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1

Electrical field control of interface magnetic anisotropy  

NASA Astrophysics Data System (ADS)

The interface magnetic anisotropy of ferromagnetic metals comes from the spin-orbit interaction. By explicitly taking into account the interaction between the symmetry-broken interface potential and the spin-dependent electric dipoles of the Bloch states, we find that the interface spin-orbit coupling can be modeled by the Rashba spin-orbit Hamiltonian (RSOH). Due to the presence of the RSOH, the spin up and down states of the ferromagnet are spin mixed at the interface. Among other consequences, the RSOH induces a perpendicular surface magnetic anisotropy whose magnitude is comparable to the observed values in transition metals. When an external electric field is applied across the interface, the induced screening potential modifies the RSOH and thus the perpendicular anisotropy can be manipulated. Our calculated results are in agreement with the experiments [1]. [4pt] [1] Endo et al., Appl. Phys. Lett. 96, 212503 (2010); T. Nozaki et al, Appl. Phys. Lett. 96, 022506 (2010).

Xu, Lei; Zhang, Shufeng

2011-03-01

2

Electric field control of interface magnetic anisotropy  

NASA Astrophysics Data System (ADS)

The interface magnetic anisotropy of ferromagnetic metals comes from the spin-orbit interaction. But unlike the semiconductor heterostructures, the strong electron screening would make the Rashba spin-orbit coupling (RSOC) localized within the election screening length at metallic interface. Now by explicitly taking into account the interaction between the symmetry-broken interface potential and the spin-dependent electric dipoles of the Bloch states, we find that this interaction may generate a RSOC, which is much stronger than the direct Pauli spin-orbit coupling. Due to the presence of the RSOC, the spin up and down states of the ferromagnet are spin mixed at the interface. Among other consequences, the RSOC induces a perpendicular surface magnetic anisotropy whose magnitude is comparable to the observed values in transition metals. When we apply an external electric field across the interface, the induced screening potential modifies the RSOC and thus the perpendicular anisotropy can be manipulated.

Xu, Lei; Zhang, Shufeng

2011-10-01

3

Induced Magnetic Anisotropy of Ferrofluid Frozen in Magnetic Fields  

Microsoft Academic Search

The magnetization process of a ferrofluid whose carrier fluid is paraffin was investigated in the temperature range from 77 K to 300 K, as a function of the cooling field intensity and freezing rate. Phase transitions between the liquid and solid states can be simulated by using the ferrofluids as a magnetic probe. A uniaxial magnetic anisotropy was induced by

N. Inaba; H. Miyajima; S. Taketomi; S. Chikazumi

1989-01-01

4

CMB anisotropies in the presence of a stochastic magnetic field  

SciTech Connect

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

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

2011-01-15

5

Electric Field Induced Magnetic Anisotropy in a Ferromagnet  

SciTech Connect

We report the first observation of a transient all electric field induced magnetic anisotropy in a thin film metallic ferromagnet. We generate the anisotropy with a strong (-10{sup 9} V/m) and short (70 fs) {rvec E}-field pulse. This field is large enough to distort the valence charge distribution in the metal, yet its duration is too brief to change the atomic positions. This pure electronic structure alteration of the sample generates a new type of transient anisotropy axis and strongly influences the magnetization dynamics. The successful creation of such an anisotropy opens the possibility for all {rvec E}-field induced magnetization reversal in thin metallic films - a greatly desired yet unachieved process.

Gamble, S. J.

2010-02-24

6

Antiferromagnetic superconductors with effective-mass anisotropy in magnetic fields  

Microsoft Academic Search

We derive critical field Hc2 equations for antiferromagnetic s -wave, dx2-y2 -wave, and dxy -wave superconductors with effective-mass anisotropy in three dimensions, where we take into account (i) the Jaccarino-Peter mechanism of magnetic-field-induced superconductivity (FISC) at high fields, (ii) an extended Jaccarino-Peter mechanism that reduces the Pauli paramagnetic pair-breaking effect at low fields where superconductivity and an antiferromagnetic long-range order

Yuuichi Suginishi; Hiroshi Shimahara

2006-01-01

7

Magnetic stress anisotropy field in plated cylindrical permalloy films  

Microsoft Academic Search

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 Hksto uniaxial film stress, average composition, and amplitude of composition variation. A result of particular importance is that even

O. Lutes

1971-01-01

8

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

2013-05-08

9

Magnetic fields from inflation: The CMB temperature anisotropies  

NASA Astrophysics Data System (ADS)

The cosmic microwave background (CMB) temperature anisotropies from primordial magnetic fields are studied. In addition to the known passive and compensated modes we discuss an inflationary magnetic mode in the curvature perturbation, present when magnetic fields are generated during inflation. This mode is absent if the generation mechanism is causal, e.g. a phase transition. We compute and discuss the effect of this mode on the observed CMB anisotropy spectrum, in comparison with the passive and compensated ones. We find that it dominates the CMB anisotropy, and consequently leads to stronger constraints on the amplitude B1Mpc and spectral index nB of the magnetic field than what is usually found in CMB analyses from the compensated mode. This happens in particular for spectral indexes nB>-3: the inflationary magnetic mode is always scale invariant; therefore through this mode even a magnetic field with a spectrum which is not scale invariant can leave a detectable signal in the CMB at large scales.

Bonvin, Camille; Caprini, Chiara; Durrer, Ruth

2013-10-01

10

Magnetic anisotropy transformation of Co-Fe-B nanowire arrays synthesized under the magnetic field  

NASA Astrophysics Data System (ADS)

The effects of magnetic field on the magnetic anisotropy of amorphous Co-Fe-B nanowire arrays during the electroless plating process have been investigated. The results show that the easy magnetization direction of the Co-Fe-B nanowire array rotated from in-plane to out-of-plane with the applied magnetic field increasing. A mechanism based on the variation of atomic short-range ordering induced by the applied magnetic field is proposed to interpret this unique anisotropy transformation.

Liu, Z.; Li, W. L.; Jin, P. P.; Fei, W. D.

2013-11-01

11

Anisotropies in magnetic field evolution and local Lyapunov exponents  

SciTech Connect

The natural occurrence of small scale structures and the extreme anisotropy in the evolution of a magnetic field embedded in a conducting flow is interpreted in terms of the properties of the local Lyapunov exponents along the various local characteristic (un)stable directions for the Lagrangian flow trajectories. The local Lyapunov exponents and the characteristic directions are functions of Lagrangian coordinates and time, which are completely determined once the flow field is specified. The characteristic directions that are associated with the spatial anisotropy of the problem, are prescribed in both Lagrangian and Eulerian frames. Coordinate transformation techniques are employed to relate the spatial distributions of the magnetic field, the induced current density, and the Lorentz force, which are usually followed in Eulerian frame, to those of the local Lyapunov exponents, which are naturally defined in Lagrangian coordinates.

Tang, X.Z.; Boozer, A.H.

2000-01-13

12

Magnetic Anisotropy and the Orientation of Retinal Rods in a Homogeneous Magnetic Field  

PubMed Central

The reported orientation of retinal rods in a homogeneous magnetic field can be explained by the magnetic anisotropy of oriented molecules in the disc membranes of the rods. The energy of a single rod as a function of orientation in the magnetic field, the time required for alingment of the rod in a viscous medium, and the fluctuations of orientation are calculated. Arguments that rhodopsin is the constituent responsible for the effect are given. The possibility of orientation due to inhomogeneity of the magnetic field is ruled out. The application of magnetic anisotropy as an experimental tool in biology is indicated.

Hong, Felix T.; Mauzerall, David; Mauro, Alexander

1971-01-01

13

Linear Birefringence and Linear Dichroism Coupled Optical Anisotropy of Magnetic Fluids by External Magnetic Fields  

Microsoft Academic Search

The optical anisotropy of magnetic fluids, including linear birefringence and linear dichroism simultaneously, under externally applied magnetic fields is investigated in this work. Analytical expressions to describe the polarization properties (direction of main polarization and degree of polarization) of the transmitted elliptically polarized light after the optically anisotropic magnetic fluids are obtained by theoretical derivation. Numerical examples are presented to

Shengli Pu; Min Dai; Guoqing Sun; Ming Liu

2009-01-01

14

Antiferromagnetic superconductors with effective-mass anisotropy in magnetic fields  

NASA Astrophysics Data System (ADS)

We derive critical field Hc2 equations for antiferromagnetic s -wave, dx2-y2 -wave, and dxy -wave superconductors with effective-mass anisotropy in three dimensions, where we take into account (i) the Jaccarino-Peter mechanism of magnetic-field-induced superconductivity (FISC) at high fields, (ii) an extended Jaccarino-Peter mechanism that reduces the Pauli paramagnetic pair-breaking effect at low fields where superconductivity and an antiferromagnetic long-range order with a canted spin structure coexist, and (iii) the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO or LOFF) state. As an example, experimental phase diagrams observed in organic superconductor ?-(BETS)2FeBr4 are theoretically reproduced. In particular, the upper critical field of low-field superconductivity is well reproduced without any additional fitting parameter other than those determined from the critical field curves of the FISC at high fields. Therefore, the extended Jaccarino-Peter mechanism seems to occur actually in the present compound. It is predicted that the FFLO state does not occur in the FISC at high fields in contrast to the compound ?-(BETS)2FeCl4 , but it may occur in low-field superconductivity for s -wave and dx2-y2 -wave pairings. We also briefly discuss a possibility of compounds that exhibit unconventional behaviors of upper critical fields.

Suginishi, Yuuichi; Shimahara, Hiroshi

2006-07-01

15

Two-dimensional field-sensing map and magnetic anisotropy dispersion in magnetic tunnel junction arrays  

NASA Astrophysics Data System (ADS)

Due to the inherent disorder in local structures, anisotropy dispersion exists in almost all systems that consist of multiple magnetic tunnel junctions (MTJs). Aided by micromagnetic simulations based on the Stoner-Wohlfarth (S-W) model, we used a two-dimensional field-sensing map to study the effect of anisotropy dispersion in MTJ arrays. First, we recorded the field sensitivity value of an MTJ array as a function of the easy- and hard-axis bias fields, and then extracted the anisotropy dispersion in the array by comparing the experimental sensitivity map to the simulated map. Through a mean-square-error-based image processing technique, we found the best match for our experimental data, and assigned a pair of dispersion numbers (anisotropy angle and anisotropy constant) to the array. By varying each of the parameters one at a time, we were able to discover the dependence of field sensitivity on magnetoresistance ratio, coercivity, and magnetic anisotropy dispersion. The effects from possible edge domains are also discussed to account for a correction term in our analysis of anisotropy angle distribution using the S-W model. We believe this model is a useful tool for monitoring the formation and evolution of anisotropy dispersion in MTJ systems, and can facilitate better design of MTJ-based devices.

Zhang, Wenzhe; Xiao, Gang; Carter, Matthew J.

2011-04-01

16

Magnetic Anisotropy of CoFeB Amorphous Nanotubes Prepared by Electroless Plating in Magnetic Field  

NASA Astrophysics Data System (ADS)

CoFeB nanotubes were fabricated by electroless plating in magnetic field using anodized aluminum oxide template, and the structural and magnetic properties of CoFeB nanotubes were investigated. It is found that some nano-scale particles form on the wall of nanotubes. Both coercivity ratio and squareness ratio of out-of-plane to in-plane are significantly changed by the applied magnetic field during electroless plating, which indicates that directional ordering in amorphous CoFeB nanotubes are achieved during electroless plating under magnetic field. The results show that the applied field impacts the magnetic anisotropy of amorphous nanotubes. The anisotropy is stronger with the magnitude of applied field increasing.

Liu, Z.; Li, W. L.; Fei, W. D.

2013-07-01

17

Analysis of the magnetic anisotropy induced by applying a magnetic field during the quenching process in amorphous ribbons  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy induced in amorphous magnetic ribbons by applying a magnetic field to the melt during the solidification process is analyzed. Using a model based on the magnetization curve and on the evolution of the uniaxial torque with the applied magnetic field, the volume fractions of the sample affected by the different magnetic anisotropies are obtained for the ribbons of composition Fe80B20 and Co70Mn5Fe1Mo1Si14B9. The results are compared with those obtained in the ribbons of the same composition but with anisotropies induced by the static magnetic annealing. From these results, the different sources of the field-quenching-induced magnetic anisotropy in those amorphous magnetic ribbons are analyzed.

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

2004-11-01

18

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

National Technical Information Service (NTIS)

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 extragal...

T. M. Venters V. Pavlidou

2012-01-01

19

CMB temperature anisotropy from broken spatial isotropy due to a homogeneous cosmological magnetic field  

SciTech Connect

We derive the cosmic microwave background temperature anisotropy two-point correlation function (including off-diagonal correlations) from broken spatial isotropy due to an arbitrarily oriented homogeneous cosmological magnetic field.

Kahniashvili, Tina [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States); Department of Physics, Laurentian University, Ramsey Lake Road, Sudbury, ON P3E 2C6 (Canada); National Abastumani Astrophysical Observatory, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Lavrelashvili, George [Department of Theoretical Physics, A. Razmadze Mathematical Institute, 1 M. Aleksidze, Tbilisi, GE-0193 (Georgia); Ratra, Bharat [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States)

2008-09-15

20

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

Microsoft Academic Search

We investigate the use of intermolecular multiple-quantum coherence to probe structural anisotropy in trabecular bone. Despite the low volume fraction of bone, the bone–water interface produces internal magnetic field gradients which modulate the dipolar field, depending on sample orientation, choice of dipolar correlation length, correlation gradient direction, and evolution time. For this system, the probing of internal magnetic field gradients

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

2005-01-01

21

Nucleation field of a soft magnetic nanotube with uniaxial anisotropy  

NASA Astrophysics Data System (ADS)

We have performed both one-dimensional variational and two-dimensional numerical calculations of the magnetic curling structure near the ends of soft magnetic nanotubes whose axes are magnetically favored, and compared the two. The variational calculation is based on the observation that the numerical simulation results for ending curling structure are similar to those for head-to-head domain walls. Except for magnetic fields opposing the average magnetization and larger than a critical value, the wall centers are outside the tube, and there is an appreciable energy barrier against penetration of the tube by the wall. The two calculations are in reasonable agreement for a range of tube dimensions and material parameters. Both predict critical fields lower than those for infinite tubes.

Usov, N. A.; Chen, A. P.; Zhukov, A.; González, J.

2008-10-01

22

Magnetic anisotropy in a permalloy microgrid fabricated by near-field optical lithography  

SciTech Connect

We report the fabrication and magnetic properties of permalloy microgrids prepared by near-field optical lithography and characterized using high-sensitivity magneto-optical Kerr effect techniques. A fourfold magnetic anisotropy induced by the grid architecture is identified. {copyright} 2001 American Institute of Physics.

Li, S. P.; Lebib, A.; Peyrade, D.; Natali, M.; Chen, Y.; Lew, W. S.; Bland, J. A. C.

2001-07-01

23

Effects of magnetic field and transverse anisotropy on full counting statistics in single-molecule magnet  

NASA Astrophysics Data System (ADS)

We have theoretically studied the full counting statistics of electron transport through a single-molecule magnet (SMM) with an arbitrary angle between the applied magnetic field and the SMM's easy axis above the sequential tunneling threshold, since the angle ? cannot be controlled in present-day SMM experiments. In the absence of the small transverse anisotropy, when the coupling of the SMM with the incident-electrode is stronger than that with the outgoing-electrode, i.e., ?L/?R>>1, the maximum peak of shot noise first increases and then decreases with increasing ? from 0 to 0.5?. In particular, the shot noise can reach up to a super-Poissonian value from a sub-Poissonian value when considering the small transverse anisotropy. For ?L/?R<<1, the maximum peaks of the shot noise and skewness can be reduced from a super-Poissonian to a sub-Poissonian value with increasing ? from 0 to 0.5? the super-Poissonian behavior of the skewness is more sensitive to the small ? than shot noise, which is suppressed when taking into account the small transverse anisotropy. These characteristics of shot noise can be qualitatively attributed to the competition between the fast and slow transport channels. The predictions regarding the ?- dependence of high order current cumulants are very interesting for a better understanding of electron transport through SMM, and will allow for experimental tests in the near future.

Xue, Hai-Bin; Nie, Y.-H.; Li, Z.-J.; Liang, J.-Q.

2011-04-01

24

Nonlinear evolution of cosmic magnetic fields and cosmic microwave background anisotropies  

NASA Astrophysics Data System (ADS)

In this work we investigate the effects of primordial magnetic fields on cosmic microwave background anisotropies (CMB). Based on cosmological magneto-hydro dynamic (MHD) simulations [R. Banerjee and K. Jedamzik, Phys. Rev. DPRVDAQ0556-2821 70, 123003 (2004).10.1103/PhysRevD.70.123003] we calculate the CMB anisotropy spectra and polarization induced by fluid fluctuations (Alfvén modes) generated by primordial magnetic fields. The strongest effect on the CMB spectra comes from the transition epoch from a turbulent regime to a viscous regime. The balance between magnetic and kinetic energy until the onset of the viscous regime provides a one to one relation between the comoving coherence length L and the comoving magnetic field strength B, such as L˜30(B/10-9Gauss)3pc. The resulting CMB temperature and polarization anisotropies for the initial power law index of the magnetic fields n>3/2 are somewhat different from the ones previously obtained by using linear perturbation theory. In particular, differences can appear on intermediate scales l<2000 and small scales l>20000. On scales l<2000 the CMB anisotropy and polarization spectra are flat in the case of our nonlinear calculations whereas the spectra have a blue index calculated with linear perturbation theory if we assume the velocity fields of baryons induced by the magnetic fields achieved Alfvén velocity due to the turbulent motions on large scales in the early universe. Our calculation gives a constraint on the magnetic field strength in the intermediate scale of CMB observations. Upper limits are set by WMAP and BOOMERANG results for comoving magnetic field strength of B<28nGauss with a comoving coherence length of L>0.7Mpc for the most extreme case, or B<30nGauss and L>0.8Mpc for the most conservative case. We may also expect higher signals on large scales of the polarization spectra compared to linear calculations. The signal may even exceed the B-mode polarization from gravitational lensing depending on the strength of the primordial magnetic fields. On very small scales, the diffusion damping scale of nonlinear calculations turns out to be much smaller than the one of linear calculations if the comoving magnetic field strength B>16nGauss. If the magnetic field strength is smaller, the diffusion scales become smaller too. Therefore we expect to have both, temperature and polarization anisotropies, even beyond l>10000 regardless of the strength of the magnetic fields. The peak values of the temperature anisotropy and the B-mode polarization spectra are approximately 40?K and a few ?K, respectively.

Tashiro, Hiroyuki; Sugiyama, Naoshi; Banerjee, Robi

2006-01-01

25

Magnetic anisotropy of chloritoid  

NASA Astrophysics Data System (ADS)

The magnetocrystalline anisotropy of monoclinic chloritoid, a relatively common mineral in aluminum-rich, metapelitic rocks, has been determined for the first time by measuring the high-field anisotropy of magnetic susceptibility (HF-AMS), using two independent approaches, i.e., (a) directional magnetic hysteresis measurements and (b) torque magnetometry, on a collection of single crystals collected from different tectonometamorphic settings worldwide. Magnetic remanence experiments show that all specimens contain ferromagnetic (s.l.) impurities, being mainly magnetite. The determined 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 degree of anisotropy 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 the AMS of siliciclastic rocks. The obtained values for the paramagnetic Curie temperature parallel (??) and perpendicular (??) to the basal plane indicate that this pronounced magnetocrystalline anisotropy is related to strong antiferromagnetic exchange interactions in the direction of the crystallographic c-axis (?? < 0) and rather weak ferromagnetic exchange interactions within the basal plane (?? > 0). As a consequence, chloritoid-bearing metapelites with a pronounced mineral alignment can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic, ferromagnetic (s.l.) minerals. The newly discovered magnetocrystalline anisotropy of chloritoid thus calls for a revised approach of magnetic fabric interpretations in chloritoid-bearing rocks.

Haerinck, Tom; Debacker, Timothy N.; Sintubin, Manuel

2013-08-01

26

Quantum teleportation via a two-qubit Heisenberg XXZ chain effects of anisotropy and magnetic field  

NASA Astrophysics Data System (ADS)

We study quantum teleportation via a two-qubit Heisenberg XXZ chain under an inhomogeneous magnetic field. We first consider entanglement teleportation, and then focus on the teleportation fidelity under different conditions. The effects of anisotropy and the magnetic field, both uniform and inhomogeneous, are discussed. We also find that, though entanglement teleportation does require an entangled quantum channel, a nonzero critical value of minimum entanglement is not always necessary.

Zhou, Y.; Zhang, G.-F.

2008-04-01

27

Effects of the magnetic field direction and anisotropy on the interband light absorption of an asymmetric quantum dot  

NASA Astrophysics Data System (ADS)

In this paper, the direct interband transition and the threshold frequency of absorption in a two-dimensional anisotropic quantum dot are studied under the influence of a tilted external magnetic field. We first calculate the analytical wave functions and energy levels using a transformation to simplify the Hamiltonian of the system. Then, we obtain the analytical expressions for the light interband absorption coefficient and the threshold frequency of absorption as a function of the magnetic field, magnetic field direction, and anisotropy of the system. According to the results obtained from the present work, we find that (i) the absorption threshold frequency (ATF) increases when the magnetic field increases for all directions. (ii) When anisotropy is increased, ATF increases. (iii) At small anisotropy, the magnetic field direction has no important effect on the ATF. In brief, the magnetic field, magnetic field direction, and anisotropy play important roles in the ATF and absorption coefficient.

Khordad, R.

2013-06-01

28

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

29

Tuning of the nucleation field in nanowires with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We report on domain nucleation in nanowires consisting of Co/Pt multilayers with perpendicular magnetic anisotropy that are patterned by electron-beam lithography, sputter deposition, and lift-off processing. It is found that the nucleation field can be tuned by changing the geometry of the wire ends. A reduction of the nucleation field by up to 60% is achieved when the wire ends are designed as tips. This contrasts with the behavior of wires with in-plane anisotropy where the nucleation field increases when triangular-pointed ends are used. In order to clarify the origin of the reduction of the nucleation field, micromagnetic simulations are employed. The effect cannot be explained by the lateral geometrical variation but is attributable to a local reduction of the perpendicular anisotropy caused by shadowing effects due to the resist mask during sputter deposition of the multilayer.

Kimling, Judith; Gerhardt, Theo; Kobs, André; Vogel, Andreas; Wintz, Sebastian; Im, Mi-Young; Fischer, Peter; Peter Oepen, Hans; Merkt, Ulrich; Meier, Guido

2013-04-01

30

Anisotropy of the magnetic and magnetooptic properties of HoIG:Al single crystals (low and high magnetic field)  

Microsoft Academic Search

Magnetization and Faraday rotation measurements at 1152 nm have been performed on Ho3Fe5?zAlzO12 (z=0.45) single crystals as a function of temperature and magnetic field oriented along the 3 crystallographic axes [100], [110], and [111] in both experiments. A strong anisotropy is observed at low temperature (T<100 K), although the Faraday susceptibility remains anisotropic until Tcomp=185 K. High field magnetization measurements

J. Ostoréro; M. Guillot

1994-01-01

31

Montmorillonite alignment induced by magnetic field: Evidence based on the diffusion anisotropy of water molecules  

Microsoft Academic Search

Diffusion coefficients of water in Na-montmorillonite (Na-mon) suspensions have been determined by pulsed-field gradient spin–echo (PGSE) NMR spectroscopy for three directions (x, y, and z), where x and y mean the directions perpendicular to the static magnetic field, and z the direction parallel to it. Diffusion anisotropy was observed in the suspensions with Na-mon weight fractions of 0.63, 1.82, and

Takafumi Takahashi; Takahiro Ohkubo; Yasuhisa Ikeda

2006-01-01

32

Effect of perpendicular uniaxial anisotropy on the annihilation fields of magnetic vortices  

NASA Astrophysics Data System (ADS)

The magnetization reversal in several nanoscopic systems is driven by the nucleation and propagation of a vortex structure that is very sensitive to the application of a magnetic field or a spin polarized current. In particular in a dot, the vortex profile is strongly affected by anisotropy, however, its role on the core behavior has not been clarified. In the present work, we investigate the influence of a perpendicular anisotropy on the annihilation and shape of magnetic vortex cores in permalloy disks. We used both micromagnetic simulations with the OOMMF code, and the analytical rigid core model that assumes that the shape of the core does not change during the hysteresis cycle. Under both approaches, the annihilation field decreases with increasing perpendicular anisotropy for almost all the structures investigated. Also a deformation of the vortex core profile is evidenced from the micromagnetic simulations, for larger anisotropy and/or dot thickness. For every dot thickness, this change does not depend on the dot radius, but on the relative distance of the core from the center of the dot.

Novais, E. R. P.; Allende, S.; Altbir, D.; Landeros, P.; Garcia, F.; Guimara~es, A. P.

2013-10-01

33

Factors determining the magnetic field generated by a solenoid made with a superconductor having critical current anisotropy  

Microsoft Academic Search

The magnetic field generation in a simple solenoid is reconsidered for the case where the magnetic field is generated by a superconductor with anisotropy in its critical current density. In this case the influence of the radial magnetic field at the solenoid ends on the weak direction of the conductor has to be taken into account. Instead of the usual

M. Däumling; R. Flükiger

1995-01-01

34

Magnetic anisotropy of Fe6 and Fe10 molecular rings by cantilever torque magnetometry in high magnetic fields  

NASA Astrophysics Data System (ADS)

We studied the magnetic anisotropy of two molecular magnets, Fe6 and Fe10, which comprise six- and ten-membered rings of antiferromagnetically coupled iron (III) ions (Si=52), respectively. Spin-flip transitions induced by the applied magnetic field (up to 23 T) were investigated by cantilever torque magnetometry on microgram single crystals at very low temperature (down to 0.45 K). From the sharp, steplike variations of magnetic anisotropy at the transition fields, we determined the singlet-triplet energy gap (?1) and the axial zero-field splitting parameter (D1) for the triplet state of Fe6 [?1=15.28(1) cm-1, D1=4.32(3) cm-1] and Fe10 [?1=4.479(4) cm-1, D1=2.24(2) cm-1]. By analyzing the additional steps observed in the Fe10 sample, we evaluated the ?S and DS parameters for the total-spin multiplets with S up to 5. On the basis of our findings, we discuss the origin of magnetic anisotropy in iron (III) rings and the application of torque magnetometry to the study of field induced level crossing in molecular magnets.

Cornia, A.; Jansen, A. G. M.; Affronte, M.

1999-11-01

35

Field-induced magnetic anisotropy in La0.7Sr0.3CoO3  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy has been measured for the ferromagnetic La0.7Sr0.3CoO3 perovskite from an analysis of the high-field part of the magnetization vs. field curves, i.e., the magnetic saturation regime. These measurements give a magnetic anistropy one order of magnitude higher than that of reference manganites. Surprisingly, the values of the magnetic anisotropy calculated in this way do not coincide with those estimated from measurements of coercive fields which are one order of magnitude smaller. It is proposed that the reason of this anomalous behaviour is a transition of the trivalent Co ions under the external magnetic field from a low-spin to an intermediate-spin state. Such a transition converts the Co3+ ions into Jahn-Teller ions having an only partially quenched orbital angular momentum, which enhances the intra-atomic spin-orbit coupling and magnetic anisotropy.

Mira, J.; Rivas, J.; Vázquez, M.; Ibarra, M. R.; Caciuffo, R.; Señarís Rodríguez, M. A.

2003-05-01

36

Enhancing weak magnetic fabrics using field-impressed anisotropy: application to the Chinese loess  

NASA Astrophysics Data System (ADS)

The anisotropy of the low-field magnetic susceptibility (AMS), alternating-field-treated AMS (AF-AMS), and anisotropy of anhysteretic remanent magnetization (AARM) have been systematically examined for a sandwich sequence of loess/palaeosols crossing the upper loess unit L2 (Marine Oxygen Isotope Stage 6, MIS6) to the last interglacial maximum (palaeosol unit S1S3, MIS5e) from the Yuanbao section, northwestern China. Results show that a weak, but detectable, magnetic lineation is controlled by coarse-grained aeolian Fe3O4 (magnetite). Because the long axes of the coarse-grained magnetites are statistically parallel to the palaeowind directions, the declination of the maximum susceptibility principal axis of AMS can be used as an indicator of palaeowind direction. In contrast, fine-grained pedogenic magnetic particles are responsible for the magnetic foliation. We found that AF-AMS can indicate the domain state of the magnetic particles, which is consistent with Potter & Stephenson's earlier model. We also found that AF demagnetization can significantly alter the AMS. In conclusion, the angular dependence of AF-AMS can enhance the weak AMS fabrics.

Liu, Qingsong; Yu, Yongjae; Deng, Chenglong; Pan, Yongxin; Zhu, Rixiang

2005-08-01

37

Magnetic multilayer interface anisotropy  

NASA Astrophysics Data System (ADS)

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 transition temperature.

Pechan, M. J.

38

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

39

Changes in mean magnetic susceptibility and its anisotropy of rock samples as a result of alternating field demagnetization  

Microsoft Academic Search

Measurements of low-field magnetic susceptibility (K) and its anisotropy (AMS) on different rock types during stepwise alternating field (AF) demagnetization in increasing fields revealed not only significant changes of the AMS principal susceptibilities, but also an increase of the mean magnetic susceptibility (Km). Studied collections of loess\\/paleosol samples from different sections in Belgium, Bulgaria, China, Siberia and Tadjikistan and diorites,

Diana Jordanova; Neli Jordanova; Bernard Henry; Jozef Hus; Jérôme Bascou; Minoru Funaki; Dimo Dimov

2007-01-01

40

Temperature dependence of magnetic anisotropy in Ni-Mn-Ga alloys exhibiting giant field-induced strain  

NASA Astrophysics Data System (ADS)

Temperature dependence of structure and magnetic anisotropy of single crystalline Ni48.8Mn28.6Ga22.6 alloy exhibiting giant field-induced strain or magnetic shape memory (MSM) effect was studied in the temperature range 80-420 K. Upon cooling the alloy transforms from cubic austenite at 307 K to the martensite which exhibits five-layered (modulated) tetragonal structure (5M) with a=0.595 nm and c=0.559 nm. Reverse transformation occurs at 317 K. An additional intermartensitic transition takes place at about 95 K. The basic mechanism of the MSM effect was corroborated by direct simultaneous measurements of strain and magnetization as a function of magnetic field. The magnetic anisotropy of the martensite exhibiting the giant strain was determined from the magnetization curves measured by a vibrating sample magnetometer at different temperatures. The anisotropy of the single variant 5M martensite is uniaxial with easy axis along the tetragonal c axis. The first magnetic anisotropy constant is Ku1=2.0×105 J/m3 at 283 K and increase to Ku1=2.65×105 J/m3 at 130 K. Above room temperature the anisotropy steeply decreases. The second anisotropy constant is negligible and less than 4% of the first anisotropy constant.

Heczko, Oleg; Straka, Ladislav; Lanska, Natalyia; Ullakko, Kari; Enkovaara, Jussi

2002-05-01

41

Power Anisotropy in the Magnetic Field Power Spectral Tensor of Solar Wind Turbulence  

NASA Astrophysics Data System (ADS)

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 (? B ) and the angle of the vector in the plane perpendicular to the velocity (phi 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, ? B , phi B ) based on a scalar field description of turbulence theory. This allows us to predict the variation in the phi 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.; Forman, M. A.; Horbury, T. S.; Oughton, S.

2012-02-01

42

Effects of skeletal muscle anisotropy on human organ dosimetry under 60 Hz uniform magnetic field exposure  

NASA Astrophysics Data System (ADS)

The recent development of anatomically derived high-resolution voxel-based models of the human body suitable for electromagnetic modelling, and of effective methods for computing the associated induction, has resulted in numerical estimates of organ-specific dosimetry for human exposure to low-frequency magnetic fields. However, these estimates have used an isotropic conductivity model for all body components. More realistic estimates should account for the anisotropy of certain tissues, particularly skeletal muscle. In this work, high-resolution finite-difference computations of induced fields are used to estimate the effects of several extremal realizations of skeletal muscle anisotropy on field levels in various organs. It is shown that, under the present assumptions (anisotropy ratios up to 3.5:1), the resulting dosimetric values can vary by factors of between two or three for tissues other than muscle and up to 5.4 for muscle, despite the unchanged nature of the conductivity model used for all other body components.

Dawson, Trevor W.; Stuchly, Maria A.

1998-05-01

43

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 transition temperature. During the next project period 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.

Pechan, M.J.

1990-01-01

44

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

45

Anisotropy of exciton spectrum and spin-orbit interactions in quantum wells in tilted magnetic field  

NASA Astrophysics Data System (ADS)

We study theoretically excitonic energy spectrum and optical absorption in narrowgap semiconductor quantum wells in strong magnetic field. We show that, in the presence of an in-plane field component, the absorption coefficient exhibit a double-peak structure due to hybridization of bright and dark excitons. If both Rashba and Dresselhaus spin-orbit terms are present, the spectrum is anisotropic in in-plane field orientation with respect to [100] axis. In particular, the magnitude of the splitting can be tuned in a wide interval by varying the azimuthal angle of the in-plane field. The absorption spectrrum anisotropy would allow simultaneous measurement Dresselhaus and Rashba spin-orbit coefficients.

Olendski, Oleg; Shahbazyan, Tigran V.

2006-05-01

46

Field Anisotropy of the Pseudogap State in Bi2Sr2CaCu2O8+y Ultrahigh Magnetic Fields  

NASA Astrophysics Data System (ADS)

The orientational anisotropy of the pseudogap closing field Hpg is investigated in magnetic fields up to 60 T applied parallel (||ab) and normal (||c) to CuO2 planes in Bi2Sr2CaCu2O8+y. We find that, in contrast to large field anisotropy related to the orbital motion of Cooper pairs below the upper critical field Hc2, the temperature-independent and small anisotropy of Hpg is due to anisotropy of the g-factor: g\\|c/g\\|ab=Hpg\\|ab/Hpg\\|c, indicating correlations only in the spin-channel.

Krusin-Elbaum, L.; Shibauchi, T.; Mielke, C. H.

47

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

48

Electric-field control of the magnetic anisotropy in an ultrathin (Ga,Mn)As/(Ga,Mn)(As,P) bilayer  

NASA Astrophysics Data System (ADS)

We report on the electric control of the magnetic anisotropy in an ultrathin ferromagnetic (Ga,Mn)As/(Ga,Mn)(As,P) bilayer with competing in-plane and out-of-plane anisotropies. The carrier distribution and therefore the strength of the effective anisotropy are controlled by the gate voltage of a field effect device. Anomalous Hall effect measurements confirm that a depletion of carriers in the upper (Ga,Mn)As layer results in the decrease of the in-plane anisotropy. The uniaxial anisotropy field is found to decrease by a factor ~4 over the explored gate-voltage range so that the transition to an out-of-plane easy-axis configuration is almost reached.

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

2013-03-01

49

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

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

50

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

51

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

52

Effect of residual strain in Fe-based amorphous alloys on field induced magnetic anisotropy and domain structure  

NASA Astrophysics Data System (ADS)

Field induced magnetic anisotropy in two Fe-based amorphous alloys with different saturation induction levels (1.56 T and 1.64 T) was investigated by varying magnetic field strength and annealing temperature and domain images were taken on these samples. Residual strain was evaluated by measuring coercivities of the materials after stress-relief annealing. These results are discussed, clarifying the difference between the two Fe-based amorphous alloys.

Azuma, Daichi; Hasegawa, Ryusuke; Saito, Shin; Takahashi, Migaku

2013-05-01

53

Susceptibility Anisotropy in an Iron Arsenide Superconductor Revealed by X-Ray Diffraction in Pulsed Magnetic Fields  

NASA Astrophysics Data System (ADS)

In addition to unconventional high-Tc superconductivity, the iron arsenides exhibit strong magnetoelastic coupling and a notable electronic anisotropy within the a-b plane. We relate these properties by studying underdoped Ba(Fe1-xCox)2As2 by x-ray diffraction in pulsed magnetic fields up to 27.5 T. We exploit magnetic detwinning effects to demonstrate anisotropy in the in-plane susceptibility, which develops at the structural phase transition despite the absence of magnetic order. The degree of detwinning increases smoothly with decreasing temperature, and a single-domain condition is realized over a range of field and temperature. At low temperatures we observe an activated behavior, with a large hysteretic remnant effect. Detwinning was not observed within the superconducting phase for accessible magnetic fields.

Ruff, J. P. C.; Chu, J.-H.; Kuo, H.-H.; Das, R. K.; Nojiri, H.; Fisher, I. R.; Islam, Z.

2012-07-01

54

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

NASA Astrophysics Data System (ADS)

FeCoB layers prepared on Ru underlayer possess a high saturation magnetization Ms and a high in-plane magnetic anisotropy filed Hk. 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 Hk 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 Hk of 500 Oe.

Hirata, Ken-Ichiro; Hashimoto, Atsuto; Matsuu, Toshimitsu; Nakagawa, Shigeki

2009-04-01

55

Magnetic anisotropy data of CHP  

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.

56

Field-induced slow magnetic relaxation in a six-coordinate mononuclear cobalt(II) complex with a positive anisotropy.  

PubMed

The novel mononuclear Co(II) complex cis-[Co(II)(dmphen)(2)(NCS)(2)]·0.25EtOH (1) (dmphen = 2,9-dimethyl-1,10-phenanthroline) features a highly rhombically distorted octahedral environment that is responsible for the strong positive axial and rhombic magnetic anisotropy of the high-spin Co(II) ion (D = +98 cm(-1) and E = +8.4 cm(-1)). Slow magnetic relaxation effects were observed for 1 in the presence of a dc magnetic field, constituting the first example of field-induced single-molecule magnet behavior in a mononuclear six-coordinate Co(II) complex with a transverse anisotropy energy barrier. PMID:22963111

Vallejo, Julia; Castro, Isabel; Ruiz-García, Rafael; Cano, Joan; Julve, Miguel; Lloret, Francesc; De Munno, Giovanni; Wernsdorfer, Wolfgang; Pardo, Emilio

2012-09-14

57

Magnetic anisotropy and crystalline electric field effects in RRh{sub 4}B{sub 4} single crystals.  

SciTech Connect

Research on polycrystalline RRh{sub 4}B{sub 4} samples has shown that crystalline electric field (CEF) effects play an important role in these compounds. The successful synthesis of single crystal samples of RRh{sub 4}B{sub 4} with R = Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu has provided an opportunity to further investigate CEF effects in these materials. Magnetization and magnetic susceptibility measurements on the RRh{sub 4}B{sub 4} single crystals revealed strong magnetic anisotropy, and the experimental results could be described well by CEF calculations based on the parameters derived from an analysis of experimental data for ErRh{sub 4}B{sub 4} single crystals. The easy directions of magnetization of these compounds are consistent with the signs of the Stevens factor {alpha}J of the CEF Hamiltonian. A strong influence of magnetic anisotropy on superconductivity was also observed.

Zhou, H.; Lambert, S. E.; Maple, M. B.; Dunlap, B. D.; Materials Science Division; Univ. of California at San Diego

2009-08-01

58

A new magnetic anisotropy  

Microsoft Academic Search

A new discovery has been made in the field of magnetic materials that manifests itself in the form of a displaced hysteresis loop. In addition, although from the same basic phenomena, the magnetic material has only one stable orientation in a magnetic field. In particular, it can be turned through 180° and it will still return to its original orientation.

William H. Meiklejohn; Charles P. Bean

2001-01-01

59

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

60

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

2013-10-15

61

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

62

Magnetic anisotropy in (Ga,Mn)As grown on vicinal GaAs: Effects of the orientation of microwave magnetic field  

SciTech Connect

Ferromagnetic resonance (FMR) study of the magnetic anisotropy in epitaxial (Ga,Mn)As grown on vicinal GaAs is presented. The data collected in the growth plane reveal very limited dependence on the miscut angle {eta}, with a negligible effect of {eta} on the in-plane uniaxial anisotropy. In the out-of-plane configuration, the substrate misorientation has a pronounced influence on FMR, which features are partially explained with a phenomenological treatment of the atomic step-induced anisotropy. This simple model, however, does not account for the miscut-induced dependence of FMR on the orientation of microwave magnetic field, that is observed with the static field applied invariably along the growth direction.

Dziatkowski, K. [Institute of Experimental Physics, University of Warsaw, 00-681 Warsaw (Poland); Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States); Liu, X.; Furdyna, J. K. [Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Twardowski, A. [Institute of Experimental Physics, University of Warsaw, 00-681 Warsaw (Poland)

2011-04-01

63

Anisotropy and symmetry of fluctuations in the solar wind magnetic field and velocity  

NASA Astrophysics Data System (ADS)

The behavior of correlation tensors of fluctuations in the solar wind magnetic field and velocity is studied during different phases of a solar cycle on the basis of a 45-year measurement series of solar wind parameters. It is found that the orientation of fluctuations in the magnetic field and velocity is approximately axisymmetric relative to the direction of a local magnetic field during high solar activity. This symmetry is violated significantly during periods of low solar activity, and deviations from the symmetry are regular and oppositely directed during minima of even and odd 11-year cycles, which is probably connected with variations in the orientation of the Sun's magnetic field. The dependence of the power of fluctuations on the local magnetic field direction reveals significant deviations from local symmetry during all phases of a solar cycle, especially for velocity fluctuations.

Erofeev, D. V.

2012-12-01

64

Critical current anisotropy in Ag\\/(Pb,Bi)2Sr2Ca2Cu3O10+x multifilamentary tapes: influence of self-magnetic field  

Microsoft Academic Search

Two factors affect critical current anisotropy in multifilamentary Ag\\/(Pb,Bi)2Sr2Ca2Cu3O10+x tapes - the intrinsic material anisotropy and the geometry. Experimental results on the magnetic field dependence and anisotropy of the critical current in a multifilamentary Ag\\/(Pb,Bi)2Sr2Ca2Cu3O10+x tape after correction for self-magnetic field effects were found to fit the anisotropic Kim relation. Based on this relation a finite-element-method numerical code for solving

M. Majoros; B. A. Glowacki; A. M. Campbell

2001-01-01

65

Effect of anisotropy in magnetic nanotubes  

NASA Astrophysics Data System (ADS)

Analytical expressions for the total magnetic energy of two characteristic internal configurations of nanometric tubes are calculated. A magnetic phase diagram with respect to the aspect ratio of the tubes is obtained considering anisotropy properties of four materials: iron, cobalt, permalloy and nickel. Conditions for low/high coercive field are discussed.

Escrig, J.; Landeros, P.; Altbir, D.; Vogel, E. E.

2007-03-01

66

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

NASA Astrophysics Data System (ADS)

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

Jedamzik, Karsten; Abel, Tom

2013-10-01

67

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

68

Analysis of the Magnetic Susceptibility Anisotropy of the Cantera Ignimbrite, San Luis Potosé­ Volcanic field, Mexico  

NASA Astrophysics Data System (ADS)

Anisotropy of Magnetic Susceptibility (AMS) results from a group of 17 - 18 sites (286 - 312 specimens) from the Cantera Ignimbrite - of Oligocene age and part of the San Luis Potosí Volcanic Filed (SLPVF), México - are presented and analysed in order to help to determine the source and flow directions. In each site a flow direction is inferred based on AMS results. As the Cantera Ignimbrite is generally dipping, AMS was structural corrected. So two sets of geographical and paleo-geographical (structural corrected) inferred-flow directions were obtained. Both sets are analysed trying to define if the source of the ignimbrite is related to a calderic (concentric structure) or to the NW-SE faulting and jointing. Geographical AMS results mostly give SW flow directions, the southernmost sites give to SSE. Meanwhile structural corrected results give a wider range of flow directions, a group of them to NW and another northerly group mostly to NE. AMS was measured in a KLY2 appliance, Jelinek and other statistics and density distributions were performed, giving all very similar results in each site. Mean susceptibilities range from 147 to 27200 x10-6 SI (average = 5713 x10-6 SI). Anisotropy degree (Pj) range from 1.011 to 1.055 with two sites of 1.134-1.254 (Pj average = 1.046). Shape is mostly oblate ranging the T-factor from 0.843 to 0.409 and only one site mainly prolate: T of -0.277 (T average = 0.550).

Caballero, C.; Torres-Hernandez, J.; Alva-Valdivia, L. M.

2007-05-01

69

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

70

Uniaxial anisotropy and novel magnetic behaviors of CoFe2O4 nanoparticles prepared in a magnetic field  

NASA Astrophysics Data System (ADS)

CoFe2O4 nanoparticles prepared by chemical coprecipitation method in a magnetic field exhibit novel magnetic properties. The average particle diameter was about 2 nm and larger depending on the post annealing temperature. Magnetization measurements indicate that smaller nanoparticles are superparamagnetic above their respective blocking temperatures. In the blocked state, these nanoparticles exhibit interesting behaviors in the magnetic hysteresis measurements. Constricted, or wasp waisted with extremely narrow waist, hysteresis curves have been observed in the magnetization versus field sweeps. For larger nanoparticles, the room temperature hysteresis is typical of a ferromagnet with an open loop, but the loop closes at lower temperature. The novel magnetic behavior is attributed to the directional order of Co ions and vacancies in CoFe2O4 established during the coprecipitation of the nanoparticles under an applied field.

Gao, Qian; Hong, Guangyan; Ni, Jiazuan; Wang, Wendong; Tang, Jinke; He, Jibao

2009-04-01

71

Electric-poling-induced magnetic anisotropy and electric-field-induced magnetization reorientation in magnetoelectric Ni/(011) [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x heterostructure  

NASA Astrophysics Data System (ADS)

This study reports the influence of poling a PMN-PT single crystal laminated structure on the magnetic properties of a 35 nm polycrystalline Ni thin film. During the poling process, a large anisotropic remanent strain is developed in the PMN-PT that is transferred to the ferromagnetic film creating a large predefined magnetic anisotropy. Test results show that operating the PMN-PT substrate in the linear regime following poling produces sufficient anisotropic strain to reversibly reorient the magnetization toward an easy axis oriented 90° to the magnetic easy axis induced during poling. The influence of poling prestress on the magnetic anisotropy field, coercive field and magnetic remanence is discussed.

Wu, Tao; Bur, Alexandre; Wong, Kin; Leon Hockel, Joshua; Hsu, Chin-Jui; Kim, Hyungsuk K. D.; Wang, Kang L.; Carman, Gregory P.

2011-04-01

72

Anisotropy of Iron-Series Permanent Magnets  

NASA Astrophysics Data System (ADS)

Element-strategic considerations have sparked renewed interest in rare-earth-free permanent magnets, but the prediction of the magnetocrystalline anisotropy from the atomic structure is still in its infancy, and there are no rules predicting the d anisotropy as function of the atomic structure. We have obtained tight-binding estimates for a variety of clusters and etxtended structures of different symmetry and d-band filling. A expected, the anisotropy strongly oscillates as a function of the d-band filling. Our calculations indicate that nearly filled d bands tend to yield anisotropy parallel to the pair axis. Sites with trigonal symmetry support bigger anisotropies than cubic and tetragonal environments, but this is a crystal- field effect similar to that in BaFe12O19 rather than a band-structure effect. Shape anisotropy is important in alnico- type nanostructured permanent magnets. We find a maximum of the energy product as a function of packing fraction, namely a maximum value of ?oMs^2/12 realized at a volume fraction of 2/3. For Fe65Co35, this yields an upper limit of 390 kJ/m^3 [49 MGOe].

Skomski, Ralph; Hadjipanayis, G. C.; Sellmyer, D. J.

2010-03-01

73

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

74

Magnetic anisotropy of strained epitaxial manganite films  

NASA Astrophysics Data System (ADS)

The in-plane magnetic anisotropy of epitaxial La0.7Sr0.3MnO3 (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 NdGaO3 (NGO) substrates in which the (110)NGO plane is tilted at an angle of 0-25.7° 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)SrTiO3, and (001)[(LaAlO3)0.3 + (Sr2AlTaO6)0.7] substrates are compared.

Demidov, V. V.; Borisenko, I. V.; Klimov, A. A.; Ovsyannikov, G. A.; Petrzhik, A. M.; Nikitov, S. A.

2011-05-01

75

Magnetic anisotropy in nanostructured gadolinium  

NASA Astrophysics Data System (ADS)

This experimental work evaluates the magnetic response of 25-nm-thick Gd thin film and 1400 × 70 × 50 nm3 Gd nanobar structures. Neither the thin film nor the nanobars exhibited single domain behavior at temperatures down to 53 K. The Gd thin film exhibited a magnetocrystalline anisotropy induced spin-reorientation due to a hexagonal close-packed (002) texture, something different from that previously reported on epitaxial Gd thin film. The discrepancy is due to grain boundary induced spin-disorder in the nanosacle. The Gd nanobars had a saturation magnetization 75% smaller than the thin film or bulk and is attributed to oxidation as well as the crystallinity changes from hexagonal close-packed to face-centered cubic caused by stress induced stacking faults. These experimental results for both thin film and nanobar show that the crystallinity has a substantial impact to the magnetic anisotropy of Gd nanostructures as well as the formation of single domain structures.

Hsu, Chin-Jui; Prikhodko, Sergey V.; Wang, Chiu-Yen; Chen, Lih-Juann; Carman, Gregory P.

2012-03-01

76

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

77

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

78

Enhancement of GMI effect in magnetic microwires through the relative temperature dependence of magnetization and anisotropy  

Microsoft Academic Search

We present the study of Giant Magneto Impedance (GMI) effect in magnetic microwires with zero magnetostriction. It is shown that the temperature response of GMI effect can be enhanced by 80% through the relative temperature dependence of magnetization and anisotropy. However, such effect appears only for low amplitudes of exciting current that induces exciting magnetic field below the anisotropy field

J. D. Santos; R. Varga; B. Hernando; A. Zhukov

2009-01-01

79

Magnetic anisotropy of ferrosmectic phases  

NASA Astrophysics Data System (ADS)

A new anisotropic magnetic fluid, called ferrosmectic, is obtained when using a colloidal suspension of submicronic magnetic particles (ferrofluid), as a component in a smectic phase of fluid membranes. These lamellar phases present specific magnetic properties. The anisotropy of their magnetic susceptilities as a function of particles concentration is studied and interpreted : a microscopic mechanism involving a steric hindrance between particles and membranes is used to understand the experimental results. Un nouveau fluide magnétique anisotrope, appelé ferrosmectique, est obtenu lorsque nous utilisons un ferrofluide, c'est-à-dire une suspension colloïdale de particules magnétiques de taille inférieure au micron, comme composant dans la fabrication d'une phase smectique de membranes fluides. Ces phases adoptent des comportements spécifiques sous champ magnétique, et nous présentons ici une étude de l'anisotropie de leur susceptibilité magnétique en fonction de la concentration en particules. Nous interprétons les résultats obtenus par un mécanisme microscopique basé sur l'existence d'une gêne stérique entre membranes et particules.

Ponsinet, Virginie; Fabre, Pascale; Veyssié, Madeleine; Cabanel, Régis

1994-10-01

80

Jc anisotropy for magnetic field angle in YBCO coated conductor on IBAD-MgO buffered metal tapes  

NASA Astrophysics Data System (ADS)

We found that YBCO films deposited by the controlled process showed improved superconducting properties in magnetic fields, even without any artificial pinning centers such as BaZrO3 and BaSnO3. The YBCO films with a thickness of 450 nm were deposited on hastelloy tapes with a textured MgO buffer deposited by IBAD (Ion Beam Assist Deposition) method (IBAD-MgO) by PLD method. In the YBCO films on the IBAD-MgO (IBAD-YBCO), the critical current density of 2.9 MA/cm2 at 77 K in self-field and the ratio of Jc(B//c)/Jc(B//a, b) at 1 T was almost unity. Furthermore, we found that the Jc anisotropy changed with surface morphology on underlying buffer layer and YBCO thickness. This means that some c-axis correlated pinning centers are included in the films. From the cross-sectional TEM images of the IBAD-YBCO, there were not so many defects such as dislocations, Y2O3 inclusions and so on. Thus it is considered that some defects such as oxygen heterogeneity, displacement of a local composition and so on are pinning centers, although such defects can not be detected by a present analytical technique.

Suzuki, H.; Yoshida, Y.; Ichino, Y.; Takai, Y.; Awaji, S.; Watanabe, K.; Yoshizumi, M.; Izumi, T.; Shiohara, Y.; Kato, T.

2010-11-01

81

Advanced magnetic anisotropy determination through isothermal remanent magnetization of nanoparticles  

NASA Astrophysics Data System (ADS)

We propose a theoretical framework enabling the simulation of isothermal remanence magnetization (IRM) curves, based on the Stoner-Wohlfarth model combined with the Néel macrospin relaxation time description. We show how low temperature IRM curves, which have many advantages compared to hysteresis loops, can be efficiently computed for realistic assemblies of magnetic particles with both a size and anisotropy constant distribution, and a biaxial anisotropy. The IRM curves, which probe the irreversible switching provoked by an applied field, are shown to be complementary to other usual measurements (in particular low-field susceptibility curves where a thermal switching is involved). As an application, the experimental IRM curve of Co clusters embedded in a carbon matrix is analyzed. We demonstrate how powerful such an analysis can be, which in the present case allows us to put into evidence an anisotropy constant dispersion among the Co nanoparticles.

Hillion, A.; Tamion, A.; Tournus, F.; Gaier, O.; Bonet, E.; Albin, C.; Dupuis, V.

2013-09-01

82

Magnetic Anisotropy in the Radula of Chiton  

NASA Astrophysics Data System (ADS)

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

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

2000-07-01

83

Role of the Fermi-surface anisotropy in angle-dependent magnetic-field oscillations for identifying the energy-gap anisotropy of A(y)Fe(2)Se(2) superconductors.  

PubMed

We present a numerical study of the field-angle resolved oscillations of the thermal conductivity and specific heat under a rotated magnetic field in the A(y)Fe(2-x)Se(2) [A = K, Rb, Cs, (Tl, K)] superconductors, using realistic two-band Fermi surface parametrization. Our key finding is that even for isotropic pairing on an anisotropic Fermi surface, the thermodynamic quantities exhibit substantial oscillatory behavior in the superconducting state, even much below the upper critical field. Furthermore, in multiband systems the competition of anisotropies between two Fermi surfaces can cause a double sign reversal of oscillations as a function of temperature, irrespective of gap anisotropy. Our findings put severe constraints on simple interpretations of field-angle resolved measurements widely used to identify the angular structure of the superconducting gap. PMID:23215321

Das, Tanmoy; Vorontsov, Anton B; Vekhter, Ilya; Graf, Matthias J

2012-11-02

84

Role of the Fermi-Surface Anisotropy in Angle-Dependent Magnetic-Field Oscillations for Identifying the Energy-Gap Anisotropy of AyFe2Se2 Superconductors  

NASA Astrophysics Data System (ADS)

We present a numerical study of the field-angle resolved oscillations of the thermal conductivity and specific heat under a rotated magnetic field in the AyFe2-xSe2 [A=K, Rb, Cs, (Tl, K)] superconductors, using realistic two-band Fermi surface parametrization. Our key finding is that even for isotropic pairing on an anisotropic Fermi surface, the thermodynamic quantities exhibit substantial oscillatory behavior in the superconducting state, even much below the upper critical field. Furthermore, in multiband systems the competition of anisotropies between two Fermi surfaces can cause a double sign reversal of oscillations as a function of temperature, irrespective of gap anisotropy. Our findings put severe constraints on simple interpretations of field-angle resolved measurements widely used to identify the angular structure of the superconducting gap.

Das, Tanmoy; Vorontsov, Anton B.; Vekhter, Ilya; Graf, Matthias J.

2012-11-01

85

A simple experiment for determination of magnetic anisotropy  

NASA Astrophysics Data System (ADS)

While experiments involving measurements of magnetic susceptibility in undergraduate laboratories are quite common, it is perhaps not fully appreciated that the anisotropy of magnetic susceptibility can be measured with the use of a small magnet, a microscope, and a stopwatch. This problem is discussed in relation to an illustrative example which involves the orientation of sickle cells in the magnetic field.

Ribeiro, P. Costa; Bemski, G.; Davidovich, M. A.; Wajnberg, E.

1983-01-01

86

Determination of magnetic anisotropy of magnetically hard materials  

SciTech Connect

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

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

1990-03-15

87

The Effects of Plasma Beta and Anisotropy Instabilities on the Dynamics of Reconnecting Magnetic Fields in the Heliosheath  

NASA Astrophysics Data System (ADS)

The plasma ? (the ratio of the plasma pressure to the magnetic pressure) of a system can have a large effect on its dynamics as high ? enhances the effects of pressure anisotropies. We investigate the effects of ? 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 ?. At low ?, growing magnetic islands are modestly elongated and become round as contraction releases magnetic stress and reduces magnetic energy. At high ?, 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 ? 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-? systems such as astrophysical accretion flows and the magnetosphere of Saturn.

Schoeffler, K. M.; Drake, J. F.; Swisdak, M.

2011-12-01

88

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

89

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

90

Goldanskii-Karyagin effect and external magnetic field method as tools to measure anisotropy of the recoilless fraction in amorphous materials  

Microsoft Academic Search

Diffraction of X-rays or neutrons can not be used to obtain details about the atomic vibrational anisotropy in the case of amorphous materials due to the lack of well-defined Bragg reflections. Mössbauer spectroscopy can yield some information in such cases, either via the Goldanskii-Karyagin effect or by applying a magnetic field, preferably along the beam axis. The latter method can

K. Ruebenbauer; B. Sepiol

1985-01-01

91

Relationship between the intrinsic thermal switching field at 10 -9 s and the anisotropy field in magnetic recording media  

Microsoft Academic Search

Recently, the time dependent remanent coercivity, HCR(t), has become a major concern in new high density recording media where the coercivity at 1 ns can be ~50% larger than that measured at 100 s. To combat this problem, an increase in the anisotropy has typically been used to make the media more thermally stable. However, the effect of increasing the

S. M. Stinnett; W. D. Doyle

2000-01-01

92

Anisotropy of the Taylor scale and the correlation scale in plasma sheet and solar wind magnetic field fluctuations  

Microsoft Academic Search

Magnetic field data from nine spacecraft in the magnetospheric plasma sheet and the solar wind are employed to determine the correlation scale and the magnetic Taylor microscale from simultaneous multiple-point measurements for multiple intervals with a range of mean magnetic field directions. We have determined that in the solar wind the Taylor scale is independent of direction relative to the

James M. Weygand; W. H. Matthaeus; S. Dasso; M. G. Kivelson; L. M. Kistler; C. Mouikis

2009-01-01

93

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

94

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

95

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

96

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

97

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

98

Novel magnetization processes in ferrimagnetic multilayers with random anisotropy  

NASA Astrophysics Data System (ADS)

We carried out a numerical study of magnetization processes in ferrimagnetic multilayers in the presence of pinning forces acting on one of the magnetic components. The multilayers consist of an alternation of two ferromagnetic materials (M and T) which are assumed antiferromagnetically coupled through the interfaces (as in Fe/Tb multilayers for instance). A random anisotropy field acts on the magnetization of material T. The reversal of the magnetization of the multilayers when the applied field is swept from positive saturation to negative saturation is characterized by a competition between coherent rotation and nucleation-propagation mechanisms. In this competition the rotational hysteresis induced by the random anisotropy on the magnetization of material T plays a crucial role. Very original features have been observed in the magnetization processes of these systems such as crossed hysteresis loops with a negative remanent magnetization. An overview of these magnetization processes below and above the compensation temperature is given in this paper.

Dieny, B.; Ribas, R.; Barbara, B.

1994-02-01

99

Combined effect of demagnetizing field and induced magnetic anisotropy on the magnetic properties of manganese-zinc ferrite composites  

Microsoft Academic Search

This work is devoted to the analysis of factors responsible for the high-frequency shift of the complex permeability ( mu * ) dispersion region in polymer composites of manganese-zinc (MnZn) ferrite, as well as to the increase in their thermomagnetic stability. The magnetic spectra of the ferrite and its composites with polyurethane (MnZn-PU) and polyaniline (MnZn-PANI) are measured in the

V. Babayan; N. E. Kazantseva; R. Moucka; I. Sapurina; Yu. M. Spivak; V. A. Moshnikov

2012-01-01

100

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

101

Anisotropy of Magnetic Susceptibility of Rocks and Minerals  

Microsoft Academic Search

There are two predominant causes for the anisotropy of magnetic susceptibility of rocks and ferrimagnetic minerals: the shape of the magnetic material and crystalline anisotropy. In general, these factors may operate simultaneously, but in rock magnetism their effects are frequently separable. In the case of shape-effect anisotropy, one can predict the degree of anisotropy by an ellipsoidal approximation, provided that

S. Uyeda; M. D. Fuller; J. C. Belshé; R. W. Girdler

1963-01-01

102

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

103

Magnetization reversal in ultrashort magnetic field pulses  

NASA Astrophysics Data System (ADS)

We report the switching properties of a thin magnetic film subject to an ultrashort, laterally localized magnetic field pulse, obtained by numerical investigations. The magnetization distribution in the film is calculated on a grid assuming Stoner-like coherent rotation within the grid square size. Perpendicularly and in-plane magnetized films exhibit a magnetization reversal due to a 4ps magnetic field pulse. Outside the central region the pulse duration is short compared to the precession period. In this area the evolution of the magnetization during the field pulse does not depend strongly on magnetic damping and/or pulse shape. However, the final magnetization distribution is affected by the magnetic damping. Although the pulse duration is short compared to the precession period, the time needed for the relaxation of the magnetization to the equilibrium state is rather large. The influence of the different magnetic anisotropy contributions and the magnetic damping parameter enters into the magnetization reversal process. Comparing the case of perpendicular anisotropy with different kinds of in-plane anisotropies, a principal difference is found due to the symmetry of the shape anisotropy with respect to the anisotropy in question.

Bauer, M.; Lopusnik, R.; Fassbender, J.; Hillebrands, B.

2000-08-01

104

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

105

Effect of the magnetic field in the plane of a garnet ferrite film with orthorhombic magnetic anisotropy on the dynamics of domain walls  

Microsoft Academic Search

The effect of an in-plane magnetic field on the dependence of the domain-wall velocity on the acting magnetic field is investigated\\u000a for bismuth-containing garnet ferrite single-crystal films of the composition (Bi,Y,Pr)3(Fe,Ga)5O12 with the (210) orientation. The in-plane magnetic field is applied along the ?120? and ?001? crystallographic axes. The domain-wall\\u000a velocity is measured in directions perpendicular and parallel to the

V. V. Randoshkin; V. A. Polezhaev; N. N. Sysoev; Yu. N. Sazhin; V. N. Dudorov

2003-01-01

106

Magnetic anisotropy in the trenton limestone: Results of a new technique, anisotropy of anhysteretic susceptibility  

Microsoft Academic Search

A new method for determining magnetic anisotropy using anhysteric remanence susceptibility is described. The magnetic fabric of a collection of Trenton Limestone specimens has been determined using this method, as well as by conventional anisotropy of magnetic susceptibility. The results demonstrate the usefulness of the new method for finding the magnetic fabric of rock units such as the Trenton in

Chad McCabe; Michael Jackson; Brooks B. Ellwood

1985-01-01

107

Magnetic anisotropy of epitaxial (Ga,Mn)As on (113)A GaAs  

NASA Astrophysics Data System (ADS)

The temperature dependence of magnetic anisotropy in (113)A (Ga,Mn)As layers grown by molecular-beam epitaxy is studied by means of superconducting quantum interference device magnetometry as well as by ferromagnetic resonance (FMR) and magnetooptical effects. Experimental results are described considering cubic and two kinds of uniaxial magnetic anisotropy. The magnitude of cubic and uniaxial anisotropy constants is found to be proportional to the fourth and second power of saturation magnetization, respectively. Similarly to the case of (001) samples, the spin reorientation transition from uniaxial anisotropy with the easy axis along the [1¯10] direction at high temperatures to the biaxial ?100? anisotropy at low temperatures is observed around 25 K. The determined values of the anisotropy constants have been confirmed by FMR studies. As evidenced by investigations of the polar magnetooptical Kerr effect, the particular combination of magnetic anisotropies allows the out-of-plane component of magnetization to be reversed by an in-plane magnetic field. Theoretical calculations within the p-d Zener model explain the magnitude of the out-of-plane uniaxial anisotropy constant caused by epitaxial strain but do not explain satisfactorily the cubic anisotropy constant. At the same time the findings point to the presence of an additional uniaxial anisotropy of unknown origin. Similarly to the case of (001) films, this additional anisotropy can be explained by assuming the existence of a shear strain. However, in contrast to the (001) samples, this additional strain has an out of the (001) plane character.

Stefanowicz, Wiktor; ?liwa, Cezary; Aleshkevych, Pavlo; Dietl, Tomasz; Döppe, Matthias; Wurstbauer, Ursula; Wegscheider, Werner; Weiss, Dieter; Sawicki, Maciej

2010-04-01

108

Magnetic Fabrics of Impact Breccias from the Chicxulub Impact Crater: Analyses of Thermal and Alternating Field Treatment on the Anisotropy of Magnetic Susceptibility  

NASA Astrophysics Data System (ADS)

We present results of a characterization study of the impact breccias sequence in the Chicxulub multiring structure. Chicxulub formed by a bolide impact some 65 Ma ago into the Yucatan carbonate platform. Chicxulub is the only large multiring structure in the terrestrial record that preserves its ejecta blanket, which includes proximal ejecta and the distal deposits. The global spherulitic-and-clay layer that marks the Cretaceous/Paleogene boundary is related to the Chicxulub impact. Impact excavated a deep transient crater into the Yucatan platform; part of the large volume of fragmented material ejected into the column plume was emplaced as breccias deposits inside the forming crater as column collapsed, also including deposits from ejecta curtain and basal surge flows. Ejecta emplacement involved highly energetic high temperature/pressure processes. Fabric analyses of the ejecta show the relative complexity of the material formed by the impact. The impact breccias and melt have been sampled in the UNAM and CSDP drilling projects. Here we report on fabric analyses of the breccias sampled in the CSDP Yaxcopoil-1 borehole. In particular, we analyze the trend AMS parameters follow in two different processes of demagnetization. Previous studies of the breccias in the UNAM boreholes documented the presence of an upper sequence of melt-and-basement-clast rich breccias and a lower sequence of carbonate-clast-rich breccias, which could be separated into various subunits with distinct petrographic and textural characteristics. Samples for this experiment were obtained from the suevitic breccias sequence in the Yaxcopoil-1 borehole. It is located about 62 km from the center of the Chicxulub impact structure in Yucatán. The Yaxcopoil-1 breccias have been subdivided into six units (Stoeffler et al., 2004; Kring et al, 2004). For the alternating field (AF) demagnetization, 8 samples were selected, and for the thermal demagnetization 16 samples. The AMS parameters analyzed include bulk susceptibility K, shape parameter T, corrected anisotropy degree Pj, lineation L, foliation F, and an analysis for the natural remanent magnetization NRM. K shows an ascendant trend with a irregular behavior in the AF process, while in thermal process, in general K shows a descendent trend with a almost constant behavior. The T parameter, in AF process shows 3 tendencies: first, T has a defined behavior in the oblate and prolate zone. Second, T trends to the prolate zone and third, is that T varies from prolate to oblate zone during this process. While in thermal process, there are three behaviours: 1) some samples show ascendent tendency and others show descendent tendency but, all are oblate (0anisotropy degree Pj. In AF process, it shows 2 groups: one for the samples from unit five and six, Pj is distributed between 1.06 and 1.1 units. Second, for the samples from unit 3 and 4, Pj varies between 1.0 y 1.03. This behavior is similar to igneous and sedimentary rocks behavior. For the thermal process, the majority of the samples show descendent trend with a behavior almost "constant" and the others show a variable trend and the same behavior. All samples are distributed in different intervals of the parameter. Lineation parameter. In AF, there’re two groups: one, for the unit 3 and 4 L varies from 1.0 to 1.01, and for the units 5 and 6, L varies from1.03 to 1.05, all of which show a regular behavior. In general, thermal process shows tree groups: (1) ascendent trend subdivided in different intervals of L. (2) descendent tendency subdivided in different intervals of L, too. (3) Behaviour irregular with no definitive trend. In AF, foliation parameter shows a similar behavior like L. For the thermal process F shows descendent tendency for the majority of the samples with a irregular behavior, and the rest samples show ascendent trend with irreg

Velasco Villarreal, M.; Urrutia Fucugauchi, J.

2010-03-01

109

Magnetic anisotropy data of C84 (D2d)  

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.

110

Magnetic anisotropy data of C82 (C2)  

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.

111

Magnetic anisotropy data of C84 (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.

112

On Cosmic Magnetic Fields  

NASA Astrophysics Data System (ADS)

Magnetic fields are present in all astrophysical media. However, many models and interpretations of observations often ignore them, because magnetic fields are difficult to handle and because they produce complicated morphological features. Here we will comment on the basic intuitive properties, which even if not completely true, provide a first guiding insight on the physics of a particular astrophysical problem. These magnetic properties are not mathematically demonstrated here. How magnetic fields evolve and how they introduce dynamical effects are considered, also including a short comment on General Relativity Magnetohydrodynamics. In a second part we consider some audacious and speculative matters. They are answers to three questions: a) How draw a cube without lifting the pencil from the paper so that when the pen passes through the same side do in the same direction? B) Are MILAGRO anisotropies miraculous? C) Do cosmic magnetic lenses exist?. The last two questions deal with issues related with the interplay between magnetic fields and cosmic ray propagation.

Florido, E.; Battaner, E.

2010-12-01

113

Effect of anisotropies on magnetic quantum phase transitions  

NASA Astrophysics Data System (ADS)

We consider the effects of superexchange anisotropy and Dzyaloshinskii--Moriya (DM) interactions on the field-- and pressure--driven magnetic phase transitions in quantum dimer systems. These two types of anisotropy term are introduced separately on the intra-- and interdimer bonds, with spatial symmetries both commensurate and incommensurate with the magnetic order, to determine the alterations of the phase diagram and magnetic excitations. Exchange anisotropy causes a general modification of the critical properties at the field--driven transition from the XY universality class (Bose--Einstein condensation) to Ising behaviour. DM interactions may act either to remove the field--driven transition completely or to create a new transition between two different antiferromagnetic states. For certain cases we compute the magnetisation and the evolution of the excitation spectra as functions of field and pressure. Our results are directly relevant to recent measurements on TlCuCl3 and CuHpCl, and may assist in the further understanding of a number of other quantum dimer systems, including BaCuSi2O6, Sr2Cu(BO3)2 and PHCC.

Normand, B.; Zhitomirsky, M. E.

2005-03-01

114

Mononuclear single-molecule magnets: tailoring the magnetic anisotropy of first-row transition-metal complexes.  

PubMed

Magnetic anisotropy is the property that confers to the spin a preferred direction that could be not aligned with an external magnetic field. Molecules that exhibit a high degree of magnetic anisotropy can behave as individual nanomagnets in the absence of a magnetic field, due to their predisposition to maintain their inherent spin direction. Until now, it has proved very hard to predict magnetic anisotropy, and as a consequence, most synthetic work has been based on serendipitous processes in the search for large magnetic anisotropy systems. The present work shows how the property can be predicted based on the coordination numbers and electronic structures of paramagnetic centers. Using these indicators, two Co(II) complexes known from literature have been magnetically characterized and confirm the predicted single-molecule magnet behavior. PMID:23586965

Gomez-Coca, Silvia; Cremades, Eduard; Aliaga-Alcalde, Núria; Ruiz, Eliseo

2013-04-25

115

Micromagnetic studies on resolution limits of magnetic force microscopy tips with different magnetic anisotropy  

NASA Astrophysics Data System (ADS)

In magnetic force microscopy (MFM), it is effective to control the magnetic properties of the coating materials on the MFM tip to achieve higher resolution. In this work, the effect of the magnetic anisotropy of the tip-coating, such as perpendicular magnetic anisotropy (PMA), in-plane magnetic anisotropy (IMA), and random magnetic anisotropy (RMA), on the MFM image resolution are studied by micromagnetics. An accurate 3 D micromagnetic model of the CoPt pyramid MFM tip, with a cone angle of 37°, tip height of 120 nm, coating thickness of 7.6 nm, and average grain size of about 8.8 nm, was setup to calculate the domain structure and the stray field of the tip. A CoPt disk medium, with a bit size of 24 × 32 nm2 and film thickness of 8 nm, was chosen for image simulation. The PMA tip is advantageous in low scan height (SH) measurement with little tip-sample interaction due to its sharp and small stray field, while the IMA tip will disturb the magnetic moments of the medium at a low SH due to its strong stray field, and the RMA tip cannot read the bits with clear image contrast due to its broader field distribution.

Li, Hongjia; Wei, Dan; Piramanayagam, S. N.

2012-04-01

116

Determination of Layer Specific Magnetization and Anisotropy Fields in Multilayer Garnet Films from FMR and VSM Measurements  

Microsoft Academic Search

A new method is developed to measure the magnetizations in each layer of a multi-layered garnet film. This method combines a single VSM and multiple FMR measurements to completely characterize the magnetic properties of layers. This method can be immediately extended to the case of multiple layers or different materials, as long as the requirement for resolving the FMR absorption

I. Nistor; C. Holthaus; C. Krafft; I. D. Mayergoyz

2006-01-01

117

Ferromagnetic Resonance Studies of Magnetic Anisotropy in Sr2FeMoO6  

NASA Astrophysics Data System (ADS)

We investigated magnetic anisotropic parameters of a 400-nm ferromagnetic half-metallic Sr2FeMoO6 thin film by ferromagnetic resonance (FMR). The resonance field and line width were recorded as a function of relative angle between applied magnetic field and crystallographic axes of the sample. The resonance field varies sinusoidally and considerable line width broadening occurs when the field aligned axis is rotated orthogonal to the spectrometer field. This is consistent with the presence of higher order components of anisotropy field. Further, we obtain the values of the cubic and the uniaxial magnetic anisotropy fields from the analysis of the FMR data.

Nosach, Tetiana; Ebrahim, Mark; Greenbaum, Steve; Ren, Yuhang; Venimadhav, Adyam; Li, Qi

2007-03-01

118

Molecular-dynamics simulation of structural anisotropy in glassy metals and its relationship to magnetic anisotropy  

Microsoft Academic Search

Creep-induced magnetic anisotropy in metallic glass was investigated using a molecular-dynamics simulation. A model binary glass structure of 2048 particles interacting via Lennard–Jones potentials was creep deformed below its glass transition temperature. Creep deformation resulted in the bond-orientational anisotropy (BOA) within the first nearest-neighbor shell with a large sixth-order spherical harmonic component. The magnetic anisotropy estimated on the basis of

T. Tomida; T. Egami

1991-01-01

119

The influence of magnetic anisotropy on magnetoelectric behavior in conical spin ordered multiferroic state  

NASA Astrophysics Data System (ADS)

For the magnetism-driven multiferroic materials, the magnetic anisotropy plays an essential role in the magnetoelectric behavior. To understand the influence of magnetic anisotropy on multiferroic state resulting from the conical spin order, we have performed Monte Carlo simulation on a three-dimensional classical Heisenberg model in spinel lattice. The single-ion anisotropy from the easy-axis type to the easy-plane type is considered in the system, and the corresponding magnetoelectric behavior is investigated under a rotating external magnetic field (h). It is revealed that the magnetic anisotropy drags the orientation of conical spin structure slightly away from the direction of h, and distorts the conical spin structure as well. The balance between h and the anisotropy results in the anisotropic magnetoelectric properties during the rotation of h.

Yao, Xiaoyan; Lo, Veng Cheong; Liu, Jun-Ming

2010-05-01

120

Anisotropy and microstructure of high-coercivity rare earth permanent magnets  

Microsoft Academic Search

In Nd2Fe14B-based permanent magnets the coercivity is in practice only 20 to 40 percent of the theoretical limits. The aim of this study is to investigate Nd-Fe-B based compounds with respect to their magnetic anisotropy behavior and to characterize the microstructure of sintered Nd-Fe-B based permanent magnets. The anisotropy field HA was determined by using the Singular Point Detection (SPD)

Josef Fidler; Roland Grossinger; Hans Kirchmayr; Peter Skalicky

1989-01-01

121

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

SciTech Connect

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

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

2008-09-11

122

Ising-Type Magnetic Anisotropy Derived by ?7(1) Crystal Electric Field Ground State in Tetragonal CeRu2Al2B: 11B and 27Al NMR Studies  

NASA Astrophysics Data System (ADS)

The magnetic properties of the new tetragonal compound CeRu2Al2B have been investigated by 11B and 27Al nuclear magnetic resonance (NMR) measurements. In the paramagnetic state, the Knight shift exhibits a strong Ising-type magnetic anisotropy. In the ferromagnetic order state, the ordered moment is estimated to be ?1.8{--}1.85?B/Ce from the magnitudes of the internal fields at the B and Al sites. These results strongly suggest that the Ising-like ferromagnetic ground state arises from the ?7(1) ground state in CeRu2Al2B.

Matsuno, Haruki; Nohara, Hiroki; Kotegawa, Hisashi; Matsuoka, Eiichi; Tomiyama, Yo; Sugawara, Hitoshi; Harima, Hisatomo; Tou, Hideki

2012-07-01

123

Perpendicular Exchange Bias and Magnetic Anisotropy in FePt\\/FeMn Multilayers  

Microsoft Academic Search

A systematic investigation of parallel and perpendicular exchange bias in FePt\\/FeMn multilayers is presented. Perpendicular magnetic anisotropy observed in FePt\\/FeMn multilayers is attributed to the surface anisotropy at the interface of FePt\\/FeMn. The surface and volume anisotropy constants are found to decrease with increasing temperature. The thickness (FePt) dependence of exchange bias field and blocking temperature are discussed. Of interest

Nguyen N. Phuoc; Takao Suzuki

2006-01-01

124

The evolution of magnetic domain structure with magnetic history in amorphous film with perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

Amorphous rare-earth-Fe-B (RE-Fe-B) films were deposited on Si substrates at 300 °C by dc magnetron sputtering. The evolution of their magnetic domain structures with magnetic history was observed by magnetic force microscopy. It was found that the remanent domain configuration can be gradually transformed from stripes to bubbles after applying different magnetic fields along the out-of-plane direction, which indicates that the film has a perpendicular magnetic anisotropy. In addition, an in situ investigation on the evolution of domain structure under an in-plane field was carried out using a homemade sample holder. The results showed that the domain structure depends on both the applied field and the magnetic history. The present work provides a feasible approach for manipulating magnetic domains in amorphous RE-Fe-B film by employing a magnetic field.

Gao, Jinlong; Tang, Shaolong; Li, Yulong; Xia, Wenbin; Tang, Tao; Du, Youwei

2012-10-01

125

Magnetic Anisotropy of R2Co17 Compounds (R = Er, Tm, Yb).  

National Technical Information Service (NTIS)

Saturation moments, easy direction of magnetization, anisotropy field, and anisotropy constants have been determined at 4.2K and room temperature for Er2Co17, Tm2Co17 and Yb2Co17. The data obtained are compared with theoretical predictions. Y and Pr were ...

K. S. V. L. Narasimhan W. E. Wallace R. D. Hutchens J. E. Greedan

1974-01-01

126

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

127

Magnetic single-ion anisotropy and zero-field splittings of Mn2+ ions in some low-dimensional chlorides  

Microsoft Academic Search

The zero-field splitting parameter D of the 6S5\\/2 ground state of Mn2+ ions with Cl- ligands is discussed. Ab initio calculations of D, based on the relativistic spin-spin and Blume-Orbach splitting mechanisms, and an electrostatic model of the crystal field, are in poor agreement with experimental measurements for Mn2+ ions in a representative group of six chloride host compounds: CdCl2,

A. Edgar; E. Siegel; W. Urban

1980-01-01

128

Precessional switching on exchange biased patterned magnetic media with perpendicular anisotropy  

Microsoft Academic Search

We propose to use an in-plane exchange bias field to assist the applied field to obtain precessional switching of the magnetization in a high perpendicular anisotropy media. Our calculation is made in the limit of a nondamped macrospin particle. From the energy conservation, we derive the magnetic trajectories for any applied field magnitude and orientation. Precessional switching is shown to

M. Belmeguenai; T. Devolder; C. Chappert

2005-01-01

129

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

130

The magnetization processes and critical transition in a nanogranular magnetic film with perpendicular anisotropy.  

PubMed

The mechanisms and properties of the equilibrium magnetization process for nanogranular films with perpendicular anisotropy placed in a tilted magnetic field are considered. The contributions of the effects of canting and flipping of the granules' magnetic moments to the process of film magnetization are studied. A critical behavior of the film magnetization at the transition, induced by a tilted magnetic field, from a state with non-uniform orientation of the granules' magnetic moments to one with a similar orientation is revealed. The results obtained within the two-level model of the orientation of the particles' magnetic moments are in good agreement with the experimental data for Co-Al(2)O(3) (61 at.% Co) granular film. The perpendicular anisotropy of the granules in this film originates mainly from their elongated shape. It is shown that in the non-uniform state the magnetostatic energy of a granular film with similarly oriented elongated granules can be described by the sum of contributions of two types: quasi-single-granular and quasi-film. The effective constant of the single-particle anisotropy of the granules in this case turns out to be dependent on the factor of volume filling of the film by granules, but not on its magnetization. PMID:23315477

Kalita, V M; Lozenko, A F; Ryabchenko, S M; Los, A V; Sitnikov, A V; Stognei, O V

2013-01-11

131

Magnetic anisotropy, magnetostatic interactions and identification of magnetofossils  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

132

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

133

Effect of magnetic field cooling and magnetization anomaly in magnetic fluids near melting point  

Microsoft Academic Search

The magnetization process of ferrofluids with carrier fluids of water, paraffin, and alkylnaphtalene was investigated in a temperature range from 77 to 300 K as functions of the freezing rate and the intensity of cooling magnetic fields. A uniaxial magnetic anisotropy is induced by field cooling in frozen ferrofluids. This induced anisotropy which is caused by the formation of clustering

H. Miyajima; N. Inaba; S. Taketomi; M. Sakurai; S. Chikazumi

1988-01-01

134

State diagram of nanopillar spin valves with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

The spin-torque switching of metallic nanopillar spin valves showing strong perpendicular anisotropy are studied. The magnetic states of the layers depend on extrinsic parameters such as the magnetic field and the dc current applied to the device. A state diagram presents a comprehensive graph of the role of those parameters on the spin-valve magnetic response. After explaining how state diagrams can be built and the different possible representation, experimental state diagrams are studied for perpendicular devices and the influence of lateral size, temperature, and field orientation are shown. An analytical model of a purely uniaxial system is presented. It is shown that this simple model does not properly reflect the experimental results, whereas if the symmetry is broken a qualitative agreement is obtained. Finally, the possible origins of the symmetry break are discussed in light of an analytical model and numerical simulations.

Le Gall, S.; Cucchiara, J.; Gottwald, M.; Berthelot, C.; Lambert, C.-H.; Henry, Y.; Bedau, D.; Gopman, D. B.; Liu, H.; Kent, A. D.; Sun, J. Z.; Lin, W.; Ravelosona, D.; Katine, J. A.; Fullerton, Eric E.; Mangin, S.

2012-07-01

135

Soft to hard magnetic anisotropy in nanostructured magnets  

NASA Astrophysics Data System (ADS)

The effective anisotropy of hard-soft magnetic nanostructures is analyzed using the concept of the exchange correlation length of both phases. The dependence of coercivity on volume fraction, fluctuation length, temperature, and magnetic properties of the components is derived from the degree of magnetic coupling, defined through an effective interphase exchange constant. Coercivity and remanence measurements carried out on devitrified FeZrBCu amorphous alloys point out the transition from an uncoupled to a coupled regime by increasing the temperature in a very diluted system, according to the predictions of the analysis.

Arcas, J.; Hernando, A.; Barandiarán, J. M.; Prados, C.; Vázquez, M.; Marín, P.; Neuweiler, A.

1998-09-01

136

In-plane magnetic anisotropy along the width in amorphous magnetic ribbons  

NASA Astrophysics Data System (ADS)

A study about the variation of the in-plane magnetic anisotropy along the width of the ribbon is carried out in Co- and Fe-based amorphous magnetic ribbons. From the measurements of the anisotropy in as-quenched, mechanical polished and annealed samples the origin of the lack of homogeneity of the in-plane magnetic anisotropy in wide amorphous ribbons is determined. In addition a shape magnetic anisotropy that we think is originated by the edge effect was found.

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

2004-05-01

137

Magnetization of densely packed interacting magnetic nanoparticles with cubic and uniaxial anisotropies: A Monte Carlo study  

NASA Astrophysics Data System (ADS)

The magnetization curves of densely packed single domain magnetic nanoparticles (MNPs) are investigated by Monte Carlo simulations in the framework of an effective one spin model. The particles whose size polydispersity is taken into account are arranged in spherical clusters, and both dipole dipole interactions (DDI) and magnetic anisotropy energy (MAE) are included in the total energy. Having in mind the special case of spinel ferrites of intrinsic cubic symmetry, combined cubic and uniaxial magnetocrystalline anisotropies are considered with different configurations for the orientations of the cubic and uniaxial axes. It is found that the DDI together with a marked reduction of the linear susceptibility are responsible for a damping of the peculiarities due to the MAE cubic component on the magnetization. As an application, we show that the simulated magnetization curves compare well to experimental results for ?-Fe2O3 MNP for small to moderate values of the field.

Russier, V.; de-Montferrand, C.; Lalatonne, Y.; Motte, L.

2013-10-01

138

The Measurement of the Anisotropy of Magnetic Susceptibility of Rocks by the Torque Method  

Microsoft Academic Search

The method of measuring magnetic anisotropy in terms of the couple acting on a sample suspended in a magnetic field is well known. In recent years it has been used by Granar and by Stacey, among others, to determine what may be called the 'magnetic fabric' of rocks. In this paper two variations on Granar's magnetometer are described, designed re-

R. F. King; A. I. Rees

1962-01-01

139

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

140

Light-induced magnetization reversal of high-anisotropy TbCo alloy films  

NASA Astrophysics Data System (ADS)

Magnetization reversal using circularly polarized light provides a way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1-x ferrimagnetic alloy compositions using fs- and ps-laser pulses and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3 × 106 ergs/cm3. Optical magnetization switching is observed only for alloy compositions where the compensation temperature can be reached through sample heating.

Alebrand, Sabine; Gottwald, Matthias; Hehn, Michel; Steil, Daniel; Cinchetti, Mirko; Lacour, Daniel; Fullerton, Eric E.; Aeschlimann, Martin; Mangin, Stéphane

2012-10-01

141

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

142

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

143

Magnetic orientation and magnetic anisotropy in paramagnetic layered oxides containing rare-earth ions  

NASA Astrophysics Data System (ADS)

The magnetic anisotropies and easy axes of magnetization at room temperature were determined, and the effects of rare-earth (RE) ions were clarified for RE-based cuprates, RE-doped bismuth-based cuprates and RE-doped Bi-based cobaltite regarding the grain orientation by magnetic field. The easy axis, determined from the powder orientation in a static field of 10 T, depended qualitatively on the type of RE ion for all three systems. On the other hand, the magnetization measurement of the c-axis oriented powders, aligned in static or rotating fields, revealed that the type of RE ion strongly affected not only the directions of the easy axis but also the absolute value of magnetic anisotropy, and an appropriate choice of RE ion is required to minimize the magnetic field used for grain orientation. We also studied the possibility of triaxial grain orientation in high-critical-temperature superconductors by a modulated oval magnetic field. In particular, triaxial orientation was attempted in a high-oxygen-pressure phase of orthorhombic RE-based cuprates Y2Ba4Cu7Oy. Although the experiment was performed in epoxy resin, which is not practical, in-plane alignment within 3° was achieved.

Horii, Shigeru; Ishihara, Atsushi; Fukushima, Takayuki; Uchikoshi, Tetsuo; Ogino, Hiraku; Suzuki, Tohru S.; Sakka, Yoshio; Shimoyama, Jun-ichi; Kishio, Kohji

2009-01-01

144

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

145

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

Microsoft Academic Search

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

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

2010-01-01

146

Ferromagnetic nanoparticles with strong surface anisotropy: Spin structures and magnetization processes  

NASA Astrophysics Data System (ADS)

Monte Carlo simulations are used to investigate the effect of surface anisotropy on the spin configurations and hysteresis loops of ferromagnetic nanoparticles. Spherical particles of radius ?a are composed of N atoms located on a simple cubic lattice with interatomic spacing a . The particles have 2???13 . A classical Heisenberg model is assumed, with surface and bulk anisotropy. When surface anisotropy is positive there are two types of ground states separated by a large energy barrier: a “throttled” configuration with reduced magnetization for intermediate values of surface anisotropy and a “hedgehog” configuration with zero magnetization in the strong surface anisotropy limit. Beyond a threshold, surface anisotropy of either sign induces ?111? easy axes for the net magnetization. Easy-axis hysteresis loops are then square, with a continuous approach to saturation, and the effective anisotropy is deduced either from the switching field or from the initial slope of the perpendicular magnetization curve. The hedgehog state shows a stepwise magnetization curve involving ? discrete configurations, and it passes to a throttled configuration before saturating. The hysteresis loop has the unusual feature that it involves a state in the first quadrant, which lies on the reversible initial magnetization curve; it is possible to recover the zero-field cooled state after saturation. A survey of the exchange and anisotropy parameters for a range of ferromagnetic materials indicates that the effects of surface anisotropy on the spin configuration should be most evident in nanoparticles of ferromagnetic actinide compounds such as US, and rare-earth metals and alloys with Curie points below room temperature; the effects in nanoparticles of 3d ferromagnets and their alloys are usually insignificant, with the possible exception of FePt.

Berger, L.; Labaye, Y.; Tamine, M.; Coey, J. M. D.

2008-03-01

147

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

148

Anisotropy of the critical temperature of a superconducting niobium thin film with an array of nanoscale holes in an external magnetic field  

NASA Astrophysics Data System (ADS)

We report on magnetotransport experiments investigating the effect of a regular array of nanoscale holes on the anisotropic response in the transition temperature of a superconducting niobium thin film. We find that the angle dependence of the critical temperature exhibits two strong anisotropic effects: Little-Parks oscillations whose period varies with field direction and a smooth background arising from one-dimensional confinement by the finite lateral space between neighboring holes. The two components of the anisotropy are intrinsically linked and appear in concert with one superimposed on top of the other.

Latimer, M. L.; Xiao, Z. L.; Hua, J.; Joshi-Imre, A.; Wang, Y. L.; Divan, R.; Kwok, W. K.; Crabtree, G. W.

2013-01-01

149

Determination of anisotropy constants of protein encapsulated iron oxide nanoparticles by electron magnetic resonance  

NASA Astrophysics Data System (ADS)

Angle-dependent electron magnetic resonance was performed on 4.9, 8.0, and 19 nm iron oxide nanoparticles encapsulated within protein capsids and suspended in water. Measurements were taken at liquid nitrogen temperature after cooling in a 1 T field to partially align the particles. The angle dependence of the shifts in the resonance field for the iron oxide nanoparticles (synthesized within Listeria-Dps, horse spleen ferritin, and cowpea chlorotic mottle virus) all show evidence of a uniaxial anisotropy. Using a Boltzmann distribution for the particles’ easy-axis direction, we are able to use the resonance field shifts to extract a value for the anisotropy energy, showing that the anisotropy energy density increases with decreasing particle size. This suggests that surface anisotropy plays a significant role in magnetic nanoparticles of this size.

Li, Hongyan; Klem, Michael T.; Sebby, Karl B.; Singel, David J.; Young, Mark; Douglas, Trevor; Idzerda, Yves U.

2009-02-01

150

Effects of transverse magnetic anisotropy on current-induced spin switching.  

PubMed

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. PMID:23931390

Misiorny, Maciej; Barna?, Józef

2013-07-23

151

Magnetic anisotropy in ferrites-spinels with frustrated magnetic structure  

Microsoft Academic Search

The investigation of magnetic properties of diluted ferrite CuGaxAlxFe2-2xO4 (\\/x=0.2-0.7), CuGaxAl2xFe2-3xO4 (\\/x=0.1-0.5), of ferrites-chromates CuxNi1-xFe0.6Cr1.4O4 (\\/x=0.0-0.4), CuFe2-xCrxO4 (\\/x=0.0, 0.2, 0.3, 1.0, 1.4 and 1.6), and of diluted ferrites-chromates GaxFe1-xNiCrO4 (\\/x=0.0, 0.2, 0.4, 0.6 and 0.8) is carried out. It is revealed that the effective magnetic anisotropy constant in ferrites with frustrated magnetic structure is less than Keff for the ferrites

L. G. Antoshina; A. N. Goryaga; A. I. Kokorev

2003-01-01

152

Perpendicular magnetic anisotropy materials for reduced current switching devices  

NASA Astrophysics Data System (ADS)

Recently, spin-transfer switching of magnetic tunnel junctions (MTJs) has become a very active area of research. It is theoretically postulated that using perpendicular magnetic anisotropy materials will substantially reduce the critical current density for switching, resulting in lower energy devices, while keeping the thermal stability high. A range of perpendicular anisotropy material systems, including (i) multilayers, (ii) crystalline alloys, and (iii) amorphous alloys have been intensively studied in this dissertation. The surface and bulk anisotropy, damping parameter, and structural properties of these material systems have been investigated. Magnetic tunnel junctions based on some of these perpendicular material schemes have been fabricated, and their transport properties have been measured and related to the anisotropy. We have found several promising approaches to magnetic tunnel junctions utilized in spin-torque transfer random access memory (STT-RAM).

Tadisina, Zeenath Reddy

153

Anisotropy and Microstructure of Rare Earth Permanent Magnet Materials.  

National Technical Information Service (NTIS)

The present report is divided into two parts, the microstructural investigations and the anisotropy measurements of rare earth permanent magnet materials. Section I shows that the hardmagnetic properties, i.e. coercivity, of the individual Nd-Fe-B permane...

P. Skalicky J. Fidler R. Groessinger H. Kirchmayr

1986-01-01

154

Magnetic susceptibility of hcp iron and the seismic anisotropy of Earth's inner core  

Microsoft Academic Search

The seismic anisotropy of the Earth's core is believed to be due to a preferred orientation of hexagonal close packed (hcp) iron crystals that constitute the dominating element in the inner core. In this connection, the magnetic properties of the hcp iron in an external magnetic field are very interesting and are studied here by employing an ab initio full-potential

G. E. Grechnev; R. Ahuja; O. Eriksson

2003-01-01

155

Magnetic configurations of Co(111) nanostripes with competing shape and crystalline anisotropies  

NASA Astrophysics Data System (ADS)

Nanostripes with varying widths are lithographed on Co thin films with strong magnetic anisotropy resulting from the epitaxial growth onto vicinal Si(111) substrate. The competition between magnetocrystalline and shape anisotropies is used to tune the magnetic behavior of Co nanostripes. Single domain configuration is observed for nanostructures where magnetocrystalline and shape anisotropies go along the same direction. However, more complicated configurations such as open stripe domains can be developed when both anisotropies compete. The nanostructures have been experimentally characterized by longitudinal magneto-optical Kerr effect and magnetic force microscopy (MFM). Micromagnetic simulations performed by finite-element and finite difference codes are in good agreement with the experimental results. The use of MFM based techniques such as the variable field magnetic force microscopy and the so-called three-dimensional modes has allowed us to follow the evolution of the domains and domain walls under externally applied magnetic fields, i.e., to deeply understand the magnetization reversal process in the multidomain nanostripes. In particular, the nanostripes with competing anisotropies and a high aspect ratio present vortex configuration along the domain walls which have a key role in the magnetization reversal process.

Ivanov, Yu. P.; Iglesias-Freire, O.; Pustovalov, E. V.; Chubykalo-Fesenko, O.; Asenjo, A.

2013-05-01

156

Magnetic anisotropy of the radula of chiton Acanthochiton rubrolinestus LISCHKE.  

PubMed

The magnetic anisotropy of the whole radula, the major lateral radula teeth, and magnetic material in the major lateral radula teeth of the chiton Acanthochiton rubrolinestus LISCHKE have been studied by a magnetic torque meter and superconducting quantum interference device (SQUID) magnetometer. The length and width axes of the teeth are the easily magnetized axes, while the thickness axis is difficult to magnetize. The width and thickness axes of the radula are the easily magnetized axes, and the length axis is difficult to magnetize. The measurement results of the whole radula and the major lateral radula teeth agree well with each other. The magnetic anisotropy of the magnetic material is given as well as a possible distribution of the magnetic material in the major lateral radula teeth. PMID:12210567

Qian, Xia; Zhao, Jian-Gao; Liu, Chuan-Lin; Guo, Cheng-Hua

2002-09-01

157

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

158

Magnetic anisotropy studies on the cobalt-based chain molecular magnet CoCu(opba)(DMSO)3  

NASA Astrophysics Data System (ADS)

The present paper reports on a study of the magnetic anisotropy of the Co-based chain molecular magnet CoCu(opba)(DMSO)3. The magnetic anisotropy measurements were performed on microgram monocrystalline samples using a cantilever magnetometer at low temperatures down to 1.5K and magnetic fields up to 7T. The field dependence of the magnetic torque confirms an ordered ferrimagnetic structure at low temperature, TC=6K, with a very small coercive field. Magnetic torque measurements as a function of the angle within the /a-c and /b-c planes suggest the emergence of biaxial behavior at low temperatures. Our results suggest that the resulting ferromagnetic moment lies perpendicular to both the CuCo-chains and hard magnetic axis.

Meira-Belo, L. C.; Leita~o, U. A.; Pereira, C. L. M.; Doriguetto, A.; Fernandes, N. G.; Stumpf, H. O.

2001-05-01

159

Pulsed laser deposited Y3Fe5O12 films: Nature of magnetic anisotropy I  

NASA Astrophysics Data System (ADS)

Recently we sintered by pulsed laser deposition (PLD) technique the epitaxial Fe-deficient yttrium iron garnet (YIG) films with ferromagnetic resonance (FMR) linewidth as narrow as 0.9 Oe, the uniaxial anisotropy as high as Hu=-880 Oe, and demonstrated them feasible for magnetostatic waves band pass filter application [Manuilov et al., J. Appl. Phys. 105, 033917 (2009)]. Here we explore the origin of unusually high noncubic magnetic anisotropy. Using the angular resolved FMR spectroscopy we found that in addition to strong uniaxial anisotropy, cubic magnetic anisotropy experienced almost fivefold reduction compared to standard YIG grown by liquid phase epitaxy. Molecular field theory was employed to calculate saturation magnetization 4?Ms, cubic magnetocrystalline K1, and uniaxial anisotropy Ku in garnets with Fe vacancies. The modeling utilizes crystal field parameters that we revealed from earlier published experimental data on diamagnetic ion substituted Y3Fe5O12 and Fe-substituted isomorphous diamagnetic garnets. Consistent single ion anisotropy crystal field theory perfectly fits experimentally observed high saturation magnetization, reduction in cubic, and appearance of strong uniaxial anisotropy in PLD-grown Fe-deficient YIG films. The redistribution of Fe vacancies between different magnetic sublattices was quantified and confirmed that in YIG(111) films ferric ions preferentially leave vacant octahedrally coordinated sites. Simulation of growth induced anisotropy proves the ordering of Fe3+ vacancies within octahedral sites. At equal number of available ferric ions and vacancies, the latter populate the octahedrons with distortion axis perpendicular to the film surface with the probability equal to 0.67. Deformation blockage of octahedral complexes with distortion axes directed along the film surface reduces this probability down to 0.14.

Manuilov, S. A.; Khartsev, S. I.; Grishin, A. M.

2009-12-01

160

Uniaxial anisotropy and high-frequency permeability of novel soft magnetic FeCoTaN and FeCoAlN films field-annealed at CMOS temperatures  

NASA Astrophysics Data System (ADS)

In order to investigate the anisotropy and high-frequency behaviour, soft magnetic FeCoTaN and FeCoAlN films were fabricated by reactive RF-magnetron sputtering. Six-inch targets consisting of Fe47Co36Ta17 and Fe49Co36Al15 were used to grow the films on oxidized (100)-silicon substrates with a TiN seed layer for better film adhesion. The concentration of nitrogen was adjusted by a flow control system. For applications in, e.g., aluminium CMOS processed components the films were annealed at temperatures of about 400?C in a static magnetic field of 50mT to induce a uniaxial anisotropy in the film plane by activating an atomic ordering process. Controlling the anisotropy by annealing demands a specified elaboration and results in an in-plane uniaxial anisotropy between 3 and 4mT. Nitrogen in both materials caused the formation of TaN or AlN which mainly supported the suppression of polycrystalline film growth. After deposition the films showed an amorphous structure and turned to be nanocrystalline after the annealing procedure. A saturation polarization in both materials amounted to between 1.1 and 1.2T. Ferromagnetic resonance frequencies of about 1.9GHz for FeCoTaN and 1.8GHz for FeCoAlN, determined by measuring the frequency-dependent permeability by means of a strip line permeameter up to 5GHz, were observed. The experimental results where compared with a spin dynamic model based on the Landau-Lifschitz and Maxwell's eddy current equation in the total frequency range.

Seemann, K.; Leiste, H.; Bekker, V.

2004-12-01

161

Optimization of perpendicular magnetic anisotropy tips for high resolution magnetic force microscopy by micromagnetic simulations  

NASA Astrophysics Data System (ADS)

Magnetic Force Microscopy (MFM) tip coated with perpendicular magnetic anisotropy film (PMA tip) is one of the choices for high resolution imaging at low scan height (SH), since it has negligible tip-sample interaction related to its stable magnetic state, sharp, and small tip stray field. In this work, detailed micromagnetic studies are carried out to understand the effect of geometrical and magnetic parameters including the cone angle ? of the PMA tip, intergrain exchange constant , saturation magnetization M s and uniaxial crystalline anisotropy constant K 1 of the tip coating on the MFM tip resolution. To evaluate the resolution performance of the optimized PMA tip, MFM images of high-density granular recording media and patterned media are simulated. We find that, for the PMA tip and its coating, a cone angle in a range of 36.9? to 53.1?, a saturation M s of 700 emu/cm3, a large uniaxial crystalline anisotropy constant K 1 (>4.9×106 erg/cm3) and a high intergrain exchange constant of (0.3-1.0)×10-6 erg/cm are optimized conditions for high resolution imaging. The optimized PMA tip has an excellent performance on imaging of high-density thin film media (bit size of 8×16 nm2) at low SH of 2-8 nm and bit pattern media with a pitch of 50 nm, edge-edge spacing of 5-15 nm at SH of 8-15 nm.

Li, Hongjia; Wei, Dan; Piramanayagam, S. N.

2013-09-01

162

Transversal magnetic anisotropy in nanoscale PdNi-strips  

NASA Astrophysics Data System (ADS)

We investigate submicron ferromagnetic PdNi thin-film strips intended as contact electrodes for carbon nanotube-based spintronic devices. The magnetic anisotropy and micromagnetic structure are measured as function of temperature. Contrary to the expectation from shape anisotropy, magnetic hysteresis measurements of Pd0.3Ni0.7 on arrays containing strips of various width point towards a magnetically easy axis in the sample plane, but transversal to the strip direction. Anisotropic magnetoresistance measured on individual Pd0.3Ni0.7 contact strips and magnetic force microscopy images substantiate that conclusion.

Steininger, D.; Hüttel, A. K.; Ziola, M.; Kiessling, M.; Sperl, M.; Bayreuther, G.; Strunk, Ch.

2013-01-01

163

Electric field control of thermal stability and magnetization switching in (Ga,Mn)As  

NASA Astrophysics Data System (ADS)

Magnetization switching induced by electric fields in the absence of external magnetic field has been demonstrated in a field effect structure with a (Ga,Mn)As layer having an in-plane magnetic anisotropy. The switching is related to the modulation of the in-plane magnetic anisotropy by electric fields. Reducing magnetic anisotropy energy height by electric fields, we observe stochastic magnetization switching.

Chiba, D.; Ono, T.; Matsukura, F.; Ohno, H.

2013-09-01

164

Anisotropy and Microstructure Analysis by Magnetic Measurement.  

National Technical Information Service (NTIS)

Analysis of digital data from the approach-to-saturation region of the hysteresis loop has been made convenient through the use of a microprocessor controlled hysteresigraph. To evaluate microstructure and magnetocrystalline anisotropy effects on the high...

G. F. Dionne J. A. Weiss G. A. Allen

1986-01-01

165

Understanding the magnetic anisotropy in Fe-Si amorphous alloys  

SciTech Connect

The origin of the magnetic anisotropy in a very disordered Fe-Si alloy has been investigated. The alloy containing 40 percent at. Si was prepared in the form of a thin film in a DC magnetron sputtering chamber. Structural disorder was obtained from Extended X-ray Absorption Fine Structure spectroscopy. The uniformity and lack of inhomogeneities at a microscopic level was checked by measuring their transverse magnetic susceptibility and hysteresis loops. The orbital component of the magnetic moment was measured by X-ray Magnetic Circular Dichroism spectroscopy. The orbital moment was extraordinary high, 0.4mB. Such a high value contrasted with the relatively small uniaxial anisotropy energy of the thin film (2kJ/m3). This suggests that the cause of the magnetic anisotropy in this alloy was a small degree of correlation in the orientation of the local orbital moments along a preferential direction.

Diaz, J.; Hamdan, N.M.; Jalil, P.; Hussain, Z.; Valvidares, S.M.; Alameda, J.M.

2002-08-01

166

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

National Technical Information Service (NTIS)

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...

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

2003-01-01

167

The magnetic anisotropy of samarium-alnico pseudobinary alloys  

NASA Astrophysics Data System (ADS)

The anisotropy properties of samarium-Alnico V pseudobinary alloys have been investigated. With alloys containing less than 12.0 mol% samarium, the K1 values are negative at 77 K and increase with increasing temperature to approximately zero at room temperature. The K2 values remain positive at all temperatures. We do not find the easy cone that has long been thought to be existed in those alloys with K1 < 0 and K2 #62; 0. In alloys with samarium contents between 13.3 and 19.0 mol%, the K1 and K2 values are positive at all temperatures. The anisotropy fields are not changed monotonically in the whole range of 10.1 to 19.0 mol% of samarium. It is concluded that the alloys are characteristics in thermodynamically of first-order transition. We have found that the ``hard cone'' exists in each of those alloys with samarium content more than 16.0 mol% and at temperatures above 77 K. The alloys with samarium less that 13.4 mol% also have ``hard cone'' under 77 K. However, the observed ``hard cone'' is different from the well known one in the first-order magnetization process, and it will collapse to the easy axis when the measuring field and temperature increase while under room temperature.

Chang, Y. H.; Weng, C. I.; Hsu, T. K.

1984-01-01

168

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

169

Tilted Uniaxial Magnetic Anisotropy in Sputtered TbFeCo Films  

NASA Astrophysics Data System (ADS)

Tb x(Fe50Co50)1- x films were deposited on glass slides using a DC sputtering apparatus. Torque measurements revealed that both perpendicular and in-plane uniaxial anisotropy components are induced in resputtered films with FeCo-dominant composition. The easy axis of the in-plane anisotropy component is aligned with the magnetic field applied during deposition. Torque curve analysis revealed that tilting of the easy axis from the film normal in alternate directions can reproduce the measured torque curves very well. In GdCo, DyCo and ErCo films, however, no appreciable in-plane uniaxial anisotropy was induced.

Shiomi, Shigeru; Kato, Junji; Saito, Seiji; Kobayashi, Tadashi; Masuda, Morio

1994-08-01

170

Giant magnetic anisotropy in Mn3O4 investigated by 55Mn2+ and 55Mn3+ NMR  

NASA Astrophysics Data System (ADS)

In Mn3O4, the magnetization along the c axis is different from that along the ab plane even in the strong field of 30 T. To investigate the origin of the huge magnetic anisotropy, Mn2+ and Mn3+ nuclear magnetic resonance spectra were measured in the 7-T magnetic field. The canting angle of the magnetic moments was estimated for various directions of field by rotating a single-crystalline Mn3O4 sample. One of the main results is that Mn3+ moments lie nearly in the ab plane in the external field perpendicular to the plane, meaning that the macroscopic magnetic anisotropy of Mn3O4 originates from the magnetic anisotropy of Mn3+ in the ab plane. The anisotropy field is estimated to be about 65 T. It is obvious that the Yafet-Kittel structure made of Mn2+ and Mn3+ spins lies in the ab plane due to this huge magnetic anisotropy, contrary to the previous reports. By the least-squares fit of the canting angle data for various field directions to a simple model, we obtained that JBB=1.88JAB-0.09 meV and KA=-14.7JAB+2.0 meV, where JAB, JBB, and KA are the exchange interaction constants between Mn2+ moments, Mn2+ and Mn3+ moments, and an anisotropy constant of Mn2+, respectively.

Kim, Changsoo; Jo, Euna; Kang, Byeongki; Kwon, Sangil; Lee, Soonchil; Shim, Jeong Hyun; Suzuki, Takehiko; Katsufuji, Takuro

2012-12-01

171

Determination of the distribution of transverse magnetic anisotropy in thin films from the second harmonic of Kerr signal  

NASA Astrophysics Data System (ADS)

We describe a method to determine the magnetic anisotropy distribution in thin films based on Kerr magnetometry, well adapted for single micro- and nanostructures. When the sample is excited by an ac field of small amplitude, for each value of a longitudinal dc field H, the second harmonic of the Kerr signal gives the contribution of the corresponding transverse anisotropy field Hk=H to the anisotropy distribution. The method is tested on a Permalloy-based multilayer microstructure, revealing two anisotropy contributions, one of them deviated from the perfect transverse direction. This confirms and extends a previous characterization performed by far more sophisticated methods.

García-Arribas, A.; Fernández, E.; Orue, I.; Barandiaran, J. M.

2013-09-01

172

Effect of anisotropy and dipole interaction on long-range order magnetic structures generated by Dzyaloshinskii-Moriya interaction  

NASA Astrophysics Data System (ADS)

Self-organized long-range order structures, such as stripe domains and magnetic skyrmion lattices, are formed by the competition between ferromagnetic exchange interaction and Dzyaloshinskii-Moriya (DM) interaction. We investigated the properties of the magnetic structures generated by a DM interaction under the influence of anisotropy or magnetic dipole interaction, by performing Monte-Carlo simulated annealing. We constructed phase maps in external-field and anisotropy space to study the effect of anisotropy or dipole interaction on the phase boundaries between the magnetic structures. The simulation results show that the phase boundaries are sensitive to perpendicular anisotropy and that the skyrmion lattice region in phase space is extended under easy-plane anisotropy. The effect of the long-range dipole interaction was studied and was found to stabilize the skyrmion lattice phase and reduce the size of the magnetic structures.

Kwon, H. Y.; Bu, K. M.; Wu, Y. Z.; Won, C.

2012-07-01

173

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

174

Orienting Paramecium with intense static magnetic fields  

NASA Astrophysics Data System (ADS)

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 fields, 2.5 T < B < 8 T were applied to immobilized (non-swimming) Paramecium Caudatum that were suspended in a density matched medium. The organisms align with their long axis parallel to the applied magnetic field. Their intrinsic diamagnetic anisotropy is 3x10-11 in cgs units. We will discuss the implications of these results for employing magnetic fields to probe the behavior of swimming Paramecium. [1] J. M. Valles, Jr. et al., Expt. Cell Res.274, 112-118 (2002).

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

2004-03-01

175

Field-induced energy band and effective mass anisotropy in coupled double quantum wells  

NASA Astrophysics Data System (ADS)

The effects of the field-induced conduction band anisotropy on the electron effective mass and electrical transport properties of coupled double quantum well structures are discussed. This anisotropy is due to the formation of a partial energy gap in the dispersion curves of coupled double quantum wells by an in-plane magnetic field. The reported data show that the magnitude of this gap is mainly dependent on the interwell coupling, although it also depends on the magnitude of the applied magnetic field. A field-induced anisotropy of the electron effective mass and the in-plane electrical transport properties, due to the formation of a saddle point at the lower edge of this gap, is predicted. Further, a simple model to estimate the critical field at which a saddle point appears is also discussed.

Velásquez, R.; Pankiewicz, C. G.

2008-07-01

176

VELOCITY ANISOTROPY AS A DIAGNOSTIC OF THE MAGNETIZATION OF THE INTERSTELLAR MEDIUM AND MOLECULAR CLOUDS  

SciTech Connect

We use a set of magnetohydrodynamic simulations of fully developed (driven) turbulence to study the anisotropy in the velocity field that is induced by the presence of the magnetic field. In our models, we study turbulence characterized by sonic Mach numbers M{sub s} from 0.7 to 7.5 and Alfven Mach numbers from 0.4 to 7.7. These are used to produce synthetic observations (centroid maps) that are then analyzed. To study the effect of large-scale density fluctuations and of white noise, we have modified the density fields and obtained new centroid maps, which are analyzed. We show that restricting the range of scales at which the anisotropy is measured makes the method robust against such fluctuations. We show that the anisotropy in the structure function of the maps reveals the direction of the magnetic field for M{sub A} {approx}< 1.5, regardless of the sonic Mach number. We find that the degree of anisotropy can be used to determine the degree of magnetization (i.e., M{sub A} ) for M{sub A} {approx}< 1.5. To do this, one needs an additional measure of the sonic Mach number and an estimate of the line of sight magnetic field, both feasible by other techniques, offering a new opportunity to study the magnetization state of the interstellar medium.

Esquivel, A. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, 04510 Mexico D.F. (Mexico); Lazarian, A., E-mail: esquivel@nucleares.unam.mx, E-mail: lazarian@astro.wisc.edu [Astronomy Department, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706-1582 (United States)

2011-10-20

177

Velocity Anisotropy as a Diagnostic of the Magnetization of the Interstellar Medium and Molecular Clouds  

NASA Astrophysics Data System (ADS)

We use a set of magnetohydrodynamic simulations of fully developed (driven) turbulence to study the anisotropy in the velocity field that is induced by the presence of the magnetic field. In our models, we study turbulence characterized by sonic Mach numbers Ms from 0.7 to 7.5 and Alfvén Mach numbers from 0.4 to 7.7. These are used to produce synthetic observations (centroid maps) that are then analyzed. To study the effect of large-scale density fluctuations and of white noise, we have modified the density fields and obtained new centroid maps, which are analyzed. We show that restricting the range of scales at which the anisotropy is measured makes the method robust against such fluctuations. We show that the anisotropy in the structure function of the maps reveals the direction of the magnetic field for MA <~ 1.5, regardless of the sonic Mach number. We find that the degree of anisotropy can be used to determine the degree of magnetization (i.e., MA ) for MA <~ 1.5. To do this, one needs an additional measure of the sonic Mach number and an estimate of the line of sight magnetic field, both feasible by other techniques, offering a new opportunity to study the magnetization state of the interstellar medium.

Esquivel, A.; Lazarian, A.

2011-10-01

178

Simulation of magnetization ripples on Permalloy caused by surface anisotropy  

NASA Astrophysics Data System (ADS)

A micromagnetic study of the magnetization distribution near the surface of bulk Permalloy shows the presence of periodic rippling in the magnetization. The dependence of the wavelength of these ripples on the strength of the surface anisotropy, together with their energy, depth of penetration and general structure, is reported.

Tucker, J. W.; Bishop, J. E. L.; Hua, Lu.

1995-02-01

179

Modification of Magnetic Anisotropy in Garnets by Ion Implantation  

Microsoft Academic Search

Ion implantation into epitaxial films of certain magnetic garnets grown on nonmagnetic substrates has produced layers with uniaxial anisotropy suitable for magnetic ``bubble'' formation and propagation. Implantation of hydrogen or lithium ions causes the garnet lattice to expand and the constraint of the unimplanted material places the implanted layer in lateral compression. In garnets with positive magnetostriction, this stress results

R. Wolfe; J. C. North; R. L. Barns; M. Robinson; H. J. Levinstein

1971-01-01

180

High-anisotropy nanocomposite films for magnetic recording  

Microsoft Academic Search

This paper presents results on the synthesis and properties of FePt- and CoPt-based high-anisotropy nanocomposite films. These films consist of high anisotropy L10 CoPt or FePt particles embedded in a nonmagnetic matrix such as C, SiO2, or B2 O3. The grain size and magnetic properties of these films ran he controlled by the processing temperatures and the film compositions. Particularly

D. J. Sellimyer; C. P. Luo; M. L. Yan; Y. Liu

2001-01-01

181

The magnetic anisotropy and its distribution in CoCrPtTa\\/CrV thin film recording media  

Microsoft Academic Search

CoCrPtTa\\/CrV thin films for longitudinal media, with high coercivity and small thickness, are studied. Particularly, the magnetic anisotropy is analyzed with determination of the distribution of anisotropy fields and measurement of rotational hysteresis energy losses. The results are correlated to the basic processes of magnetization and to the thermal stability of the magnetization. The role of the grain segregation state

G. Bottoni; D. Candolfo; A. Cecchetti

2002-01-01

182

Hyperfine field anisotropy of Co in C15 RCo2 compounds (R = rare earth)  

Microsoft Academic Search

Results of 59Co NMR investigation on the C15 type RCo2 compounds (R = rare earth) in the ferro-, ferri-, and paramagnetic states are reviewed. An enormous anisotropy in the 59Co hyperfine fields, which results in antiparallel hyperfine fields at two magnetically inequivalent Co sites in RCo2 compounds with the [111] or [011] easy axis, is attributed to unquenched orbital moment

S. Hirosawa; Y. Nakamura

1982-01-01

183

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

184

Structural origin of perpendicular magnetic anisotropy in Ni-W thin films  

NASA Astrophysics Data System (ADS)

The magnetic properties and microstructure of electrodeposited Ni-W thin films (0-11.7at% W in composition) were studied. The film structures were divided into three regions: an FCC nanocrystalline phase (0-2at% W), a transition region from FCC nanocrystalline to amorphous phase (2-7at% W), and an amorphous phase (>7at% W). In the transition region, (4-5at% W) films with perpendicular magnetic anisotropy (PMA) were found. The saturation magnetization, magnetic anisotropy field, perpendicular magnetic anisotropy and perpendicular coercivity for a typical Ni-W film (4.5at% W) were 420kA/m, 451kA/m, 230kJ/m and 113kA/m, respectively. The microstructure of Ni-W films with PMA is composed of isolated columnar crystalline grains (27-36nm) with the FCC phase surrounded by the Ni-W amorphous phase. The appearance of the interface between the magnetic core of Ni crystalline grains and the Ni-W non-magnetic boundary layer seems to be the driving mechanism for the appearance of PMA. The origin of PMA in Ni-W films is mainly attributed to the magnetoelastic anisotropy associated with in-plane internal stress and positive magnetostriction. The secondary source of PMA is believed to be the magnetocrystalline anisotropy of <111> columnar grains and its shape magnetic anisotropy. It is concluded that Ni-W electrodeposited films (4-5at% W) may be applicable for perpendicular magnetic recording media.

Sulitanu, N.

2001-05-01

185

Effect of in-plane uniaxial anisotropy on self-organized magnetic structures generated by the Dzyaloshinskii-Moriya interaction  

NASA Astrophysics Data System (ADS)

The influences of uniaxial in-plane anisotropy on the properties of ordered magnetic structures generated by the DM interaction were investigated by performing Monte-Carlo simulated annealing. The uniaxial anisotropy aligns the magnetic structure along a specific direction and helps to organize magnetic skyrmions to form either a horizontal or a vertical hexagonal structure, depending on the anisotropy strength. The uniaxial in-plane anisotropy not only enhances the ordering of the structure but also enriches the phases of the system, which include a rectangular lattice structure of skyrmions and 1D skyrmion arrays separated by stripe domains. We investigate the formation conditions of the anisotropy strength and the external field for various magnetic phases.

Oh, S. W.; Kwon, H. Y.; Won, C.

2013-03-01

186

An algorithm to extract effective magnetic parameters of thin film with in-plane uniaxial magnetic anisotropy  

Microsoft Academic Search

The calculation of high frequency complex permeability of thin ferromagnetic film requires the measured values of its saturation magnetization, anisotropic magnetic field intensity, resistivity, and thickness. It is often observed that the calculated permeability using the Landau-Lifshitz-Gilbert (LLG) theory does not agree well with the measured permeability of thin film with in-plane uniaxial magnetic anisotropy, owing to the measured anisotropic

C. P. Neo; J. Ding

2010-01-01

187

A model-assisted technique for characterization of in-plane magnetic anisotropy  

NASA Astrophysics Data System (ADS)

This paper describes a novel technique for characterizing in-plane magnetic anisotropy, such as stress anisotropy. The method involves applying a radially spreading ac field to a test sample, and detects simultaneously the field signals emanating from the sample surface along different directions using an angular array of Hall effect sensors. The technique was applied to detect the stress-induced anisotropy in an annealed Fe plate. Under uniaxial tension, the field signal measured along the stress axis increases while that along the transverse axis decreases. The stress sensitivity of the technique was characterized in terms of the ratio of the field signals measured along and perpendicular to the stress axis. The ratios measured at both the first- and third-order harmonic frequencies increase monotonically with stress, with the latter showing a higher stress sensitivity. The stress dependence of the field signal ratio was modeled based on the magnetomechanical effect theory, and was found to agree with the experimental results.

Fan, B.; Lo, C. C. H.

2012-04-01

188

Effect of Electron and Phonon Anisotropy on the Phonon-Drag Thermopower of a Classical Two-Dimensional Electron Gas in a Magnetic Field  

Microsoft Academic Search

The standard theory of the phonon-drag thermopower tensor S^ for a classical two-dimensional electron gas in a perpendicular magnetic field B describes fairly well the longitudinal tensor element Sgxx. However, the transverse tensor element Sgyx is only ~0.5% of what is measured in a GaAs\\/AlGaAs quantum well. This large error can be removed when B<3 T by allowing for the

P. N. Butcher; M. Tsaousidou

1998-01-01

189

Magnetic anisotropy and vortex dynamics in LCMO/YBCO heterostructures  

NASA Astrophysics Data System (ADS)

Interplay of ferromagnetism and superconductivity in heterostructures of highly spin polarized CMR oxides and cuprate superconductors, is of topical interest. We have used a sensitive radio-frequency (RF) resonant method based on a tunnel-diode oscillator (TDO) to simultaneously probe the dynamic magnetic susceptibility and the vortex penetration depth in well characterized sputtered bi-layers (LCMO/YBCO) and tri-layers (LCMO/YBCO/LCMO), grown on STO substrates with the thickness of LCMO and YBCO being 40 u.c. and 15 u.c., respectively. Transverse susceptibility in the normal state shows distinct peaks associated with the anisotropy fields in LCMO. In the superconducting state, complex coupled response is observed with the region just below Tc dominated by flux flow in a vortex liquid state. Experimental results with various field orientations are reported and analyzed in the context of proximity effect, spin diffusion, flux penetration and dissipation in the presence of geometrical barriers. Overall, our work demonstrates the effectiveness of RF experiments in probing the magnetization and vortex dynamics in these systems.

Srikanth, H.; Frey, N. A.; Visani, C.; Santamaria, J.

2007-03-01

190

Relationship between Magnetic Anisotropy and Syndeformational Remagnetization Inferred from Experimental Study  

NASA Astrophysics Data System (ADS)

Experimental investigations of deformation-induced remagnetization demonstrate that a primary remanence can survive conditions equivalent to moderate metamorphism in certain cases and that pre-deformation magnetic fabric can play an important role in determining the remanence stability. Results from shear experiments at elevated temperatures on magnetite-bearing rock-analogues demonstrate that complex interactions between temperature, applied field, stress, and anisotropy are responsible for determining the robustness of a pre-deformation magnetization. Syndeformational remagnetization is partly attributed to a stress-softening mechanism resulting in a piezoremanent magnetization, but the extent of remagnetization was largely dependent on the initial anisotropy, and generally unrelated to the deformation fabric. Similarly, the initial anisotropy of deformed samples is found to strongly influence the development of deformation fabrics and overprinting causes the deformation geometry to be obscured at low strains. These results raise several questions concerning paleomagnetic study in tectonized terranes and highlight a research area with much potential for future study.

Till, Jessica; Jackson, Mike; Moskowitz, Bruce

2013-04-01

191

Origin of easy magnetization switching in magnetic tunnel junctions with voltage-controlled interfacial anisotropy.  

PubMed

Spin-polarized currents represent an efficient tool for manipulating ferromagnetic nanostructures but the critical current density necessary for the magnetization switching is usually too high for applications. Here we show theoretically that, in magnetic tunnel junctions having electric-field-dependent interfacial anisotropy, the critical density may reduce down to a very low level (~10(4)?A cm(-2)) when the junction combines small conductance with the proximity of free layer to a size-driven spin reorientation transition. The theory explains easy magnetization switching recently discovered in CoFeB/MgO/CoFeB tunnel junctions, surprisingly showing that it happens when the spin-transfer torque is relatively small, and provides a recipe for the fabrication of magnetic tunnel junctions suitable for industrial memory applications. PMID:24067783

Pertsev, Nikolay A

2013-09-25

192

Critical Properties of Mixed Ising Spin System with Different Trimodal Transverse Fields in the Presence of Single-Ion Anisotropy  

Microsoft Academic Search

Within the framework of an effective field approximation, the effects of single-ion anisotropy and different trimodal transverse fields of two sublattices on the critical properties of the mixed spin-1\\/2 and spin-1 Ising system are investigated on the simple cubic lattice. A smaller single-ion anisotropy can magnify magnetic ordering phases and a larger one can depress magnetic ordering phase for T-?1\\/2

Chen Qiang; Yan Shi-Lei

2006-01-01

193

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

194

Magnetic anisotropy in strained manganite films and bicrystal junctions  

NASA Astrophysics Data System (ADS)

Transport and magnetic properties of La0.67Sr0.33MnO3 (LSMO) manganite thin films and bicrystal junctions were investigated. Epitaxial manganite films were grown on SrTiO3, LaAlO3, NdGaO3 (NGO), and (LaAlO3)0.3 + (Sr2AlTaO6)0.7 substrates, and their magnetic anisotropy were determined by two independent techniques of magnetic resonance spectroscopy. It was demonstrated that by using these techniques, a small (0.3%) anisotropy of crystal structure at the (110) surface plane of the orthorhombic NGO substrate leads to uniaxial magnetic anisotropy of the films in the plane of the substrate at least at the room temperature. It was found that on vicinal NGO substrates, the value of magnetic anisotropy strength can be varied in the range 100-200 Oe at T = 295 K by changing the substrate vicinal angle from 0° to 25°. Measurement of the magnetic anisotropy of manganite bicrystal junction demonstrated the presence of two ferromagnetic spin subsystems for both types of bicrystal boundaries with tilting of basal plane of manganite tilted bicrystal (TB-junction) and with rotation of crystallographic axes (RB-junction) used for comparison. The magnetoresistance of TB-junctions increases with decreasing temperature and the misorientation angle. Variation of bicrystal misorientation angle does not lead to change of misorientation of easy magnetic axes in the film parts forming TB-junction. Analysis of the voltage dependencies of bicrystal junction conductivity show that the low value of the magnetoresistance for the LSMO bicrystal junctions can be caused by two scattering mechanisms. The first one is the spin-flip of spin-polarized carriers due to the strong electron-electron interactions in a disordered layer at the bicrystal boundary at low temperatures and the second one is spin-flip by antiferromagnetic magnons at high temperatures.

Demidov, V. V.; Ovsyannikov, G. A.; Petrzhik, A. M.; Borisenko, I. V.; Shadrin, A. V.; Gunnarsson, R.

2013-04-01

195

[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

196

Magnetostriction of rare-earth random magnetic anisotropy spin glasses  

Microsoft Academic Search

A model of magnetostriction for single-ion random magnetic anisotropy (RMA) spin glasses (SG) is developed, the calculation being based on the replica technique. An overall uniform strain is assumed and coupled to the local easy axis (or easy plane) by an adequate projection. The obtained bulk magnetostriction becomes proportional to the average quadrupolar moment, which depends upon the assumed ferromagnetic

A. del Moral; J. I. Arnaudas

1989-01-01

197

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

198

Ab initio calculations of magnetic anisotropy in transition metals  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy is the physical phenomenon that determines the direction of the magnetization in a sample. It plays an important role in applications like computer disks. Spin orbit coupling is responsible for relating the direction of the spin magnetic moment and the crystalline axes in a solid. The changes in energy as a function of the direction of the magnetization are very small, and numerical calculations have to be performed very precisely. Numerical errors are responsible for the large discrepancy between published theoretical results. Reliable results, however, still differ from experiment, which shows that additional correlation effects between the electrons have to be taken into account. Changes in the magnetocrystalline anisotropy as a function of changes in the interatomic hopping parameters are very subtle, and show that the necessary integrals are long range both in real space and in reciprocal space.

Jansen, Henri

2000-05-01

199

Dependence of hard-axis anisotropy field on domain wall width for current-induced domain wall motion in nanowires  

NASA Astrophysics Data System (ADS)

The dependence of the hard-axis anisotropy field on the domain wall width for current-induced domain wall motion in perpendicularly magnetized anisotropic nanowires was investigated using micromagnetic simulations. The hard-axis anisotropy field in nanowires was estimated by varying the magnetic anisotropy constant and the exchange stiffness constant, and the hard-axis anisotropy constant was calculated from the energy differences of the Bloch and Néel walls. As a result, when the stable domain wall is a Bloch wall, the hard-axis anisotropy field and the intrinsic critical current velocity decrease with increasing domain wall width, whereas when the stable domain wall is a Néel wall, they increase with increasing domain wall width. It was clarified that the intrinsic critical current velocity can be expressed as a function of the domain wall width, even though the analytical solution indicated that the critical current velocity would be monotonically reduced by decreasing the domain wall width.

Ito, Makoto; Ooba, Ayaka; Komine, Takashi; Sugita, Ryuji

2013-08-01

200

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

201

Doping effects of Fe ion on magnetic anisotropy of YBa2Cu3Oy  

NASA Astrophysics Data System (ADS)

We report magnetic alignment of YBa2(Cu1-xFex)3Oy (Fe-doped Y123, x = 0-0.1) powders under modulated rotation magnetic fields (MRFs) and roles of Fe ion as a determination factor of magnetic anisotropy in Y123. The Fe-free and Fe-doped Y123 powder samples aligned in the MRF of 10 T showed two different orientation types of the hard axis in Y123 grains. From an X-ray rocking curve measurement for the magnetically aligned powder samples of the Fe-doped Y123, inplane magnetic anisotropy for Y123 grains with the hard axis parallel to the [1 1 0] direction was found to be higher than that for Y123 grains with the hard axis parallel to the [0 1 0] direction.

Ugawa, T.; Horii, S.; Maeda, T.; Haruta, M.; Shimoyama, J.

2013-11-01

202

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

203

Chemical trends of the magnetocrystalline anisotropy of magnetic monolayers  

Microsoft Academic Search

The in-plane and out-of-plane magnetocrystalline anisotropy energies of 3d, 4d, and 5d magnetic monolayers are calculated using the self-consistent density functional theory in the local spin density approximation (LSDA) and the generalized gradient approximation (GGA), as implemented by the film and bulk FLAPW code FLEUR. The spin-orbit interaction is included using a second variation method. The magnetic monolayers are treated

X. Nie; Su-Huai Wei; Stefan Blügel

2001-01-01

204

The effect of uniaxial pressure on the magnetic anisotropy of the Mn12-Ac single-molecule magnet  

NASA Astrophysics Data System (ADS)

We study the effect of uniaxial pressure on the magnetic hysteresis loops of the single-molecule magnet Mn12-Ac. We find that the application of pressure along the easy axis increases the fields at which quantum tunneling of magnetization occurs. The observations are attributed to an increase in the molecule's magnetic anisotropy constant D of 0.142(1)%/kbar. The increase in D produces a small, but measurable increase in the effective energy barrier for magnetization reversal. Density-functional theory calculations also predict an increase in the barrier with applied pressure.

Atkinson, James H.; Park, K.; Beedle, C. C.; Hendrickson, D. N.; Myasoedov, Y.; Zeldov, E.; Friedman, Jonathan R.

2013-05-01

205

Magnetization configurations and reversal of thin magnetic nanotubes with uniaxial anisotropy  

NASA Astrophysics Data System (ADS)

We present calculations of the magnetization configuration and reversal behavior of magnetic nanotubes with uniaxial anisotropy by means of two-dimensional micromagnetic simulations and analytical methods. The tube radii R from 50 to 150 nm and the tube length /radius aspect ratio L/R<=20 were explored. For a finite length of magnetic nanotubes the magnetization configuration is characterized by a uniformly magnetized along the tube axis middle part and two nonuniform curling states of a length Lc in two ends of the tube with the same or opposite magnetization rotating senses, referring as C-state or B-state, respectively. We found that the magnetization configuration of the C-state exists for thin nanotubes with the tube thickness, ?R, in the range of ?R/R<=0.2. For thicker nanotubes the strong magnetostatic stray field forces the change of rotating senses of the end domains in opposite directions (the B-state). The transition from the C-state to a vortex state with in-plane magnetization is described as function of the tube geometrical parameters. The nanotube hysteresis loops and switching fields were calculated. The simple analytical model was developed to describe the nanotube magnetization reversal reducing its description to the Stoner-Wohlfarth model with effective parameters. The equilibrium state of nanotube is described in terms of ?, the angle of the magnetization deviation from the intrinsic tube easy axis. The L/R dependence of the C-state magnetization, the shape of hysteresis loops and the switching field values are described by a dependence of ? on L/R.

Chen, A. P.; Guslienko, K. Y.; Gonzalez, J.

2010-10-01

206

Reconstructing the Depositional Environment at the Dolni Vestonice (Czech Republic) Loess Site from Magnetic Anisotropy  

NASA Astrophysics Data System (ADS)

Loess and paleosol deposits, worldwide, have provided an important medium from which paleoclimatic conditions and paleoenvironments could be reconstructed. Within the field of environmental magnetism, the most fruitful data have been time series of various common magnetic parameters, such as, but not exclusively, bulk magnetic susceptibility and its frequency dependence, magnetic hysteresis derived parameters, and remanent magnetizations. Magnetic anisotropy data, capable of determined the orientation distribution of mineral particles within oriented bulk specimens, have proven to be a powerful tool even in non-lithified and poorly consolidated aeolian sediment. A 15 meter long loess and paleosol section at the Dolni Vestonice site in the Czech Republic (48°53'11.5''N 16°39'15.8''E) was investigated within the framework of a multi-disciplinary funded research project (ANR-08-BLAN-0227-CSD6). Here we present the interpretation of the anisotropy of magnetic susceptibility data set. Oriented specimens were collected from the 1 meter depth mark to the base of the section at a 5 or 10 cm depth sampling interval. Overall, 2 to 4 specimens were obtained at each sampling depth for a total of 632 specimens. The mean bulk magnetic susceptibility along the deposit is everywhere below 56 x 10-8 m3/kg and the degree of magnetic anisotropy (Pj) does not exceed 1.05. Intra-sampling depth reproducibility between specimens is good except in sand rich loess of the upper rapidly accumulating intervals. The magnetic anisotropy data, combined with field observations, optically stimulated luminescence chronology and other analytical data, reveal a fairly complete history of loess accumulation since the last interglacial. Nonetheless, the depositional environment was likely marked by hiatus, by erosional surfaces, and by post-depositional deformations driven by the local geomorphology and the regional tectonic setting.

Lagroix, F.; Rousseau, D.; Antoine, P.; Fuchs, M.; Hatté, C.; Moine, O.; Gauthier, C.; Lisa, L.; Svoboda, J.

2011-12-01

207

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

208

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

Microsoft Academic Search

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

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

2010-01-01

209

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

210

Magnetic anisotropy and high-spin effects in single-molecule transistors  

NASA Astrophysics Data System (ADS)

Fabrication of single-molecule transistors where electron transport occurs through an individual molecule has become possible due to the recent progress in molecular electronics. Three-terminal configuration allows charging molecules and performing transport spectroscopy in multiple redox states. Single-molecule magnets combining large spin with uniaxial anisotropy are of special interest as appealing candidates for high density memory applications and quantum information processing. We study single-molecule magnets Fe4. Three-terminal junctions are fabricated using electromigration of gold nanowires followed by a self-breaking. High-spin Kondo effect and inelastic cotunneling excitations show up in transport measurements. Several excitations feature the energy close to the energy of zero-field splitting (ZFS) of a ground spin multiplet in bulk. This splitting is caused by the anisotropy and is a hallmark of single-molecule magnets. We observe nonlinear Zeeman effect due to a misalignment of an anisotropy axis and a magnetic field direction. The ZFS energy is increased in oxidized and reduced states of the molecule indicating enhancement of the anisotropy in these states.

Zyazin, Alexander; van den Berg, Johan; Osorio, Edgar; Konstantinidis, Nikos; Leijnse, Martin; May, Falk; Hofstetter, Walter; Danieli, Chiara; Cornia, Andrea; Wegewijs, Maarten; van der Zant, Herre

2011-03-01

211

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

212

Rotatable magnetic anisotropy in Si/SiO2/(Co2Fe)xGe1-x Heusler alloy films.  

PubMed

Polycrystalline (Co2Fe)xGe1-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

2013-09-11

213

Rotatable magnetic anisotropy in Si/SiO2/(Co2Fe)xGe1-x Heusler alloy films  

NASA Astrophysics Data System (ADS)

Polycrystalline (Co2Fe)xGe1-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.

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.

2013-10-01

214

Investigation of magnetic anisotropy in Co nanoparticles using ferromagnetic resonance technique  

NASA Astrophysics Data System (ADS)

Using ferromagnetic resonance (FMR) technique, we have investigated the temperature dependence and angular dependence of line width and resonance magnetic field of Co nanoparticles capped with novel alkane carboxylic acids of varying chain lengths. The magnetic properties such as blocking temperature and anisotropy sensitively depend on the chain length as evidenced by the temperature dependence of line width. These results indicate that the magnetic properties of these samples are critically governed by the interparticle interactions which are decided by the chain length. The presence of anisotropy even up to very high temperature above the blocking temperature observed in these studies confirms the presence of inter-particle magnetic interactions as well as intra-particle exchange interaction between the core and shell regions as evidenced by our earlier ac susceptibility and transverse susceptibility measurements on similar system.

Sendilkumar, A.; Kasture, Manasi; Patel, Pitamber; Ramana, C. V.; Prasad, B. L. V.; Srinath, S.

2010-01-01

215

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

216

Determination of the Fe Magnetic Anisotropies and the CoO Frozen Spins in Epitaxial CoO/Fe/Ag(001).  

National Technical Information Service (NTIS)

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 o...

A. Scholl C. A. Jenkins E. Areholz J. Li Y. Meng

2011-01-01

217

Induced magnetic anisotropy in stress-annealed Galfenol laminated rods  

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

218

Anisotropy and microstructure of rare-earth permanent-magnet materials. Final report, December 1083-March 1986  

SciTech Connect

This report is divided into two parts, the microstructural investigations and the anisotropy measurements of rare-earth permanent-magnet materials. Section I shows that the hard magnetic properties, i.e. coercivity, of the individual Nd-Fe-B permanent magnet material strongly depends on the compositional and processing parameters (milling, blending, annealing, etc.) and are directly correlated to the microstructural properties (grain size, composition and distribution of phases, crystal defects and precipitates) and to the magnetocrystalline anisotropy of the material. By means of transmission electron microscopy together with STEM x-ray microanalysis, at least three categories of phases were identified in sintered rare earth-iron permanent magnets. From microstructural investigations it can be assumed that the coercivity of sintered rare earth-iron permanent magnet materials is controlled by the nucleation and expansion fields for reversed domains. In Section II the magnetic anisotropy measurements of various rare earth-iron based magnets between 80 K and the Curie temperature are shown and the results are discussed by means of a expanded model for the anisotropy field. From the study of the temperature dependence of the anisotropy field of the mixed crystal series (N,RE)15Fe77B8 (RE=Y, La, Ce) the ine ion character of the Nd sublattice is shown.

Skalicky; Fidler; Groessinger; Kirchmayr

1986-01-01

219

Domain structure in biaxial Fe/Cr films induced by lateral fluctuations of the magnetic anisotropy  

NASA Astrophysics Data System (ADS)

The magnetic microstructure of single-crystalline Fe(001) thin films has been studied by magnetic second harmonic generation and conventional magneto-optical Kerr effect methods. The layers were grown on GaAs/Fe/Ag(100) substrates, capped by a Cr overlayer, and displayed a fourfold in-plane magnetic anisotropy. We observe the formation of a multidomain structure at magnetic fields |H|?0.5kOe , when the field is applied in a narrow range of azimuthal angles close to the hard axis direction (|??|<1°) . The domains are characterized by the same longitudinal magnetization component Mx and transverse components My of opposite signs. We developed an approach to extract the change of the relative contributions of domains with different magnetization directions during magnetization reversal from the experimental data. The formation of a domain structure can be explained by taking into account the lateral fluctuations of the magnetic anisotropy energy caused by defects and stress at the interfaces and the role of the biquadratic exchange coupling between interfacial Fe and Cr magnetic moments.

Rzhevsky, A. A.; Krichevtsov, B. B.; Bürgler, D. E.; Schneider, C. M.

2008-05-01

220

Role of anisotropy and interactions in magnetic nanoparticle systems  

Microsoft Academic Search

.  Magnetic nanoparticle systems are characterized by several competing effects like anisotropy, an inherent disorder, the long\\u000a range dipolar and the short range exchange interactions due to clustering effects. The sensitivity of the observed static\\u000a and dynamical properties of these systems like the blocking temperature, the hysteresis and the susceptibility, to the methods\\u000a of preparation, annealing and the resulting morphology is

R. Malik; S. Lamba; R. K. Kotnala; S. Annapoorni

2010-01-01

221

Spin-orbit effect and magnetic anisotropy in Pt clusters  

NASA Astrophysics Data System (ADS)

Based on the non-collinear (NCL) and spin-orbit coupling (SOC) implementation of the density-functional theory (DFT) calculations, isomeric structures, spin and orbital moments, magnetic anisotropies, as well as magnetic anisotropy energy (MAE) are investigated for Ptn clusters (n=2-8, 13). Our studies show that the planar structures are superior to the three-dimensional structures in stabilizing Pt clusters up to n=7, favored by both scalar relativistic calculations and SOC calculations. For each cluster size, relative stabilities of different low-lying energy isomers are not alternated by the SOC effects. Strong magnetic anisotropies and remarkable orbital moments (0.1-0.4?B/atom) are found in Pt clusters. The easy axes usually prefer the orientations that are in the basal planes of the structures and parallel to the principal axes of symmetry. There is always collinearity between total spin moments and total orbital moments, favoring a strict ferromagnetic coupling. It is revealed that small Pt clusters mostly exhibit large MAEs.

Yuan, H. K.; Chen, H.; Kuang, A. L.; Wu, B.

2013-04-01

222

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

223

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

224

Effect of pressure anisotropy and flow velocity on Kelvin-Helmholtz instability of anisotropic magnetized plasma using generalized polytrope laws  

Microsoft Academic Search

The effect of pressure anisotropy and flow velocity on the Kelvin-Helmholtz (KH) instability of two magnetized anisotropic pressure plasmas flowing relative to each other is investigated using generalized polytrope laws. The anisotropic pressure with the generalized polytrope laws is considered with three-dimensional perturbations in the description of plasma using relevant magnetohydrodynamic (MHD) set of equations. The magnetic field is assumed

R. P. Prajapati; R. K. Chhajlani

2010-01-01

225

Effect of pressure anisotropy and flow velocity on Kelvin–Helmholtz instability of anisotropic magnetized plasma using generalized polytrope laws  

Microsoft Academic Search

The effect of pressure anisotropy and flow velocity on the Kelvin–Helmholtz (KH) instability of two magnetized anisotropic pressure plasmas flowing relative to each other is investigated using generalized polytrope laws. The anisotropic pressure with the generalized polytrope laws is considered with three-dimensional perturbations in the description of plasma using relevant magnetohydrodynamic (MHD) set of equations. The magnetic field is assumed

R. P. Prajapati; R. K. Chhajlani

2010-01-01

226

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,

227

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

228

Confined stripe structure in periodically grooved NdCo Films with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Magnetic multilayers are broad research field with many interesting phenomena depending on interlayer coupling. Also, since the development of nanolithography techniques, magnetic nanowires and dots have been intensively investigated [1]. Recently, as a combination of these two fields, the concept of magnetic lateral superlattice has emerged: continuous magnetic films with a lateral modulation of their magnetic properties at submicrometric length scale [2]. In this work, we have fabricated amorphous Nd-Co films with perpendicular magnetic anisotropy and a periodic thickness modulation by e-beam lithography and ion milling. Lateral periods range from 2 ?m - 500 nm and groove depths from 10 to 30 nm. MFM and Kerr magnetometry have been used for characterization. Lateral patterning modifies the interplay between magnetostatic energy, perpendicular and in plane anisotropy and exchange interaction resulting in confined magnetic stripe structures. The different regimes that appear depending on the size of the periodic thickness modulation relative to the magnetic stripe period will be discussed. [1] J.I Martin et al, JMMM, 256 (2003) 449 [2] S. P. Li et al, PRL 88 (2002) 087202; N. Martin et al, PRB 83 (2010) 174423

Martin, Jose I.; Hierro-Rodriguez, Aurelio; Cid, Rosalia; Rodriguez-Rodriguez, Gabriel; Velez, Maria; Alvarez-Prado, Luis M.; Alameda, Jose M.

2012-02-01

229

Intrinsic anomalous magnetic anisotropy of CdCr2S4  

NASA Astrophysics Data System (ADS)

The magnetocrystalline anisotropy of the ferromagnetic spinel CdCr2S4 was investigated by ferromagnetic resonance measurements. By avoiding any contact to iron during the sample preparation we can exclude that the anisotropy is due to ferrous impurities, and by performing wavelength dispersive electron probe microanalysis as well as annealing experiments, it is demonstrated that the samples possess almost ideal stoichiometry. The resonance data suggest that compositional deviations from the stoichiometry up to 10-3 have no influence on our conclusion that the magnetocrystalline anisotropy is an intrinsic property of CdCr2S4, caused by trigonal distortion of the sulfur octahedra surrounding the Cr3+ ions. Anomalous low-temperature linewidth maxima in the <111> directions can be understood by considering the crystal fields acting on inequivalent sites of the magnetic ions in the spinel structure and by taking into account the effect of exchange narrowing.

Ehlers, D.; Tsurkan, V.; von Nidda, H.-A. Krug; Loidl, A.

2012-11-01

230

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

Microsoft Academic Search

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

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

1981-01-01

231

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)

1998-07-01

232

Magnetic anisotropy of antiferromagnet and its role on the exchange bias in ferromagnetic\\/antiferromagnetic bilayers  

Microsoft Academic Search

The origin of the magnetic anisotropy of the antiferromagnetic (AF) layer and the role of it on the magnetization process of exchange-coupled ferromagnetic\\/AF bilayers are discussed. Through the magnetic torque analysis of a polycrystalline Ni-Fe\\/Mn-Ir bilayer and a pseudo-single crystalline Ni-Fe\\/Mn-Ni bilayer, the magnetocrystalline anisotropy of the antiferromagnet is strongly suggested to be the origin of the magnetic anisotropy of

Migaku Takahashi; Masakiyo Tsunoda

2002-01-01

233

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

234

Magnetic field line Hamiltonian  

SciTech Connect

The basic properties of the Hamiltonian representation of magnetic fields in canonical form are reviewed. The theory of canonical magnetic perturbation theory is then developed and applied to the time evolution of a magnetic field embedded in a toroidal plasma. Finally, the extension of the energy principle to tearing modes, utilizing the magnetic field line Hamiltonian, is outlined.

Boozer, A.H.

1985-02-01

235

Anisotropy in Magnetic Properties and Electronic Structure of Single Crystal LiFePO4  

SciTech Connect

We report the experimental and theoretical results on the anisotropies in the magnetic properties and x-ray absorption spectra of single-crystal LiFePO4. A mean-field theory is developed to explain the observed strong anisotropies in Lande g-factor, paramagnetic Curie temperature, and effective moment for LiFePO4 single crystals. The values of the in-plane nearest- and next-nearest-neighbor spin exchange (J1 and J2), interplane spin exchange (J{perpendicular}), and single-ion anisotropy (D), obtained recently from neutron scattering measurements, are used for calculating the Curie temperatures with the formulas derived from the mean-field Hamiltonian. It is found that the calculated Curie temperatures match well with that obtained by fitting the magnetic susceptibility curves to the modified Curie-Weiss law. For the polarized Fe K-edge x-ray absorption spectra of single-crystal LiFePO4, a different feature assignment for the 1s4p transition features is proposed and the anisotropy in the intensities of the 1s3d transition features is explained adequately by a one-electron theory calculation of the electric quadrupole transition terms in the absorption coefficient.

Liang,G.; Park, K.; Li, J.; Benson, R.; Vaknin, D.; Markert, J.; Croft, M.

2008-01-01

236

Anisotropy in magnetic properties and electronic structure of single-crystal LiFePO4  

SciTech Connect

We report the experimental and theoretical results on the anisotropies in the magnetic properties and x-ray absorption spectra of single-crystal LiFePO{sub 4}. A mean-field theory is developed to explain the observed strong anisotropies in Lande g-factor, paramagnetic Curie temperature, and effective moment for LiFePO{sub 4} single crystals. The values of the in-plane nearest- and next-nearest-neighbor spin exchange (J{sub 1} and J{sub 2}), interplane spin exchange (J{perpendicular}), and single-ion anisotropy (D), obtained recently from neutron scattering measurements, are used for calculating the Curie temperatures with the formulas derived from the mean-field Hamiltonian. It is found that the calculated Curie temperatures match well with that obtained by fitting the magnetic susceptibility curves to the modified Curie-Weiss law. For the polarized Fe K-edge x-ray absorption spectra of single-crystal LiFePO{sub 4}, a different feature assignment for the 1s {yields} 4p transition features is proposed and the anisotropy in the intensities of the 1s {yields} 3d transition features is explained adequately by a one-electron theory calculation of the electric quadrupole transition terms in the absorption coefficient.

Liang, G.; Park, K.; Li, J.; Benson, R.; Vaknin, D; Markert, J.; Croft, M.

2008-02-12

237

Anisotropy of the Reflected Radiation Field Over Melting Glacier Ice  

Microsoft Academic Search

In this article we analyze the anisotropy of the reflected radiation field over melting glacier ice using 118 ground-based radiance measurements in Landsat TM Bands 2 and 4. The measurements were carried out on the tongue of the Morteratschgletscher, Switzerland. On the basis of directional measurements several bidirectional reflectance distribution functions (BRDFs) were derived for dirty and clean glacier ice

Wouter H. Knap; Carleen H. Reijmer

1998-01-01

238

Anisotropy in the sound field generated by a bubble chain  

Microsoft Academic Search

A vertical chain of rising bubbles represents a transition from individual to continuum behaviour in a compressible gas–liquid flow. Experiments on the distribution of acoustic pressure around a bubble chain revealed a strong anisotropy in the acoustic field in the frequency band generated by individual bubbles. Sound appeared to propagate much more efficiently along the chain than normal to it.

Richard Manasseh; Aneta Nikolovska; Andrew Ooi; Shizuo Yoshida

2004-01-01

239

Anisotropy in the sound field generated by a bubble chain  

Microsoft Academic Search

A vertical chain of rising bubbles represents a transition from individual to contin- uum behaviour in a compressible gas-liquid flow. Experiments on the distribution of acoustic pressure around a bubble chain revealed a strong anisotropy in the acous- tic field in the frequency band generated by individual bubbles. Sound appeared to propagate much more eciently along the chain than normal

Richard Manasseh; Aneta Nikolovska; Andrew Ooi; Shizuo Yoshida

2003-01-01

240

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

241

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

242

Dipole interaction and magnetic anisotropy in gadolinium compounds  

NASA Astrophysics Data System (ADS)

The influence of the dipole interaction on the magnetic anisotropy of Gd compounds is investigated. Available data on ferromagnets and antiferromagnets with different crystal structures are discussed and complemented by new neutron scattering experiments on GdCu2In, GdAu2Si2, GdAu2, and GdAg2. If the propagation vector of the magnetic structure is known, the orientation of the magnetic moments as caused by the dipole interaction can be predicted by a straightforward numerical method for compounds with a single Gd atom in the primitive unit cell. The moment directions found by magnetic diffraction on GdAu2Si2, GdAu2, GdAg2, GdCu2Si2, GdNi2B2C, GdNi2Si2, GdBa2Cu3O7, GdNi5, GdCuSn, GdCu2In, GdCu4In, and GdX (X=Ag, Cu, S, Se, Sb, As, Bi, P) are compared to the predicted directions resulting in an almost complete accordance. Therefore, the dipole interaction is identified as the dominating source of anisotropy for most Gd compounds. The numerical method can be applied to a large number of other compounds with zero angular momentum.

Rotter, M.; Loewenhaupt, M.; Doerr, M.; Lindbaum, A.; Sassik, H.; Ziebeck, K.; Beuneu, B.

2003-10-01

243

Piezoelectric enhancement of giant magnetoresistance in spin-valves with different magnetic anisotropies  

NASA Astrophysics Data System (ADS)

The phenomenon of giant magnetoresistance (GMR) in spin-valves under applied magnetic field is well established. We present piezoelectric control of the GMR ratio at room temperature for standard multilayered spin-valve structure fabricated on (011)-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) piezoelectric substrate. Four samples namely, S1, S2, S3, and S4 were, respectively, fabricated such that the magnetic easy axis makes an initial angle of 0°, 30°, 45°, and 60° with magnetic field applied during measurement. For S1, the GMR ratio decreases under electric field whereas it increases for the samples making progressively larger initial magnetization angles with the external field. We suggest that for S1, magnetic alignment between the two magnetic layers decreases due to the rotation of bottom free layer magnetization resulting in the decrease of antiparallel resistance as well as the GMR ratio under applied electric field whereas for the other samples, the antiparallel resistance increases due to improvement in antiparallel alignment between the two magnetic layers causing increase in the GMR ratio at room temperature. Our results establish new way to control and even enhance the magnetoresistance via converse piezoelectric effect in spin-valves with different magnetic anisotropies.

Rizwan, Syed; Zhang, S.; Yu, Tian; Zhao, Y. G.; Han, X. F.

2013-01-01

244

Field induced unidirectional anisotropy in NiMn and NiMnPt alloys  

NASA Astrophysics Data System (ADS)

We report the characterization of the magnetic properties of polycrystalline disks of Ni72Mn28 and Ni(72-x)Mn28Ptx (x=1.0, 4.0, and 10.0) at 4.2 K induced by field cooling (FC). It is found that the FC-induced anisotropy field HK, and coercivity HC, are strongly enhanced by the addition of Pt impurities. The remanent magnetization in the direction of the initial applied field (in the disk plane) for each samples can be rotated from 0° to 180° and back to 0° in various stationary fields above and below HK and the parallel component is measured (the longitudinal magnetization component ML). From the analysis of the angular dependence of ML, we show that these results can be accounted for by the coexistence of Mn(Ni)-rich and/or Mn(Ni)-deficient nanoscale regions coupled antiferromagnetically. It is found that the unidirectional anisotropy originates from interfacial exchange interactions between these regions. Up to some critical angle rotation (?c) relative to H, the unidirectional anisotropy field turns rigidly with the sample, while above ?c, the coupled regions become unstable and magnetically rearrange such that a unidirectional anisotropy is induced along H. The value of ?c varies from region to region. An increase in HK and HC with increasing Pt content can be attributed to the increase in the number of antiferromagnetically coupled regions of decreasing size. In addition, it is found that some ordered single-domain clusters (presumably Ni3Mn compound) are distributed within the disordered Ni or Mn-rich regions.

Öner, Y?ld?rhan

2013-10-01

245

Magnetostriction and magnetic anisotropy in rare earth intermetallic compounds  

Microsoft Academic Search

An analysis of the magnetoelastic coupling and the magnetocrystalline anisotropy in rare earth intermetallic compounds has been undertaken on the basis of a microscopic description. Crystal electric field and exchange interaction have been considered as the main contribution to the free energy in order to explain the behaviour. Magnetostriction measurements on cubic (RAl2, RNi2) and uniaxial (RCo5 and R2Fe14B) compounds

M. R. Ibarra; A. del Moral

1990-01-01

246

Torque Measurements on Liquid Crystals in a Rotating Magnetic Field  

Microsoft Academic Search

The torque exerted on nematic liquid crystals due to a rotating magnetic field is investigated. Measurements of this torque on EBBA, MBBA and a 1:1 mixture of these as a function of temperature, magnetic field and frequency of rotation are reported. Comparison with theory shows reasonable agreement and yields the magnetic susceptibility anisotropy and the twist viscosity as a function

P. J. Flanders; S. Shtrikman

1973-01-01

247

Modeling the properties of ferrogels in uniform magnetic fields  

Microsoft Academic Search

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

Dean S. Wood; Philip J. Camp

2011-01-01

248

The influence of magnetic anisotropy on magnetoelectric behavior in conical spin ordered multiferroic state  

Microsoft Academic Search

For the magnetism-driven multiferroic materials, the magnetic anisotropy plays an essential role in the magnetoelectric behavior. To understand the influence of magnetic anisotropy on multiferroic state resulting from the conical spin order, we have performed Monte Carlo simulation on a three-dimensional classical Heisenberg model in spinel lattice. The single-ion anisotropy from the easy-axis type to the easy-plane type is considered

Xiaoyan Yao; Veng Cheong Lo; Jun-Ming Liu

2010-01-01

249

Anisotropy of magnetic interactions in the spin-ladder compound (C5H12N)2CuBr4  

NASA Astrophysics Data System (ADS)

Magnetic excitations in the spin-ladder material (C5H12N)2CuBr4 (BPCB) are probed by high-resolution multifrequency electron spin resonance (ESR) spectroscopy. Our experiments provide a direct evidence for a pronounced anisotropy ( ˜5% of the dominant exchange interaction), that is in contrast to a fully isotropic spin-ladder model employed for this system previously. It is argued that this anisotropy in BPCB is caused by spin-orbit coupling, which appears to be important for describing magnetic properties of this compound. The zero-field zone-center gap in the excitation spectrum of BPCB, ?0/kB=16.5K , is detected directly. Furthermore, an ESR signature of the interladder exchange interactions is obtained. The detailed characterization of the anisotropy in BPCB completes the determination of the full spin hamiltonian of this exceptional spin-ladder material and shows ways to study anisotropy effects in spin ladders.

?ižmár, E.; Ozerov, M.; Wosnitza, J.; Thielemann, B.; Krämer, K. W.; Rüegg, Ch.; Piovesana, O.; Klanjšek, M.; Horvati?, M.; Berthier, C.; Zvyagin, S. A.

2010-08-01

250

Magnetic anisotropy in (Tb0.3Dy0.7)45Fe55 amorphous films  

NASA Astrophysics Data System (ADS)

Giant magnetostrictive (Tb0.3Dy0.7)45Fe55 thin films were prepared by direct current (DC) magnetron sputtering. The onset temperature of crystallization of the films is found to be 407°C through differential scanning calorimetery (DSC) studies. X-ray diffraction analysis confirms that the films exhibit an amorphous phase after annealing at 400°C. The effect of annealing on the in-plane anisotropy was investigated. The in-plane anisotropy is enhanced upon increasing the annealing temperature from 200°C to 400°C. The ratio Mr/M10 is varied from 0.037 for the as-deposited sample to 0.543 after annealing at 400°C, where Mr and M10 refer to remanence and magnetization measured at the field of 10kOe, respectively. In addition, pre-stress was also applied during deposition to induce an in-plane unidirectional anisotropy in the films. This may result in an anisotropy of the in-plane magnetization and lead to a large improvement of magnetostriction.

Xu, H.; Jiang, C.; Jiang, X.; Gong, S.

2001-06-01

251

Spin wave mode transition induced by surface anisotropy and characteristic length in magnetic nanoparticles  

Microsoft Academic Search

In magnetic nanoparticles with cylindrical symmetry of the magnetization configurations, spin wave mode transition (SWMT) is predicted for the case of a surface anisotropy parallel to the uniform magnetization. Theoretical investigation has shown that a characteristic length can be determined to evaluate the spatial influence of the spin wave mode excited by surface anisotropy. This knowledge implies SWMT occurs as

Peiheng Zhou; Li Zhang; Longjiang Deng

2010-01-01

252

The Anisotropy of Magnetic Susceptibility of Some Igneous and Metamorphic Rocks  

Microsoft Academic Search

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

M. Aftab Khan

1962-01-01

253

Nanocrystalline iron nitride films with perpendicular magnetic anisotropy  

SciTech Connect

Nanocrystalline {alpha}-iron nitride films have been prepared using reactive ion-beam sputtering. Films develop significant perpendicualr magnetic anisotropy (PMA) with increasing thickness. A comparison of x-ray diffraction patterns taken with scattering vectors in the film plane and out of the film plane provides a clear evidence for development of compressive strain in the film plane with thickness. Thermal annealing results in relaxation of the strain, which correlates very well with the relaxation of PMA. This suggests that the observed PMA is a consequence of the breaking of the symmetry of the crystal structure due to the compressive strain.

Gupta, Ajay; Dubey, Ranu; Leitenberger, W.; Pietsch, U. [UGC-DAE Consortium for Scientific Research, University Campus Khandwa Road, Indore 452017 (India); Institute of Physics, University of Postdam, 14469 Potsdam (Germany); Physics Department, University of Siegen, D-57068 Siegen (Germany)

2008-02-04

254

Scattering anisotropy and giant magnetoresistance in magnetic multilayers  

SciTech Connect

We present full ab initio calculations of giant magnetoresistance (GMR) in Co/Cu (001) multilayers including self-consistent impurity scattering potentials. Starting from density functional theory the electronic structure of the multilayer and the scattering at impurities are described by means of a new Green function method. It will be demonstrated that impurity scattering in magnetic multilayers is strongly anisotropic in comparison to impurity scattering in bulk systems. Concerning transport the anisotropy of scattering leads to a formation of highly conducting channels which give rise to short circuits and cause strong variation of GMR as a function of the impurity position in the multilayer. {copyright} 2001 American Institute of Physics.

Binder, J.; Zahn, P.; Mertig, I.

2001-06-01

255

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

256

Enhancement of the magnetic anisotropy barrier in critical long range spin systems.  

PubMed

Magnetic materials are usually characterized by anisotropy energy barriers which dictate the timescale of the magnetization decay and consequently the magnetic stability of the sample. Here we consider magnetization decay for spin systems in a d = 3 cubic lattice with an isotropic Heisenberg interaction decaying as a power law with a critical exponent ? = d and on-site anisotropy. We show that the anisotropy energy barrier can be determined from the ergodicity breaking energy of the corresponding isolated system and that, unlike in the case of nearest neighbour interaction, the anisotropy energy barrier grows as the particle volume, V, and not as the cross-sectional area. PMID:23399834

Borgonovi, F; Celardo, G L

2013-02-12

257

Perpendicular Magnetic Anisotropy in Ultrathin Co/Ni Multilayer Films Studies with Ferromagnetic Resonance and Magnetic X-Ray Microspectroscopy.  

National Technical Information Service (NTIS)

Ferromagnetic resonance (FMR) spectroscopy, x-ray magnetic circular dichroism (XMCD) spectroscopy and magnetic transmission soft x-ray microscopy (MTXM) experiments have been performed to gain insight into the magnetic anisotropy and domain structure of u...

D. Bedau F. Macia M. Im P. Fischer P. Warnicke

2012-01-01

258

Large amplitude oscillation of magnetic anisotropy engineered by substrate step density  

NASA Astrophysics Data System (ADS)

Large amplitude quantum oscillations of magnetic anisotropy in Fe films grown on Ag surfaces of high step density are reported. Distortion of the film structure by the steps is found to be responsible for the anisotropy modification which oscillates with increasing film thickness. The larger the distorted fraction of the film volume, the larger the observed amplitude of the anisotropy oscillations. Such dependence of the anisotropy oscillations on the step density offers an easy tool to manipulate the strength of the anisotropy and orientation of the easy magnetization axis.

Bauer, U.; Przybylski, M.

2010-04-01

259

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.

260

Multiferroic response to magnetic field in orthorhombic manganites  

Microsoft Academic Search

The magnetoelectric coupling in Eu0.55Y0.45MnO3 is studied based on a microscopic spin model which includes the superexchange interaction, the single-ion anisotropy, the Dzyaloshinskii–Moriya interaction, and the cubic anisotropy. Our Monte Carlo simulation reproduces the experimentally observed multiferroic response to magnetic field B. It is demonstrated that the magnetic field can control the multiferroic behaviors by modulating the spin arrangements, leading

M. H. Qin; Y. M. Tao; S. Dong; H. B. Zhao; X. S. Gao; J.-M. Liu

2011-01-01

261

Multiferroic response to magnetic field in orthorhombic manganites  

Microsoft Academic Search

The magnetoelectric coupling in Eu0.55Y0.45MnO3 is studied based on a microscopic spin model which includes the superexchange interaction, the single-ion anisotropy, the Dzyaloshinskii-Moriya interaction, and the cubic anisotropy. Our Monte Carlo simulation reproduces the experimentally observed multiferroic response to magnetic field B. It is demonstrated that the magnetic field can control the multiferroic behaviors by modulating the spin arrangements, leading

M. H. Qin; Y. M. Tao; S. Dong; H. B. Zhao; X. S. Gao; J.-M. Liu

2011-01-01

262

Investigation of perpendicular magnetic anisotropy of CoFeB by x-ray magnetic circular dichroism  

NASA Astrophysics Data System (ADS)

We have studied the variation of perpendicular magnetic anisotropy (PMA) of CoFeB layers with the oxidation degree of the MgO buffer layers. After annealing at 330 °C, the out-of-plane anisotropy field (Hk) of 1.5-nm CoFeB could be optimized to 3.1 kOe. To investigate the orbital hybridization of the Fe-3d and O-2p, the orbital moments per hole (morb/Nh) of Fe in annealed CoFeB layers were extracted by using x-ray magnetic circular dichroism. The dependence of morb/Nh on the oxidation time of MgO coincided with that of Hk, which revealed that PMA of annealed CoFeB originated from the interfacial orbital hybridization.

Tsai, W. C.; Liao, S. C.; Hou, H. C.; Yen, C. T.; Wang, Y. H.; Tsai, H. M.; Chang, F. H.; Lin, H. J.; Lai, Chih-Huang

2012-04-01

263

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

264

Magnetic Domain Structure and Magnetic Anisotropy in Ga1-xMnxAs  

NASA Astrophysics Data System (ADS)

Large, well-defined magnetic domains, on the scale of hundreds of micrometers, are observed in Ga1-xMnxAs epilayers using a high-resolution magneto-optical imaging technique. The orientations of the magnetic moments in the domains clearly show in-plane magnetic anisotropy, which changes through a second-order transition from a biaxial mode (easy axes nearly along [100] and [010]) at low temperatures to an unusual uniaxial mode (easy axis along [110]) as the temperature increases above about Tc/2. This transition is a result of the interplay between the natural cubic anisotropy of the GaMnAs zinc-blende structure and a uniaxial anisotropy which attribute to the effects of surface reconstruction.

Welp, U.; Vlasko-Vlasov, V. K.; Liu, X.; Furdyna, J. K.; Wojtowicz, T.

2003-04-01

265

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

SciTech Connect

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

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

2009-01-01

266

Disclinations: The magnetism and the magnetic anisotropies of the rare-earth--3d transition-metal hard magnets (invited)  

SciTech Connect

An important class of hard magnets, involving rare earth and 3d transition metals and sometimes metalloids, includes Nd/sub 2/Fe/sub 14/B and Nd/sub 2/Fe/sub 17/. We have noted a correlation between the local site magnetism in these two compounds and whether those sites lie on nets of so-called major ligand lines or disclinations, i.e., bond lines shared by six common nearest neighbors. We have proposed that a criterion for choosing candidate alloys with strong 3d moments is the occurrence of such disclination nets, and using this criterion, have listed several structures having 3d sites with this characteristic. We have also rationalized the crystal field anisotropies as relating to the orientation of the major ligand lines.

Watson, R.E.; Bennett, L.H.; Melamud, M.

1988-04-15

267

Disclinations: The magnetism and the magnetic anisotropies of the rare earth-3d transition metal hard magnets  

SciTech Connect

An important class of hard magnets, involving rare earth and 3d transition metals and sometimes metalloids, includes Nd/sub 2/Fe/sub 14/B and Nd/sub 2/Fe/sub 17/. We have noted a correlation between the local site magnetism in these two compounds and whether those sites lie on nets of so called major ligand lines or disclinations, i.e., bond lines shared by six common nearest neighbors. We have proposed that a criterion for choosing candidate alloys with strong 3d moments is the occurrence of such disclination nets, and using this criterion, have listed several structures having 3d sites with this characteristic. We have also rationalized the crystal field anisotropies as relating to the orientation of the major ligand lines. 7 refs., 1 fig., 2 tabs.

Watson, R.E.; Bennett, L.H.; Melamud, M.

1987-01-01

268

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

269

Hetero-amorphous Fe-Co-B-C soft magnetic thin films with uniaxial magnetic anisotropy and large magnetostriction  

Microsoft Academic Search

Hetero-amorphous (Fe0.75Co0.25)1-x(B1-yC y)x films have been obtained by RF magnetron sputtering. Magnetic properties strongly depended on the hetero-amorphous substructure of the films. The film with a fine substructure less than 10 nm in mean diameter exhibited low coercive force of 40 A\\/m along the hard axis, large spontaneous magnetization of 1.6 T, and in-plane anisotropy field of 1.2 kA\\/m induced

Hiroshi Tomita; Tetsuo Inoue; Tetsuhiko Mizoguchi

1996-01-01

270

High-spin organic molecules with dominant spin-orbit contribution and unprecedentedly large magnetic anisotropy  

NASA Astrophysics Data System (ADS)

High-spin organic molecules with dominant spin-orbit contribution to magnetic anisotropy are reported. Quintet 4-azido-3,5-dibromopyridyl-2,6-dinitrene (Q-1), quintet 2-azido-3,5-dibromopyridyl-4,6-dinitrene (Q-2), and septet 3,5-dibromopyridyl-2,4,6-trinitrene (S-1) were generated in solid argon matrices by ultraviolet irradiation of 2,4,6-triazido-3,5-dibromopyridine. The zero-field splitting (ZFS) parameters, derived from electron spin resonance spectra, show unprecedentedly large magnitudes of the parameters D: |DQ1| = 0.289, |DQ2| = 0.373, and |DS1| = 0.297 cm-1. The experimental ZFS parameters were successfully reproduced by density functional theory calculations, confirming that magnetic anisotropy of high-spin organic molecules can considerably be enhanced by the ``heavy atom effect.'' In bromine-containing high-spin nitrenes, the spin-orbit term is dominant and governs both the magnitude and the sign of magnetic anisotropy. The largest negative value of D among septet trinitrenes is predicted for 1,3,5-trinitrenobenzene bearing three heavy atoms (Br) in positions 2, 4, and 6 of the benzene ring.

Misochko, Eugenii Ya.; Akimov, Alexander V.; Masitov, Artem A.; Korchagin, Denis V.; Yakushchenko, Igor K.; Chapyshev, Sergei V.

2012-08-01

271

The relationship of thermal expansion to magnetocrystalline anisotropy, spontaneous magnetization, and Tc for permanent magnets  

NASA Astrophysics Data System (ADS)

The materials studied here include SmCo5, GdCo5, Sm2TM17, Gd2TM17, Nd9.4Pr4.6Fe80B6, Alnico, SrFe12O19, and PtCo (TM=transition metal). For the first time, the thermal expansion data ?(?) and ?(?) for the eight materials from as low as -180 °C to as high as 1250 °C have been reported. ?(?) is the thermal expansion coefficient in the base plane and ?(?) is the coefficient in the c axis. All anisotropic materials tested show thermal expansion anisotropy (TEA). The degree of TEA is defined as ?=?(?)/?(?). The ? has been observed to be related to the degree of magnetocrystalline anisotropy field HA. SmCo5 has the highest HA (350 kOe) and the highest ? (2.5). All the materials show thermal anomaly with a changing slope for ?(?) near Tc and near phase transformation temperatures. The magnitude of thermal anomaly has been observed to be related to the magnitude of spontaneous magnetization (SMZ). The most distinct thermal anomalies are observed for Nd9.4Pr4.6Fe80B6, in which both ?(?) and ?(?) show a deep valley near Tc, and a peak at around the spin-tilt temperature. Nd-Fe-B type material has the highest SMZ and the largest thermal anomaly of all the permanent magnets. Spontaneous magnetostriction occurs mainly in the c axis for RE-Co alloys (RE=rare earth), and in all directions for Nd-Fe-B type alloys. A rubber band model is used to describe the spontaneous magnetostriction force.

Chen, Christina H.; Walmer, Marlin S.; Walmer, Michael H.; Gong, Wei; Ma, Bao-Min

1999-04-01

272

Magnetic field sensors and visualizers using magnetic photonic crystals  

NASA Astrophysics Data System (ADS)

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

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

2008-06-01

273

Spin dependent transport through a carbon nanotube quantum dot in magnetic field  

Microsoft Academic Search

Spin-polarized transport through a carbon nanotube quantum dot in the Kondo regime is studied by the equation of motion method. Magnetic field perpendicular to the tube axis breaks the spin degeneracy, whereas axial field breaks both the orbital and spin degeneracies. A strong magnetic field anisotropy of conductance and anisotropy of its spin polarization is observed. We propose a new

D. Krychowski; S. Lipi?ski; S. Krompiewski

2007-01-01

274

Magnetic Field Problem  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

275

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

276

Evaluation of anisotropy field in amorphous Fe 71+ x Nb 7B 22? x alloys by GMI measurement  

Microsoft Academic Search

We have measured the variation of magnetoimpedance (MI) ratio on Fe71+xNb7B22?x (x=0, 2, 6, 8) amorphous ribbons for the evaluation of anisotropy field Hk. MI at a frequency of 10MHz is related to the transverse permeability from rotational magnetization. MI varies sensitively with the various Fe-contents, reflecting the magnetic softness. The field interval of the MI peaks corresponds to the

Gil Ho Ryu; Seong Cho Yu; Cheol Gi Kim; Seok Soo Yoon

2000-01-01

277

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

278

Cylindrical magnetization model for glass-coated microwires with circumferential anisotropy: Dynamics  

NASA Astrophysics Data System (ADS)

The high frequency magnetic susceptibility of glass-coated microwires with effective circumferential anisotropy has been modeled by micromagnetics. In their amorphous and magnetically soft metallic nucleus, the negative magnetostriction induces a continuous and non-uniform vortex-like structure, with an axially magnetized core coupled to a circumferentially magnetized outer shell. The model is a one-dimensional radial micromagnetic model where exchange, magnetoelastic and magnetostatic energies are considered. The microwave permeability under AC (axial and circumferential) fields is found to be expressed as a sum over a set of eigenmodes, each with a characteristic resonance frequency. In the framework of this model, a sum rule on the frequency-dependent permeability is shown to hold. It provides a figure of merit and guidelines for the design of high permeability materials for applications in the microwave range.

Torrejon, J.; Thiaville, A.; Adenot-Engelvin, A.-L.; Vazquez, M.

2013-05-01

279

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

280

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

281

Magnetic anisotropy in isotropic and nanopatterned strongly exchange-coupled nanolayers.  

PubMed

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. PMID:23088782

Vergara, José; Favieres, Cristina; Madurga, Vicente

2012-10-22

282

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

Most of the visible matter in the Universe is ionized so that cosmic magnetic fields are quite easy to generate and, due to the lack of magnetic monopoles, hard to destroy. Magnetic fields have been measured in or around practically all celestial objects, either by in situ measurements of spacecrafts or by the electromagnetic radiation of embedded cosmic rays, gas, or dust. The Earth, the Sun, solar planets, stars, pulsars, the Milky Way, nearby galaxies, more distant (radio) galaxies, quasars, and even intergalactic space in clusters of galaxies have significant magnetic fields, and even larger volumes of the Universe may be permeated by "dark" magnetic fields. Information on cosmic magnetic fields has increased enormously as the result of the rapid development of observational methods, especially in radio astronomy. In the Milky Way, a wealth of magnetic phenomena was discovered, which are only partly related to objects visible in other spectral ranges. The large-scale structure of the Milky Way's magnetic field is still under debate. The available data for external galaxies can well be explained by field amplification and ordering via the dynamo mechanism. The measured field strengths and the similarity of field patterns and flow patterns of the diffuse ionized gas give strong indication that galactic magnetic fields are dynamically important. They may affect the formation of spiral arms, outflows, and the general evolution of galaxies. In spite of our increasing knowledge on magnetic fields, many important questions on the origin and evolution of magnetic fields, their first occurrence in young galaxies, or the existence of large-scale intergalactic fields remained unanswered. The present upgrades of existing instruments and several planned radio astronomy projects have defined cosmic magnetism as one of their key science projects.

Beck, Rainer; Wielebinski, Richard

283

Intergalactic magnetic fields  

Microsoft Academic Search

There is no observational support to the hypothesis of the most large-scale homogeneous magnetic field in the Universe. The best upper limit is given by interpretation of the Faraday rotation from the extragalactic radio sources. However the magnetic fields can be generated in the clusters of galaxies by a turbulence in the wakes of moving galaxies. These fields have an

A. A. Ruzmajkin

1991-01-01

284

Magnetic Field Example 1  

NSDL National Science Digital Library

Clicking on the different links below will produce different magnetic fields in the box above. The wires (perpendicular to the screen) or coils (in and out of the screen) are not visible, but you can determine what they are from the field. You can also click on a point to read off the magnetic field at that place.

Christian, Wolfgang; Belloni, Mario

2008-02-19

285

The Magnetic Field  

NSDL National Science Digital Library

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

Universe, Windows T.

1997-12-03

286

Tuning Transverse Anisotropy in Co(III)-Co(II)-Co(III) Mixed-Valence Complex toward Slow Magnetic Relaxation.  

PubMed

Two cobalt mixed-valence complexes with different substituents have been prepared and structurally characterized by single-crystal X-ray diffraction to alter slow magnetic relaxation by tailoring the transverse anisotropy. The trinuclear complexes [(L(1))4Co3(H2O)2](NO3)4·CH3OH·5H2O (1-NO3) and [(L(2))4Co3(H2O)2](NO3)4·6H2O (2-NO3) feature a distorted octahedral Co(II) strongly hindered in a trinuclear Co(III)-Co(II)-Co(III) mixed-valence array. Detailed magnetic studies of 1-NO3 and 2-NO3 have been conducted using direct- and alternating-current magnetic susceptibility data. In accordance with variable-field magnetic susceptibility data at low temperatures, high-field electron paramagnetic resonance (HF-EPR) spectroscopy reveals the presence of an easy-plane anisotropy (D > 0) with a significant transverse component, E, in complexes 1-NO3 and 2-NO3. These findings indicate that the onset of the variation of distortion within complex 2-NO3 leads to a suppression of quantum tunneling of the magnetization within the easy plane, resulting in magnetic bistability and slow relaxation behavior. Consequently, the anisotropy energy scale associated with the relaxation barrier, 5.46 cm(-1) (?o = 1.03 × 10(-5) s), is determined by the transverse E term. The results demonstrate that slow magnetic relaxation can be switched through optimization of the transverse anisotropy associated with magnetic ions that possess easy-plane anisotropy. PMID:24044879

Wu, Dayu; Zhang, Xingxing; Huang, Ping; Huang, Wei; Ruan, Mingyue; Ouyang, Z W

2013-09-17

287

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

288

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

289

Role of orbital polarization in calculations of the magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy is a difficult topic to describe by electronic structure theory. The results of ab initio calculations for iron and nickel are disappointing, especially since these calculations require high numerical precision and are very time consuming. For iron the value of the energy is too small by a factor of 3, while for nickel the sign is wrong and the value is too small by a factor of 5. The local density approximation can be improved by adding corrections that mimic the inclusion of Hund's second rule. This is equivalent to increasing the effective spin-orbit parameter. For iron a small increase in the effective spin-orbit parameter is sufficient to reconcile theory and experiment. For nickel, this is not possible.

Schneider, G.; Jansen, H. J. F.

2000-05-01

290

Viscous Bianchi type II universes with intergalactic magnetic field  

Microsoft Academic Search

Homogeneous Bianchi type II models are studied for universes containing a viscous fluid and a large scale magnetic field. The present values of the magnetic field, the anisotropy in the microwave radiation background and the Hubble parameters are obtained by numerical integration of the Einstein and Maxwell equations from the beginning of the lepton era (1012 K) up to the

T. Hageman; W. A. van Leeuwen

1987-01-01

291

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

NASA Astrophysics Data System (ADS)

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.

2013-06-01

292

Magnetic field generator  

DOEpatents

A magnetic field generating device provides a useful magnetic field within a specific retgion, while keeping nearby surrounding regions virtually field free. By placing an appropriate current density along a flux line of the source, the stray field effects of the generator may be contained. One current carrying structure may support a truncated cosine distribution, and it may be surrounded by a current structure which follows a flux line that would occur in a full coaxial double cosine distribution. Strong magnetic fields may be generated and contained using superconducting cables to approximate required current surfaces.

Krienin, Frank (Shoreham, NY)

1990-01-01

293

Variation of domain-wall structures and magnetization ripple spectra in permalloy films with controlled uniaxial anisotropy  

NASA Astrophysics Data System (ADS)

We have studied domain-wall structures and magnetization ripple in permalloy films with widely varying values of anisotropy field and thickness. Both the Fresnel and differential phase contrast imaging modes of Lorentz microscopy have been used, the latter proving particularly valuable for providing reliable quantitative data. Cross-tie walls were frequently observed but the density of the cross ties increased markedly with anisotropy field while the cross-tie length decreased. In accord with expectation, the mean ripple wavelength and magnitude of the ripple decreased with increasing anisotropy field, albeit the variation was more rapid than could be accounted for using simple theories. Generally the root-mean-square dispersion angle was found to be greater than that in earlier experimental work, a factor that was ascribed to the use of an incomplete analysis procedure in the past.

Gentils, A.; Chapman, J. N.; Xiong, G.; Cowburn, R. P.

2005-09-01

294

ATOMIC AND MOLECULAR PHYSICS: Mössbauer study of the field induced uniaxial anisotropy in electro-deposited FeCo alloy films  

NASA Astrophysics Data System (ADS)

Thin ferromagnetic films with in-plane magnetic anisotropy are promising materials for obtaining high microwave permeability. The paper reports a Mössbauer study of the field induced in-plane uniaxial anisotropy in electro-deposited FeCo alloy films. The FeCo alloy films were prepared by the electro-deposition method with and without an external magnetic field applied parallel to the film plane during deposition. Vibrating sample magnetometry and Mössbauer spectroscopy measurements at room temperature indicate that the film deposited in external field shows an in-plane uniaxial anisotropy with an easy direction coinciding with the external field direction and a hard direction perpendicular to the field direction, whereas the film deposited without external field does not show any in-plane anisotropy. Mössbauer spectra taken in three geometric arrangements show that the magnetic moments are almost constrained in the film plane for the film deposited with applied magnetic field. Also, the magnetic moments tend to align in the direction of the applied external magnetic field during deposition, indicating that the observed anisotropy should be attributed to directional ordering of atomic pairs.

Li, Zhi-Wei; Yang, Xu; Wang, Hai-Bo; Liu, Xin; Li, Fa-Shen

2009-11-01

295

Magnetic fields at Uranus  

Microsoft Academic Search

The conclusions drawn regarding the structure, behavior and composition of the Uranian magnetic field and magnetosphere as revealed by Voyager 2 data are summarized. The planet had a bipolar magnetotail and a bow shock wave which was observed 23.7 Uranus radii (UR) upstream and a magnetopause at 18.0 UR. The magnetic field observed can be represented by a dipole offset

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

1986-01-01

296

THE INTERPLANETARY MAGNETIC FIELD  

Microsoft Academic Search

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

V. A. BAILEY

1963-01-01

297

Cosmic Magnetic Fields  

Microsoft Academic Search

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

Elisabete M. de Gouveia Dal Pino; Dal Pino

2006-01-01

298

Uniaxial magnetic anisotropy for thin Co films on glass studied by magnetooptic Kerr effect  

NASA Astrophysics Data System (ADS)

Thin Co films of different thickness deposited on glass are investigated by magnetooptic Kerr effect to study the uniaxial magnetic anisotropy of these films. The direction of the uniaxial magnetic anisotropy is determined from the azimuthal dependence of the magnetic remanence and differs with increasing thickness of the Co film investigated by x-ray reflectivity. Our experiments reveal that preparation conditions like temperature, deposition rate, or obliqueness of deposition cannot be the reason for this rotation effect of the uniaxial magnetic anisotropy. Also, strain in the substrate and possible textures in the film structure can be excluded as the origin of the magnetic behavior as studied by grazing incidence wide angle x-ray scattering. Thus, probably only the substrate shape in connection with the amorphous or polycrystalline film structure can explain the rotation of the uniaxial magnetic anisotropy.

Kuschel, T.; Becker, T.; Bruns, D.; Suendorf, M.; Bertram, F.; Fumagalli, P.; Wollschläger, J.

2011-05-01

299

Saturation magnetization and perpendicular anisotropy of Fe/GaAs(110) epitaxial films studied by the extraordinary hall effect  

NASA Astrophysics Data System (ADS)

The magnetic field dependence of the extraordinary Hall effect (EHE) has been used to determine the sum of the perpendicular magnetic anisotropy and the saturation magnetization of thin (5-20 nm) Fe films. The films were grown on (110) surfaces of GaAs by molecular beam epitaxy. The free surface of the films was not protected thereby allowing an iron oxide layer to form upon removal from the MBE apparatus. The relation between the film thickness and the sum of the perpendicular anisotropy energy and the saturation magnetization was compared to that determined in a previous study which relied on ferromagnetic resonance (FMR) to measure the same quantity. The FMR study measured both oxide covered films and also films with a protective overcoating of Al to prevent oxidation. It is found that the data from the EHE are not in agreement with the FMR data taken on the iron oxide covered films but instead are in agreement with the FMR data of the protected or nonoxidized films. In addition a determination of the surface anisotropy energy can be made by subtracting the magnetization data measured on overcoated films from the sum determined by the EHE analysis. In this case there is no indication of a large surface anisotropy energy making the perpendicular direction an easy axis.

Riggs, K. T.; Dan Dahlberg, E.; Prinz, G. A.

1988-05-01

300

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

301

Systematic study of in-plane magnetic anisotropy in CoCrPtB/Cr media  

NASA Astrophysics Data System (ADS)

Circumferential texturing in longitudinal recording media induces in-plane magnetic anisotropy. It is characterized by orientation ratio (OR), which is an important parameter affecting media performance. Our work shows that among the media with different OR values (including isotropic media with OR=1), the ones with higher OR have both better thermal stability and better recording performance. Therefore, it is important to have a better understanding of the mechanism for in-plane anisotropy so that OR can be further increased. Several mechanisms for in-plane anisotropy have been proposed through micromagnetic analysis or empirical methods. A systematic study of OR in CoCrPtB/Cr media was performed to explore the mechanism of in-plane magnetic anisotropy. Circumferential texture roughness has the most effect on OR, but OR is also strongly affected by magnetic alloy composition and sputtering process parameters such as substrate temperature, underlayer thickness, and magnetic-layer thickness. Higher substrate temperature, thinner underlayer thickness, and thinner magnetic-layer thickness all lead to higher OR. These results suggest that the in-plane magnetic anisotropy comes from stress anisotropy via the inverse magnetostriction effect. The stress is induced at the magnetic-layer/underlayer and underlayer/substrate interfaces, while the anisotropy is suggested to arise from the topology of the circumferential texture lines.

Yu, Mingjun; Choe, Geon; Johnson, Kenneth E.

2002-05-01

302

The Earth's Magnetic Field  

NSDL National Science Digital Library

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

303

Anisotropies and spin dynamics in ultrathin magnetic multilayer structures  

NASA Astrophysics Data System (ADS)

High quality magnetic films were prepared by Molecular Beam Epitaxy (MBE) using Thermal Deposition (TD) and Pulse Laser Deposition (PLD) techniques. Ferromagnetic Resonance (FMR) and Mossbauer studies have shown that the Fe films prepared by PLD exhibited a more intermixed interface lattice structure than those prepared by TD. Dramatic decrease of the in-plane interface uniaxial anisotropy for the PLD films compared to those prepared by TD has shown that the in-plane uniaxial anisotropy is caused by magnetoelasticity driven by the Fe/GaAs(001) interface lattice shear. Magnetization dynamics of the ultrathin Fe/Au,Ag/Fe films was studied using Time-Resolved Magneto-Optical Kerr Effect (TRMOKE) and FMR in the frequency range from 1 to 73 GHz. The Gilbert damping was studied in the Au/Fe/GaAs(001) structures as a function of the Fe and Au layer thickness, respectively. The observed increase in magnetic damping in the Fe film covered with thick Au capping layers was explained by spin pumping at the Fe/Au interface accompanied by spin relaxation and diffusion of the accumulated spin density in the Au layer. The spin diffusion length in Au was found to be 34 nm at room temperature. Significant increase of the Gilbert damping was observed in the Au/Fe/GaAs structures with decreasing Fe film thickness. Its origin lies in the additional damping at the Fe/GaAs interface. Direct detection of the spin current propagating across the Ag spacer in Fe/Ag,Au/Fe/GaAs(001) structures was carried out with stroboscopic TRMOKE measurements. The Fe layer grown on GaAs served as a spin pumping source and the Fe layer grown on the Au,Ag spacer was used as a probe for detection of the spin current propagating across the Au and Ag spacers. The experimental results were interpreted using selfconsistent solution of the Landau Lifshitz Gilbert (LLG) equations of motion with the spin diffusion equation for the accumulated spin density in the Au and Ag spacers. The spin diffusion length in Ag was found to be 150 nm.

Kardasz, Bartlomiej

304

Transition States and the Energy Barrier to Magnetization Reversal of Thin Film Nanomagnets with Perpendicular Anisotropy  

NASA Astrophysics Data System (ADS)

We use the String Method [1] in conjunction with the micromagnetics OOMMF package to calculate the energy barrier for magnetization reversal of square thin film nanomagnets with perpendicular anisotropy. The lowest energy state consists of out of plane magnetization configurations. A field applied perpendicular to the plane lifts the degeneracy between the states. The effect of the element size and the consequences of breaking the square symmetry are investigated. We find that the transition state is not uniform: it starts with a localized nucleation, which expands to complete the reversal. The field dependence of the energy barrier is compared to that of macrospin model, and nonuniform reversal is shown to be the preferred transition configuration, providing a lower energy barrier to reversal. This result indicates the limits of the macrospin model. We present the dependence on the energy barrier on the exchange constant and simulation cell size. [1] W. E, W. Ren, E. Vanden-Eijnden, J. Chem. Phys. 126, 164103 (2007)

Chaves-O'Flynn, Gabriel; Bedau, Daniel; vanden-Eijnden, Eric; Stein, Daniel; Kent, Andrew

2010-03-01

305

Anisotropy and temperature dependence of the first critical field in 2H-NbS2  

NASA Astrophysics Data System (ADS)

We report on ? Hall probe measurements on single crystals of 2H-NbS2. This compound is the only superconducting 2H-dichalcogenide which does not develop a charge density wave. At low temperature and low magnetic field, a Bean profile is observed, allowing to evaluate the critical current. Moreover, the anisotropy and temperature dependence of the first critical field in 2H-NbS2 was measured down to 1.2 K. A linear temperature dependence of the first penetration field is clearly observed. The absolute magnetic penetration depth is found to be 83 nm which is slightly reduced compared to the iso-structural compound 2H-NbSe2.

Leroux, M.; Rodière, P.; Cario, L.; Klein, T.

2012-06-01

306

Development of an identification method of pressure anisotropy based on equilibrium analysis and magnetics  

NASA Astrophysics Data System (ADS)

We evaluate the fluxes measured by the magnetic flux loops installed in LHD by using a three dimensional MHD equilibrium analysis code, ANIMEC, which enable us to directly determine the calibration function between the anisotropic pressure and the measured fluxes for the non-axisymmetric plasmas for the first time. The result indicates that the diamagnetic flux represents a nearly single-valued function of the beta perpendicular with respect to the field, and the saddle loop flux represents a nearly single-valued function of an equally weighted average of the beta values parallel and perpendicular to the field, regardless of the pressure anisotropy or the amount of energetic trapped particles. The values of the beta perpendicular to the field and the equal weighting averaged beta estimated by the single-valued functions (calibration functions) are investigated in order to clarify the magnitude of deviation from those original values, and the range of anisotropy where the beta value evaluated by the magnetic flux measurement is calculated within a 10% error.

Asahi, Y.; Suzuki, Y.; Watanabe, K. Y.; Cooper, W. A.

2013-02-01

307

Holographic photon production with magnetic field in anisotropic plasmas  

NASA Astrophysics Data System (ADS)

We investigate the thermal photon production from constant magnetic field in a strongly coupled and anisotropic plasma via the gauge/gravity duality. The dual geometry with pressure anisotropy is generated from the axion-dilaton gravity action introduced by Mateos and Trancancelli and the magnetic field is coupled to fundamental matters(quarks) through the D3/D7 embeddings. We find that the photon spectra with different quark mass are enhanced at large frequency when the photons are emitted parallel to the anisotropic direction with larger pressure or perpendicular to the magnetic field. However, in the opposite conditions for the emitted directions, the spectra approximately saturate isotropic results in the absence of magnetic field. On the other hand, a resonance emerges at moderate frequency for the photon spectrum with heavy quarks when the photons move perpendicular to the magnetic field. The resonance is more robust when the photons are polarized along the magnetic field. On the contrary, in the presence of pressure anisotropy, the resonance will be suppressed. There exist competing effects of magnetic field and pressure anisotropy on meson melting in the strongly coupled super Yang-Mills plasma, while we argue that the suppression led by anisotropy may not be applied to the quark gluon plasma.

Wu, Shang-Yu; Yang, Di-Lun

2013-08-01

308

Large magnetic anisotropy of Fe2P investigated via ab initio density functional theory calculations  

NASA Astrophysics Data System (ADS)

We present an investigation of the large magnetic anisotropy of Fe2P, based on ab initio density functional theory calculations, with a full-potential linear muffin-tin orbital basis. We obtain a uniaxial magnetic anisotropy energy (MAE) of 664 ?eV/f.u., which is in decent agreement with experimental observations. Based on a band structure analysis the microscopic origin of the large magnetic anisotropy is explained. We also show that by straining the crystal structure, the MAE can be enhanced further.

Costa, M.; Grånäs, O.; Bergman, A.; Venezuela, P.; Nordblad, P.; Klintenberg, M.; Eriksson, O.

2012-08-01

309

Magnetization kinetics in tension and field annealed Fe-based amorphous alloys  

NASA Astrophysics Data System (ADS)

Magnetization kinetics in tension-annealed and field-annealed amorphous magnetic materials indicates that strain and magnetic fields are equally effective in inducing and relaxing local structural and magnetic anisotropy changes. This observation is based on the thermomagnetic aging of the magnetic properties obtained in the materials studied.

Hasegawa, Ryusuke; Takahashi, Kengo; Francoeur, Bruno; Couture, Pierre

2013-05-01

310

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

311

Evaluation of diffusional anisotropy and microscopic structure in skeletal muscles using magnetic resonance  

Microsoft Academic Search

The pulsed-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) method is used for detecting the diffusion of water molecules in biological tissues. Because tissues generally have diffusional anisotropy, their diffusion properties are denoted by a tensor. In this study, we evaluated the diffusional anisotropy and microscopic structure in atrophied skeletal muscles using the PGSE NMR method. The left sciatic nerve was

Takako Saotome; Masaki Sekino; Fumio Eto; Shoogo Ueno

2006-01-01

312

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

313

Random magnet with competing anisotropies in FexNi1-xF2 alloys  

NASA Astrophysics Data System (ADS)

A series of epitaxial (110) FexNi1-xF2 films were deposited on (110) MgF2 via molecular beam epitaxy. The Fe concentration x was determined by measuring the lattice parameter along the [110] direction using x-ray diffraction. The film thicknesses and the roughness of each interface were found by fitting of x-ray reflectivity data. The magnetic ordering as a function of x was analyzed by SQUID magnetometry. Enhancement of the N'eel temperature in alloys as well as evidence of spontaneous magnetization along the c-axis after field-cooling were observed for samples with x>0.1; for samples with x<0.1 the magnetization was perpendicular to the c-axis. Two phase transitions were observed for alloy samples with x>0.1. The phase diagram of the upper transition was consistent with mean field theory of a system with competing anisotropies. The transition at lower temperatures was unaffected by the application of a magnetic field, whereas the upper temperature transition was broadened by the application of fields as small as 50 Oe. This suggests the presence of a spin-glass phase at lower temperatures, followed by melting of the spin glass prior to the main transition to paramagnetic behavior as the temperature is raised.

Johnson, Trent; Perez, Felio; Stanescu, Tudor; Lederman, David

2012-02-01

314

First principles study on the local magnetic anisotropy near surfaces of Dy2Fe14B and Nd2Fe14B magnets  

NASA Astrophysics Data System (ADS)

The electronic structures of a (001) surface of crystalline Dy2Fe14B and Nd2Fe14B have been studied and the crystal field parameters at the rare-earth sites have been estimated by using first principles calculations. It is shown that Dy or Nd ions at the surface exhibit an in-plane magnetic anisotropy and can be nucleation sites of magnetization reversal.

Tanaka, Susumu; Moriya, Hiroshi; Tsuchiura, Hiroki; Sakuma, Akimasa; Diviš, Martin; Novák, Pavel

2011-04-01

315

Laser-Induced Fast Magnetization Precession and Gilbert Damping for CoCrPt Alloy Thin Films with Perpendicular Magnetic Anisotropy  

Microsoft Academic Search

We have investigated magnetic field strength (up to 10 kOe) and angle dependences of spin dynamics in 4-nm-thick films of CoCrPt alloys with perpendicular magnetic anisotropy using the all-optical time-resolved magneto-optical Kerr effect (TRMOKE). The comprehensive TRMOKE measurements have indicated the Gilbert damping constant alpha of 0.05 for the alloy film with low coercivity. The experiments also indicated that alpha

Shigemi Mizukami; Daisuke Watanabe; Takahide Kubota; Xianmin Zhang; Hiroshi Naganuma; Mikihiko Oogane; Yasuo Ando; Terunobu Miyazaki

2010-01-01

316

Magnetic-field-induced enhancement of crystallinity and field-effect mobilities in phthalocyanine thin films  

NASA Astrophysics Data System (ADS)

Organic semiconductor thin films were fabricated by thermal deposition of free-base and metal phthalocyanines under a static magnetic field. A vertical magnetic field enhanced the crystallinity of the edge-on orientation of the phthalocyanine discs, whereas a horizontal magnetic field had a minimal effect on the crystallinity. The major factor for the orientation change is attributed to the diamagnetic anisotropies of ?-electrons in the phthalocyanine macrocycles. Field-effect transistors of phthalocyanine films fabricated under a vertical magnetic field exhibited better hole mobilities and on-current values with smaller threshold voltages than those of phthalocyanine films fabricated without a magnetic field.

Tabata, Kenichi; Sasaki, Takayuki; Yamamoto, Yohei

2013-07-01

317

The First Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

318

Direct Observation of Field and Temperature Induced Domain Replication in Dipolar Coupled Perpendicular Anisotropy Films  

SciTech Connect

Dipolar interactions in a soft/Pd/hard [CoNi/Pd]{sub 30}/Pd/[Co/Pd]{sub 20} multilayer system, where a thick Pd layer between two ferromagnetic units prevents direct exchange coupling, are directly revealed by combining magnetometry and state-of-the-art layer resolving soft x-ray imaging techniques with sub-100-nm spatial resolution. The domains forming in the soft layer during external magnetic field reversal are found to match the domains previously trapped in the hard layer. The low Curie temperature of the soft layer allows varying its intrinsic parameters via temperature and thus studying the competition with dipolar fields due to the domains in the hard layer. Micromagnetic simulations elucidate the role of [CoNi/Pd] magnetization, exchange, and anisotropy in the duplication process. Finally, thermally driven domain replication in remanence during temperature cycling is demonstrated.

Hauet, T.; Gunther, C.M.; Pfau, B.; Eisebitt, S.; Fischer, P.; Rick, R. L.; Thiele, J.-U.; Hellwig, O.; Schabes, M.E.

2007-07-01

319

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

320

Magnetic anisotropies and magnetotransport in CeH{sub 2}/Co multilayers  

SciTech Connect

Measurements of the magnetization were performed between 4.2 and 300 K on a series of periodically stacked layers of cerium hydride and cobalt prepared by reactive ion-beam sputtering. X-ray reflectometry shows that the interfaces are sharp with a rms roughness of nominally one atomic layer. In the ground state at low temperatures, for Co-layer thicknesses up to 17 {Angstrom}, the magnetization is spontaneously oriented perpendicular to the layer planes in a multidomain configuration. A phenomenological analysis of the measured magnetic anisotropy energy reveals that the out-of-plane orientation of the magnetic easy axis is the result of a strong interface anisotropy which overcomes the shape anisotropy of the Co layers and of an additional volume anisotropy. Possible mechanisms behind the surface and volume anisotropies are discussed. Between 50 and 100 K, the magnetization turns into the layer planes in a continuous transition. The saturation magnetization, the spin-wave parameter describing its temperature dependence and the anisotropy energy vary continuously through the transition from the crystalline fcc phase to the amorphous phase of the Co sublayers near 20 {Angstrom}. This reveals the close relationship between the electronic configurations of amorphous and fcc Co. The magnetization measurements are supplemented by measurements of the anisotropic magnetoresistance and the extraordinary Hall effect. The extraordinary Hall coefficient shows contributions from skew scattering and side jump processes and scales with the ordinary electrical resistivity. {copyright} {ital 1997} {ital The American Physical Society}

Nawrath, T.; Damaske, B.; Schulte, O.; Felsch, W. [I. Physikalisches Institut, Universitaet Goettingen, Bunsenstrasse 9, 37073 Goettingen (Germany)

1997-02-01

321

Magnetic anisotropies and magnetotransport in CeH2/Co multilayers  

NASA Astrophysics Data System (ADS)

Measurements of the magnetization were performed between 4.2 and 300 K on a series of periodically stacked layers of cerium hydride and cobalt prepared by reactive ion-beam sputtering. X-ray reflectometry shows that the interfaces are sharp with a rms roughness of nominally one atomic layer. In the ground state at low temperatures, for Co-layer thicknesses up to 17 Å, the magnetization is spontaneously oriented perpendicular to the layer planes in a multidomain configuration. A phenomenological analysis of the measured magnetic anisotropy energy reveals that the out-of-plane orientation of the magnetic easy axis is the result of a strong interface anisotropy which overcomes the shape anisotropy of the Co layers and of an additional volume anisotropy. Possible mechanisms behind the surface and volume anisotropies are discussed. Between 50 and 100 K, the magnetization turns into the layer planes in a continuous transition. The saturation magnetization, the spin-wave parameter describing its temperature dependence and the anisotropy energy vary continuously through the transition from the crystalline fcc phase to the amorphous phase of the Co sublayers near 20 Å. This reveals the close relationship between the electronic configurations of amorphous and fcc Co. The magnetization measurements are supplemented by measurements of the anisotropic magnetoresistance and the extraordinary Hall effect. The extraordinary Hall coefficient shows contributions from skew scattering and side jump processes and scales with the ordinary electrical resistivity.

Nawrath, T.; Damaske, B.; Schulte, O.; Felsch, W.

1997-02-01

322

Noncollinear magnetism and single-ion anisotropy in multiferroic perovskites  

NASA Astrophysics Data System (ADS)

The link between the crystal distortions of the perovskite structure and the magnetic exchange interaction, the single-ion anisotropy (SIA), and the Dzyaloshinsky-Moriya (DM) interaction are investigated by means of density functional calculations. Using BiFeO3 and LaFeO3 as model systems, we quantify the relationship between the oxygen octahedra rotations, the ferroelectricity, and the weak ferromagnetism (wFM). We recover the fact that the wFM is due to the DM interaction induced by the oxygen octahedra rotations. We find a simple relationship between the wFM, the oxygen rotation amplitude, and the ratio between the DM vector and the exchange parameter such that the wFM increases with the oxygen octahedra rotation when the SIA does not compete with the DM forces induced on the spins. Unexpectedly, we also find that in spite of the d5 electronic configuration of Fe3+, the SIA is very large in some structures and is surprisingly strongly sensitive to the chemistry of the A-site cation of the ABO3 perovskite. In the ground R3c state phase we show that the SIA shape induced by the ferroelectricity and the oxygen octahedra rotations are in competition such that it is possible to turn the wFM “on” and “off” through the relative size of the two types of distortion.

Weingart, Carlo; Spaldin, Nicola; Bousquet, Eric

2012-09-01

323

Magnetic field dosimeter development  

SciTech Connect

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

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

1980-09-01

324

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

325

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

326

Reversible magnetization and anisotropy in YBa2Cu4O8  

NASA Astrophysics Data System (ADS)

The reversible magnetization for H?ab has been studied for grain-aligned YBa2Cu4O8 in order to determine whether the Hao-Clem theory can properly describe the vortex state in this orientation, as well as the orientation for H?c. Between temperatures of 70 and 76 K, the magnetization is reversible to better than 2% and the results scale very well to the universal Hao-Clem curve even though the supercurrents have a highly noncircular path as they circulate around a vortex parallel to the ab plane. The thermodynamic critical field is the same for H?ab as for H?c, as expected, and the Ginzburg-Landau parameter ?ab=380 compared to ?c=70 is consistent with an anisotropy value ?=5.8+/-0.4.

Xu, Ming; Sok, Junghyun; Ostenson, J. E.; Finnemore, D. K.; Dabrowski, B.

1996-06-01

327

Magnetic states of small cubic particles with uniaxial anisotropy  

Microsoft Academic Search

The lowest energy states in small cubic particles with uniaxial anisotropy are explored as a function of anisotropy strength and particle size. The investigations result in a phase diagram which contains the boundaries between the regions of one, two and three domains (flower, vortex and double vortex states). While the general features of the phase diagram are derived from energy

W. Rave; K. Fabian; A. Hubert

1998-01-01

328

Magnetic field confinement for magnetically levitated vehicles  

SciTech Connect

A magnetically levitated vehicle adapted for movement along a guide way, comprising: a passenger compartment; first and second primary magnet means secured on the vehicle to produce a magnetic field having a magnetic flux density extending outward from the primary magnet means, to support the vehicle above and spaced from the guide way; and a plurality of confining magnets disposed on the vehicle to confine the magnetic flux extending outward from the primary magnet means and to reduce the strength of the primary magnetic field in the passenger compartment; wherein the primary magnet means has a capacity to produce a primary magnetic field having a maximum strength of at least 200 gauss in the passenger compartment, and the confining magnets maintain the strength of the primary magnetic field in the passenger compartment below 5 gauss.

Proise, M.

1993-05-25

329

Magnetic surface anisotropy of amorphous Fe-B ultrathin films  

SciTech Connect

Ferromagnetic resonance experiments were performed at room temperature on amorphous ultrathin films of Fe/sub x/B/sub 100-x/ (x = 50, x = 70) at two frequencies (f = 9.515 GHz and f = 24.03 GHz). Two different configurations were employed, with the applied field being either parallel or perpendicular to the film surface. The amorphous Fe-B ultrathin film samples were successfully fabricated by d.c. sputtering deposition techniques. Their thicknesses range from about 18 A to 77 A. General formulas for the free energy were derived from Hamilton's principle and were adapted to amorphous materials. The ultrathin nature of the samples allows one to employ a surface inhomogeneity model, which involves only surface anisotropy, and to ignore any volume inhomogeneities. No approximation beyond the usual linearization of the equation of motion and the assumption of the uniformity of the microwave field throughout the sample was involved. It was found that in ultrathin films the observed FMR modes were surface-induced modes in the parallel configuration and spin-wave modes in the perpendicular configuration.

Zhang, L.

1986-01-01

330

Anisotropy in the magnetic and electrical transport properties of Fe1-xCrxSb2  

NASA Astrophysics Data System (ADS)

We have investigated anisotropy in magnetic and electrical transport properties of Fe1-xCrxSb2 (0?x?1) single crystals. The magnetic ground state of the system evolves from paramagnetic to antiferromagnetic with gradual substitution of Fe with Cr. Anisotropy in electrical transport diminishes with increased Cr substitution and fades away by x=0.5 . We find that the variable range hopping conduction mechanism dominates at low temperatures for 0.4?x?0.75 .

Hu, Rongwei; Mitrovi?, V. F.; Petrovic, C.

2007-09-01

331

Magnetic domain pattern asymmetry in (Ga, Mn)As/(Ga,In)As with in-plane anisotropy  

NASA Astrophysics Data System (ADS)

Appropriate adjustment of the tensile strain in (Ga, Mn)As/(Ga,In)As films allows for the coexistence of in-plane magnetic anisotropy, typical of compressively strained (Ga, Mn)As/GaAs films, and the so-called cross-hatch dislocation pattern seeded at the (Ga,In)As/GaAs interface. Kerr microscopy reveals a close correlation between the in-plane magnetic domain and dislocation patterns, absent in compressively strained materials. Moreover, the magnetic domain pattern presents a strong asymmetry in the size and number of domains for applied fields along the easy [110] and hard [110] directions which is attributed to different domain wall nucleation/propagation energies. This strong influence of the dislocation lines in the domain wall propagation/nucleation provides a lithography-free route to the effective trapping of domain walls in magneto-transport devices based on (Ga, Mn)As with in-plane anisotropy.

Herrera Diez, L.; Rapp, C.; Schoch, W.; Limmer, W.; Gourdon, C.; Jeudy, V.; Honolka, J.; Kern, K.

2012-04-01

332

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

333

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

334

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

335

Magnetic susceptibility anisotropy of human brain in vivo and its molecular underpinnings.  

PubMed

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

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

2011-10-20

336

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

PubMed Central

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

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

2011-01-01

337

Planetary magnetic fields  

Microsoft Academic Search

The past several years have seen dramatic developments in the study of planetary magnetic fields, including a wealth of new data, mainly from the Galilean satellites and Mars, together with major improvements in our theoretical modeling effort of the dynamo process believed responsible for large planetary fields. These dynamos arise from thermal or compositional convection in fluid regions of large

David J. Stevenson

2003-01-01

338

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

339

Magnetic Multipole Field Model  

NSDL National Science Digital Library

The EJS Magnetic Multipole Field Model shows the field of a magnetic dipole or quadrupole with little compasses that indicate direction and relative field strength. A slider changes the angular orientation of the dipole and a movable compass shows the magnetic field direction and magnitude. Compass values can be recorded into a data table and analyzed using a built-in data analysis tool. 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 Multipole 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_MagneticMultipoleField.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; Cox, Anne; Franciscouembre

2010-02-14

340

Determination of the first anisotropy constant of uniaxial anisotropic material from initial susceptibility of magnetization hard direction  

Microsoft Academic Search

A method to calculate the first anisotropy constant of a uniaxial anisotropy system from the initial susceptibility of magnetization hard direction have been studied. The formulas for single crystal and magnetically aligned powder based on rigid coupled magnetization model or two sublattice magnetization model have been derived and applied to determine the anisotropy constant of RE2Fe14B (RE=Ce, Pr, Gd, Tb,

Y. B Kim; Han-Min Jin

1998-01-01

341

Epitaxial thin film deposition of magnetostrictive materials and its effect on magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Magnetostriction means that the dimensions of a material depend on its magnetization. The primary goal of this dissertation was to understand the effect of magnetostriction on the magnetic anisotropy of single crystal magnetostrictive thin films, where the epitaxial pinning of the material to a substrate could inhibit its conversion to new dimensions. In order to address this goal, several Fe-based binary alloys were deposited onto various substrates by molecular beam epitaxy. The samples were characterized by an array of techniques including electron diffraction, Rutherford backscattering, vibrating sample magnetometry, ferromagnetic resonance, and x-ray absorption spectroscopies. The attempted growths of crystalline magnetostrictive thin films resulted in successful depositions of Fe1-xGax and Fe1-x Znx. Depositions onto MgO(001) substrates result in an in-plane cubic magnetic anisotropy, as expected from the cubic symmetry of the Fe-based thin films, and a strong out-of-plane uniaxial anisotropy that forces the magnetization to lie in the plane of the films. Depositions onto ZnSe/GaAs(001) substrates feature an additional in-plane uniaxial anisotropy. The magnitudes and signs of the in-plane anisotropies depend on the Ga content. Furthermore, the cubic anisotropy constant of Fe1-xGax samples deposited onto MgO substrates switches sign at a lower Ga concentration than is seen in bulk Fe1-xGax. The effect on the magnetic anisotropy of depositing a magnetostrictive material as an epitaxial thin film is influenced by the material's magnetostrictive properties and the substrate upon which it is deposited. In particular, pinning a magnetoelastic material to a substrate will modify its cubic anisotropy, and depositions on substrates compliant to an anisotropic strain relaxation may result in a strong in-plane uniaxial anisotropy.

McClure, Adam Marc

342

Magnetic Field Measurement System  

SciTech Connect

A magnetic field measurement system was designed, built and installed at MAX Lab, Sweden for the purpose of characterizing the magnetic field produced by Insertion Devices (see Figure 1). The measurement system consists of a large granite beam roughly 2 feet square and 14 feet long that has been polished beyond laboratory grade for flatness and straightness. The granite precision coupled with the design of the carriage yielded minimum position deviations as measured at the probe tip. The Hall probe data collection and compensation technique allows exceptional resolution and range while taking data on the fly to programmable sample spacing. Additional flip coil provides field integral data.

Kulesza, Joe; Johnson, Eric; Lyndaker, Aaron; Deyhim, Alex; Waterman, Dave; Blomqvist, K. Ingvar [Advanced Design Consulting USA, 126 Ridge Road, P.O. Box 187, Lansing, NY 14882 (United States); Dunn, Jonathan Hunter [MAX-lab, SE-221 00 Lund (Sweden)

2007-01-19

343

Magnetic Field Problem: Current  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2007-03-03

344

Crustal magnetic field of Mars  

Microsoft Academic Search

The equivalent source dipole technique is used to model the three components of the Martian lithospheric magnetic field. We use magnetic field measurements made on board the Mars Global Surveyor spacecraft. Different input dipole meshes are presented and evaluated. Because there is no global, Earth-like, inducing magnetic field, the magnetization directions are solved for together with the magnetization intensity. A

B. Langlais; M. E. Purucker; M. Mandea

2004-01-01

345

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

346

Co monolayers and adatoms on Pd(100), Pd(111), and Pd(110): Anisotropy of magnetic properties  

NASA Astrophysics Data System (ADS)

We investigate to what extent the magnetic properties of deposited nanostructures can be influenced by selecting as a support different surfaces of the same substrate material. Fully relativistic ab initio calculations were performed for Co monolayers and adatoms on Pd(100), Pd(111), and Pd(110) surfaces. Changing the crystallographic orientation of the surface has a moderate effect on the spin magnetic moment, a larger effect on the orbital magnetic moment, but sometimes a dramatic effect on the magnetocrystalline anisotropy energy and on the magnetic dipole term T?. The dependence of T? on the magnetization direction ? can lead to a strong apparent anisotropy of the spin magnetic moment as deduced from the x-ray magnetic circular dichroism sum rules. For systems in which the spin-orbit coupling is not very strong, the T? term can be understood as arising from the differences between components of the spin magnetic moment associated with different magnetic quantum numbers m.

Šipr, O.; Bornemann, S.; Ebert, H.; Mankovsky, S.; Vacká?, J.; Minár, J.

2013-08-01

347

Magnetic Domains and Anisotropy in the Magnetic Semiconductor GaMnAs  

NASA Astrophysics Data System (ADS)

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

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

2003-03-01

348

In-plane anisotropy in the magnetic and transport properties of manganite ultrathin films  

SciTech Connect

To analyze the conducting and magnetic properties near the film and substrate interface in manganites, ultrathin films (thickness{<=}100 A ) of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} were epitaxially grown by molecular-beam epitaxy on single-crystal (001) LaAlO{sub 3} (110) NdGaO{sub 3}, and (001) SrTiO{sub 3} substrates. Structural, magnetic, and magnetoresistive properties were investigated. All samples exhibit a substrate-independent decrease of the c-lattice parameter for thinnest films. Highly anisotropic behavior in both transport and magnetic properties were measured along the in-plane directions parallel to the substrate crystallographic axes. In particular, for the thinnest films (60 A ), the negative magnetoresistance at about 120 K with the average current along one of the crystallographic directions, is larger than the room-temperature colossal value. In the same low-temperature range, with the current along the other in-plane crystallographic direction, the magnetoresistance changes sign (resulting to be magnetic field independent for T{approx}150 K). Such an in-plane anisotropy of transport and magnetic properties is investigated with respect to possible intrinsic and extrinsic physical mechanisms.

Orgiani, P.; Polichetti, M.; Zola, D. [CNR-INFM SuperMat and Department of Physics, University of Salerno, Via S. Allende, I - 84081 Baronissi (Saudi Arabia) (Italy); Petrov, A. Yu.; Adamo, C.; Aruta, C.; Barone, C.; De Luca, G. M.; Galdi, A.; Maritato, L. [CNR-INFM Coherentia and Department of Physics, University of Salerno, Via S. Allende, I - 84081 Baronissi (Saudi Arabia) (Italy)

2006-10-01

349

Consistency relation for cosmic magnetic fields  

NASA Astrophysics Data System (ADS)

If cosmic magnetic fields are indeed produced during inflation, they are likely to be correlated with the scalar metric perturbations that are responsible for the cosmic microwave background anisotropies and large scale structure. Within an archetypical model of inflationary magnetogenesis, we show that there exists a new simple consistency relation for the non-Gaussian cross correlation function of the scalar metric perturbation with two powers of the magnetic field in the squeezed limit where the momentum of the metric perturbation vanishes. We emphasize that such a consistency relation turns out to be extremely useful to test some recent calculations in the literature. Apart from primordial non-Gaussianity induced by the curvature perturbations, such a cross correlation might provide a new observational probe of inflation and can in principle reveal the primordial nature of cosmic magnetic fields.

Jain, Rajeev Kumar; Sloth, Martin S.

2012-12-01

350

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized emission traces turbulent fields which are strongest in spiral arms and bars (20-30 ?G) and in central starburst regions (50-100 ?G). Such fields are dynamically important, e.g. they can drive gas inflows in central regions. Polarized emission traces ordered fields which can be regular or anisotropic random, generated from isotropic random fields by compression or shear. The strongest ordered fields of 10-15 ?G strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several spiral galaxies reveal large-scale patterns, which are signatures of regular fields generated by a mean-field dynamo. However, in most spiral galaxies observed so far the field structure is more complicated. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Ordered magnetic fields are also observed in radio halos around edge-on galaxies, out to large distances from the plane, with X-shaped patterns. Future observations of polarized emission at high frequencies, with the EVLA, the SKA and its precursors, will trace galactic magnetic fields in unprecedented detail. Low-frequency telescopes (e.g. LOFAR and MWA) are ideal to search for diffuse emission and small RMs from weak interstellar and intergalactic fields.

Beck, Rainer

2012-05-01

351

Coexistence of magnetic domains with in-plane and out-of-plane anisotropy in a single GaMnAs film  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy of the ferromagnetic semiconductor GaMnAs film grown on a (001) GaAs substrate was investigated by using Hall effect and magnetization measurements. When field strength was swept at a fixed direction in the film plane, abrupt transitions in the Hall resistance appeared while reducing the field strength even before the field direction is reversed. We show that this phenomenon is related to the presence of magnetic domains with a vertical easy axis in the film, as identified via Hall measurements performed with a field applied normal to the plane. The coexistence of magnetic domains with both in-pane and out-of-plane anisotropies in a single film was further confirmed by direct measurement of the corresponding magnetization components of the film.

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

2013-09-01

352

Magnetic properties of nanoparticles of cobalt ferrite at high magnetic field  

Microsoft Academic Search

In this paper we report high magnetic field (? 140 ? H ? 140 kOe) magnetization data for cobalt ferrites (crystallites size ? 42 nm) for temperatures (T) varying from 5 to 340 K. The T-dependence for the cubic magnetocrystalline anisotropy constant K1 was determined by using the “law of approach” (LA) to saturation. The values of K1 were found

A. Franco; F. L. A. Machado; V. S. Zapf

2011-01-01

353

Magnetic properties of nanoparticles of cobalt ferrite at high magnetic field  

Microsoft Academic Search

In this paper we report high magnetic field (- 140 <= H <= 140 kOe) magnetization data for cobalt ferrites (crystallites size ~ 42 nm) for temperatures (T) varying from 5 to 340 K. The T-dependence for the cubic magnetocrystalline anisotropy constant K1 was determined by using the ``law of approach'' (LA) to saturation. The values of K1 were found

A. Franco; F. L. A. Machado; V. S. Zapf

2011-01-01

354

Asymmetric hysteresis loops and its dependence on magnetic anisotropy in exchange biased Co/CoO core-shell nanoparticles  

NASA Astrophysics Data System (ADS)

The origin of asymmetry in field cooled (FC) hysteresis loops exhibiting exchange bias (EB) is investigated by studying the static and dynamic magnetic properties of core-shell Co/CoO nanoparticles. Two distinct freezing temperatures coresponding to the core (Tf-cr ~ 190 K) and the shell moments (Tf-sh ~ 95 K) are obtained from the energy barrier distribution. The FC loops are symmetric in the temperature range Tf-sh <= T <= Tf-cr, however, asymmetry in hysteresis is observed immediately below Tf-sh. These intriguing features are also probed by radio frequency transverse susceptibility (TS) experiments. We show that the first anisotropy fields obtained from the demagnetization and return curves of field cooled TS measurement, shift along the negative field axis and strikingly resemble the temperature dependence of EB. Field cooled TS measurements reveal the effect of competing Zeeman and anisotropy energy above and below Tf-sh to account for the development of asymmetry. Our study indicates that asymmetry in FC hysteresis loops is intrinsic to core-shell nanoparticles and develops only below the freezing temperature of the shell due to enhanced magnetic anisotropy.

Chandra, Sayan; Khurshid, Hafsa; Phan, Manh-Huong; Srikanth, Hariharan

2012-12-01

355

Development of a tensile-stress-induced anisotropy in amorphous magnetic thin films  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy was induced in positive magnetostrictive Fe80B20 and negative magnetostrictive Co75Si15B10 thin films by developing a tensile stress within the samples. The films were grown on the concave surfaces of mechanically bowed glass substrates. On releasing the substrates from the substrate holders, a tensile stress was developed within the samples that modified the domain structure. As a result of it, a magnetic easy axis parallel to the direction of the stress was induced in FeB sample whereas in CoSiB sample the induced easy axis was perpendicular to the direction of the developed stress. To produce magnetic multilayers with crossed anisotropy, FeB/CoSiB bilayers and FeB/Cu/CoSiB trilayers were grown on bowed substrates. The study of magnetic properties of the multilayers indicates the development of crossed anisotropy within them, particularly when the magnetic layers are separated by a nonmagnetic Cu layer.

Mandal, K.; Vázquez, M.; García, D.; Castaño, F. J.; Prados, C.; Hernando, A.

2000-10-01

356

CMB anisotropies due to cosmological magnetosonic waves  

SciTech Connect

We study scalar mode perturbations (magnetosonic waves) induced by a helical stochastic cosmological magnetic field and derive analytically the corresponding cosmic microwave background (CMB) temperature and polarization anisotropy angular power spectra. We show that the presence of a stochastic magnetic field, or an homogeneous magnetic field, influences the acoustic oscillation pattern of the CMB anisotropy power spectrum, effectively acting as a reduction of the baryon fraction. We find that the scalar magnetic energy density perturbation contribution to the CMB temperature anisotropy is small compared to the contribution to the CMB E-polarization anisotropy.

Kahniashvili, Tina [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States); CCPP, Department of Physics, New York University, 4 Washington Place, New York 10003 (United States); National Abastumani Astrophysical Observatory, 2A Kazbegi Ave, GE-0160 Tbilisi (Georgia); Ratra, Bharat [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States)

2007-01-15

357

The induced magnetic field.  

PubMed

Aromaticity is indispensable for explaining a variety of chemical behaviors, including reactivity, structural features, relative energetic stabilities, and spectroscopic properties. When interpreted as the spatial delocalization of ?-electrons, it represents the driving force for the stabilization of many planar molecular structures. A delocalized electron system is sensitive to an external magnetic field; it responds with an induced magnetic field having a particularly long range. The shape of the induced magnetic field reflects the size and strength of the system of delocalized electrons and can have a large influence on neighboring molecules. In 2004, we proposed using the induced magnetic field as a means of estimating the degree of electron delocalization and aromaticity in planar as well as in nonplanar molecules. We have since tested the method on aromatic, antiaromatic, and nonaromatic compounds, and a refinement now allows the individual treatment of core-, ?-, and ?-electrons. In this Account, we describe the use of the induced magnetic field as an analytical probe for electron delocalization and its application to a large series of uncommon molecules. The compounds include borazine; all-metal aromatic systems Al(4)(n-); molecular stars Si(5)Li(n)(6-n); electronically stabilized planar tetracoordinate carbon; planar hypercoordinate atoms inside boron wheels; and planar boron wheels with fluxional internal boron cluster moieties. In all cases, we have observed that planar structures show a high degree of electron delocalization in the ?-electrons and, in some examples, also in the ?-framework. Quantitatively, the induced magnetic field has contributions from the entire electronic system of a molecule, but at long range the contributions arising from the delocalized electronic ?-system dominate. The induced magnetic field can only indirectly be confirmed by experiment, for example, through intermolecular contributions to NMR chemical shifts. We show that calculating the induced field is a useful method for understanding any planar organic or inorganic system, as it corresponds to the intuitive Pople model for explaining the anomalous proton chemical shifts in aromatic molecules. Indeed, aromatic, antiaromatic, and nonaromatic molecules show differing responses to an external field; that is, they reduce, augment, or do not affect the external field at long range. The induced field can be dissected into different orbital contributions, in the same way that the nucleus-independent chemical shift or the shielding function can be separated into component contributions. The result is a versatile tool that is particularly useful in the analysis of planar, densely packed systems with strong orbital contributions directly atop individual atoms. PMID:21848282

Islas, Rafael; Heine, Thomas; Merino, Gabriel

2011-08-17

358

Origin of Magnetic Anisotropy of Iron Films Evaporated at Oblique Incidence  

Microsoft Academic Search

Detailed electron microscopic investigations confirmed that the shape anisotropies of the columnar grains grown in iron films evaporated at oblique incidence, which are parallel and perpendicular to the columnar grain axis, are principally responsible for both of the anisotropy fields Hk(1) and Hk(2) analyzed from torque measurements, respectively. Fiber textures found by X-ray diffraction were of the types of {111}

Kunito Okamoto; Takashi Hashimoto; Kazuhiro Hara; Eiji Tatsumoto

1971-01-01

359

Multiferroic response to magnetic field in orthorhombic manganites  

NASA Astrophysics Data System (ADS)

The magnetoelectric coupling in Eu0.55Y0.45MnO3 is studied based on a microscopic spin model which includes the superexchange interaction, the single-ion anisotropy, the Dzyaloshinskii-Moriya interaction, and the cubic anisotropy. Our Monte Carlo simulation reproduces the experimentally observed multiferroic response to magnetic field B. It is demonstrated that the magnetic field can control the multiferroic behaviors by modulating the spin arrangements, leading to various flops of electric polarization. In addition, an interesting state in which both the electric polarizations along the a-axis and c-axis are activated under high B is predicted and discussed.

Qin, M. H.; Tao, Y. M.; Dong, S.; Zhao, H. B.; Gao, X. S.; Liu, J.-M.

2011-03-01

360

Magnetism of filled skutterudites under high magnetic fields  

NASA Astrophysics Data System (ADS)

We measured the high-field magnetization M for skutterudite compounds of a paramagnet PrFe4Sb12 and a ferromagnet SmOs4Sb12 to investigate the characteristic magnetic properties. In PrFe4Sb12, we observed a peak structure in the dM/dH curve, which might be a level crossing effect between the singlet ground state and the excited state with a splitting energy of about 20 K in the crystalline electric field (CEF) scheme. In SmOs4Sb12, the anisotropy of magnetization for H?[100] and [1 1 0] was not observed, which is inconsistent with the quartet ground state in the CEF scheme.

Yamada, T.; Nakashima, H.; Sugiyama, K.; Hagiwara, M.; Kindo, K.; Tanaka, K.; Kikuchi, D.; Aoki, Y.; Sugawara, H.; Sato, H.; Settai, R.; ?nuki, Y.; Harima, H.

2007-03-01

361

Gd-Based Single-Ion Magnets with Tunable Magnetic Anisotropy: Molecular Design of Spin Qubits  

NASA Astrophysics Data System (ADS)

We report ac susceptibility and continuous wave and pulsed EPR experiments performed on GdW10 and GdW30 polyoxometalate clusters, in which a Gd3+ ion is coordinated to different polyoxometalate moieties. Despite the isotropic character of gadolinium as a free ion, these molecules show slow magnetic relaxation at very low temperatures, characteristic of single molecule magnets. For T?200mK, the spin-lattice relaxation becomes dominated by pure quantum tunneling events, with rates that agree quantitatively with those predicted by the Prokof’ev and Stamp model [Phys. Rev. Lett. 80, 5794 (1998)PRLTAO0031-900710.1103/PhysRevLett.80.5794]. The sign of the magnetic anisotropy, the energy level splittings, and the tunneling rates strongly depend on the molecular structure. We argue that GdW30 molecules are also promising spin qubits with a coherence figure of merit QM?50.

Martínez-Pérez, M. J.; Cardona-Serra, S.; Schlegel, C.; Moro, F.; Alonso, P. J.; Prima-García, H.; Clemente-Juan, J. M.; Evangelisti, M.; Gaita-Ariño, A.; Sesé, J.; van Slageren, J.; Coronado, E.; Luis, F.

2012-06-01

362

Gd-based single-ion magnets with tunable magnetic anisotropy: molecular design of spin qubits.  

PubMed

We report ac susceptibility and continuous wave and pulsed EPR experiments performed on GdW10 and GdW30 polyoxometalate clusters, in which a Gd3+ ion is coordinated to different polyoxometalate moieties. Despite the isotropic character of gadolinium as a free ion, these molecules show slow magnetic relaxation at very low temperatures, characteristic of single molecule magnets. For T?200??mK, the spin-lattice relaxation becomes dominated by pure quantum tunneling events, with rates that agree quantitatively with those predicted by the Prokof'ev and Stamp model [Phys. Rev. Lett. 80, 5794 (1998)]. The sign of the magnetic anisotropy, the energy level splittings, and the tunneling rates strongly depend on the molecular structure. We argue that GdW30 molecules are also promising spin qubits with a coherence figure of merit Q(M)?50. PMID:23004325

Martínez-Pérez, M J; Cardona-Serra, S; Schlegel, C; Moro, F; Alonso, P J; Prima-García, H; Clemente-Juan, J M; Evangelisti, M; Gaita-Ariño, A; Sesé, J; van Slageren, J; Coronado, E; Luis, F

2012-06-15

363

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

364

Magnetic field annihilators: invisible magnetization at the magnetic equator  

Microsoft Academic Search

Some distributions of magnetization give rise to magnetic fields that vanish everywhere above the surface, rendering these distributions of magnetization completely invisible. They are the annihilators of the magnetic inverse problem. Known examples are the infinite sheet with constant magnetization and the spherical shell of constant susceptibility magnetized by an arbitrary internal field. Here, we show that remarkably more interesting

S. Maus; V. Haak

2003-01-01

365

Anisotropy of the Lower Critical Field in YBa sub 2 Cu sub 3 O sub 7 Minus delta.  

National Technical Information Service (NTIS)

We report the first careful measurements of the two dimensional anisotropy of the lower critical field H/sub c1/. We compare the anisotropy in our values of H/sub c1/ with the anisotropy observed in H/sub c2/ and derive values for the anisotropy of the ef...

A. Umezawa G. W. Crabtree J. Z. Liu L. H. Nunez

1988-01-01

366

Synthesis of Samarium-Titanium and Neodymium Iron-Boron Magnetic Films with Special Anisotropies  

Microsoft Academic Search

Rare earth-transition metal film magnets of Nd -Fe-B and several new phases of Sm-Ti-Fe system have been synthesised by special sputtering methods to utilize the high magnetic anisotropies of these alloys. The magnetic properties of these film magnets were observed to be strongly dependent on the film textures. Thus, by varying the sputtering conditions we were able to synthesize films

Lee Wickramasekara

1986-01-01

367

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

368

Modifications of magnetic anisotropy and magnetization reversal in [Co0.4 nm/Pd0.7 nm]50 multilayers induced by 10 keV-He ion bombardment  

NASA Astrophysics Data System (ADS)

[Co0.4 nm/Pd0.7 nm]50 multilayers with Pd film thicknesses in the first ferromagnetic maximum of interlayer exchange coupling display almost purely perpendicular-to-plane anisotropy and labyrinth stripe domain patterns in remanence. Their magnetization reversal is characterized by domain nucleation starting at a defined field HN and domain wall movement in a defined magnetic field range. The modification of the magnetization reversal by 10 keV He ion bombardment due to the reduced magnetic anisotropy has been investigated by polar magneto-optical Kerr effect, by vibrating sample magnetometry, and by magnetic force microscopy at room temperature. It is shown that the ion bombardment creates and increases areas with ferromagnetic in-plane anisotropy and proportions of the sample showing superparamagnetism, the latter predominantly in the deeper layers.

Ehresmann, Arno; Hellwig, Olav; Buhl, Oliver; David Müglich, Nicolas; Weis, Tanja; Engel, Dieter

2012-09-01

369

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

370

Strain, interdiffusion, magnetism and magnetic anisotropy in Cu\\/Ni\\/Cu (0 0 1) sandwiches  

Microsoft Academic Search

The effects of interface, strain and interdiffusion on magnetic moments and magnetocrystalline anisotropy in Cu\\/Ni\\/Cu(0 0 1) trilayers have been studied by first-principles spin-polarized relativistic band-structure calculations. Ideal Cu\\/Nin\\/Cu(0 0 1) trilayers are modelled by NinCu5(0 0 1) superlattices (n = 1, 3, 5) whilst Ni\\/Cu interdiffusion is simulated by (NiCu)2Nin(NiCu)2Cu3(0 0 1) superlattices (n = 3, 5, 7) containing

G. Y. Guo

1997-01-01

371

Structural anisotropy of magnetically aligned single wall carbon nanotube films  

NASA Astrophysics Data System (ADS)

Thick films of aligned single wall carbon nanotubes and ropes have been produced by filtration/deposition from suspension in strong magnetic fields. We measured mosaic distributions of rope orientations in the film plane, for samples of different thicknesses. For an ~1 ?m film the full width at half maximum (FWHM) derived from electron diffraction is 25°-28°. The FWHM of a thicker film (~7 ?m) measured by x-ray diffraction is slightly broader, 35+/-3°. Aligned films are denser than ordinary filter-deposited ones, and much denser than as-grown material. Optimization of the process is expected to yield smaller FWHMs and higher densities.

Smith, B. W.; Benes, Z.; Luzzi, D. E.; Fischer, J. E.; Walters, D. A.; Casavant, M. J.; Schmidt, J.; Smalley, R. E.

2000-07-01

372

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

373

Tuning magnetic anisotropy in metallic multilayers by surface charging: an ab initio study.  

PubMed

Our ab initio studies show clear evidence that magnetic anisotropy (MA) and the direction of magnetization in metallic magnetic multilayers can be tailored at once by surface charging. By taking Fe-Pt multilayers as a representative example, we demonstrate that surface charging has a deep effect on the magnitude of the MA, which is composition dependent, achieving remarkably large values for systems featuring a single Fe layer capped with Pt. More intriguing is the behavior of the multilayers capped with iron bilayers, for which surface charging not only affects the value of the anisotropy but an easy-axis switching is also revealed. By analyzing the electronic structure of the magnetic layers and relating the MA to the orbital moment anisotropy, some insights about the origin of the MA from a local perspective can be inferred. PMID:23848916

Ruiz-Díaz, P; Dasa, T R; Stepanyuk, V S

2013-06-25

374

Effect of coherent to incoherent structural transition on magnetic anisotropy in Co/Pt multilayers  

NASA Astrophysics Data System (ADS)

The crystallographic structure and magnetic anisotropy have been investigated in Co/Pt multilayers deposited by direct current magnetron sputtering on two different buffer layers, Ta and Pt. Detail theoretical and experimental investigations reveal the presence of three effects: magneto-elastic, interface and shape anisotropies, and their competition results in three distinct regions based on the Co layer thickness (tCo). In the region I, with tCo< 6 A?, the coherent lattice strain modifies the volume anisotropy through magneto-elastic contribution and it leads to overall positive volume anisotropy energy. With further increase in tCo, lattice mismatch initiates and this results in a decrease in magneto-elastic effect and it enhances the interface anisotropy. The presence of both diminished magneto-elastic effect and enhanced interface anisotropy results in an intermediate region (region II) with negative volume anisotropy energy which is relatively wider (6 A? 12 A?, the magneto-elastic effect emerges as an interface phenomena and the shape anisotropy becomes dominant.

Chowdhury, P.; Kulkarni, P. D.; Krishnan, M.; Barshilia, Harish C.; Sagdeo, A.; Rai, S. K.; Lodha, G. S.; Sridhara Rao, D. V.

2012-07-01

375

Structural Control of Magnetic Anisotropy in a Multiferroic EuTiO3 Thin Film  

NASA Astrophysics Data System (ADS)

Strain control of EuTiO3 has been shown under tensile strain the system converts to a multiferroic groundstate with ferromagnetic and ferroelectric order[1]. Here we present a study of the magnetic order in thin films of EuTiO3 grown on DyScO3(110) substrates by reactive molecular-beam epitaxy (MBE). Neutron scattering and magnetic measurements show the magnetic moment orders with an easy axis along only one of the (110) pseudocubic axis of the unit cell. Such an easy axis is connected to the uniaxial crystal structure that evolves from cubic to tetragonal with octahedral tilting, which agrees well with the strain dependent structure predicted under biaxial tensile strain. The magnetic anisotropy for Eu is attributed to an asymmetric crystal field due to the uniaxial symmetry of the Eu-O coordination. Work at Argonne, including the Advanced Photon, is supported by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. [1] J.-H. Lee et al. Nature 466, 954 (2010).

Freeland, J. W.; Ke, X.; Ryan, P. J.; Kim, J. W.; Lee, J.-H.; Misra, R.; Schiffer, P.; Birol, T.; Fennie, C. J.; Schlom, D. G.

2012-02-01

376

Temperature-induced magnetic anisotropies in Co/Cu(1 1 17)  

NASA Astrophysics Data System (ADS)

The temperature dependence of magnetic anisotropy in cobalt films grown on Cu(1 1 17) has been studied by means of the magneto-optic Kerr effect. An in-plane uniaxial anisotropy is found in the as-grown films. At elevated temperatures the films exhibit changes in anisotropy. At temperatures around 100 °C a transition to nearly biaxial behavior is found which transforms again into uniaxial behavior at higher temperatures. Both transitions generate pronounced secondary maxima in the temperature-dependent susceptibility.

Wulfhekel, W.; Knappmann, S.; Gehring, B.; Oepen, H. P.

1994-12-01

377

Effect of Sample Concentration on the Determination of the Anisotropy Constant of Magnetic Nanoparticles  

Microsoft Academic Search

Techniques such as equilibrium (DC) and dynamic (AC) magnetic measurements have been used to determine the anisotropy constant of a variety of magnetic nanoparticles, obtaining values that are often an order of magnitude higher than the corresponding bulk material. Unfortunately, the effect of particle-particle interactions is often neglected, hence the reported values are an effective collective parameter , rather than

Victoria L. Calero-Diaz del Castillo; Carlos Rinaldi

2010-01-01

378

Magnetic Anisotropy and Magneto-Optical Properties of Iron Oxide Films  

Microsoft Academic Search

Iron oxide films were prepared by rf diode sputtering. Magnetic and magneto-optical properties of the iron oxide films are discussed. Perpendicular anisotropy was induced in sputtered iron oxide films (typically Ku{=}2× 105 erg\\/cm3). This perpendicular anisotropy was lost by annealing in air. The value of the Faraday constant thetaf was typically 2× 104 deg\\/cm at 633 nm. The absorption coefficient

Shuji Urabe; Takuhisa Numata; Seiji Inokuchi; Yoshifumi Sakurai

1986-01-01

379

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

380

Linear Theory of Weakly Amplified, Parallel Propagating, Transverse Temperature-anisotropy Instabilities in Magnetized Thermal Plasmas  

NASA Astrophysics Data System (ADS)

A rigorous analytical study of the dispersion relations of weakly amplified transverse fluctuations with wavevectors (\\vec{k}? \\vec{B}) parallel to the uniform background magnetic field \\vec{B} in an anisotropic bi-Maxwellian magnetized electron-proton plasma is presented. A general analytical instability condition is derived that holds for different values of the electron (Ae ) and proton (Ap ) temperature anisotropies. We determine the conditions for which the weakly amplified left-handed (LH) polarized Alfvén proton cyclotron and right-handed (RH) polarized Alfvén Whistler electron cyclotron branches can be excited. For different regimes of the electron plasma frequency phase speed w = ? p,e /(kc) these branches reduce to the RH- and LH-polarized Alfvén waves, RH-polarized high and low phase speed Whistler, RH-polarized proton, and LH-polarized electron cyclotron modes. Analytic instability threshold conditions are derived in terms of the combined temperature anisotropy A = T bottom/T par, the parallel plasma beta ?par = 8 ? nekBT par/B 2 and the electron plasma frequency phase speed w = ? p,e /(kc) for each mode. The results of our instability study are applied to the observed solar wind magnetic turbulence at values of 90 <= w <= 330. According to the existence conditions of the different instabilities, only the LH- and RH-polarized Alfvén wave instabilities can operate here. Besides the electron-proton mass ratio ? = 1836, the Alfvénic instability threshold conditions are controlled by the single observed plasma parameter w. The Alfvénic instability diagram explains well the observed confinement limits at small parallel plasma beta values in the solar wind.

Schlickeiser, R.; Skoda, T.

2010-06-01

381

LINEAR THEORY OF WEAKLY AMPLIFIED, PARALLEL PROPAGATING, TRANSVERSE TEMPERATURE-ANISOTROPY INSTABILITIES IN MAGNETIZED THERMAL PLASMAS  

SciTech Connect

A rigorous analytical study of the dispersion relations of weakly amplified transverse fluctuations with wavevectors ( k-vector {parallel} B-vector ) parallel to the uniform background magnetic field B-vector in an anisotropic bi-Maxwellian magnetized electron-proton plasma is presented. A general analytical instability condition is derived that holds for different values of the electron (A{sub e}) and proton (A{sub p}) temperature anisotropies. We determine the conditions for which the weakly amplified left-handed (LH) polarized Alfven proton cyclotron and right-handed (RH) polarized Alfven Whistler electron cyclotron branches can be excited. For different regimes of the electron plasma frequency phase speed w = {omega}{sub p,e}/(kc) these branches reduce to the RH- and LH-polarized Alfven waves, RH-polarized high and low phase speed Whistler, RH-polarized proton, and LH-polarized electron cyclotron modes. Analytic instability threshold conditions are derived in terms of the combined temperature anisotropy A = T{sub perpendicular}/T{sub {parallel}}, the parallel plasma beta {beta}{sub {parallel}} = 8 {pi} n{sub e}k{sub B}T{sub {parallel}}/B {sup 2} and the electron plasma frequency phase speed w = {omega}{sub p,e}/(kc) for each mode. The results of our instability study are applied to the observed solar wind magnetic turbulence at values of 90 {<=} w {<=} 330. According to the existence conditions of the different instabilities, only the LH- and RH-polarized Alfven wave instabilities can operate here. Besides the electron-proton mass ratio {mu} = 1836, the Alfvenic instability threshold conditions are controlled by the single observed plasma parameter w. The Alfvenic instability diagram explains well the observed confinement limits at small parallel plasma beta values in the solar wind.

Schlickeiser, R.; Skoda, T., E-mail: rsch@tp4.rub.d, E-mail: ts@tp4.rub.d [Institut fuer Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2010-06-20

382

Effect of pressure anisotropy and flow velocity on Kelvin-Helmholtz instability of anisotropic magnetized plasma using generalized polytrope laws  

SciTech Connect

The effect of pressure anisotropy and flow velocity on the Kelvin-Helmholtz (KH) instability of two magnetized anisotropic pressure plasmas flowing relative to each other is investigated using generalized polytrope laws. The anisotropic pressure with the generalized polytrope laws is considered with three-dimensional perturbations in the description of plasma using relevant magnetohydrodynamic (MHD) set of equations. The magnetic field is assumed in the x-direction and parallel to the direction of the flow of plasma streams. A complete polytrope model is given for the considered system in terms of pressure components, magnetic field, and density of the fluids to discuss the condition of KH instability, stability, and overstability. The problem is solved using the normal mode analysis and the general dispersion relation is obtained by applying the appropriate boundary conditions. The case of nonvanishing wavenumber transverse to the direction of the stream is obtained, which represents the stationery configuration without excitation of KH instability. The longitudinal mode of propagation is discussed with conditions of KH instability, stability, and overstability for collisionless (anisotropic) double-adiabatic Chew-Goldberger-Low (CGL) and collisional (isotropic) MHD media, depending on various values of polytrope indices. The effects of pressure anisotropy, different flow velocities, and magnetic field are also discussed on the growth rate of KH instability. We observe that the presence of flow velocity and pressure anisotropy of the plasmas has a destabilizing influence on the growth rate of the system. The growth rate is found larger for MHD set of equations in comparison to the CGL set of equations. The presence of magnetic field has a stabilizing role on the growth rate of the considered system.

Prajapati, R. P.; Chhajlani, R. K. [School of Studies in Physics, Vikram University, Ujjain, Madhya Pradesh 456010 (India)

2010-11-15

383

Field dependence of the superconducting basal plane anisotropy of TmNi2B2C  

SciTech Connect

The superconductor TmNi2B2C possesses a significant fourfold basal plane anisotropy, leading to a square vortex lattice (VL) at intermediate fields. However, unlike other members of the borocarbide superconductors, the anisotropy in TmNi2B2C appears to decrease with increasing field, evident by a reentrance of the square VL phase. We have used small-angle neutron scattering measurements of the VL to study the field dependence of the anisotropy. Our results provide a direct, quantitative measurement of the decreasing anisotropy. We attribute this reduction of the basal plane anisotropy to the strong Pauli paramagnetic effects observed in TmNi2B2C and the resulting expansion of vortex cores near Hc2.

Das, P.; Densmore, J.M.; Rastovski, C.; Schlesinger, K.J.; Laver, M.; Dewhurst, C.D.; Littrell, K.; Budko, Serguei L.; Canfield, Paul C.; Eskildsen, M.R.

2012-10-01

384

The Subduction Zone Flow Field from Seismic Anisotropy: A Global View  

Microsoft Academic Search

Although the morphologies of subducting slabs have been relatively well characterized, the character of the mantle flow field that accompanies subduction remains poorly understood. To analyze this pattern of flow, we compiled observations of seismic anisotropy, as manifested by shear wave splitting. Data from 13 subduction zones reveal systematic variations in both mantle-wedge and subslab anisotropy with the magnitude of

Maureen D. Long; Paul G. Silver

2008-01-01

385

Random-field and random-anisotropy O(N) spin systems with a free surface.  

PubMed

We study the surface scaling behavior of a semi-infinite d-dimensional O(N) spin system in the presence of a quenched random field and random anisotropy disorders. It is known that above the lower critical dimension d(LC) = 4 the infinite models undergo a paramagnetic-ferromagnetic transition for N > N(c) (N(c) = 2.835 for the random field and N(c) =9.441 for random anisotropy). For N < N(c) and d < d(LC) there exists a quasi-long-range-order phase with a zero order parameter and a power-law decay of spin correlations. Using a functional renormalization group, we derive the surface scaling laws that describe the ordinary surface transition for d > d(LC) and the long-range behavior of spin correlations near the surface in the quasi-long-range-order phase for d < d(LC). The corresponding surface exponents are calculated to one-loop order. The obtained results can be applied to the surface scaling of periodic elastic systems in disordered media, amorphous magnets, and (3)He-A in aerogel. PMID:23005746

Fedorenko, Andrei A

2012-08-27

386

Magnetic Field Measurements in Beam Guiding Magnets  

Microsoft Academic Search

Electromagnets used as beam guiding elements in particle accelerators and colliders require very tight tole-rances on their magnetic fields and on their alignment along the particle path. This article describes the methods and equipment used for magnetic measurements in beam transport magnets. Descriptions are given of magnetic resonance techniques, various induction coil methods, Hall generator measurements, the fluxgate magnetometer as

K. N. Henrichsen

1998-01-01

387

Growth of Cholesteric Finger under the Magnetic Field  

NASA Astrophysics Data System (ADS)

The growth of the cholesteric finger pattern under an electric field and a magnetic field was investigated experimentally.A phase diagram of the appearing patterns was constructed by changing the magnetic field H and the electric voltage V.There were six regions, numbered as I, II, III, IV, IV? and V, in the H-V phase diagram, where the growth of finger pattern was observed in the regions III and IV. It was found that in the region III the cholesteric finger grew up toward the direction of magnetic field and in the region IV the dendritic finger became elliptic due to the anisotropy of growth velocity as the increase of H. The growth velocity of the finger was enhanced by the magnetic field especially for the direction parallel to the magnetic field. The preferred direction of the finger growth was discussed by considering the interaction energy between the director and the magnetic field.

Nagaya, Tomoyuki; Hikita, Yasuhiro; Orihara, Hiroshi; Ishibashi, Yoshihiro

1998-07-01

388

Spontaneous generation of magnetic fields in astrophysical dusty plasmas  

Microsoft Academic Search

Two novel mechanisms for spontaneous generation of magnetic fields in dusty plasmas are presented. These are a new dust–plasma battery involving the cross product of the gradient of the dust charge density and the electron–ion pressures, as well as a new Weibel-like instability involving ion pressure anisotropy and resistive electron motions. The relevance of the present investigation to magnetic fields

P. K. Shukla

2003-01-01

389

Spontaneous generation of magnetic fields in astrophysical dusty plasmas  

Microsoft Academic Search

Two novel mechanisms for spontaneous generation of magnetic fields in dusty plasmas are presented. These are a new dust-plasma battery involving the cross product of the gradient of the dust charge density and the electron-ion pressures, as well as a new Weibel-like instability involving ion pressure anisotropy and resistive electron motions. The relevance of the present investigation to magnetic fields

P. K. Shukla

2003-01-01

390

Spontaneous generation of magnetic fields in astrophysical dusty plasmas  

NASA Astrophysics Data System (ADS)

Two novel mechanisms for spontaneous generation of magnetic fields in dusty plasmas are presented. These are a new dust-plasma battery involving the cross product of the gradient of the dust charge density and the electron-ion pressures, as well as a new Weibel-like instability involving ion pressure anisotropy and resistive electron motions. The relevance of the present investigation to magnetic fields in astrophysical objects is discussed.

Shukla, P. K.

2003-07-01

391

Towards an understanding of magnetic interactions and anisotropies in iron superconductors  

NASA Astrophysics Data System (ADS)

The itinerant or strong coupling origin of magnetism in iron pnictides is still unsettled. The localized description generally assumes AF exchange constants satisfying 2J2>J1, withJ1 and J2 referring to first and second nearest neighbors respectively. The itinerant picture relies on the nesting of the Fermi surface. Both descriptions reproduce the columnar ordering found experimentally. The role played by the Hund's coupling JH and the orbital degree of freedom are also highly debated. Orbital ordering has been invoked to explain the anisotropic resistivity and optical conductivity. We make connection between these two pictures by studying the same five-orbital model within Heisenberg and mean field descriptions [1]. We have found that J2/J1 strongly depends on the charge and orbital filling what results in an unexpected sensitivity of the AF ordering to crystal field parameters. J1 and J2 can become ferromagnetic at large JH. Consistent results are obtained in the mean field description. We also analyze the resistivity and optical conductivity anisotropies and show that they are a consequence of magnetism and not of orbital ordering [2].[4pt] [1] M.J. Calder'on et al, arXiv:1107.2279. E. Bascones et al, PRL 104, 227201 (2010).[0pt] [2] B. Valenzuela et al, PRL 105, 207202 (2010).

Bascones, Elena

2012-02-01

392

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

393

Perpendicular magnetic anisotropy in ultrathin Co|Ni multilayer films studied with ferromagnetic resonance and magnetic x-ray microspectroscopy  

NASA Astrophysics Data System (ADS)

Ferromagnetic resonance (FMR) spectroscopy, x-ray magnetic circular dichroism (XMCD) spectroscopy and magnetic transmission soft x-ray microscopy (MTXM) experiments have been performed to gain insight into the magnetic anisotropy and domain structure of ultrathin Co|Ni multilayer films with a thin permalloy layer underneath. MTXM images with a spatial resolution better than 25 nm were obtained at the Co L3 edge down to an equivalent thickness of Co of only 1 nm, which establishes a new lower boundary on the sensitivity limit of MTXM. Domain sizes are shown to be strong functions of the anisotropy and thickness of the film.

Macià, F.; Warnicke, P.; Bedau, D.; Im, M.-Y.; Fischer, P.; Arena, D. A.; Kent, A. D.

2012-11-01

394

Anisotropy of magnetic susceptibility and magnetic properties of obsidians: volcanic implications  

NASA Astrophysics Data System (ADS)

The anisotropy of magnetic susceptibility (AMS), hysteresis and thermomagnetic curves of two sets of obsidians with contrasting bulk compositions are reported in this work. The cooling and deformation history of one of those obsidians is perfectly known, as these specimens were produced in the laboratory using material from a basaltic lava flow. The other samples are occurrences of a more silicic composition and for which the AMS has been documented to have a close relationship with the distribution of microlites. The results of our measurements indicate that although the deformation and cooling histories of the lava might influence the exact composition of the ferromagnetic fraction, the relationship between the AMS and the deformation history does not seem to be altered. Furthermore, the results of this work indicate that the AMS can be associated to a population of ferromagnetic minerals of a submicroscopic size, despite of which it can be very well defined and yield large degrees of anisotropy. It is suggested that the AMS associated to such population of small grains might indeed be the origin of the AMS of other igneous rocks that have an optically observable fraction of mineral grains, although until present it had been overlooked in most instances. Use of tests designed to identify the contribution of a superparamagnetic fraction (SP) in the magnetic properties of a rock can help us to identify the presence of such a SP-related AMS in other cases.

Cañón-Tapia, E.; Cárdenas, K.

2012-04-01

395

Mapping magnetic susceptibility anisotropies of white matter in vivo in the human brain at 7 T.  

PubMed

High-resolution magnetic resonance phase- or frequency-shift images acquired at high field show contrast related to magnetic susceptibility differences between tissues. Such contrast varies with the orientation of the organ in the field, but the development of quantitative susceptibility mapping (QSM) has made it possible to reproducibly image the intrinsic tissue susceptibility contrast. However, recent studies indicate that magnetic susceptibility is anisotropic in brain white matter and, as such, needs to be described by a symmetric second-rank tensor( ??). To fully determine the elements of this tensor, it would be necessary to acquire frequency data at six or more orientations. Assuming cylindrical symmetry of the susceptibility tensor in myelinated white matter fibers, we propose a simplified method to reconstruct the susceptibility tensor in terms of a mean magnetic susceptibility, MMS=(?(//)+2 ?(?))/3 and a magnetic susceptibility anisotropy, MSA=?(//)-?(?), where ?(//) and ?(?) are susceptibility parallel and perpendicular to the white matter fiber direction, respectively. Computer simulations show that with a practical head rotation angle of around 20°-30°, four head orientations suffice to reproducibly reconstruct the tensor with good accuracy. We tested this approach on whole brain 1 × 1 × 1 mm(3) frequency data acquired from five healthy subjects at 7 T. The frequency information from phase images collected at four head orientations was combined with the fiber direction information extracted from diffusion tensor imaging (DTI) to map the white matter susceptibility tensor. The MMS and MSA were quantified for regions in several large white matter fiber structures, including the corona radiata, posterior thalamic radiation and corpus callosum. MMS ranged from -0.037 to -0.053 ppm (referenced to CSF being about zero). MSA values could be quantified without the need for a reference and ranged between 0.004 and 0.029 ppm, in line with the expectation that the susceptibility perpendicular to the fiber is more diamagnetic than the one parallel to it. PMID:22561358

Li, Xu; Vikram, Deepti S; Lim, Issel Anne L; Jones, Craig K; Farrell, Jonathan A D; van Zijl, Peter C M

2012-04-28

396

Transition of magnetic anisotropy in Ni\\/GaAs (0 0 1) observed by magnetization and ferromagnetic resonance  

Microsoft Academic Search

Polycrystalline thin Ni films deposited onto GaAs (001) show a transition of the magnetic anisotropy depending on its thickness. The anisotropy is perpendicular to the film plane for the thicknesses of the film ?12nm. This becomes in-plane in the films having thicknesses ?15nm. The films are deposited onto the n-type GaAs (001) substrate by the usual thermal evaporation method and

S. A. Haque; A. Matsuo; Y. Yamamoto; H. Hori

2002-01-01

397

Modeling the properties of ferrogels in uniform magnetic fields.  

PubMed

The properties of ferrogels in homogeneous magnetic fields are studied using a simple microscopic model and Monte Carlo simulations. The main phenomena of interest concern the anisotropy and enhancement of the elastic moduli that result from applying uniform magnetic fields before and after the magnetic grains are locked in to the polymer-gel matrix by cross-linking reactions. The positional organization of the magnetic grains is influenced by the application of a magnetic field during gel formation, leading to a pronounced anisotropy in the mechanical response of the ferrogel to an applied magnetic field. In particular, the elastic moduli can be enhanced to different degrees depending on the mutual orientation of the fields during and after ferrogel formation. The model represents ferrogels by ensembles of dipolar spheres dispersed in elastic matrices. Experimental trends are shown to be reflected accurately in the simulations of the microscopic model. In addition, the simulations yield microscopic insights on the organization of the magnetic grains. Finally, simple relationships between the elastic moduli and the magnetization are proposed. If supplemented by the magnetization curve, these relationships yield the dependencies of the elastic moduli on the applied magnetic field, which are often measured directly in experiments. PMID:21405693

Wood, Dean S; Camp, Philip J

2011-01-07

398

Modeling the properties of ferrogels in uniform magnetic fields  

NASA Astrophysics Data System (ADS)

The properties of ferrogels in homogeneous magnetic fields are studied using a simple microscopic model and Monte Carlo simulations. The main phenomena of interest concern the anisotropy and enhancement of the elastic moduli that result from applying uniform magnetic fields before and after the magnetic grains are locked in to the polymer-gel matrix by cross-linking reactions. The positional organization of the magnetic grains is influenced by the application of a magnetic field during gel formation, leading to a pronounced anisotropy in the mechanical response of the ferrogel to an applied magnetic field. In particular, the elastic moduli can be enhanced to different degrees depending on the mutual orientation of the fields during and after ferrogel formation. The model represents ferrogels by ensembles of dipolar spheres dispersed in elastic matrices. Experimental trends are shown to be reflected accurately in the simulations of the microscopic model. In addition, the simulations yield microscopic insights on the organization of the magnetic grains. Finally, simple relationships between the elastic moduli and the magnetization are proposed. If supplemented by the magnetization curve, these relationships yield the dependencies of the elastic moduli on the applied magnetic field, which are often measured directly in experiments.

Wood, Dean S.; Camp, Philip J.

2011-01-01

399

Rare-Earth-Dependent Tri-axial Magnetic Anisotropies and Growth Conditions in REBa2Cu4O8  

NASA Astrophysics Data System (ADS)

Tri-axial orientation under modulated rotation magnetic fields (MRFs) and the growth of single crystals in ambient pressure were demonstrated in various REBa2Cu4O8 (RE124; RE, rare earth elements) compounds. RE124 crystals have been successfully grown for RE = Y, Sm, Eu, Gd, Dy, Ho, and Er. Optimal growth temperature regions for RE124 largely depended on the type of RE and became narrower in the case of lighter RE ions. By applying an MRF of 10 T, powders of all the grown RE124 were tri-axially oriented in epoxy resin at room temperature, and their orientation axes were clearly dependent on the type of RE ions in RE124. Furthermore, it was found from the changes in the degree of orientation under three different MRF conditions that tri-axial single-ion magnetic anisotropies of heavy RE3+ ions were highest among magnetic anisotropies generated by Cu--O networks and RE3+ ions. The appropriate choice of RE ions in RE-based cuprate superconductors enables the reduction of the magnetic field required for the production of bulk and thick films based on the magnetic orientation technique.

Yamaki, Momoko; Horii, Shigeru; Haruta, Masakazu; Shimoyama, Jun-ichi

2012-01-01

400

Enhanced nucleation fields due to dipolar interactions in nanocomposite magnets  

NASA Astrophysics Data System (ADS)

One approach to construct powerful permanent magnets while using less rare-earth elements is to combine a hard magnetic material having a high coercive field with a soft magnetic material having a high saturation magnetization at the nanometer scale and create so-called nanocomposite magnets. If both materials are strongly coupled, exchange forces will form a stable magnet. We use finite element micromagnetics simulations to investigate the changing hysteresis properties for varying arrays of soft magnetic spherical inclusions in a hard magnetic body. We show that the anisotropy arising from dipolar interactions between soft magnetic particles in a hard magnetic matrix can enhance the nucleation field by more than 10% and strongly depends on the arrangement of the inclusions.

Fischbacher, Johann; Bance, Simon; Exl, Lukas; Gusenbauer, Markus; Oezelt, Harald; Reichel, Franz; Schrefl, Thomas

2013-03-01

401

Full magnetization process of 3d-4f hard magnetic materials in ultrahigh magnetic fields (an example: RFe11Ti)  

NASA Astrophysics Data System (ADS)

The prospects of using the free-powder high-field magnetization method for a quantitative study of inter-sublattice exchange interaction in 3d-4f hard magnetic materials are analyzed. Such analysis is stimulated by the availability of pulsed magnetic fields ~103 T generated by implosion. Particular attention is paid to effects due to magnetic anisotropy, essential for these materials. The 3d-4f ferrimagnets where both sublattices contribute positively to the easy-axis anisotropy are shown to be suitable objects of study by the free-powder method, because (i) anomalies in their low-temperature magnetizatization curves are sharp and (ii) anisotropic effects can be allowed for without quantitative knowledge of the anisotropy constants. Moreover, these ``good'' hard magnetic materials can be brought into metamagnetic regime by diluting the rare earth sublattice with nonmagnetic yttrium; then, regardless of the anisotropy constants, the magnetization curve at low temperatures has just one steplike anomaly, the threshold field being equal exactly to the molecular field acting on the rare earth.

Kuz'min, M. D.; Zvezdin, A. K.

1998-03-01

402

Magnetoresistance, Magnetization Characteristics and In-plan Anisotropy of the Co/Cu/Co Pseudo-Spin Valves  

NASA Astrophysics Data System (ADS)

We studied Co/Cu/Co pseudo-spin-vales (PSVs) for induced anisotropy during film growth and its effects on the magnetization and magnetoresistance (MR). Considerable improvement of MR performance was achieved in these PSVs with Fe buffer due to anisotropy induced in <100> direction compared to PSVs on Cr/Cu buffer. PSVs were deposited on Si (100) wafers with natural oxide using S-research magnetron sputtering in 3 mTorr argon and base pressure <1.0x10-7 Torr. The PSVs with different thickness values of the constituent layers were deposited to optimize their MR performance. For PVS on Fe buffer, sharp magnetization reversal results in an almost perfect ``square loop" of magnetization and a corresponding enhanced MR value (9.2%) and field sensitivity (1.0%Oe)at the switch field of 27 Oe. The dependence of the magnitude of the MR on the thickness of constituent layers of the PSVs was interpreted within the model based on first principles solution to the Boltzmann transport equations calculations. The magnetization reversal of the PSVs with Cr/Cu buffer was affected by the temperature, unlike the anisotropic PSVs with the Fe buffer layer, which showed perfect square loops and high MR sensitivity from 5 K to 300 K. In both systems the switching field between low and high resistance states decreased with increasing temperature but it is lower for the Fe/Co/Cu/Co.

Wang, Jian-Qing; Malskinski, Leszek M.; MacLaren, James M.; Ross, C. A.

2000-03-01

403

Anisotropy of Left-Handed Material Substrates Effect on Field Distributions  

NASA Astrophysics Data System (ADS)

Anisotropy may be introduced into the material properties of the left-handed material (LHM) substrate in a guided wave structure, an extension of earlier work looking at the isotropic situation [1], [2] and [3]. This is done through the introduction of uniaxial behavior on the diagonal elements of the tensor for the principal axes of the left-handed material. Using an anisotropic Greens function, ab initio calculations have been done in three different frequencies regions, centered about 0.2, 2.0 , and 20 GHz. Structure studied is microstrip whose configuration is compatible with miniaturized monolithic circuits. Field distributions, in the 2D cross-section, obtained for the electric E and magnetic H fields, demonstrate the change with introduced anisotropy. Some evidence of surface wave generation, and strong evidence, occurs at, respectively, 2 GHz and 20 GHz, for particular anisotropic LHM substrates. All of the distributions found were for the fundamental mode in the even current Jz symmetry case. Both color magnitude field distributions as well as arrow distributions were produced. Finally, in order to discern the field variation as one goes from the LHM to the ordinary right-handed material (RHM) in a different way, field component variation versus the direction normal to the material layers is plotted, showing the peculiar behavior of LHM. This last plotting technique very vividly highlights the surface waves. [1] C. M. Krowne, arXiv.org/abs/physics/0305004 (May 4, 2004). [2] C. M. Krowne and M. Daniel, IEEE Intern. Microwave Symp. Dig. 1, 309 (June 2003). [3] C. M. Krowne, IEEE Trans. Microwave Theory & Tech. 51, (Dec. 2003).

Krowne, Clifford

2004-03-01

404

Magnetic fields and cancer  

SciTech Connect

This letter is a response to an article by Savitz and Kaune, EHP 101:76-80. W-L wire code was applied to data from a 1988 Denver study, and an association was reported between high W-L wire code and childhood cancer. This author discusses several studies and provides explanations which weakens the argument that classification error resulted in an appreciable reduction in the association between W-L high wire code and childhood cancer. In conclusion, the fact that new wire code is only weakly correlated with magnetic field measurements (in the same manner as the original W-L wire code) suggests that the newly reported stronger association with childhood cancer is likely due to factors other than magnetic fields. Differential residential mobility and differential residential age are two possible explanations and are suggestive that the reported association may be false.

Jones, T.L.

1993-10-01

405

Highly asymmetric magnetic behavior in exchange biased systems induced by non-collinear field cooling.  

SciTech Connect

A detailed study of the angular dependence of the magnetization reversal in polycrystalline ferromagnetic (FM)/antiferromagnetic Co/IrMn bilayers with noncollinear FM and unidirectional anisotropies shows a peculiar asymmetric magnetic behavior. The anisotropy configuration is set via a field cooling (FC) procedure with the magnetic field misaligned with respect to the easy magnetization direction of the FM layer. Different magnetization reversal modes are observed for either positive or negative angles with respect to the FC direction. The angular dependence of both coercivity and exchange bias also clearly displays the broken symmetry of the induced noncollinearity. Our findings are reproduced with a modified Stoner-Wohlfarth model including the induced anisotropy configuration. Our results highlight the importance of the relative angle between anisotropies in exchange bias systems, opening a new path for the tailoring of their magnetic properties.

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

2009-09-21

406

Crystalline and Magnetic Anisotropy of the 3d Transistion-Metal Oxides  

NASA Astrophysics Data System (ADS)

The 3d transition-metal oxides (TMOs) are subject of debate since many decades due to their extraordinary properties, such as the formation of an antiferromagnetic ordering AFM2 below their Néel temperature. Many studies, both experimental and theoretical, focus only on MnO and NiO, where the crystalline anisotropy is solely driven by exchange striction along the unique symmetry axis in the [111] direction and where the magnetic anisotropy is explained in terms of magnetic dipole interactions. In the other TMOs, FeO and CoO, however, orbital magnetization and spin-orbit interaction play an additional, yet crucial role for both crystalline and magnetic anisotropy. We present density-functional theory (DFT) studies including an on-site interaction U of the crystalline and magnetic anisotropy of the electronic systems with non-collinear spins. The influence of the (semi-)local description of exchange and correlation (XC) by means of the local density approximation (LDA) and generalized gradient approximation (GGA) on the orbital moments in FeO and CoO and the implications on the aforementioned properties is investigated. We discuss the quenching of the orbital magnetization due to the gradient corrections.

Schrön, Andreas; Rödl, Claudia; Bechstedt, Friedhelm

2013-03-01

407

a Comparison of Anisotropy of Magnetic Susceptibility and Anisotropy of Anhysteretic Remanence Data from the Early Jurassic Basal Karoo Igneous Series, South Africa  

NASA Astrophysics Data System (ADS)

Although anisotropy of magnetic susceptibility (AMS) data from plutonic rocks has often been used as a proxy for magma flow, many studies indicate that the relationship between the principal axes of the anisotropy of magnetic susceptibility (AMS) and independently inferred flow patterns is not simple. Data from dikes show that complications may arise from the contribution of single domain (SD) magnetite grains, imbricated symmetric fabrics along dike margins and post-solidification thermal stresses. Limited studies have focused on subhorizontal tabular intrusions and their magnetic fabrics. The Karoo Large Igneous Province in South Africa hosts a well-exposed, laterally extensive set of undeformed, stacked gabbroic sills emplaced parallel to bedding in the Karoo Basin. The sills range in thickness from about 1 m up to 1000 m and have a relatively constant petrologic composition of gabbros and gabbro-norites. Theses sills are distributed throughout the entire Karoo Basin and were emplaced at several stratigraphic heights / depths in the Karoo stratigraphic column. Oriented core samples were collected from 30 different sills and yielded 1598 specimens for AMS and AARM fabric data as well as paleomagnetic measurements. The low-field magnetic susceptibility Km ranges widely from about 100 to 20,000 x 10-6 [SI Vol] and the degree of anisotropy P' ranges from 1.01 to 1.10, with a broad correlation between Km and P'. Thermomagnetic experiments reveal that the main magnetic carrier is titanomagnetite with variable ulvöspinel content; hysteresis data show a pseudo-single domain grain dominance. The AMS and AARM fabric data, collected for all sites, yield normal fabric relations and are consistent with the nearly horizontal attitude of the sills in most of the sills, with subvertical K3 AMS and AARM axes. Generally, AARM parameters are greater than AMS values, although the dispersion of AARM data is more variable among sites. In five of 30 sills, K3 and K1 AMS axes are subhorizontal, and the AARM data are similar. An explanation for this phenomenon must take into consideration the general agreement between both fabric approaches, and likely involves unusual alignment of titanomagnetite grains related to magma flow.

Geissman, J. W.; Ferre, E. C.; Mason, S. N.; Maes, S. M.; Lehman, A.; Marsh, J.

2011-12-01

408

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

SciTech Connect

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 suggestion is supported by results presented here of finite element calculations of the effects of changes in anisotropy on MFL signal amplitudes.

Leonard, S.; Atherton, D.L. [Queen`s Univ., Kingston, Ontario (Canada). Dept. of Physics

1996-05-01

409

In-plane anisotropy control of the magnetic vortex gyrotropic mode  

NASA Astrophysics Data System (ADS)

The effect of an in-plane induced uniaxial anisotropy on the magnetic vortex gyrotropic frequency is investigated by micromagnetic simulations, exemplified by the inverse magnetostriction in a uniaxially stressed circular dot. It is found that the gyrotropic frequency decreases with increasing magnitude of the induced uniaxial anisotropy. The results are analyzed by extracting the restoring forces from the vortex dynamical potential-well. The dominant contribution to the decreasing trend in frequency is found to be due to a softening of both the restoring force spring constants. This work offers an alternative method to control the gyrotropic frequency of a magnetic vortex.

Roy, P. E.

2013-04-01

410

Edge atoms effects on the perpendicular anisotropy of ultrathin magnetic layers  

NASA Astrophysics Data System (ADS)

The present work reports experimental and theoretical results for electrodeposited Co/Au(111) ultrathin layers with very specific magnetic behavior. We show that the observed two peaks in the out-of-plane magnetization versus deposition time variation could be explained by the remarkably high perpendicular anisotropy of the perimeter atoms of low-dimensional islands formed during the layer-by-layer growth, as compared to that of the surface atoms. Our results indicate that it is possible to sustain high anisotropy in very small grains without coming across the superparamagnetic limit, opening excellent opportunities for materials engineering.

Geshev, J.; Gündel, A.; Zaharieva, I.; Schmidt, J. E.

2012-09-01

411

Diffusive processes in a stochastic magnetic field  

SciTech Connect

The statistical representation of a fluctuating (stochastic) magnetic field configuration is studied in detail. The Eulerian correlation functions of the magnetic field are determined, taking into account all geometrical constraints: these objects form a nondiagonal matrix. The Lagrangian correlations, within the reasonable Corrsin approximation, are reduced to a single scalar function, determined by an integral equation. The mean square perpendicular deviation of a geometrical point moving along a perturbed field line is determined by a nonlinear second-order differential equation. The separation of neighboring field lines in a stochastic magnetic field is studied. We find exponentiation lengths of both signs describing, in particular, a decay (on the average) of any initial anisotropy. The vanishing sum of these exponentiation lengths ensures the existence of an invariant which was overlooked in previous works. Next, the separation of a particle`s trajectory from the magnetic field line to which it was initially attached is studied by a similar method. Here too an initial phase of exponential separation appears. Assuming the existence of a final diffusive phase, anomalous diffusion coefficients are found for both weakly and strongly collisional limits. The latter is identical to the well known Rechester-Rosenbluth coefficient, which is obtained here by a more quantitative (though not entirely deductive) treatment than in earlier works.

Wang, H.; Vlad, M.; Vanden Eijnden, E.; Spineanu, F.; Misguich, J.H.; Balescu, R. [Association Euratom-Etat Belge sur la Fusion, Physique Statistique et Plasmas, Code Postal 231, Universite Libre de Bruxelles, Campus Plaine, Boulevard du Triomphe, 1050 Bruxelles (Belgium)]|[Association Euratom-Commissariat a l`Energie Atomique sur la Fusion, Departement de Recherches sur la Fusion Controle, Centre d`Etudes de Cadarache, 13108 Saint-Paul-lez-Durance Cedex (France)

1995-05-01

412

The detection of magnetotactic bacteria and magnetofossils by means of magnetic anisotropy  

NASA Astrophysics Data System (ADS)

An important characteristic of magnetotactic bacteria (MTB) is the anisotropy of one-dimensionally aligned magnetite particles. This paper introduces the use of ferromagnetic resonance spectroscopy (FMR) at two different frequencies to compare the anisotropic properties of magnetite chains of cultured intact MTB with those of lake sediments of Holocene age in order to detect magnetofossils and to characterize their preservation in a geological system. Magnetite chains of intact MTB exhibit a predominantly uniaxial anisotropy. In the lake sediments, where diagenetic processes disintegrate the chains and diminish their uniaxiality, magnetite chains or chain fragments and dissociated bulk magnetite particles differ in their anisotropy properties. The two groups of assembly can be distinguished by empirical spectral separation of the FMR signal. This straightforward use of the characteristics of magnetic anisotropy provides a way to detect magnetofossils experimentally, thus allowing a better insight into microbial ecology during Earth's history.

Gehring, Andreas U.; Kind, Jessica; Charilaou, Michalis; García-Rubio, Inés

2011-09-01

413

Damping of CoxFe80-xB20 ultrathin films with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We use vector network analyzer ferromagnetic resonance to study the perpendicularly magnetized CoFeB films. We report the dependence of the anisotropy, the g-factor, and the damping upon the Fe-Co compositional ratio in the amorphous and crystalline states. The damping and the anisotropy increase upon crystallization but vary little with composition on the Fe-rich side. At high cobalt content, the anisotropy lowers while the damping and the sample inhomogeneity increase. The compositional dependences seem to extrapolate from the properties of bulk CoFe alloys, with differences that can be understood from the correlated impacts of spin-orbit interaction on anisotropy, g-factor, and damping.

Devolder, T.; Ducrot, P.-H.; Adam, J.-P.; Barisic, I.; Vernier, N.; Kim, Joo-Von; Ockert, B.; Ravelosona, D.

2013-01-01

414

Magnetic and structural anisotropies in laser ablated epitaxial thin films of full-Heusler alloy Co2MnSi on SrTiO3  

NASA Astrophysics Data System (ADS)

We present the thickness dependent magnetic properties of laser ablated epitaxial Co2MnSi (CMS)Heusler alloy thin films grown on (001) oriented SrTiO3 substrate. In order to study the intrinsic magnetic anisotropy, a highly ordered single crystal thin film of Heusler alloys is necessary. This provides a unique opportunity to determine the behavior of magnetization reversal, and affect important properties such as the coercive field and remanence. The two important sources of the magnetic anisotropy are the magnetic dipolar interaction and the spin-orbit interaction. The strain in films due to the lattice mismatch with the substrate affects the shape anisotropy while spin-orbit coupling changes magneto-crystalline anisotropy. We have observed an in-plane biaxial compressive strain in the films which relaxes with increasing film thickness. Although the hysteresis loops show an in-plane easy axis for all films, the single-domain phase diagram reveals a gradual transition from in-plane to out-of-plane transition of magnetization as the film thickness is decreased. The magnetization starts to cant as film thickness start to decrease and we found a canting angle of 31.8^o with respect to the film plane for our thinnest 5 nm CMS films.

Pandey, Himanshu; Rout, P. K.; Budhani, R. C.

2013-03-01

415

Texturing of magnetic materials at high temperature by solidification in a magnetic field  

Microsoft Academic Search

The ability to impose a preferred orientation, or 'texture', on a crystalline material is important in many fields of materials science. A new method is presented of texturing materials that have a residual anisotropy in their magnetic susceptibility at high temperature, by solidification in a magnetic field. This one-step process is demonstrated by an application to the high-temperature superconductor YBa2Cu3O7.

P. de Rango; M. Lees; P. Lejay; A. Sulpice; R. Tournier; M. Ingold; P. Germi; M. Pernet

1991-01-01

416

Magnetic anisotropy and Verwey transition of magnetosome chains in Magnetospirillum gryphiswaldense  

NASA Astrophysics Data System (ADS)

Magnetotactic bacteria (MTB) are characterized by cellular magnetic dipoles formed by the 1-D assembly of magnetite and/or greigite particles aligned along their magnetic easy axes. This alignment creates strong interaction-induced shape anisotropy. Ferromagnetic resonance (FMR) spectroscopy is applied to study the changes in anisotropy of the MTB Magnetospirillum gryphiswaldense between room temperature and 10 K. The Verwey transition is found at about 100 K. The characteristic FMR signal of the cellular dipole at room temperature vanishes upon cooling to the isotropic point at Ti? 130 K, where the magnetocrystalline anisotropy constant K1 becomes zero. Monitoring of the FMR response of intact MTB as a function of temperature is taken to discuss theoretically the reduction of the interaction-induced shape anisotropy in magnetofossils because of diagenetic processes. It is concluded that there is a similarity in the FMR response between magnetofossils at room temperature and intact MTB near Ti. This is because the critical effect of the magnetocrystalline anisotropy constant K1 and of the alignment of magnetic easy axes on the cellular dipole. Low-temperature FMR results of intact MTB can thus be used as a guideline for detecting magnetofossils in geological environments.