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1

Anisotropy of magnetic susceptibility measured in variable weak magnetic fields  

NASA Astrophysics Data System (ADS)

Theory of the low-field anisotropy of magnetic susceptibility (AMS) of rocks is based on the assumption of the linear relationship between magnetization and magnetizing field, resulting in field independent susceptibility. This relationship is by definition valid in diamagnetic and paramagnetic minerals, while in ferrimagnetic and antiferromagnetic minerals this relationship is in general non-linear (represented by hysteresis loop), being linear only in very weak fields in which the initial susceptibility is measured. Among these minerals, magnetite shows no field variation of susceptibility and its anisotropy in the low fields used in common AMS meters. In pyrrhotite, hematite and titanomagnetite bearing rocks, in which these minerals are very fine-grained, the field variation of susceptibility is insignificant. Using linear theory in calculating the AMS is fully legitimate in all these cases. In pyrrhotite, hematite, and titanomagnetite bearing rocks, in which these minerals are relatively coarse-grained (typically hundreds of micrometers), clear field variation of magnetic susceptibility may exist even in the low fields used in common AMS meters, often resulting in bad fit of the susceptibility tensor to the measured data. Strictly speaking, linear theory in calculating the AMS is in general incorrect in this case. The KLY-3S Kappabridge has been modified in such a way to enable AMS measurement also in the fields down to 3 A/m. Examples are shown of the effect of this field decrease on the measured data.

Pokorny, J.; Suza, P.; Hrouda, F.

2003-04-01

2

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

E-print Network

Magnetic anisotropy in Fe-25Cr-12Co-1Si alloy induced by external magnetic field ZHEN Liang( )1 27599-3255, USA Received 29 June 2006; accepted 15 January 2007 Abstract: Structural and magnetic properties of Fe-25Cr-12Co-1Si alloy thermo-magnetically treated under different external magnetic field

Qin, Lu-Chang

3

Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields  

NASA Astrophysics Data System (ADS)

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

Ahlers, Markus

2014-01-01

4

Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields  

E-print Network

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

Ahlers, Markus

2014-01-01

5

Anomalous anisotropies of cosmic rays from turbulent magnetic fields.  

PubMed

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

Ahlers, Markus

2014-01-17

6

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

7

Exchange anisotropy determined by magnetic field dependence of ac susceptibility  

NASA Astrophysics Data System (ADS)

ac susceptibility measurements of ferromagnetic/antiferromagnetic (FM/AF) bilayers are usually performed as a function of the temperature. In this work we describe measurements of transverse biased ac susceptibility (?t) of FM/AF bilayers as a function of the applied magnetic field H0. The measurements were carried out at room temperature by means of an ac magneto-optical Kerr effect susceptometer. The ?t-1(H0) dependence, at the saturation magnetization regime, exhibits a linear behavior with the applied field parallel and perpendicular to the exchange bias direction. The linear extrapolation of ?t-1 versus H0 cuts the abscissa at asymmetrical values of field due to the exchange bias coupling. The inverse susceptibility is calculated in the saturation regime by a model, which takes into account the free energy of both layers plus a term corresponding to the interfacial coupling. The exchange coupling field (HE) and uniaxial anisotropy (HU) are extracted from the best fit to the experimental results. The results obtained are crosschecked by those obtained from ferromagnetic resonance (FMR) and dc magnetometry. The measurements of the exchange bias and the uniaxial field in all of the three analyzed bilayers gave values that are consistently lower when measured by FMR than those obtained by ac and dc magnetometry. It is argued that the apparently discrepant values of HE and HU, obtained by different techniques, might be explained by existence of unstable AF grains at the AF/FM interface.

Rodríguez-Suárez, R. L.; Vilela Leão, L. H.; de Aguiar, F. M.; Rezende, S. M.; Azevedo, A.

2003-10-01

8

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

SciTech Connect

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

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

2014-06-28

9

The influences of transverse magnetic anisotropy on field-induced domain wall propagation in magnetic nanowires  

NASA Astrophysics Data System (ADS)

Domain wall (DW) propagation in magnetic nanowires is an important subject in nanomagnetism because of its fundamental interest and potential applications in spintronic devices. It is well known that a head-to-head (or tail-to-tail) domain wall in a nanowire will propagate along the wire under an axial magnetic field. In this talk, we shall show that a new velocity-field formula can fit well with numerical results obtained from the open-source micromagnetic simulation package OOMMF. The fitting parameters have clear physical meanings that relate to the transverse magnetic anisotropy. How the transverse magnetic anisotropy, which can be modified by both transverse magnetic field and the aspect ratio of wire cross section, affects the DW structure and hence the DW propagation velocity will be discussed systematically.

Lu, Jie; Yan, Peng; Wang, Xiangrong

2009-03-01

10

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

NASA Astrophysics Data System (ADS)

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

Iwai, Kazuhiko

2010-12-01

11

Chiral Symmetry Breaking: To Probe Anisotropy and Magnetic Field in QGP  

E-print Network

We discuss the (spontaneous) chiral symmetry breaking in a strongly coupled anisotropic quark-gluon plasma (QGP) in the presence of the magnetic field, using holography. The physical quantities related to the chiral symmetry breaking (m;B_c) distinguish between the effects of the anisotropy and magnetic field on the plasma. Anisotropy affects the system similar to the temperature and for its larger values heavier quarks can live in the QGP without getting condensed. Raising the anisotropy in the system will also increase the value of the critical magnetic field, B_c, at which the spontaneous chiral symmetry breaking happens. Both of these growths are even more when the magnetic field is applied perpendicular to the anisotropy direction. Such behaviour persists in the high temperature limit where the temperature is kept fixed. However, when the entropy density is held fixed, as one increases the anisotropy, lighter mesons melt when the magnetic field is applied along the anisotropy direction, in contrast to when the magnetic field is perpendicular to the anisotropy direction.

Mohammad Ali-Akbari; Hajar Ebrahim

2014-03-08

12

Chiral symmetry breaking: To probe anisotropy and magnetic field in quark-gluon plasma  

NASA Astrophysics Data System (ADS)

We discuss the (spontaneous) chiral symmetry breaking in a strongly coupled anisotropic quark-gluon plasma (QGP) in the presence of the magnetic field, using holography. The physical quantities related to the chiral symmetry breaking (m ,Bc) distinguish between the effects of the anisotropy and magnetic field on the plasma. Anisotropy affects the system similar to the temperature and for its larger values heavier quarks can live in the QGP without getting condensed. Raising the anisotropy in the system will also increase the value of the critical magnetic field, Bc, at which the spontaneous chiral symmetry breaking happens. Both of these growths are even more when the magnetic field is applied perpendicular to the anisotropy direction. Such behavior persists in the high temperature limit where the temperature is kept fixed. However, when the entropy density is held fixed, as one increases the anisotropy, lighter mesons melt when the magnetic field is applied along the anisotropy direction, in contrast to when the magnetic field is perpendicular to the anisotropy direction.

Ali-Akbari, Mohammad; Ebrahim, Hajar

2014-03-01

13

Magnetic anisotropy of thin sputtered MgB2 films on MgO substrates in high magnetic fields  

NASA Astrophysics Data System (ADS)

We investigated the magnetic anisotropy ratio of thin sputtered polycrystalline MgB2 films on MgO substrates. Using high magnetic field measurements, we estimated an anisotropy ratio of 1.35 for T = 0 K with an upper critical field of 31.74 T in the parallel case and 23.5 T in the perpendicular case. Direct measurements of a magnetic-field sweep at 4.2 K show a linear behavior, confirmed by a linear fit for magnetic fields perpendicular to the film plane. Furthermore, we observed a change of up to 12% of the anisotropy ratio in dependence of the film thickness.

Fabretti, Savio; Imort, Inga-Mareen; Kuschel, Timo; Dahm, Thomas; Guduru, Veerendra K.; Zeitler, Uli; Thomas, Andy

2014-03-01

14

Determination of the saturation magnetization, anisotropy field, mean field interaction, and switching field distribution for nanocrystalline hard magnets  

NASA Astrophysics Data System (ADS)

For a uniaxial nanocrystalline magnetic material, the determination of the saturation magnetization, Ms, requires measurements of the magnetization at fields which exceed the anisotropy field. For a typical RE-Tm compound, where RE=rare earth and Tm=transition metal, this may require fields above 7 T if the approach to saturation law is used. However for an isotropic material composed of a random distribution of non-interacting uniaxial grains, both Ms and the anisotropy filed, Ha, may be determined by fitting the Stoner-Wohlfarth (SW) model (Philos. Trans. Roy. Soc. 240 (1948) 599) to the reversible part of the demagnetization curve in the first quadrant. Furthermore, using the mean field interaction model of Callen, Liu and Cullen [2], a quantitative measure of the interaction strength for interacting particles may be determined. In conjunction with an analytical fit to the first quadrant demagnetization curve of the SW model, this allows Ms, Ha and the mean field interaction constant of a nanocrystalline magnet to be determined from measurements below 5 T. Furthermore, comparison of the model solution for the reversible magnetization with experimental data in the 2nd and 3rd quadrants allows the accurate determination of the switching field distribution. In many cases the hysteresis loop may be accurately described by a normal distribution of switching fields.

McCallum, R. William

2005-04-01

15

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

SciTech Connect

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

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

2014-01-20

16

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

NASA Astrophysics Data System (ADS)

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

Iwai, Kazuhiko; Niimi, Masahiro; Kohama, Takenori

2009-10-01

17

Field Variation of Low-field Anisotropy of Magnetic Susceptibility of Rocks: Measurement Problems  

NASA Astrophysics Data System (ADS)

Theory of low-field anisotropy of magnetic susceptibility (AMS) assumes linear rela- tionship between magnetization and magnetizing field. This assumption is precisely valid in diamagnetic and paramagnetic minerals by definition, while in ferrimagnetic and antiferromagnetic minerals this relationship is in general non-linear, represented by hysteresis loop, being linear only in very weak fields in which the initial suscep- tibility is measured. Recently, it has been shown that, in using common measuring fields, the initial susceptibility is always measured in magnetite, while in pyrrhotite, hematite, and titanomagnetite the measured susceptibility may often be outside the initial susceptibility range. The field variation of low-field AMS results in lowering the quality of the fit of the susceptibility ellipsoid to the measured data and in mis- estimating the degree of anisotropy. Fortunately, the orientations of the principal sus- ceptibilities are virtually field-independent. The problem can be solved in basically three ways. The simplest way is using very weak measuring fields (less than 10 A/m), but this can result in significant lowering sensitivity and precision. The other way is to respect the non-linearity and measure the susceptibility in so many directions that contour diagram of directional susceptibilities can be presented instead of suscepti- bility ellipsoid. The third way is to measure the AMS in at least two fields within the Rayleigh law range and calculate the initial directional susceptibilities from which the AMS can be correctly determined using linear theory.

Hrouda, F.

18

Effects of Anisotropies in Turbulent Magnetic Diffusion in Mean-field Solar Dynamo Models  

NASA Astrophysics Data System (ADS)

We study how anisotropies of turbulent diffusion affect the evolution of large-scale magnetic fields and the dynamo process on the Sun. The effect of anisotropy is calculated in a mean-field magnetohydrodynamics framework assuming that triple correlations provide relaxation to the turbulent electromotive force (so-called the "minimal ?-approximation"). We examine two types of mean-field dynamo models: the well-known benchmark flux-transport model and a distributed-dynamo model with a subsurface rotational shear layer. For both models, we investigate effects of the double- and triple-cell meridional circulation, recently suggested by helioseismology and numerical simulations. To characterize the anisotropy effects, we introduce a parameter of anisotropy as a ratio of the radial and horizontal intensities of turbulent mixing. It is found that the anisotropy affects the distribution of magnetic fields inside the convection zone. The concentration of the magnetic flux near the bottom and top boundaries of the convection zone is greater when the anisotropy is stronger. It is shown that the critical dynamo number and the dynamo period approach to constant values for large values of the anisotropy parameter. The anisotropy reduces the overlap of toroidal magnetic fields generated in subsequent dynamo cycles, in the time-latitude "butterfly" diagram. If we assume that sunspots are formed in the vicinity of the subsurface shear layer, then the distributed dynamo model with the anisotropic diffusivity satisfies the observational constraints from helioseismology and is consistent with the value of effective turbulent diffusion estimated from the dynamics of surface magnetic fields.

Pipin, V. V.; Kosovichev, A. G.

2014-04-01

19

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

20

Electric field controlled reversible magnetic anisotropy switching studied by spin rectification  

SciTech Connect

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

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

2014-03-10

21

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

22

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

23

Magnetic Fields and Cosmic-Ray Anisotropies at TeV Energies  

NASA Astrophysics Data System (ADS)

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

Battaner, Eduardo; Castellano, Joaquín; Masip, Manuel

2015-02-01

24

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

PubMed

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

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

2015-02-25

25

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.; Guimarães, A. P.

2013-10-01

26

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

SciTech Connect

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

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

2010-11-01

27

Phase evolution and field-induced magnetic anisotropy of the nanocomposite three-phase fcc, hcp, and amorphous  

E-print Network

Phase evolution and field-induced magnetic anisotropy of the nanocomposite three-phase fcc, hcp a relatively more significant contribution to the field-induced anisotropy of Co-based nanocomposite ribbons amorphous and nanocomposite materials can be engineered to simultaneously display low core losses, high

Laughlin, David E.

28

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

NASA Technical Reports Server (NTRS)

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

Venters, T. M.; Pavlidou, V.

2013-01-01

29

CMB distortion anisotropies due to the decay of primordial magnetic fields  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

30

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

NASA Astrophysics Data System (ADS)

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

Kaplan, B.; Kaplan, R.

2014-12-01

31

TeV Cosmic Ray Anisotropy and the Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

Cosmic rays are observed to possess a small non uniform distribution in arrival direction. Such anisotropy appears to have a roughly consistent topology between tens of GeV and hundreds of TeV, with a smooth energy dependency on phase and amplitude. Above a few hundreds of TeV a sudden change in the topology of the anisotropy is observed. The distribution of cosmic ray sources in the Milky Way is expected to inject anisotropy on the cosmic ray flux. The nearest and most recent sources, in particular, are expected to contribute more significantly than others. Moreover the interstellar medium is expected to have different characteristics throughout the Galaxy, with different turbulent properties and injection scales. Propagation effects in the interstellar magnetic field can shape the cosmic ray particle distribution as well. In particular, in the 1-10 TeV energy range, they have a gyroradius comparable to the size of the Heliosphere, assuming a typical interstellar magnetic field strength of 3 ?G. Therefore they are expected to be strongly affected by the Heliosphere in a manner ordered by the direction of the local interstellar magnetic field and of the heliotail. In this paper we discuss on the possibility that TeV cosmic rays arrival distribution might be significantly redistributed as they propagate through the Heliosphere.

Desiati, P.; Lazarian, A.

2014-10-01

32

Anisotropy-Compensated Magnetic Nanostructures  

NASA Astrophysics Data System (ADS)

Nanostructuring can be used to tailor the magnetic anisotropy K1 as function of temperature, which is important in permanent magnetism and magnetic recording. Anisotropy is an atomic quantity, but the ferromagnetic exchange ensures an anisotropy averaging over a few nanometers, in contrast to the absence of nanoscale Curie-temperature averaging [1]. An intriguing and largely overlooked feature is the possibility of temperature- dependent anisotropy zeros, which yields a potential write-field reduction in magnetic recording. On an atomic scale, this effect is well-known but limited to a relatively narrow range of rare- earth transition-metal intermetallics. Nanostructuring greatly extends the range of materials. Explicitly considered structures are thin films, where the determination of the anisotropy zero (s) yields algebraic equations whose roots depend on the thicknesses, Curie temperatures, and zero-temperature anisotropies of the involved phases. On a somewhat larger length scale (> 5 to 10 nm), there is no longer a well-defined anisotropy, but the corresponding micromagnetic corrections are easily incorporated into the theory. - [1] R. Skomski, ``Simple Models of Magnetism,'' University Press, Oxford 2008.

Skomski, Ralph; George, Tom A.; Sellmyer, D. J.

2008-03-01

33

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

34

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

SciTech Connect

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

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

2012-02-10

35

Dynamics of the magnetization of single domain particles having triaxial anisotropy subjected to a uniform dc magnetic field  

NASA Astrophysics Data System (ADS)

Thermally induced relaxation of the magnetization of single domain ferromagnetic particles with triaxial (orthorhombic) anisotropy in the presence of a uniform external magnetic field H0 is considered in the context of Brown's continuous diffusion model. Simple analytic equations, which allow one to describe qualitatively the field effects in the relaxation behavior of the system for wide ranges of the field strength and damping parameters are derived. It is shown that these formulas are in complete agreement with the exact matrix continued fraction solution of the infinite hierarchy of linear differential-recurrence equations for the statistical moments, which governs the magnetization dynamics of an individual particle (this hierarchy is derived by averaging the underlying stochastic Landau-Lifshitz-Gilbert equation over its realizations). It is also demonstrated that in strong fields the longitudinal relaxation of the magnetization is essentially modified by the contribution of the high-frequency "intrawell" modes to the relaxation process. This effect discovered for uniaxial particles by Coffey et al. [Phys. Rev. B 51, 15947 (1995)] is the natural consequence of the depletion of population of the shallow potential well. However, in contrast to uniaxial anisotropy, for orthorhombic crystals there is an inherent geometric dependence of the complex magnetic susceptibility and the relaxation time on the damping parameter ? arising from the coupling of longitudinal and transverse relaxation modes.

Ouari, Bachir; Kalmykov, Yury P.

2006-12-01

36

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

NASA Technical Reports Server (NTRS)

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

Ghosh, Sanjoy; Roberts, D. Aaron

2010-01-01

37

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

38

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

39

Low-field variation of magnetic susceptibility and its effect on the anisotropy of magnetic susceptibility of rocks  

NASA Astrophysics Data System (ADS)

The theory of the low-field anisotropy of magnetic susceptibility (AMS) assumes a linear relationship between magnetization and the magnetizing field. This assumption is precisely valid in diamagnetic and paramagnetic minerals by definition, while in ferrimagnetic and antiferromagnetic minerals this relationship is in general non-linear (represented by a hysteresis loop), being linear only with very weak fields in which the initial susceptibility is measured. Recently, it has been shown that, in using common measuring fields, the field-independent susceptibility is measured in magnetite, while in pyrrhotite, haematite and titanomagnetite it may often be outside the initial susceptibility range. The problem can be solved in three ways. The simplest way is using very weak measuring fields (less than 10 A m-1), but this can result in significant lowering of sensitivity and precision. The second way is to respect the non-linearity and measure the susceptibility in so many directions that contour diagram of directional susceptibilities can be presented instead of a susceptibility ellipsoid. The third way is to measure the AMS within the Rayleigh law range and calculate the initial directional susceptibilities from which the AMS can be correctly determined using linear theory.

Hrouda, František

2002-09-01

40

Extensions of the standard cosmological model: Anisotropy, rotation, and the magnetic field  

SciTech Connect

We show that the difference between the theoretically expected and measured by WMAP amplitude of the quadrupole fluctuations of the cosmic microwave background (CMB) can be related to the impact of the anisotropic curvature of the homogeneous universe dominated by dark energy. In such a universe the matter expansion becomes practically isotropic just after the period of inflation, and only at small redshifts is the anisotropic expansion generated again by the small curvature {omega}{sub K}=1-{omega}{sub m}-{omega}{sub {lambda}}{<=}10{sup -4}. For such models the possible deviations from the parameters derived for the standard cosmological model are evidently negligible but the correlations of large scale perturbations and distortions of their Gaussianity are possible. Such models are also compatible with the existence of a homogeneous magnetic field and matter rotation which contribute to the low l anisotropy and can be considered as ''hidden parameters'' of the model. Their influence can be observed as, for example, special correlations of small scale fluctuations and the Faraday rotation of the CMB and radiation of the farthest quasars. However, both the magnetic field and matter rotation also require modifications of the simple models of isotropic inflation, and they change the evolutionary history of the early Universe.

Demianski, M.; Doroshkevich, A. G. [Institute of Theoretical Physics, University of Warsaw, 00-681 Warsaw (Poland) and Department of Astronomy, Williams College, Williamstown, Massachusetts 01267 (United States); Astro Space Center of Lebedev Physical Institute of Russian Academy of Sciences, 117997 Moscow (Russian Federation)

2007-06-15

41

Magnetic Anisotropy of Igneous Rocks  

Microsoft Academic Search

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

F. D. Stacey

1960-01-01

42

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

43

Magnetic Anisotropy of a Single Cobalt Nanocluster  

Microsoft Academic Search

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

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

2001-01-01

44

Primordial magnetic fields in the Early Universe and anisotropies of the cosmic microwave background  

E-print Network

- Sezione di Bologna XXV Canary Island Winter School of Astrophysics, Cosmic Magnetic Fields, Tenerife) of primordial magnetic fields (PMF) · The energy-momentum tensor (EMT) for the SB of PMF · The spectrum of CMB of primordial magnetic field to less than 300 nG (3 muG would correspond to the same radiation energy density

45

Large electric tunable remanent magnetization and in-plane anisotropy field in (110) PMN-0.32PT/Cu/Fe65Co35 multiferroic heterostructures  

NASA Astrophysics Data System (ADS)

Large electric field tunable remanent magnetization and in-plane anisotropy in a Fe65Co35 film was observed in sputtered ferromagnetic/ferroelectric heterostructures. Two stable magnetization directions were established through a 90° transition of the in-plane uniaxial anisotropy of FeCo film under a positive electric field, and large nonvolatile remanence ratio tunability between 0.50 and 0.12 was realized using electric field pulses. With the increase of negative electric field, the anisotropy field increases at a rate of around 31.1 Oe/(kV cm-1). The large tunable anisotropy field and remnant magnetization may have potential applications in electrically tunable microwave magnetic devices and information storage memories.

Han, Xuemeng; Li, Yue; Guo, Xiaobin; Wang, Zhen; Zuo, Yalu; Xi, Li; Xue, Desheng

2014-04-01

46

Relationship among petrofabric, magnetic anisotropy and seismic anisotropy in dunite  

NASA Astrophysics Data System (ADS)

Physical anisotropies in rocks arise from the preferred alignment of the rock's constituents, which include mineral grains, organic matter or pore space. Different physical properties will be affected to a greater or lesser extent by these various factors. The anisotropy of magnetic susceptibility (AMS) is dependent on mineral orientation, particularly of minerals with high susceptibility and strong intrinsic anisotropy. Seismic anisotropy will also be controlled predominantly by mineral texture for rocks deformed at high pressure, where pore space or cracks are closed. During high-temperature ductile flow of the upper mantle, peridotite will develop a permanent deformation texture, which will be responsible for its physical anisotropies. Olivine develops characteristic crystal-preferred orientations (CPO) under different thermal-mechanical conditions. In this study we examine the relationship among mineral texture, magnetic anisotropy and seismic anisotropy of dunites from the Western Gneiss Region, Norway. Because dunite consists of > 90% olivine, the intrinsic magnetic anisotropy of single crystals of olivine is also investigated. AMS was measured with a high-field torsion magnetometer at room temperature and 77 K, in order to separate the paramagnetic sub-fabric from the total anisotropy. Our results indicate that olivine has a prolate anisotropy, in which the minimum, intermediate, and maximum axes of susceptibility correspond to the [010], [100] and [001] axes of olivine, respectively; this is partially contrary to an earlier investigation by Belley et al. (2009, EPSL, 284, 516-526). The degree of anisotropy increases by a factor of 7.1 - 8.2 at 77 K, and the shape becomes more triaxial. The CPO of olivine was measured using electron backscatter diffraction technique or X-ray texture goniometry. Although olivine grains in the samples develop two fabric types, namely [100](010) or [001](010), there is the same very good agreement between the orientation of the principal axes of the AMS ellipsoid and the texture ellipsoid of olivine. The minimum axes of the AMS ellipsoid are coaxial with the [010] axes in all samples, and maximum axes are coaxial with [001] in all but two samples; for these the intermediate axes are along the [100] direction of olivine. In addition, the degree of AMS increases with increasing texture strength. Seismic velocities and anisotropy are determined from the orientation distribution function and elastic constants of olivine, using the method described by Mainprice (1990, Comput. Geosci., 16, 385-393). A significant linear correlation is found between the degree of P- and S-wave anisotropies and AMS degree. Our results indicate that AMS can be used to infer the petrofabric and seismic anisotropy of olivine-rich rocks.

Hirt, A. M.; Wang, Q.; Biedermann, A. R.

2012-04-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

48

Magnetic anisotropies of quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

49

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

SciTech Connect

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

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

2013-10-01

50

A theoretical and experimental study of the electric field and magnetic anisotropy effects on proton chemical shifts  

NASA Astrophysics Data System (ADS)

Proton magnetic shielding constants are divided into different contributions using the IPPP technique (inner projections of the polarization propagator). Total magnetic shielding constants are calculated within the CHF-INDO-GIAO approach (coupled-Hartree-Fock-INDO-gauge-invariant atomic orbitals). In order to compare the electric field and magnetic anisotropy effects of neighbouring groups, two model compounds were chosen, namely, ethyl cyanoformate, I, and ethylformate, II, which show to frozen and unequally populated rotamers each at room temperature. Their proton spectra were measured and the difference in shielding of methylene protons in each pair of rotamers was theoretically analysed with the abovementioned technique. The experimental difference in chemical shifts is quantitatively reproduced with the present analysis.

Ferraro, M. B.; De Kowalewski, D. G.; Contreras, R. H.; Ortiz, F. S.

1987-12-01

51

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

52

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

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

53

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

PubMed

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

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

2012-09-01

54

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

55

Electric-field control of magnetic anisotropy in Fe81Ga19/BaTiO3 heterostructure films  

NASA Astrophysics Data System (ADS)

We investigate the control of magnetism with an electric field in Fe81Ga19(FeGa)/BaTiO3(BTO) heterostructure films. The as-prepared FeGa/BTO samples present a uniaxial magnetic anisotropy, which is ascribed to be induced by the spontaneous ferroelectric polarization of the BTO substrates. With the electric field applied on the BTO substrates increasing from 0 to 6 kV/cm, the coercivity of FeGa films measured along the BTO[110] direction increases from 28 to 41 Oe, while the squareness of the hysteresis loop decreases from 0.99 to 0.31, which indicates that the easy and hard axes of FeGa films are swapped. The ferroelectric domains of BTO substrates and the magnetic domains of FeGa films exhibit the same dependence on the applied electric fields, manifesting the strong magnetoelectric coupling between the ferroelectricity of BTO substrates and the magnetism of FeGa films.

Xie, Yali; Zhan, Qingfeng; Liu, Yiwei; Dai, Guohong; Yang, Huali; Zuo, Zhenghu; Chen, Bin; Wang, Baomin; Zhang, Yao; Rong, Xin; Li, Run-Wei

2014-11-01

56

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

PubMed

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

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

2014-06-21

57

The electric field induced in the brain by magnetic stimulation: a 3-D finite-element analysis of the effect of tissue heterogeneity and anisotropy  

Microsoft Academic Search

We investigate the effect of tissue heterogeneity and anisotropy on the electric field and current density distribution induced in the brain during magnetic stimulation. Validation of the finite-element (FE) calculations in a homogeneous isotropic sphere showed that the magnitude of the total electric field can be calculated to within an error of approximately 5% in the region of interest, even

Pedro C. Miranda; Mark Hallett; Peter J. Basser

2003-01-01

58

The Electric Field Induced in the Brain by Magnetic Stimulation: A 3-D Finite-Element Analysis of the Effect of Tissue Heterogeneity and Anisotropy  

Microsoft Academic Search

We investigate the effect of tissue heterogeneity and anisotropy on the electric field and current density distribution in- duced in the brain during magnetic stimulation. Validation of the finite-element (FE) calculations in a homogeneous isotropic sphere showed that the magnitude of the total electric field can be cal- culated to within an error of approximately 5% in the region of

Pedro C. Miranda; Mark Hallett; Peter J. Basser

2003-01-01

59

Anisotropy of the superconducting transition in magnetic fields in a Nd 1.85 Ce 0.15 CuO 4 single crystal  

Microsoft Academic Search

The anisotropy of superconducting properties of a Nd1.85Ce0.15CuO4 single crystal is studied by resistance measurements over the temperature range 2–30 K in magnetic fields of 0, 1, 2, 4,\\u000a and 6 T parallel to the a-b plane. A strong anisotropy of T\\u000a \\u000a c\\u000a (H) and H\\u000a \\u000a c\\u000a 2(T) is observed for different orientations of magnetic field in the a-b plane.

G. Kh. Panova; A. A. Shikov; N. A. Chernoplekov; G. A. Emel’chenko; A. N. Malyuk; S. T. Lin

2002-01-01

60

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

61

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

NASA Astrophysics Data System (ADS)

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

CÄ«murs, J.; CÄ`bers, A.

2013-12-01

62

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

NASA Technical Reports Server (NTRS)

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

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

2009-01-01

63

Magnetic anisotropy data of CBrN  

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.

64

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

65

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

66

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

SciTech Connect

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

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

2011-12-10

67

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

NASA Astrophysics Data System (ADS)

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

Hu, Gangsan; Zhu, Rengui

2015-02-01

68

Temperature dependence of anisotropy fields in deuterium implanted garnet films  

NASA Astrophysics Data System (ADS)

It has recently been reported that the reduction in the uniaxial anisotropy due to magnetostriction does not, by itself, account for the total implantation-induced change in the uniaxial anistropy field in magnetic garnet epitaxial films. The present investigation is concerned with the temperature dependence of the magnetostriction divided by the magnetization in the bulk lambda 111/Ms(B), and the implanted layer lambda 111/Ms(I) for deuterium implanted films. The change in uniaxial anisotropy field was measured for the temperature range from 20 to 200 C, and compared to magnetostriction. It was found that the total implantation induced uniaxial anisotropy field change decreased nearly linearly with temperature.

Krafft, C. S.; Kryder, M. H.

1984-03-01

69

Field-induced transition in the S1 antiferromagnetic chain with single-ion anisotropy in a transverse magnetic field  

E-print Network

model,6 etc., have been de- voted to verifying Haldane's conjecture7 that the uniform integer spin chain . The model Hamiltonian they adopted is expressed as H J ij Si"Sj D i Si z 2 B i Si·g~·h, 1 where J is the exchange integral for NDMAP J/kB 30 K), D is the single-ion anisotropy constant, B is the Bohr magneton

Gao, Song

70

Anisotropy of MHD Turbulence at Low Magnetic Reynolds Number  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

71

Low-temperature magnetic anisotropy in micas and chlorite  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

72

Carrier-dependent magnetic anisotropy of cobalt doped titanium dioxide.  

PubMed

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

Shao, Bin; Feng, Min; Zuo, Xu

2014-01-01

73

Electric field effects in low resistance CoFeB-MgO magnetic tunnel junctions with perpendicular anisotropy  

NASA Astrophysics Data System (ADS)

We have investigated the electric field effects in low resistance perpendicular magnetic tunnel junction (MTJ) devices and found that the electric field can effectively reduce the coercivity (Hc) of free layer (FL) by 30% for a bias voltage Vb = -0.2 V. In addition, the bias field (Hb) on free layer is almost linearly dependent on Vb yet independent on the device size. The demonstrated Vb dependences of Hc and Hb in low resistance MTJ devices present the potential to extend the scalability of the electric field assisted spin transfer torque magnetic random access memory and improve its access speed.

Meng, H.; Sbiaa, R.; Akhtar, M. A. K.; Liu, R. S.; Naik, V. B.; Wang, C. C.

2012-03-01

74

Magnetization dynamics in nanostructures with weak/strong anisotropy  

NASA Astrophysics Data System (ADS)

We investigate the high-frequency response of magnetization dynamics through magnetoimpedance (MI) effect in Permalloy-based multilayered thin films produced with two different non-magnetic metallic spacers: Cu and Ag. Due to the nature of the spacer materials, we are able to play with magnetic properties and to study both systems with weak/strong magnetic anisotropy. We verify very rich features in the magnetoimpedance behavior and high magnetoimpedance ratios, with values above 200%. We compare the MI results obtained in multilayered thin films with distinct spacers and number of bilayers, and discuss them in terms of the different mechanisms that govern the MI changes observed at distinct frequency ranges, intensity of the magnetic anisotropy, alignment between dc magnetic field and anisotropy direction. Besides, by considering a theoretical approach that takes into account two single models together and calculate the transverse magnetic permeability and the MI effect, we support our interpretation via numerical calculations modeling the effect of weak/strong magnetic anisotropy on the MI response. Thus, we confirm that these features are very important for the use of multilayered films in sensor applications and, both the frequency and field response can be tailored to fulfill the requirements of a given device.

de Andrade, A. M. H.; Corrêa, M. A.; Viegas, A. D. C.; Bohn, F.; Sommer, R. L.

2014-03-01

75

Wavenumber anisotropy in spectra, statistics and scaling in the turbulent solar wind using a locally defined background magnetic field  

NASA Astrophysics Data System (ADS)

One of the key characteristics of small-scale plasma turbulence within the solar wind that distinguishes it from hydrodynamic neutral fluids, is that the majority of the power is situated in spatial fluctuations (wavenumbers) that are perpendicular to the background magnetic field. As these fluctuations represent spatial gradients, this has been interpreted as the turbulent cascade proceeding primarily or exclusively perpendicular to the background magnetic field. However, definitions of what constitutes a background magnetic field for the turbulent magnetic fluctuations lack consensus and this topic is a subject of debate amongst researchers who study turbulence - a well-known multiscale phenomenon where there is no clear separation of scales. An appropriate and self-consistent definition of such a background field is essential if one desires to compare observational results with theoretical analysis and predictions -necessary for a deeper understanding of plasma turbulence. We present a detailed analysis on the use of a stochastic locally varying and scale-dependent background magnetic field in studies of plasma turbulence. We will attempt to clarify some of the apparent discrepancies, both in formalism and practice, between the use of such a local field and a globally varying field taken over much larger time/space scales. In particular, we present a mechanism by which the spectral exponents systematically change when a local scale-dependent field is used. We also show that the scaling seen in the spectra of the parallel wavenumber is robust with respect to extreme outliers in the distribution of fluctuations and that this distribution is highly non-Gaussian. The scaling accompanying these statistics show that the well-known and observed multiple exponent scaling of higher-order moments, actually only occurs in the perpendicular wavenumbers, in anisotropic collisionless plasma turbulence. The parallel wavenumbers show an absence of such scaling - they are monoscaling i.e. higher order moments scale as linear multiplications of a single scaling exponent. We employ the use of the Undecimated Discrete Wavelet Transform (UDWT) to separate out the signal into a scale dependent local background magnetic field, and scale-dependent local fluctuations. The UDWT not only decomposes the signals into components fluctuating at different scales, but crucially also preserves the timing of events within signals. This allows one to project the fluctuations accurately onto a locally varying background magnetic field. We use solar wind measurements from the ULYSSES and STEREO spacecraft missions to illustrate the key concepts. Lastly we discuss the relevance of using a local varying background field in observational studies that compare to theories of turbulence cast in a global field picture, and conclude with ways in which theories need to adapt in order to incorporate the local field description.

Chapman, S. C.; Kiyani, K. H.; Osman, K.

2013-12-01

76

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

77

Rock magnetism and the interpretation of anisotropy of magnetic susceptibility  

Microsoft Academic Search

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

P. Rochette; M. Jackson; C. Aubourg

1992-01-01

78

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

79

The Ligand Field of the Azido Ligand: Insights into Bonding Parameters and Magnetic Anisotropy in a Co(II)-Azido Complex.  

PubMed

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

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

2015-02-11

80

Anisotropy parameters and coercivity for sintered Co5Sm permanent magnet alloys  

NASA Astrophysics Data System (ADS)

Saturation magnetization, intrinsic coercive force, anisotropy field, and anisotropy constants were determined for a sample of sintered Co5Sm at 4.2, 77, 300, and 500 °K. The ralationship between the temperature dependence of the coercivity and the anisotropy parameters is discussed.

Benz, M. G.; Martin, D. L.

1972-11-01

81

Domain structure and magnetization reversal ofantiferromagnetically coupled perpendicular anisotropy films  

SciTech Connect

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

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

2007-03-16

82

Understanding the source of magnetic and seismic anisotropy in peridotites  

NASA Astrophysics Data System (ADS)

Peridotite, a rock consisting of more than 90% olivine, orthopyroxene and clinopyroxene, is the dominant component in the Earth's upper mantle. Olivine, which is more abundant than pyroxene in general, and rheologically weaker, controls the deformation behavior and seismic anisotropy of the Earth's upper mantle. The majority of naturally deformed peridotites develop a [100](010) olivine fabric, and this fabric is the major contributor to physical anisotropies in these rocks. Seismic anisotropy is often determined from the crystallographic-preferred orientation (CPO) of olivine and its intrinsic anisotropy in elastic properties. The relationship of the anisotropy of magnetic susceptibility (AMS), determined in low field (LF), to deformation fabrics in peridotites is more coplicated. This is due to the presence of ferromagnetic minerals that may form late in the deformation history. The isolated paramagnetic fabric, however, is controlled by the texture of the paramagnetic minerals, olivine and pyroxene. We have studied the texture, as determined by EBSD or X-ray texture goniometry, and relate this to magnetic and seismic anisotropy in a series of peridotites from Norway and northern Italy. Our peridotite samples show different olivine fabrics, e.g., weakly deformed and strongly sheared peridotites develop [100](010) and [001](010) fabrics, respectively. The LF-AMS, which is controlled by ferromagnetic minerals, is often not significant. The paramagnetic anisotropy, which is isolated using high-field torque magnetometry, shows a well-defined magnetic fabric. Often the paramagnetic anisotropy agrees with the olivine texture. When more than one mineral phase contributes to the AMS, interpretation becomes more complicated, because of the different orientation of the AMS principal axes of the intrinsic minerals with respect to their crystallographic axes. The AMS of olivine has the maximum susceptibility (k1) parallel to the c-crystallographic axis, whereas the orientation of the intermediate (k2) and minimum (k3) axes is dependent on the mineral composition; i.e., k3 is along the a-axis and k2 along the b-axis for 3 to 5 wt% FeO, but with higher iron oxide content, 7 to 9 wt%, k3 is along the b-axis. For clinopyroxene, k2 lies close to the b-crystallographic axis, independent of composition, and the k1 and k3 axes lie slightly off the a-c-plane. The orientation of the principal axes of the AMS in orthopyroxene is strongly dependent on composition; e.g., enstatite has a triaxial anisotropy with k1 along the crystallographic c-axis, k2 along the a-axis and k3 along the b-axis. Therefore contributions from different phases may weaken the net magnetic fabric. We compare magnetic anisotropy that is calculated from the CPO of the major mineral constituents in the peridotites with the measured anisotropy to gain a better understanding of the factors that control magnetic anisotropy. Further, we use the CPO of the samples together with the elastic properties of constituent minerals in a rock to calculate the seismic anisotropy. It is also possible to show under what conditions the magnetic anisotropy can be related to seismic anisotropy. Results from this work will help improve our understanding about in situ deformation mechanisms and physical fabrics of the upper mantle.

Hirt, Ann; Biedermann, Andrea; Wang, Qin; Zappone, Alba

2013-04-01

83

Thermal and surface anisotropy effects on the magnetization reversal of a nanocluster  

Microsoft Academic Search

The relaxation rate and temperature-dependent switching field curve of a spherical magnetic nanocluster are calculated by including the effect of surface anisotropy via an effective anisotropy model. In particular, it is shown that surface anisotropy may change the thermally activated magnetization reversal by more than an order of magnitude, and that temperature-dependent switching field curves noticeably deviate from the Stoner-Wohlfarth

P.-M. Dejardin; Yu. P. Kalmykova

84

LDAbold">+DMFT Approach to Magnetocrystalline Anisotropy of Strong Magnets  

NASA Astrophysics Data System (ADS)

The new challenges posed by the need of finding strong rare-earth-free magnets demand methods that can predict magnetization and magnetocrystalline anisotropy energy (MAE). We argue that correlated electron effects, which are normally underestimated in band-structure calculations, play a crucial role in the development of the orbital component of the magnetic moments. Because magnetic anisotropy arises from this orbital component, the ability to include correlation effects has profound consequences on our predictive power of the MAE of strong magnets. Here, we show that incorporating the local effects of electronic correlations with dynamical mean-field theory provides reliable estimates of the orbital moment, the mass enhancement, and the MAE of YCo5.

Zhu, Jian-Xin; Janoschek, Marc; Rosenberg, Richard; Ronning, Filip; Thompson, J. D.; Torrez, Michael A.; Bauer, Eric D.; Batista, Cristian D.

2014-04-01

85

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

NASA Astrophysics Data System (ADS)

The anisotropy of magnetic susceptibility (AMS) of the marine fine-grained Plio-Pleistocene sediments that crop out at the eastern (Adriatic) front of the central-northern Apennines (Italy) indicates a prevalent sedimentary-compactional magnetic fabric with variable overprint of the tectonic strain. The degree of anisotropy and the geometry of the AMS ellipsoids suggest a subdivision of the studied sediments in two distinct ages: Early-middle Pliocene and Late Pliocene-Early Pleistocene. The Early-middle Pliocene sediments show a weak but well defined magnetic lineation parallel to the main fold and thrust axes throughout the region, analogously to the Messinian sediments located in a more internal (western) position of the Apenninic chain. Since the Late Pliocene, the AMS data are not regionally coherent and indicate a reduced and locally variable tectonic influence on the magnetic fabrics. The AMS data have been integrated with the available geophysical information of the present-day stress in the region, with the aim to reconstruct the time-spatial evolution of the stress field in the Adriatic margin of the central-northern Apennines, during the past 5 Ma. The present-day stress field was evaluated using borehole breakout in deep wells (about 50 wells), focal mechanisms of crustal earthquakes (2.5< Md<5) that occurred in the last 10 years and a review of the historical seismicity. The synthesis of these data suggests significant changes in the time-space evolution of the stress field through the area in the last 5 Ma. In the northern sector the tectonic regime shows a maximum compressional axis trending NE-SW, that is constant at least since the Early Pliocene. In the southern sector the stress field has drastically changed: a compressional stress with a maximum compressional axis trending E-W was active during the Pliocene and was likely preserved until Early Pleistocene; then the stress field changed, presently showing a NE-SW minimum horizontal stress that mirrors the trend of the active extension observed in the southern Apennines. Between these two sectors a transitional area is identified at about 43°N, that we associate with a main NNE-SSW lithospheric discontinuity pointed out by the available geological and geophysical data.

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

1999-09-01

86

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

NASA Astrophysics Data System (ADS)

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

Fitter, Thomas

87

Quantitative Evaluation of Voltage-Induced Magnetic Anisotropy Change by Magnetoresistance Measurement  

NASA Astrophysics Data System (ADS)

We investigated the voltage-induced perpendicular magnetic anisotropy change in an epitaxial magnetic tunnel junction (MTJ) with an ultrathin FeCo layer. Tunneling magnetoresistance (TMR) curves were measured under various bias voltage applications for different FeCo thicknesses. Clear changes in the shape of TMR curves were observed depending on the voltage-controlled perpendicular magnetic anisotropy. By evaluating the relative angle of two ferromagnetic layers, we could estimate the anisotropy energy change quantitatively. The realization of voltage-induced anisotropy change in the MTJ structure makes it possible to control the magnetization dynamics, leading to a new area of electric-field-based spintronics devices.

Shiota, Yoichi; Murakami, Shinichi; Bonell, Frédéric; Nozaki, Takayuki; Shinjo, Teruya; Suzuki, Yoshishige

2011-04-01

88

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

89

Magnetic Fields  

E-print Network

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

Schöller, Markus

2015-01-01

90

Coupled stochastic dynamics of magnetic moment and anisotropy axis of a magnetic nanoparticle.  

PubMed

An algorithm is developed for numerical simulation of coupled stochastic dynamics of magnetic moment and magnetic anisotropy axis of a nanoparticle. Time-correlation functions of the magnetic moment and its components longitudinal and transverse to the magnetic anisotropy axis are calculated by averaging along the stochastic trajectory. The longitudinal and transverse relaxation times are found by fitting the time correlation functions. Existing theoretical relations derived by the effective field approach in the limit of small fields are confirmed. The time-correlation functions of magnetic moments of nanoparticles in dependence on their properties are calculated numerically for arbitrary large magnetic fields and it is shown that they may be approximated by a sum of several exponentials. These results are applied for the calculation of relaxivity parameters of nuclear magnetic resonance (NMR) imaging in dependence on the field strength. PMID:23367948

Taukulis, R; C?bers, A

2012-12-01

91

Voltage-induced perpendicular magnetic anisotropy change in magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

A voltage-induced perpendicular magnetic anisotropy change in an ultrathin FeCo layer was observed in an epitaxial magnetic tunnel junction (MTJ) structure. A spin-transfer induced ferromagnetic resonance measurement technique was used under various bias voltage applications to evaluate the anisotropy change. From the peak frequency shifts, we could estimate that a surface magnetic anisotropy change of 15 ?J/m2 was induced by an electric field application of 400 mV/nm in the MTJ with a 0.5 nm thick FeCo layer. The realization of voltage-induced anisotropy changes in an MTJ structure should have a large impact on the development of electric-field driven spintronic devices.

Nozaki, T.; Shiota, Y.; Shiraishi, M.; Shinjo, T.; Suzuki, Y.

2010-01-01

92

Finite-temperature anisotropy of magnetic alloys  

NASA Astrophysics Data System (ADS)

The temperature dependence of the magnetic anisotropy of ferromagnetic materials is analyzed. Simple ferromagnets, such as Fe and Co, obey the m=n(n+1)/2 power laws predicted by the Callen and Callen [Phys. Rev. 129, 578 (1963)] theory, but in alloys, the applicability of the theory is an exception rather than the rule. Many alloys, such as the rare-earth transition-metal intermetallics and L10 magnets, violate a basic assumption of the theory, namely, that the single-ion anisotropy and the spontaneous magnetization have the same origin. This is the reason for significant deviations from the Callen and Callen behavior, such as the m=2 law we obtained for L10 alloys.

Skomski, R.; Mryasov, O. N.; Zhou, J.; Sellmyer, D. J.

2006-04-01

93

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

94

Depth-resolved magnetization reversal in nanoporous perpendicular anisotropy multilayers  

NASA Astrophysics Data System (ADS)

We have used polarized neutron reflectometry to study the field-dependent magnetizations of Co/Pt mulitlayers patterned via deposition onto nanoporous alumina hosts with varying pore aspect ratio. Despite the porosity and lack of long-range order, robust spin-dependent reflectivities are observed, allowing us to distinguish the magnetization of the surface multilayer from that of material in the pores. We find that as the pores become wider and shallower, the surface Co/Pt multilayers have progressively smaller high field magnetization and exhibit softer magnetic reversal—consistent with increased magnetic disorder and a reduction of the perpendicular anisotropy near the pore rims. These results reveal complexities of magnetic order in nanoporous heterostructures, and help pave the way for depth-resolved studies of complex magnetic heterostructures grown on prepatterned substrates.

Kirby, B. J.; Rahman, M. T.; Dumas, R. K.; Davies, J. E.; Lai, C. H.; Liu, Kai

2013-01-01

95

Piezoelectric control of the magnetic anisotropy via interface strain coupling in a composite multiferroic structure  

NASA Astrophysics Data System (ADS)

We investigate theoretically the magnetic dynamics in a ferroelectric/ferromagnetic heterostructure mediated by a strain-induced magnetoelectric interaction. The epitaxial strain involves a strong piezoelectricity and interfacial magnetoelastic coupling, the interplay of both gives rise to an electrically tunable uniaxial magnetic anisotropy. We predict an electric-field-induced magnetic switching in the plane perpendicular to the magneto-crystalline easy axis while the total magnetization remains stable. We trace this effect back to the ferroelectric control of the magnetic anisotropy. We also inspect the magnetic remanence and the electric coercivity and demonstrate a pronounced dynamic magnetic response to an electric field in a thin ferromagnetic layer.

Jia, Chenglong; Sukhov, Alexander; Horley, Paul P.; Berakdar, Jamal

2012-07-01

96

Ligands effects on the magnetic anisotropy of tetrahedral cobalt complexes.  

PubMed

The effect of ligands with heavy donor atoms on the magnetic anisotropy of the pseudo-tetrahedral cobalt complexes, Co(quinoline)2I2 (1) and Co(EPh3)2I2 (2-3) (E = P, As) has been investigated. The axial zero-field splitting parameter D was found to vary from +9.2 cm(-1) in 1 to -36.9 cm(-1) in 2 and -74.7 cm(-1) in 3. Compounds 2 and 3 exhibit slow relaxation of the magnetization up to 4 K under an applied dc field, indicating SMM behavior. PMID:25183324

Saber, Mohamed R; Dunbar, Kim R

2014-10-21

97

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

Microsoft Academic Search

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

P. Rochette; G. Fillion

1988-01-01

98

Tri-axial magnetic anisotropies in RE2Ba4Cu7O15-y superconductors  

NASA Astrophysics Data System (ADS)

We report a novel quantification method of tri-axial magnetic anisotropy in orthorhombic substances containing rare earth (RE) ions using tri-axial magnetic alignment and tri-axial magnetic anisotropies depending on the type of RE in RE-based cuprate superconductors. From the changes in the axes for magnetization in magnetically aligned powders of (RE'1-xRE?x)2Ba4Cu7Oy [(RE',RE?)247] containing RE ions with different single-ion magnetic anisotropies, the ratios of three-dimensional magnetic anisotropies between RE'247 and RE?247 could be determined. The results in (Y,Er)247, (Dy,Er)247, (Ho,Er)247, and (Y,Eu)247 systems suggest that magnetic anisotropies largely depended on the type of RE' (or RE?), even in the heavy RE ions with higher magnetic anisotropies. An appropriate choice of RE ions in RE-based cuprate superconductors enables the reduction of the required magnetic field for the production of their bulks and thick films based on the tri-axial magnetic alignment technique using modulated rotation magnetic fields.

Horii, Shigeru; Okuhira, Shota; Yamaki, Momoko; Kishio, Kohji; Shimoyama, Jun-ichi; Doi, Toshiya

2014-03-01

99

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

100

Magnetic Fields  

NSDL National Science Digital Library

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

Stern, David

2005-01-04

101

Giant Magnetic Anisotropy of Single Cobalt Atoms and  

E-print Network

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

Brune, Harald

102

Direct probe of anisotropy field dispersion in perpendicular media  

NASA Astrophysics Data System (ADS)

A complex transverse alternating-current (ac) susceptibility (?T) technique based on magneto-optical detection has been developed with sufficient sensitivity for thin film recording media. The technique has been used to measure the dispersions in grain size and anisotropy field in perpendicular magnetic recording media. Applying a direct-current (dc) field perpendicular to the easy axis effectively reduces the thermal energy barrier, which leads to thermally activated switching on the time scale of the ac field applied in the easy-axis (perpendicular) direction. The dc field dependence of the resulting imaginary transverse ac susceptibility Im(?T) is sensitive to dispersions in both the grain size and the anisotropy field. The sensitivity has been used to extract the amount of both dispersions. It has been found that the extracted grain size dispersion values agree well with those obtained from plane-view transmission electron microscopy micrographs.

Ju, Ganping; Zhou, Hong; Chantrell, Roy; Lu, Bin; Weller, Dieter

2006-04-01

103

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

PubMed

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

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

2014-01-01

104

Anisotropy of magnetic susceptibility of some metamorphic minerals  

Microsoft Academic Search

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

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

1987-01-01

105

Inkjet printed superparamagnetic polymer composite hemispheres with programmed magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We present the fabrication and characterization of large arrays of inkjet-printed superparamagnetic polymer composite (SPMPC) hemispherical microstructures. SPMPCs are appealing for applications in microsystems and nanorobotics due to the added functionality of polymers and the significant magnetic attributes of embedded nanostructures. SPMPC-based microarchitectures can be used to perform different functions wirelessly in various media (e.g. water, solvents) using external magnetic fields: handling and assembling small objects, delivering drugs or biomass, or sensing specific physical or chemical changes. In this work superparamagnetic magnetite nanoparticles are dispersed in SU-8 to form magnetic hemispheres. Magnetically anisotropic hemispheres as well as standard SPMPC hemispheres are fabricated. Magnetic anisotropy is programmed by applying a magnetic field during curing. The distribution of nanoparticles inside the polymer matrix and magnetic characteristics of the SPMPC are investigated. Magnetic manipulation of hemispheres is demonstrated at liquid-liquid interfaces. Different assembly strategies to form lines or geometric shapes from hemispheres as well as their independent dynamic control are demonstrated. Finally, a two-interface assembly strategy is demonstrated to assemble hemispheres into complete spheres for advanced self-assembly tasks.We present the fabrication and characterization of large arrays of inkjet-printed superparamagnetic polymer composite (SPMPC) hemispherical microstructures. SPMPCs are appealing for applications in microsystems and nanorobotics due to the added functionality of polymers and the significant magnetic attributes of embedded nanostructures. SPMPC-based microarchitectures can be used to perform different functions wirelessly in various media (e.g. water, solvents) using external magnetic fields: handling and assembling small objects, delivering drugs or biomass, or sensing specific physical or chemical changes. In this work superparamagnetic magnetite nanoparticles are dispersed in SU-8 to form magnetic hemispheres. Magnetically anisotropic hemispheres as well as standard SPMPC hemispheres are fabricated. Magnetic anisotropy is programmed by applying a magnetic field during curing. The distribution of nanoparticles inside the polymer matrix and magnetic characteristics of the SPMPC are investigated. Magnetic manipulation of hemispheres is demonstrated at liquid-liquid interfaces. Different assembly strategies to form lines or geometric shapes from hemispheres as well as their independent dynamic control are demonstrated. Finally, a two-interface assembly strategy is demonstrated to assemble hemispheres into complete spheres for advanced self-assembly tasks. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06442e

Ergeneman, Olgaç; Peters, Christian; Gullo, Maurizio R.; Jacot-Descombes, Loïc; Gervasoni, Simone; Özkale, Berna; Fatio, Philipe; Cadarso, Victor J.; Mastrangeli, Massimo; Pané, Salvador; Brugger, Jürgen; Hierold, Christofer; Nelson, Bradley J.

2014-08-01

106

Magnetization and incremental susceptibilities of ferromagnets with angularly distributed uniaxial anisotropy above remanence  

Microsoft Academic Search

We calculate magnetization and incremental longitudinal and perpendicular susceptibilities for ferromagnets above remanence as functions of longitudinally applied field, assuming a local uniaxial anisotropy to have certain angular distributions. We give analytical formulas, together with computation results, under a wide range of conditions. For anisotropy uniformly oriented in all directions, the classical derivation of the law of approach to saturation

D.-X. Chen; L. Pascual

2003-01-01

107

Experimental investigation of magnetic anisotropy in spin vortex discs  

SciTech Connect

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

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

2014-05-07

108

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

SciTech Connect

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

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

2011-06-01

109

The Magnetic Anisotropy of Scandium, Dilute Scandium Alloys, and Technetium  

Microsoft Academic Search

The magnetic anisotropies, defined as the difference in magnetic susceptibility perpendicular to the c-axis and parallel to the c-axis, ??c-?∥c, of hcp scandium, dilute scandium-base alloys with both magnetic and nonmagnetic solutes, and high purity technetium have been studied as a function of temperature between 2 and 300°K. The magnetic anisotropy of scandium is not affected by small amounts of

L. L. Isaacs; D. J. Lam; J. W. Ross

1972-01-01

110

The Magnetic Anisotropy of Scandium, Dilute Scandium Alloys, and Technetium  

Microsoft Academic Search

The magnetic anisotropies, defined as the difference in magnetic susceptibility perpendicular to the c-axis and parallel to the c-axis, chi?c-chis||c, of hcp scandium, dilute scandium-base alloys with both magnetic and nonmagnetic solutes, and high purity technetium have been studied as a function of temperature between 2 and 300°K. The magnetic anisotropy of scandium is not affected by small amounts of

L. L. Isaacs; D. J. Lam; J. W. Ross

1972-01-01

111

Stability of the perpendicular magnetic anisotropy of ultrathin Ni films on Cu(100) upon multiple magnetization reversals.  

SciTech Connect

Ultrathin Ni films with perpendicular magnetic anisotropy were deposited on Cu(100) at room temperature. The magnetic properties of the films were measured upon multiple magnetization reversals in an alternating magnetic field using the magneto-optic Kerr effect. All magnetic properties remain virtually constant for up to 10{sup 6} magnetization reversals for all films studied. This finding is supported by a simple theoretical model.

Lu, X.; Berger, A.; Wuttig, M.; Materials Science Division; Inst. fur Grenzflachenforschung und Vakuumphysik; I. Physikalisches Inst. der RWTH Aachen

2001-01-01

112

Temperature dependent magnetization in Co-base nanowire arrays: Role of crystalline anisotropy  

NASA Astrophysics Data System (ADS)

Co, Co(1-x)Pdx, and Co(1-y)Niy nanowire arrays have been prepared by electrochemical template-assisted growth. Hcp, fcc or both phases are detected in Co nanowires depending on their length (300 nm to 40 ?m) and on the content of Pd (0 ? x ? 0.4) and Ni (0 ? y ? 0.8). Their magnetic behavior has been studied under longitudinal and perpendicular applied fields. The effective magnetic anisotropy is mostly determined by the balance between the shape and the crystalline terms, the latter depending on the fractional volume of hcp phase with strong perpendicular anisotropy and fcc phase with weaker longitudinal anisotropy. The temperature dependence of remanence and coercivity and the eventual observation of compensation temperature is interpreted as due to the different temperature dependence of shape and hcp crystalline anisotropy. Optimum longitudinal magnetic anisotropy is achieved in low Pd-content CoPd nanowires and in short Co nanowires.

Vivas, L. G.; Vázquez, M.; Vega, V.; García, J.; Rosa, W. O.; del Real, R. P.; Prida, V. M.

2012-04-01

113

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

PubMed

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

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

2012-12-14

114

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

115

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion.  

PubMed

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

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

2014-01-01

116

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion  

PubMed Central

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

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

2014-01-01

117

Large voltage-induced magnetic anisotropy change in a few atomic layers of iron  

NASA Astrophysics Data System (ADS)

In the field of spintronics, researchers have manipulated magnetization using spin-polarized currents. Another option is to use a voltage-induced symmetry change in a ferromagnetic material to cause changes in magnetization or in magnetic anisotropy. However, a significant improvement in efficiency is needed before this approach can be used in memory devices with ultralow power consumption. Here, we show that a relatively small electric field (less than 100 mV nm-1) can cause a large change (~40%) in the magnetic anisotropy of a bcc Fe(001)/MgO(001) junction. The effect is tentatively attributed to the change in the relative occupation of 3d orbitals of Fe atoms adjacent to the MgO barrier. Simulations confirm that voltage-controlled magnetization switching in magnetic tunnel junctions is possible using the anisotropy change demonstrated here, which could be of use in the development of low-power logic devices and non-volatile memory cells.

Maruyama, T.; Shiota, Y.; Nozaki, T.; Ohta, K.; Toda, N.; Mizuguchi, M.; Tulapurkar, A. A.; Shinjo, T.; Shiraishi, M.; Mizukami, S.; Ando, Y.; Suzuki, Y.

2009-03-01

118

Magnetic Field Safety Magnetic Field Safety  

E-print Network

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

McQuade, D. Tyler

119

Paleomagnetic, Anisotropy of Magnetic Susceptibility, and 40AR/39AR Data from the Cienega Volcano, Cerros del Rio Volcanic Field, New Mexico  

NASA Astrophysics Data System (ADS)

Cinder cone eruptions are typically interpreted to have formed by the ascension of magma through a simple conduit. Recent field work and laboratory studies on different excavated volcanoes around the world suggest that magma transport within cinder cones can involve a complex system of feeder geometries. We studied the Cienega volcano, a cinder cone in the Cerros del Rio volcanic field, northern New Mexico, in order to better understand the complexity and the evolution of volcanic plumbing systems in the development of cinder cone volcanoes. We hypothesized that cinder cone plumbing systems are inherently complex and involve numerous feeder geometries (e.g. dikes, sills) and flow patterns both towards and away from the central vent complex. The Cienega volcano comprises tephra fall deposits as well as several vents, multiple intrusions, and numerous lava flow sequences. We inspected the magmatic plumbing system using different laboratory methods including paleomagnetic, anisotropy of magnetic susceptibility (AMS), rock magnetic and thin section studies. We collected samples across each outcrop of the feeder system. The dikes are olivine porphyritic basalts with major clinopyroxene, calcic plagioclase feldspar, magnetite, and xenocrystic quartz. Most samples display a trachytic texture with plagioclase crystals showing a preferred orientation parallel to the dike margins. The magnetic information is held predominantly by a cubic phase magnetite with a low- to moderate-Ti composition of Single or Pseudo-Single Domain grains. The AMS results show various flow directions. Three of six dikes yielded magma flow directions away from the vent. The other dikes showed both a subvertical flow, which corresponds to the typical movement of magma in a dike originating from a deeper crustal level, and a downward flow direction. We concluded that magma initially flowed upward from the magma chamber until it encountered flow resistance. At this structural level (the current exposure level), the magma flowed laterally away from the ascent location. Magma transport was, therefore, not solely directed into the central conduit but actually involved numerous conduits away from the vent area. The in situ results for eight paleomagnetic sites provide a group mean of D=354.2°, I=19.7°, ?95= 4.8°, 5/8. The virtual geomagnetic pole dispersion of the group mean yields a value of 1.19, significantly lower than the predicted VGP dispersion estimate of 15° for the paleolatitude of the site (35.7°N). The results indicate that the different dikes were emplaced within a short period of time (<100 years) relative to a secular variation of the geomagnetic field. Four new whole rock 40Ar/39Ar age determinations from both vent and dike facies are indistinguishable at 2.75 Ma. These ages place the eruptive events in the latest Pliocene and indicate rapid magma injections and cone construction relative to secular variation.

Foucher, M. S.; Petronis, M. S.; Lindline, J.; Van Wyk de Vries, B.

2012-12-01

120

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

121

Probing magnetic anisotropy effects in epitaxial CrO2 thin films  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy in ferromagnetic chromium dioxide thin films (Tc~393 K) grown epitaxially on (100) TiO2 substrates, is probed using precise rf transverse susceptibility (?T) measurements. Singular peaks in ?T are observed that are associated with the anisotropy (+/-HK) and switching (+/-Hs) fields in CrO2. Theoretical calculations of ?T based on a simple coherent rotation model display remarkable agreement with the experimental data, indicating that these thin films behave like single-domain magnetic particles. Magnetoelastic contributions to the total anisotropy energy are needed to describe the evolution of ?T peaks at lower temperatures.

Spinu, L.; Srikanth, H.; Gupta, A.; Li, X. W.; Xiao, Gang

2000-10-01

122

Recognizing the threshold magnetic anisotropy for inclination shallowing: Implications for correcting inclination errors of sedimentary rocks  

NASA Astrophysics Data System (ADS)

Post-depositional compaction is an integral part of sedimentary rock formation and thus has been reasonably deemed as a major culprit for the long-recognized inclination-shallowing problem in sedimentary rocks. Although theoretical treatment elegantly envisions magnetic anisotropy (or oblate fabrics) to correspond to the degree of compaction and the magnitude of inclination flattening, such correspondence has rarely been seen in nature quantitavely, which leaves the possibility of misidentification and/or over-correction for inclination shallowing using magnetic anisotropy. This is because the extent to which oblate magnetic fabrics are developed strongly enough for inclination to start becoming shallow is not yet known. Here, we present sedimentary paleomagnetic data from two ~6 m long gravity cores GHE24L and GHE27L from the northern slope of the South China Sea to examine the down-core changes in magnetic anisotropy and inclinations, and to explore the possible connection between the two parameters. The results show that oblate fabrics are dominantly developed at depths >~2m and the degree of anisotropy displays an overall gradual increase with depth. Inclination shallowing occurs in the > 5m segment of the relatively distal core GHE27L and the amount of shallowing largely correlates with the degree of anisotropy, suggesting a causal relation between the development of magnetic anisotropy and the degree of inclination shallowing. Examination of down-core changes in inclination and magnetic anisotropy suggests that a threshold anisotropy of PAMS~1.04 and PAAR~1.10 exists for inclination shallowing in the cores. For PAAR<1.10, over-correction is mostly negligible, but can amount >10° if particle anisotropy is <1.4. This study provides strong field evidence that complements and substantiates the theoretical model and suggests that the threshold anisotropy can be used as a first-order criterion to identify inclination errors of some sedimentary rocks.

Li, Yongxiang; Wang, Shipeng; Fu, Shaoying; Jiao, Wenjun

2014-05-01

123

Magnetic and structural anisotropies of Co2FeAl Heusler alloy epitaxial thin films  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

124

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

125

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

PubMed

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

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

2014-01-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

127

Determination of the optical anisotropy of magnetic garnet films.  

PubMed

We show that the application of isotropic coupling prisms instead of birefringent prisms permits the precise determination of the optical anisotropy of magnetic garnet films; these measurements are essential for phase matching and conversion of optical modes. Using this technique, the anisotropy of a (211)-oriented film was measured with silicon prisms. PMID:19741925

Hemme, H; Dötsch, H; Middelberg, J; Kappelt, R; Tolksdorf, W

1987-11-01

128

Perpendicular magnetic recording with a composite anisotropy film  

Microsoft Academic Search

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

S. Iwasaki; Y. Nakamura; K. Ouchi

1979-01-01

129

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

130

Anisotropy of magnetic susceptibility parameters: Guidelines for their rational selection  

NASA Astrophysics Data System (ADS)

Twenty-eight parameters used to characterize measurements of the anisotropy of magnetic susceptibility are compared theoretically in this work by introducing the concept of the field of susceptibility tensors, which allows the representation of parameters as families of lines in a plane. It is demonstrated that the foliation and lineation parameters are but a special case of the shape parameters, implying that the resolution of these two rock fabric elements using AMS measurements alone is more an artifact of the numerical range of definition of some parameters than a quantification of two physically independent features. Also, it is shown that parameters presumably of the same type do not necessarily yield equivalent interpretation of results in a qualitative sense, and therefore, caution should be strongly exercised when parameters are to be selected. Paramters quantifying the degree of anisotropy are, in general, equivalent to each other because of the very small departure observed in natural rocks from the isotropic case. However, a final consideration of the possible ability to differentiate rock types and a convenient range of values allowing expression of the degree of anisotropy in a well-defined percentage are pointed out as the main factors to be considered before selecting one parameter within this class.

Cañón-Tapia, Edgardo

1994-06-01

131

Artificially modified magnetic anisotropy in interconnected nanowire networks  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

132

Artificially modified magnetic anisotropy in interconnected nanowire networks.  

PubMed

Interconnected or crossed magnetic nanowire networks have been fabricated by electrodeposition into a polycarbonate template with crossed cylindrical nanopores oriented ±30° with respect to the surface normal. Tailor-made nanoporous polymer membranes have been designed by performing a double energetic heavy ion irradiation with fixed incidence angles. The Ni and Ni/NiFe nanowire networks have been characterized by magnetometry as well as ferromagnetic resonance and compared with parallel nanowire arrays of the same diameter and density. The most interesting feature of these nanostructured materials is a significant reduction of the magnetic anisotropy when the external field is applied perpendicular and parallel to the plane of the sample. This effect is attributed to the relative orientation of the nanowire axes with the applied field. Moreover, the microwave transmission spectra of these nanowire networks display an asymmetric linewidth broadening, which may be interesting for the development of low-pass filters. Nanoporous templates made of well-defined nanochannel network constitute an interesting approach to fabricate materials with controlled anisotropy and microwave absorption properties that can be easily modified by adjusting the relative orientation of the nanochannels, pore sizes and material composition along the length of the nanowire. PMID:25501534

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

2015-01-01

133

Self-consistent mean-field theory of the XXZ ferrimagnetic spin chain with single-ion anisotropy  

NASA Astrophysics Data System (ADS)

The extended self-consistent mean-field theory is applied to study the XXZ ferrimagnetic spin chain with single-ion anisotropy. Based on the effects of XXZ anisotropy ? and single-ion anisotropy D, we calculate the energy excitation spectrums, energy gaps, static uniform susceptibility and specific heat. The magnetization plateau of ferrimagnetic spin chain with single-ion anisotropy D disappears at the critical point Dc = 1.335.

Li, Yinxiang; Chen, Bin; Zhang, Zhengfan; Han, Rushan

2015-01-01

134

Colossal anisotropy of the magnetic properties of doped lithium nitrodometalates  

SciTech Connect

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

Antropov, Vladimir P [Ames Laboratory; Antonov, Victor N [Ames Laboratory

2014-09-01

135

Electron concentration dependent magnetization and magnetic anisotropy in ZnO:Mn thin films  

E-print Network

applications.1 Diluted magnetic semiconductors DMSs can meet this expectation.1,2 ZnO based DMS materials haveElectron concentration dependent magnetization and magnetic anisotropy in ZnO:Mn thin films Z. Yang. Magnetic anisotropy was also observed in these ZnO:Mn films, which is another indication for intrinsic

Yang, Zheng

136

Anisotropy of magnetic susceptibility data indicating remagnetization in diabase dikes  

Microsoft Academic Search

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

Brooks B. Ellwood

1984-01-01

137

Depth profiles of magnetic anisotropy in annealed Co-based amorphous ribbon  

Microsoft Academic Search

For Co-Fe-Si-B amorphous ribbons the influence of weak-field annealing on transformation of magnetic field and spectral transverse Kerr effect (TKE) dependencies has been studied. The TKE spectra and magnetization curves were found to exhibit anisotropic behavior. The results indicate that the magnetic structure is inhomogeneous relative to thickness and confirm an increase of anisotropy in the near surface layer. It

E. A. Gan'shina; N. S. Perov; M. Yu. Kochneva; P. M. Sheverdyaeva; C. G. Kim; C. O. Kim

2002-01-01

138

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

139

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

140

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

141

The Effect of Cation Substitution on Magnetic Anisotropy of M-Type Hexagonal Ferrites  

Microsoft Academic Search

Anisotropic characteristics of substituted ferrimagnetics are studied on the basis of BaFe12O19. The constants of Fe3+ ion level splitting by fields with axial symmetry at various crystallographic sites are calculated in the framework of a single-ion anisotropy model. The iron cations at pseudotetrahedral sites 4e·1\\/2 are shown to have a dominating role in forming magnetic crystalline anisotropy of hexagonal ferrimagnetics

E. P. Naiden; V. Yu. Kreslin; M. V. Politov; A. G. Chesnokov

2000-01-01

142

Magnetic properties and anisotropy of CoCr thin films for perpendicular recording (abstract)  

NASA Astrophysics Data System (ADS)

The magnetic properties, microstructure, and anisotropy of CoCr thin films have been studied using VSM, x-ray, torque magnetometer, and electron microscopy techniques. These films were grown on a number of different substrates including sapphire, glass, mica, Al, and Ni-P, by rf sputtering, in the thickness range 300 Å-1 ?m. The microstructures dominate the magnetic properties of these films and the coercivity Hc continues to increase even up to the grain diameters of 1000 Å. The ??50 value for the (0002) x-ray peak reached 2°. For the sapphire the anisotropy field Hk is positive down to a film thickness of 500 Å. Effective anisotropy constants as measured by torque magnetometer increase from 1.31 to 3.16×10+5 erg/cm3 for film thicknesses ranging from 0.1 to 1 ?m. We have estimated the magnetocrystalline anisotropy from the measured anisotropy values from the torque magnetometer. In calculating the shape anisotropy, this model accounts for magnetostatically interacting cylindrical columns as opposed to the simple uniform thin-film model. Since there is experimental evidence that Cr segregates towards the grain-boundary walls, a variety of models were used where the diameter of the grains were kept constant while the diameter of the magnetic parts of the grains were gradually reduced. When the magnetic columns are in contact, the shape anisotropy field Hs is 5% lower than the uniform thin film approximation. When the magnetic radius is 80% of the grain radius, then the Hs is 34% lower, but the magnetocrystalline anisotropy constant Ku is 7% higher.

Khan, Mahbub R.; Seagle, David J.; Fernelius, Nils C.; Lee, Jae I.

1987-04-01

143

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

NASA Astrophysics Data System (ADS)

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

Hockel, Joshua Leon

144

Magnetic Anisotropy Engineering in Thin Film Ni Nanostructures by Magnetoelastic Coupling  

NASA Astrophysics Data System (ADS)

A phenomenon that can be exploited for the manipulation of magnetization without the conventional current-generated magnetic fields is magnetoelastic coupling, which might, thus, pave the way for low-power data-storage devices. Here, we report a quantitative analysis of the magnetic uniaxial anisotropy induced by piezoelectric strain in Ni nanostructured squares. By applying strain, the magnetic domains in Ni nanostructured squares can be manipulated by the magnetoelastic effect in the Ni. The strain-induced anisotropy displaces the domain walls in the square leading to changes in the domain sizes. By comparing the experiments with micromagnetic simulations, the resulting uniaxial anisotropy is quantified. We find a good agreement for a magnetostrictive constant of ?s=-26 ppm, confirming a full strain transfer from the piezoelectric to the Ni nanostructures and the retainment of a bulklike ?s.

Finizio, S.; Foerster, M.; Buzzi, M.; Krüger, B.; Jourdan, M.; Vaz, C. A. F.; Hockel, J.; Miyawaki, T.; Tkach, A.; Valencia, S.; Kronast, F.; Carman, G. P.; Nolting, F.; Kläui, M.

2014-03-01

145

Magnetic properties of the molecular nanomagnet Cr7Cd: single ion and exchange anisotropy effects.  

PubMed

In order to verify two microscopic models of the molecular nanomagnet Cr7Cd we analyze a number of thermodynamic quantities calculated for two sets of parameters. The first model, with only single ion anisotropy, was established on the basis of the thermodynamic properties (by fitting susceptibility and magnetization) whereas the second, with single ion and bond-dependent exchange anisotropies, was based on the inelastic neutron scattering and EPR spectra. The calculations are performed by means of non-perturbative, numerically exact quantum transfer matrix technique on large scale parallel computers. We demonstrate that the predictions of the models are consistent in the region of small magnetic fields which do not exceed 10 T and differ significantly in higher fields. Comparison with the experiment leads to a conclusion that better modeling of magnetic torque requires more complex microscopic model with single ion and bond-dependent exchange anisotropies. PMID:22400319

Koz?owski, P; Kamieniarz, G

2011-10-01

146

Magnetic tunnel junction sensor with Co/Pt perpendicular anisotropy ferromagnetic layer  

SciTech Connect

Linear magnetoresistance (MR) is an important attribute for magnetic sensor designs for space applications, three dimensional detection of the magnetic field, and high field measurements. Here we demonstrate that a large linear MR of up to 22% can be achieved in a magnetic tunnel junction that consists of two ferromagnetic layers, one with out of plane and one with in plane magnetic anisotropy. The tunnelling magnetoresistance (TMR) is measured with the electrical current perpendicular to the film plane. The magnetic configuration of the device is analyzed.

Wei, H. X. [Institute of Physics, Chinese Academy of Science; Qin, Q. H. [Institute of Physics, Chinese Academy of Science; Wen, Z. C. [Institute of Physics, Chinese Academy of Science; Han, Prof. X. F. [Institute of Physics, Chinese Academy of Science; Zhang, Xiaoguang [ORNL

2009-01-01

147

Origin of slow magnetic relaxation in Kramers ions with non-uniaxial anisotropy.  

PubMed

Transition metal ions with long-lived spin states represent minimum size magnetic bits. Magnetic memory has often been associated with the combination of high spin and strong uniaxial magnetic anisotropy. Yet, slow magnetic relaxation has also been observed in some Kramers ions with dominant easy-plane magnetic anisotropy, albeit only under an external magnetic field. Here we study the spin dynamics of cobalt(II) ions in a model molecular complex. We show, by means of quantitative first-principles calculations, that the slow relaxation in this and other similar systems is a general consequence of time-reversal symmetry that hinders direct spin-phonon processes regardless of the sign of the magnetic anisotropy. Its magnetic field dependence is a subtle manifestation of electronuclear spin entanglement, which opens relaxation channels that would otherwise be forbidden but, at the same time, masks the relaxation phenomenon at zero field. These results provide a promising strategy to synthesize atom-size magnetic memories. PMID:24980875

Gómez-Coca, Silvia; Urtizberea, Ainhoa; Cremades, Eduard; Alonso, Pablo J; Camón, Agustín; Ruiz, Eliseo; Luis, Fernando

2014-01-01

148

Constraints on a Primordial Magnetic Field  

SciTech Connect

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

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

1997-05-01

149

Induced anisotropy in FeCo-based nanocrystalline ferromagnetic alloys (HITPERM) by very high field annealing  

Microsoft Academic Search

Very high magnetic field annealing is shown to affect the magnetic anisotropy in FeCo-base nanocrystalline soft ferromagnetic alloys. Alloys of composition Fe44.5Co44.5Zr7B4 were prepared by melt spinning into amorphous ribbons, then wound to form toroidal bobbin cores. One set of cores was crystallized in a zero field at 600°C for 1 h, then, field annealed at 17 tesla (T) at

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

2004-01-01

150

Role of magnetic anisotropy in spin-filter junctions  

NASA Astrophysics Data System (ADS)

We have fabricated oxide-based spin-filter junctions in which we demonstrate that magnetic anisotropy can be used to tune the transport behavior of spin-filter junctions. We have demonstrated spin-filtering behavior in La0.7Sr0.3MnO3/CoCr2O4/Fe3O4 and La0.7Sr0.3MnO3/MnCr2O4/Fe3O4 junctions where the interface anisotropy plays a significant role in determining transport behavior. Detailed studies of chemical and magnetic structure at the interfaces indicate that abrupt changes in magnetic anisotropy across the nonisostructural interface is the cause of the significant suppression of junction magnetoresistance in junctions with MnCr2O4 barrier layers.

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

2011-06-01

151

Uniaxial anisotropy in magnetite thin film—Magnetization studies  

Microsoft Academic Search

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

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

2006-01-01

152

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

E-print Network

Facilities: EMR & DC field (31T, 50mm bore resistive magnet). Citation: Giant Ising-Type Magnetic and N. Guihéry, J. Am. Chem. Soc. 135, 3017­3026 (2013). Molecules that can be magnetized, so-called single-molecule magnets (SMMs), are of considerable interest in terms of their potential future use

McQuade, D. Tyler

153

Giant magnetic anisotropy and tunnelling of the magnetization in Li2(Li1?xFex)N  

SciTech Connect

Large magnetic anisotropy and coercivity are key properties of functional magnetic materials and are generally associated with rare earth elements. Here we show an extreme, uniaxial magnetic anisotropy and the emergence of magnetic hysteresis in Li2(Li1?xFex)N. An extrapolated, magnetic anisotropy field of 220?T and a coercivity field of over 11?T at 2?K outperform all known hard ferromagnets and single-molecular magnets. Steps in the hysteresis loops and relaxation phenomena in striking similarity to single-molecular magnets are particularly pronounced for x<<1 and indicate the presence of nanoscale magnetic centres. Quantum tunnelling, in the form of temperature-independent relaxation and coercivity, deviation from Arrhenius behaviour and blocking of the relaxation, dominates the magnetic properties up to 10?K. The simple crystal structure, the availability of large single crystals and the ability to vary the Fe concentration make Li2(Li1?xFex)N an ideal model system to study macroscopic quantum effects at elevated temperatures and also a basis for novel functional magnetic materials.

Jesche, Anton [Ames Laboratory; McCallum, Ralph W. [Ames Laboratory; Thimmaiah, Srinivasa [Ames Laboratory; Jacobs, Jenee L. [Ames Laboratory; Taufour, V. [Iowa State University; Kreyssig, Andreas [Ames Laboratory; Houk, Robert S. [Ames Laboratory; Bud'ko, Sergey L. [Ames Laboratory; Canfield, Paul C. [Ames Laboratory

2014-02-25

154

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

155

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

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

156

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

157

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

158

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 (J), the single-ion anisotropy (SIA), and the Dzyaloshinsky-Moriya (DM) interaction are investigated by means of density-functional calculations in AFeO3 systems. We explore the effect of the crystal distortions (Antiferrodistortive-AFD and Ferroelectric) as well as the effect of the A-cation chemistry on the 3 magnetic properties, J, SIA and DM. Our analysis shows a never explored but possible switching of the weak ferromagnetism in the R3c phase of BiFeO3 through the competition of the SIA shapes induced by the AFD and the ferroelectric distortions. We also found that-in spite of the d^5 electronic configuration of Fe^3+, 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. To clarify the origin of this unexpected effect, we analyze the crystal field splitting by means of Wannier functions.

Bousquet, Eric; Weingart, Carlo; Spaldin, Nicola

2013-03-01

159

Microscopic origin of magnetic anisotropy in martensitic Ni2MnGa  

NASA Astrophysics Data System (ADS)

The microscopic origin of magnetic anisotropy in the shape memory alloy Ni2MnGa is investigated by means of x-ray magnetic circular dichroism in transmission mode. Field- and angle-dependent dichroism spectra of epitaxial Ni2MnGa(101)/MgO(001) films reveal pronounced differences for magnetization aligned parallel and perpendicular to the film plane. These differences are related to an anisotropy of the orbital magnetic moment in agreement with the observed out-of-plane magnetocrystalline anisotropy. The spectral variation of the x-ray absorption originates from changes in the spin-projected density of states when the magnetization vector is rotated from the easy to the hard magnetic axis. Minority Ni states with d3z2-r2 symmetry close to the Fermi energy form a wide half filled band for easy axis magnetization. When the magnetization is rotated into the hard axis the band narrowing of these states causes an increase of the mean kinetic energy of the electronic system. The opposite behavior of mostly unoccupied Ni states with dxy symmetry leads to an increase of the minority orbital moment for hard-axis magnetization.

Klaer, P.; Eichhorn, T.; Jakob, G.; Elmers, H. J.

2011-06-01

160

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

161

Switching current density reduction in perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions  

SciTech Connect

We investigate the switching current density reduction of perpendicular magnetic anisotropy spin transfer torque magnetic tunneling junctions using micromagnetic simulations. We find that the switching current density can be reduced with elongated lateral shapes of the magnetic tunnel junctions, and additional reduction can be achieved by using a noncollinear polarizer layer. The reduction is closely related to the details of spin configurations during switching processes with the additional in-plane anisotropy.

You, Chun-Yeol [Department of Physics, Inha University, Incheon 402-751 (Korea, Republic of)

2014-01-28

162

Magnetic anisotropy and mechanism of magnetic relaxation in Er(III) single-ion magnets.  

PubMed

Magnetic anisotropy is a key component in the design of single-molecule magnets (SMMs) possessing a large barrier height for magnetization reversal. Lanthanide-based SMMs are the most promising candidates in this arena as they offer a large magnetic anisotropy due to the presence of strong spin-orbit coupling. Among lanthanides, Er(III) complexes are gaining attention in the area of SMMs, because of their intriguing magnetic properties and attractive blocking temperatures. Here, we have undertaken detailed ab initio calculations on four structurally diverse Er(III) SMMs to shed light on how the magnetic anisotropy is influenced by the role of symmetry and structural distortions. The employed CASSCF+RASSI calculations have offered rationale for the observed differences in the estimated Ueff values for the studied complexes and also offered hints to the mechanism of magnetic relaxation. The differences in the mechanism of magnetic relaxations are further analyzed based on the Er-ligand interactions, which is obtained by analyzing the charges, densities, luminescent behavior and the frontier molecular orbitals. Our calculations, for the first time, have highlighted the importance of high symmetry environment and ligand donor strength in obtaining large Ueff values for the Er(III) complexes. We have examined these possibilities by modeling several structures with variable coordination numbers and point group symmetry. These results signify the need of a detailed understanding on the shape of the anisotropy and the point group symmetry in order to achieve large Ueff values in Er(III) single-ion magnets. PMID:25259840

Singh, Saurabh Kumar; Gupta, Tulika; Rajaraman, Gopalan

2014-10-20

163

Using different Mn-oxides to influence the magnetic anisotropy of FePt in bilayers with little change of the exchange bias field  

NASA Astrophysics Data System (ADS)

We have investigated the exchange coupling between a bottom FePt thin film layer capped with different Mn-oxides. Results have shown that the magnetization reversal of the soft FePt layer is influenced strongly by the capped Mn-oxide layer (Mn, MnO, and Mn3O4), as revealed by the enhanced coercivities. Typical temperature dependent magnetization between zero-field cooled (ZFC) and field cooled (FC) scans was observed in the Mn-oxide (8%O2/Ar)/FePt bilayer that exhibited a blocking temperature (TB ˜ 120 K) close to the Nèel temperature, TN, of MnO. However, the Mn/FePt bilayer exhibited unusual temperature dependent of M vs. T, implying that intermixing between Mn and FePt interfaces formed an AF FeMn that may have enabled a high irreversibility temperature (Tirr. ˜ 400 K) compared to almost identical ZFC and FC curves from weaker exchange coupling between FePt and the Mn3O4 created with 21 and 30%O2/Ar deposition conditions.

Lin, K.-W.; Shueh, C.; Liu, C.-H.; Skoropata, E.; Wu, T.-H.; van Lierop, J.

2013-05-01

164

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

165

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

PubMed

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

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

2014-08-28

166

Controlling magnetic anisotropy in epitaxial FePt(001) films  

SciTech Connect

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

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

2009-07-15

167

Anisotropy of magnetic properties of Fe1+yTe  

NASA Astrophysics Data System (ADS)

The magnetic properties of Fe1+yTe single crystals (y ? 0.1 ÷ 0.18) were studied at temperatures 4.2 ÷ 300 K. At an ambient pressure, with decreasing temperature a drastic drop in ?(T) was confirmed at T ? 60 ÷ 65 K, which appears to be closely related to the antiferromagnetic (AFM) ordering. It is found that the magnitudes of the anisotropy of magnetic susceptibility ?? in the AFM phase are close in the studied samples, whereas the sign of the anisotropy apparently depends on the small variations of the excess iron y in Fe1+yTe samples. The performed DFT calculations of the electronic structure and magnetic properties for the stoichiometric FeTe compound indicate the presence of frustrated AFM ground states. There are very close energies and magnetic moments for the double stripe configurations, with the AFM axes oriented either on the basal plane or along the [0?0?1] direction. Presumably, both these configurations can be realized in Fe1+yTe single crystals, depending on the variations of the excess iron. This can provide different signs of magnetic anisotropy in the AFM phase, presently observed in the Fe1+yTe samples. For these types of AFM configuration, the calculations for the FeTe values of ?? are consistent with our experimental data.

Grechnev, G. E.; Panfilov, A. S.; Fedorchenko, A. V.; Lyogenkaya, A. A.; Zhuravleva, I. P.; Chareev, D. A.; Nekrasov, A. N.; Mitrofanova, E. S.; Volkova, O. S.; Vasiliev, A. N.; Eriksson, O.

2014-10-01

168

Anisotropy of magnetic properties of Fe(1+y)Te.  

PubMed

The magnetic properties of Fe(1+y)Te single crystals (y ? 0.1 ÷ 0.18) were studied at temperatures 4.2 ÷ 300 K. At an ambient pressure, with decreasing temperature a drastic drop in ?(T) was confirmed at T ? 60 ÷ 65 K, which appears to be closely related to the antiferromagnetic (AFM) ordering. It is found that the magnitudes of the anisotropy of magnetic susceptibility ?? in the AFM phase are close in the studied samples, whereas the sign of the anisotropy apparently depends on the small variations of the excess iron y in Fe(1+y)Te samples. The performed DFT calculations of the electronic structure and magnetic properties for the stoichiometric FeTe compound indicate the presence of frustrated AFM ground states. There are very close energies and magnetic moments for the double stripe configurations, with the AFM axes oriented either on the basal plane or along the [0?0?1] direction. Presumably, both these configurations can be realized in Fe(1+y)Te single crystals, depending on the variations of the excess iron. This can provide different signs of magnetic anisotropy in the AFM phase, presently observed in the Fe(1+y)Te samples. For these types of AFM configuration, the calculations for the FeTe values of ?? are consistent with our experimental data. PMID:25299131

Grechnev, G E; Panfilov, A S; Fedorchenko, A V; Lyogenkaya, A A; Zhuravleva, I P; Chareev, D A; Nekrasov, A N; Mitrofanova, E S; Volkova, O S; Vasiliev, A N; Eriksson, O

2014-10-29

169

Composition dependence of field induced anisotropy in ferromagnetic ,,Co,Fe...89Zr7B4 and ,,Co,Fe...88Zr7B4Cu1  

E-print Network

The composition dependence of field induced anisotropy KU of field annealed soft ferromagnetic Co1-xFex 89Zr7B4.1063/1.3021141 I. INTRODUCTION Magnetic field annealing techniques are often used to tailor the properties of softComposition dependence of field induced anisotropy in ferromagnetic ,,Co,Fe...89Zr7B4 and ,,Co

McHenry, Michael E.

170

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

PubMed

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

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

2013-10-16

171

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

172

Giant electric field controlled magnetic anisotropy in epitaxial BiFeO3-CoFe2O4 thin film heterostructures on single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrate  

NASA Astrophysics Data System (ADS)

We have deposited self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) thin films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates and studied the change in magnetic anisotropy under different strain conditions induced by an applied electric field. After electric field poling, we observed (i) giant magnetization change: magnetization of original CFO phase is three times larger than that of strained one and (ii) magnetic force microscopy line profiles that exhibited significant change in the CFO magnetic domain response in accordance to magnetization-field (M-H) loops. Together, these results demonstrate good control of the magnetic properties of CFO via an electric field induced strain.

Wang, Zhiguang; Yang, Yaodong; Viswan, Ravindranath; Li, Jiefang; Viehland, D.

2011-07-01

173

Spin disorder and magnetic anisotropy in Fe3O4 nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2006-04-01

174

Large voltage-induced magnetic anisotropy change in a few atomic layers of iron.  

PubMed

In the field of spintronics, researchers have manipulated magnetization using spin-polarized currents. Another option is to use a voltage-induced symmetry change in a ferromagnetic material to cause changes in magnetization or in magnetic anisotropy. However, a significant improvement in efficiency is needed before this approach can be used in memory devices with ultralow power consumption. Here, we show that a relatively small electric field (less than 100 mV nm(-1)) can cause a large change (approximately 40%) in the magnetic anisotropy of a bcc Fe(001)/MgO(001) junction. The effect is tentatively attributed to the change in the relative occupation of 3d orbitals of Fe atoms adjacent to the MgO barrier. Simulations confirm that voltage-controlled magnetization switching in magnetic tunnel junctions is possible using the anisotropy change demonstrated here, which could be of use in the development of low-power logic devices and non-volatile memory cells. PMID:19265844

Maruyama, T; Shiota, Y; Nozaki, T; Ohta, K; Toda, N; Mizuguchi, M; Tulapurkar, A A; Shinjo, T; Shiraishi, M; Mizukami, S; Ando, Y; Suzuki, Y

2009-03-01

175

Magnetophoresis of iron oxide nanoparticles at low field gradient: the role of shape anisotropy.  

PubMed

Magnetophoresis of iron oxide magnetic nanoparticle (IOMNP) under low magnetic field gradient (<100 T/m) is significantly enhanced by particle shape anisotropy. This unique feature of magnetophoresis is influenced by the particle concentration and applied magnetic field gradient. By comparing the nanosphere and nanorod magnetophoresis at different concentration, we revealed the ability for these two species of particles to achieve the same separation rate by adjusting the field gradient. Under cooperative magnetophoresis, the nanorods would first go through self- and magnetic field induced aggregation followed by the alignment of the particle clusters formed with magnetic field. Time scale associated to these two processes is investigated to understand the kinetic behavior of nanorod separation under low field gradient. Surface functionalization of nanoparticles can be employed as an effective strategy to vary the temporal evolution of these two aggregation processes which subsequently influence the magnetophoretic separation time and rate. PMID:24594047

Lim, Jitkang; Yeap, Swee Pin; Leow, Chee Hoe; Toh, Pey Yi; Low, Siew Chun

2014-05-01

176

Magnetic anisotropy investigation in (2 1 0)-oriented Bi-substituted magnetic garnets  

NASA Astrophysics Data System (ADS)

Different methods of describing growth- and stress-induced anisotropy are analysed. Two-parameter and quadratic models (generally five parameters) are discussed. A (2 1 0)-oriented epitaxial garnet film was chosen as an example of this analysis. Magnetic anisotropy constants were analyzed using both the traditional FMR technique and a magneto-optical anisometer based on the Faraday effect. The two-parameter model turned out to be incorrect for anisotropy description in such films. Observed differences between the experimental values of anisotropy constants from FMR and magneto-optical methods may be connected to magnetostriction influence on the resonance frequency.

Maryško, M.; Maziewski, A.; Stankiewicz, A.; Tekielak, M.; Volkov, V. V.

1993-07-01

177

A magneto-optic technique for studying magnetization reversal processes and anisotropies applied to Co/Cu/Co trilayer structures  

NASA Astrophysics Data System (ADS)

We report the magnetization reversal and magnetic anisotropy behavior of ultrathin Co/Cu(111)/Co (dCu=20 and 27 Å) trilayer structures prepared by MBE on a 500-Å Ge/GaAs(110) epilayer. We describe an arrangement in which the magnetization components parallel and perpendicular to the applied field are both determined from longitudinal MOKE measurements. For the samples examined, coherent rotation of the magnetization vector is observed when the magnetic field is applied along the hard in-plane anisotropy axis, with the magnitude of the magnetization vector constant and close to its bulk value. Results of micromagnetic calculations closely reproduce the observed parallel and perpendicular magnetization loops, and yield strong uniaxial magnetic anisotropies in both layers while the interlayer coupling appears to be absent or negligible in comparison with the anisotropy strengths. An absence of antiferromagnetic (AF) coupling has been observed previously [W. F. Egelhoff, Jr. and M. T. Kief, Phys. Rev. B 45, 7795 (1992)] in contrast to recent results, indicating that AF coupling [M. T. Johnson et al., Phys. Rev. Lett. 69, 969 (1992)] and GMR [D. Grieg et al., J. Magn. Magn. Mater. 110, L239 (1992)] can occur in Co/Cu(111)/Co structures grown by MBE, but these properties are sensitively dependent on growth conditions. The absence of coupling in our samples is attributed to the presence of a significant interface roughness induced by the Ge epilayer. The uniaxial anisotropies are assumed to arise from strain or defects induced in the film.

Daboo, C.; Bland, J. A. C.; Hicken, R. J.; Ives, A. J. R.; Baird, M. J.; Walker, M. J.

1993-05-01

178

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

NASA Astrophysics Data System (ADS)

Patterned hard-soft 2D magnetic lateral composites have been fabricated by e-beam lithography plus dry etching techniques on sputter-deposited NdCo5 thin films with perpendicular magnetic anisotropy. Their magnetic behavior is strongly thickness dependent due to the interplay between out-of-plane anisotropy and magnetostatic energy. Thus, the spatial modulation of thicknesses leads to an exchange coupled system with hard/soft magnetic regions in which rotatable anisotropy of the thicker elements provides an extra tool to design the global magnetic behavior of the patterned lateral composite. Kerr microscopy studies (domain imaging and magneto-optical Kerr effect magnetometry) reveal that the resulting hysteresis loops exhibit a tunable exchange bias-like shift that can be switched on/off by the applied magnetic field.

Hierro-Rodriguez, A.; Teixeira, J. M.; Vélez, M.; Alvarez-Prado, L. M.; Martín, J. I.; Alameda, J. M.

2014-09-01

179

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

SciTech Connect

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

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

2014-02-17

180

Exploring Magnetic Fields  

NSDL National Science Digital Library

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

181

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

182

Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy.  

PubMed

To extend density limits in magnetic recording industry, two separate strategies were developed to build the storage bit in last decade, introduction of perpendicular magnetic anisotropy (PMA) and adoption of ferrimagnetism/antiferromagnetism. Meanwhile, these properties significantly improve device performance, such as reducing spin-transfer torque energy consumption and decreasing signal-amplitude-loss. However, materials combining PMA and antiferromagnetism rather than transition-metal/rare-earth system were rarely developed. Here, we develop a new type of ferrimagnetic superlattice exhibiting PMA based on abundant Heusler alloy families. The superlattice is formed by [MnGa/Co2FeAl] unit with their magnetizations antiparallel aligned. The effective anisotropy (Ku(eff)) over 6 Merg/cm(3) is obtained, and the SL can be easily built on various substrates with flexible lattice constants. The coercive force, saturation magnetization and Ku(eff) of SLs are highly controllable by varying the thickness of MnGa and Co2FeAl layers. The SLs will supply a new choice for magnetic recording and spintronics memory application such as magnetic random access memory. PMID:25597496

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

2015-01-01

183

Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy  

PubMed Central

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

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

2015-01-01

184

Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

185

Full 180° magnetization reversal with electric fields.  

PubMed

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

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

2014-01-01

186

Full 180° Magnetization Reversal with Electric Fields  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

187

Full 180° Magnetization Reversal with Electric Fields  

PubMed Central

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

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

2014-01-01

188

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

189

Visualizing Magnetic Field Lines  

NSDL National Science Digital Library

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

VU Bioengineering RET Program, School of Engineering,

190

What are Magnetic Fields?  

NSDL National Science Digital Library

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

191

IEEE TRANSACTIONS ON MAGNETICS, VOL. 37, NO. 4, JULY 2001 2067 Magnetoresistance Anisotropy of a Bi Antidot Array  

E-print Network

IEEE TRANSACTIONS ON MAGNETICS, VOL. 37, NO. 4, JULY 2001 2067 Magnetoresistance Anisotropy of a Bi, and D. J. Bergman Abstract--We have measured the magnetoresistance of a Bi an- tidot array film. The magnetoresistance exhibits a pronounced an- gular dependence on the direction of the magnetic field, e

Strelniker, Yakov M.

192

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

193

Structural controlled magnetic anisotropy in Heusler L10-MnGa epitaxial Kangkang Wang,1  

E-print Network

- netic anisotropy in thin epitaxial MnGa films. This Heusler alloy has drawn lots of attention recentlyStructural controlled magnetic anisotropy in Heusler L10-MnGa epitaxial thin films Kangkang Wang,1

194

Photoinduced Magnetic Anisotropy and Optical Dichroism in Silicon-Doped Yttrium Iron Garnet  

Microsoft Academic Search

It has been found that an intense beam of linearly polarized light can induce a magnetic anisotropy in silicon-doped yttrium iron garnet at liquid-helium temperatures. Furthermore, there is associated with this anisotropy a substantial linear dichroism.

J. F. Dillon; E. M. Gyorgy; J. P. Remeika

1969-01-01

195

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

SciTech Connect

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

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

2014-05-07

196

Magnetic properties and anisotropy of orthorhombic DyMnO3 single crystal  

NASA Astrophysics Data System (ADS)

An orthorhombic DyMnO3 single crystal has been studied in magnetic fields up to 14 T and between 3 K and room temperature. The field dependent ordering temperature of Dy moments is deduced. The paramagnetic Curie Weiss behavior is related mainly to the Dy3+sublattice whereas the Mn sublattice contribution plays a secondary role. DC magnetization measurements show marked anisotropic features, related to the anisotropic structure of a cubic system stretched along a body diagonal, with a magnetic easy axis parallel to the crystallographic b axis. A temperature and field dependent spin flop transition is observed below 9 K, when relatively weak magnetocrystalline anisotropy is overcome by magnetic fields up to 1.6 T.

P?ka?a, M.; Wolff-Fabris, F.; Fagnard, J.-F.; Vanderbemden, Ph.; Mucha, J.; Gospodinov, M. M.; Lovchinov, V.; Ausloos, M.

2013-06-01

197

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

SciTech Connect

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

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

1999-08-19

198

Favorable magnetic fluctuation anisotropy for unconventional superconductivity in f -electron systems  

NASA Astrophysics Data System (ADS)

We report spin-lattice relaxation time measurements in isostructural ( HoCoGa5 -type) actinide compounds with different ground states (paramagnet, antiferromagnet, and superconductor) using single-crystal samples. The anisotropy of local magnetic fluctuations due to LS coupling on the actinide (magnetic) site is evaluated. In the superconductor PuRhGa5 , the XY -type magnetic anisotropy is strong compared with nonsuperconducting compounds. Favorable magnetic anisotropy for d -wave superconductivity in f -electron systems is discussed.

Kambe, S.; Sakai, H.; Tokunaga, Y.; Fujimoto, T.; Walstedt, R. E.; Ikeda, S.; Aoki, D.; Homma, Y.; Haga, Y.; Shiokawa, Y.; ?nuki, Y.

2007-04-01

199

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

SciTech Connect

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

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

2014-10-14

200

Thermoelectric effects and magnetic anisotropy of Ga1-xMnxAs thin films  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

201

Spin-orbit torque in a bulk perpendicular magnetic anisotropy Pd/FePd/MgO system  

PubMed Central

Spin-orbit torques, including the Rashba and spin Hall effects, have been widely observed and investigated in various systems. Since interesting spin-orbit torque (SOT) arises at the interface between heavy nonmagnetic metals and ferromagnetic metals, most studies have focused on the ultra-thin ferromagnetic layer with interface perpendicular magnetic anisotropy. Here, we measured the effective longitudinal and transverse fields of bulk perpendicular magnetic anisotropy Pd/FePd (1.54 to 2.43?nm)/MgO systems using harmonic methods with careful correction procedures. We found that in our range of thicknesses, the effective longitudinal and transverse fields are five to ten times larger than those reported in interface perpendicular magnetic anisotropy systems. The observed magnitude and thickness dependence of the effective fields suggest that the SOT do not have a purely interfacial origin in our samples. PMID:25293693

Lee, Hwang-Rae; Lee, Kyujoon; Cho, Jaehun; Choi, Young-Ha; You, Chun-Yeol; Jung, Myung-Hwa; Bonell, Frédéric; Shiota, Yoichi; Miwa, Shinji; Suzuki, Yoshishige

2014-01-01

202

Magnetic susceptibility anisotropies in a two-dimensional quantum Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions  

NASA Astrophysics Data System (ADS)

The magnetic and thermodynamic properties of the two-dimensional quantum Heisenberg antiferromagnet (QHAF) that incorporates both a Dzyaloshinskii-Moriya and pseudodipolar interactions are studied within the framework of a generalized nonlinear sigma model. We calculate the static uniform susceptibility and sublattice magnetization as a function of temperature and we show that (i) the magnetic response is anisotropic and differs qualitatively from the expected behavior of a conventional easy-axis QHAF; (ii) the Néel second-order phase transition becomes a crossover, for a magnetic field B?CuO2 layers. We provide a simple and clear explanation for all the recently reported unusual magnetic anisotropies in the low-field susceptibility of La2CuO4 [L. N. Lavrov , Phys. Rev. Lett. 87, 017007 (2001)], and we demonstrate explicitly why La2CuO4 cannot be classified as an ordinary easy-axis antiferromagnet.

Silva Neto, M. B.; Benfatto, L.; Juricic, V.; Morais Smith, C.

2006-01-01

203

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

204

Mapping Magnetic Fields  

NSDL National Science Digital Library

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

2012-08-03

205

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

SciTech Connect

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

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

2014-03-21

206

Magnetic resonance and magnetic anisotropy oscillations in Co/Cu (111) superlattices  

NASA Astrophysics Data System (ADS)

Magnetic resonance was studied in magnetic fields parallel or perpendicular to the film plane in magnetron-sputtered [Co(8 Å)/Cu(dCu)(111)]20 multilayers. Oscillations of the magnetic anisotropy KA and the width ?Hres of the resonance line as a function of the thickness of the copper interlayers were found in the interval dCu=7-19 Å. Extrema of KA and ?Hres were observed at dCu=nd(111), where n is an integer or half-integer, and d(111)=2.087 ŗthe distance between the (111) planes in Cu. In addition, the distances between the neighboring maxima or minima were 1, 1.5, and 2d(111). The KA and ?Hres oscillations occurred synchronously with oscillations of the resistivity at saturation (in the field H=15 kOe) and oscillations of the magnetoresistance. An interlayer antiferromagnetic exhange interaction was found in the ranges dCu=8-11 Å and dCu?18 Å. The effects observed were due to nonmonotonic variation of the interlayer interface roughness with increasing dCu.

Kaplienko, A. I.; Nikolova, É. P.; Kut'ko, K. V.; Anders, A. G.; Zorchenko, V. V.; Stetsenko, A. N.

2005-03-01

207

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

SciTech Connect

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

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

2011-06-01

208

Perpendicular-magnetic-anisotropy CoFeB racetrack memory  

NASA Astrophysics Data System (ADS)

Current-induced domain wall motion in magnetic nanowires drives the invention of a novel ultra-dense non-volatile storage device, called "racetrack memory." Combining with magnetic tunnel junctions write and read heads, CMOS integrability and fast data access speed can also be achieved. Recent experimental progress showed that perpendicular-magnetic anisotropy (PMA) CoFeB could be a good candidate to build up racetrack memory and promise high performance like high-density (e.g., ˜1 F2/bit), fast-speed, and low-power beyond classical spin transfer torque memories. In this paper, we first present the design of PMA CoFeB racetrack memory and a spice-compatible model to perform mixed simulation with CMOS circuits. Its area, speed, and power dissipation performance has been simulated and evaluated based on different technology nodes.

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

2012-05-01

209

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

210

Comment on "Frustrated magnetization in Co nanowires: Competition between crystal anisotropy and demagnetization  

E-print Network

Comment on "Frustrated magnetization in Co nanowires: Competition between crystal anisotropy anisotropy. This theory, which predicts a sinusoidal variation of the magnetization along the long axis of the wire, depends upon an assumption that "the magnetization is constant within a cross section of the wire

Donahue, Michael J.

211

Quantum effects and Haldane gap in magnetic chains with alternating anisotropy axes  

NASA Astrophysics Data System (ADS)

The isotropic quantum Heisenberg model with alternating uniaxial anisotropy axes is analyzed numerically by the density-matrix renormalization-group (DMRG) method. In the classical version, the model is applied to describe the magnetic properties of the S=2 zigzag chain containing Mn(III) acetate meso-tetraphenylporphyrin complexes coupled by the phenylphosphinate ligands which transmit antiferromagnetic interactions. Although the tensors representing the uniaxial magnetic anisotropy D and g factors are non-diagonal in the global coordination system, the DMRG approach has been successfully applied to this complex model in the entire temperature region studied. The predictions of our quantum approach are compared to those previously obtained from the classical one and the importance of quantum effects for analysis of the single-crystal susceptibility and magnetization is demonstrated. At low temperatures the magnetization in the field applied along the c direction increases much more slowly than the classical counterpart. The magnetization behavior is very sensitive to temperature. Moreover, the presence of a magnetization jump in the limit T?0 at the field H=3.8 Tesla can be an indication of the Haldane gap of the order of 10.2 K. The considerable differences are demonstrated for the temperature dependent single-crystal susceptibilities, but surprisingly they disappear after averaging over the three crystallographic directions which has not been reported before.

Barasi?ski, A.; Drzewi?ski, A.; Kamieniarz, G.

2011-09-01

212

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

NASA Astrophysics Data System (ADS)

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

Su, Lei; Wierschem, Keola; Sengupta, Pinaki

2014-06-01

213

Introduction to Magnetic Fields  

NSDL National Science Digital Library

This is an activity about magnetic fields. Learners will use various magnets, magnetic film, and a compass to see and illustrate what magnetic fields look like. This is the fourth activity as part of the iMAGiNETICspace: Where Imagination, Magnetism, and Space Collide educator's guide. Instructions for downloading the iBook educator's guide and the associated Transmedia book student guide are available at the resource link.

2013-05-06

214

Drawing Magnetic Fields  

NSDL National Science Digital Library

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

2014-09-18

215

Electricity and Magnetic Fields  

NSDL National Science Digital Library

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

VU Bioengineering RET Program,

216

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

217

Uniaxial in-plane magnetic anisotropy of a CoPt thin film induced by ion irradiation  

Microsoft Academic Search

The mechanism for ion-induced uniaxial magnetic anisotropy of ferromagnetic CoPt thin films is investigated using x-ray diffraction and soft x-ray emission spectroscopy. When Co\\/Pt multilayers 64 nm thick are irradiated with 80 keV Ar+ ions in an externally applied magnetic field, the magnetization of the ion-irradiated area shows a significant anisotropic angular dispersion in its hysteresis. Analysis of x-ray diffraction

G. S. Chang; A. Moewes; S. H. Kim; J. Lee; K. Jeong; C. N. Whang; D. H. Kim; S.-C. Shin

2006-01-01

218

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

219

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

220

Magnetic soliton transport over topological spin texture in chiral helimagnet with strong easy-plane anisotropy  

SciTech Connect

We show the existence of an isolated soliton excitation over the topological ground-state configuration in chiral helimagnet with the Dzyaloshinskii-Moryia exchange and the strong easy-plane anisotropy. The magnetic field perpendicular to the helical axis stabilizes the kink crystal state which plays a role of ''topological protectorate'' for the traveling soliton with a definite handedness. To find new soliton solution, we use the Baecklund transformation technique. It is pointed out that the traveling soliton carries the magnon density and a magnetic soliton transport may be realized.

Borisov, A. B. [Institute of Metal Physics, Ural Division, Russian Academy of Sciences, Ekaterinburg 620219 (Russian Federation); Kishine, Jun-ichiro [Department of Basic Sciences, Kyushu Institute of Technology, Kitakyushu 804-8550 (Japan); Bostrem, I. G.; Ovchinnikov, A. S. [Department of Physics, Ural State University, Ekaterinburg 620083 (Russian Federation)

2009-04-01

221

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

NASA Astrophysics Data System (ADS)

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

Kaplan, B.; Kaplan, R.

2014-04-01

222

Circuits and Magnetic Fields  

NSDL National Science Digital Library

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

VU Bioengineering RET Program,

223

Magnetic fields at Neptune  

Microsoft Academic Search

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

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

1989-01-01

224

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

225

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

226

Magnetic anisotropy engineering in in-plane magnetized ultrathin ferromagnetic films (invited)  

NASA Astrophysics Data System (ADS)

We have studied the effect of depositing submonolayer quantities of Cu onto the CO exposed Co/Cu(110) system at room temperature using the magneto-optic Kerr effect. Cu overlayers are found to completely reverse the in-plane 90° easy axis switch caused by the CO adsorption, for all Co thicknesses studied up to 40 ML. The Cu reverses the sign of the effective in-plane uniaxial anisotropy KUeff thereby switching the easy axis from the [1-10] to the [001] direction. Two modes of switching are observed depending on the magnitude of the cubic magnetocrystalline anisotropy constant K1 which is in turn dependent on the thickness of the Co films. For sufficiently thick Co films (dCo>15 ML), the easy axis is found to shift gradually from the [1-10] to the [001] direction due to the competition between the cubic and effective uniaxial anisotropy contributions. Therefore, we are able to controllably engineer the direction of the easy axis in this system as a function of Cu overlayer thickness. For thin Co films (dCu<15 ML) K1 tends to zero as revealed by BLS measurements of Hillebrands et al. and the easy axis switch is abrupt. We have engineered an experimental realization of an isotropic two-dimensional XY magnet by depositing submonolayer coverages of Cu onto a CO exposed 5 ML Co/Cu(110) film with a zero cubic anisotropy component K1 at room temperature. For a Cu coverage of 1.02 ML, the uniaxial anisotropy component vanishes also, and we observe a corresponding loss of ferromagnetic order at remanence. Further Cu deposition restores the uniaxial anisotropy and the magnetic order. Therefore we have directly observed the stabilization of ferromagnetic order by magnetic anisotropy in an ultrathin magnetic film, as theoretically predicted.

Bland, J. A. C.; Hope, S.; Choi, B.; Bode, P.

1999-04-01

227

O the Rotational Magnetic Processes and the Induced Anisotropy in Spin-Glass Alloys  

NASA Astrophysics Data System (ADS)

Measurements were made simultaneously of both the longitudinal and transverse components of the magnetization of field-cooled thin-disk, spin-glass samples of Ni-Mn, Cu-Mn and Au-Fe rotated in various fixed fields. For Ni -Mn and Cu-Mn at 4.2 K, the rotations of the magnetization (vec M_{rot}) are nearly reversible and indicate a predominantly unidirectional anisotropy (vec H_{K }) that turns rigidly with sample. Moreover, the changes in magnitude of M_{rm rot} with the sample rotation are seen to follow a universal curve as a function of an effective field that combines vectorially the anisotropy field and the applied magnetic field (vec H_{a}). At higher temperatures vec M_{rot} and vec H_{K} rotate irreversibly in the sample frame when the sample rotation angle exceeds a critical value above which they stay fixed relative to vec H_ {a}. In Au-Fe, the irreversible rotations of vec M_{rot} and vec H_{K } occur even at very low temperatures. It is deduced that vec H_{K } starts to turn relative to the sample when the torque on it, exerted by vec M_{rot}, exceeds the magnitude of a frictional torque exerted by the sample.

Alziq, Khalil Ali

228

Modifications in magnetic anisotropy of M—type strontium hexaferrite crystals by swift heavy ion irradiation.  

NASA Astrophysics Data System (ADS)

Using vibrating sample magnetometery (VSM) 50 MeV Li 3+ ion irradiation effects on magnetic properties of single crystals of SrGa xIn yFe 12-(x+y)O 19 (where x=0, 5, 7, 9; y=0, 0.8, 1.3, 1.0), are reported. The substitution of Ga and In in strontium hexaferrite crystals decreases the value of magnetization sharply, which is attributed to shifting of collinear magnetic order to a non-collinear one. Reduction of magnetization is also explained to be as a result of the occupation of the crystallographic sites of Fe 3+ by Ga 3+ and In 3+. The Li 3+ ion irradiation decreases the value of magnetization, irrespective of whether the crystals are Ga-In substituted or unsubstituted crystals of SrFe 12O 19. The result is interpreted in terms of the occurrence of a paramagnetic doublet in crystals replacing magnetic sextuplet as a result of irradiation. Substitution of Ga-In in Strontium hexaferrite decreases the value of anisotropy constant. Irradiation with Li 3+ ions increases the values of anisotropy field for both substituted as well as unsubstituted crystals. Substitution with Ga-In also decreases the Curie temperature ( Tc) but the irradiation with Li 3+ ions does not affect the curie temperature of either Ga-In substituted or pure SrFe 12O 19 crystals.

Kaur, Balwinder; Bhat, Monita; Licci, F.; Kumar, Ravi; Kulkarni, S. D.; Joy, P. A.; Bamzai, K. K.; Kotru, P. N.

2006-10-01

229

The First Magnetic Fields  

E-print Network

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 is 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 genera...

Widrow, Lawrence M; Schleicher, Dominik; Subramanian, Kandaswamy; Tsagas, Christos G; Treumann, Rudolf A

2011-01-01

230

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

SciTech Connect

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

Arranz, Miguel A. [Facultad de Ciencias Químicas, Universidad de Castilla-La Mancha, Avda. Camilo J. Cela 10, 13071 Ciudad Real (Spain); Colino, Jose M., E-mail: josemiguel.colino@uclm.es [Instituto de Nanociencia, Nanotecnología y Materiales Moleculares, Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, 45071 Toledo (Spain); Palomares, Francisco J. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, c/ Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain)

2014-05-14

231

Solar magnetic fields - Extended.  

NASA Technical Reports Server (NTRS)

Spacecraft observations of the interplanetary magnetic field have revealed that almost always each solar rotation can be divided into sectors, within each of which the field has a predominant polarity toward the sun or away from the sun. Comparisons of this interplanetary magnetic sector pattern with observations of the photospheric magnetic field have revealed a similar solar magnetic pattern. The boundaries between solar magnetic sectors are approximately in the north-south direction over a wide range of latitudes on both sides of the equator. This solar magnetic sector structure can be described as a rotating dipole whose magnetic axis makes an angle of approximately 90 deg with the axis of rotation. Possible similarities between this solar-sector magnetism and the models derived from observations of stellar magnetism are discussed.

Wilcox, J. M.

1971-01-01

232

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

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

233

Cyclic Magnetic Field Reconnection  

NASA Astrophysics Data System (ADS)

Using a 2.5D electromagnetic particle-in-cell model, we study the magnetic field reconnection around the rotating plasma embedded in a magnetic field. Considering plasma rotation driven by an external electric field, it was found that during one rotational cycle, first the magnetic field energy increases and then decreases to its initial value. The magnetic reconnection occurring during this cycle plays two roles: first, it produces the closed magnetic islands and later on it reopens them to the initial form of magnetic field lines. Thus, the magnetic reconnection can be cyclically repeated in following plasma rotations. Simultaneously, the kinetic particle energy in the system increases due to dissipative processes in this externally driven plasma system. We think that this cyclic reconnection can operate around rapidly rotating stars and in the plasma vortices formed in unstable plasma flows.

Karlický, Marian

2009-02-01

234

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

PubMed

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

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

2014-03-01

235

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

236

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

E-print Network

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

Utrecht, Universiteit

237

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

NASA Astrophysics Data System (ADS)

The influence of a gate voltage on magnetic anisotropy is investigated in a thin Fe film epitaxially grown on a Ag(1,1,10) substrate and covered by MgO. Oscillations in step-induced magnetic anisotropy due to quantum well states (QWS) confined in the Fe film are observed and shown to persist up to room temperature at low Fe thicknesses. By systematically examining the voltage and thickness dependence of the magnetic hysteresis loop characteristics, we identify two distinct effects by which an applied voltage modifies the magnetic anisotropy. The first effect is due to voltage-induced changes to interfacial perpendicular magnetic anisotropy which, due to the vicinal geometry, leads to changes in the effective in-plane uniaxial magnetic anisotropy. A second effect is observed at lower film thicknesses and shows nonmonotonic voltage-induced effects on magnetic anisotropy. This nonmonotonic behavior coincides with the onset of significant QWS-induced effects on magnetic anisotropy and suggests a link between QWS- and voltage-induced anisotropy changes.

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

2014-05-01

238

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

PubMed Central

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

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

2015-01-01

239

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

PubMed

The perpendicular magnetic anisotropy Keff, magnetization reversal, and field-driven domain wall velocity in the creep regime are modified in Pt/Co(0.85-1.0?nm)/Pt thin films by strain applied via piezoelectric transducers. Keff, measured by the extraordinary Hall effect, is reduced by 10?kJ/m(3) by tensile strain out-of-plane ?z = 9 × 10(-4), independently of the film thickness, indicating a dominant volume contribution to the magnetostriction. The same strain reduces the coercive field by 2-4?Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers. We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity. PMID:25605499

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

2015-01-01

240

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. PMID:23088782

2012-01-01

241

Excitation of Uniaxial-Anisotropy Relaxation Processes in Magnetic Films by a Rotating Magnetic Anneal  

Microsoft Academic Search

In hard-axis annealing studies of Permalloy films, which have revealed a number of discrete uniaxial-anisotropy relaxation processes, all processes are annealed simultaneously, making interpretation difficult and ambiguous. In this paper a new method is reported, in which individual processes are excited by a rotating magnetic anneal. Simple physical considerations show that the easy axes of only those processes with relaxation

K. J. Harte; D. O. Smith; R. M. Anderson; R. C. Johnston

1968-01-01

242

Uniaxial magnetic anisotropy of cobalt thin films on different substrates using CW-MOKE technique  

NASA Astrophysics Data System (ADS)

Cobalt thin films were deposited on GaAs, Si and Glass substrates by RF-magnetron sputtering. The structure was studied using atomic force microscopy, X-ray reflectivity and grazing incidence X-ray diffraction. Magnetic properties were determined with the magneto-optic Kerr effect. The deposited films have in-plane uniaxial anisotropy and after annealing the anisotropy reduces. The reduction in anisotropy may be due to release of stress and the remaining anisotropy after annealing may be due to shape anisotropy of the particulates.

Shukla, Vijay; Mukherjee, C.; Chari, R.; Rai, S.; Bindra, K. S.; Banerjee, A.

2014-12-01

243

Tuning the perpendicular magnetic anisotropy of co-based layers in multilayered systems.  

PubMed

The combination of Pt with Co either in alloy or in multilayer form is widely studied among the potential magnetic media for ultrahigh density magnetic recording. On the other hand the combination of Co with Cr in alloy form is currently providing commercial magnetic media. In an effort to further exploit and benefit from both systems, we fabricated Co(1-x)Cr(x)/Pt multilayers with two adjustable parameters. The first one is the Cr concentration on CoCr layer (x = 0, 5, 30), which modulates segregation effects on Co grains, thus tunes macroscopic magnetic features such as saturation magnetization and coercive field. The second one is the small layer thickness (< or = 0.6 nm) that affects interlayer coupling, perpendicular magnetic anisotropy and magnetization enhancement through spin polarization of Pt atoms in a ferromagnetic environment. The X-ray diffraction patterns verified the existence of multilayered structures following a preferable face-centered-cubic stacking. The Pt thickness and Cr concentration are found to significantly affect the macroscopic magnetic behavior. It is remarkable the fact that, samples present perpendicular anisotropy that scales with Pt thickness and temperature, even in the case of significant Cr concentration (30% in the alloy) when ferromagnetic behavior is expected to diminish according to relevant studies in alloys and in bulk films. Such an effect may be attributed to spin-polarization of Pt interlayers and was evidenced by X-ray magnetic circular dichroism. The spin-polarization of Pt is also the drive for the strong magneto-optic enhancement in the ultra-violet region between 4.5 and 5 eV shown by magnetooptic Kerr spectroscopy. PMID:21133152

Angelakeris, M; Papaioannou, E Th; Poulopoulos, P; Kopsidis, M; Kalogirou, O; Flevaris, N K

2010-09-01

244

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

245

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

NASA Astrophysics Data System (ADS)

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

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

2009-11-01

246

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

247

THE ROLE OF PRESSURE ANISOTROPY ON PARTICLE ACCELERATION DURING MAGNETIC RECONNECTION  

SciTech Connect

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

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

2013-02-20

248

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

249

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

250

The solar magnetic field  

Microsoft Academic Search

The magnetic field of the Sun is the underlying cause of the many diverse phenomena combined under the heading of solar activity. Here we describe the magnetic field as it threads its way from the bottom of the convection zone, where it is built up by the solar dynamo, to the solar surface, where it manifests itself in the form

Sami K. Solanki; Bernd Inhester; Manfred Schüssler

2006-01-01

251

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

SciTech Connect

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

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

2014-04-21

252

Magnetic anisotropy and evolution of ground-state domain structures in bcc Fe81Ni19/Co(001) superlattices  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy and evolution of striped magnetic domain structures in bcc Fe81Ni19/Co(001) superlattices with the total thickness ranging from 85 to 1370 nm has been studied by magneto-optical Kerr effect and magnetic force microscopy. At a thickness of about 85 nm [25 bilayers (BL)] the domains appear as stripe domains, typical for perpendicular anisotropy films, with the weak cubic anisotropy of the in-plane magnetization component stabilizing the stripe direction. The magnetic domain period strongly depends on the thickness of the superlattice. As the thickness increases, the equilibrium magnetization orients at oblique angles with respect to the film plane and continuously varies with the thickness from in-plane to out-of-plane. We first apply a simple phenomenological model which correctly predicts the transition from in-plane to out-of-plane magnetization as well as increasing domain period and saturation field with increasing BL number. The results indicate the presence of partial flux-closure domains at the film surface with the tilt angle continuously varying with the superlattice thickness. By solving a linearized Landau Lifshitz equation together with Maxwell’s equations in magnetostatic approximation for samples consisting of up to 1000 individual layers, we calculate the spin-wave dispersion and determine the stability conditions for the saturated ferromagnetic state. From these results the dependence of the saturation field on the number of layers is inferred and agrees well with the experiment. The uniaxial bulk anisotropy is attributed to distortions along the c axis and the results further show evidence for the presence of an easy-plane interface anisotropy in these samples.

Bru?as, R.; Hafermann, H.; Soroka, I. L.; Iu?an, D.; Sanyal, B.; Katsnelson, M. I.; Eriksson, O.; Hjörvarsson, B.

2008-07-01

253

Magnetic and geometric anisotropy in particle-crosslinked ferrohydrogels.  

PubMed

Particle-crosslinked polymer composites and gels have recently been shown to possess novel or improved properties due to a covalent particle-matrix interaction. We employ spindle-like hematite particles as exclusive crosslinkers in poly(acrylamide) gels, and exploit their extraordinary magnetic properties for the realization of ferrohydrogels with a perpendicular orientation of the preferred magnetic and geometric axes of the particles. The angle-dependent magnetic properties of uniaxially oriented gels are investigated and interpreted with respect to particle-matrix interactions. The impact of the particle orientation on the resulting angle-dependent magnetic performance reveals the presence of two different contributions to the magnetization: a hysteretic component ascribed to immobilized particles, and a pseudo-superparamagnetic, non-hysteretic component due to residual particle mobility. Furthermore, a plastic reorientation of magnetic particles in the matrix when subjected to a transversal field component is observed. PMID:25423114

Roeder, Lisa; Bender, Philipp; Kundt, Matthias; Tschöpe, Andreas; Schmidt, Annette M

2014-12-10

254

Interplanetary Magnetic Field Lines  

NSDL National Science Digital Library

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

Stern, David

2005-04-27

255

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

256

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

SciTech Connect

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

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

2014-10-21

257

The effect of anisotropy on the propagation of linear compressional waves in magnetic flux tubes: Applications to astrophysical plasmas  

NASA Astrophysics Data System (ADS)

The propagation of linear compressional waves is studied in magnetic flux tubes. The plasma inside and outside the tube is considered to be rarefied which confers an anisotropic character to the plasma. The anisotropy appears at different temperatures for parallel and perpendicular directions relative to the ambient magnetic field. The theoretical results are applied to study the effects of anisotropy and equilibrium steady flow on wave propagation in structures such as coronal plumes, the geomagnetic tail and anisotropic astrophysical jets. The obtained results show that the internal and/or external anisotropy has a very important effect on the propagation of linear compressional waves. The presence of a steady equilibrium flow in certain applications can change dramatically the propagation of the modes.

Ballai, I.; Marcu, A.

2004-02-01

258

The influence of phosphorus content on magnetic anisotropy in ferromagnetic (Ga, Mn) (As, P)/GaAs thin films  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy of the ferromagnetic semiconductor (Ga, Mn) (As, P) is studied in a material-specific microscopic k ?p approach. We calculate the electronic energy band structure of (Ga, Mn) (As, P) quaternary ferromagnetic alloys using a 40-band k ?p model and taking into account the s, p-d exchange interaction and the strain of the (Ga, Mn) (As, P) layer on a GaAs substrate. We determine the variations of the carrier effective masses in the strained (Ga, Mn) (As, P)/GaAs system. The magnetic anisotropy constants obtained from our simulations using a mean-field model are compared with the experimental ones determined by ferromagnetic resonance spectroscopy on a set of samples with constant manganese concentration and varying phosphorus concentration. An excellent quantitative agreement between experiment and theory is found for the uniaxial out-of-plane and cubic in-plane anisotropy parameters.

Yahyaoui, M.; Boujdaria, K.; Cubukcu, M.; Testelin, C.; Gourdon, C.

2013-08-01

259

Anisotropy of magnetic susceptibility of URu2Si2 under pressure  

NASA Astrophysics Data System (ADS)

We have carried out measurements of magnetic susceptibility on a single crystal of the heavy fermion compound URu2Si2 under pressure up to 0.7 GPa. The external magnetic fields were applied parallel to a- and c-axes. Hidden order transition at T0 and first-order phase transition between hidden ordered phase and large-staggered-moment antiferromagnetic phase at TM are observable in both measurements. Temperature dependence of magnetic susceptibility of a- and c-axes exhibits a kink and a drop at T0 and TM, respectively. However, the magnitude of the variation on a-axis at T0 and TM were about one tenth of those on c-axis, respectively. We conclude that the HO phase has a similar anisotropy to that of AFM phase.

Motoyama, Gaku; Sakai, Hideki; Yamaguchi, Akira; Sumiyama, Akihiko; Oda, Yasukage

2011-01-01

260

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

SciTech Connect

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

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

2014-02-15

261

Solar polar magnetic field  

NASA Astrophysics Data System (ADS)

The solar polar magnetic field has attracted the attention of researchers since the polar magnetic field reversal was revealed in the middle of the last century (Babcock and Livingston, 1958). The polar magnetic field has regularly reversed because the magnetic flux is transported from the sunspot formation zone owing to differential rotation, meridional circulation, and turbulent diffusion. However, modeling of these processes leads to ambiguous conclusions, as a result of which it is sometimes unclear whether a transport model is actual. Thus, according to the last Hinode data, the problem of a standard transport model (Shiota et al., 2012) consists in that a decrease in the polar magnetic flux in the Southern Hemisphere lags behind such a decrease in the flux in the Northern Hemisphere (from 2008 to June 2012). On the other hand, Svalgaard and Kamide (2012) consider that the asymmetry in the sign reversal simply results from the asymmetry in the emerging flux in the sunspot formation region. A detailed study of the polar magnetic flux evolution according to the Solar Dynamics Observatory (SDO) data for May 2010-December 2012 is illustrated in the present work. Helioseismic & Magnetic Imager (HMI) magnetic data in the form of a magnetic field component along the line of sight (the time resolution is 720 s) are used here. The magnetic fluxes in sunspot formation regions and at high latitudes have been compared.

Benevolenskaya, E. E.

2013-12-01

262

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

263

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

264

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

265

Control of the spin relaxation and magnetic anisotropy in Iron 1-x Gallium x / Zinc selenide systems  

NASA Astrophysics Data System (ADS)

Magnetostrictive materials will deform under application of a magnetic field. They can be deposited onto various substrates for engineering multifunctional materials, such as integrated micro actuators and multiferroric materials. In this dissertation clamping of a magnetostrive material onto a substrate is demonstrated to give control of the magnetic anisotropy and spin relaxation, to serve as a device with tunable spin relaxation, which uses magnetic field to change the strain and affect the relaxation. The purpose of this thesis is to use ferromagnetic resonance to investigate the interface effects (chemical bonding, interface strain...) on the magnetic anisotropy properties and the magnetic moment relaxation of Fe1-xGax /ZnSe for different Ga doping. Fe1-xGax has been deposited on ZnSe(001) and ZnSe(110) surfaces. The growth was epitaxial and the crystal axes are perfectly aligned. Angular ferromagnetic resonance in the X-band (9.4 GHz) and Q-band (34.6 GHz) have been done on samples for a veriety of Ga concentrations and thicknesses. The anisotropies for Fe1-xGax/ZnSe are found to be composed of a cubic term, an in-plane uniaxial term, and the out-of-plane uniaxial term. The in-plane uniaxial term changes its magnitude and direction with Ga doping while the cubic anisotropy term follows the same trend as the bulk material. The direction switch of the uniaxial anisotropy and the field dependence of the uniaxial term indicated that the uniaxial term is generated from anisotropic strain relaxation.

Li, Hongyan

266

Uniaxial in-plane magnetic anisotropy of a CoPt thin film induced by ion irradiation  

SciTech Connect

The mechanism for ion-induced uniaxial magnetic anisotropy of ferromagnetic CoPt thin films is investigated using x-ray diffraction and soft x-ray emission spectroscopy. When Co/Pt multilayers 64 nm thick are irradiated with 80 keV Ar{sup +} ions in an externally applied magnetic field, the magnetization of the ion-irradiated area shows a significant anisotropic angular dispersion in its hysteresis. Analysis of x-ray diffraction patterns and Co L{sub 3} emission spectra reveals that the formation of partially ordered (face-centered-tetragonal) CoPt phase and nonequivalent electronic hybridization between easy and hard axes causes the induction of a uniaxial magnetic anisotropy.

Chang, G.S.; Moewes, A.; Kim, S.H.; Lee, J.; Jeong, K.; Whang, C.N.; Kim, D.H.; Shin, S.-C. [Department of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SK 57N 5E2 (Canada); Institute of Physics and Applied Physics, Yonsei University, 134 Shinchon-dong Sudaemoon-ku, Seoul 120-749 (Korea, Republic of); Department of Physics and Center for Nanospinics of Spintronic Materials, Korea Advanced Institute of Science and Technology, Taejon 305-701 (Korea, Republic of)

2006-02-27

267

Detecting Exoplanetary Magnetic Fields  

NASA Astrophysics Data System (ADS)

Asymmetries in exoplanet transits are proving to be a useful tool for furthering our understanding of magnetic activity on both stars and planets outside our Solar System.Near-UV observations of the WASP-12 system have revealed asymmetries in the timing of the transit when compared with the optical light curve. A number of possible explanations have been suggested for this variation, including the presence of a magnetospheric bow shock arising from the interaction of the planet's magnetic field with the stellar wind from it's host star. Such observations provide the first method for directly detecting the presence of a magnetic field on exoplanets.The shape and size of such asymmetries is highly dependent on the structure of the host stars magnetic field at the time of observation. This implies we may observe highly varying near-UV transit light curves for the same system. These variations can then be used to learn about the geometry of the host star's magnetic field.In this presentation I will show modelling a bow shock around an exoplanet can help us to not only detect, but also also place constraints on the magnetic field strength of hot Jupiters. For some systems, such as HD 189733, we have maps of the surface magnetic field of the star at various epochs. I will also show how incorporating these maps into a stellar wind model, I can model the formation of a bow shock around the planet and hence demonstrate the variability of the near-UV transits.

Llama, Joe

2015-01-01

268

Eruptive solar magnetic fields  

Microsoft Academic Search

This paper considers the quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes. Special interest is taken in the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates has been treated previously, and we extend it to a field which is not force free

B. C. Low

1981-01-01

269

Competing magnetic anisotropies in an AFM-FM-AFM trilayer  

SciTech Connect

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

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

2009-08-01

270

Mapping Magnetic Field Lines  

NSDL National Science Digital Library

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

271

Diffusion of charged particles in a random magnetic field  

NASA Technical Reports Server (NTRS)

When charged particles move in a random magnetic field superimposed upon a relatively large constant field, their pitch angle distribution can be calculated to any desired precision by an iterative approximation procedure. Improved knowledge of the pitch angle distribution and of the characteristic time for relaxation of anisotropy leads to an accurate expression for the coefficient of diffusion parallel to the mean field.

Earl, J. A.

1972-01-01

272

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

E-print Network

O · (distorted) rock-salt (rs) structure Andreas Schrön, Claudia Rödl, and Friedhelm Bechstedt #12;Crystalline Anisotropy Magnetic Anisotropy Introduction · MnO, FeO, CoO, and NiO · (distorted) rock-salt (rs) structure) rock-salt (rs) structure · antiferromagnetic ordering AF2 interesting benchmark materials · series

Rossak, Wilhelm R.

273

Origin of uniaxial in-plane magnetic anisotropy in Fe 81Ni 19/Co superlattices  

NASA Astrophysics Data System (ADS)

We have studied the in-plane magnetic uniaxial anisotropy, for (0 0 1) -oriented Fe 81Ni 19/Co superlattices grown on MgO (0 0 1) by magnetron sputtering. The layers in the superlattices have a BCC structure with a slight orthorhombic distortion, which gives rise to a weak in-plane uniaxial anisotropy.

Soroka, I. L.; Hjörvarsson, B.

2004-05-01

274

Bulk Properties of a Fermi Gas in a Magnetic Field  

E-print Network

We calculate the number density, energy density, transverse pressure, longitudinal pressure, and magnetization of an ensemble of spin one-half particles in the presence of a homogenous background magnetic field. The magnetic field direction breaks spherical symmetry causing the pressure transverse to the magnetic field direction to be different than the pressure parallel to it. We present explicit formulae appropriate at zero and finite temperature for both charged and uncharged particles including the effect of the anomalous magnetic moment. We demonstrate that the resulting expressions satisfy the canonical relations, Omega = - P_parallel and P_perp = P_parallel - M B, with M = - d Omega/d B being the magnetization of the system. We numerically calculate the resulting pressure anisotropy for a gas of protons and a gas of neutrons and demonstrate that the inclusion of the anomalous magnetic increases the level of pressure anisotropy in both cases.

Michael Strickland; Veronica Dexheimer; Debora P. Menezes

2012-09-14

275

Faraday rotation and magnetic properties of erbium gallium gallate under high magnetic field  

NASA Astrophysics Data System (ADS)

Magnetization (M) and Faraday rotation (FR) have been measured in Er3Ga5O12 single crystals in the 4.2-300 K temperature range under high dc magnetic field up to 300 kOe. Experimental data are reported for H applied parallel to the [111] and [100] directions at 633 and 550 nm wavelength. A strong anisotropy of both magneto-optical and magnetic properties is observed. At low temperature, FR and M are proportional only when the magnetization is weak (small magnetic field). In medium and high magnetic field, complex relationships between M and FR are found. The magnetization cannot account for the whole Faraday rotation anisotropy. These data are discussed taking into account the magnetic and magneto-optical properties of the isomorphous erbium iron garnet ferrite.

Guillot, M.; Schmiedel, T.; Xu, You

1998-06-01

276

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

277

Solar magnetic fields  

Microsoft Academic Search

Since the structuring and variability of the Sun and other stars are governed by magnetic fields, much of present-day stellar\\u000a physics centers around the measurement and understanding of the magnetic fields and their interactions. The Sun, being a prototypical\\u000a star, plays a unique role in astrophysics, since its proximity allows the fundamental processes to be explored in detail.\\u000a The PRL

J. O. Stenflo

2008-01-01

278

Solar magnetic fields  

Microsoft Academic Search

This paper is a review of our observational knowledge on solar magnetic fields. In Section 1 we make an attempt to summarize all observations of the general magnetic field (m.f.) of the Sun. Section 2 deals with the local m.f. at low latitudes and their connection with some features on the disk. The m.f. of sunspots and their peculiar character

A. Severny

1964-01-01

279

Limitations of tensor subtraction in isolating diamagnetic fabrics by magnetic anisotropy  

NASA Astrophysics Data System (ADS)

The anisotropy of low field susceptibility (AMS) represents the orientation distribution of all minerals in a rock, whereas the anisotropy of magnetic remanence (AMR, preferably anhysteretic) isolates that of the accessory remanence-bearing minerals. The subtraction of normalized AMR from AMS, in theory and under limited practical circumstances, may isolate the paramagnetic+diamagnetic anisotropy contribution and thus the orientation distribution of the matrix minerals ( Borradaile et al., 1999. Geol. Soc. Lond., Sp. Publ. 151, 139-145). Limitations include the great sensitivity of the subtraction process to the precision of the definition of the respective (AMS, AMR) tensors, and a requirement that single-domain and superparamagnetic grains are absent. The latter is particularly important for superparamagnetic minerals because iron oxides may be part of the orientation distribution of the main group of remanence-bearing minerals, although they would be excluded from the AMR fabric. Low ratios of saturation isothermal remanence to induced susceptibility characterize those rare rocks in which superparamagnetic behavior is a significant contribution.

Hrouda, František; Henry, Bernard; Borradaile, Graham

2000-07-01

280

Dynamic optical probing of the magnetic anisotropy of nickelferrite nanoparticles  

Microsoft Academic Search

Field dependence of dynamic magneto-orientational birefringence in a ferrocolloid based on the nickel-ferrite nanoparticles is examined. The nanoparticles are electrostatically stabilized and suspended in glycerin at low-volume fractions Phi<=0.75%. The colloids are tested under crossed magnetic fields: an alternating weak (probing) and a constant strong (bias) one. By comparison to a theoretical model of the birefringence relaxation, an evaluation of

Yu. L. Raikher; V. I. Stepanov; J. Depeyrot; M. H. Sousa; F. A. Tourinho; E. Hasmonay; R. Perzynski

2004-01-01

281

Competition between cubic and uniaxial magnetic anisotropy in GaMnAs at low Mn concentrations  

NASA Astrophysics Data System (ADS)

We study the dependence of the cubic and uniaxial magnetic anisotropy terms in GaMnAs on hole concentration p and temperature T. The Ga0.99Mn0.01As layers were grown on ZnSe buffers deposited on GaAs substrates, and co-doped by Be in the range 3.0x10^19 < p < 8.5x10^19 cm-3. Due to small lattice mismatch the uniaxial and cubic anisotropy terms in these samples were comparable. The magnetic anisotropy was studied by polar magneto-optical Kerr effect, which allowed us to monitor the easy axis of magnetization. The results showed that the cubic anisotropy is highly sensitive to both p and T. Specifically, in samples with high p the cubic anisotropy term is dominant at low T, but decreases rapidly as T increases. In sharp contrast, uniaxial anisotropy shows a much weaker dependence on p and T, thus dominating at temperatures close to TC even in samples with high p. These results open the possibility of engineering magnetic anisotropy and the magnetization reversal process in GaMnAs by controlling T and/or p.

Titova, L. V.

2005-03-01

282

Anisotropy of the sublattice magnetization and magnetoresistance in Co/Re superlattices on Al2O3,,112 0...  

E-print Network

Anisotropy of the sublattice magnetization and magnetoresistance in Co/Re superlattices on Al2O3Oe. The anisotropy of the sublattice magnetization is related to the anisotropy of the magnetoresistance. This has manufactures began to use magnetoresistive read/write heads to increase the bit den- sity in hard disk drives

Lederman, David

283

Experimental and theoretical investigations of the magnetic susceptibility and anisotropy of Nd(OH)3  

NASA Astrophysics Data System (ADS)

Measurements are reported on the magnetic susceptibilities and anisotropies of single crystals of Nd(OH)3 in the temperature range between 300 and 77 K. The intermediate-coupling scheme with J mixing under the crystal field of C3h symmetry is used to obtain the crystal-field energy levels and their eigenfunctions. Matrix elements of the Coulomb, spin-orbit, and crystal-field interactions within the f3 configuration are calculated. The g values are found to be g=3.65+/-0.01 and g?=1.95+/-0.01 in close agreement with the experimental values quoted by P. D. Scott (Ph.D. dissertation, Yale University, 1970). The calculated crystal-field splitting explains successfully the temperature dependence of the specific heat as observed by Chirico and Westrum [J. Chem. Thermodyn. 12, 311 (1980)] in the temperature range between 350 and 20 K. Saturated magnetizations parallel and perpendicular to the applied magnetic field are found to be 271 and 145 emu/cm3, respectively.

Karmakar, S.

1985-08-01

284

Magnetic anisotropy of Co /Cu (111) superlattices: calculation and experiment  

NASA Astrophysics Data System (ADS)

The results of theoretical calculations and experimental data for the effective magnetic anisotropy Keff (obtained from ferromagnetic resonance measurements) of [Co(8width="0.3em"/>Å)/Cu(dCu)]20 (dCu=7-22Å) superlattices with a coherent interaction of the Co and Cu layers prepared by magnetron sputtering are presented. The experimental values of Keff are an oscillatory function of the thickness dCu interlayers. The computed and experimentally measured dependences Keff(dCu) are qualitatively similar; stable growth of the parameter Keff with increasing thickness of the nonmagnetic layers is observed (against the background of oscillations of the experimental curve), which is a direct consequence of the growth of axial distortions of the initial cubic structure of cobalt under the conditions of pseudomorphism. The reasons for the appearance of oscillations of Keff are discussed; the main one is the oscillatory behavior of the roughness of the interfaces of the layers with increasing dCu, resulting in synchronous oscillations of Keff, resistivity, magnetoresistance, and the ferromagnetic resonance linewidth.

Kut'ko, K. V.; Kaplienko, A. I.; Nikolova, É. P.; Anders, A. G.; Zorchenko, V. V.; Stetsenko, A. N.; Kaj?akova, M.

2009-11-01

285

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

286

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

E-print Network

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

Bi, Lei

287

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

288

High-Resolution SQUID imaging of Magnetic Fields Generated by Propagating Cardiac Action Currents  

Microsoft Academic Search

The heart's magnetic field is exquisitely sensitive to anisotropy ratios in the cardiac bidomain model; Therefore, magnetic imaging of cardiac action currents is an ideally suited technique for testing the accuracy of cardiac models and elucidating the effects of anisotropy in the spread of stimulus and action currents. We mapped the magnetocardiogram (MCG) as a function of position over a

Jenny R. Holzer; Veniamin Sidorov; Luis Fong; Nicholas Peters; Petra Baudenbacher; Franz Baudenbacher

2004-01-01

289

Magnetic Field Problem: Current  

NSDL National Science Digital Library

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

Wolfgang Christian

290

Magnetic Field Solver  

NASA Technical Reports Server (NTRS)

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

Ilin, Andrew V.

2006-01-01

291

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

292

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

293

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

294

Probing boundary magnetization through exchange bias in heterostructures with competing anisotropy  

NASA Astrophysics Data System (ADS)

Cr2O3 (chromia) is a magnetoelectric antiferromagnet with a bulk TN of 307 K. It has been utilized for electrically controlled exchange bias (EB) by taking advantage of voltage-controllable boundary magnetization (BM) occurring as a generic property in magnetoelectric single domain antiferromagnets.footnotetextXi He, et al., Nature Mater.9, 579-585 (2010) In the perpendicular Cr2O3(0001)/CoPd EB system the EB-field shows an order parameter type T-dependence close to TN reflecting the T-dependence of the BM. At about 150 K a decrease of the EB-field sets in with decreasing temperature suggesting canting of the BM. To evidence this mechanism we use EB as a probe. Specifically, we investigate EB in Permalloy(5nm)/Cr2O3 (0001)(100nm) with Permalloy and chromia having competing anisotropies. We measure easy axis magnetic hysteresis loops via longitudinal magneto-optical Kerr effect for various temperatures after perpendicular and in-plane magnetic field-cooling. The T-dependence of the EB field supports the canting mechanism. In addition to the all thin film EB system, we explore a Permalloy(10nm)/Cr2O3(0001 single crystal) heterostructure where magnetoelectric annealing allows selecting Cr2O3 single domain states. Here the effect of T-dependent canting of the BM is compared with findings in the complementary perpendicular EB system.

Wang, Yi; Binek, Christian

2013-03-01

295

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

PubMed

The effect of the lattice strain on magnetic anisotropy of alternately layered FeNi ultrathin films grown on a substrate, Cu(tCu = 0-70 ML)/Ni(48)Cu(52)(124 ML)/Cu(0 0 1) single crystal, is systematically studied by means of in situ x-ray magnetic circular dichroism (XMCD) and reflection high-energy electron diffraction (RHEED) analyses. To investigate the magnetic anisotropy of the FeNi layer itself, a non-magnetic substrate is adopted. From the RHEED analysis, the in-plane lattice constant, ain, of the substrate is found to shrink by 0.8% and 0.5% at tCu = 0 and 10 ML as compared to that of bulk Cu, respectively. Fe L-edge XMCD analysis is performed for n ML FeNi films grown on various ain, and perpendicular magnetic anisotropy (PMA) is observed at n = 3 and 5, whereas the film with n = 7 shows in-plane magnetic anisotropy. Moreover, it is found that PMA is enhanced with decreasing ain, in the case where a Cu spacer layer is inserted. We suppose that magnetic anisotropy in the FeNi films is mainly carried by Fe, and the delocalization of the in-plane orbitals near the Fermi level increases the perpendicular orbital magnetic moment, which leads to the enhancement of PMA. PMID:24695244

Sakamaki, M; Amemiya, K

2014-04-23

296

Solid-State Carbon-13 Nuclear Magnetic Resonance of Humic Acids at High Magnetic Field Strengths  

E-print Network

for cross state 13 C NMR spectra obtained with modern high-field spectrometers, polarization (CP). Similarly magnetic resonance (NMR) spectros- 1 H, 25 MHz 13 C) and low sample reorientation frequen-copy has become NMR spectra of humic acids at high magnetic width of the chemical shift anisotropy (CSA

Hemminga, Marcus A.

297

Determination of the magnetic anisotropy constant of Cu/Fe/SiO2/Si by a magneto-optical Kerr effect susceptometer  

NASA Astrophysics Data System (ADS)

The magneto-optical Kerr effect susceptometry technique is proposed to determine the uniaxial magnetic anisotropy (UMA) constant Ku. The magnetic properties of Cu/Fe/SiO2/Si grown by dc magnetron sputtering were investigated. The in-plane uniaxial magnetic anisotropy was probed by the magneto-optical Kerr effect (MOKE). The value of UMA, Ku = 2.5 ×103 J/m3, was simulated from the field dependence of ac susceptibility along the hard axis according to the Stoner—Wohlfarth (S—W) model, which is consistent with Ku = 2.7 × 103 J/m3 calculated from the magnetic hysteresis loops. Our results show that the magneto-optical Kerr effect susceptometry can be employed to determine the magnetic anisotropy constant owing to its high sensitivity.

Jia, Yi-Jiao; He, Wei; Ye, Jun; Hu, Bo; Chen, Zi-Yu; Gao, You-Hui; Zhang, Xiang-Qun; Yang, Hai-Tao; Cheng, Zhao-Hua

2014-01-01

298

Parametric Excitation of Spin Waves by Voltage-Controlled Magnetic Anisotropy  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

299

Magnetic Fluctuation Power Near Proton Temperature Anisotropy Instability Thresholds in the Solar Wind  

SciTech Connect

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

Bale, S. D. [Physics Department and Space Sciences Laboratory, University of California, Berkeley, California (United States); Kasper, J. C. [Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts (United States); Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa (United States); Quataert, E. [Physics Department and Astronomy Department, University of California, Berkeley, California (United States); Salem, C.; Sundkvist, D. [Space Sciences Laboratory, University of California, Berkeley, California (United States)

2009-11-20

300

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

PubMed

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

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

2009-11-20

301

Electrically silent magnetic fields.  

PubMed Central

There has been a significant controversy over the past decade regarding the relative information content of bioelectric and biomagnetic signals. In this paper we present a new, theoretical example of an electrically-silent magnetic field, based on a bidomain model of a cylindrical strand of tissue generalized to include off-diagonal components in the conductivity tensors. The physical interpretation of the off-diagonal components is explained, and analytic expressions for the electrical potential and the magnetic field are found. These expressions show that information not obtainable from electrical potential measurements can be obtained from measurements of the magnetic field in systems with conductivity tensors more complicated than those previously examined. PMID:3779008

Roth, B J; Wikswo, J P

1986-01-01

302

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

303

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

304

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

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

Beck, Rainer

305

Sixfold configurational anisotropy and magnetic reversal in nanoscale Permalloy triangles  

Microsoft Academic Search

Six-fold configurational anisotropy was studied in Permalloy triangles, in\\u000awhich the shape symmetry order yields two energetically non-degenerate\\u000amicromagnetic configurations of the spins, the so-called \\

Laura Thevenard; Dorothee Petit; Huang T. Zeng; Russell P. Cowburn

2009-01-01

306

Solar magnetic fields and convection. IX - A primordial magnetic field  

Microsoft Academic Search

Observational evidence is reviewed in an attempt to decide between a reversing (dynamo) and a nonreversing primordial solar poloidal magnetic field. The data examined include Zeeman-effect measurements, measurements of gross magnetic fluxes in individual magnetic elements, determinations of average field strength, observations of polar-cap magnetic fields, eclipse observations of coronal structure, and observations of interplanetary-magnetic-field polarity reversals. It is suggested

J. H. Piddington

1977-01-01

307

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

308

Designing magnets with prescribed magnetic fields  

NASA Astrophysics Data System (ADS)

We present a novel design method capable of finding the magnetization densities that generate prescribed magnetic fields. The method is based on the solution to a simple variational inequality and the resulting designs have simple piecewise-constant magnetization densities. By this method, we obtain new designs of magnets that generate commonly used magnetic fields: uniform magnetic fields, self-shielding fields, quadrupole fields and sextupole fields. Further, it is worth noting that this method is not limited to the presented examples, and in particular, three-dimensional designs can be constructed in a similar manner. In conclusion, this novel design method is anticipated to have broad applications where specific magnetic fields are important for the performance of the devices.

Liu, Liping

2011-03-01

309

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

SciTech Connect

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

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

2012-03-29

310

The existence of cosmic ray sidereal anisotropies of galactic and solar origins with energies lower than 104 GeV and their modulation caused by the presumed behavior pattern of the heliomagnetosphere and of its neighboring gaseous matter in interstellar magnetic field  

NASA Astrophysics Data System (ADS)

It is shown that the sidereal anisotropy (SiA) of cosmic rays (CRs) with energies smaller than 104 GeV consists of three kinds: one (GA) is of galactic origin from the direction ?G (?G = 0 hr; ?G = -20°), and the other two (tail-in TA and nose-in HA) are of solar origin from the respective directions ?T (?T = 6 hr; ?T ˜ -24°) and ?H (?H = 18 hr; ?H > 0°) and supposed to be produced by the acceleration of Crs on the tail and nose boundaries of the heliomagnetosphere (HMS). This conclusion was arrived at in 1995 after a long-term delay since the beginning of CR observations in the early 20-th century. This delay was mainly due to the inconsistency among observations caused by the belief that the sidereal anisotropy must be unidirectional in space. The inconsistency has been solved at least qualitatively by the discovery of GA and TA. These anisotropies, including also HA, are subject, respectively, to their proper solar modulations in the HMS characterized by a polarity reversal every 11 years of the solar polar magnetic field and solar activity dependence with an 11-year periodicity. By using these modulation patterns, the origins of the three anisotropies have been determined. TA and HA thus determined inversely produce the following kinds of evidence and problems in the HMS: (1) the structure of the HMS, (2) acceleration of CRs on the boundary of the HMS, (3) CR Lens Effect of the HMS for the sharp concentration of TA and HA, (4) the proper motion (VHMS) of the HMS relative to neighboring stars, (5) the proper motion of interstellar gaseous matter (including the magnetic field) relative to neighboring stars, and (6) the existence of the Subordinate HMS surrounding the HMS for the explanation of the duality of the motion of the HMS and also of the absence of the Compton-Getting (C-G) effect on the HMS. The present paper not only presents a brief summary of the studies of CR sidereal anisotropy made by many researchers during the 20th century leading to the present understanding, but also presents some problems to open up a new vista of the future.

Nagashima, K.; Morishita, I.; Fujii, Z.; Mori, S.; Kondo, I.; Jacklyn, R. M.

2012-07-01

311

High field superconducting magnets  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

312

Magnetic-field-modulated Kondo effect in a single-magnetic-ion molecule  

NASA Astrophysics Data System (ADS)

We study numerically the low-temperature electronic transport properties of a single-ion magnet with uniaxial and transverse spin anisotropies. We find clear signatures of a Kondo effect caused by the presence of a transverse (zero-field) anisotropy in the molecule. This Kondo effect has an SU(2) pseudospin character, associated with a doublet ground state of the isolated molecule, which results from the transverse anisotropy. Upon applying a transverse magnetic field to the single-ion magnet, we observe oscillations of the Kondo effect due to the presence of diabolical points (degeneracies) of the energy spectrum of the molecule caused by geometrical phase interference effects, similar to those observed in the quantum tunneling of multi-ion molecular nanomagnets. The field-induced lifting of the ground-state degeneracy competes with the interference modulation, resulting in some cases in a suppression of the Kondo peak.

Romero, Javier I.; Vernek, E.; Martins, G. B.; Mucciolo, E. R.

2014-11-01

313

Magnetic phase diagram of the low-anisotropy antiferromagnet Cs2FeCl5·H2O  

NASA Astrophysics Data System (ADS)

From magnetization and ac susceptibility measurements we obtain the complete magnetic phase diagram of single crystals of Cs2FeCl5·H2O for magnetic field up to 15 T. The magnetic field was applied along the directions parallel and perpendicular to the easy axis and the magnetization measured to temperatures down to 0.5 K. At zero magnetic field the antiferromagnetic ordering occurs at TN=6.63 K. For the field applied parallel to the easy axis the antiferromagnetic (AF) to the spin-flop (SF) transition occurs for fields from 1.4 T to 1.1 T depending on the temperature. The low temperature transition from the (SF) to the paramagnetic (P) phase occurs at 13.15 T. In the perpendicular configuration this transition occurs at fields around 13.5 T. From the extrapolation of the transition fields to zero temperature, we obtain a ratio of the anisotropy field HA to exchange field HE, ?=HA/HE=(1.4±0.2)×10-2. A comparison with the phase diagram measured for MnF2 is included.

Freitas, R. S.; Paduan-Filho, A.; Becerra, C. C.

2015-01-01

314

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

315

Magnetic anisotropy and magnetostriction in nanocrystalline Fe-Al alloys obtained by melt spinning technique  

NASA Astrophysics Data System (ADS)

A study about the magnetic anisotropy and magnetostriction in ribbons of composition Fe81Al19 and Fe70Al30 obtained by the melt spinning technique is presented. The hysteresis loops indicate that the easy magnetization direction lies in both cases on the plane of the ribbon. Torque magnetometry measurements show that the in-plane magnetic anisotropy constant results 10100 J m-3 and 490 J m-3 for the Fe81Al19 and Fe70Al30 respectively. After a thermal treatment of 2 h at 473 K to remove the residual stresses, the in-plane magnetic anisotropy constants falls down to 2500 J m-3 in the first composition and remains the same in the second one, while the easy direction remains the same. Measurements of the magnetostriction and the residual stresses of both ribbons allow us to explain the above mentioned results about the magnetic anisotropy and to conclude that the residual stresses via magnetostriction are the main source of magnetic anisotropy in the case of Fe81Al19 ribbon but they do not influence this property in the ribbon of composition Fe70Al30.

García, J. A.; Carrizo, J.; Elbaile, L.; Lago-Cachón, D.; Rivas, M.; Castrillo, D.; Pierna, A. R.

2014-12-01

316

Nuclear Magnetic Resonance and Magnetic Field Measurements  

NSDL National Science Digital Library

This laboratory is designed for students to become familiar with the principles and detection techniques of Nuclear Magnetic Resonance (NMR), examine the relationship between current and magnetic field in an electromagnet, and gain experience in the use of magnetic field measurement techniques.

2012-01-04

317

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

318

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

319

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

SciTech Connect

Nickel (Ni) based nanoparticles and nanochains were incorporated as fillers in polydimethylsiloxane (PDMS) elastomers and then these mixtures were thermally cured in the presence of a uniform magnetic field. In this way, macroscopically structured-anisotropic PDMS-Ni based magnetorheological composites were obtained with the formation of pseudo-chains-like structures (referred as needles) oriented in the direction of the applied magnetic field when curing. Nanoparticles were synthesized at room temperature, under air ambient atmosphere (open air, atmospheric pressure) and then calcined at 400?°C (in air atmosphere also). The size distribution was obtained by fitting Small Angle X-ray Scattering (SAXS) experiments with a polydisperse hard spheres model and a Schulz-Zimm distribution, obtaining a size distribution centered at (10.0?±?0.6) nm with polydispersivity given by ??=?(8.0?±?0.2) nm. The SAXS, X-ray powder diffraction, and Transmission Electron Microscope (TEM) experiments are consistent with single crystal nanoparticles of spherical shape (average particle diameter obtained by TEM: (12?±?1) nm). Nickel-based nanochains (average diameter: 360?nm; average length: 3??m, obtained by Scanning Electron Microscopy; aspect ratio?=?length/diameter ? 10) were obtained at 85?°C and ambient atmosphere (open air, atmospheric pressure). The magnetic properties of Ni-based nanoparticles and nanochains at room temperature are compared and discussed in terms of surface and size effects. Both Ni-based nanoparticles and nanochains were used as fillers for obtaining the PDMS structured magnetorheological composites, observing the presence of oriented needles. Magnetization curves, ferromagnetic resonance (FMR) spectra, and strain-stress curves of low filler's loading composites (2% w/w of fillers) were determined as functions of the relative orientation with respect to the needles. The results indicate that even at low loadings it is possible to obtain magnetorheological composites with anisotropic properties, with larger anisotropy when using nanochains. For instance, the magnetic remanence, the FMR field, and the elastic response to compression are higher when measured parallel to the needles (about 30% with nanochains as fillers). Analogously, the elastic response is also anisotropic, with larger anisotropy when using nanochains as fillers. Therefore, all experiments performed confirm the high potential of nickel nanochains to induce anisotropic effects in magnetorheological materials.

Landa, Romina A.; Soledad Antonel, Paula; Ruiz, Mariano M.; Negri, R. Martín, E-mail: rmn@qi.fcen.uba.ar [Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales, Instituto de Química Física de Materiales, Ambiente y Energía (INQUIMAE), Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, C1428EGA Buenos Aires (Argentina); Perez, Oscar E. [Departamento de Industrias, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Butera, Alejandro [Centro Atómico Bariloche (Comisión Nacional de Energía Atómica. Argentina) and Instituto Balseiro, Universidad Nacional de Cuyo, Mendoza (Argentina); Jorge, Guillermo [Instituto de Ciencias, Universidad Nacional de General Sarmiento, Buenos Aires (Argentina); Oliveira, Cristiano L. P. [Grupo de Fluidos Complexos, Instituto de Física, Universidade de São Paulo, São Paulo (Brazil)

2013-12-07

320

Fabrication of tunable Janus microspheres with dual anisotropy of porosity and magnetism.  

PubMed

This work presents a facile approach to produce a novel type of Janus microspheres with dual anisotropy of porosity and magnetism based on Pickering-type double emulsion templates. A stable aqueous Fe3O4 dispersion-in-oil-in-water (WF/O/W) double Pickering emulsion is first generated by using hydrophobic silica and hydrophilic mesoporous silica particles as stabilizers. Janus microspheres with multihollow structure possessing magnetite nanoparticles concentrated on one side of the microspheres are obtained after polymerization of the middle oil phase of the double emulsion under a magnetic field. The resultant Janus microspheres are characterized by optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDX). Moreover, we have systematically investigated the influences of Fe3O4 particle concentration, hydrophobic silica particle content, and volume ratio of the inner water phase to middle oil phase (WF/O) on the double emulsion formation and consequently on the structure of the resulting Janus microspheres. Our results show that the distribution of the multihollow structures within the prepared microspheres can be accurately tailored by adjusting the ratio of WF/O. In addition, the obtained Janus microsphere can be fairly orientated under a magnetic field, making them a potential candidate for synthesizing Janus membrane. PMID:23565899

Ning, Yin; Wang, Chaoyang; Ngai, To; Tong, Zhen

2013-04-30

321

Experimental confirmation of quantum oscillations of magnetic anisotropy in Co/Cu(001)  

E-print Network

The effect of quantum well states on the magnetic anisotropy of Co films grown on vicinal Cu(001) substrates was studied by in situ magneto-optic Kerr effect in a temperature range of 5 K to 365 K. The uniaxial magnetic ...

Dabrowski, M.

322

The Earth's Magnetic Field  

NSDL National Science Digital Library

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

Johnson, Roberta

2000-07-01

323

Capping layer-tailored interface magnetic anisotropy in ultrathin Co2FeAl films  

NASA Astrophysics Data System (ADS)

Co2FeAl (CFA) thin films of various thicknesses (2 nm ? d ? 50 nm) have been grown on (001) MgO single crystal substrates and then capped with Cr, V, and Ta. Their magnetic and structural properties have been studied by x-ray diffraction (XRD), vibrating sample magnetometry, and broadband microstrip ferromagnetic resonance (MS-FMR). The XRD revealed that the films are epitaxial with the cubic [001] CFA axis normal to the substrate plane and that the chemical order varies from the B2 phase to the A2 phase when decreasing the thickness. The deduced lattice parameters showed that the Cr-capped films exhibit a larger tetragonal distortion, as compared with the films capped with V or Ta. The presence of magnetic dead layers has been observed in CFA samples capped with V and Ta but not in the case of the Cr-capped ones. The effective magnetization, deduced from the fit of MS-FMR measurements, increases (decreases) linearly with the CFA inverse thickness (1/d) for the Cr-capped (Ta-capped) films while it is constant for the V-capped ones. This allows quantifying the perpendicular surface anisotropy coefficients of -0.46 erg/cm2 and 0.74 erg/cm2 for Cr and Ta-capped films, respectively. Moreover, the fourfold and the uniaxial anisotropy fields, measured in these films, showed different trends with a respect to the CFA inverse thickness. This allows inferring that a non-negligible part of the fourfold magnetocrystalline term is of interfacial origin.

Belmeguenai, M.; Gabor, M. S.; Petrisor, T.; Zighem, F.; Chérif, S. M.; Tiusan, C.

2015-01-01

324

Magnetic anisotropy and magnetostriction in cobalt-ferrite with lattice deformation  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy (MA) energy induced by uniform lattice deformation is calculated for cobalt-ferrites Fe(Co-Fe)2O4 (CFOs) by using an electron theory for down-spin t2g electrons of Co2+ ions in CFOs. It is shown that the MA energy depends nonlinearly and asymmetrically on the uniform lattice deformation. By comparing the calculated results with those obtained in the phenomenological theory at the small lattice deformation limit, values of the magnetoelastic coefficients B1 and B2 have been evaluated. These values semi-quantitatively agree with the experimental ones. A non-trivial appearance of crystal-field potentials produced by the uniform trigonal lattice deformation is crucial to understand the large negative value of B2.

Inoue, Jun-ichiro; Yanagihara, Hideto; Kita, Eiji

2014-12-01

325

Shock-induced anisotropy of magnetic susceptibility: impact experiment on basaltic andesite  

NASA Astrophysics Data System (ADS)

Changes in the anisotropy of the low-field magnetic susceptibility (AMS) of basaltic andesite were induced by decaying stress waves and subsequently quantified. An initial shock pressure of 5 GPa was generated in a block of the target rock through impacting with a cylindrical projectile. Following the impact, the maximum or minimum principal susceptibility axes of the target were reoriented toward the shock direction at low (0.5-3 GPa) or high (>3 GPa) estimated shock pressures, respectively. Subtraction of the initial AMS demonstrated a parallelism between the induced susceptibility axes and the shock direction. These results suggest a potential application of AMS as an indicator of the propagation directions of stress waves generated in rocks at terrestrial impact structures.

Nishioka, I.; Funaki, M.; Sekine, T.

2007-11-01

326

Reversible DC Magnetization Measurements of the Superconducting Parameters and Their Anisotropies in the Randomly-Doped Cuprates and Prelude to the Magnetic Resonance Studies of - Cuprates  

Microsoft Academic Search

The fact that there is no consensus on the microscopic origin of the high-temperature superconducting phenomenon highlights the need for accurate measurements of the parameters which characterize the superconducting state (i.e., the coherence lengths (Ginzburg-Landau), penetration depths, and critical fields) and their anisotropies in these materials. This dissertation presents the first dc magnetization measurements of these parameters in the electron-doped,

Jonathan Lynn Cobb

1995-01-01

327

Relating pore fabric geometry to acoustic and permeability anisotropy in Crab Orchard Sandstone: A laboratory study using magnetic ferrofluid  

NASA Astrophysics Data System (ADS)

Pore fabric anisotropy is a common feature of many sedimentary rocks. In this paper we report results from a comparative study on the anisotropy of a porous sandstone (Crab Orchard) using anisotropy of magnetic susceptibility (AMS), acoustic wave velocity and fluid permeability techniques. Initially, we characterise the anisotropic pore fabric geometry by impregnating the sandstone with magnetic ferro-fluid and measuring its AMS. The results are used to guide subsequent measurements of the anisotropy of acoustic wave velocity and fluid permeability. These three independent measures of anisotropy are then directly compared. Results show strong positive correlation between the principal directions given from the AMS, velocity anisotropy and permeability anisotropy. Permeability parallel to the macroscopic crossbedding observed in the sandstone is 240% higher than that normal to it. P and S-wave velocity anisotropy and AMS show mean values of 19.1%, 4.8% and 3.8% respectively, reflecting the disparate physical properties measured.

Benson, Philip M.; Meredith, Philip G.; Platzman, Ellen S.

2003-10-01

328

Magnetic phase diagram of quasi-2D quantum Heisenberg antiferromagnets with XY anisotropy  

NASA Astrophysics Data System (ADS)

The magnetic phase diagram of a quasi-2D quantum Heisenberg antiferromagnetic compound Cu(pz)2(ClO4)2 [1] has been determined by experimental measurements; TN shows a strong field dependence. The data reveal the presence of a small (0.5%) amount of XY anisotropy. QMC simulations have been performed to examine the role of the anisotropy and the interlayer exchange (') upon the phase diagram [2,3]. Comparison of the QMC results with the experimental phase diagram will be presented. [4pt] [1] F. Xiao, F. M. Woodward, C. P. Landee, M. M. Turnbull, C. Mielke, N. Harrison, T. Lancaster, S. J. Blundell, P. J. Baker, P. Babkevich, and F. L. Pratt. Phys. Rev. B, 79(13): 134412 (2009) [0pt] [2] A. Cuccoli, T. Roscilde, R. Vaia, and P. Verrucchi. Phys. Rev. B, 68(6):060402 (2003). [0pt] [3] A. Cuccoli, T. Roscilde, R. Vaia, and P. Verrucchi. Phys. Rev. Lett., 90(16): 167205 (2003).

Xiao, Fan; Landee, Christopher; Turnbull, Mark; Fortune, Nathanael; Hannahs, Scott

2012-02-01

329

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

330

Molecular anisotropy analysis of single-ion magnets using an effective electrostatic model.  

PubMed

Simple electrostatic models have been shown to successfully rationalize the magnetic properties of mononuclear single molecule magnets based on f-elements and even to predict the direction of the magnetic anisotropy axis in these nanomagnets. In this Article, we go a step forward by showing that these models, conveniently modified to account for the covalency effects, are able to predict not only the easy axis direction but also the three components of the magnetic anisotropy. Thus, by using a lone pair effective charge (LPEC) model we can fully reproduce the angular dependence of the magnetic susceptibility in single crystals of pentamethylcyclopentadienyl-Er-cyclooctatetraene single-ion magnet. Furthermore, the parametrization of the ligands obtained in this study has been extrapolated to successfully reproduce spectroscopic data of a set of mononuclear lanthanoid complexes based on the same kind of ligands, thus emphasizing the predictive character of this model. PMID:25271391

Baldoví, José J; Clemente-Juan, Juan M; Coronado, Eugenio; Gaita-Ariño, Alejandro

2014-10-20

331

Phase-field simulation of strain-induced domain switching in magnetic thin films  

E-print Network

switching based on, for example, the magnetic force microscopy11,12 or the Lorentz microscopy.13Phase-field simulation of strain-induced domain switching in magnetic thin films Jia-Mian Hu, G of the Bloch point in a magnetic film with strong uniaxial magnetic anisotropy Low Temp. Phys. 37, 690 (2011

Chen, Long-Qing

332

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

E-print Network

The proton temperature anisotropy in the solar wind is known to be constrained by the theoretical thresholds for pressure anisotropy-driven instabilities. Here we use approximately 1 million independent measurements of gyroscale magnetic fluctuations in the solar wind to show for the first time that these fluctuations are enhanced along the temperature anisotropy thresholds of the mirror, proton oblique firehose, and ion cyclotron instabilities. In addition, the measured magnetic compressibility is enhanced at high plasma beta ($\\beta_\\parallel \\gtrsim 1$) along the mirror instability threshold but small elsewhere, consistent with expectations of the mirror mode. The power in this frequency (the 'dissipation') range is often considered to be driven by the solar wind turbulent cascade, an interpretation which should be qualified in light of the present results. In particular, we show that the short wavelength magnetic fluctuation power is a strong function of collisionality, which relaxes the temperature aniso...

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

2009-01-01

333

Narrow Track Confinement by AC Field Generation Layer in Microwave Assisted Magnetic Recording  

Microsoft Academic Search

Microwave assisted magnetic recording (MAMR) has been proposed to provide sufficient writability in magnetic recording when the magnetic grain has a large crystalline anisotropy field in high recording density. In this paper, the relationship between the track width and recording head designs in this novel recording scheme is studied using micromagnetic modeling. By controlling the AC field generation layer width,

Yuhui Tang; Jian-Gang Zhu

2008-01-01

334

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

2012-08-01

335

Domain-wall structure in thin films with perpendicular anisotropy: Magnetic force microscopy and polarized neutron reflectometry study  

NASA Astrophysics Data System (ADS)

Ferromagnetic domain patterns and three-dimensional domain-wall configurations in thin CoCrPt films with perpendicular magnetic anisotropy were studied in detail by combining magnetic force microscopy and polarized neutron reflectometry with micromagnetic simulations. With the first method, lateral dimension of domains with alternative magnetization directions normal to the surface and separated by domain walls in 20-nm-thick CoCrPt films were determined in good agreement with micromagnetic simulations. Quantitative analysis of data on reflectometry shows that domain walls consist of a Bloch wall in the center of the thin film, which is gradually transformed into a pair of Néel caps at the surfaces. The width and in-depth thickness of the Bloch wall element, transition region, and Néel caps are found consistent with micromagnetic calculations. A complex structure of domain walls serves to compromise a competition between exchange interactions, keeping spins parallel, magnetic anisotropy orienting magnetization normal to the surface, and demagnetizing fields, promoting in-plane magnetization. It is shown that the result of such competition strongly depends on the film thickness, and in the thinner CoCrPt film (10 nm thick), simple Bloch walls separate domains. Their lateral dimensions estimated from neutron scattering experiments agree with micromagnetic simulations.

Navas, David; Redondo, Carolina; Badini Confalonieri, Giovanni A.; Batallan, Francisco; Devishvili, Anton; Iglesias-Freire, Óscar; Asenjo, Agustina; Ross, Caroline A.; Toperverg, Boris P.

2014-08-01

336

Mars Observer magnetic fields investigation  

Microsoft Academic Search

The magnetic fields experiment designed for the Mars Observer mission will provide definitive measurements of the Martian magnetic field from the transition and mapping orbits planned for the Mars Observer. The paper describes the instruments (which include a classical magnetometer and an electron reflection magnetometer) and techniques designed to investigate the nature of the Martian magnetic field and the Mars-solar

J. E. P. Connerney; P. Wasilewski; R. P. Lin; K. A. Anderson; C. W. Carlson; J. McFadden; D. W. Curtis; H. Reme; A. Cros; J. L. Médale; J. A. Sauvaud; C. d'Uston; S. J. Bauer; P. Cloutier; Michael Mayhew; N. F. Ness

1992-01-01

337

The WIND magnetic field investigation  

Microsoft Academic Search

The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and

R. P. Lepping; M. H. Ac?na; L. F. Burlaga; W. M. Farrell; J. A. Slavin; K. H. Schatten; F. Mariani; N. F. Ness; F. M. Neubauer; Y. C. Whang; J. B. Byrnes; R. S. Kennon; P. V. Panetta; J. Scheifele; E. M. Worley

1995-01-01

338

Anisotropy of Magnetic Suscetibility of the Aquidauana Formation (PARANÁ Basin): Preliminary Results  

NASA Astrophysics Data System (ADS)

The magnetic studies were performed on sites of reddish-brown sandstones, siltites, and mudstones, which crop out mainly in Mato Grosso do Sul State. Magnetic fabrics were determined on oriented cylindrical specimens (2.54 cm x 2.2 cm) using anisotropy of low-field magnetic susceptibility (AMS). Considering the eingenvector orientations, the sites usually gave good results. The analysis at the individual-site scale defines two AMS fabric types. The first type shows Kmin perpendicular to the bedding plane, while Kmax and Kint are scattered within the bedding plane itself. This fabric is usually interpreted as primary (sedimentary-compactional), typical of undeformed sediments and is dominant among the sites. The second type shows good clustering of the AMS principal axes with Kmin still either perpendicular or sub-perpendicular to the bedding plane. This fabric type could be interpreted as a combination of sedimentary-compactional and tectonic contributions if some strain markers or evidence for tectonic deformation had been found in the studied area. However, the tight Kmax grouping in this fabric type could be explained by the action of currents since they cause Kmax to be aligned sub-parallel to the paleocurrent direction.

Raposo, M. B.; Paranhos, A.

2013-12-01

339

Magnetic field switchable dry adhesives.  

PubMed

A magnetic field controllable dry adhesive device is manufactured. The normal adhesion force can be increased or decreased depending on the presence of an applied magnetic field. If the magnetic field is present during the entire normal adhesion test cycle which includes both applying a preloading force and measuring the pulloff pressure, a decrease in adhesion is observed when compared to when there is no applied magnetic field. Similarly, if the magnetic field is present only during the preload portion of the normal adhesion test cycle, a decrease in adhesion is observed because of an increased stiffness of the magnetically controlled dry adhesive device. When the applied magnetic field is present during only the pulloff portion of the normal adhesion test cycle, either an increase or a decrease in normal adhesion is observed depending on the direction of the applied magnetic field. PMID:25588470

Krahn, Jeffrey; Bovero, Enrico; Menon, Carlo

2015-02-01

340

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

341

A study of magnetic anisotropy energy in CuMn spin glass  

E-print Network

A STUDY OF MAGNETIC ANISOTROPY ENERGY IN CuMn SPIN GLASS A Thesis by CHRISTINE ADELE ALLEN Submitted to the Graduate College of Texas ARM University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE August 1986... Major Subject: Physics A STUDY OF MAGNETIC ANISOTROPY ENERGY IN CuMn SPIN GLASS A Thesis by CHRISTINE ADELE ALLEN Approved as to style and content by: Thomas W. Adair, III (Chai man of Committee) Robert A. enefick (Member) Donald L. Parker...

Allen, Christine Adele

2012-06-07

342

Uniaxial magnetic anisotropy of quasi-one-dimensional Fe chains on Pb/Si  

SciTech Connect

We fabricated quasi-one-dimensional Fe chains on a 4{sup o} miscut Si (111) substrate with a Pb film as a buffer layer. The magnetic properties and morphology of Fe chains were investigated by means of scanning tunneling microscope (STM) and surface magneto-optical Kerr effect (SMOKE). STM images show that Fe chains are formed by Fe random islands along the steps of the Pb film due to step decoration. SMOKE data indicate that the Fe chains exhibit in-plane uniaxial magnetic anisotropy along the step direction. The effective in-plane uniaxial anisotropy constant at room temperature was determined by means of electron spin resonance.

Sun, Da-li [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics; Wang, De-yong [Material Science and Technology Division, Oak Ridge National Laboratory; Du, Hai-Feng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics; Ning, Wei [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics; Gao, Jian-Hua [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics; Fang, Ya-Peng [Institute of High Energy Physics, Chinese Academy of Sciences, China; Zhang, Xiang-Qun [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics; Sun, Young [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics; Cheng, Zhao-Hua [ORNL; Shen, Jian [ORNL

2009-01-01

343

Strategies for assessing diffusion anisotropy on the basis of magnetic resonance images: comparison of systematic errors.  

PubMed

Diffusion weighted imaging uses the signal loss associated with the random thermal motion of water molecules in the presence of magnetic field gradients to derive a number of parameters that reflect the translational mobility of the water molecules in tissues. With a suitable experimental set-up, it is possible to calculate all the elements of the local diffusion tensor (DT) and derived parameters describing the behavior of the water molecules in each voxel. One of the emerging applications of the information obtained is an interpretation of the diffusion anisotropy in terms of the architecture of the underlying tissue. These interpretations can only be made provided the experimental data which are sufficiently accurate. However, the DT results are susceptible to two systematic error sources: On one hand, the presence of signal noise can lead to artificial divergence of the diffusivities. In contrast, the use of a simplified model for the interaction of the protons with the diffusion weighting and imaging field gradients (b matrix calculation), common in the clinical setting, also leads to deviation in the derived diffusion characteristics. In this paper, we study the importance of these two sources of error on the basis of experimental data obtained on a clinical magnetic resonance imaging system for an isotropic phantom using a state of the art single-shot echo planar imaging sequence. Our results show that optimal diffusion imaging require combining a correct calculation of the b-matrix and a sufficiently large signal to noise ratio. PMID:24761372

Boujraf, Saïd

2014-04-01

344

Strategies for Assessing Diffusion Anisotropy on the Basis of Magnetic Resonance Images: Comparison of Systematic Errors  

PubMed Central

Diffusion weighted imaging uses the signal loss associated with the random thermal motion of water molecules in the presence of magnetic field gradients to derive a number of parameters that reflect the translational mobility of the water molecules in tissues. With a suitable experimental set-up, it is possible to calculate all the elements of the local diffusion tensor (DT) and derived parameters describing the behavior of the water molecules in each voxel. One of the emerging applications of the information obtained is an interpretation of the diffusion anisotropy in terms of the architecture of the underlying tissue. These interpretations can only be made provided the experimental data which are sufficiently accurate. However, the DT results are susceptible to two systematic error sources: On one hand, the presence of signal noise can lead to artificial divergence of the diffusivities. In contrast, the use of a simplified model for the interaction of the protons with the diffusion weighting and imaging field gradients (b matrix calculation), common in the clinical setting, also leads to deviation in the derived diffusion characteristics. In this paper, we study the importance of these two sources of error on the basis of experimental data obtained on a clinical magnetic resonance imaging system for an isotropic phantom using a state of the art single-shot echo planar imaging sequence. Our results show that optimal diffusion imaging require combining a correct calculation of the b-matrix and a sufficiently large signal to noise ratio. PMID:24761372

Boujraf, Saïd

2014-01-01

345

In situ manipulation of magnetic anisotropy in magnetite thin films  

Microsoft Academic Search

We show that the ferromagnetic anisotropy of a thin crystalline Fe3O4 film can be manipulated in situ via the application of tunable stress. The stress is exerted by a piezoelectric actuator, onto which the Fe3O4 film is cemented. The strain in the sample is quantified as a function of the voltage applied to the actuator using high-resolution x-ray diffraction, and

A. Brandlmaier; S. Geprägs; M. Weiler; A. Boger; M. Opel; H. Huebl; C. Bihler; M. S. Brandt; B. Botters; D. Grundler; R. Gross; S. T. B. Goennenwein

2008-01-01

346

Perpendicular magnetic anisotropy in epitaxially strained cobalt-ferrite (001) thin films  

SciTech Connect

We investigated the dependencies of both the magnetization characteristics and the perpendicular magnetic anisotropy of Co{sub x}Fe{sub 3–x}O{sub 4}(001) epitaxial films (x?=?0.5 and 0.75) on the growth conditions of the reactive magnetron sputtering process. Both saturation magnetization and the magnetic uniaxial anisotropy constant K{sub u} are strongly dependent on the reactive gas (O{sub 2}) flow rate, although there is little difference in the surface structures for all samples observed by reflection high-energy electron diffraction. In addition, certain dead-layer-like regions were observed in the initial stage of the film growth for all films. Our results suggest that the magnetic properties of Co{sub x}Fe{sub 3–x}O{sub 4} epitaxial films are governed by the oxidation state and the film structure at the vicinity of the interface.

Yanagihara, H., E-mail: yanagiha@bk.tsukuba.ac.jp; Utsumi, Y.; Niizeki, T., E-mail: t-niizeki@imr.tohoku.ac.jp; Inoue, J.; Kita, Eiji [Institute of Applied Physics, University of Tsukuba, Tsukuba 305-8573 (Japan)

2014-05-07

347

Nonlinear turbulent magnetic diffusion and mean-field dynamo.  

PubMed

The nonlinear coefficients defining the mean electromotive force (i.e., the nonlinear turbulent magnetic diffusion, the nonlinear effective velocity, the nonlinear kappa tensor, etc.) are calculated for an anisotropic turbulence. A particular case of an anisotropic background turbulence (i.e., the turbulence with zero-mean magnetic field) with one preferential direction is considered. It is shown that the toroidal and poloidal magnetic fields have different nonlinear turbulent magnetic diffusion coefficients. It is demonstrated that even for a homogeneous turbulence there is a nonlinear effective velocity that exhibits diamagnetic or paramagnetic properties depending on the anisotropy of turbulence and the level of magnetic fluctuations in the background turbulence. The diamagnetic velocity results in the field being pushed out from the regions with stronger mean magnetic field, while the paramagnetic velocity causes the magnetic field to be concentrated in the regions with stronger field. Analysis shows that an anisotropy of turbulence strongly affects the nonlinear turbulent magnetic diffusion, the nonlinear effective velocity, and the nonlinear alpha effect. Two types of nonlinearities (algebraic and dynamic) are also discussed. The algebraic nonlinearity implies a nonlinear dependence of the mean electromotive force on the mean magnetic field. The dynamic nonlinearity is determined by a differential equation for the magnetic part of the alpha effect. It is shown that for the alphaOmega axisymmetric dynamo the algebraic nonlinearity alone (which includes the nonlinear alpha effect, the nonlinear turbulent magnetic diffusion, the nonlinear effective velocity, etc.) cannot saturate the dynamo generated mean magnetic field while the combined effect of the algebraic and dynamic nonlinearities limits the mean magnetic field growth. PMID:11736094

Rogachevskii, I; Kleeorin, N

2001-11-01

348

Domain-wall structure in thin films with perpendicular anisotropy: Magnetic force microscopy and polarized neutron reflectometry study  

E-print Network

Ferromagnetic domain patterns and three-dimensional domain-wall configurations in thin CoCrPt films with perpendicular magnetic anisotropy were studied in detail by combining magnetic force microscopy and polarized neutron ...

Navas, David

349

Fast superconducting magnetic field switch  

SciTech Connect

The superconducting magnetic switch or fast kicker magnet is employed with an electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater than the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. Magnetic switches and particularly fast kicker magnets are used in the accelerator industry to quickly deflect particle beams into and out of various transport lines, storage rings, dumps, and specifically to differentially route individual bunches of particles from a train of bunches which are injected or ejected from a given ring.

Goren, Y.; Mahale, N.K.

1995-12-31

350

Constituents of magnetic anisotropy and a screening of spin-orbit coupling in solids  

SciTech Connect

Using quantum mechanical perturbation theory (PT) we analyze how the energy of perturbation of different orders is renormalized in solids. We test the validity of PT analysis by considering a specific case of spin-orbit coupling as a perturbation. We further compare the relativistic energy and the magnetic anisotropy from the PT approach with direct density functional calculations in FePt, CoPt, FePd, MnAl, MnGa, FeNi, and tetragonally strained FeCo. In addition using decomposition of anisotropy into contributions from individual sites and different spin components we explain the microscopic origin of high anisotropy in FePt and CoPt magnets.

Antropov, Vladimir [Ames Laboratory; Ke, Liqin [Ames Laboratory; Aberg, Daniel [Lawrence Livermore National Laboratory

2014-07-11

351

Anatomy of perpendicular magnetic anisotropy in Fe/MgO magnetic tunnel junctions: First-principles insight  

NASA Astrophysics Data System (ADS)

Using first-principles calculations, we elucidate microscopic mechanisms of perpendicular magnetic anisotropy (PMA) in Fe/MgO magnetic tunnel junctions through evaluation of orbital and layer resolved contributions into the total anisotropy value. It is demonstrated that the origin of the large PMA values is far beyond simply considering the hybridization between Fe-3d and O-2p orbitals at the interface between the metal and the insulator. Onsite projected analysis shows that the anisotropy energy is not localized at the interface but it rather propagates into the bulk showing an attenuating oscillatory behavior which depends on orbital character of contributing states and interfacial conditions. Furthermore, it is found in most situations that states with dyz(xz) and dz2 character tend always to maintain the PMA while those with dxy and dx2-y2 character tend to favor the in-plane anisotropy. It is also found that while MgO thickness has no influence on PMA, the calculated perpendicular magnetic anisotropy oscillates as a function of Fe thickness with a period of 2 ML and reaches a maximum value of 3.6 mJ/m2.

Hallal, A.; Yang, H. X.; Dieny, B.; Chshiev, M.

2013-11-01

352

Pliocene and latest Miocene anisotropy of magnetic susceptibility (AMS) from the Wilkes Land margin (Invited)  

NASA Astrophysics Data System (ADS)

During IODP Expedition 318, Sites U1359 and U1361 were drilled on the continental rise offshore the Wilkes Subglacial Basin to reconstruct the stability of the East Antarctic Ice Sheet (EAIS) during Neogene warm periods, such as the late Miocene and the early Pliocene. As the drilled core contains a complex history of compaction, erosion (thus hiatuses), and likely artificial disturbances, identifying these is important for reconstructing paleoenvironments. Anisotropy of magnetic susceptibility (AMS) is sensitive to lithological changes and differential compaction. At both sites, highly anisotropic layers correspond with turbidite units, lithologic boundaries and hiatuses. In places, it appears that low anisotropy is controlled by the bioturbated units and high productivity layers. Here we present a detailed study of the relationships between sediment compaction, based on AMS fabric variations in sedimentary records, and magnetic mineralogy. A clear correlation can be found between the degree of anisotropy and moisture content and diatom abundance during the Pliocene, but this pattern breaks down in the late Miocene. There are also strong rock magnetic indications for changes in the sources of the magnetic minerals throughout the Miocene to Pliocene. Furthermore, a significant difference exists between magnetic minerals at Sites U1359 and U1361. We will use our AMS and rock magnetic study to 1) characterize sediment compaction with biological productivity, and 2) detect the source of magnetic mineralogy throughout the late Miocene to Pliocene at both sites.

Sugisaki, S.; Tauxe, L.; Iwai, M.; van de Flierdt, T.; Cook, C.; Jimenez, F. J.; Khim, B.; Patterson, M. 0; Mckay, R. M.; Passchier, S.; Roehl, U.; González, J. J.; Escutia, C.

2013-12-01

353

On the energy losses of hot worked Nd-Fe-B magnets and ferrites in a small alternating magnetic field perpendicular to a bias field  

SciTech Connect

Torsion pendulum magnetometer measurements on ferrites and on neodymium-iron-boron permanent magnets are presented. The damping of the oscillation of the pendulum leads to information on the magnetic energy losses of the magnets in a small alternating magnetic field applied perpendicular to a bias field. The origin of the energy absorption is explained by the magnetization reversal of single-domain particles. It is shown experimentally that the energy absorption mechanism requires the ferromagnetic order of the sample, and that the magnetic field strength of maximal energy absorption coincides with the effective anisotropy field strength.

Staa, F. von; Hempel, K.A.; Artz, H. [Aachen Univ. of Technology (Germany). Institut fuer Werkstoffe der Elektrotechnik] [Aachen Univ. of Technology (Germany). Institut fuer Werkstoffe der Elektrotechnik

1995-11-01

354

Photonic Magnetic Field Sensor  

NASA Astrophysics Data System (ADS)

Small, in-line polarization rotators or isolators to reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical (GMO) or Faraday effect in iron garnets, they with a magnetic field of a few hundred Gauss, (20 mT) for an interaction length for an optical beam of a few millimeters achieve a polarization rotation or phase shift of 45 deg (1/8 cycle). When powered by a small laser diode, with the induced linear phase shift recovered at the shot noise limit, we have demonstrated sensitivities at the 3.3 nT/Hz1/2 level for frequencies from less than 1 Hz to frequencies into the high kHz range. Through further improvements; an increase in interaction length, better materials and by far the greatest factor, the addition of a flux concentrator, sensitivities at the pT/Hz1/2 level appear to be within reach. We will detail such a design and discuss the issues that may limit achieving these goals.

Wyntjes, Geert

2002-02-01

355

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The heliospheric magnetic field (HMF) is the extension of the coronal magnetic field carried out into the solar system by the solar wind. It is the means by which the Sun interacts with planetary magnetospheres and channels charged particles propagating through the heliosphere. As the HMF remains rooted at the solar photosphere as the Sun rotates, the large-scale HMF traces out an Archimedean spiral. This pattern is distorted by the interaction of fast and slow solar wind streams, as well as the interplanetary manifestations of transient solar eruptions called coronal mass ejections. On the smaller scale, the HMF exhibits an array of waves, discontinuities, and turbulence, which give hints to the solar wind formation process. This review aims to summarise observations and theory of the small- and large-scale structure of the HMF. Solar-cycle and cycle-to-cycle evolution of the HMF is discussed in terms of recent spacecraft observations and pre-spaceage proxies for the HMF in geomagnetic and galactic cosmic ray records.

Owens, Mathew J.; Forsyth, Robert J.

2013-11-01

356

Magnetic state of pyrochlore Cd(2)Os(2)O(7) emerging from strong competition of ligand distortions and longer-range crystalline anisotropy.  

PubMed

By many-body quantum-chemical calculations, we investigate the role of two structural effects--local ligand distortions and the anisotropic Cd-ion coordination--on the magnetic state of Cd(2)Os(2)O(7), a spin S = 3/2 pyrochlore. We find that these effects strongly compete, rendering the magnetic interactions and ordering crucially dependent on these geometrical features. Without trigonal distortions, a large easy-plane magnetic anisotropy develops. Their presence, however, reverses the sign of the zero-field splitting and causes a large easy-axis anisotropy (D ? -6.8 meV), which in conjunction with the antiferromagnetic exchange interaction (J ? 6.4 meV) stabilizes an all-in-all-out magnetic order. The competition uncovered here is a generic feature of pyrochlore magnets. PMID:25166841

Bogdanov, Nikolay A; Maurice, Rémi; Rousochatzakis, Ioannis; van den Brink, Jeroen; Hozoi, Liviu

2013-03-22

357

Magnetic State of Pyrochlore Cd2Os2O7 Emerging from Strong Competition of Ligand Distortions and Longer-Range Crystalline Anisotropy  

NASA Astrophysics Data System (ADS)

By many-body quantum-chemical calculations, we investigate the role of two structural effects—local ligand distortions and the anisotropic Cd-ion coordination—on the magnetic state of Cd2Os2O7, a spin S=3/2 pyrochlore. We find that these effects strongly compete, rendering the magnetic interactions and ordering crucially dependent on these geometrical features. Without trigonal distortions, a large easy-plane magnetic anisotropy develops. Their presence, however, reverses the sign of the zero-field splitting and causes a large easy-axis anisotropy (D?-6.8meV), which in conjunction with the antiferromagnetic exchange interaction (J?6.4meV) stabilizes an all-in-all-out magnetic order. The competition uncovered here is a generic feature of pyrochlore magnets.

Bogdanov, Nikolay A.; Maurice, Rémi; Rousochatzakis, Ioannis; van den Brink, Jeroen; Hozoi, Liviu

2013-03-01

358

Structure and magnetic anisotropy of epitaxial fcc-Co(110) and hcp-Co(1100) films  

E-print Network

Structure and magnetic anisotropy of epitaxial fcc-Co(110) and hcp- Co(11¯00) films C. K. Lo,a) Y, Republic of China Received 8 November 1995; accepted for publication 2 February 1996 Fcc-Co 110 and hcp the crystal structure. Co films grown directly on MgO 110 were pseudomorphic fcc structure. Twofold

Huang, Jung-Chun

359

Magnetic anisotropy of rocks and its application in geology and geophysics  

Microsoft Academic Search

Magnetic anisotropy in sedimentary rocks is controlled by the processes of deposition and compaction, in volcanic rocks by the lava flow and in metamorphic and plutonic rocks by ductile deformation and mimetic crystallization. In massive ore it is due to processes associated with emplacement and consolidation of an ore body as well as to ductile deformation. Hence, it can be

Frantisek Hrouda

1982-01-01

360

Toward an understanding of grain-to-grain anisotropy field variation in thin film media  

Microsoft Academic Search

Grain-to-grain anisotropy field variation has become one of the main causes of medium noise, especially in perpendicular thin film media. In this paper, we present an electron microscopy investigation and theoretical analysis on the grain-to-grain anisotropy field variation in various types of thin film recording media. In alloyed film media, the intrinsic grain-to-grain composition variation would present a lower limit

Jian-Gang Zhu; Yingguo Peng; David E. Laughlin

2005-01-01

361

Room-temperature perpendicular magnetic anisotropy of MgO/Fe/MgO ultrathin films  

SciTech Connect

We used the anomalous Hall effect to study the magnetic properties of MgO/Fe(t)/MgO(001) structures in which the Fe thickness t ranged from 4?Å to 14?Å. For the iron deposited at 140?K, we obtained perpendicular magnetization at room temperature below the critical thickness of t{sub c}?=?(9?±?1)?Å. In the vicinity of t{sub c}, the easy magnetization axis switched from an out-of-plane orientation to an in-plane orientation, and the observed spin-reorientation transition was considered in terms of the competition among different anisotropies. The perpendicular magnetization direction was attributed to magnetoelastic anisotropy. Finally, the temperature-dependent spin-reorientation transition was analyzed for Fe thicknesses close to t{sub c}.

Kozio?-Rachwa?, A.; ?l?zak, T.; Przewo?nik, J. [Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Skowro?ski, W.; Stobiecki, T. [Department of Electronics, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Wilgocka-?l?zak, D. [Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Kraków (Poland); Qin, Q. H.; Dijken, S. van [NanoSpin, Department of Applied Physics, Aalto University School of Science, P.O. Box 15100, FI-00076 Aalto (Finland); Korecki, J. [Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków (Poland); Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, ul. Niezapominajek 8, 30-239 Kraków (Poland)

2013-12-14

362

Magnetic Propeller for Uniform Magnetic Field Levitation  

E-print Network

Three new approaches to generating thrust in uniform magnetic fields are proposed. The first direction is based on employing Lorentz force acting on partial magnetically shielded 8-shaped loop with current in external magnetic field, whereby a net force rather than a torque origins. Another approach, called a Virtual Wire System, is based on creating a magnetic field having an energetic symmetry (a virtual wire), with further superposition of external field. The external field breaks the symmetry causing origination of a net force. Unlike a wire with current, having radial energetic symmetry, the symmetry of the Virtual Wire System is closer to an axial wire. The third approach refers to the first two. It is based on creation of developed surface system, comprising the elements of the first two types. The developed surface approach is a way to drastically increase a thrust-to-weight ratio. The conducted experiments have confirmed feasibility of the proposed approaches.

Mark Krinker; Alexander Bolonkin

2008-07-12

363

Tailoring magnetism in CoNi films with perpendicular anisotropy by ion irradiation  

SciTech Connect

This paper reports on the influence of ion irradiation on the magnetic properties of Co/Ni multilayers with perpendicular magnetic anisotropy (PMA). This material is a very promising candidate for ultrahigh density spintronic applications since it exhibits high polarization and low damping parameters. We show that PMA can be tailored in a controlled way by using uniform He{sup +} ion irradiation or focused Ga{sup +} ion beam.

Stanescu, D.; Ravelosona, D.; Mathet, V.; Chappert, C. [Institut d'Electronique Fondamentale, UMR CNRS 8622, Universite Paris Sud, 91405 Orsay Cedex (France); Samson, Y.; Beigne, C. [CEA Grenoble, DRFMC/SP2M, 17 avenue des Martyrs, 38054 Grenoble (France); Vernier, N.; Ferre, J. [Laboratoire de Physique de Solide, UMR CNRS 8502, Universite Paris Sud, 91405 Orsay Cedex (France); Gierak, J.; Bouhris, E. [Laboratoire de Photonique et de Nanostructures-CNRS, route de Nozay, 91460 Marcoussis (France); Fullerton, E. E. [Center for Magnetic Recording Research, University of California, San Diego, La Jolla, California 92093-0401 (United States)

2008-04-01

364

Magnetic anisotropy of Sm2Fe(17-x)Ga(x) hydrides  

Microsoft Academic Search

The magnetic properties of single-phase 2:17 compounds of the composition Sm(2)Fe(17-x)Ga(x) H(y) were investigated. The substitution of Ga for Fe in the Sm2Fe17 compound resulted in a substantial increase in the Curie temperature and, for alloys with x greater than 2, the formation of a uniaxial magnetic anisotropy at room temperature. The diffusion of hydrogen into those compounds that exhibit

R. A. Dunlap; Z. Wang

1993-01-01

365

Simple torque magnetometer for anisotropy measurements in magnetic thin-film media  

NASA Astrophysics Data System (ADS)

A simple and novel torque magnetometer for the magnetic anisotropy measurements of magnetic thin-film samples is described. A Brookfield LVTD viscometer, normally used in the viscosity measurements of liquids and fluids, is utilized as a torque measuring device. A HP series 310 computer along with the HP 7090 measurement plotting system interfaced to the torque magnetometer perform data acquisition, any calculations required for data correction, and plotting of the torque curves.

Agarwala, A. K.

1988-10-01

366

Fast superconducting magnetic field switch  

DOEpatents

The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles.

Goren, Yehuda (Mountain View, CA); Mahale, Narayan K. (The Woodlands, TX)

1996-01-01

367

Fast superconducting magnetic field switch  

DOEpatents

The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. 6 figs.

Goren, Y.; Mahale, N.K.

1996-08-06

368

Investigating the anisotropy of magnetic susceptibility and other rock magnetic properties of the Beaver River Diabase in northeastern Minnesota  

NASA Astrophysics Data System (ADS)

The Beaver River Diabase (BRD) is a series of mafic dikes and sills within the Beaver Bay Complex (BBC) of northern Minnesota, which formed during the development of the ~1.1 Ga Midcontinent Rift (MCR). The BRD is one of the youngest and most extensive intrusive phases of the BBC. The BRD dikes and sills were emplaced into the medial levels of the 6-10 kilometer-thick North Shore Volcanic Group and occur over an arcuate area extending 120 by 20 kilometers. The BRD is composed of fine- to medium-grained ophitic olivine gabbro and does not display obvious foliation or lineation features and rarely displays modal layering. Without obvious magmatic internal structures, it is difficult to determine emplacement properties such as flow direction using standard geologic mapping or petrographic techniques. For this reason, we measured the anisotropy of magnetic susceptibility (AMS), in conjunction with other rock magnetic properties, to better understand the BRD's emplacement and deformation history in the context of the MCR. AMS measures the directional dependence of low-field magnetic susceptibility, and is used to infer a shape-preferred orientation of magnetic minerals within a rock, which can be related to specific emplacement mechanisms (e.g. directional flow or settling). Preliminary analysis of AMS at 20 sites within the southern half of the BRD (with 4-7 samples per site) shows maximum susceptibility values between 4.48 x 10-6 and 2.22 x 10-4 m3/kg (1165 and 65400 ?SI). Most specimens display nearly isotropic AMS ellipsoids (Pj < 1.15) with minor degrees of prolateness and oblateness. However, about 20% of specimens have higher anisotropies (Pj between 1.15 and 1.67) and higher degrees of oblateness and prolateness. Variations in AMS properties may reflect differences in concentration and composition, as well as emplacement mechanisms. Measurements of susceptibility as a function of temperature yield Curie points between 470 and 570 °C, indicating a presence of low-titanium titanomagnetite. Major hysteresis loops and first order reversal curve (FORC) experiments show coercivities between 1 and 125 mT, with a bulk average microcoercivity of 25 mT, consistent with titanomagnetite as the dominant remanence carrier. Further analysis will also investigate the relationship of AMS to rock fabric by measuring mineral crystal preferred orientations using electron backscatter diffraction. These measurements will supplement the AMS data, and provide links to the role of microstructure, texture and mineralogy in AMS.

Hariri, S. H.; Brownlee, S. J.; Feinberg, J. M.; Jackson, M. J.; Miller, J. D.

2013-12-01

369

[Magnetic fields and fish behavior].  

PubMed

In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25508098

2013-01-01

370

[Magnetic fields and fish behavior].  

PubMed

In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25438567

Krylov, V V; Iziumov, Iu G; Izvekov, E I; Nepomniashchikh, V A

2013-01-01

371

Exposure guidelines for magnetic fields  

SciTech Connect

The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

Miller, G.

1987-12-01

372

Magnetic-field-dosimetry system  

DOEpatents

A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.

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

1981-01-21

373

Magnetic fields in massive stars  

E-print Network

Although indirect evidence for the presence of magnetic fields in high-mass stars is regularly reported in the literature, the detection of these fields remains an extremely challenging observational problem. We review the recent discoveries of magnetic fields in different types of massive stars and briefly discuss strategies for spectropolarimetric observations to be carried out in the future.

S. Hubrig

2007-03-09

374

Voltage induced magnetic anisotropy change in ultrathin Fe80Co20/MgO junctions with Brillouin light scattering  

NASA Astrophysics Data System (ADS)

We investigate voltage induced perpendicular magnetic anisotropy (PMA) changes in MgO/Cr/Au/Fe80Co20/MgO/polyimide/ indium tin oxide (ITO). In order to observe the PMA change, spin wave frequency was measured by Brillouin light scattering with finite bias voltages applied between Au and ITO electrodes. The obtained PMA constants from spin wave frequency of Fe80Co20 layer show clear bias voltage dependences, which agree well with the previous polar-Kerr effect measurement results and theoretical study. This study suggests spintronics devices operated by an electric field for next generation devices complying with low-power consumption.

Ha, Seung-Seok; Kim, Nam-Hee; Lee, Sukmock; You, Chun-Yeol; Shiota, Yoichi; Maruyama, Takuto; Nozaki, Takayuki; Suzuki, Yoshishige

2010-04-01

375

Temperature evolution of the effective magnetic anisotropy in the MnCr2O4 spinel.  

PubMed

In this work, we present a study of the low temperature magnetic phases of polycrystalline MnCr2O4 spinel through dc magnetization and ferromagnetic resonance spectroscopy (FMR). Through these experiments, we determined the main characteristic temperatures: TC ? 41 K and TH ? 18 K corresponding, respectively, to the ferrimagnetic order and to the low temperature helicoidal transitions. The temperature evolution of the system is described by a phenomenological approach that considers the different terms that contribute to the free energy density. Below the Curie temperature, the FMR spectra were modeled by a cubic magnetocrystalline anisotropy to the second order, with K1 and K2 anisotropy constants that define the easy magnetization axis along the <1 1 0> direction. At lower temperatures, the formation of a helicoidal phase was considered by including uniaxial anisotropy axis along the [Formula: see text] propagation direction of the spiral arrange, with a Ku anisotropy constant. The values obtained from the fittings at 5 K are K1 = -2.3 × 10(4) erg cm(-3), K2 = 6.4 × 10(4) erg cm(-3) and Ku = 7.5 × 10(4) erg cm(-3). PMID:25428138

Tobia, Dina; Milano, Julián; Causa, María Teresa; Winkler, Elin L

2015-01-14

376

Temperature evolution of the effective magnetic anisotropy in the MnCr2O4 spinel  

NASA Astrophysics Data System (ADS)

In this work, we present a study of the low temperature magnetic phases of polycrystalline MnCr2O4 spinel through dc magnetization and ferromagnetic resonance spectroscopy (FMR). Through these experiments, we determined the main characteristic temperatures: TC ? 41 K and TH ? 18 K corresponding, respectively, to the ferrimagnetic order and to the low temperature helicoidal transitions. The temperature evolution of the system is described by a phenomenological approach that considers the different terms that contribute to the free energy density. Below the Curie temperature, the FMR spectra were modeled by a cubic magnetocrystalline anisotropy to the second order, with K1 and K2 anisotropy constants that define the easy magnetization axis along the <1 1 0> direction. At lower temperatures, the formation of a helicoidal phase was considered by including uniaxial anisotropy axis along the [1 \\bar{1} 0] propagation direction of the spiral arrange, with a Ku anisotropy constant. The values obtained from the fittings at 5 K are K1 = ?2.3 × 104 erg cm?3, K2 = 6.4 × 104 erg cm?3 and Ku = 7.5 × 104 erg cm?3.

Tobia, Dina; Milano, Julián; Causa, María Teresa; Winkler, Elin L.

2015-01-01

377

Ferrofilm in a magnetic field  

NASA Astrophysics Data System (ADS)

A vertically draining thin ferrofilm under the influence of gravity and a nonuniform magnetic field is considered. It is observed experimentally that the presence of the magnetic field greatly alters the drainage of the film. A mathematical model is developed to describe the behavior. Experiments are conducted for multiple magnetic field configurations. The model is solved for two different sets of boundary conditions and results are compared to experiments. It is shown that the magnetic field structure, the concentration of magnetite in the solution, and the boundary conditions all have noticeable affects on the evolution of the thinning film. Good qualitative agreement between the model and the experiments is observed.

Back, Randy; Beckham, J. Regan

2012-10-01

378

Longitudinal complex magnetic susceptibility and relaxation times of superparamagnetic particles with triaxial anisotropy  

NASA Astrophysics Data System (ADS)

The longitudinal relaxation time and spectrum of the complex magnetic susceptibility of single domain ferromagnetic particles with triaxial (orthorhombic) anisotropy are calculated by averaging the Gilbert-Langevin equation for the magnetization of an individual particle and by reducing the problem to that of solving a system of linear differential-recurrence relations for the appropriate equilibrium correlation functions. The solution of this system is obtained in terms of matrix continued fractions. It is shown that in contrast to the linear magnetic response of particles with uniaxial anisotropy, there is an inherent geometric dependence of the complex susceptibility and the relaxation time on the damping parameter arising from coupling of longitudinal and transverse relaxation modes. Simple analytic equations, which allow one to understand the qualitative behavior of the system and to accurately predict the spectrum of the longitudinal complex susceptibility in wide ranges of the barrier height and dissipation parameters, are proposed.

Kalmykov, Yuri P.; Ouari, Bachir

2005-03-01

379

Strain-induced magnetoresistance and magnetic anisotropy properties of Co/Cu multilayers  

NASA Astrophysics Data System (ADS)

[Co (tCo) nm/Cu 1.5 nm]50 multilayers were grown onto 15-nm Cu/polyimide buffer layers. The relationship between stress, ?, and strain, ?, for the [Co 1.0 nm/Cu 1.5 nm]50 multilayers has been presented. The effects of induced strain on the magnetoresistance (MR) and magnetic anisotropy have been examined. The [Co 1.0 nm/Cu 1.5 nm]50 multilayer exhibited a maximum MR ratio of 3.4% at a Co layer thickness of 1.0 nm, ? of 0.1, and a strain of 1.5%. The multilayers exhibited a remarkable magnetic anisotropy with the easy axis of magnetization always lying in a plane perpendicular to the direction of the induced strain.

Rizal, C.; Gyawali, P.; Kshattry, I.; Pokharel, R. K.

2012-04-01

380

Paleomagnetism and Magnetic Anisotropy of Neogene Red Beds from Tarim Basin, NW China  

NASA Astrophysics Data System (ADS)

Greater than 1000 km of continental shortening north of the Tarim basin has been derived from Cretaceous and Tertiary paleomagnetic data. Recent studies have shown that much of the continental shortening derived from Cretaceous results can be due to inclination error caused by deposition and compaction processes. To better understand the Tertiary paleomagnetic data from the Tarim basin, we conducted a combined paleomagnetic and magnetic anisotropy study for the Neogene red beds from the south Tianshan frontal thrust belt, north Tarim basin. A total of 11 sites of paleomagnetic cores were collected from the Neogene Kangcun Formation, and 81 samples were treated with progressive thermal demagnetization. A characteristic remanent magnetization (ChRM) was isolated at temperatures between 300 and 690°C from 9 sites. The mean ChRM direction, Dg =180.3°, Ig = -55.9°, kg = 5.5, ?95 =22.6°, in situ, and Ds = 177.7°, Is = -38.5°, ks = 15.5, ?95 = 14.4°, in stratigraphic coordinates, passes the McFadden (1990) fold test at 99% confidence level. Compared with the reference pole of Besse and Courtillot (2002), this direction implies about 23° of inclination shallowing. Anisotropy of magnetic susceptibility (AMS) reveals a triaxial, oblate fabric with foliation between 1.03 and 1.16, and minimum axis perpendicular to bedding. Each of the three axes of anisotropy ellipsoid passes the fold tests, indicating depositional and/or compaction fabrics. Measurement of high temperature component of isothermal remanent magnetization acquired in the bedding parallel and bedding perpendicular directions yielded anisotropy between 1.00 and 1.18. The remanent anisotropy shows a good relationship with paleomagnetic inclination. Linear and exponential fits yielded corrected inclinations of 56° and 57°, respectively, about 18° of inclination correction. The remaining inclination difference, 5°, can be explained by crustal shortening in Tianshan ranges.

Tan, X.; Kodama, K. P.; Chen, H.; Fang, D.; Sun, D.; Li, Y.

2009-12-01

381

Pliocene anisotropy of magnetic susceptibility (AMS) and diatom stratigraphy from the Wilkes Land margin  

NASA Astrophysics Data System (ADS)

During IODP Expedition 318, Sites U1359 and U1361 were drilled on the continental rise offshore the Wilkes subglacial basin to reconstruct the stability of the East Antarctic Ice Sheet (EAIS) during Neogene warm periods, such as the late Miocene and the early Pliocene. As the drilled core has complex story of compaction, erosion (thus hiatuses), and possibly artificial disturbance, identifying these is important for reconstructing paleoenvironments. Anisotropy of magnetic susceptibility (AMS) is sensitive to lithological changes and differential compaction. At site U1359, highly anisotropic layers correspond with lithologic boundaries and hiatuses. In places, it appeared that the degree of anisotropy was controlled by the presence or absence of diatoms. Here we present a detailed study of the relationships between sediment compaction based on AMS fabric and variations in diatom taxa and magnetic mineralogy. There is clear correlation between degree of anisotropy and moisture content; where moisture content is high, the layer is more isotropic, and vice versa. Moreover, the anisotropic layers correspond to layers with abundant fibrous diatom taxa (e.g, Thalassionema nitzschioides). In contrast, the more isotropic layers are dominated by the Pennate diatom taxa (e.g, Rouxia spp.). There are also strong rock magnetic indications for changes in the sources of the magnetic minerals. We will describe our AMS and diatom stratigraphy to 1) characterize sediments compaction with diatom taxa variation and 2) detect the source of magnetic mineralogy throughout Pliocene.

Sugisaki, S.; Iwai, M.; Tauxe, L.; van de Flierdt, T.; Cook, C.; Jimenez-Espejo, F.; Passchier, S.; Roehl, U.; González, J.; Escutia, C.

2012-12-01

382

Study of Magnetic Susceptibility Anisotropy Across The Northern Transect of Taiwan Mountain Belt  

NASA Astrophysics Data System (ADS)

Anisotropy of magnetic susceptibility (AMS) can be regarded as a useful tool for understanding the variation of finite strain pattern of regional deformation. By analyzing the directions and magnitudes of magnetic susceptibility ellipsoids across the northern Taiwan, the strain pattern and tectonic features of early deformation event of arc-continental collision of Taiwan can be investigated. Previous study suggested that metamorphic temperature overprint postdated the regional deformation across the northern Taiwan. In order to evaluate the interrelationship between maximum temperature and deformation during mountain building, we collected oriented samples of low-grade metamorphic rocks along the Northern Cross-Island Highway. In addition to the strain pattern inferred from the study of magnetic susceptibility anisotropy, experiments of natural remanent magnetization, hysteresis loop, and temperature-function magnetic susceptibility were also conducted. By these experiments, we can investigate the type and size of magnetic carriers and also can evaluate the factors of influencing magnetic parameters of AMS. Furthermore, the meaning of strain pattern deduced from AMS can be inspected. Current results show that in general K1 orientation of magnetic ellipsoids indicates northwest and southeast compression, which is consistent with plate convergence direction. Both deformation intensity and anisotropy increase from the west to east with abnormally strong intensity and oblate strain in the footwalls of major faults. The results are slightly different from the maximum temperature profile, which increases eastward and becomes almost constant temperature after cleavage development. These observations provide insights into evaluating the evolution of tectonometamorphism and exhumation process of northern Taiwan. To decipher the meaning of differences between metamorphism and deformation, integrated analysis of magnetic parameters and temperature should be carried out.

Peng, X.; Yeh, E.; Lee, T.; Aubourg, C. T.; Chen, C.; Lin, S.; Chen, C.; Chou, Y.

2013-12-01

383

Field induced anisotropic cooperativity in a magnetic colloidal glass  

E-print Network

The translational dynamics in a repulsive colloidal glass-former is probed by time-resolved X-ray Photon Correlation Spectroscopy. In this dense dispersion of charge-stabilized and magnetic nanoparticles, the interaction potential can be tuned, from quasi-isotropic to anisotropic by applying an external magnetic field. Structural and dynamical anisotropies are reported on interparticle lengthscales associated with highly anisotropic cooperativity, almost two orders of magnitude larger in the field direction than in the perpendicular direction and in zero field.

E Wandersman; Y Chushkin; E Dubois; V Dupuis; A Robert; R Perzynski

2015-02-03

384

Perpendicular magnetic anisotropy in CoFe/MgO/CoFe magnetic tunnel junctions by first-principles calculations  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy in FexCo100 -x/MgO/FexCo100 -x magnetic tunnel junctions as a function of composition is investigated on different substrates (Cu, Ag, and MgO). We use the full relativistic screened-Korringa-Kohn-Rostoker method and employ the coherent potential approximation for description of the alloys. Our findings show that the magnetocrystalline anisotropy (MCA) strongly depends on the CoFe composition and that the MCA decreases with increasing Co concentration. At a certain composition there is a transition at which the MCA changes sign from positive to negative. The origin of the MCA is related to the difference of density of states between d orbitals around Fermi energy, in particular, the difference between dy z(dz x) and d3 z2-r2 orbitals. We also calculate the shape anisotropy in order to obtain phase diagrams that show at which magnetic layer thickness and at which composition we expect perpendicular anisotropy.

Zhang, Jia; Franz, Christian; Czerner, Michael; Heiliger, Christian

2014-11-01

385

Theory of fossil magnetic field  

NASA Astrophysics Data System (ADS)

Theory of fossil magnetic field is based on the observations, analytical estimations and numerical simulations of magnetic flux evolution during star formation in the magnetized cores of molecular clouds. Basic goals, main features of the theory and manifestations of MHD effects in young stellar objects are discussed.

Dudorov, Alexander E.; Khaibrakhmanov, Sergey A.

2015-02-01

386

Cosmic Magnetic Fields - An Overview  

NASA Astrophysics Data System (ADS)

Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds' staffs get at times “glued” to a stone, a alodestone. In Europe the magnetic compass came through the Arab sailors who met the Portuguese explorers. The first scientific treatise on magnetism, “De Magnete”, was published by William Gilbert who in 1600 described his experiments and suggested that the Earth was a huge magnet. Johannes Kepler was a correspondent of Gilbert and at times suggested that planetary motion was due to magnetic forces. Alas, this concept was demolished by Isaac Newton,who seeing the falling apple decided that gravity was enough. This concept of dealing with gravitational forces only remains en vogue even today. The explanations why magnetic effects must be neglected go from “magnetic energy is only 1% of gravitation” to “magnetic fields only complicate the beautiful computer solutions”. What is disregarded is the fact that magnetic effects are very directional(not omni-directional as gravity) and also the fact that magnetic fields are seen every where in our cosmic universe.

Wielebinski, Richard; Beck, Rainer

387

CoCrPt antidot arrays with perpendicular magnetic anisotropy made on anodic alumina templates  

SciTech Connect

Ti(5 nm)/CoCrPt(5-20 nm) bilayers with perpendicular magnetic anisotropy were deposited by rf sputtering onto porous alumina films to form antidot arrays with period 105 nm and pore diameters ranging from 18 to 56 nm. The coercivities of the antidot arrays are greater than those of unpatterned films and show only a weak dependence on antidot diameter. Magnetic force microscopy of ac-demagnetized samples shows that the antidot arrays have domain sizes larger than the 105 nm period. The magnetic behavior is discussed in terms of domain wall pinning by the antidots.

Navas, D.; Ilievski, F.; Ross, C. A. [Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts 02139 (United States)

2009-06-01

388

Microstructure and magnetic anisotropy of electrospun Cu1-xZnxFe2O4 nanofibres: a local probe study  

NASA Astrophysics Data System (ADS)

Understanding phenomena at the nanometre scale is of fundamental importance for future improvements of desired properties of nanomaterials. We report a detailed investigation of the microstructure and the resulting magnetic anisotropy by magnetic, transmission electron microscopy (TEM) and Mössbauer measurements of electrospun Cu1-xZnxFe2O4 nanofibres. Our results show that the electrospun Cu1-xZnxFe2O4 nanofibres exhibit nearly isotropic magnetic anisotropy. TEM measurements indicate that the nanofibres are composed of loosely connected and randomly aligned nanograins. As revealed by the Henkel plot, these nanofibres and the nanograins within the nanofibres are dipolar coupled, which reduces the effective shape anisotropy leading to a nearly random configuration of the magnetic moments inside the nanofibres; hence, the observed nearly isotropic magnetic anisotropy can be easily understood.

Li, Zhiwei; Pan, Weiwei; Zhang, Junli; Yi, Haibo

2011-11-01

389

Measurements of magnetic field alignment  

SciTech Connect

The procedure for installing Superconducting Super Collider (SSC) dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying on these measurements is described and the measurements performed on the first few prototypes SSC magnets are presented. The field angle as a function of position in these 16.6 m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic field intensity (by NMR) characteristic for one of the prototypes is also presented. 5 refs., 7 figs.

Kuchnir, M.; Schmidt, E.E.

1987-11-06

390

CHAPTER 3. STRUCTURE OF MAGNETIC FIELDS 1 Structure of Magnetic  

E-print Network

CHAPTER 3. STRUCTURE OF MAGNETIC FIELDS 1 Chapter 3 Structure of Magnetic Fields Many of the most interesting plasmas are permeated by or imbedded in magnetic fields.1 As shown in Fig. 3.1, the magnetic field properties of magnetic fields in plasmas can be discussed without specifying a model for the plasma

Callen, James D.

391

Origin of the uniaxial magnetic anisotropy in La0.7Sr0.3MnO3 on stripe-domain BiFeO3  

NASA Astrophysics Data System (ADS)

The La0.7Sr0.3MnO3/BiFeO3 (LSMO/BFO) heterostructure has been a model system to study the interaction between ferroic order parameters at a complex oxide interface. In this study, uniaxial magnetic anisotropy is artificially induced in LSMO thin film grown on BFO with electrically patterned stripe domains. Variable-field magnetic force microscopy is exploited to investigate the in situ magnetic switching dynamics and subsequently determine the magnetic easy axis of the LSMO thin film. Intriguingly, one-to-one correspondence between the magnetization of LSMO and the polarization of BFO is found. The observed uniaxial magnetic anisotropy is attributed to the magnetocrystalline anisotropy of the LSMO, which is induced by the shear strain of the BFO lattice, rather than the interfacial magnetic coupling which would be more naturally assumed. This finding highlights the crucial role of lattice coupling at a complex oxide interface. When multiple-order parameters come into play at the heterointerface, special care is needed to deconvolute their effects on the related physical properties.

You, Lu; Wang, Baomin; Zou, Xi; Lim, Zhi Shiuh; Zhou, Yang; Ding, Hui; Chen, Lang; Wang, Junling

2013-11-01

392

Magnetic Field Problem: Measuring Current  

NSDL National Science Digital Library

A cross section of two circular wire loops carrying the exact same current is shown above (position given in centimeters and magnetic field given in milli-Tesla). You can click-drag to read the magnitude of the magnetic field.

Christian, Wolfgang; Belloni, Mario

2007-03-03

393

Studies of solar magnetic fields  

Microsoft Academic Search

An estimate of the average magnetic field strength at the poles of the Sun from Mount Wilson measurements is made by comparing low latitude magnetic measurements in the same regions made near the center of the disk and near the limb. There is still some uncertainty because the orientation angle of the field lines in the meridional plane is unknown,

Robert Howard

1977-01-01

394

Magnetic anisotropy and fabric of some progressively deformed ophiolitic gabbros  

Microsoft Academic Search

The ophiolites, considered remnants of oceanic seafloor, a fruitful source of information on the physical and chemical behavior of the deeper uncored lithosphere. A study of the gabbros in a rather well-preserved ophiolite from the western Alps (Montgenèvre, France) shows strong evidence for intraoceanic plate deformation. To characterize the different steps of deformation observed in the outcrops, a magnetic fabric

J.-J. Wagner; I. G. Hedley; D. Steen; C. Tinkler; m. Vuagnat

1981-01-01

395

Manipulation of modified clay particles in a nematic solvent by a magnetic field  

Microsoft Academic Search

The magnetic alignment of organically modified montmorillonite platelets in magnetic fields is studied using small-angle x-ray scattering. When suspended in non-mesogenic solvents such as dodecanol the platelets are found to align parallel to the magnetic field due to the negative anisotropy of the magnetic susceptibility of the montmorillonite. Alignment of the clay in the nematic phase of 5CB was possible

Joan Connolly; Jeroen S. van Duijneveldt; Susanne Klein; Claire Pizzey; Robert M. Richardson

2007-01-01

396

Relationship between Magnetocrystalline Anisotropy and Orbital Magnetic Moment in L10-Type Ordered and Disordered Alloys  

NASA Astrophysics Data System (ADS)

The magnetocrystalline anisotropy energy and orbital magnetic moment in L10-type transition metal alloys such as FePt, FePd, FeNi, CoPt, CoPd, and MnAl are evaluated while continuously varying the degree of order. The electronic structure with spin--orbit interaction is calculated by employing the tight-binding linear muffin-tin orbital method based on the local spin-density approximation. To control the degree of order, we consider a substitutional disorder and then adopt the coherent potential approximation. The magnetocrystalline anisotropy energy ? E is roughly proportional to the power of the long-range order parameter S, i.e., ? E \\propto Sn (n ˜ 1.6{--}2.4). We also discuss the relationship between the magnetocrystalline anisotropy energy and the orbital magnetic moment. In the same compositional system with different degrees of order, the difference between the orbital magnetic moment in the magnetic easy axis and that in the hard one is proportional to ? E. However, the coefficient corresponding to the effective spin--orbit coupling is inconsistent with the intrinsic one in some cases.

Kota, Yohei; Sakuma, Akimasa

2012-08-01

397

Magnetic anisotropy and chirality of frustrated Cr nanostructures on Au(1?1?1).  

PubMed

By using a fully relativistic embedded cluster Green's function technique we investigated the magnetic anisotropy properties of four different compact Cr trimers (equilateral triangles) and Cr mono-layers deposited on the Au(1?1?1) surface in both fcc and hcp stackings. For all trimers the magnetic ground state was found to be a frustrated 120° Néel configuration. Applying global spin rotations to the magnetic ground state, predictions of an appropriate second order spin Hamiltonian were reproduced with high accuracy by first principles calculations. For the Cr trimers with adjacent Au atoms in similar geometry, we obtained similar values for the in-plane and out-of-plane anisotropy parameters, however, the Dzyaloshinskii-Moriya (DM) interactions appeared to differ remarkably. For two kinds of trimers we found an unconventional magnetic ground state showing 90° in-the-plane rotation with respect to the high symmetry directions. Due to higher symmetry, the in-plane anisotropy term was missing for the mono-layers and distinctly different DM interactions were obtained for the different stackings. The chiral degeneracy of the Néel configurations was lifted by an energy less than 2 meV for the trimers, while this value increased up to about 15 meV per 3 Cr atoms for the hcp packed mono-layer. PMID:25299811

Balogh, L; Udvardi, L; Szunyogh, L

2014-10-29

398

Magnetic anisotropy and chirality of frustrated Cr nanostructures on Au(1?1?1)  

NASA Astrophysics Data System (ADS)

By using a fully relativistic embedded cluster Green's function technique we investigated the magnetic anisotropy properties of four different compact Cr trimers (equilateral triangles) and Cr mono-layers deposited on the Au(1?1?1) surface in both fcc and hcp stackings. For all trimers the magnetic ground state was found to be a frustrated 120° Néel configuration. Applying global spin rotations to the magnetic ground state, predictions of an appropriate second order spin Hamiltonian were reproduced with high accuracy by first principles calculations. For the Cr trimers with adjacent Au atoms in similar geometry, we obtained similar values for the in-plane and out-of-plane anisotropy parameters, however, the Dzyaloshinskii–Moriya (DM) interactions appeared to differ remarkably. For two kinds of trimers we found an unconventional magnetic ground state showing 90° in-the-plane rotation with respect to the high symmetry directions. Due to higher symmetry, the in-plane anisotropy term was missing for the mono-layers and distinctly different DM interactions were obtained for the different stackings. The chiral degeneracy of the Néel configurations was lifted by an energy less than 2 meV for the trimers, while this value increased up to about 15 meV per 3 Cr atoms for the hcp packed mono-layer.

Balogh, L.; Udvardi, L.; Szunyogh, L.

2014-10-01

399

NiO/Fe(001): Magnetic anisotropy, exchange bias, and interface structure  

NASA Astrophysics Data System (ADS)

The magnetic and structural properties of NiO/Fe epitaxial bilayers grown on MgO(001) were studied using magnetooptic Kerr effect (MOKE) and conversion electron Mössbauer spectroscopy (CEMS). The bilayers were prepared under ultra high vacuum conditions using molecular beam epitaxy with oblique deposition. Two systems were compared: one showing the exchange bias (100ML-NiO/24ML-Fe), ML stands for a monolayer, and another where the exchange bias was not observed (50ML-NiO/50ML-Fe). For both, the magnetic anisotropy was found to be complex, yet dominated by the growth-induced uniaxial anisotropy. The training effect was observed for the 100ML-NiO/24ML-Fe system and quantitatively described using the spin glass model. The composition and magnetic state of the interfacial Fe layers were studied using 57Fe-CEMS. An iron oxide phase (Fe3+4Fe2+1O7), as thick as 31 Å, was identified at the NiO/Fe interface in the as-deposited samples. The ferrimagnetic nature of the interfacial iron oxide film explains the complex magnetic anisotropy observed in the samples.

M?y?czak, E.; Luches, P.; Valeri, S.; Korecki, J.

2013-06-01

400

Strong magnetic surface anisotropy of ultrathin Fe on curved Pt(111).  

SciTech Connect

We investigate the step decoration growth and magnetic properties of Fe grown on a curved Pt(111) single crystal by means of low-energy electron diffraction, scanning tunneling microscopy, and the surface magneto-optical Kerr effect. We find that the step-induced magnetic anisotropy enhances the Curie temperature of Fe ultrathin films. Fe grown on high-vicinal-angle surfaces has larger values of both the saturation magnetization M{sub s} and coercivity H{sub c} compared with the flat surface. M{sub s}({alpha}) increases quadratically with the vicinal angle {alpha}. The atomic steps of the vicinal surface greatly affect the magnetic properties of ultrathin Fe films. Finally we find that the step-induced surface anisotropy K{sub s}({alpha}) is proportional to {alpha}{sup 4}. The surface anisotropy of Fe on curved Pt(111) substrate is related to the numbers of atoms at the step edges and the polarization of proximal Pt atoms.

Cheng, R.; Bader, S. D.; Fradin, F. Y.; Materials Science Division; Indiana Univ.-Purdue Univ.

2008-01-01

401

NiO/Fe(001): Magnetic anisotropy, exchange bias, and interface structure  

SciTech Connect

The magnetic and structural properties of NiO/Fe epitaxial bilayers grown on MgO(001) were studied using magnetooptic Kerr effect (MOKE) and conversion electron Moessbauer spectroscopy (CEMS). The bilayers were prepared under ultra high vacuum conditions using molecular beam epitaxy with oblique deposition. Two systems were compared: one showing the exchange bias (100ML-NiO/24ML-Fe), ML stands for a monolayer, and another where the exchange bias was not observed (50ML-NiO/50ML-Fe). For both, the magnetic anisotropy was found to be complex, yet dominated by the growth-induced uniaxial anisotropy. The training effect was observed for the 100ML-NiO/24ML-Fe system and quantitatively described using the spin glass model. The composition and magnetic state of the interfacial Fe layers were studied using {sup 57}Fe-CEMS. An iron oxide phase (Fe{sup 3+}{sub 4}Fe{sup 2+}{sub 1}O{sub 7}), as thick as 31 A, was identified at the NiO/Fe interface in the as-deposited samples. The ferrimagnetic nature of the interfacial iron oxide film explains the complex magnetic anisotropy observed in the samples.

Mlynczak, E. [Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Krakow (Poland)] [Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Krakow (Poland); Luches, P. [S3, Istituto Nanoscienze-CNR, Via G. Campi 213/a, I-41125 Modena (Italy)] [S3, Istituto Nanoscienze-CNR, Via G. Campi 213/a, I-41125 Modena (Italy); Valeri, S. [S3, Istituto Nanoscienze-CNR, Via G. Campi 213/a, I-41125 Modena (Italy) [S3, Istituto Nanoscienze-CNR, Via G. Campi 213/a, I-41125 Modena (Italy); Dipartimento di Scienze Fisiche, Matematiche e Informatiche, Universita di Modena e Reggio Emilia, Via G. Campi 213/a, 41100 Modena (Italy); Korecki, J. [Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Krakow (Poland) [Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30-239 Krakow (Poland); Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al.Mickiewicza 30, 30-059 Krakow (Poland)

2013-06-21

402

Exploration of perpendicular magnetic anisotropy material system for application in spin transfer torque - Random access memory  

NASA Astrophysics Data System (ADS)

Perpendicular magnetic anisotropy (PMA) materials have unique advantages when used in magnetic tunnel junctions (MTJ) which are the most critical part of spin-torque transfer random access memory devices (STT-RAMs) that are being researched intensively as future non-volatile memory technology. They have high magnetoresistance which improves their sensitivity. The STT-RAM has several advantages over competing technologies, for instance, low power consumption, non-volatility, ultra-fast read and write speed and high endurance. In personal computers, it can replace SRAM for high-speed applications, Flash for non-volatility, and PSRAM and DRAM for high-speed program execution. The main aim of this research is to identify and optimize the best perpendicular magnetic anisotropy (PMA) material system for application to STT-RAM technology. Preliminary search for perpendicular magnetic anisotropy (PMA) materials for pinned layer for MTJs started with the exploration and optimization of crystalline alloys such as Co50Pd50 alloy, Mn50Al50 and amorphous alloys such as Tb21Fe72Co7 and are first presented in this work. Further optimization includes the study of Co/[Pd/Pt]x multilayers (ML), and the development of perpendicular synthetic antiferromagnets (SAF) utilizing these multilayers. Focused work on capping and seed layers to evaluate interfacial perpendicular anisotropy in free layers for pMTJs is then discussed. Optimization of the full perpendicular magnetic tunnel junction (pMTJ) includes the CoFeB/MgO/CoFeB trilayer coupled to a pinned/pinning layer with perpendicular Co/[Pd/Pt]x SAF and a thin Ta seeded CoFeB free layer. Magnetometry, simulations, annealing studies, transport measurements and TEM analysis on these samples will then be presented.

Natarajarathinam, Anusha

403

Origin and Significance of Magnetic Anisotropy in the Dufek Layered Intrusion  

NASA Astrophysics Data System (ADS)

Anisotropy of magnetic susceptibility (AMS) is commonly used as a rapid, precise and nondestructive measure of fabrics in igneous rocks. In mafic intrusions that lack cumulus magnetite, magnetic susceptibility is typically low and the anisotropy reflects the combined contribution from paramagnetic Fe-bearing silicates and trace amounts of silicate-hosted magnetite. The precise origin of the AMS signal may be difficult to ascertain and, consequently, inferences about magmatic processes may be limited. Here we illustrate that combined AMS, remanence anisotropy and silicate fabric data (from electron backscatter diffraction, EBSD) from large data sets allow the origin of the magnetic fabrics to be more clearly related to the silicate fabric. We collected approximately 800 cores (3600 specimens) from the lowermost 500m of the Jurassic Dufek layered intrusion in Antarctica. AMS for these specimens reveals moderate anisotropy (mean P' = 1.09) with dominantly oblate magnetic fabrics. We also determined anisotropy of thermoremanence (ATRM) for more than 500 specimens. Remanence anisotropy is much more pronounced, with an average anisotropy of P' = 2.1 (range 1.08-10.4) and dominantly prolate fabrics. AMS and ATRM reveal a consistent fabric, with subvertical minima approximating the pole to the magmatic foliation and subhorizontal maxima clustered in the northeast quadrant. EBSD results from 13 samples, spanning a range of magnetic fabric intensities and lithologies, indicate that statistically significant mineral lineations are absent in most samples. Because silicate-hosted magnetite is expected to be the dominant magnetic carrier in these cumulates (three quarters have susceptibility < 0.001 SI and no discrete magnetite grains are observed petrographically), the lack of detectable lineation in the silicates is apparently difficult to reconcile with the pronounced magnetic fabrics. However, when crystallographic data from all samples are combined, the substantial data set (n=135,735 for plagioclase, n=48,608 for orthopyroxene, n=14,365 for clinopyroxene) allows relatively unambiguous correlation of magnetic and silicate fabrics. Crystallographic c-axes for orthopyroxene show the highest degree of clustering (maximum eigenvalue 0.53) and have a mean direction (039°/09°) that is virtually indistiguishable from the ATRM maxima (031°/03°). Clinopyroxene and plagioclase c-axes show less pronounced clustering (maximum eigenvalues 0.41 and 0.37, respectively) with more easterly, subhorizontal directions (099°/03°). Orthopyroxene-hosted magnetite needles (elongate parallel to the c-axis) are presumably the dominant source of the magnetic lineation in both ATRM and AMS. These results provide compelling evidence that magnetic fabric data can provide a robust measure of, at least, the alignment of pyroxene in the Dufek intrusion. When corroborated by silicate fabric analysis, magnetic fabrics may be a sensitive indicator of silicate mineral alignment including subtle lineations that are otherwise difficult to discern.

Gee, J. S.; Lusk, M. W.; Cheadle, M. J.; Grimes, C. B.; Meurer, W. P.

2009-12-01

404

Magnetic Field Control of the Quantum Chaotic Dynamics of Hydrogen Analogues in an Anisotropic Crystal Field  

E-print Network

We report magnetic field control of the quantum chaotic dynamics of hydrogen analogues in an anisotropic solid state environment. The chaoticity of the system dynamics was quantified by means of energy level statistics. We analyzed the magnetic field dependence of the statistical distribution of the impurity energy levels and found a smooth transition between the Poisson limit and the Wigner limit, i.e. transition between regular Poisson and fully chaotic Wigner dynamics. Effect of the crystal field anisotropy on the quantum chaotic dynamics, which manifests itself in characteristic transitions between regularity and chaos for different field orientations, was demonstrated.

Weihang Zhou; Zhanghai Chen; Bo Zhang; C. H. Yu; Wei Lu; S. C. Shen

2010-03-09

405

Electric-field control of magnetic domain wall motion and local magnetization reversal  

PubMed Central

Spintronic devices currently rely on magnetic switching or controlled motion of domain walls by an external magnetic field or spin-polarized current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including enhanced functionality and low power consumption. Here we report on an approach to electrically control local magnetic properties, including the writing and erasure of regular ferromagnetic domain patterns and the motion of magnetic domain walls, in CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer from ferroelastic domains in ferroelectric media to continuous magnetostrictive films with negligible magnetocrystalline anisotropy. Optical polarization microscopy of both ferromagnetic and ferroelectric domain structures reveals that domain correlations and strong inter-ferroic domain wall pinning persist in an applied electric field. This leads to an unprecedented electric controllability over the ferromagnetic microstructure, an accomplishment that produces giant magnetoelectric coupling effects and opens the way to electric-field driven spintronics. PMID:22355770

Lahtinen, Tuomas H. E.; Franke, Kévin J. A.; van Dijken, Sebastiaan

2012-01-01

406

Sputtering of cobalt film with perpendicular magnetic anisotropy on disorder-free graphene  

NASA Astrophysics Data System (ADS)

Growth of thin cobalt film with perpendicular magnetic anisotropy has been investigated on pristine graphene for spin logic and memory applications. By reduction of the kinetic energy of the sputtered atoms using indirect sputtered deposition, deposition induced defects in the graphene layer have been controlled. Cobalt film on graphene with perpendicular magnetic anisotropy has been developed. Raman spectroscopy of the graphene surface shows very little disorder induced in the graphene by the sputtering process. In addition, upon increasing the cobalt film thickness, the disorder density increases on the graphene and saturates for thicknesses of Co layers above 1 nm. The AFM image indicates a surface roughness of about 0.86 nm. In addition, the deposited film forms a granular structure with a grain size of about 40 nm.

Jamali, Mahdi; Lv, Yang; Zhao, Zhengyang; Wang, Jian-Ping

2014-10-01

407

Sputtering of cobalt film with perpendicular magnetic anisotropy on disorder-free graphene  

SciTech Connect

Growth of thin cobalt film with perpendicular magnetic anisotropy has been investigated on pristine graphene for spin logic and memory applications. By reduction of the kinetic energy of the sputtered atoms using indirect sputtered deposition, deposition induced defects in the graphene layer have been controlled. Cobalt film on graphene with perpendicular magnetic anisotropy has been developed. Raman spectroscopy of the graphene surface shows very little disorder induced in the graphene by the sputtering process. In addition, upon increasing the cobalt film thickness, the disorder density increases on the graphene and saturates for thicknesses of Co layers above 1 nm. The AFM image indicates a surface roughness of about 0.86 nm. In addition, the deposited film forms a granular structure with a grain size of about 40 nm.

Jamali, Mahdi; Lv, Yang; Zhao, Zhengyang; Wang, Jian-Ping, E-mail: jpwang@umn.edu [Department of Electrical and Computer Engineering, University of Minnesota, 4-174 200 Union Street SE, Minneapolis, MN 55455 (United States)

2014-10-15

408

Solar magnetic fields and convection  

Microsoft Academic Search

The solar magnetic fields observed in active regions and their residues are thought to be parts of toroidal field systems renewed every 11-yr cycle from a poloidal field. The latter may be either a reversing (dynamo) field or a non-reversing, primordial field. The latter view was held for some 70 yr, but the apparent reversals of the polar-cap fields in

J. H. Piddington

1977-01-01

409

Orientation of Conductive Polymer PEDOT:PSS Films Prepared Under Magnetic Field  

NASA Astrophysics Data System (ADS)

We report the magnetic field orientation effect of the conductive polymer poly(3,4-ethylene dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS). The films prepared under the magnetic field parallel to the substrates show clear anisotropy of the polarized infrared reflectivity and DC resistivity. The results indicate that the nano-crystals of PEDOT are aligned in the polymer films by magnetic fields.

Guziak, Milena A.; Honma, Yuta; Hashimoto, Kenichiro; Nishizaki, Terukazu; Watanabe, Kazuo; Sasaki, Takahiko

410

Anisotropy of the Magnetic Susceptibility of the Alnö alkaline and carbonatite igneous complex  

NASA Astrophysics Data System (ADS)

The Alnö igneous complex in central Sweden is one of the largest (radius ~2.5 km) of the few well-known alkaline and carbonatite ring-intrusions in the world. The lithologies span from alkaline silicate rocks (nepheline syenite, ijolite, and pyroxenite) to a range of carbonatite dykes (e.g. sövite) with variable composition. The depth extent, dip, and dip direction of the alkaline and carbonatite rocks have been inferred from surface geological mapping, and a dome-shaped magma chamber with the roof at ~2 km below the palaeosurface was inferred to have supplied steeply dipping radial dykes and (shallowly dipping) cone sheets. Recent high-resolution reflection seismic profiles and gravity and ground magnetic measurements suggest, in turn, a saucer-shaped magma chamber at ~3 km depth below present day land surface. To provide further insight into the internal flow mechanics of these dykes and into their emplacement mechanisms, we have measured the anisotropy of magnetic susceptibility (AMS). About 250 samples from 119 oriented cores were collected with a handheld drilling machine from 26 localities within the Alnö complex. Prior to preparation of discrete samples for AMS, the cores were measured for their density and for ultrasonic P- and S-wave velocities. Most of the sampling locations lie on a transect through the intrusion. Three locations have been sampled in detail, to determine the variation of AMS within individual carbonatite dykes. The AMS of samples were measured in low-field, using a KLY-2 Kappabridge. Bulk magnetic susceptibility ranges from 3.01e-5 to 2.50e-1 SI, and correlates with lithology. The sövites have the widest range of susceptibility (average 4.32e-2, with a range from 3.01e-5 to 2.50e-1 SI), whereas fenites have the lowest average susceptibility (average 2.06e-3, with a range from 9.86e-5 to 1.47e-2 SI); nepheline-syenite, ijolite and pyroxenite have susceptibilities between these two end member lithologies. Sövite consists mainly of calcite; but holds varying concentrations of magnetite, pyrochlore, and biotite. These minerals explain the wide range of susceptibilities found in the sövites. Within sövite dykes, the magnetic fabric is consistent however, and has strong association with the orientation of the dyke. Maximum susceptibility (k1) tends to be sub-parallel to the strike of the dyke, displaying mostly sub-horizontal orientations. The minimum susceptibility axes (k3) are generally oriented perpendicular to the strike of the dyke. The magnetic fabric in the transect displays greater variation and complexity in the orientation of the principal susceptibility axes. The majority of samples have an oblate shape susceptibility ellipsoid, but many have triaxial and a few have prolate shapes. The close affinity of the AMS with the orientation of the dyke, together with geological mapping of outcrops, helps to infer the flow direction of the magma. The sub-horizontal direction of the maximum susceptibility can be interpreted such that the flow direction of magma during intrusion might have been horizontal rather than vertical in the investigated sövite dykes. This assumes that the anisotropy is from primary flow, but it is also possible that it was created due to post-emplacement flattening. The full nature of fabrics will help to further unravel the history of the Alnö complex and test hypotheses of flow patterns.

Andersson, M.; Almqvist, B.; Malehmir, A.; Troll, V. R.; Snowball, I.; Lougheed, B.

2013-12-01

411

Photo-induced changes in the magnetic anisotropy of silicon-doped yttrium iron garnet  

Microsoft Academic Search

Measurements are reported of the changes in the magnetocrystalline anisotropy which were induced in specimens of silicon-doped yttrium iron garnet by irradiating them with a plane polarized infrared beam. The torque exerted by magnetically saturated samples was measured using a torque magnetometer at 4.2K. Single-crystal specimens of composition Y3Fe5-xSixO12 with x=0.035, 0.07 and 0.08 were studied. A semi phenomenological model

B. T. Sharp; R. W. Teale

1974-01-01

412

Using anisotropy of magnetic susceptibility to better constrain the tilt correction in paleomagnetism: A case study from southern Peru  

NASA Astrophysics Data System (ADS)

We report a combined study of anisotropy of low field magnetic susceptibility (AMS) and paleomagnetism from 16 sites in a sedimentary sequence of Eocene-early Oligocene red beds in southern Peru. Incipient tectonic strain is recorded during the early stages of deformation. Nonhorizontal magnetic lineation in geographic coordinate suggests either noncylindrical folding and/or interference of two phases of compressive deformation and tectonic rotation. Applying the classic tilt correction results in significant dispersion in paleomagnetic declinations and apparent clockwise and counterclockwise relative tectonic rotations. A dispersion in the orientation of the magnetic lineation also arises from a simple classic tilt correction inducing apparent local rotation in paleostress determination. The magnetic lineation is a good proxy to detect a complex history of folding when the finite strain is not large enough to reset the magnetic fabric acquired during the early stages of deformation and when detailed geological field mapping is not available or not possible. In the present study, a double correction rotating first the lineation to the horizontal reduces significantly the dispersion of the paleomagnetic data with respect to conventional tilt correction (Fisher parameter k increases from 14 to 35). The interest of this double correction must obviously be evaluated for each study according to the complexity of the folding and the intensity of the deformation. Assuming a mean age of 40 Ma for the sedimentary sequence, no significant rotation (-4.5° ± 8.4) is observed in this area of the Peruvian Andes.

Roperch, Pierrick; Carlotto, Victor; Chauvin, Annick

2010-12-01

413

Interfacial oxygen migration and its effect on the magnetic anisotropy in Pt/Co/MgO/Pt films  

SciTech Connect

This paper reports the interfacial oxygen migration effect and its induced magnetic anisotropy evolution in Pt/Co/MgO/Pt films. During depositing the MgO layer, oxygen atoms from the MgO combine with the neighboring Co atoms, leading to the formation of CoO at the Co/MgO interface. Meanwhile, the films show in-plane magnetic anisotropy (IMA). After annealing, most of the oxygen atoms in CoO migrate back to the MgO layer, resulting in obvious improvement of Co/MgO interface and the enhancement of effective Co-O orbital hybridization. These favor the evolution of magnetic anisotropy from IMA to perpendicular magnetic anisotropy (PMA). The oxygen migration effect is achieved by the redox reaction at the Co/MgO interface. On the contrary, the transfer from IMA to PMA cannot be observed in Pt/Co/Pt films due to the lack of interfacial oxygen migration.

Chen, Xi; Feng, Chun, E-mail: fengchun@ustb.edu.cn, E-mail: ghyu@mater.ustb.edu.cn; Liu, Yang; Jiang, Shaolong; Hua Li, Ming; Hua Yu, Guang, E-mail: fengchun@ustb.edu.cn, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Long Wu, Zheng [Analytical and Testing Center, Beijing Normal University, Beijing 100875 (China); Yang, Feng [State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249 (China)

2014-02-03

414

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

SciTech Connect

Amorphous CoSiB/Pt multilayer is a perpendicular magnetic anisotropy material to achieve high squareness, low coercivity, strong anisotropy, and smooth domain wall (DW) motion, because of the smoother interface compared with crystalline multilayers. For [CoSiB(6?Å)/Pt (14?Å)]{sub N} multilayers with N?=?3, 6, and 9, we studied the field-induced DW dynamics. The effective anisotropy constant K{sub 1}{sup eff} is 1.5?×?10{sup 6}?erg/cm{sup 3} for all the N values, and the linear increment of coercive field H{sub c} with N gives constant exchange coupling J. By analyzing the field dependence of DW images at room temperature, a clear creep motion with the exponent ??=?1/4 could be observed. Even though the pinning field H{sub dep} slightly increases with N, the pinning potential energy U{sub c} is constant (=35 k{sub B}T) for all the N values. These results imply that the amorphous [CoSiB/Pt]{sub N} multilayers are inherently homogeneous compared to crystalline multilayers. For N???6, the pinning site density ?{sub pin} is less than 1000/?m{sup 2}, which is about 1 pinning site per the typical device junction size of 30?×?30 nm{sup 2}. Also, the exchange stiffness constant A{sub ex} is obtained to be 0.48?×?10{sup ?6}?erg/cm, and the domain wall width is expected to be smaller than 5.5?nm. These results may be applicable for spin-transfer-torque magnetic random access memory and DW logic device applications.

Choi, Y. H.; Lee, K. J.; Jung, M. H., E-mail: mhjung@sogang.ac.kr [Department of Physics, Sogang University, Seoul 121-742 (Korea, Republic of); Yoon, J. B.; Cho, J. H.