 0.31, 0.33, 0.36, 0.41, 0.46, 0.49, 0.53, 0.56, 0.60, 0.64, 0.70, 0.80 and 0.87, were investigated in the temperature range of 1.6 K to 300 K. These powder samples were prepared starting from the nitrates, Co(NO _3)_2cdot6H _2O and Mg(NO_3)_2 cdot6H_2O. The samples were characterized by magnetic measurements for the presence of ferromagnetic impurities, by X-ray diffraction technique for the determination of crystal structure and lattice constants, and by atomic absorption spectroscopy for the determination of the composition parameter p. The lattice constant is found to vary linearly with p, in accordance with Vegard's Law. The magnetic susceptibility, chi , measurements were carried out with a Faraday balance, employing Lewis coils. The samples were cooled either in zero field (zfc) or in a field of 50 Oe (fc) to the lowest temperature (1.6 K or 4.2 K), followed by chi measurements in 50 Oe with increasing temperatures. A Neel temperature T_{ rm N}, as determined by d(chi T)/dT, is observed for all p >=q 0.17. By extrapolation and by the behavior of the low temperature magnetization, it is determined that the percolation threshold p_{rm c} = 0.13 +/- 0.01. This is in agreement with the theoretical estimate of p_{ rm c} = 0.136 for fcc lattice with nn and nnn included. The variation of T_{ rm N} with p is non-linear for p < 0.6. However no theoretical variation of T _{rm N} vs p is available for fcc lattice with both nn and nnn interactions included. For the high temperature region (T > T_{rm N}), the data is fit to the Curie-Weiss law and the Curie-Weiss temperature theta(p), the molar and gram Curie constants C_{rm M}(p) and C_{rm g}(p) respectively and the effective

  12. A structurally-controllable spin filter in a δ-doped magnetically modulated semiconductor nanostructure with zero average magnetic field

    NASA Astrophysics Data System (ADS)

    Shen, Li-Hua; Ma, Wen-Yue; Zhang, Gui-Lian; Yang, Shi-Peng

    2015-07-01

    We report on a theoretical investigation of spin-polarized transport in a δ-doped magnetically modulated semiconductor nanostructure, which can be experimentally realized by depositing a ferromagnetic stripe on the top of a semiconductor heterostructure and by using the atomic layer doping technique such as molecular beam epitaxy (MBE). It is shown that although such a nanostructure has a zero average magnetic filed, a sizable spin polarization exists due to the Zeeman splitting mechanism. It is also shown that the degree of spin polarization varies sensitively with the weight and/or position of the δ-doping. Therefore, one can conveniently tailor the behaviour of the spin-polarized electron by tuning the δ -doping, and such a device can be employed as a controllable spin filter for spintronics.

  13. Optically Detected Magnetic Resonance and Thermal Activation Spectroscopy Study of Organic Semiconductors

    SciTech Connect

    Chang-Hwan Kim

    2003-12-12

    Organic electronic materials are a new class of emerging materials. Organic light emitting devices (OLEDs) are the most promising candidates for future flat panel display technologies. The photophysical characterization is the basic research step one must follow to understand this new class of materials and devices. The light emission properties are closely related to the transport properties of these materials. The objective of this dissertation is to probe the relation between transport and photophysical properties of organic semiconductors. The transport characteristics were evaluated by using thermally stimulated current and thermally stimulated luminescence techniques. The photoluminescence detected magnetic resonance and photoluminescence quantum yield studies provide valuable photophysical information on this class of materials. OLEDs are already in the market. However, detailed studies on the degradation mechanisms are still lacking. Since both optically detected magnetic resonance and thermal activation spectroscopy probe long-lived defect-related states in organic semiconductors, the combined study generates new insight on the OLED operation and degradation mechanisms.

  14. Extremely large magnetoresistance and magnetic logic by coupling semiconductor nonlinear transport effect and anomalous Hall Effect

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaozhong; Luo, Zhaochu

    Size limitation of silicon FET hinders the further scaling down of silicon based CPU. To solve this problem, spin based magnetic logic devices were proposed but almost all of them could not be realized experimentally except for NOT logic operation. A magnetic field controlled reconfigurable semiconductor logic using InSb was reported. However, InSb is very expensive and not compatible with the silicon technology. Based on our Si based magnetoresistance (MR) device, we developed a Si based reconfigurable magnetic logic device, which could do all four Boolean logic operations including AND, OR, NOR and NAND. By coupling nonlinear transport effect of semiconductor and anomalous Hall effect of magnetic material, we propose a PMA material based MR device with a remarkable non local MR of >20000 % at ~1 mT. Based on this MR device, we further developed a PMA material based magnetic logic device which could do all four Boolean logic operations. This makes it possible that magnetic material does both memory and logic. This may result in a memory-logic integrated system leading to a non von Neumann computer

  15. Ferromagnetism of magnetic semiconductors: Zhang-Rice limit

    NASA Astrophysics Data System (ADS)

    Dietl, T.; Matsukura, F.; Ohno, H.

    2002-07-01

    It is suggested that p-d hybridization contributes significantly to the hole binding energy Eb of Mn acceptors in III-V compounds, leading in an extreme case to the formation of Zhang-Rice-like small magnetic polarons. The model explains both the strong increase of Eb and the evolution of a Mn spin-resonance spectrum with the magnitude of valence-band offsets. The high Curie temperature above room temperature is shown to be in accordance with the mean-field Zener model.

  16. Room-temperature ferromagnetism in Zn{sub 1-x}Co{sub x}O magnetic semiconductors prepared by sputtering

    SciTech Connect

    Dinia, A.; Schmerber, G.; Meny, C.; Pierron-Bohnes, V.; Beaurepaire, E.

    2005-06-15

    We have used magnetron cosputtering to grow Zn{sub 1-x}Co{sub x}O magnetic dilute semiconductors. The growth has been performed on SiO{sub 2}/Si and Al{sub 2}O{sub 3}(0001) substrates. The Co concentration has been varied between 0.1 and 0.25 and the substrate temperature between room temperature and 600 deg. C. X-ray diffraction analysis has shown that for the films grown on Si substrates the structural quality of the film is improved by increasing the growth temperature and/or postgrowth annealing. The films are textured with c axis of the wurtzite structure along the growth direction. However, for the films grown on Al{sub 2}O{sub 3} substrate quasi-epitaxial films have been obtained for 600 deg. C substrate temperature. Magnetization measurements have shown that the ferromagnetism is directly correlated to the structural quality and appears by increasing the growth temperature and/or postgrowth annealing. Moreover, for the highly textured film a clear magnetic perpendicular anisotropy has been evidenced with the easy magnetization axis along the growth direction. To evidence the intrinsic nature of the ferromagnetism in the films, transmission optical measurements have been used. They show three absorption bands that are characteristics of d-d transitions of tetrahedrally coordinated Co{sup 2+}. This has been supported by nuclear magnetic resonance and magnetic thermal variation.

  17. Transition metal doped semiconductor quantum dots: Optical and magnetic properties

    NASA Astrophysics Data System (ADS)

    Dahnovsky, Yuri; Proshchenko, Vitaly; Pimachev, Artem

    We study optical and magnetic properties of CdSe and Cd-Mn-Se quantum dots (QD). We find that there are two luminescence lines, one is fast and another is slow (~1ms). With the increase of a QD diameter the slow luminescence disappears at some critical QD size, thus only one line (fast) remains. Using the SAC SI computational method we find that D = 3.2 nm and D = 2.7 nm if the Mn impurity is located inside a QD or on a QD surface, respectively. For two or four Mn atoms in the quantum dot, now absorption takes place because the transition is spin-allowed. The DFT calculations of the magnetic state reveal that it is an antiferromagnet. We also study other quantum dots such as Cd-Mn-Se, Zn-Mn-S, and Zn-Mn-Se, doped and undoped. We find the slow luminescence energies for low concentrations of Mn impurities for each QD type. The calculations indicate that two luminescence lines, fast and slow, should always take place. However for Pb-Mn-S quantum dots there are now Mn levels inside a HOMO-LUMO gap, i.e., the Mn-levels are located in a PbS conduction band. The presence of Mn dopants increases the band gap and also removes the exciton peak. This effect is different to the other quantum dots.

  18. Temperature dependence of the magnetic hyperfine field at an s-p impurity diluted in RNi2

    NASA Astrophysics Data System (ADS)

    de Oliveira, A. L.; Chaves, C. M.; Oliveira, N. A. de; Troper, A.

    2016-03-01

    We study the formation of local magnetic moments and magnetic hyperfine fields at an s-p impurity diluted in intermetallic Laves phase compounds RNi2 (R=Nd, Sm, Gd, Tb, Dy) at finite temperatures. We start with a clean host and later the impurity is introduced. The host has two-coupled (R and Ni) sublattice Hubbard Hamiltonians but the Ni sublattice can be disregarded because its d band, being full, is magnetically ineffective. Also, the effect of the 4f electrons of R is represented by the polarization they produce on the d band. This leaves us with a lattice of effective rare earth R-ions with polarized electrons. For the dd electronic interaction we use the Hubbard-Stratonovich identity in a functional integral approach in the static saddle point approximation.

  19. Convection Induced by Traveling Magnetic Fields in Semiconductor Melts

    NASA Technical Reports Server (NTRS)

    Konstantin, Mazuruk

    2000-01-01

    Axisymmetric traveling magnetic fields (TMF) can be beneficial for crystal growth applications. such as the vertical Bridgman, float zone or traveling heater methods. TMF induces a basic flow in the form of a single roll. This type of flow can enhance mass and heat transfer to the growing crystal. More importantly, the TMF Lorentz body force induced in the system can counterbalance the buoyancy forces, so the resulting convection can be much smaller and even the direction of it can be changed. In this presentation, we display basic features of this novel technique. In particular, numerical calculations of the Lorentz force for arbitrary frequencies will be presented along with induced steady-state fluid flow profiles. Also, numerical modeling of the TMF counter-balancing natural convection in vertical Bridgman systems will be demonstrated.

  20. Magnetic fields and the technology challenges they pose to beam-based equipment: a semiconductor perspective

    NASA Astrophysics Data System (ADS)

    Esqueda, Vincent; Montoya, Julian A.

    2005-08-01

    As semiconductor devices shrink in size to accommodate faster processing speeds, the need for higher resolution beam-based metrology equipment and beam-based writing equipment will increase. The electron and ion beams used within these types of equipment are sensitive to very small variations in magnetic force applied to the beam. This phenomenon results from changes in Alternating Current (AC) and Direct Current (DC) magnetic flux density at the beam column which causes deflections of the beam that can impact equipment performance. Currently the most sensitive beam-based microscope manufacturers require an ambient magnetic field environment that does not have variations that exceed 0.2 milli-Gauss (mG). Studies have shown that such low levels of magnetic flux density can be extremely difficult to achieve. As examples, scissor lifts, vehicles, metal chairs, and doors moving in time and space under typical use conditions can create distortions in the Earth's magnetic field that can exceed 0.2 mG at the beam column. In addition it is known that changes in the Earth's magnetic field caused by solar flares, earthquakes, and variations in the Earth's core itself all cause changes in the magnetic field that can exceed 0.2 mG. This paper will provide the reader with the basic understanding of the emerging problem, will discuss the environmental and facility level challenges associated in meeting such stringent magnetic field environments, will discuss some of the mitigation techniques used to address the problem, and will close by discussing needs for further research in this area to assure semiconductor and nanotechnology industries are pre-positioned for even more stringent magnetic field environmental requirements.

  1. Detecting excitation and magnetization of individual dopants in a semiconductor two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Wiebe, Jens

    2011-03-01

    Magnetic atoms doped into a semiconductor are the building blocks for bottom up spintronic and quantum logic devices. They also provide model systems for the investigation of fundamental effects. In order to correlate the dopant's atomic structure with its magnetism magnetically sensitive techniques with atomic resolution are a prerequisite. Here, I show electrical excitation and read-out [ 1 ] of single magnetic dopant associated spins in a two-dimensional electron gas (2DEG) confined to a semiconductor surface [ 2 ] using spin-resolved scanning tunneling spectroscopy [ 3 ] . I will review our real-space study of the quantum Hall transition in the 2DEG [ 2 ] and of the magnetic properties of the dopants [ 1 ] . Finally, I will demonstrate that the dopant serves as an atomic scale probe for local magnetometry of the 2DEG. This work was done in collaboration with A. A. Khajetoorians, B. Chillian, S. Schuwalow, F. Lechermann, K. Hashimoto, C. Sohrmann, T. Inaoka, F. Meier, Y. Hirayama, R. A. Römer, M. Morgenstern, and R. Wiesendanger. [ 1 ] A. A. Khajetoorians et al., Nature 467, 1084 (2010). [ 2 ] K. Hashimoto et al., Phys. Rev. Lett. 101, 256802 (2008). [ 3 ] J. Wiebe et al., Rev. Sci. Instrum. 75, 4871 (2004). We acknowledge financial support from ERC Advanced Grant ``FURORE'', by the DFG via SFB668 and GrK1286, and by the city of Hamburg via the cluster of excellence ``Nanospintronics''.

  2. Tunable surface plasmon polaritons in metal-strip waveguides with magnetized semiconductor substrates in Voigt configuration

    NASA Astrophysics Data System (ADS)

    Mathew, Gishamol; Mathew, Vincent

    2012-05-01

    The properties of surface plasmon polaritons (SPPs) in a magnetically tunable strip waveguide geometry comprising of a metal film of finite width deposited on a magnetized semiconductor and covered by an isotropic dielectric material were studied in Voigt configuration. The method of lines was used to compute the dispersion relation of fundamental modes, and the dependence of the propagation constant on metal film dimensions, material parameters and biasing magnetic field was considered. The bounded SPPs are nonreciprocal with respect to the direction of the biasing magnetic field, producing a nonreciprocal phase shift of the order of 2-18 rad mm-1 at a wavelength of excitation 1.55 μm. Moreover, controlled propagation of SPP modes and their effective tuning are possible in this strip geometry, which enables the design and development of tunable optoelectronic devices.

  3. Emergence of competing magnetic interactions induced by Ge doping in the semiconductor FeGa3

    NASA Astrophysics Data System (ADS)

    Alvarez-Quiceno, J. C.; Cabrera-Baez, M.; Ribeiro, R. A.; Avila, M. A.; Dalpian, G. M.; Osorio-Guillén, J. M.

    2016-07-01

    FeGa3 is an unusual intermetallic semiconductor that presents intriguing magnetic responses to the tuning of its electronic properties. When doped with Ge, the system evolves from diamagnetic to paramagnetic to ferromagnetic ground states that are not well understood. In this work, we have performed a joint theoretical and experimental study of FeGa3 -xGex using density functional theory and magnetic susceptibility measurements. For low Ge concentrations we observe the formation of localized moments on some Fe atoms and, as the dopant concentration increases, a more delocalized magnetic behavior emerges. The magnetic configuration strongly depends on the dopant distribution, leading even to the appearance of antiferromagnetic interactions in certain configurations.

  4. Ab initio search for novel bipolar magnetic semiconductors: Layered YZnAsO doped with Fe and Mn

    NASA Astrophysics Data System (ADS)

    Bannikov, V. V.; Ivanovskii, A. L.

    2013-02-01

    Very recently, the newest class of spintronic materials, where reversible spin polarization can be controlled by applying gate voltage: so-called bipolar magnetic semiconductors (Xingxing Li et al., arXiv:1208.1355) was proposed. In this work, a novel way to creation of bipolar magnetic semiconductors by doping of non-magnetic semiconducting 1111 phases with magnetic d n < 10 atoms is discussed using ab initio calculations of layered YZnAsO doped with Fe and Mn. In addition, more complex materials with several spectral intervals with opposite 100% spin polarization where multiple gate-controlled spin-polarization can be expected are proposed.

  5. Unexpected magnetic semiconductor behavior in zigzag phosphorene nanoribbons driven by half-filled one dimensional band.

    PubMed

    Du, Yongping; Liu, Huimei; Xu, Bo; Sheng, Li; Yin, Jiang; Duan, Chun-Gang; Wan, Xiangang

    2015-01-01

    Phosphorene, as a novel two-dimensional material, has attracted a great interest due to its novel electronic structure. The pursuit of controlled magnetism in Phosphorene in particular has been persisting goal in this area. In this paper, an antiferromagnetic insulating state has been found in the zigzag phosphorene nanoribbons (ZPNRs) from the comprehensive density functional theory calculations. Comparing with other one-dimensional systems, the magnetism in ZPNRs display several surprising characteristics: (i) the magnetic moments are antiparallel arranged at each zigzag edge; (ii) the magnetism is quite stable in energy (about 29 meV/magnetic-ion) and the band gap is big (about 0.7 eV); (iii) the electronic and magnetic properties is almost independent on the width of nanoribbons; (iv) a moderate compressive strain will induce a magnetic to nonmagnetic as well as semiconductor to metal transition. All of these phenomena arise naturally due to one unique mechanism, namely the electronic instability induced by the half-filled one-dimensional bands which cross the Fermi level at around π/2a. The unusual electronic and magnetic properties in ZPNRs endow them possible potential for the applications in nanoelectronic devices. PMID:25747727

  6. Unexpected Magnetic Semiconductor Behavior in Zigzag Phosphorene Nanoribbons Driven by Half-Filled One Dimensional Band

    PubMed Central

    Du, Yongping; Liu, Huimei; Xu, Bo; Sheng, Li; Yin, Jiang; Duan, Chun-Gang; Wan, Xiangang

    2015-01-01

    Phosphorene, as a novel two-dimensional material, has attracted a great interest due to its novel electronic structure. The pursuit of controlled magnetism in Phosphorene in particular has been persisting goal in this area. In this paper, an antiferromagnetic insulating state has been found in the zigzag phosphorene nanoribbons (ZPNRs) from the comprehensive density functional theory calculations. Comparing with other one-dimensional systems, the magnetism in ZPNRs display several surprising characteristics: (i) the magnetic moments are antiparallel arranged at each zigzag edge; (ii) the magnetism is quite stable in energy (about 29 meV/magnetic-ion) and the band gap is big (about 0.7 eV); (iii) the electronic and magnetic properties is almost independent on the width of nanoribbons; (iv) a moderate compressive strain will induce a magnetic to nonmagnetic as well as semiconductor to metal transition. All of these phenomena arise naturally due to one unique mechanism, namely the electronic instability induced by the half-filled one-dimensional bands which cross the Fermi level at around π/2a. The unusual electronic and magnetic properties in ZPNRs endow them possible potential for the applications in nanoelectronic devices. PMID:25747727

  7. Unexpected Magnetic Semiconductor Behavior in Zigzag Phosphorene Nanoribbons Driven by Half-Filled One Dimensional Band

    NASA Astrophysics Data System (ADS)

    Du, Yongping; Liu, Huimei; Xu, Bo; Sheng, Li; Yin, Jiang; Duan, Chun-Gang; Wan, Xiangang

    2015-03-01

    Phosphorene, as a novel two-dimensional material, has attracted a great interest due to its novel electronic structure. The pursuit of controlled magnetism in Phosphorene in particular has been persisting goal in this area. In this paper, an antiferromagnetic insulating state has been found in the zigzag phosphorene nanoribbons (ZPNRs) from the comprehensive density functional theory calculations. Comparing with other one-dimensional systems, the magnetism in ZPNRs display several surprising characteristics: (i) the magnetic moments are antiparallel arranged at each zigzag edge; (ii) the magnetism is quite stable in energy (about 29 meV/magnetic-ion) and the band gap is big (about 0.7 eV) (iii) the electronic and magnetic properties is almost independent on the width of nanoribbons; (iv) a moderate compressive strain will induce a magnetic to nonmagnetic as well as semiconductor to metal transition. All of these phenomena arise naturally due to one unique mechanism, namely the electronic instability induced by the half-filled one-dimensional bands which cross the Fermi level at around π/2a. The unusual electronic and magnetic properties in ZPNRs endow them possible potential for the applications in nanoelectronic devices.

  8. Magnetic damping of thermocapillary convection in the floating-zone growth of semiconductor crystals

    NASA Astrophysics Data System (ADS)

    Morthland, Timothy Edward

    The floating zone is one process used to grow high purity semiconductor single crystals. In the floating-zone process, a liquid bridge of molten semiconductor, or melt, is held by surface tension between the upper, melting polycrystalline feed rod and the lower, solidifying single crystal. A perfect crystal would require a quiescent melt with pure diffusion of dopants during the entire period needed to grow the crystal. However, temperature variations along the free surface of the melt lead to gradients of the temperature-dependent surface tension, driving a strong and unsteady flow in the melt, commonly labeled thermocapillary or Marangoni convection. For small temperature differences along the free surface, unsteady thermocapillary convection occurs, disrupting the diffusion controlled solidification and creating undesirable dopant concentration variations in the semiconductor single crystal. Since molten semiconductors are good electrical conductors, an externally applied, steady magnetic field can eliminate the unsteadiness in the melt and can reduce the magnitude of the residual steady motion. Crystal growers hope that a strong enough magnetic field will lead to diffusion controlled solidification, but the magnetic field strengths needed to damp the unsteady thermocapillary convection as a function of floating-zone process parameters is unknown. This research has been conducted in the area of the magnetic damping of thermocapillary convection in floating zones. Both steady and unsteady flows have been investigated. Due to the added complexities in solving Maxwells equations in these magnetohydrodynamic problems and due to the thin boundary layers in these flows, a direct numerical simulation of the fluid and heat transfer in the floating zone is virtually impossible, and it is certainly impossible to run enough simulations to search for neutral stability as a function of magnetic field strength over the entire parameter space. To circumvent these difficulties

  9. Magnetic field dependence of the product yields of cycloheptanone photolysis in the dilute gas phase

    NASA Astrophysics Data System (ADS)

    Stich, E. M.; Baumeister, W. F.; Huber, J. Robert

    1984-07-01

    The product yields of the gas-phase photolysis of cycloheptanone were measured in magnetic fields up to 10 kG. The magnetic-field effect is explained in terms of the radical pair model. A reaction mechanism is proposed that explains the magnetic field dependence, pressure dependence, and excitation enegy dependence of the gas-phase photochemistry of cycloheptanone.

  10. Possible colloid crystal formation in a magnetized and inhomogeneous semiconductor plasma

    SciTech Connect

    Salimullah, M.; Ehsan, Z.; Zubia, K.; Shah, H. A.; Murtaza, G.

    2007-09-01

    We investigate the detailed properties of the modification of the Debye-Hueckel and the consequent oscillatory wake potentials in the presence of a density inhomogeneity and external static uniform electric and magnetic fields in an ion-implanted n-type piezoelectric semiconductor. It is found that the external fields and the density nonuniformity have significant effects on the static and dynamical electrostatic potentials. The possibility of the long-ranged order formation of colloids of the implanted ions, leading to modification of the electrical, thermodynamic, and optical properties of the 'soft matter', has been pointed out. The periodic wakefields besides the usual static Coulombian Debye-Hueckel potential may cause the long-range ordered structures of the charged colloidal particulates within the semiconductor to show various additional properties.

  11. Semiconductor crystal growth in crossed electric and magnetic fields: Center Director's Discretionary Fund

    NASA Technical Reports Server (NTRS)

    Mazuruk, K.; Volz, M. P.

    1996-01-01

    A unique growth cell was designed in which crossed electric and magnetic fields could be separately or simultaneously applied during semiconductor crystal growth. A thermocouple was inserted into an InSb melt inside the growth cell to examine the temperature response of the fluid to applied electromagnetic fields. A static magnetic field suppressed time-dependent convection when a destabilizing thermal field was applied. The simultaneous application of electric and magnetic fields resulted in forced convection in the melt. The InSb ingots grown in the cell were polycrystalline. An InGaSb crystal, 0.5 cm in diameter and 23-cm long, was grown without electromagnetic fields applied. The axial composition results indicated that complete mixing in the melt occurred for this large aspect ratio.

  12. Models of Mass Transport During Microgravity Crystal Growth of Alloyed Semiconductors in a Magnetic Field

    NASA Technical Reports Server (NTRS)

    Ma, Nancy

    2003-01-01

    Alloyed semiconductor crystals, such as germanium-silicon (GeSi) and various II-VI alloyed crystals, are extremely important for optoelectronic devices. Currently, high-quality crystals of GeSi and of II-VI alloys can be grown by epitaxial processes, but the time required to grow a certain amount of single crystal is roughly 1,000 times longer than the time required for Bridgman growth from a melt. Recent rapid advances in optoelectronics have led to a great demand for more and larger crystals with fewer dislocations and other microdefects and with more uniform and controllable compositions. Currently, alloyed crystals grown by bulk methods have unacceptable levels of segregation in the composition of the crystal. Alloyed crystals are being grown by the Bridgman process in space in order to develop successful bulk-growth methods, with the hope that the technology will be equally successful on earth. Unfortunately some crystals grown in space still have unacceptable segregation, for example, due to residual accelerations. The application of a weak magnetic field during crystal growth in space may eliminate the undesirable segregation. Understanding and improving the bulk growth of alloyed semiconductors in microgravity is critically important. The purpose of this grant to to develop models of the unsteady species transport during the bulk growth of alloyed semiconductor crystals in the presence of a magnetic field in microgravity. The research supports experiments being conducted in the High Magnetic Field Solidification Facility at Marshall Space Flight Center (MSFC) and future experiments on the International Space Station.

  13. Material degradation of liquid organic semiconductors analyzed by nuclear magnetic resonance spectroscopy

    SciTech Connect

    Fukushima, Tatsuya; Yamamoto, Junichi; Fukuchi, Masashi; Kaji, Hironori; Hirata, Shuzo; Jung, Heo Hyo; Adachi, Chihaya; Hirata, Osamu; Shibano, Yuki

    2015-08-15

    Liquid organic light-emitting diodes (liquid OLEDs) are unique devices consisting only of liquid organic semiconductors in the active layer, and the device performances have been investigated recently. However, the device degradation, especially, the origin has been unknown. In this study, we show that material degradation occurs in liquid OLEDs, whose active layer is composed of carbazole with an ethylene glycol chain. Nuclear magnetic resonance (NMR) experiments clearly exhibit that the dimerization reaction of carbazole moiety occurs in the liquid OLEDs during driving the devices. In contrast, cleavages of the ethylene glycol chain are not detected within experimental error. The dimerization reaction is considered to be related to the device degradation.

  14. Determining Exchange Splitting in a Magnetic Semiconductor by Spin-Filter Tunneling

    SciTech Connect

    Santos, T. S.; Moodera, J. S.; Venkataraman, K.; Negusse, E.; Holroyd, J.; Dvorak, J.; Liberati, M.; Idzerda, Y. U.; Arenholz, E.

    2008-06-24

    A large exchange splitting of the conduction band in ultrathin films of the ferromagnetic semiconductor EuO was determined quantitatively, by using EuO as a tunnel barrier and fitting the current-voltage characteristics and temperature dependence to tunneling theory. This exchange splitting leads to different tunnel barrier heights for spin-up and spin-down electrons, and is large enough to produce a near fully spin-polarized current. Moreover, the magnetic properties of these ultrathin films (<6 nm) show a reduction in Curie temperature with decreasing thickness, in agreement with theoretical calculation [R. Schiller et al., Phys. Rev. Lett. 86, 3847 (2001)].

  15. Magnetic filter apparatus and method for generating cold plasma in semiconductor processing

    DOEpatents

    Vella, M.C.

    1996-08-13

    Disclosed herein is a system and method for providing a plasma flood having a low electron temperature to a semiconductor target region during an ion implantation process. The plasma generator providing the plasma is coupled to a magnetic filter which allows ions and low energy electrons to pass therethrough while retaining captive the primary or high energy electrons. The ions and low energy electrons form a ``cold plasma`` which is diffused in the region of the process surface while the ion implantation process takes place. 15 figs.

  16. On a few properties of very dilute matter frozen in space magnetic fields

    NASA Astrophysics Data System (ADS)

    Berdichevsky, D. B.; Schefers, K.

    2014-12-01

    For a case study, the flux-rope (FR) that passed Earth on June 2, 2014(1) (see also listing of magnetic clouds and their properties in the Wind SC MFI science team site at http://wind.gsfc.nasa.gov/mfi/mag_cloud_S1.html), we proceed to interpret plasma and magnetic field observations in the context of MHD. The observations used are 3s average interplanetary magnetic field (Wind/MFI instrument) and 3s plasma (Wind/SWE instruments) data(2). After identifying the observed correlation between electron density, temperature and pressure in the plasma frame of reference we proceed to establish the existence of a relationship between these plasma observables with the magnetic field pressure. By assuming ideal MHD conditions to be valid we proceed to confirm that the medium is diamagnetic, as is to be expected for the MHD state of matter and magnetic field which is assumed to be a superconducting medium. Additionally we infer the presence of magnetization work, as well as a few other constitutive properties of this state of matter. 1 Berdichevsky D. B., R. P. Lepping, and C. J. Farrugia, Geometric considerations of the evolution of magnetic flux ropes, Phys. Rev. E67, doi:10.1103/PhysRevE.036405. Lepping R. P. et al, A summary of Wind magnetic clouds for years 1995 - 2003: model-fitted parameters, associated errors and classifications, Ann. Geophysicae, 24, 215-245, 2006.2006 2 Ogilvie, K. W., et al, SWE, A comprehensive plasma instrument for the Wind spacecraft, Space Sci. Rev., 71, 55 - 77, 1995; Lepping R. P., et al , The Wind Magnetic Field Investigation, Space Sci. Rev., 71, 207 - 229, 1995.

  17. Spin-orbit dilution effects on the magnetism of frustrated spinel Ge(Co1-xMgx)2O4

    NASA Astrophysics Data System (ADS)

    Agata, Ryotaro; Takita, Shota; Ishikawa, Takashi; Watanabe, Tadataka

    2015-03-01

    We investigated magnetic properties of spinel oxides Ge(Co1-xMgx)2O4 with x = 0 ~ 0.5 to study the spin-orbit dilution effects on the magnetism of spin-orbit frustrated spinel GeCo2O4. We discovered that the magnetic moment per single Co2+ ion is decreased with increasing nonmagnetic Mg2+ concentration, which indicates the spin-orbit decoupling caused by the spin-orbit dilution. Additionally, small-amount substitution of Mg2+ for Co2+ causes the rapid increase of the positive Weiss temperature indicating the enhancement of ferromagnetic interactions, while the Mg2+ substitution suppresses the antiferromagnetic ordering resulting in the appearance of spin glass behavior. The present results suggest that the spin-orbit dilution causes the spin-orbit decoupling and the reinforcement of ferromagnetic frustration in GeCo2O4.

  18. Magnetic Mn5Ge3 nanocrystals embedded in crystalline Ge: a magnet/semiconductor hybrid synthesized by ion implantation

    PubMed Central

    2012-01-01

    The integration of ferromagnetic Mn5Ge3 with the Ge matrix is promising for spin injection in a silicon-compatible geometry. In this paper, we report the preparation of magnetic Mn5Ge3 nanocrystals embedded inside the Ge matrix by Mn ion implantation at elevated temperature. By X-ray diffraction and transmission electron microscopy, we observe crystalline Mn5Ge3 with variable size depending on the Mn ion fluence. The electronic structure of Mn in Mn5Ge3 nanocrystals is a 3d6 configuration, which is the same as that in bulk Mn5Ge3. A large positive magnetoresistance has been observed at low temperatures. It can be explained by the conductivity inhomogeneity in the magnetic/semiconductor hybrid system. PMID:23009168

  19. Rheology of a very dilute magnetic suspension with micro-structures of nanoparticles

    NASA Astrophysics Data System (ADS)

    Cunha, Francisco Ricardo; Rosa, Adriano Possebon; Dias, Nuno Jorge

    2016-01-01

    The main objective of this present paper is to measure the apparent viscosity of a magnetic suspension in the presence of particle agglomerates of different sizes for several applied magnetic fields, shear rates and particle volume fractions. A secondary goal is to investigate suspension microstructure transition, when subjected to a magnetic field. We show that an employed like virial expansion of two empirical coefficients based only on the experimental data gives a good quantitative description of the magnetorheological suspension effective viscosity up to particle volume fraction less than 0.01. The observed shear rate dependence viscosity is a direct consequence of the stretching, breaking particle structures of different sizes and shapes formed by the action of magnetic attractive force between the polarized particles as observed previously in the context of dense ferrofluids. We have identified even in the limit of a very small particle volume fraction a strong non-linear behavior of the examined suspension due to formation of suspended blobs-like aggregates of different sizes and anisotropic chains of particles. These structures are induced by the presence of an external magnetic field and particle-particle magnetic interactions. A histogram of the structure size distribution is also examined. The results of this paper are important to those who are interested on the magnetorheological suspensions.

  20. Energy spectrum of layered semiconductors in a magnetic field parallel to the layers: Voigt geometry

    NASA Astrophysics Data System (ADS)

    Yoo, K. H.; Ram-Mohan, L. R.

    2010-11-01

    The electronic band structure of zinc-blende layered semiconductor heterostructures is investigated theoretically in the presence of an in-plane magnetic field, a configuration we label as the Voigt geometry. We use a Lagrangian formulation for modeling the band structure in the individual layers within the kṡP model. This approach has been shown by us to provide the correct ordering of the derivatives appearing in the multiband description of Schrödinger’s equations for the envelope functions through the application of the principle of stationary action. Finite element modeling of the action integral provides a natural and efficient approach to the inclusion of in-plane magnetic fields in the energy-level analysis. Calculations for quantum wells and superlattices are presented, and the complex energy-level structure obtained for the layered structures.

  1. Structural and magnetic properties of a prospective spin gapless semiconductor MnCrVAl

    NASA Astrophysics Data System (ADS)

    Huh, Y.; Gilbert, S.; Kharel, P.; Jin, Y.; Lukashev, P.; Valloppilly, S.; Sellmyer, D. J.

    Recently a new class of material, spin gapless semiconductors (SGS), has attracted much attention because of their potential for spintronic devices. We have synthesized a Heusler compound, MnCrVAl, which is theoretically predicted to exhibit SGS by arc melting, rapid quenching and thermal annealing. First principles calculations are employed to describe its structural, electronic and magnetic properties. X-ray diffraction indicates that the rapidly quenched samples crystallize in the disordered cubic structure. The crystal structure is stable against heat treatment up to 650oC. The samples show very small saturation magnetization, 0.3 emu/g, at room temperature under high magnetic field, 30 kOe. Above room temperature, the magnetization increases with increasing temperature undergoing a magnetic transition at 560oC, similar to an antiferromagnetic-to-paramagnetic transition. The prospect of this material for spintronic applications will be discussed. This research is supported by SDSU Academic/Scholarly Excellence Fund, and Research/Scholarship Support Fund. Research at UNL is supported by DOE (DE-FG02-04ER46152, synthesis, characterization), NSF (ECCS-1542182, facilities), and NRI.

  2. Nonlinear and ac Susceptibility of the Dilute Ising Magnet LiHoxY1-xF4

    NASA Astrophysics Data System (ADS)

    Quilliam, Jeffrey; Meng, Shuchao; Mugford, Chas; Kycia, Jan

    2008-03-01

    Recent work has called into question the existence of a spin glass transition in the dilute dipolar Ising magnet LiHoxY1-xF4 [1]. Other work has suggested that there is an exotic spin liquid phase found at a Ho concentration of x = 0.045 [2]. In order to carefully study the dynamics of this system, we have put together a SQUID magnetometer which allows for measurements of ac susceptibility and nonlinear susceptibility over a large frequency range. We present results from measurements on single crystals of LiHoxY1-xF4, particularly on an x = 0.045 sample, in an attempt to either reproduce the exotic ``anti-glass'' physics that was previously observed or to detect a spin glass transition. [1] P. E. Jonnson et al. PRL 98, 256403 (2007) [2] S. Ghosh et al. Science 296, 2195 (2002)

  3. Localization, lattice distortion, charge transition levels, and magnetism of small-polaronic hole- and electron-states in wide-gap semiconductors

    NASA Astrophysics Data System (ADS)

    Lany, Stephan

    2010-03-01

    The formation of a small polaron, i.e. of a localized (electron or hole) quasi-particle state that is stabilized by a lattice distortion, is a problem in solid state physics that has eluded a quantitative description by first principles Hamiltonians for a long time. Specifically, conventional density functional theory calculations typically predict a much too delocalized state and usually fail to correctly predict the lattice distortions of localized hole-states in semiconductors and insulators. While this problem has been studied in detail for some prototypical cases like the Al impurity in SiO2, it has at the same time precluded an extensive theoretical literature on the phenomenology of systems with localized hole states, despite the potentially dramatic effect of hole localization on such timely research topics as p-type doping of oxides or that of diluted magnetic semiconductors. Indeed, many predictions for hole-introducing defects and impurities that were based on local density approximations have led to a qualitatively wrong physical picture about the lattice distortion, the energies of the hole-bearing acceptor levels in the gap, and about ferro-magnetic interactions between defects. In order to stabilize the polaronic localized states in the gap, we define a parameterized hole- (or electron-) state potential which increases the energy splitting between occupied and unoccupied orbitals, where we further require that a fundamental physical condition is satisfied, i.e., the piecewise linearity of the energy as a function of the occupation number. This requirement takes the form of a generalized Koopmans conditions, which uniquely determines the one free parameter of the hole- (electron-) state potential. Applying this method to the anion-p orbitals within the II-VI series of ZnO, ZnS, ZnSe, and ZnTe, we demonstrate electronic correlation effects remove the partial band occupation and the metallic band-structure character that is predicted by local density

  4. First principles density functional calculation of magnetic moment and hyperfine fields of dilute transition metal impurities in Gd host

    NASA Astrophysics Data System (ADS)

    Mohanta, S. K.; Mishra, S. N.; Srivastava, S. K.

    2014-04-01

    We present first principles calculations of electronic structure and magnetic properties of dilute transition metal (3d, 4d and 5d) impurities in a Gd host. The calculations have been performed within the density functional theory using the full potential linearized augmented plane wave technique and the GGA+U method. The spin and orbital contributions to the magnetic moment and the hyperfine fields have been computed. We find large magnetic moments for 3d (Ti-Co), 4d (Nb-Ru) and 5d (Ta-Os) impurities with magnitudes significantly different from the values estimated from earlier mean field calculation [J. Magn. Magn. Mater. 320 (2008) e446-e449]. The exchange interaction between the impurity and host Gd moments is found to be positive for early 3d elements (Sc-V) while in all other cases an anti-ferromagnetic coupling is observed. The trends for the magnetic moment and hyperfine field of d-impurities in Gd show qualitative difference with respect to their behavior in Fe, Co and Ni. The calculated total hyperfine field, in most cases, shows excellent agreement with the experimental results. A detailed analysis of the Fermi contact hyperfine field has been made, revealing striking differences for impurities having less or more than half filled d-shell. The impurity induced perturbations in host moments and the change in the global magnetization of the unit cell have also been computed. The variation within each of the d-series is found to correlate with the d-d hybridization strength between the impurity and host atoms.

  5. Dilute plasma coupling currents to a high voltage solar array in weak magnetic fields

    NASA Technical Reports Server (NTRS)

    Grier, N. T.

    1984-01-01

    The plasma coupling current to an approximately 2000 sq cm array was measured for externally biased positive and negative voltages on the array to 1000 V in applied magnetic field strengths from 0 to 0.93 G. The plasma density varied from 2,000 to 1.3 million electrons/cu cm. It was found that the magnetic field primarily increased the plasma coupling current for negative biases. For positive bias, the current could increase or decrease depending on the voltage, field strength, and plasma density. It was also found that the plasma coupling current was not very sensitive to how the plane of the array was oriented relative to the magnetic field.

  6. Magnetism of dilute Co(Hf) and Co(Pt) nanoclusters

    SciTech Connect

    Balamurugan, B; Skomski, R; Das, B; Li, XZ; Shah, VR; Manchanda, P; Kashyap, A; Sellmyer, DJ

    2012-04-01

    An investigation of the magnetic properties of Co-rich nanoparticles alloyed with a small fraction of Pt and Hf is presented. Co(Hf) and Co(Pt) nanoparticles with less than 15 at% of dopants were produced using a cluster-deposition method. The nanoparticles have sizes of less than 10 nm and show improved magnetic properties upon doping. Maximum coercivities of 900 Oe (at 300 K) and 2000 Oe (at 10 K) were observed for Co nanoparticles alloyed with 14.1 at% of Hf. Doped nanoparticles also exhibit high anisotropies, such as K-1 = 9.98 Mergs/cm(3) (14.1 at% of Hf) and K-1 = 8.24 Mergs/cm(3) (9.5 at% of Pt), as compared to Co nanoparticles (K-1 = 6.21 Mergs/cm(3)). (C) 2012 American Institute of Physics. [doi:10.1063/1.3678582

  7. Cobalt-Doped Anatase TiO2: A Room Temperature Dilute Magnetic Dielectric Material

    SciTech Connect

    Griffin, Kelli A.; Pakhomov, Alexandre; Wang, Chong M.; Heald, Steve M.; Krishnan, Kannan M.

    2005-05-15

    Structural and magnetic properties of epitaxial CoxTi₁-xO₂ films with x~2%, grown by RF magnetron sputtering from composite oxide targets on lattice matched LaAIO₃(001) substrates have been investigated. The films were sputtered at a deposition rate of ~0.12 Å/s for a range of substrate temperatures from 300°C to 750°C, followed by UHV annealing for 1 hr at 400°C and aging in air for 3 months. XRD experiments determine the best quality of highly oriented anatase (991) phase in films deposited 500-750°C. Magnetic hysteresis loops at 5K and 300K and thermoremanence measurements from 5-365 K show ferromagnetism in all samples in the whole temperature range. Annealing and aging lead to an increase of spontaneous moment an order of magnitude of up to ~1.1 µB/ Co atom at 300 K. As=deposited, annealed, and aged films were found to be highly resistive changes both in surface morphology and distribution of spontaneous magnetization in the annealed films. Possible mechanisms of the ferromagnetic behavior of such dielectric transition metal-doped oxides will be discussed.

  8. Strong magnetic coupling in a magnetically dilute f-electron insulator: A dysprosium boron-cluster compound

    NASA Astrophysics Data System (ADS)

    Mori, T.; Sahara, R.; Kawazoe, Y.; Yubuta, K.; Shishido, T.; Grin, Y.

    2013-05-01

    Unexpectedly strong magnetic coupling is observed in boride insulators containing the B12 icosahedra as a structural unit. We have successfully synthesized Dy0.74B22C2N, which takes the RB22C2N-type crystal structure. The Dy phase was previously thought to not be possible to form. Spin glass-like behavior was observed with a broad peak in the zero field cooled (ZFC) magnetic susceptibility at T ˜ 44 K, while a large divergence for ZFC and field cooled (FC) curves is observed. The Curie-Weiss constant is determined to be θ =-43.9 K, and this system is indicated to have the strongest magnetic coupling ever observed for any rare earth boride insulator. Electronic structure and chemical bonding calculations were also made. Conventional mechanisms for f-electron magnetism cannot explain the strong coupling observed, which further indicates that the B12 icosahedra is functioning as a novel mediator of magnetic interaction.

  9. Field and dilution effects on the magnetic relaxation behaviours of a 1D dysprosium(iii)-carboxylate chain built from chiral ligands.

    PubMed

    Han, Tian; Leng, Ji-Dong; Ding, You-Song; Wang, Yanyan; Zheng, Zhiping; Zheng, Yan-Zhen

    2015-08-14

    A one-dimensional dysprosium(iii)-carboxylate chain in which the Dy(III) ions sit in a pseudo D(2d)-symmetry environment is synthesized and shows different slow magnetic relaxation behaviours depending on the field and dilution effects. Besides, the chiral ligand introduces the additional functions of the Cotton effect and polarization for this compound. PMID:26159885

  10. Liquid phase electroepitaxial bulk growth of binary and ternary alloy semiconductors under external magnetic field

    NASA Astrophysics Data System (ADS)

    Sheibani, Hamdi

    2002-01-01

    Liquid Phase Electroepitaxy (LPEE) and is a relatively new, promising technique for producing high quality, thick compound semiconductors and their alloys. The main objectives are to reduce the adverse effect of natural convection and to determine the optimum growth conditions for reproducible desired crystals for the optoelectronic and electronic device industry. Among the available techniques for suppressing the adverse effect of natural convection, the application of an external magnetic field seems the most feasible one. The research work in this dissertation consists of two parts. The first part is focused on the design and development of a state of the art LPEE facility with a novel crucible design, that can produce bulk crystals of quality higher than those achieved by the existing LPEE system. A growth procedure was developed to take advantage of this novel crucible design. The research of the growth of InGaAs single crystals presented in this thesis will be a basis for the future LPEE growth of other important material and is an ideal vehicle for the development of a ternary crystal growth process. The second part of the research program is the experimental study of the LPEE growth process of high quality bulk single crystals of binary/ternary semiconductors under applied magnetic field. The compositional uniformity of grown crystals was measured by Electron Probe Micro-analysis (EPMA) and X-ray microanalysis. The state-of-the-art LPEE system developed at University of Victoria, because of its novel design features, has achieved a growth rate of about 4.5 mm/day (with the application of an external fixed magnetic field of 4.5 KGauss and 3 A/cm2 electric current density), and a growth rate of about 11 mm/day (with 4.5 KGauss magnetic field and 7 A/cm2 electric current density). This achievement is simply a breakthrough in LPEE, making this growth technique absolutely a bulk growth technique and putting it in competition with other bulk growth techniques

  11. Linear and nonlinear optical properties of semiconductor nanorings with magnetic field and disorder - Influence on excitons and biexcitons

    NASA Astrophysics Data System (ADS)

    Meier, T.; Thomas, P.; Koch, S. W.

    2001-07-01

    Linear and nonlinear optical absorption spectra are studied theoretically for semiconductor nanorings penetrated by a magnetic field. Due to the Aharanov-Bohm effect the spectral position as well as the oscillator strength of the exciton change periodically as function of the magnetic flux enclosed by the ring. In the nonlinear differential absorption spectra it is found that the magnetic field strongly modifies Coulomb many-body correlations. In particular, the magnetic-field-induced increase of the exciton binding energy is accompanied by a decrease of the biexciton binding energy. The persistence of these effects in the presence of energetic disorder is analyzed.

  12. Ab initio predictions of the stability and structural properties of zincblende (III,TM)V magnetic semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Caetano, C.; Pela, R. R.; Martini, S.; Marques, M.; Teles, L. K.

    2016-05-01

    First-principles calculations and statistical methods were combined to study electronic, magnetic, thermodynamic and structural properties of zincblende (III,Mn)V and (III,Cr)V magnetic semiconductor alloys, including both nitride and arsenide alloys. From phase diagrams it was observed that nitride alloys are much less stable than arsenide ones, although the former ones have more localized d-states at the Fermi level. It was observed that all alloys present an anisotropic behavior, with the strongest magnetic interaction in the < 110 > direction. The relationship between the structural properties of these alloys and their electronic and magnetic characteristics (i.e., their half-metallicity) was investigated.

  13. Effects of lateral asymmetry on electronic structure of strained semiconductor nanorings in a magnetic field

    NASA Astrophysics Data System (ADS)

    Milošević, M. M.; Tadić, M.; Peeters, F. M.

    2008-11-01

    The influence of lateral asymmetry on the electronic structure and optical transitions in elliptical strained InAs nanorings is analyzed in the presence of a perpendicular magnetic field. Two-dimensional rings are assumed to have elliptical inner and outer boundaries oriented in mutually orthogonal directions. The influence of the eccentricity of the ring on the energy levels is analyzed. For large eccentricity of the ring, we do not find any Aharonov-Bohm effect, in contrast to circular rings. Rather, the single-particle states of the electrons and the holes are localized as in two laterally coupled quantum dots formed in the lobes of the nanoring. Our work indicates that the control of shape is important for the existence of the Aharonov-Bohm effect in semiconductor nanorings.

  14. Effects of lateral asymmetry on electronic structure of strained semiconductor nanorings in a magnetic field.

    PubMed

    Milošević, M M; Tadić, M; Peeters, F M

    2008-11-12

    The influence of lateral asymmetry on the electronic structure and optical transitions in elliptical strained InAs nanorings is analyzed in the presence of a perpendicular magnetic field. Two-dimensional rings are assumed to have elliptical inner and outer boundaries oriented in mutually orthogonal directions. The influence of the eccentricity of the ring on the energy levels is analyzed. For large eccentricity of the ring, we do not find any Aharonov-Bohm effect, in contrast to circular rings. Rather, the single-particle states of the electrons and the holes are localized as in two laterally coupled quantum dots formed in the lobes of the nanoring. Our work indicates that the control of shape is important for the existence of the Aharonov-Bohm effect in semiconductor nanorings. PMID:21832775

  15. Terahertz radiation induced chaotic electron transport in semiconductor superlattices with a tilted magnetic field

    SciTech Connect

    Wang, C. Wang, F.; Cao, J. C.

    2014-09-01

    Chaotic electron transport in semiconductor superlattice induced by terahertz electric field that is superimposed on a dc electric field along the superlattice axis are studied using the semiclassical motion equations including the effect of dissipation. A magnetic field that is tilted relative to the superlattice axis is also applied to the system. Numerical simulation shows that electrons in superlattice miniband exhibit complicate nonlinear oscillating modes with the influence of terahertz radiation. Transitions between frequency-locking and chaos via pattern forming bifurcations are observed with the varying of terahertz amplitude. It is found that the chaotic regions gradually contract as the dissipation increases. We attribute the appearance of complicate nonlinear oscillation in superlattice to the interaction between terahertz radiation and internal cooperative oscillating mode relative to Bloch oscillation and cyclotron oscillation.

  16. Magnetic ordering in digital alloys of group-IV semiconductors with 3d-transition metals

    SciTech Connect

    Otrokov, M. M.; Tugushev, V. V.; Ernst, A.; Ostanin, S. A.; Kuznetsov, V. M.; Chulkov, E. V.

    2011-04-15

    The ab initio investigation of the magnetic ordering in digital alloys consisting of monolayers of 3d-transition metals Ti, V, Cr, Mn, Fe, Co, and Ni introduced into the Si, Ge, and Si{sub 0.5}Ge{sub 0.5} semiconductor hosts is reported. The calculations of the parameters of the exchange interactions and total-energy calculations indicate that the ferromagnetic order appears only in the manganese monolayers, whereas the antiferromagnetic order is more probable in V, Cr, and Fe monolayers, and Ti, Co, and Ni monolayers are nonmagnetic. The stability of the ferromagnetic phase in digital alloys containing manganese monolayers has been analyzed using the calculations of magnon spectra.

  17. Magnetic susceptibility of semiconductors by an all-electron first-principles approach

    SciTech Connect

    Ohno, K. |; Mauri, F.; Louie, S.G. |

    1997-07-01

    The magnetic susceptibility ({chi}) of the semiconductors (diamond, Si, GaAs, and GaP) and of the inert-gas solids (Ne, Ar, and Kr) are evaluated within density-functional theory in the local-density approximation, using a mixed-basis all-electron approach. In Si, GaAs, GaP, Ar, and Kr, the contribution of core electrons to {chi} is comparable to that of valence electrons. However, our results show that the contribution associated with the core states is independent of the chemical environment and can be computed from the isolated atoms. Moreover, our results indicate that the use of a {open_quotes}scissor operator{close_quotes} does not improve the agreement of the theoretical {chi} with experiments. {copyright} {ital 1997} {ital The American Physical Society}

  18. Terahertz radiation induced chaotic electron transport in semiconductor superlattices with a tilted magnetic field.

    PubMed

    Wang, C; Wang, F; Cao, J C

    2014-09-01

    Chaotic electron transport in semiconductor superlattice induced by terahertz electric field that is superimposed on a dc electric field along the superlattice axis are studied using the semiclassical motion equations including the effect of dissipation. A magnetic field that is tilted relative to the superlattice axis is also applied to the system. Numerical simulation shows that electrons in superlattice miniband exhibit complicate nonlinear oscillating modes with the influence of terahertz radiation. Transitions between frequency-locking and chaos via pattern forming bifurcations are observed with the varying of terahertz amplitude. It is found that the chaotic regions gradually contract as the dissipation increases. We attribute the appearance of complicate nonlinear oscillation in superlattice to the interaction between terahertz radiation and internal cooperative oscillating mode relative to Bloch oscillation and cyclotron oscillation. PMID:25273189

  19. Towards a new class of heavy ion doped magnetic semiconductors for room temperature applications

    PubMed Central

    Lee, Juwon; Subramaniam, Nagarajan Ganapathi; Agnieszka Kowalik, Iwona; Nisar, Jawad; Lee, Jaechul; Kwon, Younghae; Lee, Jaechoon; Kang, Taewon; Peng, Xiangyang; Arvanitis, Dimitri; Ahuja, Rajeev

    2015-01-01

    The article presents, using Bi doped ZnO, an example of a heavy ion doped oxide semiconductor, highlighting a novel p-symmetry interaction of the electronic states to stabilize ferromagnetism. The study includes both ab initio theory and experiments, which yield clear evidence for above room temperature ferromagnetism. ZnBixO1−x thin films are grown using the pulsed laser deposition technique. The room temperature ferromagnetism finds its origin in the holes introduced by the Bi doping and the p-p coupling between Bi and the host atoms. A sizeable magnetic moment is measured by means of x-ray magnetic circular dichroism at the O K-edge, probing directly the spin polarization of the O(2p) states. This result is in agreement with the theoretical predictions and inductive magnetometry measurements. Ab initio calculations of the electronic and magnetic structure of ZnBixO1−x at various doping levels allow to trace the origin of the ferromagnetic character of this material. It appears, that the spin-orbit energy of the heavy ion Bi stabilizes the ferromagnetic phase. Thus, ZnBixO1−x doped with a heavy non-ferromagnetic element, such as Bi, is a credible example of a candidate material for a new class of compounds for spintronics applications, based on the spin polarization of the p states. PMID:26592564

  20. Spontaneous appearance of a low-dimensional magnetic electron system on semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Sawada, Keisuke; Iwata, Jun-Ichi; Oshiyama, Atsushi

    2016-06-01

    We report on the large-scale density-functional calculations that show the emergence of the spin-polarized ground states in nanofacets self-organized on SiC (0001) surfaces. We first reveal that the nanofacet formed by bunching of single bilayer steps induces peculiar electron states localized at but extended along step edges, showing the flat-band characteristics. The electron states are of C-dangling-bond characters mixed with the back-bond character of neighboring edge Si atoms. We find that the resulting flat bands lead to the spin polarization near the step edges by H passivation of the terrace Si atoms. Interestingly, either ferromagnetic or antiferromagnetic chains appear along the step edges on the SiC nanofacet and the location of such magnetic chains can be controlled by manipulating the H passivation of atoms near the step edges. These findings open a possibility of the appearance of new magnetic functions on the covalent semiconductor surfaces without magnetic elements.

  1. Structural, magnetic, and transport properties of (Zn,V)Te semiconductors

    NASA Astrophysics Data System (ADS)

    Wang, Weigang; Ni, Chaoying; Zhu, Tao; Zhang, Huiwu; Xiao, John Q.

    2006-04-01

    Vanadium-doped ZnTe has been predicted to be one of the candidates for ferromagnetic semiconductors with a high Curie temperature [K. Sato and H. Katayama-Yoshida, Semicond. Sci. Technol. 17, 367 (2002)]. In this paper, we report the structural, magnetic, and transport properties of (Zn,V)Te films prepared by magnetron sputtering. Samples were fabricated on both GaAs and thermally oxidized silicon substrate at elevated temperature. Oriented sample (100) can be achieved on GaAs substrates and only polycrystalline samples are observed on Si substrates. X-ray diffraction (XRD) and transmission electron spectroscopy (TEM) show no magnetic precipitates in the (Zn,V)Te film. The magnetization measurement shows that the oriented sample is paramagnetic at 5 K, while films on Si substrate shows weak ferromagnetism at 5 K. The sign of magnetoresistance (MR=[R(H)-R(0)]/R(0)) gradually changes from negative to positive with temperature, and positive MR at high temperatures shows H2 dependence, indicating ordinary MR effect. It is believed the observed negative MR corresponds to the ferromagnetic ordering at lower temperature.

  2. Structural and Magnetic Properties of Dilute Ca²⁺ Doped Iron Oxide Nanoparticles.

    PubMed

    Samar Layek; Rout, K; Mohapatra, M; Anand, S; Verma, H C

    2016-01-01

    Undoped and calcium substituted hematite (α-Fe₂O₃) nanoparticles are synthesized by surfactant-directed co-precipitation and post annealing method. The annealed nanoparticles were found to be in single phase in nature and crystallize in the rhombohedral structure with space group R3c as confirmed by Rietveld refinement of the X-ray diffraction (XRD) data. Average crystallite sizes are calculated to be 20 to 30 nm and 50 to 60 nm for the nanoparticles annealed at 400 and 600 °C respectively. Mössbauer spectra for all the nanoparticles could be fitted with a sextet corresponding to the single magnetic state of the iron atoms in its Fe³⁺ state in the hematite matrix. The FTIR and Raman spectra of all the samples correspond to specific modes of α-Fe₂O₃. UV-Vis spectra of annealed samples showed broad peaks in the range of 525-630 nm resulting from spin-forbidden ligand field transition together with the spin-flip transition among the 2t₂g states. The estimated band gap energies were in the range of 1.6 to 1.9 eV which are much lower than the reported values for nano hematite. From the room temperature magnetic hysteresis loop measurements, weak ferromagnetic behavior is observed in all undoped and Ca²⁺ doped hematite samples. Morin temperature (T(M)) is calculated to be 257 and 237 K for 1.45% doped samples with particle size 54 and 27 nm respectively. The sample with Ca content of 1.45 wt% when annealed at 400 °C showed that the particles were of different shapes which included both quasi spherical and rod shaped. On annealing the same sample at 600 °C, the nanorods collapsed to form bigger spherical and ellipsoidal particles. PMID:27398469

  3. Magnetic Fluorescent Delivery Vehicle using Uniform Mesoporous Silica Spheres Embedded with Monodisperse Magnetic and Semiconductor Nanocrystals

    SciTech Connect

    Kim, Jaeyun; Lee, Ji Eun; Lee, Jinwoo; Yu, Jung Ho; Kim, Byoung Chan; An, Kwangjin; Hwang, Yosun; Shin, Chae-Ho; Park, Je-Geun; Kim, Jungbae; Hyeon, Taeghwan

    2006-01-25

    Uniform sized colloidal nanocrystals have attracted much attention, because of their unique magnetic and optical properties, as compared with those of their bulk counterparts. Especially magnetic nanocrystals and quantum dots have been intensively pursued for biomedical applications such as contrast enhancement agents in magnetic resonance imaging, magnetic carriers for drug delivery system, biological labeling and diagnostics. Due to their large pore sizes and high surface areas, mesoporous materials and its composites with nanocrystals have attracted considerable attention. In order to use the nanocrystals as functional delivery carriers and catalytic supports, nanocrystals coated with porous silica shells are desirable. Herein, we report a synthetic procedure for the fabrication of monodisperse nanocrystals embedded in uniform pore-sized mesoporous silica spheres. As a representative example, we synthesized monodisperse magnetite (Fe3O4) nanocrystals embedded in mesoporous silica spheres and both magnetite nanocrystals and CdSe/ZnS quantum dots embedded in mesoporous silica spheres. Furthermore, these mesoporous silica spheres were applied to the uptake and controlled release of drugs.

  4. Energy Gap Dependence on Mn Content in a Diluted Magnetic Quantum Dot

    NASA Astrophysics Data System (ADS)

    Nalini, P.; John Peter, A.

    2011-04-01

    Positively charged donor exciton binding energy is computed as a function of quantum-dot size within the single band effective mass approximation for different Mn contents in Cd1-xinMnxin Te/Cd1-xoutMnxout Te. The exciton bound polaron is computed for 0 <= x <= 0.08, on the Mn mole fraction. We determine the energy gap using the mean field approximation and incorporate the exchange interaction between the carrier and the magnetic impurity. The interband emission energy is studied with the height and radius of the cylindrical quantum dot. Valence-band anisotropy is included in our theoretical model using different hole masses in different spatial directions. Spin polaronic shifts as functions of quantum-dot radius and Mn concentration are estimated using the mean field theory. It is found that (i) the energy gap depends on the Mn mole fraction, (ii) it increases linearly with an increase in Mn content, and (iii) the effect is more pronounced for a narrow dot, showing the quantum size effects. Our results are in good agreement with other recently published reports.

  5. Magnetically Suspended Linear Pulse Motor for Semiconductor Wafer Transfer in Vacuum Chamber

    NASA Technical Reports Server (NTRS)

    Moriyama, Shin-Ichi; Hiraki, Naoji; Watanabe, Katsuhide; Kanemitsu, Yoichi

    1996-01-01

    This paper describes a magnetically suspended linear pulse motor for a semiconductor wafer transfer robot in a vacuum chamber. The motor can drive a wafer transfer arm horizontally without mechanical contact. In the construction of the magnetic suspension system, four pairs of linear magnetic bearings for the lift control are used for the guidance control as well. This approach allows us to make the whole motor compact in size and light in weight. The tested motor consists of a double-sided stator and a transfer arm with a width of 50 mm and a total length of 700 mm. The arm, like a ladder in shape, is designed as the floating element with a tooth width of 4 mm (a tooth pitch of 8 mm). The mover mass is limited to about 1.6 kg by adopting such an arm structure, and the ratio of thrust to mover mass reaches to 3.2 N/kg under a broad air gap (1 mm) between the stator teeth and the mover teeth. The performance testing was carried out with a transfer distance less than 450 mm and a transfer speed less than 560 mm/s. The attitude of the arm was well controlled by the linear magnetic bearings with a combined use, and consequently the repeatability on the positioning of the arm reached to about 2 micron. In addition, the positioning accuracy was improved up to about 30 micron through a compensation of the 128-step wave current which was used for the micro-step drive with a step increment of 62.5 micron.

  6. Features of the electric-field distribution in anisotropic semiconductor wafers in a transverse magnetic field

    SciTech Connect

    Filippov, V. V.; Bormontov, E. N.

    2013-07-15

    A macroscopic model of the Hall effects and magnetoresistance in anisotropic semiconductor wafers is developed. The results obtained by solving the electrodynamic boundary problem allow the potential and eddy currents in anisotropic semiconductors to be calculated at different current-contact locations, depending on the parameters of the sample material's anisotropy. The results of this study are of great practical importance for investigating the physical properties of anisotropic semiconductors and simulating the electron-transport phenomena in devices based on anisotropic semiconductors.

  7. Electron - polar acoustical phonon interactions in nitride based diluted magnetic semiconductor quantum well via hot electron magnetotransport

    SciTech Connect

    Pandya, Ankur; Shinde, Satyam; Jha, Prafulla K.

    2015-05-15

    In this paper the hot electron transport properties like carrier energy and momentum scattering rates and electron energy loss rates are calculated via interactions of electrons with polar acoustical phonons for Mn doped BN quantum well in BN nanosheets via piezoelectric scattering and deformation potential mechanisms at low temperatures with high electric field. Electron energy loss rate increases with the electric field. It is observed that at low temperatures and for low electric field the phonon absorption is taking place whereas, for sufficient large electric field, phonon emission takes place. Under the piezoelectric (polar acoustical phonon) scattering mechanism, the carrier scattering rate decreases with the reduction of electric field at low temperatures wherein, the scattering rate variation with electric field is limited by a specific temperature beyond which there is no any impact of electric field on such scattering.

  8. Phase Transition of ZnxMn1-xS Dilute Magnetic Semiconductor Nanoparticles under Ultra-high Pressure

    SciTech Connect

    Z Zong; Y Ma; T Hu; Q Cui; M Zhang; G Zou

    2011-12-31

    The high-pressure behavior of different doping content of ZnS nanocrystals has been investigated using angle-dispersive synchrotron X-ray powder diffraction up to 45.1 GPa. A phase transformation from the zinc-blende(ZB) to the rock-salt (RS) structure is observed at pressures of about 17.7 and 18.3 GPa at room temperature, corresponding to the Mn{sup 2+} ion mole percent content solutions 0.85% and 1.26%, respectively. The obtained results indicate that the Mn{sup 2+} doping could obviously enhance the phase transition pressure of ZnS nanocrystal. The elevation of phase transition pressure could origin from the higher surface energy induced by ion doping.

  9. Zinc oxide based diluted magnetic semiconductor nanoparticles: Synthesis by laser ablation in liquids, microstructural and optical properties

    NASA Astrophysics Data System (ADS)

    Savchuk, Andriy I.; Perrone, Alessio; Stolyarchuk, Ihor D.; Savchuk, Oleksandr A.; Makoviy, Vitaliy V.; Smolinsky, Mykhailo M.; Shporta, Oleksandra A.

    2013-12-01

    Nanoparticles of ZnO and ZnO doped with transition metals (Mn, Co) were synthesized by laser ablation in liquid medium. Scanning electron microscopy (SEM) showed formation of nanostructures with different shapes. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. Absorption edge of ZnO, ZnO:Mn and ZnO:Co colloidal nanoparticles exhibits blue shift due to confinement effect. In photoluminescence spectra three peaks are attributed to the band-edge transitions and defect states. The Faraday rotation in ZnO:Mn nanoparticles gives evidence for paramagnetic behavior at room temperature.

  10. Semiconductor Nanostructures in High Magnetic Fields:. Recent Results at Hfml Nijmegen

    NASA Astrophysics Data System (ADS)

    Christianen, Peter C. M.

    A short overview of the current experimental facilities at the HFML Nijmegen, including an update on the planned development of a 45 T Hybrid magnet in conjunction with a Free Electron Laser, was presented. That was followed by a brief highlight of recent results on the high field physical properties of semiconductor nanostructures, such as quantum rings1 and dots,2 graphene3,4 and organic nanostructures.5 The majority of the talk was devoted to the investigation of negatively charged excitons (negative trions, two electrons bound to one hole) in semiconductor quantum wells in high magnetic fields. A comprehensive overview of photoluminescence (PL) experiments on GaAs and CdTe quantum wells (QWs) of variable well widths, containing a low density electron gas (2DEG) was presented. Particular interest was given to the magnetic field range where the ground state of negative trions is changing from a singlet (both electrons having opposite spin) to a triplet (parallel electron spins) state. Using polarized magneto-PL (excitation) and reflectivity spectroscopy we have identified (for both GaAs and CdTe QWs) the four typical excitonic peaks, usually denoted as the singlet, dark triplet and bright triplet trion peaks, as well as the neutral exciton peak. All peaks exhibit a pronounced dependence on polarization, 2DEG density and temperature. CdTe QWs exhibit all four peaks at the entire field range used (< 44 T), whereas the dark triplet emission disappears at high fields for GaAs QWs. We have determined the field strength at which the singlet-triplet crossover occurs for all QWs, which allows us to critically compare our experimental results with theoretical predictions. Remarkably, the actual singlet-triplet transition is hidden in GaAs QWs and a narrow (12 nm) CdTe QW. Since the PL emission energy equals the energy difference between the initial (trion) and final (electron) states, the PL lines themselves do not cross at the singlet-triplet crossover as a result of the

  11. Multifunctional semiconductor micro-Hall devices for magnetic, electric, and photo-detection

    SciTech Connect

    Gilbertson, A. M.; Cohen, L. F.; Sadeghi, Hatef; Lambert, C. J.; Panchal, V.; Kazakova, O.; Solin, S. A.

    2015-12-07

    We report the real-space voltage response of InSb/AlInSb micro-Hall devices to local photo-excitation, electric, and magnetic fields at room temperature using scanning probe microscopy. We show that the ultrafast generation of localised photocarriers results in conductance perturbations analogous to those produced by local electric fields. Experimental results are in good agreement with tight-binding transport calculations in the diffusive regime. The magnetic, photo, and charge sensitivity of a 2 μm wide probe are evaluated at a 10 μA bias current in the Johnson noise limit (valid at measurement frequencies > 10 kHz) to be, respectively, 500 nT/√Hz; 20 pW/√Hz (λ = 635 nm) comparable to commercial photoconductive detectors; and 0.05 e/√Hz comparable to that of single electron transistors. These results demonstrate the remarkably versatile sensing attributes of simple semiconductor micro-Hall devices that can be applied to a host of imaging and sensing applications.

  12. Ferromagnetism in indium manganese arsenide magnetic semiconductor thin films deposited by metalorganic vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Blattner, Aaron J.

    The structure-property relationships of (In,Mn)As magnetic semiconductor thin films have been investigated to elucidate the mechanism of ferromagnetism and to assess its viability for use in spintronic device applications. Single phase, epitaxial (In,Mn)As films were deposited for the first time using atmospheric pressure metalorganic vapor phase epitaxy. The microstructure and phase composition of these films were determined using X-ray diffraction, transmission electron microscopy, and extended x-ray absorption fine structure measurements. Magnetic properties of the films were examined using superconducting quantum interference device magnetometery. Room temperature ferromagnetism was observed in single-phase In1-xMn xAs films with x ≤ 0.10. Magnetization measurements indicated that these (In,Mn)As samples had a transition temperature of 298--333 K. The Curie temperature was effectively independent of Mn concentration over the range of 1--10%. The temperature dependent magnetization along with the magnitude of the saturation magnetization and microstructural analysis indicated that the source of the high-temperature ferromagnetism in single-phase films is not attributable to MnAs nanoprecipitates. The Curie temperatures for these films are nearly constant for hole concentrations of 8 x 1017--1.6 x 1018 cm -3. In addition, the hole concentration is at least two orders of magnitude smaller than what is required under the conventional hole-mediated theory of ferromagnetism to obtain room-temperature ferromagnetism. Consequently, this model in its current form is not sufficient to describe the ferromagnetism in (In,Mn)As deposited using MOVPE. A model based upon interacting atomic scale ferromagnetic clusters was developed. The ferromagnetic coupling between these clusters may be a hole-mediated mechanism. This model of interacting ferromagnetic clusters was very successful in describing both the temperature and field dependence of the magnetization. In addition

  13. Extraordinary Magnetoresistance At Room Temperature In Non-Magnetic Narrow-Gap Semiconductor/Metal Composites

    NASA Astrophysics Data System (ADS)

    Solin, S. A.

    2001-03-01

    The magnetoresistance (MR) of a material object contains a physical contribution from the magnetic field dependence of the material parameters such as the mobility or carrier concentration and a geometric contribution from the dependence of the current path and output voltage on the sample shape and electrode configuration. To date, only two classes of magnetic materials, artificially layered metals which exhibit giant MR (GMR) and the manganite perovskites which exhibit colossal MR (CMR) have been considered serious candidates in the effort to improve the room temperature (RT) performance of MR sensors. For both of these classes, the physical MR dominates. In contrast, we have found that non-magnetic narrow-gap semiconductors containing patterned metallic inhomogeneities (shunts), exhibit RT geometric extraordinary MR (EMR) orders of magnitude larger than the physical MR of other materials. EMR in excess of 2000% at 0.05 Tesla and 3,000,000% at 5 T, respectively, has been observed in macroscopic ( ~ 1 mm) composite structures of InSb with patterned internal or external shunts.(S.A. Solin et al., Science 289), 1530 (2000).^,(T. Zhou, D.R. Hines and S.A. Solin, Appl. Phys. Lett., submitted.) We have been able to quantitatively account for the magnitude of the observed EMR as well as its dependence on the geometry (shape, size and placement of the shunt) using both analytic (Laplace equation with boundary conditions) and computational (Finite Element Analysis)(see the talk by L.R. Ram-Mohan et al., this conference) methods. The effect of scaling EMR structures to mesoscopic dimensions and the possible technological impact of EMR will be discussed.

  14. Phase diagram and magnetic properties of the diluted fcc system NipMg1-pO

    NASA Astrophysics Data System (ADS)

    Feng, Zhen; Seehra, Mohindar S.

    1992-02-01

    Starting from Ni and Mg nitrates, about 20 samples of NipMg1-pO samples (with 0.06<=p<=0.86) were prepared and x-ray-diffraction studies showed the samples to have the NaCl structure with the lattice constant fitting the expression a(p)=4.2115-0.0340p Å. Temperature-dependent magnetic-susceptibility (χ) studies of the samples were carried out between 1.8 and 600 K using a superconducting-quantum-interference-device magnetometer and Néel temperatures TN's were determined from the peak in ∂(χT)/∂T. The variation of t=TN(p)/TN(1) vs p is compared with that of CopMg1-pO. For both systems, the variations for p>0.31 are found to fit the predicted values for a simple-cubic Heisenberg antiferromagnet and a theoretical basis for this anomalous result is advanced. The experimental percolation threshold pc=0.15+/-0.01 and for pcdiluted fcc antiferromagnets, such as CopMg1-pO and EupSr1-pTe. It is suggested that the differences in the t-vs-p variations for p<0.31 in NipMg1-pO, CopMg1-pO, and EupSr1-pTe may be related to the differences in the ratio of the next-nearest-neighbor to nearest-neighbor exchange constants in these systems.

  15. Optically Detected Magnetic Resonance Studies on π-conjugated semiconductor systems

    SciTech Connect

    Chen, Ying

    2011-01-01

    Optically Detected Magnetic Resonance (ODMR) techniques were used to investigate the dynamics of excitons and charge carriers in π-conjugated organic semiconductors. Degradation behavior of the negative spin-1/2 electroluminescence-detected magnetic resonance (ELDMR) was observed in Alq3 devices. The increase in the resonance amplitude implies an increasing bipolaron formation during degradation, which might be the result of growth of charge traps in the device. The same behavior of the negative spin-1/2 ELDMR was observed in 2wt% Rubrene doped Tris(8-hydroxyquinolinato)aluminium (Alq3) devices. However, with increasing injection current, a positive spin-1/2 ELDMR, together with positive spin 1 triplet powder patterns at ΔmS=±1 and ΔmS=±2, emerges. Due to the similarities in the frequency dependences of single and double modulated ELDMR and the photoluminescence-detected magnetic resonance (PLDMR) results in poly[2-methoxy-5-(2 -ethyl-hexyloxy)-1,4-phenyl ene vinylene] (MEH-PPV) films, the mechanism for this positive spin-1/2 ELDMR was assigned to enhanced triplet-polaron quenching under resonance conditions. The ELDMR in rubrene doped Alq3 devices provides a path to investigate charge distribution in the device under operational conditions. Combining the results of several devices with different carrier blocking properties and the results from transient EL, it was concluded trions not only exist near buffer layer but also exist in the electron transport layer. This TPQ model can also be used to explain the positive spin-1/2 PLDMR in poly(3-hexylthiophene) (P3HT) films at low temperature and in MEH-PPV films at various temperatures up to room temperature. Through quantitative analysis, TE-polaron quenching (TPQ) model is shown having the ability to explain most behaviors of the positive spin-1/2 resonance. Photocurrent detected magnetic resonance (PCDMR) studies on MEH-PPV devices revealed a novel transient resonance signal. The signal

  16. Magnetic ground state of an individual Fe(2+) ion in strained semiconductor nanostructure.

    PubMed

    Smoleński, T; Kazimierczuk, T; Kobak, J; Goryca, M; Golnik, A; Kossacki, P; Pacuski, W

    2016-01-01

    Single impurities with nonzero spin and multiple ground states offer a degree of freedom that can be utilized to store the quantum information. However, Fe(2+) dopant is known for having a single nondegenerate ground state in the bulk host semiconductors and thus is of little use for spintronic applications. Here we show that the well-established picture of Fe(2+) spin configuration can be modified by subjecting the Fe(2+) ion to high strain, for example, produced by lattice mismatched epitaxial nanostructures. Our analysis reveals that high strain induces qualitative change in the ion energy spectrum and results in nearly doubly degenerate ground state with spin projection Sz= ± 2. We provide an experimental proof of this concept using a new system: a strained epitaxial quantum dot containing individual Fe(2+) ion. Magnetic character of the Fe(2+) ground state in a CdSe/ZnSe dot is revealed in photoluminescence experiments by exploiting a coupling between a confined exciton and the single-iron impurity. We also demonstrate that the Fe(2+) spin can be oriented by spin-polarized excitons, which opens a possibility of using it as an optically controllable two-level system free of nuclear spin fluctuations. PMID:26818580

  17. Magnetic ground state of an individual Fe2+ ion in strained semiconductor nanostructure

    PubMed Central

    Smoleński, T.; Kazimierczuk, T.; Kobak, J.; Goryca, M.; Golnik, A.; Kossacki, P.; Pacuski, W.

    2016-01-01

    Single impurities with nonzero spin and multiple ground states offer a degree of freedom that can be utilized to store the quantum information. However, Fe2+ dopant is known for having a single nondegenerate ground state in the bulk host semiconductors and thus is of little use for spintronic applications. Here we show that the well-established picture of Fe2+ spin configuration can be modified by subjecting the Fe2+ ion to high strain, for example, produced by lattice mismatched epitaxial nanostructures. Our analysis reveals that high strain induces qualitative change in the ion energy spectrum and results in nearly doubly degenerate ground state with spin projection Sz=±2. We provide an experimental proof of this concept using a new system: a strained epitaxial quantum dot containing individual Fe2+ ion. Magnetic character of the Fe2+ ground state in a CdSe/ZnSe dot is revealed in photoluminescence experiments by exploiting a coupling between a confined exciton and the single-iron impurity. We also demonstrate that the Fe2+ spin can be oriented by spin-polarized excitons, which opens a possibility of using it as an optically controllable two-level system free of nuclear spin fluctuations. PMID:26818580

  18. Detection of magnetic state in a nanoscale ferromagnetic ring by using ballistic semiconductor two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Hara, Masahiro; Shibata, Junya; Kimura, Takashi; Otani, Yoshichika

    2006-02-01

    We have developed a method of measuring magnetization process in a ferromagnetic ring by analyzing a characteristic response of a semiconductor two-dimensional electron gas (2DEG) lying beneath the ring. A 2DEG microcross structure is formed underneath a ferromagnetic ring to detect the position of paired domain walls of the onion state. The variation of the bend resistance due to the rotation of the paired domain walls is quantitatively reproduced by a semiclassical billiard model.

  19. Magnetic-field-induced ferroelectric polarization reversal in the multiferroic Ge(1-x)Mn(x)Te semiconductor.

    PubMed

    Przybylińska, H; Springholz, G; Lechner, R T; Hassan, M; Wegscheider, M; Jantsch, W; Bauer, G

    2014-01-31

    Ge(1-x)Mn(x)Te is shown to be a multiferroic semiconductor, exhibiting both ferromagnetic and ferroelectric properties. By ferromagnetic resonance we demonstrate that both types of order are coupled to each other. As a result, magnetic-field-induced ferroelectric polarization reversal is achieved. Switching of the spontaneous electric dipole moment is monitored by changes in the magnetocrystalline anisotropy. This also reveals that the ferroelectric polarization reversal is accompanied by a reorientation of the hard and easy magnetization axes. By tuning the GeMnTe composition, the interplay between ferromagnetism and ferroelectricity can be controlled. PMID:24580486

  20. High temperature magnetic order in Zn1-x Mn x SnSb2+MnSb nanocomposite ferromagnetic semiconductors.

    PubMed

    Kilanski, L; Górska, M; Ślawska-Waniewska, A; Lewińska, S; Szymczak, R; Dynowska, E; Podgórni, A; Dobrowolski, W; Ralević, U; Gajić, R; Romčević, N; Fedorchenko, I V; Marenkin, S F

    2016-08-24

    We present studies of structural, magnetic, and electrical properties of Zn1-x Mn x SnSb2+MnSb nanocomposite ferromagnetic semiconductors with the average Mn-content, [Formula: see text], changing from 0.027 up to 0.138. The magnetic force microscope imaging done at room temperature shows the presence of a strong signal coming from MnSb clusters. Magnetic properties show the paramagnet-ferromagnet transition with the Curie temperature, T C, equal to about 522 K and the cluster-glass behavior with the transition temperature, T CG, equal to about 465 K, both related to MnSb clusters. The magnetotransport studies show that all investigated samples are p-type semiconductors with high hole concentration, p, changing from 10(21) to 10(22) cm(-3). A large increase in the resistivity as a function of the magnetic field is observed at T  <  10 K and small magnetic fields, [Formula: see text] mT, for all the studied samples with a maximum amplitude of the magnetoresistance about 460% at T  =  1.4 K. The large increase in the resistivity is most probably caused by the appearance of the superconducting state in the samples at T  <  4.3 K. PMID:27351672

  1. Effects of crossed electric and magnetic fields on the interband optical absorption spectra of variably spaced semiconductor superlattices

    NASA Astrophysics Data System (ADS)

    Zuleta, J. N.; Reyes-Gómez, E.

    2016-05-01

    The interband optical absorption spectra of a GaAs-Ga1-xAlxAs variably spaced semiconductor superlattice under crossed in-plane magnetic and growth-direction applied electric fields are theoretically investigated. The electronic structure, transition strengths and interband absorption coefficients are analyzed within the weak and strong magnetic-field regimes. A dramatic quenching of the absorption coefficient is observed, in the weak magnetic-field regime, as the applied electric field is increased, in good agreement with previous experimental measurements performed in a similar system under growth-direction applied electric fields. A decrease of the resonant tunneling in the superlattice is also theoretically obtained in the strong magnetic-field regime. Moreover, in this case, we found an interband absorption coefficient weakly dependent on the applied electric field. Present theoretical results suggest that an in-plane magnetic field may be used to tune the optical properties of variably spaced semiconductor superlattices, with possible future applications in solar cells and magneto-optical devices.

  2. Simultaneous monitoring of singlet and triplet exciton variations in solid organic semiconductors driven by an external static magnetic field

    SciTech Connect

    Ding, Baofu Alameh, Kamal

    2014-07-07

    The research field of organic spintronics has remarkably and rapidly become a promising research area for delivering a range of high-performance devices, such as magnetic-field sensors, spin valves, and magnetically modulated organic light emitting devices (OLEDs). Plenty of microscopic physical and chemical models based on exciton or charge interactions have been proposed to explain organic magneto-optoelectronic phenomena. However, the simultaneous observation of singlet- and triplet-exciton variations in an external magnetic field is still unfeasible, preventing a thorough theoretical description of the spin dynamics in organic semiconductors. Here, we show that we can simultaneously observe variations of singlet excitons and triplet excitons in an external magnetic field, by designing an OLED structure employing a singlet-exciton filtering and detection layer in conjunction with a separate triplet-exciton detection layer. This OLED structure enables the observation of a Lorentzian and a non-Lorentzian line-shape magnetoresponse for singlet excitons and triplet excitons, respectively.

  3. Detection Techniques for Biomolecules using Semi-Conductor Nanocrystals and Magnetic Beads as Labels

    NASA Astrophysics Data System (ADS)

    Chatterjee, Esha

    Continued interest in the development of miniaturized and portable analytical platforms necessitates the exploration of sensitive methods for the detection of trace analytes. Nanomaterials, on account of their unique physical and chemical properties, are not only able to overcome many limitations of traditional detection reagents but also enable the exploration of many new signal transduction technologies. This dissertation presents a series of investigations of alternative detection techniques for biomolecules, involving the use of semi-conductor nanocrystals and magnetic beads as labels. Initial research focused on the development of quantum dot-encapsulating liposomes as a novel fluorescent label for immunoassays. This hybrid nanomaterial was anticipated to overcome the drawbacks presented by traditional fluorophores as well as provide significant signal amplification. Quantum dot-encapsulating liposomes were synthesized by the method of thin film hydration and characterized. The utility of these composite nanostructures for bioanalysis was demonstrated. However, the longterm instability of the liposomes hampered quantitative development. A second approach for assay development exploited the ability of gold nanoparticles to quench the optical signals obtained from quantum dots. The goal of this study was to demonstrate the feasibility of using aptamer-linked nanostructures in FRET-based quenching for the detection of proteins. Thrombin was used as the model analyte in this study. Experimental parameters for the assay were optimized. The assay simply required the mixing of the sample with the reagents and could be completed in less than an hour. The limit of detection for thrombin by this method was 5 nM. This homogeneous assay can be easily adapted for the detection of a wide variety of biochemicals. The novel technique of ferromagnetic resonance generated in magnetic bead labels was explored for signal transduction. This inductive detection technique lends

  4. Interfacial Properties of Organic Semiconductor-Inorganic Magnetic Oxide Hybrid Spintronic Systems Fabricated Using Pulsed Laser Deposition.

    PubMed

    Majumdar, Sayani; Grochowska, Katarzyna; Sawczak, Miroslaw; Śliwiński, Gerard; Huhtinen, Hannu; Dahl, Johnny; Tuominen, Marjukka; Laukkanen, Pekka; Majumdar, Himadri S

    2015-10-14

    We report fabrication of a hybrid organic semiconductor-inorganic complex oxide interface of rubrene and La0.67Sr0.33MnO3 (LSMO) for spintronic devices using pulsed laser deposition (PLD) and investigate the interface structure and chemical bonding-dependent magnetic properties. Our results demonstrate that with proper control of growth parameters, thin films of organic semiconductor rubrene can be deposited without any damage to the molecular structure. Rubrene, a widely used organic semiconductor with high charge-carrier mobility and spin diffusion length, when grown as thin films on amorphous and crystalline substrates such as SiO2-glass, indium-tin oxide (ITO), and LSMO by PLD at room temperature and a laser fluence of 0.19 J/cm2, reveals amorphous structure. The Raman spectra verify the signatures of both Ag and Bg Raman active modes of rubrene molecules. X-ray reflectivity measurements indicate a well-defined interface formation between surface-treated LSMO and rubrene, whereas X-ray photoelectron spectra indicate the signature of hybridization of the electronic states at this interface. Magnetic measurements show that the ferromagnetic property of the rubrene-LSMO interface improves by >230% compared to the pristine LSMO surface due to this proposed hybridization. Intentional disruption of the direct contact between LSMO and rubrene by insertion of a dielectric AlOx layer results in an observably decreased ferromagnetism. These experimental results demonstrate that by controlling the interface formation between organic semiconductor and half-metallic oxide thin films, it is possible to engineer the interface spin polarization properties. Results also confirm that by using PLD for consecutive growth of different layers, contamination-free interfaces can be obtained, and this finding is significant for the well-controlled and reproducible design of spin-polarized interfaces for future hybrid spintronics devices. PMID:26402298

  5. First principles calculations of electronic structure and magnetic properties of Cr-based magnetic semiconductors Al{sub 1-x}Cr{sub x}X (X=N, P, As, Sb)

    SciTech Connect

    Saeed, Y.; Shaukat, A.; Nazir, S.; Ikram, N.; Hussain Reshak, Ali

    2010-01-15

    First principles calculations based on the density functional theory (DFT) within the local spin density approximation are performed to investigate the electronic structure and magnetic properties of Cr-based zinc blende diluted magnetic semiconductors Al{sub 1-x}Cr{sub x}X (X=N, P, As, Sb) for 0<=x<=0.50.The behaviour of magnetic moment of Al{sub 1-x}Cr{sub x}X at each Cr site as well as the change in the band gap value due to spin down electrons has been studied by increasing the concentration of Cr atom and through changing X from N to Sb. Furthermore, the role of p-d hybridization is analyzed in the electronic band structure and exchange splitting of d-dominated bands. The interaction strength is stronger in Al{sub 1-x}Cr{sub x}N and becomes weaker in Al{sub 1-x}Cr{sub x}Sb. The band gap due to the spin down electrons decreases with the increased concentration of Cr in Al{sub 1-x}Cr{sub x}X, and as one moves down along the isoelectronic series in the group V from N to Sb. Our calculations also verify the half-metallic ferromagnetic character in Cr doped AlX. - Graphical abstract: The prototype structures of Cr doped AlX (X=N, P, As, Sb) compounds: (A) zinc blende AlP for x=0, (B) Cr{sub 1}Al{sub 7}P{sub 8} for x=0.125, (C) Cr{sub 1}Al{sub 3}P{sub 4} for x=0.25, (D) Cr{sub 1}Al{sub 1}P{sub 2} for x=0.5.

  6. Anomalous D'yakonov-Perel' spin relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration

    NASA Astrophysics Data System (ADS)

    Zhou, Y.; Yu, T.; Wu, M. W.

    2013-06-01

    We report an anomalous scaling of the D’yakonov-Perel’ spin relaxation with the momentum relaxation in semiconductor quantum wells under a strong magnetic field in the Voigt configuration. We focus on the case in which the external magnetic field is perpendicular to the spin-orbit-coupling-induced effective magnetic field and its magnitude is much larger than the latter one. It is found that the longitudinal spin relaxation time is proportional to the momentum relaxation time even in the strong-scattering limit, indicating that the D’yakonov-Perel’ spin relaxation demonstrates Elliott-Yafet-like behavior. Moreover, the transverse spin relaxation time is proportional (inversely proportional) to the momentum relaxation time in the strong- (weak-) scattering limit, both in the opposite trends against the well-established conventional D’yakonov-Perel’ spin relaxation behaviors. We further demonstrate that all the above anomalous scaling relations come from the unique form of the effective inhomogeneous broadening.

  7. Mn-based ferromagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Dietl, Tomasz; Sawicki, Maciej

    2003-07-01

    The present status of research and prospects for device applications of ferromagnetic (diluted magnetic) semiconductors (DMS) is presented. We review the nature of the electronic states and the mechanisms of the carrier-mediated exchange interactions (mean-field Zener model) in p-type Mn-based III-V and II-VI compounds, highlighting a good correspondence of experimental findings and theoretical predictions. An account of the latest progress on the road of increasing the Currie point to above the room temperature is given for both families of compounds. We comment on a possibility of obtaining ferromagnetism in n-type materials, taking (Zn,Mn)O:Al as the example. Concerning technologically important issue of easy axis and domain engineering, we present theoretical predictions and experimental results on the temperature and carrier concentration driven change of magnetic anisotropy in (Ga,Mn)As.

  8. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure

    PubMed Central

    Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

    2015-01-01

    The anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gate-control of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured. PMID:26596472

  9. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure

    NASA Astrophysics Data System (ADS)

    Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

    2015-11-01

    The anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gate-control of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured.

  10. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure.

    PubMed

    Oveshnikov, L N; Kulbachinskii, V A; Davydov, A B; Aronzon, B A; Rozhansky, I V; Averkiev, N S; Kugel, K I; Tripathi, V

    2015-01-01

    The anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gate-control of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured. PMID:26596472

  11. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure.

    SciTech Connect

    Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

    2015-11-24

    In this study, the anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gatecontrol of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured.

  12. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure.

    DOE PAGESBeta

    Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

    2015-11-24

    In this study, the anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gatecontrol of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHEmore » in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured.« less

  13. The role of iron(II) dilution in the magnetic and photomagnetic properties of the series [Fe(x)Zn(1-x)(bpp)₂](NCSe)₂.

    PubMed

    Baldé, Chérif; Desplanches, Cédric; Le Gac, Fréderic; Guionneau, Philippe; Létard, Jean-François

    2014-06-01

    The effects of metal dilution on the spin-crossover behavior of iron(II) in the mixed crystal series [Fe(x)Zn(1-x)(bpp)2](NCSe)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) have been studied using magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. For each mixed-crystal system, the thermal spin transition temperature, T(1/2), and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T(1/2) decreases with the metal dilution while T(LIESST) remains unchanged. Dilution also tends to decrease the hysteresis width and smooth the transition curves. These effects were discussed first qualitatively and then quantitatively on the basis of a kinetic study governing the photo-induced back conversion taking into account the relative sizes of Zn(II) and Fe(II) ions. Interestingly, single crystals were obtained for [Fe(0.6)Zn(0.4)(bpp)2](NCSe)2 allowing the X-ray diffraction crystal-structure determination. PMID:24699627

  14. Proposal of a general scheme to obtain room-temperature spin polarization in asymmetric antiferromagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Li, Xingxing; Wu, Xiaojun; Li, Zhenyu; Yang, Jinlong

    2015-09-01

    Exploring magnetic semiconductors is one of the most important questions for spintronic applications. Although various solutions, such as dilute magnetic semiconductors, have been proposed, a practical spintronic device working at room temperature has not been realized. The key to address this issue is to find magnetic materials with both room-temperature magnetic ordering and large spin polarization around the Fermi energy level. Here, we predict a new concept of asymmetric antiferromagnetic (AFM) semiconductors (AAFMSs) with both features. The high temperature magnetic ordering originates from the AFM coupling between different transition metal ions with strong super-exchange interaction, whereas the large spin polarization around the Fermi energy level owes to d orbital mismatch among these ions. Through first-principles calculations, a family of double perovskites A2Cr M O6 (A =Ca ,Sr ,Ba , and M =Ru ,Os ) are predicted to be AAFMSs. This paper provides a way for developing spintronic devices working at room temperature.

  15. High accuracy NMR chemical shift corrected for bulk magnetization as a tool for structural elucidation of dilutable microemulsions. Part 1 - Proof of concept.

    PubMed

    Hoffman, Roy E; Darmon, Eliezer; Aserin, Abraham; Garti, Nissim

    2016-02-01

    In microemulsions, changes in droplet size and shape and possible transformations occur under various conditions. They are difficult to characterize by most analytical tools because of their nano-sized structure and dynamic nature. Several methods are usually combined to obtain reliable information, guiding the scientist in understanding their physical behavior. We felt that there is a need for a technique that complements those in use today in order to provide more information on the microemulsion behavior, mainly as a function of dilution with water. The improvement of NMR chemical shift measurements independent of bulk magnetization effects makes it possible to study the very weak intermolecular chemical shift effects. In the present study, we used NMR high resolution magic angle spinning to measure the chemical shift very accurately, free of bulk magnetization effects. The chemical shift of microemulsion components is measured as a function of the water content in order to validate the method in an interesting and promising, U-type dilutable microemulsion, which had been previously studied by a variety of techniques. Phase transition points of the microemulsion (O/W, bicontinuous, W/O) and changes in droplet shape were successfully detected using high-accuracy chemical shift measurements. We analyzed the results and found them to be compatible with the previous studies, paving the way for high-accuracy chemical shifts to be used for the study of other microemulsion systems. We detected two transition points along the water dilution line of the concentrate (reverse micelles) corresponding to the transition from swollen W/O nano-droplets to bicontinuous to the O/W droplets along with the changes in the droplets' sizes and shapes. The method seems to be in excellent agreement with other previously studied techniques and shows the advantage of this easy and valid technique. PMID:25113928

  16. Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields.

    PubMed

    Misra, S; Zhou, B B; Drozdov, I K; Seo, J; Urban, L; Gyenis, A; Kingsley, S C J; Jones, H; Yazdani, A

    2013-10-01

    We describe the construction and performance of a scanning tunneling microscope capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of performance as typical machines with more modest refrigeration by measuring spectroscopic maps at base temperature both at zero field and in an applied magnetic field. PMID:24182125

  17. Dilution Confusion: Conventions for Defining a Dilution

    ERIC Educational Resources Information Center

    Fishel, Laurence A.

    2010-01-01

    Two conventions for preparing dilutions are used in clinical laboratories. The first convention defines an "a:b" dilution as "a" volumes of solution A plus "b" volumes of solution B. The second convention defines an "a:b" dilution as "a" volumes of solution A diluted into a final volume of "b". Use of the incorrect dilution convention could affect…

  18. Investigation at the atomic scale of the Co spatial distribution in Zn(Co)O magnetic semiconductor oxide

    SciTech Connect

    Larde, R.; Talbot, E.; Vurpillot, F.; Pareige, P.; Schmerber, G.; Beaurepaire, E.; Dinia, A.; Pierron-Bohnes, V.

    2009-06-15

    A sputtered Zn{sub 0.95}Co{sub 0.05}O layer was chemically analyzed at the atomic scale in order to provide an accurate image of the distribution of Co atoms in the ZnO matrix. The investigation of the magnetic properties shows that the as-deposited Zn{sub 0.95}Co{sub 0.05}O is ferromagnetic at room temperature. Atom probe tomography reveals a homogeneous distribution of all chemical species in the layer and the absence of any Co clustering. This result proves that the ferromagnetic properties of this magnetic semiconductor cannot be attributed to a secondary phase or to metallic Co precipitates within the layer.

  19. Spin dynamics in p-doped semiconductor nanostructures subject to a magnetic field tilted from the Voigt geometry

    NASA Astrophysics Data System (ADS)

    Korzekwa, K.; Gradl, C.; Kugler, M.; Furthmeier, S.; Griesbeck, M.; Hirmer, M.; Schuh, D.; Wegscheider, W.; Kuhn, T.; Schüller, C.; Korn, T.; Machnikowski, P.

    2013-10-01

    We develop a theoretical description of the spin dynamics of resident holes in a p-doped semiconductor quantum well (QW) subject to a magnetic field slightly tilted from the Voigt geometry. We find the expressions for the signals measured in time-resolved Faraday rotation (TRFR) and resonant spin amplification (RSA) experiments and study their behavior for a range of system parameters. We find that an inversion of the RSA peaks can occur for long hole spin dephasing times and tilted magnetic fields. We verify the validity of our theoretical findings by performing a series of TRFR and RSA experiments on a p-modulation doped GaAs/Al0.3Ga0.7As single QW and showing that our model can reproduce experimentally observed signals.

  20. Néel-type skyrmion lattice with confined orientation in the polar magnetic semiconductor GaV4S8

    NASA Astrophysics Data System (ADS)

    Kézsmárki, I.; Bordács, S.; Milde, P.; Neuber, E.; Eng, L. M.; White, J. S.; Rønnow, H. M.; Dewhurst, C. D.; Mochizuki, M.; Yanai, K.; Nakamura, H.; Ehlers, D.; Tsurkan, V.; Loidl, A.

    2015-11-01

    Following the early prediction of the skyrmion lattice (SkL)--a periodic array of spin vortices--it has been observed recently in various magnetic crystals mostly with chiral structure. Although non-chiral but polar crystals with Cnv symmetry were identified as ideal SkL hosts in pioneering theoretical studies, this archetype of SkL has remained experimentally unexplored. Here, we report the discovery of a SkL in the polar magnetic semiconductor GaV4S8 with rhombohedral (C3v) symmetry and easy axis anisotropy. The SkL exists over an unusually broad temperature range compared with other bulk crystals and the orientation of the vortices is not controlled by the external magnetic field, but instead confined to the magnetic easy axis. Supporting theory attributes these unique features to a new Néel-type of SkL describable as a superposition of spin cycloids in contrast to the Bloch-type SkL in chiral magnets described in terms of spin helices.

  1. Ferromagnets based on diamond-like semiconductors GaSb, InSb, Ge, and Si supersaturated with manganese or iron impurities during laser-plasma deposition

    SciTech Connect

    Demidov, E. S. Podol'skii, V. V.; Lesnikov, V. P.; Sapozhnikov, M. V.; Druzhnov, D. M.; Gusev, S. N.; Gribkov, B. A.; Filatov, D. O.; Stepanova, Yu. S.; Levchuk, S. A.

    2008-01-15

    Properties of thin (30-100 nm) layers of diluted magnetic semiconductors based on diamond-like compounds III-V (InSb and GaSb) and elemental semiconductors Ge and Si doped with 3d impurities of manganese and iron up to 15% were measured and discussed. The layers were grown by laser-plasma deposition onto heated single-crystal gallium arsenide or sapphire substrates. The ferromagnetism of layers with the Curie temperature up to 500 K appeared in observations of the ferromagnetic resonance, anomalous Hall effect, and magneto-optic Kerr effect. The carrier mobility of diluted magnetic semiconductors is a hundred times larger than that of the previously known highest temperature magnetic semiconductors, i.e., copper and chromium chalcogenides. The difference between changes in the magnetization with temperature in diluted semiconductors based on III-V, Ge, and Si was discussed. A complex structure of the ferromagnetic resonance spectrum in Si:Mn/GaAs was observed. The results of magnetic-force microscopy showed a weak correlation between the surface relief and magnetic inhomogeneity, which suggests that the ferromagnetism is caused by the 3d-impurity solid solution, rather than ferromagnetic phase inclusions.

  2. Newtype single-layer magnetic semiconductor in transition-metal dichalcogenides VX2 (X = S, Se and Te).

    PubMed

    Fuh, Huei-Ru; Chang, Ching-Ray; Wang, Yin-Kuo; Evans, Richard F L; Chantrell, Roy W; Jeng, Horng-Tay

    2016-01-01

    We present a newtype 2-dimensional (2D) magnetic semiconductor based on transition-metal dichalcogenides VX2 (X = S, Se and Te) via first-principles calculations. The obtained indirect band gaps of monolayer VS2, VSe2, and VTe2 given from the generalized gradient approximation (GGA) are respectively 0.05, 0.22, and 0.20 eV, all with integer magnetic moments of 1.0 μB. The GGA plus on-site Coulomb interaction U (GGA + U) enhances the exchange splittings and raises the energy gap up to 0.38~0.65 eV. By adopting the GW approximation, we obtain converged G0W0 gaps of 1.3, 1.2, and 0.7 eV for VS2, VSe2, and VTe2 monolayers, respectively. They agree very well with our calculated HSE gaps of 1.1, 1.2, and 0.6 eV, respectively. The gap sizes as well as the metal-insulator transitions are tunable by applying the in-plane strain and/or changing the number of stacking layers. The Monte Carlo simulations illustrate very high Curie-temperatures of 292, 472, and 553 K for VS2, VSe2, and VTe2 monolayers, respectively. They are nearly or well beyond the room temperature. Combining the semiconducting energy gap, the 100% spin polarized valence and conduction bands, the room temperature TC, and the in-plane magnetic anisotropy together in a single layer VX2, this newtype 2D magnetic semiconductor shows great potential in future spintronics. PMID:27601195

  3. Newtype single-layer magnetic semiconductor in transition-metal dichalcogenides VX2 (X = S, Se and Te)

    PubMed Central

    Fuh, Huei-Ru; Chang, Ching-Ray; Wang, Yin-Kuo; Evans, Richard F. L.; Chantrell, Roy W.; Jeng, Horng-Tay

    2016-01-01

    We present a newtype 2-dimensional (2D) magnetic semiconductor based on transition-metal dichalcogenides VX2 (X = S, Se and Te) via first-principles calculations. The obtained indirect band gaps of monolayer VS2, VSe2, and VTe2 given from the generalized gradient approximation (GGA) are respectively 0.05, 0.22, and 0.20 eV, all with integer magnetic moments of 1.0 μB. The GGA plus on-site Coulomb interaction U (GGA + U) enhances the exchange splittings and raises the energy gap up to 0.38~0.65 eV. By adopting the GW approximation, we obtain converged G0W0 gaps of 1.3, 1.2, and 0.7 eV for VS2, VSe2, and VTe2 monolayers, respectively. They agree very well with our calculated HSE gaps of 1.1, 1.2, and 0.6 eV, respectively. The gap sizes as well as the metal-insulator transitions are tunable by applying the in-plane strain and/or changing the number of stacking layers. The Monte Carlo simulations illustrate very high Curie-temperatures of 292, 472, and 553 K for VS2, VSe2, and VTe2 monolayers, respectively. They are nearly or well beyond the room temperature. Combining the semiconducting energy gap, the 100% spin polarized valence and conduction bands, the room temperature TC, and the in-plane magnetic anisotropy together in a single layer VX2, this newtype 2D magnetic semiconductor shows great potential in future spintronics. PMID:27601195

  4. Type-II superconductivity in a dilute magnetic system: La1-xTmxRu3Si2

    NASA Astrophysics Data System (ADS)

    Escorne, M.; Mauger, A.; Gupta, L. C.; Godart, C.

    1994-05-01

    Superconducting and magnetic properties of La1-xTmxRu3Si2 (x=0, 0.08, and 0.16) have been investigated through measurements of both electric and magnetic properties. Tm is in a trivalent state and carries a magnetic moment ~=8μB. We find that the magnetic measurements are not suited to the determination of the critical line Hc(T) for the onset of type-II superconductivity in materials where one has at the same time superconducting diamagnetic shielding and paramagnetic contribution due to the localized spins. On the other hand, transport experiments are much less ambiguous, and allow us to determine accurately the critical temperature in a given applied magnetic field. In particular, they allow us to suggest a more appropriate interpretation of the maximum in the magnetic-susceptibility curve already observed in materials of the same family: this maximum results from a competition between the incomplete diamagnetic shielding and the paramagnetic contribution from the magnetic ions in the mixed phase, rather than from a spin-glass freezing of the paramagnetic ions. In zero field, the rate of depression of the critical temperature upon substituting nonmagnetic La ions by magnetic Tm ions is dT/dx=-8+/-1 K/at. % Tm.

  5. Magnetic disorder in diluted FexM100-x granular thin films (M=Au, Ag, Cu; x < 10 at.%).

    PubMed

    Alba Venero, D; Fernández Barquín, L; Alonso, J; Fdez-Gubieda, M L; Rodríguez Fernández, L; Boada, R; Chaboy, J

    2013-07-10

    Nanogranular thin films of Fe7Au93, Fe7Ag93 and Fe9Cu91 have been sputtered onto Si(100) substrates with the aim of studying the magnetic interactions. X-ray diffraction shows a major noble metal matrix with broad peaks stemming from (111) textured fcc-Au, Ag and Cu. The noble metal forms a nanogranular environment, as confirmed by transmission electron microscopy, with mean particle sizes below 10 nm. The high magnetoresistance (>6%) reveals the existence of Fe nanoparticles. X-ray absorption near edge spectroscopy confirms the presence of a bcc-Fe atom arrangement and some dissolved Fe atoms in the matrix, and XMCD shows the polarization of Au by the Fe nanoparticles. DC-magnetization displays a field-dependent irreversibility produced by the freezing of magnetic nanoparticles into a superspin-glass state. The hysteresis loops remain unsaturated at 5 K and 45 kOe. The coercivity displays a sharp temperature decrease towards a minimum below 50 K, levelling off at higher values, reaching Hc = 200 Oe at 300 K. Annealing of FeAu results in a double-peak zero field cooled magnetization and a slight decrease of the coercivity. The interpretation of the results supports the presence of Fe nanoparticles embedded in the major noble matrix, with some diluted Fe atoms/clusters. PMID:23765439

  6. Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1‑xMnxTe

    NASA Astrophysics Data System (ADS)

    Kriener, M.; Nakajima, T.; Kaneko, Y.; Kikkawa, A.; Yu, X. Z.; Endo, N.; Kato, K.; Takata, M.; Arima, T.; Tokura, Y.; Taguchi, Y.

    2016-05-01

    Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) – is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures Tc of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum Tc ≈ 180 K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-Tc phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change-memory functionality.

  7. Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1−xMnxTe

    PubMed Central

    Kriener, M.; Nakajima, T.; Kaneko, Y.; Kikkawa, A.; Yu, X. Z.; Endo, N.; Kato, K.; Takata, M.; Arima, T.; Tokura, Y.; Taguchi, Y.

    2016-01-01

    Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) – is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures Tc of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum Tc ≈ 180 K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-Tc phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change-memory functionality. PMID:27160657

  8. Heat-Treatment-Induced Switching of Magnetic States in the Doped Polar Semiconductor Ge1-xMnxTe.

    PubMed

    Kriener, M; Nakajima, T; Kaneko, Y; Kikkawa, A; Yu, X Z; Endo, N; Kato, K; Takata, M; Arima, T; Tokura, Y; Taguchi, Y

    2016-01-01

    Cross-control of a material property - manipulation of a physical quantity (e.g., magnetisation) by a nonconjugate field (e.g., electrical field) - is a challenge in fundamental science and also important for technological device applications. It has been demonstrated that magnetic properties can be controlled by electrical and optical stimuli in various magnets. Here we find that heat-treatment allows the control over two competing magnetic phases in the Mn-doped polar semiconductor GeTe. The onset temperatures Tc of ferromagnetism vary at low Mn concentrations by a factor of five to six with a maximum Tc ≈ 180 K, depending on the selected phase. Analyses in terms of synchrotron x-ray diffraction and energy dispersive x-ray spectroscopy indicate a possible segregation of the Mn ions, which is responsible for the high-Tc phase. More importantly, we demonstrate that the two states can be switched back and forth repeatedly from either phase by changing the heat-treatment of a sample, thereby confirming magnetic phase-change-memory functionality. PMID:27160657

  9. Spin and orbital magnetic moments of Fe in the n-type ferromagnetic semiconductor (In,Fe)As

    SciTech Connect

    Kobayashi, M. Oshima, M.; Anh, L. D.; Hai, P. N.; Tanaka, M.; Takeda, Y.; Okane, T.; Saitoh, Y.; Yamagami, H.; Sakamoto, S.; Kadono, T.; Fujimori, A.; Harada, Y.

    2014-07-21

    The electronic and magnetic properties of Fe atoms in the ferromagnetic semiconductor (In,Fe)As codoped with Be have been studied by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Fe L{sub 2,3} edge. The XAS and XMCD spectra showed simple spectral line shapes similar to Fe metal, but the ratio of the orbital and spin magnetic moments (M{sub orb}/M{sub spin}) estimated using the XMCD sum rules was significantly larger than that of Fe metal, indicating a significant orbital moment of Fe 3d electrons in (In,Fe)As:Be. The positive value of M{sub orb}/M{sub spin} implies that the Fe 3d shell is more than half-filled, which arises from the hybridization of the Fe{sup 3+} (d{sup 5}) state with the charge-transfer d{sup 6}L{sub ¯} states, where L{sub ¯} is a ligand hole in the host valence band. The XMCD intensity as a function of magnetic field indicated hysteretic behavior of the superparamagnetic-like component due to discrete ferromagnetic domains.

  10. Study of the oxygen vacancy influence on magnetic properties of Fe- and Co-doped SnO2 diluted alloys

    PubMed Central

    2012-01-01

    Transition-metal (TM)-doped diluted magnetic oxides (DMOs) have attracted attention from both experimental and theoretical points of view due to their potential use in spintronics towards new nanostructured devices and new technologies. In the present work, we study the magnetic properties of Sn0.96TM0.04O2 and Sn0.96TM0.04O1.98(VO)0.02, where TM = Fe and Co, focusing in particular in the role played by the presence of O vacancies nearby the TM. The calculated total energy as a function of the total magnetic moment per cell shows a magnetic metastability, corresponding to a ground state, respectively, with 2 and 1 μB/cell, for Fe and Co. Two metastable states, with 0 and 4 μB/cell were found for Fe, and a single value, 3 μB/cell, for Co. The spin-crossover energies (ES) were calculated. The values are ES0/2 = 107 meV and ES4/2 = 25 meV for Fe. For Co, ES3/1 = 36 meV. By creating O vacancies close to the TM site, we show that the metastablity and ES change. For iron, a new state appears, and the state with zero magnetic moment disappears. The ground state is 4 μB/cell instead of 2 μB/cell, and the energy ES2/4 is 30 meV. For cobalt, the ground state is then found with 3 μB/cell and the metastable state with 1 μB/cell. The spin-crossover energy ES1/3 is 21 meV. Our results suggest that these materials may be used in devices for spintronic applications that require different magnetization states. PMID:23020790

  11. LDRD-LW Final Report: 07-LW-041 "Magnetism in Semiconductor Nanocrystals: New Physics at the Nanoscale"

    SciTech Connect

    Meulenberg, R W; Lee, J I; McCall, S K

    2009-10-19

    The work conducted in this project was conducted with the aim of identifying and understanding the origin and mechanisms of magnetic behavior in undoped semiconductor nanocrystals (NCs), specifically those composed of CdSe. It was anticipated that the successful completion of this task would have the effect of addressing and resolving significant controversy over this topic in the literature. Meanwhile, application of the resultant knowledge was expected to permit manipulation of the magnetic properties, particularly the strength of any magnetic effects, which is of potential relevance in a range of advanced technologies. More specifically, the project was designed and research conducted with the goal of addressing the following series of questions: (1) How does the magnitude of the magnetism in CdSe NCs change with the organic molecules used to passivate their surface the NC size? i.e. Is the magnetism an intrinsic effect in the nanocrystalline CdSe (as observed for Au NCs) or a surface termination driven effect? (2) What is the chemical (elemental) nature of the magnetism? i.e. Are the magnetic effects associated with the Cd atoms or the Se atoms or both? (3) What is/are the underlying mechanism(s)? (4) How can the magnetism be controlled for further applications? To achieve this goal, several experimental/technical milestones were identified to be fulfilled during the course of the research: (A) The preparation of well characterized CdSe NCs with varying surface termination (B) Establishing the extent of the magnetism of these NCs using magnetometry (particularly using superconducting interference device [SQUID]) (C) Establishing the chemical nature of the magnetism using x-ray magnetic circular dichroism (XMCD) - the element specific nature of the technique allows identification of the element responsible for the magnetism (D) Identification of the effect of surface termination on the empty densities of states (DOS) using x-ray absorption spectroscopy (XAS

  12. Absence of exchange interaction between localized magnetic moments and conduction-electrons in diluted Er{sup 3+} gold-nanoparticles

    SciTech Connect

    Lesseux, G. G. Urbano, R. R.; Iwamoto, W.; García-Flores, A. F.; Rettori, C.

    2014-05-07

    The Electron Spin Resonance (ESR) of diluted Er{sup 3+} magnetic ions in Au nanoparticles (NPs) is reported. The NPs were synthesized by reducing chloro triphenyl-phosphine gold(I) and erbium(III) trifluoroacetate. The Er{sup 3+} g-value along with the observed hyperfine splitting indicate that the Er{sup 3+} impurities are in a local cubic symmetry. Furthermore, the Er{sup 3+} ESR spectra show that the exchange interaction between the 4f and the conduction electrons (ce) is absent or negligible in Au{sub 1–x}Er{sub x} NPs, in contrast to the ESR results in bulk Au{sub 1–x}Er{sub x}. Therefore, the nature of this interaction needs to be reexamined at the nano scale range.

  13. Evidence of dilute ferromagnetism in rare-earth doped yttrium aluminium garnet

    SciTech Connect

    Farr, Warrick G.; Goryachev, Maxim; Le Floch, Jean-Michel; Tobar, Michael E.; Bushev, Pavel

    2015-09-21

    This work demonstrates strong coupling regime between an erbium ion spin ensemble and microwave hybrid cavity-whispering gallery modes in a yttrium aluminium garnet dielectric crystal. Coupling strengths of 220 MHz and mode quality factors in excess of 10{sup 6} are demonstrated. Moreover, the magnetic response of high-Q modes demonstrates behaviour which is unusual for paramagnetic systems. This behaviour includes hysteresis and memory effects. Such qualitative change of the system's magnetic field response is interpreted as a phase transition of rare earth ion impurities. This phenomenon is similar to the phenomenon of dilute ferromagnetism in semiconductors. The clear temperature dependence of the phenomenon is demonstrated.

  14. Propagation of electro-kinetic waves in magnetized GaN semiconductor with nano-sized ion colloids

    SciTech Connect

    Saxena, Ajay; Sharma, Giriraj; Jat, K. L.; Rishi, M. P.

    2015-07-31

    Based on hydrodynamic model of multi-component plasma, an analytical study on propagation of longitudinal electro-kinetic (LEK) waves in wurtzite and zincblende structures of GaN is carried out. Nano-sized ion colloids (NICs) are embedded in the sample by the technique of ion-implantation. The implanted NICs are considered massive by an order as compared to the host lattice points and do not participate in Based LEK perturbations. Though, the NICs are continuously bombarded by the electrons as well as the holes yet, the former acquires a net negative charge owing to relatively higher mobility of electrons and consequently results into depletion of electron density in the medium. It i s found that the presence of charged NICs significantly modifies the dispersion and amplification characteristics of LEK waves in magnetized GaN semiconductor plasma and their role becomes increasingly effective as the fraction of charge on them increases.

  15. Magnetic properties of first-row element-doped ZnS semiconductors: A density functional theory investigation

    NASA Astrophysics Data System (ADS)

    Long, Run; English, Niall J.

    2009-09-01

    Based on first-principles calculations, we have investigated the magnetic properties of the first-row element-doped ZnS semiconductors. Calculations reveal that Be, B, and C dopants can induce magnetism while N cannot lead to spin polarization in ZnS. A possible explanation has been rationalized from the elements’ electronegativity and interaction between dopant and host atoms. The total magnetic moments are 2.00, 3.16, and 2.38μB per 2×2×2 supercell for Be, B, and C doping, respectively, and ferromagnetic coupling is generally observed in these cases. The ferromagnetism of Be-, B-, and C-doped ZnS can be explained by hole-mediated s-p or p-p interactions’ coupling mechanisms. The clustering effect was found to be present in Be-, B-, and C-doped ZnS but the degree is more obvious in the former two cases than in the latter case. Analysis revealed that C-doped ZnS displays better potential ferromagnetic behavior than Be- and B-doped ZnS due to its semimetallic characteristics.

  16. Investigating the magnetic field effect on electron-hole pair in organic semiconductor devices

    NASA Astrophysics Data System (ADS)

    Qin, W.; Gao, K.; Yin, S.; Xie, S. J.

    2013-05-01

    By constructing dynamic equations including electrons, holes and their pair densities, we calculate the magnetoconductance (MC) and the magnetoelectroluminescence (MEL) separately. It is indicated that MC and MEL may result from different response on the applied magnetic field. MC is from the scattering of polarons by magnetic field related triplet excitons, while MEL is mainly from magnetic field related conversion between singlet and triplet electron-hole pairs. Furthermore, we discuss the relation between MC and MEL. The theoretical calculations are well consistent with the experimental results.

  17. Barrier-bound resonances in semiconductor superlattices in strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Duffield, T.; Bhat, R.; Koza, M.; Derosa, F.; Rush, K. M.; Allen, S. J., Jr.

    1987-12-01

    The effective ``miniband'' mass approximation is shown to break down in strong magnetic fields when the magnetic length is smaller than the superlattice period. Under these conditions a real-space description must be used and features in the inhomogeneously broadened cyclotron resonance can be indexed by the position of the cyclotron orbit with respect to the barriers and wells. The line shape agrees with a calculation of the quantum states in a magnetic field in a one-dimensional periodic potential and these experiments give us a rare view of Landau states in the limit where the periodic potential has a period that is larger than the cyclotron diameter.

  18. Magnetic ordering in the ultrapure site-diluted spin chain materials SrCu1 -xNixO2

    NASA Astrophysics Data System (ADS)

    Simutis, G.; Thede, M.; Saint-Martin, R.; Mohan, A.; Baines, C.; Guguchia, Z.; Khasanov, R.; Hess, C.; Revcolevschi, A.; Büchner, B.; Zheludev, A.

    2016-06-01

    The muon spin rotation technique is used to study magnetic ordering in ultrapure samples of SrCu1 -xNixO2 , an archetypical S =1 /2 antiferromagnetic Heisenberg chain system with a small number of S =1 defects. The ordered state in the parent compound is shown to be highly homogeneous, contrary to a previous report [M. Matsuda et al., Phys. Rev. B 55, R11953 (1997), 10.1103/PhysRevB.55.R11953]. Even a minute number of Ni impurities results in inhomogeneous order and a decrease of the transition temperature. At as little as 0.5 % Ni concentration, magnetic ordering is entirely suppressed. The results are compared to previous theoretical studies of weakly coupled spin chains with site defects.

  19. Enhancement of magnetic moment in ZnxFe3-xO4 thin films with dilute Zn substitution

    NASA Astrophysics Data System (ADS)

    Yuan, Honglei; Liu, Er; Yin, Yuli; Zhang, Wen; Wong, P. K. Johnny; Zheng, Jian-Guo; Huang, Zhaocong; Ou, Huiling; Zhai, Ya; Xu, Qingyu; Du, Jun; Zhai, Hongru

    2016-06-01

    Highly (111)-textured ZnxFe3-xO4 thin films were grown by pulsed laser deposition on silicon substrates. The spin and orbital magnetic moments of the ZnxFe3-xO4 thin films have been obtained by X-ray magnetic circular dichroism (XMCD) and sum rule analysis. The total magnetic moments thus extracted are in good agreement with the values obtained by vibrating sample magnetometer. Both the unquenched orbital moment and the ratio of orbital-to-spin moment first increase significantly with increasing Zn substitution at a low concentration range ( 0 ≤x ≤0.1 ), and then decrease at a higher concentration (x = 0.3). The underlying site-specific doping mechanisms involved here have been elucidated by detailed analysis of the XMCD of ZnxFe3-xO4 films. Our work demonstrates a practical means to manipulate the spin-orbit coupling in the ZnxFe3-xO4 thin films via Zn impurity doping.

  20. Magnetoamplification in a Bipolar Magnetic Junction Transistor

    NASA Astrophysics Data System (ADS)

    Rangaraju, N.; Peters, J. A.; Wessels, B. W.

    2010-09-01

    We have demonstrated the first bipolar magnetic junction transistor using a dilute magnetic semiconductor. For an InMnAs p-n-p transistor magnetoamplification is observed at room temperature. The observed magnetoamplification is attributed to the magnetoresistance of the magnetic semiconductor InMnAs heterojunction. The magnetic field dependence of the transistor characteristics confirm that the magnetoamplification results from the junction magnetoresistance. To describe the experimentally observed transistor characteristics, we propose a modified Ebers-Moll model that includes a series magnetoresistance attributed to spin-selective conduction. The capability of magnetic field control of the amplification in an all-semiconductor transistor at room temperature potentially enables the creation of new computer logic architecture where the spin of the carriers is utilized.

  1. Magnetic field dependence of the energy of negatively charged excitons in semiconductor quantum wells

    SciTech Connect

    Riva, C.; Peeters, F. M.; Varga, K.

    2001-03-15

    We present a variational calculation of the spin-singlet and spin-triplet states of a negatively charged exciton (trion) confined to a single quantum well in the presence of a perpendicular magnetic field. We calculated the probability density and the pair correlation function of the singlet and triplet trion states. The dependence of the energy levels and of the binding energy on the well width and on the magnetic field strength was investigated. We compared our results with the available experimental data on GaAs/AlGaAs quantum wells and find that in the low-magnetic-field region (B<18 T) the observed transitions are those of the singlet and the dark triplet trion (with angular momentum L{sub z}=-1), while for high magnetic fields (B>25 T) the dark trion becomes optically inactive and possibly a transition to a bright triplet trion (angular momentum L{sub z}=0) state is observed.

  2. On the role of diluted magnetic cobalt-doped ZnO electrodes in efficiency improvement of InGaN light emitters

    NASA Astrophysics Data System (ADS)

    Liu, Hong-Ru; Ou, Sin-Liang; Wang, Shih-Yin; Wuu, Dong-Sing

    2016-07-01

    The 120-nm-thick cobalt-doped ZnO (Co-doped ZnO, CZO) dilute magnetic films deposited by pulsed laser deposition were employed as the n-electrodes for both lateral-type blue (450 nm) and green (520 nm) InGaN light emitters. In comparison to the conventional blue and green emitters, there were 15.9% and 17.7% enhancements in the output power (@350 mA) after fabricating the CZO n-electrode on the n-GaN layer. Observations on the role of CZO n-electrodes in efficiency improvement of InGaN light emitters were performed. Based on the results of Hall measurements, the carrier mobilities were 176 and 141 cm2/V s when the electrons passed through the n-GaN and the patterned-CZO/n-GaN, respectively. By incorporating the CZO n-electrode into the InGaN light emitters, the electrons would be scattered because of the collisions between the magnetic atoms and the electrons as the device is driven, leading to the reduction of the electron mobility. Therefore, the excessively large mobility difference between electron and hole carriers occurred in the conventional InGaN light emitter can be efficiently decreased after preparing the CZO n-electrode on the n-GaN layer, resulting in the increment of carrier recombination rate and the improvement of light output power.

  3. Precise tuning of the Curie temperature of (Ga,Mn)As-based magnetic semiconductors by hole compensation: Support for valence-band ferromagnetism

    NASA Astrophysics Data System (ADS)

    Zhou, Shengqiang; Li, Lin; Yuan, Ye; Rushforth, A. W.; Chen, Lin; Wang, Yutian; Böttger, R.; Heller, R.; Zhao, Jianhua; Edmonds, K. W.; Campion, R. P.; Gallagher, B. L.; Timm, C.; Helm, M.

    2016-08-01

    For the prototype diluted ferromagnetic semiconductor (Ga,Mn)As, there is a fundamental concern about the electronic states near the Fermi level, i.e., whether the Fermi level resides in a well-separated impurity band derived from Mn doping (impurity-band model) or in the valence band that is already merged with the Mn-derived impurity band (valence-band model). We investigate this question by carefully shifting the Fermi level by means of carrier compensation. We use helium-ion implantation, a standard industry technology, to precisely compensate the hole doping of GaAs-based diluted ferromagnetic semiconductors while keeping the Mn concentration constant. We monitor the change of Curie temperature (TC) and conductivity. For a broad range of samples including (Ga,Mn)As and (Ga,Mn)(As,P) with various Mn and P concentrations, we observe a smooth decrease of TC with carrier compensation over a wide temperature range while the conduction is changed from metallic to insulating. The existence of TC below 10 K is also confirmed in heavily compensated samples. Our experimental results are naturally explained within the valence-band picture.

  4. A pH-responsive and magnetically separable dynamic system for efficient removal of highly dilute antibiotics in water.

    PubMed

    Liu, Wanpeng; Ma, Jianqing; Shen, Chensi; Wen, Yuezhong; Liu, Weiping

    2016-03-01

    In order to control the antibiotic-related crisis and reduce the negative impacts on the environment and human health, it is urgent to develop effective technologies to eliminate residual antibiotics in water. Herein, we successfully fabricated a novel, pH-responsive and magnetically separable dynamic system for micropollutant adsorption and oxidation degradation in graphene oxide (GO)/nanoscale zero-valent iron (nZVI) composite with macroscopic structure. The pH-responsive self-assembly behavior of GO/nZVI composite was explored. The macroscopic structure of GO/nZVI composite serves as an excellent adsorbent for antibiotic removal in water. The adsorption process is fast and highly efficient even in high salty and humic acid containing water under acid to neutral conditions. After removal antibiotics, GO/nZVI composite is conveniently separated by magnetic system and put into alkaline solution (pH > 9) for adsorbent regeneration. Interestingly, it is found that at pH > 9, GO/nZVI composite disassembles partly upon increasing pH values, leading to the elution of antibiotics for efficient antibiotics degradation by ozonization. More importantly, this pH-responsive GO/nZVI system exhibits high removal efficiency, high stability, reusability and easily separation, making it a promising method for treatment of water with micropollutants. PMID:26724436

  5. Ab-initio study of magnetism behavior in TiO2 semiconductor with structural defects

    NASA Astrophysics Data System (ADS)

    Zarhri, Z.; Houmad, M.; Ziat, Y.; El Rhazouani, O.; Slassi, A.; Benyoussef, A.; El Kenz, A.

    2016-05-01

    Magnetic, electronic and structural properties of titanium dioxide material with different structural defects are studied using the first-principles ab-initio calculations and the Korringa-Kohn-Rostoker method (KKR) combined with the coherent potential approximation (CPA) method in connection with the local density approximation (LDA). We investigated all structural defects in rutile TiO2 such as Titanium interstitial (Tii), Titanium anti-sites (Tio), Titanium vacancies (VTi), Oxygen interstitial (Oi), Oxygen anti-sites (OTi) and oxygen vacancies (Vo). Mechanisms of hybridization and interaction between magnetic atoms are investigated. The transition temperature is computed using the Mean Field Approximation (MFA).Magnetic stability energy of ferromagnetic and disordered local moment states is calculated to determine the most stable state. Titanium anti-sites have a half-metallic aspect. We also studied the change type caused by structural defects in this material.

  6. Inelastic tunneling spectroscopy study on organic semiconductor tunnel barriers with magnetic electrodes

    NASA Astrophysics Data System (ADS)

    Raman, K. V.; Shim, J. H.; Moodera, J. S.

    2008-03-01

    Spin injection and transport through organic semiconductor (OS) is recently being researched extensively. Exploring the interfacial structural and chemical modifications in FM/OS/FM tunnel junctions can lead to a better understanding of spin injection and transport in OS. Inelastic tunneling spectroscopy (IETS), a high sensitivity technique, measures the vibrational and excitational modes of the molecules within a tunnel barrier, which are greatly influenced by any distortions in the molecules. These measurements are performed on thin films of OS, rubrene and pentacene, using Co/seed/OS/Py and Al/seed/OS/Al junctions, all grown in-situ, for two different seed layers viz. Al2O3 and LiF. The IETS spectra matches well with the reported Raman and IR spectroscopy measurements performed for powder and bulk single crystal samples. In addition, the IETS spectra show weak signatures of the molecular distortions through modifications to certain phonon peaks. Due to the amorphous nature of the films certain electronic states are also observed at higher bias voltages. The effect of vibrational modes on the spin conserved tunneling and the effect of different electrodes on the IETS spectra will also be presented and discussed.

  7. Manipulable GMR Effect in a δ-Doped Magnetically Confined Semiconductor Heterostructure

    NASA Astrophysics Data System (ADS)

    Jiang, Ya-Qing; Lu, Mao-Wang; Huang, Xin-Hong; Yang, Shi-Peng; Tang, Qiang

    2016-06-01

    A giant magnetoresistance (GMR) device formed by depositing two parallel nanosized ferromagnetic strips on top of a semiconductor heterostructure has been proposed theoretically (Zhai et al. in Phys Rev B 66:125305, 2002). For the sake of manipulating its performance, we introduce a tunable δ-potential into this device with the help of atomic-layer doping techniques such as molecular beam epitaxy (MBE) or metal-organic chemical-vapor deposition. We investigate theoretically the impact of such δ-doping on the magnetoresistance ratio (MR) of the GMR device. We find that, although the δ-doping is embedded in the device, a considerable GMR effect still exists due to the significant difference in electronic transmission between parallel (P) and antiparallel (AP) configurations. Moreover, the calculated results show that the MR of the GMR device varies sensitively with the weight and/or position of the δ-doping. Thus, the GMR device can be controlled by changing the δ-doping to obtain an adjustable GMR device for magnetoelectronics applications.

  8. Spectroscopic study of partially-ordered semiconductor heterojunction under high pressure and high magnetic field

    SciTech Connect

    Yu, P.Y.; Martinez, G.; Zeman, J.; Uchida, K.

    2000-12-31

    Photoluminescence upconversion (PLU) is a phenomenon in which a sample emits photons with energy higher than that of the excitation photon. This effect has been observed in many materials including rare earth ions doped in insulating hosts and semiconductor heterostructures without using high power lasers as the excitation source. Recently, this effect has been observed also in partially CuPt-ordered GaInP{sub 2} epilayers grown on GaAs substrates. As a spectroscopic technique photoluminescence upconversion is particularly well suited for studying band alignment at heterojunction interface. The value of band-offset has been determined with meV precision using magneto-photoluminescence. Using the fact that the pressure coefficient of electrons in GaAs is higher than those in GaInP{sub 2} they have been able to manipulate the band-offset at the GaInP/GaAs interface. By converting the band-offset from Type I to Type II they were able to demonstrate that the efficiency of the upconversion process is greatly enhanced by a Type II band-offset.

  9. Structural disorder and magnetism in the spin-gapless semiconductor CoFeCrAl

    NASA Astrophysics Data System (ADS)

    Choudhary, Renu; Kharel, Parashu; Valloppilly, Shah R.; Jin, Yunlong; O'Connell, Andrew; Huh, Yung; Gilbert, Simeon; Kashyap, Arti; Sellmyer, D. J.; Skomski, Ralph

    2016-05-01

    Disordered CoFeCrAl and CoFeCrSi0.5Al0.5 alloys have been investigated experimentally and by first-principle calculations. The melt-spun and annealed samples all exhibit Heusler-type superlattice peaks, but the peak intensities indicate a substantial degree of B2-type chemical disorder. Si substitution reduces the degree of this disorder. Our theoretical analysis also considers several types of antisite disorder (Fe-Co, Fe-Cr, Co-Cr) in Y-ordered CoFeCrAl and partial substitution of Si for Al. The substitution transforms the spin-gapless semiconductor CoFeCrAl into a half-metallic ferrimagnet and increases the half-metallic band gap by 0.12 eV. Compared CoFeCrAl, the moment of CoFeCrSi0.5Al0.5 is predicted to increase from 2.01 μB to 2.50 μB per formula unit, in good agreement with experiment.

  10. Novel room temperature ferromagnetic semiconductors

    SciTech Connect

    Gupta, Amita

    2004-11-01

    for Zn a 2+ state in the ZnO lattice. Ferromagnetic Resonance (FMR) technique is used to confirm the existence of ferromagnetic ordering at temperatures as high as 425K. The ab initio calculations were found to be consistent with the observation of ferromagnetism arising from fully polarized Mn 2+ state. The key to observed room temperature ferromagnetism in this system is the low temperature processing, which prevents formation of clusters, secondary phases and the host ZnO from becoming n-type. The electronic structure of the same Mn doped ZnO thin films studied using XAS, XES and RIXS, revealed a strong hybridization between Mn 3d and O 2p states, which is an important characteristic of a Dilute magnetic Semiconductor (DMS). It is shown that the various processing conditions like sintering temperature, dopant concentration and the properties of precursors used for making of DMS have a great influence on the final properties. Use of various experimental techniques to verify the physical properties, and to understand the mechanism involved to give rise to ferromagnetism is presented. Methods to improve the magnetic moment in Mn doped ZnO are also described. New promising DMS materials (such as Cu doped ZnO are explored). The demonstrated new capability to fabricate powder, pellets, and thin films of room temperature ferromagnetic semiconductors thus makes possible the realization of a wide range of complex elements for a variety of new multifunctional phenomena related to Spintronic devices as well as magneto-optic components.

  11. High sensitivity detection of radio-frequency modulated magnetic moment in semiconductors.

    PubMed

    Guite, Chinkhanlun; Venkataraman, V

    2011-10-01

    An experimental setup has been realized to measure weak magnetic moments which can be modulated at radio frequencies (~1-5 MHz). Using an optimized radio-frequency (RF) pickup coil and lock-in amplifier, an experimental sensitivity of 10(-15) Am(2) corresponding to 10(-18) emu has been demonstrated with a 1 s time constant. The detection limit at room temperature is 9.3 × 10(-16) Am(2)/√Hz limited by Johnson noise of the coil. The setup has been used to directly measure the magnetic moment due to a small number (~7 × 10(8)) of spin polarized electrons generated by polarization modulated optical radiation in GaAs and Ge. PMID:22047310

  12. Origins of large light induced voltage in magnetic tunnel junctions grown on semiconductor substrates

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Lin, W.; Petit-Watelot, S.; Hehn, M.; Rinnert, H.; Lu, Y.; Montaigne, F.; Lacour, D.; Andrieu, S.; Mangin, S.

    2016-01-01

    Recently, the study of interactions between electron spins and heat currents has given rise to the field of "Spin Caloritronics". Experimental studies of these interactions have shown a possibility to combine the use of heat and light to power magnetic tunnel junction (MTJ) devices. Here we present a careful study of an MTJ device on Si substrate that can be powered entirely by light. We analyze the influence of the material properties, device geometry, and laser characteristics on the electric response of the sample. We demonstrate that by engineering the MTJ and its electrical contact, a large photovoltage reaching 100 mV can be generated. This voltage originates from the Si substrate and depends on the MTJ magnetic configuration. Finally, we discuss the origin of the photo-voltage in terms of Seebeck and photovoltaic effects.

  13. Application of a rotating magnetic field to semiconductor crystal growth in Space

    NASA Astrophysics Data System (ADS)

    Senchenkov, A. S.; Barmin, I. V.

    2003-12-01

    To eliminate the tremendous influence of the residual accelerations on homogeneity of the crystal growing in a space experiment, a rotating magnetic field (RMF) is used. A number of the experiments have been performed in space within the RMF both in the frame of the Russian national program and together with European scientists. In the paper some theoretical and experimental results illustrating the effectiveness of RMF application to crystal growth under microgravity conditions are presented. Tables 2, Figs 5, Refs 8.

  14. Magnetic and transport properties of degenerate ferromagnetic semiconductor EuO

    NASA Astrophysics Data System (ADS)

    Takahashi, Masao

    2016-06-01

    By applying the coherent potential approximation (CPA) to simple models, we have studied the temperature (T ) dependence of the normalized magnetization M (T ) , and electrical resistivity ρ (T ) of highly rare-earth-doped EuO. The present result reveals that in degenerate EuO, the magnetization is described by an electron-doped EuO model; the strong double-dome feature of M (T ) of Gd-doped EuO is a consequence of the half-metallicity and low dopant activation. In degenerate EuO, the temperature dependence of the resistivity is well described by Matthiessen's rule as ρ (T ) =ρC+ρm(M ) , where ρC is the nonmagnetic scattering contribution (independent of T ) and ρm(M ) is the magnetic scattering contribution due to the exchange interaction with localized f spins. ρC is proportional to x (1 -x ) /n2/3 , while the amplitude of the change in ρm(M ) is proportional to n-2/3, where x is the doped rare-earth density and n is the electron density. The difference in M (T ) and ρ (T ) between Gd- and La-doped EuO is also discussed.

  15. Optical Spin-Transfer-Torque-Driven Domain-Wall Motion in a Ferromagnetic Semiconductor

    NASA Astrophysics Data System (ADS)

    Ramsay, A. J.; Roy, P. E.; Haigh, J. A.; Otxoa, R. M.; Irvine, A. C.; Janda, T.; Campion, R. P.; Gallagher, B. L.; Wunderlich, J.

    2015-02-01

    We demonstrate optical manipulation of the position of a domain wall in a dilute magnetic semiconductor, GaMnAsP. Two main contributions are identified. First, photocarrier spin exerts a spin-transfer torque on the magnetization via the exchange interaction. The direction of the domain-wall motion can be controlled using the helicity of the laser. Second, the domain wall is attracted to the hot spot generated by the focused laser. Unlike magnetic-field-driven domain-wall depinning, these mechanisms directly drive domain-wall motion, providing an optical tweezerlike ability to position and locally probe domain walls.

  16. Spin-based logic in semiconductors for reconfigurable large-scale circuits

    NASA Astrophysics Data System (ADS)

    Dery, H.; Dalal, P.; Cywiński, Ł.; Sham, L. J.

    2007-05-01

    Research in semiconductor spintronics aims to extend the scope of conventional electronics by using the spin degree of freedom of an electron in addition to its charge. Significant scientific advances in this area have been reported, such as the development of diluted ferromagnetic semiconductors, spin injection into semiconductors from ferromagnetic metals and discoveries of new physical phenomena involving electron spin. Yet no viable means of developing spintronics in semiconductors has been presented. Here we report a theoretical design that is a conceptual step forward-spin accumulation is used as the basis of a semiconductor computer circuit. Although the giant magnetoresistance effect in metals has already been commercially exploited, it does not extend to semiconductor/ferromagnet systems, because the effect is too weak for logic operations. We overcome this obstacle by using spin accumulation rather than spin flow. The basic element in our design is a logic gate that consists of a semiconductor structure with multiple magnetic contacts; this serves to perform fast and reprogrammable logic operations in a noisy, room-temperature environment. We then introduce a method to interconnect a large number of these gates to form a `spin computer'. As the shrinking of conventional complementary metal-oxide-semiconductor (CMOS) transistors reaches its intrinsic limit, greater computational capability will mean an increase in both circuit area and power dissipation. Our spin-based approach may provide wide margins for further scaling and also greater computational capability per gate.

  17. Effect of Sb incorporation on structure and magnetic properties of quaternary ferromagnetic semiconductor (Ga, Mn)(As, Sb) thin films

    SciTech Connect

    Deng, J. J.; Che, J. T.; Chen, J.; Wang, W. J.; Hu, B.; Wang, H. L.; Zhao, J. H.

    2013-12-28

    GaAs-based quaternary ferromagnetic semiconductor (Ga, Mn)(As, Sb) has been successfully prepared by molecular-beam epitaxy. High-resolution x-ray diffraction measurements indicate that the lattice constant has a notable alteration with changing Sb content. Magnetic measurements demonstrate the same evolution of the Curie temperature T{sub C} and the effective Mn content x{sub eff} with increasing Sb content. The incorporation of low Sb content is of benefit to increasing x{sub eff}, thus, increasing T{sub C}. However, higher Sb content degrades the crystal quality, resulting in a decrease of x{sub eff}. Experimental results show that T{sub C} is proportional to the product of x{sub eff} and p{sup 1/3}, which is consistent with the Zener Model. The exchange energy N{sub 0}β is calculated to be −1.09 eV, which is similar to that of (Ga, Mn)As.

  18. Superfluorescence from photoexcited semiconductor quantum wells: Magnetic field, temperature, and excitation power dependence

    NASA Astrophysics Data System (ADS)

    Cong, Kankan; Wang, Yongrui; Kim, Ji-Hee; Noe, G. Timothy; McGill, Stephen A.; Belyanin, Alexey; Kono, Junichiro

    2015-06-01

    Superfluorescence (SF) is a many-body process in which a macroscopic polarization spontaneously builds up from an initially incoherent ensemble of excited dipoles and then cooperatively decays, producing a delayed pulse of coherent radiation. SF arising from electron-hole recombination has recently been observed in In0.2Ga0.8As /GaAs quantum wells [G. T. Noe et al., Nature Phys. 8, 219 (2012), 10.1038/nphys2207 and J.-H. Kim et al., Sci. Rep. 3, 3283 (2013), 10.1038/srep03283], but its observability conditions have not been fully established. Here, by performing magnetic field (B ), temperature (T ), and pump power (P ) dependent studies of SF intensity, linewidth, and delay time through time-integrated and time-resolved magnetophotoluminescence spectroscopy, we have mapped out the B -T -P region in which SF is observable. In general, SF can be observed only at sufficiently low temperatures, sufficiently high magnetic fields, and sufficiently high laser powers with characteristic threshold behavior. We provide theoretical insights into these behaviors based primarily on considerations on how the growth rate of macroscopic coherence depends on these parameters. These results provide fundamental new insight into electron-hole SF, highlighting the importance of Coulomb interactions among photogenerated carriers as well as various scattering processes that are absent in SF phenomena in atomic and molecular systems.

  19. Thermodynamics of Dilute Solutions.

    ERIC Educational Resources Information Center

    Jancso, Gabor; Fenby, David V.

    1983-01-01

    Discusses principles and definitions related to the thermodynamics of dilute solutions. Topics considered include dilute solution, Gibbs-Duhem equation, reference systems (pure gases and gaseous mixtures, liquid mixtures, dilute solutions), real dilute solutions (focusing on solute and solvent), terminology, standard states, and reference systems.…

  20. Time-resolved spin-dependent processes in magnetic field effects in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Peng, Qiming; Li, Xianjie; Li, Feng

    2012-12-01

    We investigated the time-resolved magnetic field effects (MFEs) in tri-(8-hydroxyquinoline)-aluminum (Alq3) based organic light-emitting diodes (OLEDs) through the transient electroluminescence (EL) method. The values of magneto-electroluminescence (MEL) decrease with the time, and the decreasing slope is proportional to the driving voltage. Specifically, negative MELs are seen when the driving voltage is high enough (V > 11 V). We propose a model to elucidate the spin-dependent processes and theoretically simulate the time-resolved MELs. In particular, this dynamic analysis of time-resolved MELs reveals that the intersystem crossing between singlet and triplet electron-hole pairs and the triplet-triplet annihilation are responsible for the time-resolved MELs at the beginning and enduring periods of the pulse, respectively.

  1. High temperature magnetic order in Zn1‑x Mn x SnSb2+MnSb nanocomposite ferromagnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Kilanski, L.; Górska, M.; Ślawska-Waniewska, A.; Lewińska, S.; Szymczak, R.; Dynowska, E.; Podgórni, A.; Dobrowolski, W.; Ralević, U.; Gajić, R.; Romčević, N.; Fedorchenko, I. V.; Marenkin, S. F.

    2016-08-01

    We present studies of structural, magnetic, and electrical properties of Zn1‑x Mn x SnSb2+MnSb nanocomposite ferromagnetic semiconductors with the average Mn-content, \\bar{x} , changing from 0.027 up to 0.138. The magnetic force microscope imaging done at room temperature shows the presence of a strong signal coming from MnSb clusters. Magnetic properties show the paramagnet-ferromagnet transition with the Curie temperature, T C, equal to about 522 K and the cluster-glass behavior with the transition temperature, T CG, equal to about 465 K, both related to MnSb clusters. The magnetotransport studies show that all investigated samples are p-type semiconductors with high hole concentration, p, changing from 1021 to 1022 cm‑3. A large increase in the resistivity as a function of the magnetic field is observed at T  <  10 K and small magnetic fields, |B|<100 mT, for all the studied samples with a maximum amplitude of the magnetoresistance about 460% at T  =  1.4 K. The large increase in the resistivity is most probably caused by the appearance of the superconducting state in the samples at T  <  4.3 K.

  2. Separation of Contributions from the Ion Core and Free Charge Carriers to the Magnetic Susceptibility of an Anisotropic Semiconductor Bi2Te3-Sb2Te3 Crystal

    NASA Astrophysics Data System (ADS)

    Stepanov, N. P.; Nalivkin, V. Yu.

    2016-05-01

    A technique is presented, by which the magnetic susceptibility χ | G of the ion core of an anisotropic semiconductor Bi2Te3-Sb2Te3 crystal is determined from experimental data on the magnetic susceptibility χ ∥ and χ ⊥ obtained with allowance for the orientation of the magnetic field vector H with respect to the trigonal C3 axis of the crystal in accordance with the expression χ ∥/ χ ⊥ = ( χ ∥ eh + χ G )/( χ ⊥ eh + χ G ).In this expression, the value of the magnetic susceptibility of free charge carriers χ ∥ eh and χ ⊥ eh depending on their effective masses m ∥ * and m ⊥ * known from the experiment is calculated within the framework of the Pauli and Landau- Peierls approaches. The found value of χ | G for Bi2Te3-Sb2Te3 crystals is in good agreement with experimental data, as well as with the estimates obtained in the framework of the Larmor approach explaining, in particular, a linear dependence of the molar magnetic susceptibility on the number of electrons in the molecule observed for a large number of compounds. The proposed technique can be extended to other anisotropic semiconductors.

  3. Separation of Contributions from the Ion Core and Free Charge Carriers to the Magnetic Susceptibility of an Anisotropic Semiconductor Bi2Te3-Sb2Te3 Crystal

    NASA Astrophysics Data System (ADS)

    Stepanov, N. P.; Nalivkin, V. Yu.

    2016-05-01

    A technique is presented, by which the magnetic susceptibility χ {|/ G } of the ion core of an anisotropic semiconductor Bi2Te3-Sb2Te3 crystal is determined from experimental data on the magnetic susceptibility χ ∥ and χ ⊥ obtained with allowance for the orientation of the magnetic field vector H with respect to the trigonal C3 axis of the crystal in accordance with the expression χ ∥/χ ⊥ = (χ {∥/ eh } + χ G )/(χ {⊥/ eh } + χ G ).In this expression, the value of the magnetic susceptibility of free charge carriers χ {∥/ eh } and χ {⊥/ eh } depending on their effective masses m {∥/*} and m {⊥/*} known from the experiment is calculated within the framework of the Pauli and Landau- Peierls approaches. The found value of χ {|/ G }for Bi2Te3-Sb2Te3 crystals is in good agreement with experimental data, as well as with the estimates obtained in the framework of the Larmor approach explaining, in particular, a linear dependence of the molar magnetic susceptibility on the number of electrons in the molecule observed for a large number of compounds. The proposed technique can be extended to other anisotropic semiconductors.

  4. Magneto-optical garnet waveguides on semiconductor platforms: Magnetics, mechanics, and photonics

    NASA Astrophysics Data System (ADS)

    Sung, Sang-Yeob; Sharma, Anirudh; Block, Andrew; Keuhn, Katherine; Stadler, Bethanie J. H.

    2011-04-01

    Garnet films with thicknesses of 100-1000 nm and waveguides with widths of 700-2000 nm were grown onto Si to characterize the mechanical stresses that occurred upon crystallization (700-800 °C) by rapid thermal annealing. These magneto-optical garnet films and also photonic crystals have proposed uses in magnetic flux indicator films, integrated photonic devices, such as isolators, circulators, and polarization transformers, because their Verdet constants per unit loss are orders of magnitude better than other magneto-optical materials. However, garnet does not match Si-based materials mechanically with thermal expansion coefficients of 10.4 ppm/°C. These waveguides were optimized to have low losses in the near infrared, including the telecommunication wavelengths (1.0-2.3 dB/mm at 1.3 μm and 0.9-1.7 at 1.55 μm). The waveguide losses increased with waveguide width. Finite difference time domain simulations were used to estimate the number, effective index, and profile of modes in each guide. The polarization and localization of modes near guide surfaces effectively explain the trend in losses versus width. With Faraday rotations of 0.2 dB/μm and 1.0 dB/mm loss, this integrated garnet has great potential for a multitude of photonic devices, including isolators, circulators, and mode converters.

  5. Lithographically Patterned Nanoscale Electrodeposition of Plasmonic, Bimetallic, Semiconductor, Magnetic, and Polymer Nanoring Arrays

    PubMed Central

    2015-01-01

    Large area arrays of magnetic, semiconducting, and insulating nanorings were created by coupling colloidal lithography with nanoscale electrodeposition. This versatile nanoscale fabrication process allows for the independent tuning of the spacing, diameter, and width of the nanorings with typical values of 1.0 μm, 750 nm, and 100 nm, respectively, and was used to form nanorings from a host of materials: Ni, Co, bimetallic Ni/Au, CdSe, and polydopamine. These nanoring arrays have potential applications in memory storage, optical materials, and biosensing. A modified version of this nanoscale electrodeposition process was also used to create arrays of split gold nanorings. The size of the split nanoring opening was controlled by the angle of photoresist exposure during the fabrication process and could be varied from 50% down to 10% of the ring circumference. The large area (cm2 scale) gold split nanoring array surfaces exhibited strong polarization-dependent plasmonic absorption bands for wavelengths from 1 to 5 μm. Plasmonic nanoscale split ring arrays are potentially useful as tunable dichroic materials throughout the infrared and near-infrared spectral regions. PMID:25553204

  6. Convection and segregation in directional solidification of dilute and non-dilute binary alloys - Effects of ampoule and furnace design

    NASA Technical Reports Server (NTRS)

    Adornato, Peter M.; Brown, Robert A.

    1987-01-01

    A Petrov-Galerkin/finite-element method is used to analyze the effect of furnace configuration and ampoule design on the temperature field, the convection in the melt, the shape of the melt-solid interface, and the segregation of solute in the crystal, in the directional solidification of several dilute and nondilute binary semiconductor alloys. The vertical Bridgman-Stockbarger system leads to a two-cell flow structure, and the constant gradient furnace has only a single cell near the interface. Radial temperature gradients interact with the solute field to cause the previously predicted sideways diffusive instability, and addition of a solute that is less dense than the bulk melt and that is incorporated upon solidification decreases the intensity of the flow near the interface by increasing the melt density there. The present results have application to understanding of the effects on solute segregation of microgavity solidification and of applied magnetic fields.

  7. Spin transistor action via tunable Landau-Zener transitions in magnetic semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Weiss, Dieter

    2013-03-01

    Spin-transistors, employing spin-orbit interaction like Datta-Das prototypes, principally suffer from low signal levels due to limitations in spin injection efficiency, fast spin relaxation and dephasing processes. Here we present an alternative concept to implement spin transistor action where efficiency is improved by keeping spin transport adiabatic. To this end a helical stray field B, generated by ferromagnetic Dysprosium stripes, is superimposed upon a two-dimensional electron system in (Cd,Mn)Te, containing Mn ions with spin 5/2. Due to the giant spin splitting, occurring at low temperatures and small B in (Cd,Mn)Te quantum wells, the B-helix translates into a spin-helix and the electron spins follow adiabatically the imposed spin texture. Within this approach the transmission of spin-polarized electrons between two contacts is regulated by changing the degree of adiabaticity, i.e. an electron's ability to follow the spin helix. This is done by means of a small applied homogeneous magnetic field while the degree of adiabaticity is monitored by the channel resistance. Our scheme allows spin information to propagate efficiently over typical device distances and provides an alternative route to realize spintronics applications. We note that our concept is not restricted to a particular choice of materials, temperature, methods of spin injection, manipulation as well as detection. Work done in cooperation with Christian Betthausen, Institute of Experimental and Applied Physics, University of Regensburg, D-93040 Regensburg, Germany; Tobias Dollinger, Henri Saarikosi, Institute of Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany; Valeri Kolkovsky, Grzegorz Karczewski, Tomasz Wojtowicz, Institute of Physics, Polish Academy of Sciences, PL-02668 Warsaw, Poland; and Klaus Richter, Institute of Theoretical Physics, University of Regensburg. Financial support from the Deutsche Forschungsgemeinschaft through SFB 689, WE 247618, and FOR 1483 is

  8. Long-lived emission in Mn doped CdS, ZnS, and ZnSe diluted magnetic semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Proshchenko, Vitaly; Dahnovsky, Yuri

    2015-11-01

    Slow luminescence is studied in Mn doped CdS, ZnS, and ZnSe quantum dots. Because of the high degeneracy of Mn d-orbitals, we employ the multi-determinant SAC-CI computational method to determine the spin-forbidden transition from the 4T1 first excited to 6A1 ground state. We find that the transition energies for each material are in the excellent agreement with the experimental data. The computations reveal that the absorption spectra are independent of the presence of Mn impurities in quantum dots. The calculations show that the Mn impurity levels are located inside the QD gaps and the slow emission energies are independent of QD sizes. These features allow us to conclude that there are two luminescence peaks in the spectrum with fast (the higher energy) and slow (the lower energy) relaxations. In experiments sometimes the fast luminescence band disappears. This effect depends on Mn concentrations and a doping method. For different QD crystal structures the Mn-S (Se) bond lengths can vary. Therefore we find that the slow luminescence energy is very sensitive to a bond length. Indeed if we change the Mn-S bond length by 0.1 Å , the energy increases by 0.2 eV within the calculated range of bond lengths.

  9. Dilutions Made Easy.

    ERIC Educational Resources Information Center

    Kamin, Lawrence

    1996-01-01

    Presents problems appropriate for high school and college students that highlight dilution methods. Promotes an understanding of dilution methods in order to prevent the unnecessary waste of chemicals and glassware in biology laboratories. (JRH)

  10. Serial Dilution Simulation Lab

    ERIC Educational Resources Information Center

    Keler, Cynthia; Balutis, Tabitha; Bergen, Kim; Laudenslager, Bryanna; Rubino, Deanna

    2010-01-01

    Serial dilution is often a difficult concept for students to understand. In this short dry lab exercise, students perform serial dilutions using seed beads. This exercise helps students gain skill at performing dilutions without using reagents, bacterial cultures, or viral cultures, while being able to visualize the process.

  11. Exploration of Porphyrin-based Semiconductors for Negative Charge Transport Applications Using Synthetic, Spectroscopic, Potentiometric, Magnetic Resonance, and Computational Methods

    NASA Astrophysics Data System (ADS)

    Rawson, Jeffrey Scott

    Organic pi-conjugated materials are emerging as commercially relevant components in electronic applications that include transistors, light-emitting diodes, and solar cells. One requirement common to all of these functions is an aptitude for accepting and transmitting charges. It is generally agreed that the development of organic semiconductors that favor electrons as the majority carriers (n-type) lags behind the advances in hole transporting (p-type) materials. This shortcoming suggests that the design space for n-type materials is not yet well explored, presenting researchers with the opportunity to develop unconventional architectures. In this regard, it is worth noting that discrete molecular materials are demonstrating the potential to usurp the preeminent positions that pi-conjugated polymers have held in these areas of organic electronics research. This dissertation describes how an extraordinary class of molecules, meso-to-meso ethyne-bridged porphyrin arrays, has been bent to these new uses. Chapter one describes vis-NIR spectroscopic and magnetic resonance measurements revealing that these porphyrin arrays possess a remarkable aptitude for the delocalization of negative charge. In fact, the miniscule electron-lattice interactions exhibited in these rigid molecules allow them to host the most vast electron-polarons ever observed in a pi-conjugated material. Chapter two describes the development of an ethyne-bridged porphyrin-isoindigo hybrid chromophore that can take the place of fullerene derivatives in the conventional thin film solar cell architecture. Particularly noteworthy is the key role played by the 5,15-bis(heptafluoropropyl)porphyrin building block in the engineering of a chromophore that, gram for gram, is twice as absorptive as poly(3-hexyl)thiophene, exhibits a lower energy absorption onset than this polymer, and yet possesses a photoexcited singlet state sufficiently energetic to transfer a hole to this polymer. Chapter three describes

  12. PREFACE: 19th International Conference on the Application of High Magnetic Fields in Semiconductor Physics and Nanotechnology (HMF-19)

    NASA Astrophysics Data System (ADS)

    Muraki, Koji; Takeyama, Shojiro

    2011-12-01

    This volume contains invited and contributed papers from the 19th International Conference on the Application of High Magnetic Fields in Semiconductor Physics and Nanotechnology (HMF-19) held in Fukuoka, Japan, from 1-6 August 2010. This conference was mainly sponsored by the Tokyo University-'Horiba International fund', which was donated by Dr Masao Horiba, the founder of Horiba Ltd. The scientific program of HMF-19 consisted of 37 invited talks, 24 contributed talks, and 83 posters, which is available from the conference homepage http://www.hmf19.iis.u-tokyo.ac.jp/index.html. Each manuscript submitted for publication in this volume has been independently reviewed. The Editor is very grateful to all the reviewers for their quick responses and helpful reports and to all the authors for their submissions and patience for the delay in the editorial process. Finally, the Editor would like to express his sincere gratitude to all the individuals involved in the conference organization and all the attendees, who made this conference so successful. Koji Muraki Conference photograph Committees Chair Conference chairS Takeyama(ISSP-UT) Conference secretary T Machida (IIS-UT) Program chair K Muraki (NTT) Local organizing chair K Oto (Chiba Univ.) Advisory Committee International Domestic L Brey (ES) T Ando (TIT) Z H Chen (CN) Y Hirayama (Tohoku Univ.) S Das Sarma (US) G Kido (NIMS) L Eaves (GB) N Miura (JP) J P Eisenstein (US) J Nitta (Tohoku Univ.) K Ensslin (CH) T Takamasu (NIMS) J Furdyna (US) G M Gusev (BR) I Kukushkin (RU) Z D Kvon (RU) G Landwehr (DE) J C Maan (NL) A H MacDonald (US) N F Oliveira Jr (BR) A Pinczuk (US) J C Portal (FR) A Sachrajda (CA) M K Sanyal(IN) R Stepniewski(PL) Program Committee Chair: K Muraki(NTT) International Domestic G Bauer (AU) H Ajiki (Osaka Univ.) G Boebinger (US) H Aoki (Hongo, UT) S Ivanov (RU) K Nomura (RIKEN) K von Klitzing (DE) T Okamoto (Hongo, UT) R Nicholas (GB) T Osada (ISSP-UT ) M Potemski (FR) N Studart (BR) U Zeitler (NL

  13. Magnetic field effects on the Rabi splitting and radiative decay rates of the exciton-polariton states in a semiconductor microcavity

    NASA Astrophysics Data System (ADS)

    Fenniche, H.; Jaziri, S.; Bennaceur, R.

    1998-12-01

    We study theoretically a particular type of semiconductor microcavity formed by a quantum well embedded inside it and the distributed Bragg reflectors presenting a gradual structure. We apply to this structure a static magnetic field along the growth direction. In the strong coupling regime between the confined exciton and cavity modes, we evaluate the polariton Rabi splitting corresponding to the two lowest lying exciton states: HH1-CB1 and HH2-CB2 as a function of the applied magnetic field. In high magnetic field and for distinct reflectivities, we find that the Rabi splitting magnitude of the HH2-CB2 exciton is close to the fundamental one (HH1-CB1). In the presence of the magnetic field, the polariton Rabi splitting can be obtained even in low reflectivity. The dispersion polariton radiative decay rates related to the two lowest lying exciton states: HH1-CB1 and HH2-CB2 are calculated for different magnetic field values. At k //=0 and in the weak coupling regime, the polariton radiative decay rates are evaluated for both the HH1-CB1 and HH2-CB2 excitons. We show that for the fundamental excitonic state, the magnetic field value which determines the transition from the weak to the strong coupling regime is different from the HH2-CB2 exciton state.

  14. An electrically detected magnetic resonance study of performance limiting defects in SiC metal oxide semiconductor field effect transistors

    NASA Astrophysics Data System (ADS)

    Cochrane, C. J.; Lenahan, P. M.; Lelis, A. J.

    2011-01-01

    In this study, we utilize electrically detected magnetic resonance (EDMR) techniques and electrical measurements to study defects in SiC based metal oxide semiconductor field effect transistors (MOSFETs). We compare results on a series of SiC MOSFETs prepared with significantly different processing parameters. The EDMR is detected through spin dependent recombination (SDR) in most cases. However, in some devices at a fairly high negative bias, the EDMR likely also involves spin dependent trap-assisted tunneling (SDT) between defects on both sides of the SiC/SiO2 interface. At least three different defects have been detected in the magnetic resonance measurements. The defects observed include two at the SiC/SiO2 interface or on the SiC side of the SiC/SiO2 interface: one is very likely a vacancy center with a distribution which extends into the bulk of the SiC and the other is likely a "dangling bond" defect. A third defect, located on the SiO2 side of the SiC/SiO2 interface, has a spectrum very similar to that previously reported for an oxygen deficient silicon coupled to a hydrogen atom. In nearly all cases, we observe a strong dominating single line EDMR spectrum with an isotropic g≈2.0027. In some samples, this strong central line is accompanied by two pairs of considerably weaker side peaks which we link to hyperfine interactions with nearby Si and C atoms. The pattern is physically reasonable for a silicon vacancy in SiC. We therefore tentatively assign it to a silicon vacancy or silicon vacancy associated defect in the SiC. In one set of devices with very high interface trap density we observe another dominating spectrum with g∥=2.0026 and g⊥=2.0010 with the symmetry axis coincident with the [0001] and nearly the SiC/SiO2 interface normal. We ascribe this EDMR spectrum to a "dangling bond" defect. A third EDMR spectrum shows up in some devices at a fairly large negative gate bias. The phase of this spectrum is quite consistently opposite to that of the

  15. High-temperature ferromagnetism in transition metal implanted wide-bandgap semiconductors

    NASA Astrophysics Data System (ADS)

    Raley, Jeremy A.

    The field of spin transport electronics (spintronics) is a viable candidate for advancing computing and communication technologies. Material with both semiconductor and magnetic properties, which is commonly called a dilute magnetic semiconductor (DMS), will prove most useful in the fabrication of spintronic devices. In order to produce a DMS at above room temperature, transition metals (TMs) were implanted into host semiconductors of p-GaN, Al0.35Ga0.65N, or ZnO. Magnetic hysteresis measurements using a superconducting quantum interference device (SQUID) magnetometer show that some of the material combinations clearly exhibit ferromagnetism above room temperature. The most promising materials for creating spintronic devices using ion implantation are p-GaN:Mn, Al0.35Ga0.65N:Cr, and Fe-implanted ZnO nanotips on Al2O3. Temperature-dependent magnetization measurements confirm that indications of ferromagnetism are due to DMS behavior. Photo- and cathodoluminescence measurements show that implantation damage is recovered and the implanted TMs are incorporated into the semiconductor. As progress is made toward realizing practical spintronic devices, the work reported here will be useful for determining material combinations and implantation conditions that will yield the needed materials.

  16. Magnetically modulated laser-induced resistance effect observed in Metal-Oxide-Semiconductor structure of Cr/SiO(2)/Si.

    PubMed

    Xie, Xin; Liu, Shuai; Huang, Meizhen; Wang, Hui

    2015-09-21

    In this study, we report our finding of laser-induced resistance effect in metal-oxide-semiconductor (MOS) structure of Cr/SiO(2)/Si. Under the irradiation of a laser beam, the effect shows a large linear resistance change ratio of 92% with a spatial sensitivity of 0.79 MΩ/mm. In particular, by the application of an external magnetic field perpendicular to the Cr film, the resistance change ratio is increased to 110%. This effect is attributed to the Lorentz force acting on the photo-generated carriers in the inversion layer of MOS structures. The work suggests an approach for the development of new type magnetically modulated photoelectric devices. PMID:26406634

  17. Quantum size effects on spin-transfer torque in a double barrier magnetic tunnel junction with a nonmagnetic-metal (semiconductor) spacer

    NASA Astrophysics Data System (ADS)

    Daqiq, Reza; Ghobadi, Nader

    2016-07-01

    We study the quantum size effects of an MgO-based double barrier magnetic tunnel junction with a nonmagnetic-metal (DBMTJ-NM) (semiconductor (DBMTJ-SC)) spacer on the charge current and the spin-transfer torque (STT) components using non-equilibrium Green's function (NEGF) formalism. The results show oscillatory behavior due to the resonant tunneling effect depending on the structure parameters. We find that the charge current and the STT components in the DBMTJ-SC demonstrate the magnitude enhancement in comparison with the DBMTJ-NM. The bias dependence of the STT components in a DBMTJ-NM shows different behavior in comparison with spin valves and conventional MTJs. Therefore, by choosing a specific SC spacer with suitable thickness in a DBMTJ the charge current and the STT components significantly increase so that one can design a device with high STT and faster magnetization switching.

  18. Microfluidic serial dilution ladder.

    PubMed

    Ahrar, Siavash; Hwang, Michelle; Duncan, Philip N; Hui, Elliot E

    2014-01-01

    Serial dilution is a fundamental procedure that is common to a large number of laboratory protocols. Automation of serial dilution is thus a valuable component for lab-on-a-chip systems. While a handful of different microfluidic strategies for serial dilution have been reported, approaches based on continuous flow mixing inherently consume larger amounts of sample volume and chip real estate. We employ valve-driven circulatory mixing to address these issues and also introduce a novel device structure to store each stage of the dilution process. The dilution strategy is based on sequentially mixing the rungs of a ladder structure. We demonstrate a 7-stage series of 1 : 1 dilutions with R(2) equal to 0.995 in an active device area of 1 cm(2). PMID:24231765

  19. Néel-type skyrmion lattice with confined orientation in the polar magnetic semiconductor GaV4S8.

    PubMed

    Kézsmárki, I; Bordács, S; Milde, P; Neuber, E; Eng, L M; White, J S; Rønnow, H M; Dewhurst, C D; Mochizuki, M; Yanai, K; Nakamura, H; Ehlers, D; Tsurkan, V; Loidl, A

    2015-11-01

    Following the early prediction of the skyrmion lattice (SkL)--a periodic array of spin vortices--it has been observed recently in various magnetic crystals mostly with chiral structure. Although non-chiral but polar crystals with Cnv symmetry were identified as ideal SkL hosts in pioneering theoretical studies, this archetype of SkL has remained experimentally unexplored. Here, we report the discovery of a SkL in the polar magnetic semiconductor GaV4S8 with rhombohedral (C3v) symmetry and easy axis anisotropy. The SkL exists over an unusually broad temperature range compared with other bulk crystals and the orientation of the vortices is not controlled by the external magnetic field, but instead confined to the magnetic easy axis. Supporting theory attributes these unique features to a new Néel-type of SkL describable as a superposition of spin cycloids in contrast to the Bloch-type SkL in chiral magnets described in terms of spin helices. PMID:26343913

  20. Enhanced photophysical properties of plasmonic magnetic metal-alloyed semiconductor heterostructure nanocrystals: a case study for the Ag@Ni/Zn1-xMgxO system.

    PubMed

    Paul, Sumana; Ghosh, Sirshendu; Saha, Manas; De, S K

    2016-05-14

    Understanding the effect of homovalent cation alloying in wide band gap ZnO and the formation of metal-semiconductor heterostructures is very important for maximisation of the photophysical properties of ZnO. Nearly monodisperse ZnO nanopyramid and Mg alloyed ZnO nanostructures have been successfully synthesized by one pot decomposition of metal stearate by using oleylamine both as activating and capping agent. The solid solubility of Mg(ii) ions in ZnO is limited to ∼30% without phase segregation. An interesting morphology change is found on increasing Mg alloying: from nanopyramids to self-assembled nanoflowers. The morphology change is explained by the oriented attachment process. The introduction of Mg into the ZnO matrix increases the band gap of the materials and also generates new zinc interstitial (Zni) and oxygen vacancy related defects. Plasmonic magnetic Ag@Ni core-shell (Ag as core and Ni as shell) nanocrystals are used as a seed material to synthesize Ag@Ni/Zn1-xMgxO complex heterostructures. Epitaxial growth is established between Ag(111) and ZnO(110) planes in the heterostructure. An epitaxial metal-semiconductor interface is very crucial for complete electron-hole (e-h) separation and enhancement of the exciton lifetime. The alloyed semiconductor-metal heterostructure is observed to be highly photocatalytically active for dye degradation as well as photodetection. Incorporation of magnetic Ni(0) makes the photocatalyst superparamagnetic at room temperature which is found to be helpful for catalyst regeneration. PMID:27113320

  1. 3D magnetometer for a dilution refrigerator

    NASA Astrophysics Data System (ADS)

    Uchaikin, S.; Likhachev, A.; Cioata, F.; Perminov, I.; Sanghera, H.; Singh, I.; Spear, P.; Chavez, P.; Han, X.; Petroff, C.; Rich, C.

    2012-12-01

    In this report, we describe a development of a three dimensional system for measurements of magnetic field at a wide temperature range of 300K-4K. The system is based on 8 AMR sensors and allows for control of the magnetic environment in a dilution refrigerator during the cool down of a superconducting processor. With a low noise signal processing electronics and a special sensor saturation circuit, a magnetic induction resolution below of 1 nT was achieved.

  2. Magnetic-Polaron-Induced Enhancement of Surface Raman Scattering.

    PubMed

    Shao, Qi; Liao, Fan; Ruotolo, Antonio

    2016-01-01

    The studies of the effects of magnetic field on surface enhanced Raman scattering (SERS) have been so far limited to the case of ferromagnetic/noble-metal, core/shell nano-particles, where the influence was always found to be negative. In this work, we investigate the influence of magnetic field on a diluted magnetic semiconductor/metal SERS system. Guided by three dimensional finite-difference time-domain simulations, a high efficient SERS substrate was obtained by diluting Mn into Au-capped ZnO, which results in an increase of the dielectric constant and, therefore, an enhancement of Raman signals. More remarkably, an increase of intensities as well as a reduction of the relative standard deviation (RSD) of Raman signals have been observed as a function of the external magnetic strength. We ascribe these positive influences to magnetic-field induced nucleation of bound magnetic polarons in the Mn doped ZnO. The combination of diluted magnetic semiconductors and SERS may open a new avenue for future magneto-optical applications. PMID:26754049

  3. Magnetic-Polaron-Induced Enhancement of Surface Raman Scattering

    PubMed Central

    Shao, Qi; Liao, Fan; Ruotolo, Antonio

    2016-01-01

    The studies of the effects of magnetic field on surface enhanced Raman scattering (SERS) have been so far limited to the case of ferromagnetic/noble-metal, core/shell nano-particles, where the influence was always found to be negative. In this work, we investigate the influence of magnetic field on a diluted magnetic semiconductor/metal SERS system. Guided by three dimensional finite-difference time-domain simulations, a high efficient SERS substrate was obtained by diluting Mn into Au-capped ZnO, which results in an increase of the dielectric constant and, therefore, an enhancement of Raman signals. More remarkably, an increase of intensities as well as a reduction of the relative standard deviation (RSD) of Raman signals have been observed as a function of the external magnetic strength. We ascribe these positive influences to magnetic-field induced nucleation of bound magnetic polarons in the Mn doped ZnO. The combination of diluted magnetic semiconductors and SERS may open a new avenue for future magneto-optical applications. PMID:26754049

  4. First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors

    NASA Astrophysics Data System (ADS)

    Jakobsson, A.; Mavropoulos, P.; Şaşıoǧlu, E.; Blügel, S.; Ležaić, M.; Sanyal, B.; Galanakis, I.

    2015-05-01

    Employing first-principles electronic-structure calculations in conjunction with the frozen-magnon method, we calculate exchange interactions, spin-wave dispersion, and spin-wave stiffness constants in inverse-Heusler-based spin gapless semiconductor (SGS) compounds Mn2CoAl , Ti2MnAl , Cr2ZnSi , Ti2CoSi , and Ti2VAs . We find that their magnetic behavior is similar to the half-metallic ferromagnetic full-Heusler alloys, i.e., the intersublattice exchange interactions play an essential role in the formation of the magnetic ground state and in determining the Curie temperature Tc. All compounds, except Ti2CoSi , possess a ferrimagnetic ground state. Due to the finite energy gap in one spin channel, the exchange interactions decay sharply with the distance, and hence magnetism of these SGSs can be described considering only nearest- and next-nearest-neighbor exchange interactions. The calculated spin-wave dispersion curves are typical for ferrimagnets and ferromagnets. The spin-wave stiffness constants turn out to be larger than those of the elementary 3 d ferromagnets. Calculated exchange parameters are used as input to determine the temperature dependence of the magnetization and Tc of the SGSs. We find that the Tc of all compounds is much above the room temperature. The calculated magnetization curve for Mn2CoAl as well as the Curie temperature are in very good agreement with available experimental data. This study is expected to pave the way for a deeper understanding of the magnetic properties of the inverse-Heusler-based SGSs and enhance the interest in these materials for application in spintronic and magnetoelectronic devices.

  5. Semiconductor photoelectrochemistry

    NASA Technical Reports Server (NTRS)

    Buoncristiani, A. M.; Byvik, C. E.

    1983-01-01

    Semiconductor photoelectrochemical reactions are investigated. A model of the charge transport processes in the semiconductor, based on semiconductor device theory, is presented. It incorporates the nonlinear processes characterizing the diffusion and reaction of charge carriers in the semiconductor. The model is used to study conditions limiting useful energy conversion, specifically the saturation of current flow due to high light intensity. Numerical results describing charge distributions in the semiconductor and its effects on the electrolyte are obtained. Experimental results include: an estimate rate at which a semiconductor photoelectrode is capable of converting electromagnetic energy into chemical energy; the effect of cell temperature on the efficiency; a method for determining the point of zero zeta potential for macroscopic semiconductor samples; a technique using platinized titanium dioxide powders and ultraviolet radiation to produce chlorine, bromine, and iodine from solutions containing their respective ions; the photoelectrochemical properties of a class of layered compounds called transition metal thiophosphates; and a technique used to produce high conversion efficiency from laser radiation to chemical energy.

  6. Semiconductor sensors

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C. (Inventor); Lagowski, Jacek (Inventor)

    1977-01-01

    A semiconductor sensor adapted to detect with a high degree of sensitivity small magnitudes of a mechanical force, presence of traces of a gas or light. The sensor includes a high energy gap (i.e., .about. 1.0 electron volts) semiconductor wafer. Mechanical force is measured by employing a non-centrosymmetric material for the semiconductor. Distortion of the semiconductor by the force creates a contact potential difference (cpd) at the semiconductor surface, and this cpd is determined to give a measure of the force. When such a semiconductor is subjected to illumination with an energy less than the energy gap of the semiconductors, such illumination also creates a cpd at the surface. Detection of this cpd is employed to sense the illumination itself or, in a variation of the system, to detect a gas. When either a gas or light is to be detected and a crystal of a non-centrosymmetric material is employed, the presence of gas or light, in appropriate circumstances, results in a strain within the crystal which distorts the same and the distortion provides a mechanism for qualitative and quantitative evaluation of the gas or the light, as the case may be.

  7. A hybrid magnetic/complementary metal oxide semiconductor three-context memory bit cell for non-volatile circuit design

    SciTech Connect

    Jovanović, B. E-mail: lionel.torres@lirmm.fr; Brum, R. M.; Torres, L.

    2014-04-07

    After decades of continued scaling to the beat of Moore's law, it now appears that conventional silicon based devices are approaching their physical limits. In today's deep-submicron nodes, a number of short-channel and quantum effects are emerging that affect the manufacturing process, as well as, the functionality of the microelectronic systems-on-chip. Spintronics devices that exploit both the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, are promising solutions to circumvent these scaling threats. Being compatible with the CMOS technology, such devices offer a promising synergy of radiation immunity, infinite endurance, non-volatility, increased density, etc. In this paper, we present a hybrid (magnetic/CMOS) cell that is able to store and process data both electrically and magnetically. The cell is based on perpendicular spin-transfer torque magnetic tunnel junctions (STT-MTJs) and is suitable for use in magnetic random access memories and reprogrammable computing (non-volatile registers, processor cache memories, magnetic field-programmable gate arrays, etc). To demonstrate the potential our hybrid cell, we physically implemented a small hybrid memory block using 45 nm × 45 nm round MTJs for the magnetic part and 28 nm fully depleted silicon on insulator (FD-SOI) technology for the CMOS part. We also report the cells measured performances in terms of area, robustness, read/write speed and energy consumption.

  8. A hybrid magnetic/complementary metal oxide semiconductor three-context memory bit cell for non-volatile circuit design

    NASA Astrophysics Data System (ADS)

    Jovanović, B.; Brum, R. M.; Torres, L.

    2014-04-01

    After decades of continued scaling to the beat of Moore's law, it now appears that conventional silicon based devices are approaching their physical limits. In today's deep-submicron nodes, a number of short-channel and quantum effects are emerging that affect the manufacturing process, as well as, the functionality of the microelectronic systems-on-chip. Spintronics devices that exploit both the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, are promising solutions to circumvent these scaling threats. Being compatible with the CMOS technology, such devices offer a promising synergy of radiation immunity, infinite endurance, non-volatility, increased density, etc. In this paper, we present a hybrid (magnetic/CMOS) cell that is able to store and process data both electrically and magnetically. The cell is based on perpendicular spin-transfer torque magnetic tunnel junctions (STT-MTJs) and is suitable for use in magnetic random access memories and reprogrammable computing (non-volatile registers, processor cache memories, magnetic field-programmable gate arrays, etc). To demonstrate the potential our hybrid cell, we physically implemented a small hybrid memory block using 45 nm × 45 nm round MTJs for the magnetic part and 28 nm fully depleted silicon on insulator (FD-SOI) technology for the CMOS part. We also report the cells measured performances in terms of area, robustness, read/write speed and energy consumption.

  9. Semiconductor processing

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The primary thrust of the semiconductor processing is outlined. The purpose is to (1) advance the theoretical basis for bulk growth of elemental and compound semiconductors in single crystal form, and (2) to develop a new experimental approaches by which semiconductor matrices with significantly improved crystalline and chemical perfection can be obtained. The most advanced approaches to silicon crystal growth is studied. The projected research expansion, directed toward the capability of growth of 4 inch diameter silicon crystals was implemented. Both intra and interdepartmental programs are established in the areas of process metallurgy, heat transfer, mass transfer, and systems control. Solutal convection in melt growth systems is also studied.

  10. High-temperature antiferromagnetism in molecular semiconductor thin films and nanostructures.

    PubMed

    Serri, Michele; Wu, Wei; Fleet, Luke R; Harrison, Nicholas M; Hirjibehedin, Cyrus F; Kay, Christopher W M; Fisher, Andrew J; Aeppli, Gabriel; Heutz, Sandrine

    2014-01-01

    The viability of dilute magnetic semiconductors in applications is linked to the strength of the magnetic couplings, and room temperature operation is still elusive in standard inorganic systems. Molecular semiconductors are emerging as an alternative due to their long spin-relaxation times and ease of processing, but, with the notable exception of vanadium-tetracyanoethylene, magnetic transition temperatures remain well below the boiling point of liquid nitrogen. Here we show that thin films and powders of the molecular semiconductor cobalt phthalocyanine exhibit strong antiferromagnetic coupling, with an exchange energy reaching 100 K. This interaction is up to two orders of magnitude larger than in related phthalocyanines and can be obtained on flexible plastic substrates, under conditions compatible with routine organic electronic device fabrication. Ab initio calculations show that coupling is achieved via superexchange between the singly occupied a1g () orbitals. By reaching the key milestone of magnetic coupling above 77 K, these results establish quantum spin chains as a potentially useable feature of molecular films. PMID:24445992

  11. High-temperature antiferromagnetism in molecular semiconductor thin films and nanostructures

    PubMed Central

    Serri, Michele; Wu, Wei; Fleet, Luke R.; Harrison, Nicholas M.; Hirjibehedin, Cyrus F.; Kay, Christopher W.M.; Fisher, Andrew J.; Aeppli, Gabriel; Heutz, Sandrine

    2014-01-01

    The viability of dilute magnetic semiconductors in applications is linked to the strength of the magnetic couplings, and room temperature operation is still elusive in standard inorganic systems. Molecular semiconductors are emerging as an alternative due to their long spin-relaxation times and ease of processing, but, with the notable exception of vanadium-tetracyanoethylene, magnetic transition temperatures remain well below the boiling point of liquid nitrogen. Here we show that thin films and powders of the molecular semiconductor cobalt phthalocyanine exhibit strong antiferromagnetic coupling, with an exchange energy reaching 100 K. This interaction is up to two orders of magnitude larger than in related phthalocyanines and can be obtained on flexible plastic substrates, under conditions compatible with routine organic electronic device fabrication. Ab initio calculations show that coupling is achieved via superexchange between the singly occupied a1g () orbitals. By reaching the key milestone of magnetic coupling above 77 K, these results establish quantum spin chains as a potentially useable feature of molecular films. PMID:24445992

  12. Magnetization and spin distribution of single sub-monolayers of MnTe in semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Prechtl, G.; Heiss, W.; Bonanni, A.; Jantsch, W.; Mackowski, S.; Janik, E.

    2003-10-01

    The magnetization of single, ultrathin MnTe layers embedded in nonmagnetic quantum wells is studied by magneto-optical spectroscopy as well as by numerical simulations. It is shown to be proportional to the Zeeman splitting and thus it can be directly deduced from the magneto-optical experiments. The inverse of the experimentally determined magnetization measured as a function of temperature clearly demonstrates deviations from Curie-Weiss behavior due to the antiferromagnetic coupling between the Mn ions. By fitting this temperature dependence, an approximate Mn diffusion profile is obtained for each sample. The fitting procedure takes into account the antiferromagnetic coupling between the Mn ions as well as the exchange interactions between the Mn ions and the photoexcited electrons. For this purpose we have numerically solved the two-dimensional Ising model by a Monte Carlo method giving the magnetization of two-dimensional layers as a function of magnetic field, temperature, and Mn concentration.

  13. Pr- and La-doping effects on the magnetic anisotropy in the antiferromagnetic phase of Kondo semiconductor CeRu2Al10

    NASA Astrophysics Data System (ADS)

    Yoshida, K.; Okubo, R.; Tanida, H.; Matsumura, T.; Sera, M.; Nishioka, T.; Matsumura, M.; Moriyoshi, C.; Kuroiwa, Y.

    2015-06-01

    We have studied the Pr- and La-doping effects on the magnetic anisotropy in the antiferro-magnetic (AFM) phase of CeRu2Al10 . The crystalline electric field (CEF) splitting in PrRu2Al10 was found to be as large as ˜800 K with a singlet ground state. In Ce1 -xPrxRu2Al10 , the CEF level scheme of the Pr ion is not changed with x . The AFM moment (mAF) is rotated from c to b axis in both systems at xcsr˜0.03 and ˜0.07 for Ln=Pr and La, respectively. As the ionic radius of La and Pr is larger and smaller than that of Ce, respectively, these results indicate that the chemical pressure effect is not associated with the rotation of mAF, but is caused by the suppression of the c -f hybridization originating from the decrease of 4 f electrons of Ce ions by Ce-site substitution. Since a small amount of Pr or La doping changes easily the magnetization easy axis of all the moments on Ce sites, the origin of the magnetic anisotropy is not the local single ion effect but the bandlike effect through the anisotropic c -f hybridization. The magnetic phase diagrams of Ce1 -xLnxRu2Al10 indicate that above xcsr, the AFM order with mAF∥b continues to exist up to xc, which is ˜0.4 and ˜0.6 in Ln=Pr and Ln=La, respectively. This indicates that even in the sample with an AFM transition temperature (T0) near xc, the anisotropic c -f hybridization dominates the AFM order. A large positive transverse magnetoresistance is seen below T0, but a very small one above T0. Together with the results of Hall resistivity and the observation of Shubnikov-de Haas oscillation, we propose that there exist large Fermi surfaces above T0 and small ones below T0. A gap is opened by the AFM order on almost the area of the large Fermi surface, and small Fermi surfaces are constructed below T0, although we do not know the mechanism, which might be specific to the AFM order in Kondo semiconductors. The largest suppression of the magnetic scattering below T0 is observed for the current I ∥a and the

  14. Enhanced magnetic and photocatalytic properties of Bi2Fe4O9 semiconductor with large exposed (001) surface

    NASA Astrophysics Data System (ADS)

    Wu, Tianli; Liu, Lin; Pi, Mingyu; Zhang, Dingke; Chen, Shijian

    2016-07-01

    Magnetic photocatalysts have attracted an increasing attention for photodegradation of organic containments and easy recycling. In this work, magnetic, single-crystalline Bi2Fe4O9 samples have been synthesized through a facile hydrothermal process and the morphologies were modulated by adjusting the Bi3+/Fe3+ precursor molar ratio and NaOH concentration. The most well crystalline Bi2Fe4O9 nanoplates were formed by self-assembled anisotropic growth along the (001) plane, with large exposed (001) surface. The Bi2Fe4O9 nanoplates exhibit excellent photocatalytic degradation of rhodamine b (RhB) under visible light irradiation with the assistant of a small amount of H2O2. The excellent photocatalytic performance of the Bi2Fe4O9 nanoplates was ascribed to the lower recombination rate of the photogenerated electrons and holes on the (001) surface, which was confirmed by detecting the hydroxyl radicals. In addition, Bi2Fe4O9 samples exhibit morphology-dependent magnetic properties. The mechanisms of morphology-dependent magnetic, photoadsorbing and photocatalytic properties of Bi2Fe4O9 crystals are discussed systematically. The magnetic Bi2Fe4O9 photocatalyst allows efficient utilization of solar energy and possible catalyst recovery via magnetically-enhanced gravity separation.

  15. Monoclinic Cc-phase stabilization in magnetically diluted lead free Na1/2Bi1/2TiO3—Evolution of spin glass like behavior with enhanced ferroelectric and dielectric properties

    NASA Astrophysics Data System (ADS)

    Thangavelu, Karthik; Asthana, Saket

    2015-09-01

    The effect of magnetic cation substitution on the phase stabilization, ferroelectric, dielectric and magnetic properties of a lead free Na0.5Bi0.5TiO3 (NBT) system prepared by O2 atmosphere solid state sintering were studied extensively. Cobalt (Co) was chosen as the magnetic cation to substitute at the Ti-site of NBT with optimized 2.5 mol%. Rietveld analysis of x-ray diffraction data favours the monoclinic Cc phase stabilization strongly rather than the parent R3c phase. FE-SEM micrograph supports the single phase characteristics without phase segregation at the grain boundaries. The stabilized Cc space group was explained based on the collective local distortion effects due to spin-orbit stabilization at Co3+ and Co2+ functional centres. The phonon mode changes as observed in the TiO6 octahedral modes also support the Cc phase stabilization. The major Co3+-ion presence was revealed from corresponding crystal field transitions observed through solid state diffuse reflectance spectroscopy. The enhanced spontaneous polarization (Ps) from ≅38 μC cm-2 to 45 μC cm-2 could be due to the easy rotation of polarization vector along the {(1\\bar{1}0)}{{pc}} in Cc phase. An increase in static dielectric response (ɛ) from ɛ ≅ 42 to 60 along with enhanced diffusivity from γ ≅ 1.53 to 1.75 was observed. Magneto-thermal irreversibility and their magnetic field dependent ZFC/FC curves suggest the possibility of a spin glass like behaviour below 50 K. The monoclinic Cc phase stabilization as confirmed from structural studies was well correlated with the observed ferroic properties in magnetically diluted NBT.

  16. Trend of tunnel magnetoresistance and variation in threshold voltage for keeping data load robustness of metal–oxide–semiconductor/magnetic tunnel junction hybrid latches

    SciTech Connect

    Ohsawa, T.; Ikeda, S.; Hanyu, T.; Ohno, H.; Endoh, T.

    2014-05-07

    The robustness of data load of metal–oxide–semiconductor/magnetic tunnel junction (MOS/MTJ) hybrid latches at power-on is examined by using Monte Carlo simulation with the variations in magnetoresistances for MTJs and in threshold voltages for MOSFETs involved in 90 nm technology node. Three differential pair type spin-transfer-torque-magnetic random access memory cells (4T2MTJ, 6T2MTJ, and 8T2MTJ) are compared for their successful data load at power-on. It is found that the 4T2MTJ cell has the largest pass area in the shmoo plot in TMR ratio (tunnel magnetoresistance ratio) and V{sub dd} in which a whole 256 kb cell array can be powered-on successfully. The minimum TMR ratio for the 4T2MTJ in 0.9 V < V{sub dd} < 1.9 V is 140%, while the 6T2MTJ and the 8T2MTJ cells require TMR ratio larger than 170%.

  17. Mesoporous silica beads embedded with semiconductor quantum dots and iron oxide nanocrystals: dual-function microcarriers for optical encoding and magnetic separation.

    PubMed

    Sathe, Tushar R; Agrawal, Amit; Nie, Shuming

    2006-08-15

    Mesoporous beads are promising materials for embedding functional nanoparticles because of their nanometer-sized pores and large surface areas. Here we report the development of silica microbeads embedded with both semiconductor quantum dots (QD) and iron oxide (Fe3O4) nanocrystals as a new class of dual-function carriers for optical encoding and magnetic separation. The embedding (doping) process is carried out by either simultaneous or sequential addition of quantum dots and iron oxide (Fe3O4) nanocrystals in solution. The doping process is fast and quantitative, but the incorporated iron oxide strongly attenuates the signal intensity of QD fluorescence. We find that this attenuation is not due to conventional fluorescence quenching but is caused by the broad optical absorption spectrum of mixed-valence Fe3O4. For improved biocompatibility and reduced nonspecific binding, the encoded beads are further coated with amphiphilic polymers such as octylamine poly(acrylic acid). The results indicate that the polymer-coated beads are well suited for target capturing and enrichment, yielding magnetic separation efficiencies higher than 99%. By combining the multiplexing capability of QDs with the superparamagnetic properties of iron oxide nanocrystals, this class of encoded beads is expected to find broad applications in high-throughput and multiplexed biomolecular assays. PMID:16906704

  18. Negative magnetophoresis in diluted ferrofluid flow.

    PubMed

    Hejazian, Majid; Nguyen, Nam-Trung

    2015-07-21

    We report magnetic manipulation of non-magnetic particles suspended in diluted ferrofluid. Diamagnetic particles were introduced into a circular chamber to study the extent of their deflection under the effect of a non-uniform magnetic field of a permanent magnet. Since ferrofluid is a paramagnetic medium, it also experiences a bulk magnetic force that in turn induces a secondary flow opposing the main hydrodynamic flow. Sheath flow rate, particle size, and magnetic field strength were varied to examine this complex behaviour. The combined effect of negative magnetophoresis and magnetically induced secondary flow leads to various operation regimes, which can potentially find applications in separation, trapping and mixing of diamagnetic particles such as cells in a microfluidic system. PMID:26054840

  19. Exciton Transport in Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Menke, Stephen Matthew

    Photovoltaic cells based on organic semiconductors are attractive for their use as a renewable energy source owing to their abundant feedstock and compatibility with low-cost coating techniques on flexible substrates. In contrast to photovoltaic cells based traditional inorganic semiconductors, photon absorption in an organic semiconductor results in the formation of a coulombically bound electron-hole pair, or exciton. The transport of excitons, consequently, is of critical importance as excitons mediate the interaction between charge and light in organic photovoltaic cells (OPVs). In this dissertation, a strong connection between the fundamental photophysical parameters that control nanoscopic exciton energy transfer and the mesoscopic exciton transport is established. With this connection in place, strategies for enhancing the typically short length scale for exciton diffusion (L D) can be developed. Dilution of the organic semiconductor boron subphthalocyanine chloride (SubPc) is found to increase the LD for SubPc by 50%. In turn, OPVs based on dilute layers of SubPc exhibit a 30% enhancement in power conversion efficiency. The enhancement in power conversion efficiency is realized via enhancements in LD, optimized optical spacing, and directed exciton transport at an exciton permeable interface. The role of spin, energetic disorder, and thermal activation on L D are also addressed. Organic semiconductors that exhibit thermally activated delayed fluorescence and efficient intersystem and reverse intersystem crossing highlight the balance between singlet and triplet exciton energy transfer and diffusion. Temperature dependent measurements for LD provide insight into the inhomogeneously broadened exciton density of states and the thermal nature of exciton energy transfer. Additional topics include energy-cascade OPV architectures and broadband, spectrally tunable photodetectors based on organic semiconductors.

  20. Electro- and magneto-optic properties of photorefractive semiconductors

    NASA Astrophysics Data System (ADS)

    Dinu, Mihaela

    The photorefractive effect is a low intensity, nonlocal optical nonlinearity which has been studied extensively because of its potential uses. Photorefractive quantum wells exhibit record sensitivities and speeds, and are prime candidates for optical processing applications, both in the spatial (for images) and in the time domain (for the shaping of femtosecond pulses). For this latter application, multiple quantum well devices have to overcome a large bandwidth mismatch with femtosecond pulses, which arises from the resonant nature of photorefractivity at the bandgap. By engineering the excitonic transition spectrum of multiple quantum wells, the bandwidth of photorefractive multiple quantum well devices is increased to match that of ultrafast pulses. In superlattices, breaking of the spatial periodicity leads to the emergence of a wide distribution of critical points and transition energies; we have explored the effect of quasiperiodicity in Fibonacci superlattices, where excitonic interactions concentrate the oscillator strength at low energies and limit the useful diffractive bandwidth. Multiple quantum well structures in which the quantum wells are isolated and the quantum confinement can be tuned along the thickness of the device offer a wide parameter space for bandwidth design. In quantum well devices, almost dispersion-free diffraction can be achieved due to the Kramers-Kronig relationship between the real and imaginary parts of the electro-refraction, which makes the phase of the diffracted pulse linear in frequency. The second part of the thesis concentrates on the photorefractive effect in diluted magnetic semiconductors. In ZnMnSe epilayers, we demonstrate resonant photorefractive diffraction in the blue spectral region. Wide-gap II-VI semiconductors have characteristic properties (such as high absorption coefficients at the gap and low sensitivity to electric fields) which make the fabrication of resonant photorefractive devices in the transverse

  1. Resonantly enhanced spin-lattice relaxation of Mn2 + ions in diluted magnetic (Zn,Mn)Se/(Zn,Be)Se quantum wells

    NASA Astrophysics Data System (ADS)

    Debus, J.; Ivanov, V. Yu.; Ryabchenko, S. M.; Yakovlev, D. R.; Maksimov, A. A.; Semenov, Yu. G.; Braukmann, D.; Rautert, J.; Löw, U.; Godlewski, M.; Waag, A.; Bayer, M.

    2016-05-01

    The dynamics of spin-lattice relaxation in the magnetic Mn2 + ion system of (Zn,Mn)Se/(Zn,Be)Se quantum-well structures are studied using optical methods. Pronounced cusps are found in the giant Zeeman shift of the quantum-well exciton photoluminescence at specific magnetic fields below 10 T, when the Mn spin system is heated by photogenerated carriers. The spin-lattice relaxation time of the Mn ions is resonantly accelerated at the cusp magnetic fields. Our theoretical analysis demonstrates that a cusp occurs at a spin-level mixing of single Mn2 + ions and a quick-relaxing cluster of nearest-neighbor Mn ions, which can be described as intrinsic cross-relaxation resonance within the Mn spin system.

  2. Effects of sintering temperature variation on microstructure and magnetic nature of Al diluted La0.7Ca0.3MnO3

    NASA Astrophysics Data System (ADS)

    Kumar, Manish; Choudhary, R. J.; Phase, D. M.

    2013-02-01

    The samples of La0.7Ca0.3Mn1-XAlXO3 (X=0,0.05,0.15) are synthesized at two different sintering temperature 1200°C and 1400°C. The phase purity of the samples is analyzed using x-ray diffraction measurements. The microstructural evolution for different sintering temperatures is carefully tracked using scanning electron microscope (SEM). Increase in grain size with increasing sintering temperature is well identified in SEM images. Variation in the magnetic nature of the samples sintered at different temperature is seen in temperature dependent magnetization M(T) measurements. M(T) results reveal that Al doped samples show strong dependence of their magnetic behavior on sintering temperature as compared to undoped La0.7Ca0.3MnO3.

  3. Optical exciton Aharonov-Bohm effect, persistent current, and magnetization in semiconductor nanorings of type I and II

    NASA Astrophysics Data System (ADS)

    Grochol, M.; Grosse, F.; Zimmermann, R.

    2006-09-01

    The optical exciton Aharonov-Bohm effect—i.e., an oscillatory component in the energy of optically active (bright) states—is investigated in nanorings. It is shown that a small effective electron mass, strong confinement of the electron, and high barrier for the hole, achieved, e.g., by an InAs nanoring embedded in an AlGaSb quantum well, are favorable for observing the optical exciton Aharonov-Bohm effect. The second derivative of the exciton energy with respect to the magnetic field is utilized to extract Aharonov-Bohm oscillations even for the lowest bright state unambiguously. A connection between the theories for infinitesimal narrow and finite width rings is established. Furthermore, the magnetization is compared to the persistent current, which oscillates periodically with the magnetic field and confirms thus the nontrivial (connected) topology of the wave function in the nanoring.

  4. Field-effect modulation of anomalous Hall effect in diluted ferromagnetic topological insulator epitaxial films

    NASA Astrophysics Data System (ADS)

    Chang, CuiZu; Liu, MinHao; Zhang, ZuoCheng; Wang, YaYu; He, Ke; Xue, QiKun

    2016-03-01

    High quality chromium (Cr) doped three-dimensional topological insulator (TI) Sb2Te3 films are grown via molecular beam epitaxy on heat-treated insulating SrTiO3 (111) substrates. We report that the Dirac surface states are insensitive to Cr doping, and a perfect robust long-range ferromagnetic order is unveiled in epitaxial Sb2- x Cr x Te3 films. The anomalous Hall effect is modulated by applying a bottom gate, contrary to the ferromagnetism in conventional diluted magnetic semiconductors (DMSs), here the coercivity field is not significantly changed with decreasing carrier density. Carrier-independent ferromagnetism heralds Sb2- x Cr x Te3 films as the base candidate TI material to realize the quantum anomalous Hall (QAH) effect. These results also indicate the potential of controlling anomalous Hall voltage in future TI-based magneto-electronics and spintronics.

  5. Dilution, Concentration, and Flotation

    ERIC Educational Resources Information Center

    Liang, Ling; Schmuckler, Joseph S.

    2004-01-01

    As both classroom teaching practice and literature show, many students have difficulties learning science concepts such as density. Here are some investigations that identify the relationship between density and floating through experimenting with successive dilution of a liquid, or the systematic change of concentration of a saltwater solution.…

  6. Helium dilution refrigeration system

    DOEpatents

    Roach, P.R.; Gray, K.E.

    1988-09-13

    A helium dilution refrigeration system operable over a limited time period, and recyclable for a next period of operation is disclosed. The refrigeration system is compact with a self-contained pumping system and heaters for operation of the system. A mixing chamber contains [sup 3]He and [sup 4]He liquids which are precooled by a coupled container containing [sup 3]He liquid, enabling the phase separation of a [sup 3]He rich liquid phase from a dilute [sup 3]He-[sup 4]He liquid phase which leads to the final stage of a dilution cooling process for obtaining low temperatures. The mixing chamber and a still are coupled by a fluid line and are maintained at substantially the same level with the still cross sectional area being smaller than that of the mixing chamber. This configuration provides maximum cooling power and efficiency by the cooling period ending when the [sup 3]He liquid is depleted from the mixing chamber with the mixing chamber nearly empty of liquid helium, thus avoiding unnecessary and inefficient cooling of a large amount of the dilute [sup 3]He-[sup 4]He liquid phase. 2 figs.

  7. Helium dilution refrigeration system

    DOEpatents

    Roach, Patrick R.; Gray, Kenneth E.

    1988-01-01

    A helium dilution refrigeration system operable over a limited time period, and recyclable for a next period of operation. The refrigeration system is compact with a self-contained pumping system and heaters for operation of the system. A mixing chamber contains .sup.3 He and .sup.4 He liquids which are precooled by a coupled container containing .sup.3 He liquid, enabling the phase separation of a .sup.3 He rich liquid phase from a dilute .sup.3 He-.sup.4 He liquid phase which leads to the final stage of a dilution cooling process for obtaining low temperatures. The mixing chamber and a still are coupled by a fluid line and are maintained at substantially the same level with the still cross sectional area being smaller than that of the mixing chamber. This configuration provides maximum cooling power and efficiency by the cooling period ending when the .sup.3 He liquid is depleted from the mixing chamber with the mixing chamber nearly empty of liquid helium, thus avoiding unnecessary and inefficient cooling of a large amount of the dilute .sup.3 He-.sup.4 He liquid phase.

  8. Investigation of local structural environments and room-temperature ferromagnetism in (Fe,Cu)-codoped In2O3 diluted magnetic oxide films.

    PubMed

    An, Yukai; Xing, Yaya; Pan, Fei; Wu, Zhonghua; Liu, Jiwen

    2016-05-11

    The local structural, optical, magnetic and transport properties of (In0.95-xFexCu0.05)2O3 (0.06 ≤ x ≤ 0.20) films deposited by RF-magnetron sputtering have been systemically studied by different experimental techniques. Detailed structural analyses using XRD, XPS, EXAFS and full multiple-scattering ab initio theoretical calculations of Fe K-edge XANES show that the (In0.95-xFexCu0.05)2O3 films have the same cubic bixbyite structure as pure In2O3. The doped Fe ions exist at both +2 and +3 oxidation states, substituting for the In(3+) sites in the In2O3 lattice and forming a FeIn + 2VO complex with the O vacancy in the first coordination shell of Fe. However, the co-doped Cu atoms are not incorporated into the In2O3 lattice and form the Cu metal clusters due to high ionization energy. UV-Vis measurements show that the optical band gap Eg decreases monotonically with the increase of Fe concentration, implying an increasing s-pd exchange interaction in the films. All the films display intrinsic room-temperature (RT) ferromagnetism and the saturated magnetization (Ms) increases monotonically with Fe doping. The temperature dependence of the resistivity data suggests the conduction mechanism of Mott variable-range hopping (VRH) at low temperature, confirming that the carriers are localized. It can be concluded that the observed RT ferromagnetism in the films originates from the overlapping of polarons mediated by oxygen vacancies based on the bound magnetic polaron (BMP) model. The variation of the localization effect of carriers with Fe doping can obviously adjust the magnetic exchange interaction in the (In0.95-xFexCu0.05)2O3 films. PMID:27139011

  9. Fabrication and characterization of magnetically tunable metal-semiconductor schottky diode using barium hexaferrite thin film on gold

    NASA Astrophysics Data System (ADS)

    Kaur, Jotinder; Sharma, Vinay; Sharma, Vipul; Veerakumar, V.; Kuanr, Bijoy K.

    2016-05-01

    Barium Hexaferrite (BaM) is an extensively studied magnetic material due to its potential device application. In this paper, we study Schottky junction diodes fabricated using gold and BaM and demonstrate the function of a spintronic device. Gold (50 nm)/silicon substrate was used to grow the BaM thin films (100-150 nm) using pulsed laser deposition. I-V characteristics were measured on the Au/BaM structure sweeping the voltage from ±5 volts. The forward and reverse bias current-voltage curves show diode like rectifying characteristics. The threshold voltage decreases while the output current increases with increase in the applied external magnetic field showing that the I-V characteristics of the BaM based Schottky junction diodes can be tuned by external magnetic field. It is also demonstrated that, the fabricated Schottky diode can be used as a half-wave rectifier, which could operate at high frequencies in the range of 1 MHz compared to the regular p-n junction diodes, which rectify below 10 kHz. In addition, it is found that above 1 MHz, Au/BaM diode can work as a rectifier as well as a capacitor filter, making the average (dc) voltage much larger.

  10. Low temperature, high magnetic field investigations of the nature of magnetism in the molecular semiconductor β- cobalt phthalocyanine (C32H16CoN8)

    NASA Astrophysics Data System (ADS)

    Wang (王正君), Zhengjun; Lee, M.; Choi, E. S.; Poston, J.; Seehra, M. S.

    2016-06-01

    Results from detailed investigations of the magnetic properties of a powder sample of β-CoPc for the temperatures T=0.4 K to 300 K and in magnetic fields H up to 90 kOe are reported. X-ray diffraction confirmed the β-phase and scanning electron microscopy showed plate-like morphology of the sample. For T>3 K, the data of magnetic susceptibility χ vs. T fit the Curie-Weiss (CW) law yielding θ=-2.5 K, μ=2.16 μB per Co2+ and g=2.49 for spin S=1/2 of the low spin-state of Co2+. However for T<3 K, the χ vs. T data deviates from the CW law yielding a peak in χ at Tmax=1.9 K. It is shown that the χ vs. T data from 0.4 K to 300 K fits well with the predictions of the Bonner-Fisher (BF) model for S=1/2 Heisenberg linear chain antiferromagnet with the Co2+-Co2+ exchange J/kB = -1.5 K (Ĥ=-2J Σ Si•Si+1). The data of magnetization M vs. H at T=1 K agrees with the predictions of the BF model with J/kB=-1.5 K, yielding saturation magnetization MS=12.16 emu/g above 60 kOe corresponding to complete alignment of the spins.

  11. The ratio of the hole and electron exchange integrals in a CdMnSe/ZnSe diluted magnetic structure with quantum dots

    SciTech Connect

    Reshina, I. I. Ivanov, S. V.

    2011-02-15

    Measurements of photoluminescence and resonance Raman scattering spectra of a CdMnSe/ZnSe structure with self-assembled quantum dots in magnetic fields up to 6 T in the Faraday and Voigt configurations show that the ratio of the valence- and conduction-band exchange integrals exceeds the known value for bulk CdMnSe by a factor of 1.5. This effect is attributed mainly to a decrease in the conduction-band exchange integral caused by a contribution from the kinetic s-d exchange mechanism, forbidden in the bulk.

  12. Magnetic dilution of the iron sublattice in CoFe{sub 2-x}Sc{sub x}O{sub 4} (0{<=}x{<=}1)

    SciTech Connect

    Lefevre, C.; Roulland, F.; Viart, N.; Greneche, J.M.; Pourroy, G.

    2010-11-15

    Substitution of Fe for Sc in CoFe{sub 2}O{sub 4} spinel structure is presented. All CoFe{sub 2-x}Sc{sub x}O{sub 4} compounds crystallize in the spinel type structure (space group Fd3-bar m). By using X-ray diffraction studies, magnetic measurements and in-field {sup 57}Fe Moessbauer spectrometry, the limit of substitution has been determined to be equal to x=0.56. An increase in the cell parameter and the strains and a decrease in the apparent crystallites size are observed. For x>0.3, a partial oxidation of cobalt is evidenced and Co{sup 3+} is stabilized in the structure. A ferromagnetic behavior has been observed for all investigated compounds. As x increases, the Curie temperature and the hyperfine fields decrease. Following the Stephenson model, the diminution of T{sub C} is ascribed to a decrease of the main J{sub AB} interaction. -- Graphical abstract: Evolution of the cell parameters, the magnetic properties and the Moessbauer spectra in CoFe{sub 2-r}Sc{sub r}O{sub 4} (0{<=}r{<=}1). Display Omitted

  13. Automatic diluter for bacteriological samples.

    PubMed

    Trinel, P A; Bleuze, P; Leroy, G; Moschetto, Y; Leclerc, H

    1983-02-01

    The described apparatus, carrying 190 tubes, allows automatic and aseptic dilution of liquid or suspended-solid samples. Serial 10-fold dilutions are programmable from 10(-1) to 10(-9) and are carried out in glass tubes with screw caps and split silicone septa. Dilution assays performed with strains of Escherichia coli and Bacillus stearothermophilus permitted efficient conditions for sterilization of the needle to be defined and showed that the automatic dilutions were as accurate and as reproducible as the most rigorous conventional dilutions. PMID:6338826

  14. Automatic diluter for bacteriological samples.

    PubMed Central

    Trinel, P A; Bleuze, P; Leroy, G; Moschetto, Y; Leclerc, H

    1983-01-01

    The described apparatus, carrying 190 tubes, allows automatic and aseptic dilution of liquid or suspended-solid samples. Serial 10-fold dilutions are programmable from 10(-1) to 10(-9) and are carried out in glass tubes with screw caps and split silicone septa. Dilution assays performed with strains of Escherichia coli and Bacillus stearothermophilus permitted efficient conditions for sterilization of the needle to be defined and showed that the automatic dilutions were as accurate and as reproducible as the most rigorous conventional dilutions. Images PMID:6338826

  15. Hybrid ferromagnetic-semiconductor structures

    SciTech Connect

    Prinz, G.A. )

    1990-11-23

    Ultrahigh-vacuum growth techniques are now being used to grow single-crystal films of magnetic materials. These growth procedures, carried out in the same molecular beam epitaxy systems commonly used for the growth of semiconductor films, have yielded a variety of new materials and structures that may prove useful for integrated electronics and integrated optical device applications. Examples are given for growth on GaAs and ZnSe, including magnetic sandwiches and patterned structures. 14 refs., 9 figs.

  16. High-κ GdTixOy sensing membrane-based electrolyte-insulator-semiconductor with magnetic nanoparticles as enzyme carriers for protein contamination-free glucose biosensing.

    PubMed

    Wu, Min-Hsien; Yang, Hung-Wei; Hua, Mu-Yi; Peng, Yen-Bo; Pan, Tung-Ming

    2013-09-15

    This paper reports an electrolyte-insulator-semiconductor (EIS) device featuring a novel high-κ GdTixOy sensing membrane for high-performance pH sensing and glucose biosensing. The effect of the annealing temperature (700, 800, or 900°C) on the sensing properties of the GdTixOy membranes was investigated. The GdTixOy EIS device annealed at 900°C exhibited the greatest pH sensing performance, including the highest sensitivity (62.12mV/pH), the smallest hysteresis voltage (5mV), and the lowest drift rate (0.4mV/h), presumably because of its well-crystallized GdTixOy structure. To overcome the problems typically encountered during the practical application of biosensors (e.g., protein adsorption; preservation of enzymatic activity), we employed Fe3O4-based magnetic nanoparticles (MNPs) as enzyme carriers. The adsorption of serum protein on the unmodified sensing membrane led to poor EIS-based pH sensing (r(2)=0.71); the performance was greatly improved, however, after attaching the MNPs to the sensing membrane, thereby blocking protein adsorption significantly (by 98%) and allowing excellent pH sensing (r(2)=0.99). Moreover, we prepared a hybrid configuration of the proposed GdTixOy membrane-EIS, with magnetically attached glucose oxidase-immobilized MNPs, for glucose biosensing. The use of MNPs as enzyme carriers effectively preserved the enzymatic activity of glucose oxidase, with 45.3% of the original enzymatic activity retained after 120h of storage at 4°C (compared with complete loss of the free enzyme's activity under the same storage conditions). In addition, the proposed biosensor exhibited superior detection sensitivity of 11.03mV/mM relative to that (8.17mV/mM) obtained using the conventional enzyme immobilization method. Finally, we established the accuracy of the proposed method for blood glucose measurement; gratifyingly, blood glucose detection was comparable with the high-sensitivity glucose quantification obtained using a commercial glucose assay

  17. Semiconductor Cubing

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Through Goddard Space Flight Center and Jet Propulsion Laboratory Small Business Innovation Research contracts, Irvine Sensors developed a three-dimensional memory system for a spaceborne data recorder and other applications for NASA. From these contracts, the company created the Memory Short Stack product, a patented technology for stacking integrated circuits that offers higher processing speeds and levels of integration, and lower power requirements. The product is a three-dimensional semiconductor package in which dozens of integrated circuits are stacked upon each other to form a cube. The technology is being used in various computer and telecommunications applications.

  18. Magnetism, Magnetic Materials and their Applications III - Proceedings of the III Latin American Workshop

    NASA Astrophysics Data System (ADS)

    Leccabue, F.; Sagredo, V.

    1996-08-01

    The Table of Contents for the full book PDF is as follows: * Preface * Section I: Fundamental, Techniques and Materials * Magnetism in finite size Ising aggregates * Magnetic anisotropy in thin films * Magnetocrystalline anisotropy in rare earth intermetallics * Ferromagnetism vs Kondo effect in normal and superconducting CeTyX4-y * Magnetic phase transition and magnetocrystalline anisotropy of rare-earth transition-metal alloys * Giant magnetoresistance and related effects in multilayer and granular magnetic materials for practical applications * Magnetic properties of dilute PdMn alloys * TbFe amorphous thin films. Structural, magnetic and magnetoelastic studies * Nanophase exchange coupled alloys with enhanced hard magnetic properties * Exchange interactions in ferrimagnetic rare earth-transition metal multilayers * Superparamagnetic relaxation in interacting γ-Fe2O3 particles * Magnetic circular X-ray dichroism * Non-frustrated domains in Ising lattices with competing interactions * Thermomagnetic and X-ray diffraction analysis of Nd3Fe29-xTix and (Nd1-xYx)3Fe27.3Ti1.7 alloys * Electron paramagnetic resonance above the ordering temperature in La1-xCaxMnO3+δ * Spin-polarisation at Cr/Fe and Mn/Fe interfaces * Interplay of segregation, phase separation and magnetism in cobalt-copper slabs * High temperature behaviour of amorphous and nanocrystalline soft magnetic materials * Preparation of magnetic oxide thin films * Magnetic interactions in enhanced-remanence permanent magnets * Section II: Poster Session : Fundamental, Techniques and Materials * Magnetic properties in inorganic materials * Thermoreflactance measurements on Cd1-xCoxSe magnetic semiconductors * Analytical solutions of the NCA equations for the Coqblin-Schrieffer model in the zero temperature limit * Magneto-structural and spectroscopic investigation of MnxCd1-xIn2Te4 solid solutions * Magnetic after-effect processes in barium hexagonal ferrites * Electron paramagnetic resonance in PtFe alloys

  19. Device Concepts in Semiconductor Spintronics

    NASA Astrophysics Data System (ADS)

    Molenkamp, Laurens W.

    Semiconductor spintronics has now reached a stage where the basic physical mechanisms controlling spin injection and detection are understood. Moreover, some critical technological issues involved in the growth and lithography of the magnetic semiconductors have been solved. This has allowed us to explore the physics of meanwhile quite complex spintronic devices. The lectures will start with an introduction to spin transport in metals and semiconductors. Building upon this, I will discuss various simple devices that demonstrate this basic physics in action. Subsequently, more advanced devices will be covered. For example, I will discuss resonant tunneling diodes (RTDs) fabricated from paramagnetic II-VI semiconductors that can be operated as a voltage controlled spin-switch. A quantum dot version of these RTDs exhibits, unexpectedly, remanent magnetism at zero external field, which we interpret as resulting from tunneling through a single magnetic polaron. In the ferromagnetic semiconductor (Ga, Mn)As we have observed a very large spin valve effect due to domain wall pinning at sub-10 nm sized constrictions. Furthermore, we have found a novel magnetoresistance effect in this material, dubbed tunnel anisotropic magnetoresistance (TAMR), which is due to the strongly (magneto-)anisotropic density of states in a ferromagnetic semiconductor. The effect leads to the observation of a spin valve-like behavior in tunnel structures containg a single ferromagnetic layer and also dominates the spin-valve signal obtained from structures containing two (Ga, Mn)As layers, where the effect may cause resistance changes of five orders of magnitude. Note from Publisher: This article contains the abstract only.

  20. THE ANISOTROPIC TRANSPORT EFFECTS ON DILUTE PLASMAS

    SciTech Connect

    Devlen, Ebru

    2011-04-20

    We examine the linear stability analysis of a hot, dilute, and differentially rotating plasma by considering anisotropic transport effects. In dilute plasmas, the ion Larmor radius is small compared with its collisional mean free path. In this case, the transport of heat and momentum along the magnetic field lines becomes important. This paper presents a novel linear instability that may be more powerful and greater than ideal magnetothermal instability and ideal magnetorotational instability in the dilute astrophysical plasmas. This type of plasma is believed to be found in the intracluster medium (ICM) of galaxy clusters and radiatively ineffective accretion flows around black holes. We derive the dispersion relation of this instability and obtain the instability condition. There is at least one unstable mode that is independent of the temperature gradient direction for a helical magnetic field geometry. This novel instability is driven by the gyroviscosity coupled with differential rotation. Therefore, we call it gyroviscous-modified magnetorotational instability (GvMRI). We examine how the instability depends on signs of the temperature gradient and the gyroviscosity and also on the magnitude of the thermal frequency and on the values of the pitch angle. We provide a detailed physical interpretation of the obtained results. The GvMRI is applicable not only to the accretion flows and ICM but also to the transition region between cool dense gas and the hot low-density plasma in stellar coronae, accretion disks, and the multiphase interstellar medium because it is independent of the temperature gradient direction.

  1. Dilution jet mixing program

    NASA Technical Reports Server (NTRS)

    Srinivasan, R.; Coleman, E.; Johnson, K.

    1984-01-01

    Parametric tests were conducted to quantify the mixing of opposed rows of jets (two-sided injection) in a confined cross flow. Results show that jet penetrations for two sided injections are less than that for single-sided injections, but the jet spreading rates are faster for a given momentum ratio and orifice plate. Flow area convergence generally enhances mixing. Mixing characteristics with asymmetric and symmetric convergence are similar. For constant momentum ratio, the optimum S/H(0) with in-line injections is one half the optimum value for single sided injections. For staggered injections, the optimum S/H(0) is twice the optimum value for single-sided injection. The correlations developed predicted the temperature distributions within first order accuracy and provide a useful tool for predicting jet trajectory and temperature profiles in the dilution zone with two-sided injections.

  2. Standard dilution analysis.

    PubMed

    Jones, Willis B; Donati, George L; Calloway, Clifton P; Jones, Bradley T

    2015-02-17

    Standard dilution analysis (SDA) is a novel calibration method that may be applied to most instrumental techniques that will accept liquid samples and are capable of monitoring two wavelengths simultaneously. It combines the traditional methods of standard additions and internal standards. Therefore, it simultaneously corrects for matrix effects and for fluctuations due to changes in sample size, orientation, or instrumental parameters. SDA requires only 200 s per sample with inductively coupled plasma optical emission spectrometry (ICP OES). Neither the preparation of a series of standard solutions nor the construction of a universal calibration graph is required. The analysis is performed by combining two solutions in a single container: the first containing 50% sample and 50% standard mixture; the second containing 50% sample and 50% solvent. Data are collected in real time as the first solution is diluted by the second one. The results are used to prepare a plot of the analyte-to-internal standard signal ratio on the y-axis versus the inverse of the internal standard concentration on the x-axis. The analyte concentration in the sample is determined from the ratio of the slope and intercept of that plot. The method has been applied to the determination of FD&C dye Blue No. 1 in mouthwash by molecular absorption spectrometry and to the determination of eight metals in mouthwash, wine, cola, nitric acid, and water by ICP OES. Both the accuracy and precision for SDA are better than those observed for the external calibration, standard additions, and internal standard methods using ICP OES. PMID:25599250

  3. A Novel Class of High-TC Ferromagnetic Semiconductors

    SciTech Connect

    Shlyk, L. V.; Kryukov, S. A.; De Long, L. E.; Schupp-Niewa, B.; Niewa, R.; Lynn, J. W.; Huang, Qing; Arenholz, E.; Piamonteze, C.

    2008-05-30

    We have grown single crystals of novel ruthenates (Sr,Ba)(Fe,Co){sub 2+x}Ru{sub 4-x}O{sub 11} that exhibit long-range ferromagnetic order well above room temperature, accompanied by narrow-gap semiconducting properties that include a large anomalous Hall conductance, low resistivity, high carrier concentration and low coercive field, which are properties well suited to spintronic applications. X-ray diffraction, EDX, neutron diffraction and x-ray absorption measurements on single crystals firmly establish the 'R-Type' hexagonal ferrite structure (space group P6{sub 3}/mmc, No 194) and single-phase nature of all samples. The electronic structure and physical properties can be tuned by simple chemical substitution of two elements, M = Fe or Co, or by varying the relative concentration of 3d solutes and 4d Ru. Our magnetotransport, x-ray magnetic circular dichroism and magnetic moment data suggest the mechanism for FM order is quite different from that governing known dilute magnetic semiconductors.

  4. Field-induced spin-flop in antiferromagnetic semiconductors with commensurate and incommensurate magnetic structures: Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS).

    PubMed

    Brant, Jacilynn A; dela Cruz, Clarina; Yao, Jinlei; Douvalis, Alexios P; Bakas, Thomas; Sorescu, Monica; Aitken, Jennifer A

    2014-12-01

    Li2FeGeS4 (LIGS) and Li2FeSnS4 (LITS), which are among the first magnetic semiconductors with the wurtz-kesterite structure, exhibit antiferromagnetism with TN ≈ 6 and 4 K, respectively. Both compounds undergo a conventional metamagnetic transition that is accompanied by a hysteresis; a reversible spin-flop transition is dominant. On the basis of constant-wavelength neutron powder diffraction data, we propose that LIGS and LITS exhibit collinear magnetic structures that are commensurate and incommensurate with propagation vectors km = [1/2, 1/2, 1/2] and [0, 0, 0.546(1)], respectively. The two compounds exhibit similar magnetic phase diagrams, as the critical fields are temperature-dependent. The nuclear structures of the bulk powder samples were verified using time-of-flight neutron powder diffraction along with synchrotron X-ray powder diffraction. (57)Fe and (119)Sn Mössbauer spectroscopy confirmed the presence of Fe(2+) and Sn(4+) as well as the number of crystallographically unique positions. LIGS and LITS are semiconductors with indirect and direct bandgaps of 1.42 and 1.86 eV, respectively, according to optical diffuse-reflectance UV-vis-NIR spectroscopy. PMID:25397682

  5. Electronic structures and magnetism for carbon doped CdSe: Modified Becke-Johnson density functional calculations

    NASA Astrophysics Data System (ADS)

    Fan, S. W.; Song, T.; Huang, X. N.; Yang, L.; Ding, L. J.; Pan, L. Q.

    2016-09-01

    Utilizing the full potential linearized augment plane wave method, the electronic structures and magnetism for carbon doped CdSe are investigated. Calculations show carbon substituting selenium could induce CdSe to be a diluted magnetic semiconductor. Single carbon dopant could induce 2.00 μB magnetic moment. Electronic structures show the long-range ferromagnetic coupling mainly originates from the p-d exchange-like p-p coupling interaction. Positive chemical pair interactions indicate carbon dopants would form homogeneous distribution in CdSe host. The formation energy implies the non-equilibrium fabricated technology is necessary during the samples fabricated.

  6. Growth and characterization of semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Philipose, Usha

    This thesis describes a catalytic growth approach to synthesize semiconductor nanowires with good control over their physical dimensions, chemical composition, and optical/electronic properties. Using the Vapour-Liquid-Solid growth mechanism, gold nanoclusters serve as the catalytic sites directing the growth of crystalline Zinc Selenide (ZnSe), Zinc Oxide (ZnO) and Zinc Sulphide (ZnS) nanowires with length of several microns and diameters varying from 15 nm to 100 nm. The morphology and properties of the nanowires were found to be strongly dependent on growth conditions. Optical characterization by photoluminescence spectroscopy show that the spectra is dominated by near band edge emission for low defect density nanowires in contrast to the high level of defect related emission from high defect density nanowires. The growth parameters were optimized leading to the synthesis of nanowires with minimum defect concentration. Electrical transport studies on an array of ZnSe nanowires confirm that there exists a non-uniform carrier distribution along the nanowires leading to 'super-linear' current-voltage behaviour with carrier mobilities comparable to that of bulk material. Photoconductivity measurements on ZnSe nanoribbons show that they are of good quality, enabling realization of a nanoscale photodetector with a peak efficiency of 43%. Spectral response of photoconductivity had a threshold character with edge corresponding to the ZnSe bandgap, which makes it an ideal candidate for blue and ultraviolet light detection. The effect of doping of these nanowires with transition elements such as manganese (Mn) has been studied. In this effort, the first successful attempt at synthesizing room temperature ferromagnetic nanowires has been realized. Above room temperature ferromagnetism has been observed for the first time in dilute Mn-doped crystalline ZnO nanowires. From the observed saturation magnetization, the magnetic moment per Mn atom is estimated to be in the range

  7. Breakdown of cyclotron resonance in semiconductor superlattices

    NASA Astrophysics Data System (ADS)

    Duffield, T.; Bhat, R.; Koza, M.; Hwang, D. M.; DeRosa, F.; Grabbe, P.; Allen, S. J.

    1988-03-01

    We have observed breakdown of cyclotron resonance in large magnetic fields oriented perpendicular to the growth direction in semiconductor superlattices. At small magnetic fields conventional cyclotron resonance is observed with the mass related to the miniband mass. At large magnetic fields, when the cyclotron diameter approaches the superlattice period, the resonance frequency appears to saturate and is determined by orbits impaled on the barrier. A model calculation gives good account of the magnetic field dependence of the resonance position and line width.

  8. Lattice location and local magnetism of recoil implanted Fe impurities in wide and narrow band semiconductors CdTe, CdSe, and InSb: Experiment and theory

    SciTech Connect

    Mohanta, S. K.; Mishra, S. N.

    2014-05-07

    Employing the time differential perturbed angular distribution method, we have measured local susceptibility and spin relaxation rate of {sup 54}Fe nuclei implanted in III-V and II-VI semiconductors, CdTe, CdSe, and InSb. The magnetic response of Fe, identified to occupy the metal as well as the semi-metal atom sites, exhibit Curie-Weiss type susceptibility and Korringa like spin relaxation rate, revealing the existence of localized moments with small spin fluctuation temperature. The experimental results are supported by first principle electronic structure calculations performed within the frame work of density functional theory.

  9. Isotope dilution mass spectrometry

    NASA Astrophysics Data System (ADS)

    Heumann, Klaus G.

    1992-09-01

    In the past isotope dilution mass spectrometry (IDMS) has usually been applied using the formation of positive thermal ions of metals. Especially in calibrating other analytical methods and for the certification of standard reference materials this type of IDMS became a routine method. Today, the progress in this field lies in the determination of ultra trace amounts of elements, e.g. of heavy metals in Antarctic ice and in aerosols in remote areas down to the sub-pg g-1 and sub-pg m-3 levels respectively, in the analysis of uranium and thorium at concentrations of a few pg g-1 in sputter targets for the production of micro- electronic devices or in the determination of sub-picogram amounts of230Th in corals for geochemical age determinations and of226Ra in rock samples. During the last few years negative thermal ionization IDMS has become a frequently used method. The determination of very small amounts of selenium and technetium as well as of other transition metals such as vanadium, chromium, molybdenum and tungsten are important examples in this field. Also the measurement of silicon in connection with a re-determination of Avogadro's number and osmium analyses for geological age determinations by the Re/Os method are of special interest. Inductively-coupled plasma mass spectrometry is increasingly being used for multi-element analyses by the isotope dilution technique. Determinations of heavy metals in samples of marine origin are representative examples for this type of multi-element analysis by IDMS. Gas chromatography-mass spectrometry systems have also been successfully applied after chelation of metals (for example Pt determination in clinical samples) or for the determination of volatile element species in the environment, e.g. dimethyl sulfide. However, IDMS--specially at low concentration levels in the environment--seems likely to be one of the most powerful analytical methods for speciation in the future. This has been shown, up to now, for species of

  10. Stress in dilute suspensions

    NASA Technical Reports Server (NTRS)

    Passman, Stephen L.

    1989-01-01

    Generally, two types of theory are used to describe the field equations for suspensions. The so-called postulated equations are based on the kinetic theory of mixtures, which logically should give reasonable equations for solutions. The basis for the use of such theory for suspensions is tenuous, though it at least gives a logical path for mathematical arguments. It has the disadvantage that it leads to a system of equations which is underdetermined, in a sense that can be made precise. On the other hand, the so-called averaging theory starts with a determined system, but the very process of averaging renders the resulting system underdetermined. A third type of theory is proposed in which the kinetic theory of gases is used to motivate continuum equations for the suspended particles. This entails an interpretation of the stress in the particles that is different from the usual one. Classical theory is used to describe the motion of the suspending medium. The result is a determined system for a dilute suspension. Extension of the theory to more concentrated systems is discussed.

  11. Electronic and magnetic behaviors of graphene with 5d series transition metal atom substitutions: A first-principles study

    NASA Astrophysics Data System (ADS)

    Sun, Minglei; Tang, Wencheng; Ren, Qingqiang; Zhao, Yiming; Wang, Sake; Yu, Jin; Du, Yanhui; Hao, Yitong

    2016-06-01

    The electronic structures and magnetic behaviors of graphene with 5d series transition metal atom substitutions are investigated by performing first-principles calculations. All the impurities are tightly bonded to single vacancy in a graphene sheet. The substitutions of La and Ta lead to Fermi level shifting to valence and conduction band, respectively. Both the two substitutions result in metallic properties. Moreover, the Hf, Os and Pt-substituted systems exhibit semiconductor properties, while the Re and Ir-substituted ones exhibit robust half-metallic properties. Interestingly, W-substituted system shows dilute magnetic semiconductor property. On the other hand, the substitution of Ta, W, Re and Ir induce 0.86 μB, 2 μB, 1 μB and 0.99 μB magnetic moment, respectively. Our studies demonstrate that the 5d series transition metal substituted graphene have potential applications in nanoelectronics, spintronics and magnetic storage devices.

  12. Hydrogen in semiconductors and metals

    SciTech Connect

    Nickel, N.H.; Jackson, W.B.; Bowman, R.C.; Leisure, R.G.

    1998-12-31

    Major highlights of the conference include further understanding of the structure of extended hydrogen clusters in semiconductors, switchable optical properties of metal-hydride films, reversible changes in the magnetic coupling in metallic superlattices, and increased lifetime of integrated circuits due to deuterium device passivation. Continued progress has also been achieved in understanding hydrogenation of defects in compound semiconductors and on surfaces. Total energy calculations in semiconductors have progressed sufficiently to predict energetics and vibration frequencies as measured by experiment. Similarly, electronic structure calculations of hydrogen-metal systems provide a deeper understanding of stability, bonding, and phase changes. Various nuclear techniques have been refined to yield important information regarding the concentration and transport of hydrogen in condensed matter. Finally, the interaction of hydrogen to create thermal donors has been used to create deep p-n junctions without the need for deep diffusion of dopants. The volume has been organized along the order of presentation within the conference. Similar methods and subjects have been grouped together. The authors have attempted to keep similar metal and semiconductor papers together in order to further promote cross-fertilization between the fields. Major categories include hydrogen on surfaces, theory and thermodynamics, hydrogen transport phenomena, nuclear characterization techniques, compound semiconductors, metal bulk, devices and applications, bulk silicon, and carbon and carbon-like materials. Separate abstracts were prepared for most papers.

  13. Dilution refrigeration for space applications

    NASA Technical Reports Server (NTRS)

    Israelsson, U. E.; Petrac, D.

    1990-01-01

    Dilution refrigerators are presently used routinely in ground based applications where temperatures below 0.3 K are required. The operation of a conventional dilution refrigerator depends critically on the presence of gravity. To operate a dilution refrigerator in space many technical difficulties must be overcome. Some of the anticipated difficulties are identified in this paper and possible solutions are described. A single cycle refrigerator is described conceptually that uses forces other than gravity to function and the stringent constraints imposed on the design by requiring the refrigerator to function on the earth without using gravity are elaborated upon.

  14. Voltage-controlled spin selection in a magnetic resonant tunneling diode.

    PubMed

    Slobodskyy, A; Gould, C; Slobodskyy, T; Becker, C R; Schmidt, G; Molenkamp, L W

    2003-06-20

    We have fabricated all II-VI semiconductor resonant tunneling diodes based on the (Zn,Mn,Be)Se material system, containing dilute magnetic material in the quantum well, and studied their current-voltage characteristics. When subjected to an external magnetic field the resulting spin splitting of the levels in the quantum well leads to a splitting of the transmission resonance into two separate peaks. This is interpreted as evidence of tunneling transport through spin polarized levels, and could be the first step towards a voltage controlled spin filter. PMID:12857209

  15. Structural and Magnetic Analysis of Nanocrystalline Lead Europium Sulfide (PbxEuyS)

    SciTech Connect

    Somarajan, Suseela; Harrison, Melissa A; Koktysh, Dmitry S.; He, Weidong; Stillwell, Ryan L; Harl, Bobby; Schmidt, Ben; Rogers, Bridget; Payzant, E Andrew; Dickerson, II, James H.

    2012-01-01

    The authors report the synthesis of nanocrystalline, alloyed PbEuS, a potentially important dilute magnetic semiconductor. The thermolysis of mixed precursors has been adapted for the formation of homogeneous alloyed nanocrystals. X-ray diffraction and magnetization measurements of ternary PbEuS nanocrystals provide convincing evidence that no phase separation occurs in these nanomaterials for europium concentrations up to x = 0.17. X-ray photoelectron spectroscopy provides the atomic composition for PbEuS alloy nanocrystals juxtaposed with the ratio of the starting precursors.

  16. Etching Of Semiconductor Wafer Edges

    DOEpatents

    Kardauskas, Michael J.; Piwczyk, Bernhard P.

    2003-12-09

    A novel method of etching a plurality of semiconductor wafers is provided which comprises assembling said plurality of wafers in a stack, and subjecting said stack of wafers to dry etching using a relatively high density plasma which is produced at atmospheric pressure. The plasma is focused magnetically and said stack is rotated so as to expose successive edge portions of said wafers to said plasma.

  17. Intermittency in dilute granular flows

    NASA Astrophysics Data System (ADS)

    Guo, Wenxuan; Zhang, Qiang; Wylie, Jonathan J.

    2016-07-01

    In this letter, we show that dilute granular systems can exhibit a type of intermittency that has no analogue in gas dynamics. We consider a simple system in which a very dilute set of granular particles falls under gravity through a nozzle. This setting is analogous to the classical problem of high-speed nozzle flow in the study of compressible gases. It is well known that very dilute granular systems exhibit behavior qualitatively similar to gases, and that gas flowing through a nozzle does not exhibit intermittency. Nevertheless, we show that the intermittency in dilute granular nozzle flows can occur and corresponds to complicated transitions between supersonic and subsonic regimes. We also provide detailed explanations of the mechanism underlying this phenomenon.

  18. Optical sensor of magnetic fields

    DOEpatents

    Butler, M.A.; Martin, S.J.

    1986-03-25

    An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

  19. Chain Dynamics in a Dilute Magnetorheological Fluid

    NASA Technical Reports Server (NTRS)

    Liu, Jing; Hagenbuchle, Martin

    1996-01-01

    The structure, formation, and dynamics of dilute, mono-dispersive ferrofluid emulsions in an external magnetic field have been investigated using dynamic light scattering techniques. In the absence of the magnetic field, the emulsion particles are randomly distributed and behave like hard spheres in Brownian motion. An applied magnetic field induces a magnetic dipole moment in each particle. Dipolar interactions between particles align them into chains where correlation functions show two decay processes. The short-time decay shows the motion of straight chains as a whole where the apparent chain length increases with the applied magnetic field and the particle volume fraction. Good scaling results are obtained showing that the apparent chain length grows with time following a power law with exponent of 0.6 and depends on the applied field, particle volume fraction, and diffusion constant of the particles. The long-time decay in the correlation function shows oscillation when the chains reach a certain length with time and stiffness with threshold field This result shows that chains not only fluctuate, but move in a periodic motion with a frequency of 364 Hz at lambda = 15. It may suggest the existence of phonons. This work is the first step in the understanding of the structure formation, especially chain coarsening mechanism, of magnetorheological (MR) fluids at higher volume fractions.

  20. Band modification in (Ga, Mn)As evidenced by new measurement scheme - photoresistance magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Huang, X. J.; Wang, L. G.; Chen, L.; Zhao, J. H.; Zheng, H. Z.

    2012-11-01

    A new scheme for measuring magneto-optical (MO) effect is developed in the present work, called photoresistance magnetic circular dichroism (PR-MCD). It detects the differential photoresistance of materials between two circularly polarized excitations. That allows us to detect the MO effect induced mainly by interband transitions, as evidenced by the appearance of a clear long wavelength cutoff at 840 nm in PR-MCD spectrum. Our results provide unambiguous evidence that the host semiconductor band structure of (Ga, Mn)As is indeed modified by the strong exchange interactions. It is also found that the interband-induced MO effect decays rather fast with increasing temperatures as compared to MO effects observed in conventional MCD measurements. Moreover, our PR-MCD measurements show interesting feature of diluted magnetic semiconductor Ga1- x Mn x As of a high mole fraction x. PR-MCD signal persists in a reentrant insulating phase at temperatures blow half of Curie temperature (~80 K), and disappears right above it. Such an intrigue feature might be self-consistently explained by recent theory, developed for diluted magnetic semiconductors in the strong correlation regime.

  1. Sr0.9K0.1Zn1.8Mn0.2As2: A ferromagnetic semiconductor with colossal magnetoresistance

    NASA Astrophysics Data System (ADS)

    Yang, Xiaojun; Chen, Qian; Li, Yupeng; Wang, Zhen; Bao, Jinke; Li, Yuke; Tao, Qian; Cao, Guanghan; Xu, Zhu-An

    2014-09-01

    A bulk diluted magnetic semiconductor (Sr,K)(Zn,Mn)2As2 was synthesized with decoupled charge and spin doping. It has a hexagonal CaAl2Si2-type structure with the (Zn,Mn)2As2 layer forming a honeycomb-like network. Magnetization measurements show that the sample undergoes a ferromagnetic transition with a Curie temperature of 12 K and magnetic moment reaches about 1.5 μ\\textit{B}/\\text{Mn} under μ_0H= 5 \\text{T} and T= 2 \\text{K} . Surprisingly, a colossal negative magnetoresistance, defined as [ρ(H)-ρ(0)]/ρ(0) , up to -38{%} under a low field of μ_0H= 0.1 \\text{T} and to -99.8{%} under μ_0H= 5 \\text{T} , was observed at T= 2 \\text{K} . The colossal magnetoresistance can be explained based on the Anderson localization theory.

  2. Boron doping a semiconductor particle

    SciTech Connect

    Stevens, G.D.; Reynolds, J.S.; Brown, L.K.

    1998-06-09

    A method of boron doping a semiconductor particle using boric acid to obtain a p-type doped particle. Either silicon spheres or silicon powder is mixed with a diluted solution of boric acid having a predetermined concentration. The spheres are dried, with the boron film then being driven into the sphere. A melt procedure mixes the driven boron uniformly throughout the sphere. In the case of silicon powder, the powder is metered out into piles and melted/fused with an optical furnace. Both processes obtain a p-type doped silicon sphere with desired resistivity. Boric acid is not a restricted chemical, is inexpensive, and does not pose any special shipping, handling, or disposal requirements. 2 figs.

  3. Phosphorus doping a semiconductor particle

    DOEpatents

    Stevens, G.D.; Reynolds, J.S.

    1999-07-20

    A method of phosphorus doping a semiconductor particle using ammonium phosphate is disclosed. A p-doped silicon sphere is mixed with a diluted solution of ammonium phosphate having a predetermined concentration. These spheres are dried with the phosphorus then being diffused into the sphere to create either a shallow or deep p-n junction. A good PSG glass layer is formed on the surface of the sphere during the diffusion process. A subsequent segregation anneal process is utilized to strip metal impurities from near the p-n junction into the glass layer. A subsequent HF strip procedure is then utilized to removed the PSG layer. Ammonium phosphate is not a restricted chemical, is inexpensive, and does not pose any special shipping, handling, or disposal requirement. 1 fig.

  4. Phosphorous doping a semiconductor particle

    DOEpatents

    Stevens, Gary Don; Reynolds, Jeffrey Scott

    1999-07-20

    A method (10) of phosphorus doping a semiconductor particle using ammonium phosphate. A p-doped silicon sphere is mixed with a diluted solution of ammonium phosphate having a predetermined concentration. These spheres are dried (16, 18), with the phosphorus then being diffused (20) into the sphere to create either a shallow or deep p-n junction. A good PSG glass layer is formed on the surface of the sphere during the diffusion process. A subsequent segregation anneal process is utilized to strip metal impurities from near the p-n junction into the glass layer. A subsequent HF strip procedure is then utilized to removed the PSG layer. Ammonium phosphate is not a restricted chemical, is inexpensive, and does not pose any special shipping, handling, or disposal requirement.

  5. Boron doping a semiconductor particle

    DOEpatents

    Stevens, Gary Don; Reynolds, Jeffrey Scott; Brown, Louanne Kay

    1998-06-09

    A method (10,30) of boron doping a semiconductor particle using boric acid to obtain a p-type doped particle. Either silicon spheres or silicon powder is mixed with a diluted solution of boric acid having a predetermined concentration. The spheres are dried (16), with the boron film then being driven (18) into the sphere. A melt procedure mixes the driven boron uniformly throughout the sphere. In the case of silicon powder, the powder is metered out (38) into piles and melted/fused (40) with an optical furnace. Both processes obtain a p-type doped silicon sphere with desired resistivity. Boric acid is not a restricted chemical, is inexpensive, and does not pose any special shipping, handling, or disposal requirements.

  6. 2010 Defects in Semiconductors GRC

    SciTech Connect

    Shengbai Zhang

    2011-01-06

    Continuing its tradition of excellence, this Gordon Conference will focus on research at the forefront of the field of defects in semiconductors. The conference will have a strong emphasis on the control of defects during growth and processing, as well as an emphasis on the development of novel defect detection methods and first-principles defect theories. Electronic, magnetic, and optical properties of bulk, thin film, and nanoscale semiconductors will be discussed in detail. In contrast to many conferences, which tend to focus on specific semiconductors, this conference will deal with point and extended defects in a broad range of electronic materials. This approach has proved to be extremely fruitful for advancing fundamental understanding in emerging materials such as wide-band-gap semiconductors, oxides, sp{sup 2} carbon based-materials, and photovoltaic/solar cell materials, and in understanding important defect phenomena such as doping bottleneck in nanostructures and the diffusion of defects and impurities. The program consists of about twenty invited talks and a number of contributed poster sessions. The emphasis should be on work which has yet to be published. The large amount of discussion time provides an ideal forum for dealing with topics that are new and/or controversial.

  7. Oxygen vacancy and dilute ferromagnetism of ZnGa2O4 doped with Co at the octahedral site

    NASA Astrophysics Data System (ADS)

    Nakai, Ikuo; Hisamatsu, Ryouhei; Li, Yingjie; Kurisu, Makio

    2016-05-01

    We report magnetism and structure of a diluted magnetic semiconductor Zn[Ga0.97Co0.03]2O4 preferentially doped with Co ions in the octahedral site of zinc gallate ZnGa2O4. Zn[Ga0.97Co0.03]2O4 has a small ferromagnetic component superimposed on a large paramagnetic contribution to the magnetization at room temperature, whereas ZnGa2O4 is diamagnetic. The X-ray powder diffraction confirms that both ZnGa2O4 and Zn[Ga0.97Co0.03]2O4 have a normal spinel structure (space group Fd-3m) without any impurity phases. From X-ray absorption fine structure measurements we find the following features in Zn[Ga0.97Co0.03]2O4; all of the Co dopants occupy the octahedral site, about half of which are divalent; around the Co cations there exist the oxygen vacancies and the local distortion of shrink in pair distance, while the local structure around Zn and Ga ions coincides with that expected from the X-ray diffraction. These features suggest that the local disorder including oxygen vacancies and distortions only around Co ions plays an important role in stabilizing the ferromagnetic order between some Co ions in Zn[Ga0.97Co0.03]2O4.

  8. Magnetic circular dichroism in the hard X-ray range

    NASA Astrophysics Data System (ADS)

    Rogalev, A.; Wilhelm, F.

    2015-12-01

    An overview of X-ray magnetic circular dichroism (XMCD) spectroscopy in the hard X-ray range is presented. A short historical overview shows how this technique has evolved from the early days of X-ray physics to become a workhorse technique in the modern magnetism research As with all X-ray spectroscopies, XMCD has the advantage of being element specific. Interpretation of the spectra based on magneto-optical sum rules can provide unique information about spin and orbital moment carried by absorbing atom in both amplitude and direction, can infer magnetic interactions from element selective magnetization curves, can allow separation of magnetic and non-magnetic components in heterogeneous systems. The review details the technology currently available for XMCD measurements in the hard X-ray range referring to the ESRF beamline ID12 as an example. The strengths of hard X-ray magnetic circular dichroism technique are illustrated with a wide variety of representative examples, such as actinide based ferromagnets, paramagnetism in metals, pure metallic nanoparticles, exchange spring magnets, half metallic ferromagnets, magnetism at interfaces, and dilute magnetic semiconductors. In this way, we aim to encourage researchers from various scientific communities to consider XMCD as a tool to understanding the electronic and magnetic properties of their samples.

  9. Photoelectrosynthesis at semiconductor electrodes

    SciTech Connect

    Nozik, A. J.

    1980-12-01

    The general principles of photoelectrochemistry and photoelectrosynthesis are reviewed and some new developments in photoelectrosynthesis are discussed. Topics include energetics of semiconductor-electrolyte interfaces(band-edge unpinning); hot carrier injection at illuminated semiconductor-electrolyte junctions; derivatized semiconductor electrodes; particulate photoelectrochemical systems; layered compounds and other new materials; and dye sensitization. (WHK)

  10. Photorefractive Semiconductors and Applications

    NASA Technical Reports Server (NTRS)

    Chen, Li-Jen; Luke, Keung L.

    1993-01-01

    Photorefractive semiconductors are attractive for information processing, becuase of fast material response, compatibility with semiconductor lasers, and availability of cross polarization diffraction for enhancing signal-to-noise ration. This paper presents recent experimental results on information processing using photorefractive GaAs, InP and CdTe, including image processing with semiconductor lasers.

  11. High field magnetotransport and point contact Andreev reflection measurements on CuCr{sub 2}Se{sub 4} and CuCr{sub 2}Se{sub 3}Br—Degenerate magnetic semiconductor single crystals

    SciTech Connect

    Borisov, K. Coey, J. M. D.; Stamenov, P.; Alaria, J.

    2014-05-07

    Single crystals of the metallically degenerate fully magnetic semiconductors CuCr{sub 2}Se{sub 4} and CuCr{sub 2}Se{sub 3}Br have been prepared by the Chemical Vapour Transport method, using either Se or Br as transport agents. The high-quality, millimetre-sized, octahedrally faceted, needle- and platelet-shaped crystals are characterised by means of high field magnetotransport (μ{sub 0}H≤ 14 T) and Point Contact Andreev Reflection. The relatively high spin polarisation observed |P|>0.56, together with the relatively low minority carrier effective mass of 0.25 m{sub e}, and long scattering time  10{sup −13} s, could poise these materials for integration in low- and close-to-room temperature minority injection bipolar heterojunction transistor demonstrations.

  12. Design and implementation of a 1-V transformer magnetic feedback low-noise amplifier (LNA) at 5-6 GHz, in a 90 nm complementary metal-oxide-semiconductor (CMOS) process

    NASA Astrophysics Data System (ADS)

    Kytonaki, Eleni-Sotiria; Simitsakis, Paschalis; Bazigos, Antonios; Papananos, Yannis

    2011-02-01

    In this study, a low-noise amplifier (LNA) suitable for low-voltage operation is presented. The LNA operates at a frequency range between 5 and 6 GHz. Its topology exploits magnetic feedback to achieve high reverse isolation and low noise performance without a significant degradation of the gain and linearity of the circuit. The design has been fabricated, considering full electrostatic discharge protection, in a modern 90 nm complementary metal-oxide-semiconductor process. The measured performance, at 5.4 GHz, shows a reverse isolation of -17.3 dB, a gain of 10.4 dB, a noise figure of 0.98 dB and an input intercept point of 1.4 dBm. The circuit dissipates 12.5 mW from a 1 V supply, while it occupies 0.162 mm2 of the die area.

  13. Unique Static Magnetic and Dynamic Electromagnetic Behaviors in Titanium Nitride/Carbon Composites Driven by Defect Engineering.

    PubMed

    Gong, Chunhong; Meng, Hongjie; Zhao, Xiaowei; Zhang, Xuefeng; Yu, Laigui; Zhang, Jingwei; Zhang, Zhijun

    2016-01-01

    Recently, the defect-induced static magnetic behaviours of nanomaterials have been a cutting-edge issue in diluted magnetic semiconductor materials. However, the dynamic magnetic properties of nanomaterials are commonly ignored if their bulk counterparts are non-magnetic. In the present research, titanium nitride-carbon (TiN/C) nanocomposites were found to exhibit both static and dynamic magnetic properties that vary in the opposite trend. Moreover, novel unconventional electromagnetic resonance behaviour was demonstrated in TiN/C systems, and their permeability and permittivity show similar trend. This is challenging for the traditional understanding of electromagnetism and makes it possible to achieve an appropriate balance between the permeability and permittivity simultaneously in a simple system. Hopefully, the results could provide some valuable clues to revealing the magnetism and electromagnetism of nanostructures. PMID:26739853

  14. Unique Static Magnetic and Dynamic Electromagnetic Behaviors in Titanium Nitride/Carbon Composites Driven by Defect Engineering

    PubMed Central

    Gong, Chunhong; Meng, Hongjie; Zhao, Xiaowei; Zhang, Xuefeng; Yu, Laigui; Zhang, Jingwei; Zhang, Zhijun

    2016-01-01

    Recently, the defect-induced static magnetic behaviours of nanomaterials have been a cutting-edge issue in diluted magnetic semiconductor materials. However, the dynamic magnetic properties of nanomaterials are commonly ignored if their bulk counterparts are non-magnetic. In the present research, titanium nitride-carbon (TiN/C) nanocomposites were found to exhibit both static and dynamic magnetic properties that vary in the opposite trend. Moreover, novel unconventional electromagnetic resonance behaviour was demonstrated in TiN/C systems, and their permeability and permittivity show similar trend. This is challenging for the traditional understanding of electromagnetism and makes it possible to achieve an appropriate balance between the permeability and permittivity simultaneously in a simple system. Hopefully, the results could provide some valuable clues to revealing the magnetism and electromagnetism of nanostructures. PMID:26739853

  15. Unique Static Magnetic and Dynamic Electromagnetic Behaviors in Titanium Nitride/Carbon Composites Driven by Defect Engineering

    NASA Astrophysics Data System (ADS)

    Gong, Chunhong; Meng, Hongjie; Zhao, Xiaowei; Zhang, Xuefeng; Yu, Laigui; Zhang, Jingwei; Zhang, Zhijun

    2016-01-01

    Recently, the defect-induced static magnetic behaviours of nanomaterials have been a cutting-edge issue in diluted magnetic semiconductor materials. However, the dynamic magnetic properties of nanomaterials are commonly ignored if their bulk counterparts are non-magnetic. In the present research, titanium nitride-carbon (TiN/C) nanocomposites were found to exhibit both static and dynamic magnetic properties that vary in the opposite trend. Moreover, novel unconventional electromagnetic resonance behaviour was demonstrated in TiN/C systems, and their permeability and permittivity show similar trend. This is challenging for the traditional understanding of electromagnetism and makes it possible to achieve an appropriate balance between the permeability and permittivity simultaneously in a simple system. Hopefully, the results could provide some valuable clues to revealing the magnetism and electromagnetism of nanostructures.

  16. Unitary lens semiconductor device

    DOEpatents

    Lear, K.L.

    1997-05-27

    A unitary lens semiconductor device and method are disclosed. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors. 9 figs.

  17. Unitary lens semiconductor device

    DOEpatents

    Lear, Kevin L.

    1997-01-01

    A unitary lens semiconductor device and method. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors.

  18. Spectroscopy of single emitters using a scanning optical microscope in a dilution refrigerator

    NASA Astrophysics Data System (ADS)

    Ghosh, Saikat; Heikes, Colin; Wise, Frank; Gaeta, Alexander; Ralph, Dan

    2010-03-01

    We report the design and implementation of a fiber-based optical scanning microscope, capable of operating at temperatures down to 20 mK and in magnetic fields in excess of 9 Tesla, with sub-micron spatial resolution and ultra-low light levels. A home-made modular, piezo-based scanning head is at the heart of the design, with optical fibers coupling light in and out of a commercial dilution refrigerator. The microscope can be operated both in transmission and reflection modes. In the transmission mode, we can analyze the polarization of the light transmitted through the sample down to femto-Watt light levels, using detectors and polarizers integrated with the scanning head inside the refrigerator. In the reflection mode, the instrument can be operated in a confocal geometry in conjunction with single photon counting modules to measure anti-bunching and the decay times of fluorescent photons. We are using this microscope to study individual nano- emitters, focusing initially on spin dynamics in semiconductor quantum dots.

  19. Crystallization of a dilute atomic dipolar condensate

    NASA Astrophysics Data System (ADS)

    Bisset, Russell; Blakie, Blair

    2016-05-01

    A recent experiment found that a dilute BEC of highly-magnetic dysprosium atoms may spontaneously break up into a crystal of droplets, a process reminiscent of the Rosensweig instability [ArXiv:1508.05007]. We dynamically simulate this scenario and find that the standard dipolar Gross-Pitaevskii equation (GPE) cannot explain such a droplet crystal. Indeed, the GPE predicts too much heating during the violent droplet formation, and a droplet lifetime that is much shorter than observed in the experiment. We investigate the requisite properties of the unknown stabilization mechanism, and find that an effective repulsive interaction with a higher order density dependence than the usual two-body interactions is required to quantitatively reproduce the experimental results.

  20. Hydrogen effect on electronic and magnetic properties of Cd1-xMnxTe: Ab initio study

    NASA Astrophysics Data System (ADS)

    Larabi, A.; Merad, G.; Abdelaoui, I.; Sari, A.

    2016-07-01

    Hydrogen effect on electronic and magnetic properties of diluted magnetic semiconductor (DMS) Cd1-xMnxTe for x composition of 0.125 has been investigated using the projected augmented wave (PAW) based on density functional theory (DFT) formalism within the generalized gradient approximation (GGA). The results show that the Mn dopant is spin-polarized with magnetic moment of 4.189 μB per Mn atom at x≈0.125. The calculated formation energies indicate that the hydrogen is not stable in CdTe and the lowest energy position for H is at the Cd-Mn bond center in Cd0.875Mn0.125Te. We find also that the existence of interstitial hydrogen decreases the magnetic moment of Cd0.875Mn0.125Te diluted magnetic semiconductor. From the calculated density of state, we observed that the presence of hydrogen does not cause a change in electronic properties of Cd0.875Mn0.125Te.

  1. The Effect of SF6 dilution in an Argon plasma

    NASA Astrophysics Data System (ADS)

    Koirala, Sudip; Gordon, Matt

    2010-02-01

    Plasma etching is widely used in semiconductor industries. There have been extensive studies in the dilution of rare gases; however, limited studies are found in the dilution of electronegative gases. In this work, SF6 content is varied from 5% to 60% in an Ar plasma in a deep reactive ion etching system. A Langmuir probe is used to measure electron temperature (Te), electron density (ne), and electron energy distribution function (eedf). Te decreases monotonically with increasing SF6 at first, and then increases for SF6 content greater than 20%. This increase is attributed to the loss of low energy electrons in attachment and high energy electrons in excitation and ionization. As the content of SF6 is increased above 20%, the dissociation of SF6 increases and most of the low energy electrons are lost in attachment and hence the average electron temperature increases. ne decreases by an order of magnitude as the SF6 dilution is increased from 5% to 60%. eedf shows that the distribution shifts towards high energy with the increase of SF6 content, which is because of the depletion of low energy electrons. )

  2. The Physics of Semiconductors

    NASA Astrophysics Data System (ADS)

    Grundmann, Marius

    The historic development of semiconductor physics and technology began in the second half of the 19th century. Interesting discussions of the early history of the physics and chemistry of semiconductors can be found in treatises of G. Busch [2] and Handel [3]. The history of semiconductor industry can be followedin the text of Morris [4] and Holbrook et al. [5]. In 1947, the realization of the transistor was the impetus to a fast-paced development that created the electronics and photonics industries. Products founded on the basis of semiconductor devices such as computers (CPUs, memories), optical-storage media (lasers for CD, DVD), communication infrastructure (lasers and photodetectors for optical-fiber technology, high frequency electronics for mobile communication), displays (thin film transistors, LEDs), projection (laser diodes) and general lighting (LEDs) are commonplace. Thus, fundamental research on semiconductors and semiconductor physics and its offspring in the form of devices has contributed largely to the development of modern civilization and culture.

  3. Magnetic-field-induced photocurrent in metal-dielectric-semiconductor heterostructures based on cobalt nanoparticles SiO2(Co)/GaAs

    NASA Astrophysics Data System (ADS)

    Pavlov, V. V.; Lutsev, L. V.; Usachev, P. A.; Astretsov, A. A.; Stognij, A. I.; Novitskii, N. N.; Pisarev, R. V.

    2016-02-01

    Magnetic-field influence on photocurrent in heterostructures of silicon dioxide films with cobalt nanoparticles SiO2(Co) grown on gallium arsenide GaAs substrate has been studied in the avalanche regime at room temperature. High values of magnetic-field-induced photocurrent were found in the vicinity and above the GaAs bandgap of ∼1.4 eV. For photon energies E > 1.4 eV the photocurrent significantly increases, while the avalanche process is suppressed by the magnetic field, and the current flowing through the heterostructure decreases. The photocurrent is enhanced in the SiO2(Co 60 at%)/GaAs heterostructure at the magnetic field H=1.65 kOe by factor of about 10 for the photon energy E=1.5 eV. This phenomenon is explained by a model based on electronic transitions in magnetic fields with the spin-dependent recombination process at deep impurity centers in the SiO2(Co)/GaAs interface region.

  4. Semiconductor microcavity lasers

    SciTech Connect

    Gourley, P.L.; Wendt, J.R.; Vawter, G.A.; Warren, M.E.; Brennan, T.M.; Hammons, B.E.

    1994-02-01

    New kinds of semiconductor microcavity lasers are being created by modern semiconductor technologies like molecular beam epitaxy and electron beam lithography. These new microcavities exploit 3-dimensional architectures possible with epitaxial layering and surface patterning. The physical properties of these microcavities are intimately related to the geometry imposed on the semiconductor materials. Among these microcavities are surface-emitting structures which have many useful properties for commercial purposes. This paper reviews the basic physics of these microstructured lasers.

  5. Influence of temperature on spin polarization dynamics in dilute nitride semiconductors—Role of nonparamagnetic centers

    SciTech Connect

    Baranowski, M.; Misiewicz, J.

    2015-10-21

    We report theoretical studies of spin polarization dynamics in dilute nitride semiconductors. We develop a commonly used rate equation model [Lagarde et al., Phys. Status Solidi A 204, 208 (2007) and Kunold et al. Phys. Rev. B 83, 165202 (2011)] to take into account the influence of shallow localizing states on the temperature dependence of spin polarization dynamics and a spin filtering effect. Presented investigations show that the experimentally observed temperature dependence of a spin polarization lifetime in dilute nitrides can be related to the electron capture process by shallow localizing states without paramagnetic properties. This process reduces the efficiency of spin filtering effect by deep paramagnetic centers, especially at low temperatures.

  6. Semiconductor bridge (SCB) detonator

    DOEpatents

    Bickes, Jr., Robert W.; Grubelich, Mark C.

    1999-01-01

    The present invention is a low-energy detonator for high-density secondary-explosive materials initiated by a semiconductor bridge igniter that comprises a pair of electrically conductive lands connected by a semiconductor bridge. The semiconductor bridge is in operational or direct contact with the explosive material, whereby current flowing through the semiconductor bridge causes initiation of the explosive material. Header wires connected to the electrically-conductive lands and electrical feed-throughs of the header posts of explosive devices, are substantially coaxial to the direction of current flow through the SCB, i.e., substantially coaxial to the SCB length.

  7. Semiconductor bridge (SCB) detonator

    DOEpatents

    Bickes, R.W. Jr.; Grubelich, M.C.

    1999-01-19

    The present invention is a low-energy detonator for high-density secondary-explosive materials initiated by a semiconductor bridge (SCB) igniter that comprises a pair of electrically conductive lands connected by a semiconductor bridge. The semiconductor bridge is in operational or direct contact with the explosive material, whereby current flowing through the semiconductor bridge causes initiation of the explosive material. Header wires connected to the electrically-conductive lands and electrical feed-throughs of the header posts of explosive devices, are substantially coaxial to the direction of current flow through the SCB, i.e., substantially coaxial to the SCB length. 3 figs.

  8. Interconnected semiconductor devices

    DOEpatents

    Grimmer, Derrick P.; Paulson, Kenneth R.; Gilbert, James R.

    1990-10-23

    Semiconductor layer and conductive layer formed on a flexible substrate, divided into individual devices and interconnected with one another in series by interconnection layers and penetrating terminals.

  9. Electronic structure of magnetic semiconductor CdCr{sub 2}Te{sub 4}: A possible spin-dependent symmetry filter

    SciTech Connect

    Sims, H.; Butler, W. H.; Ramasamy, K.; Gupta, A.

    2013-11-04

    We present a theoretical investigation of the electronic and magnetic structure of spinel CdCr{sub 2}Te{sub 4} using density functional theory, its extensions via onsite Hubbard U interactions, and a screened-hybrid-functional exchange potential. We find that the ground state is semiconducting within the latter approach, and within this magnetic-semiconducting system, we compute the complex band structure, finding a slowly decaying evanescent Δ{sup ~}{sub 1} state possibly suitable for realizing a spin-dependent symmetry filter effect.

  10. Voltage controlled magnetism in 3d transitional metals

    NASA Astrophysics Data System (ADS)

    Wang, Weigang

    2015-03-01

    Despite having attracted much attention in multiferroic materials and diluted magnetic semiconductors, the impact of an electric field on the magnetic properties remains largely unknown in 3d transitional ferromagnets (FMs) until recent years. A great deal of effort has been focused on the voltage-controlled magnetic anisotropy (VCMA) effect where the modulation of anisotropy field is understood by the change of electron density among different d orbitals of FMs in the presence of an electric field. Here we demonstrate another approach to alter the magnetism by electrically controlling the oxidation state of the 3d FM at the FM/oxide interface. The thin FM film sandwiched between a heavy metal layer and a gate oxide can be reversibly changed from an optimally-oxidized state with a strong perpendicular magnetic anisotropy to a metallic state with an in-plane magnetic anisotropy, or to a fully-oxidized state with nearly zero magnetization, depending on the polarity and time duration of the applied electric fields. This is a voltage controlled magnetism (VCM) effect, where both the saturation magnetization and anisotropy field of the 3d FM layer can be simultaneously controlled by voltage in a non-volatile fashion. We will also discuss the impact of this VCM effect on magnetic tunnel junctions and spin Hall switching experiments. This work, in collaboration with C. Bi, Y.H. Liu, T. Newhouse-Illige, M. Xu, M. Rosales, J.W. Freeland, O. Mryasov, S. Zhang, and S.G.E. te Velthuis, was supported in part by NSF (ECCS-1310338) and by C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program, sponsored by MARCO and DARPA.

  11. Electronic and magnetic properties of Co doped MoS2 monolayer

    PubMed Central

    Wang, Yiren; Li, Sean; Yi, Jiabao

    2016-01-01

    First principle calculations are employed to calculate the electronic and magnetic properties of Co doped MoS2 by considering a variety of defects including all the possible defect complexes. The results indicate that pristine MoS2 is nonmagnetic. The materials with the existence of S vacancy or Mo vacancy alone are non-magnetic either. Further calculation demonstrates that Co substitution at Mo site leads to spin polarized state. Two substitutional CoMo defects tend to cluster and result in the non-magnetic behaviour. However, the existence of Mo vacancies leads to uniform distribution of Co dopants and it is energy favourable with ferromagnetic coupling, resulting in an intrinsic diluted magnetic semiconductor. PMID:27052641

  12. Electronic and magnetic properties of Co doped MoS2 monolayer

    NASA Astrophysics Data System (ADS)

    Wang, Yiren; Li, Sean; Yi, Jiabao

    2016-04-01

    First principle calculations are employed to calculate the electronic and magnetic properties of Co doped MoS2 by considering a variety of defects including all the possible defect complexes. The results indicate that pristine MoS2 is nonmagnetic. The materials with the existence of S vacancy or Mo vacancy alone are non-magnetic either. Further calculation demonstrates that Co substitution at Mo site leads to spin polarized state. Two substitutional CoMo defects tend to cluster and result in the non-magnetic behaviour. However, the existence of Mo vacancies leads to uniform distribution of Co dopants and it is energy favourable with ferromagnetic coupling, resulting in an intrinsic diluted magnetic semiconductor.

  13. Science Notes: Dilution of a Weak Acid

    ERIC Educational Resources Information Center

    Talbot, Christopher; Wai, Chooi Khee

    2014-01-01

    This "Science note" arose out of practical work involving the dilution of ethanoic acid, the measurement of the pH of the diluted solutions and calculation of the acid dissociation constant, K[subscript a], for each diluted solution. The students expected the calculated values of K[subscript a] to be constant but they found that the…

  14. The extrinsic hysteresis behavior of dilute binary ferrofluids.

    PubMed

    Lin, Lihua; Li, Jian; Lin, Yueqiang; Liu, Xiaodong; Chen, Longlong; Li, Junming; Li, Decai

    2014-10-01

    We report on the magnetization behavior of dilute binary ferrofluids based on γ-Fe(2)O(3)/Ni(2)O(3) composite nanoparticles (A particles), with diameter about 11 nm, and ferrihydrite (Fe(5)O(7)(OH) ・4H2O) nanoparticles (B particles), with diameter about 6 nm. The results show that for the binary ferrofluids with A-particle volume fraction φ(A) = 0.2% and B-particle volume fractions φ(B) = 0.1% and φ(B) = 0.6%, the magnetization curves exhibit quasi-magnetic hysteresis behavior. The demagnetizing curves coincide with the magnetizing curves at high fields. However, for single γ-Fe(2)O(3)/Ni(2)O(3) ferrofluids with φ(A) = 0.2% and binary ferrofluids with φ(A) = 0.2% and φ(B) = 1.0%, the magnetization curves do not behave in this way. Additionally, at high field (750 kA/m), the binary ferrofluid with φ(B) = 1.0% has the smallest magnetization. From the model-of-chain theory, the extrinsic hysteresis behavior of these samples is attributed to the field-induced effects of pre-existing A particle chains, which involve both Brownian rotation of the chains'moments and a Néel rotation of the particles' moments in the chains. The loss of magnetization for the ferrofluids with φ(B) = 1.0% is attributed to pre-existing ring-like A-particle aggregates. These magnetization behaviors of the dilute binary ferrofluids not only depend on features of the strongly magnetic A-particle system, but also modifications of the weaker magnetic B-particle system. PMID:25365919

  15. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Formation of the intermediate semiconductor layer for the Ohmic contact to silicon carbide using Germanium implantation

    NASA Astrophysics Data System (ADS)

    Guo, Hui; Wang, Yue-Hu; Zhang, Yu-Ming; Qiao, Da-Yong; Zhang, Yi-Men

    2009-10-01

    By formation of an intermediate semiconductor layer (ISL) with a narrow band gap at the metallic contact/SiC interface, this paper realises a new method to fabricate the low-resistance Ohmic contacts for SiC. An array of transfer length method (TLM) test patterns is formed on N-wells created by P+ ion implantation into Si-faced p-type 4H-SiC epilayer. The ISL of nickel-metal Ohmic contacts to n-type 4H-SiC could be formed by using Germanium ion implantation into SiC. The specific contact resistance ρc as low as 4.23 × 10-5 Ωcm2 is achieved after annealing in N2 at 800 °C for 3 min, which is much lower than that (> 900 °C) in the typical SiC metallisation process. The sheet resistance Rsh of the implanted layers is 1.5 kΩ/□. The technique for converting photoresist into nanocrystalline graphite is used to protect the SiC surface in the annealing after Ge+ ion implantations.

  16. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: A Novel Fully Depleted Air AlN Silicon-on-Insulator Metal-Oxide-Semiconductor Field Effect Transistor

    NASA Astrophysics Data System (ADS)

    Yang, Yuan; Gao, Yong; Gong, Peng-Liang

    2008-08-01

    A novel fully depleted air AlN silicon-on-insulator (SOI) metal-oxide-semiconductor field effect transistor (MOS-FET) is presented, which can eliminate the self-heating effect and solve the problem that the off-state current of SOI MOSFETs increases and the threshold voltage characteristics become worse when employing a high thermal conductivity material as a buried layer. The simulation results reveal that the lattice temperature in normal SOI devices is 75 K higher than the atmosphere temperature, while the lattice temperature is just 4K higher than the atmosphere temperature resulting in less severe self-heating effect in air AlN SOI MOSFETs and AlN SOI MOSFETs. The on-state current of air AlN SOI MOSFETs is similar to the AlN SOI structure, and improves 12.3% more than that of normal SOI MOSFETs. The off-state current of AlN SOI is 6.7 times of normal SOI MOSFETs, while the counterpart of air AlN SOI MOSFETs is lower than that of SOI MOSFETs by two orders of magnitude. The threshold voltage change of air AlN SOI MOSFETs with different drain voltage is much less than that of AlN SOI devices, when the drain voltage is biased at 0.8 V, this difference is 28mV, so the threshold voltage change induced by employing high thermal conductivity material is cured.

  17. Half-metallic ferromagnetic properties of Cr- and V-doped AlP semiconductors

    NASA Astrophysics Data System (ADS)

    Boutaleb, M.; Doumi, B.; Tadjer, A.; Sayede, A.

    2016-01-01

    Using the full-potential linearized augmented plane-wave (FP-LAPW) calculations with generalized gradient approximation functional (GGA), we investigated the structural, electronic and magnetic properties of the family compounds AlP as ternary diluted semiconductors (DMS)s Al1-x(TM=Cr,V)xP with concentration of 0.25 and 0.125 in zinc blende phase (B3). The interaction of 3d orbital of transition metal with the 3p states of the four phosphorus atoms who occupy the summits of the tetrahedron resulting from SP3 hybridization, stabilize more the phenomena of magnetization by the effect of Zener's p-d exchange. The analyses of electronic and magnetic properties using the total and partial density of state and bands structure show that Al1-xCrxP and Al1-xVxP are spin-polarized with a half-metallic band gap. We seem that these materials will be among the good candidates for spintronic applications.

  18. Exciton Kinetics in Strained II-Vi Semiconductor Multiple Quantum Wells.

    NASA Astrophysics Data System (ADS)

    Hefetz, Yaron

    1987-09-01

    Two groups of wide gap II-VI semiconductor superlattices based on ZnSe/Zn(,1-x)Mn(,x)Se and CdTe/ZnTe were investigated using CW and time-resolved photoluminescence, excitation, reflectance, and photomodulated reflectance spectroscopy at various temperatures and under an external magnetic field. All these lattice mismatch strained layer structures were grown by MBE technique and exhibit strong excitonic photoluminescence at low temperatures. By studying the dynamics of the exciton recombination processes, the role of strain, quantum confinement and localization effects were revealed. In the CdTe/ZnTc system where the lattice mismatch is (DELTA)a/a (TURNEQ) 6% the inhomogeneously broadened ((TURN)40 mev) luminescence line is governed by excitonic localization in well width fluctuations. Exchange interactions of the carriers with the Mn('++) ions in the dilute magnetic semiconductor Zn(,1-x)Mn(,x)Se in thin film and the barrier of the MQW structures influence their optical behavior in an exernal magnetic field. "Giant" Zeeman splittings of up to (TURN)10 mev/Tesla were measured in samples with moderate Mn concentration (x = .23). Antiferromagnetic interaction reduces these splittings in samples with higher Mn concentrations. In observing the time evolution of the carrier in Zn(,1-x)Mn(,x)Se MQW we found that the capture time of these carriers into the well is on the order of 1 psec but the last stages of thermalization, exciton formations and localization is (TURN)70 ps. The fast capture of electrons and holes into the quantum wells bypass the energy transfer into the Mn internal transition that is responsible to the efficient "yellow" luminescence in ZnMnSe mixed crystals.

  19. Element-resolved orbital polarization in (III,Mn)As ferromagnetic semiconductors from K -edge x-ray magnetic circular dichroism

    NASA Astrophysics Data System (ADS)

    Wadley, P.; Freeman, A. A.; Edmonds, K. W.; van der Laan, G.; Chauhan, J. S.; Campion, R. P.; Rushforth, A. W.; Gallagher, B. L.; Foxon, C. T.; Wilhelm, F.; Smekhova, A. G.; Rogalev, A.

    2010-06-01

    Using x-ray magnetic circular dichroism (XMCD), we determine the element-specific character and polarization of unoccupied states near the Fermi level in (Ga,Mn)As and (In,Ga,Mn)As thin films. The XMCD at the AsK absorption edge consists of a single peak located on the low-energy side of the edge, which increases with the concentration of ferromagnetic Mn moments. The XMCD at the MnK edge is more detailed and is strongly concentration dependent, which is interpreted as a signature of hole localization for low Mn doping. The results indicate a markedly different character of the polarized holes in low-doped insulating and high-doped metallic films, with a transfer of the hole orbital magnetic moment from Mn to As sites on crossing the metal-insulator transition.

  20. Semiconductor materials: From gemstone to semiconductor

    NASA Astrophysics Data System (ADS)

    Nebel, Christoph E.

    2003-07-01

    For diamond to be a viable semiconductor it must be possible to change its conductivity by adding impurities - known as dopants. With the discovery of a new dopant that generates electron conductivity at room temperature, diamond emerges as an electronic-grade material.

  1. Dilute acid and autohydrolysis pretreatment.

    PubMed

    Yang, Bin; Wyman, Charles E

    2009-01-01

    Exposure of cellulosic biomass to temperatures of about 120-210 degrees C can remove most of the hemicellulose and produce cellulose-rich solids from which high glucose yields are possible with cellulase enzymes. Furthermore, the use of dilute sulfuric acid in this pretreatment operation can increase recovery of hemicellulose sugars substantially to about 85-95% of the maximum possible versus only about 65% if no acid is employed. The use of small-diameter tubes makes it possible to employ high solids concentrations similar to those preferred for commercial operations, with rapid heat-up, good temperature control, and accurate closure of material balances. Mixed reactors can be employed to pretreat larger amounts of biomass than possible in such small-diameter tubes, but solids concentrations are limited to about 15% or less to provide uniform temperatures. Pretreatment of large amounts of biomass at high solids concentrations is best carried out using direct steam injection and rapid pressure release, but closure of material balances in such "steam gun" devices is more difficult. Although flow of water alone or containing dilute acid is not practical commercially, such flow-through configurations provide valuable insight into biomass deconstruction kinetics not possible in the batch tubes, mixed reactors, or steam gun systems. PMID:19768619

  2. A Microgravity Helium Dilution Cooler

    NASA Technical Reports Server (NTRS)

    Roach, Pat R.; Sperans, Joel (Technical Monitor)

    1994-01-01

    We are developing a He-3-He-4 dilution cooler to operate in microgravity. It uses charcoal adsorption pumps and heaters for its operation; it has no moving parts. It currently operates cyclically to well below 0.1 K and we have designed a version to operate continuously. We expect that the continuous version will be able to provide the long-duration cooling that many experiments need at temperatures down to 0.040 K. More importantly, such a dilution cooler could provide the precooling that enables the use of adiabatic demagnetization techniques that can reach temperatures below 0.001 K. At temperatures below 0.002 K many fascinating microgravity experiments on superfluid He-3 become possible. Among the possibilities are: research into a superfluid He-3 gyroscope, study of the nucleation of the B-phase of superfluid He-3 when the sample is floating out of contact with walls, study of the anisotropy of the surface tension of the B-phase, and NMR experiments on tiny free-floating clusters of superfluid He-3 atoms that should model the shell structure of nuclei.

  3. Magnetoviscosity in dilute ferrofluids from rotational brownian dynamics simulations.

    PubMed

    Soto-Aquino, D; Rinaldi, C

    2010-10-01

    Ferrofluids are suspensions of magnetic nanoparticles which respond to imposed magnetic fields by changing their viscosity without losing their fluidity. Prior work on modeling the behavior of ferrofluids has focused on using phenomenological suspension-scale continuum equations. A disadvantage of this approach is the controversy surrounding the equation describing the rate of change of the ferrofluid magnetization, the so-called magnetization relaxation equation. In this contribution the viscosity of dilute suspensions of spherical magnetic nanoparticles suspended in a Newtonian fluid and under applied shear and constant magnetic fields is studied through rotational brownian dynamics simulations. Simulation results are compared with the predictions of suspension-scale models based on three magnetization relaxation equations. Excellent agreement is observed between simulation results and the predictions of an equation due to Martsenyuk, Raikher, and Shliomis. Good qualitative agreement is observed with predictions of other equations, although these models fail to accurately predict the magnitude and shear rate dependence of the magnetic-field-dependent effective viscosity. Finally, simulation results over a wide range of conditions are collapsed into master curves using a Mason number defined based on the balance of hydrodynamic and magnetic torques. PMID:21230393

  4. Electronic structure study of wide band gap magnetic semiconductor (La0.6Pr0.4)0.65Ca0.35MnO3 nanocrystals in paramagnetic and ferromagnetic phases

    NASA Astrophysics Data System (ADS)

    Dwivedi, G. D.; Joshi, Amish G.; Kumar, Shiv; Chou, H.; Yang, K. S.; Jhong, D. J.; Chan, W. L.; Ghosh, A. K.; Chatterjee, Sandip

    2016-04-01

    X-ray circular magnetic dichroism (XMCD), X-ray photoemission spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) techniques were used to study the electronic structure of nanocrystalline (La0.6Pr0.4)0.65Ca0.35MnO3 near Fermi-level. XMCD results indicate that Mn3+ and Mn4+ spins are aligned parallel to each other at 20 K. The low M-H hysteresis curve measured at 5 K confirms ferromagnetic ordering in the (La0.6Pr0.4)0.65Ca0.35MnO3 system. The low temperature valence band XPS indicates that coupling between Mn3d and O2p is enhanced and the electronic states near Fermi-level have been suppressed below TC. The valence band UPS also confirms the suppression of electronic states near Fermi-level below Curie temperature. UPS near Fermi-edge shows that the electronic states are almost absent below 0.5 eV (at 300 K) and 1 eV (at 115 K). This absence clearly demonstrates the existence of a wide band-gap in the system since, for hole-doped semiconductors, the Fermi-level resides just above the valence band maximum.

  5. Reduction in the interface-states density of metal-oxide-semiconductor field-effect transistors fabricated on high-index Si (114) surfaces by using an external magnetic field

    SciTech Connect

    Molina, J. De La Hidalga, J.; Gutierrez, E.

    2014-08-14

    After fabrication of Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices on high-index silicon (114) surfaces, their threshold voltage (Vth) and interface-states density (Dit) characteristics were measured under the influence of an externally applied magnetic field of B = 6 μT at room temperature. The electron flow of the MOSFET's channel presents high anisotropy on Si (114), and this effect is enhanced by using an external magnetic field B, applied parallel to the Si (114) surface but perpendicular to the electron flow direction. This special configuration results in the channel electrons experiencing a Lorentzian force which pushes the electrons closer to the Si (114)-SiO{sub 2} interface and therefore to the special morphology of the Si (114) surface. Interestingly, Dit evaluation of n-type MOSFETs fabricated on Si (114) surfaces shows that the Si (114)-SiO{sub 2} interface is of high quality so that Dit as low as ∼10{sup 10 }cm{sup −2}·eV{sup −1} are obtained for MOSFETs with channels aligned at specific orientations. Additionally, using both a small positive Vds ≤ 100 mV and B = 6 μT, the former Dit is reduced by 35% in MOSFETs whose channels are aligned parallel to row-like nanostructures formed atop Si (114) surfaces (channels having a 90° rotation), whereas Dit is increased by 25% in MOSFETs whose channels are aligned perpendicular to these nanostructures (channels having a 0° rotation). From these results, the special morphology of a high-index Si (114) plane having nanochannels on its surface opens the possibility to reduce the electron-trapping characteristics of MOSFET devices having deep-submicron features and operating at very high frequencies.

  6. A comprehensive study of the magnetic, structural, and transport properties of the III-V ferromagnetic semiconductor InMnP

    SciTech Connect

    Khalid, M.; Hübner, R.; Baehtz, C.; Skorupa, W.; Zhou, Shengqiang; Gao, Kun; Helm, M.; Weschke, E.; Gordan, O.; Salvan, G.; Zahn, D. R. T.

    2015-01-28

    The manganese induced magnetic, electrical, and structural modification in InMnP epilayers, prepared by Mn ion implantation and pulsed laser annealing, are investigated in the following work. All samples exhibit clear hysteresis loops and strong spin polarization at the Fermi level. The degree of magnetization, the Curie temperature, and the spin polarization depend on the Mn concentration. The bright-field transmission electron micrographs show that InP samples become almost amorphous after Mn implantation but recrystallize after pulsed laser annealing. We did not observe an insulator-metal transition in InMnP up to a Mn concentration of 5 at. %. Instead all InMnP samples show insulating characteristics up to the lowest measured temperature. Magnetoresistance results obtained at low temperatures support the hopping conduction mechanism in InMnP. We find that the Mn impurity band remains detached from the valence band in InMnP up to 5 at. % Mn doping. Our findings indicate that the local environment of Mn ions in InP is similar to GaMnAs, GaMnP, and InMnAs; however, the electrical properties of these Mn implanted III-V compounds are different. This is one of the consequences of the different Mn binding energy in these compounds.

  7. Resistance transition assisted geometry enhanced magnetoresistance in semiconductors

    SciTech Connect

    Luo, Zhaochu; Zhang, Xiaozhong

    2015-05-07

    Magnetoresistance (MR) reported in some non-magnetic semiconductors (particularly silicon) has triggered considerable interest owing to the large magnitude of the effect. Here, we showed that MR in lightly doped n-Si can be significantly enhanced by introducing two diodes and proper design of the carrier path [Wan, Nature 477, 304 (2011)]. We designed a geometrical enhanced magnetoresistance (GEMR) device whose room-temperature MR ratio reaching 30% at 0.065 T and 20 000% at 1.2 T, respectively, approaching the performance of commercial MR devices. The mechanism of this GEMR is: the diodes help to define a high resistive state (HRS) and a low resistive state (LRS) in device by their openness and closeness, respectively. The ratio of apparent resistance between HRS and LRS is determined by geometry of silicon wafer and electrodes. Magnetic field could induce a transition from LRS to HRS by reshaping potential and current distribution among silicon wafer, resulting in a giant enhancement of intrinsic MR. We expect that this GEMR could be also realized in other semiconductors. The combination of high sensitivity to low magnetic fields and large high-field response should make this device concept attractive to the magnetic field sensing industry. Moreover, because this MR device is based on a conventional silicon/semiconductor platform, it should be possible to integrate this MR device with existing silicon/semiconductor devices and so aid the development of silicon/semiconductor-based magnetoelectronics. Also combining MR devices and semiconducting devices in a single Si/semiconductor chip may lead to some novel devices with hybrid function, such as electric-magnetic-photonic properties. Our work demonstrates that the charge property of semiconductor can be used in the magnetic sensing industry, where the spin properties of magnetic materials play a role traditionally.

  8. Semiconductor sensor embedded microfluidic chip for protein biomarker detection using a bead-based immunoassay combined with deoxyribonucleic acid strand labeling.

    PubMed

    Lin, Yen-Heng; Peng, Po-Yu

    2015-04-15

    Two major issues need to be addressed in applying semiconductor biosensors to detecting proteins in immunoassays. First, the length of the antibody on the sensor surface surpasses the Debye lengths (approximately 1 nm, in normal ionic strength solution), preventing certain specifically bound proteins from being tightly attached to the sensor surface. Therefore, these proteins do not contribute to the sensor's surface potential change. Second, these proteins carry a small charge and can be easily affected by the pH of the surrounding solution. This study proposes a magnetic bead-based immunoassay using a secondary antibody to label negatively charged DNA fragments for signal amplification. An externally imposed magnetic force attaches the analyte tightly to the sensor surface, thereby effectively solving the problem of the analyte protein's distance to the sensor surface surpassing the Debye lengths. In addition, a normal ion intensity buffer can be used without dilution for the proposed method. Experiments revealed that the sensitivity can be improved by using a longer DNA fragment for labeling and smaller magnetic beads as solid support for the antibody. By using a 90 base pair DNA label, the signal was 15 times greater than that without labeling. In addition, by using a 120 nm magnetic bead, a minimum detection limit of 12.5 ng mL(-1) apolipoprotein A1 can be measured. Furthermore, this study integrates a semiconductor sensor with a microfluidic chip. With the help of microvalves and micromixers in the chip, the length of the mixing step for each immunoassay has been reduced from 1h to 20 min, and the sample volume has been reduced from 80 μL to 10 μL. In practice, a protein biomarker in a urinary bladder cancer patient's urine was successfully measured using this technique. This study provides a convenient and effective method to measure protein using a semiconductor sensor. PMID:25818137

  9. Structure, stability and magnetism of cobalt doped (ZnO)n clusters.

    PubMed

    Yang, Jack; Zhang, Y B; Li, Sean

    2011-03-01

    Clusters of magnetic impurities are believed to play an important role in retaining ferromagnetism in diluted magnetic semiconductors (DMS), the origin of which has been a long debated issue. Controlling the dopant homogeneity in magnetic semiconductors is therefore a critical issue for the fabrication of high performance DMS. The current paper presents a first principle study on the stability and magnetic properties of Co doped (ZnO)n (n = 12 and 15) clusters using density functional theory. The results show that cobalt ions in these clusters tend to increase their stabilities by maximizing their co-ordination numbers to oxygen. This will likely to be the case for (ZnO)n clusters with n other than 12 and 15 in order for Co to reside in a stable local crystal field. Expansive (shrinkage) stress is introduced when cobalt resides in exohedral substitutional (endohedral interstitial) sites; such strain can be offset by the cluster deformation. Bidoped cluster is found to be unstable due to the increase of system strain energy. All the doped clusters were found to preserve 3 microg of magnetic moments from Co in the overall clusters, but with part of the local moments on cobalt re-distributed onto neighboring oxygen atoms. Current findings may provide a better understanding on the structural chemistry of magnetic dopants in nanocrystallined DMS materials. PMID:21449427

  10. Contrasting effect of La substitution on the magnetic moment direction in the Kondo semiconductors Ce T2Al10 (T =Ru ,Os )

    NASA Astrophysics Data System (ADS)

    Adroja, D. T.; Hillier, A. D.; Ritter, C.; Bhattacharyya, A.; Khalyavin, D. D.; Strydom, A. M.; Peratheepan, P.; Fâk, B.; Koza, M. M.; Kawabata, J.; Yamada, Y.; Okada, Y.; Muro, Y.; Takabatake, T.; Taylor, J. W.

    2015-09-01

    The opening of a spin gap in the orthorhombic compounds Ce T2Al10 (T =Ru andOs ) is followed by antiferromagnetic ordering at TN=27 and 28.5 K, respectively, with a small ordered moment (0.29 -0.34 μB ) along the c axis, which is not an easy axis of the crystal field (CEF). In order to investigate how the moment direction and the spin gap energy change with La doping in Ce1 -xLaxT2Al10 (T = Ru and Os) and also to understand the microscopic nature of the magnetic ground state, we here report on magnetic, transport, and thermal properties, neutron diffraction (ND), and inelastic neutron scattering (INS) investigations on these compounds. Our INS study reveals the persistence of spin gaps of 7 and 10 meV in the 10% La-doped T = Ru and Os compounds, respectively. More interestingly our ND study shows a very small ordered moment of 0.18 μB along the b axis in Ce0.9La0.1Ru2Al10 , however a moment of 0.23 μB still along the c axis in Ce0.9La0.1Os2Al10 . This contrasting behavior can be explained by a different degree of hybridization in CeRu2Al10 and CeOs2Al10 , being stronger in the latter than in the former. Muon spin rotation (μ SR ) studies on Ce1 -xLaxRu2Al10 (x =0 , 0.3, 0.5, and 0.7), reveal the presence of coherent frequency oscillations indicating a long-range magnetically ordered ground state for x =0 to 0.5, but an almost temperature independent Kubo-Toyabe response between 45 mK and 4 K for x =0.7 . We compare the results of the present investigations with those reported on the electron and hole doping in Ce T2Al10 .

  11. Residual Resistivity of Dilute Alloys

    NASA Astrophysics Data System (ADS)

    Vora, Aditya M.

    The residual resistivity for 156 dilute alloys of 19 hosts of different groups of the periodic table has been studied on the basis of the single parametric model potential formalism. Ashcroft's empty core model (EMC) potential is explored for the first time with five different local field correction functions, viz, Hartree (H), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F), and Sarkar et al. (S) to investigate the effect of the exchange and correlation on the aforesaid properties. The comparison of the presently computed outcomes with the available theoretical and experimental data is highly encouraging. The investigation of residual resistivity is found to be quite sensitive to the selection of local field correction function, showing a significant variation with the change in the function.

  12. Band anticrossing in dilute nitrides

    SciTech Connect

    Shan, W.; Yu, K.M.; Walukiewicz, W.; Wu, J.; Ager III, J.W.; Haller, E.E.

    2003-12-23

    Alloying III-V compounds with small amounts of nitrogen leads to dramatic reduction of the fundamental band-gap energy in the resulting dilute nitride alloys. The effect originates from an anti-crossing interaction between the extended conduction-band states and localized N states. The interaction splits the conduction band into two nonparabolic subbands. The downward shift of the lower conduction subband edge is responsible for the N-induced reduction of the fundamental band-gap energy. The changes in the conduction band structure result in significant increase in electron effective mass and decrease in the electron mobility, and lead to a large enhance of the maximum doping level in GaInNAs doped with group VI donors. In addition, a striking asymmetry in the electrical activation of group IV and group VI donors can be attributed to mutual passivation process through formation of the nearest neighbor group-IV donor nitrogen pairs.

  13. Desynchronization in diluted neural networks

    SciTech Connect

    Zillmer, Ruediger; Livi, Roberto; Politi, Antonio; Torcini, Alessandro

    2006-09-15

    The dynamical behavior of a weakly diluted fully inhibitory network of pulse-coupled spiking neurons is investigated. Upon increasing the coupling strength, a transition from regular to stochasticlike regime is observed. In the weak-coupling phase, a periodic dynamics is rapidly approached, with all neurons firing with the same rate and mutually phase locked. The strong-coupling phase is characterized by an irregular pattern, even though the maximum Lyapunov exponent is negative. The paradox is solved by drawing an analogy with the phenomenon of 'stable chaos', i.e., by observing that the stochasticlike behavior is 'limited' to an exponentially long (with the system size) transient. Remarkably, the transient dynamics turns out to be stationary.

  14. Isotopically controlled semiconductors

    SciTech Connect

    Haller, E.E.

    2004-11-15

    A review of recent research involving isotopically controlled semiconductors is presented. Studies with isotopically enriched semiconductor structures experienced a dramatic expansion at the end of the Cold War when significant quantities of enriched isotopes of elements forming semiconductors became available for worldwide collaborations. Isotopes of an element differ in nuclear mass, may have different nuclear spins and undergo different nuclear reactions. Among the latter, the capture of thermal neutrons which can lead to neutron transmutation doping, can be considered the most important one for semiconductors. Experimental and theoretical research exploiting the differences in all the properties has been conducted and will be illustrated with selected examples. Manuel Cardona, the longtime editor-in-chief of Solid State Communications has been and continues to be one of the major contributors to this field of solid state physics and it is a great pleasure to dedicate this review to him.

  15. Optical pumping in semiconductors

    NASA Astrophysics Data System (ADS)

    Hermann, C.; Lampel, G.; Safarov, V. I.

    Optical Pumping in Semiconductors (OPS) arises from the transfer of angular momentum from light to the localized states of a semiconductor. Spin polarized electrons are thus excited in the conduction band; their polarization is convenient measured through the circular polarization of photoluminescence. This review gives an insight of the various studies based on OPS. After describing the first OPS experiment, we show that this technique allows the determination of band structure properties, and the optical detection of conduction electron spin resonance. The nuclei are polarized by hyperfine interaction, which permits the optical detection of nuclear resonance. A magnetic field transverse to the direction of light propagation produces an electronic depolarization analogous to the Hanle effect. The electron lifetime and spin relaxation time are measured under steady-state conditions by comparison to their Larmor frequency in this transverse field. By activation to Negative Electron Affinity of a GaAs surface, electrons oriented by OPS can be photoemitted into vacuum, leading to a highly spin-polarized beam : we describe a collision experiment in which such a beam transfers angular momentum to atoms. Le Pompage Optique dans les semiconducteurs (POS) provient du transfert de moment angulaire de la lumière vers les états délocalisés d'un semiconducteur. On excite ainsi dans la bande de conduction des électrons polarisés de spin, dont on mesure commodément la polarisation à partir de la polarisation circulaire de la photoluminescence. Cet article de revue présente un aperçu des différentes études fondées sur le POS. Après avoir décrit la première expérience de POS, nous montrons que par cette technique on peut déterminer des propriétés liées à la structure de bande, et détecter optiquement la résonance de spin des électrons de conduction. Les noyaux sont polarisés grâce au couplage hyperfin qui permet également la détection optique de la r

  16. Force Detected Nuclear Magnetic Resonance on ammonium sulfate and magnesium diboride

    NASA Astrophysics Data System (ADS)

    Chia, Han-Jong

    Nuclear magnetic resonance force microscopy (NMRFM) is a technique that combines aspects of scanning probe microscopy (SPM) and nuclear magnetic resonance (NMR) to obtain 3 dimensional nanoscale spatial resolution and perform spectroscopy. We describe the components of a helium-3 NM-RFM probe and studies of ammonium sulfate ((NH4)2SO4) and magnesium dibordie (MgB2). For our room temperature (NH4)2SO 4 studies we were able to perform a 1-D scan and perform nutation and spin echo experiments. In our 77 K MgB2 we demonstrate a 1-D scan of a 30 mum powder sample. In addition, we describe magnetic measurements of the possible dilute semiconductors MnxSc 1-xN and Fe0:1Sc 0:9N.

  17. EDITORIAL: Oxide semiconductors

    NASA Astrophysics Data System (ADS)

    Kawasaki, M.; Makino, T.

    2005-04-01

    growth of p-type layers, ferromagnetic behaviour in transition-metal doped oxide is also fuelling renewed interest from the spintronic point of view. Since some of the related reports remain controversial, a critical discussion of the magnetic properties of these doped oxides is made by Fukumura et al. Before the observation of electro-luminescence from the ZnO p-n homojunction reported by Tsukazaki et al (2005 Nature Mater. 4 42), the afore-mentioned advantages have been explored and exploited by alternative methods, such as heteroepitaxy in which p-n heterostructures can be obtained by depositing n-type ZnO films on other p-type oxides while still utilizing ZnO as their active layer. Researchers in Hosono's group observed the high-intensity band-edge emission from such heterostructures for the first time (Ohta H et al 2000 Appl. Phys. Lett. 77 475). They have also successfully extended their research fields to the development of a transparent oxide transistor based on homologous compounds, which is reviewed by Kamiya and Hosono in this special issue. As can be seen from these demonstrations, the advantage of oxides is, of course, based on the fact that many elements in the periodic table can form compounds with oxygen. Since the discovery of high-temperature superconductors, these multi-component oxides have exploited the new field known as the science of strongly correlated-electron materials, whose recent progress is reviewed by Inoue. Although the collection of papers included in this special issue covers a good cross-section of the development of oxide semiconductors and correlated-electron oxides to date, this is not meant to be exhaustive. There are a number of unavoidable omissions, such as theoretical studies except for some theoretical predictions on the room-temperature Bose-Einstein condensation of exciton-polaritons found in the article by Chichibu et al. We hope this issue promotes further development of this exciting field. The guest editors would like to

  18. Optoelectronic bistability effect in semiconductors

    NASA Astrophysics Data System (ADS)

    Lagomarsino, Stefano

    2008-09-01

    A recombination bistability driven only by light irradiance, without any intervention of an externally imposed electric or magnetic field, is possible in doped semiconductors in which recombination is assured by multiply charged centers. This effect is allowed by the competition between two or more different recombination channels, providing that the shallower charged centers capture more likely charge carriers of the same polarity than the deep neutral ones, in spite of columbic repulsion. A close algebraic condition guaranteeing this effect is given, involving the trap parameters of the recombination centers. Deep multiple recombination centers in germanium, silicon, and silicon carbide are identified whose trap parameters make those materials good candidates to the realization of optoelectronic switching devices based on this effect.

  19. Raman spectra of Cu{sub 2}B{sup II}C{sup IV}X{sub 4}{sup VI} magnetic quaternary semiconductor compounds with tetragonal stannite type structure

    SciTech Connect

    Rincón, C. Quintero, M.; Power, Ch.; Moreno, E.; Quintero, E.; Morocoima, M.; Henao, J. A.; Macías, M. A.

    2015-05-28

    A comparative study of the Raman spectra of Cu{sub 2}B{sup II}C{sup IV}S{sub 4}{sup VI} and Cu{sub 2}B{sup II}C{sup IV}Se{sub 4}{sup VI}(where B = Mn or Fe) magnetic quaternary semiconductor compounds with stannite-type structure (I4{sup ¯}2m) has been done. Most of the fourteen Raman lines expected for these materials were observed in the spectra. The two strongest lines observed have been assigned to the IR inactive A{sub 1}{sup 1} and A{sub 1}{sup 2} stannite modes that originated from the motion of the S or Se anion around the Cu and C{sup IV} cations remaining at rest. The shift in the frequency of these two lines of about 150 cm{sup −1} to lower energies observed in Cu{sub 2}B{sup II}C{sup IV}Se{sub 4}{sup VI} compounds as compared to those in Cu{sub 2}B{sup II}C{sup IV}S{sub 4}{sup VI} ones, can then be explained as due to the anion mass effect. Based on the fact that values of these frequencies depend mainly on anion mass and bond-stretching forces between nearest-neighbor atoms, the vibrational frequencies v{sup ¯}(A{sub 1}{sup 2}) and v{sup ¯}(A{sub 1}{sup 2}) of both modes for several Cu{sub 2}B{sup II}C{sup IV}X{sub 4}{sup VI} stannite compounds (where X = S, Se, or Te) very close to the experimental data reported for these materials were calculated from a simple model that relates these stretching forces to the anion-cation bond-distances.

  20. Electrocoalescence based serial dilution of microfluidic droplets

    PubMed Central

    Bhattacharjee, Biddut; Vanapalli, Siva A.

    2014-01-01

    Dilution of microfluidic droplets where the concentration of a reagent is incrementally varied is a key operation in drop-based biological analysis. Here, we present an electrocoalescence based dilution scheme for droplets based on merging between moving and parked drops. We study the effects of fluidic and electrical parameters on the dilution process. Highly consistent coalescence and fine resolution in dilution factor are achieved with an AC signal as low as 10 V even though the electrodes are separated from the fluidic channel by insulator. We find that the amount of material exchange between the droplets per coalescence event is high for low capillary number. We also observe different types of coalescence depending on the flow and electrical parameters and discuss their influence on the rate of dilution. Overall, we find the key parameter governing the rate of dilution is the duration of coalescence between the moving and parked drop. The proposed design is simple incorporating the channel electrodes in the same layer as that of the fluidic channels. Our approach allows on-demand and controlled dilution of droplets and is simple enough to be useful for assays that require serial dilutions. The approach can also be useful for applications where there is a need to replace or wash fluid from stored drops. PMID:25379096