Zn(1-x)MnxTe diluted magnetic semiconductor nanowires grown by molecular beam epitaxy.

PubMed

Zaleszczyk, Wojciech; Janik, Elzbieta; Presz, Adam; Dłuzewski, Piotr; Kret, Sławomir; Szuszkiewicz, Wojciech; Morhange, Jean-François; Dynowska, Elzbieta; Kirmse, Holm; Neumann, Wolfgang; Petroutchik, Aleksy; Baczewski, Lech T; Karczewski, Grzegorz; Wojtowicz, Tomasz

2008-11-01

It is shown that the growth of II-VI diluted magnetic semiconductor nanowires is possible by the catalytically enhanced molecular beam epitaxy (MBE). Zn(1-x)MnxTe NWs with manganese content up to x=0.60 were produced by this method. X-ray diffraction, Raman spectroscopy, and temperature dependent photoluminescence measurements confirm the incorporation of Mn(2+) ions in the cation substitutional sites of the ZnTe matrix of the NWs.

Spin diffusion in the Mn2+ ion system of II-VI diluted magnetic semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Maksimov, A. A.; Yakovlev, D. R.; Debus, J.; Tartakovskii, I. I.; Waag, A.; Karczewski, G.; Wojtowicz, T.; Kossut, J.; Bayer, M.

2010-07-01

The magnetization dynamics in diluted magnetic semiconductor heterostructures based on (Zn,Mn)Se and (Cd,Mn)Te were studied optically and simulated numerically. In samples with inhomogeneous magnetic ion distribution, these dynamics are contributed by spin-lattice relaxation and spin diffusion in the Mn spin system. A spin-diffusion coefficient of 7×10-8cm2/s was evaluated for Zn0.99Mn0.01Se from comparison of experiment and theory. Calculations of the exciton giant Zeeman splitting and the magnetization dynamics in ordered alloys and digitally grown parabolic quantum wells show perfect agreement with the experimental data. In both structure types, spin diffusion contributes essentially to the magnetization dynamics.

A room-temperature magnetic semiconductor from a ferromagnetic metallic glass

NASA Astrophysics Data System (ADS)

Liu, Wenjian; Zhang, Hongxia; Shi, Jin-An; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V.; Chen, Mingwei; Yao, Kefu; Chen, Na

2016-12-01

Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III-V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p-n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V-1 s-1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities.

A room-temperature magnetic semiconductor from a ferromagnetic metallic glass.

PubMed

Liu, Wenjian; Zhang, Hongxia; Shi, Jin-An; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V; Chen, Mingwei; Yao, Kefu; Chen, Na

2016-12-08

Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III-V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co 28.6 Fe 12.4 Ta 4.3 B 8.7 O 46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p-n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm 2  V -1  s -1 . Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities.

A room-temperature magnetic semiconductor from a ferromagnetic metallic glass

PubMed Central

Liu, Wenjian; Zhang, Hongxia; Shi, Jin-an; Wang, Zhongchang; Song, Cheng; Wang, Xiangrong; Lu, Siyuan; Zhou, Xiangjun; Gu, Lin; Louzguine-Luzgin, Dmitri V.; Chen, Mingwei; Yao, Kefu; Chen, Na

2016-01-01

Emerging for future spintronic/electronic applications, magnetic semiconductors have stimulated intense interest due to their promises for new functionalities and device concepts. So far, the so-called diluted magnetic semiconductors attract many attentions, yet it remains challenging to increase their Curie temperatures above room temperature, particularly those based on III–V semiconductors. In contrast to the concept of doping magnetic elements into conventional semiconductors to make diluted magnetic semiconductors, here we propose to oxidize originally ferromagnetic metals/alloys to form new species of magnetic semiconductors. We introduce oxygen into a ferromagnetic metallic glass to form a Co28.6Fe12.4Ta4.3B8.7O46 magnetic semiconductor with a Curie temperature above 600 K. The demonstration of p–n heterojunctions and electric field control of the room-temperature ferromagnetism in this material reflects its p-type semiconducting character, with a mobility of 0.1 cm2 V−1 s−1. Our findings may pave a new way to realize high Curie temperature magnetic semiconductors with unusual multifunctionalities. PMID:27929059

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.

Local atomic and magnetic structure of dilute magnetic semiconductor (Ba ,K ) (Zn,Mn ) 2As2

NASA Astrophysics Data System (ADS)

Frandsen, Benjamin A.; Gong, Zizhou; Terban, Maxwell W.; Banerjee, Soham; Chen, Bijuan; Jin, Changqing; Feygenson, Mikhail; Uemura, Yasutomo J.; Billinge, Simon J. L.

2016-09-01

We have studied the atomic and magnetic structure of the dilute ferromagnetic semiconductor system (Ba ,K )(Zn ,Mn )2As2 through atomic and magnetic pair distribution function analysis of temperature-dependent x-ray and neutron total scattering data. We detected a change in curvature of the temperature-dependent unit cell volume of the average tetragonal crystallographic structure at a temperature coinciding with the onset of ferromagnetic order. We also observed the existence of a well-defined local orthorhombic structure on a short length scale of ≲5 Å , resulting in a rather asymmetrical local environment of the Mn and As ions. Finally, the magnetic PDF revealed ferromagnetic alignment of Mn spins along the crystallographic c axis, with robust nearest-neighbor ferromagnetic correlations that exist even above the ferromagnetic ordering temperature. We discuss these results in the context of other experiments and theoretical studies on this system.

Magneto-Transpots in Interband Resonant Tunneling Diodes (I-RTDs) and Dilute Magnetic Semiconductor (DMS) I-RTDs

DTIC Science & Technology

2011-03-02

Woolard, "Far- infrared and Terahertz lasing based upon resonant and interband tunneling in InAs/GaSb heterostructure," Applied Physics Letter, vol. 98...REPORT FINAL REPORT: Magneto-Transpots in interband Resonant Tunneling Diodes (I-RTDs) and Dilute Magnetic Semiconductor (DMS) I-RTDs 14. ABSTRACT 16...diodes (RTDs). This DB-BG-RTD device will utilizes two distinct innovations. First, ultra-fast heavy-hole (HH) interband tunneling is leveraged to

Local atomic and magnetic structure of dilute magnetic semiconductor ( Ba , K ) ( Zn , Mn ) 2 As 2

DOE PAGES

Frandsen, Benjamin A.; Gong, Zizhou; Terban, Maxwell W.; ...

2016-09-06

We studied the atomic and magnetic structure of the dilute ferromagnetic semiconductor system (Ba,K)(Zn,Mn) 2As 2 through atomic and magnetic pair distribution function analysis of temperature-dependent x-ray and neutron total scattering data. Furthermore, we detected a change in curvature of the temperature-dependent unit cell volume of the average tetragonal crystallographic structure at a temperature coinciding with the onset of ferromagnetic order. We also observed the existence of a well-defined local orthorhombic structure on a short length scale of ≲5Å, resulting in a rather asymmetrical local environment of the Mn and As ions. Finally, the magnetic PDF revealed ferromagnetic alignment ofmore » Mn spins along the crystallographic c axis, with robust nearest-neighbor ferromagnetic correlations that exist even above the ferromagnetic ordering temperature. Finally, we discuss these results in the context of other experiments and theoretical studies on this system.« less

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

PubMed

Mizokawa, Takashi

2012-10-23

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.

Curie temperatures of cubic (Ga, Mn)N diluted magnetic semiconductors from the RKKY spin model.

PubMed

Zhu, Li-Fang; Liu, Bang-Gui

2009-11-04

We explore how much the RKKY spin interaction can contribute to the high-temperature ferromagnetism in cubic (Ga, Mn)N diluted magnetic semiconductors. The usual coupling constant is used and effective carriers are considered independent of doped magnetic atoms, as is shown experimentally. Our Monte Carlo simulated results show that maximal Curie temperature is reached at the optimal carrier concentration for a given Mn concentration, equaling 373 K for 5% Mn and 703 K for 8% Mn. Because such a Monte Carlo method does not overestimate transition temperatures, these calculations indicate that the RKKY spin interaction alone can yield high-enough Curie temperatures in cubic (Ga, Mn)N under optimized conditions.

Transition-metal-doped group-IV monochalcogenides: a combination of two-dimensional triferroics and diluted magnetic semiconductors

NASA Astrophysics Data System (ADS)

Yang, Liu; Wu, Menghao; Yao, Kailun

2018-05-01

We report the first-principles evidence of a series of two-dimensional triferroics (ferromagnetic + ferroelectric + ferroelastic), which can be obtained by doping transition-metal ions in group-IV monochalcogenide (SnS, SnSe, GeS, GeSe) monolayers, noting that a ferromagnetic Fe-doped SnS2 monolayer has recently been realized (Li B et al 2017 Nat. Commun. 8 1958). The ferroelectricity, ferroelasticity and ferromagnetism can be coupled and the magnetization direction may be switched upon ferroelectric/ferroelastic switching, rendering electrical writing + magnetic reading possible. They can be also two-dimensional half-metals or diluted magnetic semiconductors, where p/n channels or even multiferroic tunneling junctions can be designed by variation in doping and incorporated into a monolayer wafer.

Transition-metal-doped group-IV monochalcogenides: a combination of two-dimensional triferroics and diluted magnetic semiconductors.

PubMed

Yang, Liu; Wu, Menghao; Yao, Kailun

2018-05-25

We report the first-principles evidence of a series of two-dimensional triferroics (ferromagnetic + ferroelectric + ferroelastic), which can be obtained by doping transition-metal ions in group-IV monochalcogenide (SnS, SnSe, GeS, GeSe) monolayers, noting that a ferromagnetic Fe-doped SnS 2 monolayer has recently been realized (Li B et al 2017 Nat. Commun. 8 1958). The ferroelectricity, ferroelasticity and ferromagnetism can be coupled and the magnetization direction may be switched upon ferroelectric/ferroelastic switching, rendering electrical writing + magnetic reading possible. They can be also two-dimensional half-metals or diluted magnetic semiconductors, where p/n channels or even multiferroic tunneling junctions can be designed by variation in doping and incorporated into a monolayer wafer.

Holistic electronic response underlying the development of magnetism in co-doped diluted magnetic semiconductors

NASA Astrophysics Data System (ADS)

Andriotis, Antonis N.; Menon, Madhu

2018-05-01

A systematic analysis of the properties of codoped diluted magnetic semiconductors (DMSs) reveals the role and the effect of the codopants in dictating the magnetic features of the DMSs. Our results indicate that the magnetic features of a codoped DMS is the outcome of synergistic electronic processes of the whole system rather than a local hybridization process isolated from the rest of the system. Specifically, the d-orbital hybridization of the (co)dopants and the introduction of their impurity bands lead to the readjustment of the position of the p-band center of the host’s anions and that of the valence band maximum (VBM). The overall effect of these is to pull the hybridized d-bands of the (co)dopants relative to the Fermi energy, E F , which in turn dictate the value of the magnetic moment of both the dopant as well as the codopant. More precisely, the magnetic moment of a dopant shows an almost linearly increasing (decreasing) variation as the dopant’s d-band center (the latter dictated by the codopant) moves away from (gets closer to) E F . Our results thus suggest a completely new approach in the investigation and understanding of the origin of the defect induced magnetism and support previous reports suggesting the Fermi-energy engineering as a mean for developing high T C DMSs. These trends are demonstrated with results obtained for GaN, GaP, and CdS doped with one of the V, Mn, Co and Cu dopants and codoped with the transition metals of the 3d-series.

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rani, Anita; Kaur, Kulwinder; Kumar, Ranjan, E-mail: ranianita64@gmail.com

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 foundmore » 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.« less

Universal features underlying the magnetism in diluted magnetic semiconductors

NASA Astrophysics Data System (ADS)

Andriotis, Antonis N.; Menon, Madhu

2018-04-01

Investigation of a diverse variety of wide band gap semiconductors and metal oxides that exhibit magnetism on substitutional doping has revealed the existence of universal features that relate the magnetic moment of the dopant to a number of physical properties inherent to the dopants and the hosts. The investigated materials consist of ZnO, GaN, GaP, TiO2, SnO2, Sn3N4, MoS2, ZnS and CdS doped with 3d-transition metal atoms. The primary physical properties contributing to magnetism include the orbital hybridization and charge distribution, the d-band filling, d-band center, crystal field splitting, electron pairing energy and electronegativity. These features specify the strength of the spin-polarization induced by the dopants on their first nearest neighboring anions which in turn specify the long range magnetic coupling among the dopants through successively induced spin polarizations (SSP) on neighboring dopants. The proposed local SSP process for the establishment of the magnetic coupling among the TM-dopants appears as a competitor to other classical processes (superexchange, double exchange, etc). Furthermore, these properties can be used as a set of descriptors suitable for developing statistical predictive theories for a much larger class of magnetic materials.

STRUCTURAL, SURFACE MORPHOLOGICAL AND MAGNETIC STUDIES OF Zn1-xFexS (x=0.00-0.10) DILUTED MAGNETIC SEMICONDUCTORS GROWN BY CO-PRECIPITATION METHOD

NASA Astrophysics Data System (ADS)

Hassan, M.; Ghazanfar, M.; Arooj, N.; Riaz, S.; Hussain, S. Sajjad; Naseem, S.

We have fabricated Zn1-xFexS (x=0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) diluted magnetic semiconductors using co-precipitation method. X-ray diffraction patterns depict that Zn1-xFexS appears as a dominant phase with cubic zinc blende structure and nanoscale crystallite size. In addition, a secondary phase of rhombohedral ZnS also appears; however, no additional phase arises that primarily belongs to Fe dopant. Using Debye-Scherrer relation, the crystallite size is found to be in the range of 20-27nm, which is in good agreement with the crystallite size calculated using the Williamson-Hall (WH) plot method. The appearance of secondary phase provoked to study the residual strain using Stokes-Wilson equation, which is nearly consistent to that observed using WH plot method. The surface morphology, revealed using scanning electron microscopy, depicts non-uniform surface structure with a variety of grains and void dimensions. Hysteresis loops measured for Zn1-xFexS at room temperature (RT) illustrate a paramagnetic behavior at higher fields; however, small ferromagnetic behavior is evident due to the small openings of the measured hysteresis loops around the origin. The measured RT ferromagnetism reveals the potential spintronic device applications of the studied diluted magnetic semiconductors.

Optical, electrical and ferromagnetic studies of ZnO:Fe diluted magnetic semiconductor nanoparticles for spintronic applications

NASA Astrophysics Data System (ADS)

Elilarassi, R.; Chandrasekaran, G.

2017-11-01

In the present investigation, diluted magnetic semiconductor (Zn1-xFexO) nanoparticles with different doping concentrations (x = 0, 0.02, 0.04, 0.06, and 0.08) were successfully synthesized by sol-gel auto-combustion method. The crystal structure, morphology, optical, electrical and magnetic properties of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis using x-rays (EDAX), ultraviolet-visible spectrophotometer, fluorescence spectroscope (FS), vibrating sample magnetometer (VSM) and broad band dielectric spectrometer (BDS). XRD results reveal that all the samples possess hexagonal wurtzite crystal structure with good crystalline quality. The absence of impurity phases divulge that Fe ions are well incorporated into the ZnO crystal lattice. The substitutional incorporation of Fe3+ at Zn sites is reflected in optical absorption spectra of the samples. Flouorescence spectra of the samples show a strong near-band edge related UV emission as well as defect related visible emissions. The semiconducting behavior of the samples has been confirmed through electrical conductivity measurements. Magnetic measurements indicated that all the samples possess ferromagnetism at room temperature.

Effective equations for the precession dynamics of electron spins and electron-impurity correlations in diluted magnetic semiconductors

NASA Astrophysics Data System (ADS)

Cygorek, M.; Axt, V. M.

2015-08-01

Starting from a quantum kinetic theory for the spin dynamics in diluted magnetic semiconductors, we derive simplified equations that effectively describe the spin transfer between carriers and magnetic impurities for an arbitrary initial impurity magnetization. Taking the Markov limit of these effective equations, we obtain good quantitative agreement with the full quantum kinetic theory for the spin dynamics in bulk systems at high magnetic doping. In contrast, the standard rate description where the carrier-dopant interaction is treated according to Fermi’s golden rule, which involves the assumption of a short memory as well as a perturbative argument, has been shown previously to fail if the impurity magnetization is non-zero. The Markov limit of the effective equations is derived, assuming only a short memory, while higher order terms are still accounted for. These higher order terms represent the precession of the carrier-dopant correlations in the effective magnetic field due to the impurity spins. Numerical calculations show that the Markov limit of our effective equations reproduces the results of the full quantum kinetic theory very well. Furthermore, this limit allows for analytical solutions and for a physically transparent interpretation.

Optical, electrical and ferromagnetic studies of ZnO:Fe diluted magnetic semiconductor nanoparticles for spintronic applications.

PubMed

Elilarassi, R; Chandrasekaran, G

2017-11-05

In the present investigation, diluted magnetic semiconductor (Zn 1-x Fe x O) nanoparticles with different doping concentrations (x=0, 0.02, 0.04, 0.06, and 0.08) were successfully synthesized by sol-gel auto-combustion method. The crystal structure, morphology, optical, electrical and magnetic properties of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis using x-rays (EDAX), ultraviolet-visible spectrophotometer, fluorescence spectroscope (FS), vibrating sample magnetometer (VSM) and broad band dielectric spectrometer (BDS). XRD results reveal that all the samples possess hexagonal wurtzite crystal structure with good crystalline quality. The absence of impurity phases divulge that Fe ions are well incorporated into the ZnO crystal lattice. The substitutional incorporation of Fe 3+ at Zn sites is reflected in optical absorption spectra of the samples. Flouorescence spectra of the samples show a strong near-band edge related UV emission as well as defect related visible emissions. The semiconducting behavior of the samples has been confirmed through electrical conductivity measurements. Magnetic measurements indicated that all the samples possess ferromagnetism at room temperature. Copyright © 2017 Elsevier B.V. All rights reserved.

Dependence of the magnetic properties of the dilute magnetic semiconductor Zn1-xMnxO nanorods on their Mn doping levels

NASA Astrophysics Data System (ADS)

Thongjamroon, S.; Ding, J.; Herng, T. S.; Tang, I. M.; Thongmee, S.

2017-10-01

The effects of Mn doping on the ferromagnetic properties of the dilute magnetic semiconductor Zn1-xMnxO nanorods (NR's) having the nominal composit-ions x = 0, 0.01, 0.03, 0.04 and 0.05 grown by a low temperature hydrothermal method are studied. Energy dispersive X-ray (EDX) is used to determine the actual amounts of the elements in each NR's. X-ray diffraction, scanning electron microscopy, photoluminescence and vibrating sample magnetometer measurements are used to observe the effects of the Mn substitution on the properties of the doped ZnO and to relate the changes in the properties to changes in the defect content. It is observed that the saturation magnetization of the Mn ions in the wurtzite structure varies from 0.0210 μB/Mn2+ to 0.0234 μB/Mn2+ reaching a high of 0.0251 μB/Mn2+ as the Mn concentrations is varied from 0.9 to 7.36 atomic%. It is argued that the changes in the saturation magnetization are due to the competition between the direct Mn-Mn exchange interaction and the indirect Mn-O-Mn exchange interaction in the doped Mn ZnO NP's.

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.

Experimentally evaluating the origin of dilute magnetism in nanomaterials

NASA Astrophysics Data System (ADS)

Pereira, L. M. C.

2017-10-01

Reports of room-temperature ferromagnetism continue to emerge for an ever-growing range of nanomaterials with a small or even vanishing concentration of magnetic atoms. Dilute magnetic semiconductors (DMS) are the most representative class of such materials, but similar magnetic properties have been reported in many others. Challenging our understanding of magnetic order in solids, as well as our ability to experimentally assess it, these remarkable magnetic phenomena have become one of the most controversial topics in magnetism. Various non-intrinsic sources of ferromagnetism (e.g. instrumental artifacts and magnetic contamination) are becoming well documented, and rarely are all of them taken into account when room-temperature ferromagnetism is reported. This topical review is intended to serve as a guide when evaluating to what extent a given data set supports the claim of intrinsic ferromagnetism in dilute nanomaterials. It compiles the most relevant sources of non-intrinsic ferromagnetism which have been reported, as well as guidelines for how to minimize them. It also provides an overview of complementary structural and magnetic characterization techniques which can be combined to provide different levels of scrutiny of the intrinsic nature of experimentally observed ferromagnetism. In particular, it gives some notable examples of how comprehensive studies based on those techniques have led to a remarkably detailed understanding of model DMS materials, with strong evidence of absence of room-temperature ferromagnetism. Although mostly based on DMS research, this review provides a set of guidelines and cautionary notes of broader relevance, including some emerging new fields of dilute nanomagnetism such as magnetically doped 3D topological insulators, 3D Dirac semimetals, and 2D materials.

Defect-Rich Dopant-Free ZrO2 Nanostructures with Superior Dilute Ferromagnetic Semiconductor Properties.

PubMed

Rahman, Md Anisur; Rout, S; Thomas, Joseph P; McGillivray, Donald; Leung, Kam Tong

2016-09-14

Control of the spin degree of freedom of an electron has brought about a new era in spin-based applications, particularly spin-based electronics, with the potential to outperform the traditional charge-based semiconductor technology for data storage and information processing. However, the realization of functional spin-based devices for information processing remains elusive due to several fundamental challenges such as the low Curie temperature of group III-V and II-VI semiconductors (<200 K), and the low spin-injection efficiencies of existing III-V, II-VI, and transparent conductive oxide semiconductors in a multilayer device structure, which are caused by precipitation and migration of dopants from the host layer to the adjacent layers. Here, we use catalyst-assisted pulsed laser deposition to grow, for the first time, oxygen vacancy defect-rich, dopant-free ZrO2 nanostructures with high TC (700 K) and high magnetization (5.9 emu/g). The observed magnetization is significantly greater than both doped and defect-rich transparent conductive oxide nanomaterials reported to date. We also provide the first experimental evidence that it is the amounts and types of oxygen vacancy defects in, and not the phase of ZrO2 that control the ferromagnetic order in undoped ZrO2 nanostructures. To explain the origin of ferromagnetism in these ZrO2 nanostructures, we hypothesize a new defect-induced bound polaron model, which is generally applicable to other defect-rich, dopant-free transparent conductive oxide nanostructures. These results provide new insights into magnetic ordering in undoped dilute ferromagnetic semiconductor oxides and contribute to the design of exotic magnetic and novel multifunctional materials.

Control of magnetism in dilute magnetic semiconductor (Ga,Mn)As films by surface decoration of molecules

NASA Astrophysics Data System (ADS)

Wang, Hailong; Wang, Xiaolei; Xiong, Peng; Zhao, Jianhua

2016-03-01

The responses of magnetic moments to external stimuli such as magnetic-field, heat, light and electric-field have been utilized to manipulate the magnetism in magnetic semiconductors, with many of the novel ideas applied even to ferromagnetic metals. Here, we review a new experimental development on the control of magnetism in (Ga,Mn)As thin films by surface decoration of organic molecules: Molecules deposited on the surface of (Ga,Mn)As thin films are shown to be capable of significantly modulating their saturation magnetization and Curie temperature. These phenomena are shown to originate from the carrier-mediated ferromagnetism in (Ga,Mn)As and the surface molecules acting as acceptors or donors depending on their highest occupied molecular orbitals, resembling the charge transfer mechanism in a pn junction in which the equilibrium state is reached on the alignment of Fermi levels.

Out-of-plane easy-axis in thin films of diluted magnetic semiconductor Ba1-xKx(Zn1-yMny)2As2

NASA Astrophysics Data System (ADS)

Wang, R.; Huang, Z. X.; Zhao, G. Q.; Yu, S.; Deng, Z.; Jin, C. Q.; Jia, Q. J.; Chen, Y.; Yang, T. Y.; Jiang, X. M.; Cao, L. X.

2017-04-01

Single-phased, single-oriented thin films of Mn-doped ZnAs-based diluted magnetic semiconductor (DMS) Ba1-xKx(Zn1-yMny)2As2 (x = 0.03, 0.08; y = 0.15) have been deposited on Si, SrTiO3, LaAlO3, (La,Sr)(Al,Ta)O3, and MgAl2O4 substrates, respectively. Utilizing a combined synthesis and characterization system excluding the air and further optimizing the deposition parameters, high-quality thin films could be obtained and be measured showing that they can keep inactive-in-air up to more than 90 hours characterized by electrical transport measurements. In comparison with films of x = 0.03 which possess relatively higher resistivity, weaker magnetic performances, and larger energy gap, thin films of x = 0.08 show better electrical and magnetic performances. Strong magnetic anisotropy was found in films of x = 0.08 grown on (La,Sr)(Al,Ta)O3 substrate with their magnetic polarization aligned almost solely on the film growth direction.

Magnetization and photomagnetic effects in diluted magnetic microcrystalline Cd 1-xMn xTe

NASA Astrophysics Data System (ADS)

He, X.-F.; Kotlicki, A.; Dosanjh, P.; Turrell, B. G.; Carolan, J. F.; Jimenez-Sandoval, S.; Lozano-Tovar, P.

1993-12-01

We have investigated the magnetic and photomagnetic properties of microcrystalline Cd 1-xMn xTe prepared by rf sputtering. Magnetization measurements were carried out using an rf SQUID magnetometer in the temperature range of 1.8 to 300 K at various magnetic fields up to 5.5 T. For temperatures above 40 K, the sample showed Curie-Weiss behaviour with a Curie temperature indicating predominantly antiferromagnetic interactions. A spin-glass phase transition was also observed. Photomagnetization measurements were performed using a fibre-optic system. The light was shone onto the sample utilizing an optical fibre and the subsequent change in the magnetization was sensed by the SQUID. Photo-induced magnetization was observed when the sample was illuminated by unpolarized light. Our results enable qualitative and quantitative conclusions to be drawn on the magnetic behaviour and the interplay between optical and magnetic properties of the diluted magnetic microcrystalline semiconductors. PACS: 68.55.Gi; 75.50.Pp.

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).

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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 exchangemore » 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.« less

Magnetic field induced optical gain in a dilute nitride quaternary semiconductor quantum dot

NASA Astrophysics Data System (ADS)

Mageshwari, P. Uma; Peter, A. John; Lee, Chang Woo

2016-10-01

Effects of magnetic field strength on the electronic and optical properties are brought out in a Ga0.661In0.339N0.0554As0.9446/GaAs quantum dot for the applications of desired wavelength in opto-electronic devices. The band alignment is obtained using band anticrossing model and the model solid theory. The magnetic field dependent electron-heavy hole transition energies with the dot radius in a GaInNAs/GaAs quantum dot are investigated. The magnetic field induced oscillator strength as a function of dot radius is studied. The resonant peak values of optical absorption coefficients and the changes of refractive index with the application of magnetic field strength in a GaInNAs/GaAs quantum dot are obtained. The magnetic field induced threshold current density and the maximum optical gain are found in a GaInNAs/GaAs quantum dot. The results show that the optimum wavelength for fibre optical communication networks can be obtained with the variation of applied magnetic field strength and the outcomes may be useful for the design of efficient lasers based on the group III-N-V semiconductors.

Particles size distribution in diluted magnetic fluids

NASA Astrophysics Data System (ADS)

Yerin, Constantine V.

2017-06-01

Changes in particles and aggregates size distribution in diluted kerosene based magnetic fluids is studied by dynamic light scattering method. It has been found that immediately after dilution in magnetic fluids the system of aggregates with sizes ranging from 100 to 250-1000 nm is formed. In 50-100 h after dilution large aggregates are peptized and in the sample stationary particles and aggregates size distribution is fixed.

New diluted ferromagnetic semiconductor with Curie temperature up to 180 K and isostructural to the '122' iron-based superconductors.

PubMed

Zhao, K; Deng, Z; Wang, X C; Han, W; Zhu, J L; Li, X; Liu, Q Q; Yu, R C; Goko, T; Frandsen, B; Liu, Lian; Ning, Fanlong; Uemura, Y J; Dabkowska, H; Luke, G M; Luetkens, H; Morenzoni, E; Dunsiger, S R; Senyshyn, A; Böni, P; Jin, C Q

2013-01-01

Diluted magnetic semiconductors have received much attention due to their potential applications for spintronics devices. A prototypical system (Ga,Mn)As has been widely studied since the 1990s. The simultaneous spin and charge doping via hetero-valent (Ga(3+),Mn(2+)) substitution, however, resulted in severely limited solubility without availability of bulk specimens. Here we report the synthesis of a new diluted magnetic semiconductor (Ba(1-x)K(x))(Zn(1-y)Mn(y))(2)As(2), which is isostructural to the 122 iron-based superconductors with the tetragonal ThCr(2)Si(2) (122) structure. Holes are doped via (Ba(2+), K(1+)) replacements, while spins via isovalent (Zn(2+),Mn(2+)) substitutions. Bulk samples with x=0.1-0.3 and y=0.05-0.15 exhibit ferromagnetic order with T(C) up to 180 K, which is comparable to the highest T(C) for (Ga,Mn)As and significantly enhanced from T(C) up to 50 K of the '111'-based Li(Zn,Mn)As. Moreover, ferromagnetic (Ba,K)(Zn,Mn)(2)As(2) shares the same 122 crystal structure with semiconducting BaZn(2)As(2), antiferromagnetic BaMn(2)As(2) and superconducting (Ba,K)Fe(2)As(2), which makes them promising for the development of multilayer functional devices.

Excitations and magnetization density distribution in the dilute ferromagnetic semiconductor Yb 14 MnSb 11

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stone, M. B.; Garlea, V. O.; Gillon, B.

2017-01-23

One rare example of a Kondo lattice compound with ferromagnetic dominated RKKY interactions is Ybmore » $$_{14}$$MnSb$$_{11}$$. As a ferromagnetic semiconductor with $$T_c \\approx 53$$~K, it is also a potential compound for exploration of spintronic devices. This material is furthermore one of the most efficient high temperature thermoelectrics. We describe measurements which answer remaining questions regarding the energy scales of the exchange interactions, the valence and the magnetization density distribution in this system. We also find that the system consists of RKKY exchange coupled Mn$$^{2+}$$ sites with nearest and next nearest exchange interactions dominating the magnetic spectrum with no significant magnetization density localized on other atomic sites. The extended spread of a negative magnetization around each of the Mn ions supports a Kondo screening cloud scenario for Yb$$_{14}$$MnSb$$_{11}$$.« less

Carrier-induced ferromagnetism in half-metallic Co-doped ZnS-diluted magnetic semiconductor: a DFT study

NASA Astrophysics Data System (ADS)

Saikia, D.; Borah, J. P.

2018-03-01

Systematic experimental and theoretical calculations have been performed to investigate the origin of the carrier-induced ferromagnetism in the Co-doped ZnS-diluted magnetic semiconductors. The crystalline structure, morphology of the chemically synthesized Co-doped ZnS nanoparticles are evaluated using X-ray diffraction (XRD) and transmission electron microscopy (TEM) and obtained the average crystallite size in the range 5-8 nm. Fourier transform-infrared spectra reveal the characteristic Zn-S vibrations of cubic ZnS and also show the splitting of peaks with increasing Co concentration which indicates that the Co-doping level beyond 3% affects the structure of ZnS. The room temperature ferromagnetic behavior analyzed by M- H curve exhibited up to the doping level 5%, achieving due to the indirect ` p- d' exchange interactions between the localized ` d' spins of Co2+ ion and the free-delocalized carriers in the host lattice. The existence of the antiferromagnetic coupling is discernable beyond the 5% doping level, owing to the short-range super-exchange interactions between the characteristic ` d' spins of the Co2+ ions which minimize the ferromagnetic ordering. Band structure and density of states (DOS) calculations demonstrate the p- d hybridization mechanism in Co-doped ZnS system which is the main cause of realizing ferromagnetic ordering in the system and also shows the half-metallic characteristics with the combination of semiconducting and metallic nature in the spin-up and spin-down states, respectively.

Diluted magnetic oxides

NASA Astrophysics Data System (ADS)

Li, XiaoLi; Qi, ShiFei; Jiang, FengXian; Quan, ZhiYong; Xu, XiaoHong

2013-01-01

In this review, we review the progress of research on ZnO- and In2O3-based diluted magnetic oxides (DMOs). Firstly, we present the preparation and characterization of DMOs. The former includes the preparation methods and conditions, and the latter includes the characterization techniques for measuring microstructures. Secondly, we introduce the magnetic and transport properties of DMOs, as well as the relationship between them. Thirdly, the origin and mechanism of the ferromagnetism are discussed. Fourthly, we introduce other related work, including computational work and pertinent heterogeneous structures, such as multilayers and magnetic tunnel junctions. Finally, we provide an overview and outlook for DMOs.

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

Electron-nuclear spin dynamics of Ga centers in GaAsN dilute nitride semiconductors probed by pump-probe spectroscopy

NASA Astrophysics Data System (ADS)

Sandoval-Santana, J. C.; Ibarra-Sierra, V. G.; Azaizia, S.; Carrère, H.; Bakaleinikov, L. A.; Kalevich, V. K.; Ivchenko, E. L.; Marie, X.; Amand, T.; Balocchi, A.; Kunold, A.

2018-03-01

We propose an experimental procedure to track the evolution of electronic and nuclear spins in Ga2+ centers in GaAsN dilute semiconductors. The method is based on a pump-probe scheme that enables to monitor the time evolution of the three components of the electronic and nuclear spin variables. In contrast to other characterization methods, as nuclear magnetic resonance, this one only needs moderate magnetic fields (B≈ 10 mT), and does not require microwave irradiation. Specifically, we carry out a series of tests for different experimental conditions in order to optimize the procedure for maximum sensitivity in the measurement of the circular degree of polarization. Based on previous experimental results and the theoretical calculations presented here, we estimate that the method could yield a time resolution of about 10ps.

Effect of Al doping on the magnetic and electrical properties of Zn(Cu)O based diluted magnetic semiconductors

NASA Astrophysics Data System (ADS)

Chakraborti, D.; Trichy, G.; Narayan, J.; Prater, J. T.; Kumar, D.

2007-12-01

The effect of Al doping on the magnetic properties of Zn(Cu)O based dilute magnetic semiconducting thin films has been systematically investigated. Epitaxial thin films have been deposited onto sapphire c-plane single crystals using pulsed laser deposition technique. X-ray diffraction and high resolution transmission electron microscopy studies show that the Zn(Cu,Al)O films are epitaxially grown onto (0001) sapphire substrates with a 30°/90° rotation in the basal plane. The large lattice misfit of the order of 16% is accommodated by matching integral multiples of lattice and substrate planes. In these large mismatch systems, the resulting films are fully relaxed following deposition of the first complete monolayer of ZnO (consistent with a critical thickness that is less than one monolayer). Magnetic hysteresis measurements indicate that the pure Zn(Cu)O thin films are ferromagnetic at room temperature. Doping with up to 5% Al (n type) does not significantly affect the ferromagnetism even though it results in an increase in carrier densities of more than 3 orders of magnitude, rising from 1×1017 to 1.5×1020 cm-3. However, for Al additions above 5%, a drop in net magnetization is observed. Annealing the films in an oxygen atmosphere at 600 °C also resulted in a dramatic drop in magnetic moment of the samples. These results strongly suggest that carrier induced exchange is not directly responsible for the magnetic properties of these materials. Rather, a defect mediated exchange mechanism needs to be invoked for this system.

Photoemission and x-ray absorption studies of the isostructural to Fe-based superconductors diluted magnetic semiconductor Ba1 -xKx(Zn1 -yMny)2As2

NASA Astrophysics Data System (ADS)

Suzuki, H.; Zhao, K.; Shibata, G.; Takahashi, Y.; Sakamoto, S.; Yoshimatsu, K.; Chen, B. J.; Kumigashira, H.; Chang, F.-H.; Lin, H.-J.; Huang, D. J.; Chen, C. T.; Gu, Bo; Maekawa, S.; Uemura, Y. J.; Jin, C. Q.; Fujimori, A.

2015-04-01

The electronic and magnetic properties of a new diluted magnetic semiconductor (DMS) Ba1 -xKx (Zn1 -yMny )2As2 , which is isostructural to so-called 122-type Fe-based superconductors, are investigated by x-ray absorption spectroscopy (XAS) and resonance photoemission spectroscopy (RPES). Mn L2 ,3-edge XAS indicates that the doped Mn atoms have a valence 2+ and strongly hybridize with the 4 p orbitals of the tetrahedrally coordinating As ligands. The Mn 3 d partial density of states obtained by RPES shows a peak around 4 eV and is relatively high between 0 and 2 eV below the Fermi level (EF) with little contribution at EF, similar to that of the archetypal DMS Ga1 -xMnxAs . This energy level creates a d5 electron configuration with S =5 /2 local magnetic moments at the Mn atoms. Hole carriers induced by K substitution for Ba atoms go into the top of the As 4 p valence band and are weakly bound to the Mn local spins. The ferromagnetic correlation between the local spins mediated by the hole carriers induces ferromagnetism in Ba1 -xKx (Zn1 -yMny )2As2 .

Magnetic properties of the layered III-VI diluted magnetic semiconductor Ga{sub 1−x}Fe{sub x}Te

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pekarek, T. M.; Edwards, P. S.; Olejniczak, T. L.

2016-05-15

Magnetic properties of single crystalline Ga{sub 1−x}Fe{sub x}Te (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 Ga{sub 1−x}Mn{sub x}Se and Ga{sub 1−x}Mn{sub x}S and reaches a maximum of 0.68 emu/g at 2 K in 7 T. The magnetization of Ga{sub 1−x}Fe{sub x}Te 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 atmore » 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 Ga{sub 1−x}Fe{sub x}Se. Neither the broad thermal hysteresis observed from 100-300 K in In{sub 1−x}Mn{sub x}Se nor the spin-glass behavior observed around 10.9 K in Ga{sub 1−x}Mn{sub x}S are observed in Ga{sub 1−x}Fe{sub x}Te. 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 Å{sup 3}.« less

Diluted Magnetic Semiconductors for Magnetic Field Tunable Infrared Detectors

DTIC Science & Technology

2005-06-30

significantly improved performance and technological advances of quantum well infrared photodetectors (QWIPs)14 and quantum cascade lasers (QCLs)15...NUMBER FA8655-04-1-3069 5b. GRANT NUMBER 4. TITLE AND SUBTITLE Magnetic Field Tunable Terahertz Quantum Well Infrared Photodetector 5c...fabrication in II-VI materials, quantum well infrared photodetector device design and magneto-optical characterisation are all well understood

Bipolar magnetic semiconductor in silicene nanoribbons

NASA Astrophysics Data System (ADS)

Farghadan, Rouhollah

2017-08-01

A theoretical study was presented on generation of spin polarization in silicene nanoribbons using the single-band tight-binding approximation and the non-equilibrium Green's function formalism. We focused on the effect of electric and exchange magnetic fields on the spin-filter capabilities of zigzag-edge silicene nanoribbons in the presence of the intrinsic spin-orbit interaction. The results show that a robust bipolar magnetic semiconductor with controllable spin-flip and spin-conserved gaps can be obtained when exchange magnetic and electric field strengths are both larger than the intrinsic spin-orbit interaction. Therefore, zigzag silicene nanoribbons could act as bipolar and perfect spin filter devices with a large spin-polarized current and a reversible spin polarization in the vicinity of the Fermi energy. We also investigated the effect of edge roughness and found that the bipolar magnetic semiconductor features are robust against edge disorder in silicene nanoribbon junctions. These results may be useful in multifunctional spin devices based on silicene nanoribbons.

A Designed Room Temperature Multilayered Magnetic Semiconductor

NASA Astrophysics Data System (ADS)

Bouma, Dinah Simone; Charilaou, Michalis; Bordel, Catherine; Duchin, Ryan; Barriga, Alexander; Farmer, Adam; Hellman, Frances; Materials Science Division, Lawrence Berkeley National Lab Team

2015-03-01

A room temperature magnetic semiconductor has been designed and fabricated by using an epitaxial antiferromagnet (NiO) grown in the (111) orientation, which gives surface uncompensated magnetism for an odd number of planes, layered with the lightly doped semiconductor Al-doped ZnO (AZO). Magnetization and Hall effect measurements of multilayers of NiO and AZO are presented for varying thickness of each. The magnetic properties vary as a function of the number of Ni planes in each NiO layer; an odd number of Ni planes yields on each NiO layer an uncompensated moment which is RKKY-coupled to the moments on adjacent NiO layers via the carriers in the AZO. This RKKY coupling oscillates with the AZO layer thickness, and it disappears entirely in samples where the AZO is replaced with undoped ZnO. The anomalous Hall effect data indicate that the carriers in the AZO are spin-polarized according to the direction of the applied field at both low temperature and room temperature. NiO/AZO multilayers are therefore a promising candidate for spintronic applications demanding a room-temperature semiconductor.

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.

Magnetic-field-controlled reconfigurable semiconductor logic.

PubMed

Joo, Sungjung; Kim, Taeyueb; Shin, Sang Hoon; Lim, Ju Young; Hong, Jinki; Song, Jin Dong; Chang, Joonyeon; Lee, Hyun-Woo; Rhie, Kungwon; Han, Suk Hee; Shin, Kyung-Ho; Johnson, Mark

2013-02-07

Logic devices based on magnetism show promise for increasing computational efficiency while decreasing consumed power. They offer zero quiescent power and yet combine novel functions such as programmable logic operation and non-volatile built-in memory. However, practical efforts to adapt a magnetic device to logic suffer from a low signal-to-noise ratio and other performance attributes that are not adequate for logic gates. Rather than exploiting magnetoresistive effects that result from spin-dependent transport of carriers, we have approached the development of a magnetic logic device in a different way: we use the phenomenon of large magnetoresistance found in non-magnetic semiconductors in high electric fields. Here we report a device showing a strong diode characteristic that is highly sensitive to both the sign and the magnitude of an external magnetic field, offering a reversible change between two different characteristic states by the application of a magnetic field. This feature results from magnetic control of carrier generation and recombination in an InSb p-n bilayer channel. Simple circuits combining such elementary devices are fabricated and tested, and Boolean logic functions including AND, OR, NAND and NOR are performed. They are programmed dynamically by external electric or magnetic signals, demonstrating magnetic-field-controlled semiconductor reconfigurable logic at room temperature. This magnetic technology permits a new kind of spintronic device, characterized as a current switch rather than a voltage switch, and provides a simple and compact platform for non-volatile reconfigurable logic devices.

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.

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.

DARPA-URI Consortium Meetings on Submicron Heterostructures of Diluted Magnetic Semiconductors.

DTIC Science & Technology

1987-01-01

Acta Physica Polonica (to be published). 89. B.E. Larson, K.C. Hass, H. Ehrenreich and A.E. Carlsson, "Theory of Exchange Interactions and Chemical...Rodriguez, "Parity Violation and Electron-Spin Resonance of Donors in Semiconductors" (to appear in Physica ). 45. Z. Barticevic, M. Dobrowolska, J.K. Furdyna

Hole doping and pressure effects on the II-II-V-based diluted magnetic semiconductor (B a1 -xKx ) (Zn1-yM ny ) 2A s2

NASA Astrophysics Data System (ADS)

Sun, F.; Zhao, G. Q.; Escanhoela, C. A.; Chen, B. J.; Kou, R. H.; Wang, Y. G.; Xiao, Y. M.; Chow, P.; Mao, H. K.; Haskel, D.; Yang, W. G.; Jin, C. Q.

2017-03-01

We investigate doping- and pressure-induced changes in the electronic state of Mn 3 d and As 4 p orbitals in II-II-V-based diluted magnetic semiconductor (B a1 -xKx ) (Zn1-yM ny ) 2A s2 to shed light into the mechanism of indirect exchange interactions leading to high ferromagnetic ordering temperature (T c =230 K in optimally doped samples). A suite of x-ray spectroscopy experiments (emission, absorption, and dichroism) show that the emergence and further enhancement of ferromagnetic interactions with increased hole doping into the As 4 p band is accompanied by a decrease in local 3 d spin density at Mn sites. This is a result of increasing Mn 3 d -As 4 p hybridization with hole doping, which enhances indirect exchange interactions between Mn dopants and gives rise to induced magnetic polarization in As 4 p states. On the contrary, application of pressure suppresses exchange interactions. While Mn K β emission spectra show a weak response of 3 d states to pressure, clear As 4 p band broadening (hole delocalization) is observed under pressure, ultimately leading to loss of ferromagnetism concomitant with a semiconductor to metal transition. The pressure response of As 4 p and Mn 3 d states is intimately connected with the evolution of the As-As interlayer distance and the geometry of the MnA s4 tetrahedral units, which we probed with x-ray diffraction. Our results indicate that hole doping increases the degree of covalency between the anion (As) p states and cation (Mn) d states in the MnA s4 tetrahedron, a crucial ingredient to promote indirect exchange interactions between Mn dopants and high T c ferromagnetism. The instability of ferromagnetism and semiconducting states against pressure is mainly dictated by delocalization of anion p states.

Spin manipulation with magnetic semiconductor barriers.

PubMed

Miao, Guo-Xing; Moodera, Jagadeesh S

2015-01-14

Magnetic semiconductors are a class of materials with special spin-filtering capabilities with magnetically tunable energy gaps. Many of these materials also possess another intrinsic property: indirect exchange interaction between the localized magnetic moments and the adjacent free electrons, which manifests as an extremely large effective magnetic field applying only on the spin degrees of freedom of the free electrons. Novel device concepts can be created by taking advantage of these properties. We discuss in the article the basic principles of these phenomena, and potential ways of applying them in constructing spintronic devices.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Banerjee, Ananya, E-mail: banerjee.ananya2008@gmail.com; Sarkar, A.

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 andmore » agreement between theory and experiment are good.« less

Probing the magnetic profile of diluted magnetic semiconductors using polarized neutron reflectivity.

PubMed

Luo, X; Tseng, L T; Lee, W T; Tan, T T; Bao, N N; Liu, R; Ding, J; Li, S; Lauter, V; Yi, J B

2017-07-24

Room temperature ferromagnetism has been observed in the Cu doped ZnO films deposited under an oxygen partial pressure of 10 -3 and 10 -5 torr on Pt (200 nm)/Ti (45 nm)/Si (001) substrates using pulsed laser deposition. Due to the deposition at relatively high temperature (873 K), Cu and Ti atoms diffuse to the surface and interface, which significantly affects the magnetic properties. Depth sensitive polarized neutron reflectometry method provides the details of the composition and magnetization profiles and shows that an accumulation of Cu on the surface leads to an increase in the magnetization near the surface. Our results reveal that the presence of the copper at Zn sites induces ferromagnetism at room temperature, confirming intrinsic ferromagnetism.

Route to the Smallest Doped Semiconductor: Mn(2+)-Doped (CdSe)13 Clusters.

PubMed

Yang, Jiwoong; Fainblat, Rachel; Kwon, Soon Gu; Muckel, Franziska; Yu, Jung Ho; Terlinden, Hendrik; Kim, Byung Hyo; Iavarone, Dino; Choi, Moon Kee; Kim, In Young; Park, Inchul; Hong, Hyo-Ki; Lee, Jihwa; Son, Jae Sung; Lee, Zonghoon; Kang, Kisuk; Hwang, Seong-Ju; Bacher, Gerd; Hyeon, Taeghwan

2015-10-14

Doping semiconductor nanocrystals with magnetic transition-metal ions has attracted fundamental interest to obtain a nanoscale dilute magnetic semiconductor, which has unique spin exchange interaction between magnetic spin and exciton. So far, the study on the doped semiconductor NCs has usually been conducted with NCs with larger than 2 nm because of synthetic challenges. Herein, we report the synthesis and characterization of Mn(2+)-doped (CdSe)13 clusters, the smallest doped semiconductors. In this study, single-sized doped clusters are produced in large scale. Despite their small size, these clusters have semiconductor band structure instead of that of molecules. Surprisingly, the clusters show multiple excitonic transitions with different magneto-optical activities, which can be attributed to the fine structure splitting. Magneto-optically active states exhibit giant Zeeman splittings up to elevated temperatures (128 K) with large g-factors of 81(±8) at 4 K. Our results present a new synthetic method for doped clusters and facilitate the understanding of doped semiconductor at the boundary of molecules and quantum nanostructure.

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

X-ray Characterization of Oxide-based Magnetic Semiconductors

NASA Astrophysics Data System (ADS)

Idzerda, Yves

2008-05-01

Although the evidence for magnetic semiconductors (not simply semiconductors which are ferromagnetic) is compelling, there is much uncertainty in the mechanism for the polarization of the carriers, suggesting that it must be quite novel. Recent experimental evidence suggests that this mechanism is similar to the polaron percolation theory proposed by Kaminski and Das Sarma,ootnotetextKaminski and S. Das Sarma, Physical Review Letters 88, 247202 (2002). which was recently applied specifically to doped oxides by Coey et al.ootnotetextJ. M. D. Coey, M. Venkatesan, and C. B. Fitzgerald, Nature Materials 4, 173 (2005). where the ferromagnetism is driven by the percolation of polarons generated by defects or dopants. We have used X-ray absorption spectroscopy at the L-edges and K-edges for low concentrations transition metal (TM) doped magnetic oxides (including TiO2, La1-xSrxO3, HfO2, and In2O3). We have found that in most cases, the transition metal assumes a valence consistent with being at a substitutional, and not interstitial site. We have also measured the X-ray Magnetic Circular Dichroism spectra. Although these materials show strong bulk magnetization, we are unable to detect a robust dichroism feature associated with magnetic elements in the host semiconductor. In the cases where a dichroism signal was observed, it was very weak and could be ascribed to a distinct ferromagnetic phase (TM metal cluster, TM oxide particulate, etc.) separate from the host material. This fascinating absence of a dichroic signal and its significant substantiation of important features of the polaron percolation model may help to finally resolve the issue of ferromagnetism in magnetically doped oxides.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garza-Navarro, Marco; Torres-Castro, Alejandro, E-mail: alejandro.torrescs@uanl.edu.m; Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Universidad Autonoma de Nuevo Leon, Apodaca, Nuevo Leon 66600

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 behaviormore » 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.« less

Hole doping and pressure effects on the II-II-V-based diluted magnetic semiconductor ( B a 1 - x K x ) ( Z n 1 - y M n y ) 2 A s 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, F.; Zhao, G. Q.; Escanhoela, Jr., C. A.

We investigate doping- and pressure-induced changes in the electronic state of Mn 3d and As 4p orbitals in II-II-V based diluted magnetic semiconductor (Ba 1-x,K x)(Zn 1-y,Mn y) 2As 2 to shed light into the mechanism of indirect exchange interactions leading to high ferromagnetic ordering temperature (T c = 230 K in optimally doped samples). A suite of x-ray spectroscopy experiments (emission, absorption and dichroism) show that the emergence, and further enhancement of ferromagnetic interactions with increased hole doping into the As 4p band is accompanied by a decrease in local 3d spin density at Mn sites. This is amore » result of increasing Mn 3d - As 4p hybridization with hole doping which enhances indirect exchange interactions between Mn dopants and gives rise to induced magnetic polarization in As 4p states. On the contrary, application of pressure suppresses exchange interactions. While Mn Kβ emission spectra show a weak response of 3d state to pressure, clear As 4p band broadening (hole delocalization) is observed under pressure ultimately leading to loss of ferromagnetism concomitant with a semiconductor to metal transition. The pressure response of As 4p and Mn 3d states is intimately connected with the evolution of the As-As interlayer distance and the geometry of the MnAs 4 tetrahedral units, which we probed with X-ray diffraction. Our results indicate that hole doping increases the degree of covalency between the anion (As) p states and cation (Mn) d states in the MnA s4 tetrahedron, a crucial ingredient to promote indirect exchange interactions between Mn dopants and high T c ferromagnetism. As a result, the instability of ferromagnetism and semiconducting state against pressure is mainly dictated by delocalization of anion p states.« less

Hole doping and pressure effects on the II-II-V-based diluted magnetic semiconductor ( B a 1 - x K x ) ( Z n 1 - y M n y ) 2 A s 2

DOE PAGES

Sun, F.; Zhao, G. Q.; Escanhoela, Jr., C. A.; ...

2017-03-13

We investigate doping- and pressure-induced changes in the electronic state of Mn 3d and As 4p orbitals in II-II-V based diluted magnetic semiconductor (Ba 1-x,K x)(Zn 1-y,Mn y) 2As 2 to shed light into the mechanism of indirect exchange interactions leading to high ferromagnetic ordering temperature (T c = 230 K in optimally doped samples). A suite of x-ray spectroscopy experiments (emission, absorption and dichroism) show that the emergence, and further enhancement of ferromagnetic interactions with increased hole doping into the As 4p band is accompanied by a decrease in local 3d spin density at Mn sites. This is amore » result of increasing Mn 3d - As 4p hybridization with hole doping which enhances indirect exchange interactions between Mn dopants and gives rise to induced magnetic polarization in As 4p states. On the contrary, application of pressure suppresses exchange interactions. While Mn Kβ emission spectra show a weak response of 3d state to pressure, clear As 4p band broadening (hole delocalization) is observed under pressure ultimately leading to loss of ferromagnetism concomitant with a semiconductor to metal transition. The pressure response of As 4p and Mn 3d states is intimately connected with the evolution of the As-As interlayer distance and the geometry of the MnAs 4 tetrahedral units, which we probed with X-ray diffraction. Our results indicate that hole doping increases the degree of covalency between the anion (As) p states and cation (Mn) d states in the MnA s4 tetrahedron, a crucial ingredient to promote indirect exchange interactions between Mn dopants and high T c ferromagnetism. As a result, the instability of ferromagnetism and semiconducting state against pressure is mainly dictated by delocalization of anion p states.« less

Tailoring Magnetism in Bulk Semiconductors and Quantum Dots

NASA Astrophysics Data System (ADS)

Zutic, Igor

2008-03-01

Carrier-mediated magnetism in semiconductors shows important and potentially useful differences from their metallic counterparts [1]. For example, in magnetically doped semiconductors the change in carrier density induced by light or bias could be sufficient to turn the ferromagnetism on and off. However, there remain many important challenges to fully understand these materials. Our density functional theory study of Mn- doped II-IV-V2 chalcopyrites [2] reveals that variation of magnetic properties across 64 different materials cannot be explained by the dominant models of ferromagnetism in semiconductors. We observe no qualitative similarity with the suggested Curie temperature scaling with the inverse cube of the lattice constant [3]. In contrast to most of the theoretical studies, we explicitly include the temperature dependence of the carrier density and propose a model which permits analysis of the thermodynamic stability of the competing magnetic states [4]. As an example we analyze the stability of a possible reentrant ferromagnetic semiconductor and discuss the experimental support for this prediction. An increasing temperature leads to an increased carrier density such that the enhanced coupling between magnetic impurities results in the onset of ferromagnetism as temperature is raised. We also use the real space finite-temperature local spin density approximation to examine magnetically doped quantum dots in which the interplay of quantum confinement and strong Coulomb interactions can lead to novel possibilities to tailor magnetism. We reveal that, even at a fixed number of carriers, the gate induced changes in the screening [5] or deviations from isotropic quantum confinement [6] could allow for a reversible control of magnetism and switching between zero and finite magnetization. Such magnetic quantum dots could also provide versatile voltage-control of spin currents and spin filtering. The work done in collaboration with S. C. Erwin (Naval Research

Towards improved photovoltaic conversion using dilute magnetic semiconductors (abstract only)

NASA Astrophysics Data System (ADS)

Olsson, Pär; Guillemoles, J.-F.; Domain, C.

2008-02-01

Present photovoltaic devices, based on p/n junctions, are limited from first principles to maximal efficiencies of 31% (40% under full solar concentration; Shockley and Queisser 1961 J. Appl. Phys. 32 510). However, more innovative schemes may overcome the Shockley-Queisser limit since the theoretical maximal efficiency of solar energy conversion is higher than 85% (Harder and Würfel 2003 Semicond. Sci. Technol. 18 S151). To date, the only practical realization of such an innovative scheme has been multi-junction devices, which at present hold the world record for efficiency at nearly 41% at significant solar concentration (US DOE news site: http://www.energy.gov/news/4503.htm). It has been proposed that one could make use of the solar spectrum in much the same way as the multi-junction devices do but in a single cell, using impurity induced intermediate levels to create gaps of different sizes. This intermediate level semiconductor (ILSC) concept (Green and Wenham 1994 Appl. Phys. Lett. 65 2907; Luque and Martí1997 Phys. Rev. Lett. 78 5014) has a maximal efficiency similar to that of multi-junction devices but suffers from prohibitively large non-radiative recombination rates. We here propose to use a ferromagnetic impurity scheme in order to reduce the non-radiative recombination rates while maintaining the high theoretical maximum efficiency of the ILSC scheme, that is about 46%. Using density functional theory calculations, the electronic and energetic properties of transition metal impurities for a wide range of semiconductors have been analysed. Of the several hundred compounds studied, only a few fulfil the design criteria that we present here. As an example, wide gap AlP is one of the most promising compounds. It was found that inclusion of significant amounts of Mn in AlP induces band structures providing conversion efficiencies potentially close to the theoretical maximum, with an estimated Curie temperature reaching above 100 K.

Size and diluted magnetic properties of diamond shaped graphene quantum dots: Monte Carlo study

NASA Astrophysics Data System (ADS)

Masrour, R.; Jabar, A.

2018-05-01

The magnetic properties of diamond shaped graphene quantum dots have been investigated by varying their sizes with the Monte Carlo simulation. The magnetizations and magnetic susceptibilities have been studied with dilutions x (magnetic atom), several sizes L (carbon atom) and exchange interaction J between the magnetic atoms. The all magnetic susceptibilities have been situated at the transitions temperatures of each parameters. The obtained values increase when increases the values of x, L and J. The effect of exchanges interactions and crystal field on the magnetization has been discussed. The magnetic hysteresis cycles for several dilutions x, sizes L, exchange interactions J and temperatures T. The magnetic coercive increases with increasing the exchange interactions and decreases when the temperatures values increasing.

Unraveling the Origin of Magnetism in Mesoporous Cu-Doped SnO₂ Magnetic Semiconductors.

PubMed

Fan, Junpeng; Menéndez, Enric; Guerrero, Miguel; Quintana, Alberto; Weschke, Eugen; Pellicer, Eva; Sort, Jordi

2017-10-25

The origin of magnetism in wide-gap semiconductors doped with non-ferromagnetic 3d transition metals still remains intriguing. In this article, insights in the magnetic properties of ordered mesoporous Cu-doped SnO₂ powders, prepared by hard-templating, have been unraveled. Whereas, both oxygen vacancies and Fe-based impurity phases could be a plausible explanation for the observed room temperature ferromagnetism, the low temperature magnetism is mainly and unambiguously arising from the nanoscale nature of the formed antiferromagnetic CuO, which results in a net magnetization that is reminiscent of ferromagnetic behavior. This is ascribed to uncompensated spins and shape-mediated spin canting effects. The reduced blocking temperature, which resides between 30 and 5 K, and traces of vertical shifts in the hysteresis loops confirm size effects in CuO. The mesoporous nature of the system with a large surface-to-volume ratio likely promotes the occurrence of uncompensated spins, spin canting, and spin frustration, offering new prospects in the use of magnetic semiconductors for energy-efficient spintronics.

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.

Fe implantation effect in the 6H-SiC semiconductor investigated by Mössbauer spectrometry

NASA Astrophysics Data System (ADS)

Diallo, M. L.; Diallo, L.; Fnidiki, A.; Lechevallier, L.; Cuvilly, F.; Blum, I.; Viret, M.; Marteau, M.; Eyidi, D.; Juraszek, J.; Declémy, A.

2017-08-01

P-doped 6H-SiC substrates were implanted with 57Fe ions at 380 °C or 550 °C to produce a diluted magnetic semiconductor with an Fe homogeneous concentration of about 100 nm thickness. The magnetic properties were studied with 57Fe Conversion Electron Mössbauer Spectrometry at room temperature (RT). Results obtained by this technique on annealed samples prove that ferromagnetism in 57Fe-implanted SiC for Fe concentrations close to 2% and 4% is mostly due to Fe atoms diluted in the matrix. In contrast, for Fe concentrations close to 6%, it also comes from Fe in magnetic phase nano-clusters. This study allows quantifying the Fe amount in the interstitial and substitutional sites and the nanoparticles and shows that the majority of the diluted Fe atoms are substituted on Si sites inducing ferromagnetism up to RT.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rana, Amit Kumar; Kumar, Yogendra; Arjunan, M.S.

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.more » 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.« less

METHODOLOGICAL NOTES: Integrating magnetism into semiconductor electronics

NASA Astrophysics Data System (ADS)

Zakharchenya, Boris P.; Korenev, Vladimir L.

2005-06-01

The view of a ferromagnetic-semiconducting hybrid structure as a single tunable system is presented. Based on an analysis of existing experiments it is shown that, contrary to a 'common sense', a nonmagnetic semiconductor is capable of playing an important role in controlling ferromagnetism. Magnetic properties of a hybrid (the hysteresis loop and the spatial orientation of magnetization) can be tuned both optically and electrically by utilizing semiconductor—making the hybrid an electronic-write-in and electronic-read-out elementary storage unit.

Spatially selective hydrogen irradiation of dilute nitride semiconductors: a brief review

NASA Astrophysics Data System (ADS)

Felici, Marco; Pettinari, Giorgio; Biccari, Francesco; Capizzi, Mario; Polimeni, Antonio

2018-05-01

We provide a brief survey of the most recent results obtained by performing spatially selective hydrogen irradiation of dilute nitride semiconductors. The striking effects of the formation of stable N–H complexes in these compounds—coupled to the ultrasharp diffusion profile of H therein—can be exploited to tailor the structural (lattice constant) and optoelectronic (energy gap, refractive index, electron effective mass) properties of the material in the growth plane, with a spatial resolution of a few nm. This can be applied to the fabrication of site-controlled quantum dots (QDs) and wires, but also to the realization of the optical elements required for the on-chip manipulation and routing of qubits in fully integrated photonic circuits. The fabricated QDs—which have shown the ability to emit single photons—can also be deterministically coupled with photonic crystal microcavities, proving their inherent suitability to act as integrated light sources in complex nanophotonic devices.

Magnetic polarons in a nonequilibrium polariton condensate

NASA Astrophysics Data System (ADS)

Mietki, Paweł; Matuszewski, Michał

2017-09-01

We consider a condensate of exciton polaritons in a diluted magnetic semiconductor microcavity. Such a system may exhibit magnetic self-trapping in the case of sufficiently strong coupling between polaritons and magnetic ions embedded in the semiconductor. We investigate the effect of the nonequilibrium nature of exciton polaritons on the physics of the resulting self-trapped magnetic polarons. We find that multiple polarons can exist at the same time, and we derive a critical condition for self-trapping that is different from the one predicted previously in the equilibrium case. Using the Bogoliubov-de Gennes approximation, we calculate the excitation spectrum and provide a physical explanation in terms of the effective magnetic attraction between polaritons, mediated by the ion subsystem.

Analytical study of acoustically perturbed Brillouin active magnetized semiconductor plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shukla, Arun, E-mail: arunshuklaujn@gmail.com; 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 foundmore » 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.« less

(Sr{sub 1-x}Na{sub x})(Cd{sub 1-x}Mn{sub x}){sub 2}As{sub 2}: A new charge and spin doping decoupled diluted magnetic semiconductors with CaAl{sub 2}Si{sub 2}-type structure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Bijuan; Deng, Zheng; Li, Wenmin

2016-08-28

We report the synthesis and characterization of a new bulk diluted ferromagnetic semiconductor via Na and Mn co-doping in SrCd{sub 2}As{sub 2} with a hexagonal CaAl{sub 2}Si{sub 2}-type structure. Together with carrier doping via (Sr,Na) substitution, spin doping via (Cd,Mn) substitution results in ferromagnetic order with Curie temperature of T{sub C} up to 13 K. Negative magnetoresistance is assigned to weak localization at low temperatures, where the magnetization of samples becomes saturated. The hexagonal structure of (Sr{sub 1−x}Na{sub x})(Cd{sub 1−x}Mn{sub x}){sub 2}As{sub 2} can be acted as a promising candidate for spin manipulations owing to its relatively small coercive field ofmore » less than 24 Oe.« less

Magneto-optical Faraday rotation of semiconductor nanoparticles embedded in dielectric matrices.

PubMed

Savchuk, Andriy I; Stolyarchuk, Ihor D; Makoviy, Vitaliy V; Savchuk, Oleksandr A

2014-04-01

Faraday rotation has been studied for CdS, CdTe, and CdS:Mn semiconductor nanoparticles synthesized by colloidal chemistry methods. Additionally these materials were prepared in a form of semiconductor nanoparticles embedded in polyvinyl alcohol films. Transmission electron microscopy and atomic force microscopy analyses served as confirmation of nanocrystallinity and estimation of the average size of the nanoparticles. Spectral dependence of the Faraday rotation for the studied nanocrystals and nanocomposites is correlated with a blueshift of the absorption edge due to the confinement effect in zero-dimensional structures. Faraday rotation spectra and their temperature behavior in Mn-doped nanocrystals demonstrates peculiarities, which are associated with s, p-d exchange interaction between Mn²⁺ ions and band carriers in diluted magnetic semiconductor nanostructures.

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.

Stretching magnetism with an electric field in a nitride semiconductor

PubMed Central

Sztenkiel, D.; Foltyn, M.; Mazur, G. P.; Adhikari, R.; Kosiel, K.; Gas, K.; Zgirski, M.; Kruszka, R.; Jakiela, R.; Li, Tian; Piotrowska, A.; Bonanni, A.; Sawicki, M.; Dietl, T.

2016-01-01

The significant inversion symmetry breaking specific to wurtzite semiconductors, and the associated spontaneous electrical polarization, lead to outstanding features such as high density of carriers at the GaN/(Al,Ga)N interface—exploited in high-power/high-frequency electronics—and piezoelectric capabilities serving for nanodrives, sensors and energy harvesting devices. Here we show that the multifunctionality of nitride semiconductors encompasses also a magnetoelectric effect allowing to control the magnetization by an electric field. We first demonstrate that doping of GaN by Mn results in a semi-insulating material apt to sustain electric fields as high as 5 MV cm−1. Having such a material we find experimentally that the inverse piezoelectric effect controls the magnitude of the single-ion magnetic anisotropy specific to Mn3+ ions in GaN. The corresponding changes in the magnetization can be quantitatively described by a theory developed here. PMID:27782126

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.

Anti-site-induced diverse diluted magnetism in LiMgPdSb-type CoMnTiSi alloy

NASA Astrophysics Data System (ADS)

Lin, T. T.; Dai, X. F.; Guo, R. K.; Cheng, Z. X.; Wang, L. Y.; Wang, X. T.; Liu, G. D.

2017-02-01

The effect of three kinds of anti-site disorder to electronic structure and magnetic properties of the LiMgPdSb-type CoMnTiSi alloy are investigated. It was found the Mn-Ti anti-site disorder can induce the diluted magnetism in CoMnTiSi matrix. The magnetic structure has an oscillation between the ferromagnetic and antiferromagnetic states with the different degree of Mn-Ti anti-site disorder. Two novel characteristics: the diluted antiferromagnetic half-metallicity and the diluted zero-gap half-metallity are found in the different degree range of the Mn-Ti anti-site disorder. The Co-Mn and Co-Ti anti-site disorder have little effect on the magnetic properties. The width of energy gap and the intensity of DOS at the Fermi level can be adjusted by the degree of Co-Mn or Co-Ti anti-site disorder. The independent control to the carrier concentration and magnetization can be realized by introducing the different anti-site disorder.

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.

Evidence of dilute ferromagnetism in rare-earth doped yttrium aluminium garnet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farr, Warrick G.; Goryachev, Maxim; Le Floch, Jean-Michel

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 themore » phenomenon is demonstrated.« less

Electronic structure of the dilute magnetic semiconductor G a1 -xM nxP from hard x-ray photoelectron spectroscopy and angle-resolved photoemission

NASA Astrophysics Data System (ADS)

Keqi, A.; Gehlmann, M.; Conti, G.; Nemšák, S.; Rattanachata, A.; Minár, J.; Plucinski, L.; Rault, J. E.; Rueff, J. P.; Scarpulla, M.; Hategan, M.; Pálsson, G. K.; Conlon, C.; Eiteneer, D.; Saw, A. Y.; Gray, A. X.; Kobayashi, K.; Ueda, S.; Dubon, O. D.; Schneider, C. M.; Fadley, C. S.

2018-04-01

We have investigated the electronic structure of the dilute magnetic semiconductor (DMS) G a0.98M n0.02P and compared it to that of an undoped GaP reference sample, using hard x-ray photoelectron spectroscopy (HXPS) and hard x-ray angle-resolved photoemission spectroscopy (HARPES) at energies of about 3 keV. We present experimental data, as well as theoretical calculations, to understand the role of the Mn dopant in the emergence of ferromagnetism in this material. Both core-level spectra and angle-resolved or angle-integrated valence spectra are discussed. In particular, the HARPES experimental data are compared to free-electron final-state model calculations and to more accurate one-step photoemission theory. The experimental results show differences between G a0.98M n0.02P and GaP in both angle-resolved and angle-integrated valence spectra. The G a0.98M n0.02P bands are broadened due to the presence of Mn impurities that disturb the long-range translational order of the host GaP crystal. Mn-induced changes of the electronic structure are observed over the entire valence band range, including the presence of a distinct impurity band close to the valence-band maximum of the DMS. These experimental results are in good agreement with the one-step photoemission calculations and a prior HARPES study of G a0.97M n0.03As and GaAs [Gray et al., Nat. Mater. 11, 957 (2012), 10.1038/nmat3450], demonstrating the strong similarity between these two materials. The Mn 2 p and 3 s core-level spectra also reveal an essentially identical state in doping both GaAs and GaP.

Solar energy harvesting by magnetic-semiconductor nanoheterostructure in water treatment technology.

PubMed

Mahmoodi, Vahid; Bastami, Tahereh Rohani; Ahmadpour, Ali

2018-03-01

Photocatalytic degradation of toxic organic pollutants in the wastewater using dispersed semiconductor nanophotocatalysts has a number of advantages such as high activity, cost effectiveness, and utilization of free solar energy. However, it is difficult to recover and recycle nanophotocatalysts since the fine dispersed nanoparticles are easily suspended in waters. Furthermore, a large amount of photocatalysts will lead to color contamination. Thus, it is necessary to prepare photocatalysts with easy separation for the reusable application. To take advantage of high photocatalysis activity and reusability, magnetic photocatalysts with separation function were utilized. In this review, the photocatalytic principle, structure, and application of the magnetic-semiconductor nanoheterostructure photocatalysts under solar light are evaluated. Graphical abstract ᅟ.

Destabilization of Magnetic Order in a Dilute Kitaev Spin Liquid Candidate

NASA Astrophysics Data System (ADS)

Lampen-Kelley, P.; Banerjee, A.; Aczel, A. A.; Cao, H. B.; Stone, M. B.; Bridges, C. A.; Yan, J.-Q.; Nagler, S. E.; Mandrus, D.

2017-12-01

The insulating honeycomb magnet α -RuCl3 exhibits fractionalized excitations that signal its proximity to a Kitaev quantum spin liquid state; however, at T =0 , fragile long-range magnetic order arises from non-Kitaev terms in the Hamiltonian. Spin vacancies in the form of Ir3 + substituted for Ru are found to destabilize this long-range order. Neutron diffraction and bulk characterization of Ru1 -xIrxCl3 show that the magnetic ordering temperature is suppressed with increasing x , and evidence of zizag magnetic order is absent for x >0.3 . Inelastic neutron scattering demonstrates that the signature of fractionalized excitations is maintained over the full range of x investigated. The depleted lattice without magnetic order thus hosts a spin-liquid-like ground state that may indicate the relevance of Kitaev physics in the magnetically dilute limit of RuCl3 .

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.

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.

Concentration dependence of the wings of a dipole-broadened magnetic resonance line in magnetically diluted lattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zobov, V. E., E-mail: rsa@iph.krasn.ru; Kucherov, M. M.

2017-01-15

The singularities of the time autocorrelation functions (ACFs) of magnetically diluted spin systems with dipole–dipole interaction (DDI), which determine the high-frequency asymptotics of autocorrelation functions and the wings of a magnetic resonance line, are studied. Using the self-consistent fluctuating local field approximation, nonlinear equations are derived for autocorrelation functions averaged over the independent random arrangement of spins (magnetic atoms) in a diamagnetic lattice with different spin concentrations. The equations take into account the specificity of the dipole–dipole interaction. First, due to its axial symmetry in a strong static magnetic field, the autocorrelation functions of longitudinal and transverse spin components aremore » described by different equations. Second, the long-range type of the dipole–dipole interaction is taken into account by separating contributions into the local field from distant and near spins. The recurrent equations are obtained for the expansion coefficients of autocorrelation functions in power series in time. From them, the numerical value of the coordinate of the nearest singularity of the autocorrelation function is found on the imaginary time axis, which is equal to the radius of convergence of these expansions. It is shown that in the strong dilution case, the logarithmic concentration dependence of the coordinate of the singularity is observed, which is caused by the presence of a cluster of near spins whose fraction is small but contribution to the modulation frequency is large. As an example a silicon crystal with different {sup 29}Si concentrations in magnetic fields directed along three crystallographic axes is considered.« less

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.

Destabilization of Magnetic Order in a Dilute Kitaev Spin Liquid Candidate

DOE PAGES

Lampen-Kelley, Paige; Banerjee, Arnab; Aczel, Adam A.; ...

2017-12-06

The insulating honeycomb magnet α–RuCl 3 exhibits fractionalized excitations that signal its proximity to a Kitaev quantum spin liquid state; however, at T=0, fragile long-range magnetic order arises from non-Kitaev terms in the Hamiltonian. Spin vacancies in the form of Ir 3+ substituted for Ru are found to destabilize this long-range order. Neutron diffraction and bulk characterization of Ru 1–xIr xCl 3 show that the magnetic ordering temperature is suppressed with increasing x, and evidence of zizag magnetic order is absent for x > 0.3. Inelastic neutron scattering demonstrates that the signature of fractionalized excitations is maintained over the fullmore » range of x investigated. In conclusion, the depleted lattice without magnetic order thus hosts a spin-liquid-like ground state that may indicate the relevance of Kitaev physics in the magnetically dilute limit of RuCl 3.« less

Asymptotic Analysis of Melt Growth for Antimonide-Based Compound Semiconductor Crystals in Magnetic and Electric Fields

DTIC Science & Technology

2006-10-01

F. Bliss, Gerald W. Iseler and Piotr Becla, "Combining static and rotating magnetic fields during modified vertical Bridgman crystal growth ," AIAA...Wang and Nancy Ma, "Semiconductor crystal growth by the vertical Bridgman process with rotating magnetic fields," ASME Journal of Heat Transfer...2005. 15. Stephen J. LaPointe, Nancy Ma and Donald W. Mueller, Jr., " Growth of binary alloyed semiconductor crystals by the vertical Bridgman

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.

Electronic and magnetic properties of Mn-doped WSe2 monolayer under strain

NASA Astrophysics Data System (ADS)

Xin, Qianqian; Zhao, Xu; Wang, Tianxing

2017-04-01

Electronic and magnetic properties of Mn-doped WSe2 monolyer subject to isotropic strain are investigated using the first-principles methods based on the density functional theory. Our results indicate that Mn-doped WSe2 monolayer is a magnetic semiconductor nanomaterial with strong spontaneous magnetism without strain and the total magnetic moment of Mn-doped system is 1.038μB. We applied strain to Mn-doped WSe2 monolayer from -10% to 10%. The doped system transforms from magnetic semiconductor to half-metallic material from -10% to -2% compressive strain and from 2% to 6% tensile strain. The largest half-metallic gap is 0.450 eV at -2% compressive strain. The doped system shows metal property from 7% to 10%. Its maximum magnetic moment comes to 1.181μB at 6% tensile strain. However, the magnetic moment of system decreases to zero sharply when tensile strain arrived at 7%. Strain changes the redistribution of charges and arises to the magnetic effect. The coupling between the 3d orbital of Mn atom, 5d orbital of W atom and 4p orbital of Se atom is analyzed to explain the strong strain effect on the magnetic properties. Our studies predict Mn-doped WSe2 monolayers under strain to be candidates for thin dilute magnetic semiconductors, which is important for application in semiconductor spintronics.

Magnetoreflection spectroscopy of monolayer transition-metal dichalcogenide semiconductors in pulsed magnetic fields

DOE PAGES

Stier, Andreas V.; McCreary, Kathleen M.; Jonker, Berend T.; ...

2016-05-13

The authors describe recent experimental efforts to perform polarization-resolved optical spectroscopy of monolayer transition-metal dichalcogenide semiconductors in very large pulsed magnetic fields to 65 T. The experimental setup and technical challenges are discussed in detail, and temperature-dependent magnetoreflection spectra from atomically thin tungsten disulphide are presented. The data clearly reveal not only the valley Zeeman effect in these two-dimensional semiconductors but also the small quadratic exciton diamagnetic shift from which the very small exciton size can be directly inferred. Lastly, the authors present model calculations that demonstrate how the measured diamagnetic shifts can be used to constrain estimates of themore » exciton binding energy in this new family of monolayer semiconductors.« less

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.

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

Ballistic transport in nanowires through non-magnetic or magnetic cavity

NASA Astrophysics Data System (ADS)

Nonoyama, Shinji; Honma, Yukari; Ono, Miyuki; Nakamura, Atsunobu

2015-07-01

Ballistic transport phenomena through a region containing a cavity in a quasi-one-dimensional quantum nanowire are investigated. Conductance curves calculated as a function of a structural parameter show quantum interference effects on transport clearly. In a special geometry, very narrow periodic dips, which are attributable to the anti-resonance, appear on the conductance curve. The nature of the virtual bound state resulting in the anti-resonance is studied in detail. Electron conductions through a small dilute magnetic semiconductor are also investigated.

Ultrafast magnetization modulation induced by the electric field component of a terahertz pulse in a ferromagnetic-semiconductor thin film.

PubMed

Ishii, Tomoaki; Yamakawa, Hiromichi; Kanaki, Toshiki; Miyamoto, Tatsuya; Kida, Noriaki; Okamoto, Hiroshi; Tanaka, Masaaki; Ohya, Shinobu

2018-05-02

High-speed magnetization control of ferromagnetic films using light pulses is attracting considerable attention and is increasingly important for the development of spintronic devices. Irradiation with a nearly monocyclic terahertz pulse, which can induce strong electromagnetic fields in ferromagnetic films within an extremely short time of less than ~1 ps, is promising for damping-free high-speed coherent control of the magnetization. Here, we successfully observe a terahertz response in a ferromagnetic-semiconductor thin film. In addition, we find that a similar terahertz response is observed even in a non-magnetic semiconductor and reveal that the electric-field component of the terahertz pulse plays a crucial role in the magnetization response through the spin-carrier interactions in a ferromagnetic-semiconductor thin film. Our findings will provide new guidelines for designing materials suitable for ultrafast magnetization reversal.

Frustrated spin chains in strong magnetic field: Dilute two-component Bose gas regime

NASA Astrophysics Data System (ADS)

Kolezhuk, A. K.; Heidrich-Meisner, F.; Greschner, S.; Vekua, T.

2012-02-01

We study the ground state of frustrated spin-S chains in a strong magnetic field in the immediate vicinity of saturation. In strongly frustrated chains, the magnon dispersion has two degenerate minima at inequivalent momenta ±Q, and just below the saturation field the system can be effectively represented as a dilute one-dimensional lattice gas of two species of bosons that correspond to magnons with momenta around ±Q. We present a theory of effective interactions in such a dilute magnon gas that allows us to make quantitative predictions for arbitrary values of the spin. With the help of this method, we are able to establish the magnetic phase diagram of frustrated chains close to saturation and study phase transitions between several nontrivial states, including a two-component Luttinger liquid, a vector chiral phase, and phases with bound magnons. We study those phase transitions numerically and find a good agreement with our analytical predictions.

Self-bound droplets of a dilute magnetic quantum liquid

NASA Astrophysics Data System (ADS)

Schmitt, Matthias; Wenzel, Matthias; Böttcher, Fabian; Ferrier-Barbut, Igor; Pfau, Tilman

2016-11-01

Self-bound many-body systems are formed through a balance of attractive and repulsive forces and occur in many physical scenarios. Liquid droplets are an example of a self-bound system, formed by a balance of the mutual attractive and repulsive forces that derive from different components of the inter-particle potential. It has been suggested that self-bound ensembles of ultracold atoms should exist for atom number densities that are 108 times lower than in a helium droplet, which is formed from a dense quantum liquid. However, such ensembles have been elusive up to now because they require forces other than the usual zero-range contact interaction, which is either attractive or repulsive but never both. On the basis of the recent finding that an unstable bosonic dipolar gas can be stabilized by a repulsive many-body term, it was predicted that three-dimensional self-bound quantum droplets of magnetic atoms should exist. Here we report the observation of such droplets in a trap-free levitation field. We find that this dilute magnetic quantum liquid requires a minimum, critical number of atoms, below which the liquid evaporates into an expanding gas as a result of the quantum pressure of the individual constituents. Consequently, around this critical atom number we observe an interaction-driven phase transition between a gas and a self-bound liquid in the quantum degenerate regime with ultracold atoms. These droplets are the dilute counterpart of strongly correlated self-bound systems such as atomic nuclei and helium droplets.

Self-bound droplets of a dilute magnetic quantum liquid.

PubMed

Schmitt, Matthias; Wenzel, Matthias; Böttcher, Fabian; Ferrier-Barbut, Igor; Pfau, Tilman

2016-11-10

Self-bound many-body systems are formed through a balance of attractive and repulsive forces and occur in many physical scenarios. Liquid droplets are an example of a self-bound system, formed by a balance of the mutual attractive and repulsive forces that derive from different components of the inter-particle potential. It has been suggested that self-bound ensembles of ultracold atoms should exist for atom number densities that are 10 8 times lower than in a helium droplet, which is formed from a dense quantum liquid. However, such ensembles have been elusive up to now because they require forces other than the usual zero-range contact interaction, which is either attractive or repulsive but never both. On the basis of the recent finding that an unstable bosonic dipolar gas can be stabilized by a repulsive many-body term, it was predicted that three-dimensional self-bound quantum droplets of magnetic atoms should exist. Here we report the observation of such droplets in a trap-free levitation field. We find that this dilute magnetic quantum liquid requires a minimum, critical number of atoms, below which the liquid evaporates into an expanding gas as a result of the quantum pressure of the individual constituents. Consequently, around this critical atom number we observe an interaction-driven phase transition between a gas and a self-bound liquid in the quantum degenerate regime with ultracold atoms. These droplets are the dilute counterpart of strongly correlated self-bound systems such as atomic nuclei and helium droplets.

Optical third harmonic generation in the magnetic semiconductor EuSe

NASA Astrophysics Data System (ADS)

Lafrentz, M.; Brunne, D.; Kaminski, B.; Pavlov, V. V.; Pisarev, R. V.; Henriques, A. B.; Yakovlev, D. R.; Springholz, G.; Bauer, G.; Bayer, M.

2012-01-01

Third harmonic generation (THG) has been studied in europium selenide EuSe in the vicinity of the band gap at 2.1-2.6 eV and at higher energies up to 3.7 eV. EuSe is a magnetic semiconductor crystalizing in centrosymmetric structure of rock-salt type with the point group m3m. For this symmetry the crystallographic and magnetic-field-induced THG nonlinearities are allowed in the electric-dipole approximation. Using temperature, magnetic field, and rotational anisotropy measurements, the crystallographic and magnetic-field-induced contributions to THG were unambiguously separated. Strong resonant magnetic-field-induced THG signals were measured at energies in the range of 2.1-2.6 eV and 3.1-3.6 eV for which we assign to transitions from 4f7 to 4f65d1 bands, namely involving 5d(t2g) and 5d(eg) states.

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.

Combined use of fluorescence with a magnetic tracer and dilution effect upon sentinel node localization in a murine model.

PubMed

Kuwahata, Akihiro; Ahmed, Muneer; Saeki, Kohei; Chikaki, Shinichi; Kaneko, Miki; Qiu, Wenqi; Xin, Zonghao; Yamaguchi, Shinji; Kaneko, Akiko; Douek, Michael; Kusakabe, Moriaki; Sekino, Masaki

2018-01-01

Sentinel node biopsy using radioisotope and blue dye remains a gold standard for axillary staging in breast cancer patients with low axillary burden. However, limitations in the use of radioisotopes have resulted in emergence of novel techniques. This is the first in vivo study to assess the feasibility of combining the two most common novel techniques of using a magnetic tracer and indocyanine green (ICG) fluorescence. A total of 48 mice were divided into eight groups. Groups 1 and 2, the co-localization groups, received an injection of magnetic tracers (Resovist ® and Sienna+ ® , respectively) and ICG fluorescence; distilled water was used as the solvent of ICG. Groups 3 and 4, the diluted injection groups, received an injection of magnetic tracers (Resovist and Sienna+, respectively) and saline for dilution. Groups 5, 6, and 7, the control groups, received magnetic tracer (Resovist, Sienna+) and ICG alone, respectively. Fluorescent intensity assessment and iron quantification of excised popliteal lymph nodes were performed. Group 1', a co-localization group, received an injection of magnetic tracers (Resovist) and ICG' fluorescence: saline was used as the solvent for ICG. Lymphatic uptake of all tracers was confined to the popliteal nodes only, with co-localization confirmed in all cases and no significant difference in fluorescent intensity or iron content of ex vivo nodes between the groups (except for Group 1'). There was no impact of dilution on the iron content in the diluted Sienna+ group, but it significantly enhanced Resovist uptake ( P =0.005). In addition, there was a significant difference in iron content ( P =0.003) in Group 1'. The combination of a magnetic tracer (Resovist or Sienna+) and ICG fluorescence is feasible for sentinel node biopsy and will potentially allow for precise transcutaneous node identification, in addition to accurate intraoperative assessment. This radioisotope-free "combined technique" warrants further assessment within a

Novel room temperature ferromagnetic semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, Amita

2004-06-01

substituting 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.« less

AB INITIO Investigations of the Magnetism in Diluted Magnetic Semiconductor Fe-DOPED GaN

NASA Astrophysics Data System (ADS)

Cheng, Jie; Zhou, Jing; Xu, Wei; Dong, Peng

2014-01-01

In this paper, we present a first principle investigation on Fe-doped GaN with wurtzite and zinc-blend structure using full potential density functional calculations. Data point out that the magnetic behavior of Fe-doped GaN system is strongly dependent on Fe doping configurations. In agreement with the experimental reports, and independently by doping, antiferromagnetism occurs in the zinc-blend structure, while in the wurtzite structure ferromagnetism depends on the Fe doping configurations. Detailed analyses combined with density of state calculations support the assignment that the ferromagnetism is closely related to the impurity band at the origin of the hybridization of Fe 3d and N 2p states in the Fe-doped GaN of wurtzite phase.

Periodic multilayer magnetized cold plasma containing a doped semiconductor

NASA Astrophysics Data System (ADS)

Nayak, Chittaranjan; Saha, Ardhendu; Aghajamali, Alireza

2018-07-01

The present work is to numerically investigate the properties of the defect mode in a one-dimensional photonic crystal made of magnetized cold plasma, doped by semiconductor. The defect mode of such kind of multilayer structure is analyzed by applying the character matrix method to each individual layer. Numerical results illustrate that the defect mode frequency can be tuned by varying the external magnetic field, the electron density, and the thickness of the defect layer. Moreover, the behavior of the defect mode was found to be quite interesting when study the oblique incidence. It was found that for both right- and left-hand polarized transversal magnetic waves, the defect mode of the proposed defective structure disappears when the angle of incidence is larger than a particular oblique incidence. For the left-hand polarized transversal electric wave, however, an additional defect mode was noticed. The results lead to some new information concerning the designing of new types of tunable narrowband microwave filters.

Periodic multilayer magnetized cold plasma containing a doped semiconductor

NASA Astrophysics Data System (ADS)

Nayak, Chittaranjan; Saha, Ardhendu; Aghajamali, Alireza

2018-02-01

The present work is to numerically investigate the properties of the defect mode in a one-dimensional photonic crystal made of magnetized cold plasma, doped by semiconductor. The defect mode of such kind of multilayer structure is analyzed by applying the character matrix method to each individual layer. Numerical results illustrate that the defect mode frequency can be tuned by varying the external magnetic field, the electron density, and the thickness of the defect layer. Moreover, the behavior of the defect mode was found to be quite interesting when study the oblique incidence. It was found that for both right- and left-hand polarized transversal magnetic waves, the defect mode of the proposed defective structure disappears when the angle of incidence is larger than a particular oblique incidence. For the left-hand polarized transversal electric wave, however, an additional defect mode was noticed. The results lead to some new information concerning the designing of new types of tunable narrowband microwave filters.

Carrier-dependent magnetic anisotropy of cobalt doped titanium dioxide

PubMed Central

Shao, Bin; Feng, Min; Zuo, Xu

2014-01-01

Using first-principles calculations, we predict that the magnetic anisotropy energy of Co-doped TiO2 sensitively depends on carrier accumulation. This magnetoelectric phenomenon provides a potential route to a direct manipulation of the magnetization direction in diluted magnetic semiconductor by external electric-fields. We calculate the band structures and reveal the origin of the carrier-dependent magnetic anisotropy energy in k-space. It is shown that the carrier accumulation shifts the Fermi energy, and consequently, regulates the competing contributions to the magnetic anisotropy energy. The calculations provide an insight to understanding this magnetoelectric phenomenon, and a straightforward way to search prospective materials for electrically controllable spin direction of carriers. PMID:25510846

Optimal doping control of magnetic semiconductors via subsurfactant epitaxy.

PubMed

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

2008-02-15

"Subsurfactant epitaxy" is established as a conceptually new approach for introducing manganese as a magnetic dopant into germanium. A kinetic pathway is devised in which the subsurface interstitial sites on Ge(100) are first selectively populated with Mn, while lateral diffusion and clustering on or underneath the surface are effectively suppressed. Subsequent Ge deposition as a capping layer produces a novel surfactantlike phenomenon as the interstitial Mn atoms float towards newly defined subsurface sites at the growth front. Furthermore, the Mn atoms that failed to float upwards are uniformly distributed within the Ge capping layer. The resulting doping levels of order 0.25 at. % would normally be considered too low for ferromagnetic ordering, but the Curie temperature exceeds room temperature by a comfortable margin. Subsurfactant epitaxy thus enables superior dopant control in magnetic semiconductors.

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.

Evolution of magnetic and orbital properties in the magnetically diluted A -site spinel Cu1 -xZnxRh2O4

NASA Astrophysics Data System (ADS)

Zakrzewski, A. V.; Gangopadhyay, S.; MacDougall, G. J.; Aczel, A. A.; Calder, S.; Williams, T. J.

2018-06-01

In frustrated spinel antiferromagnets, dilution with nonmagnetic ions can be a powerful strategy for probing unconventional spin states or uncovering interesting phenomena. Here, we present x-ray, neutron scattering, and thermodynamic studies of the effects of magnetic dilution of the tetragonally distorted A -site spinel antiferromagnet, CuRh2O4 , with nonmagnetic Zn2 + ions. Our data confirm the helical spin order recently identified at low temperatures in this material, and further demonstrate a systematic suppression of the associated Néel temperature with increasing site dilution towards a continuous transition with critical doping of xspin˜0.44 . Interestingly, this critical doping is demonstrably distinct from a second structural critical point at xJ T˜0.6 , which is consistent with the suppression of orbital order on the A site through a classical percolative mechanism. This anomalously low value for xspin is confirmed via multiple measurements, and is inconsistent with predictions of classical percolation theory, suggesting that the spin transition in this material is driven by an enhancement of preexisting spin fluctuations with weak dilution.

Excitonic pathway to photoinduced magnetism in colloidal nanocrystals with nonmagnetic dopants

NASA Astrophysics Data System (ADS)

Pinchetti, Valerio; Di, Qiumei; Lorenzon, Monica; Camellini, Andrea; Fasoli, Mauro; Zavelani-Rossi, Margherita; Meinardi, Francesco; Zhang, Jiatao; Crooker, Scott A.; Brovelli, Sergio

2018-02-01

Electronic doping of colloidal semiconductor nanostructures holds promise for future device concepts in optoelectronic and spin-based technologies. Ag+ is an emerging electronic dopant in iii-v and ii-vi nanostructures, introducing intragap electronic states optically coupled to the host conduction band. With its full 4d shell Ag+ is nonmagnetic, and the dopant-related luminescence is ascribed to decay of the conduction-band electron following transfer of the photoexcited hole to Ag+. This optical activation process and the associated modification of the electronic configuration of Ag+ remain unclear. Here, we trace a comprehensive picture of the excitonic process in Ag-doped CdSe nanocrystals and demonstrate that, in contrast to expectations, capture of the photohole leads to conversion of Ag+ to paramagnetic Ag2+. The process of exciton recombination is thus inextricably tied to photoinduced magnetism. Accordingly, we observe strong optically activated magnetism and diluted magnetic semiconductor behaviour, demonstrating that optically switchable magnetic nanomaterials can be obtained by exploiting excitonic processes involving nonmagnetic impurities.

Electronic and magnetic properties of SnS2 monolayer doped with 4d transition metals

NASA Astrophysics Data System (ADS)

Xiao, Wen-Zhi; Xiao, Gang; Rong, Qing-Yan; Chen, Qiao; Wang, Ling-Ling

2017-09-01

We investigate the electronic structures and magnetic properties of SnS2 monolayers substitutionally doped with 4-d transition-metal through systematic first principles calculations. The doped complexes exhibit interesting electronic and magnetic behaviors, depending on the interplay between crystal field splitting, Hund's rule, and 4d levels. The system doped with Y is nonmagnetic metal. Both the Zr- and Pd-doped systems remain nonmagnetic semiconductors. Doping results in half-metallic states for Nb-, Ru-, Rh-, Ag, and Cd doped cases, and magnetic semiconductors for systems with Mo and Tc dopants. In particular, the Nb- and Mo-doped systems display long-ranged ferromagnetic ordering with Curie temperature above room temperature, which are primarily attributable to the double-exchange mechanism, and the p-d/p-p hybridizations, respectively. Moreover, The Mo-doped system has excellent energetic stability and flexible mechanical stability, and also possesses remarkable dynamic and thermal (500 K) stability. Our studies demonstrate that Nb- and Mo-doped SnS2 monolayers are promising candidates for preparing 2D diluted magnetic semiconductors, and hence will be a helpful clue for experimentalists.

Structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kanzyuba, Vasily; Dong, Sining; Liu, Xinyu; Li, Xiang; Rouvimov, Sergei; Okuno, Hanako; Mariette, Henri; Zhang, Xueqiang; Ptasinska, Sylwia; Tracy, Brian D.; Smith, David J.; Dobrowolska, Margaret; Furdyna, Jacek K.

2017-02-01

We describe the structural evolution of dilute magnetic (Sn,Mn)Se films grown by molecular beam epitaxy on GaAs (111) substrates, as revealed by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. When the Mn concentration is increased, the lattice of the ternary (Sn,Mn)Se films evolves quasi-coherently from a SnSe2 two-dimensional (2D) crystal structure into a more complex quasi-2D lattice rearrangement, ultimately transforming into the magnetically concentrated antiferromagnetic MnSe 3D rock-salt structure as Mn approaches 50 at. % of this material. These structural transformations are expected to underlie the evolution of magnetic properties of this ternary system reported earlier in the literature.

Electrodynamic properties of a hypercrystal with ferrite and semiconductor layers in an external magnetic field

NASA Astrophysics Data System (ADS)

Fedorin, Illia V.

2018-01-01

Electrodynamic properties of a photonic hypercrystal formed by periodically alternating two types of anisotropic metamaterials are studied. The first metamaterial consists of ferrite and dielectric layers, while the second metamaterial consists of semiconductor and dielectric layers. The system is assumed to be placed in an external magnetic field, which applied parallel to the boundaries of the layers. An effective medium theory which is suitable for calculation of properties of long-wavelength electromagnetic modes is applied in order to derive averaged expressions for effective constitutive parameters. It has been shown that providing a conscious choice of the constitutive parameters and material fractions of magnetic, semiconductor, and dielectric layers, the system under study shows hypercrystal properties for both TE and TM waves in the different frequency ranges.

Tuning the antiferromagnetic helical pitch length and nanoscale domain size in Fe3PO4O3 by magnetic dilution

NASA Astrophysics Data System (ADS)

Tarne, M. J.; Bordelon, M. M.; Calder, S.; Neilson, J. R.; Ross, K. A.

2017-12-01

The insulating magnetic material Fe3PO4O3 features a noncentrosymmetric lattice composed of Fe3 + triangular units. Frustration, due to competing near-neighbor (J1) and next-nearest-neighbor (J2) antiferromagnetic interactions, was recently suggested to be the origin of an antiferromagnetic helical ground state with unusual needlelike nanoscale magnetic domains in Fe3PO4O3 . Magnetic dilution is shown here to tune the ratio of these magnetic interactions, thus providing deeper insight into this unconventional antiferromagnet. Dilution of the Fe3 + lattice in Fe3PO4O3 was accomplished by substituting nonmagnetic Ga3 + to form the solid solution series Fe3-xGaxPO4O3 with x =0.012 , 0.06, 0.25, 0.5, 1.0, 1.5. Magnetic susceptibility and neutron powder diffraction data from this series are presented. A continuous decrease of both the helical pitch length and the domain size is observed with increasing dilution up to at least x =0.25 , while for x ≥0.5 , the compounds lack long-range magnetic order entirely. The decrease in the helical pitch length with increasing x can be qualitatively understood by reduction of the ratio of J2/J1 in the Heisenberg model, consistent with mean-field considerations. Intriguingly, the magnetic correlation length in the a b plane remains nearly equal to the pitch length for each value of x ≤0.25 , showing that the two quantities are intrinsically connected in this unusual antiferromagnet.

A comparison study of Co and Cu doped MgO diluted magnetic thin films

NASA Astrophysics Data System (ADS)

Sarıtaş, S.; ćakıcı, T.; Muǧlu, G. Merhan; Kundakcı, M.; Yıldırım, M.

2017-02-01

Transition metal-doped MgO diluted magnetic thin films are appropriate candidates for spintronic applications and designing magnetic devices and sensors. Therefore, MgO:Co and MgO:Cu films were deposited on glass substrates by Chemical Spray Pyrolysis (CSP) method different thin film deposition parameters. Deposited different transition metal doped MgO thin films were compared in terms of optic and structural properties. Comparison optic analysis of the films was investigated spectral absorption and transmittance measurements by UV-Vis double beam spectrophotometer technique. Comparison structural analysis of the thin films was examined by using XRD, Raman Analysis, SEM, EDX and AFM techniques. The transition metal-doped; MgO:Co and MgO:Cu thin films maybe have potential applications in spintronics and magnetic data storage.

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.

Charged excitons in a dilute two-dimensional electron gas in a high magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wojs, Arkadiusz; Institute of Physics, Wroclaw University of Technology, Wroclaw 50-370,; Quinn, John J.

2000-08-15

A theory of charged excitons X{sup -} in a dilute two-dimensional (2D) electron gas in a high-magnetic field is presented. In contrast to previous calculations, three bound X{sup -} states (one singlet and two triplets) are found in a narrow and symmetric GaAs quantum well. The singlet and a ''bright'' triplet are the two optically active states observed in experiments. The bright triplet has the binding energy of about 1 meV, smaller than the singlet and a ''dark'' triplet. The interaction of bound X{sup -}'s with a dilute 2D electron gas is investigated using exact diagonalization techniques. It is foundmore » that the short-range character of the e-X{sup -} interactions effectively isolates bound X{sup -} states from a dilute e-h plasma. This results in the insensitivity of the photoluminescence spectrum to the filling factor {nu}, and a rapid decrease of the oscillator strength of the dark triplet X{sup -} as a function of {nu}{sup -1}. (c) 2000 The American Physical Society.« less

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.

Production and distribution of dilute species in semiconducting materials

DOEpatents

James, Ralph B.; Camarda, Giuseppe; Bolotnikov, Aleksey E.; Hossain, Anwar; Yang, Ge; Kim, Kihyun

2016-09-06

Technologies are described effective to implement systems and methods of producing a material. The methods comprise receiving a tertiary semiconductor sample with a dilute species. The sample has two ends. The first end of the sample includes a first concentration of the dilute species lower than a second concentration of the dilute species in the second end of the sample. The method further comprises heating the sample in a chamber. The chamber has a first zone and a second zone. The first zone having a first temperature higher than a second temperature in the second zone. The sample is orientated such that the first end is in the first zone and the second end is in the second zone.

Temperature-dependent magnetic anisotropy in the layered magnetic semiconductors Cr I3 and CrB r3

NASA Astrophysics Data System (ADS)

Richter, Nils; Weber, Daniel; Martin, Franziska; Singh, Nirpendra; Schwingenschlögl, Udo; Lotsch, Bettina V.; Kläui, Mathias

2018-02-01

Chromium trihalides are layered and exfoliable semiconductors and exhibit unusual magnetic properties with a surprising temperature dependence of the magnetization. By analyzing the evolution of the magnetocrystalline anisotropy with temperature in chromium iodide Cr I3 , we find it strongly changes from Ku=300 ±50 kJ / m3 at 5 K to Ku=43 ±7 kJ / m3 at 60 K , close to the Curie temperature. We draw a direct comparison to CrB r3 , which serves as a reference, and where we find results consistent with literature. In particular, we show that the anisotropy change in the iodide compound is more than 3 times larger than in the bromide. We analyze this temperature dependence using a classical model, showing that the anisotropy constant scales with the magnetization at any given temperature below the Curie temperature, indicating that the temperature dependence can be explained by a dominant uniaxial anisotropy where this scaling results from local spin clusters having thermally induced magnetization directions that deviate from the overall magnetization.

First-principles study of ZnSnAs2-based dilute magnetic semiconductors

NASA Astrophysics Data System (ADS)

Kizaki, Hidetoshi; Morikawa, Yoshitada

2018-02-01

The electronic structure and magnetic properties of chalcopyrite Zn(Sn,TM)As2 and (Zn,TM)SnAs2 have been investigated by the Korringa-Kohn-Rostoker method combined with the coherent potential approximation within the local spin density approximation, where TM denotes a 3d transition metal element. We find that the half-metallic and high-spin ferromagnetic state can be obtained in Zn(Sn,V)As2, Zn(Sn,Cr)As2, Zn(Sn,Mn)As2, (Zn,V)SnAs2, and (Zn,Cr)SnAs2. The calculated result of Zn(Sn,Mn)As2 is in good agreement with the experimentally observed room-temperature ferromagnetism if we can control selective Mn doping at Sn sites. In addition, (Zn,V)SnAs2 and (Zn,Cr)SnAs2 are predicted to exhibit high-Curie-temperature ferromagnetism.

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.

Magnetization dynamics in dilute Pd1-xFex thin films and patterned microstructures considered for superconducting electronics

NASA Astrophysics Data System (ADS)

Golovchanskiy, I. A.; Bolginov, V. V.; Abramov, N. N.; Stolyarov, V. S.; Ben Hamida, A.; Chichkov, V. I.; Roditchev, D.; Ryazanov, V. V.

2016-10-01

Motivated by recent burst of applications of ferromagnetic layers in superconducting digital and quantum elements, we study the magnetism of thin films and patterned microstructures of Pd0.99Fe0.01. In this diluted ferromagnetic system, a high-sensitivity ferromagnetic resonance (FMR) experiment reveals spectroscopic signatures of re-magnetization and enables the estimation of the saturation magnetization, the anisotropy field, and the Gilbert damping constant. The detailed analysis of FMR spectra links the observed unexpectedly high reduced anisotropy field (0.06-0.14) with the internal anisotropy, points towards a cluster nature of the ferromagnetism, and allows estimating characteristic time scale for magnetization dynamics in Pd-Fe based cryogenic memory elements to ( 3 - 5 ) × 10 - 9 s.

Optical orientation in ferromagnet/semiconductor hybrids

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2008-11-01

The physics of optical pumping of semiconductor electrons in ferromagnet/semiconductor hybrids is discussed. Optically oriented semiconductor electrons detect the magnetic state of a ferromagnetic film. In turn, the ferromagnetism of the hybrid can be controlled optically with the help of a semiconductor. Spin-spin interactions near the ferromagnet/semiconductor interface play a crucial role in the optical readout and the manipulation of ferromagnetism.

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)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saeed, Y., E-mail: yasir_saeed54321@yahoo.co; Shaukat, A., E-mail: schaukat@gmail.co; Nazir, S., E-mail: nazirsafdar@gmail.co

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 structuremore » 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.« less

Spin-dependent transport phenomena in organic semiconductors

NASA Astrophysics Data System (ADS)

Bergeson, Jeremy D.

Thin-film organic semiconductors transport can have an anomalously high sensitivity to low magnetic fields. Such a response is unexpected considering that thermal fluctuation energies are greater than the energy associated with the intrinsic spin of charge carriers at a modest magnetic field of 100 Oe by a factor of more than 104 at room temperature and is still greater by 102 even at liquid helium temperatures. Nevertheless, we report experimental characterization of (1) spin-dependent injection, detection and transport of spin-polarized current through organic semiconductors and (2) the influence of a magnetic field on the spin dynamics of recombination-limited transport. The first focus of this work was accomplished by fabricating basic spin-valve devices consisting of two magnetic layers spatially separated by a nonmagnetic organic semiconductor. The spin-valve effect is a change in electrical resistance due to the magnetizations of the magnetic layers changing from parallel to antiparallel alignment, or vice versa. The conductivities of the metallic contacts and that of the semiconductor differed by many orders of magnitude, which inhibited the injection of a spin-polarized current from the magnet into the nonmagnet. We successfully overcame the problem of conductivity mismatch by inserting ultra-thin tunnel barriers at the metal/semiconductor interfaces which aided in yielding a ˜20% spin-valve effect at liquid helium temperatures and the effect persisted up to 150 K. We built on this achievement by constructing spin valves where one of the metallic contacts was replaced by the organic-based magnetic semiconductor vanadium tetracyanoethylene (V[TCNE]2). At 10 K these devices produced the switching behavior of the spin-valve effect. The second focus of this work was the bulk magnetoresistance (MR) of small molecule, oligomer and polymer organic semiconductors in thin-film structures. At room temperature the resistance can change up to 8% at 100 Oe and 15% at

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.

Nature of magnetization and lateral spin-orbit interaction in gated semiconductor nanowires.

PubMed

Karlsson, H; Yakimenko, I I; Berggren, K-F

2018-05-31

Semiconductor nanowires are interesting candidates for realization of spintronics devices. In this paper we study electronic states and effects of lateral spin-orbit coupling (LSOC) in a one-dimensional asymmetrically biased nanowire using the Hartree-Fock method with Dirac interaction. We have shown that spin polarization can be triggered by LSOC at finite source-drain bias,as a result of numerical noise representing a random magnetic field due to wiring or a random background magnetic field by Earth magnetic field, for instance. The electrons spontaneously arrange into spin rows in the wire due to electron interactions leading to a finite spin polarization. The direction of polarization is, however, random at zero source-drain bias. We have found that LSOC has an effect on orientation of spin rows only in the case when source-drain bias is applied.

Nature of magnetization and lateral spin–orbit interaction in gated semiconductor nanowires

NASA Astrophysics Data System (ADS)

Karlsson, H.; Yakimenko, I. I.; Berggren, K.-F.

2018-05-01

Semiconductor nanowires are interesting candidates for realization of spintronics devices. In this paper we study electronic states and effects of lateral spin–orbit coupling (LSOC) in a one-dimensional asymmetrically biased nanowire using the Hartree–Fock method with Dirac interaction. We have shown that spin polarization can be triggered by LSOC at finite source-drain bias,as a result of numerical noise representing a random magnetic field due to wiring or a random background magnetic field by Earth magnetic field, for instance. The electrons spontaneously arrange into spin rows in the wire due to electron interactions leading to a finite spin polarization. The direction of polarization is, however, random at zero source-drain bias. We have found that LSOC has an effect on orientation of spin rows only in the case when source-drain bias is applied.

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

Analysis of Magnetic Anisotropy and the Role of Magnetic Dilution in Triggering Single-Molecule Magnet (SMM) Behavior in a Family of CoII YIII Dinuclear Complexes with Easy-Plane Anisotropy.

PubMed

Palacios, María A; Nehrkorn, Joscha; Suturina, Elizaveta A; Ruiz, Eliseo; Gómez-Coca, Silvia; Holldack, Karsten; Schnegg, Alexander; Krzystek, Jurek; Moreno, José M; Colacio, Enrique

2017-08-25

Three new closely related Co II Y III complexes of general formula [Co(μ-L)(μ-X)Y(NO 3 ) 2 ] (X - =NO 3 - 1, benzoate 2, or 9-anthracenecarboxylato 3) have been prepared with the compartmental ligand N,N',N''-trimethyl-N,N''-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H 2 L). In these complexes, Co II and Y III are triply bridged by two phenoxide groups belonging to the di-deprotonated ligand (L 2- ) and one ancillary anion X - . The change of the ancillary bridging group connecting Co II and Y III ions induces small differences in the trigonally distorted CoN 3 O 3 coordination sphere with a concomitant tuning of the magnetic anisotropy and intermolecular interactions. Direct current magnetic, high-frequency and -field EPR (HFEPR), frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) measurements, and ab initio theoretical calculations demonstrate that Co II ions in compounds 1-3 have large and positive D values (≈50 cm -1 ), which decrease with increasing the distortion of the pseudo-octahedral Co II coordination sphere. Dynamic ac magnetic susceptibility measurements indicate that compound 1 exhibits field-induced single-molecule magnet (SMM) behavior, whereas compounds 2 and 3 only display this behavior when they are magnetically diluted with diamagnetic Zn II (Zn/Co=10:1). In view of this, it is always advisable to use magnetically diluted complexes, in which intermolecular interactions and quantum tunneling of magnetism (QTM) would be at least partly suppressed, so that "hidden single-ion magnet (SIM)" behavior could emerge. Field- and temperature-dependence of the relaxation times indicate the prevalence of the Raman process in all these complexes above approximately 3 K. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

Unraveling the temperature and voltage dependence of magnetic field effects in organic semiconductors

NASA Astrophysics Data System (ADS)

Janssen, Paul; Wouters, Steinar H. W.; Cox, Matthijs; Koopmans, Bert

2013-11-01

In recent years, it was discovered that the current through an organic semiconductor, sandwiched between two non-magnetic electrodes, can be changed significantly by applying a small magnetic field. This surprisingly large magnetoresistance effect, often dubbed as organic magnetoresistance (OMAR), has puzzled the young field of organic spintronics during the last decade. Here, we present a detailed study on the voltage and temperature dependence of OMAR, aiming to unravel the lineshapes of the magnetic field effects and thereby gain a deeper fundamental understanding of the underlying microscopic mechanism. Using a full quantitative analysis of the lineshapes, we are able to extract all linewidth parameters and the voltage and temperature dependencies are explained with a recently proposed trion mechanism. Moreover, explicit microscopic simulations show a qualitative agreement to the experimental results.

Ab initio calculations of the concentration dependent band gap reduction in dilute nitrides

NASA Astrophysics Data System (ADS)

Rosenow, Phil; Bannow, Lars C.; Fischer, Eric W.; Stolz, Wolfgang; Volz, Kerstin; Koch, Stephan W.; Tonner, Ralf

2018-02-01

While being of persistent interest for the integration of lattice-matched laser devices with silicon circuits, the electronic structure of dilute nitride III/V-semiconductors has presented a challenge to ab initio computational approaches. The origin of the computational problems is the strong distortion exerted by the N atoms on most host materials. Here, these issues are resolved by combining density functional theory calculations based on the meta-GGA functional presented by Tran and Blaha (TB09) with a supercell approach for the dilute nitride Ga(NAs). Exploring the requirements posed to supercells, it is shown that the distortion field of a single N atom must be allowed to decrease so far that it does not overlap with its periodic images. This also prevents spurious electronic interactions between translational symmetric atoms, allowing us to compute band gaps in very good agreement with experimentally derived reference values. In addition to existing approaches, these results offer a promising ab initio avenue to the electronic structure of dilute nitride semiconductor compounds.

Magnetic analysis of a melt-spun Fe-dilute Cu60Ag35Fe5 alloy

NASA Astrophysics Data System (ADS)

Kondo, Shin-ichiro; Kaneko, Kazuhiro; Morimura, Takao; Nakashima, Hiromichi; Kobayashi, Shin-Taro; Michioka, Chishiro; Yoshimura, Kazuyoshi

2015-04-01

The magnetic properties of a melt-spun Fe-dilute Cu60Ag35Fe5 alloy are examined by X-ray diffraction, magnetic measurements, and transmission electron microscopy (TEM). The X-ray diffraction patterns show that the as-spun and annealed (773 K×36 ks) samples contain Cu and Ag phases and no Fe phases; thus, most Fe atoms are dispersed as clusters. Magnetic measurements indicate that the as-spun and annealed samples exhibit superparamagnetic behavior at 300 K, whereas ferromagnetic and superparamagnetic behaviors coexist at 4.2 K. The magnetic moments of small clusters at 300 K are determined by the nonlinear least squares method as 5148 and 4671 μB for as-spun and annealed samples, respectively, whereas those at 300 K are experimentally determined as 3500 and 3200 μB. This decrease in magnetic moments may imply the formation of anti-ferromagnetic coupling by annealing. TEM observation of the melt-spun sample suggests that there are three regions with different compositions: Cu-rich, Ag-rich, and Fe-rich with no precipitation in the matrix. In addition, these regions have obscure interfaces. The magnetic clusters are attributed to the Fe-rich regions.

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.

Anisotropic magnetic properties of the ferromagnetic semiconductor CrSbSe3

NASA Astrophysics Data System (ADS)

Kong, Tai; Stolze, Karoline; Ni, Danrui; Kushwaha, Satya K.; Cava, Robert J.

2018-01-01

Single crystals of CrSbSe3, a structurally pseudo-one-dimensional ferromagnetic semiconductor, were grown using a high-temperature solution growth technique and were characterized by x-ray diffraction, anisotropic temperature- and field-dependent magnetization, temperature-dependent resistivity, and optical absorption measurements. A band gap of 0.7 eV was determined from both resistivity and optical measurements. At high temperatures, CrSbSe3 is paramagnetic and isotropic, with a Curie-Weiss temperature of ˜145 K and an effective moment of ˜4.1 μB /Cr. A ferromagnetic transition occurs at Tc=71 K. The a axis, perpendicular to the chains in the structure, is the magnetic easy axis, while the chain axis direction, along b , is the hard axis. Magnetic isotherms measured around Tc do not follow the behavior predicted by simple mean-field critical exponents for a second-order phase transition. A tentative set of critical exponents is estimated based on a modified Arrott plot analysis, giving β ˜0.25 , γ ˜1.38 , and δ ˜6.6 .

Computational Studies of Magnetically Doped Semiconductor Nanoclusters

NASA Astrophysics Data System (ADS)

Gutsev, Lavrenty Gennady

Spin-polarized unrestricted density functional theory is used to calculate the molecular properties of magnetic semiconductor quantum dots doped with 3d-metal atoms. We calculate total energies of the low spin antiferromagnetically coupled states using a spin-flipping algorithm leading to the broken-symmetry states. Given the novel nature of the materials studied, we simulate experimental observables such as hyperfine couplings, ionization/ energies, electron affinities, first and second order polarizabilities, band gaps and exchange coupling constants. Specifically, we begin our investigation with pure clusters of (CdSe )16 and demonstrate the dependence of molecular observables on geometrical structures. We also show that the many isomers of this cluster are energetically quite closely spaced, and thus it would be necessary to employ a battery of tests to experimentally distinguish them. Next, we discuss Mn-doping into the cage (CdSe)9 cluster as well as the zinc-blende stacking type cluster (CdSe)36. We show that the local exchange coupling mechanism is ligand-mediated superexchange and simulate the isotropic hyperfine constants. Finally, we discuss a novel study where (CdSe)9 is doped with Mn or Fe up to a full replacement of all the Cd's and discuss the transition points for the magnetic behavior and specifically the greatly differing band-gap shifts. We also outline an unexpected pattern in the polarizability of the material as metals are added and compare our results with the results from theoretical studies of the bulk material.

Electronic and magnetic properties of second main-group and second sub-group metals substitution for Al in delafossite CuAlO2

NASA Astrophysics Data System (ADS)

Liu, Qi-Jun; Liu, Fu-Sheng; Liu, Zheng-Tang

2015-07-01

A systematic theoretical investigation has been carried out for the structural, electronic and magnetic properties of second main-group and second sub-group metals substitution for Al in delafossite CuAlO2 in the framework of density functional theory. The structural parameters and formation energies were calculated and discussed. The appearance of enhanced p-type conductivity after doping has been analyzed. Moreover, it is shown that all dopants have relatively large magnetic moments, but their ferromagnetic states are unstable, showing that their potential application in dilute magnetic semiconductors is not applicable.

Ab initio study of (Fe, Ni) doped GaAs: Magnetic, electronic properties and Faraday rotation

NASA Astrophysics Data System (ADS)

Sbai, Y.; Ait Raiss, A.; Bahmad, L.; Benyoussef, A.

2017-06-01

The interesting diluted magnetic semiconductor (DMS), Gallium Arsenide (GaAs), was doped with the transition metals magnetic impurities: iron (Fe) and Nickel (Ni), in one hand to study the magnetic and magneto-optical properties of the material Ga(Fe, Ni) As, in the other hand to investigate the effect of the doping on the properties of this material, the calculations were performed within the spin polarized density functional theory (DFT) and generalized gradient approximation (GGA) with AKAI KKR-CPA method, the density of states (DOS) for different doping concentrations were calculated, giving the electronical properties, as well as the magnetic state and magnetic states energy, also the effect of these magnetic impurities on the Faraday rotation as magneto-optical property. Furthermore, we found the stable magnetic state for our doped material GaAs.

Electronic bandstructure of semiconductor dilute bismide structures

NASA Astrophysics Data System (ADS)

Erucar, T.; Nutku, F.; Donmez, O.; Erol, A.

2017-02-01

In this work electronic band structure of dilute bismide GaAs/GaAs1-xBix quantum well structures with 1.8% and 3.75% bismuth compositions have been investigated both experimentally and theoretically. Photoluminescence (PL) measurements reveal that effective bandgap of the samples decreases approximately 65 meV per bismuth concentration. Temperature dependence of the effective bandgap is obtained to be higher for the sample with higher bismuth concentration. Moreover, both asymmetric characteristic at the low energy tail of the PL and full width at half maximum (FWHM) of PL peak increase with increasing bismuth composition as a result of increased Bi related defects located above valence band (VB). In order to explain composition dependence of the effective bandgap quantitatively, valence band anti-crossing (VBAC) model is used. Bismuth composition and temperature dependence of effective bandgap in a quantum well structure is modeled by solving Schrödinger equation and compared with experimental PL data.

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.

Femtosecond optical characterization and applications in cadmium(manganese) telluride diluted magnetic semiconductors

NASA Astrophysics Data System (ADS)

Wang, Daozhi

This thesis is devoted to the optical characterization of Cd(Mn)Te single crystals. I present the studies of free-carrier dynamics and generation and detection of coherent acoustic phonons (CAPS) using time-resolved femtosecond pump-probe spectroscopy. The giant Faraday effect and ultrafast responsivity of Cd(Mn)Te to sub-picosecond electromagnetic transients are also demonstrated and discussed in detail. The first, few-picosecond-long electronic process after the initial optical excitation exhibits very distinct characteristic dependence on the excitation condition, and in case of Cd(Mn)Te, it has been attributed to the collective effects of band filling, band renormalization, and two-photon absorption. A closed-form, analytic expression for the differential reflectivity induced by the CAPs is derived based on the propagating-strain-pulse model and it accounts very well for our experimental observations. The accurate values of the Mn concentration and longitudinal sound velocity nu s in Cd(Mn)Te were obtained by fitting the data of the refractive index dependence on the probe wavelength to the Schubert model. In Cd 0.91Mn0.09Te, nus was found to be 3.6x103 m/s. Our comparison studies from the one-color and two-color experiments reveal that the intrinsic phonon lifetime in Cd(Mn)Te was at least on the order of nanoseconds, and the observed exponential damping of the CAP oscillations was due to the finite absorption depth of the probe light. Optically-induced electronic stress has been demonstrated to be the main generation mechanism of CAPs. We also present the giant Faraday effect in the Cd(Mn)Te and the spectra of the Verdet constant, which is mainly due to the exchange interaction between the Mn ions and band electrons. The spectral characteristics of the Verdet constant in Cd(Mn)Te exhibit very unique features compared to that in pure semiconductors. In our time-resolved sampling experiments at the room temperature, the response of the Cd(Mn)Te, particularly

Exciting transition metal doped dilute magnetic thin films: MgO:Er and ZnO:Er

NASA Astrophysics Data System (ADS)

Ćakıcı, T.; Sarıtaş, S.; Muǧlu, G. Merhan; Yıldırım, M.

2017-02-01

Erbium doped MgO and doped ZnO thin films have reasonably important properties applications in spintronic devices. These films were synthesized on glass substrates by Chemical Spray Pyrolysis (CSP) method. In the literature there has been almost no report on preparation of MgO:Er dilute magnetic thin films by means of CSP. Because doped thin films show different magnetic behaviors, depending upon the type of magnetic material ions, concentration of them, synthesis route and experimental conditions, synthesized MgO:Er and ZnO:Er films were compared to thin film properties. Optical analyses of the synthesized thin films were examined spectral absorption and transmittance measurements by UV-Vis double beam spectrophotometer technique. Structural analysis of the thin films was examined by using XRD, Raman Analysis, FE-SEM, EDX and AFM techniques. Also, magnetic properties of the MgO:Er and ZnO:Er films were investigated by vibrating sample magnetometer (VSM) which show that diamagnetic behavior of the MgO:Er thin film and ferromagnetic (FM) behavior of the ZnO:Er film were is formed.

Model of Anisotropic Magnetization of In(1-x)Mn(x)S: Comparison to Experiment

NASA Astrophysics Data System (ADS)

Garner, J.; Franzese, G.; Byrd, Ashlee; Pekarek, T. M.; Miotkowski, I.; Ramdas, A. K.

2004-03-01

Calculations of and experimental results for the anisotropic magnetization of the new III-VI dilute magnetic semiconductor, In(1-x)Mn(x)S, are presented. The model Hamiltonian incorporates the interaction of the incomplete shell of Mn 3d-electrons with the crystal lattice within the point-ion approximation. Other terms in the Hamiltonian include the Zeeman interaction, the spin-orbit and the spin-spin terms. It is assumed the Mn atoms do not interact with each other (this is the singlet model, which is appropriate when x is small, here 2%). The temperature- and field- dependent magnetization is found from the energy eigenvalues of the Hamiltonian matrix, which was expressed in terms of an uncoupled angular momentum basis set. Magnetization versus temperature results are found for several field values, B, pointing along various directions relative to the underlying dilute magnetic semiconductor crystal lattice. In addition, the magnetization versus field is computed for several fixed temperatures and for various B-field directions and magnitudes. Overall, the agreement of this simple model with the experimental data is very good except at low temperatures (< 20 K) and high fields (> a few Tesla). It would be useful for quantitative comparison purposes to have optical absorption data in order to better fix the crystal potential parameters that are input parameters in the theory. In addition, the model could be improved by going beyond the point-ion approximation to better model the covalent bonds in the crystal.* Supported by UNF Research Grants, Research Corporation Award, CC4845, NSF Grant Nos. DMR-03-05653, DMR-01-02699, and ECS-01-29853 and Donors of the American Chemical Society Petroleum Research Fund PRF#40209-B5M, and a Purdue Univ. Academic Reimbursement Grant.

Interface magnetism and electronic structure: ZnO(0001)/Co3O4 (111)

NASA Astrophysics Data System (ADS)

Kupchak, I. M.; Serpak, N. F.; Shkrebtii, A.; Hayn, R.

2018-03-01

We have studied the structural, electronic, and magnetic properties of spinel Co3O4 (111) surfaces and their interfaces with ZnO(0001) using density functional theory within the generalized gradient approximation with the on-site Coulomb repulsion term. Two possible forms of spinel surface, containing Co2 + or Co3 + ions and terminated with either cobalt or oxygen ions, were considered, as well as their interface with zinc oxide. Our calculations demonstrate that Co3 + ions attain nonzero magnetic moments at the surface and interface, in contrast to the bulk, where they are not magnetic, leading to the ferromagnetic ordering. Since heavily Co doped ZnO samples can contain a Co3O4 secondary phase, such magnetic ordering at the interface might explain the origin of the magnetism in such diluted magnetic semiconductors.

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.

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

DOE PAGES

Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; ...

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

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

Influence of quantizing magnetic field and Rashba effect on indium arsenide metal-oxide-semiconductor structure accumulation capacitance

NASA Astrophysics Data System (ADS)

Kovchavtsev, A. P.; Aksenov, M. S.; Tsarenko, A. V.; Nastovjak, A. E.; Pogosov, A. G.; Pokhabov, D. A.; Tereshchenko, O. E.; Valisheva, N. A.

2018-05-01

The accumulation capacitance oscillations behavior in the n-InAs metal-oxide-semiconductor structures with different densities of the built-in charge (Dbc) and the interface traps (Dit) at temperature 4.2 K in the magnetic field (B) 2-10 T, directed perpendicular to the semiconductor-dielectric interface, is studied. A decrease in the oscillation frequency and an increase in the capacitance oscillation amplitude are observed with the increase in B. At the same time, for a certain surface accumulation band bending, the influence of the Rashba effect, which is expressed in the oscillations decay and breakdown, is traced. The experimental capacitance-voltage curves are in a good agreement with the numeric simulation results of the self-consistent solution of Schrödinger and Poisson equations in the magnetic field, taking into account the quantization, nonparabolicity of dispersion law, and Fermi-Dirac electron statistics, with the allowance for the Rashba effect. The Landau quantum level broadening in a two-dimensional electron gas (Lorentzian-shaped density of states), due to the electron scattering mechanism, linearly depends on the magnetic field. The correlation between the interface electronic properties and the characteristic scattering times was established.

Bound magnetic polaron in a semimagnetic double quantum well

NASA Astrophysics Data System (ADS)

Kalpana, P.; Jayakumar, K.

2017-09-01

The effect of different combinations of the concentration of Mn2+ ion in the Quantum well Cd1-xinMnxin Te and the barrier Cd1-xoutMnxout Te on the Bound Magnetic Polaron (BMP) in a Diluted Magnetic Semiconductors (DMS) Double Quantum Well (DQW) has been investigated. The Schrodinger equation is solved variationally in the effective mass approximation through which the Spin Polaronic Shift (SPS) due to the formation of BMP has been estimated for various locations of the donor impurity in the DQW. The results show that the effect of the increase of Mn2+ ion composition with different combinations on SPS is predominant for On Centre Well (OCW) impurity when compared to all other impurity locations when there is no application of magnetic field (γ = 0), γ being a dimensionless parameter for the magnetic field, and the same is predominant for On Centre Barrier (OCB) impurity with the application of external magnetic field (γ = 0.15).

Transport and magnetic properties of dilute rare-earth-PbSe alloys

NASA Astrophysics Data System (ADS)

Jovovic, V.; Joottu-Thiagarajan, S.; West, J.; Heremans, J. P.; Story, T.; Golacki, Z.; Paszkowicz, W.; Osinniy, V.

2007-03-01

An increase in the density of states is predicted [1] to increase the thermoelectric (TE) figure of merit, and could be induced by doping TE materials with rare-earth elements. This was attempted here: the galvanomagnetic and thermomagnetic properties of dilute alloys of PbSe and Ce, Pr, Nd, Eu, Gd and Yb were measured from 80 to 380K; magnetic susceptibilities were measured from 4 to 120K. The density of states effective mass, the relaxation time, and the carrier density and mobility are calculated from measurements of the electrical conductivity and the Hall, Seebeck and transverse Nernst-Ettingshausen coefficients. The Eu, Gd, Nd and Yb-alloyed samples are paramagnetic; the concentrations of rare-earth atoms are determined from fitting a Curie-Weiss law. The magnetic behavior of the Ce and Pr-alloyed samples is different. Ce, Pr, Nd, Gd and Yb act as donors with efficiencies that will be reported. Alloying with divalent Eu does not affect carrier density but increases the energy gap. This work suggests that the 4f orbitals preserve their atomic-like localized character and exhibit only weak sp-f hybridization. 1 G. D. Mahan and J. O. Sofo, Proc. Natl. Acad. Sci. USA 93 7436 (1996)

Magnetic order in a frustrated two-dimensional atom lattice at a semiconductor surface.

PubMed

Li, Gang; Höpfner, Philipp; Schäfer, Jörg; Blumenstein, Christian; Meyer, Sebastian; Bostwick, Aaron; Rotenberg, Eli; Claessen, Ralph; Hanke, Werner

2013-01-01

Two-dimensional electron systems, as exploited for device applications, can lose their conducting properties because of local Coulomb repulsion, leading to a Mott-insulating state. In triangular geometries, any concomitant antiferromagnetic spin ordering can be prevented by geometric frustration, spurring speculations about 'melted' phases, known as spin liquid. Here we show that for a realization of a triangular electron system by epitaxial atom adsorption on a semiconductor, such spin disorder, however, does not appear. Our study compares the electron excitation spectra obtained from theoretical simulations of the correlated electron lattice with data from high-resolution photoemission. We find that an unusual row-wise antiferromagnetic spin alignment occurs that is reflected in the photoemission spectra as characteristic 'shadow bands' induced by the spin pattern. The magnetic order in a frustrated lattice of otherwise non-magnetic components emerges from longer-range electron hopping between the atoms. This finding can offer new ways of controlling magnetism on surfaces.

Absolute instability of polaron mode in semiconductor magnetoplasma

NASA Astrophysics Data System (ADS)

Paliwal, Ayushi; Dubey, Swati; Ghosh, S.

2018-01-01

Using coupled mode theory under hydrodynamic regime, a compact dispersion relation is derived for polaron mode in semiconductor magnetoplasma. The propagation and amplification characteristics of the wave are explored in detail. The analysis deals with the behaviour of anomalous threshold and amplification derived from dispersion relation, as function of external parameters like doping concentration and applied magnetic field. The results of this investigation are hoped to be useful in understanding electron-longitudinal optical phonon interplay in polar n-type semiconductor plasmas under the influence of coupled collective cyclotron excitations. The best results in terms of smaller threshold and higher gain of polaron mode could be achieved by choosing moderate doping concentration in the medium at higher magnetic field. For numerical appreciation of the results, relevant data of III-V n-GaAs compound semiconductor at 77 K is used. Present study provides a qualitative picture of polaron mode in magnetized n-type polar semiconductor medium duly shined by a CO2 laser.

Landau quantization effects on hole-acoustic instability in semiconductor plasmas

NASA Astrophysics Data System (ADS)

Sumera, P.; Rasheed, A.; Jamil, M.; Siddique, M.; Areeb, F.

2017-12-01

The growth rate of the hole acoustic waves (HAWs) exciting in magnetized semiconductor quantum plasma pumped by the electron beam has been investigated. The instability of the waves contains quantum effects including the exchange and correlation potential, Bohm potential, Fermi-degenerate pressure, and the magnetic quantization of semiconductor plasma species. The effects of various plasma parameters, which include relative concentration of plasma particles, beam electron temperature, beam speed, plasma temperature (temperature of electrons/holes), and Landau electron orbital magnetic quantization parameter η, on the growth rate of HAWs, have been discussed. The numerical study of our model of acoustic waves has been applied, as an example, to the GaAs semiconductor exposed to electron beam in the magnetic field environment. An increment in either the concentration of the semiconductor electrons or the speed of beam electrons, in the presence of magnetic quantization of fermion orbital motion, enhances remarkably the growth rate of the HAWs. Although the growth rate of the waves reduces with a rise in the thermal temperature of plasma species, at a particular temperature, we receive a higher instability due to the contribution of magnetic quantization of fermions to it.

Effect of temperature and magnetic field on disorder in semiconductor structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agrinskaya, N. V., E-mail: nina.agrins@mail.ioffe.ru; Kozub, V. I.

We present the results of consistent theoretical analysis of various factors that may lead to influence of temperature and external magnetic field on disorder in semiconductor structures. Main attention is paid to quantum well (QW) structures in which only QWs or both QW and barriers are doped (the doping level is assumed to be close to the value corresponding to the metal–insulator transition). The above factors include (i) ionization of localized states to the region of delocalized states above the mobility edge, which is presumed to exist in the impurity band; (ii) the coexistence in the upper and lower Hubbardmore » bands (upon doping of QWs as well as barriers); in this case, in particular, the external magnetic field determines the relative contribution of the upper Hubbard band due to spin correlations at doubly filled sites; and (iii) the contribution of the exchange interaction at pairs of sites, in which the external magnetic field can affect the relation between ferromagnetic and antiferromagnetic configurations. All these factors, which affect the structure and degree of disorder, lead to specific features in the temperature dependence of resistivity and determine specific features of the magnetoresistance. Our conclusions are compared with available experimental data.« less

Properties of self-assembled diluted magnetic semiconductor nanostructures =

NASA Astrophysics Data System (ADS)

Ankiewicz, Amelia Olga Goncalves

Este trabalho centra-se na investigacao da possibilidade de se conseguir um semicondutor magnetico diluido (SMD) baseado em ZnO. Foi levado a cabo um estudo detalhado das propriedades magneticas e estruturais de estruturas de ZnO, nomeadamente nanofios (NFs), nanocristais (NCs) e filmes finos, dopadas com metais de transicao (MTs). Foram usadas varias tecnicas experimentais para caracterizar estas estruturas, designadamente difraccao de raios-X, microscopia electronica de varrimento, ressonancia magnetica, SQUID, e medidas de transporte. Foram incorporados substitucionalmente nos sitios do Zn ioes de Mn2+ e Co2+ em ambos os NFs e NCs de ZnO. Revelou-se para ambos os ioes dopantes, que a incorporacao e heterogenea, uma vez que parte do sinal de ressonancia paramagnetica electronica (RPE) vem de ioes de MTs em ambientes distorcidos ou enriquecidos com MTs. A partir das intensidades relativas dos espectros de RPE e de modificacoes da superficie, demonstra-se ainda que os NCs exibem uma estrutura core-shell. Os resultados, evidenciam que, com o aumento da concentracao de MTs, a dimensao dos NCs diminui e aumentam as distorcoes da rede. Finalmente, no caso dos NCs dopados com Mn, obteve-se o resultado singular de que a espessura da shell e da ordem de 0.3 nm e de que existe uma acumulacao de Mn na mesma. Com o objectivo de esclarecer o papel dos portadores de carga na medicao das interaccoes ferromagneticas, foram co-dopados filmes de ZnO com Mn e Al ou com Co e Al. Os filmes dopados com Mn, revelaram-se simplesmente paramagneticos, com os ioes de Mn substitucionais nos sitios do Zn. Por outro lado, os filmes dopados com Co exibem ferromagnetismo fraco nao intrinseco, provavelmente devido a decomposicao spinodal. Foram ainda efectuados estudos comparativos com filmes de ligas de Zn1-xFexO. Como era de esperar, detectaram-se segundas fases de espinela e de oxido de ferro nestas ligas; todas as amostras exibiam curvas de histerese a 300 K. Estes resultados suportam a hipotese de que as segundas fases sao responsaveis pelo comportamento magnetico observado em muitos sistemas baseados em ZnO. Nao se observou nenhuma evidencia de ferromagnetismo mediado por portadores de carga. As experiencias mostram que a analise de RPE permite demonstrar directamente se e onde estao incorporados os ioes de MTs e evidenciam a importancia dos efeitos de superficie para dimensoes menores que 15 nm, para as quais se formam estruturas core-shell. As investigacoes realizadas no ambito desta tese demonstram que nenhuma das amostras de ZnO estudadas exibiram propriedades de um SMD intrinseco e que, no futuro, sao necessarios estudos teoricos e experimentais detalhados das interaccoes de troca entre os ioes de MTs e os atomos do ZnO para determinar a origem das propriedades magneticas observadas.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilbertson, A. M.; Cohen, L. F.; Sadeghi, Hatef

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;more » 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.« less

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.

The effects of Peltier marking on semiconductor growth in a magnetic field

NASA Astrophysics Data System (ADS)

Sellers, Cheryl Casper

This research represents a model for three dimensional semiconductor growth in a vertical Bridgman process within an externally applied magnetic field with the additional effects of Peltier marking. The magnetic field is strong enough that inertial effects can be neglected and that viscous effects are confined to boundary layers. The objective of this research is a first step in the development of a method to accurately predict the distribution of dopants and species in the melt after a current pulse with a given duration and strength, with a given magnetic field and with a given crystal-melt interface shape. The first model involves an asymptotic solution to provide physical clarification of the flow. In both models the crystal/melt interface is modeled as fr=3r2 where 3≪1 . The first model incorporates a variable, a which ranges from 0.25 to 1.0. The second model involves an analytical solution with an arbitrary Ha and a≪1 . These models show the how the azimuthal velocity varies with increasing Ha and how the stream function varies in the meridional problem. This gives insight into how the dopant is mixed during the crystal growth process. The results demonstrate that current pulses with relatively weak magnetic fields and modest interface curvature can lead to very strong mixing in the melt.

Energy states, transport, and magnetotransport in diluted magnetic semiconductor (Ga, Mn)As with quantum well InGaAs.

PubMed

Shchurova, L Yu; Kulbachinskii, V A

2011-03-01

We investigate energy levels, thermodynamic, transport and magnetotransport properties of holes in GaAs structure with quantum well InGaAs delta-doped by C and Mn. We present self-consistent calculations for energy levels in the quantum well for different degrees of ionization of Mn impurity. The magnetoresistance of holes in the quantum well is calculated. We explain observed negative magnetoresistance by the reduction of spin-flip scattering on magnetic ions due to aligning of spins with magnetic field.

D Haas-Van Alphen Oscillations in the Diluted Magnetic Semiconductor MERCURY(1-X)IRON(X)SELENIUM.

NASA Astrophysics Data System (ADS)

Miller, Michael Montgomery

de Haas-van Alphen measurements are performed in oriented single crystals of Hg_{ rm 1-x}Fe_{rm x}Se in the range 0.0 <=q x <=q 0.05 for 0.5 < T < 4.2K for the magnetic field range 0.2 T < H < 1.0 T. These data can be interpreted in terms of a closed orbit magnetic breakdown model. The effect of Fe on the conduction band is explored in some detail. It is found that the presence of Fe lowers the Dingle temperature in a non-monotonic fashion, i.e., there is a minimum in the Dingle temperature for x ~ 0.001. This effect cannot be attributed to a gross modification of the band structure. Effective mass measurements are in good agreement with those expected for HgSe. However, the presence of Fe is seen to have a subtle effect on the band structure. The overall symmetry of the band structure may be modified by the addition of Fe. Furthermore, the presence of Fe tends to decrease the inversion asymmetry splitting of the conduction band as evidenced in the low-field beating.

Newtype single-layer magnetic semiconductor in transition-metal dichalcogenides VX2 (X = S, Se and Te)

NASA Astrophysics Data System (ADS)

Fuh, Huei-Ru; Chang, Ching-Ray; Wang, Yin-Kuo; Evans, Richard F. L.; Chantrell, Roy W.; Jeng, Horng-Tay

2016-09-01

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.

Local structure analysis of diluted magnetic semiconductor Co and Al co-doped ZnO nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hyodo, K.; Morimoto, S.; Yamazaki, T.

2016-02-01

In this study, Co and Al ions co-doped ZnO nanoparticles (Zn(Al, Co)O NPs) were prepared by our original chemical preparation method. The obtained samples prepared by this method, were encapsulated in amorphous SiO{sub 2}. X-ray diffraction (XRD) results showed Zn(Al, Co)O NPs had a single-phase nature with hexagonal wurtzite structure. These particle sizes could be controlled to be approximately 30 nm. We investigate the effect that the increase in the carrier has on the magnetization by doping Al to Co-doped ZnO NPs. The local structures were qualitatively analyzed using X-ray absorption fine structure (XAFS) measurements.

Stepping Stone Mechanism: Carrier-Free Long-Range Magnetism Mediated by Magnetized Cation States in Quintuple Layer

NASA Astrophysics Data System (ADS)

Chan, Chunkai; Zhang, Xiaodong; Zhang, Yiou; Tse, Kinfai; Deng, Bei; Zhang, Jingzhao; Zhu, Junyi

2018-01-01

The long-range magnetism observed in group-V tellurides quintuple layers is the only working example of carrier-free dilute magnetic semiconductors (DMS), whereas the physical mechanism is unclear, except the speculation on the band topology enhanced van Vleck paramagnetism. Based on DFT calculations, we find a stable long-range ferromagnetic order in a single quintuple layer of Cr-doped Bi2Te3 or Sb2Te3, with the dopant separation more than 9 Å. This configuration is the global energy minimum among all configurations. Different from the conventional super exchange theory, the magnetism is facilitated by the lone pair derived anti-bonding states near the cations. Such anti-bonding states work as stepping stones merged in the electron sea and conduct magnetism. Further, spin orbit coupling induced band inversion is found to be insignificant in the magnetism. Therefore, our findings directly dismiss the common misbelief that band topology is the only factor that enhances the magnetism. We further demonstrate that removal of the lone pair derived states destroys the long-range magnetism. This novel mechanism sheds light on the fundamental understanding of long-range magnetism and may lead to discoveries of new classes of DMS. Supported by Chinese University of Hong Kong (CUHK) under Grant No 4053084, University Grants Committee of Hong Kong under Grant No 24300814, and the Start-up Funding of CUHK.

Phase diagram as a function of temperature and magnetic field for magnetic semiconductors

NASA Astrophysics Data System (ADS)

González, I.; Castro, J.; Baldomir, D.

2002-10-01

Using an extension of the Nagaev model of phase separation [E. L. Nagaev and A. I. Podel'shchikov, Sov. Phys. JETP, 71, 1108 (1990)] we calculate the phase diagram for degenerate antiferromagnetic semiconductors in the T-H plane for different current carrier densities. Both wide-band semiconductors and double-exchange materials are investigated.

Thermodynamics of a dilute XX chain in a field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Timonin, P. N., E-mail: pntim@live.ru

Gapless phases in ground states of low-dimensional quantum spin systems are rather ubiquitous. Their peculiarity is a remarkable sensitivity to external perturbations due to permanent criticality of such phases manifested by a slow (power-low) decay of pair correlations and the divergence of the corresponding susceptibility. A strong influence of various defects on the properties of the system in such a phase can then be expected. Here, we consider the influence of vacancies on the thermodynamics of the simplest quantum model with a gapless phase, the isotropic spin-1/2 XX chain. The existence of the exact solution of this model gives amore » unique opportunity to describe in detail the dramatic effect of dilution on the gapless phase—the appearance of an infinite series of quantum phase transitions resulting from level crossing under the variation of a longitudinal magnetic field. We calculate the jumps in the field dependences of the ground-state longitudinal magnetization, susceptibility, entropy, and specific heat appearing at these transitions and show that they result in a highly nonlinear temperature dependence of these parameters at low T. Also, the effect of enhancement of the magnetization and longitudinal correlations in the dilute chain is established. The changes of the pair spin correlators under dilution are also analyzed. The universality of the mechanism of the quantum transition generation suggests that similar effects of dilution can also be expected in gapless phases of other low-dimensional quantum spin systems.« less

Magnetism in Mn-nanowires and -clusters as δ-doped layers in group IV semiconductors (Si, Ge)

NASA Astrophysics Data System (ADS)

Simov, K. R.; Glans, P.-A.; Jenkins, C. A.; Liberati, M.; Reinke, P.

2018-01-01

Mn doping of group-IV semiconductors (Si/Ge) is achieved by embedding nanostructured Mn-layers in group-IV matrix. The Mn-nanostructures are monoatomic Mn-wires or Mn-clusters and capped with an amorphous Si or Ge layer. The precise fabrication of δ-doped Mn-layers is combined with element-specific detection of the magnetic signature with x-ray magnetic circular dichroism. The largest moment (2.5 μB/Mn) is measured for Mn-wires with ionic bonding character and a-Ge overlayer cap; a-Si capping reduces the moment due to variations of bonding in agreement with theoretical predictions. The moments in δ-doped layers dominated by clusters is quenched with an antiferromagnetic component from Mn-Mn bonding.

Shell Filling and Magnetic Anisotropy In A Few Hole Silicon Metal-Oxide-Semiconductor Quantum Dot

NASA Astrophysics Data System (ADS)

Hamilton, Alex; Li., R.; Liles, S. D.; Yang, C. H.; Hudson, F. E.; Veldhorst, M. E.; Dzurak, A. S.

There is growing interest in hole spin states in group IV materials for quantum information applications. The near-absence of nuclear spins in group IV crystals promises long spin coherence times, while the strong spin-orbit interaction of the hole states provides fast electrical spin manipulation methods. However, the level-mixing and magnetic field dependence of the p-orbital hole states is non-trivial in nanostructures, and is not as well understood as for electron systems. In this work, we study the hole states in a gate-defined silicon metal-oxide-semiconductor quantum dot. Using an adjacent charge sensor, we monitor quantum dot orbital level spacing down to the very last hole, and find the standard two-dimensional (2D) circular dot shell filling structure. We can change the shell filling sequence by applying an out-of-plane magnetic field. However, when the field is applied in-plane, the shell filling is not changed. This magnetic field anisotropy suggests that the confined hole states are Ising-like.

Density functional theory study of bulk and single-layer magnetic semiconductor CrPS4

NASA Astrophysics Data System (ADS)

Zhuang, Houlong L.; Zhou, Jia

2016-11-01

Searching for two-dimensional (2D) materials with multifunctionality is one of the main goals of current research in 2D materials. Magnetism and semiconducting are certainly two desirable functional properties for a single 2D material. In line with this goal, here we report a density functional theory (DFT) study of bulk and single-layer magnetic semiconductor CrPS4. We find that the ground-state magnetic structure of bulk CrPS4 exhibits the A-type antiferromagnetic ordering, which transforms to ferromagnetic (FM) ordering in single-layer CrPS4. The calculated formation energy and phonon spectrum confirm the stability of single-layer CrPS4. The band gaps of FM single-layer CrPS4 calculated with a hybrid density functional are within the visible-light range. We also study the effects of FM ordering on the optical absorption spectra and band alignments for water splitting, indicating that single-layer CrPS4 could be a potential photocatalyst. Our work opens up ample opportunities of energy-related applications of single-layer CrPS4.

Specific features of the structural and magnetic states of a Zn1 - x Ni x Se crystal ( x = 0.0025) at low temperatures

NASA Astrophysics Data System (ADS)

Dubinin, S. F.; Sokolov, V. I.; Parkhomenko, V. D.; Teploukhov, S. G.; Gruzdev, N. B.

2008-12-01

The magnetic state and the structure of a Zn1 - x Ni x Se ( x = 0.0025) bulk crystal were studied at low temperatures. It is revealed that the magnetic and crystal structures below T ≅ 15 K are dependent on the cooling rate of this dilute semiconductor. For example, on fast cooling to 4.2 K, about 10% hexagonal ferromagnetic phase is formed in the crystal. During heating, the phase disappears at T ≅ 15 K. The results obtained are discussed with allowance for the specific features of the Jahn-Teller distortions in this compound.

DFT calculation and experimental study on structural, optical and magnetic properties of Co-doped SrTiO3

NASA Astrophysics Data System (ADS)

Sikam, Pornsawan; Moontragoon, Pairot; Sararat, Chayanin; Karaphun, Attaphol; Swatsitang, Ekaphan; Pinitsoontorn, Supree; Thongbai, Prasit

2018-07-01

SrTiO3 (STO) is an attractive material that offers a wide range of technological applications, e.g., ferroelectricity, solar cell and photocatalysis. An application that the STO might be utilized is diluted magnetic semiconductors. Here, we would like to improve magnetic property of the STO by Ti site substitution using Co atoms. In this work, we present the structural, optical and magnetic properties of perfect and oxygen defect structures of STO and Co-doped SrTiO3 via experimental and theoretical aspects. In first-principles calculation, the structural properties, electronic band structure and magnetic properties of undoped STO and Co-doped STO supercells have been investigated by density functional theory using GGA with Hubbard model scheme (GGA+U) on Vienna Ab initio Simulation Package (VASP). In calculation detail, pure phase of STO with nanometer scale size of undoped STO and Co-doped STO have been synthesized using hydrothermal technique. The findings obtained from DFT computation reveal that the new states in gap between the valence band and conduction band of the STO were induced after Co atom was doped into the host structure. These impurity states narrow the band gap corresponding to experimental results. In addition, band splitting was observed on O defect and dopant systems, indicating that missing O and doping Co on STO could induce magnetization on none-magnetic material of STO. In case of synthesized powder, ferromagnetic behaviors are determined in the dopant system annealed in Ar. Additionally, another appreciated point of Co doping is that surface area of the STO is improved. Thus, it is expected that the surface activity, such as photocatalytic performance, of the STO will be enhanced. From all referred results, they introduce that the Co-doped STO might be a potential candidate to be a photocatalyst for the high photocatalytic performance under visible light radiation and the diluted magnetic semiconductor in spintronic devices.

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…

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

Dielectric response of a nondegenerate electron gas in semiconductor nanocrystallites

NASA Astrophysics Data System (ADS)

van Faassen, E.

1998-12-01

We investigate the low-frequency dielectric response of a dilute electron gas in a small spherical semiconductor particle. The flow of the electrons is described by hydrodynamic equations which incorporate the electrostatic interactions between the electrons in a self-consistent fashion. In the low-frequency regime, the dielectric loss is small and proportional to the frequency, despite substantial field penetration into the semiconductor. The loss remains small even for high doping levels due to effective cancellation between field-induced drift and diffusion. The model is used to estimate the complex dielectric constant of a system of weakly conducting nanosized semiconductor particles. The most prominent manifestation of spatial dispersion is that photoinduced changes in the real and imaginary parts of the dielectric constant are positive and of comparable magnitude.

Dynamics of exciton magnetic polarons in CdMnSe/CdMgSe quantum wells: Effect of self-localization

NASA Astrophysics Data System (ADS)

Akimov, I. A.; Godde, T.; Kavokin, K. V.; Yakovlev, D. R.; Reshina, I. I.; Sedova, I. V.; Sorokin, S. V.; Ivanov, S. V.; Kusrayev, Yu. G.; Bayer, M.

2017-04-01

We study the exciton magnetic polaron (EMP) formation in (Cd,Mn)Se/(Cd,Mg)Se diluted-magnetic-semiconductor quantum wells by using time-resolved photoluminescence (PL). The magnetic-field and temperature dependencies of this dynamics allow us to separate the nonmagnetic and magnetic contributions to the exciton localization. We deduce the EMP energy of 14 meV, which is in agreement with time-integrated measurements based on selective excitation and the magnetic-field dependence of the PL circular polarization degree. The polaron formation time of 500 ps is significantly longer than the corresponding values reported earlier. We propose that this behavior is related to strong self-localization of the EMP, accompanied with a squeezing of the heavy-hole envelope wave function. This conclusion is also supported by the decrease of the exciton lifetime from 600 ps to 200-400 ps with increasing magnetic field and temperature.

Optical and Magnetic Properties of ZnO Nanoparticles Doped with Co, Ni and Mn and Synthesized at Low Temperature.

PubMed

Hancock, Jared M; Rankin, William M; Hammad, Talaat M; Salem, Jamil S; Chesnel, Karine; Harrison, Roger G

2015-05-01

Zinc oxide nanomaterials were synthesized with small amounts of magnetic ions to create dilute magnetic semiconductors (DMS), by using a low temperature sol-gel method. Conditions were controlled such that a range of amounts of Co, Ni and Mn were incorporated. The incorporation could be tracked by color changes in the powders to blue for Co, green for Ni and yellow for Mn. XRD measurements showed the ZnO has the wurtzite structure with crystallites 8-12 nm in diameter. Nanoparticles were observed by SEM and TEM and TEM showed that the lattice fringes of different nanoparticles align. Nanoparticle alignment was disrupted when high concentrations of metal dopants were incorporated. Magnetic measurements showed a change in behavior from diamagnetic to paramagnetic with increasing concentration of metal dopants.

Effect of Ga doping and point defect on magnetism of ZnO

NASA Astrophysics Data System (ADS)

Hou, Qingyu; Zhao, Chunwang; Jia, Xiaofang; Qu, Lingfeng

2017-02-01

The combined influence mechanism of Ga doping and Zn vacancy or O vacancy on magnetism of ZnO is studied using the first-principle calculation. The coexistence of Ga doping and Zn vacancy can achieve a Curie temperature higher than room temperature and the Ga doped ZnO system is a p-type diluted degenerate semiconductor with metalized ferromagnetism. The magnetism of the doping system of Ga doping and Zn vacancy is mainly contributed by double-exchange interaction through the holes of Zn vacancy taking carrier as medium. However, the system of Ga doping and O vacancy is non-magnetic. In the coexistence of Ga doping and Zn vacancy or O vacancy, a close relative distance between doping and vacancy will reduce the formation energy of the doping system but increase the easiness of doping and vacancy, as well as enhance the stability of the doping system.

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.

Electrical control of 2D magnetism in bilayer CrI 3

DOE PAGES

Huang, Bevin; Clark, Genevieve; Klein, Dahlia R.; ...

2018-04-23

Controlling magnetism via electric fields addresses fundamental questions of magnetic phenomena and phase transitions, and enables the development of electrically coupled spintronic devices, such as voltage-controlled magnetic memories with low operation energy. Previous studies on dilute magnetic semiconductors such as (Ga,Mn)As and (In,Mn)Sb have demonstrated large modulations of the Curie temperatures and coercive fields by altering the magnetic anisotropy and exchange interaction. Owing to their unique magnetic properties, the recently reported two-dimensional magnets provide a new system for studying these features. For instance, a bilayer of chromium triiodide (CrI 3) behaves as a layered antiferromagnet with a magnetic field-driven metamagneticmore » transition. Here, we demonstrate electrostatic gate control of magnetism in CrI 3 bilayers, probed by magneto-optical Kerr effect (MOKE) microscopy. At fixed magnetic fields near the metamagnetic transition, we realize voltage-controlled switching between antiferromagnetic and ferromagnetic states. At zero magnetic field, we demonstrate a time-reversal pair of layered antiferromagnetic states that exhibit spin-layer locking, leading to a linear dependence of their MOKE signals on gate voltage with opposite slopes. Here, our results allow for the exploration of new magnetoelectric phenomena and van der Waals spintronics based on 2D materials.« less

Electrical control of 2D magnetism in bilayer CrI 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Bevin; Clark, Genevieve; Klein, Dahlia R.

Controlling magnetism via electric fields addresses fundamental questions of magnetic phenomena and phase transitions, and enables the development of electrically coupled spintronic devices, such as voltage-controlled magnetic memories with low operation energy. Previous studies on dilute magnetic semiconductors such as (Ga,Mn)As and (In,Mn)Sb have demonstrated large modulations of the Curie temperatures and coercive fields by altering the magnetic anisotropy and exchange interaction. Owing to their unique magnetic properties, the recently reported two-dimensional magnets provide a new system for studying these features. For instance, a bilayer of chromium triiodide (CrI 3) behaves as a layered antiferromagnet with a magnetic field-driven metamagneticmore » transition. Here, we demonstrate electrostatic gate control of magnetism in CrI 3 bilayers, probed by magneto-optical Kerr effect (MOKE) microscopy. At fixed magnetic fields near the metamagnetic transition, we realize voltage-controlled switching between antiferromagnetic and ferromagnetic states. At zero magnetic field, we demonstrate a time-reversal pair of layered antiferromagnetic states that exhibit spin-layer locking, leading to a linear dependence of their MOKE signals on gate voltage with opposite slopes. Here, our results allow for the exploration of new magnetoelectric phenomena and van der Waals spintronics based on 2D materials.« less

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. Copyright © 2015 Elsevier B.V. All rights reserved.

Doping of Ga in antiferromagnetic semiconductor α-Cr2O3 and its effects on magnetic and electronic properties

NASA Astrophysics Data System (ADS)

Bhowmik, R. N.; Venkata Siva, K.; Ranganathan, R.; Mazumdar, Chandan

2017-06-01

The samples of Ga-doped Cr2O3 have been prepared using chemical co-precipitation route. X-ray diffraction pattern and Raman spectra have indicated rhombohedral crystal structure with space group R 3 bar C. Magnetic measurements indicated diluted antiferromagnetic (AFM) spin order in Ga-doped α-Cr2O3 and ferrimagnetic ordering of spins at about 50-60 K is confirmed from the analysis of the temperature dependence of dc magnetization and ac susceptibility data. Apart from magnetic dilution effect, the samples have shown superparamagnetic behavior below 50 K due to frustrated surface spins of the nano-sized grains. The samples have shown non-linear electronic properties. The current-voltage (I-V) characteristics of the Ga-doped α-Cr2O3 samples are remarkably different from α-Cr2O3 sample. The bi-stable electronic states and negative differential resistance are some of the unique non-linear electronic properties that the I-V curves of Ga-doped samples have exhibited. Optical study revealed three electronic transitions in the samples associated with band gap energy at about 2.67-2.81 eV, 1.91-2.11 eV, 1.28-1.35 eV, respectively. The results indicated multi-level electronic structure in Ga-doped α-Cr2O3 system.

Slow dynamics in the geometrically frustrated magnet ZnFe2O4: Universal features of aging phenomena in spin glasses

NASA Astrophysics Data System (ADS)

Mamiya, H.; Tsujii, N.; Terada, N.; Nimori, S.; Kitazawa, H.; Hoshikawa, A.; Ishigaki, T.

2014-07-01

To clarify the universal features of spin glasses, we carefully studied slow dynamics in a geometrically frustrated magnet ZnFe2O4 with slight disorders, regarded as an "unconventional" Heisenberg spin glass, using time-resolved neutron diffractometry and magnetometry. The results indicate that "aging" can be attributed not to growth of the short-range order detected by a diffuse scattering but to aging of a hidden aperiodic correlation, as expected from theories for spin glasses. Concerning aging, peculiar behavior was found; the decay of thermoremanent magnetization is extremely accelerated if the sample is heated/cooled briefly midway through the isothermal slow relaxation. Conversely, magnetization surprisingly increases despite the absence of a magnetic field when the temperature returns after the brief heating/cooling. The behavior can be explained as a destabilization of the aged spin configuration due to the thermal perturbations and subsequent spontaneous restoration of the original spin configuration after the destabilization. Whereas such destabilization and restoration do not occur during freezing into numerous metastable states in a fixed energy landscape, these are possible in an energy landscape with a temperature-sensitive funnel-like structure. These features, consistent with the ghost domain scenario of the droplet picture, are the same as for conventional Heisenberg spin glasses such as dilute magnetic alloys and dilute magnetic semiconductors. In other words, they are universal features in Heisenberg spin glasses including unconventional ones.

Hybrid semiconductor nanomagnetoelectronic devices

NASA Astrophysics Data System (ADS)

Bae, Jong Uk

2007-12-01

The subject of this dissertation is the exploration of a new class of hybrid semiconductor nanomagnetoelectronic devices. In these studies, single-domain nanomagnets are used as the gate in a transistor structure, and the spatially non-uniform magnetic fields that they generate provide an additional means to modulate the channel conductance. A quantum wire etched in a high-mobility GaAs/AlGaAs quantum well serves as the channel of this device and the current flow through it is modulated by a high-aspect-ratio Co nanomagnet. The conductance of this device exhibits clear hysteresis in a magnetic field, which is significantly enhanced when the nanomagnet is used as a gate to form a local tunnel barrier in the semiconductor channel. A simple theoretical model, which models the tunnel barrier as a simple harmonic saddle, is able to account for the experimentallyobserved behavior. Further improvements in the tunneling magneto-resistance of this device should be possible in the future by optimizing the gate and channel geometries. In addition to these investigations, we have also explored the hysteretic magnetoresistance of devices in which the tunnel barrier is absent and the behavior is instead dominated by the properties of the magnetic barrier alone. We show experimentally how quantum corrections to the conductance of the quantum wire compete against the magneto-transport effects induced by the non-uniform magnetic field.

Magnetic Correlations in the Quasi-Two-Dimensional Semiconducting Ferromagnet CrSiTe 3

DOE PAGES

Williams, Travis J.; Aczel, Adam A.; Lumsden, Mark D.; ...

2015-10-02

Intrinsic, 2D ferromagnetic semiconductors are an important class of materials for overcoming dilute magnetic semiconductors’ limitations for spintronics. CrSiTe 3 is a particularly interesting material of this class, since it can likely be exfoliated to single layers, for which T c is predicted to increase dramatically. Establishing the nature of the bulk material’s magnetism is necessary for understanding the thin-film magnetic behavior and the material’s possible applications. In this work, we use elastic and inelastic neutron scattering to measure the magnetic properties of single crystalline CrSiTe 3. We find a very small single ion anisotropy that favors magnetic ordering alongmore » the c-axis and that the measured spin waves fit well to a model in which the moments are only weakly coupled along that direction. Then, we find that both static and dynamic correlations persist within the ab-plane up to at least 300 K, which is strong evidence of the material's 2D characteristics that are relevant for future studies on thin film and monolayer samples.« less

Magnetic refrigeration capabilities of magnetocaloric Ni2Mn:75Cu:25Ga

NASA Astrophysics Data System (ADS)

Mishra, S. K.; Jenkins, C. A.; Dubenko, I.; Samanta, T.; Ali, N.; Roy, S.

2013-03-01

Doping-driven competition between energetically similar ground states leads to many exciting materials phenomena such as the emergence of high-Tc superconductivity, diluted magnetic semiconductors, and colossal magnetoresistance. Doped Ni2MnGa Heusler alloy, which is a multifunctional ferromagnetic alloy with various exotic physical properties demonstrates this notion of rich phenomenology via modified ground spin states. Adopting this generic concept, here we will present a novel doped Ni2Mn.75Cu.25Ga alloy that offers unprecedented co-existence of the magnetocaloric effect and fully controlled ferromagnetism at room temperature. Application of site engineering enables us to manipulate the ground spin state that leads to the decrease in magnetic transition temperature and also increases the delocalization of the Mn magnetism. SQUID magnetometery suggests that Cu doping enhances the saturation magnetization, coercive field and clarity of magnetic hysteresis loops. By exploiting x-ray absorption techniques and measuring element specific magnetic hysteresis loops, here we will describe the microscopic origin of enhnaced magnetocaloric properties and d-d interaction driven charge transfer effects in Ni2Mn.75Cu.25Ga This work was supported by DOE Grant No. DE-FG02-06ER46291

EPR Studies of Magnetically Dilute Ga-Doped Single Crystals of Fe18 Antiferromagnetic Molecular Wheels

NASA Astrophysics Data System (ADS)

Henderson, John; Ramsey, Christopher; Del Barco, Enrique; Stamatatos, Theocharis; Christou, George

2008-03-01

Studies of the quantum dynamics of the electron spins in solid state systems has gained considerable interest recently due to their potential for use as quantum computing substrates. One class of materials, molecular magnets, are of particular importance, owing to the seemingly limitless array of spin configurations due to synthetic chemical flexibility. Efforts are currently devoted to minimizing decoherence times by diminishing dipolar effects. In this regard, we have carried out EPR measurements on small single crystals of 0.5% Ga doped Fe18 molecular antiferromagnetic wheels at temperatures down to 300 mK using planar resonators patterned on GaAs wafers. This system constitutes a dilute sample of S = 5/2 molecules dispersed within a sea of S = 0 (at low temperature) molecules, which significantly reduces dipolar interactions and might provide a means of observing Rabi oscillations in crystals of molecular magnets. Detailed angular dependence studies reveal significant anisotropy with D = 500 mK and E = 20 mK. The presence of second order anisotropy (E) is very unusual for such a high symmetry system and its interpretation will be discussed. Pulsed-EPR measurements and doping concentration dependence will also be discussed.

Multistage ordering and critical singularities in C o1 -xZ nxA l2O4(0 ≤x ≤1 ) : Dilution and pressure effects in a magnetically frustrated system

NASA Astrophysics Data System (ADS)

Naka, Takashi; Sato, Koichi; Matsushita, Yoshitaka; Terada, Noriki; Ishii, Satoshi; Nakane, Takayuki; Taguchi, Minori; Nakayama, Minako; Hashishin, Takeshi; Ohara, Satoshi; Takami, Seiichi; Matsushita, Akiyuki

2015-06-01

We report comprehensive studies of the crystallographic, magnetic, and thermal properties of a spinel-type magnetically frustrated compound, CoA l2O4 , and a magnetically diluted system, C o1- xZ nxA l2O4 . These studies revealed the effects of dilution and disorder when the tetrahedral magnetic Co ion was replaced by the nonmagnetic Zn ion. Low-temperature anomalies were observed in magnetic susceptibility at x <0.6 . A multicritical point was apparent at T =3.4 K and x =0.12 , where the antiferromagnetic, spin-glass-like, and paramagnetic phases met. At that point, the quenched ferromagnetic component induced by a magnetic field during cooling was sharply enhanced and was observable below x =0.6 . At x ˜0.6 , magnetic susceptibility and specific heat were described by temperature power laws, χ ˜C /T ˜T-δ , in accord with the site percolation threshold of the diamond lattice. This behavior is reminiscent of a quantum critical singularity. We propose an x -temperature phase diagram in the range 0 ≤x ≤1 for C o1- xZ nxA l2O4 . The transition temperature of CoA l2O4 determined from magnetic susceptibility measured under hydrostatic pressure increased with increasing pressure.

Structure and magnetism of Fe-doped BaSnO 3 thin films

DOE PAGES

Alaan, Urusa S.; N’Diaye, Alpha T.; Shafer, Padraic; ...

2017-02-28

BaSnO 3 is an excellent candidate system for developing a new class of perovskite-based dilute magnetic semiconductors. Here in this study, we show that BaSn 0.95Fe 0.05O 3 can be grown from a background pressure of ~2×10-3 mTorr to oxygen pressures of 300 mTorr with high crystallinity and excellent structural quality. When grown in vacuum, the films may be weakly ferromagnetic with a nonzero x-ray magnetic circular dichroism signal on the Fe L 3 edge. Growth with oxygen flow appears to suppress magnetic ordering. Even for very thick films grown in 100 mTorr O 2, the films are paramagnetic. Finally,more » the existence of ferromagnetism in vacuum-grown BaSnO 3 may be attributed to the F-center exchange mechanism, which relies on the presence of oxygen vacancies to facilitate the ferromagnetism. However, other possible extrinsic contributions to the magnetic ordering, such as clusters of Fe 3O 4 and FeO or contamination can also explain the observed behavior.« less

Effects of Eu doping and O vacancy on the magnetic and optical properties of ZnO

NASA Astrophysics Data System (ADS)

Ling-Feng, Qu; Qing-Yu, Hou; Xiao-Fang, Jia; Zhen-Chao, Xu; Chun-Wang, Zhao

2018-02-01

We calculated the electronic structure and optical properties of Eu mono-doped ZnO systems with or without O vacancy. We also determined the relative energy of ferromagnetic and antiferromagnetic orders of Eu-double-doped ZnO systems. The double-doped systems possess high Curie temperature and achieve room temperature ferromagnetism. The magnetism in the Eu mono-doped system without O vacancy is caused by the -Eu3+-O2--Eu3+- bound magnetopolaron (BMP) model. The magnetism of Eu mono-doped ZnO systems with O vacancy is more stable than that without O vacancy, and such magnetism is attributed to the -Eu3+-VO++-Eu3+- BMP model. The absorption spectrum for mono-doped systems is red shifted, and this finding confirms that Eu-mono-doped ZnO is a candidate photocatalyst for various applications. Therefore, Eu-double-doped ZnO can be practically used as an unambiguous diluted magnetic semiconductor.

Engineered Transition Metal Chalcogenides for Photovoltaic, Thermoelectric, and Magnetic Applications

NASA Astrophysics Data System (ADS)

Moroz, Nicholas Anton

This work focuses on the development of ternary and quaternary chalcogenide compounds featuring transition metal cations through careful engineering of the electronic and thermal transport as well as magnetic properties by traditional solid-state doping techniques and novel template structure synthesis methods for improvements in thermoelectric performance, diluted magnetic semiconductors, and photovoltaic conversion. Presented here is an innovative low-temperature batch synthesis that was developed to create hexagonal nanoplatelets of thermoelectrically interesting CuAgSe. This process utilized room temperature ion exchange reactions to convert cubic Cu2-xSe nanoplatelets into CuAgSe by replacing a portion of the Cu+ ions with Ag+ while maintaining the morphology of the nanoplatelet. This simple reaction process offers an energy efficient and versatile strategy to create interesting materials with superior thermoelectric performance. An investigation of the thermal and electronic transport of CuAl(S xSe1-x)2 solid solutions was also conducted. While these compounds yielded low thermal conductivity, they also exhibited low electronic conductivity. Doping with transition metals Ag, Hf, and Ti further reduced the thermal conductivity below 1 W/mK; however, most exciting was the determination that the thermal transport of the system could be modified by doping at the Al3+ site without affecting the electronic structure of the system, potentially leading to the use of CuAl(SxSe 1-x)2 as a heavily doped thermoelectric material. The effect of local carrier concentration in the diluted magnetic semiconductor FeSb2Se4 was studied by substitution of In3+ for Sb3+. Using systematic Rietveld refinement, it was determined that In3+ resides in the semiconducting layer of the structure for concentrations of x ≤ 0.1, and the magnetic layer for x > 0.1. The increase in local carrier concentration has an appreciable effect on the electronic and magnetic properties of the material

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

2014-06-07

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.

MBE Growth of Ferromagnetic Metal/Compound Semiconductor Heterostructures for Spintronics

ScienceCinema

Palmstrom, Chris [University of California, Santa Barbara, California, United States

2017-12-09

Electrical transport and spin-dependent transport across ferromagnet/semiconductor contacts is crucial in the realization of spintronic devices. Interfacial reactions, the formation of non-magnetic interlayers, and conductivity mismatch have been attributed to low spin injection efficiency. MBE has been used to grow epitaxial ferromagnetic metal/GA(1-x)AL(x)As heterostructures with the aim of controlling the interfacial structural, electronic, and magnetic properties. In situ, STM, XPS, RHEED and LEED, and ex situ XRD, RBS, TEM, magnetotransport, and magnetic characterization have been used to develop ferromagnetic elemental and metallic compound/compound semiconductor tunneling contacts for spin injection. The efficiency of the spin polarized current injected from the ferromagnetic contact has been determined by measuring the electroluminescence polarization of the light emitted from/GA(1-x)AL(x)As light-emitting diodes as a function of applied magnetic field and temperature. Interfacial reactions during MBE growth and post-growth anneal, as well as the semiconductor device band structure, were found to have a dramatic influence on the measured spin injection, including sign reversal. Lateral spin-transport devices with epitaxial ferromagnetic metal source and drain tunnel barrier contacts have been fabricated with the demonstration of electrical detection and the bias dependence of spin-polarized electron injection and accumulation at the contacts. This talk emphasizes the progress and achievements in the epitaxial growth of a number of ferromagnetic compounds/III-V semiconductor heterostructures and the progress towards spintronic devices.

Optical characteristics of p-type GaAs-based semiconductors towards applications in photoemission infrared detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lao, Y. F.; Perera, A. G. U., E-mail: uperera@gsu.edu; Center for Nano-Optics

2016-03-14

Free-carrier effects in a p-type semiconductor including the intra-valence-band and inter-valence-band optical transitions are primarily responsible for its optical characteristics in infrared. Attention has been paid to the inter-valence-band transitions for the development of internal photoemission (IPE) mid-wave infrared (MWIR) photodetectors. The hole transition from the heavy-hole (HH) band to the spin-orbit split-off (SO) band has demonstrated potential applications for 3–5 μm detection without the need of cooling. However, the forbidden SO-HH transition at the Γ point (corresponding to a transition energy Δ{sub 0}, which is the split-off gap between the HH and SO bands) creates a sharp drop around 3.6 μmmore » in the spectral response of p-type GaAs/AlGaAs detectors. Here, we report a study on the optical characteristics of p-type GaAs-based semiconductors, including compressively strained InGaAs and GaAsSb, and a dilute magnetic semiconductor, GaMnAs. A model-independent fitting algorithm was used to derive the dielectric function from experimental reflection and transmission spectra. Results show that distinct absorption dip at Δ{sub 0} is observable in p-type InGaAs and GaAsSb, while GaMnAs displays enhanced absorption without degradation around Δ{sub 0}. This implies the promise of using GaMnAs to develop MWIR IPE detectors. Discussions on the optical characteristics correlating with the valence-band structure and free-hole effects are presented.« less

Mn concentration and quantum size effects on spin-polarized transport through CdMnTe based magnetic resonant tunneling diode.

PubMed

Mnasri, S; Abdi-Ben Nasrallahl, S; Sfina, N; Lazzari, J L; Saïd, M

2012-11-01

Theoretical studies on spin-dependent transport in magnetic tunneling diodes with giant Zeeman splitting of the valence band are carried out. The studied structure consists of two nonmagnetic layers CdMgTe separated by a diluted magnetic semiconductor barrier CdMnTe, the hole is surrounded by two p-doped CdTe layers. Based on the parabolic valence band effective mass approximation and the transfer matrix method, the magnetization and the current densities for holes with spin-up and spin-down are studied in terms of the Mn concentration, the well and barrier thicknesses as well as the voltage. It is found that, the current densities depend strongly on these parameters and by choosing suitable values; this structure can be a good spin filter. Such behaviors are originated from the enhancement and suppression in the spin-dependent resonant states.

Dynamic spin polarization by orientation-dependent separation in a ferromagnet-semiconductor hybrid

NASA Astrophysics Data System (ADS)

Korenev, V. L.; Akimov, I. A.; Zaitsev, S. V.; Sapega, V. F.; Langer, L.; Yakovlev, D. R.; Danilov, Yu. A.; Bayer, M.

2012-07-01

Integration of magnetism into semiconductor electronics would facilitate an all-in-one-chip computer. Ferromagnet/bulk semiconductor hybrids have been, so far, mainly considered as key devices to read out the ferromagnetism by means of spin injection. Here we demonstrate that a Mn-based ferromagnetic layer acts as an orientation-dependent separator for carrier spins confined in a semiconductor quantum well that is set apart from the ferromagnet by a barrier only a few nanometers thick. By this spin-separation effect, a non-equilibrium electron-spin polarization is accumulated in the quantum well due to spin-dependent electron transfer to the ferromagnet. The significant advance of this hybrid design is that the excellent optical properties of the quantum well are maintained. This opens up the possibility of optical readout of the ferromagnet's magnetization and control of the non-equilibrium spin polarization in non-magnetic quantum wells.

Dynamic spin polarization by orientation-dependent separation in a ferromagnet-semiconductor hybrid.

PubMed

Korenev, V L; Akimov, I A; Zaitsev, S V; Sapega, V F; Langer, L; Yakovlev, D R; Danilov, Yu A; Bayer, M

2012-07-17

Integration of magnetism into semiconductor electronics would facilitate an all-in-one-chip computer. Ferromagnet/bulk semiconductor hybrids have been, so far, mainly considered as key devices to read out the ferromagnetism by means of spin injection. Here we demonstrate that a Mn-based ferromagnetic layer acts as an orientation-dependent separator for carrier spins confined in a semiconductor quantum well that is set apart from the ferromagnet by a barrier only a few nanometers thick. By this spin-separation effect, a non-equilibrium electron-spin polarization is accumulated in the quantum well due to spin-dependent electron transfer to the ferromagnet. The significant advance of this hybrid design is that the excellent optical properties of the quantum well are maintained. This opens up the possibility of optical readout of the ferromagnet's magnetization and control of the non-equilibrium spin polarization in non-magnetic quantum wells.

Electron spin resonance study of CuGa1-xMnxSe2 magnetic semiconducting compounds

NASA Astrophysics Data System (ADS)

Fermin, José R.; Nava, Alexander; Durante-Rincón, C. A.; Castro, Jaime; Silva, Pedro J.

2013-02-01

We report on the magnetic properties of the diluted magnetic semiconductor CuGa1-xMnxSe2. For this, Electron spin resonance (ESR) experiments in the temperature range 70 Kmagnetic phase not well identified. The inclusion of Mn induces local fields that increase the resonance field, with resulting g-values less than 2.0. The behavior of the ESR linewidth is similar to that observed in II-Mn-VI alloys, and can be described by the modified Huber equation.

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

Doping of epitaxial III-V semiconductors for optoelectronic and magnetoelectronic applications

NASA Astrophysics Data System (ADS)

Overberg, Mark Eddy

Doped III-V semiconducting materials were studied in this dissertation for use in optoelectronic and magnetoelectronic applications. The specific areas of use are emitters for fiber optic communication and room temperature ferromagnetic layers for spintronic devices. The general requirement for both application areas is the ability to heavily dope (or alloy) the III-Vs with the intended active element, while still maintaining good crystallinity and semiconducting properties. Four dopant/semiconductor systems were investigated: erbium in gallium nitride (GaN:Er), europium in gallium nitride (GaN:Eu), manganese in gallium nitride (GaMnN), and manganese in gallium phosphide (GaMnP). These materials were fabricated using variants of the molecular beam epitaxy (MBE) technique, where beams of the constituent elements are produced in a high vacuum environment. The technique allows for a wide variety of parameters to be adjusted during the material preparation. The materials were deposited on sapphire, gallium nitride, and gallium phosphide surfaces; with particular emphasis on the correlation between growth conditions and the final chemical, structural, morphological, electronic, optical, and magnetic properties. The materials were characterized using a variety of techniques. Results with the GaN:Er material indicated that several percent of Er could be successfully incorporated into the material, and that the optical emission could be increased by incorporating C impurities into the film. These impurities were found to increase the overall emission and decrease the quenching of the emission with temperature. Optical emission results for GaN:Eu indicated that this material produced a visible red emission that was brighter under optical excitation than the AlGaAs used in commercial red emitting devices. The dilute magnetic semiconductors n-GaMnN and p-GaMnP were produced for the first time by the MBE technique. The SQUID magnetometry and magnetotransport results for n

Oxidized Mn:Ge magnetic semiconductor: Observation of anomalous Hall effect and large magnetoresistance

NASA Astrophysics Data System (ADS)

Duc Dung, Dang; Choi, Jiyoun; Feng, Wuwei; Cao Khang, Nguyen; Cho, Sunglae

2018-03-01

We report on the structural and magneto-transport properties of the as-grown and oxidized Mn:Ge magnetic semiconductors. Based on X-ray diffraction and X-ray photoelectron spectroscopy results, the samples annealed at 650 and 700 °C became fully oxidized and the chemical binding energies of Mn was found to be Mn3O4. Thus, the system became Mn3O4 clusters embedded in Ge1-yOy. The as-grown sample showed positive linear Hall effect and negligible negative magnetoresistance (MR), which trend remained for the sample annealed up to 550 °C. Interestingly, for the samples annealed at above 650 °C, we observed the anomalous Hall effect around 45 K and the giant positive MR, which are respectively 59.2% and 78.5% at 7 kOe annealed at 650 °C and 700 °C.

Boron doping a semiconductor particle

DOEpatents

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.

Hole-cyclotron instability in semiconductor quantum plasmas

NASA Astrophysics Data System (ADS)

Areeb, F.; Rasheed, A.; Jamil, M.; Siddique, M.; Sumera, P.

2018-01-01

The excitation of electrostatic hole-cyclotron waves generated by an externally injected electron beam in semiconductor plasmas is examined using a quantum hydrodynamic model. The quantum effects such as tunneling potential, Fermi degenerate pressure, and exchange-correlation potential are taken care of. The growth rate of the wave is analyzed on varying the parameters normalized by hole-plasma frequency, like the angle θ between propagation vector and B0∥z ̂ , speed of the externally injected electron beam v0∥k , thermal temperature of the electron beam τ, external magnetic field B0∥z ̂ that modifies the hole-cyclotron frequency, and finally, the semiconductor electron number density. The instability of the hole-cyclotron wave seeks its applications in semiconductor devices.

32nd International Conference on the Physics of Semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chelikowsky, James

The International Conference on the Physics of Semiconductors (ICPS) continues a series of biennial conferences that began in the 1950's. ICPS is the premier meeting for reporting all aspects of semiconductor physics including electronic, structural, optical, magnetic and transport properties with an emphasis on new materials and their applications. The meeting will reflect the state of art in the semiconductor physics field and will serve as a forum where scholars, researchers, and specialists can interact to discuss future research directions and technological advancements. The conference typically draws 1,000 international physicists, scientists, and students. This is one of the largest sciencemore » meetings on semiconductors and related materials to be held in the United States.« less

Defect-mediated magnetism of transition metal doped zinc oxide thin films

NASA Astrophysics Data System (ADS)

Roberts, Bradley Kirk

Magnetism in transition metal doped wide band-gap materials is of interest to further the fundamental science of materials and future spintronics applications. Large inter-dopant separations require mediation of ferromagnetism by some method; carrier-mediated mechanisms are typically applicable to dilute magnetic semiconductors with low Curie temperatures. Dilute magnetic oxides, commonly with poor conductivity and TC above room temperature, cannot be described within this theory. Recent experiment and theory developments suggest that ferromagnetic exchange in these materials can be mediated by defects. This research includes experimental results justifying and developing this approach. Thin films of Cr doped ZnO (band gap ˜3.3 eV) were deposited with several processing variations to enhance the effects of either 0-dimensional (vacancy, hydrogen-related defect) or two-dimensional defects (surface/interface) and thereby affect magnetism and conductivity. We observe surface magnetism in dielectric thin films of oxygen-saturated ZnO:Cr with spontaneous magnetic moment and conductance dropping approximately exponentially with increasing thickness. Uniform defect concentrations would not result in such magnetic ordering behavior indicating that magnetism is mediated either by surface defects or differing concentrations of point defects near the surface. Polarized neutron reflectivity profiling confirms a magnetically active region of ˜8 nm at the film surface. Hydrogen is notoriously present as a defect and carrier dopant in ZnO, and artificial introduction of hydrogen in dielectric ZnO:Cr films results in varying electronic and magnetic behavior. Free carriers introduced with hydrogen doping are not spin-polarized requiring an alternative explanation for ferromagnetism. We find from positron annihilation spectroscopy measurements that hydrogen doping increases the concentration of an altered VZn-related defect (a preliminary interpretation) throughout the film, which

Diamagnetic excitons and exciton magnetopolaritons in semiconductors

NASA Astrophysics Data System (ADS)

Seisyan, R. P.

2012-05-01

Interband magneto-absorption in semiconductors is reviewed in the light of the diamagnetic exciton (DE) concept. Beginning with a proof of the exciton nature of oscillating-magnetoabsorption (the DE discovery), development of the DE concept is discussed, including definition of observation conditions, quasi-cubic approximation for hexagonal crystals, quantum-well effects in artificial structures, and comprehension of an important role of the DE polariton. The successful use of the concept application to a broad range of substances is reviewed, namely quasi-Landau magnetic spectroscopy of the ‘Rydberg’ exciton states in cubic semiconductors such as InP and GaAs and in hexagonal ones such as CdSe, the proof of exciton participation in the formation of optical spectra in narrow-gap semiconductors such as InSb, InAs, and, especially, PbTe, observation of DE spectra in semiconductor solid solutions like InGaAs. The most fundamental findings of the DE spectroscopy for various quantum systems are brought together, including the ‘Coulomb-well’ effect, fine structure of discrete oscillatory states in the InGaAs/GaAs multiple quantum wells, the magneto-optical observation of above-barrier exciton. Prospects of the DE physics in ultrahigh magnetic field are discussed, including technological creation of controllable low-dimensional objects with extreme oscillator strengths, formation of magneto-quantum exciton polymer, and even modelling of the hydrogen behaviour in the atmosphere of a neutron star.

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.

Overview of the 1997 Dirac High-Magnetic Series at LOS Alamos

NASA Astrophysics Data System (ADS)

Clark, D. A.; Campbell, L. J.; Forman, K. C.; Fowler, C. M.; Goettee, J. D.; Mielke, C. H.; Rickel, D. G.; Marshall, B. R.

2004-11-01

During the summer of 1997, a series of high magnetic field experiments was conducted at Los Alamos National Laboratory. Four experiments utilizing Russian built MC-1 generators, which can reach fields as high as 10 Megagauss, and four smaller strip generator experiments at fields near 1.5 Megagauss were conducted. Experiments mounted on the devices included magnetoresistance of high temperature superconductors and semiconductors, optical reflectivity (conductivity) of semiconductors, magnetization of a magnetic cluster material and a semiconductor, Faraday rotation in a semiconductor and a magnetic cluster material, and transmission spectroscopy of molecules. Brief descriptions of the experimental setups, magnetic field measurement techniques, field results and various experiments are presented. Magnetic field data and other information on Dirac `97 can be found at .

Tunnel based spin injection devices for semiconductor spintronics

NASA Astrophysics Data System (ADS)

Jiang, Xin

This dissertation summarizes the work on spin-dependent electron transport and spin injection in tunnel based spintronic devices. In particular, it focuses on a novel three terminal hot electron device combining ferromagnetic metals and semiconductors---the magnetic tunnel transistor (MTT). The MTT has extremely high magnetic field sensitivity and is a useful tool to explore spin-dependent electron transport in metals, semiconductors, and at their interfaces over a wide energy range. In Chap. 1, the basic concept and fabrication of the MTT are discussed. Two types of MTTs, with ferromagnetic single and spin-valve base layers, respectively, are introduced and compared. In the following chapters, the transport properties of the MTT are discussed in detail, including the spin-dependent hot electron attenuation lengths in CoFe and NiFe thin films on GaAs (Chap. 2), the bias voltage dependence of the magneto-current (Chap. 3), the giant magneto-current effect in MTTs with a spin-valve base (Chap. 4), and the influence of non-magnetic seed layers on magneto-electronic properties of MTTs with a Si collector (Chap. 5). Chap. 6 concentrates on electrical injection of spin-polarized electrons into semiconductors, which is an essential ingredient in semiconductor spintronics. Two types of spin injectors are discussed: an MTT injector and a CoFe/MgO tunnel injector. The spin polarization of the injected electron current is detected optically by measuring the circular polarization of electroluminescence from a quantum well light emitting diode. Using an MTT injector a spin polarization of ˜10% is found for injection electron energy of ˜2 eV at 1.4K. This moderate spin polarization is most likely limited by significant electron spin relaxation at high energy. Much higher spin injection efficiency is obtained by using a CoFe/MgO tunnel injector with spin polarization values of ˜50% at 100K. The temperature and bias dependence of the electroluminescence polarization provides

Optical gain in 1.3-μm electrically driven dilute nitride VCSOAs

PubMed Central

2014-01-01

We report the observation of room-temperature optical gain at 1.3 μm in electrically driven dilute nitride vertical cavity semiconductor optical amplifiers. The gain is calculated with respect to injected power for samples with and without a confinement aperture. At lower injected powers, a gain of almost 10 dB is observed in both samples. At injection powers over 5 nW, the gain is observed to decrease. For nearly all investigated power levels, the sample with confinement aperture gives slightly higher gain. PMID:24417791

Assembling non-ferromagnetic materials to ferromagnetic architectures using metal-semiconductor interfaces

PubMed Central

Ma, Ji; Liu, Chunting; Chen, Kezheng

2016-01-01

In this work, a facile and versatile solution route was used to fabricate room-temperature ferromagnetic fish bone-like, pteridophyte-like, poplar flower-like, cotton-like Cu@Cu2O architectures and golfball-like Cu@ZnO architecture. The ferromagnetic origins in these architectures were found to be around metal-semiconductor interfaces and defects, and the root cause for their ferromagnetism lay in charge transfer processes from metal Cu to semiconductors Cu2O and ZnO. Owing to different metallization at their interfaces, these architectures exhibited different ferromagnetic behaviors, including coercivity, saturation magnetization as well as magnetic interactions. PMID:27680286

Theoretical Study of Defect Signatures in III-V and II-VI Semiconductors

DTIC Science & Technology

2006-03-01

collaboration with experimentalists at Linköpin University (Sweden), we identified the recently observed EPR signals in diluted GaPN to be Gallium ...the results from USPP calculations to all electron calculations. o Study NO-Zni complexes and other point defects in ZnO using USPP calculations...parameters for point defects in semiconductors. o Results on stability of NO-Zni complexes in ZnO and preliminary results on their electronic

Realisation of magnetically and atomically abrupt half-metal/semiconductor interface: Co2FeSi0.5Al0.5/Ge(111)

PubMed Central

Nedelkoski, Zlatko; Kuerbanjiang, Balati; Glover, Stephanie E.; Sanchez, Ana M.; Kepaptsoglou, Demie; Ghasemi, Arsham; Burrows, Christopher W.; Yamada, Shinya; Hamaya, Kohei; Ramasse, Quentin M.; Hasnip, Philip J.; Hase, Thomas; Bell, Gavin R.; Hirohata, Atsufumi; Lazarov, Vlado K.

2016-01-01

Halfmetal-semiconductor interfaces are crucial for hybrid spintronic devices. Atomically sharp interfaces with high spin polarisation are required for efficient spin injection. In this work we show that thin film of half-metallic full Heusler alloy Co2FeSi0.5Al0.5 with uniform thickness and B2 ordering can form structurally abrupt interface with Ge(111). Atomic resolution energy dispersive X-ray spectroscopy reveals that there is a small outdiffusion of Ge into specific atomic planes of the Co2FeSi0.5Al0.5 film, limited to a very narrow 1 nm interface region. First-principles calculations show that this selective outdiffusion along the Fe-Si/Al atomic planes does not change the magnetic moment of the film up to the very interface. Polarized neutron reflectivity, x-ray reflectivity and aberration-corrected electron microscopy confirm that this interface is both magnetically and structurally abrupt. Finally, using first-principles calculations we show that this experimentally realised interface structure, terminated by Co-Ge bonds, preserves the high spin polarization at the Co2FeSi0.5Al0.5/Ge interface, hence can be used as a model to study spin injection from half-metals into semiconductors. PMID:27869132

Electronic and magnetic properties of transition metal decorated monolayer GaS

NASA Astrophysics Data System (ADS)

Lin, Heng-Fu; Liu, Li-Min; Zhao, Jijun

2018-07-01

Inducing controllable magnetism in two dimensional non-magnetic materials is very important for realizing dilute magnetic semiconductor. Using density functional theory, we have systematically investigated the effect of surface adsorption of various 3d transition metal (TM) atoms (Sc-Cu) on the electronic and magnetic properties of the monolayer GaS as representative of group-IIIA metal-monochalcogenide. We find that all adatoms favor the top site on the Ga atom. All the TM atoms, except for the Cr and Mn, can bond strongly to the GaS monolayer with sizable binding energies. Moreover, the TM decorated GaS monolayers exhibit interesting magnetic properties, which arise from the strong spin-dependent hybridization of the TM 3d orbitals with S 3p and Ga 4s orbitals. After examining the magnetic interaction between two same types of TM atoms, we find that most of them exhibit antiferromagnetic coupling, while Fe and Co atoms can form long-range ferromagnetism. Furthermore, we find that the electronic properties of metal decorated systems strongly rely on the type of TM adatom and the adsorption concentration. In particular, the spin-polarized semiconducting state can be realized in Fe doped system for a large range of doping concentrations. These findings indicate that the TM decorated GaS monolayers have potential device applications in next-generation electronics and spintronics.

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.

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.

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.

EDITORIAL: Semiconductor lasers: the first fifty years Semiconductor lasers: the first fifty years

NASA Astrophysics Data System (ADS)

Calvez, S.; Adams, M. J.

2012-09-01

achievements in the June 1987 Special Issue of IEEE Journal of Quantum Electronics. The Millennium Issue of IEEE Journal of Selected Topics in Quantum Electronics presented a further set of articles on historical aspects of the subject as well as a 'snapshot' of current research in June 2000. It is not the intention here to duplicate any of this historical material that is already available, but rather to complement it with personal recollections from researchers who were involved in laser development in the USA, France, Russia and the UK. Hence, in addition to fascinating accounts of the discovery of the theoretical condition for stimulated emission from semiconductors and of the pioneering work at IBM, there are two complementary views of the laser research at the Lebedev Institute, and personal insights into the developments at STL and at Bell Laboratories. These are followed by an account of the scientific and technological connections between the early pioneering breakthroughs and the commercialisation of semiconductor laser products. Turning to the papers from today's researchers, there is coverage of many of the current 'hot' topics including quantum cascade lasers, mid-infrared lasers, high-power lasers, the exciting developments in understanding and exploiting the nonlinear dynamics of lasers, and photonic integrated circuits with extremely high communication data capacity, as well as reports of recent progress on laser materials such as dilute nitrides and bismides, photonic crystals, quantum dots and organic semiconductors. Thanks are due to Jarlath McKenna for sterling support from IOP Publishing and to Peter Blood for instigating this Special Issue and inviting us to serve as Guest Editors.

Van der Waals engineering of ferromagnetic semiconductor heterostructures for spin and valleytronics

DOE PAGES

Zhong, Ding; Seyler, Kyle L.; Linpeng, Xiayu; ...

2017-05-31

The integration of magnetic material with semiconductors has been fertile ground for fundamental science as well as of great practical interest toward the seamless integration of information processing and storage. We create van der Waals heterostructures formed by an ultrathin ferromagnetic semiconductor CrI 3 and a monolayer of WSe 2. We observe unprecedented control of the spin and valley pseudospin in WSe 2, where we detect a large magnetic exchange field of nearly 13 T and rapid switching of the WSe 2 valley splitting and polarization via flipping of the CrI 3 magnetization. The WSe2 photoluminescence intensity strongly depends onmore » the relative alignment between photoexcited spins in WSe 2 and the CrI 3 magnetization, because of ultrafast spin-dependent charge hopping across the heterostructure interface. The photoluminescence detection of valley pseudospin provides a simple and sensitive method to probe the intriguing domain dynamics in the ultrathin magnet, as well as the rich spin interactions within the heterostructure.« less

Van der Waals engineering of ferromagnetic semiconductor heterostructures for spin and valleytronics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Ding; Seyler, Kyle L.; Linpeng, Xiayu

The integration of magnetic material with semiconductors has been fertile ground for fundamental science as well as of great practical interest toward the seamless integration of information processing and storage. We create van der Waals heterostructures formed by an ultrathin ferromagnetic semiconductor CrI 3 and a monolayer of WSe 2. We observe unprecedented control of the spin and valley pseudospin in WSe 2, where we detect a large magnetic exchange field of nearly 13 T and rapid switching of the WSe 2 valley splitting and polarization via flipping of the CrI 3 magnetization. The WSe2 photoluminescence intensity strongly depends onmore » the relative alignment between photoexcited spins in WSe 2 and the CrI 3 magnetization, because of ultrafast spin-dependent charge hopping across the heterostructure interface. The photoluminescence detection of valley pseudospin provides a simple and sensitive method to probe the intriguing domain dynamics in the ultrathin magnet, as well as the rich spin interactions within the heterostructure.« less

Theory of electron g-tensor in bulk and quantum-well semiconductors

NASA Astrophysics Data System (ADS)

Lau, Wayne H.; Flatte', Michael E.

2004-03-01

We present quantitative calculations for the electron g-tensors in bulk and quantum-well semiconductors based on a generalized P.p envelope function theory solved in a fourteen-band restricted basis set. The dependences of g-tensor on structure, magnetic field, carrier density, temperature, and spin polarization have been explored and will be described. It is found that at temperatures of a few Kelvin and fields of a few Tesla, the g-tensors for bulk semiconductors develop quasi-steplike dependences on carrier density or magnetic field due to magnetic quantization, and this effect is even more pronounced in quantum-well semiconductors due to the additional electric quantization along the growth direction. The influence of quantum confinement on the electron g-tensors in QWs is studied by examining the dependence of electron g-tensors on well width. Excellent agreement between these calculated electron g-tensors and measurements [1-2] is found for GaAs/AlGaAs QWs. This work was supported by DARPA/ARO. [1] A. Malinowski and R. T. Harley, Phys. Rev. B 62, 2051 (2000);[2] Le Jeune et al., Semicond. Sci. Technol. 12, 380 (1997).

Effect of disorder on the magnetic and electronic structure of a prospective spin-gapless semiconductor MnCrVAl

DOE PAGES

Kharel, P.; Herran, J.; Lukashev, P.; ...

2016-12-19

Recent discovery of a new class of materials, spin-gapless semiconductors (SGS), has attracted considerable attention in the last few years, primarily due to potential applications in the emerging field of spin-based electronics (spintronics). Here, we investigate structural, electronic, and magnetic properties of one potential SGS compound, MnCrVAl, using various experimental and theoretical techniques. Our calculations show that this material exhibits ≈ 0.5 eV band gap for the majority-spin states, while for the minority-spin it is nearly gapless. The calculated magnetic moment for the completely ordered structure is 2.9 μB/f.u., which is different from our experimentally measured value of almost zero.more » Here, this discrepancy is explained by the structural disorder. In particular, A2 type disorder, where Mn or Cr atoms exchange their positions with Al atoms, results in induced antiferromagnetic exchange coupling, which, at a certain level of disorder, effectively reduces the total magnetic moment to zero. This is consistent with our x-ray diffraction measurements which indicate the presence of A2 disorder in all of our samples. In addition, we also show that B2 disorder does not result in antiferromagnetic exchange coupling and therefore does not significantly reduce the total magnetic moment.« less

Physics and application of persistent spin helix state in semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Kohda, Makoto; Salis, Gian

2017-07-01

In order to utilize the spin degree of freedom in semiconductors, control of spin states and transfer of the spin information are fundamental requirements for future spintronic devices and quantum computing. Spin orbit (SO) interaction generates an effective magnetic field for moving electrons and enables spin generation, spin manipulation and spin detection without using external magnetic field and magnetic materials. However, spin relaxation also takes place due to a momentum dependent SO-induced effective magnetic field. As a result, SO interaction is considered to be a double-edged sword facilitating spin control but preventing spin transport over long distances. The persistent spin helix (PSH) state solves this problem since uniaxial alignment of the SO field with SU(2) symmetry enables the suppression of spin relaxation while spin precession can still be controlled. Consequently, understanding the PSH becomes an important step towards future spintronic technologies for classical and quantum applications. Here, we review recent progress of PSH in semiconductor heterostructures and its device application. Fundamental physics of SO interaction and the conditions of a PSH state in semiconductor heterostructures are discussed. We introduce experimental techniques to observe a PSH and explain both optical and electrical measurements for detecting a long spin relaxation time and the formation of a helical spin texture. After emphasizing the bulk Dresselhaus SO coefficient γ, the application of PSH states for spin transistors and logic circuits are discussed.

Simplified Modeling of Steady-State and Transient Brillouin Gain in Magnetoactive Non-Centrosymmetric Semiconductors

NASA Astrophysics Data System (ADS)

Singh, M.; Aghamkar, P.; Sen, P. K.

With the aid of a hydrodynamic model of semiconductor-plasmas, a detailed analytical investigation is made to study both the steady-state and the transient Brillouin gain in magnetized non-centrosymmetric III-V semiconductors arising from the nonlinear interaction of an intense pump beam with the internally-generated acoustic wave, due to piezoelectric and electrostrictive properties of the crystal. Using the fact that the origin of coherent Brillouin scattering (CBS) lies in the third-order (Brillouin) susceptibility of the medium, we obtained an expression of the gain coefficient of backward Stokes mode in steady-state and transient regimes and studied the dependence of piezoelectricity, magnetic field and pump pulse duration on its growth rate. The threshold-pump intensity and optimum pulse duration for the onset of transient CBS are estimated. The piezoelectricity and externally-applied magnetic field substantially enhances the transient CBS gain coefficient in III-V semiconductors which can be of great use in the compression of scattered pulses.

Pre-earthquake Magnetic Pulses

NASA Astrophysics Data System (ADS)

Scoville, J.; Heraud, J. A.; Freund, F. T.

2015-12-01

A semiconductor model of rocks is shown to describe unipolar magnetic pulses, a phenomenon that has been observed prior to earthquakes. These pulses are suspected to be generated deep in the Earth's crust, in and around the hypocentral volume, days or even weeks before earth quakes. Their extremely long wavelength allows them to pass through kilometers of rock. Interestingly, when the sources of these pulses are triangulated, the locations coincide with the epicenters of future earthquakes. We couple a drift-diffusion semiconductor model to a magnetic field in order to describe the electromagnetic effects associated with electrical currents flowing within rocks. The resulting system of equations is solved numerically and it is seen that a volume of rock may act as a diode that produces transient currents when it switches bias. These unidirectional currents are expected to produce transient unipolar magnetic pulses similar in form, amplitude, and duration to those observed before earthquakes, and this suggests that the pulses could be the result of geophysical semiconductor processes.

Pre-earthquake magnetic pulses

NASA Astrophysics Data System (ADS)

Scoville, J.; Heraud, J.; Freund, F.

2015-08-01

A semiconductor model of rocks is shown to describe unipolar magnetic pulses, a phenomenon that has been observed prior to earthquakes. These pulses are suspected to be generated deep in the Earth's crust, in and around the hypocentral volume, days or even weeks before earthquakes. Their extremely long wavelength allows them to pass through kilometers of rock. Interestingly, when the sources of these pulses are triangulated, the locations coincide with the epicenters of future earthquakes. We couple a drift-diffusion semiconductor model to a magnetic field in order to describe the electromagnetic effects associated with electrical currents flowing within rocks. The resulting system of equations is solved numerically and it is seen that a volume of rock may act as a diode that produces transient currents when it switches bias. These unidirectional currents are expected to produce transient unipolar magnetic pulses similar in form, amplitude, and duration to those observed before earthquakes, and this suggests that the pulses could be the result of geophysical semiconductor processes.

Effect of Cobalt Concentration and Oxygen Vacancy on Magnetism of Co Doped ZnO Nanorods.

PubMed

Li, Congli; Che, Ping; Sun, Changyan; Li, Wenjun

2016-03-01

Zn(1-x)Co(x)O (x = 0-0.07) single-crystalline nanorods were prepared by a modified microemulsion route. The crystalline structure, morphology, optical, and hysteresis loop at low and room temperature of as-prepared materials were characterized by XRD, TEM, PL spectra, and magnetic measurement respectively. The nanorods are 80-250 nm in diameter and about 3 μm in length. X-ray diffraction data, TEM images confirm that the materials synthesized in optimal conditions are ZnO:Co single crystalline solid solution without any impurities related to Co. The PL spectra show that the ferromagnetic samples exhibit strong Zn interstitials and oxygen vacancy emission indicating defects may stabilize ferromagnetic order in the obtained diluted magnetic semiconductors. Magnetic measurements show that the Zn(1-x)Co(x)O nanorods exist obvious ferromagnetic characteristics with T(c) above 300 K. M(s) and coercivities first increase and then decrease with dopant concentration increasing, reaching the highest for 3% doping level. The structural and magnetic properties of these samples support the hypothesis that the FM of DMS nanorods is due to a defect mediated mechanism instead of cobalt nanoclusters and carrier mediated.

High-throughput ab-initio dilute solute diffusion database.

PubMed

Wu, Henry; Mayeshiba, Tam; Morgan, Dane

2016-07-19

We demonstrate automated generation of diffusion databases from high-throughput density functional theory (DFT) calculations. A total of more than 230 dilute solute diffusion systems in Mg, Al, Cu, Ni, Pd, and Pt host lattices have been determined using multi-frequency diffusion models. We apply a correction method for solute diffusion in alloys using experimental and simulated values of host self-diffusivity. We find good agreement with experimental solute diffusion data, obtaining a weighted activation barrier RMS error of 0.176 eV when excluding magnetic solutes in non-magnetic alloys. The compiled database is the largest collection of consistently calculated ab-initio solute diffusion data in the world.

Absence of exchange interaction between localized magnetic moments and conduction-electrons in diluted Er{sup 3+} gold-nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lesseux, G. G., E-mail: lesseux@ifi.unicamp.br; Urbano, R. R.; Iwamoto, W.

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 reexaminedmore » at the nano scale range.« less

Probing and manipulating magnetization at the nanoscale

NASA Astrophysics Data System (ADS)

Samarth, Nitin

2012-02-01

Combining semiconductors with magnetism in hetero- and nano-structured geometries provides a powerful means of exploring the interplay between spin-dependent transport and nanoscale magnetism. We describe two recent studies in this context. First, we use spin-dependent transport in ferromagnetic semiconductor thin films to provide a new window into nanoscale magnetism [1]: here, we exploit the large anomalous Hall effect in a ferromagnetic semiconductor as a nanoscale probe of the reversible elastic behavior of magnetic domain walls and gain insight into regimes of domain wall behavior inaccessible to more conventional optical techniques. Next, we describe novel ways to create self-assembled hybrid semiconductor/ferromagnet core-shell nanowires [2] and show how magnetoresistance measurements in single nanowires, coupled with micromagnetic simulations, can provide detailed insights into the magnetization reversal process in nanoscale ferromagnets [3]. The work described here was carried out in collaboration with Andrew Balk, Jing Liang, Nicholas Dellas, Mark Nowakowski, David Rench, Mark Wilson, Roman Engel-Herbert, Suzanne Mohney, Peter Schiffer and David Awschalom. This work is supported by ONR, NSF and the NSF-MRSEC program.[4pt] [1] A. L. Balk et al., Phys. Rev.Lett. 107, 077205 (2011).[0pt] [2] N. J. Dellas et al., Appl. Phys. Lett. 97, 072505 (2010).[0pt] [3] J. Liang et al., in preparation.

An impedance analysis of double-stream interaction in semiconductors

NASA Technical Reports Server (NTRS)

Chen, P. W.; Durney, C. H.

1972-01-01

The electromagnetic waves propagating through a drifting semiconductor plasma are studied from a macroscopic point of view in terms of double-stream interaction. The possible existing waves (helicon waves, longitudinal waves, ordinary waves, and pseudolongitudinal waves) which depend upon the orientation of the dc external magnetic field are derived. A powerful impedance concept is introduced to investigate the wave behavior of longitudinal (space charge) waves or pseudolongitudinal waves in a semiconductor plasma. The impedances due to one- and two-carrier stream interactions were calculated theoretically.

Defect-induced ferromagnetism in semiconductors: A controllable approach by particle irradiation

NASA Astrophysics Data System (ADS)

Zhou, Shengqiang

2014-05-01

Making semiconductors ferromagnetic has been a long dream. One approach is to dope semiconductors with transition metals (TM). TM ions act as local moments and they couple with free carriers to develop collective magnetism. However, there are no fundamental reasons against the possibility of local moment formation from localized sp states. Recently, ferromagnetism was observed in nonmagnetically doped, but defective semiconductors or insulators including ZnO and TiO2. This kind of observation challenges the conventional understanding of ferromagnetism. Often the defect-induced ferromagnetism has been observed in samples prepared under non-optimized condition, i.e. by accident or by mistake. Therefore, in this field theory goes much ahead of experimental investigation. To understand the mechanism of the defect-induced ferromagnetism, one needs a better controlled method to create defects in the crystalline materials. As a nonequilibrium and reproducible approach of inducing defects, ion irradiation provides such a possibility. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies, interstitials or antisites. The amount and the distribution of defects can be controlled by the ion fluence and energy. By ion irradiation, we have generated defect-induced ferromagnetism in ZnO, TiO2 and SiC. In this short review, we also summarize some results by other groups using energetic ions to introduce defects, and thereby magnetism in various materials. Ion irradiation combined with proper characterizations of defects could allow us to clarify the local magnetic moments and the coupling mechanism in defective semiconductors. Otherwise we may have to build a new paradigm to understand the defect-induced ferromagnetism.

Study of magnetism in Ni-Cr hardface alloy deposit on 316LN stainless steel using magnetic force microscopy

NASA Astrophysics Data System (ADS)

Kishore, G. V. K.; Kumar, Anish; Chakraborty, Gopa; Albert, S. K.; Rao, B. Purna Chandra; Bhaduri, A. K.; Jayakumar, T.

2015-07-01

Nickel base Ni-Cr alloy variants are extensively used for hardfacing of austenitic stainless steel components in sodium cooled fast reactors (SFRs) to avoid self-welding and galling. Considerable difference in the compositions and melting points of the substrate and the Ni-Cr alloy results in significant dilution of the hardface deposit from the substrate. Even though, both the deposit and the substrate are non-magnetic, the diluted region exhibits ferromagnetic behavior. The present paper reports a systematic study carried out on the variations in microstructures and magnetic behavior of American Welding Society (AWS) Ni Cr-C deposited layers on 316 LN austenitic stainless steels, using atomic force microscopy (AFM) and magnetic force microscopy (MFM). The phase variations of the oscillations of a Co-Cr alloy coated magnetic field sensitive cantilever is used to quantitatively study the magnetic strength of the evolved microstructure in the diluted region as a function of the distance from the deposit/substrate interface, with the spatial resolution of about 100 nm. The acquired AFM/MFM images and the magnetic property profiles have been correlated with the variations in the chemical compositions in the diluted layers obtained by the energy dispersive spectroscopy (EDS). The study indicates that both the volume fraction of the ferromagnetic phase and its ferromagnetic strength decrease with increasing distance from the deposit/substrate interface. A distinct difference is observed in the ferromagnetic strength in the first few layers and the ferromagnetism is observed only near to the precipitates in the fifth layer. The study provides a better insight of the evolution of ferromagnetism in the diluted layers of Ni-Cr alloy deposits on stainless steel.

Optically programmable electron spin memory using semiconductor quantum dots.

PubMed

Kroutvar, Miro; Ducommun, Yann; Heiss, Dominik; Bichler, Max; Schuh, Dieter; Abstreiter, Gerhard; Finley, Jonathan J

2004-11-04

The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled and embedded into active devices. It has been predicted that the atomic-like electronic structure of such quantum dots suppresses coupling of the spin to the solid-state quantum dot environment, thus protecting the 'spin' quantum information against decoherence. Here we demonstrate a single electron spin memory device in which the electron spin can be programmed by frequency selective optical excitation. We use the device to prepare single electron spins in semiconductor quantum dots with a well defined orientation, and directly measure the intrinsic spin flip time and its dependence on magnetic field. A very long spin lifetime is obtained, with a lower limit of about 20 milliseconds at a magnetic field of 4 tesla and at 1 kelvin.

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.…

First-principles calculations of electronic, magnetic and optical properties of HoN doped with TM (Ti, V, Cr, Mn, Co and Ni)

NASA Astrophysics Data System (ADS)

Rouchdi, M.; Salmani, E.; Dehmani, M.; Ez-Zahraouy, H.; Hassanain, N.; Benyoussef, A.; Mzerd, A.

2018-02-01

Using the first-principles calculations within the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA), the structural, optical and magnetic properties of rare-earth nitride Ho0.95TM0.05N doped with transition metal (TM) atoms (Ti, V, Cr, Mn, Co and Ni) are investigated as a function the generalized gradient approximation and self-interaction correction (GGA-SIC) approximation. The optical properties are studied in detail by using ab-initio calculations. Using GGA-SIC we have showed that the bandgap value is in good agreement with the experimental value. Using GGA-SIC approximation for HoN, we have obtained a bandgap of 0.9 eV. Some of the dilute magnetic semiconductors (DMS) like Ho0.95TM0.05N under study exhibit a half-metallic behavior, which makes them suitable for spintronic applications. Moreover, the optical absorption spectra confirm the ferromagnetic stability based on the charge state of magnetic impurities.

Anomalous effective magnetoconductivity in disordered bipolar semiconductors: Theory and experimental simulation

NASA Astrophysics Data System (ADS)

Chaikovsky, Isaak; Alperovich, Leonid; Gurvich, Yuri; Melnikov, Andrey; Biryukov, Sergey

2002-05-01

We present the results of measuring transverse conductivity α⊥c of bipolar heterogeneous semiconductors in classical strong magnetic fields. A stochastic distribution of current carriers (electrons and holes) was created by interband illumination through special masks. The main parameters of crystalline p-Si:B placed in liquid He were the concentrations of the main and compensating impurities, 7×1015 and 4×1012 cm-3, respectively; and the mobilities of electrons and holes, 1×106 and 5×104 cm2/V s, respectively. An anomaly in α⊥c was observed: the ratio of α⊥c for heterogeneous and homogeneous samples depended on magnetic field in a nonmonotonic way, i.e., alternation of increasing and decreasing regions of relative α⊥c for H=0-10 kGs and monotonic growth for H=10-40 kGs. To explain this effect, a theory is presented which is a development of the α⊥c theory for heterogeneous semiconductors with one kind of carrier. It is shown that the effect is due to the redistribution of roles of electrons and holes in magnetoconductivity of homogeneous semiconductors. This effect has high sensitivity to degree of disorder and can be used for detection of small irregularities and as a diagnostic of semiconductor purity.

A primary exploration to quasi-two-dimensional rare-earth ferromagnetic particles: holmium-doped MoS2 sheet as room-temperature magnetic semiconductor

NASA Astrophysics Data System (ADS)

Chen, Xi; Lin, Zheng-Zhe

2018-05-01

Recently, two-dimensional materials and nanoparticles with robust ferromagnetism are even of great interest to explore basic physics in nanoscale spintronics. More importantly, room-temperature magnetic semiconducting materials with high Curie temperature is essential for developing next-generation spintronic and quantum computing devices. Here, we develop a theoretical model on the basis of density functional theory calculations and the Ruderman-Kittel-Kasuya-Yoshida theory to predict the thermal stability of two-dimensional magnetic materials. Compared with other rare-earth (dysprosium (Dy) and erbium (Er)) and 3 d (copper (Cu)) impurities, holmium-doped (Ho-doped) single-layer 1H-MoS2 is proposed as promising semiconductor with robust magnetism. The calculations at the level of hybrid HSE06 functional predict a Curie temperature much higher than room temperature. Ho-doped MoS2 sheet possesses fully spin-polarized valence and conduction bands, which is a prerequisite for flexible spintronic applications.

Structural and Magnetic Properties of Transition-Metal-Doped Zn 1-x Fe x O.

PubMed

Abdel-Baset, T A; Fang, Yue-Wen; Anis, B; Duan, Chun-Gang; Abdel-Hafiez, Mahmoud

2016-12-01

The ability to produce high-quality single-phase diluted magnetic semiconductors (DMS) is the driving factor to study DMS for spintronics applications. Fe-doped ZnO was synthesized by using a low-temperature co-precipitation technique producing Zn 1-x Fe x O nanoparticles (x= 0, 0.02, 0.04, 0.06, 0.08, and 0.1). Structural, Raman, density functional calculations, and magnetic studies have been carried out in studying the electronic structure and magnetic properties of Fe-doped ZnO. The results show that Fe atoms are substituted by Zn ions successfully. Due to the small ionic radius of Fe ions compared to that of a Zn ions, the crystal size decreases with an increasing dopant concentration. First-principle calculations indicate that the charge state of iron is Fe (2+) and Fe (3+) with a zinc vacancy or an interstitial oxygen anion, respectively. The calculations predict that the exchange interaction between transition metal ions can switch from the antiferromagnetic coupling into its quasi-degenerate ferromagnetic coupling by external perturbations. This is further supported and explains the observed ferromagnetic bahaviour at magnetic measurements. Magnetic measurements reveal that decreasing particle size increases the ferromagnetism volume fraction. Furthermore, introducing Fe into ZnO induces a strong magnetic moment without any distortion in the geometrical symmetry; it also reveals the ferromagnetic coupling.

Tunability of room-temperature ferromagnetism in spintronic semiconductors through nonmagnetic atoms

NASA Astrophysics Data System (ADS)

Leedahl, Brett; Abooalizadeh, Zahra; LeBlanc, Kyle; Moewes, Alexander

2017-07-01

The implementation and control of room-temperature ferromagnetism (RTFM) by adding magnetic atoms to a semiconductor's lattice has been one of the most important problems in solid-state physics in the last decade. Herein we report on the mechanism that allows RTFM to be tuned by the inclusion of nonmagnetic aluminum in nickel ferrite. This material, NiFe2 -xAlxO4 (x =0 ,0.5 ,1.5 ), has already shown much promise for magnetic semiconductor technologies, and we are able to add to its versatility technological viability with our results. The site occupancies and valencies of Fe atoms (Fe3 +Td , Fe2 +Oh , and Fe3 +Oh ) can be methodically controlled by including aluminum. Using the fact that aluminum strongly prefers a 3+ octahedral environment, we can selectively fill iron sites with aluminum atoms, and hence specifically tune the magnetic contributions for each of the iron sites, and therefore the bulk material as well. Interestingly, the influence of the aluminum is weak on the electronic structure, allowing one to retain the desirable electronic properties while achieving desirable magnetic properties.

Magnetoviscous effect in ferrofluids diluted with sheep blood

NASA Astrophysics Data System (ADS)

Nowak, J.; Borin, D.; Haefner, S.; Richter, A.; Odenbach, S.

2017-11-01

Suspensions of magnetic nanoparticles in suitable carrier liquids, denoted as ferrofluids, are in the focus of current research in the biomedical area. Those fluids can be potentially used for the treatment of cancer by coupling chemotherapeutic agents and accumulating them in the diseased region with the help of external magnetic fields or by artificially local induced heating. Those applications rely on the help of external magnetic fields, which are well known to drastically influence the physical behaviour of ferrofluids. This study investigates the changing viscosity of a biocompatible ferrofluid in a flow situation close to the situation found in a biomedical application. For this purpose blood as diluting agent and thin capillaries have been utilised. The strong magnetoviscous effects found lead to the assumption of quite big changes of the microstructure due to the external magnetic fields, which was investigated and quantified using a microscopic setup. In the result an increases of the structure size as well as faster structure formation in the stronger magnetic fields were observed. Moreover, with increasing duration of the applied magnetic field the size of the structures increases too. The observed process of the structure formation is reversible.

Diluted-Magenetic Semiconductor (DMS) Tunneling Devices for the Terahertz Regime

DTIC Science & Technology

2014-12-10

that utilize electron spin properties for achieving higher- level functionality (e.g., transistor action) at very high switching speeds and...influence of the carrier-ion interaction on the properties of a semi-magnetic semi- conductor with a moderate energy gap it is important to keep in mind...the relative numbers: Some of the double barrier experiments, particularly those with II-VI materials are constructed with materials in which the

High-throughput ab-initio dilute solute diffusion database

PubMed Central

Wu, Henry; Mayeshiba, Tam; Morgan, Dane

2016-01-01

We demonstrate automated generation of diffusion databases from high-throughput density functional theory (DFT) calculations. A total of more than 230 dilute solute diffusion systems in Mg, Al, Cu, Ni, Pd, and Pt host lattices have been determined using multi-frequency diffusion models. We apply a correction method for solute diffusion in alloys using experimental and simulated values of host self-diffusivity. We find good agreement with experimental solute diffusion data, obtaining a weighted activation barrier RMS error of 0.176 eV when excluding magnetic solutes in non-magnetic alloys. The compiled database is the largest collection of consistently calculated ab-initio solute diffusion data in the world. PMID:27434308

Helicon wave excitation to produce energetic electrons for manufacturing semiconductors

DOEpatents

Molvik, Arthur W.; Ellingboe, Albert R.

1998-01-01

A helicon plasma source is controlled by varying the axial magnetic field or rf power controlling the formation of the helicon wave. An energetic electron current is carried on the wave when the magnetic field is 90 G; but there is minimal energetic electron current when the magnetic field is 100 G in one particular plasma source. Similar performance can be expected from other helicon sources by properly adjusting the magnetic field and power to the particular geometry. This control for adjusting the production of energetic electrons can be used in the semiconductor and thin-film manufacture process. By applying energetic electrons to the insulator layer, such as silicon oxide, etching ions are attracted to the insulator layer and bombard the insulator layer at higher energy than areas that have not accumulated the energetic electrons. Thus, silicon and metal layers, which can neutralize the energetic electron currents will etch at a slower or non-existent rate. This procedure is especially advantageous in the multilayer semiconductor manufacturing because trenches can be formed that are in the range of 0.18-0.35 mm or less.

Helicon wave excitation to produce energetic electrons for manufacturing semiconductors

DOEpatents

Molvik, A.W.; Ellingboe, A.R.

1998-10-20

A helicon plasma source is controlled by varying the axial magnetic field or rf power controlling the formation of the helicon wave. An energetic electron current is carried on the wave when the magnetic field is 90 G; but there is minimal energetic electron current when the magnetic field is 100 G in one particular plasma source. Similar performance can be expected from other helicon sources by properly adjusting the magnetic field and power to the particular geometry. This control for adjusting the production of energetic electrons can be used in the semiconductor and thin-film manufacture process. By applying energetic electrons to the insulator layer, such as silicon oxide, etching ions are attracted to the insulator layer and bombard the insulator layer at higher energy than areas that have not accumulated the energetic electrons. Thus, silicon and metal layers, which can neutralize the energetic electron currents will etch at a slower or non-existent rate. This procedure is especially advantageous in the multilayer semiconductor manufacturing because trenches can be formed that are in the range of 0.18--0.35 mm or less. 16 figs.

Bipolar Spintronics: From magnetic diodes to magnetic bipolar transistors

NASA Astrophysics Data System (ADS)

Zutic, Igor

2004-03-01

We develop a theory of bipolar (electrons and holes) spin-polarized transport [1,2] in semiconductors and discuss its implications for spintronic devices [3]. In our proposal for magnetic bipolar transistors [4,5] we show how bipolar spintronics can lead to spin and magnetic field controlled active devices, not limited by the magnetoresistive effects used in all-metallic structures [3]. We focus on magnetic p-n diodes [1,2] with spatially dependent spin splitting (Zeeman or exchange) of carrier bands. An exchange splitting can be provided by ferromagnetic semiconductors [6], while a large Zeeman splitting can be realized in the presence of magnetic field in magnetically doped or narrow band gap semiconductors [3]. Our theory of magnetic diodes [1,2] can be directly applied to magnetic bipolar transistors--the three-terminal devices which consist of two magnetic p-n diodes connected in series [4,5]. Predictions of exponentially large magnetoresistance [1] and a strong coupling between the spin and charge transport leading to the spin-voltaic effect [1,7] for magnetic diodes are also relevant for magnetic bipolar transistors. In particular, in n-p-n transistors, we show the importance of considering the nonequilibrium spin leading to the spin-voltaic effect. In addition to the applied magnetic filed, the injected nonequilibrium spin can be used to dynamically control the current amplification (gain). Recent experimental progress [8,9] supports the viability of our theoretical proposals. [1] I. Zutic, J. Fabian, S. Das Sarma, Phys. Rev. Lett. 88, 066603 (2002). [2] J. Fabian, I. Zutic, S. Das Sarma, Phys. Rev. B 66, 165301 (2002). [3] I. Zutic, J. Fabian, S. Das Sarma, Rev. Mod. Phys., in press. [4] J. Fabian, I. Zutic, S. Das Sarma, cond-mat/0211639; cond-mat/0307014, Appl. Phys. Lett., in press. [5] J. Fabian and I. Zutic, cond-mat/0311456. [6] H. Ohno, Science 281, 951 (1998). [7] I. Zutic, J. Fabian, S. Das Sarma, Appl. Phys. Lett. 82, 221 (2003). [8] N. Samarth

Magnetosonic solitons in semiconductor plasmas in the presence of quantum tunneling and exchange correlation effects

NASA Astrophysics Data System (ADS)

Hussain, S.; Mahmood, S.

2018-01-01

Low frequency magnetosonic wave excitations are investigated in semiconductor hole-electron plasmas. The quantum mechanical effects such as Fermi pressure, quantum tunneling, and exchange-correlation of holes and electrons in the presence of the magnetic field are considered. The two fluid quantum magnetohydrodynamic model is used to study magnetosonic wave dynamics, while electric and magnetic fields are coupled via Maxwell equations. The dispersion relation of the magnetosonic wave in electron-hole semiconductor plasma propagating in the perpendicular direction of the magnetic field is obtained, and its dispersion effects are discussed. The Korteweg-de Vries equation (KdV) for magnetosonic solitons is derived by employing the reductive perturbation method. For numerical analysis, the plasma parameters are taken from the semiconductors such as GaAs, GaSb, GaN, and InP already existing in the literature. It is found that the phase velocity of the magnetosonic wave is increased with the inclusion of exchange-correlation force in the model. The soliton dip structures of the magnetosonic wave in GaN semiconductor plasma are obtained, which satisfy the quantum plasma conditions for electron and hole fluids. The magnetosonic soliton dip structures move with speed less than the magnetosonic wave phase speed in the lab frame. The effects of exchange-correlation force in the model and variations of magnetic field intensity and electron/hole density on the magnetosonic wave dip structures are also investigated numerically for illustration.

Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sachleben, Joseph Robert

1993-09-01

Semiconductor nanocrystals, small biomolecules, and 13C enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution 1H and 13C 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 Å. Internal motion is estimated to be slow with a correlation time > 10 -8 s -1. The surface thiophenol ligands react to form a dithiophenol when the nanocrystals were subjected to O 2 and ultraviolet. A method formore » measuring 14N- 1H J-couplings is demonstrated on pyridine and the peptide oxytocin; selective 2D T 1 and T 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 13C enriched solids is demonstrated by experiments on zinc acetate and L-alanine.« less

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.

Co-Doped ZnO nanoparticles: minireview.

PubMed

Djerdj, Igor; Jaglicić, Zvonko; Arcon, Denis; Niederberger, Markus

2010-07-01

Diluted magnetic semiconductors with a Curie temperature exceeding 300 K are promising candidates for spintronic devices and spin-based electronic technologies. We review recent achievements in the field of one of them: Co-doped ZnO at the nanoparticulate scale.

Revisiting spin-lattice relaxation time measurements for dilute spins in high-resolution solid-state NMR spectroscopy

NASA Astrophysics Data System (ADS)

Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua

2016-07-01

Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as 13C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. 13C) and abundant I (e.g. 1H) spins affects the measured T1S values in solid-state NMR in the absence of 1H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance L-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions.

40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

Code of Federal Regulations, 2010 CFR

2010-07-01

... interval. You may use the difference between a diluted exhaust flow meter and a dilution air meter to.... We recommend that you use a diluted exhaust flow meter that meets the specifications in Table 1 of... verification in § 1065.307 and the calibration and verifications in § 1065.340 and § 1065.341. You may use the...

Improvement of charge-pumping electrically detected magnetic resonance and its application to silicon metal-oxide-semiconductor field-effect transistor

NASA Astrophysics Data System (ADS)

Hori, Masahiro; Tsuchiya, Toshiaki; Ono, Yukinori

2017-01-01

Charge-pumping electrically detected magnetic resonance (CP EDMR), or EDMR in the CP mode, is improved and applied to a silicon metal-oxide-semiconductor field-effect transistor (MOSFET). Real-time monitoring of the CP process reveals that high-frequency transient currents are an obstacle to signal amplification for EDMR. Therefore, we introduce cutoff circuitry, leading to a detection limit for the number of spins as low as 103 for Si MOS interface defects. With this improved method, we demonstrate that CP EDMR inherits one of the most important features of the CP method: the gate control of the energy window of the detectable interface defects for spectroscopy.

Origin of band gap bowing in dilute GaAs1-xNx and GaP1-xNx alloys: A real-space view

NASA Astrophysics Data System (ADS)

Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.

2013-07-01

The origin of the band gap bowing in dilute nitrogen doped gallium based III-V semiconductors is largely debated. In this paper we show the dilute GaAs1-xNx and GaP1-xNx as representative examples that the nitrogen-induced states close to the conduction band minimum propagate along the zigzag chains on the {110} planes. Thereby states originating from different N atoms interact with each other resulting in broadening of the nitrogen-induced states which narrows the band gap. Our modeling based on ab initio theoretical calculations explains the experimentally observed N concentration dependent band gap narrowing both qualitatively and quantitatively.

EDITORIAL: (Nano)characterization of semiconductor materials and structures (Nano)characterization of semiconductor materials and structures

NASA Astrophysics Data System (ADS)

Bonanni, Alberta

2011-06-01

The latest impressive advancements in the epitaxial fabrication of semiconductors and in the refinement of characterization techniques have the potential to allow insight into the deep relation between materials' structural properties and their physical and chemical functionalities. Furthermore, while the comprehensive (nano)characterization of semiconductor materials and structures is becoming more and more necessary, a compendium of the currently available techniques is lacking. We are positive that an overview of the hurdles related to the specific methods, often leading to deceptive interpretations, will be most informative for the broad community working on semiconductors, and will help in shining some light onto a plethora of controversial reports found in the literature. From this perspective, with this special issue we address and highlight the challenges and misinterpretations related to complementary local (nanoscale) and more global experimental methods for the characterization of semiconductors. The six topical reviews and the three invited papers by leading experts in the specific fields collected in here are intended to provide the required broad overview on the possibilities of actual (nano)characterization methods, from the microscopy of single quantum structures, over the synchrotron-based absorption and diffraction of nano-objects, to the contentious detection of tiny magnetic signals by quantum interference and resonance techniques. We are grateful to all the authors for their valuable contributions. Moreover, I would like to thank the Editorial Board of the journal for supporting the realization of this special issue and for inviting me to serve as Guest Editor. We greatly appreciate the work of the reviewers, of the editorial staff of Semiconductor Science and Technology and of IOP Publishing. In particular, the efforts of Alice Malhador in coordinating this special issue are acknowledged.

Decoherence of spin states induced by Rashba coupling for an electron confined to a semiconductor quantum dot in the presence of a magnetic field

NASA Astrophysics Data System (ADS)

Poszwa, A.

2018-05-01

We investigate quantum decoherence of spin states caused by Rashba spin-orbit (SO) coupling for an electron confined to a planar quantum dot (QD) in the presence of a magnetic field (B). The Schrödinger equation has been solved in a frame of second-order perturbation theory. The relationship between the von Neumann (vN) entropy and the spin polarization is obtained. The relation is explicitly demonstrated for the InSb semiconductor QD.

Magnetic field tunability of spin polarized excitations in a high temperature magnet

NASA Astrophysics Data System (ADS)

Holinsworth, Brian; Sims, Hunter; Cherian, Judy; Mazumdar, Dipanjan; Harms, Nathan; Chapman, Brandon; Gupta, Arun; McGill, Steve; Musfeldt, Janice

Magnetic semiconductors are at the heart of modern device physics because they naturally provide a non-zero magnetic moment below the ordering temperature, spin-dependent band gap, and spin polarization that originates from exchange-coupled magnetization or an applied field creating a spin-split band structure. Strongly correlated spinel ferrites are amongst the most noteworthy contenders for semiconductor spintronics. NiFe2O4, in particular, displays spin-filtering, linear magnetoresistance, and wide application in the microwave regime. To unravel the spin-charge interaction in NiFe2O4, we bring together magnetic circular dichroism, photoconductivity, and prior optical absorption with complementary first principles calculations. Analysis uncovers a metamagnetic transition modifying electronic structure in the minority channel below the majority channel gap, exchange splittings emerging from spin-split bands, anisotropy of excitons surrounding the indirect gap, and magnetic-field dependent photoconductivity. These findings open the door for the creation and control of spin-polarized excitations from minority channel charge charge transfer in NiFe2O4 and other members of the spinel ferrite family.

High Temperature Superconductor/Semiconductor Hybrid Microwave Devices and Circuits

NASA Technical Reports Server (NTRS)

Romanofsky, Robert R.; Miranda, Felix A.

1999-01-01

Contents include following: film deposition technique; laser ablation; magnetron sputtering; sequential evaporation; microwave substrates; film characterization at microwave frequencies; complex conductivity; magnetic penetration depth; surface impedance; planar single-mode filters; small antennas; antenna arrays phase noise; tunable oscillations; hybrid superconductor/semiconductor receiver front ends; and noise modeling.

Spin-glass behaviors in carrier polarity controlled Fe{sub 3−x}Ti{sub x}O{sub 4} semiconductor thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamahara, H., E-mail: yamahara@bioxide.t.u-tokyo.ac.jp; Seki, M.; Adachi, M.

2015-08-14

Carrier-type control of spin-glass (cluster spin-glass) is studied in order to engineer basic magnetic semiconductor elements using the memory functions of spin-glass. A key of carrier-polarity control in magnetite is the valence engineering between Fe(II) and Fe(III) that is achieved by Ti(IV) substitution. Single phases of (001)-oriented Fe{sub 3−x}Ti{sub x}O{sub 4} thin films have been obtained on spinel MgAl{sub 2}O{sub 4} substrates by pulsed laser deposition. Thermoelectric power measurements reveal that Ti-rich films (x = 0.8) show p-type conduction, while Ti-poor films (x = 0.6–0.75) show n-type conduction. The systematic Fe(III) reduction to Fe(II) followed by Ti(IV) substitution in the octahedral sublattice is confirmedmore » by the X-ray absorption spectra. All of the Fe{sub 3−x}Ti{sub x}O{sub 4} films (x = 0.6–0.8) exhibit ferrimagnetism above room temperature. Next, the spin-glass behaviors of Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film are studied, since this magnetically diluted system is expected to exhibit the spin-glass behaviors. The DC magnetization and AC susceptibility measurements for the Ti-rich Fe{sub 2.2}Ti{sub 0.8}O{sub 4} film reveal the presence of the spin glass phase. Thermal- and magnetic-field-history memory effects are observed and are attributed to the long time-decay nature of remanent magnetization. The detailed analysis of the time-dependent thermoremanent magnetization reveals the presence of the cluster spin glass state.« less

Structurally controllable spin spatial splitter in a hybrid ferromagnet and semiconductor nanostructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Mao-Wang, E-mail: maowanglu@126.com; Cao, Xue-Li; Huang, Xin-Hong

2014-05-07

We theoretically investigate modulation of a tunable δ-potential to the lateral displacement of electrons across a magnetically modulated semiconductor nanostructure. Experimentally, this nanostructure can be produced by depositing a nanosized ferromagnetic stripe with in-plane magnetization on top of a semiconductor heterostructure, while the δ-potential can be realized by means of the atomic layer doping technique. Theoretical analysis reveals that this δ-doping can break the intrinsic symmetry in nanostructure and a considerable spin polarization in the lateral displacement will appear. Numerical calculations demonstrate that both magnitude and sign of spin polarization can be manipulated by changing the height and/or position ofmore » the δ-doping, giving rise to a structurally tunable spin spatial splitter.« less

Diluting the burden of load: perceptual load effects are simply dilution effects.

PubMed

Tsal, Yehoshua; Benoni, Hanna

2010-12-01

The substantial distractor interference obtained for small displays when the target appears alone is reduced in large displays when the target is embedded among neutral letters. This finding has been interpreted as reflecting low-load and high-load processing, respectively, thereby supporting the theory of perceptual load (Lavie & Tsal, 1994). However, a possible alternative interpretation of this effect is that the distractor is similarly processed in both displays, yet its interference in the large ones is diluted by the presence of the neutral letters. We separated the effects of load and dilution by introducing dilution displays. They contained as many letters as the high-load displays but were clearly distinguished from the target, thus allowing for a low-load processing mode. Distractor interference obtained under both the low-load and high-load conditions disappeared under the dilution condition. Hence, the display size effect traditionally misattributed to perceptual load is fully accounted for by dilution. Furthermore, when dilution is controlled for, it is high load not low load producing greater interference.

Ba2NiOsO6: a Dirac-Mott insulator with ferromagnetism near 100 K

NASA Astrophysics Data System (ADS)

Feng, Hl; Calder, S.; Ghimire, M.; Yuan, Yh; Shirako, Y.; Tsujimoto, Y.; Matsushita, Y.; Hu, Z.; Kuo, Cy; Tjeng, Lh; Pi, Tw; Soo, Yl; He, Jf; Tanaka, M.; Katsuya, Y.; Richte, M.; Yamaura, Kazunari

The ferromagnetic semiconductor Ba2NiOsO6(Tmag 100 K) was synthesized at 6 GPa and 1500 ° C. It crystallizes into a double perovskite structure [Fm-3 m; a = 8.0428(1)], where the Ni2+ and Os6+ ions are perfectly ordered at the perovskite B-site. We show that the spin-orbit coupling of Os6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21-kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag<180 K), the spin-gapless semiconductor Mn2CoAl (Tmag 720 K), and the ferromagnetic insulators EuO (Tmag 70 K) and Bi3Cr3O11(Tmag 220 K). It is also qualitatively different from known ferrimagnetic insulator/semiconductors, which are characterized by an antiparallel spin arrangement. Our report of cubic Ba2NiOsO6 heralds a new class of FM insulator oxides, which may be useful in developing a practical magnetic semiconductor that can be employed in spintronic and quantum magnetic devices.

A scanning tunneling microscope for a dilution refrigerator.

PubMed

Marz, M; Goll, G; Löhneysen, H v

2010-04-01

We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T approximately 30 mK, and in applied magnetic fields up to 13 T. The topography of both highly ordered pyrolytic graphite and the dichalcogenide superconductor NbSe(2) has been imaged with atomic resolution down to T approximately 50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe(2) in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence proportional to 1/square root of B and measurements in the scanning tunneling spectroscopy mode clearly show the superconductive density of states with Andreev bound states in the vortex core.

High-temperature ferromagnetism in new n-type Fe-doped ferromagnetic semiconductor (In,Fe)Sb

NASA Astrophysics Data System (ADS)

Thanh Tu, Nguyen; Hai, Pham Nam; Anh, Le Duc; Tanaka, Masaaki

2018-06-01

Over the past two decades, intensive studies on various ferromagnetic semiconductor (FMS) materials have failed to realize reliable FMSs that have a high Curie temperature (T C > 300 K), good compatibility with semiconductor electronics, and characteristics superior to those of their nonmagnetic host semiconductors. Here, we demonstrate a new n-type Fe-doped narrow-gap III–V FMS, (In1‑ x ,Fe x )Sb. Its T C is unexpectedly high, reaching ∼335 K at a modest Fe concentration (x) of 16%. The anomalous Hall effect and magnetic circular dichroism (MCD) spectroscopy indicate that the high-temperature ferromagnetism in (In,Fe)Sb thin films is intrinsic and originates from the zinc-blende (In,Fe)Sb alloy semiconductor.

Tailoring magnetic nanoparticle for transformers application.

PubMed

Morais, P C; Silva, A S; Leite, E S; Garg, V K; Oliveira, A C; Viali, W R; Sartoratto, P P C

2010-02-01

In this study photoacoustic spectroscopy was used to investigate the effect of dilution of an oil-based magnetic fluid sample on the magnetic nanoparticle surface-coating. Changes of the photoacoustic signal intensity on the band-L region (640 to 830 nm) upon dilution of the stock magnetic fluid sample were discussed in terms of molecular surface desorption. The model proposed here assumes that the driving force taking the molecules out from the nanoparticle surface into the bulk solvent is the gradient of osmotic pressure. This gradient of osmotic pressure is established between the nanoparticle surface and the bulk suspension. It is further assumed that the photoacoustic signal intensity (area under the photoacoustic spectra) scales linearly with the number of coating molecules (surface grafting) at the nanoparticle surface. This model picture provides a non-linear analytical description for the reduction of the surface grafting coefficient upon dilution, which was successfully-used to curve-fit the photoacoustic experimental data.

Capsize of polarization in dilute photonic crystals.

PubMed

Gevorkian, Zhyrair; Hakhoumian, Arsen; Gasparian, Vladimir; Cuevas, Emilio

2017-11-29

We investigate, experimentally and theoretically, polarization rotation effects in dilute photonic crystals with transverse permittivity inhomogeneity perpendicular to the traveling direction of waves. A capsize, namely a drastic change of polarization to the perpendicular direction is observed in a one-dimensional photonic crystal in the frequency range 10 ÷ 140 GHz. To gain more insights into the rotational mechanism, we have developed a theoretical model of dilute photonic crystal, based on Maxwell's equations with a spatially dependent two dimensional inhomogeneous dielectric permittivity. We show that the polarization's rotation can be explained by an optical splitting parameter appearing naturally in Maxwell's equations for magnetic or electric fields components. This parameter is an optical analogous of Rashba like spin-orbit interaction parameter present in quantum waves, introduces a correction to the band structure of the two-dimensional Bloch states, creates the dynamical phase shift between the waves propagating in the orthogonal directions and finally leads to capsizing of the initial polarization. Excellent agreement between theory and experiment is found.

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)

Upward magnetic relaxation in self organizing Fe nanoparticle system

NASA Astrophysics Data System (ADS)

Pal, Satyendra Prakash; Sharma, Gyaneshwar; Sen, P.

2018-04-01

Study of the thermoremanent magnetic relaxation behavior of Fe nanoparticles and its nanocomposite with activated carbon has been systematically performed. Magnetic relaxation data shows the spontaneous collective periodic oscillations of the spins superimposed on the magnetic decay curves. At sufficiently high temperature, due to thermal noise induced ordering of the magnetic moment an inflexion with an increase in the absolute value of the magnetization takes place. Due to insufficient interaction on account of dilution in the case of nanocomposite, the spin - spin interaction which was responsible for magnetic ordering in the case of bare Fe nanoparticles, collective oscillations of the system do not sustain upto longer times in the case of carbon diluted system.

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.

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.

Modulating the electronic and magnetic properties of bilayer borophene via transition metal atoms intercalation: from metal to half metal and semiconductor.

PubMed

Zhang, Xiuyun; Sun, Yi; Ma, Liang; Zhao, Xinli; Yao, Xiaojing

2018-07-27

Borophene, a two-dimensional monolayer made of boron atoms, has attracted wide attention due to its appealing properties. Great efforts have been devoted to fine tuning its electronic and magnetic properties for desired applications. Herein, we theoretically investigate the versatile electronic and magnetic properties of bilayer borophene (BLB) intercalated by 3d transition metal (TM) atoms, TM@BLBs (TM = Ti-Fe), using ab initio calculations. Four allotropes of AA-stacking (α 1 -, β-, β 12 - and χ 3 -) BLBs with different intercalation concentrations of TM atoms are considered. Our results show that the TM atoms are strongly bonded to the borophene layers with fairly large binding energies, around 6.31 ∼ 15.44 eV per TM atom. The BLBs with Cr and Mn intercalation have robust ferromagnetism, while for the systems decorated with Fe atoms, fruitful magnetic properties, such as nonmagnetic, ferromagnetic or antiferromagnetic, are identified. In particular, the α 1 - and β-BLBs intercalated by Mn or Fe atom can be transformed into a semiconductor, half metal or graphene-like semimetal. Moreover, some heavily doped TM@BLBs expose high Curie temperatures above room temperature. The attractive properties of TM@BLBs entail an efficient way to modulate the electronic and magnetic properties of borophene sheets for advanced applications.

Modulating the electronic and magnetic properties of bilayer borophene via transition metal atoms intercalation: from metal to half metal and semiconductor

NASA Astrophysics Data System (ADS)

Zhang, Xiuyun; Sun, Yi; Ma, Liang; Zhao, Xinli; Yao, Xiaojing

2018-07-01

Borophene, a two-dimensional monolayer made of boron atoms, has attracted wide attention due to its appealing properties. Great efforts have been devoted to fine tuning its electronic and magnetic properties for desired applications. Herein, we theoretically investigate the versatile electronic and magnetic properties of bilayer borophene (BLB) intercalated by 3d transition metal (TM) atoms, TM@BLBs (TM = Ti-Fe), using ab initio calculations. Four allotropes of AA-stacking (α 1-, β-, β 12- and χ 3-) BLBs with different intercalation concentrations of TM atoms are considered. Our results show that the TM atoms are strongly bonded to the borophene layers with fairly large binding energies, around 6.31 ∼ 15.44 eV per TM atom. The BLBs with Cr and Mn intercalation have robust ferromagnetism, while for the systems decorated with Fe atoms, fruitful magnetic properties, such as nonmagnetic, ferromagnetic or antiferromagnetic, are identified. In particular, the α 1- and β-BLBs intercalated by Mn or Fe atom can be transformed into a semiconductor, half metal or graphene-like semimetal. Moreover, some heavily doped TM@BLBs expose high Curie temperatures above room temperature. The attractive properties of TM@BLBs entail an efficient way to modulate the electronic and magnetic properties of borophene sheets for advanced applications.

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.

Planar Nernst effect and Mott relation in (In,Fe)Sb ferromagnetic semiconductor

NASA Astrophysics Data System (ADS)

Bui, Cong Tinh; Garcia, Christina A. C.; Tu, Nguyen Thanh; Tanaka, Masaaki; Hai, Pham Nam

2018-05-01

Transverse magneto-thermoelectric effects were studied in an (In,Fe)Sb ferromagnetic semiconductor thin film under an in-plane magnetic field. We find that the thermal voltage is governed by the planar Nernst effect. We show that the magnetic field intensity dependence, magnetic field direction dependence, and temperature dependence of the transverse Seebeck coefficient can be explained by assuming a Mott relation between the in-plane magneto-transport and magneto-thermoelectric phenomena in (In,Fe)Sb.

Magnetic quantum phase transition in Cr-doped Bi2(SexTe1-x)3 driven by the Stark effect

NASA Astrophysics Data System (ADS)

Zhang, Zuocheng; Feng, Xiao; Wang, Jing; Lian, Biao; Zhang, Jinsong; Chang, Cuizu; Guo, Minghua; Ou, Yunbo; Feng, Yang; Zhang, Shou-Cheng; He, Ke; Ma, Xucun; Xue, Qi-Kun; Wang, Yayu

2017-10-01

The recent experimental observation of the quantum anomalous Hall effect has cast significant attention on magnetic topological insulators. In these magnetic counterparts of conventional topological insulators such as Bi2Te3, a long-range ferromagnetic state can be established by chemical doping with transition-metal elements. However, a much richer electronic phase diagram can emerge and, in the specific case of Cr-doped Bi2(SexTe1-x)3, a magnetic quantum phase transition tuned by the actual chemical composition has been reported. From an application-oriented perspective, the relevance of these results hinges on the possibility to manipulate magnetism and electronic band topology by external perturbations such as an electric field generated by gate electrodes—similar to what has been achieved in conventional diluted magnetic semiconductors. Here, we investigate the magneto-transport properties of Cr-doped Bi2(SexTe1-x)3 with different compositions under the effect of a gate voltage. The electric field has a negligible effect on magnetic order for all investigated compositions, with the remarkable exception of the sample close to the topological quantum critical point, where the gate voltage reversibly drives a ferromagnetic-to-paramagnetic phase transition. Theoretical calculations show that a perpendicular electric field causes a shift in the electronic energy levels due to the Stark effect, which induces a topological quantum phase transition and, in turn, a magnetic phase transition.

Electrical spin injection from CoFe2O4 into p-Si semiconductor across MgO tunnel barrier for spin electronics

NASA Astrophysics Data System (ADS)

Panda, J.; Maji, Nilay; Nath, T. K.

2017-05-01

The room temperature spin injection and detection in non magnetic p-Si semiconductor have been studied in details in our CoFe2O4 (CFO)/MgO/p-Si heterojunction. The 3-terminal tunnel contacts have been made on the device for transport measurements. The electrical transport properties have been investigated at different isothermal conditions in the temperature range of 10-300 K. The spin accumulation in non magnetic p-Si semiconductor has been observed at different bias current under the applied magnetic field parallel to the film plane in the temperature range of 40-300 K. We have observed a giant spin accumulation in p-Si semiconductor using MgO/CFO tunnel contact. The Hanley effect is used to control the reduction of spin accumulation by applying magnetic field perpendicular to the carrier spin in the p-Si. The accumulated spin signal decays as a function of applied magnetic field for fixed bias current. These results will enable utilization of the spin degree of freedom in complementary Si devices and its further development.

Hybridizing pines with diluted pollen

Treesearch

Robert Z. Callaham

1967-01-01

Diluted pollens would have many uses by the tree breeder. Dilutions would be particularly advantageous in making many controlled pollinations with a limited amount of pollen. They also would be useful in artificial mass pollinations of orchards or single trees. Diluted pollens might help overcome troublesome genetic barriers to crossing. Feasibility o,f using diluted...

Controlling ferromagnetism of (In,Fe)As semiconductors by electron doping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dang Vu, Nguyen; Fukushima, Tetsuya; Katayama-Yoshida, Hiroshi

2014-02-21

Based on experimental results, using the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method and Monte Carlo simulation, we study the mechanism of ferromagnetic behavior of (In,Fe)As. We show that with doped Be atoms occupying in interstitial sites, chemical pair interactions between atoms and magnetic exchange interactions between Fe atoms change due to electron concentration. Therefore, by controlling the doping process, magnetic behavior of (In,Fe)As is controlled and ferromagnetism is observed in this semiconductor.

Antiferromagnetic phase of the gapless semiconductor V3Al

NASA Astrophysics Data System (ADS)

Jamer, M. E.; Assaf, B. A.; Sterbinsky, G. E.; Arena, D.; Lewis, L. H.; Saúl, A. A.; Radtke, G.; Heiman, D.

2015-03-01

Discovering new antiferromagnetic (AF) compounds is at the forefront of developing future spintronic devices without fringing magnetic fields. The AF gapless semiconducting D 03 phase of V3Al was successfully synthesized via arc-melting and annealing. The AF properties were established through synchrotron measurements of the atom-specific magnetic moments, where the magnetic dichroism reveals large and oppositely oriented moments on individual V atoms. Density functional theory calculations confirmed the stability of a type G antiferromagnetism involving only two-thirds of the V atoms, while the remaining V atoms are nonmagnetic. Magnetization, x-ray diffraction, and transport measurements also support the antiferromagnetism. This archetypal gapless semiconductor may be considered as a cornerstone for future spintronic devices containing AF elements.

Electric-field-controlled ferromagnetism in high-Curie-temperature Mn0.05Ge0.95 quantum dots.

PubMed

Xiu, Faxian; Wang, Yong; Kim, Jiyoung; Hong, Augustin; Tang, Jianshi; Jacob, Ajey P; Zou, Jin; Wang, Kang L

2010-04-01

Electric-field manipulation of ferromagnetism has the potential for developing a new generation of electric devices to resolve the power consumption and variability issues in today's microelectronics industry. Among various dilute magnetic semiconductors (DMSs), group IV elements such as Si and Ge are the ideal material candidates because of their excellent compatibility with the conventional complementary metal-oxide-semiconductor (MOS) technology. Here we report, for the first time, the successful synthesis of self-assembled dilute magnetic Mn(0.05)Ge(0.95) quantum dots with ferromagnetic order above room temperature, and the demonstration of electric-field control of ferromagnetism in MOS ferromagnetic capacitors up to 100 K. We found that by applying electric fields to a MOS gate structure, the ferromagnetism of the channel layer can be effectively modulated through the change of hole concentration inside the quantum dots. Our results are fundamentally important in the understanding and to the realization of high-efficiency Ge-based spin field-effect transistors.

Electronic and Magnetic Properties of Ni-Doped Zinc-Blende ZnO: A First-Principles Study.

PubMed

Xue, Suqin; Zhang, Fuchun; Zhang, Shuili; Wang, Xiaoyang; Shao, Tingting

2018-04-26

The electronic structure, band structure, density of state, and magnetic properties of Ni-doped zinc-blende (ZB) ZnO are studied by using the first-principles method based on the spin-polarized density-functional theory. The calculated results show that Ni atoms can induce a stable ferromagnetic (FM) ground state in Ni-doped ZB ZnO. The magnetic moments mainly originate from the unpaired Ni 3 d orbitals, and the O 2 p orbitals contribute a little to the magnetic moments. The magnetic moment of a supercell including a single Ni atom is 0.79 μ B . The electronic structure shows that Ni-doped ZB ZnO is a half-metallic FM material. The strong spin-orbit coupling appears near the Fermi level and shows obvious asymmetry for spin-up and spin-down density of state, which indicates a significant hybrid effects from the Ni 3 d and O 2 p states. However, the coupling of the anti-ferromagnetic (AFM) state show metallic characteristic, the spin-up and spin-down energy levels pass through the Fermi surface. The magnetic moment of a single Ni atom is 0.74 μ B . Moreover, the results show that the Ni 3 d and O 2 p states have a strong p - d hybridization effect near the Fermi level and obtain a high stability. The above theoretical results demonstrate that Ni-doped zinc blende ZnO can be considered as a potential half-metal FM material and dilute magnetic semiconductors.

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.

Physicochemical and Electrophysical Properties of Metal/Semiconductor Containing Nanostructured Composites

NASA Astrophysics Data System (ADS)

Gerasimov, G. N.; Gromov, V. F.; Trakhtenberg, L. I.

2018-06-01

The properties of nanostructured composites based on metal oxides and metal-polymer materials are analyzed, along with ways of preparing them. The effect the interaction between metal and semiconductor nanoparticles has on the conductivity, photoconductivity, catalytic activity, and magnetic, dielectric, and sensor properties of nanocomposites is discussed. It is shown that as a result of this interaction, a material can acquire properties that do not exist in systems of isolated particles. The transfer of electrons between metal particles of different sizes in polymeric matrices leads to specific dielectric losses, and to an increase in the rate and a change in the direction of chemical reactions catalyzed by these particles. The interaction between metal-oxide semiconductor particles results in the electronic and chemical sensitization of sensor effects in nanostructured composite materials. Studies on creating molecular machines (Brownian motors), devices for magnetic recording of information, and high-temperature superconductors based on nanostructured systems are reviewed.

Extremely Low Frequency-Magnetic Field (ELF-MF) Exposure Characteristics among Semiconductor Workers

PubMed Central

Choi, Sangjun; Cha, Wonseok; Kim, Won; Yoon, Chungsik; Park, Ju-Hyun; Ha, Kwonchul; Park, Donguk

2018-01-01

We assessed the exposure of semiconductor workers to extremely low frequency-magnetic fields (ELF-MF) and identified job characteristics affecting ELF-MF exposure. These were demonstrated by assessing the exposure of 117 workers involved in wafer fabrication (fab) and chip packaging wearing personal dosimeters for a full shift. A portable device was used to monitor ELF-MF in high temporal resolution. All measurements were categorized by operation, job and working activity during working time. ELF-MF exposure of workers were classified based on the quartiles of ELF-MF distribution. The average levels of ELF-MF exposure were 0.56 µT for fab workers, 0.59 µT for chip packaging workers and 0.89 µT for electrical engineers, respectively. Exposure to ELF-MF differed among types of factory, operation, job and activity. Workers engaged in the diffusion and chip testing activities showed the highest ELF-MF exposure. The ELF-MF exposures of process operators were found to be higher than those of maintenance engineers, although peak exposure and/or patterns varied. The groups with the highest quartile ELF-MF exposure level are operators in diffusion, ion implantation, module and testing operations, and maintenance engineers in diffusion, module and testing operations. In conclusion, ELF-MF exposure among workers can be substantially affected by the type of operation and job, and the activity or location. PMID:29614730

Toward designing semiconductor-semiconductor heterojunctions for photocatalytic applications

NASA Astrophysics Data System (ADS)

Zhang, Liping; Jaroniec, Mietek

2018-02-01

Semiconductor photocatalysts show a great potential for environmental and energy-related applications, however one of the major disadvantages is their relatively low photocatalytic performance due to the recombination of electron-hole pairs. Therefore, intensive research is being conducted toward design of heterojunctions, which have been shown to be effective for improving the charge-transfer properties and efficiency of photocatalysts. According to the type of band alignment and direction of internal electric field, heterojunctions are categorized into five different types, each of which is associated with its own charge transfer characteristics. Since the design of heterojunctions requires the knowledge of band edge positions of component semiconductors, the commonly used techniques for the assessment of band edge positions are reviewed. Among them the electronegativity-based calculation method is applied for a large number of popular visible-light-active semiconductors, including some widely investigated bismuth-containing semiconductors. On basis of the calculated band edge positions and the type of component semiconductors reported, heterojunctions composed of the selected bismuth-containing semiconductors are proposed. Finally, the most popular synthetic techniques for the fabrication of heterojunctions are briefly discussed.

40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

Code of Federal Regulations, 2014 CFR

2014-07-01

...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements... interval. You may use the difference between a diluted exhaust flow meter and a dilution air meter to... compression-ignition engines, two-stroke spark-ignition engines, or four-stroke spark-ignition engines at or...

Technical note: Evaluating nuclear magnetic resonance spectroscopy for determining body composition in Holstein dairy calves using deuterium oxide dilution methods.

PubMed

Chapman, C E; Wilkinson, P Stone; Murphy, M R; Erickson, P S

2017-04-01

Deuterium oxide (D 2 O) dilution methods have been used to assess body composition in live animals. Estimated body water content can be used to predict body fat and protein, and thus, the amount of energy reserves. It is an alternative method to direct chemical analysis and considered a noninvasive technique that is economical and repeatable. Deuterium oxide use is considered easy, safe, and accurate; however, the traditional methods of analyzing D 2 O are expensive, tedious, and time consuming. The objective of this study was to evaluate the potential for using nuclear magnetic resonance spectroscopy (NMR) to determine body composition in Holstein dairy heifers. Nuclear magnetic resonance is less expensive and requires minutes to calculate the percentage of D 2 O in the blood. This study used 24 newborn dairy heifer calves blocked by birth and randomly assigned to 1 of 3 treatments: (1) 446 g dry matter (DM) of a conventional milk replacer (MR) [CON; 20% crude protein (CP), 20% fat], (2) 669 g DM of a moderately high protein MR (MOD; 26% CP, 18% fat), or (3) 892 g DM of a moderately high protein MR (aggressive, AGG; 26% CP, 18% fat). All calves had free-choice access to starter and water. Both MR and starter were medicated with decoquinate. During weaning (d 43 to 49), the morning MR feeding ceased. On d 50, all MR feedings ended but starter and water intakes were continuously recorded until d 56. When calves were 50 d of age, a baseline blood sample was taken followed by injection of 300 mg of D 2 O/kg of body weight in sterile physiological saline (0.9%). The syringes containing the D 2 O in physiological saline were weighed before and after administration to record the actual dose of D 2 O injected gravimetrically. After injection, the D 2 O was allowed to equilibrate with body water for 1 h. Six blood samples were taken over 6 d (1/d) at 1630 h to estimate the dilution of the tracer. The plasma was aspirated and stored at -20°C until further D 2 O analysis

Modulation of structural, electrical, and magnetic features with dilute Zr substitution in Bi0.8La0.2Fe1-xZrxO3 system

NASA Astrophysics Data System (ADS)

Usama, Hasan M.; Akter, Ayesha; Zubair, M. A.

2017-12-01

A significant structural modification and enhancement of the electrical and magnetic properties with dilute substitution of Zr (≤1 mol. %) in the Bi0.8La0.2Fe1-xZrxO3 system has been reported. A mixture of rhombohedral and orthorhombic phases was detected in these conventionally sintered ceramics. Transition from a leaky state to an insulating state was observed upon Zr substitution. This is the first time that a drop in the electrical conductivity as large as 6 orders of magnitude for doping as small as 0.25 mol. % in bismuth ferrite systems has been reported. An investigation on the nature of this abrupt transition revealed the dominant role of defects. A proper consideration of possible defect reactions taking place during and after sintering satisfactorily accounts for the observed modulation in the electrical properties. Both AC and DC measurements indicate that, before Zr substitution, p-type hopping conduction prevails with an activation energy as low as ˜0.57 eV, whereas the Zr substitution makes oxide ion migration the central mechanism for conduction with the activation energy of ˜0.96-1.08 eV. In contrast to that, the magnetic properties of the compounds experience a more subtle effect; a gradual modification of saturation magnetization and coercivity with Zr substitution is observed. Curve fitting of the magnetic hysteresis loops not only allowed extraction of three separate contributions from the magnetic response but also helped to explain the effects of Zr on the magnetic properties. Modifications of structural characteristics and magnetic anisotropy of the samples are believed to be the primary driving force behind the improvement in the magnetic properties.

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.

40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

Code of Federal Regulations, 2013 CFR

2013-07-01

...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements... interval. You may use the difference between a diluted exhaust flow meter and a dilution air meter to... compression-ignition engines, 2-stroke spark-ignition engines, and 4-stroke spark-ignition engines below 19 kW...

40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

Code of Federal Regulations, 2011 CFR

2011-07-01

...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements... interval. You may use the difference between a diluted exhaust flow meter and a dilution air meter to... compression-ignition engines, 2-stroke spark-ignition engines, and 4-stroke spark-ignition engines below 19 kW...

40 CFR 1065.240 - Dilution air and diluted exhaust flow meters.

Code of Federal Regulations, 2012 CFR

2012-07-01

...) AIR POLLUTION CONTROLS ENGINE-TESTING PROCEDURES Measurement Instruments Flow-Related Measurements... interval. You may use the difference between a diluted exhaust flow meter and a dilution air meter to... compression-ignition engines, 2-stroke spark-ignition engines, and 4-stroke spark-ignition engines below 19 kW...

Semirelativity in semiconductors: a review.

PubMed

Zawadzki, Wlodek

2017-09-20

An analogy between behavior of electrons in narrow-gap semiconductors (NGS) and relativistic electrons in vacuum is reviewed. Energy band structures [Formula: see text] are considered for various NGS materials and their correspondence to the energy-momentum relation in special relativity is emphasized. It is indicated that special relativity for vacuum is analogous to a two-band [Formula: see text] description for NGS. The maximum electron velocity in NGS is [Formula: see text], which corresponds to the light velocity in vacuum. An effective mass of charge carriers in semiconductors is introduced, relating their velocity to quasimomentum and it is shown that this mass depends on electron energy (or velocity) in a way similar to the mass of free relativistic electrons. In [Formula: see text] alloys one can reach vanishing energy gap at which electrons and light holes become three-dimensional massless Dirac fermions. A wavelength [Formula: see text] is defined for NGS, in analogy to the Compton wavelength in relativistic quantum mechanics. It is estimated that [Formula: see text] is on the order of tens of Angstroms in typical semiconducting materials which is experimentally confirmed in tunneling experiments on energy dispersion in the forbidden gap. Statistical properties of the electron gas in NGS are calculated and their similarity is demonstrated to those of the Juttner gas of relativistic particles. Interband electron tunneling in NGS is described and shown to be in close analogy to the predicted but unobserved tunneling between negative and positive energies resulting from the Dirac equation for free electrons. It is demonstrated that the relativistic analogy holds for orbital and spin properties of electrons in the presence of an external magnetic field. In particular, it is shown that the spin magnetic moment of both NGS electrons and relativistic electrons approaches zero with increasing energy. This conclusion is confirmed experimentally for NGS. Electrons

Semirelativity in semiconductors: a review

NASA Astrophysics Data System (ADS)

Zawadzki, Wlodek

2017-09-01

An analogy between behavior of electrons in narrow-gap semiconductors (NGS) and relativistic electrons in vacuum is reviewed. Energy band structures \\varepsilon ≤ft(\\mathbf{k}\\right) are considered for various NGS materials and their correspondence to the energy-momentum relation in special relativity is emphasized. It is indicated that special relativity for vacuum is analogous to a two-band \\mathbf{k}\\centerdot \\mathbf{p} description for NGS. The maximum electron velocity in NGS is u≃ 1× {{10}8}~\\text{cm}~{{\\text{s}}-1} , which corresponds to the light velocity in vacuum. An effective mass of charge carriers in semiconductors is introduced, relating their velocity to quasimomentum and it is shown that this mass depends on electron energy (or velocity) in a way similar to the mass of free relativistic electrons. In \\text{H}{{\\text{g}}1-x}\\text{C}{{\\text{d}}x}\\text{Te} alloys one can reach vanishing energy gap at which electrons and light holes become three-dimensional massless Dirac fermions. A wavelength {λz} is defined for NGS, in analogy to the Compton wavelength in relativistic quantum mechanics. It is estimated that {λz} is on the order of tens of Angstroms in typical semiconducting materials which is experimentally confirmed in tunneling experiments on energy dispersion in the forbidden gap. Statistical properties of the electron gas in NGS are calculated and their similarity is demonstrated to those of the Juttner gas of relativistic particles. Interband electron tunneling in NGS is described and shown to be in close analogy to the predicted but unobserved tunneling between negative and positive energies resulting from the Dirac equation for free electrons. It is demonstrated that the relativistic analogy holds for orbital and spin properties of electrons in the presence of an external magnetic field. In particular, it is shown that the spin magnetic moment of both NGS electrons and relativistic electrons approaches zero with increasing

Doping of wide-bandgap titanium-dioxide nanotubes: optical, electronic and magnetic properties

NASA Astrophysics Data System (ADS)

Alivov, Yahya; Singh, Vivek; Ding, Yuchen; Cerkovnik, Logan Jerome; Nagpal, Prashant

2014-08-01

Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO2) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications.Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO2) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications. Electronic supplementary information (ESI) available: See DOI: 10.1039/c4nr02417f

Hg-Based Epitaxial Materials for Topological Insulators

DTIC Science & Technology

2014-07-01

Research Laboratory for investigation of properties. 15. SUBJECT TERMS EOARD, topological insulator , diluted magnetic ...topological superconductors and spintronics to quantum computation (e.g. see C.L.Kane and J.E.Moore "Topological Insulators " Physics World (2011) 24...tetradymite semiconductors Bi2Te3, Bi2Se3, and Sb2Te3 which form magnetically ordered insulators when doped with transition metal elements Cr or Fe (Rui Yu et

Additional compound semiconductor nanowires for photonics

NASA Astrophysics Data System (ADS)

Ishikawa, F.

2016-02-01

GaAs related compound semiconductor heterostructures are one of the most developed materials for photonics. Those have realized various photonic devices with high efficiency, e. g., lasers, electro-optical modulators, and solar cells. To extend the functions of the materials system, diluted nitride and bismide has been paid attention over the past decade. They can largely decrease the band gap of the alloys, providing the greater tunability of band gap and strain status, eventually suppressing the non-radiative Auger recombinations. On the other hand, selective oxidation for AlGaAs is a vital technique for vertical surface emitting lasers. That enables precisely controlled oxides in the system, enabling the optical and electrical confinement, heat transfer, and mechanical robustness. We introduce the above functions into GaAs nanowires. GaAs/GaAsN core-shell nanowires showed clear redshift of the emitting wavelength toward infrared regime. Further, the introduction of N elongated the carrier lifetime at room temperature indicating the passivation of non-radiative surface recombinations. GaAs/GaAsBi nanowire shows the redshift with metamorphic surface morphology. Selective and whole oxidations of GaAs/AlGaAs core-shell nanowires produce semiconductor/oxide composite GaAs/AlGaOx and oxide GaOx/AlGaOx core-shell nanowires, respectively. Possibly sourced from nano-particle species, the oxide shell shows white luminescence. Those property should extend the functions of the nanowires for their application to photonics.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chou, Hsiung, E-mail: hchou@mail.nsysu.edu.tw; Yang, Kung-Shang; Tsao, Yao-Chung

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 (V{sub O}) on SPC, which are controlled by growing the Co-doped ZnO thin-films at room temperature in a reducing atmosphere [Ar + (1%–30%)H{sub 2}].more » We found that the conductivity increases with an increase of V{sub O} 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 V{sub O} and increase in its concentration. The transport measurement shows that by manipulating V{sub O}, 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%.« less

Microfluidic Serial Dilution Circuit

PubMed Central

Paegel, Brian M.; Grover, William H.; Skelley, Alison M.; Mathies, Richard A.; Joyce, Gerald F.

2008-01-01

In vitro evolution of RNA molecules requires a method for executing many consecutive serial dilutions. To solve this problem, a microfluidic circuit has been fabricated in a three-layer glass-PDMS-glass device. The 400-nL serial dilution circuit contains five integrated membrane valves: three two-way valves arranged in a loop to drive cyclic mixing of the diluent and carryover, and two bus valves to control fluidic access to the circuit through input and output channels. By varying the valve placement in the circuit, carryover fractions from 0.04 to 0.2 were obtained. Each dilution process, which is comprised of a diluent flush cycle followed by a mixing cycle, is carried out with no pipeting, and a sample volume of 400 nL is sufficient for conducting an arbitrary number of serial dilutions. Mixing is precisely controlled by changing the cyclic pumping rate, with a minimum mixing time of 22 s. This microfluidic circuit is generally applicable for integrating automated serial dilution and sample preparation in almost any microfluidic architecture. PMID:17073422

Exchange and spin-orbit induced phenomena in diluted (Ga,Mn)As from first principles

NASA Astrophysics Data System (ADS)

Kudrnovský, J.; Drchal, V.; Turek, I.

2016-08-01

Physical properties induced by exchange interactions (Curie temperature and spin stiffness) and spin-orbit coupling (anomalous Hall effect, anisotropic magnetoresistance, and Gilbert damping) in the diluted (Ga,Mn)As ferromagnetic semiconductor are studied from first principles. Recently developed Kubo-Bastin transport theory and nonlocal torque operator formulation of the Gilbert damping as formulated in the tight-binding linear muffin-tin orbital method are used. The first-principles Liechtenstein mapping is employed to construct an effective Heisenberg Hamiltonian and to estimate Curie temperature and spin stiffness in the real-space random-phase approximation. Good agreement of calculated physical quantities with experiments on well-annealed samples containing only a small amount of compensating defects is obtained.

Self-assembled molecular magnets on patterned silicon substrates: bridging bio-molecules with nanoelectronics.

PubMed

Chang, Chia-Ching; Sun, Kien Wen; Lee, Shang-Fan; Kan, Lou-Sing

2007-04-01

The paper reports the methods of preparing molecular magnets and patterning of the molecules on a semiconductor surface. A highly magnetically aligned metallothionein containing Mn and Cd (Mn,Cd-MT-2) is first synthesized, and the molecules are then placed into nanopores prepared on silicon (001) surfaces using electron beam lithography and reactive ion-etching techniques. We have observed the self-assemble growth of the MT molecules on the patterned Si surface such that the MT molecules have grown into rod or ring type three-dimensional nanostructures, depending on the patterned nanostructures on the surface. We also provide scanning electron microscopy, atomic force microscopy, and magnetic force microscope studies of the molecular nanostructures. This engineered molecule shows molecular magnetization and is biocompatible with conventional semiconductors. These features make Mn,Cd-MT-2 a good candidate for biological applications and sensing sources of new nanodevices. Using molecular self-assembly and topographical patterning of the semiconductor substrate, we can close the gap between bio-molecules and nanoelectronics built into the semiconductor chip.

Mesoscopic spin Hall effect in semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Zarbo, Liviu

The spin Hall effect (SHE) is a name given to a collection of diverse phenomena which share two principal features: (i) longitudinal electric current flowing through a paramagnetic semiconductor or metallic sample leads to transverse spin current and spin accumulation of opposite sign at opposing lateral edges; (ii) SHE does not require externally applied magnetic field or magnetic ordering in the equilibrium state of the sample, instead it relies on the presence of spin-orbit (SO) couplings within the sample. This thesis elaborates on a new type of phenomenon within the SHE family, predicted in our recent studies [Phys. Rev. B 72, 075361 (2005); Phys. Rev. Lett. 95, 046601 (2005); Phys. Rev. B 72, 075335 (2005); Phys. Rev. B 73 , 075303 (2006); and Europhys. Lett. 77, 47004 (2007)], where pure spin current flows through the transverse electrodes attached to a clean finitesize two-dimensional electron gas (2DEG) due to unpolarized charge current injected through its longitudinal leads. If transverse leads are removed, the effect manifests as nonequilibrium spin Hall accumulation at the lateral edges of 2DEG wires. The SO coupling driving this SHE effect is of the Rashba type, which arises due to structural inversion asymmetry of semiconductor heterostructure hosting the 2DEG. We term the effect "mesoscopic" because the spin Hall currents and accumulations reach optimal value in samples of the size of the spin precession length---the distance over which the spin of an electron precesses by an angle pi. In strongly SO-coupled structures this scale is of the order of ˜100 nm, and, therefore, mesoscopic in the sense of being much larger than the characteristic microscopic scales (such as the Fermi wavelength, screening length, or the mean free path in disordered systems), but still much smaller than the macroscopic ones. Although the first theoretical proposal for SHE, driven by asymmetry in SO-dependent scattering of spin-up and spin-down electrons off impurities

Voltage-controlled quantum light from an atomically thin semiconductor

NASA Astrophysics Data System (ADS)

Chakraborty, Chitraleema; Kinnischtzke, Laura; Goodfellow, Kenneth M.; Beams, Ryan; Vamivakas, A. Nick

2015-06-01

Although semiconductor defects can often be detrimental to device performance, they are also responsible for the breadth of functionality exhibited by modern optoelectronic devices. Artificially engineered defects (so-called quantum dots) or naturally occurring defects in solids are currently being investigated for applications ranging from quantum information science and optoelectronics to high-resolution metrology. In parallel, the quantum confinement exhibited by atomically thin materials (semi-metals, semiconductors and insulators) has ushered in an era of flatland optoelectronics whose full potential is still being articulated. In this Letter we demonstrate the possibility of leveraging the atomically thin semiconductor tungsten diselenide (WSe2) as a host for quantum dot-like defects. We report that this previously unexplored solid-state quantum emitter in WSe2 generates single photons with emission properties that can be controlled via the application of external d.c. electric and magnetic fields. These new optically active quantum dots exhibit excited-state lifetimes on the order of 1 ns and remarkably large excitonic g-factors of 10. It is anticipated that WSe2 quantum dots will provide a novel platform for integrated solid-state quantum photonics and quantum information processing, as well as a rich condensed-matter physics playground with which to explore the coupling of quantum dots and atomically thin semiconductors.

Multi-scale modeling of spin transport in organic semiconductors

NASA Astrophysics Data System (ADS)

Hemmatiyan, Shayan; Souza, Amaury; Kordt, Pascal; McNellis, Erik; Andrienko, Denis; Sinova, Jairo

In this work, we present our theoretical framework to simulate simultaneously spin and charge transport in amorphous organic semiconductors. By combining several techniques e.g. molecular dynamics, density functional theory and kinetic Monte Carlo, we are be able to study spin transport in the presence of anisotropy, thermal effects, magnetic and electric field effects in a realistic morphologies of amorphous organic systems. We apply our multi-scale approach to investigate the spin transport in amorphous Alq3 (Tris(8-hydroxyquinolinato)aluminum) and address the underlying spin relaxation mechanism in this system as a function of temperature, bias voltage, magnetic field and sample thickness.

The mathematics of dilution.

PubMed

Chatterjee, Barun Kumar

2014-04-01

The major objection to homeopathic medicine is that the doses of medicine prescribed in some cases are too dilute for any active ingredient to be present. The medicines would hence be rendered inactive, necessitating novel explanations for the action. A further examination of dilution in the light of the Langmuir equation shows that homeopathic medicines may not be as dilute as a simplistic application of Avogadro's Principle suggests, due to surface effects. Copyright © 2013 The Faculty of Homeopathy. Published by Elsevier Ltd. All rights reserved.

Magnetooptics of Exciton Rydberg States in a Monolayer Semiconductor

NASA Astrophysics Data System (ADS)

Stier, A. V.; Wilson, N. P.; Velizhanin, K. A.; Kono, J.; Xu, X.; Crooker, S. A.

2018-02-01

We report 65 T magnetoabsorption spectroscopy of exciton Rydberg states in the archetypal monolayer semiconductor WSe2 . The strongly field-dependent and distinct energy shifts of the 2 s , 3 s , and 4 s excited neutral excitons permits their unambiguous identification and allows for quantitative comparison with leading theoretical models. Both the sizes (via low-field diamagnetic shifts) and the energies of the n s exciton states agree remarkably well with detailed numerical simulations using the nonhydrogenic screened Keldysh potential for 2D semiconductors. Moreover, at the highest magnetic fields, the nearly linear diamagnetic shifts of the weakly bound 3 s and 4 s excitons provide a direct experimental measure of the exciton's reduced mass mr=0.20 ±0.01 m0.

Nanosized solvent superstructures in ultramolecular aqueous dilutions: twenty years' research using water proton NMR relaxation.

PubMed

Demangeat, Jean-Louis

2013-04-01

proton nuclear magnetic resonance (NMR) relaxation times T1, T2, T1/T2 are sensitive to motion and organization of water molecules. Especially, increase in T1/T2 reflects a higher degree of structuring. My purpose was to look at physical changes in water in ultrahigh aqueous dilutions. Samples were prepared by iterative centesimal (c) dilution with vigorous agitation, ranging between 3c and 24c (Avogadro limit 12c). Solutes were silica-lactose, histamine, manganese-lactose. Solvents were water, NaCl 0.15 M or LiCl 0.15 M. Solvents underwent strictly similar, simultaneous dilution/agitation, for each level of dilution, as controls. NMR relaxation was studied within 0.02-20 MHz. No changes were observed in controls. Increasing T1 and T1/T2 were found in dilutions, which persisted beyond 9c (manganese-lactose), 10c (histamine) and 12c (silica-lactose). For silica-lactose in LiCl, continuous decrease in T2 with increase in T1/T2 within the 12c-24c range indicated growing structuring of water despite absence of the initial solute. All changes vanished after heating/cooling. These findings were interpreted in terms of nanosized (>4-nm) supramolecular structures involving water, nanobubbles and ions, if any. Additional study of low dilutions of silica-lactose revealed increased T2 and decreased T1/T2 compared to solvent, within the 10(-3)-10(-6) range, reflecting transient solvent destructuring. This could explain findings at high dilution. Proton NMR relaxation demonstrated modifications of the solvent throughout the low to ultramolecular range of dilution. The findings suggested the existence of superstructures that originate stereospecifically around the solute after an initial destructuring of the solvent, developing more upon dilution and persisting beyond 12c. Copyright © 2013 The Faculty of Homeopathy. Published by Elsevier Ltd. All rights reserved.

Opto-valleytronic imaging of atomically thin semiconductors

DOE PAGES

Neumann, Andre; Lindlau, Jessica; Colombier, Léo; ...

2017-01-16

Transition metal dichalcogenide semiconductors represent elementary components of layered heterostructures for emergent technologies beyond conventional opto-electronics. In their monolayer form they host electrons with quantized circular motion and associated valley polarization and valley coherence as key elements of opto-valleytronic functionality. Here, we introduce two-dimensional polarimetry as means of direct imaging of the valley pseudospin degree of freedom in monolayer transition metal dichalcogenides. Using MoS 2 as a representative material with valley-selective optical transitions, we establish quantitative image analysis for polarimetric maps of extended crystals, and identify valley polarization and valley coherence as sensitive probes of crystalline disorder. Moreover, we findmore » site-dependent thermal and non-thermal regimes of valley-polarized excitons in perpendicular magnetic fields. Finally, we demonstrate the potential of widefield polarimetry for rapid inspection of opto-valleytronic devices based on atomically thin semiconductors and heterostructures.« less

Opto-valleytronic imaging of atomically thin semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Neumann, Andre; Lindlau, Jessica; Colombier, Léo

Transition metal dichalcogenide semiconductors represent elementary components of layered heterostructures for emergent technologies beyond conventional opto-electronics. In their monolayer form they host electrons with quantized circular motion and associated valley polarization and valley coherence as key elements of opto-valleytronic functionality. Here, we introduce two-dimensional polarimetry as means of direct imaging of the valley pseudospin degree of freedom in monolayer transition metal dichalcogenides. Using MoS 2 as a representative material with valley-selective optical transitions, we establish quantitative image analysis for polarimetric maps of extended crystals, and identify valley polarization and valley coherence as sensitive probes of crystalline disorder. Moreover, we findmore » site-dependent thermal and non-thermal regimes of valley-polarized excitons in perpendicular magnetic fields. Finally, we demonstrate the potential of widefield polarimetry for rapid inspection of opto-valleytronic devices based on atomically thin semiconductors and heterostructures.« less

New Icosahedral Boron Carbide Semiconductors

NASA Astrophysics Data System (ADS)

Echeverria Mora, Elena Maria

Novel semiconductor boron carbide films and boron carbide films doped with aromatic compounds have been investigated and characterized. Most of these semiconductors were formed by plasma enhanced chemical vapor deposition. The aromatic compound additives used, in this thesis, were pyridine (Py), aniline, and diaminobenzene (DAB). As one of the key parameters for semiconducting device functionality is the metal contact and, therefore, the chemical interactions or band bending that may occur at the metal/semiconductor interface, X-ray photoemission spectroscopy has been used to investigate the interaction of gold (Au) with these novel boron carbide-based semiconductors. Both n- and p-type films have been tested and pure boron carbide devices are compared to those containing aromatic compounds. The results show that boron carbide seems to behave differently from other semiconductors, opening a way for new analysis and approaches in device's functionality. By studying the electrical and optical properties of these films, it has been found that samples containing the aromatic compound exhibit an improvement in the electron-hole separation and charge extraction, as well as a decrease in the band gap. The hole carrier lifetimes for each sample were extracted from the capacitance-voltage, C(V), and current-voltage, I(V), curves. Additionally, devices, with boron carbide with the addition of pyridine, exhibited better collection of neutron capture generated pulses at ZERO applied bias, compared to the pure boron carbide samples. This is consistent with the longer carrier lifetimes estimated for these films. The I-V curves, as a function of external magnetic field, of the pure boron carbide films and films containing DAB demonstrate that significant room temperature negative magneto-resistance (> 100% for pure samples, and > 50% for samples containing DAB) is possible in the resulting dielectric thin films. Inclusion of DAB is not essential for significant negative magneto

Graphene-based half-metal and spin-semiconductor for spintronic applications.

PubMed

Qi, Jingshan; Chen, Xiaofang; Hu, Kaige; Feng, Ji

2016-03-31

In this letter we propose a strategy to make graphene become a half-metal or spin-semiconductor by combining the magnetic proximity effects and sublattice symmetry breaking in graphone/graphene and graphone/graphene/BN heterostructures. Exchange interactions lift the spin degeneracy and sublattice symmetry breaking opens a band gap in graphene. More interestingly, the gap opening depends on the spin direction and the competition between the sublattice asymmetry and exchange field determines the system is a half-metal or a spin-semiconductor. By first-principles calculations and a low-energy effective model analysis, we elucidate the underlying physical mechanism of spin-dependent gap opening and spin degeneracy splitting. This offers an alternative practical platform for graphene-based spintronics.

Formation and photoluminescence of GaAs1-xNx dilute nitride achieved by N-implantation and flash lamp annealing

NASA Astrophysics Data System (ADS)

Gao, Kun; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, Shengqiang

2014-07-01

In this paper, we present the fabrication of dilute nitride semiconductor GaAs1-xNx by nitrogen-ion-implantation and flash lamp annealing (FLA). N was implanted into the GaAs wafers with atomic concentration of about ximp1 = 0.38% and ximp2 = 0.76%. The GaAs1-xNx layer is regrown on GaAs during FLA treatment in a solid phase epitaxy process. Room temperature near band-edge photoluminescence (PL) has been observed from the FLA treated GaAs1-xNx samples. According to the redshift of the near band-edge PL peak, up to 80% and 44% of the implanted N atoms have been incorporated into the lattice by FLA for ximp1 = 0.38% and ximp2 = 0.76%, respectively. Our investigation shows that ion implantation followed by ultrashort flash lamp treatment, which allows for large scale production, exhibits a promising prospect on bandgap engineering of GaAs based semiconductors.

Sensitizing solid state nuclear magnetic resonance of dilute nuclei by spin-diffusion assisted polarization transfers.

PubMed

Lupulescu, Adonis; Frydman, Lucio

2011-10-07

Recent years have witnessed efforts geared at increasing the sensitivity of NMR experiments, by relying on the suitable tailoring and exploitation of relaxation phenomena. These efforts have included the use of paramagnetic agents, enhanced (1)H-(1)H incoherent and coherent transfers processes in 2D liquid state spectroscopy, and homonuclear (13)C-(13)C spin diffusion effects in labeled solids. The present study examines some of the opportunities that could open when exploiting spontaneous (1)H-(1)H spin-diffusion processes, to enhance relaxation and to improve the sensitivity of dilute nuclei in solid state NMR measurements. It is shown that polarization transfer experiments executed under sufficiently fast magic-angle-spinning conditions, enable a selective polarization of the dilute low-γ spins by their immediate neighboring protons. Repolarization of the latter can then occur during the time involved in monitoring the signal emitted by the low-γ nuclei. The basic features involved in the resulting approach, and its potential to improve the effective sensitivity of solid state NMR measurements on dilute nuclei, are analyzed. Experimental tests witness the advantages that could reside from utilizing this kind of approach over conventional cross-polarization processes. These measurements also highlight a number of limitations that will have to be overcome for transforming selective polarization transfers of this kind into analytical methods of choice. © 2011 American Institute of Physics

Ab-Initio Investigations of Magnetic Properties and Induced Half-Metallicity in Ga1-xMnxP (x = 0.03, 0.25, 0.5, and 0.75) Alloys.

PubMed

Laref, Amel; AlMudlej, Abeer; Laref, Slimane; Yang, Jun Tao; Xiong, Yong-Chen; Luo, Shi Jun

2017-07-07

Ab-initio calculations are performed to examine the electronic structures and magnetic properties of spin-polarized Ga 1- x Mn x P ( x = 0.03, 0.25, 0.5, and 0.75) ternary alloys. In order to perceive viable half-metallic (HM) states and unprecedented diluted magnetic semiconductors (DMSs) such as spintronic materials, the full potential linearized augmented plane wave method is utilized within the generalized gradient approximation (GGA). In order to tackle the correlation effects on 3d states of Mn atoms, we also employ the Hubbard U (GGA + U) technique to compute the magnetic properties of an Mn-doped GaP compound. We discuss the emerged global magnetic moments and the robustness of half-metallicity by varying the Mn composition in the GaP compound. Using GGA + U, the results of the density of states demonstrate that the incorporation of Mn develops a half-metallic state in the GaP compound with an engendered band gap at the Fermi level ( E F ) in the spin-down state. Accordingly, the half-metallic feature is produced through the hybridization of Mn-d and P-p orbitals. However, the half-metallic character is present at a low x composition with the GGA procedure. The produced magnetic state occurs in these materials, which is a consequence of the exchange interactions between the Mn-element and the host GaP system. For the considered alloys, we estimated the X-ray absorption spectra at the K edge of Mn. A thorough clarification of the pre-edge peaks is provided via the results of the theoretical absorption spectra. It is inferred that the valence state of Mn in Ga 1- x Mn x P alloys is +3. The predicted theoretical determinations surmise that the Mn-incorporated GaP semiconductor could inevitably be employed in spintronic devices.

Binding of two-electron metastable states in semiconductor quantum dots under a magnetic field

NASA Astrophysics Data System (ADS)

Garagiola, Mariano; Pont, Federico M.; Osenda, Omar

2018-04-01

Applying a strong enough magnetic field results in the binding of few-electron resonant states. The mechanism was proposed many years ago but its verification in laboratory conditions is far more recent. In this work we study the binding of two-electron resonant states. The electrons are confined in a cylindrical quantum dot which is embedded in a semiconductor wire. The geometry considered is similar to the one used in actual experimental setups. The low-energy two-electron spectrum is calculated numerically from an effective-mass approximation Hamiltonian modelling the system. Methods for binding threshold calculations in systems with one and two electrons are thoroughly studied; in particular, we use quantum information quantities to assess when the strong lateral confinement approximation can be used to obtain reliable low-energy spectra. For simplicity, only cases without bound states in the absence of an external field are considered. Under these conditions, the binding threshold for the one-electron case is given by the lowest Landau energy level. Moreover, the energy of the one-electron bounded resonance can be used to obtain the two-electron binding threshold. It is shown that for realistic values of the two-electron model parameters it is feasible to bind resonances with field strengths of a few tens of tesla.

Color-dilution alopecia in dogs.

PubMed

Kim, Jae Hoon; Kang, Kyung Il; Sohn, Hyun Joo; Woo, Gye Hyeong; Jean, Young Hwa; Hwang, Eui Kyung

2005-09-01

Color-dilution alopecia is a relatively uncommon hereditary skin disease seen in "Blue" and other color-diluted dogs. This syndrome is associated with a color-dilution gene. The initial clinical signs are the gradual onset of a dry, dull and poor hair coat quality. Hair shafts and hair regrowth are poor, and follicular papules may develop and progress to frank comedones. Hair loss and comedo formation are usually most severe on the trunk, especially color-diluted area on the skin. Six cases of color-dilution alopecia are reported in 3 months to 10 years old dogs. The breeds of dogs are blue Doberman Pinscher, Miniature Pinscher, Dachshund, and Schnauzer. Grossly, extensive partial hair loss was seen on the skin. Histopathologically, the epidermis is relatively normal but may be hyperplastic. Hair follicles are characterized by atrophy and distortion. Heavily clumped melanin is present in the epidermis, dermis and hair follicles.

Study of static and dynamic magnetic properties of Fe nanoparticles composited with activated carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pal, Satyendra Prakash, E-mail: sppal85@gmail.com; Department of Physical Sciences, Indian Institute of Science Education and Research, Mohali, Knowledge city, Sector81, SAS Nagar, Manauli-140306, Punjab; Kaur, Guratinder

2016-05-23

Nanocomposite of Fe nanoparticles with activated carbon has been synthesized to alter the magnetic spin-spin interaction and hence study the dilution effect on the static and dynamic magnetic properties of the Fe nanoparticle system. Transmission electron microscopic (TEM) image shows the spherical Fe nanoparticles dispersed in carbon matrix with 13.8 nm particle size. Temperature dependent magnetization measurement does not show any blocking temperature at all, right up to the room temperature. Magnetic hysteresis curve, taken at 300 K, shows small value of the coercivity and this small hysteresis indicates the presence of an energy barrier and inherent magnetization dynamics. Langevinmore » function fitting of the hysteresis curve gives almost similar value of particle size as obtained from TEM analysis. Magnetic relaxation data, taken at a temperature of 100 K, were fitted with a combination of two exponentially decaying function. This diluted form of nanoparticle system, which has particles size in the superparamagnetic limit, behaves like a dilute ensemble of superspins with large value of the magnetic anisotropic barrier.« less

Development of a thermodynamic model for a cold cycle 3He-4He dilution refrigerator

NASA Astrophysics Data System (ADS)

Mueller, B. W.; Miller, F. K.

2016-10-01

A thermodynamic model of a 3He-4He cold cycle dilution refrigerator with no actively-driven mechanical components is developed and investigated. The refrigerator employs a reversible superfluid magnetic pump, passive check valves, a phase separation chamber, and a series of recuperative heat exchangers to continuously circulate 3He-4He and maintain a 3He concentration gradient across the mixing chamber. The model predicts cooling power and mixing chamber temperature for a range of design and operating parameters, allowing an evaluation of feasibility for potential 3He-4He cold cycle dilution refrigerator prototype designs. Model simulations for a prototype refrigerator design are presented.

Modified transverse phonon-helicon interaction in colloids laden semiconductor plasmas due to Bohm potential and Fermi degenerate pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Aartee, E-mail: aartee.sharma08@gmail.com; Yadav, N.; Ghosh, S.

2015-07-31

A detailed study of the quantum modification of acousto-helicon wave spectra due to Bohm potential and Fermi degenerate pressure in colloids laden semiconductor plasma has been presented. We have used quantum hydrodynamic model of plasmas to arrive at most general dispersion relation in presence of magnetic field. This dispersion relation has been analyzed in three different velocity regimes and the expressions for gain constants have been obtained. From the present study it has been concluded that the quantum effect and the magnetic field significantly modify the wave characteristics particularly in high doping regime in semiconductor plasma medium in presence ofmore » colloids in it.« less

Testing methodologies and systems for semiconductor optical amplifiers

NASA Astrophysics Data System (ADS)

Wieckowski, Michael

Semiconductor optical amplifiers (SOA's) are gaining increased prominence in both optical communication systems and high-speed optical processing systems, due primarily to their unique nonlinear characteristics. This in turn, has raised questions regarding their lifetime performance reliability and has generated a demand for effective testing techniques. This is especially critical for industries utilizing SOA's as components for system-in-package products. It is important to note that very little research to date has been conducted in this area, even though production volume and market demand has continued to increase. In this thesis, the reliability of dilute-mode InP semiconductor optical amplifiers is studied experimentally and theoretically. The aging characteristics of the production level devices are demonstrated and the necessary techniques to accurately characterize them are presented. In addition, this work proposes a new methodology for characterizing the optical performance of these devices using measurements in the electrical domain. It is shown that optical performance degradation, specifically with respect to gain, can be directly qualified through measurements of electrical subthreshold differential resistance. This metric exhibits a linear proportionality to the defect concentration in the active region, and as such, can be used for prescreening devices before employing traditional optical testing methods. A complete theoretical analysis is developed in this work to explain this relationship based upon the device's current-voltage curve and its associated leakage and recombination currents. These results are then extended to realize new techniques for testing semiconductor optical amplifiers and other similarly structured devices. These techniques can be employed after fabrication and during packaged operation through the use of a proposed stand-alone testing system, or using a proposed integrated CMOS self-testing circuit. Both methods are capable

Theory of Magnetic Bipolar Transistors

NASA Astrophysics Data System (ADS)

Zutic, Igor; Fabian, Jaroslav; Das Sarma, S.

2003-03-01

We introduce the concept of a magnetic bipolar transistor (MBT) (J. Fabian, I. Zutic, S. Das Sarma, cond-mat/0211639.), which can be realized using already available materials. The transistor has at least one magnetic region (emitter, base, or collector) characterized by spin-splitting of the carrier bands. In addition, nonequilibrium (source) spin in MBTs can be induced by external means (electrically or optically). The theory of ideal MBTs is developed and discussed in the forward active regime where the transistors can amplify signals. It is shown that source spin can be injected from the emitter to the collector. It is predicted that electrical current gain (amplification) can be controlled effectively by magnetic field and source spin. If a base is a ferromagnetic semiconductor we suggest several methods for using spin-polarized bipolar transport (I. Zutic, J. Fabian, S. Das Sarma, Phys. Rev. Lett. f 88, 066603 (2002); J. Fabian, I. Zutic, S. Das Sarma, Phys. Rev. B f 66, 165301 (2002).) to manipulate semiconductor ferromagnetism.

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2010-08-13

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Room Temperature Ferromagnetic Mn:Ge(001).

PubMed

Lungu, George Adrian; Stoflea, Laura Elena; Tanase, Liviu Cristian; Bucur, Ioana Cristina; Răduţoiu, Nicoleta; Vasiliu, Florin; Mercioniu, Ionel; Kuncser, Victor; Teodorescu, Cristian-Mihail

2013-12-27

We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 °C) exhibited the formation of ~5-8 nm diameter Mn₅Ge₃ and Mn 11 Ge₈ agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe ~2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge-Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed.

Dilution in single pass arc welds

DOE Office of Scientific and Technical Information (OSTI.GOV)

DuPont, J.N.; Marder, A.R.

1996-06-01

A study was conducted on dilution of single pass arc welds of type 308 stainless steel filler metal deposited onto A36 carbon steel by the plasma arc welding (PAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and submerged arc welding (SAW) processes. Knowledge of the arc and melting efficiency was used in a simple energy balance to develop an expression for dilution as a function of welding variables and thermophysical properties of the filler metal and substrate. Comparison of calculated and experimentally determined dilution values shows the approach provides reasonable predictions of dilution when the melting efficiencymore » can be accurately predicted. The conditions under which such accuracy is obtained are discussed. A diagram is developed from the dilution equation which readily reveals the effect of processing parameters on dilution to aid in parameter optimization.« less

One-Shot Coherence Dilution.

PubMed

Zhao, Qi; Liu, Yunchao; Yuan, Xiao; Chitambar, Eric; Ma, Xiongfeng

2018-02-16

Manipulation and quantification of quantum resources are fundamental problems in quantum physics. In the asymptotic limit, coherence distillation and dilution have been proposed by manipulating infinite identical copies of states. In the nonasymptotic setting, finite data-size effects emerge, and the practically relevant problem of coherence manipulation using finite resources has been left open. This Letter establishes the one-shot theory of coherence dilution, which involves converting maximally coherent states into an arbitrary quantum state using maximally incoherent operations, dephasing-covariant incoherent operations, incoherent operations, or strictly incoherent operations. We introduce several coherence monotones with concrete operational interpretations that estimate the one-shot coherence cost-the minimum amount of maximally coherent states needed for faithful coherence dilution. Furthermore, we derive the asymptotic coherence dilution results with maximally incoherent operations, incoherent operations, and strictly incoherent operations as special cases. Our result can be applied in the analyses of quantum information processing tasks that exploit coherence as resources, such as quantum key distribution and random number generation.

One-Shot Coherence Dilution

NASA Astrophysics Data System (ADS)

Zhao, Qi; Liu, Yunchao; Yuan, Xiao; Chitambar, Eric; Ma, Xiongfeng

2018-02-01

Manipulation and quantification of quantum resources are fundamental problems in quantum physics. In the asymptotic limit, coherence distillation and dilution have been proposed by manipulating infinite identical copies of states. In the nonasymptotic setting, finite data-size effects emerge, and the practically relevant problem of coherence manipulation using finite resources has been left open. This Letter establishes the one-shot theory of coherence dilution, which involves converting maximally coherent states into an arbitrary quantum state using maximally incoherent operations, dephasing-covariant incoherent operations, incoherent operations, or strictly incoherent operations. We introduce several coherence monotones with concrete operational interpretations that estimate the one-shot coherence cost—the minimum amount of maximally coherent states needed for faithful coherence dilution. Furthermore, we derive the asymptotic coherence dilution results with maximally incoherent operations, incoherent operations, and strictly incoherent operations as special cases. Our result can be applied in the analyses of quantum information processing tasks that exploit coherence as resources, such as quantum key distribution and random number generation.

Transport Optical and Magnetic Properties of Solids.

DTIC Science & Technology

Solid state physics, Band theory of solids, Semiconductors, Strontium compounds, Superconductors, Magnetic properties, Chalcogens, Transport properties, Optical properties, Bibliographies, Scientific research, Magnons

Ferromagnetic properties of Mn-doped HfS2 monolayer under strain

NASA Astrophysics Data System (ADS)

Ma, Xu; Zhao, Xu; Wu, Ninghua; Xin, Qianqian; Liu, Xiaomeng; Wang, Tianxing; Wei, Shuyi

2017-12-01

Using the first-principles calculations, we investigated electronic and magnetic properties of Mn-doped HfS2 monolayer for 4% and 8% Mn concentration. We study the strain tuning of electronic and magnetic properties of 4% Mn-doped HfS2 monolayer firstly. Our results show that the Mn-doped HfS2 monolayer is magnetic nanomaterial without strain. It keeps this character until the compressive strain comes to -8%, and the magnetism disappear with lager compressive strain. With the increasing tensile strain, the doped system transforms from semiconductor to half-metallic when the tensile strain is equivalent to or greater than 5%. The largest half-metallic gap is 1.307 eV at 5% tensile strain and the magnetic moment always keeps about 3μB, which indicates that Mn-doped HfS2 monolayer can be a candidate for superior half-metallic namomaterial. Furthermore, we find two Mn dopants couple ferromagnetically via antiferromagnetic (AFM) p-d exchange interaction at the environment of 8% concentration. It keeps the properties of magnetic semiconductor under two Mn-doped configurations with different Mn-Mn separations. Our studies predict Mn-doped HfS2 monolayer under strain to be candidates for dilute magnetic semiconductors.

Macroporous Semiconductors

PubMed Central

Föll, Helmut; Leisner, Malte; Cojocaru, Ala; Carstensen, Jürgen

2010-01-01

Pores in single crystalline semiconductors come in many forms (e.g., pore sizes from 2 nm to > 10 µm; morphologies from perfect pore crystal to fractal) and exhibit many unique properties directly or as nanocompounds if the pores are filled. The various kinds of pores obtained in semiconductors like Ge, Si, III-V, and II-VI compound semiconductors are systematically reviewed, emphasizing macropores. Essentials of pore formation mechanisms will be discussed, focusing on differences and some open questions but in particular on common properties. Possible applications of porous semiconductors, including for example high explosives, high efficiency electrodes for Li ion batteries, drug delivery systems, solar cells, thermoelectric elements and many novel electronic, optical or sensor devices, will be introduced and discussed.

Synthesis and Magnetic Properties of Ni-DOPED ZnO Thin Films: Experimental and AB INITIO Study

NASA Astrophysics Data System (ADS)

Rouchdi, M.; Salmani, E.; Hat, A. El; Hassanain, N.; Mzerd, A.

Structural and magnetic properties of Zn1-xNixO thin films and diluted magnetic semiconductors have been investigated. This sample has been synthesized using a spray pyrolysis technique with a stoechiometric mixture of zinc acetate (C4H6O4Znṡ2H2O) and Nickel acetate (C4H6O4Niṡ 2H2O) on a heated glass substrate at 450∘C. The films were characterized by X-ray diffraction (XRD), UV-Vis spectrophotometry and Hall Effect measurements. These films of ZnO crystallized in the hexagonal Wurtzite structure. The optical study showed that the band-gap energy was increased, from 3.3eV to 3.5eV, with increasing the Ni concentration. The film resistivity was affected by Ni-doping, and the best resistivity value 1.15×10-2 (Ω cm) was obtained for the film doped with 2 at.% Ni. The electronic structure and optical properties of the Wurtzite structure Zn1-xNixO were obtained by first-principles calculations using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation (CPA), as well as CPA confirm our results.

FOREWORD: Focus on Superconductivity in Semiconductors Focus on Superconductivity in Semiconductors

NASA Astrophysics Data System (ADS)

Takano, Yoshihiko

2008-12-01

Since the discovery of superconductivity in diamond, much attention has been given to the issue of superconductivity in semiconductors. Because diamond has a large band gap of 5.5 eV, it is called a wide-gap semiconductor. Upon heavy boron doping over 3×1020 cm-3, diamond becomes metallic and demonstrates superconductivity at temperatures below 11.4 K. This discovery implies that a semiconductor can become a superconductor upon carrier doping. Recently, superconductivity was also discovered in boron-doped silicon and SiC semiconductors. The number of superconducting semiconductors has increased. In 2008 an Fe-based superconductor was discovered in a research project on carrier doping in a LaCuSeO wide-gap semiconductor. This discovery enhanced research activities in the field of superconductivity, where many scientists place particular importance on superconductivity in semiconductors. This focus issue features a variety of topics on superconductivity in semiconductors selected from the 2nd International Workshop on Superconductivity in Diamond and Related Materials (IWSDRM2008), which was held at the National Institute for Materials Science (NIMS), Tsukuba, Japan in July 2008. The 1st workshop was held in 2005 and was published as a special issue in Science and Technology of Advanced Materials (STAM) in 2006 (Takano 2006 Sci. Technol. Adv. Mater. 7 S1). The selection of papers describe many important experimental and theoretical studies on superconductivity in semiconductors. Topics on boron-doped diamond include isotope effects (Ekimov et al) and the detailed structure of boron sites, and the relation between superconductivity and disorder induced by boron doping. Regarding other semiconductors, the superconducting properties of silicon and SiC (Kriener et al, Muranaka et al and Yanase et al) are discussed, and In2O3 (Makise et al) is presented as a new superconducting semiconductor. Iron-based superconductors are presented as a new series of high

Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals

DOE PAGES

Rice, William D.; Liu, Wenyong; Baker, Thomas A.; ...

2015-11-23

Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn 2+, Co 2+ and so on) couple to band carriers via strong sp–d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical √N fluctuations of N spins are expected to generate giant effective magnetic fields B eff, whichmore » should dramatically impact carrier spin dynamics, even in the absence of any applied field. In this paper, we directly and unambiguously reveal the large B eff that exist in Mn 2+-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300–600 GHz) spin precession of photoinjected electrons is observed, indicating B eff ~ 15-30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. Finally, these signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn 2+ moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.« less

Anisotropic dependence of the magnetic transition on uniaxial pressure in the Kondo semiconductors Ce T2A l10 (T =Ru and Os)

NASA Astrophysics Data System (ADS)

Hayashi, K.; Umeo, K.; Takeuchi, T.; Kawabata, J.; Muro, Y.; Takabatake, T.

2017-12-01

We have measured the strain, magnetization, and specific heat of the antiferromagnetic (AFM) Kondo semiconductors Ce T2A l10 (T =Ru and Os) under uniaxial pressures applied along the orthorhombic axes. We found a linear dependence of TN on the b -axis parameter for both compounds under uniaxial pressure P ∥b and hydrostatic pressure. This relation indicates that the distance between the Ce-T layers along the b axis is the key structural parameter determining TN. Furthermore, the pressure dependence of the spin-flop transition field indicates that Ce-Ce interchain interactions stabilize the AFM state with the ordered moments pointing to the c axis.

New oil-in-water magnetic emulsion as contrast agent for in vivo magnetic resonance imaging (MRI).

PubMed

Ahmed, Naveed; Jaafar-Maalej, Chiraz; Eissa, Mohamed Mahmoud; Fessi, Hatem; Elaissari, Abdelhamid

2013-09-01

Nowadays, bio-imaging techniques are widely applied for the diagnosis of various diseased/tumoral tissues in the body using different contrast agents. Accordingly, the advancement in bionanotechnology research is enhanced in this regard. Among contrast agents used, superparamagnetic iron oxide nanoparticles were developed by many researchers and applied for in vive magnetic resonance imaging (MRI). In this study, a new oil-in-water magnetic emulsion was used as contrast agent in MRI, after being characterized in terms of particle size, iron oxide content, magnetic properties and colloidal stability using dynamic light scattering (DLS), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM) and zeta potential measurement techniques, respectively. The hydrodynamic size and magnetic content of the magnetic colloidal particles were found to be 250 nm and 75 wt%, respectively. In addition, the used magnetic emulsion possesses superparamagentic properties and high colloidal stability in aqueous medium. Then, the magnetic emulsion was highly diluted and administered intravenously to the Sprague dawley rats to be tested as contrast agent for in vivo MRI. In this preliminary study, MRI images showed significant enhancement in contrast, especially for T2 (relaxation time) contrast enhancement, indicating the distribution of magnetic colloidal nanoparticles within organs, like liver, spleen and kidneys of the Sprague dawley rats. In addition, it was found that 500 microL of the highly diluted magnetic emulsion (0.05 wt%) was found adequate for MRI analysis. This seems to be useful for further investigations especially in theranostic applications of magnetic emulsion.

Magnetic Polarons in Anisotropic Quantum Dots

NASA Astrophysics Data System (ADS)

Oszwaldowski, Rafal; Petukhov, Andre; Zutic, Igor

2010-03-01

Tunability of confinement in magnetically-doped quantum dots (QDs) allows to tailor magnetism to an extent not available in bulk semiconductors. Versatile control of magnetic ordering, along with piezomagnetism, has been predicted even at a fixed number of carriers [1]. Recent experiments on colloidal QDs revealed strongly bound magnetic polarons (MPs) [2]. Previous studies of MPs in bulk semiconductors showed that the mean-field theory predicts a spurious magnetic phase transition, which is removed by taking into account spin fluctuations [3]. Here we present our theoretical results for MPs forming in QDs with pronounced magnetic anisotropy, which influences the spin fluctuations. We apply our findings to explain some peculiarities of the magnetic behavior of type-II ZnSe/(Zn,Mn)Te QDs, where magnetic polarons are found to persist to at least 200K [4]. Supported by ONR, AFOSR, and NSF-ECCS CAREER. [4pt] [1] R. M. Abolfath, A. G. Petukhov, and I. Zutic, Phys. Rev. Lett. 101, 207202 (2008); I. Zutic and A. G. Petukhov, Nature Mater.4, 623 (2009). [0pt] [2] R. Beaulac et al., Science 325, 973 (2009). [0pt] [3] T. Dietl and J. Spalek, Phys. Rev. Lett. 48, 355 (1982). [0pt] [4] I. R. Sellers, R. Oszwaldowski, et al., preprint; I. R. Sellers et al., Phys. Rev. Lett. 100, 136405 (2008).

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

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.

Dilution effects on combined magnetic and electric dipole interactions: A study of ferromagnetic cobalt nanoparticles with tuneable interactions

NASA Astrophysics Data System (ADS)

Hod, M.; Dobroserdova, A.; Samin, S.; Dobbrow, C.; Schmidt, A. M.; Gottlieb, M.; Kantorovich, S.

2017-08-01

Improved understanding of complex interactions between nanoparticles will facilitate the control over the ensuing self-assembled structures. In this work, we consider the dynamic changes occurring upon dilution in the self-assembly of a system of ferromagnetic cobalt nanoparticles that combine magnetic, electric, and steric interactions. The systems examined here vary in the strength of the magnetic dipole interactions and the amount of point charges per particle. Scattering techniques are employed for the characterization of the self-assembly aggregates, and zeta-potential measurements are employed for the estimation of surface charges. Our experiments show that for particles with relatively small initial number of surface electric dipoles, an increase in particle concentration results in an increase in diffusion coefficients; whereas for particles with relatively high number of surface dipoles, no effect is observed upon concentration changes. We attribute these changes to a shift in the adsorption/desorption equilibrium of the tri-n-octylphosphine oxide (TOPO) molecules on the particle surface. We put forward an explanation, based on the combination of two theoretical models. One predicts that the growing concentration of electric dipoles, stemming from the addition of tri-n-octylphosphine oxide (TOPO) as co-surfactant during particle synthesis, on the surface of the particles results in the overall repulsive interaction. Secondly, using density functional theory, we explain that the observed behaviour of the diffusion coefficient can be treated as a result of the concentration dependent nanoparticle self-assembly: additional repulsion leads to the reduction in self-assembled aggregate size despite the shorter average interparticle distances, and as such provides the growth of the diffusion coefficient.

Dilution effects on combined magnetic and electric dipole interactions: A study of ferromagnetic cobalt nanoparticles with tuneable interactions.

PubMed

Hod, M; Dobroserdova, A; Samin, S; Dobbrow, C; Schmidt, A M; Gottlieb, M; Kantorovich, S

2017-08-28

Improved understanding of complex interactions between nanoparticles will facilitate the control over the ensuing self-assembled structures. In this work, we consider the dynamic changes occurring upon dilution in the self-assembly of a system of ferromagnetic cobalt nanoparticles that combine magnetic, electric, and steric interactions. The systems examined here vary in the strength of the magnetic dipole interactions and the amount of point charges per particle. Scattering techniques are employed for the characterization of the self-assembly aggregates, and zeta-potential measurements are employed for the estimation of surface charges. Our experiments show that for particles with relatively small initial number of surface electric dipoles, an increase in particle concentration results in an increase in diffusion coefficients; whereas for particles with relatively high number of surface dipoles, no effect is observed upon concentration changes. We attribute these changes to a shift in the adsorption/desorption equilibrium of the tri-n-octylphosphine oxide (TOPO) molecules on the particle surface. We put forward an explanation, based on the combination of two theoretical models. One predicts that the growing concentration of electric dipoles, stemming from the addition of tri-n-octylphosphine oxide (TOPO) as co-surfactant during particle synthesis, on the surface of the particles results in the overall repulsive interaction. Secondly, using density functional theory, we explain that the observed behaviour of the diffusion coefficient can be treated as a result of the concentration dependent nanoparticle self-assembly: additional repulsion leads to the reduction in self-assembled aggregate size despite the shorter average interparticle distances, and as such provides the growth of the diffusion coefficient.

Berezinskii-Kosterlitz-Thouless phase transition for the dilute planar rotator model on a triangular lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun Yunzhou; Yi Lin; Wysin, G. M.

2008-10-15

The Berezinskii-Kosterlitz-Thouless (BKT) phase transition for the dilute planar rotator model on a triangular lattice is studied by using a hybrid Monte Carlo method. The phase-transition temperatures for different nonmagnetic impurity densities are obtained by three approaches: finite-size scaling of plane magnetic susceptibility, helicity modulus, and Binder's fourth cumulant. It is found that the phase-transition temperature decreases with increasing impurity density {rho} and the BKT phase transition vanishes when the magnetic occupancy falls to the site percolation threshold: 1-{rho}{sub c}=p{sub c}=0.5.

Entrainment vs. Dilution in Tropical Deep Convection

NASA Astrophysics Data System (ADS)

Hannah, W.

2017-12-01

The distinction between entrainment and dilution is investigated with cloud resolving simulations of deep convection in a tropical environment. A method for estimating the rate of dilution by entrainment and detrainment is calculated for a series of bubble simulations with a range of initial radii. Entrainment generally corresponds to dilution of convection, but the two quantities are not well correlated. Core dilution by entrainment is significantly reduced by the presence of a shell of moist air around the core. Entrainment contributes significantly to the total net dilution, but detrainment and the various source/sink terms play large roles depending on the variable in question. Detrainment has a concentrating effect on average that balances out the dilution by entrainment. The experiments are also used to examine whether entrainment or dilution scale with cloud radius. The results support a weak negative relationship for dilution, but not for entrainment. The sensitivity to resolution is briefly discussed. A toy Lagrangian thermal model is used to demonstrate the importance of the cloud shell as a thermodynamic buffer to reduce the dilution of the core by entrainment. The results suggest that explicit cloud heterogeneity may be a useful consideration for future convective parameterization development.

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.

Entrainment versus Dilution in Tropical Deep Convection

DOE PAGES

Hannah, Walter M.

2017-11-01

In this paper, the distinction between entrainment and dilution is investigated with cloud-resolving simulations of deep convection in a tropical environment. A method for estimating the rate of dilution by entrainment and detrainment is presented and calculated for a series of bubble simulations with a range of initial radii. Entrainment generally corresponds to dilution of convection, but the two quantities are not well correlated. Core dilution by entrainment is significantly reduced by the presence of a shell of moist air around the core. Dilution by entrainment also increases with increasing updraft velocity but only for sufficiently strong updrafts. Entrainment contributesmore » significantly to the total net dilution, but detrainment and the various source/sink terms play large roles depending on the variable in question. Detrainment has a concentrating effect on average that balances out the dilution by entrainment. The experiments are also used to examine whether entrainment or dilution scale with cloud radius. The results support a weak negative relationship for dilution but not for entrainment. The sensitivity to resolution is briefly discussed. A toy Lagrangian thermal model is used to demonstrate the importance of the cloud shell as a thermodynamic buffer to reduce the dilution of the core by entrainment. Finally, the results suggest that explicit cloud heterogeneity may be a useful consideration for future convective parameterization development.« less

Alteration of magnetic and optical properties of ultrafine dilute magnetic semiconductor ZnO:Co2+ nanoparticles.

PubMed

Sharma, Prashant K; Dutta, Ranu K; Pandey, Avinash C

2010-05-15

Single-phase ZnO:Co(2+) nanoparticles of mean size 2-8 nm were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO nanoparticles crystallize in wurtzite structure without any impurity phase. The wurtzite structure (lattice constants) of ZnO nanoparticles decrease slightly with increasing Co doping concentration. Optical absorption spectra show an increase in the band gap with increasing Co content and also give an evidence of the presence of Co(2+) ions at tetrahedral sites of ZnO and substituted for the Zn site with no evidence of metallic Co. Initially these nanoparticles showed strong ferromagnetic behavior at room temperature, however at higher doping percentage of Co(2+), the ferromagnetic behavior was suppressed, and antiferromagnetic nature was enhanced. The enhanced antiferromagnetic interaction between neighboring Co-Co ions suppressed the ferromagnetism at higher doping concentrations of Co(2+). Photoluminescence intensity owing to the vacancies varies with the Co concentration because of the increment of oxygen vacancies. Copyright © 2010 Elsevier Inc. All rights reserved.

Helicity moduli of three-dimensional dilute XY models

NASA Astrophysics Data System (ADS)

Garg, Anupam; Pandit, Rahul; Solla, Sara A.; Ebner, C.

1984-07-01

The helicity moduli of various dilute, classical XY models on three-dimensional lattices are studied with a view to understanding some aspects of the superfluidity of 4He in Vycor glass. A spinwave calculation is used to obtain the low-temperature helicity modulus of a regularly-diluted XY model. A similar calculation is performed for the randomly bond-diluted and site-diluted XY models in the limit of low dilution. A Monte Carlo simulation is used to obtain the helicity modulus of the randomly bond-diluted XY model over a wide range of temperature and dilution. It is found that the randomly diluted models do agree and the regularly diluted model does not agree with certain experimentally found features of the variation in superfluid fraction with coverage of 4He in Vycor glass.

Plasmon-induced carrier polarization in semiconductor nanocrystals.

PubMed

Yin, Penghui; Tan, Yi; Fang, Hanbing; Hegde, Manu; Radovanovic, Pavle V

2018-06-01

Spintronics 1 and valleytronics 2 are emerging quantum electronic technologies that rely on using electron spin and multiple extrema of the band structure (valleys), respectively, as additional degrees of freedom. There are also collective properties of electrons in semiconductor nanostructures that potentially could be exploited in multifunctional quantum devices. Specifically, plasmonic semiconductor nanocrystals 3-10 offer an opportunity for interface-free coupling between a plasmon and an exciton. However, plasmon-exciton coupling in single-phase semiconductor nanocrystals remains challenging because confined plasmon oscillations are generally not resonant with excitonic transitions. Here, we demonstrate a robust electron polarization in degenerately doped In 2 O 3 nanocrystals, enabled by non-resonant coupling of cyclotron magnetoplasmonic modes 11 with the exciton at the Fermi level. Using magnetic circular dichroism spectroscopy, we show that intrinsic plasmon-exciton coupling allows for the indirect excitation of the magnetoplasmonic modes, and subsequent Zeeman splitting of the excitonic states. Splitting of the band states and selective carrier polarization can be manipulated further by spin-orbit coupling. Our results effectively open up the field of plasmontronics, which involves the phenomena that arise from intrinsic plasmon-exciton and plasmon-spin interactions. Furthermore, the dynamic control of carrier polarization is readily achieved at room temperature, which allows us to harness the magnetoplasmonic mode as a new degree of freedom in practical photonic, optoelectronic and quantum-information processing devices.

Plasmon-induced carrier polarization in semiconductor nanocrystals

NASA Astrophysics Data System (ADS)

Yin, Penghui; Tan, Yi; Fang, Hanbing; Hegde, Manu; Radovanovic, Pavle V.

2018-06-01

Spintronics1 and valleytronics2 are emerging quantum electronic technologies that rely on using electron spin and multiple extrema of the band structure (valleys), respectively, as additional degrees of freedom. There are also collective properties of electrons in semiconductor nanostructures that potentially could be exploited in multifunctional quantum devices. Specifically, plasmonic semiconductor nanocrystals3-10 offer an opportunity for interface-free coupling between a plasmon and an exciton. However, plasmon-exciton coupling in single-phase semiconductor nanocrystals remains challenging because confined plasmon oscillations are generally not resonant with excitonic transitions. Here, we demonstrate a robust electron polarization in degenerately doped In2O3 nanocrystals, enabled by non-resonant coupling of cyclotron magnetoplasmonic modes11 with the exciton at the Fermi level. Using magnetic circular dichroism spectroscopy, we show that intrinsic plasmon-exciton coupling allows for the indirect excitation of the magnetoplasmonic modes, and subsequent Zeeman splitting of the excitonic states. Splitting of the band states and selective carrier polarization can be manipulated further by spin-orbit coupling. Our results effectively open up the field of plasmontronics, which involves the phenomena that arise from intrinsic plasmon-exciton and plasmon-spin interactions. Furthermore, the dynamic control of carrier polarization is readily achieved at room temperature, which allows us to harness the magnetoplasmonic mode as a new degree of freedom in practical photonic, optoelectronic and quantum-information processing devices.

Dynamic detection of spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance (Conference Presentation)

NASA Astrophysics Data System (ADS)

Crowell, Paul A.; Liu, Changjiang; Patel, Sahil; Peterson, Tim; Geppert, Chad C.; Christie, Kevin; Stecklein, Gordon; Palmstrøm, Chris J.

2016-10-01

A distinguishing feature of spin accumulation in ferromagnet-semiconductor devices is its precession in a magnetic field. This is the basis for detection techniques such as the Hanle effect, but these approaches become ineffective as the spin lifetime in the semiconductor decreases. For this reason, no electrical Hanle measurement has been demonstrated in GaAs at room temperature. We show here that by forcing the magnetization in the ferromagnet to precess at resonance instead of relying only on the Larmor precession of the spin accumulation in the semiconductor, an electrically generated spin accumulation can be detected up to 300 K. The injection bias and temperature dependence of the measured spin signal agree with those obtained using traditional methods. We further show that this new approach enables a measurement of short spin lifetimes (< 100 psec), a regime that is not accessible in semiconductors using traditional Hanle techniques. The measurements were carried out on epitaxial Heusler alloy (Co2FeSi or Co2MnSi)/n-GaAs heterostructures. Lateral spin valve devices were fabricated by electron beam and photolithography. We compare measurements carried out by the new FMR-based technique with traditional non-local and three-terminal Hanle measurements. A full model appropriate for the measurements will be introduced, and a broader discussion in the context of spin pumping experimenments will be included in the talk. The new technique provides a simple and powerful means for detecting spin accumulation at high temperatures. Reference: C. Liu, S. J. Patel, T. A. Peterson, C. C. Geppert, K. D. Christie, C. J. Palmstrøm, and P. A. Crowell, "Dynamic detection of electron spin accumulation in ferromagnet-semiconductor devices by ferromagnetic resonance," Nature Communications 7, 10296 (2016). http://dx.doi.org/10.1038/ncomms10296

Biomolecular Recognition of Semiconductors and Magnetic Materials to Assemble Nanoparticle Heterostructures

DTIC Science & Technology

2002-01-01

shown that engineered viruses can recognize specific semiconductor surfaces through the selection by combinatorial phage display method. These specific... phage display libraries. The screening method selected for binding affinity of a population of random peptides displayed as part of the pIII minor coat...shorter spacing than expected distance ( M13 phage length: 880 nm) corresponds to the length scale imposed by the phage which formed the tilted

Magnetic Control of Concentration Gradient in Microgravity

NASA Technical Reports Server (NTRS)

Leslie, Fred; Ramachandran, Narayanan

2005-01-01

A report describes a technique for rapidly establishing a fluid-concentration gradient that can serve as an initial condition for an experiment on solutal instabilities associated with crystal growth in microgravity. The technique involves exploitation of the slight attractive or repulsive forces exerted on most fluids by a magnetic-field gradient. Although small, these forces can dominate in microgravity and therefore can be used to hold fluids in position in preparation for an experiment. The magnetic field is applied to a test cell, while a fluid mixture containing a concentration gradient is prepared by introducing an undiluted solution into a diluting solution in a mixing chamber. The test cell is then filled with the fluid mixture. Given the magnetic susceptibilities of the undiluted and diluting solutions, the magnetic-field gradient must be large enough that the magnetic force exceeds both (1) forces associated with the flow of the fluid mixture during filling of the test cell and (2) forces imposed by any residual gravitation and fluctuations thereof. Once the test cell has been filled with the fluid mixture, the magnetic field is switched off so that the experiment can proceed, starting from the proper initial conditions.

Magnetic particles

NASA Technical Reports Server (NTRS)

Chang, Manchium (Inventor); Colvin, Michael S. (Inventor)

1989-01-01

Magnetic polymer particles are formed by swelling porous, polymer particles and impregnating the particles with an aqueous solution of precursor magnetic metal salt such as an equimolar mixture of ferrous chloride and ferric chloride. On addition of a basic reagent such as dilute sodium hydroxide, the metal salts are converted to crystals of magnetite which are uniformly contained througout the pores of the polymer particle. The magnetite content can be increased and neutral buoyancy achieved by repetition of the impregnaton and neutralization steps to adjust the magnetite content to a desired level.

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

Effect of copper and nickel doping on the optical and structural properties of ZnO

NASA Astrophysics Data System (ADS)

Muǧlu, G. Merhan; Sarıtaş, S.; ćakıcı, T.; Şakar, B.; Yıldırım, M.

2017-02-01

The present study is focused on the Cu doped ZnO and Ni doped ZnO dilute magnetic semiconductor thin films. ZnO:Cu and ZnO:Ni thin films were grown by Chemically Spray Pyrolysis (CSP) method on glass substrates. Optical analysis of the films was done spectral absorption and transmittance measurements by UV-Vis double beam spectrophotometer technique. The structure, morphology, topology and elemental analysis of ZnO:Cu and ZnO:Ni dilute magnetic thin films were investigated by X-ray diffraction (XRD), Raman Analysis, field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) techniques, respectively. Also The magnetic properties of the ZnO:Ni thin film was investigated by vibrating sample magnetometer (VSM) method. VSM measurements of ZnO:Ni thin film showed that the ferromagnetic behavior.

Magnetofluidic concentration and separation of non-magnetic particles using two magnet arrays

PubMed Central

Hejazian, Majid

2016-01-01

The present paper reports the use of diluted ferrofluid and two arrays of permanent magnets for the size-selective concentration of non-magnetic particles. The micro magnetofluidic device consists of a straight channels sandwiched between two arrays of permanent magnets. The permanent magnets create multiple capture zones with minimum magnetic field strength along the channel. The complex interaction between magnetic forces and hydrodynamic force allows the device to operate in different regimes suitable for concentration of non-magnetic particles with small difference in size. Our experimental results show that non-magnetic particles with diameters of 3.1 μm and 4.8 μm can be discriminated and separated with this method. The results from this study could be used as a guide for the design of size-sensitive separation devices for particle and cell based on negative magnetophoresis. PMID:27478527

Sub-ppb Oxygen Contaminant Detection in Semi-Conductor Processing

NASA Technical Reports Server (NTRS)

Man, K. F.

1995-01-01

Gaseous contaminants such as oxygen, water vapor, nitrogen and hydrocarbons are often present in the processing environment in semiconductor device fabrication and in containerless materials processing. The contaminants arise as a result of outgassing from hot surfaces or they may be part of the impurities in commercial ultra-high purity gases. Among these gaseous contaminants, oxygen is the most reactive and, therefore, has the most adverse effects on the end product. There has been an intense effort at the Jet Propulsion Laboratory to develop different types of oxygen sorbents to reduce oxygen concentration in a microgravity processing environment to sub-ppb (parts-per-billion) levels. Higher concentrations can lead to rapid surface oxide formation, hence reducing the quality of semiconductor devices. If the concentration of oxygen in a processing chamber at 1000oC is in the ppb level, it will only take approximately 10 seconds for an oxide layer to form on the surface of a sample. The interaction of oxygen with the water surface can lead to the formation of localized defects in semi-conductor devices, hence decreasing the manufacturing yield. For example, efficient production of 64 Mb RAM chips requires contaminations below ppb levels. This paper describes a technique for measuring trace quantities of oxygen contaminants by recording the monoatomic negative ions, O-, using mass spectrometry. The O- formation from the e--O2 interaction utilizes the electron dissociative attachment method that is greatly enhanced at the resonant energy (6.8 eV). The device combines a small gridded electron ionizer with a compact mass spectrometer. The concentrations of oxygen have been measured using the method of standard additions by diluting O2 in N2. The lowest detection limit obtained was 1.2 kHz (O- count rate) at a concentration of 10-10, corresponding to 0.1 ppb.

High Tc Superconducting Magnet Excited by a Semiconductor Thermoelectric Element

NASA Astrophysics Data System (ADS)

Kuriyama, T.; Ono, M.; Tabe, S.; Oguchi, A.; Okamura, T.

2006-04-01

A high Tc superconducting (HTS) magnet excited by a thermal electromotive force of a thermoelectric element is studied. This HTS magnet has the advantages of compactness, lightweight and continuous excitation in comparison with conventional HTS magnets, because this HTS magnet does not need a large external power source. In this system, a heat input into the cryogenic environment is necessary to excite the thermoelectric element for constant operation. This heat generation, however, causes a rise in temperature of an HTS coil and reduces the system performance. In this paper, a newly designed magnet system which adopted a two-stage GM cryocooler was investigated. It enabled us to control the temperature of a thermoelectric element and that of an HTS coil independently. The temperature of the HTS coil could be kept at 10-20 K at the second stage of the GM cryocooler, while the thermoelectric element could be excited at higher temperature in the range of 50-70 K at the first stage, where the performance of the thermoelectric element was higher. The experimental results on this HTS magnet are shown and the possibility of the thermoelectric element as a main power source of the HTS magnets is discussed.

Nonlinear generation of sum and difference frequency waves by two helicon waves in a semiconductor

NASA Astrophysics Data System (ADS)

Salimullah, M.; Ferdous, T.

1984-05-01

This paper presents a theoretical investigation of the nonlinear generation of electrostatic waves at the sum and the difference frequency when two high amplitude elliptically polarized helicon waves propagate along the direction of the externally applied static magnetic field in an n-type semiconductor. The nonlinearity arises through the ponderomotive force on electrons. It is noticed that the power conversion efficiency of the difference frequency generation is much larger than that of the sum frequency generation. The power conversion efficiency may be easily increased by increasing the density of electrons in the semiconductor.

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.

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.

Nonthermal Photocoercivity Effect in a Low-Doped (Ga,Mn)As Ferromagnetic Semiconductor

NASA Astrophysics Data System (ADS)

Astakhov, G. V.; Hoffmann, H.; Korenev, V. L.; Kiessling, T.; Schwittek, J.; Schott, G. M.; Gould, C.; Ossau, W.; Brunner, K.; Molenkamp, L. W.

2009-05-01

We report a photoinduced change of the coercive field, i.e., a photocoercivity effect (PCE), under very low intensity illumination of a low-doped (Ga,Mn)As ferromagnetic semiconductor. We find a strong correlation between the PCE and the sample resistivity. Spatially resolved dynamics of the magnetization reversal rule out any role of thermal heating in the origin of this PCE, and we propose a mechanism based on the light-induced lowering of the domain wall pinning energy. The PCE is local and reversible, allowing writing and erasing of magnetic images using light.

Nonthermal photocoercivity effect in a low-doped (Ga,Mn)As ferromagnetic semiconductor.

PubMed

Astakhov, G V; Hoffmann, H; Korenev, V L; Kiessling, T; Schwittek, J; Schott, G M; Gould, C; Ossau, W; Brunner, K; Molenkamp, L W

2009-05-08

We report a photoinduced change of the coercive field, i.e., a photocoercivity effect (PCE), under very low intensity illumination of a low-doped (Ga,Mn)As ferromagnetic semiconductor. We find a strong correlation between the PCE and the sample resistivity. Spatially resolved dynamics of the magnetization reversal rule out any role of thermal heating in the origin of this PCE, and we propose a mechanism based on the light-induced lowering of the domain wall pinning energy. The PCE is local and reversible, allowing writing and erasing of magnetic images using light.

Modeling Magnetic Properties in EZTB

NASA Technical Reports Server (NTRS)

Lee, Seungwon; vonAllmen, Paul

2007-01-01

A software module that calculates magnetic properties of a semiconducting material has been written for incorporation into, and execution within, the Easy (Modular) Tight-Binding (EZTB) software infrastructure. [EZTB is designed to model the electronic structures of semiconductor devices ranging from bulk semiconductors, to quantum wells, quantum wires, and quantum dots. EZTB implements an empirical tight-binding mathematical model of the underlying physics.] This module can model the effect of a magnetic field applied along any direction and does not require any adjustment of model parameters. The module has thus far been applied to study the performances of silicon-based quantum computers in the presence of magnetic fields and of miscut angles in quantum wells. The module is expected to assist experimentalists in fabricating a spin qubit in a Si/SiGe quantum dot. This software can be executed in almost any Unix operating system, utilizes parallel computing, can be run as a Web-portal application program. The module has been validated by comparison of its predictions with experimental data available in the literature.

Itinerant magnetism in doped semiconducting β-FeSi2 and CrSi2

PubMed Central

Singh, David J.; Parker, David

2013-01-01

Novel or unusual magnetism is a subject of considerable interest, particularly in metals and degenerate semiconductors. In such materials the interplay of magnetism, transport and other Fermi liquid properties can lead to fascinating physical behavior. One example is in magnetic semiconductors, where spin polarized currents may be controlled and used. We report density functional calculations predicting magnetism in doped semiconducting β-FeSi2 and CrSi2 at relatively low doping levels particularly for n-type. In this case, there is a rapid cross-over to a half-metallic state as a function of doping level. The results are discussed in relation to the electronic structure and other properties of these compounds. PMID:24343332

Coupling between crystal structure and magnetism in transition-metal oxides

NASA Astrophysics Data System (ADS)

Barton, Phillip Thomas

-temperature synchrotron X-ray diffraction reveal a magnetostructural transition and capacitance measurements show evidence for magnetodielectric behavior. The above work uncovered a Co10Ge3O16 phase that had a known structure but whose physical properties were largely uncharacterized. This project examined its metamagnetic properties using detailed magnetometry experiments. Upon the application of a magnetic field, this material goes through a first-order phase transition from a noncollinear antiferromagnet to an unknown ferrimagnetic state. Lastly, this thesis explored the chemical dilution of magnetism in some perovskite and delafossite solid solutions. In the perovskite structure, compositions intermediate to the endmembers SrRuO3, a ferromagnetic metal, and LaRhO3, a diamagnetic semiconductor, were investigated. While the magnetism of this system is poised between localized and itinerant behavior, a compositionally-driven metal to insulator transition, revealed by electrical resistivity measurements, did not strongly impact the magnetic properties. Instead, both octahedral tilting and magnetic dilution had strong effects, and comparison of this characterization to Sr1-- x CaxRuO3 reinforces the important role of structural distortions in determining magnetic ground state. The final materials studied were of composition CuAl1-- xCrxO2 (0 < x < 1) in the delafossite structure. The primary interest was the geometric frustration of antiferromagnetism in CuCrO 2 and significant short-range correlations were observed above TN. The analysis found that reducing the number of degenerate states through Al substitution did not enhance magnetic ordering because of the weakening of magnetic exchange.

Electron transport through magnetic quantum point contacts

NASA Astrophysics Data System (ADS)

Day, Timothy Ellis

Spin-based electronics, or spintronics, has generated a great deal of interest as a possible next-generation integrated circuit technology. Recent experimental and theoretical work has shown that these devices could exhibit increased processing speed, decreased power consumption, and increased integration densities as compared with conventional semiconductor devices. The spintronic device that was designed, fabricated, and tested throughout the course of this work aimed to study the generation of spin-polarized currents in semiconductors using magnetic fringe fields. The device scheme relied on the Zeeman effect in combination with a quantum mechanical barrier to generate spin-polarized currents. The Zeeman effect was used to break the degeneracy of spin-up and spin-down electrons and the quantum mechanical potential to transmit one while rejecting the other. The design was dictated by the drive to maximize the strength of the magnetic fringe field and in turn maximize the energy separation of the two spin species. The device was fabricated using advanced techniques in semiconductor processing including electron beam lithography and DC magnetron sputtering. Measurements were performed in a 3He cryostat equipped with a superconducting magnet at temperatures below 300 mK. Preliminary characterization of the device revealed magnetoconductance oscillations produced by the effect of the transverse confining potential on the density of states and the mobility. Evidence of the effect of the magnetic fringe fields on the transport properties of electrons in the device were observed in multiple device measurements. An abrupt washout of the quantized conductance steps was observed over a minute range of the applied magnetic field. The washout was again observed as electrons were shifted closer to the magnetic gates. In addition, bias spectroscopy demonstrated that the washout occurred despite stronger electron confinement, as compared to a non-magnetic split-gate. Thus, the

Channeling Excitons to Emissive Defect Sites in Carbon Nanotube Semiconductors beyond the Dilute Regime.

PubMed

Powell, Lyndsey R; Piao, Yanmei; Ng, Allen L; Wang, YuHuang

2018-06-07

The exciton photoluminescence of carbon nanotube semiconductors has been intensively exploited for bioimaging, anticounterfeiting, photodetection, and quantum information science. However, at high concentrations, photoluminescence is lost to self-quenching because of the nearly complete overlap of the absorption and emissive states (∼10 meV Stokes shift). Here we show that by introducing sparse fluorescent quantum defects via covalent chemistry, self-quenching can be efficiently bypassed by means of the new emission route. The defect photoluminescence is significantly red-shifted by 190 meV for p-nitroaryl tailored (6,5)-single-walled carbon nanotubes (SWCNTs) from the native emission of the nanotube. Notably, the defect photoluminescence is more than 34 times brighter than the native photoluminescence of unfunctionalized SWCNTs in the most concentrated nanotube solution tested (2.7 × 10 14 nanotubes/mL). Moreover, we show that defect photoluminescence is more resistant to self-quenching than the native state in a dense film, which is the upper limit of concentration. Our findings open opportunities to harness nanotube excitons in highly concentrated systems for applications where photoluminescence brightness and light-collecting efficiency are mutually important.

Trend of tunnel magnetoresistance and variation in threshold voltage for keeping data load robustness of metal–oxide–semiconductor/magnetic tunnel junction hybrid latches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohsawa, T.; Ikeda, S.; Hanyu, T.

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 TMRmore » 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%.« less

Organic semiconductor crystals.

PubMed

Wang, Chengliang; Dong, Huanli; Jiang, Lang; Hu, Wenping

2018-01-22

Organic semiconductors have attracted a lot of attention since the discovery of highly doped conductive polymers, due to the potential application in field-effect transistors (OFETs), light-emitting diodes (OLEDs) and photovoltaic cells (OPVs). Single crystals of organic semiconductors are particularly intriguing because they are free of grain boundaries and have long-range periodic order as well as minimal traps and defects. Hence, organic semiconductor crystals provide a powerful tool for revealing the intrinsic properties, examining the structure-property relationships, demonstrating the important factors for high performance devices and uncovering fundamental physics in organic semiconductors. This review provides a comprehensive overview of the molecular packing, morphology and charge transport features of organic semiconductor crystals, the control of crystallization for achieving high quality crystals and the device physics in the three main applications. We hope that this comprehensive summary can give a clear picture of the state-of-art status and guide future work in this area.

Design of a Dry Dilution Refrigerator for MMC Gamma Detector Arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedrich, Stephan; Boyd, Stephen; Cantor, Robin

2017-04-03

The goal of this LCP is to develop an ultra-high resolution gamma detector based on magnetic microcalorimeters (MMCs) for accurate non-destructive analysis (NDA) of nuclear materials. For highest energy resolution, we will introduce erbium-doped silver (Ag:Er) as a novel sensor material to replace current Au:Er sensors. The detector sensitivity will be increased by developing arrays of 32 Ag:Er pixels read out by 16 SQUID preamplifiers. MMC detectors require operating temperatures of ~15 mK and thus the use of a dilution refrigerator, and the desire for user-friendly operation without cryogenic liquids requires that this refrigerator use pulse-tube pre-cooling to ~4 K.more » For long-term reliability, we intend to re-design the heat switch that is needed to apply the magnetizing current to the Ag:Er sensor and that used to fail in earlier designs after months of operation. A cryogenic Compton veto will be installed to reduce the spectral background of the MMC, especially at low energies where ultra-high energy resolution is most important. The goals for FY16 were 1) to purchase a liquid-cryogen-free dilution refrigerator and adapt it for MMC operation, and 2) to fabricate Ag:Er-based MMC γ-detectors with improved performance and optimize their response. This report discusses the design of the instruments, and progress in MMC detector fabrication. Details of the MMC fabrication have been discussed in an April 2016 report to DOE.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seña, N.; Dussan, A.; Mesa, F.

We have carried out first-principles spin polarized calculations to obtain comprehensive information regarding the structural, magnetic, and electronic properties of the Mn-doped GaSb compound with dopant concentrations: x = 0.062, 0.083, 0.125, 0.25, and 0.50. The plane-wave pseudopotential method was used in order to calculate total energies and electronic structures. It was found that the Mn{sub Ga} substitution is the most stable configuration with a formation energy of ∼1.60 eV/Mn-atom. The calculated density of states shows that the half-metallic ferromagnetism is energetically stable for all dopant concentrations with a total magnetization of about 4.0 μ{sub B}/Mn-atom. The results indicate that the magnetic ground statemore » originates from the strong hybridization between Mn-d and Sb-p states, which agree with previous studies on Mn-doped wide gap semiconductors. This study gives new clues to the fabrication of diluted magnetic semiconductors.« less

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.

Room Temperature Ferromagnetic Mn:Ge(001)

PubMed Central

Lungu, George Adrian; Stoflea, Laura Elena; Tanase, Liviu Cristian; Bucur, Ioana Cristina; Răduţoiu, Nicoleta; Vasiliu, Florin; Mercioniu, Ionel; Kuncser, Victor; Teodorescu, Cristian-Mihail

2014-01-01

We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 °C) exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed. PMID:28788444

Seed-induced growth of flower-like Au-Ni-ZnO metal-semiconductor hybrid nanocrystals for photocatalytic applications.

PubMed

Chen, Yuanzhi; Zeng, Deqian; Cortie, Michael B; Dowd, Annette; Guo, Huizhang; Wang, Junbao; Peng, Dong-Liang

2015-03-25

The combination of metal and semiconductor components in nanoscale to form a hybrid nanocrystal provides an important approach for achieving advanced functional materials with special optical, magnetic and photocatalytic functionalities. Here, a facile solution method is reported for the synthesis of Au-Ni-ZnO metal-semiconductor hybrid nanocrystals with a flower-like morphology and multifunctional properties. This synthetic strategy uses noble and magnetic metal Au@Ni nanocrystal seeds formed in situ to induce the heteroepitaxial growth of semiconducting ZnO nanopyramids onto the surface of metal cores. Evidence of epitaxial growth of ZnO{0001} facets on Ni {111} facets is observed on the heterojunction, even though there is a large lattice mismatch between the semiconducting and magnetic components. Adjustment of the amount of Au and Ni precursors can control the size and composition of the metal core, and consequently modify the surface plasmon resonance (SPR) and magnetic properties. Room-temperature superparamagnetic properties can be achieved by tuning the size of Ni core. The as-prepared Au-Ni-ZnO nanocrystals are strongly photocatalytic and can be separated and re-cycled by virtue of their magnetic properties. The simultaneous combination of plasmonic, semiconducting and magnetic components within a single hybrid nanocrystal furnishes it multifunctionalities that may find wide potential applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Motor-mediated microtubule self-organization in dilute and semi-dilute filament solutions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swaminathan, S.; Ziebert, F.; Aranson, I. S.

We study molecular motor-induced microtubule self-organization in dilute and semi-dilute filament solutions. In the dilute case, we use a probabilistic model of microtubule interaction via molecular motors to investigate microtubule bundle dynamics. Microtubules are modeled as polar rods interacting through fully inelastic, binary collisions. Our model indicates that initially disordered systems of interacting rods exhibit an orientational instability resulting in spontaneous ordering. We study the existence and dynamic interaction of microtubule bundles analytically and numerically. Our results reveal a long term attraction and coalescing of bundles indicating a clear coarsening in the system; microtubule bundles concentrate into fewer orientations onmore » a slow logarithmic time scale. In semi-dilute filament solutions, multiple motors can bind a filament to several others and, for a critical motor density, induce a transition to an ordered phase with a nonzero mean orientation. Motors attach to a pair of filaments and walk along the pair bringing them into closer alignment. We develop a spatially homogenous, mean-field theory that explicitly accounts for a force-dependent detachment rate of motors, which in turn affects the mean and the fluctuations of the net force acting on a filament. We show that the transition to the oriented state can be both continuous and discontinuous when the force-dependent detachment of motors is important.« less

Method of doping a semiconductor

DOEpatents

Yang, Chiang Y.; Rapp, Robert A.

1983-01-01

A method for doping semiconductor material. An interface is established between a solid electrolyte and a semiconductor to be doped. The electrolyte is chosen to be an ionic conductor of the selected impurity and the semiconductor material and electrolyte are jointly chosen so that any compound formed from the impurity and the semiconductor will have a free energy no lower than the electrolyte. A potential is then established across the interface so as to allow the impurity ions to diffuse into the semiconductor. In one embodiment the semiconductor and electrolyte may be heated so as to increase the diffusion coefficient.

Melt Stabilization of PbSnTe in a Magnetic Field

NASA Technical Reports Server (NTRS)

Fripp, Archibald L.; Debnam, William J.; Rosch, William; Chait, Arnon; Yao, Minwu; Szofran, Frank R.

1999-01-01

Both the experimental observation and numerical simulation indicate that the Bridgman growth of PbSnTe under the microgravity environment in space is still greatly influenced by buoyancy-induced convection. The application of a magnetic field during the semiconductor growth can dampen the convective flow in the metal-like melt. However, for Bridgman growth of PbSnTe on earth (with either vertical or horizontal configuration), both experimental observation and numerical modeling suggest that even with a strong magnetic furnace (5-Tesla constant axial magnetic field), the convective flow in the melt still cannot be sufficiently suppressed to reach the diffusion-controlled level. In order to completely dampen the buoyancy-induced convection on earth, estimates based on scaling analysis indicate that for common experimental conditions, an extremely high magnetic field is required, far beyond the capacity of the experimental apparatus currently available. Therefore, it is proposed that only the combination of microgravity environment and magnetic damping will produce the desired diffusion-controlled growth state for this particular material. The primary objectives of this study are to provide a quantitative understanding of the complex transport phenomena during solidification of non-dilute binarys, to furnish a numerical tool for furnace design and growth condition optimization, to provide estimates of the required magnetic field strength for low gravity growth, and to assess the role of magnetic damping for space and earth control of the double-diffusive convection. As an integral part of a NASA research program, our numerical simulation supports both the flight and ground-based experiments in an effort to bring together a complete picture of the complex physical phenomena involved in the crystal growth process. For Bridgman growth of PbSnTe under microgravity (with both vertical and horizontal configurations), the simulations suggest that a moderate axial magnetic

Randomly diluted eg orbital-ordered systems.

PubMed

Tanaka, T; Matsumoto, M; Ishihara, S

2005-12-31

Dilution effects on the long-range ordered state of the doubly degenerate e(g) orbital are investigated. Quenched impurities without the orbital degree of freedom are introduced in the orbital model where the long-range order is realized by the order-from-disorder mechanism. It is shown by Monte Carlo simulations and the cluster-expansion method that a decrease in the orbital-ordering temperature by dilution is substantially larger than that in the randomly diluted spin models. Tilting of orbital pseudospins around impurities is the essence of this dilution effect. The present theory provides a new viewpoint for the recent resonant x-ray scattering experiments in KCu(1-x)Zn(x)F(3).

B a 2 NiOs O 6 : A Dirac-Mott insulator with ferromagnetism near 100 K

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad

In this study, the ferromagnetic semiconductor Ba 2NiOsO 6 ( T mag ~ 100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm - 3m ; a = 8.0428 ( 1 ) Å], where the Ni 2+ and Os 6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os 6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >more » 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te ( T mag < 180 K ), the spin-gapless semiconductor Mn 2 CoAl ( T mag ~ 720 K ), and the ferromagnetic insulators EuO ( T mag ~ 70 K ) and Bi 3Cr 3O 11 ( T mag ~ 220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba 2NiOsO 6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.« less

B a2NiOs O6 : A Dirac-Mott insulator with ferromagnetism near 100 K

NASA Astrophysics Data System (ADS)

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad; Yuan, Ya-Hua; Shirako, Yuichi; Tsujimoto, Yoshihiro; Matsushita, Yoshitaka; Hu, Zhiwei; Kuo, Chang-Yang; Tjeng, Liu Hao; Pi, Tun-Wen; Soo, Yun-Liang; He, Jianfeng; Tanaka, Masahiko; Katsuya, Yoshio; Richter, Manuel; Yamaura, Kazunari

2016-12-01

The ferromagnetic semiconductor B a2NiOs O6 (Tmag˜100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [F m -3 m ; a =8.0428 (1 )Å ], where the N i2 + and O s6 + ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of O s6 + plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te (Tmag<180 K ), the spin-gapless semiconductor M n2CoAl (Tmag˜720 K ), and the ferromagnetic insulators EuO (Tmag˜70 K ) and B i3C r3O11 (Tmag˜220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of B a2NiOs O6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.

B a 2 NiOs O 6 : A Dirac-Mott insulator with ferromagnetism near 100 K

DOE PAGES

Feng, Hai L.; Calder, Stuart; Ghimire, Madhav Prasad; ...

2016-12-28

In this study, the ferromagnetic semiconductor Ba 2NiOsO 6 ( T mag ~ 100 K ) was synthesized at 6 GPa and 1500 °C. It crystallizes into a double perovskite structure [Fm - 3m ; a = 8.0428 ( 1 ) Å], where the Ni 2+ and Os 6+ ions are perfectly ordered at the perovskite B site. We show that the spin-orbit coupling of Os 6+ plays an essential role in opening the charge gap. The magnetic state was investigated by density functional theory calculations and powder neutron diffraction. The latter revealed a collinear ferromagnetic order in a >more » 21 kOe magnetic field at 5 K. The ferromagnetic gapped state is fundamentally different from that of known dilute magnetic semiconductors such as (Ga,Mn)As and (Cd,Mn)Te ( T mag < 180 K ), the spin-gapless semiconductor Mn 2 CoAl ( T mag ~ 720 K ), and the ferromagnetic insulators EuO ( T mag ~ 70 K ) and Bi 3Cr 3O 11 ( T mag ~ 220 K ). It is also qualitatively different from known ferrimagnetic insulators and semiconductors, which are characterized by an antiparallel spin arrangement. Our finding of the ferromagnetic semiconductivity of Ba 2NiOsO 6 should increase interest in the platinum group oxides, because this alternative class of materials should be useful in the development of spintronic, quantum magnetic, and related devices.« less

Selection of peptides for binding semiconductor and magnetic materials for the purpose of organizing nanoscaled materials

NASA Astrophysics Data System (ADS)

Whaley, Sandra Renee

A peptide combinatorial approach, also known as phage display, was used to isolate peptides with the ability to bind semiconductor (GaAs, GaN, and InP) and magnetic (Fe2O3 and Fe3O4) materials. The commercially available combinatorial libraries contain randomized peptides either twelve (Ph.D-12(TM)) or seven (Ph.D-C7C(TM)) amino acids in length. The peptides are displayed on the pIII protein of M13 bacteriophage, which have been imaged by atomic force microscopy and transmission electron microscopy. After seven rounds of phage selection with a constrained seven amino acid sequence library (Ph.D-C7C(TM)), two sequences were isolated for binding Fe3O4 (MG-127 and MG-78). The haematite surface was screened with the same library and four unique sequences were isolated after six rounds of selection (HM-95, HM-101, HM-103, and HM-111). According to binding experiments (MG-78 v. MG-127 on Fe3O 4, MG-127 v. HM-95 on Fe3O4 and Fe2O 3, and MG-127 v. HM-95 on gamma-Fe2O3), the MG-127 clone had the highest affinity for iron oxide surfaces (magnetite, haematite, and maghemite) among the clones tested. The Fe3O 4 clone MG-127 displayed the ability to organize Fe3O 4 nanoparticles along bundles of phage. The synthetic peptide analog of this clone was used in the organization of nanoparticles onto the surface of latex beads. The surfaces of the III-V semiconductors were studied using x-ray photoelectron spectroscopy to determine their reactivity in the aqueous conditions used for phage selection. The GaN surface was shown to oxidize the least under these conditions, aiding in the ability to isolate a consensus amino acid sequence responsible for binding to this surface. The G1-3 clone isolated for binding the GaAs (100) surface displayed preferential binding to the GaAs (100) surface over Si (100), GaAs (111) A, GaAs (111) B, and AlGaAs. The synthetic peptide analog of the G12-3 clone was found to preferentially bind to GaAs (100) over either GaAs (111) surfaces or InP (100). This

Zero-field random-field effect in diluted triangular lattice antiferromagnet CuFe1-xAlxO2

NASA Astrophysics Data System (ADS)

Nakajima, T.; Mitsuda, S.; Kitagawa, K.; Terada, N.; Komiya, T.; Noda, Y.

2007-04-01

We performed neutron scattering experiments on a diluted triangular lattice antiferromagnet (TLA), CuFe1-xAlxO2 with x = 0.10. The detailed analysis of the scattering profiles revealed that the scattering function of magnetic reflection is described as the sum of a Lorentzian term and a Lorentzian-squared term with anisotropic width. The Lorentzian-squared term dominating at low temperature is indicative of the domain state in the prototypical random-field Ising model. Taking account of the sinusoidally amplitude-modulated magnetic structure with incommensurate wavenumber in CuFe1-xAlxO2 with x = 0.10, we conclude that the effective random field arises even at zero field, owing to the combination of site-random magnetic vacancies and the sinusoidal structure that is regarded as a partially disordered (PD) structure in a wide sense, as reported in the typical three-sublattice PD phase of a diluted Ising TLA, CsCo0.83Mg0.17Br3 (van Duijn et al 2004 Phys. Rev. Lett. 92 077202). While the previous study revealed the existence of a domain state in CsCo0.83Mg0.17Br3 by detecting magnetic reflections specific to the spin configuration near the domain walls, our present study revealed the existence of a domain state in CuFe1-xAlxO2 (x = 0.10) by determination of the functional form of the scattering function.

Rare earth doped III-nitride semiconductors for spintronic and optoelectronic applications (Conference Presentation)

NASA Astrophysics Data System (ADS)

Palai, Ratnakar

2016-10-01

Since last four decades the information and communication technologies are relying on the semiconductor materials. Currently a great deal of attention is being focused on adding spin degree-of-freedom into semiconductor to create a new area of solid-state electronics, called spintronics. In spintronics not only the current but also its spin state is controlled. Such materials need to be good semiconductors for easy integration in typical integrated circuits with high sensitivity to the spin orientation, especially room temperature ferromagnetism being an important desirable property. GaN is considered to be the most important semiconductor after silicon. It is widely used for the production of green, blue, UV, and white LEDs in full color displays, traffic lights, automotive lightings, and general room lighting using white LEDs. GaN-based systems also show promise for microwave and high power electronics intended for radar, satellite, wireless base stations and spintronic applications. Rare earth (Yb, Eu, Er, and Tm) doped GaN shows many interesting optoelectronic and magnetoptic properties e. g. sharp emission from UV through visible to IR, radiation hardness, and ferromagnetism. The talk will be focused on fabrication, optoelectronic (photoluminescence, cathodeluminescence, magnetic, and x-ray photoelectron spectroscopy) properties of some rare earth doped GaN and InGaN semiconductor nanostructures grown by plasma assisted molecular beam epitaxy (MBE) and future applications.

Magnetoconductance signatures of subband structure in semiconductor nanowires

NASA Astrophysics Data System (ADS)

Holloway, Gregory; Haapamaki, Chris; Lapierre, Ray; Baugh, Jonathan

2015-03-01

Understanding the subband structure due to radial confinement in semiconductor nanowires can benefit technologies ranging from optical sensors to quantum information processing. An axial magnetic field couples to the orbital angular momentum, giving rise to non-trivial features in electronic transport as a function of magnetic field. Previous reports focused on conduction electrons confined to a thin shell near the nanowire surface, which lead to flux-periodic energies and conductance oscillations. Here, we calculate the eigenstates for more general radial potentials with moderate to low surface band bending such that electrons are distributed more uniformly across the nanowire cross-section. It is found that the energy spectrum becomes aperiodic in both gate voltage and magnetic field as the radial potential becomes flatter. The behavior of an energy level is dictated by its angular momentum, and this allows, in principle, each state to be identified based on its dependence on magnetic field and the chemical potential. We experimentally investigate a short-channel InAs nanowire FET in search of conductance features that reveal this subband structure. A quantitative measure for assigning conductance features to specific transverse states is introduced and applied to this device.

Measuring Dilution of Microbicide Gels with Optical Imaging

PubMed Central

Drake, Tyler K.; Shah, Tejen; Peters, Jennifer J.; Wax, Adam; Katz, David F.

2013-01-01

We present a novel approach for measuring topical microbicide gel dilution using optical imaging. The approach compares gel thickness measurements from fluorimetry and multiplexed low coherence interferometry in order to calculate dilution of a gel. As a microbicide gel becomes diluted at fixed thickness, its mLCI thickness measurement remains constant, while the fluorimetry signal decreases in intensity. The difference between the two measurements is related to the extent of gel dilution. These two optical modalities are implemented in a single endoscopic instrument that enables simultaneous data collection. A preliminary validation study was performed with in vitro placebo gel measurements taken in a controlled test socket. It was found that change in slope of the regression line between fluorimetry and mLCI based measurements indicates dilution. A dilution calibration curve was then generated by repeating the test socket measurements with serial dilutions of placebo gel with vaginal fluid simulant. This methodology can provide valuable dilution information on candidate microbicide products, which could substantially enhance our understanding of their in vivo functioning. PMID:24340006

Structural transformations in diluted micellar and lamellar systems

NASA Astrophysics Data System (ADS)

Zelaya-Rincon, Blanca

The role of dilution by artificial hard water on nanostructures present in body wash samples provided by Procter and Gamble were investigated using time-resolved cryogenic transmission electron microscopy (cryo-TEM). Samples with and without perfume were examined at 10X, 20X, and 50X dilution. Micellar samples transformed to mostly unilamellar vesicles at 50X dilution, in contrast to the micelle to monomer transition seen in typical samples. At lower dilutions, a change in morphology from spherical to wormlike micelles was observed. For lamellar samples, lower dilution ratios show tightly packed multilamellar vesicles, while higher dilution ratios show more dispersed vesicles with less bilayers. Nanostructural transformations upon dilution were attributed to changes in curvature/packing parameters, which occurred due to dilution with hard water and addition of perfume. The systems experience changes in curvature in order to maintain equilibrium. Also, the addition of perfume in the lamellar samples caused an increase in the number of bilayers present in multilamellar vesicles, because of its role in increasing the packing parameter in the system.

Magnetic properties of spinels GeNi2-xCoxO4 systems: Green's function and high-temperature series expansions

NASA Astrophysics Data System (ADS)

El Grini, A.; Salmi, S.; Masrour, R.; Hamedoun, M.; Bouslykhane, K.; Marzouk, A.; Hourmatallah, A.; Benzakour, N.

2018-06-01

The Green's function theory and high-temperature series expansions technical have been developed for magnetic systems GeNi2-xCoxO4. We have applied the Green's function theory to evaluate thermal magnetization and magnetic susceptibility for different values of magnetic field and dilution x, considering all components of the magnetization when an external magnetic field is applied in (x,z)-plane. The second theory combined with the Padé approximants method for a randomly diluted Heisenberg magnet is used to deduce the magnetic phase diagram of GeNi2 - xCoxO4 systems. The critical exponents ? and ? associated with the magnetic susceptibility ? and the correlation length ξ, respectively, have been deduced. The theoretical results are compared with those given by magnetic measurements.

Variable temperature semiconductor film deposition

DOEpatents

Li, X.; Sheldon, P.

1998-01-27

A method of depositing a semiconductor material on a substrate is disclosed. The method sequentially comprises (a) providing the semiconductor material in a depositable state such as a vapor for deposition on the substrate; (b) depositing the semiconductor material on the substrate while heating the substrate to a first temperature sufficient to cause the semiconductor material to form a first film layer having a first grain size; (c) continually depositing the semiconductor material on the substrate while cooling the substrate to a second temperature sufficient to cause the semiconductor material to form a second film layer deposited on the first film layer and having a second grain size smaller than the first grain size; and (d) raising the substrate temperature, while either continuing or not continuing to deposit semiconductor material to form a third film layer, to thereby anneal the film layers into a single layer having favorable efficiency characteristics in photovoltaic applications. A preferred semiconductor material is cadmium telluride deposited on a glass/tin oxide substrate already having thereon a film layer of cadmium sulfide.

Variable temperature semiconductor film deposition

DOEpatents

Li, Xiaonan; Sheldon, Peter

1998-01-01

A method of depositing a semiconductor material on a substrate. The method sequentially comprises (a) providing the semiconductor material in a depositable state such as a vapor for deposition on the substrate; (b) depositing the semiconductor material on the substrate while heating the substrate to a first temperature sufficient to cause the semiconductor material to form a first film layer having a first grain size; (c) continually depositing the semiconductor material on the substrate while cooling the substrate to a second temperature sufficient to cause the semiconductor material to form a second film layer deposited on the first film layer and having a second grain size smaller than the first grain size; and (d) raising the substrate temperature, while either continuing or not continuing to deposit semiconductor material to form a third film layer, to thereby anneal the film layers into a single layer having favorable efficiency characteristics in photovoltaic applications. A preferred semiconductor material is cadmium telluride deposited on a glass/tin oxide substrate already having thereon a film layer of cadmium sulfide.

Controlling Thermodynamic Properties of Ferromagnetic Group-IV Graphene-Like Nanosheets by Dilute Charged Impurity

NASA Astrophysics Data System (ADS)

Yarmohammadi, Mohsen; Mirabbaszadeh, Kavoos

2017-05-01

Using the Kane-Mele Hamiltonian, Dirac theory and self-consistent Born approximation, we investigate the effect of dilute charged impurity on the electronic heat capacity and magnetic susceptibility of two-dimensional ferromagnetic honeycomb structure of group-IV elements including silicene, germanene and stanene within the Green’s function approach. We also find these quantities in the presence of applied external electric field. Our results show that the silicene (stanene) has the maximum (minimum) heat capacity and magnetic susceptibility at uniform electric fields. From the behavior of theses quantities, the band gap has been changed with impurity concentration, impurity scattering strength and electric field. The analysis on the impurity-dependent magnetic susceptibility curves shows a phase transition from ferromagnetic to paramagnetic and antiferromagnetic phases. Interestingly, electronic heat capacity increases (decreases) with impurity concentration in silicene (germanene and stanene) structure.

Electric-field switching of two-dimensional van der Waals magnets

NASA Astrophysics Data System (ADS)

Jiang, Shengwei; Shan, Jie; Mak, Kin Fai

2018-05-01

Controlling magnetism by purely electrical means is a key challenge to better information technology1. A variety of material systems, including ferromagnetic (FM) metals2-4, FM semiconductors5, multiferroics6-8 and magnetoelectric (ME) materials9,10, have been explored for the electric-field control of magnetism. The recent discovery of two-dimensional (2D) van der Waals magnets11,12 has opened a new door for the electrical control of magnetism at the nanometre scale through a van der Waals heterostructure device platform13. Here we demonstrate the control of magnetism in bilayer CrI3, an antiferromagnetic (AFM) semiconductor in its ground state12, by the application of small gate voltages in field-effect devices and the detection of magnetization using magnetic circular dichroism (MCD) microscopy. The applied electric field creates an interlayer potential difference, which results in a large linear ME effect, whose sign depends on the interlayer AFM order. We also achieve a complete and reversible electrical switching between the interlayer AFM and FM states in the vicinity of the interlayer spin-flip transition. The effect originates from the electric-field dependence of the interlayer exchange bias.

Back-side readout semiconductor photomultiplier

DOEpatents

Choong, Woon-Seng; Holland, Stephen E

2014-05-20

This disclosure provides systems, methods, and apparatus related to semiconductor photomultipliers. In one aspect, a device includes a p-type semiconductor substrate, the p-type semiconductor substrate having a first side and a second side, the first side of the p-type semiconductor substrate defining a recess, and the second side of the p-type semiconductor substrate being doped with n-type ions. A conductive material is disposed in the recess. A p-type epitaxial layer is disposed on the second side of the p-type semiconductor substrate. The p-type epitaxial layer includes a first region proximate the p-type semiconductor substrate, the first region being implanted with p-type ions at a higher doping level than the p-type epitaxial layer, and a second region disposed on the first region, the second region being doped with p-type ions at a higher doping level than the first region.

Estimation method for serial dilution experiments.

PubMed

Ben-David, Avishai; Davidson, Charles E

2014-12-01

Titration of microorganisms in infectious or environmental samples is a corner stone of quantitative microbiology. A simple method is presented to estimate the microbial counts obtained with the serial dilution technique for microorganisms that can grow on bacteriological media and develop into a colony. The number (concentration) of viable microbial organisms is estimated from a single dilution plate (assay) without a need for replicate plates. Our method selects the best agar plate with which to estimate the microbial counts, and takes into account the colony size and plate area that both contribute to the likelihood of miscounting the number of colonies on a plate. The estimate of the optimal count given by our method can be used to narrow the search for the best (optimal) dilution plate and saves time. The required inputs are the plate size, the microbial colony size, and the serial dilution factors. The proposed approach shows relative accuracy well within ±0.1log10 from data produced by computer simulations. The method maintains this accuracy even in the presence of dilution errors of up to 10% (for both the aliquot and diluent volumes), microbial counts between 10(4) and 10(12) colony-forming units, dilution ratios from 2 to 100, and plate size to colony size ratios between 6.25 to 200. Published by Elsevier B.V.

Avian plasma chemistry analysis using diluted samples.

PubMed

Waldoch, Jennifer; Wack, Raymund; Christopher, Mary

2009-12-01

Clinical chemistry tests are essential for the diagnosis and monitoring of disease in birds. The small volume of blood that can be obtained from many avian species limits the use of routine in-house chemistry analyzers. The aim of this study was to examine the accuracy and precision of avian plasma chemistry values obtained by use of a benchtop analyzer in samples diluted with sterile water, as compared with undiluted samples. Whole blood samples were collected from 13 clinically healthy thick-billed parrots (Rhynchopsitta pachyrhyncha). The samples were placed in lithium heparin tubes and centrifuged and the plasma decanted. One aliquot was analyzed immediately using a VetScan benchtop analyzer with an avian-reptile-specific rotor that included 12 analytes. The remainder of the plasma was divided into two aliquots and stored at -80 degrees C until analysis. One of these aliquots was diluted 1:1, 1:1.5, 1:2, and 1:2.5 with sterile water to give final dilutions of 1:2, 1:2.5, 1:3, and 1:3.5, respectively. The other aliquot was pooled with the 12 other samples to create a plasma pool. The undiluted plasma pool and two final dilutions (1:2 and 1:3) of the pooled plasma were analyzed in replicate (n = 20) to determine intra- and interassay imprecision. Each dilution was analyzed using the avian-reptile rotor and the results multiplied by the appropriate dilution factor to obtain the final result. Significant differences were observed in clinical chemistry results obtained from diluted plasma samples for all analytes except aspartate aminotransferase, creatine kinase, and glucose. Uric acid concentration was not significantly different at dilutions of up to 1:3. Bile acids, globulins, and sodium concentrations were below the limit of detection in all diluted samples and were not statistically analyzed. Based on these results, dilution with sterile water is not recommended for biochemical analysis of avian plasma using the VetScan benchtop analyzer.

Hydrogenated arsenenes as planar magnet and Dirac material

NASA Astrophysics Data System (ADS)

Zhang, Shengli; Hu, Yonghong; Hu, Ziyu; Cai, Bo; Zeng, Haibo

2015-07-01

Arsenene and antimonene are predicted to have 2.49 and 2.28 eV band gaps, which have aroused intense interest in the two-dimensional (2D) semiconductors for nanoelectronic and optoelectronic devices. Here, the hydrogenated arsenenes are reported to be planar magnet and 2D Dirac materials based on comprehensive first-principles calculations. The semi-hydrogenated (SH) arsenene is found to be a quasi-planar magnet, while the fully hydrogenated (FH) arsenene is a planar Dirac material. The buckling height of pristine arsenene is greatly decreased by the hydrogenation, resulting in a planar and relatively low-mass-density sheet. The electronic structures of arsenene are also evidently altered after hydrogenating from wide-band-gap semiconductor to metallic material for SH arsenene, and then to Dirac material for FH arsenene. The SH arsenene has an obvious magnetism, mainly contributed by the p orbital of the unsaturated As atom. Such magnetic and Dirac materials modified by hydrogenation of arsenene may have potential applications in future optoelectronic and spintronic devices.

Spin-orbit induced electronic spin separation in semiconductor nanostructures.

PubMed

Kohda, Makoto; Nakamura, Shuji; Nishihara, Yoshitaka; Kobayashi, Kensuke; Ono, Teruo; Ohe, Jun-ichiro; Tokura, Yasuhiro; Mineno, Taiki; Nitta, Junsaku

2012-01-01

The demonstration of quantized spin splitting by Stern and Gerlach is one of the most important experiments in modern physics. Their discovery was the precursor of recent developments in spin-based technologies. Although electrical spin separation of charged particles is fundamental in spintronics, in non-uniform magnetic fields it has been difficult to separate the spin states of charged particles due to the Lorentz force, as well as to the insufficient and uncontrollable field gradients. Here we demonstrate electronic spin separation in a semiconductor nanostructure. To avoid the Lorentz force, which is inevitably induced when an external magnetic field is applied, we utilized the effective non-uniform magnetic field which originates from the Rashba spin-orbit interaction in an InGaAs-based heterostructure. Using a Stern-Gerlach-inspired mechanism, together with a quantum point contact, we obtained field gradients of 10(8) T m(-1) resulting in a highly polarized spin current.

Spin–orbit induced electronic spin separation in semiconductor nanostructures

PubMed Central

Kohda, Makoto; Nakamura, Shuji; Nishihara, Yoshitaka; Kobayashi, Kensuke; Ono, Teruo; Ohe, Jun-ichiro; Tokura, Yasuhiro; Mineno, Taiki; Nitta, Junsaku

2012-01-01

The demonstration of quantized spin splitting by Stern and Gerlach is one of the most important experiments in modern physics. Their discovery was the precursor of recent developments in spin-based technologies. Although electrical spin separation of charged particles is fundamental in spintronics, in non-uniform magnetic fields it has been difficult to separate the spin states of charged particles due to the Lorentz force, as well as to the insufficient and uncontrollable field gradients. Here we demonstrate electronic spin separation in a semiconductor nanostructure. To avoid the Lorentz force, which is inevitably induced when an external magnetic field is applied, we utilized the effective non-uniform magnetic field which originates from the Rashba spin–orbit interaction in an InGaAs-based heterostructure. Using a Stern–Gerlach-inspired mechanism, together with a quantum point contact, we obtained field gradients of 108 T m−1 resulting in a highly polarized spin current. PMID:23011136

First Principles Electronic Structure of Mn doped GaAs, GaP, and GaN Semiconductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schulthess, Thomas C; Temmerman, Walter M; Szotek, Zdzislawa

We present first-principles electronic structure calculations of Mn doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extractingmore » binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn-d levels in GaAs. We find good agreement between computed values and estimates from photoemisison experiments.« less

Dilution Refrigerator for Nuclear Refrigeration and Cryogenic Thermometry Studies

NASA Astrophysics Data System (ADS)

Nakagawa, Hisashi; Hata, Tohru

2014-07-01

This study explores the design and construction of an ultra-low temperature facility in order to realize the Provisional low-temperature scale from 0.9 mK to 1 K (PLTS-2000) in Japan, to disseminate its use through calibration services, and to study thermometry at low temperatures below 1 K. To this end, a dilution refrigerator was constructed in-house that has four sintered silver discrete heat exchangers for use as a precooling stage of a copper nuclear demagnetization stage. A melting curve thermometer attached to the mixing chamber flange could be cooled continuously to 4.0 mK using the refrigerator. The dependence of minimum temperatures on circulation rates can be explained by the calculation of Frossati's formula based on a perfect continuous counterflow heat exchanger model, assuming that the Kapitza resistance has a temperature dependence. Residual heat leakage to the mixing chamber was estimated to be around 86 nW. A nuclear demagnetization cryostat with a nuclear stage containing an effective amount of copper (51 mol in a 9 T magnetic field) is under construction, and we will presently start to work toward the realization of the PLTS-2000. In this article, the design and performance of the dilution refrigerator are reported.

Effect of an external magnetic field on the mass attenuation coefficients of p-Si and n-Si

NASA Astrophysics Data System (ADS)

Yılmaz, D.; Önder, P.

2018-05-01

In this study, the mass attenuation coefficients of p-Si and n-Si semiconductor samples have been determined in an external magnetic field. The semiconductor samples were located to the external magnetic field of intensities 0.2 T, 0.4 T, 0.6 T and 0.8 T. The samples were bombarded by 59.5 keV, 80.1 keV, 121.8 keV and 244.7 keV gamma-rays emitted from Am241, Ba133 and Eu152 radioactive sources. The transmitted photons were detected by a CdTe detector. It was observed that the mass attenuation coefficients of p-Si and n-Si semiconductor samples decrease with increasing gamma-ray energy. Also, the mass attenuation coefficients of the samples increase with applying magnetic field intensity.

Stability of purified tuberculin in high dilution

PubMed Central

Magnus, Knut; Guld, Johannes; Waaler, Hans; Magnusson, Mogens

1958-01-01

The authors have investigated the effect of storage on the potency of 5 TU dilutions (5 TU per 0.1 ml) of the purified tuberculin RT 19-21 (Statens Seruminstitut, Copenhagen). Dilutions stored at 2-4°C, 20°C and 37°C for different periods up to 18 months were compared by intradermal testing. About 900 BCG-vaccinated schoolchildren were given duplicate tests and in addition 500 tests were made in BCG-vaccinated guinea-pigs. The results showed unexpected variability. It appeared that this variability was due to unsystematic variations in potency both between dilutions prepared at different times and between ampoules of the same dilution. Because of this variability only limited conclusions could be drawn. At 2-4°C the effect of storage seemed to be very slight, the potency of the dilutions being reduced by less than 25% after 18 months. At the higher temperatures, the decrease in activity was more rapid. Nevertheless, the dilutions could be stored at room temperature (20°C) for some months without any practically significant loss of potency. PMID:13618718

Plated lamination structures for integrated magnetic devices

DOEpatents

Webb, Bucknell C.

2014-06-17

Semiconductor integrated magnetic devices such as inductors, transformers, etc., having laminated magnetic-insulator stack structures are provided, wherein the laminated magnetic-insulator stack structures are formed using electroplating techniques. For example, an integrated laminated magnetic device includes a multilayer stack structure having alternating magnetic and insulating layers formed on a substrate, wherein each magnetic layer in the multilayer stack structure is separated from another magnetic layer in the multilayer stack structure by an insulating layer, and a local shorting structure to electrically connect each magnetic layer in the multilayer stack structure to an underlying magnetic layer in the multilayer stack structure to facilitate electroplating of the magnetic layers using an underlying conductive layer (magnetic or seed layer) in the stack as an electrical cathode/anode for each electroplated magnetic layer in the stack structure.

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.

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.

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…

Wafer-fused semiconductor radiation detector

DOEpatents

Lee, Edwin Y.; James, Ralph B.

2002-01-01

Wafer-fused semiconductor radiation detector useful for gamma-ray and x-ray spectrometers and imaging systems. The detector is fabricated using wafer fusion to insert an electrically conductive grid, typically comprising a metal, between two solid semiconductor pieces, one having a cathode (negative electrode) and the other having an anode (positive electrode). The wafer fused semiconductor radiation detector functions like the commonly used Frisch grid radiation detector, in which an electrically conductive grid is inserted in high vacuum between the cathode and the anode. The wafer-fused semiconductor radiation detector can be fabricated using the same or two different semiconductor materials of different sizes and of the same or different thicknesses; and it may utilize a wide range of metals, or other electrically conducting materials, to form the grid, to optimize the detector performance, without being constrained by structural dissimilarity of the individual parts. The wafer-fused detector is basically formed, for example, by etching spaced grooves across one end of one of two pieces of semiconductor materials, partially filling the grooves with a selected electrical conductor which forms a grid electrode, and then fusing the grooved end of the one semiconductor piece to an end of the other semiconductor piece with a cathode and an anode being formed on opposite ends of the semiconductor pieces.

Capital investment in semiconductors: The lifeblood of the US semiconductor industry

NASA Astrophysics Data System (ADS)

Finan, William F.

1990-09-01

An analysis is given of four proposals designed to improve capital formation for U.S. industry in general, and the semiconductor industry in particular. The National Advisory Committee on Semiconductors recommendations were to make the current research and experimentation (R and E) tax credit more effective, to reduce taxes on capital gains, to increase personal savings incentives, and to improve semiconductor manufacturing equipment depreciation rules. The results of the qualitative analysis of the proposals as well as a description of the methodology employed are given.

Heterogeneous immunoassays using magnetic beads on a digital microfluidic platform.

PubMed

Sista, Ramakrishna S; Eckhardt, Allen E; Srinivasan, Vijay; Pollack, Michael G; Palanki, Srinivas; Pamula, Vamsee K

2008-12-01

A digital microfluidic platform for performing heterogeneous sandwich immunoassays based on efficient handling of magnetic beads is presented in this paper. This approach is based on manipulation of discrete droplets of samples and reagents using electrowetting without the need for channels where the droplets are free to move laterally. Droplet-based manipulation of magnetic beads therefore does not suffer from clogging of channels. Immunoassays on a digital microfluidic platform require the following basic operations: bead attraction, bead washing, bead retention, and bead resuspension. Several parameters such as magnetic field strength, pull force, position, and buffer composition were studied for effective bead operations. Dilution-based washing of magnetic beads was demonstrated by immobilizing the magnetic beads using a permanent magnet and splitting the excess supernatant using electrowetting. Almost 100% bead retention was achieved after 7776-fold dilution-based washing of the supernatant. Efficient resuspension of magnetic beads was achieved by transporting a droplet with magnetic beads across five electrodes on the platform and exploiting the flow patterns within the droplet to resuspend the beads. All the magnetic-bead droplet operations were integrated together to generate standard curves for sandwich heterogeneous immunoassays on human insulin and interleukin-6 (IL-6) with a total time to result of 7 min for each assay.

Heterogeneous Immunoassays Using Magnetic beads On a Digital Microfluidic Platform

PubMed Central

Sista, Ramakrishna S.; Eckhardt, Allen E.; Srinivasan, Vijay; Pollack, Michael G.; Palanki, Srinivas; Pamula, Vamsee K.

2009-01-01

A digital microfluidic platform for performing heterogeneous sandwich immunoassays based on efficient handling of magnetic beads is presented in this paper. This approach is based on manipulation of discrete droplets of samples and reagents using electrowetting without the need for channels where the droplets are free to move laterally. Droplet-based manipulation of magnetic beads therefore does not suffer from clogging of channels. Immunoassays on a digital microfluidic platform require the following basic operations: bead attraction, bead washing, bead retention, and bead resuspension. Several parameters such as magnetic field strength, pull force, position, and buffer composition were studied for effective bead operations. Dilution-based washing of magnetic beads was demonstrated by immobilizing the magnetic beads using a permanent magnet and splitting the excess supernatant using electrowetting. Almost 100% bead retention was achieved after 7776 fold dilution-based washing of the supernatant. Efficient resuspension of magnetic beads was achieved by transporting a droplet with magnetic beads across five electrodes on the platform and exploiting the flow patterns within the droplet to resuspend the beads. All the magnetic-bead droplet operations were integrated together to generate standard curves for sandwich heterogeneous immunoassays on Human Insulin and Interleukin-6 (IL-6) with a total time to result of seven minutes for each assay. PMID:19023486

Magnetic and photocatalytic studies on Zn1-xMgxFe2O4 nanocolloids synthesized by solvothermal reflux method.

PubMed

Manohar, A; Krishnamoorthi, C

2017-12-01

Biocompatible magnetic semiconductor Zn 1-x Mg x Fe 2 O 4 (x=0, 0.1, 0.3, 0.5 & 0.7) nanoparticles of around 10nm diameter were synthesized by solvothermal reflux method. The method produces well separated and narrow size distributed nanoparticles. Crystal structure, morphology, particles surface properties, surfactant quantity, colloidal stability, magnetic properties and photocatalytic properties of the synthesized nanoparticles were studied. Different characterizations confirmed that all compounds were single crystals and superparamagnetic at room temperature. Saturation mass magnetization (M s =57.5emu/g) enhances with substituent Mg 2+ concentration due to promotion of mixed spinel (normal and inverse) structure. Photocatalytic activity of all synthesized magnetic semiconductor nanoparticles were studied through methylene blue degradation. The degradation of 98% methylene blue was observed on 60 min irradiation of light. It is observed that photocatalytic activity slightly enhances with substituent Mg 2+ concentration. The synthesized biocompatible magnetic semiconductor nanoparticles can be utilized as photocatalysts and could also be recycled and separated by applying an external magnetic field. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of structural defects on electronic and magnetic properties of ZrS2 monolayer

NASA Astrophysics Data System (ADS)

Wang, Haiyang; Zhao, Xu; Gao, Yonghui; Wang, Tianxing; Wei, Shuyi

2018-04-01

We aimed at ten configurations of vacancy defects and used the first-principles methods based on density functional theory to research electronic and magnetic properties of ZrS2 monolayer. Results show that the system of two-zirconium vacancy (V2zr) and one Zr atom + one S atom vacancy (V1Zr+1S) can induce to total spin magnetic moment of 0.245μB and 0.196μB, respectively. In addition, three and six S atoms vacancy can induce corresponding system to manifest spin magnetic moment of 0.728μB and 3.311μB, respectively. In S atom vacancy defects, vacancy defects can transform the system from semiconductor to metal, several of the Zr atoms and adjacent S atoms display antiferromagnetism coupling in three apart S atom vacancy defects. Vacancy defects can make the intrisic monolayer ZrS2 transform semiconductor into metal. These results are important for the achievement of spin devices based on ZrS2 semiconductor.

Tunneling conductance in semiconductor-superconductor hybrid structures

NASA Astrophysics Data System (ADS)

Stenger, John; Stanescu, Tudor D.

2017-12-01

We study the differential conductance for charge tunneling into a semiconductor wire-superconductor hybrid structure, which is actively investigated as a possible scheme for realizing topological superconductivity and Majorana zero modes. The calculations are done based on a tight-binding model of the heterostructure using both a Blonder-Tinkham-Klapwijk approach and a Keldysh nonequilibrium Green's function method. The dependence of various tunneling conductance features on the coupling strength between the semiconductor and the superconductor, the tunnel barrier height, and temperature is systematically investigated. We find that treating the parent superconductor as an active component of the system, rather than a passive source of Cooper pairs, has qualitative consequences regarding the low-energy behavior of the differential conductance. In particular, the presence of subgap states in the parent superconductor, due to disorder and finite magnetic fields, leads to characteristic particle-hole asymmetric features and to the breakdown of the quantization of the zero-bias peak associated with the presence of Majorana zero modes localized at the ends of the wire. The implications of these findings for the effort toward the realization of Majorana bound states with true non-Abelian properties are discussed.

EDITORIAL The 23rd Nordic Semiconductor Meeting The 23rd Nordic Semiconductor Meeting

NASA Astrophysics Data System (ADS)

Ólafsson, Sveinn; Sveinbjörnsson, Einar

2010-12-01

A Nordic Semiconductor Meeting is held every other year with the venue rotating amongst the Nordic countries of Denmark, Finland, Iceland, Norway and Sweden. The focus of these meetings remains 'original research and science being carried out on semiconductor materials, devices and systems'. Reports on industrial activity have usually featured. The topics have ranged from fundamental research on point defects in a semiconductor to system architecture of semiconductor electronic devices. Proceedings from these events are regularly published as a topical issue of Physica Scripta. All of the papers in this topical issue have undergone critical peer review and we wish to thank the reviewers and the authors for their cooperation, which has been instrumental in meeting the high scientific standards and quality of the series. This meeting of the 23rd Nordic Semiconductor community, NSM 2009, was held at Háskólatorg at the campus of the University of Iceland, Reykjavik, Iceland, 14-17 June 2009. Support was provided by the University of Iceland. Almost 50 participants presented a broad range of topics covering semiconductor materials and devices as well as related material science interests. The conference provided a forum for Nordic and international scientists to present and discuss new results and ideas concerning the fundamentals and applications of semiconductor materials. The meeting aim was to advance the progress of Nordic science and thus aid in future worldwide technological advances concerning technology, education, energy and the environment. Topics Theory and fundamental physics of semiconductors Emerging semiconductor technologies (for example III-V integration on Si, novel Si devices, graphene) Energy and semiconductors Optical phenomena and optical devices MEMS and sensors Program 14 June Registration 13:00-17:00 15 June Meeting program 09:30-17:00 and Poster Session I 16 June Meeting program 09:30-17:00 and Poster Session II 17 June Excursion and dinner

Magnetic tunnel spin injectors for spintronics

NASA Astrophysics Data System (ADS)

Wang, Roger

Research in spin-based electronics, or "spintronics", has a universal goal to develop applications for electron spin in a broad range of electronics and strives to produce low power nanoscale devices. Spin injection into semiconductors is an important initial step in the development of spintronic devices, with the goal to create a highly spin polarized population of electrons inside a semiconductor at room temperature for study, characterization, and manipulation. This dissertation investigates magnetic tunnel spin injectors that aim to meet the spin injection requirements needed for potential spintronic devices. Magnetism and spin are inherently related, and chapter 1 provides an introduction on magnetic tunneling and spintronics. Chapter 2 then describes the fabrication of the spin injector structures studied in this dissertation, and also illustrates the optical spin detection technique that correlates the measured electroluminescence polarization from quantum wells to the electron spin polarization inside the semiconductor. Chapter 3 reports the spin injection from the magnetic tunnel transistor (MTT) spin injector, which is capable of producing highly spin polarized tunneling currents by spin selective scattering in its multilayer structure. The MTT achieves ˜10% lower bound injected spin polarization in GaAs at 1.4 K. Chapter 4 reports the spin injection from CoFe-MgO(100) tunnel spin injectors, where spin dependent tunneling through MgO(100) produces highly spin polarized tunneling currents. These structures achieve lower bound spin polarizations exceeding 50% at 100 K and 30% in GaAs at 290 K. The CoFe-MgO spin injectors also demonstrate excellent thermal stability, maintaining high injection efficiencies even after exposure to temperatures of up to 400 C. Bias voltage and temperature dependent studies on these structures indicate a significant dependence of the electroluminescence polarization on the spin and carrier recombination lifetimes inside the

Helium 3/Helium 4 dilution cryocooler for space

NASA Technical Reports Server (NTRS)

Hendricks, John B.; Dingus, Michael L.

1991-01-01

Prototype dilution cryocoolers based on dilution refrigeration and adiabatic demagnetization refrigeration (ADR) cycles were designed, constructed, and tested. Although devices the devices did not operate as fully functional dilution cryocoolers, important information was gathered. The porous metal phase separator was demonstrated to operate in the -1-g configuration; this phase separation is the critical element in the He-3 circulation dilution cryocooler. Improvements in instrumentation needed for additional tests and development were identified.

Dilute acid/metal salt hydrolysis of lignocellulosics

DOEpatents

Nguyen, Quang A.; Tucker, Melvin P.

2002-01-01

A modified dilute acid method of hydrolyzing the cellulose and hemicellulose in lignocellulosic material under conditions to obtain higher overall fermentable sugar yields than is obtainable using dilute acid alone, comprising: impregnating a lignocellulosic feedstock with a mixture of an amount of aqueous solution of a dilute acid catalyst and a metal salt catalyst sufficient to provide higher overall fermentable sugar yields than is obtainable when hydrolyzing with dilute acid alone; loading the impregnated lignocellulosic feedstock into a reactor and heating for a sufficient period of time to hydrolyze substantially all of the hemicellulose and greater than 45% of the cellulose to water soluble sugars; and recovering the water soluble sugars.

Efficient photocatalytic degradation of rhodamine-B by Fe doped CuS diluted magnetic semiconductor nanoparticles under the simulated sunlight irradiation

NASA Astrophysics Data System (ADS)

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

2016-12-01

The present work is planned for a simple, inexpensive and efficient approach for the synthesis of Cu1-xFexS (x = 0.00, 0.01, 0.03, 0.05 and 0.07) nanoparticles via simplistic chemical co-precipitation route by using ethylene diamine tetra acetic acid (EDTA) as a capping molecules. As synthesized nanoparticles were used as competent catalysts for degradation of rhodamine-B organic dye pollutant. The properties of prepared samples were analyzed with energy dispersive analysis of X-rays (EDAX), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible optical absorption spectroscopy, Fourier transform infrared (FTIR) spectra, Raman spectra and vibrating sample magnetometer (VSM). EDAX spectra corroborated the existence of Fe in prepared nanoparticles within close proximity to stoichiometric ratio. XRD, FTIR and Raman patterns affirmed that configuration of single phase hexagonal crystal structure as that of (P63/mmc) CuS, without impurity crystals. The average particle size estimated by TEM scrutiny is in the assortment of 5-10 nm. UV-visible optical absorption measurements showed that band gap narrowing with increasing the Fe doping concentration. VSM measurements revealed that 3% Fe doped CuS nanoparticles exhibited strong ferromagnetism at room temperature and changeover of magnetic signs from ferromagnetic to the paramagnetic nature with increasing the Fe doping concentration in CuS host lattice. Among all Fe doped CuS nanoparticles, 3% Fe inclusion CuS sample shows better photocatalytic performance in decomposition of RhB compared with the pristine CuS. Thus as synthesized Cu0·97Fe0·03S nanocatalysts are tremendously realistic compounds for photocatalytic fictionalization in the direction of organic dye degradation under visible light.

Semiconductor nanocrystal-based phagokinetic tracking

DOEpatents