These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Anisotropy of magnetic emulsions induced by magnetic and electric fields  

E-print Network

The anisotropy of magnetic emulsions induced by simultaneously acting electric and magnetic fields is theoretically and experimentally investigated. Due to the anisotropy, the electric conductivity and magnetic permeability of a magnetic emulsion are no longer scalar coefficients, but are tensors. The electric conductivity and magnetic permeability tensors of sufficiently diluted emulsions in sufficiently weak electric and magnetic fields are found as functions of the electric and magnetic intensity vectors. The theoretically predicted induced anisotropy was verified experimentally. The experimental data are analyzed and compared with theoretical predictions. The results of the analysis and comparison are discussed.

Yury I. Dikansky; Alexander N. Tyatyushkin; Arthur R. Zakinyan

2011-09-10

2

Anisotropy in MHD turbulence due to a mean magnetic field  

NASA Technical Reports Server (NTRS)

The development of anisotropy in an initially isotropic spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops due to the combined effects of an externally imposed dc magnetic field and viscous and resistive dissipation at high wave numbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wave numbers.

Shebalin, J. V.; Matthaeus, W. H.; Montgomery, D.

1982-01-01

3

CMB anisotropies in the presence of a stochastic magnetic field  

SciTech Connect

Primordial magnetic fields present since before the epoch of matter-radiation equality have an effect on the anisotropies of the cosmic microwave background (CMB). The CMB anisotropies due to scalar perturbations are calculated in the gauge-invariant formalism for magnetized adiabatic initial conditions. Furthermore, the linear matter power spectrum is calculated. Numerical solutions are complemented by a qualitative analysis.

Kunze, Kerstin E. [Departamento de Fisica Fundamental and IUFFyM, Universidad de Salamanca, Plaza de la Merced s/n, E-37008 Salamanca (Spain)

2011-01-15

4

Anisotropy of photon production: initial eccentricity or magnetic field.  

PubMed

Recent measurements of the azimuthal anisotropy of direct photons in heavy-ion collisions at the energies of Relativistic Heavy Ion Collider show that it is of the same order as the hadronic one. This finding appears to contradict the expected dominance of photon production from a quark-gluon plasma at an early stage of a heavy-ion collision. A possible explanation of the strong azimuthal anisotropy of the photons, given recently, is based on the presence of a large magnetic field in the early phase of a collision. In this Letter, we propose a method to experimentally measure the degree to which a magnetic field in heavy-ion collisions is responsible for the observed anisotropy of photon production. The experimental test proposed in this Letter may potentially change our understanding of the nonequilibrium stage and possible thermalization in heavy-ion collisions. PMID:23705700

Bzdak, Adam; Skokov, Vladimir

2013-05-10

5

Tensor Microwave Anisotropies from a Stochastic Magnetic Field  

E-print Network

We derive an expression for the angular power spectrum of cosmic microwave background anisotropies due to gravity waves generated by a stochastic magnetic field and compare the result with current observations; we take into account the non-linear nature of the stress energy tensor of the magnetic field. For almost scale invariant spectra, the amplitude of the magnetic field at galactic scales is constrained to be of order 10^{-9} Gauss. If we assume that the magnetic field is damped below the Alfven damping scale, we find that its amplitude at 0.1 h^{-1}Mpc, B_\\lambda, is constrained to be B_\\lambda-3/2, where n is the spectral index of the magnetic field and H_0=100h km s^{-1}Mpc^{-1} is the Hubble constant today.

R. Durrer; P. G. Ferreira; T. Kahniashvili

1999-11-03

6

Structural anisotropy of silica hydrogels prepared under magnetic field  

E-print Network

Birefringence measurements have been carried out on the Pb-doped silica hydrogels prepared under various magnetic fields up to 5T. The silica gels prepared at 5T were used as a medium of crystal growth of PbBr2, whose result implied the structural anisotropy; an aligned array of crystallites was obtained by transmission electron microscopy. While the samples prepared at 0, 1, and 3T have no birefringence, we found that the samples have negative birefringence on the order of magnitude 10^-6 as if the direction of the magnetic field is the optic axis of a uniaxal crystal. To the authors' knowledge, the birefringent silica hydrogels were obtained by gelation under magnetic field for the first time. Also, scanning microscopic light scattering experiments have been performed. The results indicate that the characteristic length distribution for birefringent samples is narrower than that for non-birefringent ones.

Atsushi Mori; Takamasa Kaito; Hidemitsu Furukawa

2008-03-19

7

Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields  

NASA Astrophysics Data System (ADS)

The propagation of cosmic rays (CRs) in turbulent interstellar magnetic fields is typically described as a spatial diffusion process. This formalism predicts only a small deviation from an isotropic CR distribution in the form of a dipole in the direction of the CR density gradient or relative background flow. We show that the existence of a global CR dipole moment necessarily generates a spectrum of higher multipole moments in the local CR distribution. These anomalous anisotropies are a direct consequence of Liouville's theorem in the presence of a local turbulent magnetic field. We show that the predictions of this model are in excellent agreement with the observed power spectrum of multi-TeV CRs.

Ahlers, Markus

2014-01-01

8

Anomalous anisotropies of cosmic rays from turbulent magnetic fields.  

PubMed

The propagation of cosmic rays (CRs) in turbulent interstellar magnetic fields is typically described as a spatial diffusion process. This formalism predicts only a small deviation from an isotropic CR distribution in the form of a dipole in the direction of the CR density gradient or relative background flow. We show that the existence of a global CR dipole moment necessarily generates a spectrum of higher multipole moments in the local CR distribution. These anomalous anisotropies are a direct consequence of Liouville's theorem in the presence of a local turbulent magnetic field. We show that the predictions of this model are in excellent agreement with the observed power spectrum of multi-TeV CRs. PMID:24484000

Ahlers, Markus

2014-01-17

9

Manipulation of magnetic state in nanostructures by perpendicular anisotropy and magnetic field  

SciTech Connect

We investigate the transitions of spin configurations in ultrathin nanostructures by tuning the perpendicular anisotropy (K{sub z}) and out-of-plane magnetic field (H), using the Monte Carlo simulation. It is revealed that enhancing the anisotropy K{sub z} can drive the evolution of in-plane vortex state into intriguing saturated magnetization states under various H, such as the bubble domain state and quadruple-block-domain state etc. The spin configurations of these states exhibit remarkable H-dependence. In addition, the strong effects of geometry and size on the spin configurations of nanostructures are observed. In particular, a series of edged states occur in the circular disk-shaped lattices, and rich intricate saturated magnetization patterns appear in big lattices. It is suggested that the magnetic states can be manipulated by varying the perpendicular anisotropy, magnetic field, and geometry/size of the nanostructures. Furthermore, the stability (retention capacity) of the saturated magnetization states upon varying magnetic field is predicted, suggesting the potential applications of these saturated magnetization states in magnetic field-controlled data storages.

Chen, J. P.; Xie, Y. L.; Chu, P.; Wang, Y. L. [Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Wang, Z. Q.; Gao, X. S. [Institute for Advanced Materials and Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006 (China); Liu, J.-M. [Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093 (China); Institute for Advanced Materials and Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006 (China)

2014-06-28

10

Uniaxial magnetic anisotropy induced low field anomalous anisotropic magnetoresistance in manganite thin films  

NASA Astrophysics Data System (ADS)

La2/3Sr1/3MnO3 films with uniaxial magnetic anisotropy were coherently grown on NdGaO3 (110) substrates. The uniaxial anisotropy has strong effect on magnetoresistance (MR). A positive MR was observed when the current is along magnetic easy axis under the current-field perpendicular geometry. In contrast, no positive MR is observed when current is along the magnetic hard axis regardless of the field direction. Our analysis indicates that the anomalous anisotropic MR effect arises from the uniaxial magnetic anisotropy caused stripe domains which contribute to strong anisotropic domain wall resistivity.

Liao, Zhaoliang; Huijben, Mark; Koster, Gertjan; Rijnders, Guus

2014-09-01

11

Current induced perpendicular-magnetic-anisotropy racetrack memory with magnetic field assistance  

NASA Astrophysics Data System (ADS)

High current density is indispensable to shift domain walls (DWs) in magnetic nanowires, which limits the using of racetrack memory (RM) for low power and high density purposes. In this paper, we present perpendicular-magnetic-anisotropy (PMA) Co/Ni RM with global magnetic field assistance, which lowers the current density for DW motion. By using a compact model of PMA RM and 40 nm design kit, we perform mixed simulation to validate the functionality of this structure and analyze its density potential. Stochastic DW motion behavior has been taken into account and statistical Monte-Carlo simulations are carried out to evaluate its reliability performance.

Zhang, Y.; Zhao, W. S.; Klein, J.-O.; Chappert, C.; Ravelosona, D.

2014-01-01

12

Current induced perpendicular-magnetic-anisotropy racetrack memory with magnetic field assistance  

SciTech Connect

High current density is indispensable to shift domain walls (DWs) in magnetic nanowires, which limits the using of racetrack memory (RM) for low power and high density purposes. In this paper, we present perpendicular-magnetic-anisotropy (PMA) Co/Ni RM with global magnetic field assistance, which lowers the current density for DW motion. By using a compact model of PMA RM and 40?nm design kit, we perform mixed simulation to validate the functionality of this structure and analyze its density potential. Stochastic DW motion behavior has been taken into account and statistical Monte-Carlo simulations are carried out to evaluate its reliability performance.

Zhang, Y.; Klein, J.-O.; Chappert, C.; Ravelosona, D. [IEF, University of Paris-Sud, Orsay 91405 (France); UMR8622, CNRS, Orsay 91405 (France); Zhao, W. S., E-mail: weisheng.zhao@u-psud.fr [IEF, University of Paris-Sud, Orsay 91405 (France); UMR8622, CNRS, Orsay 91405 (France); Electronics and Information Engineering School, University of Beihang, Beijing 100191 (China)

2014-01-20

13

Rashba Spin-Orbit Anisotropy and the Electric Field Control of Magnetism  

PubMed Central

The control of the magnetism of ultra-thin ferromagnetic layers using an electric field, rather than a current, has many potential technologically important applications. It is usually insisted that such control occurs via an electric field induced surface charge doping that modifies the magnetic anisotropy. However, it remains the case that a number of key experiments cannot be understood within such a scenario. Much studied is the spin-splitting of the conduction electrons of non-magnetic metals or semi-conductors due to the Rashba spin-orbit coupling. This reflects a large surface electric field. For a magnet, this same splitting is modified by the exchange field resulting in a large magnetic anisotropy energy via the Dzyaloshinskii-Moriya mechanism. This different, yet traditional, path to an electrically induced anisotropy energy can explain the electric field, thickness, and material dependence reported in many experiments. PMID:24531151

Barnes, Stewart E.; Ieda, Jun'ichi; Maekawa, Sadamichi

2014-01-01

14

Nonlinear dynamics of a continuum Heisenberg spin chain with an anisotropy and an external magnetic field  

Microsoft Academic Search

By stereographically projecting the spin vector onto a complex plane in the equations of motion for a continuum Heisenberg spin chain with an anisotropy (an easy plane and an easy axis) and an external magnetic field, the effect of the magnetic field for integrability of the system is discussed. Then, introducing an auxiliary parameter, the Lax equations for Darboux matrices

Wu-Ming Liu; Shu-Li Yang; Fu-Cho Pu; Nian-Ning Huang

1997-01-01

15

Effect of magnetic field on optical anisotropy of CdZnSe quantum dots  

Microsoft Academic Search

The effect of magnetic field on the electronic structure and optical anisotropy of Zn1-xCdxSe\\/ZnSe quantum dots (QDs) has been analyzed for varying geometrical confinement related to the in-plane asymmetry. The disk-shaped QD is modeled by anisotropic parabolic potential with the magnetic field considered in Faraday geometry. The multiple band Hamiltonian in presence of magnetic field has been numerically diagonalized using

Jitendra Kumar; Sheetal Kapoor

2010-01-01

16

Implementation of magnetic field assistance to current-induced perpendicular-magnetic-anisotropy racetrack memory  

NASA Astrophysics Data System (ADS)

Due to the increase of resistance of nanowire as the technology continuously scales down, generating a current enough high for shifting domain wall (DW) becomes one of the most serious issues to hinder the progress of Racetrack memory (RM). It is recently reported that magnetic field can assist to trigger the DW motion below intrinsic current threshold, which can be a promising alternative to help RM address this current threshold issue. In this paper, we present an implementation of magnetic field assistance to perpendicular-magnetic-anisotropy Co/Ni RM. By using a spice-compatible model and CMOS 40 nm design kit, we perform mixed simulation to validate its functionality. Storage capacity and power analyses demonstrate that lowering the critical current density of DW shifting allows higher feasibility for ultra-denser RM and provides a relatively acceptable energy performance.

Zhang, Y.; Zhao, W. S.; Klein, J.-O.; Chappert, C.; Ravelosona, D.

2014-05-01

17

Approach to fabricating Co nanowire arrays with perpendicular anisotropy: Application of a magnetic field during deposition  

SciTech Connect

Cobalt (Co) nanowire arrays were electrodeposited into the pores of polycarbonate membranes. A magnetic field parallel or perpendicular to the membrane plane was applied during deposition to control the wire growth. X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer were employed to investigate the structure as well as the magnetic properties of the nanowire arrays. The results show that the magnetic field applied during deposition strongly influences the growth of Co nanowires, inducing variations in their crystalline structure and magnetic properties. The sample deposited with the field perpendicular to the membrane plane exhibits a perpendicular magnetic anisotropy with greatly enhanced coercivity and squareness as a result of the preferred growth of Co grains with the c axis perpendicular to the film plane. In contrast, the deposition in a parallel magnetic field forces Co grains to grow with the c axis parallel to the film plane, resulting in in-plane anisotropy. {copyright} 2001 American Institute of Physics.

Ge, Shihui; Li, Chao; Ma, Xiao; Li, Wei; Xi, Li; Li, C. X.

2001-07-01

18

Scaling anisotropy of the power in parallel and perpendicular components of the solar wind magnetic field  

E-print Network

Scaling anisotropy of the power in parallel and perpendicular components of the solar wind magnetic of the Power in Parallel and Perpendicular Components of the Solar Wind Magnetic Field Miriam A. Forman1, London SW7 2AZ, UK; 4 Department of Mathematics, University of Waikato, Hamilton 3240, NZ Abstract. Power

Oughton, Sean

19

Two-sublattice magnetic system with fourth-order uniaxial anisotropy and strong antisymmetric exchange in a transverse magnetic field  

Microsoft Academic Search

Discusses the equilibrium configurations and the phase transitions of a semi-classical model system consisting of two equal magnetic moments coupled by isotropic, anisotropic and antisymmetric exchange, with uniaxial anisotropy terms up to fourth order, in the presence of a transverse magnetic field. No restriction is imposed on the values of the interaction parameters. Magnetic configurations of the 'conical' type appear

M. Acquarone

1979-01-01

20

Magnetic anisotropy induced by field applied during deposition in sputtered amorphous CoZr-rare earth thin films  

Microsoft Academic Search

The formation of coherent magnetic anisotropy is investigated in amorphous (Co0.93Zr0.07)100-x (RE)x (RE=rare earth) films as a function of the magnitude of the magnetic field, Hd, applied during deposition. The direction of the induced anisotropy depends upon the peculiar rare earth substituted. For RE=Sm and Gd, a biaxial anisotropy is formed composed of a perpendicular anisotropy, Kp, and of Ku.

G. Suran; H. Ouahmane; J. Sztern

1993-01-01

21

Electric field controlled reversible magnetic anisotropy switching studied by spin rectification  

SciTech Connect

In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg{sub 1?3}Nb{sub 2?3})O{sub 3}-PbTiO{sub 3} substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropy field. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

Zhou, Hengan; Fan, Xiaolong, E-mail: fanxiaolong@lzu.edu.cn; Wang, Fenglong; Jiang, Changjun; Rao, Jinwei; Zhao, Xiaobing; Xue, Desheng [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China)] [Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Gui, Y. S.; Hu, C.-M. [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada)] [Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada)

2014-03-10

22

ANISOTROPY AS A PROBE OF THE GALACTIC COSMIC-RAY PROPAGATION AND HALO MAGNETIC FIELD  

SciTech Connect

The anisotropy of cosmic rays (CRs) in the solar vicinity is generally attributed to CR streaming due to the discrete distribution of CR sources or local magnetic field modulation. Recently, the two-dimensional large-scale CR anisotropy has been measured by many experiments in the TeV-PeV energy range in both hemispheres. The tail-in excess along the tangential direction of the local spiral arm and the loss cone deficit pointing to the north Galactic pole direction agree with what have been obtained in tens to hundreds of GeV. The persistence of the two large-scale anisotropy structures in such a wide energy range suggests that the anisotropy might be due to global streaming of the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy picture from the solar system to the whole galaxy. In such a case, we can find a new interesting signature, a loop of GCR streaming, of the GCR propagation. We further calculate the overall GCR streaming induced magnetic field, and find a qualitative consistency with the observed structure of the halo magnetic field.

Qu, Xiao-bo; Zhang, Yi; Liu, Cheng; Hu, Hong-bo [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Xue, Liang, E-mail: zhangyi@mail.ihep.ac.cn [School of Physics, Shandong University, Ji'nan 250100 (China)

2012-05-01

23

Relationship between coercive force and anisotropy field for oriented barium ferrite tapes and magnets  

Microsoft Academic Search

The approximate anisotropy field (Han) has been determined for twelve experimental oriented barium ferrite recording tapes and magnets with coercive force (Hc) between 715 Oe and 5250 Oe, and squareness ratio greater than 0.80. The Han values were taken as the ratio of saturation magnetic moment (ms) to the initial hard-axis susceptibility (m\\/H). Han values were generally within the 12.6–19.8

R. E. Fayling

1978-01-01

24

Relationship between coercive force and anisotropy field for oriented barium ferrite tapes and magnets  

Microsoft Academic Search

The approximate anisotropy field (Han) has been determined for twelve experimental oriented barium ferrite recording tapes and magnets with coercive force (Hc) between 715 Oe and 5250 Oe, and squareness ratio greater than 0.80. The Han values were taken as the ratio of saturation magnetic moment (ms) to the initial hard-axis susceptibility (m\\/H). Han values were generally within the 12.6-19.8

R. E. Fayling

1978-01-01

25

Magnetic Fields and Cosmic-Ray Anisotropies at TeV Energies  

NASA Astrophysics Data System (ADS)

Several cosmic-ray (CR) observatories have provided high-accuracy maps of the sky at TeV-PeV energies. The data reveal an O(0.1%) deficit from north galactic directions that peaks at 10 TeV and then evolves with the energy, together with other anisotropies at smaller angular scales. Using the Boltzmann equation, we derive expressions for the CR flux that fit these features. The anisotropies depend on the local interstellar magnetic field \\boldsymbol {B}IS, on the average galactic field \\boldsymbol {B}R in our vicinity, and on correlations between fluctuating quantities. We show that the initial dipole anisotropy along \\boldsymbol {B}IS can be modulated by changes in the global CR flow, and that a variation in the dipole direction would imply a given radius of coherence for the local \\boldsymbol {B}IS. We also show that small- and medium-scale anisotropies may appear when the full-sky anisotropy finds a field configuration acting as a magnetic lens.

Battaner, Eduardo; Castellano, Joaquín; Masip, Manuel

2015-02-01

26

Engineering the magnetic anisotropy of atomic-scale nanostructure under electric field  

NASA Astrophysics Data System (ADS)

Atomic-scale magnetic nanostructures are promising candidates for future information processing devices. Utilizing external electric field to manipulate their magnetic properties is an especially thrilling project. Here, by carefully identifying the different contributions of each atomic orbital to the magnetic anisotropy energy (MAE) of the ferromagnetic metal films, we argue that it is possible to engineer both the MAE and the magnetic response to the electric field of atomic-scale magnetic nanostructures. Taking the iron monolayer as a matrix, we propose several interesting iron nanostructures with dramatically different magnetic properties. Such nanostructures could exhibit a strong magnetoelectric effect. Our work may open new avenues to the artificial design of electrically controlled magnetic devices.

Zhu, Wanjiao; Ding, Hang-Chen; Tong, Wen-Yi; Gong, Shi-Jing; Wan, Xiangang; Duan, Chun-Gang

2015-02-01

27

Engineering the magnetic anisotropy of atomic-scale nanostructure under electric field.  

PubMed

Atomic-scale magnetic nanostructures are promising candidates for future information processing devices. Utilizing external electric field to manipulate their magnetic properties is an especially thrilling project. Here, by carefully identifying the different contributions of each atomic orbital to the magnetic anisotropy energy (MAE) of the ferromagnetic metal films, we argue that it is possible to engineer both the MAE and the magnetic response to the electric field of atomic-scale magnetic nanostructures. Taking the iron monolayer as a matrix, we propose several interesting iron nanostructures with dramatically different magnetic properties. Such nanostructures could exhibit a strong magnetoelectric effect. Our work may open new avenues to the artificial design of electrically controlled magnetic devices. PMID:25629772

Zhu, Wanjiao; Ding, Hang-Chen; Tong, Wen-Yi; Gong, Shi-Jing; Wan, Xiangang; Duan, Chun-Gang

2015-02-25

28

Ferroelectric control of magnetic anisotropy.  

PubMed

We demonstrate unambiguous evidence of the electric field control of magnetic anisotropy in a wedge-shaped Co film of varying thickness. A copolymer ferroelectric of 70% vinylidene fluoride with 30% trifluoroethylene, P(VDF-TrFE) overlays the Co wedge, providing a large switchable electric field. As the ferroelectric polarization is switched from up to down, the magnetic anisotropy of the Co films changes by as much as 50%. At the lowest Co thickness the magnetic anisotropy switches from out-of-plane to in-plane as the ferroelectric polarization changes from up to down, enabling us to rotate the magnetization through a large angle at constant magnetic field merely by switching the ferroelectric polarization. The large mismatch in the stiffness coefficients between the polymer ferroelectric and metallic ferromagnet excludes typical magnetoelectric strain coupling; rather, the magnetic changes arise from the large electric field at the ferroelectric/ferromagnet interface. PMID:21823660

Mardana, A; Ducharme, Stephen; Adenwalla, S

2011-09-14

29

Effects of the galactic magnetic field upon large scale anisotropies of extragalactic cosmic rays  

SciTech Connect

The large scale pattern in the arrival directions of extragalactic cosmic rays that reach the Earth is different from that of the flux arriving to the halo of the Galaxy as a result of the propagation through the galactic magnetic field. Two different effects are relevant in this process: deflections of trajectories and (de)acceleration by the electric field component due to the galactic rotation. The deflection of the cosmic ray trajectories makes the flux intensity arriving to the halo from some direction to appear reaching the Earth from another direction. This applies to any intrinsic anisotropy in the extragalactic distribution or, even in the absence of intrinsic anisotropies, to the dipolar Compton-Getting anisotropy induced when the observer is moving with respect to the cosmic rays rest frame. For an observer moving with the solar system, cosmic rays traveling through far away regions of the Galaxy also experience an electric force coming from the relative motion (due to the rotation of the Galaxy) of the local system in which the field can be considered as being purely magnetic. This produces small changes in the particles momentum that can originate large scale anisotropies even for an isotropic extragalactic flux.

Harari, D.; Mollerach, S.; Roulet, E., E-mail: harari@cab.cnea.gov.ar, E-mail: mollerach@cab.cnea.gov.ar, E-mail: roulet@cab.cnea.gov.ar [CONICET, Centro Atómico Bariloche, Bustillo 9500, 8400 Bariloche (Argentina)

2010-11-01

30

Effects of the applied magnetic field and anisotropy on the spin wave gap in ultrathin magnetic films at zero temperature  

NASA Astrophysics Data System (ADS)

We investigate the calculated spin wave gap of two-dimensional magnetic films under the combined influence of the in-plane direction of the applied magnetic field and different kinds of magnetic anisotropies. We also compute the spin wave gap as a function of the applied magnetic field at zero temperature. We discuss the results in connection with experimental data reported for epitaxial Fe-deficient yttrium garnet (YIG) films grown by pulsed laser deposition (PLD) technique onto the different faces of the Gd3Ga5O12 single crystal.

Kaplan, B.; Kaplan, R.

2014-12-01

31

Probing the Intergalactic Magnetic Field with the Anisotropy of the Extragalactic Gamma-ray Background  

NASA Technical Reports Server (NTRS)

The intergalactic magnetic field (IGMF) may leave an imprint on the angular anisotropy of the extragalactic gamma-ray background through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thereby inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that current Fermi data already seem to prefer nonnegligible IGMF values. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

Venters, T. M.; Pavlidou, V.

2013-01-01

32

CMB distortion anisotropies due to the decay of primordial magnetic fields  

NASA Astrophysics Data System (ADS)

We investigate the power spectrum of the distortion of the cosmic microwave background (CMB) due to the decay of the primordial magnetic fields. It is known that there are two types of the CMB distortions, so-called ? and y types, and we find that the signal of the y-type distortion becomes larger than that of the ?-type one. We also discuss cross power spectra between the CMB distortions and the CMB temperature anisotropy, which are naturally generated due to the existence of the primordial magnetic fields. We find that such cross power spectra have small amplitudes compared with the autopower spectra of the CMB distortions because of the Silk damping effect of the temperature anisotropy. We also investigate the possibility of detecting such a signal in the future CMB experiments, including not only absolutely calibrated experiments such as PIXIE but also relatively calibrated experiments such as LiteBIRD and CMBpol.

Miyamoto, Koichi; Sekiguchi, Toyokazu; Tashiro, Hiroyuki; Yokoyama, Shuichiro

2014-03-01

33

Structural anisotropy and internal magnetic fields in trabecular bone: Coupling solution and solid dipolar interactions  

NASA Astrophysics Data System (ADS)

We investigate the use of intermolecular multiple-quantum coherence to probe structural anisotropy in trabecular bone. Despite the low volume fraction of bone, the bone-water interface produces internal magnetic field gradients which modulate the dipolar field, depending on sample orientation, choice of dipolar correlation length, correlation gradient direction, and evolution time. For this system, the probing of internal magnetic field gradients in the liquid phase permits indirect measurements of the solid phase dipolar field. Our results suggest that measurements of volume-averaged signal intensity as a function of gradient strength and three orthogonal directions could be used to non-invasively measure the orientation of structures inside a sample or their degree of anisotropy. The system is modeled as having two phases, solid and liquid (bone and water), which differ in their magnetization density and magnetic susceptibility. A simple calculation using a priori knowledge of the material geometry and distribution of internal magnetic fields verifies the experimental measurements as a function of gradient strength, direction, and sample orientation.

Bouchard, Louis-S.; Wehrli, Felix W.; Chin, Chih-Liang; Warren, Warren S.

2005-09-01

34

Magnetic anisotropy of asbestos fibers  

NASA Astrophysics Data System (ADS)

The anisotropy of magnetic susceptibility of single asbestos fibers is measured. The alignment of both chrysotile and crocidolite fibers in magnetic fields is found to be due to the anisotropy. The average measured anisotropy of volume susceptibility is 0.40×10-6 for chrysotile and 83×10-6 for crocidolite. Fiber shape effects are estimated to contribute, on average, about 10% and 6%, respectively, to the total anisotropy of the two types of fiber. There is no evidence of significant permanent magnetic moments. The magnitude of the observed alignment makes the effect potentially useful in real-time detection of airborne asbestos fibers. The experimental technique developed in the study can be used for measuring the anisotropy of small particles of well-defined shape. High sensitivity of the technique permits the measurement of torques lower than 10-21 Nm on particles down to picogram mass.

Ulanowski, Z.; Kaye, P. H.

1999-04-01

35

Magnetic anisotropy in Fe25Cr12Co1Si alloy induced by external magnetic field  

Microsoft Academic Search

Structural and magnetic properties of Fe-25Cr-12Co-1Si alloy thermo-magnetically treated under different external magnetic field conditions were investigated. Orientation and morphology of the ferromagnetic a1 phase embedded in a2 phase matrix before and after step ageing are characterized by transmission electron microscope(TEM). The results show that the ellipsoidal particles of ferromagnetic a1 phase are aligned along the direction of external magnetic

Liang ZHEN; Xue-yin SUN; Cheng-yan XU; Run-sheng GAO; Ren-gen XU; Lu-chang QIN

2007-01-01

36

Tailoring the interfacial magnetic anisotropy in multiferroic field-effect devices  

NASA Astrophysics Data System (ADS)

Ferroelectric field-effect devices based on perovskite oxide materials offer a new possibility to exploit emergent interfacial effects such as the electrostatic modification of the transport and magnetic properties of strongly correlated materials and to prove the magneto-electric coupling at the interface between the two different ferroic materials. Here we report on the reversible modulation of the interfacial magnetic and magnetotransport properties of La0.825Sr0.175MnO3 thin films induced by switching the ferroelectric polarization of a top PbZr0.2Ti0.8O3 layer. Anisotropic magnetoresistance (AMR) measurements were performed applying a magnetic field H in a plane perpendicular to the current density. By rotating H from the out-of-plane towards the in-plane direction, upon the ferroelectric polarization switching, a modulation of the normalized AMR amplitude was achieved. The dynamical electrostatic coupling at the interface of the two oxides is responsible for a reconstruction of the Mn3deg orbitals which in turn affects the surface magnetic anisotropy of the magneto-electric system. The present work might have a broader impact, including in the field of multiferroic tunnel junctions, due to a better understanding of the coupling at the interface of the two ferroic oxides where the influence of the polarization on the magnetic degree of freedom is accomplished.

Preziosi, Daniele; Fina, Ignasi; Pippel, Eckhard; Hesse, Dietrich; Marti, Xavi; Bern, Francis; Ziese, Michael; Alexe, Marin

2014-09-01

37

The effect of the in-plane demagnetizing field on films with weak perpendicular magnetic anisotropy  

Microsoft Academic Search

The effect of reduced lateral dimension on the magnetic behavior of long microstrips with weak perpendicular magnetic anisotropy has been studied. The hysteresis loops of the surface and the whole volume of microstrips and large films have been recorded by magneto-optic Kerr effect magnetometry and vibrating sample magnetometry. Also, the magnetic structure of the microstrips and its evolution under an

Oscar de Abril; María Del Carmen Sánchez; Claudio Aroca

2006-01-01

38

Enhancement of thermopower anisotropy in Bi and Bi-Sn wires under elastic deformation and magnetic field  

NASA Astrophysics Data System (ADS)

In this work we have studied the possibility to enhance the thermopower anisotropy in Bi and Bi-Sn nanowires under the influence of elastic tension and low magnetic field. Glass coated single-crystal Bi and Bi-Sn wires with diameters 100 nm - 2 ?m were manufactured by the liquid phase casting method. The wires with trigonal orientation were prepareded by the method of zone recrystallization of wires with standard orientation (1011). This made it possible to study the thermopower anisotropy of the wires without magnetic field. It is shown that low magnetic field, Sn doping and elastic tension leads to a significant increase in the absolute value of thermopower and in its anisotropy at 250-300 K. This is important for the design of transverse anisotropic thermoelements with low useful current. The stable thermoelectric properties, high flexural strength, and long wire length allow designing anisotropic thermoelectric devices of various configurations.

Nikolaeva, Albina A.; Konopko, Leonid A.; Huber, Tito E.; Tsurkan, Anna K.; Botnari, Oxana V.

2012-06-01

39

Attempts to Simulate Anisotropies of Solar Wind Fluctuations Using MHD with a Turning Magnetic Field  

NASA Technical Reports Server (NTRS)

We examine a "two-component" model of the solar wind to see if any of the observed anisotropies of the fields can be explained in light of the need for various quantities, such as the magnetic minimum variance direction, to turn along with the Parker spiral. Previous results used a 3-D MHD spectral code to show that neither Q2D nor slab-wave components will turn their wave vectors in a turning Parker-like field, and that nonlinear interactions between the components are required to reproduce observations. In these new simulations we use higher resolution in both decaying and driven cases, and with and without a turning background field, to see what, if any, conditions lead to variance anisotropies similar to observations. We focus especially on the middle spectral range, and not the energy-containing scales, of the simulation for comparison with the solar wind. Preliminary results have shown that it is very difficult to produce the required variances with a turbulent cascade.

Ghosh, Sanjoy; Roberts, D. Aaron

2010-01-01

40

Petrophysical Characterization of Stony Meteorites Using Low Field Magnetic Susceptibility: Initial Results From Anisotropy Measurements  

NASA Astrophysics Data System (ADS)

Low field magnetic susceptibility represents a fast, systematic and non-destructive technique of meteorite classification [1-4]. We previously reported measurements of bulk susceptibility, and its frequency dependence, along with a `proxy' measure of anisotropy, on 204 specimens from 108 different meteorites in the National Meteorite Collection of Canada [5,6]. Measurements were performed on a Sapphire Instruments Model 2B. Bulk susceptibility values followed expected trends, governed by metal content, with values increasing from LL, to L, to H, to E chondrites. Frequency dependence (19000 vs 825 Hz) was greatest in H and C chondrites. Aubrites (AUB) and Howardites (HOW) had the lowest. Anisotropy of magnetic susceptibility (AMS) was measured using a `proxy' approach: the mean value determined from a series of random sample orientations was compared with repeated measurements in one orientation. AUB, E chondrites and Martian SNCs had the largest inferred anisotropies, while LL and C chondrites had the lowest. Here we report initial results from a follow-up study. Quantitative measurements of the AMS were made on 67 stony meteorite specimens. AMS measurements [3,5,6,7,8,9] can provide information on the physical fabric of the meteorite, and may relate to its deformational history. Samples measured show significant degrees of anisotropy ranging from 1-50 % for an individual specimen (in parentheses is the number of specimens used in the class mean): AUB (5), Acapulcoites (1) and E chondrites (10) display the largest degrees of anisotropy, 40±11 (1 standard deviation), 34, and 24±10, respectively. These classes are followed by Diogenite (1) 20, H (13) 14±7 and L (10) 13±6 chondrites, Brachinite (1) 11, Ureilite (2) 8, Eucrite (4) 7±4, C chondrites (14) 6±3, and Rumurutiite (1) 4. These results match a similar trend based on the `proxy' method [5,6]: AUB and E chondrites were found to have the highest inferred anisotropies followed by tightly grouped H and L chondrites, with C and LL chondrites having the lowest inferred anisotropies. The magnitudes of the ellipsoid shape varied significantly within meteorite class, and there is variability between classes. The mean ellipsoid shape and standard deviation for each class follows. Prolate ellipsoids: AUB (+17±15), Diogenite (+8), E chondrites (+4±13), and Ureilite (+4). Oblate ellipsoids dominate the remaining classes: Acapulcoite (-31), Brachinite (-15), L chondrites (-7±10), H (-5±12), Eucrite (-6±4), C (4±3) and Rumurutiite (-3). There is consistency of AMS among multiple specimens of the same meteorite. Future work on samples from the National Meteorite Collection of Canada will also include measurements of the intensity of natural remanent magnetization, and of bulk density. These techniques, measuring several physical properties non-destructively, show great promise for characterizing meteorites. References: [1] Kukkonen I.T. & Pesonen L.J. (1983) Bull. Geol. Soc. Finland 55: 157-177. [2] Terho M. et al. (1993) Studia geoph. et geod. 37: 65-82. [3] Rochette P. et al. (2001) Quaderni di Geofisica, 18, 30 p. [4] Rochette P. et al. (2003) Meteor. Planet. Sci. 2002, 38(2). [5] Smith D.L. et al. (2003) Abstract 1939, Lunar Planet. Sci. XXXIV. [6] Smith D.L. (2003). B.Sc. Thesis, Carleton U., Ottawa. [7] Sneed et al. (1988) Meteoritics. 23, 139-149. [8] Morden S.J & Collinson D.W. (1992) Earth Planet Sci. Lett. 109, 185-204. [9] Smith D.L. et al. (2003) Abstract 5275, Met. Soc. 66.

Smith, D. L.; Ernst, R. E.; Herd, R. K.; Claire, S.

2004-05-01

41

Inducing anisotropy in bulk Nd-Fe-Co-Al-B nanocrystalline alloys by quenching in magnetic field  

NASA Astrophysics Data System (ADS)

We have observed magnetic anisotropy in bulk Nd55-xCoxFe30Al10B5 (x=10, 15 and 20) alloys prepared by copper mold suction casting method with a presence of external magnetic field (quenching field) ?0H=0.25 T. By changing direction of the measuring field from perpendicular to parallel one in comparison with that of the quenching field, coercive force of the alloys slightly decreases while remanent magnetization and squareness of hysteresis loop increase more clearly. It is also found that the higher Co-concentration in the alloys the larger magnetic anisotropy is induced. The structure analyses manifest nanocrystalline particles embedded in residual amorphous matrix of the alloys. The size of the particles is in range of 10-30 nm and their crystalline phases consist of Nd2(Fe,Co)14B, Nd3Co, Nd3Al, NdAl2 and Nd.

Dan, Nguyen Huy; Thanh, Pham Thi; Yen, Nguyen Hai; Thanh Huyen, Nguyen Thi; Thang, Duong Dinh; Hung, Luu Tien

2012-04-01

42

The Cosmic Ray Anisotropy Mystery: Turbulent Anisotropic Interstellar Medium Magnetic Field Effects  

NASA Astrophysics Data System (ADS)

The distribution of cosmic rays observed at Earth by a host of experiments, including IceCube, has been found to be anisotropic for a wide range of energies, spanning from ~TeV to ~PeV. The anisotropic distribution consists of both large angular scale and small angular scale components. The cause of the anisotropic distribution of cosmic rays, especially in the case of the small scale anisotropies, is a hotly debated topic in contemporary plasma physics and astrophysics. We perform simulations of cosmic rays propagating through the anisotropic, turbulent magnetic field of the interstellar medium to test hypotheses attempting to explain the observed anisotropy. We find that the mean free path of the cosmic rays is ~half the injection scale of the turbulence, indicating that the diffusion approximation for propagating cosmic rays may not be applicable. We also find that the angular power spectra derived from our simulations matches well the angular power spectra derived from observations. In this work, we discuss the implications of our findings.This work was supported by the National Science Foundation's REU program through NSF Award AST-1004881.

Farber, Ryan; Lopez-Barquero, Vanessa; Desiati, Paolo; Lazarian, Alex

2015-01-01

43

Low depinning fields in Ta-CoFeB-MgO ultrathin films with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We have studied the domain-wall dynamics in Ta-CoFeB-MgO ultra-thin films with perpendicular magnetic anisotropy for various Co and Fe concentrations in both the amorphous and crystalline states. We observe three motion regimes with increasing magnetic field, which are consistent with a low fields creep, transitory depinning, and high fields Walker wall motion. The depinning fields are found to be as low as 2 mT, which is significantly lower than the values typically observed in 3d ferromagnetic metal films with perpendicular magnetic anisotropy. This work highlights a path toward advanced spintronics devices based on weak random pinning in perpendicular CoFeB films.

Burrowes, C.; Vernier, N.; Adam, J.-P.; Herrera Diez, L.; Garcia, K.; Barisic, I.; Agnus, G.; Eimer, S.; Kim, Joo-Von; Devolder, T.; Lamperti, A.; Mantovan, R.; Ockert, B.; Fullerton, E. E.; Ravelosona, D.

2013-10-01

44

Magnetic anisotropy in single clusters  

NASA Astrophysics Data System (ADS)

The magnetic measurements on single cobalt and iron nanoclusters containing almost 1000 atoms are presented. Particles are directly buried within the superconducting film of a micro-SQUID (superconducting quantum interference device) which leads to the required sensitivity. The angular dependence of the switching field in three dimensions turns out to be in good agreement with a uniform rotation of cluster magnetization. The Stoner and Wohlfarth model yields therefore an estimation of magnetic anisotropy in a single cluster. In particular, uniaxial, biaxial, and cubic contributions can be separated. Results are interpreted on the basis of a simple atomic model in which clusters are assimilated to “giant spins.” We present an extension of the Néel model to clusters in order to estimate surface anisotropy. In the case of cobalt, this last contribution dominates and numerical simulations allow us to get the morphology of the investigated clusters.

Jamet, Matthieu; Wernsdorfer, Wolfgang; Thirion, Christophe; Dupuis, Véronique; Mélinon, Patrice; Pérez, Alain; Mailly, Dominique

2004-01-01

45

Re-evaluation of the magnetic anisotropy of phyllosilicates using high-field methods: biotite, muscovite and chlorite single crystals  

NASA Astrophysics Data System (ADS)

The anisotropy of magnetic susceptibility (AMS) of single crystals is one of the most important pieces of information required in the evaluation of mathematical models of AMS. Phyllosilicates, which are an important constituent in the matrix of natural rocks, are often the main carriers of the AMS. Thus, it is important to have reliable values of the single crystal properties of these minerals. The main parameters of the AMS in biotite, muscovite and chlorite, have been reevaluated by means of high-field torque magnetometry and high-field magnetization curves. The main problem in the evaluation of the anisotropy of single crystals is the presence of ferromagnetic inclusions that also contribute to the low-field AMS. High-field methods, which measure the deviatoric susceptibility tensor, have been used to separate the paramagnetic from the ferrimagnetic signal. Combining high-field paramagnetic bulk susceptibility, derived from magnetization curves, with the paramagnetic deviatoric tensor it is possible to obtain anisotropy ellipsoid of the individual minerals. The ferromagnetic phases present in the single crystals have also been identified. The degree of anisotropy (P) obtained from these studies is in agreement with values reported in the literature. The shape of the AMS ellipsoid (T) is highly oblate, in contrast with the high variability of shapes reported in earlier studies. The nearly perfectly oblate shape is in accord with the crystallographic structure of the phyllosilicates and the distribution of iron in the structure.

Martin Hernandez, F.; Hirt, A. M.

2003-04-01

46

Magnetic Anisotropy of Igneous Rocks  

Microsoft Academic Search

A torque-meter method of measuring the magnetic anisotropy of rocks has been used in a study of a 1050-foot bore core from a Tasmanian dolerite sill. Each cylindrical specimen was suspended in a uniform field of 10.6 kilo-oersteds perpendicular to its axis, and the torque T exerted on it was measured at 10 ø intervals of the angle # between

F. D. Stacey

1960-01-01

47

Theoretical evaluation of the temperature dependence of magnetic anisotropy constants of Nd2Fe14B: Effects of exchange field and crystal field strength  

NASA Astrophysics Data System (ADS)

To identify the possible mechanism of the coercivity (Hc) degradation of Nd–Fe–B sintered magnets, we study the roles of the exchange field acting on the 4f electrons in Nd ions and theoretically investigate how variation in the exchange field affects the values of the magnetic anisotropy constants K1 and K2. We find that, with decreasing exchange field strength, both values decrease as a result of the lower asphericity of the 4f electron cloud, indicating that the local anisotropy constants might become small around the grain boundaries, where the exchange fields are reduced owing to the smaller coordination number.

Sasaki, Ryo; Miura, Daisuke; Sakuma, Akimasa

2015-04-01

48

Attempt to detect diamagnetic anisotropy of oxides with isotropic crystal structure by measuring its rotational oscillation in strong magnetic field  

Microsoft Academic Search

Sensitivity to detect diamagnetic anisotropy DeltachiDIA of inorganic oxides was improved by increasing intensity of horizontal field from 1.6 T to 5.0 Tesla. The field induced a rotational oscillation of a magnetically stable axis of a sample, which was suspended with a thin fiber. Accurate Deltachi values are obtained when restoration torque of the fiber is negligibly small compared to

S. Kano; K. Hisayoshi; T. Kashiwagi; T. Kida; M. Hagiwara; C. Uyeda

2009-01-01

49

Anisotropies in TeV Cosmic Rays Related to the Local Interstellar Magnetic Field from the IBEX Ribbon  

NASA Astrophysics Data System (ADS)

The Interstellar Boundary Explorer (IBEX) observes enhanced Energetic Neutral Atoms (ENAs) emission in the keV energy range from a narrow (~20° wide) "ribbon" in the sky that appears to be centered on the direction of the local interstellar (LIS) magnetic field. The Milagro collaboration, the As? collaboration and the IceCube observatory have recently made global maps of cosmic ray fluxes in the TeV energy range, revealing anisotropic structures ordered in part by the local interstellar magnetic field and the interstellar flow. This paper following from a recent publication in Science makes the link between these disparate observations by developing a simple model of the magnetic structure surrounding the heliosphere in the Local Interstellar Medium (LISM) that is consistent with both IBEX ENA fluxes and TeV cosmic ray anisotropies. The model also employs the revised velocity direction of the LIC derived from neutral He observations by IBEX. By modeling the propagation of cosmic rays through this magnetic field structure, we specifically show that (1) the large-scale TeV anisotropy provides a roughly consistent orientation for the local interstellar magnetic field at the center of the IBEX Ribbon and corroborates the ~ 3 ?G magnitude of the local interstellar magnetic field derived from IBEX observations of the global heliosphere; (2) and small-scale structures in cosmic rays (over < 30° angular scales) are influenced by the interstellar field interaction with the heliosphere at energies < 10 TeV. Thus, we provide a link between IBEX ENA observations, IBEX neutral observations of interstellar He, and TeV cosmic ray anisotropies, which are strongly influenced by the interactions between the local interstellar magnetic field, the flow of the local interstellar plasma, and the global heliosphere.

Schwadron, N. A.; Adams, F. C.; Christian, E.; Desiati, P.; Frisch, P.; Funsten, H. O.; Jokipii, J. R.; McComas, D. J.; Moebius, E.; Zank, G. P.

2015-01-01

50

Tailoring magnetic anisotropy gradients by ion bombardment for domain wall positioning in magnetic multilayers with perpendicular anisotropy  

PubMed Central

Graded anisotropy magnetic materials possess a coercive field changing laterally with position. A simple fabrication procedure to produce such an anisotropy gradient in a polycrystalline Au/Co layer system without lateral thickness variation and with perpendicular magnetic anisotropy, prototypical for a large variety of thin film systems, is shown. The procedure uses light-ion bombardment without the use of a mask. Magnetization reversal in this polycrystalline layer system takes place by unidirectional movement of a single domain wall only in regions with larger anisotropies and anisotropy gradients. In this anisotropy/anisotropy gradient regime, the domain wall is oriented perpendicular to the coercive field gradient, and it can be positioned along the gradient by an appropriate magnetic field pulse. For smaller anisotropies/anisotropy gradients, the natural anisotropy fluctuations of the polycrystalline layer system induce magnetization reversal dominated by domain nucleation. PACS 75.30.Gw; 75.70.Cn; 75.60.Ch PMID:25232291

2014-01-01

51

Electric-field-induced magnetization reorientation in a (Ga,Mn)As/(Ga,Mn)(As,P) bilayer with out-of-plane anisotropy  

NASA Astrophysics Data System (ADS)

Combined electric- and magnetic-field control of magnetization orientation and reversal is studied using anomalous Hall effect in an ultrathin ferromagnetic (Ga,Mn)As/(Ga,Mn)(As,P) bilayer. Its anisotropy results from the electrically tunable competition between the in-plane and out-of-plane anisotropies of both layers. The magnetic hysteresis loop shape is sensitive to the bias electric field. In the loop reversible part, an electric-field variation is found to reorient reversibly the magnetization. In this case, the magnetization direction follows the easy anisotropy direction controlled by electric field. In contrast, in the hysteretic part, an almost complete nonreversible magnetization reversal is achieved. This is interpreted as resulting from the electric-field-induced enhancement of domain nucleation and domain-wall propagation.

Cormier, M.; Jeudy, V.; Niazi, T.; Lucot, D.; Granada, M.; Cibert, J.; Lemaître, A.

2014-11-01

52

Magnetic anisotropy in Fe-25Cr-12Co-1Si alloy induced by external magnetic field  

E-print Network

of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China; 2. Department. Curriculum in Applied and Materials Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC on Fe-Cr-Co system have found applications in magnetic sensors, telephone receivers, hysteresis motors

Qin, Lu-Chang

53

Faraday rotation limits on a primordial magnetic field from Wilkinson Microwave Anisotropy Probe five-year data  

SciTech Connect

A primordial magnetic field in the early universe will cause Faraday rotation of the linear polarization of the cosmic microwave background generated via Compton scattering at the surface of last scattering. This rotation induces a nonzero parity-odd (B-mode) polarization component. The Wilkinson Microwave Anisotropy Probe 5-year data puts an upper limit on the magnitude of the B-polarization power spectrum; assuming that the B-polarization signal is totally due to the Faraday rotation effect, the upper limits on the comoving amplitude of a primordial stochastic magnetic field range from 6x10{sup -8} to 2x10{sup -6} G on a comoving length scale of 1 Mpc, depending on the power spectrum of the magnetic field.

Kahniashvili, Tina [Department of Physics and McWilliams Center for Cosmology, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States); Department of Physics, Laurentian University, Ramsey Lake Road, Sudbury, ON P3E 2C6 (Canada); National Abastumani Astrophysical Observatory, Ilia Chavchavadze State University, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Maravin, Yurii [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States); Kosowsky, Arthur [Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, Pennsylvania 15260 (United States)

2009-07-15

54

Faraday rotation limits on a primordial magnetic field from Wilkinson Microwave Anisotropy Probe five-year data  

NASA Astrophysics Data System (ADS)

A primordial magnetic field in the early universe will cause Faraday rotation of the linear polarization of the cosmic microwave background generated via Compton scattering at the surface of last scattering. This rotation induces a nonzero parity-odd (B-mode) polarization component. The Wilkinson Microwave Anisotropy Probe 5-year data puts an upper limit on the magnitude of the B-polarization power spectrum; assuming that the B-polarization signal is totally due to the Faraday rotation effect, the upper limits on the comoving amplitude of a primordial stochastic magnetic field range from 6×10-8 to 2×10-6G on a comoving length scale of 1 Mpc, depending on the power spectrum of the magnetic field.

Kahniashvili, Tina; Maravin, Yurii; Kosowsky, Arthur

2009-07-01

55

Towards nonvolatile magnetic crossbar arrays: A three-dimensional-integrated field-coupled domain wall gate with perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

A novel three-dimensional (3D)-integrated domain wall gate (DWG) providing direct control of the DW propagation in a magnetic nanowire with perpendicular magnetic anisotropy is presented. The pinning of field-driven DWs in a notch is controlled by the fringing fields of a subjacent gate magnet. Depending on the state of the gate magnet, the propagating DW is either pinned in the notch or its movement is supported. Theoretical calculations of controlled DW pinning are shown. We experimentally demonstrate control of the DW motion in magnetic nanowires by other domains in a separated gate layer using magnetic force microscopy. Regarding potential applications, the 3D DWG enables storing and buffering of magnetic domains in order to control the signal flow of 3D-integrated perpendicular nanomagnetic logic. Furthermore, due to the uniformity of input, output, and gate contact, the 3D DWG can act as nonvolatile logic device in order to realize field-driven logic gates and magnetic crossbar arrays.

Breitkreutz, Stephan; Eichwald, Irina; Ziemys, Grazvydas; Hiblot, Gaspard; Csaba, György; Schmitt-Landsiedel, Doris; Becherer, Markus

2015-05-01

56

Anisotropy and magnetic field effects on the entanglement of a two qubit Heisenberg XY chain.  

PubMed

We investigate the entanglement of a two-qubit anisotropic Heisenberg XY chain in thermal equilibrium at temperature T in the presence of an external magnetic field B along the z axis. By means of the combined influences of anisotropic interactions and a magnetic field B, one is able to produce entanglement for any finite T, by adjusting the magnetic field strength. This contrasts with the isotropic interaction or the B = 0 cases, for which there is no entanglement above a critical temperature T(c) that is independent of the external B field. PMID:11909386

Lagmago Kamta, G; Starace, Anthony F

2002-03-11

57

Magnetic anisotropies of quantum dots  

NASA Astrophysics Data System (ADS)

Magnetic anisotropies in quantum dots (QDs) doped by magnetic ions are discussed in terms of two frameworks: anisotropic g-factors and magnetocrystalline anisotropy energy [1]. Two examples, related to zinc-blende p-doped materials, are given of how these frameworks are utilized: four-level Hamiltonian of a flat QD and a cuboid infinite-well QD containing a single hole. The latter model, despite being an idealization of a real QD, displays a rich phenomenology of anisotropies. We quantify the anisotropy constants for ZnSe and CdTe QDs, confirming that the Ising-like effective Hamiltonians apply to magnetic QDs [2]. Compared to bulk systems, confinement tuning offers a new way to control easy axes in magnetic QDs. [1] K. Vyborny et al., preprint (2011). [2] C. Le Gall et al., Phys. Rev. Lett. 107, 057401 (2011).

Vyborny, Karel; Han, J. E.; Oszwaldowski, Rafal; Zutic, Igor; Petukhov, A. G.

2012-02-01

58

Crystal structures and magnetic anisotropy properties of Ni-Mn-Ga martensitic phases with giant magnetic-field-induced strain  

Microsoft Academic Search

Summary form only given. Magnetic shape memory materials are expected to have potential for a variety of actuating devices and sensors. Magnetic-field-induced rearrangement of the crystallographic domains (twin variants) can produce a large strain similar to a stress-induced one. We have found a giant magnetic field-induced strain approximately 10% at ambient temperature in a magnetic field less then 1 T

A. Sozinov; A. A. Likhachev; K. Ullakko

2002-01-01

59

Small-scale primordial magnetic fields and anisotropies in the cosmic microwave background radiation  

SciTech Connect

It is shown that small-scale magnetic fields present before recombination induce baryonic density inhomogeneities of appreciable magnitude. The presence of such inhomogeneities changes the ionization history of the Universe, which in turn decreases the angular scale of the Doppler peaks and increases Silk damping by photon diffusion. This unique signature could be used to (dis)prove the existence of primordial magnetic fields of strength as small as B ? 10{sup ?11} Gauss by cosmic microwave background observations.

Jedamzik, Karsten [Laboratoire de Univers et Particules, UMR5299-CNRS, Université de Montpellier II, F-34095 Montpellier (France); Abel, Tom, E-mail: karsten.jedamzik@um2.fr, E-mail: tabel@slac.stanford.edu [Kavli Institute for Particle Astrophysics and Cosmology, SLAC/Stanford University, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States)

2013-10-01

60

Magnetic nanoparticles with combined anisotropy  

NASA Astrophysics Data System (ADS)

We study the influence of the distribution of the particles' aspect ratio on the magnetostatic properties of an assembly of nanoparticles with cubic magnetocrystalline anisotropy, such as iron, nickel, iron oxides, and ferrites. Because of the large values of the dimensionless ratio Ms2/|Kc| for these particles, the shape anisotropy energy makes considerable contribution to the total nanoparticle energy even for relatively small shape distortions, with equivalent ellipsoids having aspect ratios ? ? 1.1. As a result, the magnetostatic properties of a randomly oriented assembly of particles with combined anisotropy at ? ? 1.1 are similar to those for an assembly of particles with purely uniaxial magnetic anisotropy. This conclusion is shown to be valid not only for the assembly hysteresis loops but also for the magnetic relaxation characteristics, at least in the high damping limit.

Usov, N. A.; Barandiarán, J. M.

2012-09-01

61

Effect of electric-field on the perpendicular magnetic anisotropy and strain properties in CoFeB/MgO magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

In this article, we investigate the effect of electric-field on the perpendicular magnetic anisotropy (PMA) and strain properties in nanoscaled CoFeB/MgO magnetic tunnel junction using tunnel magnetoresistance and piezoresponse force microscopy (PFM) measurements, respectively. We show that while the PMA change under electric-field is consistent with the previous reports, the PFM data show that the applied electric-field induces strain in a nanoscaled MgO. We demonstrate that the development of compressive and tensile strains corresponding to different polarities of applied electric-field. We discuss the interplay between the electric-field controlled PMA and strain properties. Our results may accelerate the development of magnetoelectrically controlled spintronic devices for low-power and high-density magnetic data storage applications.

Naik, V. B.; Meng, H.; Xiao, J. X.; Liu, R. S.; Kumar, A.; Zeng, K. Y.; Luo, P.; Yap, S.

2014-08-01

62

Out-of-plane anisotropy and low field induced magnetic domain reorientation in Al/Metglas-2605S2/Al trilayer sensors  

NASA Astrophysics Data System (ADS)

Local magnetism of Al/Metglas-2605S2/Al trilayer-like sensors prepared by dc sputtering has been studied at room temperature by both in-field and zero-field Mössbauer spectroscopy for a maximum field of 60 mT. Ferromagnetic domain reorientation from out-of-ribbon plane to in-plane, induced by low applied fields, was measured by monitoring the intensities of lines 2 and 5 in the Mössbauer sextet spectra obtained for different magnitudes of applied magnetic field. Coating the Metglas-2605S2 with Al layers of 20 ?m thickness, a stress-field is induced, allowing to distinguish different in-plane magnetic anisotropy distributions along the ribbon length (˜4 mT) as well along its width (˜10 mT). Using a phenomenological model for the magnetization reversal, out-of-plane anisotropies ranging up to 3 kJ/m3 were estimated for the Metglas-2605S2 alloy ribbons. This anisotropy range is similar to that observed for the in-plane case previously reported. The methodology applied in this work can be used to determine native out-of-plane anisotropy distributions for different melt-spun ribbons. It also allows understanding magnetization reversal associated with the ferromagnetic domains reorientation caused either by induced stress or by applied magnetic field.

Passamani, E. C.; Larica, C.; Moscon, P. S.; Mendoza Zélis, P.; Sánchez, F. H.

2011-08-01

63

Effect of a pinning field on the critical current density for current-induced domain wall motion in perpendicular magnetic anisotropy nanowires.  

PubMed

In this study, the effect of a pinning field on the critical current density for current-induced domain wall motion in nanowires with perpendicular magnetic anisotropy was investigated using micromagnetic simulations. In order to estimate the pinning field in notched nanowires, we conducted wall energy calculations for nanowires with various saturation magnetizations. The pinning field increased as the notch size increased. The pinning field decreased as the saturation magnetization decreased. As a result, the decreased in the pinning field causes the reduction of the critical current density. Therefore, a significant reduction of the critical current density can be obtained by decreasing the saturation magnetization, even if wall pinning occurs. PMID:23035485

Ooba, Ayaka; Fujimura, Yuma; Takahashi, Kota; Komine, Takashi; Sugita, Ryuji

2012-09-01

64

The theoretical account of the ligand field bonding regime and magnetic anisotropy in the DySc2N@C80 Single Ion Magnet endohedral fullerene.  

PubMed

Considering the DySc2N@C80 system as a prototype for Single Ion Magnets (SIMs) based on endohedral fullerenes, we present methodological advances and state-of-the art computations analysing the electronic structure and its relationship with the magnetic properties due to the Dy(III) ion. The results of the quantum chemical calculations are quantitatively decrypted in the framework of ligand field (LF) theory, extracting the full parametric sets and interpreting in heuristic key the outcome. An important result is the characterization of the magnetic anisotropy in the ground and excited states, drawing the polar maps of the state-specific magnetization functions that offer a clear visual image of the easy axes and account for the pattern of response to perturbations by the magnetic field applied from different space directions. The state-specific magnetization functions are derivatives with respect to the magnetic field, taken for a given eigenvalue of the computed spectrum. The methodology is based on the exploitation of the data from the black box of the ab initio spin-orbit (SO) calculations. The ground state is characterized by the Jz = ±15/2 quantum numbers with easy axis along the Dy-N bond. The implemented dependence on the magnetic field allowed the first-principles simulation of the magnetic properties. The computational approach to the properties of endohedral fullerenes is an important goal, helping to complement the scarcity of the experimental data on such systems, determined by the limited amount of samples. PMID:24789320

Cimpoesu, Fanica; Dragoe, Nita; Ramanantoanina, Harry; Urland, Werner; Daul, Claude

2014-06-21

65

Crystal structures and magnetic anisotropy properties of Ni-Mn-Ga martensitic phases with giant magnetic-field-induced strain  

Microsoft Academic Search

Several kinds of martensitic phases have been found in nonstoichiometric Ni2MnGa alloys in numerous recent studies. The structural, magnetic, and mechanical properties important for a giant magnetic-field-induced strain response in these alloys are presented. Depending on the martensite crystal structure Ni-Mn-Ga alloys are able to show a really giant (about 6% or 10%) strain response in a magnetic field less

A. Sozinov; A. A. Likhachev; K. Ullakko

2002-01-01

66

Magnetocrystalline anisotropy and its electric-field-assisted switching of Heusler-compound-based perpendicular magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

Employing density functional theory combined with the non-equilibrium Green's function formalism, we systematically investigate the structural, magnetic and magnetoelectric properties of the Co2FeAl(CFA)/MgO interface, as well as the spin-dependent transport characteristics of the CFA/MgO/CFA perpendicular magnetic tunnel junctions (p-MTJs). We find that the structure of the CFA/MgO interface with the oxygen-top FeAl termination has high thermal stability, which is protected by the thermodynamic equilibrium limit. Furthermore, this structure is found to have perpendicular magnetocrystalline anisotropy (MCA). Giant electric-field-assisted modifications of this interfacial MCA through magnetoelectric coupling are demonstrated with an MCA coefficient of up to 10-7 erg V-1 cm. In addition, our non-collinear spin transport calculations of the CFA/MgO/CFA p-MTJ predict a good magnetoresistance performance of the device.

Bai, Zhaoqiang; Shen, Lei; Cai, Yongqing; Wu, Qingyun; Zeng, Minggang; Han, Guchang; Feng, Yuan Ping

2014-10-01

67

Measuring low alternating magnetic fields by means of Bi-containing rare-earth ferrite-garnet films with planar anisotropy  

Microsoft Academic Search

A method of magnetization control through homogeneous rotation has been applied to Bi-containing rare-earth ferrite-garnet films with planar anisotropy. A dynamical range of 160 dB for low alternating magnetic fields detected at f=50 kHz is shown. A minimum detectable field (10?7 Oe) is limited by the sensitivity of polarimeter at the wavelength of the Ar-ion laser ?=514.5 nm, and the

Peter M. Vetoshko; Vadim B. Volkovoy; Vladimir N. Zalogin; Andrey Yu. Toporov

1991-01-01

68

Tailoring the exciton fine structure of cadmium selenide nanocrystals with shape anisotropy and magnetic field.  

PubMed

We use nominally spheroidal CdSe nanocrystals with a zinc blende crystal structure to study how shape perturbations lift the energy degeneracies of the band-edge exciton. Nanocrystals with a low degree of symmetry exhibit splitting of both upper and lower bright state degeneracies due to valence band mixing combined with the isotropic exchange interaction, allowing active control of the level splitting with a magnetic field. Asymmetry-induced splitting of the bright states is used to reveal the entire 8-state band-edge fine structure, enabling complete comparison with band-edge exciton models. PMID:25329623

Sinito, Chiara; Fernée, Mark J; Goupalov, Serguei V; Mulvaney, Paul; Tamarat, Philippe; Lounis, Brahim

2014-11-25

69

Electric field switching of the magnetic anisotropy of a ferromagnetic layer exchange coupled to the multiferroic compound BiFeO3.  

PubMed

We report here that a Permalloy layer deposited on top of a multiferroic BiFeO3 single crystal acquires an easy magnetic direction along the propagation vector of the cycloidal arrangement of antiferromagnetic moments in BiFeO3. This anisotropy originates from a direct magnetic coupling with the canted spins forming the cycloid. Moreover, we show that an electric field-induced change of electric polarization is able to toggle the direction of anisotropy in the ferromagnet through the magnetoelectric effect, which links the antiferromagnetic spins to the local polarization in BiFeO3. PMID:20366284

Lebeugle, D; Mougin, A; Viret, M; Colson, D; Ranno, L

2009-12-18

70

Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films with Perpendicular Magnetic Anisotropy  

NASA Technical Reports Server (NTRS)

L1(sub 0)-ordered FePd epitaxial thin films were prepared using dc magnetron sputter deposition on MgO (001) substrates. The films were grown with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured domain size/period and magnetic anisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

Skuza, J. R.; Clavero, C.; Yang, K.; Wincheski, B.; Lukaszew, R. A.

2009-01-01

71

Cotton-mouton effects, magnetic hyperpolarizabilities, and magnetic anisotropies of the methyl halides. Comparison with molecular Zeeman and high-field NMR spectroscopic results  

SciTech Connect

Measurements of the vapor-phase Cotton-Mouton effects of methyl fluoride, methyl bromide, and methyl iodide are reported. Analysis of the results, in conjunction with those of an earlier study of methane and methyl chloride, shows that in the series CH{sub 3}X (X = H, F, Cl, Br, I) the magnetic hyperpolarizabiity anisotropy, which is related to the quadratic response of the molecular polarizability to a magnetic field, is positive in sign and roughly proportional in magnitude to the mean polarizability. The magnetic anisotropies (10{sup 29}{Delta}{sub {chi}}/J T{sup {minus}2}) found for methyl chloride,methyl bromide, and methyl iodide (CH{sub 3}Cl, {minus}15.0 {plus minus} 1.3; CH{sub 3}Br, -15.1 {plus minus} 0.8; CH{sub 3}I, {minus}18.0 {plus minus} 1.5) are compared with values obtained by the molecular Zeeman and high-field {sup 2}H NMR spectroscopic methods.

Coonan, M.H.; Ritchie, G.L.D. (Univ. of New England, Armidale, New South Wales (Australia))

1991-02-07

72

Magnetic Anisotropy in the Radula of Chiton  

NASA Astrophysics Data System (ADS)

Radular teeth of chitons were studied by using magnetic torque-meter and transmission electron microscopy (TEM). The magnetic torque curves give clear evidence of presence of strong uni-axial magnetic anisotropy. The easy axis is along the length direction of tongue-like radula. The TEM pattern shows that long chip-like magnetite nano-scaled particles packed in the radular teeth with both uni-axial shape anisotropy and magneto-crystalline anisotropy.

Zhao, Jian-Gao; Qian, Xia; Liu, Wei; Liu, Chuan-Lin; Zhan, Wen-Shan

2000-07-01

73

The Large Scale Structure of the Galactic Magnetic Field and High Energy Cosmic Ray Anisotropy  

E-print Network

Galactic hemisphere if the field is of even parity and axi-symmetric (ASS). There is no sensitivity to the BSS or ASS configurations if the field is of odd parity. 1. Introduction The position of the Solar of the spiral field, axi-symmetric (ASS) or bi-symmetric (BSS) [2, 9]. The number of field reversals is still

74

Determination of magnetic anisotropy of magnetically hard materials  

SciTech Connect

The determination of the first-order anisotropy field strength using the torsion pendulum method is described. Since the applied field need not necessarily be in the range of the anisotropy field, this method is particularly useful for characterizing modern permanent magnet materials which have a very high uniaxial anisotropy. The method requires oriented samples. Measurements were made on polycrystalline samples of NdFeB, SmCo, and barium ferrite. The method is described and error sources are discussed. It is pointed out that the torsion pendulum method is closely related to reversible transverse susceptibility measurements. It is shown both experimentally and theoretically, that using susceptibility measurements similar results can be obtained. The susceptibility method is, however, not applicable to conducting materials at present.

Richter, H.J. (Institut fuer Werkstoffe der Elektrotechnik, RWTH Aachen, University of Technology, 5100 Aachen, Templergraben 55, Federal Republic of Germany (DE))

1990-03-15

75

The magnetic anisotropy of mantle peridotites  

NASA Astrophysics Data System (ADS)

Previous magnetic anisotropy studies in peridotites have shown that secondary magnetite dominates their low-field AMS. This magnetite is formed during serpentinization processes along the foliation plane and along fractures. In serpentinized peridotites from the Mid-Atlantic Ridge, the long axis of the low-field AMS ellipsoid, was reported to be parallel to the [100] olivine axis while the short axis was parallel to [001]. In extensively serpentinized peridotites of the same area, secondary pseudo-single domain (PSD) magnetite was dispersed and no relationship between olivine LPO and magnetic fabric existed. In general, the shape fabric of magnetite does not relate to either the olivine LPO or the primary silicate flow fabrics. Therefore, the low-field AMS of mantle peridotites cannot provide useful information on mantle flow fabrics. The separation of the primary silicate paramagnetic fabric component from the bulk, i.e., ferromagnetic and paramagnetic, AMS fabric is necessary for flow studies in peridotites. In a previous study of serpentinized harzburgites from an ophiolite, others proposed to isolate the ferromagnetic component from the bulk AMS by using the anisotropy of anhysteretic remanence. This approach, based on the subtraction of the AARM tensor (carried by ferromagnetic phases only) from the low-field AMS tensor, may be misleading because the AARM fabric of ferromagnetic phases does not exactly correspond to their low-field AMS fabric. This is particularly true with regards to the degree of anisotropy. The normalized AARM tensor theoretically solves this problem in the case of multi-domain magnetic fabrics. However the AARM tensor normalization cannot be easily applied to rocks with a range of grain-sizes from single domain to multi-domain. At this point the paramagnetic component of the AMS fabric can be isolated only by using torque magnetometry a technique requiring 4 to 6 hours per specimen. More recently we have developed a new magnetic fabric method, based on high-field measurements, above the saturation of ferromagnetic phases, using a vibrating sample magnetometer. This technique has been succesfully tested on the Twin Sisters dunite massif, in Washington State, which was chosen because of its petrological simplicity and moderate degree of serpentinization. The paramagnetic component of the AMS is controlled by the magnetocrystalline anisotropy of mafic silicates which, in turn, should coincide with olivine LPOs. The principal current challenge is to investigate the geometric relationship between the high-field magnetic fabrics and the olivine LPOs measured on the same specimens.

Ferre, E. C.

2003-12-01

76

Influence of ferroelectric polarization on magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Thin film heterostructures of transition metal ferromagnets (FM) and polymer ferroelectrics (FE) are investigated to look for changes in the magnetic anisotropy of the FM layer that occur on switching the FE polarization (with an ensuing change in the electric field direction).[1] Samples of [Glass/ Pd (50 nm)/Co wedge (0.9-2.6nm)/ferroelectric P(VDF-TrFE) (53 nm)/Al (30nm)] are deposited via sputtering or evaporation for the metallic layers and via Langmuir-Schaefer deposition for the polymer ferroelectric. [2] Magnetic and FE properties have been characterized using the Magneto-Optical Kerr Effect (MOKE) and the pyroelectric effect. Polar and longitudinal MOKE loops are measured across the Co wedge for both positive and negative FE polarization and the difference in the two MOKE loops is ascribed to the changes in the magnetic anisotropy of the FM layer. [3] These changes are most apparent in the region where the Co undergoes a transition from in-plane to out-of-plane anisotropy. This research is supported by the NSF MRSEC through Grant No. DMR- 0820521 1. Chun-Gang Duan et al, Appl. Phys. Lett. 92, 122905 (2008) 2. A. V. Bune, et al, Nature (London) 391, 874 (1998) 3. P. F. Carcia, J.Appl. Phys. 63, 5066 (1988)

Mardana, A.; Ducharme, S.; Adenwalla, S.

2010-03-01

77

THE EFFECTS OF PLASMA BETA AND ANISOTROPY INSTABILITIES ON THE DYNAMICS OF RECONNECTING MAGNETIC FIELDS IN THE HELIOSHEATH  

SciTech Connect

The plasma {beta} (the ratio of the plasma pressure to the magnetic pressure) of a system can have a large effect on its dynamics as high {beta} enhances the effects of pressure anisotropies. We investigate the effects of {beta} in a system of stacked current sheets that break up into magnetic islands due to magnetic reconnection, which is analogous to the compressed heliospheric current sheet in the heliosheath. We find significant differences between systems with low and high initial values of {beta}. At low {beta}, growing magnetic islands are modestly elongated and become round as contraction releases magnetic stress and reduces magnetic energy. At high {beta}, the increase of the parallel pressure in contracting islands causes saturation of modestly elongated islands as island cores approach the marginal firehose condition. Only highly elongated islands reach finite size. The anisotropy within these islands prevents full contraction, leading to a final state of highly elongated islands in which further reconnection is suppressed. The elongation of islands at finite {beta} is further enhanced by reducing the electron-to-ion mass ratio to more realistic values. The results are directly relevant to reconnection in the sectored region of the heliosheath where there is evidence that elongated islands are present, and possibly to other high-{beta} systems such as astrophysical accretion flows and the magnetosphere of Saturn.

Schoeffler, K. M.; Drake, J. F.; Swisdak, M. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742-3511 (United States)

2011-12-10

78

The influence of magnetic aftereffects on the magnetic anisotropy  

NASA Astrophysics Data System (ADS)

There were investigated the time dependences of the magnetic anisotropy characteristics of artificial depositions received in the geomagnetic field. The content of magnetite in the nonmagnetic matrix of kaolin did not exceed 1%. The Co content in the grains of magnetite Fe3 O4 was 0.0018%. The viscous magnetization was created in the depositions with grain sizes of Fe3O4 in micrometers (0 ÷ 8), (9 ÷ 16), (17 ÷ 32), (33 ÷ 64), (65 ÷ 100), (101 ÷ 150). The X-ray method of direct pole figures indicates that the intensity of the ordering of the ferromagnetic grains in the depositions depends strongly on the grain size in the above-mentioned ranges, getting reduced from 1.9 to 1.1. Compared with the characteristics received immediately after drying the samples and after holding them for two years in the earth's magnetic field in the direction of In, one could observe increase in all the characteristics of the magnetic anisotropy. The magnitude Hd of the magnetic field having the periodicity change of Hd 2? to ? increases. This indicates the stabilization of the new domain structure. The increase in the uniaxial anisotropy constant (K) is associated with the emergence of the large induced anisotropy due to the diffusion of Co ions. It was found out that the constant K decreases markedly with increasing particle size in the range from 8 mm to 40 microns. Based on the results of the X-ray analysis by using the method direct pole figures, it may be explained by the creation of the axial texture in the depositions with grains having the size less than 40 microns. The intensity of more than 40 microns decreases insignificantly - from 1.3 to 1.1. After creating the viscous magnetization in two years, the constant K has increased by 1.5 - 2 times. The influence of the magnetic after-effects on K in strong magnetic fields denotes the diffusion nature of the viscous magnetization. The losses of the rotational magnetic hysteresis (W) also rise in the presence of the structural defects and internal stresses. The value of the maximum loss (Wm) increases the more the smaller the grain size Fe3O4.The greatest influence of magnetic viscosity is exercised on the depositions having d < 40 microns. It is shown that there is a correlation between the dependence of the temporal variation of Wm and the dependence of the coefficients of the magnetic viscosity on the ferromagnetic grain size. The magnitude of the magnetic field (HW), corresponding to the maximum losses and characterizing the beginning of the transition of the spins from the connection with the crystal lattice to the connection with the external magnetic field, does not change. So, the magnetic field HW can be considered as an indicator of the composition of the ferromagnetic fraction. Depending on the composition of the ferromagnetic, value HW has a wide range of values. For the depositions, containing magnetite grains, the value of HW makes up 1.8 kOe, and for the grains of hematite it is 9 kOe. Thus, the contribution to the effective anisotropy of rocks containing large particles of the ferromagnetic fraction, can not be explained by the energy of crystallographic anisotropy. Diffusion magnetic anisotropy is a widely spread phenomenon in the rocks.

Mashukov, A.; Mashukova, A.

2012-04-01

79

The magnetic properties of the spin-1 Heisenberg antiferromagnetic chain with single-ion anisotropy  

NASA Astrophysics Data System (ADS)

The magnetic properties of the spin-1 Heisenberg antiferromagnetic chain with exchange anisotropy and single-ion anisotropy are studied by the double-time Green's function method. The determinative equations for the critical temperature, the magnetization, and the zero-field susceptibility are derived analytically. The effects of the anisotropies on the magnetic properties are presented.

Hu, Gangsan; Zhu, Rengui

2015-02-01

80

Iron-gallium alloys : temperature and field effects on [lambda]100 and magnetic anisotropy measurements  

E-print Network

Magnetostriction measurements were taken on samples of Fe-Ga alloys (Galfenol) containing between 18% and 35% Ga in fields of 5 kOe to 24 kOe from room temperature to liquid nitrogen temperature. In addition, room temperature ...

Lichter, Jenny, 1982-

2004-01-01

81

Growth anisotropy effect of bulk high temperature superconductors on the levitation performance in the applied magnetic field  

NASA Astrophysics Data System (ADS)

Growth anisotropies of bulk high temperature superconductors (HTSCs) fabricated by a top-seeded melt texture growth process, that is, different pinning effect in the growth sectors (GSs) and growth sector boundaries (GSBs), possess effect on the macro flux trapping and levitation performance of bulk HTSCs. Previous work (Physics Procedia, 36 (2012) 1043) has found that the bulk HTSC array with aligned GSB pattern (AGSBP) exhibits better capability for levitation and suppression of levitation force decay above a permanent magnet guideway (PMG) compared with misaligned GSB pattern (MGSBP). In this paper, we further examine this growth anisotropy effect on the maglev performance of a double-layer bulk HTSC. In contrast to reported trapped flux cases (Supercond. Sci. Technol. 19 (2006) S466), the two superposed bulk HTSCs with same AGSBP with PMG are found to show better maglev performance. These series of results are helpful and support a new way for the performance optimization of present HTS maglev systems.

Zheng, J.; Liao, X. L.; Jing, H. L.; Deng, Z. G.; Yen, F.; Wang, S. Y.; Wang, J. S.

2013-10-01

82

Magnetic Moment and Anisotropy of Individual Co Atoms on Graphene  

NASA Astrophysics Data System (ADS)

We report on the magnetic properties of single Co atoms on graphene on Pt(111). By means of scanning tunneling microscopy spin-excitation spectroscopy, we infer a magnetic anisotropy of K=-8.1meV with out-of-plane hard axis and a magnetic moment of 2.2?B. Co adsorbs on the sixfold graphene hollow site. Upon hydrogen adsorption, three differently hydrogenated species are identified. Their magnetic properties are very different from those of clean Co. Ab initio calculations support our results and reveal that the large magnetic anisotropy stems from strong ligand field effects due to the interaction between Co and graphene orbitals.

Donati, F.; Dubout, Q.; Autès, G.; Patthey, F.; Calleja, F.; Gambardella, P.; Yazyev, O. V.; Brune, H.

2013-12-01

83

Anisotropy of MHD Turbulence at Low Magnetic Reynolds Number  

NASA Technical Reports Server (NTRS)

Turbulent fluctuations in MHD flows are known to become dimensionally anisotropic under the action of a sufficiently strong magnetic field. We consider the technologically relevant case of low magnetic Reynolds number and apply the method of DNS of forced flow in a periodic box to generate velocity fields. The analysis based on different anisotropy characteristics shows that the dimensional anisotropy is virtually scale-independent. We also find that, except for the case of very strong magnetic field, the flow is componentally isotropic. Its kinetic energy is practically uniformly distributed among the velocity components.

Zikanov, O.; Vorobev, A.; Thess, A.; Davidson, P. A.; Knaepen, B.

2004-01-01

84

Low-temperature magnetic anisotropy in micas and chlorite  

NASA Astrophysics Data System (ADS)

Phyllosilicates, such as micas and chlorite, are common rock-forming minerals and often show preferred orientation in deformed rocks. In combination with single-crystal anisotropy, this leads to anisotropy of physical properties in the rock, such as magnetic susceptibility. In order to effectively use the magnetic anisotropy to understand a rock fabric, it is necessary to identify the minerals responsible for the magnetic anisotropy. Techniques have been developed to separate contributions of the ferrimagnetic, antiferromagnetic, paramagnetic, and diamagnetic susceptibilities to the anisotropy of magnetic susceptibility. Because diamagnetic and paramagnetic susceptibility are both linearly dependent on field, separation of the anisotropic contributions requires understanding how the degree of anisotropy of the paramagnetic susceptibility changes as a function of temperature. Note that diamagnetic susceptibility is not dependent on temperature. The increase in paramagnetic anisotropy at low temperature is used to separate the paramagnetic and diamagnetic subfabrics, and can be expressed by the p77 factor. In this study, we determined p77, which is the change in the degree of anisotropy (?k) between room temperature (298 K) and liquid nitrogen temperature (77 K), for a series of micas and chlorite. The paramagnetic susceptibility ellipsoid is highly oblate with the minimum principal susceptibility normal to the silicate layers at both 77 K and RT. The degree of anisotropy ?k increases by a factor of approximately 6.3-8.7 for individual samples of muscovite, phlogopite and chlorite on cooling from RT to 77 K and between 11.2 and 12.4 for biotite. A decrease in temperature enhances the paramagnetic anisotropy in a mineral. Biotite exhibits a relatively stronger enhancement due to the onset of magnetic ordering below ~ 100 K. This can have important implications for interpreting low temperature anisotropy in mudstones, mica schists and gneisses.

Biedermann, Andrea R.; Bender Koch, Christian; Lorenz, Wolfram E. A.; Hirt, Ann M.

2014-08-01

85

ANISOTROPY DETERMINATIONS IN EXCHANGE SPRING MAGNETS.  

SciTech Connect

Ferromagnetic nanocomposites, or ''exchange spring'' magnets, possess a nanoscaled microstructure that allows intergrain magnetic exchange forces to couple the constituent grains and alter the system's effective magnetic anisotropies. While the effects of the anisotropy alterations are clearly seen in macroscopic magnetic measurement, it is extremely difficult to determine the detailed effects of the system's exchange coupling, such as the interphase exchange length, the inherent domain wall widths or the effective anisotropies of the system. Clarification of these materials parameters may be obtained from the ''micromagnetic'' phenomenological model, where the assumption of magnetic reversal initiating in the magnetically-soft regions of the exchange-spring maqet is explicitly included. This approach differs from that typically applied by other researchers and allows a quantitative estimate of the effective anisotropies of an exchange spring system. Hysteresis loops measured on well-characterized nanocomposite alloys based on the composition Nd{sub 2}Fe{sub 14}B + {alpha}-Fe at temperatures above the spin reorientation temperature were analyzed within the framework of the micromagnetic phenomenological model. Preliminary results indicate that the effective anisotropy constant in the material is intermediate to that of bulk {alpha}-Fe and bulk Nd{sub 2}Fe{sub 14}B and increases with decreasing temperature. These results strongly support the idea that magnetic reversal in nanocomposite systems initiates in the lower-anisotropy regions of the system, and that the soft-phase regions become exchange-hardened by virtue of their proximity to the magnetically-hard regions.

LEWIS,L.H.; HARLAND,C.L.

2002-08-18

86

Magnetic anisotropy due to the Casimir effect  

SciTech Connect

We consider the Casimir interaction between a ferromagnetic and a nonmagnetic mirror and show how the Casimir effect gives rise to a magnetic anisotropy in the ferromagnetic layer. The anisotropy is out of plane if the nonmagnetic plate is optically isotropic. If the nonmagnetic plate shows a uniaxial optical anisotropy (with optical axis in the plate plane), we find an in-plane magnetic anisotropy. In both cases, the energetically most favorable magnetization orientation is given by the competition between polar, longitudinal, and transverse contributions to the magneto-optical Kerr effect and will therefore depend on the interplate distance. Numerical results will be presented for a magnetic plate made out of Fe and nonmagnetic plates of Au (optically isotropic), quartz, calcite, and barium titanate (all uniaxially birefringent).

Metalidis, G.; Bruno, P. [Institut fuer Theoretische Festkoerperphysik, Karlsruhe Institut fuer Technologie (KIT), D-76131 Karlsruhe (Germany); European Synchrotron Radiation Facility, Boite Postale 220, F-38043 Grenoble Cedex (France)

2010-02-15

87

Carrier-dependent magnetic anisotropy of cobalt doped titanium dioxide.  

PubMed

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

Shao, Bin; Feng, Min; Zuo, Xu

2014-01-01

88

Carrier-dependent magnetic anisotropy of cobalt doped titanium dioxide  

PubMed Central

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

Shao, Bin; Feng, Min; Zuo, Xu

2014-01-01

89

Magnetization reversal of patterned disks with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Magnetic vortex dynamics in magnetic disks have been extensively studied. However, spin dynamics in magnetic disks with perpendicular magnetic anisotropy (PMA) still remain to be fully understood. Magnetic configurations in disks with strong PMA are more complicated than magnetic vortices, resulting in novel spin dynamics with potential applications. In this work, we study the magnetization reversal of Co/Pd multilayered disks with PMA. Magnetic disks (3-8 microns in diameter) with the structure of [Co (0.3 nm)/Pd (0.5 nm)]5/Co(0.3nm) were patterned on Si substrates via direct laser writing lithography, electron beam evaporation, and lift-off methods. A Kerr microscope was used to image magnetization reversal processes at various bias fields. The imaging results revealed a nucleation dominated magnetization reversal process with the growth of dendritic domains. The coercivity of the disks is significantly bigger than that of thin films with the same structure. Quantitative analysis of the real time Kerr imaging results shed light on the magnetization reversal mechanism of the patterned disks with PMA. Work at Bryn Mawr is supported by NSF under Grant No. 1053854. Work at Argonne National Laboratory and use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Xiao, Zhuyun; Wang, Xiao; Cheng, X. M.; Liu, Yaohua; Te Velthuis, Suzanne G. E.; Rosenmann, Daniel; Divan, Ralu

2013-03-01

90

Magnetic anisotropy in a heavy atom radical ferromagnet.  

PubMed

High-field, single-crystal EPR spectroscopy on a tetragonal bisdiselenazolyl ferromagnet has provided evidence for the presence of easy-axis magnetic anisotropy, with the crystallographic c axis as the easy axis and the ab plane as the hard plane. The observation of a zero-field gap in the resonance frequency is interpreted in terms of an anisotropy field several orders of magnitude larger than that observed in light-heteroatom, nonmetallic ferromagnets and comparable (on a per-site basis) to that observed in hexagonal close packed cobalt. The results indicate that large spin-orbit-induced magnetic anisotropies, typically associated with 3d-orbital-based ferromagnets, can also be found in heavy p-block radicals, suggesting that there may be major opportunities for the development of heavy p-block organic magnetic materials. PMID:21553880

Winter, Stephen M; Datta, Saiti; Hill, Stephen; Oakley, Richard T

2011-06-01

91

Three-dimensional mapping of single-atom magnetic anisotropy.  

PubMed

Magnetic anisotropy plays a key role in the magnetic stability and spin-related quantum phenomena of surface adatoms. It manifests as angular variations of the atom's magnetic properties. We measure the spin excitations of individual Fe atoms on a copper nitride surface with inelastic electron tunneling spectroscopy. Using a three-axis vector magnet we rotate the magnetic field and map out the resulting variations of the spin excitations. We quantitatively determine the three-dimensional distribution of the magnetic anisotropy of single Fe atoms by fitting the spin excitation spectra with a spin Hamiltonian. This experiment demonstrates the feasibility of fully mapping the vector magnetic properties of individual spins and characterizing complex three-dimensional magnetic systems. PMID:25664924

Yan, Shichao; Choi, Deung-Jang; Burgess, Jacob A J; Rolf-Pissarczyk, Steffen; Loth, Sebastian

2015-03-11

92

Cotton-mouton effects, magnetic hyperpolarizabilities, and magnetic anisotropies of the methyl halides. Comparison with molecular Zeeman and high-field NMR spectroscopic results  

Microsoft Academic Search

Measurements of the vapor-phase Cotton-Mouton effects of methyl fluoride, methyl bromide, and methyl iodide are reported. Analysis of the results, in conjunction with those of an earlier study of methane and methyl chloride, shows that in the series CHâX (X = H, F, Cl, Br, I) the magnetic hyperpolarizabiity anisotropy, which is related to the quadratic response of the molecular

Michael H. Coonan; Geoffrey L. D. Ritchie

1991-01-01

93

Constraint on the primordial vector mode and its magnetic field generation from seven-year Wilkinson Microwave Anisotropy Probe observations  

NASA Astrophysics Data System (ADS)

It is often stated that the cosmological vector mode has only a decaying mode and gives negligible effects on cosmological observations. The vector mode, however, has a growing mode if there exists anisotropic stress in energy distributions in the universe. In this paper, we consider a primordial vector mode sustained by free-streaming neutrinos and its associated magnetic field generation. First, we put an observational constraint on the amount of the vector mode from the 7-year WMAP data. The constraint is found as rv?-(r)/(40)+0.012, where rv and r are the amounts of vector and tensor perturbation amplitudes with respect to the scalar one, respectively. Second, we calculate the spectrum of magnetic fields inevitably created from the primordial vector mode, given the constraint on rv. It is found that the maximum amount of magnetic fields generated from the vector mode is given by B?10-22G((rv)/(0.012))1/2((k)/(0.002))(nv+1)/2, with nv being a spectral index of the vector mode. We find a nontrivial cancellation of the magnetic field generation in the radiation-dominated era, which creates a characteristic cutoff in the magnetic field spectrum around k?1.0Mpc-1.

Ichiki, Kiyotomo; Takahashi, Keitaro; Sugiyama, Naoshi

2012-02-01

94

Rock magnetism and the interpretation of anisotropy of magnetic susceptibility  

Microsoft Academic Search

The conventional rules, derived from empirical and theoretical considerations, for the interpretation of anisotropy of magnetic susceptibility (AMS) in terms of microstructure and deformation are subject to numerous exceptions as a result of particular rock magnetic effects. Unusual relationships between structural and magnetic axes (so-called inverse or intermediate magnetic fabrics) can occur because of the presence of certain magnetic minerals,

P. Rochette; M. Jackson; C. Aubourg

1992-01-01

95

First-Principles Study of Electric Field Effects on Magnetic Anisotropy in Ultrathin Ferromagnetic TM (TM = Fe, Co) Films on Pt(111) Underlayer  

NASA Astrophysics Data System (ADS)

We study the electric field (EF) effects on the magnetic anisotropy in the ultrathin ferromagnetic TM (TM = Fe, Co) films on the Pt(111) underlayer using relativistic first-principles calculations based on the density functional theory with a special attention on the effects of Pt segregation. The magnetic anisotropy energy, MAE, and the spin magnetic moment, Mspin, of the Pt/TM/Pt(111) and BeO/Pt/TM/Pt(111) systems as well as those of the TM/Pt(111) and BeO/TM/Pt(111) systems are calculated in the absence of or under the EF. It is found that the MAE and its EF dependence of the BeO/Pt/TM/Pt(111) systems, especially those of the BeO/Pt/Co/Pt(111) system, are considerably large. The sign of the EF dependence is such that the MAE and Mspin are increased (decreased) when the EF increases (decreases) the number of electrons in the system. We attribute this unique behavior to the formation of the hybridized majority-spin states originated in the O 2pz, Pt 5d3z2 - r2, and TM 3d orbitals of the interfacial atoms.

Suzuki, Shugo; Shiota, Masashi; Fukuchi, Yasushi; Seki, Saori

2015-01-01

96

Bulk modulus of the nanoparticle system in concentrated magnetic fluids and local field-induced structural anisotropy  

E-print Network

In the present study we probe the bulk modulus and the structure of concentrated magnetic fluids by Small Angle X-ray Scattering. The electrostatically stabilized nanoparticles experience a repulsive interparticle potential modulated by dipolar magnetic interactions. On the interparticle distance lengthscale, we show that nanoparticles are trapped under-field in oblate cages formed by their first neighbours. We propose a theoretical model of magnetostriction for the field-induced deformation of the cage. This model captures the anisotropic features of the experimentally observed scattering pattern on the local scale in these strongly interacting colloidal dispersions.

E. Wandersman; A. C?bers; E. Dubois; G. Mériguet; A. Robert; R. Perzynski

2013-09-25

97

The ligand field of the azido ligand: insights into bonding parameters and magnetic anisotropy in a Co(II)-azido complex.  

PubMed

The azido ligand is one of the most investigated ligands in magnetochemistry. Despite its importance, not much is known about the ligand field of the azido ligand and its influence on magnetic anisotropy. Here we present the electronic structure of a novel five-coordinate Co(II)-azido complex (1), which has been characterized experimentally (magnetically and by electronic d-d absorption spectroscopy) and theoretically (by means of multireference electronic structure methods). Static and dynamic magnetic data on 1 have been collected, and the latter demonstrate slow relaxation of the magnetization in an applied external magnetic field of H = 3000 Oe. The zero-field splitting parameters deduced from static susceptibility and magnetizations (D = -10.7 cm(-1), E/D = 0.22) are in excellent agreement with the value of D inferred from an Arrhenius plot of the magnetic relaxation time versus the temperature. Application of the so-called N-electron valence second-order perturbation theory (NEVPT2) resulted in excellent agreement between experimental and computed energies of low-lying d-d transitions. Calculations were performed on 1 and a related four-coordinate Co(II)-azido complex lacking a fifth axial ligand (2). On the basis of these results and contrary to previous suggestions, the N3(-) ligand is shown to behave as a strong ? and ? donor. Magnetostructural correlations show a strong increase in the negative D with increasing Lewis basicity (shortening of the Co-N bond distances) of the axial ligand on the N3(-) site. The effect on the change in sign of D in going from four-coordinate Co(II) (positive D) to five-coordinate Co(II) (negative D) is discussed in the light of the bonding scheme derived from ligand field analysis of the ab initio results. PMID:25588991

Schweinfurth, David; Sommer, Michael G; Atanasov, Mihail; Demeshko, Serhiy; Hohloch, Stephan; Meyer, Franc; Neese, Frank; Sarkar, Biprajit

2015-02-11

98

Voltage controlled magnetic anisotropy in magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

Recently, voltage controlled magnetic anisotropy (VCMA) in 3d transitional ferromagnets (FM) has attracted a great deal of attentions. VCMA has traditionally been explored in multiferroic materials and diluted magnetic semiconductors, but not in metals because of the anticipated negligible effects since the electric field would be screened within 1-2 å at the metal surface. However, a voltage may exert marked effects if the magnetic properties of ultrathin films are dominated by interfacial magnetic anisotropy. Here we demonstrate a large VCMA effect in perpendicular MgO magnetic tunnel junctions (p-MTJs) with very thin CoFeB layers. The p-MTJs have the key structure of Co40Fe40B20(1.2-1.3nm)/MgO(1.2-2nm)/Co40Fe40B20(1.6nm) exhibiting at room temperature tunneling magnetoresistance in excess of 100%. The perpendicular magnetic anisotropy (PMA) in this system is believed to be stabilized by hybridization between the out-of-plane 3d orbitals of the FM and oxygen 2p orbitals. We show that both the magnitude and the direction of the electric field can systematically alter the PMA of the thin CoFeB layers interfaced with the MgO barrier. Furthermore, under a given electric field, the two CoFeB layers on either side of the MgO barrier respond in the opposite manner as expected. By exploiting the combined effect of spin transfer torque and VCMA in CoFeB/MgO/CoFeB nanopillars, we have accomplished voltage controlled spintronic devices, where the MTJ can be manipulated by a unipolar switching process using consecutive negative voltages less than 1.5 V in magnitude. In this manner, voltage can access the high resistance or the low resistance state of an MTJ with very small current densities. Wang, W.-G., Li, M., Hageman, S. & Chien, C. L. Electric-field-assisted switching in magnetic tunnel junctions. Nature Materials 11, 64 (2012).

Wang, Weigang

2013-03-01

99

Magnetic anisotropy of Plio–Pleistocene sediments from the Adriatic margin of the northern Apennines (Italy): implications for the time–space evolution of the stress field  

Microsoft Academic Search

The anisotropy of magnetic susceptibility (AMS) of the marine fine-grained Plio–Pleistocene sediments that crop out at the eastern (Adriatic) front of the central–northern Apennines (Italy) indicates a prevalent sedimentary-compactional magnetic fabric with variable overprint of the tectonic strain. The degree of anisotropy and the geometry of the AMS ellipsoids suggest a subdivision of the studied sediments in two distinct ages:

Leonardo Sagnotti; Aldo Winkler; Paola Montone; Letizia Di Bella; Fabio Florindo; Maria Teresa Mariucci; Fabrizio Marra; Laura Alfonsi; Alberto Frepoli

1999-01-01

100

Shape effect on in-plane anisotropy in magnetic dots  

Microsoft Academic Search

We have studied the spin waves in square and rectangular dots by Brillouin light scattering. The effects of the demagnetizing field are investigated and commented. In square dots, the observed fourfold symmetry configurational in-plane anisotropy is qualitatively interpreted as resulting from the non-homogeneous profile of the static magnetization.

S. M. Chérif; Y. Roussigné; C. Dugautier; P. Moch

2002-01-01

101

Magnetic Fields  

NSDL National Science Digital Library

Students visualize the magnetic field of a strong permanent magnet using a compass. The lesson begins with an analogy to the effect of the Earth's magnetic field on a compass. Students see the connection that the compass simply responds to the Earth's magnetic field since it is the closest, strongest field, and thus the compass responds to the field of the permanent magnets, allowing them the ability to map the field of that magnet in the activity. This information will be important in designing a solution to the grand challenge in activity 4 of the unit.

2014-09-18

102

Domain structure and magnetization reversal ofantiferromagnetically coupled perpendicular anisotropy films  

SciTech Connect

We describe experimental and theoretical investigations ofthe magnetic domain formation and the field reversal behavior inantiferromagnetically coupled perpendicular anisotropy multilayers thatmimic A-type antiferromagnet (AF) structures. The samples are sputterdeposited Co/Pt multilayers with perpendicular anisotropy that areperiodically interleaved with Ru to mediate an antiferromagneticinterlayer exchange. This structure allows precise tuning of thedifferent magnetic energy terms involved. Using various magnetometry andmagnetic imaging techniques as well as resonant soft X-ray scattering weprovide a comprehensive study of the remanent and demagnetizedconfigurations as well as the corresponding reversal mechanisms. We findthat adding AF exchange to perpendicular anisotropy system alters thetypical energy balance that controls magnetic stripe domain formation,thus resulting in two competing reversal modes for the composite system.In the AF-exchange dominated regime the magnetization isferromagnetically ordered within the film plane with the magnetization ofadjacent layers anti-parallel thus minimizing the interlayer AF exchangeenergy. In the dipolar dominated regime the magnetization pattern formsferromagnetic (FM) stripe domains where adjacent layers are verticallycorrelated, but laterally anti-correlated thus minimizing the dipolarenergy at the expense of the AF interlayer coupling. By tuning the layerthickness or applying a magnetic field, we observed the co-existence ofAF domains and FM stripe domains. We find that a FM phase exists at AFdomain boundaries, causing complex mesoscopic domain patterns withsurprising reversibility during minor loop field cycling.

Hellwig, Olav; Berger, Andreas; Kortright, Jeffrey B.; Fullerton,Eric E.

2007-03-16

103

Cosmological magnetic fields  

E-print Network

Magnetic fields are observed not only in stars, but in galaxies, clusters, and even high redshift Lyman-alpha systems. In principle, these fields could play an important role in structure formation and also affect the anisotropies in the cosmic microwave background radiation (CMB). The study of cosmological magnetic fields aims not only to quantify these effects on large-scale structure and the CMB, but also to answer one of the outstanding puzzles of modern cosmology: when and how do magnetic fields originate? They are either primordial, i.e. created before the onset of structure formation, or they are generated during the process of structure formation itself.

Roy Maartens

2000-07-24

104

Anisotropy of magnetic susceptibility (AMS) and anisotropy of remanent magnetization (ARM) data from Miocene ignimbrites, western Great Basin: A magnetic fabric study and comparison of magnetic fabric methods  

NASA Astrophysics Data System (ADS)

Magnetic fabric studies have become an integral part of any paleomagnetic investigation, and are especially pertinent to studies of ignimbrites, revealing inferred pyroclastic transport/source directions. Anisotropy of magnetic susceptibility (AMS) data were collected from regionally extensive ignimbrites in the southern Walker Lane area, including 226 sites in tuffs of the Timber Mountain Group, Tuff of Stonewall Flat, and Tuff of Mount Dunfee to infer local and regional transport/source directions based on imbrication fabrics. Anisotropy of remanent magnetization (ARM) data were obtained to refine the origin of AMS by isolating the ferro/ferrimagnetic minerals, and also to compare the fabric data for all anisotropy methods. Selected sites were analyzed to determine the effect of progressive alternating field (AF) demagnetization has on the magnetic fabric revealed by AMS on the ignimbrites.

Fitter, Thomas

105

Magnetic Fields  

E-print Network

In this chapter, we give a brief introduction into the use of the Zeeman effect in astronomy and the general detection of magnetic fields in stars, concentrating on the use of FORS2 for longitudinal magnetic field measurements.

Schöller, Markus

2015-01-01

106

Magnetic domain pinning in an anisotropy-engineered GdTbFe thin film  

SciTech Connect

Focused ion beam irradiation was used to reduce locally the perpendicular anisotropy of magnetic thin films in rectangular lattices of 50 nm sized dots. The effect of the anisotropy patterns, differing in ion fluence and interdot spacing, on the magnetization reversal process was determined in q space with x-ray resonant magnetic scattering and in real space with magnetic force microscopy. At remanence only a slight alignment of the irregularly shaped domains is observed. In perpendicular magnetic fields, however, the high field bubble domains display a pronounced localization on the dots, showing that this form of local anisotropy reduction is a highly efficient way of domain positioning.

Konings, Stan; Miguel, Jorge; Goedkoop, Jeroen; Camarero, Julio; Vogel, Jan [Van der Waals-Zeeman Institute, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam (Netherlands); Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Laboratoire Louis Neel, CNRS, BP 166, F-38042 Grenoble (France)

2006-08-01

107

Origin of the Magnetic Anisotropy Energy of Cobalt Ferrite  

Microsoft Academic Search

The magnetic anisotropy of cobalt ferrite is considered to arise from the cobaltous ions in the crystalline field of a low symmetry. The crystalline field due to the averaged-out charge distribution of Co^{2+} and Fe^{3+} ions in the octahedral sites gives the lowest-lying twofold degenerate orbital level of the Co^{2+} ion and to this level are associated four spin levels,

Masashi Tachiki

1960-01-01

108

Anisotropy in the EoS of Magnetized Quark Matter  

E-print Network

The anisotropies in the pressure obtained from the energy-momentum tensor are studied for magnetized quark matter within the su(3) Nambu-Jona-Lasinio model for both $\\beta$-equilibrium matter and quark matter with equal quark chemical potentials. The effect of the magnetic field on the particle polarization, magnetization and quark matter constituents is discussed. It is shown that the onset of the $s$-quark after chiral symmetry restoration of the $u$ and $d$-quarks gives rise to a special effect on the magnetization in the corresponding density range: a quite small magnetization just before the $s$ onset is followed by a strong increase of this quantity as soon as the $s$ quark sets in. It is also demonstrated that for $B<10^{18}$ G within the two scenarios discussed, always considering a constant magnetic field, the two components of pressure are practically coincident.

Menezes, Débora P; Providência, Constança

2015-01-01

109

Magnetic edge anisotropy in graphenelike honeycomb crystals.  

PubMed

The independent predictions of edge ferromagnetism and the quantum spin Hall phase in graphene have inspired the quest of other two-dimensional honeycomb systems, such as silicene, germanene, stanene, iridates, and organometallic lattices, as well as artificial superlattices, all of them with electronic properties analogous to those of graphene, but a larger spin-orbit coupling. Here, we study the interplay of ferromagnetic order and spin-orbit interactions at the zigzag edges of these graphenelike systems. We find an in-plane magnetic anisotropy that opens a gap in the otherwise conducting edge channels that should result in large changes of electronic properties upon rotation of the magnetization. PMID:25062225

Lado, J L; Fernández-Rossier, J

2014-07-11

110

Magnetic Edge Anisotropy in Graphenelike Honeycomb Crystals  

NASA Astrophysics Data System (ADS)

The independent predictions of edge ferromagnetism and the quantum spin Hall phase in graphene have inspired the quest of other two-dimensional honeycomb systems, such as silicene, germanene, stanene, iridates, and organometallic lattices, as well as artificial superlattices, all of them with electronic properties analogous to those of graphene, but a larger spin-orbit coupling. Here, we study the interplay of ferromagnetic order and spin-orbit interactions at the zigzag edges of these graphenelike systems. We find an in-plane magnetic anisotropy that opens a gap in the otherwise conducting edge channels that should result in large changes of electronic properties upon rotation of the magnetization.

Lado, J. L.; Fernández-Rossier, J.

2014-07-01

111

Spin splitting anisotropy in single diluted magnetic nanowire heterostructures.  

PubMed

We study the impact of the nanowire shape anisotropy on the spin splitting of excitonic photoluminescence. The experiments are performed on individual ZnMnTe/ZnMgTe core/shell nanowires as well as on ZnTe/ZnMgTe core/shell nanowires containing optically active magnetic CdMnTe insertions. When the magnetic field is oriented parallel to the nanowire axis, the spin splitting is several times larger than for the perpendicular field. We interpret this pronounced anisotropy as an effect of mixing of valence band states arising from the strain present in the core/shell geometry. This interpretation is further supported by theoretical calculations which allow to reproduce experimental results. PMID:25710186

Szymura, Ma?gorzata; Wojnar, Piotr; K?opotowski, ?ukasz; Suffczy?ski, Jan; Goryca, Mateusz; Smole?ski, Tomasz; Kossacki, Piotr; Zaleszczyk, Wojciech; Wojciechowski, Tomasz; Karczewski, Grzegorz; Wojtowicz, Tomasz; Kossut, Jacek

2015-03-11

112

Tailoring of magnetic anisotropy of Fe-rich microwires by stress induced anisotropy  

NASA Astrophysics Data System (ADS)

We report on tailoring of magnetic properties and GMI of Fe 69B 12Si 14C 5 glass-coated microwires by stress annealing. The induced magnetic anisotropy field depend on temperature and time of annealing and applied stress. At certain conditions considerable GMI effect (up to 65%) has been achieved. Application of the tensile stress drastically affects the shape of the hysteresis loop of stress-annealed sample and its GMI effect. In this way the shape of the hysteresis loop and GMI effect can by tailored by controllable way.

Zhukov, A.; Zhukova, V.; Larin, V.; Gonzalez, J.

2006-10-01

113

Stress induced magnetic anisotropy and giant magnetoimpedance in Fe-rich glass-coated magnetic microwires  

NASA Astrophysics Data System (ADS)

The effect of conventional (CA) and stress annealing (SA) on magnetic properties of Fe74B13Si11C2 glass-coated microwires has been studied. CA treatment does not significantly change the character of the hysteresis loop. Under certain annealing conditions (annealing temperature, Tann>300 °C, applied stress, ?>700 MPa) rectangular hysteresis loop transforms into the inclined with magnetic anisotropy field above 1000 A/m. Such phenomenology has been related to the induction of transverse magnetic anisotropy by SA treatment. Under tensile stress the SA annealed microwire recovers rectangular hysteresis loop. Samples subjected to stress annealing show noticeable magnetoimpedance and stress impedance effects in spite of their large magnetostriction.

Zhukova, V.; Larin, V. S.; Zhukov, A.

2003-07-01

114

Perpendicular magnetic anisotropy and magnetization of L10 FePt/FeCo bilayer films  

NASA Astrophysics Data System (ADS)

Fe40Co60 epitaxial thin films are prepared on L10 ordered Fe60Pt40 underlayer by ultrahigh vacuum multiple dc-sputtering systems. Magnetic properties of the Fe60Pt40 (10 nm)/Fe40Co60 (t nm) bilayer films are investigated. When the FeCo thickness is less than 3 nm, the easy magnetization axis of FePt/FeCo bilayer film is perpendicular to the film plane. Compared with FePt/Fe and FePt/Co films, FePt/FeCo bilayer films possess not only higher anisotropy field Hk but also larger magnetic anisotropy energy Ku, which may be due to the perpendicular magnetic anisotropy yielded by the tetragonal distorted FeCo layer on FePt, while the magnetic easy axes of Fe and Co layers lie in the film plane. Meanwhile, saturation magnetization of FePt/FeCo film increases reasonably because of the high Ms value of FeCo component. These results indicate that the FePt/FeCo bilayer films which possess both large magnetic anisotropy energy Ku and high saturation magnetization Ms have great potential for using as the magnetic recording media, and also give a clue to develop a new type of permanent magnet without rare-earth metals.

Wang, Bochong; Oomiya, Hiroyuki; Arakawa, Akira; Hasegawa, Takashi; Ishio, Shunji

2014-04-01

115

Enhancing Magnetic Properties of Molecular Magnetic Materials: The Role of Single-Ion Anisotropy  

E-print Network

) as determined by magnetic measurements. Such findings support the idea that controlling the axial crystal field distortion is an excellent way to enhance single-ion anisotropy. High Field-High Frequency EPR measurements on 4 revealed an even higher D value, -40...

Saber, Mohamed Rashad Mohamed

2013-07-09

116

Fabric evolution across a discontinuity between lower and upper crustal domains from field, microscopic, and anisotropy of magnetic susceptibility studies in central eastern Eritrea, NE Africa  

NASA Astrophysics Data System (ADS)

In the Neoproterozoic East African Orogen (EAO) of Eritrea, lower to middle crustal high-grade metamorphic rocks are juxtaposed against low-grade upper crustal rocks along diffuse tectonic contact zones or discontinuities. In the central eastern part of Eritrea, such a tectonic zone is exposed as a low-angle shear zone separating two distinct high- and low-grade domains, the Ghedem and Bizen, respectively. Integrated field, microfabric, and anisotropy of magnetic susceptibility (AMS) studies show that this low-angle shear zone formed during late deformation, D2, with top-to-the-E/SE sense of motion. The hanging wall upper crustal volcanosedimentary schists are mainly paramagnetic and the footwall middle crustal mylonitized orthogneisses are mainly ferrimagnetic. Magnetic fabric studies revealed a good agreement between metamorphic/mylonitic and magnetic foliations (Kmin) and helped to explain fabric development in the shear zone. The magnetic lineations (Kmax) reflect stretching lineations where stretched mineral aggregates dominate fine-grained mylonitic matrices and intersection lineations where microstructural studies revealed two fabric elements. AMS directional plots indicate that the orientations of the magnetic lineation and of the pole to the magnetic foliation vary systematically across the shear zone. While Kmax axes form two broad maxima oriented approximately N-S and E-W, the Kmin axes change from subhorizontal, generally westward inclination in the west to moderate to steep inclination in the direction of tectonic movement to the east. Because there is a systematic change in inclination of Kmin for individual samples, all samples together form a fairly well defined cluster distribution. The distribution of Kmin in combination with the E-W scattered plot of the Kmax is in accordance with the E/SE flow of mylonites over exhumed Damas core complex in the late Neoproterozoic. During the Cenozoic, the Red Sea rift-related detachments exploited the late orogenic shear zone, indicating that the discontinuities between ductile middle and brittle upper crustal layers in the region are reactivated low-angle shear zones and possible sites of core complexes.

Ghebreab, W.; Kontny, A.; Greiling, R. O.

2007-06-01

117

Giant Magnetic Anisotropy of Single Cobalt Atoms and  

E-print Network

Giant Magnetic Anisotropy of Single Cobalt Atoms and Nanoparticles P. Gambardella,1,2 * S. Rusponi. Dederichs,5 K. Kern,1,2 C. Carbone,3,5 H. Brune1 The isotropic magnetic moment of a free atom is shown to develop giant magnetic anisotropy energy due to symmetry reduction at an atomically ordered surface

Brune, Harald

118

Contribution of Eu 4f states to the magnetic anisotropy of EuO  

SciTech Connect

Anisotropic x-ray magnetic linear dichroism (AXMLD) provides a novel element-, site-, shell-, and symmetry-selective techniques to study the magnetic anisotropy induced by a crystalline electric field. The weak Eu2+ M4,5 AXMLD observed in EuO(001) indicates that the Eu 4f states are not rotationally invariant and hence contribute weakly to the magnetic anisotropy of EuO. The results are contrasted with those obtained for 3d transition metal oxides.

Arenholz, E.; Schmehl, A.; Schlom, D.G.; van der Laan, G.

2008-09-11

119

Modification of crystal anisotropy and enhancement of magnetic moment of Co-doped SnO2 thin films annealed under magnetic field  

PubMed Central

Co-doped SnO2 thin films were grown by sputtering technique on SiO2/Si(001) substrates at room temperature, and then, thermal treatments with and without an applied magnetic field (HTT) were performed in vacuum at 600°C for 20 min. HTT was applied parallel and perpendicular to the substrate surface. Magnetic M(H) measurements reveal the coexistence of a strong antiferromagnetic (AFM) signal and a ferromagnetic (FM) component. The AFM component has a Néel temperature higher than room temperature, the spin axis lies parallel to the substrate surface, and the highest magnetic moment m =7 ?B/Co at. is obtained when HTT is applied parallel to the substrate surface. Our results show an enhancement of FM moment per Co+2 from 0.06 to 0.42 ?B/Co at. for the sample on which HTT was applied perpendicular to the surface. The FM order is attributed to the coupling of Co+2 ions through electrons trapped at the site of oxygen vacancies, as described by the bound magnetic polaron model. Our results suggest that FM order is aligned along [101] direction of Co-doped SnO2 nanocrystals, which is proposed to be the easy magnetization axis. PMID:25489286

2014-01-01

120

Modification of crystal anisotropy and enhancement of magnetic moment of Co-doped SnO2 thin films annealed under magnetic field  

NASA Astrophysics Data System (ADS)

Co-doped SnO2 thin films were grown by sputtering technique on SiO2/Si(001) substrates at room temperature, and then, thermal treatments with and without an applied magnetic field (HTT) were performed in vacuum at 600°C for 20 min. HTT was applied parallel and perpendicular to the substrate surface. Magnetic M(H) measurements reveal the coexistence of a strong antiferromagnetic (AFM) signal and a ferromagnetic (FM) component. The AFM component has a Néel temperature higher than room temperature, the spin axis lies parallel to the substrate surface, and the highest magnetic moment m =7 ?B/Co at. is obtained when HTT is applied parallel to the substrate surface. Our results show an enhancement of FM moment per Co+2 from 0.06 to 0.42 ?B/Co at. for the sample on which HTT was applied perpendicular to the surface. The FM order is attributed to the coupling of Co+2 ions through electrons trapped at the site of oxygen vacancies, as described by the bound magnetic polaron model. Our results suggest that FM order is aligned along [101] direction of Co-doped SnO2 nanocrystals, which is proposed to be the easy magnetization axis.

Loya-Mancilla, Sagrario M.; Poddar, Pankaj; Das, Raja; Ponce, Hilda E. Esparza; Templeton-Olivares, Ivan L.; Solis-Canto, Oscar O.; Ornelas-Gutierrez, Carlos E.; Espinosa-Magaña, Francisco; Olive-Méndez, Sion F.

2014-11-01

121

Strong magnetic anisotropy in Co thin films via nanotextured Ta underlayers  

Microsoft Academic Search

The ability to control magnetization in thin films is a basic requirement for device applications. We have produced 3 nm thick polycrystalline films of Co with anisotropy fields in excess of 120 kA\\/m (1500 Oe), hundreds of times larger than the typical anisotropy of polycrystalline Co films in this thickness range, and large enough for application as a robust ``pinned''

R. D. McMichael; C. G. Lee; J. E. Bonevich; P. J. Chen; W. Miller; W. F. Egelhoff

2000-01-01

122

Anisotropy of magnetic susceptibility of some metamorphic minerals  

Microsoft Academic Search

The anisotropy of susceptibility of metamorphic rocks can be due to paramagnetic rock-forming silicates such as amphiboles, chlorites and micas. It is not always necessary to invoke fabrics of separate grains of iron oxide to explain the anisotropy. Minimum estimates of lattice anisotropies of typical samples of silicates have maximum-to-minimum ratios of 1.1-1.7. Since the magnetic anisotropies of most metamorphic

G. Borradaile; W. Keeler; C. Alford; P. Sarvas

1987-01-01

123

Transfer matrices for magnetized CMB anisotropies  

E-print Network

Large-scale magnetic fields can affect scalar cosmological perturbations whose evolution is described in the conformally Newtonian gauge and within the tight coupling approximation. The magnetized curvature perturbations present after matter radiation equality (and prior to decoupling) are computed in terms of an appropriate transfer matrix allowing a general estimate of the Sachs-Wolfe plateau. From the observation that CMB initial conditions should be (predominantly) adiabatic, the contribution of the magnetic field intensity can be constrained.

Massimo Giovannini

2006-04-02

124

The peculiarities of magnetization reversal process in magnetic nanotube with helical anisotropy  

NASA Astrophysics Data System (ADS)

The magnetization reversal process in a soft magnetic nanotube with a weak helical magnetic anisotropy is studied by means of numerical simulation. The origin of a helical anisotropy is a small off-diagonal correction to the magneto-elastic energy density. The change of the external magnetic field parallel to the nanotube axis is shown to initiate a magnetic hysteresis associated with the jumps of the circular magnetization component of the nanotube at a critical magnetic field Hs. For a uniform nanotube, the critical magnetic field Hs is investigated as a function of geometrical and magnetic parameters of the nanotube. Using 2D micromagnetic simulation, we study the behavior of a nanotube having magnetic defects in its middle part. In this case, the jump of the circular magnetization component starts at the defect. As a result, two bamboo domain walls appear near the defect and propagate to the nanotube ends. Similar effect may explain the appearance of the bamboo domain walls in a slightly non uniform amorphous ferromagnetic microwire with negative magnetostriction during magnetization reversal process.

Usov, N. A.; Serebryakova, O. N.

2014-10-01

125

Manifestation of coherent magnetic anisotropy in a carbon nanotube matrix with low ferromagnetic nanoparticle content  

NASA Astrophysics Data System (ADS)

The influence of the magnetic medium can lead to peculiar interaction between ferromagnetic nanoparticles (NPs). Most research in this area involves analysis of the interplay between magnetic anisotropy and exchange coupling. Increasing the average interparticle distance leads to the dominant role of the random magnetic anisotropy. Here we study the interparticle interaction in a carbon nanotube (CNT) matrix with low ferromagnetic NP content. Samples were synthesized by floating catalyst chemical vapor deposition. We found that below some critical NP concentration, when NPs are intercalated only inside CNTs, and at low temperatures, the extended magnetic order, of up to 150 nm, presents in our samples. It is shown by analyzing the correlation functions of the magnetic anisotropy axes that the extended order is not simply due to random anisotropy but is associated with the coherent magnetic anisotropy, which is strengthened by the CNT alignment. With increasing temperature the extended magnetic order is lost. Above the critical NP concentration, when NPs start to be intercalated not only into inner CNT channels, but also outside CNTs, the coherent anisotropy weakens and the exchange coupling dominates in the whole temperature range. We can make a connection with the various correlation functions using the generalized expression for the law of the approach to saturation and show that these different correlation functions reflect the peculiarities in the interparticle interaction inside CNTs. Moreover, we can extract such important micromagnetic parameters like the exchange field, local fields of random and coherent anisotropies, as well as their temperature and NP concentration dependencies.

Danilyuk, A. L.; Komissarov, I. V.; Labunov, V. A.; Le Normand, F.; Derory, A.; Hernandez, J. M.; Tejada, J.; Prischepa, S. L.

2015-02-01

126

Magnetic anisotropy, magnetostatic interactions and identification of magnetofossils  

NASA Astrophysics Data System (ADS)

Single-domain magnetite particles produced by magnetotactic bacteria (MTB) and aligned in chains, called magnetosomes, are potentially important recorders of paleomagnetic, paleoenvironmental and paleolife signals. Rock magnetic properties related to the anisotropy of magnetosome chains have been widely used to identify fossilized magnetosomes (magnetofossils) preserved in geological materials. However, ambiguities exist when linking magnetic properties to the chain structure because of the complexity of chain integrity and magnetostatic interactions among magnetofossils that results from chain collapse during post-depositional diagenesis. In this paper, magnetic properties of three sets of samples containing extracted magnetosomes of the cultured Magnetospirillum magneticum strain AMB-1 were analyzed to determine how chain integrity and particle concentration influence magnetic properties. Intact MTB and well-dispersed magnetosome chains are characterized by strong magnetic anisotropy and weak magnetostatic interactions, but progressive chain breakup and particle clumping significantly increase the degree of magnetostatic interaction. This results in a change of the magnetic signature toward properties typical of interacting, single-domain particles, i.e., a decrease of the ratio of anhysteretic remanent magnetization to the saturation isothermal remanent magnetization, decreasing in the crossing point of the Wohlfarth-Cisowski test and in the delta ratio between losses of field and zero-field cooled remanent magnetization across the Verwey transition, as well as vertical broadening of the first-order reversal curve distribution. We propose a new diagram that summarizes the Verwey transition properties, with diagnostic limits for intact and collapsed chains of magnetosomes. This diagram can be used, in conjunction with other parameters, to identify unoxidized magnetofossils in sediments and rocks.

Li, Jinhua; Wu, Wenfang; Liu, Qingsong; Pan, Yongxin

2012-12-01

127

Magnetic anisotropy, magnetostatic interactions and identification of magnetofossils  

NASA Astrophysics Data System (ADS)

Single-domain magnetite particles produced by magnetotactic bacteria (MTB) and aligned in chains, called magnetosomes, are potentially important recorders of paleomagnetic, paleoenvironmental and paleolife signals. Rock magnetic properties related to the anisotropy of magnetosome chains have been widely used to identify fossilized magnetosomes (magnetofossils) preserved in geological materials. However, ambiguities exist when linking magnetic properties to the chain structure because of the complexity of chain integrity and magnetostatic interactions among magnetofossils that results from chain collapse during post-depositional diagenesis. In this paper, magnetic properties of three sets of samples containing extracted magnetosomes of the culturedMagnetospirillum magneticumstrain AMB-1 were analyzed to determine how chain integrity and particle concentration influence magnetic properties. Intact MTB and well-dispersed magnetosome chains are characterized by strong magnetic anisotropy and weak magnetostatic interactions, but progressive chain breakup and particle clumping significantly increase the degree of magnetostatic interaction. This results in a change of the magnetic signature toward properties typical of interacting, single-domain particles, i.e., a decrease of the ratio of anhysteretic remanent magnetization to the saturation isothermal remanent magnetization, decreasing in the crossing point of the Wohlfarth-Cisowski test and in the delta ratio between losses of field and zero-field cooled remanent magnetization across the Verwey transition, as well as vertical broadening of the first-order reversal curve distribution. We propose a new diagram that summarizes the Verwey transition properties, with diagnostic limits for intact and collapsed chains of magnetosomes. This diagram can be used, in conjunction with other parameters, to identify unoxidized magnetofossils in sediments and rocks.

Li, Jinhua; Wu, Wenfang; Liu, Qingsong; Pan, Yongxin

2012-12-01

128

Experimental investigation of magnetic anisotropy in spin vortex discs  

SciTech Connect

We present experimental 2D vector vibrating sample magnetometer measurements to demonstrate the shape anisotropy effects occurring in micrometer-diameter supermalloy spin vortex discs. Measurements made for different disc sizes and orientations confirm the out-of-plane susceptibility is several orders of magnitude smaller than the in-plane susceptibility. These results validate with a high certitude that spin vortices with high diameter to thickness ratio retain in-plane-only magnetization, even when subjected to fields in the out-of-plane direction. These results contribute to further computational simulations of the dynamics of spin vortex structures in colloidal suspensions where external fields may be applied in any arbitrary direction.

Garraud, N., E-mail: ngarraud@ufl.edu; Arnold, D. P. [Department of Electrical and Computer Engineering, University of Florida, Gainesville, Florida 32611 (United States)

2014-05-07

129

Anisotropy of the molecular magnet V15 spin Hamiltonian detected by high-field electron spin resonance  

NASA Astrophysics Data System (ADS)

The molecular compound K6[V15IVAs6IIIO42(H2O)] . 8H2O, in short V15, has shown important quantum effects such as coherent spin oscillations. The details of the spin quantum dynamics depend on the exact form of the spin Hamiltonian. In this study, we present a precise analysis of the intramolecular interactions in V15. To that purpose, we performed high-field electron spin resonance measurements at 120 GHz and extracted the resonance fields as a function of crystal orientation and temperature. The data are compared against simulations using exact diagonalization to obtain the parameters of the molecular spin Hamiltonian.

Martens, M.; van Tol, J.; Dalal, N. S.; Bertaina, S.; Barbara, B.; Tsukerblat, B.; Müller, A.; Garai, S.; Miyashita, S.; Chiorescu, I.

2014-05-01

130

Study of YBCO tape anisotropy as a function of field, field orientation and operating temperature  

SciTech Connect

Superconducting magnets with magnetic fields above 20 T will be needed for a Muon Collider and possible LHC energy upgrade. This field level exceeds the possibilities of traditional Low Temperature Superconductors (LTS) such as Nb{sub 3}Sn and Nb{sub 3}Al. Presently the use of high field high temperature superconductors (HTS) is the only option available for achieving such field levels. Commercially available YBCO comes in tapes and shows noticeable anisotropy with respect to field orientation, which needs to be accounted for during magnet design. In the present work, critical current test results are presented for YBCO tape manufactured by Bruker. Short sample measurements results are presented up to 14 T, assessing the level of anisotropy as a function of field, field orientation and operating temperature.

Lombardo, v.; Barzi, E.; Turrioni, D.; Zlobin, A.V.

2011-06-01

131

Magnetic anisotropy of epitaxial Cu/Ni/Cu nanolines  

NASA Astrophysics Data System (ADS)

Continuous nickel films grown pseudoepitaxially between copper layers have been shown to have strong perpendicular magnetic anisotropy due to large magnetoelastic and interface magnetocrystalline anisotropy energies. These Cu/Ni/Cu films with tNi=6.9 nm have been patterned into lines approximately 200 nm wide using interferometric lithography and ion milling. Torque magnetometer measurements show the anisotropy of the nanolines to be significantly different from that of the continuous films. The magnetoelastic anisotropy (favoring perpendicular magnetization) decreases in the patterned films due to strain relaxation at the line edges. Although the anisotropy change for this line width is most likely due to shape anisotropy, we anticipate observation of magnetoelastic anisotropy due to strain relief at the edges of the lines at narrower line widths in future work.

Lyons, E. S.; O'Handley, R. C.; Ross, C. A.

2004-06-01

132

Physical properties of elongated magnetic particles: magnetization and friction coefficient anisotropies.  

PubMed

Anisotropy counts: A brief review of the main physical properties of elongated magnetic particles (EMPs) is presented. The most important characteristic of an EMP is the additional contribution of shape anisotropy to the total anisotropy energy of the particle, when compared to spherical magnetic particles. The electron micrograph shows Ni-ferrite microrods fabricated by the authors.We present an overview of the main physical properties of elongated magnetic particles (EMPs), including some of their more relevant properties in suspension. When compared to a spherical magnetic particle, the most important characteristic of an EMP is an additional contribution of shape anisotropy to the total anisotropy energy of the particle. Increasing aspect ratios also lead to an increase in both the critical single-domain size of a magnetic particle and its resistance to thermally activated spontaneous reversal of the magnetization. For single-domain EMPs, magnetization reversal occurs primarily by one of two modes, coherent rotation or curling, the latter being facilitated by larger aspect ratios. When EMPs are used to prepare colloidal suspensions, other physical properties come into play, such as their anisotropic friction coefficient and the consequent enhanced torque they experience in a shear flow, their tendency to align in the direction of an external field, to form less dense sediments and to entangle into more intricate aggregates. From a more practical point of view, EMPs are discussed in connection with two interesting types of magnetic colloids: magnetorheological fluids and suspensions for magnetic hyperthermia. Advances reported in the literature regarding the use of EMPs in these two systems are included. In the final section, we present a summary of the most relevant methods documented in the literature for the fabrication of EMPs, together with a list of the most common ferromagnetic materials that have been synthesized in the form of EMPs. PMID:19434654

Vereda, Fernando; de Vicente, Juan; Hidalgo-Alvarez, Roque

2009-06-01

133

Effects of domain, grain, and magnetic anisotropy distributions on magnetic permeability: Monte-Carlo approach  

SciTech Connect

Existing approaches for prediction of the tensor permeability of polycrystalline ferrites may not provide reasonable estimates of demagnetized permeability below the spin resonance (i.e., low-field loss region) or in cases of partial magnetization. We propose an approach which solves the coupled Landau-Lifshitz-Gilbert equation for the dynamic magnetic fields including the minimization of free energy to determine the equilibrium magnetization direction. Unlike previous models, we employ a Monte-Carlo approach to easily calculate the (ensemble) averages of permeability over various domain/grain structures and magnetic anisotropy conditions. Material differences, such as those resulting from different preparation methods, are expressed by using probability density functions (p.d.f.) for anisotropy angle (easy axis angle), grain demagnetization factor (ng), and domain demagnetization factor (nd). Effects on the permeability tensor of grain and domain demagnetization factors and anisotropy field relative to saturation magnetization are discussed for the partially magnetized states for polycrystalline ferrites. It is found that the grain structure (i.e., grain demagnetization distribution) has a smaller effect on the frequency dependent permeability than does the same distribution of domains (i.e., domain demagnetization distribution).

Chun, Jaehun; Jones, Anthony M.; McCloy, John S.

2012-07-23

134

Magnetic Field Safety Magnetic Field Safety  

E-print Network

Magnetic Field Safety Training #12;Magnetic Field Safety Strong Magnetic Fields exist around energized magnets. High magnetic fields alone are a recognized hazard only for personnel with certain medical conditions such as pacemakers, magnetic implants, or embedded shrapnel. In addition, high magnetic

McQuade, D. Tyler

135

Modulation of unidirectional anisotropy for Co-based amorphous ribbons by longitudinal pulse field  

NASA Astrophysics Data System (ADS)

Field-induced unidirectional anisotropy of Co-based amorphous ribbons was discussed by magnetization measurement. The shifted hysteresis loops of Co58Fe5Ni10Si11B16 amorphous ribbons were obtained by annealing the samples in longitudinal magnetic field. Here, the feasibility of employing the longitudinal pulse field to tailor the anisotropy characteristic is demonstrated. It is found that the shifted loops can be technically controlled by enhancing the pulse field to modulate the magnetic anisotropy from unidirectional to uniaxial, and even back to unidirectional. The surface domains scan gives strong evidence that the pulse field can be one of the skillful methods to navigate the unidirectional anisotropy in the amorphous ribbons for potential applications.

He, J.; An, J.; Xia, Z. J.; Yang, L.; Zhao, D. L.; You, C. Y.; Ren, W. J.

2015-05-01

136

Magnetic anisotropy considerations in magnetic force microscopy studies of single superparamagnetic nanoparticles.  

PubMed

In recent years, superparamagnetic nanoparticles (SPNs) have become increasingly important in applications ranging from solid state memory devices to biomedical diagnostic and therapeutic tools. However, detection and characterization of the small and unstable magnetic moment of an SPN at the single particle level remains a challenge. Further, depending on their physical shape, crystalline structure or orientation, SPNs may also possess magnetic anisotropy, which can govern the extent to which their magnetic moments can align with an externally applied magnetic field. Here, we demonstrate how we can exploit the magnetic anisotropy of SPNs to enable uniform, highly-sensitive detection of single SPNs using magnetic force microscopy (MFM) in ambient air. Superconducting quantum interference device magnetometry and analytical transmission electron microscopy techniques are utilized to characterize the collective magnetic behavior, morphology and composition of the SPNs. Our results show how the consideration of magnetic anisotropy can enhance the ability of MFM to detect single SPNs at ambient room temperature with high force sensitivity and spatial resolution. PMID:23149438

Nocera, Tanya M; Chen, Jun; Murray, Christopher B; Agarwal, Gunjan

2012-12-14

137

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion  

PubMed Central

We observed interfacial chemical sharpening due to uphill diffusion in post annealed ultrathin multilayer stack of Co and Pt, which leads to enhanced interfacial perpendicular magnetic anisotropy (PMA). This is surprising as these elements are considered as perfectly miscible. This chemical sharpening was confirmed through quantitative energy dispersive x-ray (EDX) spectroscopy and intensity distribution of images taken on high angle annular dark field (HAADF) detector in Scanning Transmission Electron Microscopic (STEM) mode. This observation demonstrates an evidence of miscibility gap in ultrathin coherent Co/Pt multilayer stacks. PMID:24937637

Das, Tanmay; Kulkarni, Prabhanjan D.; Purandare, S. C.; Barshilia, Harish C.; Bhattacharyya, Somnath; Chowdhury, Prasanta

2014-01-01

138

Visualizing magnetocrystalline anisotropy field distribution of patterned triangular L10 FePt nanodots  

NASA Astrophysics Data System (ADS)

Measuring magnetocrystalline anisotropy field distribution of patterned magnetic nanodots using a microscopically visualizing way is important for understanding some important magnetic behaviors such as switching field distribution (SFD) of patterned recording media. We present a detailed analysis of the remanent domain structures of L10-FePt triangular nanodots as revealed by high resolution magnetic force microscopy (MFM) with the help of micromagnetic simulation, showing that the domain structure diversity can effectively account for a dot-to-dot variation of the magnetocrystalline anisotropy field. Our method could shed light not only on understanding the fundamental causes of a wider SFD but also on designing future nanostructured magnetic devices.

Zhong, Hai; Zhang, Kaiming; Wei, Dan; Wang, Sumei; Yuan, Jun

2015-02-01

139

Perpendicular magnetic anisotropy of Co–Ag granular thin films  

Microsoft Academic Search

The perpendicular magnetic anisotropy constant in giant magnetoresistive granular Co22Ag78 thin films is found to increase and then decrease with annealing temperature, the maximum being about 5×105 ergs\\/cc at an annealing temperature of about 600 K. The observation of domain patterns by magnetic force microscopy is consistent with this result. The origin of the perpendicular magnetic anisotropy is not clear,

Y. J. Chen; T. Suzuki; S. P. Wong; H. Sang

1999-01-01

140

Phase diagram of a three-dimensional antiferromagnet with random magnetic anisotropy.  

PubMed

Three-dimensional antiferromagnets with random magnetic anisotropy (RMA) that have been experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of Fe_{x}Ni_{1-x}F_{2} epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean-field theory. Regions with uniaxial, oblique, and easy-plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs. PMID:25793845

Perez, Felio A; Borisov, Pavel; Johnson, Trent A; Stanescu, Tudor D; Trappen, Robbyn; Holcomb, Mikel B; Lederman, David; Fitzsimmons, M R; Aczel, Adam A; Hong, Tao

2015-03-01

141

Phase Diagram of a Three-Dimensional Antiferromagnet with Random Magnetic Anisotropy  

NASA Astrophysics Data System (ADS)

Three-dimensional antiferromagnets with random magnetic anisotropy (RMA) that have been experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of FexNi1 -xF2 epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean-field theory. Regions with uniaxial, oblique, and easy-plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs.

Perez, Felio A.; Borisov, Pavel; Johnson, Trent A.; Stanescu, Tudor D.; Trappen, Robbyn; Holcomb, Mikel B.; Lederman, David; Fitzsimmons, M. R.; Aczel, Adam A.; Hong, Tao

2015-03-01

142

Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films With Perpendicular Magnetic Anisotropy  

Microsoft Academic Search

L10 order was optimized in FePd epitaxial thin films prepared using dc magnetron sputter deposition on MgO(001) substrates by investigating various growth temperatures. A series of films was grown at the optimal temperature with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured magnetic domain size\\/period

J. R. Skuza; C. Clavero; K. Yang; B. Wincheski; R. A. Lukaszew

2010-01-01

143

Positive temperature coefficient of magnetic anisotropy in polyvinylidene fluoride (PVDF)-based magnetic composites.  

PubMed

The magnetic anisotropy is decreased with increasing temperature in normal magnetic materials, which is harmful to the thermal stability of magnetic devices. Here, we report the realization of positive temperature coefficient of magnetic anisotropy in a novel composite combining ?-phase polyvinylidene fluoride (PVDF) with magnetostrictive materials (magnetostrictive film/PVDF bilayer structure). We ascribe the enhanced magnetic anisotropy of the magnetic film at elevated temperature to the strain-induced anisotropy resulting from the anisotropic thermal expansion of the ?-phase PVDF. The simulation based on modified Stoner-Wohlfarth model and the ferromagnetic resonance measurements confirms our results. The positive temperature coefficient of magnetic anisotropy is estimated to be 1.1 × 10(2)?J m(-3) K(-1). Preparing the composite at low temperature can enlarge the temperature range where it shows the positive temperature coefficient of magnetic anisotropy. The present results may help to design magnetic devices with improved thermal stability and enhanced performance. PMID:25311047

Liu, Yiwei; Wang, Baomin; Zhan, Qingfeng; Tang, Zhenhua; Yang, Huali; Liu, Gang; Zuo, Zhenghu; Zhang, Xiaoshan; Xie, Yali; Zhu, Xiaojian; Chen, Bin; Wang, Junling; Li, Run-Wei

2014-01-01

144

Positive temperature coefficient of magnetic anisotropy in polyvinylidene fluoride (PVDF)-based magnetic composites  

PubMed Central

The magnetic anisotropy is decreased with increasing temperature in normal magnetic materials, which is harmful to the thermal stability of magnetic devices. Here, we report the realization of positive temperature coefficient of magnetic anisotropy in a novel composite combining ?-phase polyvinylidene fluoride (PVDF) with magnetostrictive materials (magnetostrictive film/PVDF bilayer structure). We ascribe the enhanced magnetic anisotropy of the magnetic film at elevated temperature to the strain-induced anisotropy resulting from the anisotropic thermal expansion of the ?-phase PVDF. The simulation based on modified Stoner-Wohlfarth model and the ferromagnetic resonance measurements confirms our results. The positive temperature coefficient of magnetic anisotropy is estimated to be 1.1 × 102?J m?3 K?1. Preparing the composite at low temperature can enlarge the temperature range where it shows the positive temperature coefficient of magnetic anisotropy. The present results may help to design magnetic devices with improved thermal stability and enhanced performance. PMID:25311047

Liu, Yiwei; Wang, Baomin; Zhan, Qingfeng; Tang, Zhenhua; Yang, Huali; Liu, Gang; Zuo, Zhenghu; Zhang, Xiaoshan; Xie, Yali; Zhu, Xiaojian; Chen, Bin; Wang, Junling; Li, Run-Wei

2014-01-01

145

Magnetic and structural anisotropies of Co2FeAl Heusler alloy epitaxial thin films  

NASA Astrophysics Data System (ADS)

This paper shows the correlation between chemical order, lattice strains, and magnetic properties of Heusler Co2FeAl films epitaxially grown on MgO(001). A detailed magnetic characterization is performed using vector-field magnetometery combined with a numerical Stoner-Wohlfarth analysis. We demonstrate the presence of three types of in-plane anisotropies: one biaxial, as expected for the cubic symmetry, and two uniaxial. The three anisotropies show different behavior with the annealing temperature. The biaxial anisotropy shows a monotonic increase. The uniaxial anisotropy that is parallel to the hard biaxial axes (related to chemical homogeneity) decreases, while the anisotropy that is supposed to have a magnetostatic origin remains constant.

Gabor, M. S.; Petrisor, T., Jr.; Tiusan, C.; Hehn, M.; Petrisor, T.

2011-10-01

146

Temperature dependence of surface magnetic anisotropy energy constant in magnetic semiconductor thin films  

NASA Astrophysics Data System (ADS)

We report on temperature dependence of surface magnetic anisotropy energy constant in magnetic semiconductor thin films of CdCr 2-2 xIn 2 xSe 4 at spin glass state. Coexistence of the infinite ferromagnetic network (IFN) and finite spin clusters (FSC) in the spin glass state (SG) is a known phenomena. The spin wave resonance experiment (microwave spectrometer at X-band) with excited surface modes was applied to describe the energy state of surface spins. We determined the surface magnetic anisotropy energy constant versus temperature using the surface inhomogeneities model of magnetic thin films. It was found that two components contribute to the surface energy. One originates from the exchange interaction term due to the lack of translation symmetry for surface spin as well as from the surface stray field of the surface roughness. The second one comes from the demagnetizing field of the close-to-surface layer with grad M. Both terms of surface magnetic anisotropy energy, decrease when the temperature is increased from 5 to 125 K, but the dominant contribution is from the first compound.

Maksymowicz, L. J.; Lubecka, M.; Jab?o?ski, R.

1999-02-01

147

Determining anisotropy constants from a first-order magnetization process in Tb2Fe17  

NASA Astrophysics Data System (ADS)

The critical parameters of a first-order magnetization process, Hcr and mcr , are used to determine the anisotropy constants K1 and K2 of Tb2Fe17 in the temperature range between 5 and 300K . Both anisotropy constants are proportional to the critical field Hcr (times spontaneous magnetization), whereas their ratio is independent of Hcr and depends solely on the dimensionless reduced critical magnetization mcr . The employed method of determining K1 and K2 is complementary to the classical Sucksmith-Thompson technique, which is inapplicable in the case of a first-order magnetization process.

Kuz'Min, M. D.; Skourski, Y.; Skokov, K. P.; Müller, K.-H.; Gutfleisch, O.

2008-04-01

148

Artificially modified magnetic anisotropy in interconnected nanowire networks  

NASA Astrophysics Data System (ADS)

Interconnected or crossed magnetic nanowire networks have been fabricated by electrodeposition into a polycarbonate template with crossed cylindrical nanopores oriented +/-30° with respect to the surface normal. Tailor-made nanoporous polymer membranes have been designed by performing a double energetic heavy ion irradiation with fixed incidence angles. The Ni and Ni/NiFe nanowire networks have been characterized by magnetometry as well as ferromagnetic resonance and compared with parallel nanowire arrays of the same diameter and density. The most interesting feature of these nanostructured materials is a significant reduction of the magnetic anisotropy when the external field is applied perpendicular and parallel to the plane of the sample. This effect is attributed to the relative orientation of the nanowire axes with the applied field. Moreover, the microwave transmission spectra of these nanowire networks display an asymmetric linewidth broadening, which may be interesting for the development of low-pass filters. Nanoporous templates made of well-defined nanochannel network constitute an interesting approach to fabricate materials with controlled anisotropy and microwave absorption properties that can be easily modified by adjusting the relative orientation of the nanochannels, pore sizes and material composition along the length of the nanowire.

Araujo, Elsie; Encinas, Armando; Velázquez-Galván, Yenni; Martínez-Huerta, Juan Manuel; Hamoir, Gaël; Ferain, Etienne; Piraux, Luc

2015-01-01

149

Magnetic anisotropy of Co/Pt/FeMn multilayers grown on polystyrene nanospheres  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy of Co/Pt/FeMn multilayers grown onto two-dimensional arrays of nanospherical polystyrene particles is studied at room temperature using Ferromagnetic Resonance measurements with X-band microwave frequency. The in-plane and out-of-plane resonance spectra display two uniform absorption modes due to two distinct magnetic phases, revealing an inhomogeneous magnetization profile through the thickness and at the top and the equator of the magnetic caps. The in-plane measurements of the angular dependence of the two absorption fields reveal that the distinct magnetic phases exhibit the effects of twofold and fourfold magnetic anisotropy fields. Out-of-plane measurements show that the magnetization of each magnetic phase depends on the structure of the multilayer and is oriented at a specific direction oblique to the plane of the film.

Martins, A.; Pelegrini, F.; Soares, M. M.; Garcia, F.

2013-02-01

150

Colossal anisotropy of the magnetic properties of doped lithium nitrodometalates  

NASA Astrophysics Data System (ADS)

We present a first-principles investigation of the electronic structure and physical properties of doped lithium nitridometalates Li2(Li1-xMx)N (LiMN) with M = Cr, Mn, Fe, Co, and Ni. The diverse properties include the equilibrium magnetic moments, magneto-crystalline anisotropy, magneto-optical Kerr spectra, and x-ray magnetic circular dichroism. We explain the colossal magnetic anisotropy in LiFeN by its unique electronic structure which ultimately leads to a series of unusual physical properties. The most unique property is a complete suppression of relativistic effects and freezing of orbital moments for in-plane orientation of the magnetization. This leads to the colossal spatial anisotropy of many magnetic properties including energy, Kerr, and dichroism effects. LiFeN is identified as an ultimate single-ion anisotropy system where a nearly insulating state can be produced by a spin orbital coupling alone. A very nontrivial strongly fluctuating and sign changing character of the magnetic anisotropy with electronic 3d-atomic doping is predicted theoretically. A large and highly anisotropic Kerr effect due to the interband transitions between atomic-like Fe 3d bands is found for LiFeN. A giant anisotropy of the x-ray magnetic circular dichroism for the Fe K spectrum and a very weak one for the Fe L2,3 spectra in LiFeN are also predicted.

Antropov, V. P.; Antonov, V. N.

2014-09-01

151

Reduction of low frequency magnetic noise by voltage-induced magnetic anisotropy modulation in tunneling magnetoresistance sensors  

NASA Astrophysics Data System (ADS)

We demonstrate the reduction and control of magnetic noise by voltage-induced perpendicular anisotropy modulation in CoFeB/MgO/CoFeB sensors. The noise decreases with the increase of the perpendicular anisotropy energy induced by the bias voltage polarity reversal. The bias reversal between -1 and +1 V results in a reduction of the normalized 1/f magnetic noise parameters by a factor of 7.3 and the thermal magnetic noise by a factor of 6.8. In the state of the highest field sensitivity, the lowest normalized 1/f magnetic noise parameter reaches 6.45 × 10-14 ?m3T. The results indicate that voltage-induced anisotropy modulation can be used to control and suppress magnetization fluctuations in the sensing layer and thus, significantly reduce the magnetic noise.

Wisniowski, P.; D?bek, M.; Skowronski, W.; Stobiecki, T.; Cardoso, S.; Freitas, P. P.

2014-08-01

152

Anisotropy of the magnetic susceptibility of gallium  

USGS Publications Warehouse

The bulk magnetic susceptibilities of single gallium crystals and polycrystalline gallium spheres were measured at 25??C. The following anisotropic diamagnetic susceptibilities were found: a axis (-0.119??0. 001)??10-6 emu/g, b axis (-0.416??0.002)??10 -6 emu/g, and c axis (-0.229??0.001) emu/g. The susceptibility of the polycrystalline spheres, assumed to be the average value for the bulk susceptibility of gallium, was (-0.257??0.003)??10-6 emu/g at 25??C, and (-0.299??0.003)??10-6 emu/g at -196??C. The susceptibility of liquid gallium was (0.0031??0.001) ??10-6 emu/g at 30??C and 100??C. Rotational diagrams of the susceptibilities in the three orthogonal planes of the unit cell were not sinusoidal. The anisotropy in the single crystals was presumably caused by the partial overlap of Brillouin zone boundaries by the Fermi-energy surface. The large change in susceptibility associated with the change in state was attributed to the absence of effective mass influence in the liquid state. ?? 1960 The American Institute of Physics.

Pankey, T., Jr.

1960-01-01

153

Magnetic Anisotropies in Samarium-Cobalt Thin Films  

Microsoft Academic Search

A systemic study of the deposition processes and magnetic properties for the Sm-Co film system has been carried out. Films of Sm-Co system with various magnetic anisotropies have been synthesized through sputter deposition in both crystalline and amorphous phases. The origins of various anisotropies have been studied. Thermallized sputter deposition process control was used to synthesize Fe enriched Sm-Co films

Kailai Chen

1993-01-01

154

Magnetic anisotropies in SmCo thin films  

Microsoft Academic Search

A systemic study of the deposition processes and magnetic properties for the Sm-Co film system has been carried out. Films of Sm-Co system with various magnetic anisotropies have been synthesized through sputter deposition in both crystalline and amorphous phases. The origins of various anisotropies have been studied. Thermalized sputter deposition process control was used to synthesize Fe enriched Sm-Co films

1993-01-01

155

Anisotropy of magnetic susceptibility data indicating remagnetization in diabase dikes  

Microsoft Academic Search

Induced and remanent magnetic analyses have been performed on drilled samples from 2 generations of unweathered diabase dikes, a breccia dike, and the host tonalite which make up the basement on which the Russell Dam foundation was poured. The maximum magnetic foliation plane for most samples, defined by anisotropy of magnetic susceptibility (AMS) data, is vertical and is oriented perpendicular

Brooks B. Ellwood

1984-01-01

156

Anisotropies of partial anhysteretic remanence and susceptibility in compacted black shales: Grainsize- and composition-dependent magnetic fabric  

Microsoft Academic Search

We have quantified the magnetic fabric of the highly-compacted Heebner Shale (Pennsylvanian) of Kansas in terms of the anisotropies of partial anhysteretic remanent magnetization (pARM) and low-field susceptibility. Hysteresis loops exhibit almost purely paramagnetic behavior, and the ratio of high-field linear susceptibility to low-field susceptibility is very close to one; the susceptibility anisotropy therefore reflects the fabric of the paramagnetic

Mike Jackson; Don Sprowl; Brooks Ellwood

1989-01-01

157

Origin and spectroscopic determination of trigonal anisotropy in a heteronuclear single-molecule magnet  

NASA Astrophysics Data System (ADS)

W-band (? ? 94 GHz) electron paramagnetic resonance (EPR) spectroscopy was used for a single-crystal study of a star-shaped Fe3Cr single-molecule magnet (SMM) with crystallographically imposed trigonal symmetry. The high resolution and sensitivity accessible with W-band EPR allowed us to determine accurately the axial zero-field splitting terms for the ground (S = 6) and first two excited states (S = 5 and S = 4). Furthermore, spectra recorded by applying the magnetic field perpendicular to the trigonal axis showed a ?/6 angular modulation. This behavior is a signature of the presence of trigonal transverse magnetic anisotropy terms whose values had not been spectroscopically determined in any SMM prior to this work. Such in-plane anisotropy could only be justified by dropping the so-called “giant spin approach” and by considering a complete multispin approach. From a detailed analysis of experimental data with the two models, it emerged that the observed trigonal anisotropy directly reflects the structural features of the cluster, i.e., the relative orientation of single-ion anisotropy tensors and the angular modulation of single-ion anisotropy components in the hard plane of the cluster. Finally, since high-order transverse anisotropy is pivotal in determining the spin dynamics in the quantum tunneling regime, we have compared the angular dependence of the tunnel splitting predicted by the two models upon application of a transverse field (Berry-phase interference).

Sorace, L.; Boulon, M.-E.; Totaro, P.; Cornia, A.; Fernandes-Soares, J.; Sessoli, R.

2013-09-01

158

Local stress engineering of magnetic anisotropy in soft magnetic thin films  

SciTech Connect

The magnetic anisotropy of amorphous thin films was modified laterally by masked ion irradiation without alteration of the intrinsic magnetic properties. The changes were introduced by local ion implantation in a protection layer, causing additional stress-induced magnetic anisotropy in the magnetostrictive layer. The underlying local variation in magnetic anisotropy was modeled and confirmed experimentally. The described method, relying purely on magnetoelastics, introduces a new path to the alteration of magnetic properties subsequent to magnetic film preparation. With the use of the resulting artificial magnetization patterns, it is possible to tailor the ferromagnetic thin film structure used in magnetoelectronic applications.

Martin, Norbert; McCord, Jeffrey; Gemming, Thomas; Moench, Ingolf; Schaefer, Rudolf; Schultz, Ludwig [Leibniz Institute for Solid State and Materials Research IFW Dresden, Postfach 270116, 01171 Dresden (Germany); Gerber, Andreas; Quandt, Eckhard [Chair for Inorganic Functional Materials, CAU Kiel, Kaiserstrasse 2, 24143 Kiel (Germany); Strache, Thomas; Fassbender, Juergen [Forschungszentrum Dresden Rossendorf e. V., P.O. Box 510119, 01314 Dresden (Germany); Farag, Nayel [Institute for Materials Science and Max Bergmann Center of Biomaterials, Dresden University of Technology, 01062 Dresden (Germany)

2009-02-09

159

Static magnetic solution in magnetic composites with arbitrary susceptibility inhomogeneity and anisotropy  

NASA Astrophysics Data System (ADS)

The static magnetic solutions in magnetic composites with arbitrary susceptibility inhomogeneity and anisotropy are accurately computed using an efficient numerical algorithm based on a proposed Fourier spectral iterative perturbation method for 3-dimensional systems. An advantage of this method is that the interphase boundary conditions are automatically considered without explicitly tracking interphase interfaces in the composites. This method can be conveniently implemented in phase-field modeling of microstructure evolution in systems with inhomogeneous susceptibility as well as inhomogeneous spontaneous magnetization distributions. Based on the proposed method, the effects of microstructures including the susceptibility mismatch between the inclusions and matrix, inclusions volume fraction, and inclusions arrangement on the effective susceptibility and local static magnetic field distribution of the composite are investigated. It is found that the interactions among the inclusions embedded in the matrix play critical roles in determining the composite properties.

Wang, J. J.; Song, Y.; Ma, X. Q.; Chen, Long-Qing; Nan, Ce-Wen

2015-01-01

160

Magnetic anisotropies in ultrathin bismuth iron garnet films  

NASA Astrophysics Data System (ADS)

Ultrathin bismuth iron garnet Bi3Fe5O12 films were grown epitaxially on (001)-oriented gadolinium gallium garnet substrates. Film thickness varied from two to three dozens of unit cells. Bi3Fe5O12 films grow pseudomorphically on substrates up to a thickness of 20 nm, and then a lattice relaxation occurs. Magnetic properties of the films were studied as a function of bismuth iron garnet thickness. The magnetization and cubic anisotropy decrease with decreasing film thickness. The uniaxial magnetocrystalline anisotropy is constant for all film thicknesses. For two unit cell thick films, the easy magnetization axis changes from in-plane to perpendicular to the plane direction. Such a reorientation takes place as a result of the competition of constant uniaxial perpendicular anisotropy with weakening film magnetization.

Popova, Elena; Franco Galeano, Andres Felipe; Deb, Marwan; Warot-Fonrose, Bénédicte; Kachkachi, Hamid; Gendron, François; Ott, Frédéric; Berini, Bruno; Keller, Niels

2013-06-01

161

Constraints on a Primordial Magnetic Field  

SciTech Connect

We derive an upper limit of B{sub 0}{lt}3.4{times}10{sup -9}({Omega}{sub 0}h{sup 2}{sub 50}){sup 1/2} G on the present strength of any primordial homogeneous magnetic field. The microwave background anisotropy created by cosmological magnetic fields is calculated in the most general flat and open anisotropic cosmologies containing expansion-rate and 3-curvature anisotropies. Our limit is derived from a statistical analysis of the 4-year Cosmic Background Explorer (COBE) data for anisotropy patterns characteristic of homogeneous anisotropy averaged over all possible sky orientations with respect to the COBE receiver. The limits we obtain on homogeneous magnetic fields are stronger than those imposed by nucleosynthesis. {copyright} {ital 1997} {ital The American Physical Society}

Barrow, J.D.; Ferreira, P.G.; Silk, J. [Center for Particle Astrophysics, and Departments of Astronomy and Physics, University of California, Berkely, California 94720-7304 (United States)] [Center for Particle Astrophysics, and Departments of Astronomy and Physics, University of California, Berkely, California 94720-7304 (United States); Barrow, J.D. [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom)] [Astronomy Centre, University of Sussex, Brighton BN1 9QH (United Kingdom)

1997-05-01

162

Magnetic anisotropy and sub-lattice magnetization study of polycrystalline magneto-electric GaFexO3  

NASA Astrophysics Data System (ADS)

Polycrystalline magneto-electric GaFexO3 (0.8?x?1.2) ceramics are studied with bulk magnetization and 57Fe Mössbauer measurements. The ferrimagnetic to paramagnetic transition temperature (TC), saturation magnetization (MS) and the magnetic anisotropy values are found to vary significantly with the site-disorder of Fe3+ and Ga3+ cations. With the increase of iron content, increase of TC and MS, and decrease of magnetic anisotropy are observed. Using low temperature high magnetic field 57Fe Mössbauer measurements, individual temperature dependence of hyperfine fields and hence magnetization of the three sub-lattices are measured. It is observed that the three sub-lattices have quite a different temperature dependence resulting in the non-monotonous variation of resultant magnetization as measured by bulk magnetic measurements. Definite evidence, using 57Fe Mössbauer measurements, is submitted to show that the Fe ions at Fe2 and Ga2 sites are responsible for the observed magnetic anisotropy, site-disorder induced magnetism and thermo-magnetic irreversible features in GaFexO3.

Raghavendra Reddy, V.; Sharma, Kavita; Gupta, Ajay; Banerjee, A.

2014-08-01

163

Uniaxial anisotropy in magnetite thin film—Magnetization studies  

Microsoft Academic Search

Magnetization and electrical resistivity measurements have been performed on a stoichiometric single crystalline magnetite Fe3O4 thin film (thickness of ca. 500nm) MBE deposited on MgO (100) substrate. The aim of these studies was to check the influence of preparation method and sample form (bulk vs. thin film) on magnetic anisotropy properties in magnetite. The film magnetization along ?001? versus applied

A. Wiechec; J. Korecki; B. Handke; Z. Kakol; D. Owoc; D. A. Antolak; A. Kozlowski

2006-01-01

164

Transition-metal dimers and physical limits on magnetic anisotropy  

Microsoft Academic Search

Recent advances in nanoscience have raised interest in the minimum bit size\\u000arequired for classical information storage, i.e. for bistability with\\u000asuppressed quantum tunnelling and energy barriers that exceed ambient\\u000atemperatures. In the case of magnetic information storage much attention has\\u000acentred on molecular magnets[1] with bits consisting of ~ 100 atoms, magnetic\\u000auniaxial anisotropy energy barriers ~ 50 K,

Carlo M. Canali; Allan H. MacDonald; Tor O. Strandberg

2007-01-01

165

Local magnetic anisotropy in Sn-doped Gd metal  

Microsoft Academic Search

The parameters of the magnetic structure near an impurity ion have been measured using the Mssbauer effect at 119Sn impurity nuclei in a Gd single crystal. The local change in the magnetic anisotropy is calculated. The role of the orbital\\u000a angular momentum of the matrix ion in the local-magnetic-perturbation mechanism in the heavy rare-earth metals series is estimated.

S. K. Godovikov; A. I. Firov

1997-01-01

166

Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films  

SciTech Connect

OAK B204 Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films. The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and hTi-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials.

Hellman, Frances

1998-10-03

167

Giant magnetic anisotropy and tunnelling of the magnetization in Li?(Li(1-x)Fe(x))N.  

PubMed

Large magnetic anisotropy and coercivity are key properties of functional magnetic materials and are generally associated with rare earth elements. Here we show an extreme, uniaxial magnetic anisotropy and the emergence of magnetic hysteresis in Li?(Li(1-x)Fe(x))N. An extrapolated, magnetic anisotropy field of 220?T and a coercivity field of over 11?T at 2?K outperform all known hard ferromagnets and single-molecular magnets. Steps in the hysteresis loops and relaxation phenomena in striking similarity to single-molecular magnets are particularly pronounced for x?1 and indicate the presence of nanoscale magnetic centres. Quantum tunnelling, in the form of temperature-independent relaxation and coercivity, deviation from Arrhenius behaviour and blocking of the relaxation, dominates the magnetic properties up to 10?K. The simple crystal structure, the availability of large single crystals and the ability to vary the Fe concentration make Li?(Li(1-x)Fe(x))N an ideal model system to study macroscopic quantum effects at elevated temperatures and also a basis for novel functional magnetic materials. PMID:24566374

Jesche, A; McCallum, R W; Thimmaiah, S; Jacobs, J L; Taufour, V; Kreyssig, A; Houk, R S; Bud'ko, S L; Canfield, P C

2014-01-01

168

Induced magnetic anisotropy in Co-Mn-Si-B amorphous microwires  

NASA Astrophysics Data System (ADS)

The effect of both thermal treatments as well as chemical etching treatments on the magnetic behavior has been investigated in nearly-zero magnetostriction glass-coated amorphous (Co1-xMnx)75Si10B15 (x=0.08, 0.09, and 0.10) microwires. Such a small change in x results in rather strong changes in the hysteresis loop parameters including coercitivity, Hc, and initial magnetic permeability, ?15. This effect was ascribed to the change of sign of the magnetostriction constant with a proper combination of the coercivity and relatively high initial permeability for the as-cast x=0.09 sample. Thermal treatment (temperatures 100-200 °C for 0.5-2 h) as well as chemical etching in 20% diluted fluoridric acid with duration from 0.5 up to 50 min modify this magnetic parameters owing to the internal stresses relaxation process. In particular, annealing under applied magnetic field (field annealing) can improve more significantly these magnetic parameters: increasing both Hc and ?15. Such phenomenology can be interpreted considering the noticeable longitudinal magnetic anisotropy induced by the combined effects of the magnetic field and strong internal stresses arising from the coating during the thermal treatment. The reduction of the glass coating thickness by chemical etching leads to a decrease of the internal stresses from a coating and, consequently, to a decrease of the transverse magnetoelastic anisotropy. Such decrease of anisotropy plays a role similar to that induced by field annealing on the hysteretic behavior.

Zhukov, A.; Blanco, J. M.; González, J.; Garcia Prieto, M. J.; Pina, E.; Vázquez, M.

2000-02-01

169

Anisotropy-based mechanism for zigzag striped patterns in magnetic thin films  

NASA Astrophysics Data System (ADS)

In this work, we studied a two-dimensional ferromagnetic system using Monte Carlo simulations. Our model includes exchange and dipolar interactions, a cubic anisotropy term, and uniaxial out-of-plane and in-plane ones. According to the set of parameters chosen, the model including uniaxial out-of-plane anisotropy has a ground state which consists of a canted state with stripes of opposite out-of-plane magnetization. When the cubic anisotropy is introduced, zigzag patterns appear in the stripes at fields close to the remanence. An analysis of the anisotropy terms of the model shows that this configuration is related to specific values of the ratio between the cubic and the effective uniaxial anisotropy. The mechanism behind this effect is related to particular features of the anisotropy's energy landscape since a global minima transition as a function of the applied field is required in the anisotropy terms. This mechanism for zigzag formation could be present in monocrystal ferromagnetic thin films in a given range of thicknesses.

Billoni, O. V.; Bustingorry, S.; Barturen, M.; Milano, J.; Cannas, S. A.

2014-05-01

170

Magnetic anisotropy and stacking faults in Co and Co84Pt16 epitaxially grown thin films  

E-print Network

. 110, 113902 (2011) Giant magnetoelectric torque effect and multicoupling in two phases ferromagnetic concurrent with an increase in magnetic anisotropy and a compression of the crystallographic lattice thermal instability and reduced switching field. A stacking fault in the HCP structure creates a layer

Laughlin, David E.

171

Magnetic circular dichroism anisotropy from coherent Raman detected electron paramagnetic resonance spectroscopy: Application to spin-12  

E-print Network

in the understanding of molecular structure.1,2 The MCD field and temperature dependencies of samples con- taining ion centers in enzymes and other proteins. When combined with infor- mation from complementary methods anisotropy. In addition, magnetic relaxation effects cross-relaxation13 and spectral diffusion can remove

Suter, Dieter

172

Resolving the controversy of a possible relationship between perpendicular magnetic anisotropy and the magnetic damping parameter  

SciTech Connect

We use broadband ferromagnetic resonance spectroscopy to systematically measure the Landau-Lifshitz damping parameter, perpendicular anisotropy, and the orbital moment asymmetry in Co{sub 90}Fe{sub 10}/Ni multilayers. No relationship is found between perpendicular magnetic anisotropy and the damping parameter in this material. However, inadequate accounting for inhomogeneous linewidth broadening, spin-pumping, and two-magnon scattering could give rise to an apparent relationship between anisotropy and damping. In contrast, the orbital-moment asymmetry and the perpendicular anisotropy are linearly proportional to each other. These results demonstrate a fundamental mechanism by which perpendicular anisotropy can be varied independently of the damping parameter.

Shaw, Justin M.; Nembach, Hans T.; Silva, T. J. [National Institute of Standards and Technology, Electromagnetics Division, Boulder, Colorado 80305 (United States)

2014-08-11

173

Magnetic field sensor for isotropically sensing an incident magnetic field in a sensor plane  

NASA Technical Reports Server (NTRS)

A magnetic field sensor that isotropically senses an incident magnetic field. This is preferably accomplished by providing a magnetic field sensor device that has one or more circular shaped magnetoresistive sensor elements for sensing the incident magnetic field. The magnetoresistive material used is preferably isotropic, and may be a CMR material or some form of a GMR material. Because the sensor elements are circular in shape, shape anisotropy is eliminated. Thus, the resulting magnetic field sensor device provides an output that is relatively independent of the direction of the incident magnetic field in the sensor plane.

Pant, Bharat B. (Inventor); Wan, Hong (Inventor)

2001-01-01

174

Magnetic fields in astrophysics  

Microsoft Academic Search

The evidence of cosmic magnetism is examined, taking into account the Zeeman effect, beats in atomic transitions, the Hanle effect, Faraday rotation, gyro-lines, and the strength and scale of magnetic fields in astrophysics. The origin of magnetic fields is considered along with dynamos, the conditions for magnetic field generation, the topology of flows, magnetic fields in stationary flows, kinematic turbulent

Ia. B. Zeldovich; A. A. Ruzmaikin; D. D. Sokolov

1983-01-01

175

Control of magnetism by electric fields  

NASA Astrophysics Data System (ADS)

The electrical manipulation of magnetism and magnetic properties has been achieved across a number of different material systems. For example, applying an electric field to a ferromagnetic material through an insulator alters its charge-carrier population. In the case of thin films of ferromagnetic semiconductors, this change in carrier density in turn affects the magnetic exchange interaction and magnetic anisotropy; in ferromagnetic metals, it instead changes the Fermi level position at the interface that governs the magnetic anisotropy of the metal. In multiferroics, an applied electric field couples with the magnetization through electrical polarization. This Review summarizes the experimental progress made in the electrical manipulation of magnetization in such materials, discusses our current understanding of the mechanisms, and finally presents the future prospects of the field.

Matsukura, Fumihiro; Tokura, Yoshinori; Ohno, Hideo

2015-03-01

176

Control of magnetism by electric fields.  

PubMed

The electrical manipulation of magnetism and magnetic properties has been achieved across a number of different material systems. For example, applying an electric field to a ferromagnetic material through an insulator alters its charge-carrier population. In the case of thin films of ferromagnetic semiconductors, this change in carrier density in turn affects the magnetic exchange interaction and magnetic anisotropy; in ferromagnetic metals, it instead changes the Fermi level position at the interface that governs the magnetic anisotropy of the metal. In multiferroics, an applied electric field couples with the magnetization through electrical polarization. This Review summarizes the experimental progress made in the electrical manipulation of magnetization in such materials, discusses our current understanding of the mechanisms, and finally presents the future prospects of the field. PMID:25740132

Matsukura, Fumihiro; Tokura, Yoshinori; Ohno, Hideo

2015-03-01

177

In-plane anisotropy of a nano-scaled magnetic tunnel junction with perpendicular magnetic easy axis  

NASA Astrophysics Data System (ADS)

We investigate magnetic properties of a 100-nm-diameter CoFeB/MgO magnetic tunnel junction (MTJ) with perpendicular magnetic easy axis by homodyne-detected ferromagnetic resonance (FMR) and junction resistance measurements. The resonant frequency depends clearly on the direction of the in-plane magnetic field, which is also the case for the angle dependence of the junction resistance. A good correspondence between the two independent measurements indicates the presence of unintentionally introduced in-plane magnetic anisotropy in the present MTJ.

Hirayama, Eriko; Kanai, Shun; Sato, Koji; Yamanouchi, Michihiko; Sato, Hideo; Ikeda, Shoji; Matsukura, Fumihiro; Ohno, Hideo

2015-04-01

178

Properties of a large-scale interplanetary loop structure as deduced from low-energy proton anisotropy and magnetic field measurements  

NASA Technical Reports Server (NTRS)

Correlated particle and magnetic field measurements by the ISEE 3 spacecraft are presented for the loop structure behind the interplanetary traveling shock event of Nov. 12, 1978. Following the passage of the turbulent shock region, strong bidirectional streaming of low-energy protons is observed for approximately 6 hours, corresponding to a loop thickness of about 0.07 AU. This region is also characterized by a low relative variance of the magnetic field, a depressed proton intensity, and a reduction in the magnetic power spectral density. Using quasi-linear theory applied to a slab model, a value of 3 AU is derived for the mean free path during the passage of the closed loop. It is inferred from this observation that the proton regime associated with the loop structure is experiencing scatter-free transport and that either the length of the loop is approximately 3 AU between the sun and the earth or else the protons are being reflected at both ends of a smaller loop.

Tranquille, C.; Sanderson, T. R.; Marsden, R. G.; Wenzel, K.-P.; Smith, E. J.

1987-01-01

179

Proximity effect between a topological insulator and a magnetic insulator with large perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

We report that thin films of a prototype topological insulator, Bi2Se3, can be epitaxially grown onto the (0001) surface of BaFe12O19 (BaM), a magnetic insulator with high Curie temperature and large perpendicular anisotropy. In the Bi2Se3 thin films grown on non-magnetic substrates, classic weak antilocalization (WAL) is manifested as cusp-shaped positive magnetoresistance (MR) in perpendicular magnetic fields and parabola-shaped positive MR in parallel fields, whereas in Bi2Se3/BaM heterostructures the low field MR is parabola-shaped, which is positive in perpendicular fields and negative in parallel fields. The magnetic field and temperature dependence of the MR is explained as a consequence of the suppression of WAL due to strong magnetic interactions at the Bi2Se3/BaM interface.

Yang, Wenmin; Yang, Shuo; Zhang, Qinghua; Xu, Yang; Shen, Shipeng; Liao, Jian; Teng, Jing; Nan, Cewen; Gu, Lin; Sun, Young; Wu, Kehui; Li, Yongqing

2014-09-01

180

Giant Modification of the Magnetocrystalline Anisotropy in Transition-Metal Monolayers by an External Electric Field  

Microsoft Academic Search

Controlling and designing quantum magnetic properties by an external electric field is a key challenge in modern magnetic physics. Here, from first principles, the effects of an external electric field on the magnetocrystalline anisotropy (MCA) in ferromagnetic transition-metal monolayers are demonstrated which show that the MCA in an Fe(001) monolayer [but not in Co(001) and Ni(001) monolayers] can be controlled

Kohji Nakamura; Riki Shimabukuro; Yuji Fujiwara; Toru Akiyama; Tomonori Ito; A. J. Freeman

2009-01-01

181

Physical Structure and Magnetic Anisotropy of Alnico 5. Part I  

Microsoft Academic Search

It is concluded from electron metallographic results that the high coercive force and anisotropy of Alnico 5 are caused by a very finely divided precipitate produced by the permanent magnet heat treatment. This precipitate is a transition structure rich in cobalt and is face-centered cubic with a0 = 10A and appears as rods growing along the [100] directions of the

R. D. Heidenreich; E. A. Nesbitt

1952-01-01

182

Structural and magnetic properties of granular Co-Pt multilayers with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We present a study of granular Co-Pt multilayers by means of high-resolution transmission electron microscopy (HRTEM), extended x-ray absorption fine structure (EXAFS), SQUID-based magnetic measurements, anomalous Hall effect (AHE), and x-ray magnetic circular dichroism (XMCD). We describe these granular films as composed of particles with a pure cobalt core surrounded by an alloyed Co-Pt interface, embedded in a Pt matrix. The alloy between the Co and Pt in these granular films, prepared by room temperature sputter deposition, results from interdiffusion of the atoms. The presence of this alloy gives rise to a high perpendicular magnetic anisotropy (PMA) in the granular films, as consequence of the anisotropy of the orbital moment in the Co atoms in the alloy, and comparable to that of highly-ordered CoPt L 10 alloy films. Their magnetic properties are those of ferromagnetically coupled particles, whose coupling is strongly temperature dependent: at low temperatures, the granular sample is ferromagnetic with a high coercive field; at intermediate temperatures the granular film behaves as an amorphous asperomagnet, with a coupling between the grains mediated by the polarized Pt, and at high temperatures, the sample has a superparamagnetic behavior. The coupling/decoupling between the grains in our Co-Pt granular films can be tailored by variation of the amount of Pt in the samples.

Figueroa, A. I.; Bartolomé, J.; García, L. M.; Bartolomé, F.; Bun?u, O.; Stankiewicz, J.; Ruiz, L.; González-Calbet, J. M.; Petroff, F.; Deranlot, C.; Pascarelli, S.; Bencok, P.; Brookes, N. B.; Wilhelm, F.; Smekhova, A.; Rogalev, A.

2014-11-01

183

Facilities: EMR & DC field (31T, 50mm bore resistive magnet). Citation: Giant Ising-Type Magnetic Anisotropy in Trigonal Bipyramidal Ni(II) Complexes: Experiment and Theory, R. Ruamps, R.  

E-print Network

Facilities: EMR & DC field (31T, 50mm bore resistive magnet). Citation: Giant Ising-Type Magnetic). If the correct symmetry is achieved, there may be a strong orbital contribution to the magnetic moment in addition to the spin moment. The combined ligand-orbital and spin-orbital interactions can then give rise

McQuade, D. Tyler

184

Competing anisotropies and complex magnetism in SrRuO3\\/SrMnO3 superlattices  

Microsoft Academic Search

Using element-specific x-ray resonance techniques, we have investigated the interfacial magnetic coupling in SrRuO3\\/SrMnO3 superlattices. A strong out-of-plane SRO anisotropy coupled with AFM Ru-Mn interactions result in a canted Mn structure with a significant induced net Mn moment that reduces to zero under a strong magnetic field. At T > TC SRO, the SRO anisotropy is removed and the planar

Omar Chmaissem; Y. Choi; Y. C. Tseng; D. Haskel; D. E. Brown; S. Kolesnik; D. Danaher

2009-01-01

185

Magnetic anisotropy of epitaxial cobalt ferrite thin films  

Microsoft Academic Search

We have fabricated epitaxial single crystalline cobalt ferrite (CoFe2O4) thin films on CoCr2O4 buffered SrTiO3 and MgAl2O4 substrates. Structural characterization by X-ray diffraction, Rutherford backscattering spectroscopy and atomic force microscopy indicates excellent crystallinity. Magnetic anisotropy measurements in the in-plane and perpendicular directions as a function of film thickness provide strong evidence for the dominant role of strain in the magnetic

Y. Suzuki; G. Hu; R. B. van Dover; R. J. Cava

1999-01-01

186

Giant induced magnetic anisotropy In strain annealed Co-based nanocomposite alloys  

E-print Network

Giant induced magnetic anisotropy In strain annealed Co-based nanocomposite alloys Samuel J://apl.aip.org/about/rights_and_permissions #12;Giant induced magnetic anisotropy In strain annealed Co-based nanocomposite alloys Samuel J in this process can mitigate eddy-current losses. Giant induced magnetic anisotropies are discussed in light

McHenry, Michael E.

187

Microstructural, magnetic anisotropy, and magnetic domain structure correlations in L10 FePd thin films  

Microsoft Academic Search

Understanding microstructural, magnetic anisotropy, and magnetic domain structure correlations in materials with large perpendicular magnetic anisotropy (PMA) is of fundamental interest and it is also important in many technological applications such as next generation magneto-recording media and spin-transfer torque devices. L10 ordered phases in some binary alloys (FePd, FePt, MnAl) have PMA due to chemical ordering that can be controlled

J. R. Skuza; C. Clavero; B. Wincheski; W. Chen; O. Amponsah; N. Noginova; R. A. Lukaszew

2010-01-01

188

Nonlinear susceptibility and dynamic hysteresis loops of magnetic nanoparticles with biaxial anisotropy  

NASA Astrophysics Data System (ADS)

The nonlinear ac susceptibility and dynamic magnetic hysteresis (DMH) of a single domain ferromagnetic particle with biaxial anisotropy subjected to both external ac and dc fields of arbitrary strength and orientation are treated via Brown's continuous diffusions model [W. F. Brown, Jr., Phys. Rev. 130, 1677 (1963)] of magnetization orientations. The DMH loops and nonlinear ac susceptibility strongly depend on the dc and ac field strengths, the polar angle between the easy axis of the particle, the external field vectors, temperature, and damping. In contrast to uniaxial particles, the nonlinear ac stationary response and DMH strongly depend on the azimuthal direction of the ac field and the biaxiality parameter ?.

Ouari, Bachir; Titov, Serguey V.; El Mrabti, Halim; Kalmykov, Yuri P.

2013-02-01

189

Magnetic field sensor  

NASA Astrophysics Data System (ADS)

Earlier papers1-3 in this journal have described experiments on measuring the magnetic fields of current-carrying wires and permanent magnets using magnetic field probes of various kinds. This paper explains how to use an iPad and the free app MagnetMeter-3D Vector Magnetometer and Accelerometer4 (compass HD) to measure the magnetic fields.

Silva, Nicolas

2012-09-01

190

Exploring Magnetic Field Lines  

NSDL National Science Digital Library

In this activity, learners explore the magnetic field of a bar magnet as an introduction to understanding Earth's magnetic field. First, learners explore and play with magnets and compasses. Then, learners trace the field lines of the magnet using the compass on a large piece of paper. This activity will also demonstrate why prominences are always "loops."

2012-06-26

191

Fabrication and characterization of thin films with perpendicular magnetic anisotropy for high-density magnetic recording  

Microsoft Academic Search

Perpendicular magnetic anisotropy (PMA) was first observed in thin films of cobalt-chromium alloys in 1974, and perpendicular magnetic recording was proposed in 1977. After less than ten years, a new technology for high-density magnetic recording is firmly established. This breakthrough of the science and technology of magnetic recording has been made possible mainly through the ingenuity and concerted efforts of

C. W. Chen

1991-01-01

192

Magnetic anisotropy as a tracer of crystal accumulation and transport, Middle Banded Series, Stillwater Complex, Montana  

NASA Astrophysics Data System (ADS)

Fabric studies of layered mafic intrusions have led to improved understanding of the mechanical processes operating in large magma chambers, including crystal accumulation and crystal mush deformation. Such studies, however, are typically limited by a tradeoff between breadth (number of sites studied, characteristic of field-focused work) and sensitivity (ability to discern subtle fabric elements, characteristic of laboratory fabric analyses). Magnetic anisotropy, if analyzed in a systematic way and supported by single-crystal and petrofabric measurements, permits relatively rapid characterization of magmatic fabrics for large numbers of samples. Here we present the results of a study of remanence and susceptibility anisotropy from three transects through the Middle Banded Series of the Stillwater Complex, Montana. All three transects exhibit a magnetic foliation that increases with stratigraphic height up to the top of Olivine Bearing Zone III, consistent with crystal mush compaction. Perhaps more importantly, each transect is characterized by a subtle lineation in the anisotropy of magnetic susceptibility with a consistent direction within that transect. The magnetic lineation directions, which generally coincide with crystallographic preferred orientations of silicate minerals, likely record a pre-compaction fabric. Lineation directions differ from one transect to another, implying that the process generating the lineation - either slumping of a semiconsolidated crystal mush or magma transport - acted on length scales of at most a few km. These results demonstrate the sensitivity of magnetic anisotropy to petrofabric in mafic rocks.

Selkin, Peter A.; Gee, Jeffrey S.; Meurer, William P.

2014-08-01

193

Rotatable magnetic anisotropy in Si/SiO2/(Co2Fe)(x)Ge(1-x) Heusler alloy films.  

PubMed

Polycrystalline (Co2Fe)(x)Ge(1-x) Heusler alloy films are fabricated by sputtering on amorphous substrates and shown to possess three types of magnetic anisotropy. The nearly stoichiometric composition of x = 50 m.f.% shows a rectangular hysteresis loop and isotropic coercive and ferromagnetic resonance fields when the film is field-magnetized along any in-plane direction, thus predominantly possessing rotatable in-plane magnetic anisotropy. Higher-x compositions show evidence of two- and fourfold in-plane anisotropy superposed on the rotatable one. A qualitative model of the observed anisotropic magnetic properties is proposed. The model explains the rotatable anisotropy by taking into account dry friction for the in-plane rotation of the magnetization direction in a fine-grained polycrystalline film with the magnetic grain size smaller than the correlation length of the inter-grain exchange interaction. The observed two- and fourfold magnetic anisotropy contributions are attributed to partial texturing of the fine-grained films, even though the films are grown on amorphous SiO2 substrates. These results should be valuable for understanding and controlling the magnetic behaviour of highly spin-polarized Heusler alloy films used in various magnetic nanodevices. PMID:24025408

Ryabchenko, S M; Kalita, V M; Kulik, M M; Lozenko, A F; Nevdacha, V V; Pogorily, A N; Kravets, A F; Podyalovskiy, D Y; Vovk, A Ya; Borges, R P; Godinho, M; Korenivski, V

2013-10-16

194

Large magnetic anisotropy in ferrihydrite nanoparticles synthesized from reverse micelles  

NASA Astrophysics Data System (ADS)

Six-line ferrihydrite (FH) nanoparticles have been synthesized in the core of reverse micelles, used as nanoreactors to obtain average particle sizes \\langle d\\rangle \\approx 2 \\mbox {--} 4~\\mathrm {nm} . The blocking temperatures TBm extracted from magnetization data increased from ap10 to 20 K for increasing particle size. Low-temperature Mössbauer measurements allowed us to observe the onset of differentiated contributions from the particle core and surface as the particle size increases. The magnetic properties measured in the liquid state of the original emulsion showed that the ferrihydrite phase is not present in the liquid precursor, but precipitates in the micelle cores after the free water is freeze-dried. Systematic susceptibility ?ac(f,T) measurements showed the dependence of the effective magnetic anisotropy energies Ea with particle volume, and yielded an effective anisotropy value of Keff = 312 ± 10 kJ m-3.

Duarte, E. L.; Itri, R.; Lima, E., Jr.; Baptista, M. S.; Berquó, T. S.; Goya, G. F.

2006-11-01

195

Controlling magnetic anisotropy in epitaxial FePt(001) films  

SciTech Connect

Epitaxial equiatomic Fe{sub 50}Pt{sub 50} thin films with a variable order parameter ranging from 0 to 0.9 and Fe{sub 100-x}Pt{sub x} thin films with x ranging from 33 to 50 were deposited on MgO (001) substrates by dc sputtering. A seed layer consisting of nonmagnetic Cr (4 nm)/Pt (12 nm) was used to promote the crystallinity of the magnetic films. The crystal structure and magnetic properties were gauged using x-ray diffraction and magnetometry. The magnetic anisotropy can be controlled by changing the order parameter. For Fe{sub 100-x}Pt{sub x} films, the increase in Fe composition leads to an increase in coercivity in the hard axis loop and causes a loss of perpendicular anisotropy.

Lu Zhihong; Walock, M. J.; LeClair, P.; Butler, W. H.; Mankey, G. J. [MINT Center and Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487-0209 (United States)

2009-07-15

196

Magnetic anisotropy and thermal stability of magnetite particle assemblies in magnetotactic bacteria  

NASA Astrophysics Data System (ADS)

The formation of nanoparticle assemblies in nature is characteristic for magnetotactic bacteria (MTB), where magnetite (Fe3O4) nanocrystals are formed intracellularly. The nanocrystals are usually aligned along their [111] axis and are held in chain configuration by a skeletal filament. This alignment, with [111] being the magnetization easy axis of magnetite, generates a strong interaction-induced dipole field along the cellular body axes, which gives rise to a distinct uniaxial anisotropy. The anisotropy properties of MTB are readily detectable by ferromagnetic resonance spectroscopy (FMR), where spectra of randomly oriented MTB show characteristic features with two low-field peaks and a strong high-field minimum. The anisotropy properties of such chain assemblies of nanocrystals are examined in detail by approximating the chain as a single ellipsoid. In this approximation both the cubic magnetocrystalline anisotropy field (Hcub) and the effective uniaxial field (Huni) are considered, and used to simulate FMR spectra [1]. By varying the two parameters Huni and Hcub we can simulate signals that fit the experimental FMR spectra obtained from cultured intact MTB, thus easily extracting the anisotropy fields in the samples. We find that this method can be used with good precision to model the behavior of MTB quantitatively. Moreover, this method is applied to investigate the evolution of the magnetic anisotropy in a growth series of MTB under laboratory conditions. Special focus is given on the superparamagnetic effects due to small particle sizes in the initial growth stages. The effective uniaxiality in MTB, which is essential for magnetotaxis, is evident after the cubic anisotropy field is strong enough to hold the magnetic moments along the [111] direction of the crystallites [2]. The quantitative analysis of anisotropy traits in intact cultured MTB could be valuable for the detection of MTB in geological systems that can contribute to a better insight into microbial ecology during Earth's history. References: [1] M. Charilaou, M. Winklhofer, A. U. Gehring, J. Appl. Phys. 109, 093903 (2011). [2] M. Charilaou, K. K. Sahu, D. Faivre, A. Fischer, I. García-Rubio, A. U. Gehring, Appl. Phys. Lett. 99, 182504 (2011).

Charilaou, M.; Winklhofer, M.; Gehring, A. U.

2012-12-01

197

Exploring Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetic fields. Using iron filings, learners will observe magnets in various arrangements to investigate the magnetic field lines of force. This information is then related to magnetic loops on the Sun's surface and the magnetic field of the Earth. This is the second activity in the Exploring the Earth's Magnetic Field: An IMAGE Satellite Guide to the Magnetosphere educators guide.

2012-08-03

198

Tailoring magnetic anisotropy in epitaxial half metallic La0.7Sr0.3MnO3 thin P. Perna,1, a)  

E-print Network

Tailoring magnetic anisotropy in epitaxial half metallic La0.7Sr0.3MnO3 thin films P. Perna,1, a) C present a detailed study on the magnetic properties, including anisotropy, reversal fields, and magnetiza temperature high resolution vectorial Kerr magnetometry measurements have been performed at different applied

Boyer, Edmond

199

Exploring Magnetic Fields  

NSDL National Science Digital Library

In this activity, students investigate the presence of magnetic fields around magnets, the sun and the earth. They will explore magnetic field lines, understand that magnetic lines of force show the strength and direction of magnetic fields, determine how field lines interact between attracting and repelling magnetic poles, and discover that the earth and sun have magnetic properties. They will also discover that magnetic force is invisible and that a "field of force" is a region or space in which one object can attract or repel another.

200

Magnetic Fields Matter  

NSDL National Science Digital Library

This lesson introduces students to the effects of magnetic fields in matter addressing permanent magnets, diamagnetism, paramagnetism, ferromagnetism, and magnetization. First students must compare the magnetic field of a solenoid to the magnetic field of a permanent magnet. Students then learn the response of diamagnetic, paramagnetic, and ferromagnetic material to a magnetic field. Now aware of the mechanism causing a solid to respond to a field, students learn how to measure the response by looking at the net magnetic moment per unit volume of the material.

2014-09-18

201

Control of single-spin magnetic anisotropy by exchange coupling.  

PubMed

The properties of quantum systems interacting with their environment, commonly called open quantum systems, can be affected strongly by this interaction. Although this can lead to unwanted consequences, such as causing decoherence in qubits used for quantum computation, it can also be exploited as a probe of the environment. For example, magnetic resonance imaging is based on the dependence of the spin relaxation times of protons in water molecules in a host's tissue. Here we show that the excitation energy of a single spin, which is determined by magnetocrystalline anisotropy and controls its stability and suitability for use in magnetic data-storage devices, can be modified by varying the exchange coupling of the spin to a nearby conductive electrode. Using scanning tunnelling microscopy and spectroscopy, we observe variations up to a factor of two of the spin excitation energies of individual atoms as the strength of the spin's coupling to the surrounding electronic bath changes. These observations, combined with calculations, show that exchange coupling can strongly modify the magnetic anisotropy. This system is thus one of the few open quantum systems in which the energy levels, and not just the excited-state lifetimes, can be renormalized controllably. Furthermore, we demonstrate that the magnetocrystalline anisotropy, a property normally determined by the local structure around a spin, can be tuned electronically. These effects may play a significant role in the development of spintronic devices in which an individual magnetic atom or molecule is coupled to conducting leads. PMID:24317285

Oberg, Jenny C; Calvo, M Reyes; Delgado, Fernando; Moro-Lagares, María; Serrate, David; Jacob, David; Fernández-Rossier, Joaquín; Hirjibehedin, Cyrus F

2014-01-01

202

Induced magnetic anisotropy in stress-annealed Galfenol laminated rods  

NASA Astrophysics Data System (ADS)

Iron-gallium (Galfenol) is a promising transducer material that combines high magnetostriction, desirable mechanical properties and a high permeability. The high permeability of this material causes a relatively low cutoff frequency in dynamic applications, above which eddy currents form and introduce significant power losses. To reduce the eddy current losses, magnetostrictive drivers are commonly laminated. A second transducer design consideration is the introduction of an initial alignment of domains inside of the material to maximize the magnetostriction performance without a prestress mechanism. Built-in uniaxial magnetic anisotropy through stress annealing aligns magnetic moments perpendicular to the direction of actuation. Stress annealing is a high temperature process with simultaneous application of an external load and subsequent cooling under load in which the magnetic moment alignment developed at temperature is retained. The external load needed to build in a useful uniaxial magnetic anisotropy in Galfenol is greater than the buckling load for Galfenol laminae sized for use in high frequency dynamic applications. In this study, stress annealing of highly textured polycrystalline Galfenol is successfully extended to thin laminae by introducing fixtures to avoid buckling of the laminae under compression during the heat treatment process. The maximum built-in uniaxial anisotropy was 11.2 kJ m-3.

Yoo, J.-H.; Restorff, J. B.; Wun-Fogle, M.; Flatau, A. B.

2009-10-01

203

Mechanism of tailored magnetic anisotropy in amorphous Co{sub 68}Fe{sub 24}Zr{sub 8} thin films  

SciTech Connect

The mechanism of tailored magnetic anisotropy in amorphous Co{sub 68}Fe{sub 24}Zr{sub 8} thin films was investigated by ferromagnetic resonance (FMR) on samples deposited without an applied magnetic field, with an out-of-plane field and an in-plane field. Analysis of FMR spectra profiles, high frequency susceptibility calculations, and statistical simulations using a distribution of local uniaxial magnetic anisotropy reveal the presence of atomic configurations with local uniaxial anisotropy, of which the direction can be tailored while the magnitude remains at an intrinsically constant value of 3.0(2) kJ/m{sup 3}. The in-plane growth field remarkably sharpens the anisotropy distribution and increases the sample homogeneity. The results benefit designing multilayer spintronic devices based on highly homogeneous amorphous layers with tailored magnetic anisotropy.

Fu, Yu, E-mail: yu.fu@uni-due.de, E-mail: cangcangzhulin@gmail.com; Meckenstock, R.; Farle, M. [Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, 47057 Duisburg (Germany); Barsukov, I., E-mail: ibarsuko@uci.edu [Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, 47057 Duisburg (Germany); Physics and Astronomy, University of California, Irvine, California 92697 (United States); Lindner, J. [Fakultät für Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universität Duisburg-Essen, 47057 Duisburg (Germany); Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf e.V., Bautzner Landstr. 400, 01328 Dresden (Germany); Raanaei, H. [Department of Physics, Persian Gulf University, Bushehr 75169 (Iran, Islamic Republic of); Hjörvarsson, B. [Department of Physics and Astronomy, Uppsala University, Box 516 SE-75120 Uppsala (Sweden)

2014-02-17

204

Tunable exchange bias-like effect in patterned hard-soft two-dimensional lateral composites with perpendicular magnetic anisotropy  

SciTech Connect

Patterned hard-soft 2D magnetic lateral composites have been fabricated by e-beam lithography plus dry etching techniques on sputter-deposited NdCo{sub 5} thin films with perpendicular magnetic anisotropy. Their magnetic behavior is strongly thickness dependent due to the interplay between out-of-plane anisotropy and magnetostatic energy. Thus, the spatial modulation of thicknesses leads to an exchange coupled system with hard/soft magnetic regions in which rotatable anisotropy of the thicker elements provides an extra tool to design the global magnetic behavior of the patterned lateral composite. Kerr microscopy studies (domain imaging and magneto-optical Kerr effect magnetometry) reveal that the resulting hysteresis loops exhibit a tunable exchange bias-like shift that can be switched on/off by the applied magnetic field.

Hierro-Rodriguez, A., E-mail: ahierro@fc.up.pt; Alvarez-Prado, L. M.; Martín, J. I.; Alameda, J. M. [Departamento de Física, Universidad de Oviedo, C/Calvo Sotelo S/N, 33007 Oviedo (Spain); Centro de Investigación en Nanomateriales y Nanotecnología—CINN (CSIC—Universidad de Oviedo—Principado de Asturias), Parque Tecnológico de Asturias, 33428 Llanera (Spain); Teixeira, J. M. [IN-IFIMUP, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre 687, 4169-007 Porto (Portugal); Vélez, M. [Departamento de Física, Universidad de Oviedo, C/Calvo Sotelo S/N, 33007 Oviedo (Spain)

2014-09-08

205

Full 180° Magnetization Reversal with Electric Fields  

NASA Astrophysics Data System (ADS)

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals.

Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

2014-12-01

206

Full 180° magnetization reversal with electric fields.  

PubMed

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Wang, J J; Hu, J M; Ma, J; Zhang, J X; Chen, L Q; Nan, C W

2014-01-01

207

Full 180° Magnetization Reversal with Electric Fields  

PubMed Central

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

2014-01-01

208

Visualizing Magnetic Field Lines  

NSDL National Science Digital Library

In this activity, students take the age old concept of etch-a-sketch a step further. Using iron filings, students begin visualizing magnetic field lines. To do so, students use a compass to read the direction of the magnet's magnetic field. Then, students observe the behavior of iron filings near that magnet as they rotate the filings about the magnet. Finally, students study the behavior of iron filings suspended in mineral oil which displays the magnetic field in three dimensions.

VU Bioengineering RET Program, School of Engineering,

209

What are Magnetic Fields?  

NSDL National Science Digital Library

This is an activity about magnetic fields. Using iron filings, learners will observe magnets in various arrangements to investigate the magnetic field lines of force. This information is then related to magnetic loops on the Sun's surface and the magnetic field of the Earth. This is the second activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website.

2012-08-03

210

Magnetic fields of galaxies  

Microsoft Academic Search

The current state of the understanding of the magnetic fields of galaxies is reviewed. A simple model of the turbulent dynamo is developed which explains the main observational features of the global magnetic fields of spiral galaxies. The generation of small-scale chaotic magnetic fields in the interstellar medium is also examined. Attention is also given to the role of magnetic

Aleksandr A. Ruzmaikin; Dmitrii D. Sokolov; Anvar M. Shukurov

1988-01-01

211

Anisotropy study of grain oriented steels with Magnetic Barkhausen Noise  

NASA Astrophysics Data System (ADS)

Grain oriented electrical steels present strong anisotropy, due to a {110} <001> texture (Goss), with [100] direction parallel to rolling direction (RD) and [110] direction parallel to transverse direction (TD). MBN (Magnetic Barkhausen Noise) were employed to measure magnetic properties in several angles towards RD using a 15° step. For 90° to the rolling direction (i.e., TD), the MBN signal changes, decreasing the MBNrms. It is found a connection between initial permeability and MBNrms. The lower initial permeability for the TD is related to a larger contribution of irreversible rotation in the hysteresis. The MBN procedure is non-destructive and provides rapid understanding of the anisotropy of the material, without the use of laborious methods like Epstein frame or toroidal coils.

de Campos, M. F.; Campos, M. A.; Landgraf, F. J. G.; Padovese, L. R.

2011-07-01

212

Thermomagnetic Properties, Natural Magnetic Moments, and Magnetic Anisotropies of Some Chondritic Meteorites  

Microsoft Academic Search

Thermomagnetic analyses, thermal demagnetization of natural and laboratory- induced remanent magnetic moments, and measurements of magnetic anisotropy have been carried out on a number of chondritic stony meteorites. Eighty to ninety per cent of the saturation magnetic moments were due to a-phase iron-nickel (kamacite) containing 5 to 6 per cent of nickel, and this phase was also responsible for most

F. D. Stacey; J. F. Lovering; L. G. Parry

1961-01-01

213

Perpendicular magnetic anisotropy in NdFeB thin films  

Microsoft Academic Search

The perpendicular magnetic anisotropy (PMA) in NdFeB thin films is investigated. PMA was observed when the c axis of Nd2Fe14B phase orients perpendicular to the film plane. The c-axis orientation and hence the PMA was found to be very sensitive to composition and substrate temperature. The change of composition or substrate temperature leads to a deterioration in the c-axis orientation

S. N. Piramanayagam; M. Matsumoto; A. Morisako

1999-01-01

214

Pressure anisotropy effects on nonlinear electrostatic excitations in magnetized electron-positron-ion plasmas  

NASA Astrophysics Data System (ADS)

The propagation of linear and nonlinear electrostatic waves is investigated in a magnetized anisotropic electron-positron-ion (e-p-i) plasma with superthermal electrons and positrons. A two-dimensional plasma geometry is assumed. The ions are assumed to be warm and anisotropic due to an external magnetic field. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low (CGL) theory. In the linear regime, two normal modes are predicted, whose characteristics are investigated parametrically, focusing on the effect of superthermality of electrons and positrons, ion pressure anisotropy, positron concentration and magnetic field strength. A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential (disturbance) via a reductive perturbation method. The parametric role of superthermality, positron content, ion pressure anisotropy and magnetic field strength on the characteristics of solitary wave structures is investigated. Following Allen and Rowlands [J. Plasma Phys. 53, 63 (1995)], we have shown that the pulse soliton solution of the ZK equation is unstable to oblique perturbations, and have analytically traced the dependence of the instability growth rate on superthermality and ion pressure anisotropy.

Adnan, Muhammad; Williams, Gina; Qamar, Anisa; Mahmood, Shahzad; Kourakis, Ioannis

2014-09-01

215

Protein crystals orientation in a magnetic field.  

PubMed

Nucleation and crystal growth of hen egg-white lysozyme, bovine pancreatic trypsin inhibitor and porcine pancreatic alpha-amylase were carried out in the presence of a magnetic field of 1.25 T produced by small permanent magnets. Crystals were oriented in the magnetic field, except when heterogeneous nucleation occurred. The orientation of protein crystals in the presence of a magnetic field can be attributed to the anisotropic diamagnetic susceptibility of proteins resulting from the large anisotropy of the alpha-helices due to the axial alignment of the peptide bonds. PMID:9761881

Astier, J P; Veesler, S; Boistelle, R

1998-07-01

216

Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy  

PubMed Central

To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory. PMID:25597496

Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.

2015-01-01

217

Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Kueff) over 6 Merg/cm3 is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Kueff of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory.

Ma, Q. L.; Zhang, X. M.; Miyazaki, T.; Mizukami, S.

2015-01-01

218

Role of magnetic anisotropy in spin-filter junctions  

SciTech Connect

We have fabricated oxide-based spin-filter junctions in which we demonstrate that magnetic anisotropy can be used to tune the transport behavior of spin-filter junctions. We have demonstrated spin-filtering behavior in La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/CoCr{sub 2}O{sub 4}/Fe{sub 3}O{sub 4} and La{sub 0.7}Sr{sub 0.3}MnO{sub 3}/MnCr{sub 2}O{sub 4}/Fe{sub 3}O{sub 4} junctions where the interface anisotropy plays a significant role in determining transport behavior. Detailed studies of chemical and magnetic structure at the interfaces indicate that abrupt changes in magnetic anisotropy across the nonisostructural interface is the cause of the significant suppression of junction magnetoresistance in junctions with MnCr{sub 2}O{sub 4} barrier layers.

Chopdekar, R.V.; Wong, F.; Nelson-Cheeseman, B.B.; Liberati, M.; Arenholz, E.; Suzuki, Y.

2011-01-10

219

Three-terminal magnetic tunneling junction device with perpendicular anisotropy CoFeB sensing layer  

SciTech Connect

We demonstrated read and write characteristics of a three terminal memory device with a perpendicular anisotropy-free layer of a strip of [Co/Ni] and a low-switching perpendicular-anisotropy CoFeB/MgO sensing layer. This new design of the cell results in a small cell area. The switching magnetic field of the sensing layer can be decreased by changing sputtering gas for the Ta-cap from Ar to Kr. An electron energy-loss spectroscopy analysis of the cross-section of the magnetic tunneling junction (MTJ) revealed that the boron content in CoFeB with a Kr-sputtered Ta-cap was smaller than that with an Ar-sputtered one. A change in resistance for the MTJ was observed that corresponded to the magnetic switching of the Co/Ni wire and its magnetoresistance ratio and critical current were 90% and 0.8?mA, respectively.

Honjo, H., E-mail: hr-honjou@aist.go.jp; Nebashi, R.; Tokutome, K.; Miura, S.; Sakimura, N.; Sugibayashi, T. [Green Platform Research Laboratories, NEC Corporation, Tsukuba (Japan); Fukami, S.; Kinoshita, K.; Murahata, M.; Kasai, N. [Center for Spintronics Integrated Systems, Tohoku University, Sendai (Japan); Ishihara, K. [Smart Energy Research Laboratories, NEC Corporation, Tsukuba (Japan); Ohno, H. [Center for Spintronics Integrated Systems, Tohoku University, Sendai (Japan); Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, Sendai (Japan); WPI Advanced Institute for Materials Research, Tohoku University, Sendai (Japan)

2014-05-07

220

Three-terminal magnetic tunneling junction device with perpendicular anisotropy CoFeB sensing layer  

NASA Astrophysics Data System (ADS)

We demonstrated read and write characteristics of a three terminal memory device with a perpendicular anisotropy-free layer of a strip of [Co/Ni] and a low-switching perpendicular-anisotropy CoFeB/MgO sensing layer. This new design of the cell results in a small cell area. The switching magnetic field of the sensing layer can be decreased by changing sputtering gas for the Ta-cap from Ar to Kr. An electron energy-loss spectroscopy analysis of the cross-section of the magnetic tunneling junction (MTJ) revealed that the boron content in CoFeB with a Kr-sputtered Ta-cap was smaller than that with an Ar-sputtered one. A change in resistance for the MTJ was observed that corresponded to the magnetic switching of the Co/Ni wire and its magnetoresistance ratio and critical current were 90% and 0.8 mA, respectively.

Honjo, H.; Fukami, S.; Ishihara, K.; Nebashi, R.; Kinoshita, K.; Tokutome, K.; Murahata, M.; Miura, S.; Sakimura, N.; Sugibayashi, T.; Kasai, N.; Ohno, H.

2014-05-01

221

Magnetic susceptibility anisotropy, strain, and progressive deformation in Permian sediments from the Maritime Alps (France)  

Microsoft Academic Search

The relationships among magnetic susceptibility anisotropy, finite strain, and progressive deformation have been studied in Permian red shales and slates of the Maritime Alps (southeastern France). These rocks contain deformed reduction spots which serve as finite strain indicators. The magnetic fabric of undeformed regions is modified during deformation to yield characteristic magnetic susceptibility anisotropy patterns and a magnetic equivalent of

Roy Kligfield; W. H. Owens; W. Lowrie

1981-01-01

222

Superparamagnetic relaxation and magnetic anisotropy energy distribution in CoFe{sub 2}O{sub 4} spinel ferrite nanocrystallites  

SciTech Connect

Superparamagnetism is a unique feature of magnetic nanoparticles. Spinel ferrite nanoparticles provide great opportunities for studying the mechanism of superparamagnetic properties. CoFe{sub 2}O{sub 4} nanocrystallites have been synthesized with a microemulsion method. The neutron diffraction studies and the temperature-dependent decay of magnetization show the superparamagnetic relaxation occurring in these nanoparticles. The neutron diffraction shows a high degree of inversion with the 78% tetrahedral sites occupied by Fe{sup 3+} cations. The nanoparticles with a 12 nm diameter have a blocking temperature around 320 K. The field-cooled and zero-field-cooled magnetization measurements display a divergence below the blocking temperature. The energy barrier distribution of magnetic anisotropy is derived from the temperature-dependent decay of magnetization. The magnetic anisotropy is clearly the origin of the divergence in the field-cooled and zero-field-cooled magnetization measurements. The energy barrier distribution function is used in a computer simulation of the zero-field-cooled magnetization, and the calculated magnetization has a great consistency with experimentally measured values. These studies on the magnetic anisotropy distribution elucidate the mechanism of superparamagnetic relaxation and facilitate the design and control of superparamagnetic properties in nanoparticles.

Rondinone, A.J.; Samia, A.C.S.; Zhang, Z.J. [Georgia Inst. of Tech., Atlanta, GA (United States). School of Chemistry and Biochemistry] [Georgia Inst. of Tech., Atlanta, GA (United States). School of Chemistry and Biochemistry

1999-08-19

223

Spatial modulation of in-plane magnetic anisotropy in epitaxial Co(111) films grown on macrostep-bunched Si(111)  

SciTech Connect

We compared magnetic properties of epitaxial Co(111) films grown on microstep- and macrostep-bunched vicinal Si(111) substrates. A surface of the microstep-bunched Si(111) substrate represents regular array of step-bunches with height of 1.7?nm divided from each other by flat microterraces with a width of 34?nm. A surface of the macrostep-bunched Si(111) substrate is constituted by macrostep bunches with a height of 75–85?nm divided by atomically flat macroterraces. The average sum width of a macrostep bunch and a macroterrace is 2.3??m. While in-plane magnetic anisotropy was spatially uniform in Co(111) films grown on the microstep-bunched Si(111), periodic macromodulation of the topography of the Si(111) substrate induced spatial modulation of in-plane magnetic anisotropy in Co(111) film grown on the macrostep-bunched Si(111) surface. The energy of uniaxial magnetic anisotropy in the areas of the Co(111) film deposited on the Si(111) macrosteps was higher more than by the order of magnitude than the energy of the magnetic anisotropy in the areas grown on macroterraces. Magnetization reversal in the areas with different energy of the magnetic anisotropy occurred in different magnetic fields. We showed the possibility of obtaining high density of domain walls in Co(111) film grown on the macrostep-bunched Si(111) by tuning the spatial step density of the Si(111) substrate.

Davydenko, A. V., E-mail: avdavydenko@gmail.com; Kozlov, A. G.; Chebotkevich, L. A. [Laboratory of Thin Film Technologies, Far Eastern Federal University, Vladivostok 690950 (Russian Federation)

2014-10-14

224

Crystalline and Magnetic Anisotropy of the 3d Transition-Metal Monoxides  

E-print Network

O · (distorted) rock-salt (rs) structure Andreas Schrön, Claudia Rödl, and Friedhelm Bechstedt #12;Crystalline Anisotropy Magnetic Anisotropy Introduction · MnO, FeO, CoO, and NiO · (distorted) rock-salt (rs) structure #12;Crystalline Anisotropy Magnetic Anisotropy Introduction · MnO, FeO, CoO, and NiO · (distorted

Rossak, Wilhelm R.

225

Mapping Magnetic Fields  

NSDL National Science Digital Library

This is an activity about bar magnets and their invisible magnetic fields. Learners will experiment with magnets and a compass to detect and draw magnetic fields. This is Activity 1 of a larger resource, entitled Exploring the Sun. The NASA spacecraft missions represented by this material include SOHO, TRACE, STEREO, Hinode, and SDO.

2012-08-03

226

Spin-flop transition on Gd5Ge4 observed by x-ray resonant magnetic scattering and first-principles calculations of magnetic anisotropy  

SciTech Connect

X-ray resonant magnetic scattering was employed to study a fully reversible spin-flop transition in orthorhombic Gd{sub 5}Ge{sub 4} and to elucidate details of the magnetic structure in the spin-flop phase. The orientation of the moments at the three Gd sites flop 90{sup o} from the c axis to the a axis when a magnetic field, H{sub sf} = 9 kOe, is applied along the c axis at T = 9 K. The magnetic space group changes from Pnm'a to Pn'm'a' for all three Gd sublattices. The magnetic anisotropy energy determined from experimental measurements is in good agreement with the calculations of the magnetic anisotropy based on the spin-orbit coupling of the conduction electrons and an estimation of the dipolar interactions anisotropy. No significant magnetostriction effects were observed at the spin-flop transition.

Tan, L.; Kreyssig, A.; Nandi, S.; Jia, S.; Lee, Y. B.; Lang, J. C.; Islam, Z.; Lograsso, T.; Schlagel, D.; Pecharsky, V.; Gschneidner, K.; Canfield, P.; Harmon, B.; McQueeney, R.; Goldman, A.

2008-02-21

227

Thermoelectric effects and magnetic anisotropy of Ga1-xMnxAs thin films  

NASA Astrophysics Data System (ADS)

The transverse voltages generated in a Ga1-xMnxAs ferromagnetic semiconductor in planar Hall effect and transverse spin Seebeck effect configurations are systematically analyzed. The observed field dependences consist of symmetric and asymmetric contributions. The former is attributed to the planar Nernst effect in the magnetic film in the presence of an in-plane temperature gradient, while the latter is caused by the anomalous Nernst effect due to spurious out-of-plane temperature gradients with a coefficient as high as 500 ?V/K. We also report on the experimental observation of the planar Hall effect measured at different temperatures. Using a Stoner-Wohlfarth model for data analysis, the anisotropy constants Ku and Kc of superimposed uniaxial and cubic anisotropies in the magnetic film are determined. The temperature dependence of the Ku/Kc ratio reveals a gradual substitution of the cubic anisotropy dominating at low temperatures with the uniaxial anisotropy as the temperature rises. This behavior is confirmed by the simultaneous domain observation using Kerr microscopy, demonstrating different field evolutions of the domain structure at different temperatures.

Soldatov, I. V.; Panarina, N.; Hess, C.; Schultz, L.; Schäfer, R.

2014-09-01

228

The Effect of Cr-Substitution on the Magnetic Anisotropy and Its Temperature Dependence in Cr-Substituted Cobalt Ferrite  

Microsoft Academic Search

The temperature dependence of the magnetic anisotropy of magnetoelastic chromium-substituted cobalt ferrites (CoCrxFe 2-xO4 with 0 les x les 0.8) was investigated over the temperature range 10-400 K. The first-order cubic anisotropy coefficient K1 was calculated by fitting the high-field regimes of the major hysteresis loops to the law of approach to saturation, which is based on the assumption that

Y. Melikhov; J. E. Snyder; C. C. H. Lo; P. N. Matlage; S. H. Song; K. W. Dennis; D. C. Jiles

2006-01-01

229

Thickness dependence of uniaxial anisotropy fields in GaMnAs films  

NASA Astrophysics Data System (ADS)

Our investigation of thin GaMnAs films with different thicknesses revealed that the magnetic properties of this material strongly depend on film thickness. For this study, a single GaMnAs film was selectively etched, and its properties were then investigated by planar Hall effect measurements. A particularly important conclusion from the results is the emergence of a uniaxial anisotropy field along the [100] crystalline direction, which increases rapidly with increasing film thickness. We argue that such thickness dependence of the [100] uniaxial anisotropy results from the crystal structure of the film, rather than from the effects of the interface between the GaMnAs and the substrate.

Bac, Seul-Ki; Lee, Hakjoon; Lee, Sangyeop; Choi, Seonghoon; Yoo, Taehee; Lee, Sanghoon; Liu, Xinyu; Furdyna, Jacek

2015-03-01

230

Magnetic anisotropy barrier for spin tunneling in Mn{sub 12}O{sub 12} molecules  

SciTech Connect

Electronic structure calculations on the nature of electronic states and the magnetic coupling in Mn-acetate [Mn{sub 12}O{sub 12}(RCOO){sub 16}(H{sub 2}O){sub 4}] molecules have been been carried out within the generalized gradient approximation to the density functional formalism. Our studies on this 100-atom molecule illustrate the role of the nonmagnetic carboxyl host in stabilizing the ferrimagnetic Mn{sub 12}O{sub 12} core and provide estimates of the local magnetic moment at the various sites. We provide a first density-functional-based prediction of the second-order magnetic anisotropy energy of this system. Results are in excellent agreement with experiment. To perform these calculations we introduce a simplified exact method for spin-orbit coupling and magnetic anisotropy energies in multicenter systems. This method is free of shape approximations and has other advantages as well. First, it is valid for periodic boundary conditions or finite systems and is independent of basis set choice. Second, the method does not require the calculation of electric field. Third, for applications to systems with a finite energy gap between occupied and unoccupied electronic states, a perturbative expansion allows for a simple determination of the magnetic anisotropy energy. {copyright} {ital 1999} {ital The American Physical Society}

Pederson, M.R. [Center for Computational Materials Science--6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)] [Center for Computational Materials Science--6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States); Khanna, S.N. [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000 (United States)] [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000 (United States)

1999-10-01

231

Microwave assisted magnetization reversal in cylindrical antidot arrays with in-plane and perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

Porous anodic alumina is a particularly attractive self-ordered system used as template to fabricate nanostructures. The anodic film contains a self-ordered hexagonal array of parallel pores with tunable pore size and interpore distance, and whose pore locations can be templated. Deposition of magnetic films onto porous alumina leads to the formation of porous magnetic films, whose properties differ significantly from those of unpatterned films. The study of antidot arrays has both technological and fundamental importance. Although porous alumina films are typically synthesized in a planar geometry, in this work we deposited NiFe and Ti/CoCrPt magnetic films with in-plane and out-of-plane anisotropy onto cylindrical-geometry porous anodic alumina substrates to achieve cylindrical antidot arrays. The effect of both, the magnitude of the AC current and the circular magnetic field on the magnetization reversal has been studied for in-plane and perpendicular anisotropies. The level of reduction in the switching field was found to be dependent on the power, the frequency of the microwave pulses and the circular applied magnetic field. Such a reduction is associate with the competition between pumping and damping processes.

Yumak, Mehmet; Ture, Kerim; Aktas, Gulen; Vega, Victor; Prida, Victor; Garcia, Carlos

2012-02-01

232

Modeling the properties of ferrogels in uniform magnetic fields  

Microsoft Academic Search

The properties of ferrogels in homogeneous magnetic fields are studied using a simple microscopic model and Monte Carlo simulations. The main phenomena of interest concern the anisotropy and enhancement of the elastic moduli that result from applying uniform magnetic fields before and after the magnetic grains are locked in to the polymer-gel matrix by cross-linking reactions. The positional organization of

Dean S. Wood; Philip J. Camp

2011-01-01

233

Irreversibility and anisotropy of the low-temperature magnetization in manganites. Spin-glass polyamorphism  

NASA Astrophysics Data System (ADS)

The temperature dependences of the magnetization in manganites of different composition and structural morphology were measured in two cooling regimes, field cooling (FC) and zero-field cooling (ZFC), for two different orientations of a magnetic field, parallel and perpendicular to the c-axis. The following general tendencies were found: (1) The difference between the magnetizations MFC and MZFC at T = 5 K increases with increasing magnetic field, reaching the maximum value in a magnetic field of about 2 kOe, and then drops in the range 2-5 kOe; (2) The field dependence of the "splitting" temperature T* below which the difference between the magnetizations MFC and MZFC appears can be reasonably well described by a power law with the exponent 2/3 as predicted by the theory of spin glasses. Both results are characteristic for single crystals, as well as for ceramics and films. On the other hand, the field dependence of the anisotropy of magnetic susceptibility is different for samples with different degrees of magnetic ordering (?/TC). These results are consistent with the detected in the present study universality of the line separating the low-temperature region of irreversibility in the H-T phase diagram of manganites. Deviations from the T*-H-line with the exponent 2/3 in strong magnetic fields, which are commonly associated with the appearance of the magnetization component transverse to the magnetic field, are typical for samples containing the antiferromagnetic phase. The interpretation takes into account the multi-phase nature of the systems, i.e., coexistence of spin glass with ferromagnetism and antiferromagnetism. The observed change in the anisotropy of magnetic susceptibility with increasing magnetic field and the behavior of magnetic and thermomagnetic irreversibility are regarded as a manifestation of the spin-reorientation phase transition in an antiferromagnetic environment. This in turn initiates the transformation of the spin-glass—from the Ising- to the Heisenberg-type—which leads to the change in the exponent in the T*-H diagram from 2/3 to 2. The observed phenomenon is universal—it was observed in manganites of different composition and structural morphology—and represents a particular type of polyamorphism, namely, spin-glass polyamorphism.

Sirenko, V. A.; Eremenko, V. V.

2014-02-01

234

Anisotropies of partial anhysteretic remanence and susceptibility in compacted black shales: Grainsize- and composition-dependent magnetic fabric  

Microsoft Academic Search

We have quantified the magnetic fabric of the high-compacted Heebner Shale (Pennsylvanian) of Kansas in terms of the anisotropies of partial anhysteretic remanent magnetization (pARM) and low-field susceptibility. Hysteresis loops exhibit almost purely paramagnetic behavior, and the ratio of the high-field linear susceptibility to low-field susceptibility is very close to one; the susceptibility aniostropy therefore reflects the fabric of the

Mike Jackson; Don Sprowl; Brooks Ellwood

1989-01-01

235

The Declining Magnetic Field  

NSDL National Science Digital Library

This is an activity about the declining strength of Earth's magnetic field. Learners will review a graph of magnetic field intensity and calculate the amount by which the field has changed its intensity in the last century, the rate of change of its intensity, and when the field should decrease to zero strength at the current rate of change. Learners will also use evidence from relevant sources to create a conjecture on the effects on Earth of a vanished magnetic field. Access to information sources about Earth's magnetic field strength is needed for this activity. This is Activity 7 in the Exploring Magnetism on Earth teachers guide.

236

Tri-axial magnetic anisotropies in RE{sub 2}Ba{sub 4}Cu{sub 7}O{sub 15?y} superconductors  

SciTech Connect

We report a novel quantification method of tri-axial magnetic anisotropy in orthorhombic substances containing rare earth (RE) ions using tri-axial magnetic alignment and tri-axial magnetic anisotropies depending on the type of RE in RE-based cuprate superconductors. From the changes in the axes for magnetization in magnetically aligned powders of (RE?{sub 1?x}RE?{sub x}){sub 2}Ba{sub 4}Cu{sub 7}O{sub y} [(RE?,RE?)247] containing RE ions with different single-ion magnetic anisotropies, the ratios of three-dimensional magnetic anisotropies between RE?247 and RE?247 could be determined. The results in (Y,Er)247, (Dy,Er)247, (Ho,Er)247, and (Y,Eu)247 systems suggest that magnetic anisotropies largely depended on the type of RE? (or RE?), even in the heavy RE ions with higher magnetic anisotropies. An appropriate choice of RE ions in RE-based cuprate superconductors enables the reduction of the required magnetic field for the production of their bulks and thick films based on the tri-axial magnetic alignment technique using modulated rotation magnetic fields.

Horii, Shigeru, E-mail: horii.shigeru.7e@kyoto-u.ac.jp; Doi, Toshiya [Graduate School of Energy Science, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501 (Japan); Okuhira, Shota; Yamaki, Momoko [Department of Environmental Systems Engineering, Kochi University of Technology, Tosa-Yamada, Kami-shi, Kochi 782-8502 (Japan); Kishio, Kohji; Shimoyama, Jun-ichi [Department of Applied Chemistry, University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan)

2014-03-21

237

Towards Detection of Magnetofossils in Sediments: Magnetostatic Interaction and Magnetic Anisotropy Effects  

NASA Astrophysics Data System (ADS)

Magnetotactic bacteria (MTB) synthesize intracellular single-domain (SD) magnetites or occasionally greigites magnetosomes, which are commonly assembled into chain(s) and server as navigation device in bacterial magnetotaxis. MTB are ubiquitous in aquatic environments ranging from freshwater to saline water. When MTB die, magnetosomes could be preserved in lake and marine sediments in forms of fossilized magnetosomes (also called magnetofossils). SD magnetofossils are stable carriers of natural remanent magnetization, and potential indicators for paleoenvironments. Our recent studies have revealed that MTB communities and their magnetosome formation are sensitive to oxygen, salinity, iron source and other environmental factors. Therefore, identification of magnetofossils is of great interests in the study of paleomagnetism, environmental magnetism, sedimentary magnetism and paleoenvironmental or paleoclimate reconstruction. Magnetic methods are widely used as fast, economic and effective approaches in detection of magnetofossils. Thee most distinctive features of magnetofossils are their uniformed nano-size range and unique chain structure. Consequently, anhysteretic remanent magnetization, first-order reversal curve diagram (FORC), low-temperature magnetic measurements (e.g. delta ratio, so-called the Moskowitz test) and ferromagnetic resonance (FMR) are often used for magnetic detection of magnetofossils. However, ambiguities remain because these magnetic properties can be seriously affected by magnetostatic interaction and magnetic anisotropy, e.g., as the chain collapse during deposition and post-depositional diagenesis. In this paper we analyzed magnetic properties of three sets of synthesized samples containing extracted magnetosomes of the cultured Magnetospirillum magneticum strain AMB-1, to determine how the chain integrity dependent magnetostatic interaction and anisotropy influence the magnetic parameters, which in turn can be used as indication of the state of magnetofossils. Results show that intact MTB and well-dispersed magnetosome chains are characterized by strong magnetic anisotropy and weak magnetostatic interactions, but progressive chain breakup and particle clumping significantly increases the degree of the magnetostatic interaction and a change of magnetic signature towards the typical properties of interacting, single-domain particles. Specifically, the progressive chain breakup and particle clumping systematically decrease of the ratio of anhysteretic remanent magnetization to the saturation isothermal remanent magnetization (ARM/SIRM or ?ARM/SIRM), the crossing point of the Wohlfarth-Cisowski test, and the delta ratio (?FC/?ZFC) between losses of field and zero-field cooled remanent magnetization across the Verwey transition. We hence propose a delta-plot (?FC/?ZFC vs. ?ZFC) as a new approach to diagnose magnetosome chains of magnetosomes, and detect magnetofossils in sediments and rocks.

Pan, Y.; Li, J.

2012-12-01

238

The Magnetic Field  

NSDL National Science Digital Library

This demonstration of the magnetic field lines of Earth uses a bar magnet, iron filings, and a compass. The site explains how to measure the magnetic field of the Earth by measuring the direction a compass points from various points on the surface. There is also an explanation of why the north magnetic pole on Earth is actually, by definition, the south pole of a magnet.

Jeffrey Barker

239

Drawing Magnetic Fields  

NSDL National Science Digital Library

Students use a compass and a permanent magnet to trace the magnetic field lines produced by the magnet. By positioning the compass in enough spots around the magnet, the overall magnet field will be evident from the collection of arrows representing the direction of the compass needle. In activities 3 and 4 of this unit, students will use this information to design a way to solve the grand challenge of separating metal for a recycling company.

2014-09-18

240

Electricity and Magnetic Fields  

NSDL National Science Digital Library

The grand challenge for this legacy cycle unit is for students to design a way to help a recycler separate aluminum from steel scrap metal. In previous lessons, they have looked at how magnetism might be utilized. In this lesson, students think about how they might use magnets and how they might confront the problem of turning the magnetic field off. Through the accompanying activity students explore the nature of an electrically induced magnetic field and its applicability to the needed magnet.

VU Bioengineering RET Program,

241

Mean magnetic field generation in sheared rotators  

E-print Network

A generalized mean magnetic field induction equation for differential rotators is derived, including a compressibility, and the anisotropy induced on the turbulent quantities from the mean magnetic field itself and a mean velocity shear. Derivations of the mean field equations often do not emphasize that there must be anisotropy and inhomogeneity in the turbulence for mean field growth. The anisotropy from shear is the source of a term involving the product of the mean velocity gradient and the cross-helicity correlation of the isotropic parts of the fluctuating velocity and magnetic field, $\\lb{\\bfv}\\cdot{\\bfb}\\rb^{(0)}$. The full mean field equations are derived to linear order in mean fields, but it is also shown that the cross-helicity term survives to all orders in the velocity shear. This cross-helicity term can obviate the need for a pre-existing seed mean magnetic field for mean field growth: though a fluctuating seed field is necessary for a non-vanishing cross-helicity, the term can produce linear (in time) mean field growth of the toroidal field from zero mean field. After one vertical diffusion time, the cross-helicity term becomes sub-dominant and dynamo exponential amplification/sustenance of the mean field can subsequently ensue. The cross-helicity term should produce odd symmetry in the mean magnetic field, in contrast to the usually favored even modes of the dynamo amplification in sheared discs. This may be important for the observed mean field geometries of spiral galaxies. The strength of the mean seed field provided by the cross- helicity depends linearly on the magnitude of the cross-helicity.

Eric G. Blackman

1999-08-31

242

Magnetic ordering and slow dynamics in a Ho-based bulk metallic glass with moderate random magnetic anisotropy  

SciTech Connect

Results of magnetic measurements are presented for a Ho-based bulk metallic glass, which shows similarities and differences with conventional spin glasses (SGs), and significant differences with weak random magnetic anisotropy (RMA) systems. Both ac and dc magnetic measurements indicate a single transition from paramagnetic to speromagnetic or spin glasslike state around 5.6 K. The moderate RMA prevents the formation of long- (or quasilong)-range magnetic order and slows down the spin dynamics in the critical region. Further its isothermal remnant magnetization exhibits a small maximum, instead of a gradual increase with field in SGs. The roles of RMA in the magnetic structure and dynamics of disordered and frustrated systems are discussed by comparisons between the weak RMA system, the moderate or strong RMA system, and conventional SG.

Luo, Q.; Schwarz, B.; Mattern, N. [IFW Dresden, Institute for Complex Materials, Helmholtzstr. 20, D-01069 Dresden (Germany); Eckert, J. [IFW Dresden, Institute for Complex Materials, Helmholtzstr. 20, D-01069 Dresden (Germany); TU Dresden, Institute of Materials Science, D-01062 Dresden (Germany)

2011-06-01

243

Tailoring of magnetic anisotropy in amorphous and nanocrystalline soft magnetic alloys using swift heavy ions  

Microsoft Academic Search

Amorphous films of Fe0.85N0.15 and Fe73.9Cu0.9Nb3.1Si 13.2B8.9 have been prepared by using ion-beam sputtering. Magneto-optic Kerr effect (MOKE) and Mössbauer measurement shows that the FeN film has a perpendicular magnetic anisotropy while the finemet film has a uniaxial in-plane anisotropy. The anisotropy in as-deposited state may be attributed to some quenched-in stresses present in the film during deposition. Films have

Ranu Dubey; Ajay Gupta; Pooja Sharma; Nora Darowski; G. Schumacher

2007-01-01

244

Influence of magnetocrystalline anisotropy on the magnetization dynamics of magnetic microstructures.  

PubMed

The study of magnetodynamics using stroboscopic time-resolved x-ray photoemission electron microscopy (TR-XPEEM) involves an intrinsic timescale provided by the pulse structure of the synchrotron radiation. In the usual multi-bunch operation mode, the time span between two subsequent light pulses is too short to allow a relaxation of the system into the ground state before the next pump-probe cycle starts. Using a deflection gating mechanism described in this paper we are able to pick the photoemission signal resulting from selected light pulses. Thus, PEEM measurements can be carried out in a flexible timing scheme with longer delays between two light pulses. Using this technique, the magnetodynamics of both Permalloy and iron structures have been investigated. The differences in the dynamic response on a short magnetic field pulse are discussed with respect to the magnetocrystalline anisotropy. PMID:21828569

Kaiser, A; Wiemann, C; Cramm, S; Schneider, C M

2009-08-01

245

Magnetic fields at Neptune  

Microsoft Academic Search

The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magnetic field experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magnetic field of Neptune and an associated magnetosphere and magnetic tail. A maximum magnetic field of nearly 10,000 nanoteslas (1 nanotesla = 10⁻⁵ gauss) was observed near closest approach, at a

N. F. Ness; M. H. Acuna; L. F. Burlaga; J. E. P. Connerney; R. P. Lepping; F. M. Neubauer

1989-01-01

246

Evidence for dynamically important magnetic fields in molecular clouds  

Microsoft Academic Search

Recent observational evidence that magnetic fields are dynamically important in molecular clouds, compared to self-gravity and turbulence, is reviewed and illustrated with data from the NGC 2024 region. One piece of evidence, turbulence anisotropy, was found in the diffuse envelope of a cloud (Av≈ 1; Heyer et al. 2008); our data further suggest turbulence anisotropy in the cloud (Av >

Hua-Bai Li; Raymond Blundell; Abigail Hedden; Jonathan Kawamura; Scott Paine; Edward Tong

2011-01-01

247

Large perpendicular magnetic anisotropy at Fe/MgO interface  

NASA Astrophysics Data System (ADS)

A large perpendicular magnetic anisotropy (PMA) of 1.4 MJ/m3 was observed from ultrathin Fe/MgO(001) bilayers grown on Cr-buffered MgO(001). The PMA strongly depends on the surface state of Fe prior to the MgO deposition. A large PMA energy density of 1.4 MJ/m3 was achieved for a 0.7 nm thick Fe layer having adsorbate-induced surface reconstruction, which is likely to originate from oxygen atoms floating up from the Cr buffer layer. This large magnitude of PMA satisfies the criterion that is required for thermal stability of magnetization in a few tens nanometer-sized magnetic memory elements.

Koo, J. W.; Mitani, S.; Sasaki, T. T.; Sukegawa, H.; Wen, Z. C.; Ohkubo, T.; Niizeki, T.; Inomata, K.; Hono, K.

2013-11-01

248

Elastic Constants and Magnetic Anisotropy of Co\\/Pt Superlattice: Resonance-Ultrasound-Spectroscopy Method  

Microsoft Academic Search

The Co\\/Pt superlattice shows perpendicular magnetic anisotropy, which makes the magnetization direction of the Co layer perpendicular to the film surface when the Co layer is less than about 20 Å thick. One possible cause of perpendicular magnetic anisotropy is large elastic strain at the interfaces between the Co and Pt layers. The elastic strain also changes the macroscopic elastic

Nobutomo Nakamura; Hirotsugu Ogi; Teruo Ono; Masahiko Hirao; Masayoshi Nishiyama

2005-01-01

249

Magnetic properties of nanocrystalline FeCuNbSiB with huge creep induced anisotropy  

NASA Astrophysics Data System (ADS)

Ribbons of originally amorphous Fe73.5Cu1Nb3Si15.5B7 have been annealed under tensile stress for about 4 seconds at temperatures between 450°C and 750°C. Under such short time conditions the optimum nanocrystalline state is achieved for annealing temperatures between 600°C and 720°C. This is about 100°C higher than in more conventional heat treatments with annealing times in the order of an hour. The stress annealed ribbons reveal an almost perfectly linear hysteresis loop and a transverse domain pattern with zigzag domain walls characteristic for a magnetic easy plane perpendicular to the stress axis. The induced magnetic anisotropy increases proportional to the annealing stress and is comparable to that obtained after more prolonged annealing. We succeeded to induce anisotropy constants as high as Ku approx 12 kJ/m3 which even exceed the local magneto-crystalline anisotropy (K1 approx 8 kJ/m3) of the crystalline Fe-Si phase. Nonetheless, the coercivity is still as small as Hc approx 8 A/m. This is to be compared to Hc approx 0.5 A/m for field annealed samples where Ku (approx 20 J/m3) is smaller by more than two orders of magnitude. The behaviour of Hc can be understood within the framework of the random anisotropy model.

Herzer, Giselher; Budinsky, Viktoria; Polak, Christian

2011-01-01

250

The Anisotropy of Magnetic Susceptibility of Some Igneous and Metamorphic Rocks  

Microsoft Academic Search

The anisotropy of magnetic susceptibility of some basic igneous and metamor- phic rocks has been found to be due to the preferred orientation of the long axes of grains of magnetite. The degree of anisotropy is in a few samples as great as 40 per cent but usually is less than 10 per cent. The variation in anisotropy is believed

M. Aftab Khan

1962-01-01

251

Magnetic Fields Analogous to electric field, a magnet  

E-print Network

Magnetic Fields Analogous to electric field, a magnet produces a magnetic field, B Set up a B field two ways: Moving electrically charged particles Current in a wire Intrinsic magnetic field Basic) Opposite magnetic poles attract like magnetic poles repel #12;Like the electric field lines

Bertulani, Carlos A. - Department of Physics and Astronomy, Texas A&M University

252

Magnetic field sensors and visualizers using magnetic photonic crystals  

NASA Astrophysics Data System (ADS)

Magneto-optical imaging is widely used to observe the domain patterns in magnetic materials, visualize defects in ferromagnetic objects, and measure the spatial distribution of stray magnetic fields. Optimized 1D magneto-photonic crystals enable a significant increase in the sensitivity of magneto-optical sensors. The properties of such devices based on the optimized reflection (doubled Faraday rotation) mode and the use of 1D magnetic photonic crystals as sensors are discussed. Experimental results of the fabrication and characterization of ferrite-garnet layers possessing uniaxial magnetic anisotropy are shown, and an optimized film structure suitable for magneto-optical imaging is proposed.

Vasiliev, Mikhail; Alameh, Kamal E.; Kotov, Viatcheslav

2008-04-01

253

Detection of electron energy distribution function anisotropy in a magnetized electron cyclotron resonance plasma by using a directional Langmuir probe  

SciTech Connect

Anisotropy in the electron energy distribution function (EEDF) in an electron cyclotron resonance plasma with magnetized electrons and weakly magnetized ions is experimentally investigated using a directional Langmuir probe. Under an assumption of independent EEDFs in the directions parallel and perpendicular to the magnetic field, the directional variation of the EEDF is evaluated. In the measured EEDFs, a significantly large population density of electrons with energies larger than 30?eV is found in one of the cross-field directions depending on the magnetic field direction. With the aid of an electron trajectory calculation, it is suggested that the observed anisotropic electrons originate from the EEDF anisotropy and the cross-field electron drift.

Shikama, T., E-mail: shikama@me.kyoto-u.ac.jp; Hasuo, M. [Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto University, Kyoto 615-8540 (Japan); Kitaoka, H. [Faculty of Engineering, Undergraduate School of Engineering Science, Kyoto University, Kyoto 615-8540 (Japan)

2014-07-15

254

Anisotropy effects on the spin wave gap of two dimensional magnets at zero temperature  

NASA Astrophysics Data System (ADS)

The principal purpose of this paper is to report an estimate of spin-wave gap of two-dimensional magnets taking into account both the anisotropy and the Zeeman energy sufficiently large to dominate over the dipolar interaction. The spin-wave gap is calculated for a magnetic field which is perpendicular to the plane at zero temperature. The results are discussed in connection with experimental data reported for epitaxial Fe-deficient yttrium garnet (YIG) films pulsed laser deposited onto the different faces of Gd3Ga5O12 single crystal.

Kaplan, B.; Kaplan, R.

2014-04-01

255

A study of magnetic anisotropy energy in CuMn spin glass  

E-print Network

. Adair, III The magnetic anisotropy energy in a CuMn, 0. 5 at%, spin glass has been investigated through torque measurements. The sample is cooled below the spin glass transition temperature T in the presence of a strong external magnetic field Hc... for stretched exponential fit . . III. I'; for summation f1t at T= 2. 4 K . . 36 IV. rt for summation fit at T= 2. 4 K. LIST OF FIGURES FIGURE PAGE 1. Spin Glass Freezing Temperature vs. Concentration for CuMn. . . . . . 2 2. Two-dimensional spin glass...

Allen, Christine Adele

1986-01-01

256

Seedlayer interface enhanced magnetic anisotropy in CoPt (0 0 0 2)-textured films  

Microsoft Academic Search

The effects of interface roughness of Ta seedlayer on the structural and magnetic properties of Co72Pt28(20nm)\\/Ru(30nm)\\/Pt(2nm)\\/Ta(5nm)\\/glass were investigated. Uniaxial perpendicular magnetic anisotropy (8.6×106ergs\\/cc), coercivity (5.5kOe) and nucleation field (?2.8kOe) in the Co72Pt28 thin film sputter-deposited on relatively smooth surface of Ta seedlayer were achieved. The results showed that relatively smoother interface roughness of Ta seedlayer improved the CoPt\\/Ru (0002) texture

K. K. M. Pandey; J. S. Chen; G. M. Chow; B. C. Lim

2009-01-01

257

Seedlayer interface enhanced magnetic anisotropy in CoPt (0 0 0 2)-textured films  

Microsoft Academic Search

The effects of interface roughness of Ta seedlayer on the structural and magnetic properties of Co72Pt28(20 nm)\\/Ru(30 nm)\\/Pt(2 nm)\\/Ta(5 nm)\\/glass were investigated. Uniaxial perpendicular magnetic anisotropy (8.6×106 ergs\\/cc), coercivity (5.5 kOe) and nucleation field (-2.8 kOe) in the Co72Pt28 thin film sputter-deposited on relatively smooth surface of Ta seedlayer were achieved. The results showed that relatively smoother interface roughness of

K. K. M. Pandey; J. S. Chen; G. M. Chow; B. C. Lim

2009-01-01

258

Magnetic Field Problem  

NSDL National Science Digital Library

The above animations represent two typical bar magnets each with a North and South pole. The arrows represent the direction of the magnetic field. The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black. You may drag either magnet and double-click anywhere inside the animation to add a magnetic field line, and mouse-down to read the magnitude of the magnetic field at that point.

Wolfgang Christian

259

Impurity-induced enhancement of perpendicular magnetic anisotropy in Fe/MgO tunnel junctions  

NASA Astrophysics Data System (ADS)

Using first-principles calculations, we investigated the impact of chromium (Cr) and vanadium (V) impurities on the magnetic anisotropy and spin polarization in Fe/MgO magnetic tunnel junctions. It is demonstrated, using layer resolved anisotropy calculation technique, that while the impurity near the interface has a drastic effect in decreasing the perpendicular magnetic anisotropy (PMA), its position within the bulk allows maintaining high interfacial PMA while reducing the bulk magnetization and correlatively the easy-plane demagnetizing energy. As a result, the effective magnetic anisotropy tends to increase as a function of the Cr or V concentration resulting in an increase in the critical magnetic thickness at which the crossover from out-of-plane to in-plane anisotropy takes place. At the same time, the interfacial spin polarization is not affected by the magnetic layer bulk doping by Cr or V impurities and even enhanced in most situations thus favoring an increase of tunnel magnetoresistance (TMR) amplitude.

Hallal, A.; Dieny, B.; Chshiev, M.

2014-08-01

260

Magnetic structure and anisotropy of [Co/Pd ] 5/NiFe multilayers  

NASA Astrophysics Data System (ADS)

The magnetization behavior, magnetic anisotropy, and domain configurations of Co/Pd multilayers with perpendicular magnetic anisotropy capped with permalloy is investigated using magnetometry, magnetic force microscopy, and ferromagnetic resonance. The thickness of the Ni80Fe20 layer in [Co/Pd ] 5/NiFe (t ) was varied from t =0 to 80 nm in order to study the interplay between the anisotropy and magnetization directions of Co/Pd and NiFe. By varying the thickness of the NiFe layer, the net anisotropy changes sign, but domains with plane-normal magnetization are present even for the thickest NiFe. Ferromagnetic resonance measurements show a decrease in damping with increasing NiFe thickness. The results demonstrate how the magnetic behavior of mixed-anisotropy thin films can be controlled.

Tryputen, Larysa; Guo, Feng; Liu, Frank; Nguyen, T. N. Anh; Mohseni, Majid S.; Chung, Sunjae; Fang, Yeyu; Åkerman, Johan; McMichael, R. D.; Ross, Caroline A.

2015-01-01

261

Magnetic anisotropy and organization of nanoparticles in heads and antennae of neotropical leaf-cutter ants, Atta colombica  

NASA Astrophysics Data System (ADS)

Oriented magnetic nanoparticles have been suggested as a good candidate for a magnetic sensor in ants. Behavioural evidence for a magnetic compass in neotropical leaf-cutter ants, Atta colombica (Formicidae: Attini), motivated a study of the arrangement of magnetic particles in the ants’ four major body parts by measuring the angular dependence of the ferromagnetic resonance spectra at room temperature. Spectra of the thoraces and those of the abdomens showed no significant angular dependence, while those of the antennae and those of the heads exhibited a periodic dependence relative to the magnetic field. Fitting of the angular dependence of the resonant field resulted in an unexpected magnetic anisotropy with uniaxial symmetry. High values of the first order anisotropy constant were observed for the magnetic material in antennae (?2.9? × ?105?erg?cm?3) and heads (?1? × ?106?erg?cm?3) as compared to body parts of other social insects. In addition, the magnitude of the anisotropy in the heads was comparable to that observed in magnetite nanoparticles of 4–5?nm diameter. For the antennae, the mean angle of the particles’ easy magnetization axis (EA) was estimated to be 41° relative to the straightened antenna’s long axis. For the heads, EA was approximately 60° relative to the head’s axis running from midway between the spines to the clypeus. These physical characteristics indicate organized magnetic nanoparticles with a potential for directional sensitivity, which is an important feature of magnetic compasses.

Alves, Odivaldo C.; Srygley, Robert B.; Riveros, Andre J.; Barbosa, Marcia A.; Esquivel, Darci M. S.; Wajnberg, Eliane

2014-10-01

262

Emergence of noncollinear anisotropies from interfacial magnetic frustration in exchange-bias systems.  

SciTech Connect

Exchange bias, referred to the interaction between a ferromagnet (FM) and an antiferromagnet (AFM), is a fundamental interfacial magnetic phenomenon, which is key to current and future applications. The effect was discovered half a century ago, and it is well established that the spin structures at the FM/AFM interface play an essential role. However, currently, ad hoc phenomenological anisotropies are often postulated without microscopic justification or sufficient experimental evidence to address magnetization-reversal behavior in exchange-bias systems. We advance toward a detailed microscopic understanding of the magnetic anisotropies in exchange-bias FM/AFM systems by showing that symmetry-breaking anisotropies leave a distinct fingerprint in the asymmetry of the magnetization reversal and we demonstrate how these emerging anisotropies are correlated with the intrinsic anisotropy. Angular and vectorial resolved Kerr hysteresis loops from FM/AFM bilayers with varying degree of ferromagnetic anisotropy reveal a noncollinear anisotropy, which becomes important for ferromagnets with vanishing intrinsic anisotropy. Numerical simulations show that this anisotropy naturally arises from the inevitable spin frustration at an atomically rough FM/AFM interface. As a consequence, we show in detail how the differences observed for different materials during magnetization reversal can be understood in general terms as originating from the interplay between interfacial frustration and intrinsic anisotropies. This understanding will certainly open additional avenues to tailor future advanced magnetic materials.

Jimenez, E.; Camarero, J.; Sort, J.; Nogues, J.; Mikuszeit, N.; Garcia-Martin, J. M.; Hoffmann, A.; Dieny, B.; Miranda, R.; Univ. Autonoma de Madrid; Univ. Autonoma de Barcelona; Inst. de Microelectronica de Madrid; SPINTEC

2009-01-01

263

Alignment of magnetic uniaxial particles in a magnetic field: Simulation  

NASA Astrophysics Data System (ADS)

The numerical investigations of the process of alignment of magnetically uniaxial Nd-Fe-B powders in an applied magnetic field were carried out using the discrete element method (DEM). It is shown that magnetic alignment of ensemble of spherical particles provides extremely high degree of alignment, which is achieved in low magnetic fields. A model of formation of anisotropic particles as a combination of spherical particles is suggested. The influence of the shape anisotropy and friction coefficient on the alignment degree was analyzed. The increase in the friction coefficient leads to a decrease in the alignment degree; the simulation results are in qualitative agreement with experimental dependences. It is shown that in magnetic fields higher than 5 T, the calculated field dependences of the alignment degree quantitatively render the experimental data. The increase of about 6% in the alignment degree in the experiments with addition of internal lubricant can be explained by the decrease of 14% in friction coefficient.

Golovnia, O. A.; Popov, A. G.; Sobolev, A. N.; Hadjipanayis, G. C.

2014-09-01

264

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

This is a lesson about the magnetic field of a bar magnet. The lesson begins with an introductory discussion with learners about magnetism to draw out any misconceptions that may be in their minds. Then, learners freely experiment with bar magnets and various materials, such as paper clips, rulers, copper or aluminum wire, and pencils, to discover that magnets attract metals containing iron, nickel, and/or cobalt but not most other materials. Next, learners experiment with using a magnetic compass to discover how it is affected by the magnet and then draw the magnetic field lines of the magnet by putting dots at the location of the compass arrow. This is the first lesson in the first session of the Exploring Magnetism teacher guide.

2012-08-03

265

Determination of the Fe magnetic anisotropies and the CoO frozen spins in epitaxial CoO/Fe/Ag(001)  

SciTech Connect

CoO/Fe/Ag(001) films were grown epitaxially and studied by X-ray Magnetic Circular Dichroism (XMCD) and X-ray Magnetic Linear Dichroism (XMLD). After field cooling along the Fe[100] axis to 80 K, exchange bias, uniaxial anisotropy, and 4-fold anisotropy of the films were determined by hysteresis loop and XMCD measurements by rotating the Fe magnetization within the film plane. The CoO frozen spins were determined by XMLD measurement as a function of CoO thickness.We find that among the exchange bias, uniaxial anisotropy, and 4-fold anisotropy, only the uniaxial magnetic anisotropy follows thickness dependence of the CoO frozen spins.

Meng, J. Li, Y.; Park, J. S.; Jenkins, C. A.; Arenholz, E.; Scholl, A.; Tan, A.; Son, H.; Zhao, H. W.; Hwang, Chanyong; Qiu, Z. Q.

2011-04-28

266

Mapping Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetism. Using bar magnets, classroom materials, and a compass, learners will explore how bar magnets interact with one another and with other materials, use a compass to find the direction north, and use various materials to make magnetic field lines visible around a bar magnet. This is an activity in a larger poster resource, entitled The Sun Like It's Never Been Seen Before: In 3D.

267

The Magnetic Field  

NSDL National Science Digital Library

This webpage is part of the University Corporation for Atmospheric Research (UCAR) Windows to the Universe program. It describes the nature and configuration of magnetic fields, which are the result of moving electric charges, including how they cause magnetic objects to orient themselves along the direction of the magnetic force points, which are illustrated as lines. Magnetic field lines by convention point outwards at the north magnetic pole and inward at the south magnetic pole. The site features text, scientific illustrations and an animation. Text and vocabulary are selectable for the beginning, intermediate, or advanced reader.

Windows to the Universe

1997-12-03

268

Magnetic ordering and anisotropy in heavy atom radicals.  

PubMed

Recent developments in stable radical chemistry have afforded "heavy atom" radicals, neutral open-shell (S = 1/2) molecular species containing heavy p-block elements (S, Se), which display solid-state magnetic properties once considered exclusive to conventional metal-based magnets. These highly spin-delocalized radicals do not associate in the solid state and yet display extensive networks of close intermolecular interactions. Spin density on the heavy atoms allows for increased isotropic and spin-orbit mediated anisotropic exchange effects. Structural variations induced by chemical modification and physical pressure, coupled with ab-initio methods to estimate exchange energies, have facilitated the development of predictive structure/property relationships. These results, coupled with detailed theoretical analyses and magnetic resonance spectroscopic measurements, have provided insight into the magnetic structure of ferromagnetic and spin-canted antiferromagnetic ordered materials as well as an understanding of the importance of spin-orbit coupling contributions to magnetic hysteresis and anisotropy. Isotropic and anisotropic ferromagnetic exchange can also be enhanced indirectly by the incorporation of heavy atoms into nonspin-bearing sites, where they can contribute to multi-orbital spin-orbit coupling. PMID:25767934

Winter, Stephen M; Hill, Stephen; Oakley, Richard T

2015-03-25

269

Competing anisotropies and complex magnetism in SrRuO3/SrMnO3 superlattices  

NASA Astrophysics Data System (ADS)

Using element-specific x-ray resonance techniques, we have investigated the interfacial magnetic coupling in SrRuO3/SrMnO3 superlattices. A strong out-of-plane SRO anisotropy coupled with AFM Ru-Mn interactions result in a canted Mn structure with a significant induced net Mn moment that reduces to zero under a strong magnetic field. At T > TC SRO, the SRO anisotropy is removed and the planar Mn AFM structure cants to produce a net Mn moment along the field direction. Below TC, the net development of in-plane Mn moment is suppressed by partially frustrated exchange interactions at the AFM-SMO/FM-SRO interfaces and competing Mn-Ru anisotropies. Hysteretic magnetization curves show a two-step magnetization reversal and enhanced coercivity. X-ray measurements confirm that the low-field magnetization reversal coincides with ``free'' Ru moments inside the SRO layers and that the high-field magnetization reversal involves the interfacial magnetization in the SMO layers and provide strong evidence for the presence of pinned SRO moments at the SRO/SMO interface.

Chmaissem, Omar; Choi, Y.; Tseng, Y. C.; Haskel, D.; Brown, D. E.; Kolesnik, S.; Danaher, D.

2009-03-01

270

Magnetic domain structure and transverse induced magnetic anisotropy in CoFeCuNbSiB alloys  

NASA Astrophysics Data System (ADS)

The magnetic domain structure is a specific property of ferromagnetic materials. The main magnetic properties and core losses depend on its configuration and dimensions. The aim of this work was to determine a relationship between the domain structure, observed by means of magneto-optic Kerr effect on the surface of the Fe14.7Co58.8Cu1Nb3Si13.5B9 (FeCo58) and Fe13.8Co65Cu0.6Nb2.6Si9B9 (FeCo65) toroidal cores, and the induced transverse magnetic anisotropy Ku and magnetic characteristics B = f(H). The transverse magnetic anisotropy has been induced in the FeCo58 and FeCo65 amorphous cores by annealing at the temperature of 420-500 °C under an external magnetic field of 500 kA/m. It was found that the FeCo58 cores, characterized by three times smaller Ku compared to the FeCo65 cores, had different domain structures than those of the FeCo65 cores. The domain structure of the FeCo65 cores is characterized by almost parallel domains of an average width d varying from 28 to 50 ?m after heat treatment at the temperatures ranging from 420 to 500 °C.

Kolano-Burian, A.

2013-10-01

271

Magnetic anisotropies of ultrathin Co films on Cu(001) and Cu (1113) substrates (abstract)  

NASA Astrophysics Data System (ADS)

The stabilization of long-range ferromagnetic order in two-dimensional systems at finite temperatures is presently discussed very controversially. Among the mechanisms dipolar interactions or magnetic anisotropies are currently most considered. For experimental clarification all relevant magnetic anisotropy constants of ultrathin Co layers on Cu(001) as well as on Cu(1 1 13) substrates using Brillouin light scattering.1,2 Due to the fourfold symmetry of Co(001) films the relevant anisotropy contributions are a fourfold in-plane anisotropy Kin-plane(4)=Kp(4)+2kp(4)/d and a perpendicular anisotropy Kperp=Ks+2ks/d with Kp(4) and Ks (kp(4) and ks) the in-plane and out-of-plane volume (surface) anisotropy constants, respectively, and d the film thickness. For Co films prepared on Cu(1 1 13) substrates an additional uniaxial in-plane anisotropy (Kin-plane(2)) is generated by the rotation of the (001) surface about the [11¯0]-in-plane axis by 6.2°. The symmetry axis of this anisotropy lies along the [11¯0] axis. Co films with film thicknesses between 1.5 and 14 monolayers (ML) were prepared in an ultrahigh vacuum (UHV) system and characterized with low-energy electron diffraction (LEED) and Auger spectroscopy as well as by in situ magneto-optic Kerr effect, as described elsewhere.1,2 The Brillouin light scattering experiments were performed in situ in the UHV system for Co/Cu (001) with the external field aligned parallel to the [100] hard axis The light scattering measurements on Co/Cu (1 1 13) with a Cu overlayer were performed ex situ with the external field direction aligned along different in-plane directions. From a fit to the measured spin wave frequencies as a function of the applied field and the Co film thickness the anisotropy constants are obtained. The Co/Cu (001) system is discussed first. Ferromagnetic order is observed for film thickness d larger than dc=(1.6±0.3) ML for uncovered Co films and dc=(1.9±0.3) ML for Co films covered by a 2-ML thick Cu overlayer. From the fits to data for different film thicknesses it was found that Kp(4)=(-2.32±0.15)×106 erg/cm3 and kp(4)=(0.034±0.004)erg/cm2 for the uncovered films, and Kp(4)=(-2.17±0.15)×106 erg/cm3 and kp(4)=(0.031±0.003)erg/cm2 for the Co layers covered with 2-ML Cu.1 Due to their opposite sign, the contributions of Kp(4) and kp(4) to Kin-plane(4) cancel each other at dc*=(1.55±0.3)ML for the uncovered films and at dc*=(1.7±0.3)ML for the films covered with 2-ML Cu. The out-of-plane anisotropy constant ks was found as ks=(-1.06±0.17)erg/cm2 for the Co/vacuum interface and ks=(0.15±0.04)erg/cm2 for the Co/Cu interface. The negative sign indicates that the surface normal is a magnetic hard axis for this anisotropy. No volume out-of-plane contribution, Ks, was found. From the observed agreement between the critical thickness for ferromagnetic order dc, with the thickness dc* at which the contributions to the in-plane anisotropy cancel, it can be concluded that the symmetry breaking interaction for stabilizing ferromagnetic order in Co(001) films at room temperature is indeed given by the magnetic in-plane anisotropy contribution. For Co/Cu(1 1 13) an additional large uniaxial in-plane anisotropy contribution of Kin-plane(2)=(-4.4±0.4)×105 erg/cm3 was found.2 The negative sign indicates that the easy axis is parallel to the step edges. The fourfold in-plane anisotropy constant, Kin-plane(4), is reduced by a factor of 2 to 4 compared to the (001)-oriented films. For the Co/Cu(1 1 13) system the uniaxial in-plane anisotropy can be described as magnetoelastic in origin: The determined value of Kin-plane(2) agrees well with the calculated in-plane magnetoelastic anisotropy constant of Kin-plane(2)=-3.5×105 erg/cm3.

Krams, P.; Lauks, F.; Stamps, R. L.; Hillebrands, B.; Güntherodt, G.; Oepen, H. P.

1993-05-01

272

Magnetic Field Distribution of Permanent Magnet Magnetized by Static Magnetic Field Generated by HTS Bulk Magnet  

Microsoft Academic Search

Demagnetized rare earth magnets (Nd-Fe-B) can be fully magnetized by scanning them in the intense static fields over 3 T of a HTS bulk magnet which was cooled to the temperature range lower than 77K with use of cryo-coolers and activated by the field of 5 T. We precisely examined the magnetic field distributions of magnetized permanent magnets. The magnetic

Tetsuo Oka; Nobutaka Kawasaki; Satoshi Fukui; Jun Ogawa; Takao Sato; Toshihisa Terasawa; Yoshitaka Itoh; Ryohei Yabuno

2012-01-01

273

Modification of perpendicular magnetic anisotropy and domain wall velocity in Pt/Co/Pt by voltage-induced strain  

PubMed Central

The perpendicular magnetic anisotropy Keff, magnetization reversal, and field-driven domain wall velocity in the creep regime are modified in Pt/Co(0.85–1.0?nm)/Pt thin films by strain applied via piezoelectric transducers. Keff, measured by the extraordinary Hall effect, is reduced by 10?kJ/m3 by tensile strain out-of-plane ?z = 9 × 10?4, independently of the film thickness, indicating a dominant volume contribution to the magnetostriction. The same strain reduces the coercive field by 2–4?Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers. We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity. PMID:25605499

Shepley, P. M.; Rushforth, A. W.; Wang, M.; Burnell, G.; Moore, T. A.

2015-01-01

274

Modification of perpendicular magnetic anisotropy and domain wall velocity in Pt/Co/Pt by voltage-induced strain  

NASA Astrophysics Data System (ADS)

The perpendicular magnetic anisotropy Keff, magnetization reversal, and field-driven domain wall velocity in the creep regime are modified in Pt/Co(0.85-1.0 nm)/Pt thin films by strain applied via piezoelectric transducers. Keff, measured by the extraordinary Hall effect, is reduced by 10 kJ/m3 by tensile strain out-of-plane ?z = 9 × 10-4, independently of the film thickness, indicating a dominant volume contribution to the magnetostriction. The same strain reduces the coercive field by 2-4 Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers. We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity.

Shepley, P. M.; Rushforth, A. W.; Wang, M.; Burnell, G.; Moore, T. A.

2015-01-01

275

Anisotropy Effect on Levitation Performance of Bulk High-Tc Superconductors Above a Permanent Magnet Guideway  

NASA Astrophysics Data System (ADS)

The anisotropy properties of bulk high-temperature superconductors (HTSCs) are taken into consideration for the application of high-temperature superconducting (HTS) Maglev systems, which are especially based on the different flux-trapping capabilities as well as critical current density, Jc, values between the growth section boundary (GSB) and the growth sections (GS) in bulk superconductors. By adjusting the angle between the GSB of bulk HTSCs and the strongest magnetic field position of a permanent magnet guideway (PMG), the levitation force and its relaxation processes are compared at different field-cooling conditions. Experimental results show that the levitation capability and the suppression of levitation force decay can be enhanced by optimizing the GS/GSB alignment of every bulk HTSC above the PMG. Meanwhile, our conclusions may provide references to other HTS maglev systems with small levitation gaps, i.e., superconducting magnetic bearings.

Zheng, Jun; Liao, Xinglin; Jing, Hailian; Lin, Qunxu; Ma, Guangtong; Yen, Fei; Wang, Suyu; Wang, Jiasu

276

Voltage control of magnetic anisotropy in Fe films with quantum well states  

E-print Network

The influence of a gate voltage on magnetic anisotropy is investigated in a thin Fe film epitaxially grown on a Ag(1,1,10) substrate and covered by MgO. Oscillations in step-induced magnetic anisotropy due to quantum well ...

Bauer, Uwe

277

MAGNETIC ANISOTROPY AS AN AID TO IDENTIFYING CRM AND DRM IN RED SEDIMENTARY ROCKS  

E-print Network

MAGNETIC ANISOTROPY AS AN AID TO IDENTIFYING CRM AND DRM IN RED SEDIMENTARY ROCKS K.P. KODAMA1 techniques for determining the origin of the natural remanent magnetization (NRM) in sedimentary rocks of the remanence anisotropy of magnetite and hematite in the same sedimentary rock sample was the goal. In one

Utrecht, Universiteit

278

The observation of multi-axial anisotropy in ultrafine cobalt ferrite particles used in magnetic fluids  

Microsoft Academic Search

It has been shown that nano-sized particles of cobalt ferrite produced by the coprecipitation method for use in magnetic fluids exhibit multiaxial anisotropy, which has not previously been reported for ferrite particles. The value of the magnetic anisotropy constant calculated from measurements of the decay of remanence is similar to that reported for bulk cobalt ferrite.

K. J. Davies; S. Wells; R. V. Upadhyay; S. W. Charles; K. O'Grady; M. El Hilo; T. Meaz; S. Mørup

1995-01-01

279

Phyllosilicate fabric characterization by Low-Temperature Anisotropy of Magnetic Susceptibility (LT-AMS)  

E-print Network

Phyllosilicate fabric characterization by Low-Temperature Anisotropy of Magnetic Susceptibility (LT rock fabrics. INDEX TERMS: 1518 Geomagnetism and Paleomagnetism: Magnetic fabrics and anisotropy; 1540: Microstructures. Citation: Pare´s, J. M., and B. A. van der Pluijm, Phyllosilicate fabric characterization by Low

280

Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar wind  

E-print Network

Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar 10, 2009) The proton temperature anisotropy in the solar wind is known to be constrained by the theo independent measurements of gyroscale magnetic fluctuations in the solar wind to show for the first time

California at Berkeley, University of

281

Switching distributions in Co-Ni nanopillars with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

This thesis reports on measurements of the switching distributions in Co-Ni nanopillars with perpendicular magnetic anisotropy. The Co-Ni nanopillars are incorporated into a spin-valve device - a two terminal device consisting of two ultrathin (1-3 nm) Co-Ni ferromagnets separated by a thin (4 nm) Cu spacer patterned into ellipses and circles with lateral sizes ranging from 40-300 nm. Magnetic fields applied along the uniaxial anisotropy axis can switch the alignment of the constituent ferromagnetic layers between anti-parallel and parallel. Electric currents flowing can also switch the nanopillar through the spin-transfer torque effect - an electric current transfers spin-angular momentum from conduction electrons to the background magnetization of a ferromagnet, ultimately manifesting as a torque on the magnetization. Lateral geometry effects were studied on nanopillars with notches along the perimeter. Switching field measurements revealed an asymmetry between the anti-parallel (AP) to parallel (P) and P to AP switching field distributions. A phenomenological model that considers the spatially inhomogeneous dipole field from the polarizing layer explains this asymmetry. In nanopillars with an 80 nm circular diameter, switching field measurements taken in a cryostat reveal non-uniform magnetization configurations during reversal. At the lowest temperatures (12 K), the transition between uniform states (P to AP) shows three consecutive hysteretic jumps. The thermal stability of the transition states was investigated for temperatures between 12 K and room temperature. The thermally activated magnetization reversal model by Neel and Brown was tested on 75 nm diameter spin-valves between 20 and 400 K. The temperature dependence of the statistics of switching reflects enhanced thermal fluctuations and cannot be modeled by the Neel expression for the energy barrier. Taking into account the implicit temperature dependence of the energy barrier from the saturation magnetization and perpendicular anisotropy energy explains this discrepancy. The effective barrier model for spin-torque thermally-activated switching of Co-Ni nanopillars was investigated. We extracted an effective energy barrier height for switching field distributions under several dc currents. The results mostly agree with the prediction that the current modifies the barrier height. However, rare switching events at the tails of the distributions reveal qualitative deviations from this model.

Gopman, Daniel Bernard

282

Magnetically enhanced bicelles delivering switchable anisotropy in optical gels.  

PubMed

Mesostructures responding to external triggers such as temperature, pH, or magnetic field have the potential to be used as self-acting sensors, detectors, or switches. Key features are a strong and well-defined response to the external trigger. Here, we present magnetic alignable bicelles embedded into a gelatin matrix generating magnetically switchable structures, which can reversibly be locked and unlocked by adjusting the temperature. We show that the disk-like aggregates can be orientated in magnetic fields, and such orientation can be preserved after embedding into gelatin. The resulting gel cubes show an anisotropic transfer for electromagnetic waves, i.e., a different spatial birefringence. Cycling through the melting point of gelatin sets the structure back to its isotropic state providing a read-out of the thermal history. Stacking of the bicelles induced by the gelatin promotes magnetic aligning, as an increased aggregation number in the stacks increases the magnetic orientation energy. PMID:24369041

Liebi, Marianne; Kuster, Simon; Kohlbrecher, Joachim; Ishikawa, Takashi; Fischer, Peter; Walde, Peter; Windhab, Erich J

2014-01-22

283

Magnetic Anisotropy of Chloritoid and its Significance in Magnetic Fabric Studies of Low-Grade Metamorphic Rocks  

NASA Astrophysics Data System (ADS)

The magnetocrystalline anisotropy of monoclinic chloritoid, a relatively common mineral in aluminium-rich, metapelitic rocks, has been determined for the first time by measuring the anisotropy of magnetic susceptibility (AMS), using two independent high-field approaches, i.e. (a) directional magnetic hysteresis measurements and (b) torque magnetometry, on a collection of single crystals collected from different tectonometamorphic settings worldwide [Haerinck et al., 2013a]. Magnetic remanence experiments show that all specimens contain ferromagnetic (s.l.) impurities, being mainly magnetite. The determined (paramagnetic) high-field-AMS (HF-AMS) ellipsoids have a highly oblate shape with the minimum susceptibility direction subparallel to the crystallographic c-axis of chloritoid. In the basal plane of chloritoid, though, the HF-AMS can be considered isotropic. The corrected degree of anisotropy (PJHF) is found to be 1.47, which is significantly higher than the anisotropy of most paramagnetic silicates and even well above the frequently used upper limit (i.e. 1.35) for the paramagnetic contribution to AMS of siliciclastic rocks. As there is no apparent relationship between PJHF and the high-field bulk susceptibility, it seems that the remarkably high magnetic anisotropy of chloritoid is not simply the result of more Fe (& Mn) cations and hence, a stronger ferrimagnetic interaction within the basal plane of the chloritoid lattice. Instead, an analysis of the paramagnetic Curie temperature, parallel (?par.) and perpendicular (?perp.) to the basal plane of the chloritoid crystals, indicates that this pronounced magnetocrystalline anisotropy is related to strong antiferromagnetic exchange interactions in the direction of the crystallographic c-axis (?perp. < 0) and rather weak ferromagnetic exchange interactions within the basal plane (?par. > 0). As a consequence, chloritoid-bearing metapelites with a pronounced mineral alignment can have a high degree of AMS without the need of invoking a significant contribution of strongly anisotropic, ferromagnetic (s.l.) minerals. This is tested by a magnetic fabric study of a particular stratigraphic horizon of Armorican metasiltstones, that covers both an area with chloritoid and white mica-bearing metasiltstones, associated with an epizonal metamorphic grade, and an area with chlorite and white mica-bearing metasiltstones, associated with an anchizonal metamorphic grade [Haerinck et al., 2013b]. It was found that the epizonal chloritoid-bearing metasiltstones show (dominantly paramagnetic) PJ values up to 1.45, whereas the anchizonal, chlorite and white mica-bearing metasiltstones show PJ values only up to 1.27. These observations clearly show that the presence of chloritoid in low-grade metamorphic rocks has a profound impact on the rock's magnetic fabric (AMS) which can be attributed to the very high intrinsic magnetic anisotropy of chloritoid. Therefore, our work calls for a revised approach of magnetic fabric interpretations in chloritoid-bearing rocks. Haerinck et al. 2013a, JGR-B, 118, 13-13, doi: 10.1002/jgrb.50276. Haerinck et al. 2013b, JGS of London, 170 (2), 263-280, doi: 10.1144/jgs2012-062.

Haerinck, T.; Debacker, T. N.; Sintubin, M.

2013-12-01

284

Growth-induced uniaxial magnetic anisotropy in Co/Cu(100)  

NASA Astrophysics Data System (ADS)

Growth-induced uniaxial magnetic anisotropy and the surface morphology of Co/Cu(100) films were investigated using Surface Magneto-Optic Kerr Effect (SMOKE), Low Energy Electron Diffractions (LEED), and Scanning Tunneling Microscopy (STM). We found that the Co film grown at low temperature (230K) at 63 degrees of off-normal growth direction processes an in-plane uniaxial magnetic anisotropy with the easy magnetization axis perpendicular to the growth incident plane. LEED measurement reveals a rougher Co surface than room temperature grown film. STM measurements show that the low temperature grown Co film consists of small islands without obvious anisotropic roughness or elongated islands. This result rules out the dipolar origin of the uniaxial magnetic anisotropy. Cu and CO absorption experiments suggest that the uniaxial magnetic anisotropy originates from the magneto crystalline anisotropy of the Co film surface.

Zhao, Hongwu; Wu, Yizheng; Won, Changyeon; Qiu, Ziqiang

2003-03-01

285

Crack-induced anisotropy models in The Geysers geothermal field  

Microsoft Academic Search

High quality observations of shear-wave anisotropy in the shallow crust have allowed us to detect subsurface crack systems in the NW and the SE Geysers geothermal fields, CA. Shear-wave splitting (SWS) parameters, fast shear-wave polarizations (phi) and time delays (deltat), are highly sensitive to the anisotropic fabric of the medium through which shear-waves propagate and constitute the basic dataset to

Maya Elkibbi; Ming Yang; J. A. Rial

2005-01-01

286

Photodetachment in magnetic fields  

Microsoft Academic Search

The behavior of the photodetachment cross section, near threshold, for atomic negative ioris in a magnetic field is described and illustrated with data on photodetachment of electrons from negative sulfur ions. The effect of the final state interaction is discussed and the photodetachment of atomic negative ions in a magnetic field is compared to photoionization of neutral atoms in a

D. J. Larson; R. Stoneman

1982-01-01

287

THE INTERPLANETARY MAGNETIC FIELD  

Microsoft Academic Search

A new analysis of magnetic and concurrent plasma data collected from the ; space probes Pionecr 5, Explorer 10, and Mariner 2 yields a new model of the ; interplanetary magnetic field. It is hypothesized that the observed ; interplanetary field F\\/sub i\\/ is due to motion of the magnetometer relative to a ; negatively charged rotating sun from which

V. A. BAILEY

1963-01-01

288

Magnetic field line Hamiltonian  

SciTech Connect

The magnetic field line Hamiltonian and the associated canonical form for the magnetic field are important concepts both for understanding toroidal plasma physics and for practical calculations. A number of important properties of the canonical or Hamiltonian representation are derived and their importance is explained.

Boozer, A.H.

1984-03-01

289

Cosmic Magnetic Fields  

Microsoft Academic Search

Most of the visible matter in the Universe is in a plasma state, or more specifically is composed of ionized or partially ionized gas permeated by magnetic fields. Thanks to recent advances on the theory and detection of cosmic magnetic fields there has been a worldwide growing interest in the study of their role on the formation of astrophysical sources

Elisabete M. de Gouveia Dal Pino; Dal Pino

2006-01-01

290

Exchange bias and magnetic anisotropy in ultrathin iron films grown on (001) GaAs  

NASA Astrophysics Data System (ADS)

Ultrathin iron films grown by MBE on GaAs substrates were studied by SQUID and by ferromagnetic resonance (FMR). Exchange bias (EB) was observed in this system at temperatures below 20 K, but disappeared at higher temperatures. The angular dependence of asymmetric hysteresis loops of the sample were understood as resulting from the coexistence of the cubic and uniaxial magnetic anisotropy fields of the Fe film and the EB field arising from a yet unidentified inter-layer between Fe and GaAs (possibly Fe2As). Magnetic anisotropy of the Fe films was investigated by FMR in a manner similar to that described by Aktas et al. [1]. By fitting the angular dependence of the FMR field we have obtained magnetic parameters of the sample, which are similar to those reported in Ref. [1]. However, the g- factor obtained from the fitting shows an unexpected anomalous increase in the low temperature range. Since this behavior occurs exactly in the range where EB appears, it is tempting to speculate that these two effects are causally related.[4pt] [1] B. Aktas et al., J. Appl. Phys. 102, 013912 (2007).

Tivakornsasithorn, Kritsanu; Liu, Xinyu; Dobrowolska, Malgorzata; Furdyna, Jacek

2011-03-01

291

SmCo5-based thin films with high magnetic anisotropy for perpendicular magnetic recording  

Microsoft Academic Search

An investigation was carried out on the effects of the addition of Cu and the thickness of the SmCo5-based thin film with perpendicular magnetic anisotropy upon its magnetic properties, with the aim of reducing the Cu\\/Ti underlayer thickness. As a result, the Cu\\/Ti underlayer thickness necessary to obtain the squareness ratio of unity was successfully reduced from 125 to 50

Junichi Sayama; Kazuki Mizutani; Yuki Yamashita; Toru Asahi; Tetsuya Osaka

2005-01-01

292

Determination of the heat diffusion anisotropy by comparing measured and simulated electron temperature profiles across magnetic islands  

NASA Astrophysics Data System (ADS)

The ratio between the heat diffusion coefficients parallel and perpendicular to the magnetic field lines, ?||/?bottom, influences the flattening of the temperature profile inside magnetic islands and the driving term of neoclassical tearing modes (Fitzpatrick 1995 Phys. Plasmas 2 825). The value of this anisotropy is, however, not easily accessible experimentally. This paper presents a method to determine it from a systematic comparison of temperature measurements at magnetic islands with numerical heat diffusion simulations. The application of the method is demonstrated for a 2/1 magnetic island in the TEXTOR tokamak, where a heat diffusion anisotropy of 108 is observed. This is lower by a factor of 40 than predicted by Spitzer and Härm (Spitzer and Härm 1953 Phys. Rev. 89 997) and a strong indication that the heat flux limit determines the flattening of the electron temperature across magnetic islands.

Hölzl, M.; Günter, S.; Classen, I. G. J.; Yu, Q.; TEXTOR Team; Delabie, E.

2009-11-01

293

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

This web page, authored and curated by David P. Stern, provides information and a graphical exercise for students regarding the interaction between magnetic field lines and a plasma. The activity involves tracing a typical interplanetary magnetic field line, dragged out of a location on the Sun by the radial flow of the solar wind. This illustrates the way magnetic field lines are "frozen to the plasma" and the wrapping of field lines due to the rotation of the sun. This is part of the work "The Exploration of the Earth's Magnetosphere". A Spanish translation is available.

Mendez, J.

294

The Earth's Magnetic Field  

NSDL National Science Digital Library

The magnetic field of the Earth is contained in a region called the magnetosphere. The magnetosphere prevents most of the particles from the sun, carried in solar wind, from hitting the Earth. This site, produced by the University Corporation for Atmospheric Research (UCAR), uses text, scientific illustrations,and remote imagery to explain the occurrence and nature of planetary magnetic fields and magnetospheres, how these fields interact with the solar wind to produce phenomena like auroras, and how magnetic fields of the earth and other planets can be detected and measured by satellite-borne magnetometers.

295

THE ROLE OF PRESSURE ANISOTROPY ON PARTICLE ACCELERATION DURING MAGNETIC RECONNECTION  

SciTech Connect

Voyager spacecraft observations have revealed that contrary to expectations, the source of anomalous cosmic rays (ACRs) is not at the local termination shock. A possible mechanism of ACR acceleration is magnetic reconnection in the heliosheath. Using a particle-in-cell code, we investigate the effects of {beta} on reconnection-driven particle acceleration by studying island growth in multiple interacting Harris current sheets. Many islands are generated, and particles are dominantly heated through Fermi reflection in contracting islands during island growth and merging. There is a striking difference between the heating of electrons versus the heating of ions. There is a strong dependence of {beta} on electron heating, while the ion heating is insensitive to {beta}. Anisotropies develop with T {sub Parallel-To} {ne} T for both electrons and ions. The electron anisotropies support the development of a Weibel instability that suppresses the Fermi acceleration of the electrons. Since the Weibel instability develops at a larger T {sub Parallel-To }/T in lower {beta} systems, electrons are able to accelerate more efficiently by the Fermi mechanism at low {beta}. The variance in anisotropy implies less electron acceleration in higher {beta} systems, and thus less heating. This study sheds light on particle acceleration mechanisms within the sectored magnetic field regions of the heliosheath and the dissipation of turbulence such as that produced by the magnetorotational instability in accreting systems.

Schoeffler, K. M.; Drake, J. F.; Swisdak, M. [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742-3511 (United States)] [Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742-3511 (United States); Knizhnik, K. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218-2686 (United States)] [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218-2686 (United States)

2013-02-20

296

Monte Carlo studies of two-dimensional random-anisotropy magnets  

NASA Astrophysics Data System (ADS)

We have carried out a systematic set of Monte Carlo simulations of the Harris-Plischke-Zuckermann lattice model of random magnetic anisotropy on a two-dimensional square lattice, using the classical Metropolis algorithm. We have considered varying temperature T, external magnetic field H (both in the reproducible and irreproducible limits), time scale of the simulation ? in Monte Carlo steps and anisotropy ratio D/J. In the absence of randomness this model reduces to the XY model in two dimensions, which possesses the familiar Kosterlitz-Thouless low-temperature phase with algebraic but no long-range order. In the presence of random anisotropy we find evidence of a low-temperature phase with some disordered features, which might be identified with a spin-glass phase. The low-temperature Kosterlitz-Thouless phase survives at intermediate temperatures for low randomness, but is no longer present for large D/J. We have also studied the high-H approach to perfect order, for which there are theoretical predictions due to Chudnovsky.

Denholm, D. R.; Sluckin, T. J.

1993-07-01

297

INTERPRETING MAGNETIC VARIANCE ANISOTROPY MEASUREMENTS IN THE SOLAR WIND  

SciTech Connect

The magnetic variance anisotropy (A{sub m}) of the solar wind has been used widely as a method to identify the nature of solar wind turbulent fluctuations; however, a thorough discussion of the meaning and interpretation of the A{sub m} has not appeared in the literature. This paper explores the implications and limitations of using the A{sub m} as a method for constraining the solar wind fluctuation mode composition and presents a more informative method for interpreting spacecraft data. The paper also compares predictions of the A{sub m} from linear theory to nonlinear turbulence simulations and solar wind measurements. In both cases, linear theory compares well and suggests that the solar wind for the interval studied is dominantly Alfvenic in the inertial and dissipation ranges to scales of k{rho}{sub i} {approx_equal} 5.

TenBarge, J. M.; Klein, K. G.; Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA (United States); Podesta, J. J., E-mail: jason-tenbarge@uiowa.edu [Space Science Institute, Boulder, CO (United States)

2012-07-10

298

Anisotropies of partial anhysteretic remanence and susceptibility in compacted black shales: Grainsize- and composition-dependent magnetic fabric  

NASA Astrophysics Data System (ADS)

We have quantified the magnetic fabric of the highly-compacted Heebner Shale (Pennsylvanian) of Kansas in terms of the anisotropies of partial anhysteretic remanent magnetization (pARM) and low-field susceptibility. Hysteresis loops exhibit almost purely paramagnetic behavior, and the ratio of high-field linear susceptibility to low-field susceptibility is very close to one; the susceptibility anisotropy therefore reflects the fabric of the paramagnetic matrix, while the remanent anisotropies are due to the preferred orientations of ferrimagnetic grains. Both the paramagnetic and ferrimagnetic fabrics are dominated by a horizontal foliation, with a weak northeasterly lineation, but the pARM anisotropies are generally much larger than the susceptibility anisotropy. The degree of foliation measured with pARM's decreases markedly with increasing coercivities, indicating stronger foliation in the coarser grainsize fraction. In contrast, the pARM mean lineations are grainsize-independent, suggesting a post-compactional origin, related to tectonic compression. The susceptibility lineation appears to have a slightly different azimuth, and may therefore be due to paleocurrents.

Jackson, Mike; Sprowl, Don; Ellwood, Brooks

299

Domain wall motion driven by spin Hall effect—Tuning with in-plane magnetic anisotropy  

SciTech Connect

This letter investigates the effects of in-plane magnetic anisotropy on the current induced motion of magnetic domain walls in systems with dominant perpendicular magnetic anisotropy, where accumulated spins from the spin Hall effect in an adjacent heavy metal layer are responsible for driving the domain wall motion. It is found that that the sign and magnitude of the domain wall velocity in the uniform flow regime can be tuned significantly by the in-plane magnetic anisotropy. These effects are sensitive to the ratio of the adiabatic and non-adiabatic spin transfer torque parameters and are robust in the presence of pinning and thermal fluctuations.

Rushforth, A. W., E-mail: andrew.rushforth@nottingham.ac.uk [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD (United Kingdom)

2014-04-21

300

Temperature dependence of magnetization and anisotropy in uniaxial NiFe{sub 2}O{sub 4} nanomagnets: Deviation from the Callen-Callen power law  

SciTech Connect

The thermal variation of magnetic anisotropy (K) and saturation magnetization (M{sub S}) for uniaxial nickel ferrite (NiFe{sub 2}O{sub 4}) nanomagnets are investigated. Major magnetic hysteresis loops are measured for the sample at temperatures over the range 5–280?K using a vibrating sample magnetometer. The high-field regimes of the hysteresis loops are modeled using the law of approach to saturation, based on the assumption that at sufficiently high field only direct rotation of spin-moment take place, with an additional forced magnetization term that is linear with applied field. The uniaxial anisotropy constant K is calculated from the fitting of the data to the theoretical equation. As temperature increases from 5?K to 280?K, a 49% reduction of K, accompanied by an 85% diminution of M{sub S} is observed. Remarkably, K is linearly proportional to M{sub S}{sup 2.6} in the whole temperature range violating the existing theoretical model by Callen and Callen. The unusual power-law behavior for the NiFe{sub 2}O{sub 4} uniaxial nanomagnets is ascribed to the non-negligible contributions from inter-sublattice pair interactions, Neel surface anisotropy, and higher order anisotropies. A complete realization of the unusual anisotropy-magnetization scaling behavior for nanoscale two-sublattice magnetic materials require a major modification of the existing theory by considering the exact mechanism of each contributions to the effective anisotropy.

Chatterjee, Biplab K.; Ghosh, C. K. [School of Materials Science and Nanotechnology, Jadavpur University, Jadavpur, Kolkata 700032 (India); Chattopadhyay, K. K., E-mail: kalyan-chattopadhyay@yahoo.com [School of Materials Science and Nanotechnology, Jadavpur University, Jadavpur, Kolkata 700032 (India); Thin Film and Nanoscience Laboratory, Department of Physics, Jadavpur University, Jadavpur, Kolkata 700032 (India)

2014-10-21

301

Temperature dependence of magnetization and anisotropy in uniaxial NiFe2O4 nanomagnets: Deviation from the Callen-Callen power law  

NASA Astrophysics Data System (ADS)

The thermal variation of magnetic anisotropy (K) and saturation magnetization (MS) for uniaxial nickel ferrite (NiFe2O4) nanomagnets are investigated. Major magnetic hysteresis loops are measured for the sample at temperatures over the range 5-280 K using a vibrating sample magnetometer. The high-field regimes of the hysteresis loops are modeled using the law of approach to saturation, based on the assumption that at sufficiently high field only direct rotation of spin-moment take place, with an additional forced magnetization term that is linear with applied field. The uniaxial anisotropy constant K is calculated from the fitting of the data to the theoretical equation. As temperature increases from 5 K to 280 K, a 49% reduction of K, accompanied by an 85% diminution of MS is observed. Remarkably, K is linearly proportional to MS2.6 in the whole temperature range violating the existing theoretical model by Callen and Callen. The unusual power-law behavior for the NiFe2O4 uniaxial nanomagnets is ascribed to the non-negligible contributions from inter-sublattice pair interactions, Neel surface anisotropy, and higher order anisotropies. A complete realization of the unusual anisotropy-magnetization scaling behavior for nanoscale two-sublattice magnetic materials require a major modification of the existing theory by considering the exact mechanism of each contributions to the effective anisotropy.

Chatterjee, Biplab K.; Ghosh, C. K.; Chattopadhyay, K. K.

2014-10-01

302

Observing magnetic anisotropy in electronic transport through individual single-molecule magnets  

NASA Astrophysics Data System (ADS)

We review different electron transport methods to probe the magnetic properties, such as the magnetic anisotropy, of an individual Fe4 SMM. The different approaches comprise first and higher order transport through the molecule. Gate spectroscopy, focusing on the charge degeneracy-point, is presented as a robust technique to quantify the longitudinal magnetic anisotropy of the SMM in different redox states. We provide statistics showing the robustness and reproducibility of the different methods. In addition, conductance measurements typically show high-energy excited states well beyond the ground spin multiplet of SMM. Some of these excitations have their origin in excited spin multiplets, others in vibrational modes of the molecule. The interplay between vibrations, charge and spin may yield a new approach for spin control.

Burzurí, E.; Gaudenzi, R.; van der Zant, H. S. J.

2015-03-01

303

Observing magnetic anisotropy in electronic transport through individual single-molecule magnets.  

PubMed

We review different electron transport methods to probe the magnetic properties, such as the magnetic anisotropy, of an individual Fe4 SMM. The different approaches comprise first and higher order transport through the molecule. Gate spectroscopy, focusing on the charge degeneracy-point, is presented as a robust technique to quantify the longitudinal magnetic anisotropy of the SMM in different redox states. We provide statistics showing the robustness and reproducibility of the different methods. In addition, conductance measurements typically show high-energy excited states well beyond the ground spin multiplet of SMM. Some of these excitations have their origin in excited spin multiplets, others in vibrational modes of the molecule. The interplay between vibrations, charge and spin may yield a new approach for spin control. PMID:25721135

Burzurí, E; Gaudenzi, R; van der Zant, H S J

2015-03-25

304

Electron theory of perpendicular magnetic anisotropy of Co-ferrite thin films  

SciTech Connect

We develop an electron theory for the t{sub 2g} electrons of Co{sup 2+} ions to clarify the perpendicular magnetic anisotropy (PMA) mechanism of Co-ferrite thin films by considering the spin-orbit interaction (SOI) and crystal-field (CF) potentials induced by the local symmetry around the Co ions and the global tetragonal symmetry of the film. Uniaxial and in-plane MA constants K{sub u} and K{sub 1} at 0 K, respectively, are calculated for various values of SOI and CF. We show that reasonable parameter values explain the observed PMA and that the orbital moment for the in-plane magnetization reduces to nearly half of that of the out-of-plane magnetization.

Inoue, Jun-ichiro; Yanagihara, Hideto; Kita, Eiji [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan)] [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan); Niizeki, Tomohiko [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan) [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan); AIMR, Tohoku University, Sendai 980-8577 (Japan); Itoh, Hiroyoshi [Department of Pure and Applied Physics, Kansai University, Suita 564-8680 (Japan)] [Department of Pure and Applied Physics, Kansai University, Suita 564-8680 (Japan)

2014-02-15

305

Sources of Magnetic Field Magnetic Phenomena  

E-print Network

push on currents Moving charges can make and feel magnetic forces. We don't understand how permanent will consider the last piece of the puzzle in electromagnetic - changing magnetic fields can make induction. 15Lecture 9 Sources of Magnetic Field 1 Magnetic Phenomena 1. Magnets can push on each other (and

Tobar, Michael

306

Correlation between nanocrystalline and magnetic structure of Co-based alloys with the induced transverse magnetic anisotropy  

NASA Astrophysics Data System (ADS)

The magnetic domain structure is a specific property of ferromagnetic materials influencing their main magnetic properties. The aim of this work was to determine a relationship between nanocrystalline and the domain structure observed by means of magneto-optic Kerr effect on the surface of the Fe14.7Co58.8Cu1Nb3Si13.5B9 and Fe13.8Co65Cu0.6Nb2.6Si9B9 toroidal cores, and the induced transverse magnetic anisotropy Ku. The transverse magnetic anisotropy was induced in the Fe14.7Co58.8Cu1Nb3Si13.5B9 and Fe13.8Co65Cu0.6Nb2.6Si9B9 amorphous cores by annealing them at the temperature of 460 °C, under an external magnetic field of 500 kA/m. It was found that the appearance of nanocrystalline phase in the Fe13.8Co65Cu0.6Nb2.6Si9B9 alloy resulted in considerable increase of the magnetic anisotropy constant to 900 J/m3 already after 40 minutes of heating, whereas the nanocrystallization process in the Fe14.7Co58.8Cu1Nb3Si13.5B9 alloy proceeded much slower (after 240 minutes of heating the content of nanocrystalline phase was at the level of about 18%, and the induced magnetic anisotropy constant reached 190 J/m3). Observations of the domain structure were also made showing that the 180° domains were obtained in the Fe14.7Co58.8Cu1Nb3Si13.5B9 alloy only after 240 min of heating, whereas similar structure was observed in the Fe13.8Co65Cu0.6Nb2.6Si9B9 alloy already after 40 min of treatment.

Kolano-Burian, A.; Kolano, R.; Hawe?ek, ?.; Szynowski, J.; W?odarczyk, P.

2014-05-01

307

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

This is an activity about electromagnetism. Learners will use a compass to map the magnetic field lines surrounding a coil of wire that is connected to a battery. This activity requires a large coil or spool of wire, a source of electricity such as 3 D-cell batteries or an AC to DC power adapter, alligator-clipped wire, and magnetic compasses. This is the third lesson in the second session of the Exploring Magnetism teachers guide.

2012-08-03

308

The First Magnetic Fields  

NASA Astrophysics Data System (ADS)

We review current ideas on the origin of galactic and extragalactic magnetic fields. We begin by summarizing observations of magnetic fields at cosmological redshifts and on cosmological scales. These observations translate into constraints on the strength and scale magnetic fields must have during the early stages of galaxy formation in order to seed the galactic dynamo. We examine mechanisms for the generation of magnetic fields that operate prior during inflation and during subsequent phase transitions such as electroweak symmetry breaking and the quark-hadron phase transition. The implications of strong primordial magnetic fields for the reionization epoch as well as the first generation of stars are discussed in detail. The exotic, early-Universe mechanisms are contrasted with astrophysical processes that generate fields after recombination. For example, a Biermann-type battery can operate in a proto-galaxy during the early stages of structure formation. Moreover, magnetic fields in either an early generation of stars or active galactic nuclei can be dispersed into the intergalactic medium.

Widrow, Lawrence M.; Ryu, Dongsu; Schleicher, Dominik R. G.; Subramanian, Kandaswamy; Tsagas, Christos G.; Treumann, Rudolf A.

2012-05-01

309

Cationic distribution, magnetization and magnetic anisotropy of Co2+ doped M-type barium ferrite  

Microsoft Academic Search

The cation distribution and the high field magnetization of the Co-Ti M-type barium ferrites have been investigated by means of neutron powder diffraction and high field isothermal magnetic measurements. The composition dependence of the experimental magnetization is compared to that obtained from the cationic distribution assuming a collinear magnetic structure. A considerable amount of Co ions occupy tetrahedral sites being

X. Batlle; X. Obradors; M. Pernet; M. Vallet; M. Cabañas; J. Rodríguez; J. Fontcuberta

1990-01-01

310

Theoretical calculations of magnetic order and anisotropy energies in molecular magnets  

SciTech Connect

We present theoretical electronic structure calculations on the nature of electronic states and the magnetic coupling in the Mn{sub 12}O{sub 12} free cluster and the Mn{sub 12}O{sub 12}(RCOO){sub 16}(H{sub 2}O){sub 4} molecular magnetic crystal. The calculations have been performed with the all-electron full-potential NRLMOL code. We find that the free Mn{sub 12}O{sub 12} cluster relaxes to an antiferromagnetic cluster with no net moment. However, when coordinated by sixteen HCOO ligands and four H{sub 2}O groups, as it is in the molecular crystal, we find that the ferrimagnetic ordering and geometrical and magnetic structure observed in the experiments is restored. Local Mn moments for the free and ligandated molecular magnets are presented and compared to experiment. We identify the occupied and unoccupied electronic states that are most responsible for the formation of the large anisotropy barrier and use a recently developed full-space and full-potential method for calculating the spin-orbit coupling interaction and anisotropy energies. Our calculated second-order anisotropy energy is in excellent agreement with experiment. (c) 2000 American Institute of Physics.

Pederson, M. R. [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)] [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States); Porezag, D. V. [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)] [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States); Kortus, J. [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States)] [Center for Computational Materials Science - 6392, Naval Research Laboratory, Washington, D.C. 20375-5000 (United States); Khanna, S. N. [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000 (United States)] [Department of Physics, Virginia Commonwealth University, Richmond, Virginia 23284-2000 (United States)

2000-05-01

311

Electric-field-induced thermally assisted switching of monodomain magnetic bits  

NASA Astrophysics Data System (ADS)

We present a study of the electric-field-induced switching of magnetic memory bits exhibiting interfacial voltage-controlled magnetic anisotropy (VCMA). Switching is analyzed in the single-domain approximation and in the thermally activated regime. The effects of external magnetic fields, magnitudes of the perpendicular anisotropy and VCMA effect, and voltage pulse width on the switching voltage are discussed. Both in-plane and perpendicular magnetic memory bits are considered. Experimental results are presented and compared to the theoretical model.

Khalili Amiri, P.; Upadhyaya, P.; Alzate, J. G.; Wang, K. L.

2013-01-01

312

Anomalous Magnetic Anisotropy of Caged Cubic Compound SmRu2Zn20  

NASA Astrophysics Data System (ADS)

The magnetic susceptibility ?, magnetization M, and specific heat C were measured for the caged cubic compound SmRu2Zn20 at temperatures down to 2 K in a magnetic field H along the three principal axes of [111], [101], and [001]. A ferromagnetic phase transition was observed at TC = 7.8 K in the temperature dependences of both ?(T) and C(T). The Sm ion in SmRu2Zn20 is trivalent, which is shown by the experimental results of the lattice constant and ?(T) between 10 and 300 K. The easy axis of magnetization is the [111] direction, and the entropy at TC is R ln 4, indicating that the ground state is quartet. These experimental results, however, contradict the simple prediction based on the cubic crystalline electric field (CEF) of Sm3+. If the ground state is quartet ?8, the easy axis of magnetization should be in the [001] direction. We analyzed the anomalous magnetic anisotropy by taking into account quadrupole–quadrupole and octupole–octupole interactions as well as the cubic CEF effect, the usual exchange interaction, and the Zeeman effect.

Isikawa, Yosikazu; Mizushima, Toshio; Ejiri, Jun-ichi; Kuwai, Tomohiko

2014-07-01

313

Magnetic field dosimeter development  

SciTech Connect

In recent years there has been increased concern over potential health hazards related to exposure of personnel to magnetic fields. If exposure standards are to be established, then a means for measuring magnetic field dose must be available. To meet this need, the Department of Energy has funded development of prototype dosimeters at the Battelle Pacific Northwest Laboratory. This manual reviews the principle of operation of the dosimeter and also contains step-by-step instructions for its operation.

Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

1980-09-01

314

The magnetic properties and microstructure of strontium ferrite films with perpendicular and in-plane magnetic anisotropy  

Microsoft Academic Search

The texture and the easy axis of magnetization of strontium ferrite (SrFe12O19) thin films can be controlled by changing the power of the rf sputtering. In-plane magnetic anisotropy is developed at a sputtering power of 330 W (7.5 W\\/cm2), whereas strong perpendicular magnetic anisotropy (Ku~1×106 erg\\/cc) is induced at 60 W power (1.3 W\\/cm2). Further control over coercivity and morphology

B. Ramamurthy Acharya; S. Prasad; N. Venkataramani; E. N. Ebarra; T. Suzuki

1997-01-01

315

Perpendicular magnetic anisotropy in Ta/Co2FeAl/MgO multilayers  

NASA Astrophysics Data System (ADS)

In this paper, we demonstrate the stabilization of perpendicular magnetic anisotropy (PMA) in Ta/Co2FeAl/MgO multilayers sputtered on thermally oxidized Si(100) substrates. The magnetic analysis points out that these films show significant interfacial anisotropy even in the as-deposited state, KS=0.67 erg/cm2, enough to provide PMA for the as-deposited films with thicknesses below 1.5 nm. Moreover, the interfacial anisotropy is enhanced by thermal annealing up to 300 °C. The presence of a magnetic dead layer, whose thickness increases with annealing temperature, was also identified.

Gabor, M. S.; Petrisor, T.; Tiusan, C.; Petrisor, T.

2013-08-01

316

Transmission electron microscopy study of large field induced anisotropy (Co1xFex)89Zr7B4 nanocomposite ribbons with dilute Fe-contents  

E-print Network

to investigate the structure of magnetic field crystallized (Co1Ã?xFex)89Zr7B4 alloys with only dilute Fe matrix after crystallization. A number of other Co-rich compositions with high field induced anisotropies, Pittsburgh, PA 15213, USA b Magnetics, A Division of Spang & Company, Pittsburgh, PA 15238, USA a r t i c l e

Laughlin, David E.

317

Dielectric anisotropy in polar solvents under external fields  

E-print Network

We investigate dielectric saturation and increment in polar liquids under external fields. We couple a previously introduced dipolar solvent model to a uniform electric field and derive the electrostatic kernel of interacting dipoles. This procedure allows an unambiguous definition of the liquid dielectric permittivity embodying non-linear dielectric response and correlation effects.We find that the presence of the external field results in a dielectric anisotropy characterized by a two-component dielectric permittivity tensor. The increase of the electric field amplifies the permittivity component parallel to the field direction, i.e. dielectric increment is observed along the field. However, the perpendicular component is lowered below the physiological permittivity, indicating dielectric saturation perpendicular to the field. By comparison with Molecular Dynamics simulations from the literature, we show that the mean-field level dielectric response theory underestimates dielectric saturation. The inclusion of dipolar correlations at the weak-coupling level intensify the mean-field level dielectric saturation and improves the agreement with simulation data at weak electric fields. The correlation-corrected theory predicts as well the presence of a metastable configuration corresponding to the antiparallel alignment of dipoles with the field. This prediction can be verified by solvent-explicit simulations where solvent molecules are expected to be trapped transiently in this metastable state.

Sahin Buyukdagli

2014-12-14

318

Magnetic susceptibility tensor anisotropies for a lanthanide ion series in a fixed protein matrix.  

PubMed

The full series of lanthanide ions (except the radioactive promethium and the S-state gadolinium) has been incorporated into the C-terminal calcium binding site of the dicalcium protein calbindin D(9k). A fairly constant coordination environment is maintained throughout the series. At variance with several lanthanide complexes with small chelating ligands investigated in the past, the large protein moiety provides a large number of NMR signals whose hyperfine shifts can be exclusively ascribed to pseudocontact shifts (PCS). The chemical shifts of 1H and 15N backbone and side chain amide NH groups were accurately measured through HSQC experiments. 1097 PCS were estimated from these by subtracting the diamagnetic contributions measured on HSQC spectra of either the 4f(0) lanthanum(III) or the 4f(14) lutetium(III) derivatives and used to define a quality factor for the structure. The differences in diamagnetic chemical shifts between the two diamagnetic blanks were relatively small, although some were not negligible especially for the nuclei closest to the metal center. These differences were used as a tolerance for the PCS. The magnetic susceptibility tensor anisotropies for each paramagnetic lanthanide ion were obtained as the result of the solution structure determination performed by using the NOEs of the cerium(III) derivative and the PCS of all lanthanides simultaneously. This set of reliable magnetic data permits an experimental assessment of Bleaney's theory relative to the magnetic properties for an extended series of lanthanide complexes in solution. All of the obtained tensors show some rhombicity, as could be expected from the lack of symmetry of the protein environment. The directions of the largest magnetic susceptibility component for Ce, Pr, Nd, Sm, Tb, Dy, and Ho and of the smallest magnetic susceptibility component for Eu, Er, Tm, and Yb were found to be all within 15 degrees from their average (within 20 degrees for Sm), confirming the essential similarity of the coordination environment for all lanthanides. Bleaney's theory is in excellent qualitative agreement with the observed pattern of axial anisotropies. Its quantitative agreement is substantially better than that suggested by previous analyses performed on more limited sets of PCS data for small lanthanide complexes, the so-called crystal field parameter varying only within +/-30% from one lanthanide to another. These variations are even smaller (+/-15%) if a reasonable T(-3) correction is taken into consideration. A knowledge of magnetic susceptibility anisotropy properties of lanthanides is essential in determining the self-orienting properties of lanthanide complexes in solution when immersed in magnetic fields. PMID:11457182

Bertini, I; Janik, M B; Lee, Y M; Luchinat, C; Rosato, A

2001-05-01

319

Competing magnetic anisotropies in an AFM-FM-AFM trilayer  

SciTech Connect

An antiferromagnet-ferromagnet-antiferromagnet trilayer was grown in magnetic field using CoMn, permalloy (Py), and FeMn, respectively. Magnetometry studies show that the direction of exchange coupling of CoMn with Py was perpendicular to that of Py with FeMn. These results are explained by a spin flop in the CoMn layer and show that the spin structure of an antiferromagnet may undergo severe modification due to a relatively small magnetic field applied during its growth. The perpendicular exchange coupling was exploited in the CoMn-Py-FeMn trilayer to manipulate the easy axis of the ferromagnet.

Bali, R.; Nelson-Cheeseman, B.B.; Scholl, A.; Arenholz, E.; Suzuki, Y.; Blamire, M.G.

2009-08-01

320

Solar Wind Magnetic Fields  

NASA Technical Reports Server (NTRS)

The magnetic fields originate as coronal fields that are converted into space by the supersonic, infinitely conducting, solar wind. On average, the sun's rotation causes the field to wind up and form an Archimedes Spiral. However, the field direction changes almost continuously on a variety of scales and the irregular nature of these changes is often interpreted as evidence that the solar wind flow is turbulent.

Smith, E. J.

1995-01-01

321

Temperature dependence of the voltage-controlled perpendicular anisotropy in nanoscale MgO|CoFeB|Ta magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

In this work, we experimentally study the temperature dependence of the perpendicular magnetic anisotropy (PMA) and of the voltage-controlled magnetic anisotropy (VCMA) in nanoscale MgO|CoFeB|Ta-based magnetic tunnel junctions. We demonstrate that the temperature dependences of both the PMA and the VCMA coefficient follow power laws of the saturation magnetization, but with different exponents. We also find that the linear dependence of the PMA on electric field is maintained over a wide temperature range, although the VCMA strength decreases faster as a function of temperature as compared to the PMA. Possible mechanisms leading to the different exponents are discussed.

Alzate, Juan G.; Khalili Amiri, Pedram; Yu, Guoqiang; Upadhyaya, Pramey; Katine, Jordan A.; Langer, Juergen; Ocker, Berthold; Krivorotov, Ilya N.; Wang, Kang L.

2014-03-01

322

Magnetic properties of La–Co substituted barium ferrite thin films with large magnetic anisotropy  

Microsoft Academic Search

Barium ferrite thin films with lanthanum ions and cobalt ions substituted for barium ions and iron ions have been prepared by conventional diode sputtering method. The hexagonal magnetoplumbite structure was formed by an annealing at 800°C or above. La–Co-substituted barium ferrite thin films had large magnetic anisotropy compared with non-substituted barium ferrite thin films. Moreover, an attempt was also made

K. Kakizaki; H. Taguchi; N. Hiratsuka

2004-01-01

323

Magnetization Reversal and Magnetic Anisotropy in Ordered CoNiP Nanowire Arrays: Effects of Wire Diameter.  

PubMed

Ordered CoNiP nanowires with the same length of 4 µm and varying diameters (d = 100 nm-600 nm) were fabricated by electrodeposition of CoNiP onto polycarbonate templates. X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy confirmed the quality of the fabricated nanowires. Magnetic measurements and theoretical analysis revealed that the magnetization reversal and magnetic anisotropy were significantly influenced by varying of the diameters of the nanowires. There existed a critical wire diameter (dc ? 276 nm), below which the magnetization reversal occurred via a coherent rotation mode, and above which the magnetization reversal occurred via a curling rotation mode. The easy axis of the magnetization tended to change in direction from parallel to perpendicular with respect to the wire axis as the wire diameter exceeded dc ? 276 nm. With increasing wire diameter, the coercive field (Hc) and the remanent to saturation magnetization ratio (Mr/Ms) were also found to rapidly decrease in the range d = 100-400 nm and gradually decrease for d > 400 nm. PMID:25760054

Van Thiem, Luu; Tu, Le Tuan; Phan, Manh-Huong

2015-01-01

324

Magnetic Field Problem: Current  

NSDL National Science Digital Library

A cross section of a circular wire loop carrying an unknown current is shown above. The arrows represent the direction of the magnetic field. The color of the arrows represents the magnitude of the field with magnitude increasing as the color changes from blue to green to red to black. You can double-click in the animation to add magnetic field lines, click-drag the center of the loop to reposition it, and click-drag the top or bottom of the loop to change its size.

Wolfgang Christian

325

Magnetic Field Solver  

NASA Technical Reports Server (NTRS)

The Magnetic Field Solver computer program calculates the magnetic field generated by a group of collinear, cylindrical axisymmetric electromagnet coils. Given the current flowing in, and the number of turns, axial position, and axial and radial dimensions of each coil, the program calculates matrix coefficients for a finite-difference system of equations that approximates a two-dimensional partial differential equation for the magnetic potential contributed by the coil. The program iteratively solves these finite-difference equations by use of the modified incomplete Cholesky preconditioned-conjugate-gradient method. The total magnetic potential as a function of axial (z) and radial (r) position is then calculated as a sum of the magnetic potentials of the individual coils, using a high-accuracy interpolation scheme. Then the r and z components of the magnetic field as functions of r and z are calculated from the total magnetic potential by use of a high-accuracy finite-difference scheme. Notably, for the finite-difference calculations, the program generates nonuniform two-dimensional computational meshes from nonuniform one-dimensional meshes. Each mesh is generated in such a way as to minimize the numerical error for a benchmark one-dimensional magnetostatic problem.

Ilin, Andrew V.

2006-01-01

326

Determination of magnetic anisotropy constants in Fe ultrathin film on vicinal Si(111) by anisotropic magnetoresistance  

PubMed Central

The epitaxial growth of ultrathin Fe film on Si(111) surface provides an excellent opportunity to investigate the contribution of magnetic anisotropy to magnetic behavior. Here, we present the anisotropic magnetoresistance (AMR) effect of Fe single crystal film on vicinal Si(111) substrate with atomically flat ultrathin p(2 × 2) iron silicide as buffer layer. Owing to the tiny misorientation from Fe(111) plane, the symmetry of magnetocrystalline anisotropy energy changes from the six-fold to a superposition of six-fold, four-fold and a weakly uniaxial contribution. Furthermore, the magnitudes of various magnetic anisotropy constants were derived from torque curves on the basis of AMR results. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of various magnetic anisotropy constants. PMID:23828508

Ye, Jun; He, Wei; Wu, Qiong; Liu, Hao-Liang; Zhang, Xiang-Qun; Chen, Zi-Yu; Cheng, Zhao-Hua

2013-01-01

327

Determination of magnetic anisotropy constants in Fe ultrathin film on vicinal Si(111) by anisotropic magnetoresistance.  

PubMed

The epitaxial growth of ultrathin Fe film on Si(111) surface provides an excellent opportunity to investigate the contribution of magnetic anisotropy to magnetic behavior. Here, we present the anisotropic magnetoresistance (AMR) effect of Fe single crystal film on vicinal Si(111) substrate with atomically flat ultrathin p(2 × 2) iron silicide as buffer layer. Owing to the tiny misorientation from Fe(111) plane, the symmetry of magnetocrystalline anisotropy energy changes from the six-fold to a superposition of six-fold, four-fold and a weakly uniaxial contribution. Furthermore, the magnitudes of various magnetic anisotropy constants were derived from torque curves on the basis of AMR results. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of various magnetic anisotropy constants. PMID:23828508

Ye, Jun; He, Wei; Wu, Qiong; Liu, Hao-Liang; Zhang, Xiang-Qun; Chen, Zi-Yu; Cheng, Zhao-Hua

2013-01-01

328

Structure, magnetic properties and magnetoelastic anisotropy in epitaxial Sr(Ti???Co?)O? films  

E-print Network

We report the structure, magnetic properties and magnetoelastic anisotropy of epitaxial Sr(Ti???Co?)O? films grown on LaAlO? (001) and SrTiO? (001) substrates by pulsed laser deposition. Room temperature ferromagnetism was ...

Bi, Lei

329

A 3-D finite-element computation of eddy currents and losses in laminated iron cores allowing for electric and magnetic anisotropy  

SciTech Connect

A 3-D scheme based on the Finite Element Method, which takes electric and magnetic anisotropy into consideration, has been developed for computing eddy-current losses caused by stray magnetic fields in laminated iron cores of large transformers and generators. The model is applied to some laminated iron-core samples and compared with equivalent solid-iron cases.

Silva, V.C.; Meunier, G.; Foggia, A. [URA CNRS 355, Saint-Martin-d`Heres (France). Lab. d`Electrotechnique de Grenoble] [URA CNRS 355, Saint-Martin-d`Heres (France). Lab. d`Electrotechnique de Grenoble

1995-05-01

330

Interfacial perpendicular magnetic anisotropy and damping parameter in ultra thin Co2FeAl films  

NASA Astrophysics Data System (ADS)

B2-ordered Co2FeAl films were synthesized using an ion beam deposition tool. A high degree of chemical ordering ˜81.2% with a low damping parameter (?) less than 0.004 was obtained in a 50 nm thick film via rapid thermal annealing at 600 °C. The perpendicular magnetic anisotropy (PMA) was optimized in ultra thin Co2FeAl films annealed at 350 °C without an external magnetic field. The reduced thickness and annealing temperature to achieve PMA introduced extrinsic factors thus increasing ? significantly. However, the observed damping of Co2FeAl films was still lower than that of Co60Fe20B20 films prepared at the same thickness and annealing temperature.

Cui, Yishen; Khodadadi, Behrouz; Schäfer, Sebastian; Mewes, Tim; Lu, Jiwei; Wolf, Stuart A.

2013-04-01

331

Anisotropies of partial anhysteretic remanence and susceptibility in compacted black shales: Grainsize- and composition-dependent magnetic fabric  

SciTech Connect

The authors have quantified the magnetic fabric of the highly-compacted Heebner Shale (Pennsylvanian) of Kansas in terms of the anisotropies of partial anhysteretic remanent magnetization (pARM) and low-field susceptibility. Hysteresis loops exhibit almost purely paramagnetic behavior, and the ratio of high-field linear susceptibility to low-field susceptibility is very close to one; the susceptibility anistropy therefore reflects the fabric anisotropies are due to the preferred orientations of ferrimagnetic grains. Both the paramagnetic and ferrimagnetic fabrics are dominated by a horizontal foliation with a weak northeasterly lineation, but the pARM anisotropies are generally much larger than the susceptibility anisotropy. The degree of foliation measured with pARM's decreases markedly with increasing coercivities, indicating stronger foliation in the coarser grainsize fraction. In contrast, the pARM mean lineations are grainsize, independent, suggesting a post-compactional origin, related to tectonic compression. The susceptibility lineation appears to have a slightly different azimuth, and may therefore be due to paleocurrents.

Jackson, M. (Univ. of Minnesota, Minneapolis (USA)); Sprowl, D. (Univ. of Kansas, Lawrence (USA)); Ellwood, B. (Univ. of Texas, Arlington (USA))

1989-09-01

332

Pressure-induced enhancement of the magnetic anisotropy in Mn(N(CN)2)2  

NASA Astrophysics Data System (ADS)

Using dc and ac magnetometry, the pressure dependence of the magnetization of the three-dimensional antiferromagnetic coordination polymer Mn(N(CN)2)2 was studied up to 12 kbar and down to 8 K. The antiferromagnetic transition temperature, TN, increases dramatically with applied pressure (P ) , where a change from TN(P =ambient) =16.0 K to TN(P =12.1 kbar) =23.5 K was observed. In addition, a marked difference in the magnetic behavior is observed above and below 7.1 kbar. Specifically, for P <7.1 kbar, the differences between the field-cooled and zero-field-cooled magnetizations, the coercive field, and the remanent magnetization decrease with increasing pressure. However, for P >7.1 kbar, the behavior is inverted. Additionally, for P >8.6 kbar, minor hysteresis loops are observed. All of these effects are evidence of the increase of the superexchange interaction and the appearance of an enhanced exchange anisotropy with applied pressure.

Quintero, P. A.; Rajan, D.; Peprah, M. K.; Brinzari, T. V.; Fishman, R. S.; Talham, D. R.; Meisel, M. W.

2015-01-01

333

Magnetic and elastic wave anisotropy in partially molten rocks: insight from experimental melting of synthetic quartz-mica schist (Invited)  

NASA Astrophysics Data System (ADS)

We studied the magnetic and elastic wave speed anisotropy of a synthetically prepared quartz-mica schist, prior to, during and after experimental melting. The synthetic rock was manufactured from a mixture of powders with equal volumes of quartz and muscovite. The powders were initially compacted with 200 MPa uniaxial stress at room temperature and sealed in a stainless steel canister. Subsequently the sealed canister was isostatically pressed at 180 MPa and 580 °C for 24 hours. This produced a solid medium with ~25 % porosity. Mica developed a preferred grain-shape alignment due to the initial compaction with differential load, where mica flakes tend to orient perpendicular to the applied stress and hence define a synthetic foliation plane. In the last stage we used a Paterson gas-medium apparatus, to pressurize and heat the specimens up to 300 MPa and 750 °C for a six hour duration. This stage initially compacted the rock, followed by generation of melt, and finally crystallization of new minerals from the melt. Elastic wave speed measurements were performed in situ at pressure and temperature, with a transducer assembly mounted next to the sample. Magnetic measurements were performed before and after the partial melt experiments. Anisotropy was measured in low- and high-field, using a susceptibility bridge and torsion magnetometer, respectively. Additionally we performed measurements of hysteresis, isothermal remanent magnetization (IRM) and susceptibility as a function of temperature, to investigate the magnetic properties of the rock. The elastic wave speed, before the melting-stage of the experiment, exhibits a distinct anisotropy with velocities parallel to the foliation being about 15 % higher than normal to the foliation plane. Measurements of the magnetic anisotropy in the bulk sample show that anisotropy is originating from the preferred orientation of muscovite, with a prominent flattening fabric. In contrast, specimens that underwent partial melting display a weaker elastic and magnetic anisotropy, because muscovite preferentially melts due to dehydration melting at 750 °C. The decrease in anisotropy can be inferred from in situ observation of elastic wave anisotropy, but also from comparison of measurements of magnetic anisotropy prior to and subsequent to experiment. A distinct anisotropy is however identified after the experiments both in susceptibility and remanence, which appears to be controlled by the original foliation. As muscovite undergoes dehydration melting a small amount of Fe is released into the melt. Crystallization from the melt indicates that the Fe is bound in biotite and Fe-oxides. The bulk susceptibility and saturation remanence increase by more than one order of magnitude in samples after the melting experiment. The newly formed ferrimagnetic phase, identified through hysteresis, IRM and thermomagnetic measurements, have a tight grouping in the magnetite pseudo-single-domain field on a Day plot. Our experiments are pertinent to the study of partially molten rocks and provide an opportunity to help guide research in magnetic and elastic wave anisotropy of migmatite and granite. In particular the results from experiments apply to the understanding of generation and percolation of melt prior to, or coeval to, the onset of deformation.

Almqvist, B.; Misra, S.; Biedermann, A. R.; Mainprice, D.

2013-12-01

334

Thin films of SmCo5 with very high perpendicular magnetic anisotropy  

Microsoft Academic Search

Thin films of SmCo5 with extraordinarily high perpendicular magnetic anisotropy were prepared by introducing a Cu\\/Ti dual underlayer and controlling the substrate temperature during the sputter deposition. Under optimized conditions, the magnetic anisotropy constant reached 4.0×107 erg\\/cm3, and the coercivity and the remanence ratio in the direction perpendicular to the film surface were 12.0 kOe and unity, respectively. The high

J. Sayama; K. Mizutani; T. Asahi; T. Osaka

2004-01-01

335

Magnetic fields at Neptune  

NASA Technical Reports Server (NTRS)

The Voyager 2 magnetic field experiment discovered a complex and powerful magnetic field in Neptune, as well as an associated magnetosphere and magnetic tail. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar. The auroral zones are probably located far from the rotation poles, and may possess complex geometry. The Neptune rings and all its known moons are imbedded deep within the magnetosphere (except for Nereid, which is outside when it lies sunward of the planet); the radiation belts have a complex structure due to the absorption of energetic particles by the moons and rings of Neptune, as well as losses associated with the significant changes in the diurnally varying magnetosphere configuration.

Ness, Norman F.; Acuna, Mario H.; Burlaga, Leonard F.; Connerney, John E. P.; Lepping, Ronald P.

1989-01-01

336

Spectra and anisotropy of magnetic fluctuations in the Earth's magnetosheath: Cluster observations  

NASA Astrophysics Data System (ADS)

We investigate the spectral shape, the anisotropy of the wave vector distributions and the anisotropy of the amplitudes of the magnetic fluctuations in the Earth's magnetosheath within a broad range of frequencies [10-3, 10] Hz which corresponds to spatial scales from ~10 to 105 km. We present the first observations of a Kolmogorov-like inertial range of Alfvénic fluctuations ?B2⊥}~f-5/3 in the magnetosheath flanks, below the ion cyclotron frequency fci. In the vicinity of fci, a spectral break is observed, like in solar wind turbulence. Above the break, the energy of compressive and Alfvénic fluctuations generally follows a power law with a spectral index between -3 and -2. Concerning the anisotropy of the wave vector distribution, we observe a clear change in its nature in the vicinity of ion characteristic scales: if at MHD scales there is no evidence for a dominance of a slab (k?>>k⊥) or 2-D (k⊥>>k?) turbulence, above the spectral break, (f>fci, kc/?pi>1) the 2-D turbulence dominates. This 2-D turbulence is observed in six selected one-hour intervals among which the average ion ? varies from 0.8 to 10. It is observed for both the transverse and compressive magnetic fluctuations, independently on the presence of linearly unstable modes at low frequencies or Alfvén vortices at the spectral break. We then analyse the anisotropy of the magnetic fluctuations in a time dependent reference frame based on the field B and the flow velocity V directions. Within the range of the 2-D turbulence, at scales [1,30]kc/?pi, and for any ? we find that the magnetic fluctuations at a given frequency in the plane perpendicular to B have more energy along the B×V direction. This non-gyrotropy of the fluctuations at a fixed frequency is consistent with gyrotropic fluctuations at a given wave vector, with k⊥>>k?, which suffer a different Doppler shift along and perpendicular to V in the plane perpendicular to B.

Alexandrova, O.; Lacombe, C.; Mangeney, A.

2008-11-01

337

The Sun and Magnetic Fields  

NSDL National Science Digital Library

In this activity about magnetic fields and their relation to the Sun, learners will simulate sunspots by using iron filings to show magnetic fields around a bar or cow magnet, and draw the magnetic field surrounding two dipole magnets, both in parallel and perpendicular alignments. Finally, learners examine images of sunspots to relate their magnetic field drawings and observations to what is seen on the Sun.

338

The influence of structural disorder on magnetic domain formation in perpendicular anisotropy thin films  

E-print Network

The influence of structural disorder on magnetic domain formation in perpendicular anisotropy thin of California, San Diego, La Jolla CA 92093 10 Center for Magnetic Recording Research, University of California techniques we have investigated the magnetic properties and microstructure of a series of perpendicular

Fainman, Yeshaiahu

339

Graphene Magnetic Field Sensors  

Microsoft Academic Search

Graphene extraordinary magnetoresistance (EMR) devices have been fabricated and characterized in varying magnetic fields at room temperature. The atomic thickness, high carrier mobility and high current carrying capabilities of graphene are ideally suited for the detection of nanoscale sized magnetic domains. The device sensitivity can reach 10 mV\\/Oe, larger than state of the art InAs 2DEG devices of comparable size

Simone Pisana; Patrick M. Braganca; Ernesto E. Marinero; Bruce A. Gurney

2010-01-01

340

Layering and temperature-dependent magnetization and anisotropy of naturally produced Ni/NiO multilayers  

SciTech Connect

Ni/NiO multilayers were grown by magnetron sputtering at room temperature, with the aid of the natural oxidation procedure. That is, at the end of the deposition of each single Ni layer, air is let to flow into the vacuum chamber through a leak valve. Then, a very thin NiO layer ({approx}1.2 nm) is formed. Simulated x-ray reflectivity patterns reveal that layering is excellent for individual Ni-layer thickness larger than 2.5 nm, which is attributed to the intercalation of amorphous NiO between the polycrystalline Ni layers. The magnetization of the films, measured at temperatures 5-300 K, has almost bulk-like value, whereas the films exhibit a trend to perpendicular magnetic anisotropy (PMA) with an unusual significant positive interface anisotropy contribution, which presents a weak temperature dependence. The power-law behavior of the multilayers indicates a non-negligible contribution of higher order anisotropies in the uniaxial anisotropy. Bloch-law fittings for the temperature dependence of the magnetization in the spin-wave regime show that the magnetization in the multilayers decreases faster as a function of temperature than the one of bulk Ni. Finally, when the individual Ni-layer thickness decreases below 2 nm, the multilayer stacking vanishes, resulting in a dramatic decrease of the interface magnetic anisotropy and consequently in a decrease of the perpendicular magnetic anisotropy.

Pappas, S. D.; Trachylis, D.; Velgakis, M. J. [Laboratory of High-Tech Materials, School of Engineering, University of Patras, 26504 Patras (Greece); Kapaklis, V.; Joensson, P. E.; Papaioannou, E. Th. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Delimitis, A. [Chemical Process Engineering Research Institute (CPERI), Centre for Research and Technology Hellas (CERTH), 57001 Thermi, Thessaloniki (Greece); Poulopoulos, P. [Laboratory of High-Tech Materials, School of Engineering, University of Patras, 26504 Patras (Greece); Institut fuer Experimentalphysik, Freie Universitaet Berlin, Arnimallee 14, D-14195 Berlin-Dahlem (Germany); Materials Science Department, University of Patras, 26504 Patras (Greece); Fumagalli, P. [Institut fuer Experimentalphysik, Freie Universitaet Berlin, Arnimallee 14, D-14195 Berlin-Dahlem (Germany); Politis, C. [Laboratory of High-Tech Materials, School of Engineering, University of Patras, 26504 Patras (Greece); Department of Materials Science and Engineering, University of Texas at Arlington, Arlington, Texas 76019 (United States)

2012-09-01

341

Magnetic films of negative Poisson’s ratio in rotating magnetic fields  

Microsoft Academic Search

Mechanical properties of a thin magnetic film subjected to an external, rotating magnetic field have been studied by computer simulations. The film is modeled by a two-dimensional bead-spring model of a non-magnetic polymer matrix with inclusions of magnetic nanoparticles (nanograins) of uniaxial anisotropy. The isotropic polymer matrix is represented as a hexagonal structure with sites decorated with small hexagonal particles

Miros?aw R. Dudek; Krzysztof W. Wojciechowski

2008-01-01

342

Magnetic Susceptibility Anisotropy of Human Brain in vivo and its Molecular Underpinnings  

PubMed Central

Frequency shift of gradient-echo MRI provides valuable information for assessing brain tissues. Recent studies suggest that the frequency and susceptibility contrast depend on white matter fiber orientation. However, the molecular underpinning of the orientation dependence is unclear. In this study, we investigated the orientation dependence of susceptibility of human brain in vivo and mouse brains ex vivo. The source of susceptibility anisotropy in white matter is likely to be myelin as evidenced by the loss of anisotropy in the dysmyelinating shiverer mouse brain. A biophysical model is developed to investigate the effect of the molecular susceptibility anisotropy of myelin components, especially myelin lipids, on the bulk anisotropy observed by MRI. This model provides a consistent interpretation of the orientation dependence of macroscopic magnetic susceptibility in normal mouse brain ex vivo and human brain in vivo and the microscopic origin of anisotropic susceptibility. It is predicted by the theoretical model and illustrated by the experimental data that the magnetic susceptibility of the white matter is least diamagnetic along the fiber direction. This relationship allows an efficient extraction of fiber orientation using susceptibility tensor imaging. These results suggest that anisotropy on the molecular level can be observed on the macroscopic level when the molecules are aligned in a highly ordered manner. Similar to the utilization of magnetic susceptibility anisotropy in elucidating molecular structures, imaging magnetic susceptibility anisotropy may also provide a useful tool for elucidating the microstructure of ordered biological tissues. PMID:22036681

Li, Wei; Wu, Bing; Avram, Alexandru V.; Liu, Chunlei

2011-01-01

343

Influence of magnetic electrodes thicknesses on the transport properties of magnetic tunnel junctions with perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

The influence of the bottom and top magnetic electrodes thicknesses on both perpendicular anisotropy and transport properties is studied in (Co/Pt)/Ta/CoFeB/MgO/FeCoB/Ta magnetic tunnel junctions. By carefully investigating the relative magnetic moment of the two electrodes as a function of their thicknesses, we identify and quantify the presence of magnetically dead layers, likely localized at the interfaces with Ta, that is, 0.33 nm for the bottom electrode and 0.60 nm for the top one. Critical thicknesses (spin-reorientation transitions) are determined as 1.60 and 1.65 nm for bottom and top electrodes, respectively. The tunnel magnetoresistance ratio reaches its maximum value, as soon as both effective (corrected from dead layer) electrode thicknesses exceed 0.6 nm.

Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Dieny, Bernard

2014-08-01

344

Influence of magnetic electrodes thicknesses on the transport properties of magnetic tunnel junctions with perpendicular anisotropy  

SciTech Connect

The influence of the bottom and top magnetic electrodes thicknesses on both perpendicular anisotropy and transport properties is studied in (Co/Pt)/Ta/CoFeB/MgO/FeCoB/Ta magnetic tunnel junctions. By carefully investigating the relative magnetic moment of the two electrodes as a function of their thicknesses, we identify and quantify the presence of magnetically dead layers, likely localized at the interfaces with Ta, that is, 0.33?nm for the bottom electrode and 0.60?nm for the top one. Critical thicknesses (spin-reorientation transitions) are determined as 1.60 and 1.65?nm for bottom and top electrodes, respectively. The tunnel magnetoresistance ratio reaches its maximum value, as soon as both effective (corrected from dead layer) electrode thicknesses exceed 0.6?nm.

Cuchet, Léa; Rodmacq, Bernard; Auffret, Stéphane; Sousa, Ricardo C.; Dieny, Bernard [SPINTEC, UMR 8191, CEA-INAC/CNRS/UJF-Grenoble 1/Grenoble-INP, 38054 Grenoble Cedex (France)

2014-08-04

345

Magnetic Field and Life  

NSDL National Science Digital Library

This is a lesson where learners explore magnetic forces, fields, and the relationship between electricity. Learners will use this information to infer how the Earth generates a protective magnetic field. The lesson models scientific inquiry using the 5E instructional model and includes teacher notes, prerequisite concepts, common misconceptions, student journal and reading. This is lesson seven in the Astro-Venture Geology Training Unit that were developed to increase students' awareness of and interest in astrobiology and the many career opportunities that utilize science, math and technology skills. The lessons are designed for educators to use with with the Astro-Venture multimedia modules.

346

Multiwavelength Magnetic Field Modeling  

NASA Astrophysics Data System (ADS)

We model the large-scale Galactic magnetic fields, including a spiral arm compression to generate anisotropic turbulence, by comparing polarized synchrotron and thermal dust emission. Preliminary results show that in the outer Galaxy, the dust emission comes from regions where the fields are more ordered than average while the situation is reversed in the inner Galaxy. We will attempt in subsequent work to present a more complete picture of what the comparison of these observables tells us about the distribution of the components of the magnetized ISM and about the physics of spiral arm shocks and turbulence.

Jaffe, T. R.

2015-03-01

347

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

The origin and evolution of cosmic magnetic fields, their strength and structure in intergalactic space, their first occurrence in young galaxies, and their dynamical importance for galaxy evolution remain widely unknown. Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized radio synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important; they can affect gas flows and drive gas inflows in central regions. Polarized radio emission traces ordered fields which can be regular or anisotropic turbulent, generated from isotropic turbulent fields by compression or shear. The strongest ordered fields of 10-15 ?G strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. In galaxies with strong density waves, ordered (anisotropic turbulent) fields are also observed at the inner edges of the spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Irregular galaxies host isotropic turbulent fields often of similar strength as in spiral galaxies, but only weak ordered fields. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several galaxies reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by a mean-field ? -? dynamo. So far no indications were found in external galaxies of large-scale field reversals, like the one in the Milky Way. Ordered magnetic fields are also observed in radio halos around edge-on galaxies out to large distances from the plane, with X-shaped patterns. In the outflow cone above a starburst region of NGC 253, RM data indicate a helical magnetic field.

Beck, Rainer

348

Electromagnetic electron temperature anisotropy instabilities  

NASA Technical Reports Server (NTRS)

This paper considers electromagnetic Vlasov instabilities driven by electron temperature anisotropies in a homogeneous, nonrelativistic magnetized plasma. Numerical solutions of the full linear dispersion equation for bi-Maxwellian distribution functions and instabilities propagating parallel to the magnetic field are presented. Parametric dependences of the maximum growth rates of the electron fire hose and whistler anisotropy instabilities are given.

Gary, S. P.; Madland, C. D.

1985-01-01

349

Electromagnetic electron temperature anisotropy instabilities  

NASA Astrophysics Data System (ADS)

This paper considers electromagnetic Vlasov instabilities driven by electron temperature anisotropies in a homogeneous, nonrelativistic magnetized plasma. Numerical solutions of the full linear dispersion equation for bi-Maxwellian distribution functions and instabilities propagating parallel to the magnetic field are presented. Parametric dependences of the maximum growth rates of the electron fire hose and whistler anisotropy instabilities are given.

Gary, S. P.; Madland, C. D.

1985-08-01

350

Magnetic Domains and Anisotropy in the Magnetic Semiconductor GaMnAs  

NASA Astrophysics Data System (ADS)

The magnetic properties of Ga_1-xMn_xAs grown epitaxially on (001) GaAs have been investigated using magnetometry and magneto-optical domain imaging. As-grown samples with x 0.03 and Tc 60 K have been studied. The compressive strains resulting from the lattice mismatch between GaMnAs and GaAs induce magnetic moment orientation in the film plane. We observe clear evidence for a temperature dependent in-plane magnetic anisotropy. At temperatures above about T_c/2 the samples show uniaxial anisotropy unusual for (001) films with easy axis along a [110]-direction, whereas at temperatures below T_c/2 two easy axes emerge which at low temperatures approach the [100] and [010] directions. The magnetization reversal proceeds through the nucleation and expansion of large (several hundred microns), well defined domains. In the biaxial state ˜ 90-deg domains and in the uniaxial state 180-deg domains are observed. The domain boundaries show some roughness and pinning indicative of some degree of sample inhomogeneity. This work was supported by the US Department of Energy, Basic Energy Science under contract W-31-109-ENG-38; and by the NSF grant DMR02-10519.

Vlasko-Vlasov, Vitali; Welp, Ulrich; Liu, Xinyu; Furdyna, Jacek; Wojtowicz, T.

2003-03-01

351

Tailoring the magnetic anisotropy, magnetization reversal, and anisotropic magnetoresistance of Ni films by ion sputtering  

NASA Astrophysics Data System (ADS)

We studied surface morphology induced changes of magnetic anisotropy, magnetization reversal, and symmetry of the anisotropic magnetoresistance (AMR) in ion sputtered Ni films grown on MgO (001). Grazing-incidence ion sputtering generally develops anisotropic surface roughness of the Ni films, i.e., nanometer wide ripples parallel to the ion beam direction, giving rise to uniaxial magnetic anisotropy with the easy axis along the ion beam direction. The formed ripples act as domain wall nucleation and pinning sites during magnetization reversal, while two-jump domain wall motion dominates in the as-grown Ni films. More importantly, the azimuthal angular dependence of the AMR indicates a superposition of twofold symmetry and fourfold symmetry. By relying on grazing-incidence ion sputtering along specific crystallographic directions, we are able to tailor the relative weight of twofold and fourfold symmetry of AMR. We demonstrate that in contrast to the bulk case, the symmetry of the AMR becomes also sensitive to the surface morphology in thin films, which is in particular relevant for the design of magnetotransport based sensors.

Liu, Hao-liang; ŠkereÅ, Tomáš; Volodin, Alexander; Temst, Kristiaan; Vantomme, André; Van Haesendonck, Chris

2015-03-01

352

Magnetic domains and anisotropy in single crystals of Er(Co,Mn)O 3  

NASA Astrophysics Data System (ADS)

We have previously reported the magnetic properties of the Er(Co,Mn)O 3 solid solution, in which Mn atoms have been partially substituted by Co. Several magnetic entities coexist in this system (Er 3+, Mn 3+, Mn 4+, Co 2+, Co 3+), resulting into a subtle interplay between different interactions and leading to unusual phenomena such as: a spin reversal due to antiferromagnetic exchange between erbium and transition-metal spins, a step-like transition due to reorientation of magnetic domains, a relaxation mechanism connected to the rotation energy of the domains, the intersection of the increasing and decreasing branches in the magnetization loops, etc. These results have been obtained in highly dense ceramic samples for compositions near ErCo 0.50Mn 0.50O 3. In order to better understand the different mechanisms, we have started a program on crystal growth. High-quality single crystals of orthorhombic structure (S.G. Pbnm) of Er(Co,Mn)O 3 manganite were grown in a floating-zone oven under oxygen atmosphere. Although the zero-field-cooled/field cooled (ZFC/FC) curves confirm the spin reversal observed in bulk samples, the remarkable effects seen on hysteresis loops for bulk samples were not present in single crystals, probably due to oxygenation conditions. On the other hand, a very large anisotropy was observed between two perpendicular orientations of the single crystal.

Antunes, A. B.; Ceretti, M.; Paulus, W.; Roisnel, T.; Gil, V.; Moure, C.; Peña, O.

353

High field superconducting magnets  

NASA Technical Reports Server (NTRS)

A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

2011-01-01

354

A co-crystal of polyoxometalates exhibiting single-molecule magnet behavior: the structural origin of a large magnetic anisotropy  

SciTech Connect

A polyoxometalate-based {MnIII3MnIV} single-molecule magnet exhibits a large axial anisotropy (D = ?0.86 cm?1) resulting from a near-parallel alignment of Jahn–Teller axes. Its rigorous three-fold symmetry (i.e. rhombicity E ? 0) and increased intercluster separation via co-crystallization effectively hamper quantum tunnelling of the magnetization. Graphical abstract: A co-crystal of polyoxometalates exhibiting single-molecule magnet behavior: the structural origin of a large magnetic anisotropy

Fang, Xikui; McCallum, Kendall; Pratt III, Harry D.; Anderson, Travis M.; Dennis, Kevin; Luban, Marshall

2012-03-29

355

Effect of electron thermal anisotropy on the kinetic cross-field streaming instability  

NASA Technical Reports Server (NTRS)

The investigation of the kinetic cross-field streaming instability, motivated by the research of collisionless shock waves and previously studied by Wu et al. (1983), is discussed more fully. Since in the ramp region of a quasi-perpendicular shock electrons can be preferentially heated in the direction transverse to the ambient magnetic field, it is both desirable and necessary to include the effect of the thermal anisotropy on the instability associated with a shock. It is found that Te-perpendicular greater than Te-parallel can significantly enhance the peak growth rate of the cross-field streaming instability when the electron beta is sufficiently high. Furthermore, the present analysis also improves the analytical and numerical solutions previously obtained.

Tsai, S. T.; Tanaka, M.; Gaffey, J. D., Jr.; Wu, C. S.; Da Jornada, E. H.; Ziebell, L. F.

1984-01-01

356

Magnetic fields at Uranus  

NASA Technical Reports Server (NTRS)

The conclusions drawn regarding the structure, behavior and composition of the Uranian magnetic field and magnetosphere as revealed by Voyager 2 data are summarized. The planet had a bipolar magnetotail and a bow shock wave which was observed 23.7 Uranus radii (UR) upstream and a magnetopause at 18.0 UR. The magnetic field observed can be represented by a dipole offset from the planet by 0.3 UR. The field vector and the planetary angular momentum vector formed a 60 deg angle, permitting Uranus to be categorized as an oblique rotator, with auroral zones occurring far from the rotation axis polar zones. The surface magnetic field was estimated to lie between 0.1-1.1 gauss. Both the field and the magnetotail rotated around the planet-sun line in a period of about 17.29 hr. Since the ring system is embedded within the magnetosphere, it is expected that the rings are significant absorbers of radiation belt particles.

Ness, N. F.; Acuna, M. H.; Behannon, K. W.; Burlaga, L. F.; Connerney, J. E. P.; Lepping, R. P.

1986-01-01

357

Magnetic and structural characterization of high anisotropy cobalt-rich alloys: Thin films and patterns  

Microsoft Academic Search

In this dissertation the structural and magnetic characterization of high anisotropy Co-rich alloys for magnetic recording and MEMS applications has been carried out. The potential of Co78Sm22 as an ultra-high density recording medium was explored through comprehensive static and dynamic magnetic measurements. It was found out that hard magnetic properties (Hc = 4.5 kOe) can be achieved when CoSm is

Iulica Zana

2003-01-01

358

Spin-canting and magnetic anisotropy in ultrasmall CoFe2O4 nanoparticles.  

PubMed

The magnetic properties of cobalt ferrite nanoparticles dispersed in a silica matrix in samples with different concentrations (5 and 10 wt% CoFe2O 4) and same particle size (3 nm) were studied by magnetization, DC and AC susceptibility, and Mossbauer spectroscopy measurements. The results indicate that the particles are very weakly interacting. The magnetic properties (saturation magnetization, anisotropy constant, and spin-canting) are discussed in relation to the cation distribution. PMID:18590326

Peddis, D; Mansilla, M V; Mørup, S; Cannas, C; Musinu, A; Piccaluga, G; D'Orazio, F; Lucari, F; Fiorani, D

2008-07-24

359

Magnetostrictive behaviors of Fe-Si(001) single-crystal films under rotating magnetic fields  

NASA Astrophysics Data System (ADS)

Magnetostrictive behaviors under rotating magnetic fields are investigated for bcc(001) single-crystal films of Fe100-x-Six(x = 0, 6, 10 at. %). The magnetostriction observation directions are along bcc[100] and bcc[110] of the films. The magnetostriction waveform varies greatly depending on the observation direction. For the observation along [100], the magnetostriction waveform of all the films is bathtub-like and the amplitude stays at almost constant even when the magnetic field is increased up to the anisotropy field. On the other hand, the waveform along [110] is triangular and the amplitude increases with increasing magnetic field up to the anisotropy field and then saturates. In addition, the waveform of Fe90Si10 film is distorted triangular when the applied magnetic fields are less than its anisotropy field. These magnetostrictive behaviors under rotating magnetic fields are well explained by employing a proposed modified coherent rotation model where the anisotropy field and the magnetization reversal field are determined by using measured magnetization curves. The results show that magnetocrystalline anisotropy plays important role on magnetostrictive behavior under rotating magnetic fields.

Kawai, Tetsuroh; Aida, Takuya; Ohtake, Mitsuru; Futamoto, Masaaki

2015-05-01

360

Fiber Optic Magnetic Field Sensors Using Metallic Glass Coatings  

Microsoft Academic Search

In this thesis we have investigated the use of a magnetostrictive material with a single-mode optical fiber for detecting weak magnetic fields. The amorphous alloy Metglas^circler 2605SC (Fe_{81}B_ {13.5}Si_{3.5} C_2) was chosen as the magnetostrictive material because of the combination of its large magnetostriction and small magnetic anisotropy field among all available metals. For efficient coupling between the magnetostrictive material

Yu. Wang

1990-01-01

361

Evolution of Stellar Magnetic Fields  

NASA Astrophysics Data System (ADS)

Stellar magnetic fields can reliably be characterized by several magnetic activity indicators, such as X-ray or radio luminosity. Physical processes leading to such emission provide important information on dynamic processes in stellar atmospheres and magnetic structuring.

Güdel, Manuel

2015-03-01

362

Ferroelectric switching induced magnetic anisotropy in Fe/BaTiO3 bilayers  

NASA Astrophysics Data System (ADS)

Ferromagnetic/ferroelectric heterostructures have recently attracted significantly interest due to their potential applications in multifunctional electronic devices. We have recently predicted a magnetoelectric effect at the Fe/BaTiO3 interface induced by ferroelectric polarization reversal [1]. In this report, calculations are being carried out on the magnetic anisotropy of Fe/BaTiO3 films. Preliminary results show that the ferroelectric switching of the BaTiO3 has appreciable effect on the magnetic anisotropy of magnetic Fe films. This should be of interest in multiferroic device applications. [1] Chun-gang Duan, S. S. Jaswal, E. Y. Tsymbal, Phys. Rev. Lett. 97, 047201 (2006).

Duan, Chun-Gang; Jaswal, S. S.; Tsymbal, E. Y.

2007-03-01

363

Magnetic Fields and Forces in Permanent Magnet Levitated Bearings  

Microsoft Academic Search

Magnetic fields and magnetic forces from magnetic bearings made of circular Halbach permanent-magnet arrays are computed and analyzed. The magnetic fields are calculated using superposition of fields due to patches of magnetization charge at surfaces where the magnetization is discontinuous. The magnetic force from the magnetic bearing is computed using superposition of forces on each patch of magnetization charge. The

Kevin D. Bachovchin; James F. Hoburg; Richard F. Post

2012-01-01

364

Magnetic and elastic anisotropy in magnetorheological elastomers using nickel-based nanoparticles and nanochains  

SciTech Connect

Nickel (Ni) based nanoparticles and nanochains were incorporated as fillers in polydimethylsiloxane (PDMS) elastomers and then these mixtures were thermally cured in the presence of a uniform magnetic field. In this way, macroscopically structured-anisotropic PDMS-Ni based magnetorheological composites were obtained with the formation of pseudo-chains-like structures (referred as needles) oriented in the direction of the applied magnetic field when curing. Nanoparticles were synthesized at room temperature, under air ambient atmosphere (open air, atmospheric pressure) and then calcined at 400?°C (in air atmosphere also). The size distribution was obtained by fitting Small Angle X-ray Scattering (SAXS) experiments with a polydisperse hard spheres model and a Schulz-Zimm distribution, obtaining a size distribution centered at (10.0?±?0.6) nm with polydispersivity given by ??=?(8.0?±?0.2) nm. The SAXS, X-ray powder diffraction, and Transmission Electron Microscope (TEM) experiments are consistent with single crystal nanoparticles of spherical shape (average particle diameter obtained by TEM: (12?±?1) nm). Nickel-based nanochains (average diameter: 360?nm; average length: 3??m, obtained by Scanning Electron Microscopy; aspect ratio?=?length/diameter ? 10) were obtained at 85?°C and ambient atmosphere (open air, atmospheric pressure). The magnetic properties of Ni-based nanoparticles and nanochains at room temperature are compared and discussed in terms of surface and size effects. Both Ni-based nanoparticles and nanochains were used as fillers for obtaining the PDMS structured magnetorheological composites, observing the presence of oriented needles. Magnetization curves, ferromagnetic resonance (FMR) spectra, and strain-stress curves of low filler's loading composites (2% w/w of fillers) were determined as functions of the relative orientation with respect to the needles. The results indicate that even at low loadings it is possible to obtain magnetorheological composites with anisotropic properties, with larger anisotropy when using nanochains. For instance, the magnetic remanence, the FMR field, and the elastic response to compression are higher when measured parallel to the needles (about 30% with nanochains as fillers). Analogously, the elastic response is also anisotropic, with larger anisotropy when using nanochains as fillers. Therefore, all experiments performed confirm the high potential of nickel nanochains to induce anisotropic effects in magnetorheological materials.

Landa, Romina A.; Soledad Antonel, Paula; Ruiz, Mariano M.; Negri, R. Martín, E-mail: rmn@qi.fcen.uba.ar [Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Instituto de Química Física de Materiales, Ambiente y Energía (INQUIMAE), Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, C1428EGA Buenos Aires (Argentina); Perez, Oscar E. [Departamento de Industrias, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Butera, Alejandro [Centro Atómico Bariloche (Comisión Nacional de Energía Atómica. Argentina) and Instituto Balseiro, Universidad Nacional de Cuyo, Mendoza (Argentina); Jorge, Guillermo [Instituto de Ciencias, Universidad Nacional de General Sarmiento, Buenos Aires (Argentina); Oliveira, Cristiano L. P. [Grupo de Fluidos Complexos, Instituto de Física, Universidade de São Paulo, São Paulo (Brazil)

2013-12-07

365

Magnetic Field of the Earth  

NSDL National Science Digital Library

Students can learn about how the magnetic field of the earth is similar to magnets. Go to the following link: Magnetic Field of the Earth 1. What makes the earth like a magnet? 2. How do we measure magnetism? Be sure to check out the fun games and activities on this web site too!! Now click on the following link and listen to a 2 minute presentation about magnetism: Pulse Planet Next go to ...

Mrs. Merritt

2005-10-18

366

Effect of Resputtering on Perpendicular Magnetic Anisotropy in Amorphous GdCo Thin Films  

Microsoft Academic Search

In order to control resputtering during the sputtering formation of amorphous thin films, a wire mesh in DC sputtering equipment were used to suppress resputtering, and the effects of resputtering on magnetic anisotropy in GdCo films were studied. The measured values for Keff and Ms indicated that nearly all films had in-plane magnetizations, and under the film deposition conditions, through

M. Nakahashi; S. Shiomi; M. Masuda

1985-01-01

367

Correlation between magnetic anisotropy and fabric for Devonian shales on the Appalachian Plateau  

Microsoft Academic Search

The magnetic anisotropy of Devonian black shale samples was measured from two cores drilled in the Appalachian Plateau. The mineralogy of the shales is predominantly clay, with small quantities of quartz and minor amounts of opaques and chlorite. Magnetite is the predominant ferromagnetic mineral present in the samples. The magnetic fabric was measured at both room temperature and liquid-nitrogen temperature

A. M. Hirt; K. F. Evans; T. Engelder

1995-01-01

368

Full magnetization process of 3d-4f hard magnetic materials in ultrahigh magnetic fields (an example: RFe11Ti)  

NASA Astrophysics Data System (ADS)

The prospects of using the free-powder high-field magnetization method for a quantitative study of inter-sublattice exchange interaction in 3d-4f hard magnetic materials are analyzed. Such analysis is stimulated by the availability of pulsed magnetic fields ˜103 T generated by implosion. Particular attention is paid to effects due to magnetic anisotropy, essential for these materials. The 3d-4f ferrimagnets where both sublattices contribute positively to the easy-axis anisotropy are shown to be suitable objects of study by the free-powder method, because (i) anomalies in their low-temperature magnetizatization curves are sharp and (ii) anisotropic effects can be allowed for without quantitative knowledge of the anisotropy constants. Moreover, these "good" hard magnetic materials can be brought into metamagnetic regime by diluting the rare earth sublattice with nonmagnetic yttrium; then, regardless of the anisotropy constants, the magnetization curve at low temperatures has just one steplike anomaly, the threshold field being equal exactly to the molecular field acting on the rare earth.

Kuz'min, M. D.; Zvezdin, A. K.

1998-03-01

369

Ferromagnetic resonance, magnetic susceptibility, and transformation of domain structure in CoFeB film with growth induced anisotropy  

NASA Astrophysics Data System (ADS)

Field dependence of magnetic susceptibility in nanocrystalline CoFeB film was studied in a wide frequency range from 500 kHz to 15 GHz. Anomalies of the susceptibility were detected exciting CoFeB film with a solenoidal coil, microwave strip line, in the tunable microwave cavity as well as employing magneto-optical domains imaging. Critical spin fluctuations in the form of "soft" modes were observed in a whole range of orientations of magnetic field perpendicular to the "easy" magnetic axis. A sequence of domain structure transformations was extensively examined in a "hard" direction in in-plane magnetic field reduced below the field of uniaxial anisotropy Hp = 535 Oe. At first, uniformly magnetized state in CoFeB film transforms to stripe domains separated by low angle Néel domain walls (DWs) parallel to the "hard"-axis. Then, at critical field Hcr = 232 Oe, Néel DWs gradually convert to the"easy"-axis oriented Bloch DWs loaded with vertical Bloch lines (VBLs). After field reversal at H = -Hcr, backward conversion of VBL-loaded Bloch DWs to Néel DWs results in instantaneous energy release and sharp anomaly of magnetic susceptibility. Appearance of critical spin fluctuations accomplishes domains transformation to the uniformly magnetized state at H = -535 Oe.

Manuilov, S. A.; Grishin, A. M.; Munakata, M.

2011-04-01

370

Crustal Magnetic Fields  

NASA Technical Reports Server (NTRS)

Cosmos 49, Polar Orbit Geophysical Observatory (POGO) (Orbiting Geophysical Observatory (OGO-2, 4 and 6)) and Magsat have been the only low-earth orbiting satellites to measure the crustal magnetic field on a global scale. These missions revealed the presence of long- wavelength (> 500 km) crustal anomalies predominantly located over continents. Ground based methods were, for the most part, unable to record these very large-scale features; no doubt due to the problems of assembling continental scale maps from numerous smaller surveys acquired over many years. Questions arose as to the source and nature of these long-wave length anomalies. As a result there was a great stimulant given to the study of the magnetic properties of the lower crust and upper mantle. Some indication as to the nature of these deep sources has been provided by the recent results from the deep crustal drilling programs. In addition, the mechanism of magnetization, induced or remanent, was largely unknown. For computational ease these anomalies were considered to result solely from induced magnetization. However, recent results from Mars Orbiter Laser Altimeter (MOLA), a magnetometer-bearing mission to Mars, have revealed crustal anomalies with dimensions similar to the largest anomalies on Earth. These Martian features could only have been produced by remanent magnetization, since Mars lacks an inducing field. The origin of long-wavelength crustal anomalies, however, has not been completely determined. Several large crustal magnetic anomalies (e.g., Bangui, Kursk, Kiruna and Central Europe) will be discussed and the role of future satellite magnetometer missions (Orsted, SUNSAT and Champ) in their interpretation evaluated.

Taylor, Patrick T.; Ravat, D.; Frawley, James J.

1999-01-01

371

Capping layer-tailored interface magnetic anisotropy in ultrathin Co2FeAl films  

NASA Astrophysics Data System (ADS)

Co2FeAl (CFA) thin films of various thicknesses (2 nm ? d ? 50 nm) have been grown on (001) MgO single crystal substrates and then capped with Cr, V, and Ta. Their magnetic and structural properties have been studied by x-ray diffraction (XRD), vibrating sample magnetometry, and broadband microstrip ferromagnetic resonance (MS-FMR). The XRD revealed that the films are epitaxial with the cubic [001] CFA axis normal to the substrate plane and that the chemical order varies from the B2 phase to the A2 phase when decreasing the thickness. The deduced lattice parameters showed that the Cr-capped films exhibit a larger tetragonal distortion, as compared with the films capped with V or Ta. The presence of magnetic dead layers has been observed in CFA samples capped with V and Ta but not in the case of the Cr-capped ones. The effective magnetization, deduced from the fit of MS-FMR measurements, increases (decreases) linearly with the CFA inverse thickness (1/d) for the Cr-capped (Ta-capped) films while it is constant for the V-capped ones. This allows quantifying the perpendicular surface anisotropy coefficients of -0.46 erg/cm2 and 0.74 erg/cm2 for Cr and Ta-capped films, respectively. Moreover, the fourfold and the uniaxial anisotropy fields, measured in these films, showed different trends with a respect to the CFA inverse thickness. This allows inferring that a non-negligible part of the fourfold magnetocrystalline term is of interfacial origin.

Belmeguenai, M.; Gabor, M. S.; Petrisor, T.; Zighem, F.; Chérif, S. M.; Tiusan, C.

2015-01-01

372

Nonlithographic fabrication of 25 nm magnetic nanodot arrays with perpendicular anisotropy over a large area  

SciTech Connect

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm{sup 2} coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO{sub 2} dot arrays formed on a Si wafer. At first, arrays of the SiO{sub 2} dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO{sub 2} dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO{sub 2} dots are about 24, 43, and 17 nm, respectively. Then (Co(0.4 nm)/Pt(0.08 nm)){sub 8} MLs with a 3 nm Pt buffer layer is deposited onto the SiO{sub 2} dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO{sub 2} substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner-Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array.

Rahman, M. Tofizur; Shams, Nazmun N.; Lai, C.-H. [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

2009-04-01

373

Anisotropy of the magnetic properties and the electronic structure of transition-metal diborides  

Microsoft Academic Search

The temperature dependences of the magnetic susceptibility chi and its anisotropy Deltachi=chi||-chi? have been measured for hexagonal single crystals of transition-metal diborides MB2 (M=Sc,Ti,V,Zr,Hf) in the temperature interval 4.2-300 K. It is found that the anisotropy Deltachi is weakly temperature-dependent, a nonmonotonic function of the filling of the hybridized p-d conduction band, and largest for group-IV transition metals. First-principles calculations

A. V. Fedorchenko; G. E. Grechnev; A. S. Panfilov; A. V. Logosha; I. V. Svechkarev; V. B. Filippov; A. B. Lyashchenko; A. V. Evdokimova

2009-01-01

374

Magnetic anisotropy and magnetostriction in cobalt-ferrite with lattice deformation  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy (MA) energy induced by uniform lattice deformation is calculated for cobalt-ferrites Fe(Co-Fe)2O4 (CFOs) by using an electron theory for down-spin t2g electrons of Co2+ ions in CFOs. It is shown that the MA energy depends nonlinearly and asymmetrically on the uniform lattice deformation. By comparing the calculated results with those obtained in the phenomenological theory at the small lattice deformation limit, values of the magnetoelastic coefficients B1 and B2 have been evaluated. These values semi-quantitatively agree with the experimental ones. A non-trivial appearance of crystal-field potentials produced by the uniform trigonal lattice deformation is crucial to understand the large negative value of B2.

Inoue, Jun-ichiro; Yanagihara, Hideto; Kita, Eiji

2014-12-01

375

The WIND magnetic field investigation  

Microsoft Academic Search

The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and

R. P. Lepping; M. H. Ac?na; L. F. Burlaga; W. M. Farrell; J. A. Slavin; K. H. Schatten; F. Mariani; N. F. Ness; F. M. Neubauer; Y. C. Whang; J. B. Byrnes; R. S. Kennon; P. V. Panetta; J. Scheifele; E. M. Worley

1995-01-01

376

Magnetic Field Topology in Jets  

NASA Technical Reports Server (NTRS)

We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.

Gardiner, T. A.; Frank, A.

2000-01-01

377

Low field magnetic resonance imaging  

DOEpatents

A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.

Pines, Alexander (Berkeley, CA); Sakellariou, Dimitrios (Billancourt, FR); Meriles, Carlos A. (Fort Lee, NJ); Trabesinger, Andreas H. (London, GB)

2010-07-13

378

Magnetic Field Problem: Current and Magnets  

NSDL National Science Digital Library

The above animations represent two typical bar magnets each with a North and South pole. The arrows represent the direction of the magnetic field. A wire is placed between the magnets and a current that comes out of the page can be turned on.

Wolfgang Christian

379

Magnetic behavior of cosputtered Fe-Zr amorphous thin films exhibiting perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Excellent mechanical properties of amorphous or glassy metals along with the capability to fabricate sub-50-nm patterns promise their application as a futuristic material for production of various nano- or microelectromechanical systems. In addition to their applications, these materials pose a lot of challenges in understanding their fundamental properties because of their random structure and involvement of three or more different kinds of atoms. The amorphous Fe-Zr system which is reported to exhibit superconductivity, ferromagnetism, spin glass, and antiferromagnetism is an ideal system to understand. The controversial magnetic properties of this system are still a subject of debate. In the present paper we revisited Fe-Zr system and studied their detailed magnetic properties in the temperature range of 5-330 K. FexZr100-x ( x=63 , 68, 76, 86, 92, and 93at.% ) thin films were deposited on silicon (100) substrate by a cosputtering technique. The Curie temperature (Tc) is shown to increase almost linearly with an increase in Fe concentration, but it decreases rapidly for the Fe-rich films. The films with x up to ˜86at.% have a strange shape of the hysteresis loop and are shown to exhibit perpendicular magnetic anisotropy with a stripe domain structure. Hysteresis loop shapes are correlated with the magnetic structure of the films, and provide an easy understanding of magnetic properties. It has been shown that the Fe-rich films are composed of antiferromagnetic Fe clusters which are embedded in the ferromagnetic amorphous FeZr.

Sharma, Parmanand; Kimura, Hisamichi; Inoue, Akihisa

2008-10-01

380

Probing Magnetic Fields With SNRs  

NASA Astrophysics Data System (ADS)

As supernova remnants (SNRs) expand, their shock waves freeze in and compress magnetic field lines they encounter; consequently we can use SNRs as magnifying glasses for interstellar magnetic fields. A simple model is used to derive polarization and rotation measure (RM) signatures of SNRs. This model is exploited to gain knowledge about the large-scale magnetic field in the Milky Way. Three examples are given which indicate a magnetic anomaly, an azimuthal large-scale magnetic field towards the anti-centre, and a chimney that releases magnetic energy from the plane into the halo.

Kothes, Roland

2015-03-01

381

The Galactic Magnetic Field  

NASA Astrophysics Data System (ADS)

With this Letter, we complete our model of the Galactic magnetic field (GMF), by using the WMAP7 22 GHz total synchrotron intensity map and our earlier results to obtain a 13-parameter model of the Galactic random field, and to determine the strength of the striated random field. In combination with our 22-parameter description of the regular GMF, we obtain a very good fit to more than 40,000 extragalactic Faraday rotation measures and the WMAP7 22 GHz polarized and total intensity synchrotron emission maps. The data call for a striated component to the random field whose orientation is aligned with the regular field, having zero mean and rms strength ?20% larger than the regular field. A noteworthy feature of the new model is that the regular field has a significant out-of-plane component, which had not been considered earlier. The new GMF model gives a much better description of the totality of data than previous models in the literature.

Jansson, Ronnie; Farrar, Glennys R.

2012-12-01

382

THE GALACTIC MAGNETIC FIELD  

SciTech Connect

With this Letter, we complete our model of the Galactic magnetic field (GMF), by using the WMAP7 22 GHz total synchrotron intensity map and our earlier results to obtain a 13-parameter model of the Galactic random field, and to determine the strength of the striated random field. In combination with our 22-parameter description of the regular GMF, we obtain a very good fit to more than 40,000 extragalactic Faraday rotation measures and the WMAP7 22 GHz polarized and total intensity synchrotron emission maps. The data call for a striated component to the random field whose orientation is aligned with the regular field, having zero mean and rms strength Almost-Equal-To 20% larger than the regular field. A noteworthy feature of the new model is that the regular field has a significant out-of-plane component, which had not been considered earlier. The new GMF model gives a much better description of the totality of data than previous models in the literature.

Jansson, Ronnie; Farrar, Glennys R. [Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10003 (United States)

2012-12-10

383

A large scale coherent magnetic field: interactions with free streaming particles and limits from the CMB  

SciTech Connect

We study a homogeneous and nearly-isotropic Universe permeated by a homogeneous magnetic field. Together with an isotropic fluid, the homogeneous magnetic field, which is the primary source of anisotropy, leads to a plane-symmetric Bianchi I model of the Universe. However, when free-streaming relativistic particles are present, they generate an anisotropic pressure which counteracts the one from the magnetic field such that the Universe becomes isotropized. We show that due to this effect, the CMB temperature anisotropy from a homogeneous magnetic field is significantly suppressed if the neutrino masses are smaller than 0.3 eV.

Adamek, Julian [Institut für theoretische Physik und Astrophysik, Universität Würzburg, Am Hubland, 97074 Würzburg (Germany); Durrer, Ruth; Fenu, Elisa; Vonlanthen, Marc, E-mail: jadamek@physik.uni-wuerzburg.de, E-mail: ruth.durrer@unige.ch, E-mail: elisa.fenu@unige.ch, E-mail: marc.vonlanthen@unige.ch [Institut de Physique Théorique, Université de Genève, 24 quai E. Ansermet, 1211 Genève 4 (Switzerland)

2011-06-01

384

Domain-wall structure in thin films with perpendicular anisotropy: Magnetic force microscopy and polarized neutron reflectometry study  

NASA Astrophysics Data System (ADS)

Ferromagnetic domain patterns and three-dimensional domain-wall configurations in thin CoCrPt films with perpendicular magnetic anisotropy were studied in detail by combining magnetic force microscopy and polarized neutron reflectometry with micromagnetic simulations. With the first method, lateral dimension of domains with alternative magnetization directions normal to the surface and separated by domain walls in 20-nm-thick CoCrPt films were determined in good agreement with micromagnetic simulations. Quantitative analysis of data on reflectometry shows that domain walls consist of a Bloch wall in the center of the thin film, which is gradually transformed into a pair of Néel caps at the surfaces. The width and in-depth thickness of the Bloch wall element, transition region, and Néel caps are found consistent with micromagnetic calculations. A complex structure of domain walls serves to compromise a competition between exchange interactions, keeping spins parallel, magnetic anisotropy orienting magnetization normal to the surface, and demagnetizing fields, promoting in-plane magnetization. It is shown that the result of such competition strongly depends on the film thickness, and in the thinner CoCrPt film (10 nm thick), simple Bloch walls separate domains. Their lateral dimensions estimated from neutron scattering experiments agree with micromagnetic simulations.

Navas, David; Redondo, Carolina; Badini Confalonieri, Giovanni A.; Batallan, Francisco; Devishvili, Anton; Iglesias-Freire, Óscar; Asenjo, Agustina; Ross, Caroline A.; Toperverg, Boris P.

2014-08-01

385

The Martian magnetic field  

NASA Technical Reports Server (NTRS)

The paper presents an overview of the Martian magnetic field measurements and the criticisms made of them. The measurements of the Mars 2, 3, and 5 spacecraft were interpreted by Dolginov et al. (1976, 1978) to be consistent with an intrinsic planetary magnetic moment of 2.5 times 10 to the 22nd power gauss cu cm, basing this result on the apparent size of the obstacle responsible for deflecting the solar wind and an apparent encounter of the spacecraft with the planetary field. It is shown that if the dependence of the Martian magnetic moment on the rotation rate was linear, the estimate of the moment would be far larger than reported by Dolginov et al. An upper limit of 250 km is calculated for the dynamo radius using the similarity law, compared with 500 km obtained by Dolginov et al. It is concluded that the possible strength of a Martian dynamo is below expectations, and it is likely that the Mars dynamo is not presently operative.

Russell, C. T.

1979-01-01

386

Control of the magnetic in-plane anisotropy in off-stoichiometric NiMnSb  

SciTech Connect

NiMnSb is a ferromagnetic half-metal which, because of its rich anisotropy and very low Gilbert damping, is a promising candidate for applications in information technologies. We have investigated the in-plane anisotropy properties of thin, molecular beam epitaxy-grown NiMnSb films as a function of their Mn concentration. Using ferromagnetic resonance to determine the uniaxial and four-fold anisotropy fields, (2K{sub U})/(M{sub s}) and (2K{sub 1})/(M{sub s}) , we find that a variation in composition can change the strength of the four-fold anisotropy by more than an order of magnitude and cause a complete 90° rotation of the uniaxial anisotropy. This provides valuable flexibility in designing new device geometries.

Gerhard, F.; Schumacher, C.; Gould, C.; Molenkamp, L. W. [Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074 Würzburg (Germany)

2014-03-07

387

Electric and magnetic fields  

NASA Technical Reports Server (NTRS)

A number of energy momentum anomalies are described that result from the use of Abraham-Lorentz electromagnetic theory. These anomalies have in common the motion of charged bodies or current carrying conductors relative to the observer. The anomalies can be avoided by using the nonflow approach, based on internal energy of the electromagnetic field. The anomalies can also be avoided by using the flow approach, if all contributions to flow work are included. The general objective of this research is a fundamental physical understanding of electric and magnetic fields which, in turn, might promote the development of new concepts in electric space propulsion. The approach taken is to investigate quantum representations of these fields.

Kaufman, H. R.; Robinson, R. S.; Etters, R. D.

1982-01-01

388

Magnetic anisotropy observed at surface of amorphous silicate and its implications for the mechanism of dust alignment  

NASA Astrophysics Data System (ADS)

Amorphous silicate is considered to be one of the major dust-forming material, however its possibility of magnetic alignment by magnetic anisotropy has not been considered as yet. This is because the anisotropy of an amorphous material is generally considered to be negligibly small. In the present study, depth profile of paramagnetic anisotropy ??para was experimentally obtained for the first time on an amorphous silicate sample, namely moldavite, with a spatial resolution of 0.5 mm. For the above purpose, ??para of square plate (2 mm×2 mm×0.5 mm), separated from a quadrangular prism (2 mm×2 mm×10 mm), were measured one by one; the prism was cut from the amorphous sample with its long axis directed normal to the surface. In order to realize the above measurement, a new experimental device was adopted which could detect ??para of a sub-mm sized sample by measuring its field-induced rotational oscillation in an ?G area. The observed magnetic unstable axis of the plate was always normal to surface plane. The magnitude of ??para at the surface was at a level of 10-6 emu/g, which was comparable to the value previously obtained for of olivine and pyroxene, which are major dust components in the proto-planetary disk region. Accordingly, most of the dust forming materials in the above region is expected to possess finite amount of ?? to cause partial dust alignment.

Yokoi, M.; Katsura, M.; Hisayoshi, K.; Uyeda, C.

2014-10-01

389

Field dependence of the superconducting basal plane anisotropy of TmNi2B2C  

SciTech Connect

The superconductor TmNi2B2C possesses a significant fourfold basal plane anisotropy, leading to a square vortex lattice (VL) at intermediate fields. However, unlike other members of the borocarbide superconductors, the anisotropy in TmNi2B2C appears to decrease with increasing field, evident by a reentrance of the square VL phase. We have used small-angle neutron scattering measurements of the VL to study the field dependence of the anisotropy. Our results provide a direct, quantitative measurement of the decreasing anisotropy. We attribute this reduction of the basal plane anisotropy to the strong Pauli paramagnetic effects observed in TmNi2B2C and the resulting expansion of vortex cores near Hc2.

Das, P.; Densmore, J.M.; Rastovski, C.; Schlesinger, K.J.; Laver, M.; Dewhurst, C.D.; Littrell, K.; Budko, Serguei L.; Canfield, Paul C.; Eskildsen, M.R.

2012-10-01

390

The Structure of a Lyotropic Liquid Crystalline Phase that Orients in a Magnetic Field  

Microsoft Academic Search

The structure of a lyotropic liquid crystalline phase with positive diamagnetic anisotropy (type I), that spontaneously orients in a magnetic field has been studied by means of water NMR quadrupole splittings, NMR diffusion and polarized absorption spectroscopy. It is concluded that this phase is built up of long rodlike aggregates. A preliminary study of a sample with negative diamagnetic anisotropy

Olle Söderman; Göran Lindblom; Lennart B.-Å. Johansson; Krister Fontell

1980-01-01

391

Entanglement and sources of magnetic anisotropy in radical pair-based avian magnetoreceptors.  

PubMed

One of the principal models of magnetic sensing in migratory birds rests on the quantum spin dynamics of transient radical pairs created photochemically in ocular cryptochrome proteins. We consider here the role of electron spin entanglement and coherence in determining the sensitivity of a radical pair-based geomagnetic compass and the origins of the directional response. It emerges that the anisotropy of radical pairs formed from spin-polarized molecular triplets could form the basis of a more sensitive compass sensor than one founded on the conventional hyperfine-anisotropy model. This property offers new and more flexible opportunities for the design of biologically inspired magnetic compass sensors. PMID:23368109

Hogben, Hannah J; Biskup, Till; Hore, P J

2012-11-30

392

Entanglement and Sources of Magnetic Anisotropy in Radical Pair-Based Avian Magnetoreceptors  

NASA Astrophysics Data System (ADS)

One of the principal models of magnetic sensing in migratory birds rests on the quantum spin dynamics of transient radical pairs created photochemically in ocular cryptochrome proteins. We consider here the role of electron spin entanglement and coherence in determining the sensitivity of a radical pair-based geomagnetic compass and the origins of the directional response. It emerges that the anisotropy of radical pairs formed from spin-polarized molecular triplets could form the basis of a more sensitive compass sensor than one founded on the conventional hyperfine-anisotropy model. This property offers new and more flexible opportunities for the design of biologically inspired magnetic compass sensors.

Hogben, Hannah J.; Biskup, Till; Hore, P. J.

2012-11-01

393

Strain and magnetic anisotropy of epitaxial Ni/Cu(001) nanostructures  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy of isolated epitaxial Ni/Cu(001) nanostructure on Si(001) has been studied together with structural characterization. The strain of the Ni nanostructure is released such that the perpendicular strain of nanostructure with tNi=10 nm decreases to -0.48% from -1.17% of film with the same thickness. Because of this, strain becomes the main factor in determining magnetic anisotropy of Ni/Cu nanostructure in the investigated Ni thickness range (tNi=4.5-10 nm).

Lee, S. G.; Shin, S. W.; Jang, J. W.; Hwang, H. M.; Jang, H. K.; Lee, J.; Lee, J. H.; Song, J. H.; Choi, J.-Y.; Lee, H. S.

2006-04-01

394

Uniaxial magnetic anisotropy of quasi-one-dimensional Fe chains on Pb /Si  

NASA Astrophysics Data System (ADS)

We fabricated quasi-one-dimensional Fe chains on a 4° miscut Si (111) substrate with a Pb film as a buffer layer. The magnetic properties and morphology of Fe chains were investigated by means of scanning tunneling microscope (STM) and surface magneto-optical Kerr effect (SMOKE). STM images show that Fe chains are formed by Fe random islands along the steps of the Pb film due to step decoration. SMOKE data indicate that the Fe chains exhibit in-plane uniaxial magnetic anisotropy along the step direction. The effective in-plane uniaxial anisotropy constant at room temperature was determined by means of electron spin resonance.

Sun, Da-Li; Wang, De-Yong; Du, Hai-Feng; Ning, Wei; Gao, Jian-Hua; Fang, Ya-Peng; Zhang, Xiang-Qun; Sun, Young; Cheng, Zhao-Hua; Shen, Jian

2009-01-01

395

Chemically manipulated anomalous Hall effect and perpendicular magnetic anisotropy in Co/Pt multilayers  

NASA Astrophysics Data System (ADS)

Chemically manipulated anomalous Hall effect (AHE) and perpendicular magnetic anisotropy (PMA) have been studied in MgO/[Co/Pt]3/MgO multilayers by introducing a Mg metal layer between the Co layer and the top MgO layer. It is shown that the saturation anomalous Hall resistivity (?AH) and effective magnetic anisotropy (Keff) are 125% and 26% larger than those in the multilayers without Mg insertion, respectively. The X-ray photoelectron spectroscopy (XPS) analysis shows that the enhancement of AHE and PMA is primarily ascribed to effective control of chemical states at the Co/MgO interface.

Jiang, Shao-Long; Chen, Xi; Zhang, Jing-Yan; Yang, Guang; Teng, Jiao; Li, Xu-Jing; Cao, Yi; Zhao, Zhi-Duo; Yang, Kang; Liu, Yang; Yu, Guang-Hua

2014-11-01

396

Magnetic field programming in quadrupole magnetic field-flow fractionation  

NASA Astrophysics Data System (ADS)

Magnetic field-flow fractionation (MgFFF) is a technique for the separation and characterization of magnetic nanoparticles. It is explained that the analysis of polydisperse samples requires a programmed decay of field and field gradient during sample elution. A procedure for achieving reproducible field decay with asymptotic approach to zero field using a quadrupole electromagnet is described. An example of an analysis of a polydisperse sample under programmed field decay is given.

Stephen Williams, P.; Carpino, Francesca; Moore, Lee R.; Zborowski, Maciej

397

The detection of magnetotactic bacteria and magnetofossils by means of magnetic anisotropy  

NASA Astrophysics Data System (ADS)

An important characteristic of magnetotactic bacteria (MTB) is the anisotropy of one-dimensionally aligned magnetite particles. This paper introduces the use of ferromagnetic resonance spectroscopy (FMR) at two different frequencies to compare the anisotropic properties of magnetite chains of cultured intact MTB with those of lake sediments of Holocene age in order to detect magnetofossils and to characterize their preservation in a geological system. Magnetite chains of intact MTB exhibit a predominantly uniaxial anisotropy. In the lake sediments, where diagenetic processes disintegrate the chains and diminish their uniaxiality, magnetite chains or chain fragments and dissociated bulk magnetite particles differ in their anisotropy properties. The two groups of assembly can be distinguished by empirical spectral separation of the FMR signal. This straightforward use of the characteristics of magnetic anisotropy provides a way to detect magnetofossils experimentally, thus allowing a better insight into microbial ecology during Earth's history.

Gehring, Andreas U.; Kind, Jessica; Charilaou, Michalis; García-Rubio, Inés

2011-09-01

398

Scattering by magnetic fields  

Microsoft Academic Search

Consider the scattering amplitude $s(\\\\omega,\\\\omega^\\\\prime;\\\\lambda)$,\\u000a$\\\\omega,\\\\omega^\\\\prime\\\\in{\\\\Bbb S}^{d-1}$, $\\\\lambda > 0$, corresponding to an\\u000aarbitrary short-range magnetic field $B(x)$, $x\\\\in{\\\\Bbb R}^d$. This is a smooth\\u000afunction of $\\\\omega$ and $\\\\omega^\\\\prime$ away from the diagonal\\u000a$\\\\omega=\\\\omega^\\\\prime$ but it may be singular on the diagonal. If $d=2$, then\\u000athe singular part of the scattering amplitude (for example, in the transversal\\u000agauge) is a

D. R. Yafaev

2005-01-01

399

Origin of `in-plane' and `out-of-plane' magnetic anisotropies in as-deposited and annealed CoFeB ferromagnetic thin films  

NASA Astrophysics Data System (ADS)

A detailed comparative Ferromagnetic resonance study of pulsed laser deposited Co40Fe40B20 thin films, before and after annealing, was under taken. The dependence of resonance field (Hres) and peak-to-peak linewidth (?Hpp) on film thickness, annealing temperature, and magnetic field orientation is examined. `In-plane' (IP) and `out-of-plane' (OP) angular dependence of the resonance fields, (IP:Hres(?); OP:Hres(?)), were measured at T = 150 and 295 K for the as deposited (as-) to annealed (an-) thin film samples to determine IP ( HK ? ) and OP ( HK ? ) uniaxial anisotropy fields. Variation of Hres(?) and Hres(?) on sample geometry demonstrate that the uniaxial magnetic anisotropy is present in as- and an-thin films of Co40Fe40B20. The effective magnetic anisotropy ( Ku e f f ) increases after nanocrystallization in CoFeB films indicates that the exchange interactions are unable to average out the local-magnetocrystalline anisotropy of the nanocrystalline grains and thereby lead to magnetic hardening in the early stages of crystallization.

Swamy, G. Venkat; Rakshit, R. K.; Pant, R. P.; Basheed, G. A.

2015-05-01

400

Large coercive field in magnetic-field oriented ?-Fe 2O 3 nanorods  

NASA Astrophysics Data System (ADS)

We report the fabrication and magnetic coercive field of oriented ?-Fe 2O 3 nanorods. Oriented ?-Fe 2O 3 nanorods embedded in SiO 2 matrix were obtained by a sol-gel method under an applied external magnetic field. The longitudinal axis, which corresponds to a-axis of the crystal structure of ?-Fe 2O 3 nanorods, was oriented parallel to the direction of external magnetic field. The sample achieved a magnetic coercive field along the longitudinal axis of 23.4 kOe, which is the largest value among metal oxide-based magnetic materials. The shape of the magnetic hysteresis loop is well understood by considering the magnetization rotation process and the uniaxial magnetic anisotropy.

Sakurai, Shunsuke; Shimoyama, Jun-ichi; Hashimoto, Kazuhito; Ohkoshi, Shin-ichi

2008-06-01

401

Perpendicular magnetic anisotropy in epitaxially strained cobalt-ferrite (001) thin films  

SciTech Connect

We investigated the dependencies of both the magnetization characteristics and the perpendicular magnetic anisotropy of Co{sub x}Fe{sub 3–x}O{sub 4}(001) epitaxial films (x?=?0.5 and 0.75) on the growth conditions of the reactive magnetron sputtering process. Both saturation magnetization and the magnetic uniaxial anisotropy constant K{sub u} are strongly dependent on the reactive gas (O{sub 2}) flow rate, although there is little difference in the surface structures for all samples observed by reflection high-energy electron diffraction. In addition, certain dead-layer-like regions were observed in the initial stage of the film growth for all films. Our results suggest that the magnetic properties of Co{sub x}Fe{sub 3–x}O{sub 4} epitaxial films are governed by the oxidation state and the film structure at the vicinity of the interface.

Yanagihara, H., E-mail: yanagiha@bk.tsukuba.ac.jp; Utsumi, Y.; Niizeki, T., E-mail: t-niizeki@imr.tohoku.ac.jp; Inoue, J.; Kita, Eiji [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan)

2014-05-07

402

In situ manipulation of magnetic anisotropy in magnetite thin films  

Microsoft Academic Search

We show that the ferromagnetic anisotropy of a thin crystalline Fe3O4 film can be manipulated in situ via the application of tunable stress. The stress is exerted by a piezoelectric actuator, onto which the Fe3O4 film is cemented. The strain in the sample is quantified as a function of the voltage applied to the actuator using high-resolution x-ray diffraction, and

A. Brandlmaier; S. Geprägs; M. Weiler; A. Boger; M. Opel; H. Huebl; C. Bihler; M. S. Brandt; B. Botters; D. Grundler; R. Gross; S. T. B. Goennenwein

2008-01-01

403

Perpendicularizing magnetic anisotropy of full-Heusler Co2FeAl films by cosputtering with terbium  

NASA Astrophysics Data System (ADS)

In this letter, we fabricated Co2FeAl films with perpendicular-to-plane magnetic anisotropy by cosputtering with terbium (Tb). The as-prepared (Tb+Co2FeAl) films (TCFA) consists of nanocrystalline L21 Co2FeAl and amorphous alloy of Tb(Co, Fe, and Al). The coercivity field (Hc) of the TCFA films is adjustable from 200 to 800 Oe. After annealing, the Hc decreases to 70 Oe. A perpendicularly magnetized spin valve with the TCFA films as free and reference layers shows a current-perpendicular-to-plane magnetoresistance of 1.8% at room temperature. Our result opens a way to fabricate perpendicularly magnetized full-Heusler alloys and makes it possible to realize faster and simple structured magnetic storage bits in the future.

Li, X. Q.; Xu, X. G.; Zhang, D. L.; Miao, J.; Zhan, Q.; Jalil, M. B. A.; Yu, G. H.; Jiang, Y.

2010-04-01

404

Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO3  

NASA Astrophysics Data System (ADS)

We report on domain formation and magnetization reversal in epitaxial Fe films on ferroelectric BaTiO3 substrates with ferroelastic a-c stripe domains. The Fe films exhibit biaxial magnetic anisotropy on top of c domains with out-of-plane polarization, whereas the in-plane lattice elongation of a domains induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The strong modulation of magnetic anisotropy symmetry results in full imprinting of the a-c domain pattern in the Fe films. Exchange and magnetostatic interactions between neighboring magnetic stripes further influence magnetization reversal and pattern formation within the a and c domains.

Lahtinen, Tuomas H. E.; Shirahata, Yasuhiro; Yao, Lide; Franke, Kévin J. A.; Venkataiah, Gorige; Taniyama, Tomoyasu; van Dijken, Sebastiaan

2012-12-01

405

ccsd-00004894,version1-10May2005 Interplay between magnetic anisotropy and interlayer coupling in nanosecond  

E-print Network

) The influence of magnetic anisotropy on nanosecond magnetization reversal in coupled FeNi/Cu/Co trilayers-valve like FeNi/Cu/Co tri- layers using time and layer-resolved photoelectron emis- sion microscopy (PEEM

Boyer, Edmond

406

Domain-wall structure in thin films with perpendicular anisotropy: Magnetic force microscopy and polarized neutron reflectometry study  

E-print Network

Ferromagnetic domain patterns and three-dimensional domain-wall configurations in thin CoCrPt films with perpendicular magnetic anisotropy were studied in detail by combining magnetic force microscopy and polarized neutron ...

Navas, David

407

Threshold magnetic fields and Fréedericksz transition in a ferronematic  

Microsoft Academic Search

Continuum theory is used to analyze the effect of an applied magnetic field on a ferronematic (i.e. dilute suspension of needle-like magnetic particles in nematic liquid crystal) with soft homeotropic anchoring between the ferroparticles and the director, and positive diamagnetic anisotropy of the liquid-crystalline matrix. It is shown that in infinite ferronematic a peculiar Fréedericksz-like transition takes place, at which

A. N. Zakhlevnykh

2004-01-01

408

Magnetic anisotropy and Verwey transition of magnetosome chains in Magnetospirillum gryphiswaldense  

NASA Astrophysics Data System (ADS)

Magnetotactic bacteria (MTB) are characterized by cellular magnetic dipoles formed by the 1-D assembly of magnetite and/or greigite particles aligned along their magnetic easy axes. This alignment creates strong interaction-induced shape anisotropy. Ferromagnetic resonance (FMR) spectroscopy is applied to study the changes in anisotropy of the MTB Magnetospirillum gryphiswaldense between room temperature and 10 K. The Verwey transition is found at about 100 K. The characteristic FMR signal of the cellular dipole at room temperature vanishes upon cooling to the isotropic point at Ti? 130 K, where the magnetocrystalline anisotropy constant K1 becomes zero. Monitoring of the FMR response of intact MTB as a function of temperature is taken to discuss theoretically the reduction of the interaction-induced shape anisotropy in magnetofossils because of diagenetic processes. It is concluded that there is a similarity in the FMR response between magnetofossils at room temperature and intact MTB near Ti. This is because the critical effect of the magnetocrystalline anisotropy constant K1 and of the alignment of magnetic easy axes on the cellular dipole. Low-temperature FMR results of intact MTB can thus be used as a guideline for detecting magnetofossils in geological environments.

Gehring, Andreas U.; Fischer, Hâkon; Charilaou, Michalis; García-Rubio, Inés.

2011-12-01

409

Pulse electrodeposition and electrochemical quartz crystal microbalance techniques for high perpendicular magnetic anisotropy cobalt nanowire arrays  

SciTech Connect

This research is focused on the development of pulse electrodeposition techniques to fabricate a high-density array of vertically oriented, high-magnetic anisotropy cobalt nanowires using a porous polymer film template. This type of array is a competitive candidate for future perpendicular magnetic media capable of storage densities exceeding 1 Terabit/in.{sup 2} The polymer template, derived from a self-assembling P(S-b-MMA) diblock copolymer film, provides precise control over the nanowire diameter (15 nm) and interwire spacing (24 nm), whereas nanowire length (typically 50 to 1000 nm) is controlled accurately with the aid of real-time electrochemical quartz crystal monitoring. Pulse and pulse-reversed electrodeposition techniques, as compared to dc, are shown to significantly enhance the perpendicular magnetic anisotropy of the magnetic nanowire array and ultimately result in coercivity as large as 2.7 kOe at 300 K. Magnetic and structural characterizations suggest that these properties arise from an improved degree of magnetocrystalline anisotropy (due to c-axis oriented crystal growth and improvements in crystal quality) that strongly supplements the basic shape anisotropy of the nanowires. Low temperature magnetometry is used to investigate exchange bias effects due to the incorporation of CoO antiferromagnetic impurities during the electrodeposition process and subsequent Co oxidation in air.

Ursache, Andrei; Goldbach, James T.; Russell, Thomas P.; Tuominen, Mark T. [Department of Physics, University of Massachusetts, 666 N Pleasant St., Hasbrouck Lab, Room 411, Amherst, Massachusetts 01003 (United States); Department of Polymer Science and Engineering, University of Massachusetts, 120 Governors Drive Amherst, Massachusetts 01003 (United States); Department of Physics, University of Massachusetts, 666 N Pleasant St., Hasbrouck Lab, Room 411, Amherst, Massachusetts 01003 (United States)

2005-05-15

410

Magnetic Fields: Visible and Permanent.  

ERIC Educational Resources Information Center

Children will be able to see the concept of a magnetic field translated into a visible reality using the simple method outlined. Standard shelf paper, magnets, iron filings, and paint in a spray can are used to prepare a permanent and well-detailed picture of the magnetic field. (Author/JN)

Winkeljohn, Dorothy R.; Earl, Robert D.

1983-01-01

411

On the energy losses of hot worked Nd-Fe-B magnets and ferrites in a small alternating magnetic field perpendicular to a bias field  

SciTech Connect

Torsion pendulum magnetometer measurements on ferrites and on neodymium-iron-boron permanent magnets are presented. The damping of the oscillation of the pendulum leads to information on the magnetic energy losses of the magnets in a small alternating magnetic field applied perpendicular to a bias field. The origin of the energy absorption is explained by the magnetization reversal of single-domain particles. It is shown experimentally that the energy absorption mechanism requires the ferromagnetic order of the sample, and that the magnetic field strength of maximal energy absorption coincides with the effective anisotropy field strength.

Staa, F. von; Hempel, K.A.; Artz, H. [Aachen Univ. of Technology (Germany). Institut fuer Werkstoffe der Elektrotechnik] [Aachen Univ. of Technology (Germany). Institut fuer Werkstoffe der Elektrotechnik

1995-11-01

412

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as the interplanetary manifestations of transient solar eruptions called coronal mass ejections. On the smaller scale, the HMF exhibits an array of waves, discontinuities, and turbulence, which give hints to the solar wind formation process. This review aims to summarise observations and theory of the small- and large-scale structure of the HMF. Solar-cycle and cycle-to-cycle evolution of the HMF is discussed in terms of recent spacecraft observations and pre-spaceage proxies for the HMF in geomagnetic and galactic cosmic ray records.

Owens, Mathew J.; Forsyth, Robert J.

2013-11-01

413

Photonic Magnetic Field Sensor  

NASA Astrophysics Data System (ADS)

Small, in-line polarization rotators or isolators to reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical (GMO) or Faraday effect in iron garnets, they with a magnetic field of a few hundred Gauss, (20 mT) for an interaction length for an optical beam of a few millimeters achieve a polarization rotation or phase shift of 45 deg (1/8 cycle). When powered by a small laser diode, with the induced linear phase shift recovered at the shot noise limit, we have demonstrated sensitivities at the 3.3 nT/Hz1/2 level for frequencies from less than 1 Hz to frequencies into the high kHz range. Through further improvements; an increase in interaction length, better materials and by far the greatest factor, the addition of a flux concentrator, sensitivities at the pT/Hz1/2 level appear to be within reach. We will detail such a design and discuss the issues that may limit achieving these goals.

Wyntjes, Geert

2002-02-01

414

Investigating the anisotropy of magnetic susceptibility and other rock magnetic properties of the Beaver River Diabase in northeastern Minnesota  

NASA Astrophysics Data System (ADS)

The Beaver River Diabase (BRD) is a series of mafic dikes and sills within the Beaver Bay Complex (BBC) of northern Minnesota, which formed during the development of the ~1.1 Ga Midcontinent Rift (MCR). The BRD is one of the youngest and most extensive intrusive phases of the BBC. The BRD dikes and sills were emplaced into the medial levels of the 6-10 kilometer-thick North Shore Volcanic Group and occur over an arcuate area extending 120 by 20 kilometers. The BRD is composed of fine- to medium-grained ophitic olivine gabbro and does not display obvious foliation or lineation features and rarely displays modal layering. Without obvious magmatic internal structures, it is difficult to determine emplacement properties such as flow direction using standard geologic mapping or petrographic techniques. For this reason, we measured the anisotropy of magnetic susceptibility (AMS), in conjunction with other rock magnetic properties, to better understand the BRD's emplacement and deformation history in the context of the MCR. AMS measures the directional dependence of low-field magnetic susceptibility, and is used to infer a shape-preferred orientation of magnetic minerals within a rock, which can be related to specific emplacement mechanisms (e.g. directional flow or settling). Preliminary analysis of AMS at 20 sites within the southern half of the BRD (with 4-7 samples per site) shows maximum susceptibility values between 4.48 x 10-6 and 2.22 x 10-4 m 3/kg (1165 and 65400 ?SI). Most specimens display nearly isotropic AMS ellipsoids (Pj < 1.15) with minor degrees of prolateness and oblateness. However, about 20% of specimens have higher anisotropies (Pj between 1.15 and 1.67) and higher degrees of oblateness and prolateness. Variations in AMS properties may reflect differences in concentration and composition of magnetic minerals, as well as emplacement mechanisms. Measurements of susceptibility as a function of temperature yield Curie points between 470 and 570 °C, indicating the presence of low-titanium titanomagnetite. Major hysteresis loops show coercivities between 1 and 25 mT, consistent with titanomagnetite as the dominant remanence carrier.

Hariri, Samer H.

415

Magnetoelastic coupling induced magnetic anisotropy in Co2(Fe/Mn)Si thin films  

NASA Astrophysics Data System (ADS)

We report the influence of in-plane strain on uniaxial magnetic anisotropy of Co2(Fe/Mn)Si [CF(M)S] films grown on SrTiO3 (STO) and MgO by varying film thickness. The analysis of magnetic free energy functional for the films on STO showed the presence of magnetoelastic anisotropy with magnetostriction constant of 12.22 × 10-6 for CFS and 2.02 × 10-6 for CMS in addition to intrinsic magnetocrystalline anisotropy. Single-domain phase diagram reveals a gradual transition from in-plane to canted state with decreasing film thickness due to strain-induced tetragonal distortion. A maximum canting angle of 41.5° with respect to film plane is predicted for CFS (12 nm)/STO film.

Pandey, Himanshu; Rout, P. K.; Anupam; Joshi, P. C.; Hossain, Z.; Budhani, R. C.

2014-01-01

416

Constituents of magnetic anisotropy and a screening of spin-orbit coupling in solids  

SciTech Connect

Using quantum mechanical perturbation theory (PT) we analyze how the energy of perturbation of different orders is renormalized in solids. We test the validity of PT analysis by considering a specific case of spin-orbit coupling as a perturbation. We further compare the relativistic energy and the magnetic anisotropy from the PT approach with direct density functional calculations in FePt, CoPt, FePd, MnAl, MnGa, FeNi, and tetragonally strained FeCo. In addition using decomposition of anisotropy into contributions from individual sites and different spin components we explain the microscopic origin of high anisotropy in FePt and CoPt magnets.

Antropov, Vladimir [Ames Laboratory; Ke, Liqin [Ames Laboratory; Aberg, Daniel [Lawrence Livermore National Laboratory

2014-07-11

417

Fast superconducting magnetic field switch  

DOEpatents

The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles.

Goren, Yehuda (Mountain View, CA); Mahale, Narayan K. (The Woodlands, TX)

1996-01-01

418

Pliocene and latest Miocene anisotropy of magnetic susceptibility (AMS) from the Wilkes Land margin (Invited)  

NASA Astrophysics Data System (ADS)

During IODP Expedition 318, Sites U1359 and U1361 were drilled on the continental rise offshore the Wilkes Subglacial Basin to reconstruct the stability of the East Antarctic Ice Sheet (EAIS) during Neogene warm periods, such as the late Miocene and the early Pliocene. As the drilled core contains a complex history of compaction, erosion (thus hiatuses), and likely artificial disturbances, identifying these is important for reconstructing paleoenvironments. Anisotropy of magnetic susceptibility (AMS) is sensitive to lithological changes and differential compaction. At both sites, highly anisotropic layers correspond with turbidite units, lithologic boundaries and hiatuses. In places, it appears that low anisotropy is controlled by the bioturbated units and high productivity layers. Here we present a detailed study of the relationships between sediment compaction, based on AMS fabric variations in sedimentary records, and magnetic mineralogy. A clear correlation can be found between the degree of anisotropy and moisture content and diatom abundance during the Pliocene, but this pattern breaks down in the late Miocene. There are also strong rock magnetic indications for changes in the sources of the magnetic minerals throughout the Miocene to Pliocene. Furthermore, a significant difference exists between magnetic minerals at Sites U1359 and U1361. We will use our AMS and rock magnetic study to 1) characterize sediment compaction with biological productivity, and 2) detect the source of magnetic mineralogy throughout the late Miocene to Pliocene at both sites.

Sugisaki, S.; Tauxe, L.; Iwai, M.; van de Flierdt, T.; Cook, C.; Jimenez, F. J.; Khim, B.; Patterson, M. 0; Mckay, R. M.; Passchier, S.; Roehl, U.; González, J. J.; Escutia, C.

2013-12-01

419

Magnetic State of Pyrochlore Cd2Os2O7 Emerging from Strong Competition of Ligand Distortions and Longer-Range Crystalline Anisotropy  

NASA Astrophysics Data System (ADS)

By many-body quantum-chemical calculations, we investigate the role of two structural effects—local ligand distortions and the anisotropic Cd-ion coordination—on the magnetic state of Cd2Os2O7, a spin S=3/2 pyrochlore. We find that these effects strongly compete, rendering the magnetic interactions and ordering crucially dependent on these geometrical features. Without trigonal distortions, a large easy-plane magnetic anisotropy develops. Their presence, however, reverses the sign of the zero-field splitting and causes a large easy-axis anisotropy (D?-6.8meV), which in conjunction with the antiferromagnetic exchange interaction (J?6.4meV) stabilizes an all-in-all-out magnetic order. The competition uncovered here is a generic feature of pyrochlore magnets.

Bogdanov, Nikolay A.; Maurice, Rémi; Rousochatzakis, Ioannis; van den Brink, Jeroen; Hozoi, Liviu

2013-03-01

420

Magnetic state of pyrochlore Cd(2)Os(2)O(7) emerging from strong competition of ligand distortions and longer-range crystalline anisotropy.  

PubMed

By many-body quantum-chemical calculations, we investigate the role of two structural effects--local ligand distortions and the anisotropic Cd-ion coordination--on the magnetic state of Cd(2)Os(2)O(7), a spin S = 3/2 pyrochlore. We find that these effects strongly compete, rendering the magnetic interactions and ordering crucially dependent on these geometrical features. Without trigonal distortions, a large easy-plane magnetic anisotropy develops. Their presence, however, reverses the sign of the zero-field splitting and causes a large easy-axis anisotropy (D ? -6.8 meV), which in conjunction with the antiferromagnetic exchange interaction (J ? 6.4 meV) stabilizes an all-in-all-out magnetic order. The competition uncovered here is a generic feature of pyrochlore magnets. PMID:25166841

Bogdanov, Nikolay A; Maurice, Rémi; Rousochatzakis, Ioannis; van den Brink, Jeroen; Hozoi, Liviu

2013-03-22

421

Spin-wave resonance and magnetic anisotropy in FePt thin films  

NASA Astrophysics Data System (ADS)

Ferromagnetic Resonance (FMR) measurements at room temperature and X-band microwave frequency were performed on polycrystalline FePt thin films with face-centered cubic structure. With the external field perpendicular to the film plane, the absorption fields H n of the odd and even spin-wave resonance modes n detected for the Fe 0.44Pt 0.56(45 nm)/Si(1 0 0) and Fe 0.51Pt 0.49(105 nm)/Pt(55 nm)/MgO(1 0 0) films, were found to obey the well-known H n× n2 ratio, giving for these films the exchange stiffness constant values of 3.9×10 -8 and 4.4×10 -7 erg/cm, respectively. The study of the out-of-plane angular dependence of the absorption field of the uniform FMR mode allowed the measurement of the effective magnetic anisotropy constants of 5.3×10 6 , 6.4×10 6 , and 6.7×10 6 erg/cm 3, related, respectively, to the [1 1 1], [1 0 0], and [1 1 0] textures present in the films.

Martins, A.; Trippe, S. C.; Santos, A. D.; Pelegrini, F.

2007-01-01

422

Magnetic field modification of optical magnetic dipoles.  

PubMed

Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate. PMID:25646869

Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David

2015-03-11

423

Exposure guidelines for magnetic fields  

SciTech Connect

The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

Miller, G.

1987-12-01

424

Enhanced interface perpendicular magnetic anisotropy in electrodeposited CoAu,,111... layers L. Cagnon,1  

E-print Network

February 2001 This work investigates the structure and interface perpendicular magnetic anisotropy PMA ever reported for the Cu/Co/Au 111 structure. While extended x-ray-absorption fine structure indicates. The correlation ob- served between the strength of PMA and film structure is discussed in details. DOI: 10

Boyer, Edmond

425

Magnetic thin films and nanostructures: Anisotropy, microstructure and their inter-relationship  

SciTech Connect

Magnetic thin films and nanostructure exhibit novel properties and have great technological potential. In particular, developing thin film structures with perpendicular anisotropy, understanding the underlying mechanisms and identifying meaningful microstructure-property relationships in such nanometer scale materials is an ongoing challenge. Here, two different approaches as well as details of the relevant microstructure are presented. 6 refs, 2 figs.

Krishnan, K.M.

1992-10-01

426

Magnetic anisotropy of rocks and its application in geology and geophysics  

Microsoft Academic Search

Magnetic anisotropy in sedimentary rocks is controlled by the processes of deposition and compaction, in volcanic rocks by the lava flow and in metamorphic and plutonic rocks by ductile deformation and mimetic crystallization. In massive ore it is due to processes associated with emplacement and consolidation of an ore body as well as to ductile deformation. Hence, it can be

Frantisek Hrouda

1982-01-01

427

A facile method to syntheses monodisperse ?-Fe2O3 nanocubes with high magnetic anisotropy density  

NASA Astrophysics Data System (ADS)

The performance of iron oxides, as a clinical tool for hyperthermia application, is strongly depending on their size and structural morphology. The precise control of the iron oxide shape and morphology offers a unique strategy to modify the strength of the dipolar interactions between iron oxide nanoparticles through the engineering of the magnetic surface anisotropy density. This article presents a novel recipe to synthesize ?-Fe2O3 nanocrystals with cubic morphology. The ?-Fe2O3 nanocubes were prepared through microwave assisted solvothermal technique. The use of 2,3-oxidosqualene results in iron oxide with cubic shape. The ?-Fe2O3 nanocubes were analyzed by X-ray diffractometer (XRD), transmission electron microscopy (TEM) and electron diffraction (SAED). The magnetic analysis revealed that the ?-Fe2O3 nanocubes have a saturation magnetization of 62 emu/g and magnetic surface anisotropy density Keff = 2 × 105 erg/cm3 compared to bulk iron oxide.

Mahmoud, Waleed E.; Al-Hazmi, Faten; Al-Noaiser, Fowzia; Al-Ghamdi, A. A.; Bronstein, Lyudmila M.

2014-04-01

428

Room-temperature perpendicular magnetic anisotropy of MgO/Fe/MgO ultrathin films  

SciTech Connect

We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4?Å to 14?Å. For the iron deposited at 140?K, we obtained perpendicular magnetization at room temperature below the critical thickness of t{sub c}?=?(9?±?1)?Å. In the vicinity of t{sub c}, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to t{sub c}.

Kozio?-Rachwa?, A.; ?l?zak, T.; Przewo?nik, J. [Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Skowro?ski, W.; Stobiecki, T. [Department of Electronics, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Wilgocka-?l?zak, D. [Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Kraków (Poland); Qin, Q. H.; Dijken, S. van [NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076 Aalto (Finland); Korecki, J. [Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Kraków (Poland)

2013-12-14

429

Magnetic fields in massive stars  

Microsoft Academic Search

Although indirect evidence for the presence of magnetic fields in high-mass stars is regularly reported in the literature, the detection of these fields remains an extremely challenging observational problem. We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

S. Hubrig; M. Scholler; M. Briquet; M. A. Pogodin; R. V. Yudin; J. F. Gonzalez; T. Morel; P. De; R. Ignace; G. Mathys; G. J. Peters

2007-01-01

430

Magnetic fields in massive stars  

E-print Network

Although indirect evidence for the presence of magnetic fields in high-mass stars is regularly reported in the literature, the detection of these fields remains an extremely challenging observational problem. We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

S. Hubrig

2007-03-09

431

Magnetic-field-dosimetry system  

SciTech Connect

A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.

Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

1981-01-21

432

The Galileo magnetic field investigation  

Microsoft Academic Search

The Galileo Orbiter carries a complement of fields and particles instruments designed to provide data needed to shed light on the structure and dynamical variations of the Jovian magnetosphere. Many questions remain regarding the temporal and spatial properties of the magnetospheric magnetic field, how the magnetic field maintains corotation of the embedded plasma and the circumstances under which corotation breaks

M. G. Kivelson; K. K. Khurana; J. D. Means; C. T. Russell; R. C. Snare

1992-01-01

433

Bosonic representation of quantum magnets with large single-ion easy-plane anisotropy  

NASA Astrophysics Data System (ADS)

We introduce a representation of an integer spin S via bosonic operators which is useful in describing the paramagnetic phase and transitions to magnetically ordered phases in magnetic systems with large single-ion easy-plane anisotropy D. Considering the exchange interaction between spins as a perturbation and using the diagram technique we derive the elementary excitation spectrum and the ground-state energy in the third order of the perturbation theory. In the special case of S=1 we obtain these expressions also using simpler spin representations some of which were introduced before. Comparison with results of previous numerical studies of 2D systems with S=1 demonstrates that our approach works better than other analytical methods applied before for such systems. We apply our results for the elementary excitation spectrum analysis obtained experimentally in NiCl2-4SC(NH2)2 (DTN). It is demonstrated that a set of model parameters (exchange constants and D) which has been used for DTN so far describes badly the experimentally obtained spectrum. A different set of parameters is proposed, using which we fit the spectrum and values of two critical fields of DTN.

Sizanov, A. V.; Syromyatnikov, A. V.

2011-08-01

434

Magnetic Anisotropy of Cobalt Ferrite (Co1.01Fe2.00O3.62) and Nickel Cobalt Ferrite (Ni0.72Fe0.20Co0.08Fe2O4)  

Microsoft Academic Search

A method of measuring the first magnetic anisotropy constant, K1, of cubic crystals having a large anisotropy was developed which utilized measurements of the torque for directions of the applied field near the direction of easy magnetization. By this method K1 of a cobalt ferrite crystal was found to be closely approximated by the empirical relationship K1=19.6×106 exp(-1.90×10- 5T2) ergs\\/cc

Henry Shenker

1957-01-01

435

Effect of a Quartic Anisotropy Energy on the Spiral Magnetic Coexistence State of Superconductivity and Ferromagnetism  

E-print Network

magnetic" state of Blount and Varma is studied near the onset temperature. For a quartic anisotropy with uniaxial symmetry, we find continuous polarization transitions from circular to elliptical and then to linear as the strength of a uni... determined that the trigonal axis is the easy axis for magnetization, and q~~[110j. The coex- istence state in this material is therefore also linearly po- larized. In order to accommodate these observed linear polar- izations into the Blount-Varma...

ROSE, GH; Hu, Chia-Ren.

1988-01-01