Note: This page contains sample records for the topic magnetic anisotropy field from Science.gov.
While these samples are representative of the content of Science.gov,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of Science.gov
to obtain the most current and comprehensive results.
Last update: August 15, 2014.
1

Magnetic field anisotropy based MR tractography  

NASA Astrophysics Data System (ADS)

Non-invasive measurements of structural orientation provide unique information regarding the connectivity and functionality of fiber materials. In the present study, we use a capillary model to demonstrate that the direction of fiber structure can be obtained from susceptibility-induced magnetic field anisotropy. The interference pattern between internal and external magnetic field gradients carries the signature of the underlying anisotropic structure and can be measured by MRI-based water diffusion measurements. Through both numerical simulation and experiments, we found that this technique can determine the capillary orientation within 3°. Therefore, susceptibility-induced magnetic field anisotropy may be useful for an alternative tractography method when diffusion anisotropy is small at higher magnetic field strength without the need to rotate the subject inside the scanner.

Han, S. H.; Song, Y. K.; Cho, F. H.; Ryu, S.; Cho, G.; Song, Y.-Q.; Cho, H.

2011-10-01

2

Anisotropy in MHD turbulence due to a mean magnetic field  

Microsoft Academic Search

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

John V. Shebalin; W. H. Matthaeus; David Montgomery

1983-01-01

3

Field-induced lattice deformation contribution to the magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Elastic and magnetoelastic effects are important to understand physical properties of many magnetic systems. Particularly, the influence of field-induced lattice deformation in the magnetic anisotropy and non-linear terms are commonly needed to describe the magnetic behavior of nanosystems. In this work, we exploit the contribution of field-induced lattice deformation to magnetic anisotropy for systems with hexagonal and cubic structures. Analytical expressions for changes in the first- and second-order magnetic anisotropy constants were obtained for systems which experience general and biaxial strains. Our estimates using bulk parameters available for ferromagnetic materials suggest that field-induced anisotropy contributions can become comparable to magnetocrystalline anisotropy, if the system possesses a strong magnetoelastic response.

Paes, V. Z. C.; Mosca, D. H.

2012-11-01

4

Magnetic stress anisotropy field in plated cylindrical Permalloy films.  

NASA Technical Reports Server (NTRS)

An analysis is made of the magnetic stress anisotropy field (Hks) arising from internal and external stress sources in plated-wire memory elements. The analysis takes into consideration circumferential composition variation and cylindrical geometry of the Permalloy film. Expressions are derived relating Hks to uniaxial film stress, average composition, and amplitude of composition variation. A result of particular importance is that even for average zeromagnetostrictive composition (ZMC) films, Hks may still make an appreciable contribution to the total anisotropy field if the composition is not uniform. Calculated Hks characteristics are shown to correlate with anisotropy field changes observed in annealing experiments. Examples are given to show the importance of composition uniformity in determining the stability of the anisotropy field. The utility of the analysis is extended by the inclusion of data expressing the inverse relation between anisotropy field and easy-axis dispersion in the film.

Lutes, O. S.

1971-01-01

5

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

6

Frequency dispersion of the magnetic anisotropy field in metallic magnetic films with the plane anisotropy of electrical conductivity  

SciTech Connect

Presence of the frequency dispersion of the field of induced single axis magnetic anisotropy and the angular position of the axis of easy magnetization in the film plane has been determined in metallic magnetic films with plane anisotropy of electrical conductivity. Theoretical dependences have been obtained which given satisfactory agreement with experimental data for cobalt and permalloy films prepared by sputtering on glass substrates and using the incident molecular beam under an angle with the substrate.

Zimin, A.B.; Kornev, Y.V.; Sementsova, T.M.; Sidorenkov, V.V.

1986-07-01

7

Banana regime pressure anisotropy in a bumpy cylinder magnetic field  

SciTech Connect

The pressure anisotropy is calculated for a plasma in a bumpy cylindrical magnetic field in the low collisionality (banana) regime for small magnetic-field modulations ({epsilon}{identical_to}{delta}B/2B<<1). Solutions are obtained by integrating the drift-kinetic equation along field lines in steady state. A closure for the local value of the parallel viscous force B{center_dot}{nabla}{center_dot}{pi}{sub parallel} is then calculated and is shown to exceed the flux-surface-averaged parallel viscous force by a factor of O(1/{epsilon}). A high-frequency limit ({omega}>>{nu}) for the pressure anisotropy is also determined and the calculation is then extended to include the full frequency dependence by using an expansion in Cordey eigenfunctions.

Garcia-Perciante, A.L.; Callen, J.D.; Shaing, K.C.; Hegna, C.C. [University of Wisconsin-Madison, Madison, Wisconsin 53706-1609 (United States)

2006-01-15

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

Magnetic susceptibilities of V3+ in corundum: Magnetic anisotropy at high fields  

NASA Astrophysics Data System (ADS)

We theoretically investigate the behavior of the V3+ ion as an impurity in Al2O3 under high magnetic fields, up to 20 T. In particular, we investigate the introduction of magnetic anisotropy that is lower than the trigonal symmetry of the host crystal. Two approaches are used for the calculations. First, fourth-order perturbation theory is used to develop quartic terms plus one sextic term in the susceptibility tensor that are good for fields up to 4 T. Then, the three-level energy matrix is reduced exactly to obtain the anisotropy at higher fields. It is found that the dominant contributions to the magnetic-induced anisotropy arise from the ?xxxx term, while the ?xxzz=?zxxz, ?zzzz, and the ?xxxxxx terms give a much lower contribution. Temperature-dependent effects are reported. There is a very small dependence of the magnetization upon the zero-field splitting.

Brumage, William H.; Quade, C. Richard; Dorman, C. Franklin

1995-08-01

10

Magnetic anisotropy study of UGe2in a static high magnetic field  

NASA Astrophysics Data System (ADS)

UGe2 has orthorhombic Cmmm crystalline symmmetry and shows ferromagnetic Heavy-Fermion (HF) Superconductor, which provides superconductivity under pressure in the range from 1.0 GPa to 1.5 GPa. Magnetic field dependence of magnetization shows strong magnetic anisotropy. When a magnetic field is applied parallel to easy axis (a-axis), magnetization presents ferromagnetic behavior. At 4.2 K, which is much lower than the Curie temperature Tc = 54 K. Spontaneous magnetization is 1.4 ?B/U, and the magnetization gradually increase with increasing field. On the contrary, when a field is applied parallel to hard axis (b-axis or c-axis), magnetization increases linearly with increasing magnetic field. As for H//b-axis, magnetization is 0.23 ? B/U even at 27 T. Magnetocrystalline anisotropy constant is obtained as 230 [T ?B] = 3.4[kJ/kg] at 4.2 K. This value is comparable with rare-earth magnet Nd2Fe17, which is typical strongly correlated ferromagnet.

Sakon, T.; Saito, S.; Koyama, K.; Awaji, S.; Sato, I.; Nojima, T.; Watanabe, K.; Motokawa, M.; Sato, N. K.

2006-11-01

11

Field dependent magnetic anisotropy of Fe1-xZnx thin films  

NASA Astrophysics Data System (ADS)

Using longitudinal magneto-optical Kerr effect in combination with a variable strength rotating magnetic field, called the Rotational Magneto-Optic Kerr Effect (ROTMOKE) method, we show that the magnetic anisotropy for thin Fe82Zn18 single crystal films, grown on MgO(001) substrates, depends linearly on the strength of the applied magnetic field at low fields but is constant (saturates) at fields greater than 350 Oe. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial and cubic anisotropy with the addition of a cubic anisotropy that depends linearly on the applied magnetic field. The field dependent term is evidence of a large effect on the effective magnetic anisotropy in Fe1-xZnx thin films by the magnetostriction.

Resnick, Damon A.; McClure, A.; Kuster, C. M.; Rugheimer, P.; Idzerda, Y. U.

2013-05-01

12

Dynamic Behavior Analysis of Crystal with Magnetic Anisotropy under Imposition of Rotating Magnetic Field  

NASA Astrophysics Data System (ADS)

The alignment behavior of a crystal with a magnetic anisotropy of ?c < ?a under the imposition of a rotating magnetic field has been investigated by numerical calculation. The promotion of the crystal alignment when the projection of the magnetically hard axis on the magnetic field rotating plane is parallel to the magnetic field direction and its suppression when the magnetically hard axis is perpendicular to the magnetic field direction can be explained by the fact that the direction of the driving torque acting on the crystal minimizes the magnetic energy. Non dimensional alignment time normalized by the alignment time under the imposition of a static field is constant in the out-of-step region where the crystal cannot follow the magnetic field rotation during its alignment. The initial phase difference between the projection of the magnetically hard axis on the magnetic field rotating plane and its direction hardly affects the alignment time in the out-of-step region but strongly affects that in the synchronous region where the crystal rotation synchronous with the magnetic field rotation. A crystal aligns quickly if the initial phase difference is between 0 and 90° in the synchronous region. The minimum alignment time is the same as that under the imposition of a static field.

Iwai, Kazuhiko

2010-12-01

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.

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

2014-01-01

14

Alignment Behavior of Crystal with Magnetic Anisotropy of ?c < ?a under Rotating Magnetic Field  

NASA Astrophysics Data System (ADS)

The alignment behavior of a crystal has been investigated by numerical calculation and an in situ observation experiment with a process combining magnetic field imposition and sample rotation to form unidirectionally aligned crystals with a magnetic anisotropy of ?c < ?a. The experimentally observed alignment behavior of a polymeric fiber and its alignment time agreed with the numerically calculated ones. Crystal alignment under the out-of-step condition alternately repeats the alignment duration and the keeping of a constant duration, and finally the crystal aligns in a specific direction. The alignment time under the synchronous condition is longer than that under the out-of-step condition if the magnetic field intensity is constant. To reduce the alignment time, a strong magnetic field under the out-of-step condition is desirable in this process.

Iwai, Kazuhiko; Niimi, Masahiro; Kohama, Takenori

2009-10-01

15

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

16

Electric-Field-Induced Magnetic Anisotropy in a Nanomagnet Investigated on the Atomic Scale  

NASA Astrophysics Data System (ADS)

Magnetoelectric coupling is studied using the electric field between the tip of a spin-polarized scanning tunneling microscope and a nanomagnet. Our experiments show that a negative (positive) electric field stabilizes (destabilizes) in-plane magnetization against thermal agitation, whereas it destabilizes (stabilizes) out-of-plane magnetization. We conclude that the electric field E induces a uniaxial anisotropy that favors in-plane magnetization for E <0 and out-of-plane magnetization for E>0. Our experiments demonstrate magnetic manipulation on the atomic scale without exploiting spin or charge currents.

Sonntag, A.; Hermenau, J.; Schlenhoff, A.; Friedlein, J.; Krause, S.; Wiesendanger, R.

2014-01-01

17

Secondary CMB anisotropies from bulk motions in the presence of stochastic magnetic fields  

NASA Astrophysics Data System (ADS)

Bulk motions of electrons along the line of sight induce secondary temperature fluctuations in the postdecoupling, reionized Universe. In the presence of a magnetic field not only the scalar mode but also the vector mode act as a source for the bulk motion. The resulting angular power spectrum of temperature anisotropies of the cosmic microwave background is calculated assuming a simple model of reionization. Contributions from the standard adiabatic, curvature mode and a nonhelical magnetic field are included. The contribution due to magnetic fields with field strengths of order nG and negative magnetic spectral indices becomes important for multipoles larger than ?˜104.

Kunze, Kerstin E.

2014-05-01

18

Electric field controlled reversible magnetic anisotropy switching studied by spin rectification  

NASA Astrophysics Data System (ADS)

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(Mg1/3Nb2/3)O3-PbTiO3 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; Wang, Fenglong; Jiang, Changjun; Rao, Jinwei; Zhao, Xiaobing; Gui, Y. S.; Hu, C.-M.; Xue, Desheng

2014-03-01

19

Controlled domain wall pinning in nanowires with perpendicular magnetic anisotropy by localized fringing fields  

NASA Astrophysics Data System (ADS)

A novel approach to directly control the domain wall (DW) pinning in a magnetic wire with perpendicular anisotropy is presented. Propagating DWs are blocked in a notch by the fringing fields of nearby gate magnets. Theoretical calculations of controlled DW pinning are confirmed by micromagnetic simulations. Experiments using magnetic force microscopy (MFM) and magneto-optical microscopy prove the functionality of the device. The presented structure enables to control the DW propagation in magnetic interconnects in order to store and buffer magnetic domains and hence, to directly control the signal flow in magnetic logic circuitry.

Breitkreutz, Stephan; Eichwald, Irina; Kiermaier, Josef; Hiblot, Gaspard; Csaba, Gyorgy; Porod, Wolfgang; Schmitt-Landsiedel, Doris; Becherer, Markus

2014-05-01

20

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

21

Impact of stochastic primordial magnetic fields on the scalar contribution to cosmic microwave background anisotropies  

SciTech Connect

We study the impact of a stochastic background of primordial magnetic fields on the scalar contribution of cosmic microwave background (CMB) anisotropies and on the matter power spectrum. We give the correct initial conditions for cosmological perturbations and the exact expressions for the energy density and Lorentz force associated to the stochastic background of primordial magnetic fields, given a power-law for their spectra cut at a damping scale. The dependence of the CMB temperature and polarization spectra on the relevant parameters of the primordial magnetic fields is illustrated.

Finelli, Fabio; Paci, Francesco; Paoletti, Daniela [INAF/IASF-BO, Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna via Gobetti 101, I-40129 Bologna (Italy); INAF/OAB, Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy); INFN, Sezione di Bologna, Via Irnerio 46, I-40126 Bologna (Italy); Dipartimento di Astronomia, Universita degli Studi di Bologna, via Ranzani 1, I-40127 Bologna (Italy); INAF/IASF-BO, Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna via Gobetti 101, I-40129 Bologna (Italy); INFN, Sezione di Bologna, Via Irnerio 46, I-40126 Bologna (Italy); Dipartimento di Fisica, Universita degli Studi di Ferrara, via Saragat 1, I-44100 Ferrara (Italy); INAF/IASF-BO, Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna via Gobetti 101, I-40129 Bologna (Italy); INFN, Sezione di Bologna, via Irnerio 46, I-40126 Bologna (Italy)

2008-07-15

22

In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB  

NASA Astrophysics Data System (ADS)

The structural and magnetic properties of as-grown 5-50 nm thin ion-beam sputter deposited transition metal-metalloid Co20Fe60B20 (CFB) films are reported in this communication. A broad peak observed at 2?˜45° in the glancing angle X-ray diffraction pattern revealed the formation of very fine nano-sized grains embedded in majority amorphous CFB matrix. Although no magnetic field is applied during deposition, the longitudinal magneto-optic Kerr effect measurements performed at 300 K in these as-grown films clearly established the presence of in-plane uniaxial magnetic anisotropy (Ku). It is argued that this observed anisotropy is strain-induced. This is supported by the observed dependence of direction of Ku on the angle between applied magnetic field and crystallographic orientation of the underlying Si(100) substrate, and increase in the coercivity with the increase of the film thickness.

Kipgen, Lalminthang; Fulara, Himanshu; Raju, M.; Chaudhary, Sujeet

2012-09-01

23

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 anisotropy properties 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, thus 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 the two extreme cases (zero IGMF and IGMF strong enough to completely isotropize cascade photons) would be separable by ten years of Fermi observations and reasonable model parameters for the gamma-ray background. 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.

2012-01-01

24

Magnetic multilayer interface anisotropy  

SciTech Connect

Ni/Mo and Ni/V multilayer magnetic anisotropy has been investigated as a function of Ni layer thickness, frequency and temperature. Variable frequency ferromagnetic resonance (FMR) measurements show, for the first time, significant frequency dependence associated with the multilayer magnetic anisotropy. The thickness dependence allows one to extract the interface contribution from the total anisotropy. Temperature dependent FMR (9 GHz) and room temperature magnetization indicate that strain between Ni and the non-magnetic layers is contributing significantly to the source of the interface anisotropy and the state of the interfacial magnetization. In order to examine the interface properties of other transition metal multilayer systems, investigations on Fe/Cu are underway and CoCr/Ag is being proposed. ESR measurements have been reported on Gd substituted YBaCuO superconductors and a novel quasi-equilibrium method has been developed to determine quickly and precisely the ransition temperature.

Pechan, M.J.

1992-01-01

25

Magnetic-field-induced optical anisotropy in ferrofluids: a time-dependent light-scattering investigation.  

PubMed

We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe3O4 nanoparticles (approximately 6 nm) under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in the sample. We propose that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes. PMID:19113131

Rablau, Corneliu; Vaishnava, Prem; Sudakar, Chandran; Tackett, Ronald; Lawes, Gavin; Naik, Ratna

2008-11-01

26

POWER ANISOTROPY IN THE MAGNETIC FIELD POWER SPECTRAL TENSOR OF SOLAR WIND TURBULENCE  

SciTech Connect

We observe the anisotropy of the power spectral tensor of magnetic field fluctuations in the fast solar wind for the first time. In heliocentric RTN coordinates, the power in each element of the tensor has a unique dependence on the angle between the magnetic field and velocity of the solar wind ({theta}{sub B}) and the angle of the vector in the plane perpendicular to the velocity ({phi}{sub B}). We derive the geometrical effect of the high speed flow of the solar wind past the spacecraft on the power spectrum in the frame of the plasma P(k) to arrive at the observed power spectrum P(f, {theta}{sub B}, {phi}{sub B}) based on a scalar field description of turbulence theory. This allows us to predict the variation in the {phi}{sub B} direction and compare it to the data. We then transform the observations from RTN coordinates to magnetic-field-aligned coordinates. The observed reduced power spectral tensor matches the theoretical predictions we derive in both RTN and field-aligned coordinates, which means that the local magnetic field we calculate with wavelet envelope functions is an accurate representation of the physical axis of symmetry for the turbulence and implies that on average the turbulence is axisymmetric. We also show that we can separate the dominant toroidal component of the turbulence from the smaller but significant poloidal component and that these have different power anisotropy. We also conclude that the magnetic helicity is anisotropic and mostly two dimensional, arising from wavevectors largely confined to the plane perpendicular to B .

Wicks, R. T.; Horbury, T. S. [Physics Department, Imperial College London, London SW7 2AZ (United Kingdom); Forman, M. A. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11790-3800 (United States); Oughton, S., E-mail: r.wicks@imperial.ac.uk [Department of Mathematics, University of Waikato, Hamilton (New Zealand)

2012-02-10

27

R.F. effects in nuclear gamma-resonance: The role of the fields of magnetic anisotropy  

NASA Astrophysics Data System (ADS)

The r.f. effects in NGR spectra of substances with magnetic order were analysed assuming the deterministic character of the hyperfine field (HF) on the nucleus: it was believed as rotating /1/ or stepwise varying in time /2/. The purpose of this paper is to show the limited nature of these models in real magnetics with magnetic anisotropy

Sadykov, E. K.; Skvortsov, A. I.

1990-08-01

28

Cosmological Constraint on "Neutrino Mass" from CMB Anisotropies with Primordial Magnetic Field  

NASA Astrophysics Data System (ADS)

It is one of the biggest challenge in particle physics and cosmology to determine the mass of neutrinos. Current neutrinoless double beta decay experiment show that the total neutrino mass is smaller than 1-6 eV. In recent years, precise CMB data make it possible to constrain neutrino masses cosmologically. It says that the total neutrino mass is smaller than 2 eV in standard ACDM model.1 But if there are other physical processes which affects the CMB anisotropies, such constraint may be changed. A primordial magnetic field (PMF) is one of such physical processes. In this work, we constrain the total neutrino mass from CMB anisotropies with the PMF effect.

Kojima, K.; Yamazaki, D. G.; Kajino, T.

2008-04-01

29

Magnetic multilayer interface anisotropy  

SciTech Connect

Ni/Mo and Ni/V multilayer magnetic anisotropy has been investigated as a function of Ni layer thickness, frequency and temperature. Variable frequency ferromagnetic resonance (FMR) measurements show, for the first time, significant frequency dependence associated with the multilayer magnetic anisotropy. The thickness dependence allows one to extract the interface contribution from the total anisotropy. Temperature dependant FMR (9 GHz) and room temperature magnetization indicate that strain between Ni and the non-magnetic layers if contributing significantly to the source of the interface anisotropy and the state of the interfacial magnetization. In order to examine the interface properties of other transition metal multilayer systems, investigations on Fe/Cu are underway and CoCr/Ag is being proposed. ESR measurements have been reported on Gd substituted YBaCuO superconductors and a novel quasi-equilibrium method has been developed to determine quickly and precisely the transition temperature. During the next project the P.I. proposes to (1) extend the variable frequency FMR measurements to low temperature, where extremely large interface anisotropies are known to obtain in Ni/Mo and Ni/V and are proposed to exist in Ni/W; (2) obtain accurate dc anisotropies via a novel, variable temperature torque magnetometer currently under construction; (3) expand upon his initial findings in Fe/Cu multilayer investigations; (4) begin anisotropy investigations on Co/Ag and CoCr/Ag multilayers where the easy magnetization direction depends upon the Cr concentration; (4) make and characterize Bi based superconductors according to resistivity, thermal conductivity and thermoelectric power and construct YBaCuO based superconducting loop-gap'' resonators for use in his magnetic resonance work. 2 figs.

Pechan, M.J.

1991-01-01

30

Magnetic-field-induced quantum criticality in a spin- S planar ferromagnet with single-ion anisotropy  

NASA Astrophysics Data System (ADS)

The effects of single-ion anisotropy on quantum criticality in a d-dimensional spin- S planar ferromagnet is explored by means of the two-time Green's function method. We work at the Tyablikov decoupling level for exchange interactions and the Anderson-Callen decoupling level for single-ion anisotropy. In our analysis a longitudinal external magnetic field is used as the non-thermal control parameter and the phase diagram and the quantum critical properties are established for suitable values of the single-ion anisotropy parameter D. We find that the single-ion anisotropy has sensible effects on the structure of the phase diagram close to the quantum critical point. However, for values of the uniaxial crystal-field parameter below a positive threshold, the conventional magnetic-field-induced quantum critical scenario remains unchanged.

Mercaldo, M. T.; Rabuffo, I.; De Cesare, L.; Caramico D'Auria, A.

2013-08-01

31

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

32

Nonlinear magnetization dynamics of the classical ferromagnet with two single-ion anisotropies in an external magnetic field  

SciTech Connect

By using a stereographic projection of the unit sphere of magnetization vector onto a complex plane for the equations of motion, the effect of an external magnetic field for integrability of the system is discussed. The properties of the Jost solutions and the scattering data are then investigated through introducing transformations other than the Riemann surface in order to avoid double-valued functions of the usual spectral parameter. The exact multisoliton solutions are investigated by means of the Binet-Cauchy formula. The results showed that under the action of an external magnetic field nonlinear magnetization depends essentially on two parameters: its center moves with a constant velocity, while its shape changes with another constant velocity; its amplitude and width vary periodically with time, while its shape is also dependent on time and is unsymmetric with respect to its center. The orientation of the nonlinear magnetization in the plane orthogonal to the anisotropy axis changes with an external magnetic field. The total magnetic momentum and the integral of the motion coincident with its {ital z} component depend on time. The mean number of spins derivated from the ground state in a localized magnetic excitations is dependent on time. The asymptotic behavior of multisoliton solutions, the total displacement of center, and the phase shift of the jth peak are also analyzed. {copyright} {ital 1999} {ital The American Physical Society}

Liu, W. [Department of Physics, The University of Texas, Austin, Texas 78712 (United States)] [Department of Physics, The University of Texas, Austin, Texas 78712 (United States); [Institute of Theoretical Physics, Chinese Academy of Sciences, P.O. Box 2735, Beijing 100 080 (China); [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6032 (United States); Zhang, W.; Pu, F. [Institute of Physics, Chinese Academy of Sciences, P.O. Box 603-99, Beijing 100 080 (China)] [Institute of Physics, Chinese Academy of Sciences, P.O. Box 603-99, Beijing 100 080 (China); Zhou, X. [Department of Mathematics, Duke University, Durham, North Carolina 27706 (United States)] [Department of Mathematics, Duke University, Durham, North Carolina 27706 (United States)

1999-11-01

33

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

34

Magnetic Anisotropy and Paleomagnetism  

Microsoft Academic Search

The natural remanent magnetization of certain Welsh slates lies in the cleavage plane, which was found to be a plane of high susceptibility defined by the alignment of aniso- tropic crystals of pyrrhotite. A correlation between the magnitude of susceptibility anisotropy and the bulk susceptibility of the slates has been observed. This is interpreted as a partial masking of the

M. D. Fuller

1963-01-01

35

Magnetic phase diagram of CeAu2Ge2: High magnetic anisotropy due to crystal electric field  

NASA Astrophysics Data System (ADS)

CeAu2Ge2 single crystals (with tetragonal ThCr2Si2 structure) have been grown in Au-Ge flux (AGF) as well as in Sn flux (SF). X-ray powder diffraction and EDX measurements indicate that in the latter case, Sn atoms from the flux are incorporated in the samples, leading to a decrease of the lattice constants by ?0.3% compared to AGF samples. For both types of samples, a strong anisotropy of the magnetization M for the magnetic field B parallel and perpendicular to the c direction is observed with M||/M??6--7 in low fields just above 10 K. This anisotropy is preserved to high fields and temperatures and can be quantitatively explained by crystal electric field effects. Antiferromagnetic ordering sets in around 10 K as previously found for polycrystalline samples. From the magnetization data of our single crystals we obtain the phase diagrams for the AGF and SF samples. The magnetic properties depend strongly on the flux employed. While the AGF samples exhibit a complex behavior indicative of several magnetic transitions, the SF samples adopt a simpler antiferromagnetic structure with a single spin-flop transition. This effect of a more ordered state induced by disorder in form of Sn impurities is qualitatively explained within the anisotropic next-nearest neighbor Ising (ANNNI) model, which assumes ferromagnetic and antiferromagnetic interactions in agreement with the magnetic structure previously inferred from neutron-scattering experiments on polycrystalline CeAu2Ge2 by Loidl [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.46.9341 46, 9341 (1992)].

Fritsch, V.; Pfundstein, P.; Schweiss, P.; Kampert, E.; Pilawa, B.; v. Löhneysen, H.

2011-09-01

36

Orientational dynamics of ferrofluids with finite magnetic anisotropy of the particles: Relaxation of magneto-birefringence in crossed fields  

NASA Astrophysics Data System (ADS)

Dynamic birefringence in a ferrofluid subjected to crossed bias (constant) and probing (pulse or ac) fields is considered, assuming that the nanoparticles have finite magnetic anisotropy. This is done on the basis of the general Fokker-Planck equation that takes into account both internal magnetic and external mechanical degrees of freedom of the particle. We describe the orientation dynamics in terms of the integral relaxation time of the macroscopic orientation order parameter. To account for an arbitrary relation between the bias (external) and anisotropy (internal) fields, an interpolation expression for the integral relaxation time is proposed and justified. A developed description is used to interpret the measurements of birefringence relaxation in magnetic fluids with nanoparticles of high (cobalt ferrite) and low (maghemite) anisotropy. The proposed theory appears to be in full qualitative agreement with all the experimental data available.

Raikher, Yu. L.; Stepanov, V. I.; Bacri, J.-C.; Perzynski, R.

2002-08-01

37

Orientational dynamics of ferrofluids with finite magnetic anisotropy of the particles: relaxation of magneto-birefringence in crossed fields.  

PubMed

Dynamic birefringence in a ferrofluid subjected to crossed bias (constant) and probing (pulse or ac) fields is considered, assuming that the nanoparticles have finite magnetic anisotropy. This is done on the basis of the general Fokker-Planck equation that takes into account both internal magnetic and external mechanical degrees of freedom of the particle. We describe the orientation dynamics in terms of the integral relaxation time of the macroscopic orientation order parameter. To account for an arbitrary relation between the bias (external) and anisotropy (internal) fields, an interpolation expression for the integral relaxation time is proposed and justified. A developed description is used to interpret the measurements of birefringence relaxation in magnetic fluids with nanoparticles of high (cobalt ferrite) and low (maghemite) anisotropy. The proposed theory appears to be in full qualitative agreement with all the experimental data available. PMID:12241160

Raikher, Yu L; Stepanov, V I; Bacri, J-C; Perzynski, R

2002-08-01

38

On the Use of Velocity Anisotropy as a Measure of the Interstellar Magnetic Field: Confluence of Observations and Numerics  

NASA Astrophysics Data System (ADS)

The dynamics of the interstellar medium (ISM) are strongly affected by turbulence, which shows increased anisotropy in the presence of a magnetic field. We present a review of a new method to estimate the magnetic field strength using position-position-velocity (PPV) radio cubes. This technique utilizes the anisotropy created by the magnetic field, which manifests in velocity centroid maps and can provide the perpendicular component of the field strength. We utilize magnetohydrodynamic (MHD) simulations of fully developed turbulence to produce synthetic observations in order to test these methods and discuss their applicability for the observations considering beam smoothing and noise. This opens up the possibility of studying the magnetic nature of the ISM using statistical methods which are easier to apply than existing observational techniques.

Burkhart, B.; Lazarian, A.; Leão, I.; de Medeiros, J. R.

2013-04-01

39

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 Nd 55- xCo xFe 30Al 10B 5 ( 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 Nd 2(Fe,Co) 14B, Nd 3Co, Nd 3Al, NdAl 2 and Nd.

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

2012-04-01

40

Energetic ion anisotropies in the geomagnetic tail. I - A statistical survey. II - Magnetic field and substorm characteristics  

NASA Technical Reports Server (NTRS)

A comprehensive data set from the ISEE 2 spacecraft is used here to perform a statistical study of events in the earth's central magnetotail that are characterized by high anisotropies of energetic ions. In about 75 percent of the cases the anisotropy vector deviates no more than 45 deg from the tidal axis. High-anisotropy samples within 45 deg of the tidal axis are dominated by the earthward fraction. High ion anisotropies are observed continuously for longer than 1 min only in a few cases. The probability of observing high ion anisotropies is significantly enhanced beyond about 16 R(E) downtail distance within a few earth radii of the neutral sheet and on the duskside of the magnetotail. The analysis is extended with respect to the local magnetic field and to the relationship between energetic ion anisotropies and substorm phases. It is found that the events can be well organized in terms of substorm expansion phase and substorm recovery. These relations and the magnetic field characteristics during the events support the notion that the near-earth source of tailward streaming ions is identical with a substorm neutral line.

Kettmann, Georg; Fritz, Theodore A.; Hones, Edward W., Jr.; Daly, Patrick W.

1993-01-01

41

A method for improving the measurement of low-field magnetic susceptibility anisotropy in weak samples  

NASA Astrophysics Data System (ADS)

Many minerals and rocks have low susceptibilities and magnetic anisotropies on the order of the noise level of the measuring instrument. Anisotropy is often not significant in these samples when using the standard measurement procedure. We propose a method that uses stacking of data to improve the signal-to-noise ratio, thus extending the dynamic range for measurement and allowing for assessment of the data quality. The method makes it possible to obtain consistent directions of the principal axes for samples with an anisotropy on the order of, or even slightly below, the noise level of the instrument. For noisy datasets, the stacking procedure makes it easier to recover correct directions. However, the degree P and shape U of the anisotropy ellipsoid show large variations. Large values of P, in combination with a badly defined U, may indicate noisy data rather than a large anisotropy. The stacking procedure is especially useful for determining the magnetic anisotropy of single crystals that often have a low susceptibility but must be measured with high accuracy.

Biedermann, Andrea R.; Lowrie, William; Hirt, Ann M.

2013-01-01

42

Giant electric-field-induced magnetic anisotropy reorientation with patterned electrodes on a Ni thin film/lead zirconate titanate heterostructure  

NASA Astrophysics Data System (ADS)

This study reports a method of using patterned electrodes on a piezoelectric substrate to generate local strain to control magnetic properties of individual magnetic units. By operating different effective electrode pairs on a piezoelectric substrate, a local bi-axial strain is generated. This rotates the magnetic anisotropy of a 35 nm thick and 0.5 mm diameter Ni island through the magnetoelastic effect. The electric-field-induced magnetic anisotropy exhibits an anisotropy field up to 600 Oe and a 75% change in magnetic remanence.

Cui, Jizhai; Hockel, Joshua L.; Nordeen, Paul K.; Pisani, David M.; Carman, Gregory P.; Lynch, Christopher S.

2014-05-01

43

Magnetic Anisotropy of a Single Cobalt Nanocluster  

Microsoft Academic Search

Using a new micro-SQUID setup, we investigate magnetic anisotropy in a single 1000-atom cobalt cluster. This system opens new fields in the characterization and understanding of the origin of magnetic anisotropy in such nanoparticles. For this purpose, we report three-dimensional switching field measurements performed on a 3 nm cobalt cluster embedded in a niobium matrix. We are able to separate

M. Jamet; W. Wernsdorfer; C. Thirion; D. Mailly; V. Dupuis; P. Mélinon; A. Pérez

2001-01-01

44

Effective anisotropy field distribution of soft magnetic nanocrystalline Fe84Zr3.5Nb3.5B8Cu1 ribbons  

NASA Astrophysics Data System (ADS)

In soft magnetic amorphous and nanocrystalline alloys where anisotropy varies randomly over a length scale determined by the micro structure, there exist a distribution of anisotropies. It is possible to determine such distribution of random anisotropies from the magnetization curve. Anisotropy field distribution of as cast and nanocrystallized ribbons of nominal composition Fe84Zr3.5Nb3.5B8Cu1 is determined using an experimental method based on second harmonic response of magnetization. Annealing treatment decides the extent to which the studied alloy samples become nanocrystalline thereby affecting the distribution of random anisotropies present. It has been observed that determination of anisotropy field distribution provides an alternative drift free method to probe the coercive behavior of the studied alloy system.

Modak, S. S.; Mazaleyrat, F.; Bue, M. Lo; Varga, L. K.; Kane, S. N.

2012-06-01

45

Limits on plasma anisotropy in a tail-like magnetic field  

NASA Technical Reports Server (NTRS)

The condition of magnetohydrostatic equilibrium implies tight constraints on the degree of anisotropy that is supportable in a magnetotail field geometry. If the plasma pressure tensor is assumed to be gyrotropic at the tail midplane (z = 0), then equilibrium requires that it also be nearly isotropic there, with P-perpendicular sub 0/P-parallel sub 0 in the range 1 +/- delta square, where delta of about 0.1 is the ratio of the normal field component at the symmetry plane to the field strength in the tail lobe. The upper and the lower limits are essentially equivalent, respectively, to the marginal mirror and firehose stability conditions evaluated at z = 0, which have been invoked previously to limit the degree of anisotropy in the plasma sheet.

Hill, T. W.; Voigt, G.-H.

1992-01-01

46

Field-induced slow relaxation of magnetization in a tetrahedral Co(II) complex with easy plane anisotropy.  

PubMed

The mononuclear Co(II) complex CoBr (dmph = 2,9-dimethyl-1,10-phenanthroline) was obtained and X-ray structurally characterized as a distorted tetrahedron environment that is responsible for the moderately strong positive anisotropy of high spin Co(II). In combination with variable-field magnetic susceptibility data at low temperature, high-field electron paramagnetic resonance (HF-EPR) spectroscopy reveals the presence of easy-plane anisotropy (D > 0) in complex CoBr. Slow magnetic relaxation effects were observed for CoBr in the presence of a dc magnetic field. At very low temperatures, ac magnetic susceptibility data show the magnetic relaxation time, ?, to be temperature-independent, while above 2.4 K thermally activated Arrhenius behavior is dominated with Ueff = 22.8(8) cm(-1) and ?0 = 3.7(5) × 10(-10) s. Upon dilution of the complex within a matrix of the isomorphous compound ZnBr, ac susceptibility data reveal the individual molecular nature of the slow magnetic relaxation and indicate that the quantum tunneling pathway observed at low temperatures is likely mediated by intermolecular dipolar interactions. PMID:24002675

Huang, Wei; Liu, Tao; Wu, Dayu; Cheng, Jiajun; Ouyang, Z W; Duan, Chunying

2013-11-21

47

Ru/FeCoB double layered film with high in-plane magnetic anisotropy field of 500 Oe  

SciTech Connect

FeCoB layers prepared on Ru underlayer possess a high saturation magnetization M{sub s} and a high in-plane magnetic anisotropy filed H{sub k}. Effects of preparation conditions were investigated. Low Ar gas pressure condition and thicker film thickness were effective to attain distortion of FeCo crystallite. As the crystallinity of Ru underlayer became higher, higher H{sub k} was induced. The accumulation of anisotropic stress in the film caused by the oblique incidences of depositing atoms with high energy seems to be one of the important effects to attain high anisotropy field. It was succeeded to prepare the Ru/FeCoB film with high H{sub k} of 500 Oe.

Hirata, Ken-ichiro; Hashimoto, Atsuto; Matsuu, Toshimitsu; Nakagawa, Shigeki [Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8552 (Japan)

2009-04-01

48

Magnetic configurations in a two-sublattice system with strong antisymmetric exchange and fourth order uniaxial anisotropy in vanishing external field  

Microsoft Academic Search

Fully general solutions to the equilibrium equations of a system of two equal magnetic moments coupled by isotropic, anisotropic and antisymmetric exchange, together with second- and fourth-order uniaxial anisotropy, in vanishing external field, are given. They depend critically upon the fourth-order anisotropy and the antisymmetric exchange, and comprise planar, axial and ''conical'' phases. The latter, stable over a wide range

M. Acquarone

1978-01-01

49

High Anisotropy Magnetic Recording Media  

NASA Astrophysics Data System (ADS)

Areal densities in magnetic recording have exhibited Moore's Law like increases in the last ten years. This is partially due to improvements in the media microstructure where reduced grain sizes, tighter grain size distribution, and chemical isolation between grains to break exchange provided increased signal-to-noise from decreased transition noise. With the recent shift from longitudinal to perpendicular recording, areal densities have again continued to increase with demonstrations of over 250 Gbits/in^2. However, areal density is limited by thermal stability considerations where the ratio of stored magnetic energy KuV (anisotropy energy times the magnetic switching volume) to the thermal energy kT must be ˜ 50-70. The projected limit for traditional CoPtCr(X) granular media is on the order of 500 Gbits/in^2. Further increases in the areal density will require greater reduction in the grain size (switching volume), which necessitates finding media with higher anisotropy to maintain thermal stability. Possible candidate materials systems include FePt and SmCo5, which have bulk Ku values 50 to 100 times greater than CoPtCr(X) media materials. High Ku allows for thermally stable grains sizes down to ˜ 2.5 nm, which would permit areal densities in the Tbit/in^2 regime. Accompanying this increase in Ku is an increase in the media switching field (H0), which is proportional to the ratio Ku/Ms where Ms is the saturation magnetization. Therefore, while providing thermal stability, these high Ku materials would potentially require writing fields greater than 50 kOe which far exceed those of available recording head materials. One possible solution is heat-assisted magnetic recording (HAMR) where a laser locally heats the media in order to reduce the coercivity so that available head fields are sufficient. Numerous challenges exist for HAMR including high cooling rates so that the heating process does not render adjacent bits thermally unstable. This paper will review recent progress in this area and concentrate on the challenges for the production of high anisotropy media for Tbit/in^2 areal densities, such as maintaining grain sizes of 2 to 4 nm with the correct crystallographic texture and sufficient grain isolation to break exchange.

Wittig, James

2007-03-01

50

Entanglement spectrum and magnetization plateaus in an S = 1 bond-alternative Heisenberg chain with single-ion anisotropy and magnetic field  

NASA Astrophysics Data System (ADS)

Entanglement spectrum and quantum phase transitions (QPTs) in S = 1 bond-alternative antiferromagnetic Heisenberg chain with single-ion anisotropy and magnetic field are investigated by the infinite time-evolving block decimation (iTEBD) method. The combined effects of the single-ion anisotropy and magnetic field have been discussed, and a rich ground-state phase diagram is obtained. We find that the single-ion anisotropy is advantageous to the stability of the 1/2 magnetization plateau. Both entanglement entropy and entanglement spectrum, as two model-independent measures, are capable of describing all the QPTs. Especially, doubly degenerate entanglement spectrum on even bond is observed in the 1/2 plateau phase. Besides constant spontaneous magnetization, three magnetization plateaus ( M z = 0, 1/2, and 1) are found to have constant entanglement entropy, entanglement spectrum, and nearest-neighbor correlation. In addition, all the QPTs in such a model have been determined to belong to the second-order category.

Liu, Guang-Hua; Qiang, Ling; Tian, Guang-Shan

2013-07-01

51

Anisotropy of the quark-antiquark potential in a magnetic field  

NASA Astrophysics Data System (ADS)

We investigate the static Q ¯Q potential for Nf=2+1 QCD at the physical point in the presence of a constant and uniform external magnetic field. The potential is found to be anisotropic and steeper in the directions transverse to the magnetic field than in the longitudinal one. In particular, when compared to the standard case with zero background field, the string tension increases (decreases) in the transverse (longitudinal) direction, while the absolute value of the Coulomb coupling and the Sommer parameter show an opposite behavior.

Bonati, Claudio; D'Elia, Massimo; Mariti, Marco; Mesiti, Michele; Negro, Francesco; Sanfilippo, Francesco

2014-06-01

52

Electronic anisotropy, magnetic field-temperature phase diagram and their dependence on resistivity in c-axis oriented MgB2 thin films  

Microsoft Academic Search

An important predicted, but so far uncharacterized, property of the new superconductor MgB2 is electronic anisotropy arising from its layered crystal structure. Here we report on three c-axis oriented thin films, showing that the upper critical field anisotropy ratio Hc2||\\/Hc2? is 1.8 to 2.0, the ratio increasing with higher resistivity. Measurements of the magnetic field-temperature phase diagram show that flux

S. Patnaik; L. D. Cooley; A. Gurevich; A. A. Polyanskii; J. Jiang; X. Y. Cai; A. A. Squitieri; M. T. Naus; M. K. Lee; J. H. Choi; L. Belenky; S. D. Bu; J. Letteri; X. Song; D. G. Schlom; S. E. Babcock; C. B. Eom; E. E. Hellstrom; D. C. Larbalestier

2001-01-01

53

Magnetic anisotropy of the visual pigment rhodopsin.  

PubMed Central

A new estimate of diamagnetic anisotropy of the frog rhodopsin is reported. The estimate is obtained by combining the data of magnetic field induced orientation of isolated frog rod outer segments as measured by Chagneux and Chalazonitis (1972) and the data of diamagnetic anisotropy of lecithin membranes as recently reported by Boroske and Helfrich (1978). The anisotropy of the volume susceptibilities of frog rhodopsin is calculated to be 4.4 X 10(-8) cgs unit/cm3, which corresponds to 1.5 X 10(-27) cgs unit/molecule, or 9.0 X 10(-4) cgs unit/mol.

Hong, F T

1980-01-01

54

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

55

Recording performance and thermal stability in perpendicular media with enhancement of grain isolation as well as magnetic anisotropy field  

NASA Astrophysics Data System (ADS)

Magnetic clustering, thermal stability, and recording performance on perpendicular media with multilayered magnetic anisotropy field (Hk)-gradient CoPtCr-oxide/Cap layers with various Ru-oxide layer thicknesses (tRu-oxide) on top of Ru/NiW layers are investigated. With increasing tRu-oxide from 0 to 1.3 nm, Hc and Hs are enhanced but Hn is reduced. Magnetic correlation length (Dn) extracted from a set of major and minor loops significantly decreases but intrinsic switching field distribution remains unaffected. A short-time switching field (Ho) proportional to Hk increases linearly while KuV/kT remains unchanged. Similar KuV/kT is explained by compensation of the reduced Dn with the enhanced Ku induced by a thin Ru-oxide. However, thermal decay rate degrades from 0.06 to 0.32%/decade, which correlates well with Hn. Similar values of initial minor loop slopes indicate no change in magnetic switching behavior. A 1 nm-thick Ru-oxide layer as a well-defined granular template significantly improves recording performance: narrower MCW at 10 T by 8 nm and higher SNR at 2 T by 1.4 dB are observed even at lower OW by 8 dB compared to the media without Ru-oxide. All the recording parameters as a function of Dn correlate well.

Jung, H. S.; Ikeda, Y.; Choe, G.; Shi, Zhupei

2012-04-01

56

Magnetization Processes in Nanocrystalline Gadolinium: Role of Magnetic Anisotropy  

NASA Astrophysics Data System (ADS)

The `zero-field-cooled' (ZFC) and `field-cooled' (FC) thermomagnetic, M(T), curves, taken at magnetic fields (H) of fixed strength on nanocrystalline Gd with an average grain size of 12 nm (18 nm), revealed irreversibility in magnetization, Mirr(T) = MFC-MZFC, below a characteristic temperature, TB?TC, at H<=3.5kOe (2.2kOe). This irreversibility in magnetization is associated with the magnetic anisotropy energy barriers and gets progressively suppressed as H increases and the temperature, TB, for the onset of irreversibility shifts to lower temperatures. At moderate fields (100Oe<=H<=1000Oe), the logarithmic growth of ZFC magnetization with time, M(t) = M(t0)+S ln(t/t0) suggests that the anisotropy energy barriers have the form E(T,H) = kBT ln[t(T,H)/t0]. The magnetic viscosity, S = (1/H)[?M(t)/?ln(t/t0)], basically reflecting the domain wall dynamics, is mainly dictated by the interfacial anisotropy rather than by the intra-grain magnetic anisotropy. Coercivity, like remanence, peaks at TP?30K and varies with T as HC = H0m(T){1-[kBTln(t/t0)/E0m2(T)]1/2}, where m(T) = M(T)/M(0), as expected for the shape anisotropy dominated magnetization reversal.

Mathew, S. P.; Kaul, S. N.

2011-06-01

57

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

58

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

NASA Astrophysics Data System (ADS)

Power spectra of the components of the magnetic field parallel (Pzz) and perpendicular (Pzz+Pyy) to the local mean magnetic field direction were determined by wavelet methods from Ulysses' MAG instrument data during eighteen 10-day segments of its first North Polar pass at high latitude at solar minimum in 1995. The power depends on frequency f and the angle ? between the solar wind direction and the local mean field, and with distance from the Sun. This data includes the solar wind whose total power (Pxx + Pyy + Pzz) in magnetic fluctuations we previously reported depends on f and the angle ? nearly as predicted by the GS95 critical balance model of strong incompressible MHD turbulence. Results at much wider range of frequencies during six evenly-spaced 10-day periods are presented here to illustrate the variability and evolution with distance from the Sun. Here we investigate the aniso tropic scaling of Pzz(f,?) in particular because it is a reduced form of the Poloidal (pseudo-Alfvenic) component of the (incompressible) fluctuations. We also report the much larger Pxx(f,?)+Pyy(f,?) which is (mostly) reduced from the Toroidal (Alfvenic, i.e., perpendicular to both B and k) fluctuations, and comprises most of the total power. These different components of the total power evolve and scale differently in the inertial range. We compare these elements of the magnetic power spectral tensor with ``critical balance'' model predictions.

Forman, Miriam A.; Wicks, Robert T.; Horbury, Timothy S.; Oughton, Sean

2013-06-01

59

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

60

The thickness, electric field, and strain effects on the magnetic anisotropy of FeCo/MgO(001) thin films: A first principles study  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy of the FeCo/MgO(001) thin films with the effects of thickness, the electric field, and the strain of the in-plane lattice constant were investigated by first-principles calculations. The thickness dependence of the magnetic anisotropy of FeCo ultrathin films in the range of one to four monolayers was explored, and the films with one, three, and four FeCo monolayers preferred the in-plane easy axis of magnetization, while the film with two FeCo monolayers occupied the perpendicular anisotropy. In the presence of an electric field, the magnetic anisotropy energies for all four films could be enhanced; moreover, the transition of the easy axis of magnetization from in-plane to out-of-plane also could be obtained, and the transition electric field was related with their thickness. It could be found that the variation of the in-plane lattice constant resulted in the switching from the perpendicular to in-plane anisotropy for the film with two FeCo monolayers.

He, K. H.; Chen, J. S.

2012-04-01

61

Interplanetary magnetic field control of drifts and anisotropy of high-latitude irregularities  

Microsoft Academic Search

The paper investigates the extent of the control exerted by the north-south component of interplanetary magnetic field (IMF) on the large-scale plasma structures in the polar cap ionosphere, using data from spaced-receiver scintillation measurements at Thule and Sondrestrom (Greenland) obtained with the 250-MHz transmissions from quasi-geostationary polar beacon satellites. Results clearly demonstrate that the strength of F region irregularities, their

Sunanda Basu; C. Bryant; C. E. Valladares; Emanoel Costa; R. C. Livingston

1991-01-01

62

Slow Magnetic Relaxation in Octahedral Cobalt(II) Field-Induced Single-Ion Magnet with Positive Axial and Large Rhombic Anisotropy.  

PubMed

Pseudooctahedral mononuclear cobat(II) complex [Co(abpt)2(tcm)2] (1), where abpt = 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole and tcm = tricyanomethanide anion, shows field-induced slow relaxation of magnetization with U = 86.2 K and large axial and rhombic single-ion zero-field-splitting parameters, D = +48(2) cm(-1) and E/D = 0.27(2) (D = +53.7 cm(-1) and E/D = 0.29 from ab initio CASSCF/NEVPT2 calculations), thus presenting a new example of a field-induced single-ion magnet with transversal magnetic anisotropy. PMID:24853769

Herchel, Radovan; Váhovská, Lucia; Poto??ák, Ivan; Trávní?ek, Zden?k

2014-06-16

63

Propagation of ultra-high-energy cosmic ray nuclei in cosmic magnetic fields and implications for anisotropy measurements  

NASA Astrophysics Data System (ADS)

Recent results from the Pierre Auger Observatory (PAO) indicate that the composition of ultra-high-energy cosmic rays (UHECRs) with energies above 1019 eV may be dominated by heavy nuclei. An important question is whether the distribution of arrival directions for such UHECR nuclei can exhibit observable anisotropy or positional correlations with their astrophysical source objects despite the expected strong deflections by intervening magnetic fields. For this purpose, we have simulated the propagation of UHECR nuclei including models for both the extragalactic magnetic field (EGMF) and the Galactic magnetic field (GMF). We find that the GMF is particularly crucial for suppressing the anisotropy as well as source correlations. Assuming that only iron nuclei are injected steadily from sources with equal luminosity and spatially distributed according to the observed large scale structure in the local Universe, at the number of events published by the PAO so far (69 events above 5.5 × 1019 eV), the arrival distribution of UHECRs would be consistent with no auto-correlation at 95% confidence if the mean number density of UHECR sources ns ? 10-6 Mpc-3, and consistent with no cross-correlation with sources within 95% errors for ns ? 10-5 Mpc-3. On the other hand, with 1000 events above 5.5 × 1019 eV in the whole sky, next generation experiments can reveal auto-correlation with more than 99% probability even for ns ? 10-3 Mpc-3, and cross-correlation with sources with more than 99% probability for ns ? 10-4 Mpc-3. In addition, we find that the contribution of Centaurus A is required to reproduce the currently observed UHECR excess in the Centaurus region. Secondary protons generated by photodisintegration of primary heavy nuclei during propagation play a crucial role in all cases, and the resulting anisotropy at small angular scales should provide a strong hint of the source location if the maximum energies of the heavy nuclei are sufficiently high.

Takami, Hajime; Inoue, Susumu; Yamamoto, Tokonatsu

2012-07-01

64

Anisotropy induced wave birefringence in bounded supercritical plasma confined in a multicusp magnetic field  

SciTech Connect

Laboratory observation of rotation of the polarization axis ({theta}{sub c{approx}}20 deg. - 40 deg. with respect to vacuum) of a penetrating electromagnetic wave through a bounded supercritical plasma (plasma frequency {omega}{sub p}>wave frequency {omega}), confined in a multicusp magnetic field is reported. Birefringence of the radial and polar wave electric field components (E{sub r} and E{sub {theta}}) has been identified as the cause for the rotation, similar to a magneto-optic medium, however, with distinct differences owing to the presence of wave induced resonances. Numerical simulation results obtained by solving the Maxwell's equations by incorporating the plasma and magnetostatic field inhomogeneities within a conducting boundary shows a reasonable agreement with the experimental results.

Dey, Indranuj; Bhattacharjee, Sudeep [Department of Physics, Indian Institute of Technology Kanpur, Kanpur 208016 (India)

2011-04-11

65

Magnetoviscosity in suspensions of grains with finite magnetic anisotropy.  

PubMed

Coupling between magnetic and mechanical rotational degrees of freedom of fine ferromagnetic grains is provided by the energy of their magnetic anisotropy. In the limiting case of strong anisotropy, an applied stationary magnetic field induces the greatest obstacles to the "rigid dipole" spin in a vortex ferrofluid flow, while in the opposite ideal case, the "soft dipoles" twist freely with the liquid. As a result, the field-dependent part of the ferrofluids viscosity depends not only on the external magnetic field strength but also on the particle magnetic anisotropy. An explicit expression coming from simple physical arguments and describing both these dependencies of magnetoviscosity is derived and discussed. PMID:16906981

Morozov, Konstantin; Shliomis, Mark; Zahn, Markus

2006-06-01

66

Micromagnetics of shape anisotropy based permanent magnets  

NASA Astrophysics Data System (ADS)

In the search for rare-earth free permanent magnets, various ideas related to shape anisotropy are being pursued. In this work we assess the limits of shape contributions to the reversal stability using micromagnetic simulations. In a first series of tests we altered the aspect ratio of single phase prolate spheroids from 1 to 16. Starting with a sphere of radius 4.3 times the exchange length Lex we kept the total magnetic volume constant as the aspect ratio was modified. For a ferromagnet with zero magnetocrystalline anisotropy the maximum coercive field reached up to 0.5 times the magnetization Ms. Therefore, in materials with moderate uniaxial magnetocrystalline anisotropy, the addition of shape anisotropy could even double the coercive field. Interestingly due to non-uniform magnetization reversal there is no significant increase of the coercive field for an aspect ratio greater than 5. A similar limit of the maximum aspect ratio was observed in cylinders. The coercive field depends on the wire diameter. By decreasing the wire diameter from 8.7Lex to 2.2Lex the coercive field increased by 40%. In the cylinders nucleation of a reversed domain starts at the corners at the end. Smoothing the edges can improve the coercive field by about 10%. In further simulations we compacted soft magnetic cylinders into a bulk-like arrangement. Misalignment and magnetostatic interactions cause a spread of 0.1Ms in the switching fields of the rods. Comparing the volume averaged hysteresis loops computed for isolated rods and the hysteresis loop computed for interacting rods, we conclude that magnetostatic interactions reduce the coercive field by up to 20%.

Bance, Simon; Fischbacher, Johann; Schrefl, Thomas; Zins, Inga; Rieger, Gotthard; Cassignol, Caroline

2014-08-01

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

Magnetic anisotropy of strained epitaxial manganite films  

SciTech Connect

The in-plane magnetic anisotropy of epitaxial La{sub 0.7}Sr{sub 0.3}MnO{sub 3} (LSMO) films is studied at room temperature by the following three independent techniques: magnetooptical Kerr effect, ferromagnetic resonance at a frequency of 9.61 GHz, and recording of absorption spectra of electromagnetic radiation at a frequency of 290.6 MHz. The films are deposited onto NdGaO{sub 3} (NGO) substrates in which the (110)NGO plane is tilted at an angle of 0-25.7 Degree-Sign to the substrate plane. The uniaxial magnetic anisotropy induced by the strain of the film is found to increase with the tilt angle of the (110)NGO plane. A model is proposed to describe the change in the magnetic anisotropy energy with the tilt angle. A sharp increase in the radio-frequency absorption in a narrow angular range of a dc magnetic field near a hard magnetization axis is detected The anisotropy parameters of the LSMO films grown on (110)NGO, (001)SrTiO{sub 3}, and (001)[(LaAlO{sub 3}){sub 0.3} + (Sr{sub 2}AlTaO{sub 6}){sub 0.7}] substrates are compared.

Demidov, V. V., E-mail: demidov@cplire.ru; Borisenko, I. V.; Klimov, A. A.; Ovsyannikov, G. A.; Petrzhik, A. M.; Nikitov, S. A. [Russian Academy of Sciences, Institute of Radio-Engineering and Electronics (Russian Federation)

2011-05-15

69

Three-dimensional dynamics of a particle with a finite energy of magnetic anisotropy in a rotating magnetic field.  

PubMed

A model of a single ferromagnetic particle with a finite coupling energy of the magnetic moment with the body of the particle is formulated, and regimes of its motion in a rotating magnetic field are investigated. Regimes are possible that are synchronous and asynchronous with the field. In a synchronous regime the easy axis of the particle is in the plane of the rotating magnetic field at low frequencies (a planar regime) and on the cone at high frequencies (a precession regime). The stability of these regimes is investigated, and it is shown that the precession regime is stable for field strengths below the critical value. In a particular range of field strength value, irreversible jumps of the magnetic moment take place in the asynchronous planar regime. The stability of this regime is investigated, and it is shown that it is stable for field strengths above the critical value, which depends on the frequency. The implications of these results for the energy dissipation in a rotating field are analyzed, and it is shown that the maximum of the heat production near the transition to the synchronous regime is flattened out by the transition to the precession regime. PMID:24483452

C?murs, J; C?bers, A

2013-12-01

70

Three-dimensional dynamics of a particle with a finite energy of magnetic anisotropy in a rotating magnetic field  

NASA Astrophysics Data System (ADS)

A model of a single ferromagnetic particle with a finite coupling energy of the magnetic moment with the body of the particle is formulated, and regimes of its motion in a rotating magnetic field are investigated. Regimes are possible that are synchronous and asynchronous with the field. In a synchronous regime the easy axis of the particle is in the plane of the rotating magnetic field at low frequencies (a planar regime) and on the cone at high frequencies (a precession regime). The stability of these regimes is investigated, and it is shown that the precession regime is stable for field strengths below the critical value. In a particular range of field strength value, irreversible jumps of the magnetic moment take place in the asynchronous planar regime. The stability of this regime is investigated, and it is shown that it is stable for field strengths above the critical value, which depends on the frequency. The implications of these results for the energy dissipation in a rotating field are analyzed, and it is shown that the maximum of the heat production near the transition to the synchronous regime is flattened out by the transition to the precession regime.

CÄ«murs, J.; CÄ`bers, A.

2013-12-01

71

Tailored magnetic anisotropy in an amorphous trilayer  

SciTech Connect

An amorphous Co{sub 68}Fe{sub 24}Zr{sub 8}(3 nm)/Al{sub 70}Zr{sub 30}(3 nm)/Co{sub 68}Fe{sub 24}Zr{sub 8}(3 nm) trilayer system has been investigated using in-plane and out-of-plane angular dependent ferromagnetic resonance at different frequencies. The in-plane magnetic anisotropy is uniaxial, retaining its value of (2.9 {+-} 0.1) x 10{sup 3} J/m{sup 3} for each magnetic layer, whereas its direction was tailored independently in an arbitrary manner by applying an external magnetic field during the film deposition. The perpendicular anisotropy constant, supposed to reflect the interface quality, is nearly identical for both layers. Furthermore, the magnetic layers act independently upon each other due to the absence of interlayer coupling.

Fu Yu [Department of Physics, Southeast University, 211189 Nanjing (China); Fakultaet fuer Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universitaet Duisburg-Essen, 47048 Duisburg (Germany); Barsukov, I.; Spasova, M.; Lindner, J.; Meckenstock, R.; Farle, M. [Fakultaet fuer Physik and Center for Nanointegration Duisburg-Essen (CeNIDE), Universitaet Duisburg-Essen, 47048 Duisburg (Germany); Raanaei, H. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala (Sweden); Department of Physics, Persian Gulf University, Bushehr 75168 (Iran, Islamic Republic of); Hjoervarsson, B. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala (Sweden)

2011-06-01

72

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

73

Magnetization process and quantum entanglement in spin-1 XXZ model with single-ion anisotropy under external field  

NASA Astrophysics Data System (ADS)

By the infinite time-evolving block decimation (iTEBD) technique, the magnetization process and the quantum phase transitions (QPTs) in the spin-1 XXZ model with single-ion anisotropy under external field are investigated. It is found that, all the phases will be destroyed by a sufficient strong magnetic field. Before they come into the ferromagnetic (fully polarized) phase, some interesting intermediate phases are induced. A pseudo order Oixy=?{<+<} with finite truncation dimension ? can be used to describe the XY1 phase. Especially, the Oxyi with finite ? is found to be nonzero in the XY1 phase, but vanishes in the XY2 phase. It means that two kinds of XY phases can be distinguished by the pseudo order parameter Oxyi. All the QPTs can be described by the behavior of the entanglement entropy and the ground-state energy. QPTs from the XY phase to the large-D, Haldane, and antiferromagnetic phases are found to be infinite-order BKT type transitions, but the QPTs from the XY1 phase to the ferromagnetic phase and XY2 have second-order characters. In addition, doubly degenerate entanglement spectra are observed in the Haldane phase.

Liu, Guang-Hua; Li, Wei; You, Wen-Long; Su, Gang; Tian, Guang-Shan

2014-06-01

74

Note on the crystal-field-induced magnetic anisotropy in R2Fe14B compounds and other rare-earth-based permanent magnet materials  

Microsoft Academic Search

The compound Gd2Fe14B was investigated by means of 155Gd Mossbauer spectroscopy. From the value of the quadrupole splitting found in this compound and in the compounds GdCo5 and Gd2Co17 investigated earlier the authors determined experimental values for the corresponding second-order crystal-field parameters V20, which mainly govern the magnetocrystalline anisotropy in related permanent magnet materials such as Nd2Fe14B, SmCo5 and Sm2Co17.

K. H. J. Buschow; J. W. C. de Vries; R. C. Thiel

1985-01-01

75

Electron mass anisotropy of BaZrO3 doped YBCO thin films in pulsed magnetic fields up to 30 T  

NASA Astrophysics Data System (ADS)

The high anisotropy of the critical current density in the high-temperature superconductor YBa2Cu3O6+x can be compensated by changing the pinning landscape, for example, through doping with BaZrO3. We measure the change due to BaZrO3 doping in the effective electron mass anisotropy, ?, by resistive measurements of the upper critical field in pulsed high magnetic fields. It is found that the angular dependence of the upper critical field follows the Blatter scaling up to 30 T but the irreversibility field does not. We also report a significant reduction in the effective electron mass anisotropy from 6.0 to 3.4 by BaZrO3 doping.

Palonen, H.; Huhtinen, H.; Shakhov, M. A.; Paturi, P.

2013-04-01

76

Scaling and anisotropy of magnetohydrodynamic turbulence in a strong mean magnetic field  

NASA Astrophysics Data System (ADS)

We present a new analysis of the anisotropic spectral energy distribution in incompressible magnetohydrodynamic (MHD) turbulence permeated by a strong mean magnetic field. The turbulent flow is generated by high-resolution pseudo-spectral direct numerical simulations with large-scale isotropic forcing. Examining the radial energy distribution for various angles ? with respect to B reveals a specific structure which remains hidden when not taking axial symmetry with respect to B0 into account. For each direction, starting at the forced large-scales, the spectrum first exhibits an amplitude drop around a wavenumber k0 which marks the start of a scaling range and goes on up to a dissipative wavenumber kd(?). The 3D spectrum for k ? k0 is described by a single ?-independent functional form F(k/kd), the scaling law being the same in every direction. The previous properties still hold when increasing the mean field from B0=5 up to B0=10 (in units of brms), as well as when passing from resistive to ideal flows. We conjecture that at fixed B0 the direction-independent scaling regime is reached when increasing the Reynolds number above a threshold which raises with increasing B0.

Mueller, W.; Grappin, R.

2010-12-01

77

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

78

Electric-field effects on thickness dependent magnetic anisotropy of sputtered MgO/Co40Fe40B20/Ta structures  

NASA Astrophysics Data System (ADS)

We have investigated the effect of applied electric field EG on thickness dependent magnetic anisotropy of sputtered Co40Fe40B20 sandwiched with MgO and Ta. The range of CoFeB thickness explored is 2 nm and below. As the thickness is reduced, the easy axis of magnetization becomes perpendicular from in-plane. We show that perpendicular magnetic anisotropy of in-plane samples and coercivity of perpendicular samples can be modified by applying EG at room temperature. Furthermore, superparamagnetic behavior is observed for CoFeB layers with further reduced thickness below ~0.9 nm, where electric-field effect is also observed below their blocking temperature.

Endo, M.; Kanai, S.; Ikeda, S.; Matsukura, F.; Ohno, H.

2010-05-01

79

Magnetic anisotropy in obliquely deposited cobalt films  

Microsoft Academic Search

The anisotropy field in cobalt films deposited obliquely by sputtering was separated into the magnetocrystalline anisotropy field, Hk(cryst), and the anisotropy field due to the shape anisotropy, Hk(shape), based on the {0002} pole figure. The incidence angle was 45° and the substrate temperature was 332 K. The film thickness ranged from 0.4 to 3.8 ?m. The thickness dependence of Hk(shape)

K. Itoh; K. Hara; M. Kamiya; K. Okamoto; T. Hashimoto; H. Fujiwara

1995-01-01

80

Neutrino mass effects on vector and tensor CMB anisotropies in the presence of a primordial magnetic field  

SciTech Connect

If a primordial magnetic field (PMF) is present during photon decoupling and afterward, a finite neutrino mass can affect all modes of the CMB. In this work, we expand on earlier studies of the scalar mode effects by constructing the vector and tensor-mode equations in the presence of massive neutrinos and a PMF. We compute the power spectrum of the various modes in an illustrative example and find that the neutrino mass can significantly affect the vector and tensor modes when a PMF exists, while the effects are negligible for no PMF. The most prominent result of the present analysis is the behavior of the EE (grad-like polarization power spectrum) component of the tensor mode at low multipoles. For massive neutrinos the EE mode can become comparable to the observed primary anisotropy. Therefore, if and when the EE mode power spectrum is measured at low multipoles the possibility exists to place a strong constraint on the sum of the neutrino masses.

Kojima, Kazuhiko; Ichiki, Kiyotomo; Yamazaki, Dai G.; Kajino, Toshitaka; Mathews, Grant J. [Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan and Division of Theoretical Astrophysics, National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Research Center for the Early Universe, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku 113-0033 (Japan); Division of Theoretical Astrophysics, National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan and Division of Theoretical Astrophysics, National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA and Division of Theoretical Astrophysics, National Astronomical Observatory, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2008-08-15

81

Hysteresis of Two Inequivalent Planar Magnets with Anisotropy  

Microsoft Academic Search

We study the hysteresis loops for two inequivalent planar magnets with equal magnetic moments and perpendicular anisotropy, which interact via the dipole-dipole interaction. We emphasize locating distinct zero net-magnetization states in zero applied field. We consider a wide range of perpendicular anisotropy constants K1 and K_2and dipole interaction strength g. For a wide range of parameter space (K_2\\/K_1, g\\/K_1) and

Benjamin T. King; M. Amin Kayali; Wayne M. Saslow

2004-01-01

82

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

83

Magnetic anisotropy of nickel nanowire array in porous silicon  

NASA Astrophysics Data System (ADS)

Ordered nickel nanowire arrays formed by electrochemical deposition in a mesoporous silicon matrix have been studied by the ferromagnetic resonance technique. It is established that the samples exhibit uniaxial magnetic anisotropy of the easy-axis or easy-plane type depending on the matrix porosity. Values of the anisotropy field and g-factor in the samples are determined.

Rusetskii, M. S.; Kazyuchits, N. M.; Baev, V. G.; Dolgii, A. L.; Bondarenko, V. P.

2011-05-01

84

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

85

Magnetic anisotropy of the Trenton limestone revisited  

SciTech Connect

Previous studies have shown clear differences between the anisotropies of low-field magnetic susceptibility (LFS) and of anhysteretic remanent magnetization (ARM) in samples of the Ordovician Trenton limestone from Trenton Falls, NY. ARM was found to be significantly more anisotropic than LFS, and to exhibit a well-defined east-northeasterly lineation which was not apparent in anisotropy of magnetic susceptibility (AMS). Because of significant local variation in mean LFS (by approximately a factor of two) at this locality, it has been possible to reanalyze the AMS of these samples by the method of Henry (1983), which in some cases allows mathematical differentiation of the ferromagnetic and paramagnetic susceptibility tensors. The ferromagnetic susceptibility tensor obtained in this way shows the same tectonic shortening apparent in the ARM anisotropy, but surprisingly, it shows no evidence of horizontal foliation. The paramagnetic tensor is horizontally foliated, with no lineation. The difference between the ferromagnetic susceptibility and ARM tensors suggests different ferrromagnetic sources of ARM and LFS.

Jackson, M. (Univ. of Minnesota, Minneapolis (USA))

1990-07-01

86

Nonvolatile electric-field modulation of magnetic anisotropy in perpendicularly magnetized L10-FePt/(001)[Pb(Mg1/3Nb2/3)]0.7-(PbTiO3)0.3 heterostructures  

NASA Astrophysics Data System (ADS)

We grow perpendicular L10-FePt films epitaxially on (001)[Pb(Mg1/3Nb2/3)]0.7-(PbTiO3)0.3 ferroelectric substrates. Due to the magnetostriction effect, the out-of-plane coercivity (Hc?) of the L10-FePt varies with applied electric fields, showing an asymmetric butterfly-like loop. The Hc? at the zero-electric-field state (Hc?,0) shows a nonvolatile change, depending on the direction of the poling electric field. The magnitude of nonvolatile magnetic anisotropy change, induced by the ferroelectric field effect, can be comparable to the anisotropy change induced by pure electric fields. The nonvolatile magnetic anisotropy change is inversely proportional to the FePt thickness and can be eliminated by inserting a metallic intermediate layer.

Tsai, Wu-Chang; Liao, Sheng-Chieh; Huang, Kuo-Feng; Wang, Ding-Shuo; Lai, Chih-Huang

2013-12-01

87

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

88

Tectonic applications of magnetic susceptibility and its anisotropy  

Microsoft Academic Search

Anisotropy of low field magnetic susceptibility (AMS) is a versatile petrofabric tool. For magnetite, AMS primarily defines grain-shape anisotropy; for other minerals, AMS expresses crystallographic control on magnetic properties. Thus, we may infer the orientation-distribution of a dominant mineral from the AMS of a rock. AMS principal directions can record current directions from sediment, flow-directions from magma, finite-strain directions from

G. J. Borradaile; B. Henry

1997-01-01

89

Tailoring the magnetic anisotropy of thin film permalloy microstrips by combined shape and induced anisotropies  

NASA Astrophysics Data System (ADS)

The sensitivity of magnetic sensors based on the Giant Magneto-Impedance effect can be enhanced using high permeability materials with a well-defined but small transverse anisotropy. We describe an experimental study performed on multilayered, permalloy-based thin films deposited by sputtering under a magnetic field that produces a homogeneous uniaxial anisotropy in the plane of the film. Patterning of the deposit by photolithographic methods into strip-shaped samples (with their long direction perpendicular to the induced anisotropy) establishes a longitudinal shape anisotropy that competes with the transversal one induced at deposition. The combination and competition of the two mutually perpendicular uniaxial anisotropies result in an effective one with a reduced magnitude (the difference between both of them) in the transversal direction. As the strength of the shape anisotropy is determined by the relation between width and length of the stripe, the magnitude of the effective anisotropy can be conveniently modulated by adequately selecting the aspect ratio of the patterned sample. The hysteresis loops measured by Kerr effect magnetometry confirm that the effective transversal anisotropy field can be reduced from 5 to 1 Oe which should concomitantly increase the sensitivity of thin film magneto-impedance sensors.

García-Arribas, Alfredo; Fernández, Eduardo; Svalov, Andrey V.; Kurlyandskaya, Galina V.; Barrainkua, Ane; Navas, David; Barandiaran, José Manuel

2013-04-01

90

Effects of hydrostatic pressure on the electron g_{\\\\parallel } factor and g-factor anisotropy in GaAs (Ga, Al)As quantum wells under magnetic fields  

Microsoft Academic Search

The hydrostatic-pressure effects on the electron-effective Landé g_{\\\\parallel } factor and g-factor anisotropy in semiconductor GaAs-Ga1-xAlxAs quantum wells under magnetic fields are studied. The g_{\\\\parallel } factor is computed by considering the non-parabolicity and anisotropy of the conduction band through the Ogg-McCombe effective Hamiltonian, and numerical results are displayed as functions of the applied hydrostatic pressure, magnetic fields, and quantum-well

N. Porras-Montenegro; C. A. Duque; E. Reyes-Gómez; L. E. Oliveira

2008-01-01

91

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

92

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

93

Pressure anisotropy along field lines in the low collisionality regime  

Microsoft Academic Search

A Chapman-Enskog-like procedure is used to calculate the neoclassical pressure anisotropy in a simple bumpy cylinder magnetic field model B(l)=B_0(1+2?sin^2fracpilL). We consider small field modulations and a steady state situation within the banana regime. Unlike the collisional regime, where particles don't experience the effect of the entire field variation, the anisotropy p_allel-p_? is not a simple sinusoidal oscillation but is

A. L. García-Perciante; J. D. Callen; K. C. Shaing; C. C. Hegna

2004-01-01

94

Magnetic anisotropy and porosity of chondrites  

NASA Astrophysics Data System (ADS)

The measured magnetic anisotropy and porosity of various chondrites are found to be inversely correlated when they are considered by class of chondrites (E, H and L + LL). For chondrites with similar porosities, the anisotropies for H and E chondrites are smaller than for L and LL chondrites, which have lower metal contents. The anisotropy and porosity are not dependent on the metamorphic grade of chondrites. K-Ar ages of strongly anisotropic and/or less porous chondrites are younger than those of less anisotropic and/or more porous chondrites. These observations suggest that impacts which reset the K-Ar ages produced the anisotropy and reduced the porosity of chondrites.

Sugiura, N.; Strangway, D. W.

1983-01-01

95

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

96

Interplay between crystal electric field and magnetic exchange anisotropies in the heavy-fermion antiferromagnet YbRhSb under pressure  

NASA Astrophysics Data System (ADS)

We report the pressure effect on the magnetic ground state of the heavy-fermion (HF) canted antiferromagnet YbRhSb (orthorhombic ?-TiNiSi-type) by means of magnetization and resistivity measurements using a single crystal. At ambient pressure, this compound undergoes a transition at TM1=2.7 K into a canted antiferromagnetic (AF) state with a small spontaneous moment of 3×10-3?B/Yb. With increasing pressure P above 1 GPa, another magnetic transition occurs at TM2 above TM1, and TM1(P) has a deep minimum of 2.5 K at 1.7 GPa. For P?2 GPa, the canted AF structure changes to a ferromagnetic (FM) one, where a large moment 0.4 ?B/Yb lies in the orthorhombic b-c plane and a metamagnetic transition occurs at B ||a = 1.5 T. This unusual FM state below TM3?4.3 K is ascribed to the balance between the single-ion crystalline electric field (CEF) anisotropy with easy direction ||a and the intersite exchange interaction with easy b-c plane. Furthermore, we have investigated the pressure dependence of TM3 up to 20.4 GPa using electrical resistivity measurements. The structural stability under pressures up to 19 GPa was examined by x-ray diffraction. We find that TM3 above 2.5 GPa steeply increases up to about 7 K, showing a broad maximum and then slightly decreases with increasing pressure above 8 GPa, while the structure remains unchanged. We attribute the enhancement of TM3 above 2.5 GPa to an increase of the CEF anisotropy with respect to magnetic exchange anisotropy. Finally, we compare and discuss the volume dependence of magnetic phase diagram of YbRhSb with the isostructural HF ferromagnet YbNiSn.

Umeo, K.; Yamane, H.; Kubo, H.; Muro, Y.; Nakamura, F.; Suzuki, T.; Takabatake, T.; Sengupta, K.; Forthaus, M. K.; Abd-Elmeguid, M. M.

2012-01-01

97

Direct Observation of Magnetic Anisotropy in an Individual Fe4 Single-Molecule Magnet  

NASA Astrophysics Data System (ADS)

We study three-terminal charge transport through individual Fe4 single-molecule magnets. Magnetic anisotropy of the single molecule is directly observed by introducing a spectroscopic technique based on measuring the position of the degeneracy point as a function of gate voltage and applied magnetic field. A nonlinear field-dependence is observed which changes by rotating the sample and is, thus, a direct proof of magnetic anisotropy. The sensitivity of this method allows us to observe small changes in the orientation and magnitude of the anisotropy in different charge states. We find that the easy axes in adjacent states are (almost) collinear.

Burzurí, E.; Zyazin, A. S.; Cornia, A.; van der Zant, H. S. J.

2012-10-01

98

On the magnetic anisotropy of superduplex stainless steel  

NASA Astrophysics Data System (ADS)

The austenite-ferrite superduplex stainless steel (SDSS) is essentially an Fe-Cr-Ni alloy to which additional elements (e.g. Mo, Mn, Si, Cu, C, P, S) were added so as to confer additional advantageous characteristics such as higher mechanical strength and resistance to corrosion. Many of its applications require the process of rolling which, due to the two-phase character, induces a marked texturing, elongation of grains, and directional ordering in each of the constituent phases. This, in turn, imprints a strong anisotropic features in the mechanical, magnetic, and other properties. Using various experimental techniques, such as magnetization and ac susceptibility, this work investigated the induced magnetic anisotropy. An easy axis (parallel to the rolling direction) anisotropy was observed. The nature of the magnetic anisotropy, manifested during low and high applied magnetic fields, will be discussed in terms of the combined influences of two main anisotropies, namely shape anisotropy (arising from demagnetizing forces) and texture anisotropy (arising from the induced preferred orientation).

ElMassalami, M.; Palatnik-de-Sousa, I.; Areiza, M. C. L.; Rebello, J. M. A.; Elzubair, A.

2011-10-01

99

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

100

Determination of the anisotropy constant and saturation magnetization of magnetic nanoparticles from magnetization relaxation curves  

Microsoft Academic Search

We have developed a new method for the determination of the anisotropy constant and saturation magnetization of magnetic nanoparticles.\\u000a This method deals with the approximation of magnetization relaxation curves measured upon application and further fast switching\\u000a off the dc magnetizing field. The relaxation process is registered in the time interval from 6 ?s to several minutes by using\\u000a a scanning high-T

Ivan Volkov; Maxim Chukharkin; Oleg Snigirev; Alexander Volkov; Saburo Tanaka; Coenrad Fourie

2008-01-01

101

Can large magnetic anisotropy and high spin really coexist?  

PubMed

This theoretical study discusses the interplay of the magnetic anisotropy and magnetic exchange interaction of two Mn6 complexes and suggests that large magnetic anisotropy is not favoured by a high spin state of the ground state. PMID:18399403

Ruiz, Eliseo; Cirera, Jordi; Cano, Joan; Alvarez, Santiago; Loose, Claudia; Kortus, Jens

2008-01-01

102

Measurements of Magnetic Anisotropy in Sickle Cells.  

National Technical Information Service (NTIS)

Room temperature magnetic measurements in deoxigenated sickle cells showed the existence of magnetic anisotropy, delta chi=1,29 x 10 exp -3 . This effect was supposed paramagnetic and considered to be due to the iron atoms of the hemoglobin molecules whic...

L. H. Salvo Souza

1982-01-01

103

Influence of Electric and Magnetic Fields on the Microwave Dielectric Constant of a Liquid Crystal with a Positive Dielectric Anisotropy.  

National Technical Information Service (NTIS)

The dielectric constant and loss in the anisotropic and normal liquid phases of anisal-p-aminoazobenzene were measured at frequencies of 6 and 24 kMc/sec. Measurements were made with an external magnetic field parallel and perpendicular to the microwave e...

E. F. Carr

1964-01-01

104

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

105

Magnetic anisotropy of polycrystalline magnetoferritin investigated by SQUID and electron magnetic resonance  

NASA Astrophysics Data System (ADS)

Magnetoferritin molecules with an average inorganic core diameter of 5.7±1.6 nm and polycrystalline internal structure were investigated by a combination of transmission electron microscopy, magnetic susceptibility, magnetization, and electron magnetic resonance (EMR) experiments. The temperature and frequency dependence of the magnetic susceptibility allowed for the determination of the magnetic anisotropy on an experimental time scale which spans from seconds to nanoseconds. In addition, angle-dependent EMR experiments were carried out for the determination of the nanoparticle symmetry and internal magnetic field. Due to the large surface to volume ratio, the nanoparticles show larger and uniaxial rather than cubic magnetic anisotropies compared to bulk maghemite and magnetite.

Moro, F.; de Miguel, R.; Jenkins, M.; Gómez-Moreno, C.; Sells, D.; Tuna, F.; McInnes, E. J. L.; Lostao, A.; Luis, F.; van Slageren, J.

2014-06-01

106

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

107

Analysis of the in-plane magnetic anisotropy in amorphous ribbons obtained by torque magnetometry  

NASA Astrophysics Data System (ADS)

The evolutions of the uniaxial torque and magnetization with the applied magnetic field allow us to discriminate the sources of in-plane magnetic anisotropy in amorphous ribbons. In order to determine the magnetic anisotropy sources, a simple model has been developed for an inhomogeneous material. We apply this model to explain the quite different behavior observed in the evolution of the uniaxial torque amplitude with the applied magnetic field of two commercial Co-based amorphous alloys.

Tejedor, M.; García, J. A.; Carrizo, J.; Elbaile, L.; Santos, J. D.; Mira, J.; Rivas, J.

1999-08-01

108

Magnetic anisotropy and domain patterning of amorphous films by He-ion irradiation  

SciTech Connect

The magnetic anisotropy in amorphous soft magnetic FeCoSiB films was modified by He-ion irradiation. A rotation of uniaxial anisotropy depending on the applied field direction in the irradiated areas is observed by magnetometry and complementary domain observation by Kerr microscopy. No significant degradation in magnetic properties relative to the as-deposited state is found from the magnetization loops on nonpatterned films. Using irradiation together with photolithography, the films were treated locally, resulting in 'anisotropy patterned' structures. Complicated periodic domain patterns form due to the locally varying anisotropy distribution. Overall magnetic properties and domain patterns are adjusted.

McCord, Jeffrey; Gemming, Thomas; Schultz, Ludwig; Fassbender, Juergen; Liedke, Maciej Oskar; Frommberger, Michael; Quandt, Eckhard [Leibniz Institute for Solid State and Materials Research IFW Dresden, Helmholtzstrasse 20, 01069 Dresden (Germany); Institut fuer Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf, Bautzner Landstrasse 128, 01328 Dresden (Germany); Research Center CAESAR, Ludwig-Erhard-Allee 2, 53175 Bonn (Germany)

2005-04-18

109

Magnetic field dependence of the basal-plane superconducting anisotropy in YBa2Cu4O8 from small-angle neutron scattering measurements of the vortex lattice  

NASA Astrophysics Data System (ADS)

We report a study of the basal-plane anisotropy of the superfluid density in underdoped YBa2Cu4O8 (Y124), showing the effects of both the CuO2 planes and the fully occupied CuO chains. From small-angle neutron scattering measurements of the vortex lattice, we can infer the superconducting (SC) properties for a temperature (T) range T = 1.5 K to Tc and magnetic induction B from 0.1 to 6 T. We find that the superfluid density along a has a simple d-wave T dependence. However, along b (the chain direction) the superfluid density falls much more rapidly with T and also with increasing field. This strongly suggests the suppression of proximity-effect-induced superconductivity in the CuO chains. In addition, our results do not support a common framework for the low-field in-plane SC response in Y124 and related YBa2Cu3O7, and also indicate that any magnetic field induced charge-density-wave order in Y124 exists only for fields above 6 T.

White, Jonathan S.; Bowell, Charlotte J.; Cameron, Alistair S.; Heslop, Richard W.; Mesot, Joël; Gavilano, Jorge L.; Strässle, Simon; Mächler, Lars; Khasanov, Rustem; Dewhurst, Charles D.; Karpinski, Janusz; Forgan, Edward M.

2014-01-01

110

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

111

Microwave studies of magnetic anisotropy of Co nanowire arrays  

NASA Astrophysics Data System (ADS)

The effect of magnetocrystalline anisotropy and dipolar interactions in Co nanowire arrays is studied by ferromagnetic resonance (FMR). Microwave measurements performed by the microstripline method are reported for two series of crystalline hcp Co (with the c axis nominally perpendicular [Co(c?)] and parallel to the wires [Co(c?)]) and an amorphous alloy with Co as the main component-Co94Fe5B1. Extrapolation of the high field linear part of the resonance curve (frequency versus dc field) permitted an evaluation of the effective anisotropy fields for saturated samples, as well as of the intrinsic fields HK, showing that the great differences between the three series are due to the magnetocrystalline anisotropy. The HK values for the two series of Co are discussed in terms of a model which accounts for the effect of the distributions of the c axis orientation in systems of uniaxial ferromagnets. The observed dependence of the effective anisotropy fields on the array geometry (wire length and diameter) is interpreted in terms of the interwire dipolar interactions and found to be in agreement with theoretical predictions based on a micromagnetic model. The fact that the resonance frequencies at Hdc=0 are geometry dependent shows that magnetostatic interactions are still significant at remanence. A second series of FMR experiments was performed at constant frequency (38 GHz), with the purpose of obtaining the angle dependence of the resonance field. These experiments provided an alternative method for the evaluation of the effective anisotropy field. The angle dependence of the resonance field for Co(c?) fitted the simplest equation for magnets with uniaxial anisotropy, obtained considering only the first order term in the expression of the magnetocrystalline energy as a function of the magnetization orientation. The same is not true for Co(c?), which required inclusion of a second order term.

Sklyuyev, A.; Ciureanu, M.; Akyel, C.; Ciureanu, P.; Yelon, A.

2009-01-01

112

Effects of Magnetic Anisotropy on Magnetization in Molecular Mesoscopic Magnet Fe8  

NASA Astrophysics Data System (ADS)

We have measured the temperature, magnetic field and angular dependences of the magnetization of a single crystal of a molecular mesoscopic magnet [(C6H15N3)6Fe8O2(OH)12]Br7(H2O)Br·8H2O, Fe8. The molecule Fe8 consists of eight Fe3+ ions with spins of s=5/2. The experimental results of the magnetizations at low temperatures show large anisotropy that is dependent on the orientation of the external magnetic field with respect to the crystal axis. These results are well explained by the Hamiltonian for an isolated molecule with total spin S=10 and anisotropies of D=-0.276 K and E=-0.035 K. The easy axis is determined to be oriented with an azimuthal angle of 16° from the a-axis in the ab-plane and an inclinational angle of 0.7° from the ab-plane.

Ueda, Miki; Maegawa, Satoru; Miyasaka, Hitoshi; Kitagawa, Susumu

2001-10-01

113

Manipulating the magnetic anisotropy of 3d transition-metal films on Cu(001) and their alloys on Rh(001) by electric field  

NASA Astrophysics Data System (ADS)

The mechanism of electric field (EF) effects on the magnetocrystalline anisotropy (MCA) in metallic films is investigated by first-principles calculations. Start with a simple system of Fe, Co and Ni monolayer on Cu(001) substrate, we show that the key factor for a large EF-induced MCA modification is that the energy bands cross of d and d (or d and d) is close to the Fermi level. In order to enhance the MCA modification by EF, 4d metal substrates (Rh, Pd) are also discussed. In particular, we find that the magnetization direction can be switched from out-of-plane to in-plane by a small EF for Fe1-xCox alloy films on Rh(001) substrate with x=0.5.

Wang, Zhe; Zhang, Yun; Cao, Juexian

2013-08-01

114

Anisotropy of Magnetic Susceptibility (AMS) of Carbonate Rocks as a Proxy for the Strain Field near the Dead Sea Transform in Northern Israel  

NASA Astrophysics Data System (ADS)

To exploit the potential of anisotropy of magnetic susceptibility (AMS) axes (k1, k2, k3) and magnitudes as a tool to estimate the strain field around major faults, the AMS of calcite-bearing diamagnetic rocks that crop out next to the Dead Sea Transform (DST) were measured. The low-field bulk-susceptibility of Bar-Kokhba limestone formation is -10.67±1.69 [µSI], very close to the value of a single calcite crystal. Thermomagnetic curves show temperature independent and reversible behavior. Chemical composition analysis indicates minor amounts of Fe contents <300 ppm. Results of XRD diffraction and petrofabric study of thin-sections and SEM images indicate that the Bar-Kokhba rocks are calcite mono-mineralic rocks. The magnetic fabrics are solely controlled by the alignment of c-axes of almost pure calcite crystals and help to assess the direction of the maximum shortening prevailing post-deposition and during the tectonic evolution of the DST. In one studied site, high Fe contents <6000 ppm were found, which are associated with young morphological processes of chemical alteration. In this site, thermomagnetic curves indicate temperature dependency and irreversibility. IRM curves show saturation around 200 mT, evidence of ferro/ferimagnetic minerals. AARM measurements reveal isotropic fabric which suggesting that the ferro/ferimagnetic minerals are contributing no anisotropy to the AMS. The AMS of the diamagnetic fabric is masked by a paramagnetic fabric of Fe-bearing minerals. Using liner correlation between Fe content and bulk susceptibility we applied a novel tensor subtraction method and successfully isolated the diamagnetic fabric from the total AMS. The paramagnetic fabric has characteristics of sedimentary fabrics, while that of the diamagnetic fabric has tectonic characteristics. The isolation process indicates that the AMS of carbonate rocks is mostly controlled by the diamagnetic phase, where the Fe content is below 500 ppm. Differences in the degree of anisotropy parameters of the Bar-Kohkba rocks are probably related to differences in strain magnitudes accumulated in the rocks. Based on the AMS measurements one major group of AMS k3 axes are defined, showing maximum horizontal shortening parallel to the N-S striking DST. The present study demonstrates the useful application of AMS measurements in "Fe-free" limestones, which serve as recorders of the strain field next to plate-bounding faults. This opens a new frontier in using AMS as a proxy for strain.

Issachar, Ran; Levi, Tsafrir; Weinberger, Ram; Marco, Shmuel

2014-05-01

115

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 therefore the compass will respond 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.

Vu Bioengineering Ret Program

116

A novel bi-directional magnetic microactuator using electroplated permanent magnet arrays with vertical anisotropy  

Microsoft Academic Search

A novel bi-directional magnetic microactuator using electroplated permanent magnet arrays has been fabricated and tested in this work. To realize the microactuator, a new electroplating technique has been developed to improve vertical magnetic anisotropy in CoNiMnP-based permanent magnet arrays. By applying magnetic field during electroplating, vertical coercivity and remanence have been increased up to 1100 Oe and 1900 G. After

Hyoung J. Cho; Chong H. Ahn

2000-01-01

117

Ag induced enhancement of perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Some interesting magnetic properties were observed after Ag ultrathin films were deposited on Co/Pt(1 1 1). The spin reversal of Co can be prevented when Ag atoms cap Co on Pt(1 1 1). The out-of-plane magnetization has a significant enhancement after annealing at high temperature. The Curie temperature increases from 625 to 710 K as 1 ML of Ag is deposited on 1 ML Co/Pt(1 1 1). The change of surface anisotropy and the formation of a Co-Pt alloy are possible mechanisms for the magnetization enhancement.

Shern, C. S.; Su, C. W.; Wu, Y. E.; Chen, S. H.

2001-12-01

118

Magnetic anisotropy in Fe nanocrystals fabricated by GDM  

NASA Astrophysics Data System (ADS)

Ferromagnetic nanocrystals composed of nano-sized grains show excellent soft magnetic characteristics and their mechanism is explained by a random anisotropy model(RAM). We have been studied nanocrystal systems with ferromagnetic 3d elements to understand the RAM. Fe nanocryatals were fabricated with a gas condensation and deposition method(GDM). The oxygen content in an as-deposited Fe nanocryatal was about 20 %. Hysteresis loop shifts observed in magnetic field cool measurements suggest the presence of antiferromagentic oxides. Dependence of room temperature coercive forces on the grain size(D) is not D6 but D3.4. Magnetization curves often seen in thin films with stripe domain structures were observed at room temperature irrespective to the sort of substrates. The presence of perpendicular magnetic anisotropy was suggested.

Kita, E.; Sato, H.; Tsukahara, N.; Lee, S. J.; Yanagihara, H.; Tanimoto, H.

2010-01-01

119

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

120

High Anisotropy Magnetic Recording Media  

Microsoft Academic Search

Areal densities in magnetic recording have exhibited Moore's Law like increases in the last ten years. This is partially due to improvements in the media microstructure where reduced grain sizes, tighter grain size distribution, and chemical isolation between grains to break exchange provided increased signal-to-noise from decreased transition noise. With the recent shift from longitudinal to perpendicular recording, areal densities

James Wittig

2007-01-01

121

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

122

Source of Magnetic Anisotropy in Andesitic Rocks: A case study from Java, Indonesia  

NASA Astrophysics Data System (ADS)

We have studied scores of intrusive and extrusive andesitic rocks from 21 sites in Java, Indonesia to gain insight into how magnetic anisotropy was developed in these rocks. The study includes measurement of anisotropy of magnetic susceptibility (AMS), anisotropy of anhysteretic susceptibility (AAS), Curie temperature, magnetic hysteresis parameters, and XRF geochemical analyses. The percent anisotropy of AMS in these rocks varies from 1.4 to 8.4%, while the percent anisotropy of AAS varies from 15% to 69%. Magnetic lineation is predominant in ten sites, while magnetic foliation is predominant in the remaining eleven sites. No direct relationship was noted between magnetic lineation or foliation and structure. Measurement of Curie temperature shows that samples from some sites have a single magnetic phase while others show the presence of two to three magnetic phases; some of them have a Curie temperature as low as 208 C suggesting high Ti content. Assuming that the predominant magnetic mineral is magnetite, estimation of grain size made by plotting anhysteretic susceptibility as a function of low-field susceptibility suggests that only five sites are dominated by magnetic grains smaller than 1 micrometer. This was supported by measurement of hysteresis parameters. Cross-parameter analyses show that the number of magnetic phases in the rocks seems to affect the AMS but not the AAS parameters. Meanwhile variations in grain size affect both AMS and AAS. For samples with smaller magnetic grains, AMS degree of anisotropy increases as grain size increases while the AAS degree of anisotropy decreases as grain size increases. For samples with larger magnetic the degree of anisotropy the degree of anisotropy the degree of anisotropy grains, both AMS and AAS degree of anisotropy decrease as grain size increases. Geochemical analyses show that the degree of anisotropy tends to be larger for andesites with FeO content of less than 9%.

Bijaksana, S.; Sastrawiharja, K.; Hodych, J. P.

2009-05-01

123

Inkjet printing of magnetic materials with aligned anisotropy  

NASA Astrophysics Data System (ADS)

3-D printing processes, which use drop-on-demand inkjet printheads, have great potential in designing and prototyping magnetic materials. Unlike conventional deposition and lithography, magnetic particles in the printing ink can be aligned by an external magnetic field to achieve both high permeability and low hysteresis losses, enabling prototyping and development of novel magnetic composite materials and components, e.g., for inductor and antennae applications. In this work, we report an inkjet printing technique with magnetic alignment capability. Magnetic films with and without particle alignment are printed, and their magnetic properties are compared. In the alignment-induced hard axis direction, an increase in high frequency permeability and a decrease in hysteresis losses are observed. Our results suggest that unique magnetic structures with arbitrary controllable anisotropy, not feasible otherwise, may be fabricated via inkjet printing.

Song, Han; Spencer, Jeremy; Jander, Albrecht; Nielsen, Jeffrey; Stasiak, James; Kasperchik, Vladek; Dhagat, Pallavi

2014-05-01

124

Orienting Paramecium with intense static magnetic fields  

Microsoft Academic Search

Recent experiments on cell division suggest the application of intense static magnetic fields as a novel tool for the manipulation of biological systems [1]. The magnetic field appears to couple to the intrinsic anisotropies in the diamagnetic components of the cells. Here, we present measurements of the intrinsic average diamagnetic anisotropy of the whole single celled ciliate, Paramecium Caudatum. Magnetic

James M. Valles Jr.; Karine Guevorkian; Carl Quindel

2004-01-01

125

Effect of planar anisotropy on damping decrement of free oscillations of magnetization in garnet-ferrite films  

Microsoft Academic Search

The results of experimental investigation of free oscillations of magnetization in garnet-ferrite films with planar anisotropy are considered. It is shown that the damping decrement of free oscillations increases with effective anisotropy field H Kp .

Yu. A. Durasova; E. I. Il'Yashenko; O. S. Kolotov; A. V. Matyunin; V. A. Pogozhev

2009-01-01

126

Slaty cleavage development and magnetic anisotropy fabrics  

NASA Astrophysics Data System (ADS)

The shale-to-slate transition preserved in the Ordovician Martinsburg Formation at the Lehigh Water Gap, Pennsylvania, provides an opportunity to study the relationship between magnetic anisotropy fabrics and the development of slaty cleavage. Our previous work has indicated that anisotropy of magnetic susceptibility (AMS) does not record changes in finite strain associated with cleavage development in these rocks but instead measures the degree of dissolution and new growth of chlorite. Additional AMS data presented in this paper lend further support to this conclusion. Conversely, anhysteretic remanent magnetization anisotropy (ARMA), which is not affected by paramagnetic chlorite, accurately reflects the strain-induced rock fabrics associated with cleavage formation. ARMA results show that magnetite dimensional orientations vary from bedding-parallel in shale samples to cleavage-parallel in samples with well-developed slaty cleavage. Samples with weak and pencil cleavage display scattered ARMA orientations which lie in between bedding and cleavage. These intermediate orientations may be due to either passive rotation of magnetite from bedding-parallel to cleavage-parallel or (re)crystallization of magnetite. If rotation occurred, grain rotation was highly heterogeneous in the samples with incipient cleavage. The intermediate ARMA orientations may also reflect the varying contribution of two magnetite preferred orientations, a depositional orientation parallel to bedding and a new growth orientation parallel to cleavage.

Housen, Bernard A.; van der Pluijm, Ben A.

1991-06-01

127

Magnetic anisotropy and magnetic phase diagram of Gd5Ge4  

NASA Astrophysics Data System (ADS)

The magnetization of single crystal Gd5Ge4 , which in a zero magnetic field orders antiferromagnetically at 128K , indicates a reversible spin-flop transition when the magnetic field is along the c axis and the absence of similar transformations when the magnetic field vector is perpendicular to the c axis. This anisotropic behavior is due to variation of magnetization energy between the c axis and the a or b axes of the orthorhombic crystal caused by a different alignment of the Gd moments with respect to the magnetic field vector. The anisotropy of the antiferromagnetic state diminishes with the increasing magnetic field and temperature. The critical magnetic field for the antiferromagnetic-ferromagnetic transition is the smallest and the ferromagnetic state is most stable when the magnetic field vector is parallel to the b axis, indicating an easy magnetization direction along this axis. The anisotropy of the magnetic field-induced transformation in Gd5Ge4 is discussed in connection with the coupled magnetic and structural transitions. Anisotropic magnetic phase diagrams along the three major crystallographic axes are constructed.

Ouyang, Z. W.; Pecharsky, V. K.; Gschneidner, K. A., Jr.; Schlagel, D. L.; Lograsso, T. A.

2006-07-01

128

Accelerating the switching of magnetic nanoclusters by anisotropy-driven magnetization dynamics  

NASA Astrophysics Data System (ADS)

In this work, the magnetization dynamics of clusters supported on nonmagnetic substrates is shown to exhibit a complex response when subjected to external magnetic fields. The field-driven magnetization reversal of small Co clusters deposited on a Cu(111) surface has been studied by means of first-principles calculations and atomistic spin dynamics simulations. For applied fields ranging from 1 to 10 Tesla, we observe a coherent magnetization reversal with switching times in the range of several tenths of picoseconds to several nanoseconds, depending on the field strength. We find a nonmonotonous dependence of the switching times with respect to the strength of the applied field, which we prove has its origin in the complex magnetic anisotropy landscape of these low-dimensional systems. This effect is shown to be stable for temperatures around 10 K, and is possible to realize over a range of exchange interactions and anisotropy landscapes. Possible experimental routes to achieve this unique switching behavior are discussed.

Etz, Corina; Costa, Marcio; Eriksson, Olle; Bergman, Anders

2012-12-01

129

On the Magnetic Susceptiability Anisotropy of Deep-Sea Sediment.  

National Technical Information Service (NTIS)

Susceptibility anisotropies in the form of vertically prolate ellipsoids have been reported in many deep-sea sediment cores. The results of the present investigation suggest that these anisotropies may not describe the original magnetic fabric of deep-sea...

D. V. Kent W. Lowrie

1975-01-01

130

Magnetic anisotropy data of C6HOCl5  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume C `Diamagnetic Susceptibility and Magnetic Anisotropy of Organic Compounds' of Volume 27 `Diamagnetic Susceptibility and Anisotropy' of Landolt-Börnstein - Group II Molecules and Radicals.

Kumar, M.; Gupta, R.

131

Magnetic anisotropy data of C76 (D2)  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume C `Diamagnetic Susceptibility and Magnetic Anisotropy of Organic Compounds' of Volume 27 `Diamagnetic Susceptibility and Anisotropy' of Landolt-Börnstein - Group II Molecules and Radicals.

Kumar, M.; Gupta, R.

132

Identification of multicomponent anisotropies in rocks using various field and temperature values in a cryogenic magnetometer  

Microsoft Academic Search

A new technique involving magnetization measurements on a rotating sample in a cryogenic magnetometer with variable field, from 0 to 4 T, and variable temperature is presented. It can be used to separate and identify multi-component anisotropy in rocks. The results obtained for anisotropy due to magnetite, haematite, pyrrhotite or phyllosilicates are interpreted according to different magnetization models.

P. Rochette; G. Fillion

1988-01-01

133

Free magnetization oscillations in garnet ferrite films with quasi-planar anisotropy  

Microsoft Academic Search

Free magnetization oscillations in garnet ferrite films with quasi-planar anisotropy was studied. The oscillations were excited\\u000a by a pulse of an in-plane magnetic field. An analytic expression relating the oscillation frequency to the film parameters\\u000a and the external magnetic field was derived; the expression is in good agreement with the experimental data. The planar anisotropy\\u000a is shown to increase the

E. N. Il’icheva; E. I. Il’yashenko; O. S. Kolotov; A. V. Matyunin; V. V. Smirnov

2003-01-01

134

Reaching the magnetic anisotropy limit of a 3d metal atom.  

PubMed

Designing systems with large magnetic anisotropy is critical to realize nanoscopic magnets. Thus far, the magnetic anisotropy energy per atom in single-molecule magnets and ferromagnetic films remains typically one to two orders of magnitude below the theoretical limit imposed by the atomic spin-orbit interaction. We realized the maximum magnetic anisotropy for a 3d transition metal atom by coordinating a single Co atom to the O site of an MgO(100) surface. Scanning tunneling spectroscopy reveals a record-high zero-field splitting of 58 millielectron volts as well as slow relaxation of the Co atom's magnetization. This striking behavior originates from the dominating axial ligand field at the O adsorption site, which leads to out-of-plane uniaxial anisotropy while preserving the gas-phase orbital moment of Co, as observed with x-ray magnetic circular dichroism. PMID:24812206

Rau, Ileana G; Baumann, Susanne; Rusponi, Stefano; Donati, Fabio; Stepanow, Sebastian; Gragnaniello, Luca; Dreiser, Jan; Piamonteze, Cinthia; Nolting, Frithjof; Gangopadhyay, Shruba; Albertini, Oliver R; Macfarlane, Roger M; Lutz, Christopher P; Jones, Barbara A; Gambardella, Pietro; Heinrich, Andreas J; Brune, Harald

2014-05-30

135

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

136

Magnetism and magnetic anisotropy of antiferromagnetic NiMn  

NASA Astrophysics Data System (ADS)

Despite the importance of magnetic anisotropy in industrial applications, the magnetic anisotropy of AFM as well as FM/AFM interfaces is not well understood. We have performed first-principles FLAPW calculations(Wimmer, Krakauer, Weinert and Freeman, PRB 24, 864(1981)) in order to understand the magnetism and magnetic anisotropy of AFM NiMn with L10 structure. The bulk system shows AFM ordering of the Mn spins while the Ni atom has almost no magnetic moment, as expected from experiment. The Mn moment at the surface is enhanced compared to the bulk case. The magneto-crystalline anisotropy (MCA) energy was calculated by the state tracking and torque approaches(D.-S. Wang, R. Wu and A. J. Freeman, PRL 70, 869(1993))^,(X. Wang, R. Wu, D.-S. Wang and A. J. Freeman, PRB 54, 61(1996)) and found to be sensitive to the environment. The case of bulk clearly exhibits in-plane MCA - in agreement with experiment. In the surface case, if Mn is at the surface the MCA exhibits qualitatively the same behavior as bulk, while for Ni at the surface there is a larger MCA energy. Work in progress on exchange bias materials includes the AFM/FM interface, NiMn/NiFe.

Freeman, A. J.; Nakamura, K.; Kim, M.; Zhong, L.; Fernandez-de-Castro, J.

2000-03-01

137

Tri-axial magnetic anisotropies in RE2Ba4Cu7O15-y superconductors  

NASA Astrophysics Data System (ADS)

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'1-xRE?x)2Ba4Cu7Oy [(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; Okuhira, Shota; Yamaki, Momoko; Kishio, Kohji; Shimoyama, Jun-ichi; Doi, Toshiya

2014-03-01

138

Magnetic Fields  

NSDL National Science Digital Library

This page and its annex describes, in trivial terms, the physics of magnetic fields and the history of its discovery. Included is the work of Halley, Oersted, Ampere and Maxwell. It also describes a way of demonstrating it in the classroom, using a vu-graph projector. Later sections #5, #5a and #6 extend this to magnetic field lines and electromagnetism.

Stern, David

2005-01-04

139

Noncubic magnetic anisotropies in bulk and thin-film garnets  

Microsoft Academic Search

Magnetic bubbles have been reported in bulk grown, chemical vapor deposition (CVD), and liquid phase epitaxy (LPE) garnets, implying the existence of noncubic anisotropies in all of these materials. Anisotropy magnitudes, directions, nonuniformities, and annealing behaviors and effects of strain relief on the anisotropies of several potentially useful garnet materials are presented and compared. These observations indicate that the noncubic

ARJEH J. KURTZIG; FRED B. HAGEDORN

1971-01-01

140

Measurement of the magnetic anisotropy energy constants for magneto-optical recording media  

NASA Technical Reports Server (NTRS)

Measurement of the magneto-optical polar Kerr effect is performed on rare earth-transition metal (RE-TM) amorphous films using in-plane fields. From this measurement and the measurement of the saturation magnetization using a vibrating sample magnetometer (VSM), the magnetic anisotropy constants are determined. The temperature dependence is presented of the magnetic anisotropy in the range of -175 to 175 C. The results show a dip in the anisotropy near magnetic compensation. This anomaly is explained based on the finite exchange coupling between the rare earth and transition metal subnetworks.

Hajjar, R. A.; Wu, T. H.; Mansuripur, M.

1992-01-01

141

The 90° pulse magnetization curve of ferrite-garnet films with planar anisotropy  

Microsoft Academic Search

The process of 90° pulse magnetization in ferrite-garnet films with planar anisotropy has been investigated. Two regions separated by a distinctly defined break point at a magnetizing field amplitude ?15 18Oe have been revealed on the pulse magnetization curve. Analysis of the magnetization signals has shown that for the description of dynamic behaviour of the films a consideration of the

E. I. Il'Yashenko; O. S. Kolotov; A. V. Matyunin; O. A. Mironets

2006-01-01

142

Low coercivity giant magnetoresistance with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We find the perpendicular magnetic anisotropy giant magnetoresistance structure, whose coercivity is less than 10 Oe. We reveal that the coercivity of free layer can be smaller than 5 Oe in Co/Pd/Cu/[Co/Pd]4 multilayer structure with a TiO2 seed layer. The TiO2 seed layer plays a critical role in the small coercivity of free layer. The GMR ratio is around 1-1.8% for the out-of-plane magnetic fields, and the maximum MR sensitivity of 0.12%/Oe is achieved.

Lee, Jeong-Seop; Yoon, Jungbum; Kang, Mool-Bit; You, Chun-Yeol

2014-05-01

143

Microwave Magnetic Properties of Nd2Fe17N3-delta with Planar Anisotropy  

Microsoft Academic Search

Microwave magnetic properties are studied for rhombohedral structure Nd2Fe17N3-? with planar magnetic anisotropy Its resin composites show the permeability ??0 = 4.15 at low frequency, the natural resonance frequency fr = 1.71 GHz and the resonance bandwidth 6.66 GHz. The calculated static permeability of Nd2Fe17N3-? reaches 133. The microwave magnetic properties are determined by the c-axis anisotropy field, basal plane

Fa-Shen Li; Fu-Sheng Wen; Dong Zhou; Liang Qiao; Wen-Liang Zuo

2008-01-01

144

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

145

Transfer matrices for magnetized CMB anisotropies  

SciTech Connect

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.

Giovannini, Massimo [Centro 'Enrico Fermi', Compendio del Viminale, Via Panisperna 89/A, 00184 Rome (Italy) and Department of Physics, Theory Division, CERN, 1211 Geneva 23 (Switzerland)

2006-05-15

146

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

147

Effect of soft underlayer magnetic anisotropy on perpendicular recording process  

NASA Astrophysics Data System (ADS)

The presence of the soft magnetic underlayer (SUL) in perpendicular magnetic recording (PMR) media is essential for the application. It is commonly understood that the SUL provides the return flux path and enhances the writing field by enhancing the recording field from the write pole. However, SUL increases the magnetic noise during the read back process due to magnetic domain walls in the SUL. Hence, it is common to grow SUL with large uniaxial or unidirectional magnetic anisotropy field ( H k) to reduce domain wall noise. In this paper, we explore the effect of increasing SUL H k on the recording process. We studied this effect by using the finite element micromagnetic simulation. Our simulation results show that the contribution of SUL to the writing field amplitude is reduced with increasing H k. This reduction in magnetic field from high H k SUL actually improves the recording performance due to the better field gradient at SUL. The simulation results are qualitatively consistent with the actual experimental data obtained from the Guzik measurement.

Lim, C. K.; Kim, E. S.; Yoon, S. Y.; Kong, S. H.; Lee, H. S.; Oh, H. S.; Kim, Y. S.

2007-03-01

148

Experimental investigation of magnetic anisotropy in spin vortex discsa)  

NASA Astrophysics Data System (ADS)

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.; Arnold, D. P.

2014-05-01

149

Magnetization reversal with variation of the ratio of the anisotropy energies in exchange bias systems  

SciTech Connect

We systematically vary the ratio of the exchange and ferromagnetic anisotropies in a single multilayered system in finally unravelling the mysteries of magnetization reversal of exchange coupled systems. This is particularly possible due to increasing unidirectional exchange anisotropies in our multilayer system which we saw earlier from sequential switching of exchange coupled layers along the stack with increasing applied field strengths. Here, by introducing different directions ({theta}) of the applied field with respect to the unidirectional anisotropy direction, we have varied two different energy parameters: (i) the exchange anisotropy for each layer (ii) the ferromagnetic anisotropy. Our polarized neutron measurements thus show a gradual crossover from layer flipping (domain-wall motion) for low torque regimes of the effective field to coherent rotation for high torque regimes. We explain these findings within a general and simple model where the angular dependencies for reversal are guided by the relative strengths of Zeeman, exchange, and anisotropy energies.

Paul, Amitesh; Kentzinger, Emmanuel; Ruecker, Ulrich; Brueckel, Thomas [Institut fuer Festkoerperforschung, Forschungszentrum Juelich GmbH, D-52425 Juelich (Germany)

2006-08-01

150

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

151

Effects of surface anisotropy on magnetic vortex core  

NASA Astrophysics Data System (ADS)

The vortex core shape in the three dimensional Heisenberg magnet is essentially influenced by a surface anisotropy. We predict that depending of the surface anisotropy type there appears barrel- or pillow-shaped deformation of the vortex core along the magnet thickness. Our theoretical study is well confirmed by spin-lattice simulations.

Pylypovskyi, Oleksandr V.; Sheka, Denis D.; Kravchuk, Volodymyr P.; Gaididei, Yuri

2014-06-01

152

High magnetic anisotropies in magnetite-bearing mylonitic garnet-micaschist of the Seve nappe, Swedish Caledonides  

Microsoft Academic Search

The first documentation of very high anisotropies (P' values up to 4.5) of the magnetic susceptibility (AMS) of mylonitic garnet micaschists of the Seve nappe near Lake Slipsiken (Swedish Caledonides) raises questions about its origin. We studied these shear zone rocks by using the anisotropy of bulk susceptibility at room and liquid nitrogen temperature and the anisotropy of high field

A. M. Kontny; J. Grimmer; R. Engelmann; R. O. Greiling

2010-01-01

153

Theoretical study of the spin dynamics in CsNiF3, a one-dimensional ferromagnet with planar anisotropy, in an external magnetic field  

Microsoft Academic Search

Using a Green's function technique we have studied the spin dynamics in the one-dimensional ferromagnetic CsNiF3 with an external field. Taking into account damping effects, the longitudinal mode becomes purely imaginary and the transverse mode is underdamped for low temperatures and overdamped near and above the critical temperature. The spin wave energy and the damping strongly depend on the anisotropy

J. M. Wesselinowa; V. P. Ivanova

1996-01-01

154

The magnetic state and its macroscopic anisotropy in amorphous rare-earth alloys (invited)  

SciTech Connect

The magnetic state and anisotropy of amorphous rare-earth transition-metal systems with a microscopic random uniaxial anisotropy are discussed. Both sputtered Tb-Fe and rapidly quenched Gd{sub 65{minus}{ital x}}R{sub {ital x}}Co{sub 35} alloys (R is a rare earth) were studied. The low-temperature magnetic state of these alloys depends on the anisotropy, exchange, and applied field strength. For the case of weak anisotropy (alloys with small concentrations of anisotropic rare earth) the low-field results can be explained in terms of a correlated spin-glass state and the higher-field magnetization curves by a ferromagnet with wandering axis state. It is also shown that a weak anisotropy such as that found in Gd{sub 65{minus}{ital x}}Er{sub {ital x}}Co{sub 35} ({ital x}{lt}8) can lead to double-transition behavior as a function of temperature. The microscopic anisotropy in Gd-Tb-Co, Gd-Er-Co, and Tb-Fe alloys leads to a large macroscopic anisotropy and hysteresis is observed in the torque at 2 K. The macroscopic anisotropy strength depends on the particular rare-earth component present in the alloy and shows a strong temperature dependence. None of the alloys of this work show a significant perpendicular anisotropy. In alloys where the macroscopic anisotropy is weak (Gd{sub 65}Co{sub 35}) a fixed in-plane anisotropy is found which is ascribed to anisotropic structural ordering in the plane of the sample. Finally, possible explanations for the movable macroscopic anisotropy found in some Tb-Fe alloys are discussed.

O'Shea, M.J.; Lee, K.M. (Kansas State University, Cardwell Hall, Department of Physics, Manhattan, Kansas 66506-2601 (USA)); Fert, A. (Laboratoire de Physique des Solides, Universite de Paris-Sud, F-91405 Orsay (France))

1990-05-01

155

Surface magnetic anisotropy of CoFe2O4 nanoparticles with a giant low-temperature hysteresis  

NASA Astrophysics Data System (ADS)

Ferrimagnetic nanoparticles of CoFe2O4 about 4-16 nm in diameter were synthesized by pyrolysis of a mixture of Fe and Co acetylacetonates. The field dependences of magnetization and hysteresis loops were investigated in magnetic fields up to 4000 kA/m at various temperatures from 4.2 to 500 K. A considerable contribution, positive or negative depending on the temperature, of ``surface'' anisotropy to the effective magnetic anisotropy of the nanoparticles was observed. A correlation was found between the magnetic properties that represent the specificity of small particles, namely, between ``surface'' anisotropy, magnetization, and high-field susceptibility.

Mozul', K. A.; Ol'khovik, L. P.; Sizova, Z. I.; Bludov, A. N.; Pashchenko, V. A.; Baumer, V. N.; Vashchenko, V. V.; Kolosov, M. O.; Kryshtal', A. P.; Prodanov, M. F.

2013-04-01

156

Magnetic anisotropy of thin Fe films on GaAs  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy of thin Fe films on (001)-oriented GaAs has been investigated using the fully relativistic TB-KKR method of band structure calculation. In line with experimental findings an in-plane anisotropy has been found with the easy axis pointing along the [110]-direction. The theoretical results for the anisotropy energy ?E are reproduced in a semi-quantitative way by the models of Bruno and van der Laan, respectively, which relate ?E to the anisotropy of the spin-orbit induced orbital magnetic moment.

Kosuth, M.; Popescu, V.; Ebert, H.; Bayreuther, G.

2005-12-01

157

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.

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

2014-01-01

158

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion.  

PubMed

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

159

Strain, anisotropy of anhysteretic remanence, and anisotropy of magnetic susceptibility in a slaty tuff  

Microsoft Academic Search

Finite strain data for the Borrowdale slaty tuffs compare variably with the anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). Finite strain, determined from lapilli-rims, shows that slaty cleavage was formed by coaxial flattening with X:Y:Z in the ratio 1.74:1.21 and 0.48. AARM was measured in different coercivity windows to isolate contributions from magnetite of different

Norihiro Nakamura; Graham J. Borradaile

2001-01-01

160

Direct observation of an anisotropic in-plane residual stress induced by B addition as an origin of high magnetic anisotropy field of Ru/FeCoB film  

SciTech Connect

Although boron-free FeCo films prepared on a Ru underlayer exhibits isotropic in-plane magnetic property, boron added FeCoB films prepared on Ru underlayer revealed large in-plane magnetic anisotropy with a high anisotropy field of 500 Oe. The effect of boron addition on the in-plane anisotropic residual stress in FeCoB film was investigated using sin{sup 2} {psi} method of x-ray diffraction analysis. Large isotropic compressive stress was observed in Ru/FeCo film. In contrast, anisotropic in-plane residual stress was observed in Ru/FeCoB film. The compressive stress along the easy axis of Ru/FeCoB film is released more than that along the hard axis. Such anisotropic residual stress is regarded as an origin of the in-plane magnetic anisotropy through inverse magnetostriction effect. Owing to the configuration of the facing targets sputtering system, boron atoms are sputtered and deposited anisotropically, and so they penetrate FeCo crystals and release the compressive stress along the incidence direction.

Hirata, Ken-ichiro; Gomi, Shunsuke; Mashiko, Yasuhiro; Nakagawa, Shigeki [Department of Physical Electronics, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro-ku, Tokyo 152-8552 (Japan)

2010-05-15

161

Extracting magnetic anisotropy energies in Co/Pd multilayers via refinement analysis of the full magnetoresistance curves  

NASA Astrophysics Data System (ADS)

We performed magnetoresistance (MR) measurements on Co/Pd multilayers with perpendicular magnetization anisotropy, as a function of external magnetic field direction and magnitude. We find that anisotropic MR for magnetization perpendicular to plane (and to the current) is surprisingly larger than the anisotropic MR when magnetization is in-plane but perpendicular to the current. We develop a refinement process for accurately and easily extracting the anisotropy energies from the full set of MR measurements. We demonstrate its effectiveness for micron-scale electrodes of the multilayers. Here, using the additional difference in MR of the out-of-plane direction, we extract both the shape anisotropy energy and perpendicular anisotropy energy.

Kachlon, Yaniv; Kurzweil, Noa; Sharoni, Amos

2014-05-01

162

Four-fold magnetic anisotropy induced by the antiferromagnetic order in FeMn/Co/Cu(001) system  

NASA Astrophysics Data System (ADS)

Single crystalline FeMn/Co bilayers were grown epitaxially on Cu(001) and investigated by magneto-optic Kerr effect (MOKE). By doing the MOKE measurement within a rotating magnetic field, we were able to retrieve quantitatively the anisotropy constant of the ferromagnetic Co layer. We show unambiguously that as the FeMn layer changes from paramagnetic (PM) to antiferromagnetic (AFM) states, it enhances the interfacial magnetic anisotropy at the FeMn/Co interface by an order of magnitude. A thickness dependent study of the magnetic anisotropy constant revealed that this induced magnetic anisotropy may originate from the FeMn/Co interfacial spin frustration.

Chen, G.; Li, J.; Liu, F. Z.; Zhu, J.; He, Y.; Wu, J.; Qiu, Z. Q.; Wu, Y. Z.

2010-10-01

163

The magnetic anisotropy change of BaFe 12?2 x Ir x Co x O 19: a single-crystal neutron diffraction study of the accompanying atomic and magnetic structures  

Microsoft Academic Search

In this paper, we present the atomic and magnetic structures accompanying the change, from axial to planar, of the magnetic anisotropy in BaFe12?2xIrxCoxO19 using magnetic measurements and single-crystal neutron diffraction. The magnetic measurements allowed us to determine the characteristic anisotropy field H? and anisotropy constants ki for the different stages. Our structure refinements show that the change of magnetic anisotropy

J. Kreisel; H. Vincent; F. Tasset; P. Wolfers

2000-01-01

164

Perpendicular magnetic anisotropy in Co-Pt granular multilayers  

NASA Astrophysics Data System (ADS)

Magnetization hysteresis curves have been measured on Co granular multilayers, (Al2O3/Co/Pt)N (N = 1 and 25), with the applied magnetic field parallel and perpendicular to the substrate plane. In all samples perpendicular magnetic anisotropy was observed. For Co particles with average diameter 3 nm, the coercive field at low temperature is ?0HC = 0.5 T. HC decreases for increasing temperature and disappears at ~200 K. A soft magnetic component is also present in all samples up to the freezing temperature Tf = 365 K. Co and Pt XMCD measurements at the L2,3 edges were performed, yielding to the orbital mL and spin mS contributions to the total magnetic moment of the system. These results, in addition to XANES ones, indicate the presence of CoxPt1-x alloy. Particles conformed of CoPt alloy, embedded in Pt and coupled magnetically by dipolar or RKKY interaction, may explain the phenomenology observed in these systems.

Bartolomé, J.; Figueroa, A. I.; García, L. M.; Bartolomé, F.; Ruiz, L.; González-Calbet, J. M.; Petroff, F.; Deranlot, C.; Wilhelm, F.; Rogalev, A.; Brookes, N.

2012-09-01

165

Anisotropy of the magnetization of single crystals and bulk high-Tc superconductors  

Microsoft Academic Search

Measurements of the angular dependence of the zero-field-cooled (ZFC), field-cooled (FC) and remanent magnetization of both high-Tc single crystals and polycrystalline samples show significant anisotropy. Comparison of the results obtained on both, prove that most anisotropy is governed by the shape of the sample via the demagnetizing factors. For ceramic samples, there is competition between the demagnetizing factors of the

U. Yaron; I. Felner; Y. Kornyushin; Y. Yeshurun

1993-01-01

166

Presence of Magnetic Surface Anisotropy in Permalloy Films  

Microsoft Academic Search

The existence of uniaxial magnetic surface anisotropy in Permalloy films has been deduced by comparing the theoretical and experimental spin-wave-resonance spectra of several films with different thicknesses. The anisotropy decreases as the film thickness decreases and, for the thinnest film, becomes comparable to that given by Néel's theory (+0.08 erg\\/cm2).

G. C. Bailey; C. Vittoria

1973-01-01

167

Measurements on the magnetic anisotropy in evaporated iron films  

Microsoft Academic Search

Summary  We have examined the problem of the magnetic anisotropy in evaporated iron films by use of the magneto-optic Kerr effect method.\\u000a As a result we found that there exists a weak anisotropy in some iron films coming from mechanical tensions.

R. Vrambout; L. de Greve

1961-01-01

168

Perpendicular magnetic recording with a composite anisotropy film  

Microsoft Academic Search

For a recently proposed perpendicular recording system, a composite anisotropy medium has been developed to improve the recording sensitivity of the perpendicular recording head. The medium is composed of a Fe-Ni soft magnetic film and a Co-Cr perpendicular anisotropy film, which are successively deposited on a base by an r. f. sputtering. By using the new double layer medium, an

S. Iwasaki; Y. Nakamura; K. Ouchi

1979-01-01

169

An enhancement behavior of coercivity near TC in ferromagnetic films with uniaxial magnetic anisotropy  

NASA Astrophysics Data System (ADS)

The temperature dependence of coercivity was investigated in CrO2 and La0.7Sr0.3MnO3 films with and without uniaxial magnetic anisotropy. When the magnetic field was applied along the uniaxial magnetic anisotropy axis, the coercivities of the CrO2 and La0.7Sr0.3MnO3 films showed remarkable enhancement behaviors near ferromagnetic transition temperature (TC). In contrast, CrO2 and La0.7Sr0.3MnO3 films without uniaxial magnetic anisotropy did not exhibit such an enhancement behavior. The temperature dependence of coercivity HC(T) for an aligned Stoner-Wohlfarth ferromagnet was theoretically studied based on a modified model of previously reported ones by He [Phys. Rev. B 75, 184424 (2007)] and Grimsditch [Phys. Rev. Lett. 90, 257201 (2003)]. Experimentally observed enhancement of coercivity near TC could be explained by an effect of a distribution of the local ordering temperatures ?(TB) for magnetic grains. The qualitative behavior of HC(T) was investigated for three different types of uniaxial anisotropies: (i) magnetocrystalline anisotropy, (ii) strain-induced anisotropy, and (iii) shape anisotropy.

Dho, Joonghoe

2012-08-01

170

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, Jr. , T.

1960-01-01

171

Induced Anisotropy in FeCo-Based Nanocrystalline Ferromagnetic Alloys (HITPERM) by Very High Field Annealing  

NASA Technical Reports Server (NTRS)

Very high magnetic field annealing is shown to affect the magnetic anisotropy in FeCo-base nanocrystalline soft ferromagnetic alloys. Alloys of composition Fe(44.5)Co(44.5)Zr(7)B(4) were prepared by melt spinning into amorphous ribbons, then wound to form toroidal bobbin cores. One set of cores was crystallized in a zero field at 600 deg. C for 1 h, then, field annealed at 17 tesla (T) at 480 deg. C for 1 h. Another set was crystallized in a 17-T field at 480 deg. C for 1 h. Field orientation was transverse to the magnetic path of the toroidal cores. An induced anisotropy is indicated by a sheared hysteresis loop. Sensitive torque magnetometry measurements with a Si cantilever sensor indicated a strong, uniaxial, longitudinal easy axis in the zero-field-crystallized sample. The source is most likely magnetoelastic anisotropy, caused by the residual stress from nanocrystallization and the nonzero magnetostriction coefficient for this material. The magnetostrictive coefficient lambda(5) is measured to be 36 ppm by a strain gage technique. Field annealing reduces the magnitude of the induced anisotropy. Core loss measurements were made in the zero-field-crystallized, zero-field-crystallized- than-field-annealed, and field-crystallized states. Core loss is reduced 30%-50% (depending on frequency) by field annealing. X-ray diffraction reveals no evidence of crystalline texture or orientation that would cause the induced anisotropy. Diffusional pair ordering is thought to be the cause of the induced anisotropy. However, reannealing the samples in the absence of a magnetic field at 480 deg. C does not completely remove the induced anisotropy.

Johnson, F.; Garmestani, H.; Chu, S.-Y.; McHenry, M. E.; Laughlin, D. E.

2004-01-01

172

Infinite susceptibility phase in planar random-anisotropy magnets  

Microsoft Academic Search

A Monte Carlo algorithm has been used to study the random-anisotropy model with two-component spins on simple cubic lattices, in the strong anisotropy limit. The magnetic susceptibility diverges at a temperature of Tc\\/J=1.91+\\/-0.03, but no singular behavior is observable in the specific heat near Tc. The two-spin correlation function at Tc is described by a critical exponent eta=0.04+\\/-0.04. The magnetization

Ronald Fisch

1991-01-01

173

Magnetic anisotropy of transition-metal dimers: Density functional calculations  

Microsoft Academic Search

We present ab initio density functional calculations of the magnetic anisotropy of dimers of the transition-metal atoms from groups 8 to 10 of the Periodic Table. Our calculations are based on a noncollinear implementation of spin-density functional theory (DFT) where spin-orbit coupling (SOC) is included self-consistently. The physical mechanism determining the sign and magnitude of the magnetic anisotropy energy (MAE)

Piotr Blonski; Jürgen Hafner

2009-01-01

174

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

175

Effects of cooling field strength on exchange anisotropy at permalloy/CoO interfaces  

SciTech Connect

We have studied exchange anisotropy at ferromagnet/antiferromagnet (FM-AFM) interfaces as a function of cooling field in Ni{sub 80}Fe{sub 20} (permalloy) films deposited on bulk single-crystal CoO substrates. Hysteresis loops measured after cooling through the antiferromagnetic ordering temperature in different magnetic fields show that the exchange bias has little dependence on cooling field. Large cooling fields produced hysteresis loops with larger remanent magnetization and larger coercivity. These trends can be explained using a model that assumes that the FM anisotropy axis directions can be influenced by the magnetic history of the AFM. Large cooling fields also led to larger CoO susceptibility, which implies rotation of the CoO spin axes. The simultaneous rotation of the FM anisotropy axes and the AFM spin axes suggests perpendicular coupling at the FM-AFM interface. {copyright} {ital 1996 American Institute of Physics.}

Moran, T.J.; Schuller, I.K. [Physics Department 0319, University of California--San Diego, La Jolla, California 92093 (United States)] [Physics Department 0319, University of California--San Diego, La Jolla, California 92093 (United States)

1996-04-01

176

Anisotropic Magnetism in Field-Structured Composites  

SciTech Connect

Magnetic field-structured-composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g. rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chain-like particle structures, and a biaxial field produces sheet-like particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCS of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material.

Anderson, Robert A.; Martin, James E.; Odinek, Judy; Venturini, Eugene

1999-06-24

177

The 90° pulse magnetization curve of ferrite-garnet films with planar anisotropy  

Microsoft Academic Search

The process of 90° pulse magnetization in ferrite-garnet films with planar anisotropy has been investigated. Two regions separated by a distinctly defined break point at a magnetizing field amplitude ?15–18Oe have been revealed on the pulse magnetization curve. Analysis of the magnetization signals has shown that for the description of dynamic behaviour of the films a consideration of the forces

E. I. Il’yashenko; O. S. Kolotov; A. V. Matyunin; O. A. Mironets

2006-01-01

178

Enhanced magnetic anisotropy in cobalt-carbide nanoparticles  

NASA Astrophysics Data System (ADS)

An outstanding problem in nano-magnetism is to stabilize the magnetic order in nanoparticles at room temperatures. For ordinary ferromagnetic materials, reduction in size leads to a decrease in the magnetic anisotropy resulting in superparamagnetic relaxations at nanoscopic sizes. In this work, we demonstrate that using wet chemical synthesis, it is possible to stabilize cobalt carbide nanoparticles which have blocking temperatures exceeding 570 K even for particles with magnetic domains of 8 nm. First principles theoretical investigations show that the observed behavior is rooted in the giant magnetocrystalline anisotropies due to controlled mixing between C p- and Co d-states.

El-Gendy, Ahmed A.; Qian, Meichun; Huba, Zachary J.; Khanna, Shiv N.; Carpenter, Everett E.

2014-01-01

179

The origin of transverse anisotropy in axially symmetric single molecule magnets.  

PubMed

Single-crystal high-frequency electron paramagnetic resonance spectroscopy has been employed on a truly axial single molecule magnet of formula [Mn(12)O(12)(tBu-CH(2)CO(2))16(CH(3)OH)4].CH(3)OH to investigate the origin of the transverse magnetic anisotropy, a crucial parameter that rules the quantum tunneling of the magnetization. The crystal structure, including the absolute structure of the crystal used for EPR experiments, has been fully determined and found to belong to I4 tetragonal space group. The angular dependence of the resonance fields in the crystallographic ab plane shows the presence of high-order tetragonal anisotropy and strong dependence on the MS sublevels with the second-highest-field transition being angular independent. This was rationalized including competing fourth- and sixth-order transverse parameters in a giant spin Hamiltonian which describes the magnetic anisotropy in the ground S = 10 spin state of the cluster. To establish the origin of these anisotropy terms, the experimental results have been further analyzed using a simplified multispin Hamiltonian which takes into account the exchange interactions and the single ion magnetic anisotropy of the Mn(III) centers. It has been possible to establish magnetostructural correlations with spin Hamiltonian parameters up to the sixth order. Transverse anisotropy in axial single molecule magnets was found to originate from the multispin nature of the system and from the breakdown of the strong exchange approximation. The tilting of the single-ion easy axes of magnetization with respect to the 4-fold molecular axis of the cluster plays the major role in determining the transverse anisotropy. Counterintuitively, the projections of the single ion easy axes on the ab plane correspond to hard axes of magnetization. PMID:17685613

Barra, Anne-Laure; Caneschi, Andrea; Cornia, Andrea; Gatteschi, Dante; Gorini, Lapo; Heiniger, Leo-Philipp; Sessoli, Roberta; Sorace, Lorenzo

2007-09-01

180

Magnetic and optical anisotropy depth profiles in obliquely deposited iron and cobalt films  

Microsoft Academic Search

The depth profiles of magnetic anisotropy field Hk and optical reflection anisotropy Deltar\\/r due to sputter etching were investigated in iron and cobalt films deposited at an incidence angle of 65°. The sputtering was carried out at a rate of about 0.3 nm\\/s. For iron films, the depth profile of Hk is similar to that of Deltar\\/r, indicating that Hk

K. Hara; K. Itoh; M. Kamiya; K. Okamoto; T. Hashimoto; H. Fujiwara

1992-01-01

181

Magnetic Anisotropy as an aid to Identifying CRM and DRM in Red Sedimentary Rocks  

NASA Astrophysics Data System (ADS)

To evaluate the usefulness of magnetic anisotropy for determining the origin of the natural remanent magnetization (NRM) in red sedimentary rocks, several new remanence anisotropy measurement techniques were investigated. The goal of the work was an accurate separation of the remanence anisotropy of magnetite and hematite in the same sedimentary rock sample. In one technique, Tertiary red and grey sedimentary rock samples from the Orera section of Spain were exposed to 13 T fields in 9 different orientations. This work was done at the High Field Magnet Laboratory of Radboud University, Nijmegen, The Netherlands. In each orientation, alternating field (af) demagnetization was used to separate the magnetite and hematite contributions to the high field isothermal remanent magnetization (IRM). Tensor subtraction was used to separate the magnetite and hematite magnetic anisotropies. Geologically interpretable fabrics did not result, probably because of the presence of goethite. In the second technique, also applied to samples from Orera, an anisotropy of anhysteretic remanence (AAR) was applied in af fields up to 240 mT to directly measure the fabric of the magnetite in the sample. IRMs applied in 2T fields followed by 240 mT af demagnetization, and thermal demagnetization at 90° C to remove the goethite contribution, were used to independently measure the hematite fabric in the same samples. This approach gave magnetic fabrics with minimum principal axes perpendicular to bedding, suggesting that the hematite and magnetite grains in the Orera samples both carry a depositional remanent magnetization (DRM). In a third experiment, IRMs applied in 13 T fields were used to measure the magnetic fabric of samples from the Dome de Barrot area in France. These samples had been demonstrated to have hematite as their only magnetic mineral. The fabrics that resulted were geologically interpretable, showing a strong NW-SE horizontal lineation consistent with AMS fabrics measured in the same samples. These fabrics suggest that the rock's remanence has may have been affected by strain and could have originated as a DRM or a CRM. Our work shows that it is important to account for goethite when using high field IRMs to measure the remanence anisotropy of hematite-bearing sedimentary rocks. It also shows that very high magnetic fields (>10 T) may be used to measure the magnetic fabric of sedimentary rocks with highly coercive magnetic minerals without complete demagnetization between each position, provided that the field magnetically saturates the rock.

Kodama, K. P.; Dekkers, M. J.

2004-12-01

182

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

183

Growth-induced magnetic anisotropy behavior in thin garnet films fabricated by pulsed laser deposition  

NASA Astrophysics Data System (ADS)

The effect of target rotation rate on the magneto-optical properties and induced magnetic anisotropy of pulse laser deposition grown Bi:YIG garnets has been investigated. The rotation rate dependence of magnetic properties of thin films has been studied using magneto-optical Faraday rotation combined with magneto-optical Kerr measurement setup. Our results show that decreasing the target rotation rate can also increase the polar coercive field and hence magnetic anisotropy. Also the spectral answer of samples show the capability of use of them in one off optical ranges such as visible, near infrared and far infrared regions.

Tehranchi, M. M.; Hamidi, S. M.

2012-10-01

184

Magnetic anisotropy and magnetization reversal in Co/Cu multilayers nanowires  

NASA Astrophysics Data System (ADS)

The Co/Cu multilayer nanowires fabricated in an array using anodized aluminum oxide (AAO) template by electrodeposition method, have been investigated. It has been observed that the magnetization reversal mode and magnetic anisotropy depend upon the Co and Cu layer thicknesses. Magnetization reversal occurs by curling mode at around Co = 400 nm and Cu = 10 nm, while for Co = 30 nm and Cu = 60 nm, magnetization reversal occurs by nucleation mode. A change of magnetic anisotropy from out of plane to in plane is observed when thickness of Cu layer tCu = 60 nm and that of Co tCo = 30 nm. Magnetic anisotropy is lost when thickness of the Co layer tCo = 400 nm and that of Cu tCu= 10 nm. Magnetic properties have been explained by the competition among shape anisotropy, magnetostatic interactions and magnetocrystalline anisotropy. Magnetic properties can be tuned accordingly depending upon the thickness of the Co and Cu nanodisks.

Ahmad, Naeem; Chen, J. Y.; Shi, D. W.; Iqbal, Javed; Han, Xiufeng

2012-04-01

185

Metastability for the Blume-Capel model with distribution of magnetic anisotropy using different dynamics  

NASA Astrophysics Data System (ADS)

We investigate the relaxation time of magnetization or the lifetime of the metastable state for a spin S=1 square-lattice ferromagnetic Blume-Capel model with distribution of magnetic anisotropy (with small variances), using two different dynamics such as Glauber and phonon-assisted dynamics. At each lattice site, the Blume-Capel model allows three spin projections (+1, 0, -1) and a site-dependent magnetic anisotropy parameter. For each dynamic, we examine the low-temperature lifetime in two dynamic regions with different sizes of the critical droplet and at the boundary between the regions, within the single-droplet regime. We compute the average lifetime of the metastable state for a fixed lattice size, using both kinetic Monte Carlo simulations and the absorbing Markov chains method in the zero-temperature limit. We find that for both dynamics the lifetime obeys a modified Arrhenius-like law, where the energy barrier of the metastable state depends on the temperature and standard deviation of the distribution of magnetic anisotropy for a given field and magnetic anisotropy and that an explicit form of this dependence differs in different dynamic regions for different dynamics. Interestingly, the phonon-assisted dynamic prevents transitions between degenerate states, which results in a large increase in the energy barrier at the region boundary compared to that for the Glauber dynamic. However, the introduction of a small distribution of magnetic anisotropy allows the spin system to relax via lower-energy pathways such that the energy barrier greatly decreases. In addition, for the phonon-assisted dynamic, even the prefactor of the lifetime is substantially reduced for a broad distribution of magnetic anisotropy in both regions considered, in contrast to the Glauber dynamic. Our findings show that overall the phonon-assisted dynamic is more significantly affected by the distribution of magnetic anisotropy than the Glauber dynamic.

Yamamoto, Yoh; Park, Kyungwha

2013-07-01

186

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

187

Deterministic Magnetization Control by Magnetoelastic Anisotropy and its Dependence on Geometry and Scale  

NASA Astrophysics Data System (ADS)

The recent interest in non-volatile memory and logic devices has encouraged the scientific community to develop improved magnetic control mechanisms. In the present work, control of magnets by magnetoelastic anisotropy is investigated within the context of magnetoelectric (ME) heterostructures of different geometry and scale. The ME heterostructure is an artificial multiferroic material which exhibits both a coexistence and coupling of ferromagnetic and ferroelectric ordering. This device architecture provides a route to control magnetism with electric fields via interfacial mechanical stress. In the present work, the initial magnetization morphology and behavior under mechanical stress is investigated for bulk laminate composites, thin film heterostructures, patterned single domain nanostructures, and ring shaped nanostructures. Significant differences were observed in the magnets' response to magnetoelastic anisotropy depending on the scale and or geometry of the magnetic material. Generally speaking, as the scale and aspect ratio of a magnetic system is reduced, the intrinsic magnetostatic and shape anisotropy energies are also reduced thus increasing the relative magnitude (and influence) of magnetoelastic anisotropy. The unambiguous control of a magnet's easy axis is here called deterministic control and this is achieved experimentally in single domain and ring shaped magnets. The magnetization of these nanostructures is shown to rotate 90° with an applied electric field, an important proof of concept for the proposed strain-based magnetic writing devices. The experimental results are confirmed by multiple characterization techniques including magnetic force microscopy (MFM), magneto optic Kerr effect (MOKE), photo emission electron microscopy (PEEM), and Lorentz transmission electron microscopy (TEM). This work thus provides significant evidence of the viability of magnetoelastic anisotropy as a means to control magnetoelectric heterostructures in future spintronic device research.

Hockel, Joshua Leon

188

Looking for higher anisotropy barriers in single-molecule magnets  

NASA Astrophysics Data System (ADS)

We report single-crystal high-frequency electron paramagnetic resonance (HFEPR) studies of a series of recently discovered Mn6^III single-molecule magnets (SMMs) with large barriers to magnetization reversal. All of the complexes consist of Mn3^III triangles with a ferromagnetic interaction between them. Recent studies have shown that the exchange interactions within the triangular Mn3^III units can be switched from antiferromagnetic to ferromagnetic,^1 resulting in a switching of the spin from S = 4 to 12 for many of the Mn6 complexes. This strategy to ``increase S'' has resulted in the highest magnetic energy barrier and blocking temperature for any known SMM to date. Extensive frequency, temperature and field-orientation dependent HFEPR measurements were performed to determine the magnetic anisotropy parameters for each complex. These studies have contributed to important new insights concerning strategies for designing SMMs with high blocking temperatures, particularly for complexes containing manganese in its +3 oxidation state. ^1 T. C. Stamatatos et al., J. Am. Chem. Soc. 129, 12505-12511, 2007.

Datta, Saiti; Milios, Constantinos; Brechin, Euan; Hill, Stephen

2008-03-01

189

Anisotropy-axis orientation effect on the magnetization of ?-Fe2O3 frozen ferrofluid  

NASA Astrophysics Data System (ADS)

The effect of magnetic anisotropy-axis alignment on the superparamagnetic (SPM) and superspin glass (SSG) states in a frozen ferrofluid has been investigated. The ferrofluid studied here consists of maghemite nanoparticles (?-Fe2O3, mean diameter = 8.6 nm) dispersed in glycerine at a volume fraction of ~15%. In the high temperature SPM state, the magnetization of aligned ferrofluid increased by a factor varying between 2 and 4 with respect to that in the randomly oriented state. The negative interaction energy obtained from the Curie-Weiss fit to the high temperature susceptibility in the SPM states as well as the SSG phase onset temperature determined from the linear magnetization curves were found to be rather insensitive to the anisotropy-axis alignment. The low temperature ageing behaviour, explored via 'zero-field cooled magnetization' relaxation measurements, however, shows a distinct difference in the ageing dynamics in the anisotropy-axis aligned and randomly oriented SSG states.

Nakamae, S.; Crauste-Thibierge, C.; Komatsu, K.; L'Hôte, D.; Vincent, E.; Dubois, E.; Dupuis, V.; Perzynski, R.

2010-12-01

190

Magnetic nanostructures as amplifiers of transverse fields in magnetic resonance.  

PubMed

We introduce the concept of amplifying the transverse magnetic fields produced and/or detected with inductive coils in magnetic resonance settings by using the reversible transverse susceptibility properties of magnetic nanostructures. First, we describe the theoretical formalism of magnetic flux amplification through the coil in the presence of a large perpendicular DC magnetic field (typical of magnetic resonance systems) achieved through the singularity in the reversible transverse susceptibility in anisotropic single domain magnetic nanoparticles. We experimentally demonstrate the concept of transverse magnetic flux amplification in an inductive coil system using oriented nanoparticles with uni-axial magnetic anisotropy. We also propose a composite ferromagnetic/anti-ferromagnetic core/shell nanostructure system with uni-directional magnetic anisotropy that, in principle, provides maximal transverse magnetic flux amplification. PMID:16039099

Barbic, Mladen; Scherer, Axel

2005-09-01

191

Critical-magnetic-field anisotropy in single-crystal YBa/sub 2/Cu/sub 3/O/sub 7/  

SciTech Connect

We have measured the critical magnetic fields H/sub c//sub 2//sub X/ (parallel to a-b plane) and H/sub c//sub 2//sub perpendicular/ (perpendicular to a-b plane) of single crystals of YBa/sub 2/Cu/sub 3/O/sub 7/ as a function of temperature in fields up to 19 T. The slope -dH/sub c//sub 2//dT is greater by about a factor of four when the field is applied parallel to the a-b plane than when it is applied parallel to the c axis.

Moodera, J.S.; Meservey, R.; Tkaczyk, J.E.; Hao, C.X.; Gibson, G.A.; Tedrow, P.M.

1988-01-01

192

Strong axial anisotropy of the magnetic penetration length in superconducting ?  

NASA Astrophysics Data System (ADS)

We report muon spin rotation measurements of the temperature dependence and anisotropy of the magnetic field penetration lengths in the heavy fermion superconductor 0953-8984/10/43/023/img9. We observe a strong axial anisotropy. At 0.05 K we obtain for the penetration length parallel and perpendicular to the c axis 0953-8984/10/43/023/img10 (150) Å and 0953-8984/10/43/023/img11 (130) Å, respectively. 0953-8984/10/43/023/img12 at low temperatures excludes a superconducting order parameter in the B phase with only a line of nodes in the equatorial plane of the Fermi surface. The combined analysis of 0953-8984/10/43/023/img13 and 0953-8984/10/43/023/img12 measured in the B phase favours an hybrid order parameter with point nodes at the poles and a line of nodes at the equatorial plane. The A phase is characterized by a larger density of nodes than the B phase.

Yaouanc, A.; Dalmas de Réotier, P.; Huxley, A.; Flouquet, J.; Bonville, P.; Gubbens, P. C. M.; Mulders, A. M.

1998-11-01

193

Estimate of the magnetic anisotropy effect on the archaeomagnetic inclination of ancient bricks  

NASA Astrophysics Data System (ADS)

The magnetic fabric of 59 bricks coming from 5 ancient kilns has been studied by measuring the anisotropy of magnetic susceptibility (AMS) and the anisotropy of isothermal (AIRM), anhysteretic (AARM) and thermal (ATRM) remanent magnetization. The bricks are characterized by a well developed magnetic fabric that matches their flat shape. The shape of the anisotropy ellipsoids is in almost all cases oblate with the maximum and intermediate axes lying parallel to the large face of the brick and the minimum axis perpendicular to it. The directions of the principal axes are almost the same irrespectively of the type of anisotropy measured, whereas the degree of anisotropy of the AIRM, AARM and ATRM is much higher than the AMS. As the bricks lie horizontally within the kiln, the planar magnetic fabric results in an inclination shallowing of the archaeomagnetic direction with respect to that of the Earth's magnetic field at the time of their last cooling. Estimation of this effect on the grounds of ATRM measurements yields a shallowing that varies from 4° to 10° for individual samples. Such inclination difference may significantly bias archeomagnetic dating; for the case of the Canosa late-Roman kiln it leads to a dating error of more than two centuries.

Tema, Evdokia

2009-10-01

194

Magnetic anisotropy of the spin-ice compound Dy2Ti2O7  

Microsoft Academic Search

We report magnetization and ac susceptibility of single crystals of the spin-ice compound Dy2Ti2O7. Saturated moments at 1.8 K along the characteristic axes [100] and [110] agree with the expected values for an effective ferromagnetic nearest-neighbor Ising pyrochlore with local anisotropy, where each magnetic moment is constrained to obey the ``ice rule.'' At high enough magnetic fields along the [111

H. Fukazawa; R. G. Melko; R. Higashinaka; Y. Maeno; M. J. Gingras

2002-01-01

195

Giant Magnetic Anisotropy of Transition-Metal Dimers on Defected Graphene  

NASA Astrophysics Data System (ADS)

Continuous miniaturization of magnetic units in spintronics and quantum computing devices inspires efforts to search for magnetic nanostructures with large magnetic anisotropy energy (MAE). Typical nanostructures including molecular magnets, magnetic nanoclusters and magnetic nanowires have MAEs of a few meV so their blocking temperature is mostly lower than 50 K. In this work, we demonstrated the feasibility of achieving giant MAE in systems with transition metal dimers on defected and decorated graphene, based on density functional theory calculations. In particular, either a Pt-Ir dimer on a single vacancy or an Os-Ru dimer on a nitrogen-decorated divacancy possesses an MAE larger than 60 meV and high structural stability. Interestingly, their magnetic anisotropy can be conveniently manipulated by using external electric field. These features make them good candidates for the use in room temperature spintronics and quantum computing devices.

Hu, Jun; Wu, Ruqian

2014-04-01

196

Numerical renormalization group calculations of the magnetization of Kondo impurities with and without uniaxial anisotropy  

NASA Astrophysics Data System (ADS)

We study a Kondo impurity model with additional uniaxial anisotropy D in a nonzero magnetic field B using the numerical renormalization group (NRG). The ratio ge/gS of electron and impurity g factor is regarded as a free parameter and, in particular, the special cases of a “local” (ge=0) and “bulk” (ge=gS) field are considered. For a bulk field, the relationship between the impurity magnetization M and the impurity contribution to the magnetization Mimp is investigated and it is shown that M and Mimp are proportional to each other for fixed coupling strength. Furthermore, we find that the g-factor ratio effectively rescales the magnetic field argument of the zero-temperature impurity magnetization. In case of an impurity with D=0 and ge=gS, it is demonstrated that at zero temperature M(B), unlike Mimp(B), does not display universal behavior. With additional “easy-axis” anisotropy, the impurity magnetization is “stabilized” at a D-dependent value for kBT?gS?BB?|D| and, for nonzero temperature, is well described by a shifted and rescaled Brillouin function on energy scales that are small compared to |D|. In the case of “hard-axis” anisotropy, the magnetization curves can feature steps which are due to field-induced pseudo-spin-(1)/(2) Kondo effects. For large hard-axis anisotropy and a local field, these screening effects are described by an exchange-anisotropic spin-(1)/(2) Kondo model with an additional scattering term that is spin dependent (in contrast to ordinary potential scattering). In accordance with the observed step widths, this effective model predicts a decrease of the Kondo temperature with every further step that occurs upon increasing the field. Our study is motivated by the question as to how the magnetic properties of a deposited magnetic molecule are modified by the interaction with a nonmagnetic metallic surface.

Höck, Martin; Schnack, Jürgen

2013-05-01

197

Double-Q magnetic structures and strong planar anisotropy in tetragonal ErRu Ge and ErRu Si  

Microsoft Academic Search

.   Single crystal magnetization measurements and powder neutron diffraction on tetragonal ErRu2Ge2 as well as anisotropy of the paramagnetic susceptibility and specific heat measurements on ErRu2Si2 are presented. Besides the huge crystal field contribution to the uniaxial anisotropy, which favors the basal plane, a strong\\u000a in-plane anisotropy is evidenced. From these features and neutron diffraction experiments it is shown that

A. Garnier; D. Gignoux; B. Ouladdiaf; D. Schmitt; T. Shigeoka

2000-01-01

198

Effect of planar anisotropy on damping decrement of free oscillations of magnetization in garnet-ferrite films  

Microsoft Academic Search

The results of experimental investigation of free oscillations of magnetization in garnet-ferrite films with planar anisotropy\\u000a are considered. It is shown that the damping decrement of free oscillations increases with effective anisotropy field H\\u000a \\u000a Kp\\u000a .

Yu. A. Durasova; E. I. Il’yashenko; O. S. Kolotov; A. V. Matyunin; V. A. Pogozhev

2009-01-01

199

Role of magnetic anisotropy in spin-filter junctions  

NASA Astrophysics Data System (ADS)

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 La0.7Sr0.3MnO3/CoCr2O4/Fe3O4 and La0.7Sr0.3MnO3/MnCr2O4/Fe3O4 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 MnCr2O4 barrier layers.

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

2011-06-01

200

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

201

Magnetic anisotropy in Ni2MnGa  

Microsoft Academic Search

We study here, within the density-functional theory, the magnetic anisotropy energy (MAE) in Ni2MnGa which is a prototype of a magnetic shape-memory alloy. We calculate the MAE, which is a key property for the magnetic shape-memory effect, for tetragonal structure with different ratios of the c and a lattice constants, reproducing the experimental easy axes both in compression and elongation

J. Enkovaara; A. Ayuela; L. Nordström; R. M. Nieminen

2002-01-01

202

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

203

Experimental study of the spindynamics in the 1-D-ferromagnet with planar anisotropy, CsNiF 3 , in an external magnetic field  

Microsoft Academic Search

The results of a detailed inelastic neutron scattering study of the spindynamics in CsNiF3 in an external magnetic field are presented. Results have been obtained for different combinations of the correlation function Sa Sa> (a=x, y, z) in order to analyse theH, T, qc-dependence of both, the central component and the spinwave scattering. These results cannot be explained by a

M. Steiner; K. Kakurai; J. K. Kjems

1983-01-01

204

Perpendicular magnetic anisotropy and noncollinear magnetic structure in ultrathin Fe films on W(110)  

NASA Astrophysics Data System (ADS)

We used nuclear resonant scattering (NRS) of synchrotron radiation to investigate the details of the thickness-induced spin reorientation transition (SRT) in ultrathin epitaxial iron films on W(110), where the thicknesses of the films ranged from 1-5 monolayers. During growth, the magnetization of the Fe film, which was probed by the hyperfine magnetic field, changes from a noncollinear configuration with an out-of-plane magnetic component to the homogeneously magnetized state with the in-plane [1-10] easy direction. The fast acquisition of the experimental NRS spectra combined with the high sensitivity of this technique to the orientation of the hyperfine magnetic fields allowed us to study the magnetic evolution during SRT in detail. Our results reveal the complex character of this transition, which has been intensively studied in the past. The noncollinear magnetic structure appears in the system of the mono-, double-, and trilayer areas that coexist due to deviation from the layer-by-layer growth of iron on W(110). We also report the observation of out-of-plane magnetic anisotropy in the double-layer areas at temperatures as high as 300 K. By comparing the experimental results with density functional theory calculations, we conclude that surface magnetic moments are enhanced by 25%.

?l?zak, M.; ?l?zak, T.; Freindl, K.; Kara?, W.; Spiridis, N.; Zaj?c, M.; Chumakov, A. I.; Stankov, S.; Rüffer, R.; Korecki, J.

2013-04-01

205

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

206

Current Induced Magnetization Switching in Small Domains of Different Anisotropies.  

NASA Astrophysics Data System (ADS)

Several recent experimental studies have confirmed the possibility of switching the magnetization direction in the small magnetic domains by pumping large spin-polarized currents through them. On the basis of equations proposed by J.Slonczewski for the case when magnetization of the domains is almost uniform, we analyze the stability and switching for two types of magnetic and shape anisotropies of a magnetic domain in a nanowire and find qualitatively different behavior, including different shapes of bistable regions. Our study is analytic as opposed to recent numeric work. Assumed anisotropies can be realized in experiments and our predictions can be used to experimentally test the theory of spin-transfer torques. Such test would be especially interesting since alternative approaches are discussed in the literature.

Bazaliy, Yaroslaw; Jones, Barbara; Zhang, Shou-Cheng

2001-03-01

207

Single-atom Magnetic Anisotropy on a Surface  

NASA Astrophysics Data System (ADS)

Studying single-atom magnetic anisotropy on surfaces enables the exploration of the smallest magnetic storage bit that can be built. In this work, magnetic anisotropy of a single rare-earth atom on a surface is studied for the first time, both computationally and theoretically. The substrate surface is chosen to be a copper-nitrite surface, where single transition-metal magnetic atoms on the same surface were previously studied one atom at a time by STM.ootnotetextC. F. Hirjibehedin, C.-Y. Lin, A. F. Otte, M. Ternes, C. P. Lutz, B. A. Jones, A. J. Heinrich, Science 317, 1199 (2007). We propose unconventional f and d subshell symmetries so that following first-principles calculations, simple pictorial analyses of such anisotropy can be performed for the first time, independently for both rare-earth and transition-metal adatoms. The analyses explain the spin-density distribution of a single adatom, and derive the spin orientation of its largest spin-orbit coupling. The magnetic anisotropy energy of the present study is calculated to be a factor of five larger than the previous highest one.

Lin, Chiung-Yuan; Yao, Jing-Neng

2012-02-01

208

Evidence of surface anisotropy in magnetic nanoparticles  

Microsoft Academic Search

Discontinuous magnetic multilayers provide a simple method of producing magnetic nanoparticles. Such systems can be viewed as two-dimensional nanosystems, depending on separation between the discontinuous magnetic layers via a non-magnetic spacer layer. We have studied the system whereby discontinuous layers of CoFe are separated by Al2O3 interlayers of 40Å (nominal). A set of samples with nominal CoFe thicknesses between 7

D. S. Schmool; R. Rocha; J. B. Sousa; J. A. M. Santos; G. Kakazei

2006-01-01

209

Evidence of surface anisotropy in magnetic nanoparticles  

Microsoft Academic Search

Discontinuous magnetic multilayers provide a simple method of producing magnetic nanoparticles. Such systems can be viewed as two-dimensional nanosystems, depending on separation between the discontinuous magnetic layers via a non-magnetic spacer layer. We have studied the system whereby discontinuous layers of CoFe are separated by Al2O3 interlayers of 40 Å (nominal). A set of samples with nominal CoFe thicknesses between

D. S. Schmool; R. Rocha; J. B. Sousa; J. A. M. Santos; G. Kakazei

2006-01-01

210

Reorientation of magnetic anisotropy in epitaxial cobalt ferrite thin films  

NASA Astrophysics Data System (ADS)

Spin reorientation has been observed in CoFe2O4 thin single crystalline films epitaxially grown on (100) MgO substrate upon varying the film thickness. The critical thickness for such a spin-reorientation transition was estimated to be 300nm . The reorientation is driven by a structural transition in the film from a tetragonal to cubic symmetry. At low thickness, the in-plane tensile stress induces a tetragonal distortion of the lattice that generates a perpendicular anisotropy, large enough to overcome the shape anisotropy and to stabilize the magnetization easy axis out of plane. However, in thicker films, the lattice relaxation toward the cubic structure of the bulk allows the shape anisotropy to force the magnetization to be in plane aligned.

Lisfi, A.; Williams, C. M.; Nguyen, L. T.; Lodder, J. C.; Coleman, A.; Corcoran, H.; Johnson, A.; Chang, P.; Kumar, A.; Morgan, W.

2007-08-01

211

Competition of perpendicular magnetic anisotropy and exchange magnetic anisotropy in a Pt\\/Co\\/alpha-Cr2O3(0001) thin film  

Microsoft Academic Search

We investigated perpendicular magnetic anisotropy and exchange magnetic anisotropy in a Pt\\/Co\\/alpha-Cr2O3(0001) thin film grown on an alpha-Al2O3(0001) substrate. The film exhibits perpendicular magnetic anisotropy below a Co thickness of 1.2 nm at room temperature. Independent of the magnetic easy direction of the Co layer, the perpendicular exchange bias (PEB) appears in a direction perpendicular to the film below 80

Yu Shiratsuchi; Hayato Noutomi; Hiroto Oikawa; Toshiaki Fujita; Ryoichi Nakatani

2011-01-01

212

[010] uniaxial-anisotropy induced asymmetry of magnetic reversal in (Ga,Mn)As  

NASA Astrophysics Data System (ADS)

We investigate the asymmetric magnetic rotation arising from [010] uniaxial anisotropy in (Ga,Mn)As thin films by measuring the planar Hall effect, with the Hall bars fabricated along [110] direction. Two modes, angle-scan and field-scan, are utilized to do the measurements, both of which show remarkably asymmetric rotations. This phenomenon is found to arise from the minimal [010] uniaxial anisotropy, which is commonly overshadowed by its strong cubic anisotropy counterpart. Besides, we also measure the temperature and film thickness dependence of asymmetric rotation, showing a more remarkable behavior with the increase of temperature or thickness. The direct demonstration of [010] uniaxial anisotropy by an electrical fashion provides useful information for designing electrically programmable memory and logic device on the basis of (Ga,Mn)As.

Lin, D. C.; Bi, G. Y.; Li, F.; Song, C.; Wang, Y. Y.; Cui, B.; Wang, G. Y.; Pan, F.

2013-01-01

213

Mathematical simulations of anisotropy of magnetic susceptibility on composite fabrics  

Microsoft Academic Search

The anisotropy of magnetic susceptibility (AMS) is an integral measure of the preferred orientation of all minerals present in a rock. When the AMS is carried by paramagnetic minerals alone, the principal directions of the susceptibility ellipsoid should reflect the crystallographic orientation of the minerals. The relationship between the AMS and deformation depends on several factors, which control the development

Fátima Martín-Hernández; Karsten Kunze; Manuel Julivert; Ann M. Hirt

2005-01-01

214

6. MAGNETIC ANISOTROPY OF BARBADOS PRISM SEDIMENTS 1  

Microsoft Academic Search

Anisotropy of magnetic susceptibility (AMS) results from sediments spanning the basal décollement of the Barbados accre- tionary prism show a striking progression across this structure that strongly supports the hypothesis that it is strongly overp res- sured. In the accretionary prism above the décollement, the minimum AMS axes are subhorizontal and nearly east-west trending, whereas the maximum AMS axes are

Bernard A. Housen

1997-01-01

215

Magnetic printing characteristics using master disk with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

With the increase in recording density and capacity of hard-disk drives (HDD), high speed, high precision and low cost servo writing method has become an issue in HDD industry. The magnetic printing was proposed as the ultimate solution for this issue [1-3]. There are two types of magnetic printing methods, which are ‘Bit Printing (BP)’ and ‘Edge Printing (EP)’. BP method is conducted by applying external field whose direction is vertical to the plane of both master disk (Master) and perpendicular magnetic recording (PMR) media (Slave). On the other hand, EP method is conducted by applying external field toward down track direction of both master and slave. In BP for bit length shorter than 100 nm, the SNR of perpendicular anisotropic master was higher than isotropic master. And the SNR of EP for the bit length shorter than 50 nm was demonstrated.

Fujiwara, Naoto; Nishida, Yoichi; Ishioka, Toshihide; Sugita, Ryuji; Yasunaga, Tadashi

216

Nanopatterned CoPt alloys with perpendicular magnetic anisotropy  

SciTech Connect

CoPt alloy films with perpendicular magnetic anisotropy were grown on SiO{sub 2} nanoparticle arrays with particle sizes as small as 10 nm. In order to induce perpendicular magnetic anisotropy in the CoPt film, a MgO seed layer was sputter deposited. Despite the fact that neighboring CoPt film caps are interconnected, individual caps appear as single domain and for most of them their magnetization orientation can be reversed individually. This behavior might be caused by domain wall nucleation and pinning preferentially at the rim of each cap. Thus, arrays of magnetic caps with defined pinning sites can be considered as a percolated perpendicular medium.

Makarov, D. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany); Bermudez-Urena, E.; Schmidt, O. G. [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden (Germany); Liscio, F.; Maret, M. [SIMAP, INP Grenoble-CNRS-UJF, 1130 rue de la Piscine, BP75, F-38402 Saint Martin d'Heres (France); Brombacher, C.; Schulze, S.; Hietschold, M.; Albrecht, M. [Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz (Germany)

2008-10-13

217

Dynamical magnetic anisotropy in spin--1 molecular systems  

NASA Astrophysics Data System (ADS)

We study electronic transport through a deformable spin-1 molecular system in a break junction setup, under the influence of a local vibrational mode. Our study shows that the magnetic anisotropy, which arises due to stretching along the transport axis[Science 328 1370 (2010)], is renormalized by the interactions with vibrations. The coupling induces additional spin--asymmetric hybridizations that contribute to the net molecular anisotropy. We show that the low temperature physics of such device can be described by an anisotropic Kondo model (J> J), with a magnetic anisotropy term, ANetSz^2, negative at zero stretching. A quantum phase transition (QPT) is explored by stretching the molecule, driving ANet into positive values, and changing the character of the device from a non--Fermi--liquid (NFL) to a Fermi liquid (FL) ground state. This transition can be directly observed through the zero--bias conductance, which we find to be finite for negative anisotropy, zero for positive anisotropy, and to reach the unitary limit at ANet 0. At that point, an underscreened spin-1 Kondo ground state appears due to the restitution of the spin-1 triplet degeneracy.

Ruiz-Tijerina, David; Cornaglia, Pablo; Balseiro, Carlos; Ulloa, Sergio

2012-02-01

218

Pattern-induced magnetic anisotropy in FePt thin films by ion irradiation  

SciTech Connect

The magnetic properties of FePt thin films have been modified by exposing the samples to irradiation of 4 MeV Cl{sup 2+} ions. Patterned magnetic films, without modified topographical profile, were fabricated by irradiating the films through a shadowing micrometric mask. The structural changes, ascribed to the ion-beam-induced amorphization of the thin films, promote the modification of the magnetic anisotropy. In particular, the out-of-plane component of the magnetization decreases simultaneously with an enhancement of in-plane anisotropy by increasing ion fluence. Moreover, the nonirradiated regions present unexpected anisotropic behavior owing to the stray field of the irradiated regions. The control of this effect, which can have unwished consequences for the patterning of magnetic properties by ion bombardment, needs to be suitably addressed.

Jaafar, M. [Instituto de Ciencia de Materiales de Madrid, CSIC, ES-28049 Madrid (Spain); Dpto. Fisica de la Materia Condensada, UAM, ES-28049 Madrid (Spain); Sanz, R. [Instituto de Ciencia de Materiales de Madrid, CSIC, ES-28049 Madrid (Spain); Nanoate SL, Poeta Rafael Morales 2, ES-28702 San Sebastian de los Reyes, Madrid (Spain); McCord, J. [Institute of Ion Beam Physics and Materials Research, FZD, D-01314 Dresden (Germany); Jensen, J. [Thin Film Physics, Department of Physics, Chemistry and Biology, Linkoeping University, SE-581 83 Linkoeping (Sweden); Schaefer, R. [Leibniz Institute for Solid State and Materials Research, IFW, Helmholtzstrasse 20, D-01069 Dresden (Germany); Vazquez, M.; Asenjo, A. [Instituto de Ciencia de Materiales de Madrid, CSIC, ES-28049 Madrid (Spain)

2011-03-01

219

Electronic structure and magnetic anisotropy of CrO2  

Microsoft Academic Search

The problem of importance of strong correlations for the electronic structure, transport and magnetic properties of half--metallic ferromagnetic CrO2 is addressed by performing density functional based electronic structure calculations in the local spin density approximation (LSDA) as well as using the LSDA+U method. In both schemes we compute electronic structure, optical conductivity and magnetic anisotropy energy for chromium dioxide. It

Antonina Toropova; Sergej Savrasov; Viktor Oudovenko

2005-01-01

220

Anisotropy of the magnetoviscous effect in ferrofluids containing nanoparticles exhibiting magnetic dipole interaction.  

PubMed

The aim of this work has been the investigation of the anisotropy of the viscosity of a ferrofluid with magnetically interacting particles which are able to form structures in an applied magnetic field. The results of the experiments show a significant deviation from the case of a fluid without strong dipolar interactions. Furthermore, we have determined the dependence of the ratio of the viscosity coefficients on shear rate providing an insight into the microstructural reasons for the observed effects. PMID:21841240

Gerth-Noritzsch, M; Yu Borin, D; Odenbach, S

2011-08-12

221

Synthesis and magnetic investigations on rare-earth-containing liquid crystals with large magnetic anisotropy  

SciTech Connect

A new series of liquid-crystalline Schiff base lanthanide compounds of the general formula (L{sup {double_prime}}H){sub 2}L{sup {double_prime}}MX{sub 2} was prepared (L{sup {double_prime}}H = H{sub 2n+1}C{sub n}OC{sub 6}H{sub 3}(OH)CHNC{sub m}H{sub 2m+1}; n = 7, 12; m = 14, 18; M =La, Tb, Dy, Er, Nd, Ho, Eu, Pr, and Gd; X = NO{sub 3} or Cl). The thermal behavior of these complexes was examined by polarizing microscopy, differential scanning calorimetry, and X-ray diffraction experiments. The ligands L {sup {double_prime}}H are nonmesomorphic, but all lanthanide complexes show smectic A mesophases. Further, temperature-dependent magnetic susceptibility measurements were carried out in order to obtain information about the magnetic anisotropy of the lanthanide compounds. The Tb(III) and Dy(III) derivatives could be oriented by a magnetic field. These liquid-crystalline lanthanide complexes display magnetic anisotropies which are two orders of magnitude greater than those of known liquid crystals. 23 refs., 8 figs., 4 tabs.

Galyametdinov, Yu.; Athanassopoulou, M.A.; Griesar, K. [Institut fuer Physikalische Chemie, Darmstadt (Germany)] [and others] [Institut fuer Physikalische Chemie, Darmstadt (Germany); and others

1996-04-01

222

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

223

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

224

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

225

Can large magnetic anisotropy and high spin really coexist?  

NASA Astrophysics Data System (ADS)

This theoretical study discusses the interplay of the magnetic anisotropy and magnetic exchange interaction of two Mn6 complexes. Our results for two polynuclear Mn6 complexes show a very strong dependence of the D value on the spin of the ground state while the energy barriers are practically constant. Thus, complex 2 with a large spin (S = 12) favoured by ferromagnetic interactions has a small D value, while the lower spin complex 1 (S = 4) has a large D value. Therefor we suggest, that a large magnetic anisotropy is not favoured by a high spin state of the ground state.E.Ruiz et al. Chem. Comm. 2008, DOI: 10.1039/b714715e

Loose, Claudia; Ruiz, Eliseo; Cirera, Jordi; Cano, Joan; Alvarez, Santiago; Kortus, Jens

2008-03-01

226

Light-induced magnetic anisotropy in Co-doped garnet films  

NASA Astrophysics Data System (ADS)

Light-induced uniaxial magnetic anisotropy characterized by amplitude, times of creation ?1, and a vanishing ?2 was studied. The investigation was performed on YIG (yttrium iron garnet):Co,Ca,Ge liquid-phase epitaxy films using a very sensitive method-observation of changes of magnetic domain structure with a different in-plane magnetization component induced by linearly polarized light pulses. An argon laser (?=488 nm) was used. The effective field HL was introduced to describe the photoinduced uniaxial magnetic-anisotropy amplitude. These domain changes were studied within the temperature range of 160-300 K. With an increase in temperature an increase in ?1, a decrease in ?2, and a drastic decrease in HL were found. The appearance of the photoinduced anisotropy is explained by light-induced rearrangement of strongly anisotropic Co2+ octahedral ions. A microscopic model was proposed where ion rearrangement is connected with electron excitations into the conducting band. Both thermal and light-induced excitations were discussed. Numerical and analytical solutions of kinetic equations describing the model are discussed. The dynamics of light-induced magnetic anisotropy both uniaxial and cubic is analyzed.

Stupakiewicz, A.; Maziewski, A.; Davidenko, I.; Zablotskii, V.

2001-08-01

227

Mapping of single-site magnetic anisotropy tensors in weakly coupled spin clusters by torque magnetometry.  

PubMed

Single-crystal torque magnetometry performed on weakly-coupled polynuclear systems provides access to a complete description of single-site anisotropy tensors. Variable-temperature, variable-field torque magnetometry was used to investigate triiron(iii) complex [Fe3La(tea)2(dpm)6] (), a lanthanum(iii)-centred variant of tetrairon(iii) single molecule magnets (Fe4) (H3tea = triethanolamine, Hdpm = dipivaloylmethane). Due to the presence of the diamagnetic lanthanoid, magnetic interactions among iron(iii) ions (si = 5/2) are very weak (<0.1 cm(-1)) and the magnetic response of is predominantly determined by single-site anisotropies. The local anisotropy tensors were found to have Di > 0 and to be quasi-axial with |Ei/Di| ? 0.05. Their hard axes form an angle of approximately 70° with the threefold molecular axis, which therefore corresponds to an easy magnetic direction for the molecule. The resulting picture was supported by a High Frequency EPR investigation and by DFT calculations. Our study confirms that the array of peripheral iron(iii) centres provides substantially noncollinear anisotropy contributions to the ground state of Fe4 complexes, which are of current interest in molecular magnetism and spintronics. PMID:25014192

Rigamonti, Luca; Cornia, Andrea; Nava, Andrea; Perfetti, Mauro; Boulon, Marie-Emmanuelle; Barra, Anne-Laure; Zhong, Xiaoliang; Park, Kyungwha; Sessoli, Roberta

2014-07-23

228

Giant magnetic anisotropy of transition-metal dimers on defected graphene.  

PubMed

Continuous miniaturization of magnetic units in spintronics and quantum computing devices inspires efforts to search for magnetic nanostructures with giant magnetic anisotropy energy (MAE) and high structural stability. Through density functional theory calculations, we found that either Pt-Ir or Os-Ru dimer forms a stable vertical structure on the defected graphene and possess an MAE larger than 60 meV, sufficient for room-temperature applications. Interestingly, their MAEs can be conveniently manipulated by using an external electric field, which makes them excellent magnetic units in spintronics and quantum computing devices. PMID:24666159

Hu, Jun; Wu, Ruqian

2014-04-01

229

Sources of anisotropy in amorphous magnetic thin films  

NASA Astrophysics Data System (ADS)

With the assistance of this grant, my laboratory has progressed substantially and is now beginning to produce results. This last year, in addition to lab build-up and student supervision, I have continued work on the amorphous rare earth transition metal alloys. There are several significant new results arising from this work. A model for the growth-induced macroscopic magnetic anisotropy: I have clear evidence against Takeshi Egami's bond-orientational anisotropy model which attributes the anisotropy to anelastic strain. He describes this model as a simple increase in the number of bonds in-plane compared to out-of-plane due to stress during the growth. I find a strong (more than an order of magnitude) dependence of the anisotropy on deposition temperature and essentially no dependence on the state of stress either during the growth or after. I believe the reason for the anisotropy is a texturing of the short-range order relative to the surface, which minimizes surface energy at every instant during the growth, and gets frozen into the structure.

Hellman, Frances

1990-11-01

230

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

231

Effects of Transverse Magnetic Anisotropy on Current-Induced Spin Switching  

NASA Astrophysics Data System (ADS)

Spin-polarized transport through bistable magnetic adatoms or single-molecule magnets (SMMs), which exhibit both uniaxial and transverse magnetic anisotropy, is considered theoretically. The main focus is on the impact of transverse anisotropy on transport characteristics and the adatom’s or SMM’s spin. In particular, we analyze the role of quantum tunneling of magnetization (QTM) in the mechanism of the current-induced spin switching, and show that the QTM phenomenon becomes revealed as resonant peaks in the average values of the molecule’s spin and in the charge current. These features appear at some resonant fields and are observable when at least one of the electrodes is ferromagnetic.

Misiorny, Maciej; Barna?, Józef

2013-07-01

232

Spin disorder and magnetic anisotropy in Fe3O4 nanoparticles  

NASA Astrophysics Data System (ADS)

We have studied the magnetic behavior of dextran-coated magnetite (Fe3O4) nanoparticles with median particle size =8 nm. Magnetization curves and in-field Mössbauer spectroscopy measurements showed that the magnetic moment MS of the particles was much smaller than the bulk material. However, we found no evidence of magnetic irreversibility or nonsaturating behavior at high fields, usually associated to spin canting. The values of magnetic anisotropy Keff from different techniques indicate that surface or shape contributions are negligible. It is proposed that these particles have bulklike ferromagnetic structure with ordered A and B sublattices, but nearly compensated the magnetic moments. The dependence of the blocking temperature with frequency and applied fields, TB(H,?), suggests that the observed nonmonotonic behavior is governed by the strength of interparticle interactions.

Lima, E.; Brandl, A. L.; Arelaro, A. D.; Goya, G. F.

2006-04-01

233

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."

Nasa

2012-06-26

234

Probing the origin of magnetic anisotropy in a dinuclear {Mn(III)Cu(II)} single-molecule magnet: the role of exchange anisotropy.  

PubMed

Using ab initio calculations all the components of the magnetic anisotropy in a dinuclear [Mn(III)Cu(II)Cl(5-Br-sap)2(MeOH)] single-molecule magnet (SMM) have been computed. These calculations reveal that apart from the single-ion anisotropy, the exchange anisotropy also plays a crucial role in determining the sign as well as the magnitude of the cluster anisotropy. Developed magneto-structural correlations suggest that a large ferromagnetic exchange can in fact reduce the ground-state anisotropy, which is an integral component in the design of SMMs. PMID:24700405

Singh, Saurabh Kumar; Rajaraman, Gopalan

2014-04-25

235

Magnetic anisotropy in Fe/Cu over- and interlayers  

NASA Astrophysics Data System (ADS)

We present an extensive study on the anisotropic magnetic properties of the high-moment ferromagnetic phase of fcc Fe/Cu over- and interlayers in terms of the Fully Realivistic Spin Polarized Screened Korringa-Kohn-Rostoker method. We calculate layer resolved anisotropy energies for various Fe overlayer thicknesses and show that the main contribution to the magnetic anisotropy energies comes from the Fe layer closest to the substrate. This is verified by calculations for the same systems but with additional Cu covering layers and for Cu/Fe/Cu sandwitched structure. We also discuss the relationship between the anisotropy energy and the orbital moment anisotropy which has been extensively studied by tight-binding models in the context of perturbation theory. The effect of intermixing between the substrate and overlayer is also demonstrated. --This paper was supported by the Austrian Minstry of Science (GZ. 45.368/2-IV/6/94), the Austrian National Bank (P4648) and the Hungarian National Scientific Research Foundation for partial financial support (OTKA F014378).

Ujfalussy, B.; Szunyogh, L.; Weinberger, P.

1996-03-01

236

Voltage-induced switching in magnetic tunnel junctions with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Spintronic devices can be operated by either a magnetic field or a spin polarized current; however, the former is not site-specific, and the latter suffers from large current density issues. In this work, we show that voltage-controlled spintronic devices offer many attributes. Although a metallic ferromagnet responds only very weakly to an electric field if at all, under special circumstances an electric field can have a profound impact on its magnetic properties. An electric field can alter the interfacial perpendicular magnetic anisotropy (PMA) of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) in a prescribed manner. By exploiting the voltage dependence of the PMA we have accomplished voltage-controlled MTJ for which the high- and low-resistance states can be accessed reversibly and repeatedly by voltage pulses associated with very low current density in the range of 104 A cm-2. This development opens up a new avenue to achieve ultra-low power consumption and ultra-fast operation in next-generation spintronic devices.

Wang, W. G.; Chien, C. L.

2013-02-01

237

Earth's Inconstant Magnetic Field  

NSDL National Science Digital Library

This NASA site describes long-term changes in Earth's magnetic field, and how magnetic stripes in the Atlantic seafloor provide evidence for reversals of this field. The site presents a model of Earth's interior that helps explain how Earth's magnetic field is generated and how the reversals occur. A computer-generated image shows the complicated magnetic field in-between reversals.

2007-04-27

238

Microwave background radiation anisotropy from scalar field gradients  

NASA Astrophysics Data System (ADS)

Analytic calculations of the cosmological density fluctuations and microwave background radiation anisotropies induced by gradients in a topologically trivial scalar field are presented. This anlaytic solution should provide a good test for numerical simulations of microwave anisotropy from scalar fields. To the extent that these results generalize to other scalar field models and configurations, they imply that (1) MBR measurements limit large-scale primordial variations greater than about 5×1016 GeV within our horizon, (2) the total scalar field variation is a fair predictor of the magnitude of the MBR anisotropy, but is only accurate to within a factor of about three, (3) scalar fields as well as other models of seeded perturbations produce a few times more anisotropy ?T/T for a given density fluctuation ??/? (on the same scale) than do primordial adiabatic perturbations, (4) models of scalar field seeds which produce a scale-invariant spectrum of perturbations seem to require galaxies to be more clustered than the mass on small scales, and (5) scalar fields do not ``tilt'' the Universe.

Stebbins, Albert; Veeraraghavan, Shoba

1993-09-01

239

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.

240

Distortions in length perception: visual field anisotropy and geometrical illusions.  

PubMed

Psychometric experiments were performed to study the effects of visual field anisotropy and geometrical illusions on the accuracy of comparison of objects in terms of length. Stimuli consisting of V-shaped symbols were used, made up of three light spots or one spot plus components of illusory figures, which were pairs of Müller-Layer wings or an interval of the Oppel-Kundt figure filled with spots of light. Relationships between the length comparison errors and the orientations of the reference and test parts of the stimulus were obtained. The experimental data showed that the simultaneous appearance of illusions and visual field anisotropy can be summed algebraically. PMID:15929571

Bertulis, A; Bulatov, A

2005-05-01

241

Magnetism and magnetic anisotropy of Ni xPd 1-x alloy  

NASA Astrophysics Data System (ADS)

Single-crystalline Ni xPd 1-x thin films with a face-centered cubic structure for the whole stoichiometry 0? x?1 have been achieved on Cu(1 0 0) via molecular beam epitaxy (MBE). The ferromagnetism shows up at x?0.25 at 300 K and the total magnetization decreases as the Pd concentration increases, which confirms our earlier first-principles calculations (Y.S. Shi, M.F. Wang, D. Qian, G.S. Dong, X.F. Jin, D.S. Wang, J. Magn. Magn. Mater. 277 (2004) 71). The magnetocrystalline anisotropy of Ni xPd 1-x is determined to be cubic with a negative K1, as measured by the magneto-optical Kerr effect (MOKE) technique with a rotating magnetic field (ROTMOKE).

Tang, Z. B.; Tian, C. S.; Yin, L. F.; Dong, G. S.; Jin, Xiaofeng

2007-03-01

242

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

243

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.

244

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.

VU Bioengineering RET Program, School of Engineering,

245

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

246

Local Spin Anisotropy Effects upon the Magnetization of Dimer Single Molecule Magnets  

NASA Astrophysics Data System (ADS)

We present an exactly soluble model of equal spin s1 dimer single molecule magnets. The dimer spins interact via the Heisenberg, Zeeman, and the most general quadratic local and global anisotropic exchange interactions. We derive the Hamiltonian matrix for the general case with each type of anisotropy. For antiferromagnetic couplings and s1 > 1/2, the low temperature T magnetization exhibits a strong influence of single-ion anisotropy. Our results suggest a substantial presence of axial single-ion anisotropy in the s1 = 5/2 Fe2 dimer, [Fe(salen)Cl]2.

Klemm, Richard A.; Efremov, Dmitri V.

2006-09-01

247

Anisotropy of magnetic susceptibility (AMS) analysis of basalt dikes at Cathedral Cliffs, WY: implications for Heart Mountain faulting  

Microsoft Academic Search

Mafic dikes pervade the upper plate of the Heart Mountain Detachment (HMD), yet the dike concentration in the lower plate is sparse. Previous workers interpreted that these dikes were emplaced either coeval with or subsequent to the emplacement of the upper plate. The magnetic fabrics of 32 mafic dikes at Cathedral Cliffs were analyzed using low-field anisotropy of magnetic susceptibility

Josh Defrates; David H. Malone; John P. Craddock

2006-01-01

248

Origin of petrofabrics and magnetic anisotropy in ordinary chondrites  

NASA Technical Reports Server (NTRS)

Three-dimensional finite strain and magnetic susceptibility anisotropy have been determined for 15 ordinary chondrites. The axes of strain and magnetic ellipsoids roughly correlate in both magnitude and orientation. The shapes of these ellipsoids are generally oblate spheroids that define a dominant foliation and a weak lineation. These characteristics suggest deformation involving uniaxial compaction. The degree of uniaxial deformation correlates with intensity of shock, as indicated by optical, TEM and chemical criteria. These data, plus the lack of a relationship between foliation and metamorphic history, indicate that dynamic processes, i.e., impacts, produced planar deformation fabrics in chondrites.

Sneyd, Deana S.; Mcsween, Harry Y., Jr.; Sugiura, Naoji; Strangway, David W.; Nord, Gordon L., Jr.

1988-01-01

249

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

250

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

NASA Astrophysics Data System (ADS)

We have investigated the effects of domain and grain anisotropy on spin-resonance in magnetic permeability, implementing a Monte-Carlo approach and a coupled Landau-Lifshitz-Gilbert equation. The Monte-Carlo approach provides great flexibility by employing different probability density functions, allowing modeling of material texture differences that may occur due to different preparation methods. Changes in the permeability tensor result from variations in grain demagnetization and domain demagnetization as well as the anisotropy field relative to saturation magnetization. Experimental permeability measurements on demagnetized polycrystalline yttrium iron garnet show for the first time that the best fit to measured data requires a complex distribution of both grain and domain demagnetization factors. Assuming that grain and domain demagnetizations are decoupled, it was 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). Implications for modeling experimental data assuming particular phenomenological loss coefficients or linewidths are also offered.

Chun, Jaehun; Mark Jones, A.; McCloy, John S.

2012-07-01

251

Measurement of magnetization using domain compressibility in CoFeB films with perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

We present a method to map the saturation magnetization of soft ultrathin films with perpendicular anisotropy, and we illustrate it to assess the compositional dependence of the magnetization of CoFeB(1 nm)/MgO films. The method relies on the measurement of the dipolar repulsion of parallel domain walls that define a linear domain. The film magnetization is linked to the field compressibility of the domain. The method also yields the minimal distance between two walls before their merging, which sets a practical limit to the storage density in spintronic devices using domain walls as storage entities.

Vernier, N.; Adam, J.-P.; Eimer, S.; Agnus, G.; Devolder, T.; Hauet, T.; Ocker, B.; Garcia, F.; Ravelosona, D.

2014-03-01

252

Tunable steady-state domain wall oscillator with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We theoretically study domain wall oscillations upon the injection of a dc current through a geometrically constrained wire with perpendicular magnetic anisotropy. The frequency spectrum of the oscillation can be tuned by the injected current density and additionally by the application of an external magnetic field. Our analytical calculations are supported by micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation. The simple concept of our localized steady-state oscillator might prove useful as a nanoscale microwave generator with possible applications in telecommunications or for rf-assisted writing in magnetic hard drives.

Bisig, A.; Heyne, L.; Boulle, O.; Kläui, M.

2009-10-01

253

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,

254

Magnetic anisotropy of amorphous alloy ribbons in as-quenched state  

Microsoft Academic Search

The in-plane magnetic anisotropy Ku in as-quenched state has been studied for amorphous Fe-based, FeNi-based and Co-based alloys. The change in anisotropy Ku with stress relief annealing has been measured and the dependence of anisotropy Kus on magnetization square M2s after annealing is linear. Results show that the anisotropy Ku consists of two parts: one is Kusigma that can be

Xiang-Yuan Xiong; Kai-Yuan Ho

1991-01-01

255

Magnetic anisotropies in (210)-oriented bismuth substituted iron garnet thin films  

NASA Astrophysics Data System (ADS)

The liquid phase epitaxy growth and characterization of single crystal (210)-oriented thin garnet films with Bi substitution up to 1.5 at./f.u. is reported. These epitaxial films exhibit an easy plane of magnetization which is inclined with respect to the film plane, making them uniquely suitable for garnet-based magneto-optic imagers (MOIs). In order to identify the optimal growth conditions to attain the highest sensitivity of such MOIs, the chemical composition of the films is discussed in relation with their magnetic and optic properties. It has been demonstrated that the increase in the amount of Pr tends to increase the in-plane orthorhombic anisotropy field HKi, while the rare-earth substitution by Bi has a strong effect on the canted orthorhombic anisotropy Kyz. The best MOI film had a saturation field of 130 Oe and a sensitivity of 175 deg/A.

Nistor, I.; Holthaus, C.; Tkachuk, S.; Mayergoyz, I. D.; Krafft, C.

2007-05-01

256

Effect of an Au underlayer on perpendicular magnetic anisotropy in Au/Co/Au(111) sandwich films  

SciTech Connect

The authors have used spin-wave Brillouin scattering to study perpendicular magnetic anisotropy in Au/Co/Au(111) sandwiched films with varying thicknesses of Au-underlayers. By using 5-monolayer (ML)-thick Co films, the transition of spin-wave frequency between out-of-plane and in-plane magnetizations can be observed by varying the in-plane field. They find that the field-dependence of the spin-wave energy is explained by a calculation including both the first-order (second power) and the second-order uniaxial perpendicular anisotropies depending on the Au-underlayer. They observe saturation of the anisotropy at 5 ML of Au-underlayer thickness, which corresponds to the saturation of in-plane lattice expansion of Co on that Au-underlayer. The contribution of interface anisotropy is evaluated from the Co-thickness dependence of the anisotropy observed. They also have observed a field-dependent broadening of the spin-wave Brillouin spectra at a critical field between out-of-plane and in-plane magnetizations, which they attribute to a distribution of the first-order anisotropy.

Murayama, Akihiro; Hyomi, Kyoko; Eickmann, J.; Falco, C.M. [Univ. of Arizona, Tucson, AZ (United States)] [Univ. of Arizona, Tucson, AZ (United States)

1998-07-01

257

Ultrafast Laser Spin Wave Measurement of Temperature Dependent Magnetic Anisotropy of Half-Metallic Chromium Dioxide  

NASA Astrophysics Data System (ADS)

Recent work has shown that the all-optical ultrafast laser production and detection of spin waves can provide useful measurements of anisotropy in magnetic thin films[1,2]. A pump laser pulse momentarily affects the magnetic anisotropy, perturbing the magnetization, which relaxes towards a new equilibrium by means of coherent oscillation. The coherent oscillation is detected by the magnetoopitcal Kerr effect. We present a study of the temperature dependence of the magnetocrystalline anisotropy of half-metallic CrO2 thin films from temperatures 10 K to 363 K. At higher temperatures, the oscillations are approximately single frequency. The anisotropy constants obtained by analyzing the oscillation frequencies as a function of applied fields using the Landau Lifshitz Gilbert equation agrees with measurements made by other techniques, particularly ferromagnetic resonance. Interesting features of the temperature dependence, as compared to ferromagnetic metals such as Co, Ni and Fe, will be highlighted. 1. M. Van Kampen et al., Phys. Rev. Lett. 88, 227201 (2002) 2. D. Talbayev et al., Appl. Phys. Lett., 86, 182501 (2005)

Reilly, Anne; Huang, Hailong; Seu, Keoki

2006-03-01

258

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

259

Magnetic anisotropy of strained MnGa alloys  

NASA Astrophysics Data System (ADS)

MnGa is a promising candidate for Rare Earth free permanent magnet applications because it has a large magnetocrystalline anisotropy. We examine the variation of the magnetocrystalline anisotropy of these alloys as function of bi-axial in-plane strain using ab-initio electronic structure calculations. We employed force theorem to calculate the MAE=E()-E() as difference of energies of the system with magnetization along and perpendicular to the easy axis. Using projector augmented wave method implemented in VASP we have calculated MAE in MnGa, Mn3Ga and Mn1+xGa1-x alloys. We find that the MAE is 2.5MJ/m^3 (0.42meV/u.c.) and 0.12MJ/m^3 (0.07meV/u.c.) in unstrained MnGa and Mn3Ga, respectively. MAE decreases if bi-axial strain is applied in MnGa. Thus, the anisotropy of this system can be affected by the strain. We also discuss the effect of Mn disorder on MAE in Mn1+xGa1-x alloys.

Sabirianov, Renat; Al-Aqtash, Nabil

2013-03-01

260

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

261

The role of erbium magnetization anisotropy during the magnetic reorientation transition in ErFeO3  

NASA Astrophysics Data System (ADS)

Magnetization of ErFeO3 single crystal was measured by a super conducting quantum interference device magnetometer with greatly improved precision. A dramatic (70%) increase of magnetization was observed in the spin-reorientation interval (88-97 K). This and the temperature dependence of the spin-rotation angle are accurately described by the modified mean field theory, which uses the key fact of the magnetic anisotropy of erbium subsystem. Calculated temperature dependence of the rotation angle shows a remarkable correspondence with the experiment with no fitting parameters. Proposed model is general and can be used to analyze orientation transitions in many orthoferrites.

Bazaliy, Ya. B.; Tsymbal, L. T.; Kakazei, G. N.; Wigen, P. E.

2004-06-01

262

Large change of perpendicular magnetic anisotropy in Cobalt ultrathin film induced by varying capping layers  

NASA Astrophysics Data System (ADS)

The magnetic films of Co with Si/SiO2/Pt/Co/molecule structure were fabricated and their structural properties and magnetic anisotropy were investigated by varying both Co (0.5-1.8 nm) thickness and molecular capping layers of 5,6,11,12-tetraphenylnaphthacene (rubrene) and copper phthalocyanine (CuPc), respectively. The crystal structures were characterized using x-ray diffraction (XRD) and the magnetization curves were measured using vibrating sample magnetometer with an applied field both in parallel and perpendicular to a film plane. It was found that the thickness of Co for the maximum perpendicular magnetic anisotropy (PMA) is around 0.7 nm for both group films. However, the estimated effective magnetic anisotropy energy for Co was 2.9 +/- 0.3 × 106 erg/cc for rubrene-capped sample, which was smaller than the value of 4.9 +/- 0.4 × 106 erg/cc for CuPc-capped sample. The XRD patterns showed the crystal structure of rubrene layer was of amorphous structure and CuPc layer was polycrystalline. The different interface effects of Co/CuPc and Co/rubrene were discussed to analyze the change of PMA.

Zhang, Xianmin; Mizukami, Shigemi; Kubota, Takahide; Ma, Qinli; Naganuma, Hiroshi; Oogane, Mikihiko; Ando, Yasuo; Miyazaki, Terunobu

2012-04-01

263

Effect of the distribution of anisotropy constants on hysteresis losses for magnetic hyperthermia applications  

NASA Astrophysics Data System (ADS)

Magnetic hyperthermia using magnetic nanoparticles is a potential remedial therapy for the reduction of cancer and other tumours. The dominant heating mechanism is hysteresis heating. This means that control of the particle size distribution is essential. However, control of the anisotropy dispersion is also required. We have calculated the effect of the anisotropy distribution on the hysteresis heating in magnetic nanoparticles for hyperthermia applications. Where there is a wide distribution of anisotropy constants the heat output is controlled by the distribution of anisotropy constants. This effect is significant in systems such as magnetite particles where shape anisotropy dominates.

Vallejo-Fernandez, G.; O'Grady, K.

2013-09-01

264

Effect of light illumination on the [100] uniaxial magnetic anisotropy of GaMnAs film  

NASA Astrophysics Data System (ADS)

The effect of light illumination on the magnetic anisotropy of GaMnAs has been investigated by using the planar Hall effect measurement. In as-grown GaMnAs, typical types of magnetic anisotropies, cubic crystalline anisotropy along the <100> directions and uniaxial anisotropy along the [110] direction, were clearly observed in the planar Hall resistance (PHR) measurements. The behavior of the PHR, however, changed after light illumination by showing significant asymmetry between the [100] and the [010] directions, which was explained by the appearance (or enhancement) of a new type of uniaxial anisotropy along the [100] direction in the film. The experiment reveals that light illumination can significantly alter the magnetic anisotropies of the GaMnAs film by changing the magnitude of existing anisotropies as well as inducing anisotropy along the [100] direction.

Lee, Hakjoon; Choi, Seonghoon; Lee, Sangyeop; Yoo, Taehee; Lee, Sanghoon; Liu, X.; Furdyna, J. K.

2014-08-01

265

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

266

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.

267

Magnetic field mapper  

NASA Technical Reports Server (NTRS)

Magnetic field mapper locates imperfections in cadmium sulphide solar cells by detecting and displaying the variations of the normal component of the magnetic field resulting from current density variations. It can also inspect for nonuniformities in other electrically conductive materials.

Masters, R. M.; Stenger, F. J.

1969-01-01

268

Exact canonical drift Hamiltonian formalism with pressure anisotropy and finite perturbed fields  

SciTech Connect

A Hamiltonian formulation of the guiding center drift orbits is extended to pressure anisotropy and field perturbations in axisymmetric systems. The Boozer magnetic coordinates are shown to retain canonical properties in anisotropic pressure plasmas with finite electrostatic perturbations and electromagnetic perturbed fields that solely affect the parallel component of the magnetic vector potential. The equations of motion developed in the Boozer coordinate frame are satisfied by direct verification of the drift velocities. A numerical application illustrates the significance of retaining all second order terms.

Cooper, G. A.; Jucker, M.; Cooper, W. A.; Graves, J. P.; Isaev, M. Yu. [Department of Physics, University of the South, Sewanee, Tennessee 37383 (United States) and Ecole Polytechnique Federale de Lausanne, Centre de Recherches en Physique des Plasmas, Association Euratom-Suisse, CH1015 Lausanne (Switzerland); Ecole Polytechnique Federale de Lausanne, Centre de Recherches en Physique des Plasmas, Association Euratom-Suisse, CH1015 Lausanne (Switzerland); Nuclear Fusion Institute, RRC Kurchatov Institute, 123182 Moscow (Russian Federation)

2007-10-15

269

Electrically induced enormous magnetic anisotropy in Terfenol-D/lead zinc niobate-lead titanate multiferroic heterostructures  

NASA Astrophysics Data System (ADS)

Electric field (E-field) tunable multiferroic devices such as tunable RF devices and memory storage mediums require strong magnetoelectric interactions. In this paper, we demonstrated a Terfenol-D/lead zinc niobate-lead titanate composite bilayer structure with an E-field-induced magnetic anisotropy field of 3500 Oe and a magnetoelectric coefficient of 580 Oe cm/kV. This is the largest E-field induced anisotropy reported to date, resulting in a strong dependence of magnetization process and tunable ferromagnetic resonance in both amorphous and crystalline Terfenol-D films. In addition, the magnetostriction constants of crystalline and amorphous Terfenol-D were estimated to be 420 ppm and 320 ppm, respectively, which are close to report values. Electrically manipulating magnetic performance holds great potential for future ultra-low power, lightweight, tunable magnetic devices, and memory storage.

Liu, Ming; Li, Shandong; Zhou, Ziyao; Beguhn, Shawn; Lou, Jing; Xu, Feng; Jian Lu, Tian; Sun, Nian X.

2012-09-01

270

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

271

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.

272

Phase Diagram for a Magnetic Thin Film with Dipolar Interactions and Magnetic Surface Anisotropy  

Microsoft Academic Search

The phase diagram of a model thin film with long-range dipole-dipole interactions and magnetic surface anisotropy is determined as a function of temperature and the surface anisotropy. We show that the model studied here exhibits a reorientation transition in the absence of an exchange interaction. Further we show that, unexpectedly, the transition is from an in-plane phase to an out-of-plane

A. B. MacIsaac; J. P. Whitehead; K. de'Bell; P. H. Poole

1996-01-01

273

Growth Induced Magnetic Anisotropy of Co-Substituted LPE Magnetic Garnet Films  

Microsoft Academic Search

The authors succeed in quantitatively explaining the uniaxial magnetic anisotropy of Co-substituted liquid-phase epitaxy (LPE) garnet films with an a-site Co2+ nonuniform distribution model. They also demonstrate that this anisotropy is induced by irregular Co2+ distribution during the growth process. A-site Co2+ makes a positive contribution to K1 and a negative one to K2, while d-site Co2+ makes a negative

M. Nakada; Y. Toriumi; A. Itoh; K. Kawanishi; F. Inoue

1987-01-01

274

Solar Magnetic Field  

NASA Astrophysics Data System (ADS)

Electrical currents flowing in the solar plasma generate a magnetic field, which is detected in the SOLAR ATMOSPHERE by spectroscopic and polarization measurements (SOLAR MAGNETIC FIELD: INFERENCE BY POLARIMETRY). The SOLAR WIND carries the magnetic field into interplanetary space where it can be measured directly by instruments on space probes....

Schüssler, M.; Murdin, P.

2000-11-01

275

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

276

Surface morphology and magnetic anisotropy of obliquely deposited Co\\/Si(111) films  

Microsoft Academic Search

We report an investigation on magnetic anisotropy of Co\\/Si(111) films deposited at oblique incidence. An in-plane uniaxial magnetic anisotropy (UMA) with the easy axis perpendicular to the incident flux plane was observed to superimpose on sixfold magnetocrystalline anisotropy of Co films. We built a total energy model to investigate the magnetization reversal mechanism around hard axis. The simulated value of

Ya-Peng Fang; Wei He; Hao-Liang Liustm; Qing-Feng Zhan; Hai-Feng Du; Qiong Wu; Hai-Tao Yang; Xiang-Qun Zhang; Zhao-Hua Cheng

2010-01-01

277

Giant Uniaxial Anisotropy in the Magnetic and Transport Properties of CePd5Al2  

NASA Astrophysics Data System (ADS)

Electrical resistivity ?, magnetic susceptibility ?, magnetization M, and specific heat measurements are reported on a singlecrystalline sample of CePd5Al2, showing successive antiferromagnetic orderings at TN1=4.1 K and TN2=2.9 K. The temperature dependence of ? shows a Kondo metal behavior with large anisotropy, ?c/?a=3.2 at 20 K, and opening of a superzone gap along the tetragonal c-direction below TN1. Both TN1 and TN2 gradually increase with applying pressure up to 2.5 GPa. The data of ?(T) and M(B) in the paramagnetic state were analyzed using a crystalline electric field (CEF) model. It led to a Kramers doublet ground state with wave functions consisting primarily of |± 5/2>, whose energy level is isolated from the excited states by 230 and 300 K. This CEF effect gives rise to the large anisotropy in the paramagnetic state. In the ordered state, the uniaxial magnetic anisotropy is manifested as Mc/Ma=20 in B=5 T and at 1.9 K, and ?c/?a=25 in B=0.1 T and at 4 K. In powder neutron diffraction experiments, magnetic reflections were observed owing to the antiferromagnetic ordered states below TN1, whereas no additional reflection was found below TN2.

Onimaru, Takahiro; Inoue, Yukihiro F.; Shigetoh, Keisuke; Umeo, Kazunori; Kubo, Hirokazu; Ribeiro, Raquel A.; Ishida, Akihiro; Avila, Marcos A.; Ohoyama, Kenji; Sera, Masafumi; Takabatake, Toshiro

2008-07-01

278

Magnetic phases in the S =1 Shastry-Sutherland model with uniaxial anisotropy  

NASA Astrophysics Data System (ADS)

We explore the field-induced magnetic phases of an S =1 XXZ model with single-ion anisotropy and large Ising-like anisotropy on a Shastry-Sutherland lattice over a wide range of Hamiltonian parameters and applied magnetic field. The multitude of ground-state phases are characterized in detail in terms of their thermodynamic properties, and the underlying classical (Ising limit) spin arrangements for the plateau phases are identified by calculating the static structure factors. The enlarged local Hilbert space of the S =1 spins results in several ground state phases that are not realized for S =1/2 spins. These include the quantum paramagnetic state that is ubiquitous to S =1 spins with single-ion anisotropy, two different spin supersolid phases (with distinct longitudinal ordering), and a magnetization plateau that arises as a direct descendant of the 1/3 plateau due to quantum fluctuations that are not possible for S =1/2 spins. We predict the same mechanism will lead to plateaus at smaller fractions of 1/3 for higher spins. The full momentum dependence of the longitudinal and transverse components of the static structure factor is calculated in the spin supersolid phase to demonstrate the simultaneous existence of diagonal and off-diagonal long-range order as well as the different longitudinal orderings.

Su, Lei; Wierschem, Keola; Sengupta, Pinaki

2014-06-01

279

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

280

Magnetic-field-induced crystallographic texture enhancement in cold-deformed FePt nanostructured magnets  

Microsoft Academic Search

This paper reports a unique approach to the fabrication of magnetically anisotropic nanostructured FePt magnets: cyclic sheath cold rolling and subsequent magnetic annealing. High magnetic fields enhance both crystallographic texture and magnetic properties of cold-deformed FePt nanostructured magnets. Magnetic annealing increases (001) out-of-plane texture of the FePt hard phase by 50% and introduces magnetic anisotropy in the annealed samples. It

B. Z. Cui; K. Han; D. S. Li; H. Garmestani; J. P. Liu; N. M. Dempsey; H. J. Schneider-Muntau

2006-01-01

281

Anisotropy barrier reduction in fast-relaxing Mn12 single-molecule magnets  

NASA Astrophysics Data System (ADS)

An angle-swept high-frequency electron paramagnetic resonance (HFEPR) technique is described that facilitates efficient in situ alignment of single-crystal samples containing low-symmetry magnetic species such as single-molecule magnets (SMMs). This cavity-based technique involves recording HFEPR spectra at fixed frequency and field, while sweeping the applied field orientation. The method is applied to the study of a low-symmetry Jahn-Teller variant of the extensively studied spin S=10 Mn12 SMMs (e.g., Mn12 -acetate). The low-symmetry complex also exhibits SMM behavior, but with a significantly reduced effective barrier to magnetization reversal (Ueff?43K) and, hence, faster relaxation at low temperature in comparison with the higher-symmetry species. Mn12 complexes that crystallize in lower symmetry structures exhibit a tendency for one or more of the Jahn-Teller axes associated with the MnIII atoms to be abnormally oriented, which is believed to be the cause of the faster relaxation. An extensive multi-high-frequency angle-swept and field-swept electron paramagnetic resonance study of [Mn12O12(O2CCH2But)16(H2O)4]?CH2Cl2?MeNO2 is presented in order to examine the influence of the abnormally oriented Jahn-Teller axis on the effective barrier to magnetization reversal. The reduction in the axial anisotropy, D , is found to be insufficient to account for the nearly 40% reduction in Ueff . However, the reduced symmetry of the Mn12 core gives rise to a very significant second-order transverse (rhombic) zero-field-splitting anisotropy, E?D/6 . This, in turn, causes a significant mixing of spin projection states well below the top of the classical anisotropy barrier. Thus, magnetic quantum tunneling is the dominant factor contributing to the effective barrier reduction in fast relaxing Mn12 SMMs.

Hill, Stephen; Murugesu, Muralee; Christou, George

2009-11-01

282

Maximizing domain-wall speed via magnetic anisotropy adjustment in Pt/Co/Pt films  

NASA Astrophysics Data System (ADS)

We report an experimental observation that indicates that a direct relation exists between the speed of the magnetic domain-wall (DW) motion and the magnitude of the perpendicular magnetic anisotropy (PMA) in Pt/Co/Pt films. It is found that by changing the thicknesses of the nonmagnetic Pt layers, the PMA magnitude can be varied significantly and the field-driven DW speed can also be modified by a factor of up to 50 under the same magnetic field. Interestingly, the DW speed exhibits a clear scaling behavior with respect to the PMA magnitude. A theory based on the DW creep criticality successfully explains the observed scaling exponent between the DW speed and the PMA magnitude. The presented results offer a method of maximizing the DW speed in DW-mediated nanodevices without altering the thickness of the magnetic Co layer.

Kim, Duck-Ho; Yoo, Sang-Cheol; Kim, Dae-Yun; Moon, Kyoung-Woong; Je, Soong-Geun; Cho, Cheong-Gu; Min, Byoung-Chul; Choe, Sug-Bong

2014-04-01

283

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.

Vu Bioengineering Ret Program

284

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.

Barker, Jeffrey

285

Magnetization reversal and magnetotransport properties of cobalt/platinum multilayers with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Due to the unique attribute of perpendicular magnetic anisotropy (PMA), [Co/Pt]n multilayers have both scientific and technological importance. [Co/Pt]n multilayers and their associated properties are presented, including (1) magnetization reversal in [Co/Pt]n multilayers with different repeat number n; and (2) antisymmetric magnetoresistance in [Co/Pt]n multilayers. Magnetization reversal in [Co/Pt]n multilayers with PMA has been found to depend sensitively on the repeat number n. In [CO/Pt]n multilayers with a large n (e.g. n=16) or a small n (e.g. n=2), magnetization reversal is dominated by nucleation or domain wall motion, respectively. Magnetization reversal in [Co/Pt]n multilayers with an intermediate n=4 provides a glimpse of the intermediate regime. During the first order reversal process, the magnetization of the [Co/Pt]4 multilayer first decreases, then reaches a plateau, and finally rises back to saturation, corresponding to expanding bubble domains, stationary domains, and domains with unchanged boundaries but fading contrast, respectively. MFM imaging reveals the existence of many submicron-sized unreversed channels within the boundary of the bubble domains, which cause the fading contrast. These unusual reversal behaviors in the [CO/Pt]4 multilayer are due to thermally activated domain wall motion, confirmed by the studies of the time dependence of magnetization. Numerical simulations show that the dependence of magnetization reversal on n is mainly due to the demagnetizing effect. Intrinsic magnetoresistance (MR), regardless of mechanisms, is symmetric with respect to the magnetic field H. A new form of MR, which is antisymmetric in H, has been demonstrated in [Co/Pt]n multilayers with PMA. By performing simultaneous MOKE imaging and transport measurements on a Pt/Co wedge/Pt trilayer with a controlled two-domain structure, it has been conclusively shown that the antisymmetric MR originates from the Hall fields due to extraordinary Hall effect on either side of the domain wall. The observed MR and Hall results can be quantitatively accounted for by a circulating-current model. This rare occurrence of antisymmetric MR is due to the special geometry afforded in multilayers with PMA, where the magnetization, current, and domain wall directions are mutually perpendicular.

Cheng, Xuemei M.

286

Circuits and Magnetic Fields  

NSDL National Science Digital Library

In this activity, students use the same method as in the activity from lesson 2 to explore the magnetism due to electric current instead of a permanent magnet. Students use a compass and circuit to trace the magnetic field lines induced by the electric current moving through the wire. Students develop an understanding of the effect of the electrical current on the compass needle through the induced magnetic field and understand the complexity of a three dimensional field system.

Vu Bioengineering Ret Program

287

Interfacial tuning of perpendicular magnetic anisotropy and spin magnetic moment in CoFe/Pd multilayers  

NASA Astrophysics Data System (ADS)

We report on a strong perpendicular magnetic anisotropy in [CoFe 0.4 nm/Pd t]6 (t=1.0-2.0 nm) multilayers fabricated by DC sputtering in an ultrahigh vacuum chamber. Saturation magnetization, Ms, and uniaxial anisotropy, Ku, of the multilayers decrease with increasing the spacing thickness; with a Ms of 155 emu/cc and a Ku of 1.14×105 J/m3 at a spacing thickness of t=2 nm. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements reveal that spin and orbital magnetic moments of Co and Fe in CoFe film decrease as a function of Pd thickness, indicating the major contribution of surface/interfacial magnetism to the magnetic properties of the film.

Ngo, D.-T.; Meng, Z. L.; Tahmasebi, T.; Yu, X.; Thoeng, E.; Yeo, L. H.; Rusydi, A.; Han, G. C.; Teo, K.-L.

2014-01-01

288

Magnetic anisotropy of NaxCoO2 single crystals  

NASA Astrophysics Data System (ADS)

We report the magnetic properties of single crystals of NaxCoO2 (x=0.42, 0.82, and 0.87). The magnetic susceptibility measurements revealed considerable anisotropy along H?ab and H?c for the as-grown single crystals. It was found that an antiferromagnetic transition with a Neel temperature TN=21 K occurred for the x=0.82 sample, and there was a paramagnetic phase for the x=0.87 sample over a wide temperature range from 2 to 300 K, but the sample with x=0.42 shows a monotonic increase of ? with increasing temperature above ~100 K. In addition, the x=0.82 sample has the largest derived anisotropic g-factor ratio (gab/gc~1.30), whereas the sample with x=0.42 is nearly isotropic (gab/gc~0.96).

Chen, D. P.; Wang, Xiaolin; Lin, C. T.; Dou, S. X.

2008-04-01

289

Photospheric magnetic fields  

NASA Technical Reports Server (NTRS)

Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

Howard, R.

1972-01-01

290

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

291

On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern  

NASA Astrophysics Data System (ADS)

Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength ? and selected, large amplitudes (?) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35-50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studied with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ?2/?/t in quantitative agreement with Schlömann's prediction for a surface anisotropy entirely ruled by dipolar interaction. The limits of UMA tuning by a ripple pattern are discussed in terms of the surface local angle with respect to the mean surface and of the onset of ripple detachment.

Arranz, Miguel A.; Colino, Jose M.; Palomares, Francisco J.

2014-05-01

292

Aligning Paramecium caudatum with static magnetic fields.  

PubMed

As they negotiate their environs, unicellular organisms adjust their swimming in response to various physical fields such as temperature, chemical gradients, and electric fields. Because of the weak magnetic properties of most biological materials, however, they do not respond to the earth's magnetic field (5 x 10(-5) Tesla) except in rare cases. Here, we show that the trajectories of Paramecium caudatum align with intense static magnetic fields >3 Tesla. Otherwise straight trajectories curve in magnetic fields and eventually orient parallel or antiparallel to the applied field direction. Neutrally buoyant immobilized paramecia also align with their long axis in the direction of the field. We model this magneto-orientation as a strictly passive, nonphysiological response to a magnetic torque exerted on the diamagnetically anisotropic components of the paramecia. We have determined the average net anisotropy of the diamagnetic susceptibility, Deltachi(p), of a whole Paramecium: Deltachi(p) = (6.7+/- 0.7) x 10(-23) m(3). We show how the measured Deltachi(p) compares to the anisotropy of the diamagnetic susceptibilities of the components in the cell. We suggest that magnetic fields can be exploited as a novel, noninvasive, quantitative means to manipulate swimming populations of unicellular organisms. PMID:16461406

Guevorkian, Karine; Valles, James M

2006-04-15

293

Topological defects and misfit strain in magnetic stripe domains of lateral multilayers with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Stripe domain patterns are characteristic of magnetic films with perpendicular magnetic anisotropy (PMA). In this work, PMA amorphous Nd-Co films have been nanostructured with a periodic thickness modulation that induces the lateral modulation of magnetic stripe periods and in-plane magnetization. Confinement effects of stripe domains within the nanostructured regions are combined with coupling effects between nearby elements through elastic interactions within the magnetic stripe pattern. The resulting ``lateral'' magnetic superlattice is the 2D equivalent of a strained superlattice controlled by interfacial misfit strain within the magnetic stripe structure and shape anisotropy: misfit dislocations appear in the stripe pattern at the boundaries between nanostructured regions and, during magnetization reversal, a 2D variable angle grain boundary is observed within the magnetic stripe pattern. Beautiful patterns appear at the point of maximum misfit strain due to the decay of dislocations in the magnetic stripe pattern into 1/2 disclination pairs. The link between topological defects in the magnetic stripe patterns and domain walls for the in-plane magnetization component allow us to tailor the whole magnetization reversal process. [1] A.Hierro-Rodriguez et al, PRL 109(2012)117202

Velez, Maria; Hierro-Rodriguez, A.; Cid, R.; Rodriguez-Rodriguez, G.; Martin, J. I.; Alvarez-Prado, L. M.; Alameda, J. M.

2013-03-01

294

Liquid crystalline order and magnetocrystalline anisotropy in magnetically doped semiconducting ZnO nanowires.  

PubMed

Controlled alignment of nanomaterials over large length scales (>1 cm) presents a challenge in the utilization of low-cost solution processing techniques in emerging nanotechnologies. Here, we report on the lyotropic liquid crystalline behavior of transition-metal-doped zinc oxide nanowires and their facile alignment over large length scales under external fields. High aspect ratio Co- and Mn-doped ZnO nanowires were prepared by solvothermal synthesis with uniform incorporation of dopant ions into the ZnO wurtzite crystal lattice. The resulting nanowires exhibited characteristic paramagnetic behavior. Suspensions of surface-functionalized doped nanowires spontaneously formed stable homogeneous nematic liquid crystalline phases in organic solvent above a critical concentration. Large-area uniaxially aligned thin films of doped nanowires were obtained from the lyotropic phase by applying mechanical shear and, in the case of Co-doped nanowires, magnetic fields. Application of shear produced thin films in which the nanowire long axes were aligned parallel to the flow direction. Conversely, the nanowires were found to orient perpendicular to the direction of the applied magnetic fields. This indicates that the doped ZnO possesses magnetocrystalline anisotropy sufficient in magnitude to overcome the parallel alignment which would be predicted based solely on the anisotropic demagnetizing field associated with the high aspect ratio of the nanowires. We use a combination of magnetic property measurements and basic magnetostatics to provide a lower-bound estimate for the magnetocrystalline anisotropy. PMID:21905709

Zhang, Shanju; Pelligra, Candice I; Keskar, Gayatri; Majewski, Pawel W; Ren, Fang; Pfefferle, Lisa D; Osuji, Chinedum O

2011-10-25

295

Structure, magnetic behavior, and anisotropy of homoleptic trinuclear lanthanoid 8-quinolinolate complexes.  

PubMed

Three complexes of the form [Ln(III)3(OQ)9] (Ln = Gd, Tb, Dy; OQ = 8-quinolinolate) have been synthesized and their magnetic properties studied. The trinuclear complexes adopt V-shaped geometries with three bridging 8-quinolinolate oxygen atoms between the central and peripheral eight-coordinate metal atoms. The magnetic properties of these three complexes differ greatly. Variable-temperature direct-current (dc) magnetic susceptibility measurements reveal that the gadolinium and terbium complexes display weak antiferromagnetic nearest-neighbor magnetic exchange interactions. This was quantified in the isotropic gadolinium case with an exchangecoupling parameter of J = -0.068(2) cm(-1). The dysprosium compound displays weak ferromagnetic exchange. Variable-frequency and -temperature alternating-current magnetic susceptibility measurements on the anisotropic cases reveal that the dysprosium complex displays single-molecule-magnet behavior, in zero dc field, with two distinct relaxation modes of differing time scales within the same molecule. Analysis of the data revealed anisotropy barriers of Ueff = 92 and 48 K for the two processes. The terbium complex, on the other hand, displays no such behavior in zero dc field, but upon application of a static dc field, slow magnetic relaxation can be observed. Ab initio and electrostatic calculations were used in an attempt to explain the origin of the experimentally observed slow relaxation of the magnetization for the dysprosium complex. PMID:24520896

Chilton, Nicholas F; Deacon, Glen B; Gazukin, Olga; Junk, Peter C; Kersting, Berthold; Langley, Stuart K; Moubaraki, Boujemaa; Murray, Keith S; Schleife, Frederik; Shome, Mahasish; Turner, David R; Walker, Julia A

2014-03-01

296

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.

297

Magnetic susceptibility curves of a nanoparticle assembly, I: Theoretical model and analytical expressions for a single magnetic anisotropy energy  

NASA Astrophysics Data System (ADS)

We study a model system made of non-interacting monodomain ferromagnetic nanoparticles, considered as macrospins, with a randomly oriented uniaxial magnetic anisotropy. We derive a simple differential equation governing the magnetic moment evolution in an experimental magnetic susceptibility measurement, at low field and as a function of temperature, following the well-known Zero-Field Cooled/Field Cooled (ZFC/FC) protocol. Exact and approximate analytical solutions are obtained, together for the ZFC curve and the FC curve. The notion of blocking temperature is discussed and the influence of various parameters on the curves is investigated. A crossover temperature is defined and a comparison is made between our progressive crossover model (PCM) and the crude "two states" or abrupt transition model (ATM), where the particles are assumed to be either fully blocked or purely superparamagnetic. We consider here the case of a single magnetic anisotropy energy (MAE), which is a prerequisite before considering the more realistic and experimentally relevant case of an assembly of particles with a MAE distribution (cf. part II that follows).

Tournus, F.; Bonet, E.

2011-05-01

298

Spin Anisotropy Effects in Dimer Single Molecule Magnets  

NASA Astrophysics Data System (ADS)

We present a model of equal spin s1 dimer single molecule magnets. The spins within each dimer interact via the Heisenberg and the most general set of four quadratic anisotropic spin interactions with respective strengths J and Jj, and with the magnetic induction B. For antiferromagnetic Heisenberg couplings (J<0) and weak anisotropy interactions (|Jj/J|1), the low temperature T magnetization M(B) exhibits 2s1 steps, the height and midpoint slope of the sth step differing from their isotropic limits by corrections of O(Jj/J)^2, but the position occurring at the energy level-crossing magnetic induction Bs,s1^lc(,), where , define the direction of B. We solve the model exactly for s1=1/2, 1, and 5/2. For weakly anisotropic dimers, the Hartree approximation yields analytic formulas for M(B) and CV(B) at arbitrary s1 that accurately fit the exact solutions at sufficiently low T or large B. Low-T formulas for the inelastic neutron scattering S(q,?) and the EPR ?(?) in an extended Hartree approximation are given. Our results are discussed with regard to existing experiments on s1=5/2 Fe2 dimers, suggesting further experiments on single crystals of these and some s1=9/2 [Mn4]2 dimers are warranted.

Efremov, Dmitri; Klemm, Richard

2006-03-01

299

Magnetic dispersion and anisotropy in multiferroic BiFeO3  

SciTech Connect

We have determined the full magnetic dispersion relations of multiferroic BiFeO3. In particular, two excitation gaps originating from magnetic anisotropies have been clearly observed. The direct observation of the gaps enables us to accurately determine the Dzyaloshinskii-Moriya (DM) interaction and the single ion anisotropy. The DM interaction supports a sizable magneto-electric coupling in this compound.

Matsuda, Masaaki [ORNL; Fishman, Randy Scott [ORNL; Hong, Tao [ORNL; Lee, C. H. [AIST, Japan; Ushiyama, T. [AIST, Japan; Yanagisawa, Y. [AIST, Japan; Tomioka, Y. [AIST, Japan; Ito, T. [AIST, Japan

2012-01-01

300

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

NASA Astrophysics Data System (ADS)

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 states (QWS) confined in the Fe film are observed and shown to persist up to room temperature at low Fe thicknesses. By systematically examining the voltage and thickness dependence of the magnetic hysteresis loop characteristics, we identify two distinct effects by which an applied voltage modifies the magnetic anisotropy. The first effect is due to voltage-induced changes to interfacial perpendicular magnetic anisotropy which, due to the vicinal geometry, leads to changes in the effective in-plane uniaxial magnetic anisotropy. A second effect is observed at lower film thicknesses and shows nonmonotonic voltage-induced effects on magnetic anisotropy. This nonmonotonic behavior coincides with the onset of significant QWS-induced effects on magnetic anisotropy and suggests a link between QWS- and voltage-induced anisotropy changes.

Bauer, Uwe; Przybylski, Marek; Beach, Geoffrey S. D.

2014-05-01

301

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

302

Uniaxial magnetic anisotropy of iron thin films deposited by oblique incidence of deposition particles  

Microsoft Academic Search

Uniaxial magnetic anisotropy induced in iron thin films by the oblique incidence of deposition particles was investigated by computer simulation. In the simulation, the self-shadowing effect was considered mainly to explain changes in the magnetic anisotropy of iron films with the incident angle. The simulated grain shape in the film changes significantly with the incident angle of deposition particles. Grains

Y. Hoshi; E. Suzuki; M. Naoe

1996-01-01

303

magnetic dispersion and anisotropy in multiferroic BiFeO3.  

PubMed

We have determined the full magnetic dispersion relations of multiferroic BiFeO3. In particular, two excitation gaps originating from magnetic anisotropies have been clearly observed. The direct observation of the gaps enables us to accurately determine the Dzyaloshinskii-Moriya (DM) interaction and the single ion anisotropy. The DM interaction supports a sizable magnetoelectric coupling in this compound. PMID:23006302

Matsuda, M; Fishman, R S; Hong, T; Lee, C H; Ushiyama, T; Yanagisawa, Y; Tomioka, Y; Ito, T

2012-08-10

304

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

305

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

306

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

307

In-plane anisotropy of coercive field in permalloy square ring arrays.  

SciTech Connect

Magnetic ring arrays are promising candidates for application in magnetic random access memory devices. The magnetic reversal processes and anisotropy of the coercivity in arrays of square-shaped nanorings with different spacings were investigated by vector magneto-optical Kerr effect magnetometry, magnetic force microscopy, and micromagnetic simulations. Two-step magnetization reversal demonstrates fourfold symmetry in the film plane resulting from the shape anisotropy in rings. Our numerical simulations show good agreement with the experiment.

Goncharov, A. V.; Zhukov, A. A.; Metlushko, V. V.; Bordignon, G.; Fangohr, H.; Karapetrov, G.; de Groot, P. A. J.; Ilic, B.; Materials Science Division; Univ. Southampton; Univ. Illinois at Chicago; Cornell Univ.

2006-04-15

308

Magnetic anisotropy in isotropic and nanopatterned strongly exchange-coupled nanolayers  

PubMed Central

In this study, the fabrication of magnetic multilayers with a controlled value of the in-plane uniaxial magnetic anisotropy field in the range of 12 to 72 kA/m was achieved. This fabrication was accomplished by the deposition of bilayers consisting of an obliquely deposited (54°) 8-nm-thick anisotropic Co layer and a second isotropic Co layer that was deposited at a normal incidence over the first layer. By changing the thickness value of this second Co layer (X) by modifying the deposition time, the value of the anisotropy field of the sample could be controlled. For each sample, the thickness of each bilayer did not exceed the value of the exchange correlation length calculated for these Co bilayers. To increase the volume of the magnetic films without further modification of their magnetic properties, a Ta spacer layer was deposited between successive Co bilayers at 54° to prevent direct exchange coupling between consecutive Co bilayers. This step was accomplished through the deposition of multilayered films consisting of several (Co8 nm-54°/CoX nm-0°/Ta6 nm-54°) trilayers.

2012-01-01

309

Melatonin and magnetic fields.  

PubMed

There is public health concern raised by epidemiological studies indicating that extremely low frequency electric and magnetic fields generated by electric power distribution systems in the environment may be hazardous. Possible carcinogenic effects of magnetic field in combination with suggested oncostatic action of melatonin lead to the hypothesis that the primary effects of electric and magnetic fields exposure is a reduction of melatonin synthesis which, in turn, may promote cancer growth. In this review the data on the influence of magnetic fields on melatonin synthesis, both in the animals and humans, are briefly presented and discussed. PMID:12019358

Karasek, Michal; Lerchl, Alexander

2002-04-01

310

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

311

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

312

The Role of Pressure Anisotropy on Particle Acceleration during Magnetic Reconnection  

NASA Astrophysics Data System (ADS)

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 ? 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 ? on electron heating, while the ion heating is insensitive to ?. Anisotropies develop with T ? ? 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 ?/T in lower ? systems, electrons are able to accelerate more efficiently by the Fermi mechanism at low ?. The variance in anisotropy implies less electron acceleration in higher ? 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.; Knizhnik, K.

2013-02-01

313

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

314

Magnetic anisotropy of amorphous alloy ribbons in as-quenched state  

NASA Astrophysics Data System (ADS)

The in-plane magnetic anisotropy Ku in as-quenched state has been studied for amorphous Fe-based, FeNi-based and Co-based alloys. The change in anisotropy Ku with stress relief annealing has been measured and the dependence of anisotropy Kus on magnetization square M2s after annealing is linear. Results show that the anisotropy Ku consists of two parts: one is Ku? that can be annealed out, which is related to the coupling between magnetostriction and internal stress; the other is Kus that originates from the surface shape effect.

Xiong, Xiang-Yuan; Ho, Kai-Yuan

1991-03-01

315

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

NASA Astrophysics Data System (ADS)

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.

2014-04-01

316

Collective oscillations of the magnetic moments of a chain of spherical magnetic nanoparticles with uniaxial magnetic anisotropy  

SciTech Connect

Magnetic particles moving freely in a fluid can organize dense phases (3D clusters or linear chains). We analyze the spectrum of magnetic oscillations of a chain of spherical magnetic particles taking into account the magnetic anisotropy of an individual particle for an arbitrary relation between the anisotropy energy and the energy of the dipole interaction of particles. For any relation between these energies, the spectrum contains three branches of collective oscillations: a high-frequency branch and a weakly split doublet of low-frequency branches. The frequency of the high-frequency branch is determined by a stronger interaction, while the frequencies of the low-frequency branches are determined by the weakest interaction. Accordingly, the dispersion is maximal for oscillations formed by the dipole-dipole interaction of particles, which have high frequencies in the case of a strong dipole interaction or low frequencies in the case of a strong anisotropy.

Dzian, S. A.; Ivanov, B. A., E-mail: bor.a.ivanov@gmail.com [Taras Shevchenko National University (Ukraine)

2013-06-15

317

Magnetic Field Viewing Cards  

NASA Astrophysics Data System (ADS)

For some years now laminated cards containing a green, magnetically sensitive film have been available from science education suppliers. When held near a magnet, these cards appear dark green in regions where the field is perpendicular to the card and light green where the field is parallel to the card. The cards can be used to explore the magnetic field near a variety of magnets as well as near wire loops. In this paper we describe how to make these cards and how we have used them in our physics classrooms and labs.

Kanim, Stephen; Thompson, John R.

2005-09-01

318

The galactic magnetic field  

Microsoft Academic Search

Estimates for the scale, geometry and strength of the magnetic field in the galactic system can be derived from observations of polarization properties of radio emission from the Galaxy, extragalactic radio sources and pulsars, and polarization of starlight. Within distances of about 500 parsecs (1 parsec = 3.26 lightyears) from the solar system the magnetic field is directed towards galactic

T A Spoelstra; T. A. T

1977-01-01

319

Hybrid wood materials with magnetic anisotropy dictated by the hierarchical cell structure.  

PubMed

Anisotropic and hierarchical structures are bound in nature and highly desired in engineered materials, due to their outstanding functions and performance. Mimicking such natural features with synthetic materials and methods has been a highly active area of research in the last decades. Unlike these methods, we use the native biomaterial wood, with its intrinsic anisotropy and hierarchy as a directional scaffold for the incorporation of magnetic nanoparticles inside the wood material. Nanocrystalline iron oxide particles were synthesized in situ via coprecipitation of ferric and ferrous ions within the interconnected pore network of bulk wood. Imaging with low-vacuum and cryogenic electron microscopy as well as spectral Raman mapping revealed layered nanosize particles firmly attached to the inner surface of the wood cell walls. The mineralogy of iron oxide was identified by XRD powder diffraction and Raman spectroscopy as a mixture of the spinel phases magnetite and maghemite. The intrinsic structural architecture of native wood entails a three-dimensional assembly of the colloidal iron oxide which results in direction-dependent magnetic features of the wood-mineral hybrid material. This superinduced magnetic anisotropy, as quantified by direction-dependent magnetic hysteresis loops and low-field susceptibility tensors, allows for directional lift, drag, alignment, (re)orientation, and actuation, and opens up novel applications of the natural resource wood. PMID:24873330

Merk, Vivian; Chanana, Munish; Gierlinger, Notburga; Hirt, Ann M; Burgert, Ingo

2014-06-25

320

Dependence of the magnetic anisotropy on the ratio of the thicknesses of the magnetic and conductive layers  

NASA Astrophysics Data System (ADS)

Control of the magnetic anisotropy is important for the sensitivity of giant Magnetoimpednace (GMI) magnetic sensors. Our research group proposed an effective magnetic anisotropy control method that uses inverse-magnetostriction and the difference in thermal expansion coefficients. If the proposed method is to be used, an investigation the ratio of the thicknesses between two layers (magnetic and conductive layers) is required because the sensitivity of proposed GMI sensor is determined by the ratio. In this paper, we introduce the dependence of magnetic anisotropy on the ratio of the thicknesses between the two layers to develop a GMI sensor with a high, and adjustable, sensitivity. The generated magnetic anisotropy ( H k( t)) in the magnetic layer depends on the shape anisotropy ( H k( s)) and the induced anisotropy ( H k( i)). To control the magnetic anisotropy, we change the thickness of the magnetic layer. The H k( s), the H k( i) and the generated bending stresses are numerically analyzed. In addition, the H k( t) is obtained experimentally. Based on this study, we found H k( t) to be inversely proportional to the stress.

Shin, Jaewon; Kim, Sung Hoon; Hashi, Shuichiro; Ishiyama, Kazushi

2013-08-01

321

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

This web page 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.

Stern, David

2005-04-27

322

Measurement of the anisotropy fields for AMR sensors  

Microsoft Academic Search

Crossfield effect of anisotropic magnetoresistive (AMR) sensors is an unwanted response to magnetic fields perpendicular to the sensitive axis. For example, the crossfield error of Honeywell HMC1002 sensors could reach 1100 nT in geomagnetic environment [1]. The cause of the effect is that crossfields could change the direction of magnetization in AMR film, which results in variation of magnetoresistance.

J. Ouyang; S. Chen; Y. Zhang; F. Jin; X. F. Yang

2011-01-01

323

M-hexaferrites with planar magnetic anisotropy and their application to high-frequency microwave absorbers  

Microsoft Academic Search

Magnetic and microwave absorbing properties have been investigated in the M-type barium ferrites (BaFe12-2xAxCox O19) with planar magnetic anisotropy. For the tetravalent A ions, Ti4+ and Ru4+ are chosen and the samples are prepared by a conventional ceramic processing technique. At the substitution ratio with in-plane anisotropy which is estimated from the minimum coercivity, the saturation magnetization of the Ru-Co

Han-Shin Cho; Sung-Soo Kim

1999-01-01

324

Ultrafast Laser Spin Wave Measurement of Temperature Dependent Magnetic Anisotropy of Half-Metallic Chromium Dioxide  

Microsoft Academic Search

Recent work has shown that the all-optical ultrafast laser production and detection of spin waves can provide useful measurements of anisotropy in magnetic thin films[1,2]. A pump laser pulse momentarily affects the magnetic anisotropy, perturbing the magnetization, which relaxes towards a new equilibrium by means of coherent oscillation. The coherent oscillation is detected by the magnetoopitcal Kerr effect. We present

Anne Reilly; Hailong Huang; Keoki Seu

2006-01-01

325

Origins of perpendicular magnetic anisotropy in Ni/Pd multilayer films  

NASA Astrophysics Data System (ADS)

Room-temperature perpendicular magnetic anisotropy (PMA) was observed in Ni/Pd multilayer films having 5.1-11 Å Ni and constant 5.7 Å Pd sublayer thicknesses, prepared by dc magnetron sputtering at 7 mTorr Ar sputtering pressure. The magnetoelastic anisotropy determined from delicate in situ stress and ex situ magnetostriction coefficient measurements was found to contribute positively to the observed PMA in those samples and its magnitude was nearly comparable to the surface anisotropy.

Jeong, Jong-Ryul; Kim, Young-Seok; Shin, Sung-Chul

1999-04-01

326

Magnetic fields at Neptune  

SciTech Connect

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{sup {minus}5} gauss) was observed near closest approach, at a distance of 1.18 R{sub N}. The planetary magnetic field between 4 and 15 R{sub N} can be well represented by an offset tilted magnetic dipole (OTD), displaced from the center of Neptune by the surprisingly large amount of 0.55 R{sub N} and inclined by 47{degrees} with respect to the rotation axis. Within 4 R{sub N}, the magnetic field representation must include localized sources or higher order magnetic multipoles, or both, which are not yet well determined. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar, and no crossings of an imbedded magnetic field reversal or plasma neutral sheet were observed. The auroral zones are most likely located far from the rotation poles and may have a complicated geometry. The rings and all the known moons of Neptune are imbedded deep inside the magnetosphere, except for Nereid, which is outside when sunward of the planet. The radiation belts will have a complex structure owing to the absorption of energetic particles by the moons and rings of Neptune and losses associated with the significant changes in the diurnally varying magnetosphere configuration. In an astrophysical context, the magnetic field of Neptune, like that of Uranus, may be described as that of an oblique rotator.

Ness, N.F. (Univ. of Delaware, Newark (USA)); Acuna, M.H.; Burlaga, L.F.; Connerney, J.E.P.; Lepping, R.P. (NASA, Greenbelt, MD (USA)); Neubauer, F.M. (Universitaet zu Koln (West Germany))

1989-12-15

327

Sonoluminescence in High Magnetic Fields  

Microsoft Academic Search

We have made a detailed study of sonoluminescence (SL) in high magnetic fields. In magnetic field sweeps at constant levels of acoustic drive, SL disappears above a pressure-dependent threshold magnetic field. Sweeps of acoustic drive at fixed magnetic fields show that the upper and lower bounds of forcing pressure that determine the region of SL increase dramatically with magnetic field.

J. B. Young; T. Schmiedel; Woowon Kang

1996-01-01

328

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

329

Single-ion magnetic anisotropy and isotropic magnetic couplings in the metal-organic framework Fe2(dobdc).  

PubMed

The metal-organic framework Fe2(dobdc) (dobdc(4-) = 2,5-dioxido-1,4-benzenedicarboxylate), often referred to as Fe-MOF-74, possesses many interesting properties such as a high selectivity in olefin/paraffin separations. This compound contains open-shell Fe(II) ions with open coordination sites which may have large single-ion magnetic anisotropies, as well as isotropic couplings between the nearest and next nearest neighbor magnetic sites. To complement a previous analysis of experimental data made by considering only isotropic couplings [Bloch et al. Science 2012, 335, 1606], the magnitude of the main magnetic interactions are here assessed with quantum chemical calculations performed on a finite size cluster. It is shown that the single-ion anisotropy is governed by same-spin spin-orbit interactions (i.e., weak crystal-field regime), and that this effect is not negligible compared to the nearest neighbor isotropic couplings. Additional magnetic data reveal a metamagnetic behavior at low temperature. This effect can be attributed to various microscopic interactions, and the most probable scenarios are discussed. PMID:23898818

Maurice, Rémi; Verma, Pragya; Zadrozny, Joseph M; Luo, Sijie; Borycz, Joshua; Long, Jeffrey R; Truhlar, Donald G; Gagliardi, Laura

2013-08-19

330

Solid-State Carbon13 Nuclear Magnetic Resonance of Humic Acids at High Magnetic Field Strengths  

Microsoft Academic Search

13 C NMR spectra of humic acids at high magnetic width of the chemical shift anisotropy (CSA) at this low field and spinning frequency. We examine the cross polarization (CP) magnetic field strength. dynamics under both traditional and ramp CP conditions on Cedar Creek humic acid. Fitted equilibrium intensities from these CP dy- Since the establishment of these conditions for

Karl J. Dria; Joseph R. Sachleben; Patrick G. Hatcher

2002-01-01

331

Magnetic Bar Field Model  

NSDL National Science Digital Library

The EJS Magnetic Bar Field Model shows the field of a bar magnet and has a movable compass that reports the magnetic field values. The bar magnet model is built by placing a group of magnetic dipoles along the bar magnet. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Magnetic Bar Field model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_MagneticBarField.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Christian, Wolfgang; Franciscouembre; Cox, Anne

2009-09-18

332

Magnetic multilayer interface anisotropy. Technical progress report, January 1, 1992--December 31, 1992  

SciTech Connect

Ni/Mo and Ni/V multilayer magnetic anisotropy has been investigated as a function of Ni layer thickness, frequency and temperature. Variable frequency ferromagnetic resonance (FMR) measurements show, for the first time, significant frequency dependence associated with the multilayer magnetic anisotropy. The thickness dependence allows one to extract the interface contribution from the total anisotropy. Temperature dependent FMR (9 GHz) and room temperature magnetization indicate that strain between Ni and the non-magnetic layers is contributing significantly to the source of the interface anisotropy and the state of the interfacial magnetization. In order to examine the interface properties of other transition metal multilayer systems, investigations on Fe/Cu are underway and CoCr/Ag is being proposed. ESR measurements have been reported on Gd substituted YBaCuO superconductors and a novel quasi-equilibrium method has been developed to determine quickly and precisely the ransition temperature.

Pechan, M.J.

1992-12-01

333

Theory of giant magneto-impedance effect in amorphous wires with different types of magnetic anisotropy  

Microsoft Academic Search

The effect of various types of magnetic anisotropy on the giant magneto-impedance spectra of amorphous wires with low magnetostriction is studied theoretically. For the first of the model considered the easy anisotropy axis is supposed to be parallel to the wire axis, whereas for the second model it has circumferential direction. In case of a wire with axial type of

N. A. Usov; A. S. Antonov; A. N. Lagar'kov

1998-01-01

334

Magnetic anisotropy in nickel and cobalt films obliquely deposited by sputtering  

Microsoft Academic Search

The in-plane magnetic anisotropy was investigated in nickel and cobalt films obliquely deposited by rf diode sputtering. The incidence angle was 45° and the substrate temperature Ts ranged from 305 to 623 K. At a pressure of 10 Pa, a uniaxial anisotropy with the easy axis parallel to the incidence plane is induced in nickel films. The magnitude of the

K. Itoh

1991-01-01

335

Origin of the magnetic anisotropy in ferromagnetic layers deposited at oblique incidence  

Microsoft Academic Search

Ferromagnetic films evaporated at oblique incidence show invariably an uniaxial in-plane magnetic anisotropy component with easy axis perpendicular to the incidence plane. Scanning Tunneling Microscopy (STM) images reveal that oblique deposition results in rough films with highly anisotropic correlation functions of the surface profile. We show that simple shape anisotropy calculations using high-quality STM roughness data as input reproduce the

J. L. Bubendorff; S. Zabrocki; G. Garreau; S. Hajjar; R. Jaafar; D. Berling; A. Mehdaoui; C. Pirri; G. Gewinner

2006-01-01

336

Magnetic tunnel junctions for low magnetic field sensing  

NASA Astrophysics Data System (ADS)

In this thesis, we did a comprehensive investigation on the relationship between spin-dependent tunneling and structural variation in junction devices. Magnetic, microstructural, and transport studies have shown a significant improvement in exchange-bias, a reduced barrier roughness, and an enhanced magnetoresistance for samples after magnetic annealing. We have examined different magnetic configurations required for sensing applications and presented some results of using MTJ sensors to detect AC magnetic fields created by electrical current flow and DC stray field distributions of patterned magnetic materials. We have studied the low frequency noise in MTJ sensors. We have found that the 1/f noise in MTJs has magnetic as well as electrical origins, and is strongly affected by the junction's internal structure. The magnetic noise comes from magnetization fluctuations in the free FM layer and can be understood using the fluctuation-dissipation theorem. While the field-independent electrical noise due to charge trapping in the barrier, is observed in the less optimized MTJs sensors, and has an amplitude at least one order of magnitude higher than the noise component due to magnetization fluctuations. In addition, we have studied the magnetization switching of Cobalt rings with varying anisotropy utilizing scanning magnetoresistive microscopy. We have for the first time observed a complicated multi-domain intermediate phase during the transition between onion states for samples with strong anisotropy. This is in contrast to as deposited samples, which reverse by simple domain wall motion and feature an intermediate vortex state. The result is further analyzed by micro magnetic simulations.

Liu, Xiaoyong

337

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.

338

Magnetic Field Lines  

NSDL National Science Digital Library

This activity will introduce students to the idea of magnetic field lines--a concept they have probably encountered but may not fully grasp. Completing this activity and reading the corresponding background information should enable students to understand

Horton, Michael

2009-05-30

339

Solar Magnetic Fields.  

National Technical Information Service (NTIS)

The research work was directed towards the following: (1) Perform necessary laboratory experiments, including a study on the Zeeman effect in absorption. Make observations of the sunspot and general magnetic fields of the sun. (2) Conduct a program of int...

M. Cimino

1966-01-01

340

Magnetic properties and microstructure of FePt\\/BN nanocomposite films with perpendicular magnetic anisotropy  

Microsoft Academic Search

We have prepared L10-FePt\\/BN nanocomposite films by depositing the FePt\\/BN mutilayers on the MgO(100) substrates using magnetron sputtering followed by a postannealing process. We found the excellent perpendicular magnetic anisotropy of [FePt (2 nm)\\/BN (0.5 nm)]10 film after annealing at 700 °C for 1 h x-ray diffraction patterns also indicate an excellent (001) texture of the film. This film shows

Bao-He Li; Chun Feng; Xin Gao; Jiao Teng; Guang-Hua Yu; Xianran Xing; Zhong-Yuan Liu

2007-01-01

341

Magnetic domain structure in thin CoPt perpendicular magnetic anisotropy films  

NASA Astrophysics Data System (ADS)

The relation between thickness and domain structure of Co80Pt20 perpendicular magnetic anisotropy films was investigated through experiments and micromagnetic simulation. The films with thickness over 10 nm exhibited clear maze domain structure, while for the films thinner than 10 nm the domain structure abruptly changed from maze domain to irregular and large domain as the thickness became thinner. The irregular domain had narrower domain wall width than maze domain.

Kawada, Y.; Onose, M.; Tojo, R.; Komine, T.; Sugita, R.

2013-01-01

342

Coronal magnetic fields  

Microsoft Academic Search

The use of coronal X-ray emission in determining the configuration of the magnetic field lines in the corona is discussed. Spatially-resolved X-ray observations provided by Skylab and subsequently by missions such as OSO-8 and SMM show the solar corona to be inhomogeneous, with open and closed structures determined by the topology of the magnetic field. The scenario provided by observations

R. Pallavicini

1986-01-01

343

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

344

Magnetization profile and magnetocrystalline anisotropy of ferromagnet-semiconductor heterostructure systems  

NASA Astrophysics Data System (ADS)

Ab initio linear-muffin-tin orbital calculations of the magnetization profile and the magnetic anisotropy of ferromagnetic-semiconductor (FM/SC) multilayers, bcc Fe/Ge (001) and bcc Fe/GaAs (001), have been carried out to find out the microscopic origin of these properties. The electronic magnetic anisotropy energy (MAE), computed with the force method, was found to favor a magnetization perpendicular to the plane of the layers and to increase with the thickness of the ferromagnetic layers. The anisotropy of the energy, i.e., the MAE, as well as the anisotropy of the orbital magnetic moment turned out to depend only slightly on the type of semiconductor, Ge or GaAs, and to come mainly from the interface Fe layers. In particular, it was found that the relationship between the electronic MAE and the anisotropy of the orbital moment proposed by van der Laan is very well satisfied in these systems. According to that relationship, the magnetic anisotropy of these FM/SC multilayers is mainly due (~80-90%) to a delicate rearrangement of the occupations of certain 3d spin down levels in the interface Fe layers caused by the change of the magnetization direction.

Cabria, I.; Perlov, A. Ya.; Ebert, H.

2001-03-01

345

Perpendicular magnetic anisotropy of Co-TiN composite film with nano-fiber structure  

NASA Astrophysics Data System (ADS)

Co-Ti-N films have been prepared by sputter deposition of Co and Ti in Ar+N2 atmosphere. Upon thermal anneal at elevated temperatures, Co (face-centered cubic) and TiN were formed in the film and separated from each other. Fiber-like microstructure developed with Co nano-fibers vertical to the substrate surface, and with their lateral size being less than 10 nm. The magnetic anisotropy of such films depends strongly on the film thickness. The Co-TiN films with their thickness above 100 nm show perpendicular magnetic anisotropy, which is explained in terms of shape anisotropy. Considering their microstructure, it is concluded that the diameter to length ratio of Co nano-fibers is an important factor controlling the magnetic anisotropy. For the Co-TiN film to show perpendicular magnetic anisotropy, the diameter to length ratio has to be smaller than 0.07 according to the experimental results. TiN in the films plays an important role in separating Co nano-fibers and thus to reduce the lateral magnetic interaction among them. The nano-scale nature and perpendicular magnetic anisotropy of the Co-TiN nanocomposite film make it a very promising candidate for future ultrahigh magnetic recording media.

Chen, C. C.; Hashimoto, M.; Shi, J.; Nakamura, Y.; Nittono, O.; Barna, P. B.

2003-05-01

346

Uniaxial magnetic anisotropy in epitaxial Fe/MgO films on GaAs(001)  

NASA Astrophysics Data System (ADS)

Magnetic and structural properties of Fe films grown on MgO buffered GaAs(001) substrates were investigated. Structural analysis using a transmission electron microscope shows that the Fe/MgO/GaAs system is fully epitaxial when MgO is grown at high temperature (~350 °C). A two-fold uniaxial magnetic anisotropy along the Fe[100]//GaAs[1¯10] was found for the epitaxial Fe/MgO/GaAs system using magnetic hysteresis loop measurements and magnetic domain imaging. However Fe grown on room temperature deposited MgO shows amorphous island morphology with discrete boundary, and no magnetic anisotropy was found.

Choi, Jun Woo; Kim, Hyung-jun; Kim, Kyung-Ho; Scholl, Andreas; Chang, Joonyeon

2014-06-01

347

Magnetocrystalline anisotropy in FePd alloys studied using transverse X-ray magnetic circular dichroism  

NASA Astrophysics Data System (ADS)

The structural and magnetic properties of Fe 0.5Pd 0.5 alloys have been correlated using X-ray diffraction (XD), vibrating sample magnetometry (VSM) and transverse X-ray magnetic circular dichroism (TXMCD) at the Pd L 2,3 edges. XD indicates that codeposition of Fe and Pd, at elevated temperatures (350°C), results in a well-ordered L1 0 phase which exhibits perpendicular magnetic anisotropy (PMA). On the other hand, codeposition at room temperature results in a disordered phase with in-plane easy-axis of magnetization. By codepositing at intermediate temperatures, a series of alloys has been produced with varying degree of compositional order. The TXMCD results show that increased compositional ordering leads to an increased orbital moment anisotropy favouring PMA. The magnetocrystalline anisotropy energy resulting from the orbital anisotropy is compared to VSM results.

Dhesi, S. S.; van der Laan, G.; Dürr, H. A.; Belakhovsky, M.; Marchesini, S.; Kamp, P.; Marty, A.; Gilles, B.; Rogalev, A.

2001-05-01

348

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

NASA Astrophysics Data System (ADS)

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.

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

2013-07-01

349

A review of pressure anisotropy caused by electron trapping in collisionless plasma, and its implications for magnetic reconnection  

SciTech Connect

From spacecraft data, it is evident that electron pressure anisotropy develops in collisionless plasmas. This is in contrast to the results of theoretical investigations, which suggest this anisotropy should be limited. Common for such theoretical studies is that the effects of electron trapping are not included; simply speaking, electron trapping is a non-linear effect and is, therefore, eliminated when utilizing the standard methods for linearizing the underlying kinetic equations. Here, we review our recent work on the anisotropy that develops when retaining the effects of electron trapping. A general analytic model is derived for the electron guiding center distribution f(v{sub ?},v{sub ?}) of an expanding flux tube. The model is consistent with anisotropic distributions observed by spacecraft, and is applied as a fluid closure yielding anisotropic equations of state for the parallel and perpendicular components (relative to the local magnetic field direction) of the electron pressure. In the context of reconnection, the new closure accounts for the strong pressure anisotropy that develops in the reconnection regions. It is shown that for generic reconnection in a collisionless plasma nearly all thermal electrons are trapped, and dominate the properties of the electron fluid. A new numerical code is developed implementing the anisotropic closure within the standard two-fluid framework. The code accurately reproduces the detailed structure of the reconnection region observed in fully kinetic simulations. These results emphasize the important role of pressure anisotropy for the reconnection process. In particular, for reconnection geometries characterized by small values of the normalized upstream electron pressure, ?{sub e?}, the pressure anisotropy becomes large with p{sub ?}?p{sub ?} and strong parallel electric fields develop in conjunction with this anisotropy. The parallel electric fields can be sustained over large spatial scales and, therefore, become important for electron acceleration.

Egedal, Jan; Le, Ari [Department of Physics, and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Department of Physics, and Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Daughton, William [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2013-06-15

350

A review of pressure anisotropy caused by electron trapping in collisionless plasma, and its implications for magnetic reconnection  

NASA Astrophysics Data System (ADS)

From spacecraft data, it is evident that electron pressure anisotropy develops in collisionless plasmas. This is in contrast to the results of theoretical investigations, which suggest this anisotropy should be limited. Common for such theoretical studies is that the effects of electron trapping are not included; simply speaking, electron trapping is a non-linear effect and is, therefore, eliminated when utilizing the standard methods for linearizing the underlying kinetic equations. Here, we review our recent work on the anisotropy that develops when retaining the effects of electron trapping. A general analytic model is derived for the electron guiding center distribution f(v?,v?) of an expanding flux tube. The model is consistent with anisotropic distributions observed by spacecraft, and is applied as a fluid closure yielding anisotropic equations of state for the parallel and perpendicular components (relative to the local magnetic field direction) of the electron pressure. In the context of reconnection, the new closure accounts for the strong pressure anisotropy that develops in the reconnection regions. It is shown that for generic reconnection in a collisionless plasma nearly all thermal electrons are trapped, and dominate the properties of the electron fluid. A new numerical code is developed implementing the anisotropic closure within the standard two-fluid framework. The code accurately reproduces the detailed structure of the reconnection region observed in fully kinetic simulations. These results emphasize the important role of pressure anisotropy for the reconnection process. In particular, for reconnection geometries characterized by small values of the normalized upstream electron pressure, ?e?, the pressure anisotropy becomes large with p?>>p? and strong parallel electric fields develop in conjunction with this anisotropy. The parallel electric fields can be sustained over large spatial scales and, therefore, become important for electron acceleration.

Egedal, Jan; Le, Ari; Daughton, William

2013-06-01

351

Size Dependence Effect in MgO-Based CoFeB Tunnel Junctions with Perpendicular Magnetic Anisotropy  

NASA Astrophysics Data System (ADS)

We examine the effect of junction sizes on the magnetization reversal process and spin-transfer torque switching of the MgO-based CoFeB magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA). From the magnetic field transport measurements, it was found that the miniaturization of MTJs inherently enhances the switching asymmetry and the PMA of the soft layer. Our micromagnetic simulations confirmed that the dipolar field from the hard layer is responsible for the switching asymmetry and the increase in perpendicular shape anisotropy induces improvement of the PMA. It was further revealed that this additional anisotropy gained from the smaller MTJ sizes is not sufficient to sustain the thermal stability to meet the long-term information storage at the state-of-the-art complementary-metal--oxide semiconductor technology node. The pulsed spin-transfer torque measurements showed that a higher current density is needed to switch the magnetization of the soft layer in MTJ with smaller lateral dimensions, which is attributed to the increase in PMA.

Chenchen, Jacob Wang; Akhtar, Mohamed Akbar Khan Bin; Sbiaa, Rachid; Hao, Meng; Sunny, Lua Yan Hwee; Kai, Wong Seng; Ping, Luo; Carlberg, Patrick; Arthur, and Ang Khoon Siah

2012-01-01

352

Influence of domain of perpendicular anisotropy master medium on perpendicular magnetic printing  

NASA Astrophysics Data System (ADS)

Magnetic printing is a promising way to write servo signals with high speed, high accuracy and low cost to fulfill the requirements for high-density hard disks. The PAMM (Perpendicular Anisotropy Master Medium) with CoPt magnetic layer has been proposed in order to improve the printing characteristics. However, it is worried that maze domain of the CoPt film may be printed on the hard disks. In this study, influence of the domain of the PAMM on the printing characteristics is analyzed by using micromagnetic simulation. As a result, it is clarified that the maze domain is not printed on the recording layer in the actual printing process even if the CoPt film has maze domain structure without external field.

Tanaka, Yasuki; Konishi, Hirotaka; Komine, Takashi; Sugita, Ryuji

353

Interfacial perpendicular magnetic anisotropy in CoFeB/MgO structure with various underlayers  

NASA Astrophysics Data System (ADS)

Interfacial perpendicular magnetic anisotropy (PMA) in CoFeB/MgO structures was investigated and found to be critically relied on underlayer material and annealing temperature. With Ta or Hf underlayer, clear PMA is observed in as-deposited samples while no PMA was shown in those with Pt or Pd. This may be attributed to smaller saturation magnetization of the films with Ta or Hf underlayer, which makes the PMA of CoFeB/MgO interface dominates over demagnetization field. On the contrary, samples with Pt or Pd demonstrate PMA only after annealing, which might be due to the CoPt (or CoPd) alloy formation that enhances PMA.

Oh, Young-Wan; Lee, Kyeong-Dong; Jeong, Jong-Ryul; Park, Byong-Guk

2014-05-01

354

Room-temperature perpendicular magnetic anisotropy in Ni/Pd (111) multilayers  

NASA Astrophysics Data System (ADS)

We report the experimental observation of room-temperature perpendicular magnetic anisotropy (PMA) in Ni/Pd (111) multilayer films having the thickness range of 5-11 Å Ni and 4-11 Å Pd sublayers, prepared by direct current magnetron sputtering on glass substrates at Ar sputtering pressure of 7 mTorr. Perpendicular magnetic anisotropy was found to be sensitively dependent on both Ni- and Pd-sublayer thicknesses, and a maximum anisotropy energy of 5.6×105 erg/cm3 was obtained for the (5 Å Ni/6 Å Pd)30 multilayer. The magnetoelastic anisotropy, quantitatively determined from in situ stress and ex situ magnetostriction coefficient measurements, was found to play an important role for the observed PMA in this system, together with the surface anisotropy.

Jeong, Jong-Ryul; Shin, Sung-Chul

1999-11-01

355

The nonequilibrium of magnetic fields  

Microsoft Academic Search

The more subtle properties of magnetic fields which create nonequilibrium and lead to vigorous activity in otherwise sluggish gas-field systems are evaluated for gross hydromagnetic effects. The gentle manipulation of magnetic fields on a large scale leads to the production of small scale variations and discontinuities, providing intense dissipation of magnetic field in a large scale system. A magnetic field

E. N. Parker

1981-01-01

356

Magnetic anisotropy of obliquely vapor-deposited CoNi films  

Microsoft Academic Search

The origin of the magnetic anisotropy in obliquely deposited Co1-x-Nix films (x = 0-1) has been investigated by using the X-ray Schulz method, reflection ellipsometry and replica electron microscopy. Films were vapor-deposited at an incidence angle of 60° on glass substrates kept at 213 K. In the x range smaller than 0.5, two kinds of large magnetic anisotropies are observed

K. Hara; K. Itoh; M. Kamiya; K. Okamoto; T. Hashimoto; H. Fujiwara

1991-01-01

357

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

358

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

359

Microinhomogeneities in Magnetic Fields  

Microsoft Academic Search

Small variations in the fields of magnets, caused by structures or domains in the pole faces, were investigated by moving a small coil in a circular path. It was found that for a given pole face the variations in the field were all about the same size, and decreased exponentially from the pole face. None of the materials tested as

H. H. Brown Jr.; F. Bitter

1956-01-01

360

Electric-field tunable magnetic-field-sensor based on CoFeB/MgO magnetic tunnel junction  

NASA Astrophysics Data System (ADS)

We demonstrate an electric-field-tunable magnetic-field-sensor based on CoFeB/MgO magnetic tunnel junction with interfacial perpendicular magnetic anisotropy (PMA). From the dynamic lock-in measurements, we show that an applied electric-field induces a peak in sensor voltage (VSENSOR) around the free layer magnetization switching regime in response to external a.c. magnetic field. Detailed measurements of VSENSOR as functions of free layer thickness, a.c. magnetic field amplitude and frequency reveal that the sensitivity of the sensor can be up to 80.8 V cm-1 Oe-1 under -0.5 V, which can be controlled by the strength and polarity of the applied electric-field via electric-field controlled PMA. We discuss the origin of our observations based on the oscillations in the tunnel magnetoresistance, and this may trigger the development of magnetoelectrically controlled magnetic-field-sensor based on magnetic tunnel junctions.

Naik, V. B.; Meng, H.; Liu, R. S.; Luo, P.; Yap, S.; Han, G. C.

2014-06-01

361

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

362

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

NASA Astrophysics Data System (ADS)

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 (~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.; Kapaklis, V.; Delimitis, A.; Jönsson, P. E.; Th. Papaioannou, E.; Poulopoulos, P.; Fumagalli, P.; Trachylis, D.; Velgakis, M. J.; Politis, C.

2012-09-01

363

Engineering Magnetic Anisotropy in Nanostructured 3d and 4f Ferromagnets  

NASA Astrophysics Data System (ADS)

Due to the increased demand for clean energy in recent years, there is a need for the scientific community to develop technology to harvest thermal energy which is ubiquitous but mostly wasted in our environment. However, there is still no efficient approach to harvest thermal energy to date. In this study, the theory of thermomagnetic energy harvesting is reviewed and unique applications of multiferroics (ferromagnetic plus ferroelectric) are introduced. Based on an efficiency analysis using experimentally measured magneto-thermal properties of 3d transitional and 4f rare earth ferromagnetic elements, the idea of using single domain ferromagnetic elements to obtain higher thermomagnetic conversion efficiencies is proposed. In order to fabricate a ferromagnetic single domain, the magnetic anisotropy of gadolinium (Gd) and nickel (Ni) is engineered at the nanoscale. Both thin films and nanostructures are fabricated and characterized with a focus on the change of magnetic anisotropy governed by shape, crystal structure, and strain. The fabrication processes include sputtering, e-beam lithography (writing and evaporation), and focused ion beam milling. Characterization techniques involving atomic/magnetic force microscopy, energy dispersive X-ray spectroscopy, magneto-optical Kerr effect magnetometry, superconducting quantum interference device magnetometry, scanning/transmission electron microscopy, and X-ray diffraction will also be discussed. Experimental results show that the magnetic domain structure of nanostructured Ni can be stably controlled with geometric constraints or by strain induced via electric field. The magnetic properties of nanostructured Gd, on the other hand, is sensitive to crystal structure. These results provide critical information toward the use of ferromagnetic nanostructures in thermomagnetic energy harvesting and multiferroic applications.

Hsu, Chin-Jui

364

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

365

Brillouin study of long-wavelength spin waves in quasimonatomic Co films with uniaxial perpendicular magnetic anisotropy  

SciTech Connect

We have observed spin-wave Brillouin light scattering from ultrathin Co/Au/Cu(111) films with Co thicknesses t{sub Co} down to 1 monolayer (ML) and with a 1-ML Au interlayer. The detection of a well-defined spin-wave spectrum and the field dependence of its frequency show directly long-range collective and ferromagnetic ordering in these films at room temperature. From the field dependence of the spin-wave frequency, we derive uniaxial perpendicular magnetic anisotropy constants as a function of t{sub Co} with various overlayer materials, including Cu, Pd, and Au. With a Cu overlayer, we observe that the first-order perpendicular anisotropy K{sub u}{sup (1)} obeys well a linear relation between K{sub u}{sup (1)}t{sub Co} and t{sub Co} for t{sub Co}{>=}1.5 ML, which indicates a constant contribution of the interface anisotropy of 0.16 mJ/m2 in addition to the volume anisotropy of 0.73 MJ/m3. With an Au or a Pd overlayer, we find that both the interface and volume anisotropies are significantly larger than those with the Cu overlayer. We quantify magnetic inhomogeneities from the field dependence of the spectrum width. With the Au or Pd overlayer, K{sub u}{sup (1)} shows a steep decrease with decreasing t{sub Co} for t{sub Co}<3.0 ML, which agrees well with a significant increase in the structure-related magnetic inhomogeneity. We show directly that long-ranged ferromagnetic ordering exists, with the perpendicular anisotropy, in our quasimonatomic Co films thinner than 1.5 ML. K{sub u}{sup (1)} for each overlayer tends to be zero at 1 ML of Co, accompanied by heavy damping of the spin wave. In addition, we find the second-order perpendicular anisotropy is still maintained with a comparable value to K{sub u}{sup (1)} in such quasimonatomic Co films, indicating significant deformation of the uniaxial anisotropy. (c) 2000 The American Physical Society.

Murayama, Akihiro [Optical Sciences Center and Surface Science Division of Arizona Research Laboratories, University of Arizona, Tucson, Arizona 85721 (United States)] [Optical Sciences Center and Surface Science Division of Arizona Research Laboratories, University of Arizona, Tucson, Arizona 85721 (United States); Hyomi, Kyoko [Optical Sciences Center and Surface Science Division of Arizona Research Laboratories, University of Arizona, Tucson, Arizona 85721 (United States)] [Optical Sciences Center and Surface Science Division of Arizona Research Laboratories, University of Arizona, Tucson, Arizona 85721 (United States); Eickmann, James [Optical Sciences Center and Surface Science Division of Arizona Research Laboratories, University of Arizona, Tucson, Arizona 85721 (United States)] [Optical Sciences Center and Surface Science Division of Arizona Research Laboratories, University of Arizona, Tucson, Arizona 85721 (United States); Falco, Charles M. [Optical Sciences Center and Surface Science Division of Arizona Research Laboratories, University of Arizona, Tucson, Arizona 85721 (United States)] [Optical Sciences Center and Surface Science Division of Arizona Research Laboratories, University of Arizona, Tucson, Arizona 85721 (United States)

2000-04-01

366

High-Field Magnetization Process and Crystalline Electric Field Interaction in Rare-Earth Permanent-Magnet Materials  

Microsoft Academic Search

\\u000a During the last two decades the performance of permanent magnets has been greatly improved by introducing rare-earth (R) elements to their constituents [1]. It is doubtless that the high coercivity of these magnets comes from the large magnetic anisotropy originated by the crystalline\\u000a electric field (CEF) acting on R ions with large orbital angular momentum. Magnetization measurements up to the

H. Kato; T. Miyazaki; M. Motokawa

367

Enhancement of perpendicular magnetic anisotropy by compressive strain in alternately layered FeNi thin films  

NASA Astrophysics Data System (ADS)

The effect of the lattice strain on magnetic anisotropy of alternately layered FeNi ultrathin films grown on a substrate, Cu(tCu = 0–70 ML)/Ni48Cu52(124 ML)/Cu(0 0 1) single crystal, is systematically studied by means of in situ x-ray magnetic circular dichroism (XMCD) and reflection high-energy electron diffraction (RHEED) analyses. To investigate the magnetic anisotropy of the FeNi layer itself, a non-magnetic substrate is adopted. From the RHEED analysis, the in-plane lattice constant, ain, of the substrate is found to shrink by 0.8% and 0.5% at tCu = 0 and 10 ML as compared to that of bulk Cu, respectively. Fe L-edge XMCD analysis is performed for n ML FeNi films grown on various ain, and perpendicular magnetic anisotropy (PMA) is observed at n = 3 and 5, whereas the film with n = 7 shows in-plane magnetic anisotropy. Moreover, it is found that PMA is enhanced with decreasing ain, in the case where a Cu spacer layer is inserted. We suppose that magnetic anisotropy in the FeNi films is mainly carried by Fe, and the delocalization of the in-plane orbitals near the Fermi level increases the perpendicular orbital magnetic moment, which leads to the enhancement of PMA.

Sakamaki, M.; Amemiya, K.

2014-04-01

368

Enhancement of perpendicular magnetic anisotropy by compressive strain in alternately layered FeNi thin films.  

PubMed

The effect of the lattice strain on magnetic anisotropy of alternately layered FeNi ultrathin films grown on a substrate, Cu(tCu = 0-70 ML)/Ni48Cu52(124 ML)/Cu(0 0 1) single crystal, is systematically studied by means of in situ x-ray magnetic circular dichroism (XMCD) and reflection high-energy electron diffraction (RHEED) analyses. To investigate the magnetic anisotropy of the FeNi layer itself, a non-magnetic substrate is adopted. From the RHEED analysis, the in-plane lattice constant, ain, of the substrate is found to shrink by 0.8% and 0.5% at tCu = 0 and 10 ML as compared to that of bulk Cu, respectively. Fe L-edge XMCD analysis is performed for n ML FeNi films grown on various ain, and perpendicular magnetic anisotropy (PMA) is observed at n = 3 and 5, whereas the film with n = 7 shows in-plane magnetic anisotropy. Moreover, it is found that PMA is enhanced with decreasing ain, in the case where a Cu spacer layer is inserted. We suppose that magnetic anisotropy in the FeNi films is mainly carried by Fe, and the delocalization of the in-plane orbitals near the Fermi level increases the perpendicular orbital magnetic moment, which leads to the enhancement of PMA. PMID:24695244

Sakamaki, M; Amemiya, K

2014-04-23

369

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

370

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

371

Magnetic ionization fronts. I. Parallel magnetic fields  

NASA Astrophysics Data System (ADS)

We solve the continuity equations across an ionization front. By including a plane parallel magnetic field we find significant differences in the allowed velocities of the R- and D-type solutions between the magnetized and non-magnetized cases. These results may have implications for the study of ionization bounded diffuse sources where a moderate or strong magnetic field is expected.

Redman, M. P.; Williams, R. J. R.; Dyson, J. E.; Hartquist, T. W.; Fernandez, B. R.

1998-03-01

372

Relaxation Phenomena of a Magnetic Nanoparticle Assembly with Randomly Oriented Anisotropy  

NASA Astrophysics Data System (ADS)

The effects of a randomly oriented anisotropy on relaxation phenomena including the memory effect of a noninteracting magnetic nanoparticle assembly, are numerically studied with a localized partition function and a master equation, leading to the following results. During the zero-field-cooled (ZFC) process, the energy barrier histogram changes with temperature, while during the field-cooled (FC) process it remains stable. In the relaxation process after ZFC initialization, the effective energy barrier distribution, which is derived from the T\\ln(t/?0) (T temperature, t time, and ?0 characteristic time constant) scaling curve, only reflects the low-energy region of the energy barrier histogram. The memory effect with temporary cooling during time evolution occurs in the studied assembly even without volume distribution and particle interaction involved.

Fang WenXiao,; He ZhenHui,; Chen DiHu,; En YunFei,; Kong XueDong,

2011-03-01

373

Parametric Excitation of Spin Waves by Voltage-Controlled Magnetic Anisotropy  

NASA Astrophysics Data System (ADS)

A theory of parametric excitation of spin waves (SWs) in ultrathin ferromagnetic strips by a microwave electric field is developed. The excitation uses the effect of voltage-controlled magnetic anisotropy in ferromagnet-dielectric heterostuctures. The characteristic values of the electric field necessary for parametric excitation of propagating SWs of 5-10 GHz frequency in Fe /MgO structure are found to be 0.1-1.5 V/nm. The minimum excitation threshold is achieved in narrow strip (strip width wx˜10-20 nm) for relatively long dipole-dominated SWs. In wider strips (wx?100 nm) electric parametric pumping excites mostly short exchange-dominated SWs having higher excitation thresholds, but substantially wider range of possible SW frequencies.

Verba, Roman; Tiberkevich, Vasil; Krivorotov, Ilya; Slavin, Andrei

2014-05-01

374

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

PubMed

The proton temperature anisotropy in the solar wind is known to be constrained by the theoretical thresholds for pressure-anisotropy-driven instabilities. Here, we use approximately 1x10;{6} independent measurements of gyroscale magnetic fluctuations in the solar wind to show for the first time that these fluctuations are enhanced along the temperature anisotropy thresholds of the mirror, proton oblique firehose, and ion cyclotron instabilities. In addition, the measured magnetic compressibility is enhanced at high plasma beta (beta_{ parallel} greater, similar1) along the mirror instability threshold but small elsewhere, consistent with expectations of the mirror mode. We also show that the short wavelength magnetic fluctuation power is a strong function of collisionality, which relaxes the temperature anisotropy away from the instability conditions and reduces correspondingly the fluctuation power. PMID:20366024

Bale, S D; Kasper, J C; Howes, G G; Quataert, E; Salem, C; Sundkvist, D

2009-11-20

375

Ferromagnetic resonance linewidth and damping in perpendicular-anisotropy magnetic multilayers thin films  

NASA Astrophysics Data System (ADS)

Transition metal ferromagnetic films with perpendicular magnetic anisotropy (PMA) have ferromagnetic resonance (FMR) linewidths that are one order of magnitude larger than soft magnetic materials, such as pure iron (Fe) and permalloy (NiFe) thin films. We have conducted systematic studies of a variety of thin film materials with perpendicular magnetic anisotropy to investigate the origin of the enhanced FMR linewidths, including Ni/Co and CoFeB/Co/Ni multilayers. In Ni/Co multilayers the PMA was systematically reduced by irradiation with Helium ions, leading to a transition from out-of-plane to in-plane easy axis with increasing He ion fluence [1,2]. The FMR linewidth depends linearly on frequency for perpendicular applied fields and increases significantly when the magnetization is rotated into the film plane with an applied in-plane magnetic field. Irradiation of the film with Helium ions decreases the PMA and the distribution of PMA parameters, leading to a large reduction in the FMR linewidth for in-plane magnetization. These results suggest that fluctuations in the PMA lead to a large two magnon scattering contribution to the linewidth for in-plane magnetization and establish that the Gilbert damping is enhanced in such materials (?˜0.04, compared to ?˜0.002 for pure Fe) [2]. We compare these results to those on CoFeB/Co/Ni and published results on other thin film materials with PMA [e.g., Ref. 3]. [1] D. Stanescu et al., J. Appl. Phys. 103, 07B529 (2008). [2] J-M. L. Beaujour, D. Ravelosona, I. Tudosa, E. Fullerton, and A. D. Kent, Phys. Rev. B RC 80, 180415 (2009). [3] N. Mo, J. Hohlfeld, M. ulIslam, C. S. Brown, E. Girt, P. Krivosik, W. Tong, A. Rebel, and C. E. Patton, Appl. Phys. Lett. 92, 022506 (2008). *Research done in collaboration with: A. D. Kent, New York University, D. Ravelosona, Institut d'Electronique Fondamentale, UMR CNRS 8622, Universit'e Paris Sud, E. E. Fullerton, Center for Magnetic Recording Research, UCSD, and supported by NSF-DMR-0706322.

Beaujour, Jean-Marc

2010-03-01

376

Oblique-Incidence Magnetic Anisotropy in Codeposited Alloy Films.  

National Technical Information Service (NTIS)

Alloy films produced by simultaneous deposition from two separate sources, one evaporating NiFe and the other evaporating a nonferromagnetic metal X, can exhibit large oblique-incidence ferromagnetic anisotropy even for small-incidence angles. The values ...

M. S. Cohen

1966-01-01

377

Anisotropies in the Magnetic Properties of Aligned HighT Superconducting YTTERIUM(1)BARIUM(2) (COPPER(1 - Powder Composites  

Microsoft Academic Search

Knowledge of the anisotropy of the penetration depth, lower critical field, and critical current density of the high-T_{c} oxide superconductors is important for the fundamental mechanism for superconductivity and as a guide for practical applications. Uniaxially -aligned powder composites of Y^1Ba_2(Cu _{1-x}Fe_{x})_3O _{z} for x <=q 0.1 were formed by magnetic alignment of particles suspended in epoxy. The volume distributions

Young Cheol Kim

1989-01-01

378

Eruptive solar magnetic fields  

NASA Technical Reports Server (NTRS)

The quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes is considered, with particular attention given to the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates is extended to a field which is not force free but in static equilibrium with plasma pressure and gravity. The basic physics is illustrated through the evolution of a loop-shaped electric current sheet enclosing a potential bipolar field with footpoints rooted in the photosphere. A free-boundary problem is posed and then solved for the equilibrium configuration of the current sheet in a hydrostatically supported isothermal atmosphere. As the footpoints move apart to spread a constant photospheric magnetic flux over a larger region, the equilibria available extend the field to increasing heights.

Low, B. C.

1981-01-01

379

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.

380

Interplay of the magnetoelastic and shape anisotropy on the evolution of magnetic domain structure of amorphous Nd-Fe-B films  

NASA Astrophysics Data System (ADS)

Amorphous Re-Fe-B (Re rare-earth) films are prepared on thermally oxidized Si substrates with Nb buffer layers by dc magnetron sputtering. We observed the evolution of magnetic domain structure in these films under the external magnetic field parallel to the film plane and discussed its origin. The magnetoelastic anisotropy and shape anisotropy can be adjusted by changing the deposition temperature and the thickness of the film. The results showed that the magnetic domain structure for a film with lower sputtering temperature (150 °C) and thinner thickness (200 nm) has changed significantly with the applied magnetic field and form stripe domains arranged along the direction of the field. However, for the film with higher sputtering temperature (300 °C) and thicker thickness (600 nm), magnetic domain structure is hardly varied with applied field. We suggest the evolution of magnetic domain structure is determined by the interplay of the magnetoelastic anisotropy and shape anisotropy energy, which will lead to the easy magnetization direction of amorphous Re-Fe-B films inclined to the normal direction instead of perpendicular to the film plane.

Liu, X. C.; Gao, J. L.; Xie, R.; Tang, T.; Tang, S. L.; Du, Y. W.

2014-05-01

381

HMI Magnetic Field Products  

NASA Astrophysics Data System (ADS)

The Helioseismic and Magnetic Imager (HMI) on SDO has measured magnetic field, velocity, and intensity in the photosphere over the full disk continuously since May 2010 with arc-second resolution. Scalar images are measured every 45 seconds. From these basic observables the pipeline automatically identifies and tracks active regions on the solar disk. The vector magnetic field and a variety of summary quantities are determined every 720s in these tracked Space-weather HMI Active Region Patches (SHARPS). Synoptic and synchronic maps are constructed daily and after each Carrington Rotation Most data products are available with definitive scientific calibration after a few day deal at and in a quick-look near-real-time version a few minutes after the observations are made. Uncertainties are determined for the derived products. All of the magnetic field products along with movies and images suitable for browsing are available at http:://Hmi.stanford.edu/magnetic. Other products, e.g. coronal field over active regions, can be computed on demand.

Hoeksema, Jon T.; HMI Magnetic Field Team

2013-07-01

382

On the magnetic dipole fields at surface atoms  

Microsoft Academic Search

The magnetic dipole fields at atoms in small particles and thin films of alpha-Fe have been calculated. Only the dipole fields in the first surface layer are significantly affected by the presence of the surface. It is shown that the shape anisotropy energy of microcrystals is influenced by these surface effects.

Per Helvig Christensen; Steen Mørup

1983-01-01

383

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.

384

Random magnetic anisotropy in thin films of amorphous Mn sub 48 B sub 52  

SciTech Connect

While crystalline MnB is a ferromagnet ({ital T}{sub {ital c}}=573 K), rf diode-sputtered thin films of composition Mn{sub 48}B{sub 52} are amorphous as ascertained by x-ray scattering and exhibit a low-field, hysteretic, static magnetization peak characteristic of a spin glass. High-field (up to 44 kG) static magnetization data at temperatures ranging between 6 and 200 K are analyzed within the random anisotropy model of Chudnovsky, Saslow, and Serota (Phys. Rev. B 33, 251 (1986)). In this model, the field-dependent magnetization at a given temperature is expressed as {ital M}({ital H})={ital M}(0)(1{minus}{ital CH}{sup {minus}1/2})+{chi}{prime}H, where the lead term follows from the analysis of a ferromagnet with a wandering axis (FWA) and the second term accounts for contributions from induced moments. The {ital T}{sup 3/2} dependence of the saturation magnetization of the FWA contribution, {ital M}(0), at low temperatures is suggestive of spin-wave excitations, while the temperature dependence of the fitting parameters {ital C} and {chi}{prime} consistently identify several characteristic temperatures associated with the magnetic behavior of {ital a}-Mn{sub 48}B{sub 52}, including the low-field spin-glass transition temperature and Curie temperature and the curvature crossover temperature (established from a classical Arrott plot) that separates the FWA state and a pseudoparamagnetic limit.

Kistenmacher, T.J.; Bryden, W.A.; Moorjani, K. (Milton S. Eisenhower Research Center, Applied Physics Laboratory, The Johns Hopkins University, Laurel, Maryland 20707-6099 (US))

1989-11-15

385

Effect of Temperature Anisotropy on Various Modes and Instabilities for a Magnetized Non-relativistic Bi-Maxwellian Plasma  

NASA Astrophysics Data System (ADS)

Using kinetic theory for homogeneous collisionless magnetized plasmas, we present an extended review of the plasma waves and instabilities and discuss the anisotropic response of generalized relativistic dielectric tensor and Onsager symmetry properties for arbitrary distribution functions. In general, we observe that for such plasmas only those modes whose magnetic-field perturbations are perpendicular to the ambient magnetic field, i.e., B 1 bot B 0, are effected by the anisotropy. However, in oblique propagation all modes do show such anisotropic effects. Considering the non-relativistic bi-Maxwellian distribution and studying the relevant components of the general dielectric tensor under appropriate conditions, we derive the dispersion relations for various modes and instabilities. We show that only the electromagnetic R- and L- waves, those derived from them (i.e., the whistler mode, pure Alfvén mode, firehose instability, and whistler instability), and the O-mode are affected by thermal anisotropies, since they satisfy the required condition {B}1bot {B}0. By contrast, the perpendicularly propagating X-mode and the modes derived from it (the pure transverse X-mode and Bernstein mode) show no such effect. In general, we note that the thermal anisotropy modifies the parallel propagating modes via the parallel acoustic effect, while it modifies the perpendicular propagating modes via the Larmor-radius effect. In oblique propagation for kinetic Alfvén waves, the thermal anisotropy affects the kinetic regime more than it affects the inertial regime. The generalized fast mode exhibits two distinct acoustic effects, one in the direction parallel to the ambient magnetic field and the other in the direction perpendicular to it. In the fast-mode instability, the magneto-sonic wave causes suppression of the firehose instability. We discuss all these propagation characteristics and present graphic illustrations. The threshold conditions for different instabilities are also obtained.

Bashir, Muhammad Fraz; Murtaza, G.

2012-12-01

386

Effects of magnetic anisotropy and exchange in Tm{sub 2}Fe{sub 17}  

SciTech Connect

Neutron diffraction experiments have been carried out to study the magnetocrystalline anisotropy of two (2b and 2d) Tm sublattices and four (4f, 6g, 12j, and 12k) Fe sublattices in ferrimagnetic compound Tm{sub 2}Fe{sub 17} (space group P6{sub 3}/mmc). We have determined the temperature dependence of the magnitude and orientation of magnetization for each of the thulium and iron sublattices in the range (10-300) K. A spontaneous rotation (at about 90 K) of the Tm and Fe sublattice magnetizations from the c-axis to the basal plane is accompanied by a drastic change in the magnetization magnitude, signifying a large magnetization anisotropy. Both Tm sublattices exhibit an easy-axis type of the magnetocrystalline anisotropy. The Fe sublattices manifest both the uniaxial and planar anisotropy types. The sublattice formed by Fe atoms at the 4f position reveals the largest planar anisotropy constant. The Fe atoms at the 12j position show a uniaxial anisotropy. We find that the inelastic neutron scattering spectra measured below and above the spin-reorientation transition are remarkably different.

Pirogov, A. N., E-mail: pirogov05@gmail.com; Bogdanov, S. G.; Rosenfeld, E. V. [Russian Academy of Sciences, Institute of Metal Physics, Ural Division (Russian Federation); Park, J.-G. [Seoul National University, FPRD, Department of Physics and Astronomy (Korea, Republic of); Choi, Y. N.; Lee, Seongsu [Korea Atomic Energy Research Institute, Neutron Science Division HANARO (Korea, Republic of); Prokes, K. [Helmholtz Centre Berlin for Materials and Energy (Germany); Golosova, N. O.; Sashin, I. L. [Joint Institute for Nuclear Research (Russian Federation); Kudrevatykh, N. V. [Ural Federal University, Institute of Physics and Applied Mathematics (Russian Federation); Skryabin, Yu. N.; Vokhmyanin, A. P. [Russian Academy of Sciences, Institute of Metal Physics, Ural Division (Russian Federation)

2012-11-15

387

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

388

The interplanetary magnetic field  

NASA Technical Reports Server (NTRS)

Large-scale properties of the interplanetary magnetic field as determined by the solar wind velocity structure are examined. The various ways in which magnetic fields affect phenomena in the solar wind are summarized. The dominant role of high and low velocity solar wind streams that persist, with fluctuations and evolution, for weeks or months is emphasized. It is suggested that for most purposes the sector structure is better identified with the stream structure than with the magnetic polarity and that the polarity does not necessarily change from one velocity sector to the next. Several mechanisms that might produce the stream structure are considered. The interaction of the high and low velocity streams is analyzed in a model that is steady state when viewed in a frame that corotates with the sun.

Davis, L., Jr.

1972-01-01

389

Exponential equilibration by slow cooling in the planar random-anisotropy magnet: Experiments and simulations  

Microsoft Academic Search

Neutron measurements of the equilibration of the staggered magnetization in DyAs0.35V0.65O4 are compared with Monte Carlo simulations of spin dynamics in a planar random-anisotropy magnet. The simulation results are in agreement with striking observed relaxation phenomena: when cooled rapidly to a low temperature, no magnetic ordering is observed; however when cooled in small steps an ordered magnetic moment appears, which

Donald R. Taylor; Orlando V. Billoni; Sergio A. Cannas; Francisco A. Tamarit

2008-01-01

390

Increase of magnetic hyperthermia efficiency due to dipolar interactions in low-anisotropy magnetic nanoparticles: Theoretical and experimental results  

NASA Astrophysics Data System (ADS)

When magnetic nanoparticles (MNPs) are single domain and magnetically independent, their magnetic properties and the conditions to optimize their efficiency in magnetic hyperthermia applications are now well understood. However, the influence of magnetic interactions on magnetic hyperthermia properties is still unclear. Here, we report hyperthermia and high-frequency hysteresis loop measurements on a model system consisting of MNPs with the same size but a varying anisotropy, which is an interesting way to tune the relative strength of magnetic interactions. A clear correlation between the MNP anisotropy and the squareness of their hysteresis loop in colloidal solution is observed: the larger the anisotropy, the smaller the squareness. Since low anisotropy MNPs display a squareness higher than the one of magnetically independent nanoparticles, magnetic interactions enhance their heating power in this case. Hysteresis loop calculations of independent and coupled MNPs are compared to experimental results. It is shown that the observed features are a natural consequence of the formation of chains and columns of MNPs during hyperthermia experiments: in these structures, when the MNP magnetocristalline anisotropy is small enough to be dominated by magnetic interactions, the hysteresis loop shape tends to be rectangular, which enhances their efficiency. On the contrary, when MNPs do not form chains and columns, magnetic interactions reduce the hysteresis loop squareness and the efficiency of MNPs compared to independent ones. Our finding can thus explain contradictory results in the literature on the influence of magnetic interactions on magnetic hyperthermia. It also provides an alternate explanation to some experiments where an enhanced specific absorption rate for MNPs in liquids has been found compared to the one of MNPs in gels, usually interpreted with some contribution of the brownian motion. The present work should improve the understanding and interpretation of magnetic hyperthermia experiments.

Mehdaoui, B.; Tan, R. P.; Meffre, A.; Carrey, J.; Lachaize, S.; Chaudret, B.; Respaud, M.

2013-05-01

391

Voltage Control of Domain Wall Motion in Perpendicular Magnetic Anisotropy Materials  

NASA Astrophysics Data System (ADS)

High-performance solid-state operation of a wide variety of spintronic devices requires efficient electrical control of domain walls (DWs). In this work we examine DW dynamics in ultrathin Co films under the influence of an electric field applied across a gadolinium oxide gate dielectric. By measuring the velocity scaling with temperature, driving field, and gate voltage, we verify domain expansion via thermally-activated creep dynamics. We show that an electric field linearly modulates the activation energy barrier EA that governs DW creep, leading to an exponential dependence of DW velocity on gate voltage. As a consequence, significant voltage-induced velocity enhancement can be achieved in the low-velocity regime, but the efficiency is diminished at high velocities where EA is correspondingly small. We overcome this limitation by engineering novel device structures with significantly larger voltage induced effects on magnetic anisotropy and demonstrate voltage modulation of the DW propagation field by hundreds of Oe. Implementation into magnetic nanowire devices allows us to engineer gate voltage controlled DW traps which are nonvolatile and robustly switchable for many cycles.

Bauer, Uwe; Emori, Satoru; Beach, Geoffrey S. D.

2013-03-01

392

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

393

Magnetic and elastic anisotropy in magnetorheological elastomers using nickel-based nanoparticles and nanochains  

NASA Astrophysics Data System (ADS)

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.; Perez, Oscar E.; Butera, Alejandro; Jorge, Guillermo; Oliveira, Cristiano L. P.; Negri, R. Martín

2013-12-01

394

Nonlinear strain dependence of magnetic anisotropy in CoFe2O4 films on MgO(001) substrates  

NASA Astrophysics Data System (ADS)

CoFe2O4 films were deposited on MgO(001) substrates using pulsed laser deposition with various laser energy densities. We found that the CoFe2O4 films were grown in the (001) orientation and that the lattice constant of the CoFe2O4 films was dependent on the laser energy densities. Perpendicular magnetic anisotropy (PMA) was observed, but the lattice strain dependence was not consistent with the phenomenological model in which the PMA is in proportion to the lattice strain. The lattice strain dependence of PMA was compared with an electron theory in which the spin-orbit interaction and the tetragonal crystal field in the electronic state of a single Co ion are considered. The experimental result does not contradict with the calculation, which shows that the magnetic anisotropy is not proportional to the lattice strain and asymmetric in respect to negative and positive lattice strain.

Tanaka, M. A.; Harada, K.; Takemura, M.; Mibu, K.; Inoue, J.

2014-05-01

395

Critical Velocities of Domain Walls in Magnetic Thin Films with Planar Anisotropy  

Microsoft Academic Search

The nonlinear dynamics of vortex-shaped domain walls in magnetic thin films with planar anisotropy is studied numerically. The critical velocity of uniform domain-wall motion is computed versus the film thickness and the saturation magnetization. It is shown that these characteristics are nonmonotonic.

B. N. Filippov; L. G. Korzunin; O. V. Sycheva; V. I. Beresnev

2001-01-01

396

Calculations of the effects of anisotropy on magnetic flux leakage detector signals  

Microsoft Academic Search

Oil and gas pipelines are inspected for corrosion using magnetic flux leakage (MFL) inspection tools. It has been found that varying line pressure, bending or residual stresses cause changes in the MFL signals. Changes in the amplitude are thought to be due to stress-induced changes in the bulk magnetic anisotropy or preferred easy axis of the steel pipe wall. This

S. Leonard; D. L. Atherton

1996-01-01

397

Room-temperature magnetic anisotropy of lanthanide complexes: A model study for various coordination polyhedra  

Microsoft Academic Search

The dependence of the room-temperature magnetic anisotropy ?? of lanthanide complexes on the type of the coordination polyhedron and on the nature of the lanthanide ion is quantitatively analyzed in terms of a model approach based on numerical calculations. The aim of this study is to establish general regularities in the variation of the sign and magnitude of the magnetic

Vladimir S. Mironov; Yury G. Galyametdinov; Arnout Ceulemans; Koen Binnemans

2002-01-01

398

Room-temperature magnetic anisotropy of lanthanide complexes: A model study for various coordination polyhedra  

Microsoft Academic Search

The dependence of the room-temperature magnetic anisotropy Deltachi of lanthanide complexes on the type of the coordination polyhedron and on the nature of the lanthanide ion is quantitatively analyzed in terms of a model approach based on numerical calculations. The aim of this study is to establish general regularities in the variation of the sign and magnitude of the magnetic

Vladimir S. Mironov; Yury G. Galyametdinov; Arnout Ceulemans; Christiane Görller-Walrand; Koen Binnemans

2002-01-01

399

Localised modification of magnetic anisotropy in LPE iron garnet films by laser annealing  

Microsoft Academic Search

A method of obtaining localized modification of magnetic anisotropy in LPE garnet film is described. Localized annealing was done by heating the film with a cw argon laser beam in a high temperature furnace. The direction change of magnetization was observed at the irradiated area.

K. Ando; Y. Yokoyama; T. Okuda; N. Koshizuka

1983-01-01

400

Magnetic anisotropy and crystalline orientation in high Hk FeCoB thin films  

NASA Astrophysics Data System (ADS)

FeCoB thin films with a high magnetic anisotropy field Hk were studied. Crystal structure of the FeCo was investigated by using x-Ray diffraction with particular interest for understanding the scheme to produce a high Hk in the FeCoB films. The as-deposited film with a high Hk of 280 Oe showed a well-crystallized bcc (110) texture of FeCo and an asymmetric profile in the rocking curve measured along the easy axis. The pole figure profile revealed that the maximum diffraction intensity was observed at the point other than the original point, namely, the tilted crystal orientation to the substrate plane. In addition, elliptical contour lines of diffraction intensity were observed and their major axis aligned with the direction of the peak shift. These results indicated the correlation among the crystal orientation and the easy axis direction and also the incident direction of the sputtering particles to the substrate.

Hashimoto, Atsuto; Matsuu, Toshimitsu; Tada, Masaru; Nakagawa, Shigeki

2008-04-01

401

Anisotropy of magnetic susceptibility as a strain gauge in the Flamanville granite, NW France  

NASA Astrophysics Data System (ADS)

The relationship between strain and anisotropy of magnetic susceptibility (AMS) has been investigated in the Carboniferous Flamanville granite in the Armorican Massif, NW France. We measured the axial ratios of elliptical inclusions and the orientation of cleavage planes at eight sites around the granite margin. Measurements of AMS were made on 73 specimens using a Schonstedt spinner magnetometer. AMS measurements are shown to provide accurate predictions of cleavage and lineation direction, even where these structures are difficult to measure in the field. The strain and AMS ellipsoids show similar regional variations in shape and intensity, and a good correlation between the lengths of the principal axes. Finally, our data are consistent with the hypothesis that the Flamanville granite was syntectonically emplaced during the late stages of the Hercynian Orogeny.

Cogné, J. P.; Perroud, H.

1988-08-01

402

Nonlithographic fabrication of 25 nm magnetic nanodot arrays with perpendicular anisotropy over a large area  

NASA Astrophysics Data System (ADS)

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm2 coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO2 dot arrays formed on a Si wafer. At first, arrays of the SiO2 dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO2 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 SiO2 dots are about 24, 43, and 17 nm, respectively. Then {Co(0.4 nm)/Pt(0.08 nm)}8 MLs with a 3 nm Pt buffer layer is deposited onto the SiO2 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 SiO2 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, Chih-Huang

2009-04-01

403

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

404

The Earth's Magnetic Field  

NSDL National Science Digital Library

This section of the Windows to the Universe website provides information and images about Earth's magnetic field (the magnetosphere), including detailed information about the aurora borealis, magnets, and solar wind. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging website that includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

Johnson, Roberta

2000-07-01

405

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The Heliospheric Magnetic Field (HMF) is the physical framework in which energetic particles and cosmic rays propagate. Changes in the large scale structure of the magnetic field lead to short- and long term changes in cosmic ray intensities, in particular in anti-phase with solar activity. The origin of the HMF in the corona is well understood and inner heliospheric observations can generally be linked to their coronal sources. The structure of heliospheric magnetic polarities and the heliospheric current sheet separating the dominant solar polarities are reviewed here over longer than a solar cycle, using the three dimensional heliospheric observations by Ulysses. The dynamics of the HMF around solar minimum activity is reviewed and the development of stream interaction regions following the stable flow patterns of fast and slow solar wind in the inner heliosphere is described. The complex dynamics that affects the evolution of the stream interaction regions leads to a more chaotic structure of the HMF in the outer heliosphere is described and discussed on the basis of the Voyager observations. Around solar maximum, solar activity is dominated by frequent transients, resulting in the interplanetary counterparts of Coronal Mass Ejections (ICMEs). These produce a complex aperiodic pattern of structures in the inner heliosphere, at all heliolatitudes. These structures continue to interact and evolve as they travel to the outer heliosphere. However, linking the observations in the inner and outer heliospheres is possible in the case of the largest solar transients that, despite their evolutions, remain recognizably large structures and lead to the formation of Merged Interaction Regions (MIRs) that may well form a quasi-spherical, "global" shell of enhanced magnetic fields around the Sun at large distances. For the transport of energetic particles and cosmic rays, the fluctuations in the magnetic field and their description in alternative turbulent models remains a very important research topic. These are also briefly reviewed in this paper.

Balogh, André; Erdõs, Géza

2013-06-01

406

Magnetic anisotropy of the antiferromagnetic ring [Cr8F8Piv16].  

PubMed

A new tetragonal (P42(1)2) crystalline form of [Cr8F8Piv16] (HPiv = pivalic acid, trimethyl acetic acid) is reported. The ring-shaped molecules, which are aligned in a parallel fashion in the unit cell, form almost perfectly planar, regular octagons. The interaction between the CrIII ions is antiferromagnetic (J = 12 cm(-1)) which results in a S = 0 spin ground state. The low-lying spin excited states were investigated by cantilever torque magnetometry (CTM) and high-frequency EPR (HFEPR). The compound shows hard-axis anisotropy. The axial zero-field splitting (ZFS) parameters of the first two spin excited states (S = 1 and S = 2, respectively) are D1 = 1.59(3) cm(-1) or 1.63 cm(-1) (from CTM and HFEPR, respectively) and D2 = 0.37 cm(-1) (from HFEPR). The dipolar contributions to the ZFS of the S = 1 and S = 2 spin states were calculated with the point dipolar approximation. These contributions proved to be less than the combined single-ion contributions. Angular overlap model calculations that used parameters obtained from the electronic absorption spectrum, showed that the unique axis of the single-ion ZFS is at an angle of 19.3(1) degrees with respect to the ring axis. The excellent agreement between the experimental and the theoretical results show the validity of the used methods for the analysis of the magnetic anisotropy in antiferromagnetic CrIII rings. PMID:11826863

van Slageren, Joris; Sessoli, Roberta; Gatteschi, Dante; Smith, Andrew A; Helliwell, Madeleine; Winpenny, Richard E P; Cornia, Andrea; Barra, Anne-Laure; Jansen, Aloysius G M; Rentschler, Eva; Timco, Grigore A

2002-01-01

407

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

408

Sizable room-temperature magnetoresistance in cobalt based magnetic tunnel junctions with out-of-plane anisotropy  

NASA Astrophysics Data System (ADS)

Submicron alumina based magnetic tunnel junctions (MTJs) using electrodes with out-of-plane magnetic anisotropy were prepared and characterized. Both electrodes are industry-compatible Co/Pt multilayers. The magnetic properties of the unpatterned samples have been investigated through superconducting quantum interference device (SQUID) magnetometry and extraordinary Hall effect: both electrodes have fully out-of-plane magnetic moments and nonoverlapping coercive fields. Transport measurements on the submicron MTJs showed a magnetoresistance (MR) ratio reaching 8% at room temperature. Nanopillars with diameters of 800, 400, and 200 nm patterned from the same wafer show the expected out-of-plane magnetic properties and similar resistance×area products (RA) and MR ratios. The I(V) characteristics of pillars with diameters of 800 and 400 nm could be accounted for with reasonable barrier heights and widths.

Carvello, Baptiste; Ducruet, Clarisse; Rodmacq, Bernard; Auffret, Stéphane; Gautier, Eric; Gaudin, Gilles; Dieny, Bernard

2008-03-01

409

Electron magnetic resonance of ferrofluids: Evidence for anisotropic resonance at 77 K in samples cooled in a magnetic field  

NASA Astrophysics Data System (ADS)

Evidence is presented from studies of electron magnetic resonance for the formation of linear chains in kerosene based Mn 0.1Fe 0.9Fe 2O 4 (MF1) ferrite ferrofluid cooled in a magnetic field. The resonance field at 77 K was found to depend on the field at which the sample was cooled. More interestingly, the samples cooled in a magnetic field exhibited anisotropy in a resonance field with 180° periodicity, giving evidence for frozen chains.

Sastry, M. D.; Babu, Y.; Goyal, P. S.; Mehta, R. V.; Upadhyay, R. V.; Srinivas, D.

1995-08-01

410

The effect of coherent uniaxial anisotropies on the grain-size dependence of coercivity in nanocrystalline soft magnetic alloys  

Microsoft Academic Search

The grain-size (D) dependence of coercivity (Hc) in various nanocrystalline soft magnetic materials has been re-analyzed with particular attention to induced uniaxial anisotropies. In addition to the well-known D6 law, a D3 dependence of Hc is observed for some nanocrystalline samples with uniaxial anisotropies larger than the random magnetocrystalline anisotropy (?K1?). The original random anisotropy model has been extended to

K. Suzuki; G. Herzer; J. M. Cadogan

1998-01-01

411

Magnetic properties and microstructure of FePt/BN nanocomposite films with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We have prepared L10-FePt/BN nanocomposite films by depositing the FePt/BN mutilayers on the MgO(100) substrates using magnetron sputtering followed by a postannealing process. We found the excellent perpendicular magnetic anisotropy of [FePt (2 nm)/BN (0.5 nm)]10 film after annealing at 700 °C for 1 h x-ray diffraction patterns also indicate an excellent (001) texture of the film. This film shows a perpendicular coercivity of 7.48 kOe and the ratio of the remnant magnetization Mr to the saturation one MS of as high as 0.93. We also found the good epitaxial growth of FePt grains on the MgO(100) substrate by cross-section high resolution transmitting microscopy.

Li, Bao-He; Feng, Chun; Gao, Xin; Teng, Jiao; Yu, Guang-Hua; Xing, Xianran; Liu, Zhong-Yuan

2007-10-01

412

Field-induced domain wall motion of amorphous [CoSiB/Pt]N multilayers with perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

Amorphous CoSiB/Pt multilayer is a perpendicular magnetic anisotropy material to achieve high squareness, low coercivity, strong anisotropy, and smooth domain wall (DW) motion, because of the smoother interface compared with crystalline multilayers. For [CoSiB(6 Å)/Pt (14 Å)]N multilayers with N = 3, 6, and 9, we studied the field-induced DW dynamics. The effective anisotropy constant K1eff is 1.5 × 106 erg/cm3 for all the N values, and the linear increment of coercive field Hc with N gives constant exchange coupling J. By analyzing the field dependence of DW images at room temperature, a clear creep motion with the exponent ? = 1/4 could be observed. Even though the pinning field Hdep slightly increases with N, the pinning potential energy Uc is constant (=35 kBT) for all the N values. These results imply that the amorphous [CoSiB/Pt]N multilayers are inherently homogeneous compared to crystalline multilayers. For N ? 6, the pinning site density ?pin is less than 1000/?m2, which is about 1 pinning site per the typical device junction size of 30 × 30 nm2. Also, the exchange stiffness constant Aex is obtained to be 0.48 × 10-6 erg/cm, and the domain wall width is expected to be smaller than 5.5 nm. These results may be applicable for spin-transfer-torque magnetic random access memory and DW logic device applications.

Choi, Y. H.; Lee, K. J.; Yoon, J. B.; Cho, J. H.; You, C.-Y.; Kim, T. W.; Jung, M. H.

2014-05-01

413

Electric-field and magnetic-field alignment of liquid-crystalline clay suspensions and clay/polymer composites  

NASA Astrophysics Data System (ADS)

Nematic and isotropic aqueous suspensions of beidellite clay sheets have been submitted to magnetic and a. c. electric fields. The nematic suspensions have positive anisotropy of magnetic susceptibility and negative anisotropy of electric susceptibility because the clay sheets orient their normals parallel to the magnetic field but perpendicular to the electric field. Moreover, the isotropic phase shows a large electric-field-induced birefringence. By dissolving acrylamide monomers in the clay suspensions and photopolymerization, clay/polymer composite gels could be elaborated. Aligned and patterned composites could be produced by application of an electric field during polymerization.

Paineau, E.; Dozov, I.; Antonova, K.; Davidson, P.; Impéror, M.; Meneau, F.; Bihannic, I.; Baravian, C.; Philippe, A. M.; Levitz, P.; Michot, L. J.

2011-10-01

414

Anisotropy of the sublattice magnetization and magnetoresistance in Co/Re superlattices on Al{sub 2}O(1120).  

SciTech Connect

[Co(20 {angstrom})/Re(6{angstrom})]{sub 20} superlattices were grown on a (11{bar 2}0) surface of a Al{sub 2}O{sub 3} single crystal, with the [0001] direction of their hcp structure in the plane of the film. The Co layers were found to be antiferromagnetically coupled (AF), with a saturating field of 6 kOe. Polarized neutron reflectivityy was used to determine the direction of the