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1

Anisotropy in MHD turbulence due to a mean magnetic field  

Microsoft Academic Search

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

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

1983-01-01

2

Anisotropy in MHD turbulence due to a mean magnetic field  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

3

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

4

Structural anisotropy of silica hydrogels prepared under magnetic field  

Microsoft Academic Search

Birefringence measurements have been carried out on the Pb-doped silica hydrogels prepared under various magnetic fields up to 5T. The silica gels prepared at 5T were used as a medium of crystal growth of PbBr2, whose result implied the structural anisotropy; an aligned array of crystallites was obtained by transmission electron microscopy. While the samples prepared at 0, 1, and

Atsushi Mori; Takamasa Kaito; Hidemitsu Furukawa

2008-01-01

5

Structural anisotropy of silica hydrogels prepared under magnetic field  

E-print Network

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

Atsushi Mori; Takamasa Kaito; Hidemitsu Furukawa

2008-03-02

6

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

7

On the Control of Magnetic Anisotropy through an External Electric Field.  

PubMed

The effect of an external electric field on the magnetic anisotropy of a single-molecule magnet has been investigated, for the first time, with the help of DFT. The application of an electric field can alter the magnetic anisotropy from "easy-plane" to "easy-axis" type. Excitation analysis performed through time-dependent DFT predicts that the external electric field facilitates metal to ?-acceptor ligand charge transfer, leading to uniaxial magnetic anisotropy and concomitant spin Hall effect in a single molecule. PMID:25154493

Goswami, Tamal; Misra, Anirban

2014-10-20

8

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

9

GALACTIC MAGNETIC FIELDS AND THE LARGE-SCALE ANISOTROPY AT MILAGRO  

SciTech Connect

The air-shower observatory Milagro has detected a large-scale anisotropy of unknown origin in the flux of TeV cosmic rays. We propose that this anisotropy is caused by galactic magnetic fields and, in particular, that it results from the combined effects of the regular and the turbulent (fluctuating) magnetic fields in our vicinity. Instead of a diffusion equation, we integrate Boltzmann's equation to show that the turbulence may define a preferred direction in the cosmic ray propagation that is orthogonal to the local regular magnetic field. The approximate dipole anisotropy that we obtain explains Milagro's data well.

Battaner, Eduardo; Castellano, JoaquIn; Masip, Manuel, E-mail: battaner@ugr.e, E-mail: jcastellano@correo.ugr.e, E-mail: masip@ugr.e [Departamento de Fisica Teorica y del Cosmos, Universidad de Granada, E-18071 Granada (Spain)

2009-09-20

10

The dependence of coercivity on anisotropy field in sintered R-Fe-B permanent magnets  

Microsoft Academic Search

To investigate the dependence of intrinsic coercivity of R-Fe-B permanent magnets (R = rare earths) on the anistropy field of R2Fe14B, the temperature dependence of the intrinsic coercivity of Pr15Fe77B8 and Nd15Fe77B8 have been measured from 4.2 K to the Curie temperature of the magnets. Study of the interrelation between coercivity and anisotropy field by modifying the anisotropy field through

S. Hirosawa; K. Tokuhara; Y. Matsuura; H. Yamamoto; S. Fujimura; M. Sagawa

1986-01-01

11

Magnetic anisotropy modified by electric field in V/Fe/MgO(001)/Fe epitaxial magnetic tunnel junction  

NASA Astrophysics Data System (ADS)

Single-crystalline V/Fe(0.7 nm)/MgO(1.2nm)/Fe(20 nm) magnetic tunnel junctions are studied to quantify the influence of an electric field on the Fe/MgO interface magnetic anisotropy. The thinnest Fe soft layer has a perpendicular magnetic anisotropy (PMA), whereas the thickest Fe layer acts as sensor for magnetic anisotropy changes. When electrons are added at the PMA Fe/MgO interface (negative voltage), no anisotropy changes are observed. For positive voltage, the anisotropy constant decreases with increasing bias voltage. A huge 1150 fJ V-1 m-1 anisotropy variation with field is observed and the magnetization is found to turn from out-of-plane to in-plane of the sample with the applied voltage.

Rajanikanth, A.; Hauet, T.; Montaigne, F.; Mangin, S.; Andrieu, S.

2013-08-01

12

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

PubMed Central

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

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

2014-01-01

13

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

14

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

Microsoft Academic Search

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) and the angle of the vector in the

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

2011-01-01

15

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

16

Temperature anisotropy instabilities; combining plasma and magnetic field data at different distances from the Sun  

NASA Astrophysics Data System (ADS)

We present a new data analysis method enabling the observation of magnetic field fluctuations associated with temperature anisotropy instabilities using the Ulysses spacecraft. The movement of the spacecraft away from the Sun causes the observed plasma conditions, turbulent fluctuation amplitude, magnetic field strength and important physical scales to change. We normalize wavelet power spectra of the magnetic field using local values for the proton gyroscale and large scale magnetic field fluctuation amplitude to remove the effects of varying heliocentric distance. We recover the enhancement of magnetic fluctuations where temperature anisotropy instability growth rates are large, as seen by previous studies in the ecliptic at 1 AU. This method can be applied to any spacecraft data that contains large changes in physical scales, magnetic field strength or other plasma parameters, for example the upcoming Solar Orbiter and Solar Probe Plus missions.

Wicks, Robert T.; Matteini, Lorenzo; Horbury, Timothy S.; Hellinger, Petr; Roberts, D. Aaron

2013-06-01

17

Investigations of cosmic ray anisotropies and their relationship to concurrent magnetic field data  

NASA Technical Reports Server (NTRS)

Investigations of cosmic ray anisotropies and their relationship to concurrent magnetic field data are reported. These investigations range in scope from the examination of data very late in the decay phase of a solar particle event where long term (approximately 6 hour) averages are used and definite interplanetary effects sought after to an examination of the change in low energy particle anisotropy as the satellite approaches the bow shock and the magnetopause.

Allum, F. R.

1974-01-01

18

Low-magnetic-field dependence and anisotropy of the critical current density in coated conductors  

Microsoft Academic Search

Many applications of ReBCO-coated conductors operate at low magnetic fields in the superconductor (below 200 mT). In order to predict the critical current and AC loss in these applications, it is necessary to know the anisotropy and field dependence of the critical current density at low magnetic fields. In this paper, we obtain a formula for the critical current density

E. Pardo; M. Vojenciak; F. Gömöry; J. Souc

2011-01-01

19

Magnetic anisotropy of chloritoid  

NASA Astrophysics Data System (ADS)

The magnetocrystalline anisotropy of monoclinic chloritoid, a relatively common mineral in aluminum-rich, metapelitic rocks, has been determined for the first time by measuring the high-field anisotropy of magnetic susceptibility (HF-AMS), using two independent approaches, i.e., (a) directional magnetic hysteresis measurements and (b) torque magnetometry, on a collection of single crystals collected from different tectonometamorphic settings worldwide. Magnetic remanence experiments show that all specimens contain ferromagnetic (s.l.) impurities, being mainly magnetite. The determined HF-AMS ellipsoids have a highly oblate shape with the minimum susceptibility direction subparallel to the crystallographic c-axis of chloritoid. In the basal plane of chloritoid, though the HF-AMS can be considered isotropic. The degree of anisotropy is found to be 1.47, which is significantly higher than the anisotropy of most paramagnetic silicates and even well above the frequently used upper limit (i.e., 1.35) for the paramagnetic contribution to the AMS of siliciclastic rocks. The obtained values for the paramagnetic Curie temperature parallel (??) and perpendicular (??) to the basal plane indicate that this pronounced magnetocrystalline anisotropy is related to strong antiferromagnetic exchange interactions in the direction of the crystallographic c-axis (?? < 0) and rather weak ferromagnetic exchange interactions within the basal plane (?? > 0). As a consequence, chloritoid-bearing metapelites with a pronounced mineral alignment can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic, ferromagnetic (s.l.) minerals. The newly discovered magnetocrystalline anisotropy of chloritoid thus calls for a revised approach of magnetic fabric interpretations in chloritoid-bearing rocks.

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

2013-08-01

20

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

E-print Network

Bulk motions of electrons along the line of sight induce secondary temperature fluctuations in the post-decoupling, reionized universe. In the presence of a magnetic field not only the scalar mode but also the vector mode act as a source for the bulk motion. The resulting angular power spectrum of temperature anisotropies of the cosmic microwave background is calculated assuming a simple model of reionization.Contributions from the standard adiabatic, curvature mode and a non helical magnetic field are included. The contribution due to magnetic fields with field strengths of order nG and negative magnetic spectral indices dominates for multipoles larger than $\\ell \\sim 10^4$.

Kunze, Kerstin E

2013-01-01

21

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

NASA Astrophysics Data System (ADS)

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

Kunze, Kerstin E.

2014-05-01

22

Possible origin of nonlinear magnetic anisotropy variation in electric field effect in a double interface system  

NASA Astrophysics Data System (ADS)

We investigated the effect of an electric field on the interface magnetic anisotropy of a thin MgO/Fe/MgO layer using density functional theory. The perpendicular magnetic anisotropy energy (MAE) increases not only under electron depletion but also under some electron accumulation conditions, showing a strong correlation with the number of electrons on the interface Fe atom. The reverse variation in the MAE under the electric field is ascribed to novel features on the charged interface, such as electron leakage. We discuss the origin of the variation in terms of the electronic structures.

Yoshikawa, Daiki; Obata, Masao; Taguchi, Yusaku; Haraguchi, Shinya; Oda, Tatsuki

2014-11-01

23

Electric field controlled reversible magnetic anisotropy switching studied by spin rectification  

NASA Astrophysics Data System (ADS)

In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg1/3Nb2/3)O3-PbTiO3 substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropy field. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

Zhou, Hengan; Fan, Xiaolong; Wang, Fenglong; Jiang, Changjun; Rao, Jinwei; Zhao, Xiaobing; Gui, Y. S.; Hu, C.-M.; Xue, Desheng

2014-03-01

24

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

25

Magnetic anisotropy of chloritoid  

NASA Astrophysics Data System (ADS)

The anisotropy of magnetic susceptibility (AMS) is commonly used as a petrofabric tool. Whereas qualitative relationships between AMS and the petrofabric are well established, quantitative correlations are often ambiguous. For a quantitative interpretation of the paramagnetic component of a rock's AMS, the mineral source(s) of the paramagnetic fabric and their intrinsic contribution(s) should be understood. This requires knowledge about the intrinsic AMS of the rock-forming, paramagnetic minerals. For this study, the magnetocrystalline anisotropy of monoclinic chloritoid, a relatively common mineral in aluminium-rich, metapelitic rocks, has been determined for the first time by measuring the high-field anisotropy of magnetic susceptibility (HF-AMS) on a collection of single crystals, collected from different tectonometamorphic settings worldwide. Magnetic remanence experiments, i.e. (a) alternating-field (AF) demagnetization of a 1 T isothermal remanent magnetization (IRM) and a 200 mT anhysteretic remanent magnetization (ARM) and (b) low-temperature cycling of a room temperature saturation isothermal remanent magnetization (RT-SIRM), show that all specimens contain ferromagnetic (s.l.) impurities, being mainly magnetite. The determined HF-AMS ellipsoids have a highly oblate shape with the minimum susceptibility direction subparallel to the crystallographic c-axis of chloritoid. In the basal plane of chloritoid, however, the HF-AMS can be considered isotropic. The paramagnetic Curie temperature (?), which has been determined parallel and perpendicular to the basal plane, indicates a weak antiferromagnetic interaction in the direction of the crystallographic c-axis and a ferromagnetic interaction within the basal plane. The degree of anisotropy is found to be 1.48, which is significantly higher than the anisotropy of most paramagnetic silicates, i.e. the Fe-bearing phyllosilicates and the mafic silicates pyroxene, orthopyroxene, amphibole and olive, and even well above the frequently used upper limit (i.e. 1.35) for the paramagnetic contribution to AMS in siliciclastic rocks. As a consequence, chloritoid-bearing metapelites with a pronounced mineral alignment can have a higher degree of anisotropy than expected, without a significant contribution of strongly anisotropic, ferromagnetic (s.l.) minerals. The newly discovered magnetocrystalline anisotropy of chloritoid thus calls for a revised approach of magnetic fabric interpretations in chloritoid-bearing rocks.

Haerinck, Tom; Debacker, Timothy; Sintubin, Manuel

2013-04-01

26

Electric field induced anisotropy modification in (Ga,Mn)As: A strategy for the precessional switching of the magnetization  

NASA Astrophysics Data System (ADS)

We propose a scheme for the precessional switching of the magnetization in the magnetic semiconductor (Ga,Mn)As using cubic anisotropy field reduction triggered by electric field and a small assisting magnetic field. We identify magnetic field regions for toggle switching and direct-overwrite of the magnetization and discuss the toggle switching critical curve dependence on the cubic anisotropy field decrease. We also determine the half-precession period of the magnetization and propose field conditions for magnetization trajectories which are optimally immune to external noise and damping.

Balestriere, P.; Devolder, T.; Wunderlich, J.; Chappert, C.

2010-04-01

27

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

28

Tuning of the nucleation field in nanowires with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

29

Magnetic fields and cosmic ray anisotropies at TeV energies  

E-print Network

Several cosmic-ray observatories have provided a high accuracy map of the sky at TeV--PeV energies. The data reveals 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 Boltzmann's equation we derive expressions for the cosmic-ray flux that fit most of these features. The anisotropies depend on the local interstellar magnetic field B_{IS}, on the average galactic field B_{R} in our vicinity, and on the distribution of dominant cosmic-ray sources. We show that the initial dipole anisotropy along B_{IS} can be modulated by changes in the global cosmic ray wind, and that a variation in the dipole direction would imply a given radius of coherence for B_{IS}. We also show that small and medium-scale anisotropies may appear when the full-sky anisotropy finds a turbulence acting as a magnetic lens.

Eduardo Battaner; Joaquin Castellano; Manuel Masip

2014-07-03

30

Magnetic-field-assisted assembly of CoFe layered double hydroxide ultrathin films with enhanced electrochemical behavior and magnetic anisotropy.  

PubMed

Magnetic films based on CoFe LDH nanoplatelets and porphyrin anions were fabricated by the layer-by-layer assembly technique with an assistance of an external magnetic field, which show enhanced electrochemical behavior and magnetic anisotropy. PMID:21283892

Shao, Mingfei; Wei, Min; Evans, David G; Duan, Xue

2011-03-21

31

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

NASA Technical Reports Server (NTRS)

The intergalactic magnetic field (IGMF) may leave an imprint on the anisotropy properties of the extragalactic gamma-ray background, through its effect on electromagnetic cascades triggered by interactions between very high energy photons and the extragalactic background light. A strong IGMF will deflect secondary particles produced in these cascades and will thus tend to isotropize lower energy cascade photons, thus inducing a modulation in the anisotropy energy spectrum of the gamma-ray background. Here we present a simple, proof-of-concept calculation of the magnitude of this effect and demonstrate that the two extreme cases (zero IGMF and IGMF strong enough to completely isotropize cascade photons) would be separable by ten years of Fermi observations and reasonable model parameters for the gamma-ray background. The anisotropy energy spectrum of the Fermi gamma-ray background could thus be used as a probe of the IGMF strength.

Venters, T. M.; Pavlidou, V.

2012-01-01

32

Hale cycle effects in cosmic ray east-west anisotropy and interplanetary magnetic field  

NASA Technical Reports Server (NTRS)

We have reanalyzed diurnal anisotropy data obtained with the shielded ion chamber (IC) at Cheltenham/Fredericksburg and the neutron monitor (NM) at Swarthmore/Newark. IC data are for the 1936-1977 period and NM data are for the 1965-1988 period. We have corrected IC data for the diurnal temperature effect. Application of this correction results in a better agreement between IC and other data sets, thereby making it possible to study the long-term changes in the diurnal anisotropy using IC data. The behavior of the annual mean east-west anisotropy is studied for 53 years of observations. The period encompasses more than two solar magnetic (Hale) cycles. Its amplitude undergoes the expected 11 and 22 year variations, with the largest changes occurring near solar activity minima. Moreover, the data indicate the presence of the subsidiary maxima for the entire 53-year period, following the solar polar field reversals, during the declining phases of activity cycles when high-speed solar wind streams are present in the heliosphere. The data suggest that the amplitude of the subsidiary maximum is large when the solar polar magnetic field points toward the sun in the Northern Hemisphere, and radial anisotropy is absent.

Ahluwalia, H. S.

1993-01-01

33

Coronal holes, solar diurnal anisotropy of cosmic rays and off-ecliptic interplanetary magnetic fields  

NASA Technical Reports Server (NTRS)

The information regarding the electromagnetic states of the interplanetary medium, derived from the analyses of the cosmic ray intensity variations observed with a global network of cosmic ray detectors such as neutron monitors and muon telescopes, is reviewed. The relation of the temporal characteristics of the cosmic ray solar diurnal anisotropy to the large scale characteristics of the interplanetary magnetic field, far away from the ecliptic plane, is addressed. A model for the phenomenon is described.

Ahluwalia, H. S.

1980-01-01

34

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

35

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

36

Low-magnetic-field dependence and anisotropy of the critical current density in coated conductors  

NASA Astrophysics Data System (ADS)

Many applications of ReBCO-coated conductors operate at low magnetic fields in the superconductor (below 200 mT). In order to predict the critical current and AC loss in these applications, it is necessary to know the anisotropy and field dependence of the critical current density at low magnetic fields. In this paper, we obtain a formula for the critical current density in a coated conductor as a function of the local magnetic field and its orientation. Afterwards, we apply this formula to predict the critical current of a pancake coil that we constructed. We extract the critical current density of the tape from measurements of the in-field critical current at several orientations. Numerical simulations correct the effect of the self-field in the measurements and successfully predict the critical current in the pancake coil. We found that a simple elliptical model is not enough to describe the anisotropy of the critical current density. In conclusion, the analytical fit that we present is useful to predict the critical current of actual coils. Therefore, it may also be useful for other structures made of coated conductor, like power-transmission cables, Roebel cables and resistive fault current limiters.

Pardo, E.; Vojen?iak, M.; Gömöry, F.; Šouc, J.

2011-06-01

37

Rare-earth magnetic anisotropy: Is the crystal field theory valid?  

NASA Astrophysics Data System (ADS)

It was suggested in recent papers that the crystal field parameters describing the rare-earth magnetic anisotropy in metals should strongly depend on the orientation of the 4f shell, in contrast to a basic assumption of crystal field theory. By comparing the results of a perturbation approach with those from self-consistent calculations within the constrained local spin density approximation - including the polarization of closed electron shells by the aspherical 4f shell - it is demonstrated that this is not the case. Results of full potential linear muffin-tin orbital calculations are presented for several rare-earth metals and for SmCo5.

Fähnle, M.; Buck, S.

1997-02-01

38

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

E-print Network

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) and the angle of the vector in the plane perpendicular to the velocity (\\phi). 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,\\phi) based on a scalar field description of turbulence theory. This allows us to predict the variation in the \\phi 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 ...

Wicks, Robert T; Horbury, Timothy S; Oughton, S

2011-01-01

39

Introduction Magnetic Anisotropy of  

E-print Network

not completely understood interesting for dilute magnetic semiconductors (DMSs) transparent ferromagnetsIntroduction Results Magnetic Anisotropy of Transition Metal Monoxides Andreas Schrön Institut für Introduction Why are Transition Metal Oxides so interesting? Theoretical Approach ­ Density Functional Theory

Rossak, Wilhelm R.

40

Tailoring the interfacial magnetic anisotropy in multiferroic field-effect devices  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

41

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

Microsoft Academic Search

Dynamic birefringence in a ferrofluid subjected to crossed bias (constant) and probing (pulse or ac) fields is considered, assuming that the nanoparticles have finite magnetic anisotropy. This is done on the basis of the general Fokker-Planck equation that takes into account both internal magnetic and external mechanical degrees of freedom of the particle. We describe the orientation dynamics in terms

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

2002-01-01

42

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

Microsoft Academic Search

Dynamic birefringence in a ferrofluid subjected to crossed bias ~constant! and probing ~pulse or ac! fields is considered, assuming that the nanoparticles have finite magnetic anisotropy. This is done on the basis of the general Fokker-Planck equation that takes into account both internal magnetic and external mechanical degrees of freedom of the particle. We describe the orientation dynamics in terms

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

2002-01-01

43

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

44

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

45

Modeling Ring Current Ion Anisotropy and Plasma Instability in Non-Dipolar Magnetic Fields  

NASA Astrophysics Data System (ADS)

Intense plasma waves, which may cause significant acceleration or loss of energetic particles, are excited in the inner magnetosphere during magnetically active periods. The free energy for these waves is supplied from the anisotropic ring current ion and electron distributions. We evaluate the spatial and temporal development of the ring current during several high-speed streams driven geomagnetic storms, using our newly improved kinetic model (RAM) which has been extended for non-dipolar magnetic field geometry. The RAM is two-way coupled with a 3-D equilibrium code that calculates self-consistently the magnetic field (SCB) in force balance with the anisotropic ring current distributions. The plasma boundary conditions of RAM-SCB are specified from LANL data measured at geosynchronous orbit. We investigate the effects of non-dipolar magnetic field configuration on ring current evolution like the formation of ion ring distributions due to energy dependent drifts, charge exchange losses, and injection boundaries between open and closed drift paths. We find that as strong depressions in the self-consistent magnetic field develop on the nightside during the main phase of a storm, the particles’ gradient-curvature drift velocity increases, the ion fluxes are reduced and the ring current is confined close to Earth. As a result of drift-shell splitting, the pitch angle anisotropy decreases at large L shells on the nightside and increases on the dayside. We calculate the linear growth rate of EMIC and magnetosonic waves in the equatorial plane and identify regions for potential excitation of these plasma instabilities in the inner magnetosphere during storm time.

Jordanova, V. K.; Chen, L.; Thorne, R. M.; Zaharia, S. G.; Welling, D. T.; Thomsen, M. F.

2010-12-01

46

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

E-print Network

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

Yue Zhou; Guofeng Zhang

2008-08-18

47

Anisotropies of the Taylor Scale, Correlation Scale, and Effective Magnetic Reynolds Number Determination from Solar Wind Magnetic Field Fluctuations  

NASA Astrophysics Data System (ADS)

ACE, Cluster, Geotail, IMP-8, Interball, THEMIS, and Wind data from many different intervals in the solar wind are employed to determine the magnetic correlation scale and the Taylor microscale from simultaneous multiple point measurements. For this study we define the correlation scale as the exponential decay constant of the correlation coefficient as a function of spacecraft separation and the Taylor scale as the radius of curvature of the correlation coefficient values at zero separation. The present determination of the Taylor scale makes use of a novel extrapolation technique to derive a statistically stable estimate from a range of measurements at small spatial separations [Weygand et al., 2007]. Using all the slow solar wind data (600 km/s), the correlation scale length is found to be smallest (about 1.3x106 km) in the direction parallel to the magnetic field and largest (about 2.2x106 km) in the direction perpendicular to the magnetic field. The anisotropies in the turbulent magnetic fluctuations in the solar wind are consistent with slow solar containing mainly two-dimensional turbulence and the fast solar wind having mostly slab type turbulence. The effective magnetic Reynolds number can be expressed in terms of the correlation scale and the Taylor scale. The difference in the Taylor and correlation scale in the parallel and perpendicular direction indicates that the effective magnetic Reynolds number varies with the direction of the magnetic field and has values between 1x106 and 8x106 . Knowledge of the effective magnetic Reynolds number may be useful in magnetohydrodynamic modeling of the solar wind and galactic cosmic ray diffusion in the heliosphere.

Weygand, J. M.; Kivelson, M. G.; Matthaeus, M. H.; Dasso, S.; Kistler, L. M.

2009-04-01

48

A six-coordinate ytterbium complex exhibiting easy-plane anisotropy and field-induced single-ion magnet behavior.  

PubMed

The field-induced blockage of magnetization behavior was first observed in an Yb(III)-based molecule with a trigonally distorted octahedral coordination environment. Ab initio calculations and micro-SQUID measurements were performed to demonstrate the exhibition of easy-plane anisotropy, suggesting the investigated complex is the first pure lanthanide field-induced single-ion magnet (field-induced SIM) of this type. Furthermore, we found the relaxation time obeys a power law instead of an exponential law, indicating that the relaxation process should be involved a direct process rather than an Orbach process. PMID:22799446

Liu, Jun-Liang; Yuan, Kang; Leng, Ji-Dong; Ungur, Liviu; Wernsdorfer, Wolfgang; Guo, Fu-Sheng; Chibotaru, Liviu F; Tong, Ming-Liang

2012-08-01

49

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

PubMed Central

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

2014-01-01

50

Probing the anisotropy constants of SmCo5 and PrCo5 by Hall resistance measurements in pulsed high magnetic fields up to 47 T  

NASA Astrophysics Data System (ADS)

In order to assess the anisotropy constants of highly anisotropic thin film samples with anisotropy fields well above 10 T, Hall resistance measurements were conducted in pulsed magnetic fields. These measurements also deliver the anomalous Hall data, which are proportional to the perpendicular magnetisation. This specific approach combines the high field values obtainable by pulsed fields with a measurement technique sensitive enough to be applied to thin film samples. Two epitaxial Rare Earth-Cobalt thin films with large in-plane uniaxial magnetocrystalline anisotropy at room temperature were studied. The resulting anisotropy fields and constants are discussed with respect to measurements on single crystals and similar films investigated in quasi-static magnetic fields well below the anisotropy field. The present technique proved to be very valuable to highly anisotropic samples, as the approach to saturation is fully monitored and the data thus provides a more extended view on the hard axis magnetisation process.

Stilp, E.; Freudenberger, J.; Seifert, M.; Patra, A. K.; Menzel, S.; Mönch, I.; Schultz, L.; Neu, V.

2012-05-01

51

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

52

Anisotropy and Magnetic Field Effects on the Genuine Multipartite Entanglement of Multi-Qubit Heisenberg {\\it XY} Chains  

E-print Network

It has been shown that, for the two-qubit Heisenberg XY model, anisotropy and magnetic field may together be used to produce entanglement for any finite temperature by adjusting the external magnetic field beyond some finite critical strength. This interesting result arises from an analysis employing the Wootters concurrence, a computable measure of entanglement for two-qubit states. Recently, Mintert {\\em et al.} proposed generalizations of Wootters concurrence for multipartite states. These MKB concurrences possess a mathematical property that enables one to understand the origin of this characteristic behavior. Here, we first study the effect of anisotropy and magnetic field on the multipartite thermal entanglement of a four-qubit Heisenberg XY chain using the MKB concurrences. We show that this model exhibits characteristic behavior similar to that of the two-qubit model. In addition, we show that this can again be understood using the same mathematical property. Next, we show that the six-qubit Heisenberg XY chain possesses properties necessary for it to have the characteristic behavior too. Most importantly, it is possible to directly measure the multipartite MKB concurrences of pure states. This may provide an experimental verification of our conjecture that for a Heisenberg XY chain of any even number of qubits, it is always possible to obtain non-zero genuine multipartite entanglement at any finite temperature by applying a sufficiently large magnetic field.

Chang Chi Kwong; Ye Yeo

2007-04-11

53

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

NASA Astrophysics Data System (ADS)

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

Erofeev, D. V.

2012-12-01

54

High Anisotropy Magnetic Recording Media  

NASA Astrophysics Data System (ADS)

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

Wittig, James

2007-03-01

55

Anisotropy of the quark-antiquark potential in a magnetic field  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

56

Magnetization Processes in Nanocrystalline Gadolinium: Role of Magnetic Anisotropy  

Microsoft Academic Search

The ‘zero-field-cooled’ (ZFC) and ‘field-cooled’ (FC) thermomagnetic, M(T), curves, taken at magnetic fields (H) of fixed strength on nanocrystalline Gd with an average grain size of 12 nm (18 nm), revealed irreversibility in magnetization, Mirr(T) = MFC?MZFC, below a characteristic temperature, TB?TC, at H?3.5kOe (2.2kOe). This irreversibility in magnetization is associated with the magnetic anisotropy energy barriers and gets progressively

S. P. Mathew; S. N. Kaul

2011-01-01

57

Magnetization Processes in Nanocrystalline Gadolinium: Role of Magnetic Anisotropy  

Microsoft Academic Search

The `zero-field-cooled' (ZFC) and `field-cooled' (FC) thermomagnetic, M(T), curves, taken at magnetic fields (H) of fixed strength on nanocrystalline Gd with an average grain size of 12 nm (18 nm), revealed irreversibility in magnetization, Mirr(T) = MFC-MZFC, below a characteristic temperature, TB?TC, at H<=3.5kOe (2.2kOe). This irreversibility in magnetization is associated with the magnetic anisotropy energy barriers and gets progressively

S. P. Mathew; S. N. Kaul

2011-01-01

58

Magnetization Processes in Nanocrystalline Gadolinium: Role of Magnetic Anisotropy  

NASA Astrophysics Data System (ADS)

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

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

2011-06-01

59

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

60

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

61

Magnetic anisotropy in nanostructured gadolinium  

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

62

Magnetic anisotropy of strained epitaxial manganite films  

NASA Astrophysics Data System (ADS)

The in-plane magnetic anisotropy of epitaxial La0.7Sr0.3MnO3 (LSMO) films is studied at room temperature by the following three independent techniques: magnetooptical Kerr effect, ferromagnetic resonance at a frequency of 9.61 GHz, and recording of absorption spectra of electromagnetic radiation at a frequency of 290.6 MHz. The films are deposited onto NdGaO3 (NGO) substrates in which the (110)NGO plane is tilted at an angle of 0-25.7° to the substrate plane. The uniaxial magnetic anisotropy induced by the strain of the film is found to increase with the tilt angle of the (110)NGO plane. A model is proposed to describe the change in the magnetic anisotropy energy with the tilt angle. A sharp increase in the radio-frequency absorption in a narrow angular range of a dc magnetic field near a hard magnetization axis is detected The anisotropy parameters of the LSMO films grown on (110)NGO, (001)SrTiO3, and (001)[(LaAlO3)0.3 + (Sr2AlTaO6)0.7] substrates are compared.

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

2011-05-01

63

Tailored magnetic anisotropy in an amorphous trilayer  

SciTech Connect

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

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

2011-06-01

64

Electric Field Switching of the Magnetic Anisotropy of a Ferromagnetic Layer Exchange Coupled to the Multiferroic Compound BiFeO3  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

65

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

Microsoft Academic Search

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

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

1985-01-01

66

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

67

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

NASA Astrophysics Data System (ADS)

We found that YBCO films deposited by the controlled process showed improved superconducting properties in magnetic fields, even without any artificial pinning centers such as BaZrO 3 and BaSnO 3. The YBCO films with a thickness of 450 nm were deposited on hastelloy tapes with a textured MgO buffer deposited by IBAD (Ion Beam Assist Deposition) method (IBAD-MgO) by PLD method. In the YBCO films on the IBAD-MgO (IBAD-YBCO), the critical current density of 2.9 MA/cm 2 at 77 K in self-field and the ratio of Jc( B// c)/ Jc( B// a, b) at 1 T was almost unity. Furthermore, we found that the Jc anisotropy changed with surface morphology on underlying buffer layer and YBCO thickness. This means that some c-axis correlated pinning centers are included in the films. From the cross-sectional TEM images of the IBAD-YBCO, there were not so many defects such as dislocations, Y 2O 3 inclusions and so on. Thus it is considered that some defects such as oxygen heterogeneity, displacement of a local composition and so on are pinning centers, although such defects can not be detected by a present analytical technique.

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

2010-11-01

68

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

E-print Network

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

69

Advanced magnetic anisotropy determination through isothermal remanent magnetization of nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

70

Magnetic anisotropy of CuMn spin glasses  

NASA Astrophysics Data System (ADS)

Hysteresis and ac-susceptibility measurements of various remanent states of CuMn have been performed to further elucidate the problem of magnetic anisotropy energy below Tf. Our experimental data are well described by a phenomenological model based on the existence of two different spin systems. We conclude that the anisotropy energy of CuMn is a field-dependent quantity.

Felten, G.; Schwink, Ch.

1986-02-01

71

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

72

An introduced effective-field theory study of spin-1 transverse Ising model with crystal field anisotropy in a longitudinal magnetic field  

NASA Astrophysics Data System (ADS)

A spin-1 transverse Ising model with longitudinal crystal field in a longitudinal magnetic field is examined by introducing an effective field approximation (IEFT) which includes the correlations between different spins that emerge when expanding the identities. The effects of the crystal field as well as the transverse and longitudinal magnetic fields on the thermal and magnetic properties of the spin system are discussed in detail. The order parameters, Helmholtz free energy, entropy and specific heat curves are calculated numerically as functions of the temperature and Hamiltonian parameters. A number of interesting phenomena such as reentrant phenomena originating from the temperature, crystal field, transverse and longitudinal magnetic fields have been found.

Yüksel, Yusuf; Polat, Hamza

2010-12-01

73

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

E-print Network

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

Lichter, Jenny, 1982-

2004-01-01

74

Upper limit of the critical currents and magnetic fields of cylindrical coils made of Bi(2223)Ag tapes with reduced ?-anisotropy  

Microsoft Academic Search

The results of model calculations of the critical currents of silver sheathed Bi(2223) multifilamentary tapes with reduced 0953-2048\\/12\\/2\\/002\\/img3-anisotropy, which can be achieved by assembling the filaments into several preferred orientations with respect to the external transverse magnetic field, are presented. Such tapes can be prepared by a two-axial rolling technique. It is shown that the properties of tape with higher

J. Pitel; P. Kovác; I. Husek

1999-01-01

75

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

Microsoft Academic Search

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

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

2009-01-01

76

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

77

Tectonic applications of magnetic susceptibility and its anisotropy  

Microsoft Academic Search

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

G. J. Borradaile; B. Henry

1997-01-01

78

Magnetic Moment and Anisotropy of Individual Co Atoms on Graphene  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

79

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

80

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

81

Magnetic anisotropy of a one-dimensional electron system  

NASA Astrophysics Data System (ADS)

We have discovered a novel anisotropy in a quasi-one-dimensional electronic system in the presence of a magnetic field. The density of states changes dramatically when a magnetic field is applied along different axes of the sample. Further, we do not observe spin splitting of one-dimensional levels in magnetic fields up to 20 T indicating that enhancement of the Landé g factor is also anisotropic. These results provide new insight into the underlying properties of quantum-confined electrons.

Smith, T. P., III; Brum, J. A.; Hong, J. M.; Knoedler, C. M.; Arnot, H.; Esaki, L.

1988-08-01

82

Neutron Scattering in Dipolar Pyrochlore Magnets with Local 111 Anisotropy  

Microsoft Academic Search

The paramagnetic neutron scattering in pyrochlore magnets with long-range dipole-dipole interactions and local Ising anisotropy is investigated within a mean field formalism. We focus on the issues of the strength of the local anisotropy and the range of the dipolar interactions necessary to capture the qualitative physics of the spin-ice materials Ho_2Ti_2O7 and Dy_2Ti_2O7 and the collective paramagnet Tb_2Ti_2O_7. In

Matthew Enjalran; Michel J. P. Gingras

2002-01-01

83

On the magnetic anisotropy of superduplex stainless steel  

NASA Astrophysics Data System (ADS)

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

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

2011-10-01

84

Revealing the volume magnetic anisotropy of Fe films epitaxied on GaAs(001) surface  

NASA Astrophysics Data System (ADS)

The in-plane magnetic anisotropy in Fe films grown on GaAs(001) was investigated quantitatively by the magneto-optic Kerr effect with a rotating magnetic field. The clear 1/dFe relation of the uniaxial magnetic anisotropy indicates a surprising volume contribution with easy axis along the GaAs [11¯0] direction. Such volume anisotropy was found to be sensitive to the growth temperature and also strongly correlate with the interface anisotropy. Our results may introduce a new aspect for further understanding the origin of uniaxial magnetic anisotropy in Fe/GaAs(001) system.

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

2011-03-01

85

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

86

Investigation of the anisotropy in frozen nickel ferrite ionic magnetic fluid using magnetic resonance  

PubMed

Magnetic resonance is used to obtain the temperature dependence of the magnetic anisotropy of noninteracting NiFe2O4 nanoparticles from 100 to 250 K. The 10.3 nm particles are dispersed as a stable ionic magnetic fluid which is frozen under the action of an external field to perform angular variation measurements. The thermal fluctuation of the easy axis and magnetic moment about the direction of the external field is included in order to obtain the anisotropy from the angular dependence of the resonance field. Copyright 1998 Academic Press. PMID:9740748

Saenger; Skeff Neto K; Morais; Sousa; Tourinho

1998-09-01

87

Effects of strain on magnetic anisotropy in Fe and Co-based heterostructures  

Microsoft Academic Search

The magnetic ordering in transition metals is strongly affected by any strain in the lattice, due to the close connection between strain and anisotropy. This article reviews recent developments, both experimental and theoretical, in the field of strain-induced magnetic anisotropies, with focus on films and multilayers based on Fe and Co. It is demonstrated that the reorientation of preferred magnetization

Gabriella Andersson; Björgvin Hjörvarsson

2008-01-01

88

Magnetic domain pinning in an anisotropy-engineered GdTbFe thin film  

SciTech Connect

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

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

2006-08-01

89

Inkjet printing of magnetic materials with aligned anisotropy  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

90

Angle-dependent radiative grain alignment. Confirmation of a magnetic field - radiation anisotropy angle dependence on the efficiency of interstellar grain alignment  

NASA Astrophysics Data System (ADS)

Context. Interstellar grain alignment studies are currently experiencing a renaissance due to the development of a new quantitative theory based on radiative alignment torques (RAT). One of the distinguishing predictions of this theory is a dependence of the grain alignment efficiency on the relative angle (?) between the magnetic field and the anisotropy direction of the radiation field. In an earlier study we found observational evidence for such an effect from observations of the polarization around the star HD 97300 in the Chamaeleon I cloud. However, due to the large uncertainties in the measured visual extinctions, the result was uncertain. Aims: By acquiring explicit spectral classification of the polarization targets, we have sought to perform a more precise reanalysis of the existing polarimetry data. Methods: We have obtained new spectral types for the stars in our for our polarization sample, which we combine with photometric data from the literature to derive accurate visual extinctions for our sample of background field stars. This allows a high accuracy test of the grain alignment efficiency as a function of ?. Results: We confirm and improve the measured accuracy of the variability of the grain alignment efficiency with ?, seen in the earlier study. We note that the grain temperature (heating) also shows a dependence on ? which we interpret as a natural effect of the projection of the grain surface to the illuminating radiation source. This dependence also allows us to derive an estimate of the fraction of aligned grains in the cloud.

Andersson, B.-G.; Pintado, O.; Potter, S. B.; Straižys, V.; Charcos-Llorens, M.

2011-10-01

91

Magnetic Edge Anisotropy in Graphenelike Honeycomb Crystals  

NASA Astrophysics Data System (ADS)

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

Lado, J. L.; Fernández-Rossier, J.

2014-07-01

92

Field-induced magnetic ordering and single-ion anisotropy in the quasi-one-dimensional Haldane chain compound SrNi2V2O8: A single-crystal investigation  

NASA Astrophysics Data System (ADS)

Field-induced magnetic ordering in the Haldane chain compound SrNi2V2O8 and the effect of anisotropy have been investigated using single crystals. Static susceptibility, inelastic neutron scattering, high-field magnetization, and low-temperature heat-capacity studies confirm a nonmagnetic spin-singlet ground state and a gap between the singlet ground state and triplet excited states. The intrachain exchange interaction is estimated to be J˜8.9±0.1 meV. Splitting of the dispersions into two modes with minimum energies 1.57 and 2.58 meV confirms the existence of single-ion anisotropy D(Sz)2. The value of D is estimated to be -0.51±0.01 meV and the easy axis is found to be along the crystallographic c axis. Field-induced magnetic ordering has been found with two critical fields (?0Hc?c=12.0±0.2 T and ?0Hc?c=20.8±0.5 T at 4.2 K). Field-induced three-dimensional magnetic ordering above the critical fields is evident from the heat-capacity, susceptibility, and high-field magnetization study. The phase diagram in the H-T plane has been obtained from the high-field magnetization. The observed results are discussed in the light of theoretical predictions as well as earlier experimental reports on Haldane chain compounds.

Bera, A. K.; Lake, B.; Islam, A. T. M. N.; Klemke, B.; Faulhaber, E.; Law, J. M.

2013-06-01

93

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

94

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

95

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

96

Intermetallic compounds containing lanthanides (studies of magnetic anisotropy)  

Microsoft Academic Search

The powerful permanent magnetism of certain rare earth intermetallics (e.g., SmCo5) is a consequence of the strong magnetic anisotropy in these materials. Both sublattices contribute to magnetic anisotropy. Usually the contribution of the rare earth predominates over that of its chemical partner, a d-transition element in systems of practical interest. The rare earth anisotropy has been treated by quantum mechanics

W. E. Wallace

1977-01-01

97

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

98

Magnetic anisotropy and domain structure in gadolinium.  

E-print Network

??The magnetocrystalline anisotropy constants of high quality single crystals of gadolinium have been measured using torque magnetometry. The redetermination of the anisotropy constants was necessary… (more)

Smith, Ronald Leslie

1978-01-01

99

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

SciTech Connect

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

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

2008-09-11

100

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

101

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

102

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

103

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

104

Anisotropy of the molecular magnet V$_{15}$ spin Hamiltonian detected by high-field electron spin resonance  

E-print Network

The molecular compound K$_6$[V$^{IV}_{15}$As$^{III}_6$O$_{42}$(H$_2$O)] $\\cdot$ 8H$_2$O, in short V$_{15}$, has shown important quantum effects such as coherent spin oscillations. The details of the spin quantum dynamics depend on the exact form of the spin Hamiltonian. In this study, we present a precise analysis of the intramolecular interactions in V$_{15}$. To that purpose, we performed high-field electron spin resonance measurements at 120 GHz and extracted the resonance fields as a function of crystal orientation and temperature. The data are compared against simulations using exact diagonalization to obtain the parameters of the molecular spin Hamiltonian.

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

2014-05-27

105

Anisotropy of magnetic susceptibility in natural olivine single crystals  

NASA Astrophysics Data System (ADS)

flow dynamics can cause preferential alignment of olivine crystals that results in anisotropy of physical properties. To interpret anisotropy in mantle rocks, it is necessary to understand the anisotropy of olivine single crystals. We determined anisotropy of magnetic susceptibility (AMS) for natural olivine crystals. High-field AMS allows for the isolation of the anisotropy due to olivine alone. The orientations of the principal susceptibility axes are related to the olivine's crystallographic structure as soon as it contains >3 wt % FeO. The maximum susceptibility is parallel to the c axis both at room temperature (RT) and at 77 K. The orientation of the minimum axis at RT depends on iron content; it is generally parallel to the a axis in crystals with 3-5 wt % FeO, and along b in samples with 6-10 wt % FeO. The AMS ellipsoid is prolate and the standard deviatoric susceptibility, k', is on the order of 8*10-10 m3/kg for the samples with <1wt % FeO, and ranges from 3.1*10-9 m3/kg to 5.7*10-9 m3/kg for samples with 3-10 wt % FeO. At 77 K, the minimum susceptibility is along b, independent of iron content. The shape of the AMS ellipsoid is prolate for samples with <5 wt % FeO, but can be prolate or oblate for higher iron content. The degree of anisotropy increases at 77 K with p'77 = 7.1 ± 0.5. The results from this study will allow AMS fabrics to be used as a proxy for olivine texture in ultramafic rocks with high olivine content.

Biedermann, Andrea R.; Pettke, Thomas; Reusser, Eric; Hirt, Ann M.

2014-07-01

106

Precessional switching on exchange biased patterned magnetic media with perpendicular anisotropy  

Microsoft Academic Search

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

M. Belmeguenai; T. Devolder; C. Chappert

2005-01-01

107

Anisotropy of the Taylor scale and the correlation scale in plasma sheet magnetic field fluctuations as a function of auroral electrojet activity  

Microsoft Academic Search

Magnetic field data from the Cluster spacecraft in the magnetospheric plasma sheet are employed to determine the correlation scale and the magnetic Taylor microscale from simultaneous multiple-point measurements for multiple intervals over a range of mean magnetic field directions for three different levels of geomagnetic activity. We have determined that in the plasma sheet the correlation scale along the mean

James M. Weygand; W. H. Matthaeus; M. El-Alaoui; S. Dasso; M. G. Kivelson

2010-01-01

108

Magnetic anisotropy in geometrically frustrated kagome staircase lattices  

Microsoft Academic Search

This paper reviews experimental results concerning magnetic anisotropy in geometrically frustrated kagome staircase lattices. Following problems are discussed: high-temperature susceptibility measurements of kagome single crystals; inelastic neutron scattering measurements on Co3V2O8 single crystals; EPR of Co2+ ions in kagome staircase Mg3V2O8 single crystals. The single-ion anisotropy Hamiltonian is used to analyze experimental results. It is suggested that the magnetic anisotropy

R. Szymczak; P. Aleshkevych; C. P. Adams; S. N. Barilo; A. J. Berlinsky; J. P. Clancy; V. Domuchowski; J. Fink-Finowicki; B. D. Gaulin; M. Ramazanoglu; S. V. Shiryaev; Z. Yamani; H. Szymczak

2009-01-01

109

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

110

Local magnetic turbulence and TeV-PeV cosmic ray anisotropies.  

PubMed

In the energy range from ?10(12) ?eV to ?10(15) ?eV, the Galactic cosmic ray flux has anisotropies both on large scales, with an amplitude of the order of 0.1%, and on scales between ?10° and ?30°, with amplitudes smaller by a factor of a few. With a diffusion coefficient inferred from Galactic cosmic ray chemical abundances, the diffusion approximation predicts a dipolar anisotropy of comparable size, but does not explain the smaller scale anisotropies. We demonstrate here that energy dependent smaller scale anisotropies naturally arise from the local concrete realization of the turbulent magnetic field within the cosmic ray scattering length. We show how such anisotropies could be calculated if the magnetic field structure within a few tens of parsecs from Earth were known. PMID:23006354

Giacinti, Gwenael; Sigl, Günter

2012-08-17

111

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

112

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

113

Magnetoelectric Control of Magnetic Anisotropy in Ultrathin Fe Films  

NASA Astrophysics Data System (ADS)

Magnetoelectric switching of the magnetization vector could enable new low-power logic devices and non-volatile memory cells. Magnetoelectric switching typically requires complex multiferroic oxides or strain coupled magnetostrictive/piezoelectric composites. However, recently it has been demonstrated that surface magnetic anisotropy in ultrathin ferromagnetic metal films can be directly controlled by application of a strong electric field [1]. In this work we apply an electric field across a high-k oxide stack of MgO and ZrO2 to induce charge at the surface of an ultrathin Fe film. By using high-k dielectric materials more charge can be induced at the surface of the ferromagnetic film and the efficiency of the magnetoelectric effect can be enhanced. Under application of just a few volts across the oxide stack we observe a strong magnetoelectric effect which results in a shift of the spin reorientation thickness by 0.5 atomic layers and a change in perpendicular surface anisotropy of ˜120?J/m^2. Moreover, by engineering the high-k oxide stack we realize a novel charge pumping mechanism that permits optical imprinting of the magnetic state in the continuous Fe film. [1] T. Maruyama et al. Nature Nanotechnology 4, 158 - 161 (2009)

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

2012-02-01

114

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

115

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

116

Magnetic anisotropy in Terfenol-D thin films (abstract)  

NASA Astrophysics Data System (ADS)

Thin-film Terfenol-D has attracted considerable attention for applications as microactuators and sensors. Depending on applications, the magnetic anisotropy plays a key role in physical property control. In this paper, the magnetic anisotropy of sputter-deposited Terfenol-D thin films on single-crystal Si substrates was studied by both dynamic torque and magnetization measurements. The evolution of magnetic anisotropy in the course of annealing treatment was followed by both types of experiments. It was found that there is a strong growth-induced anisotropy in the as-grown amorphous films, which is attributed to Fe-rare-earth bond orientation anisotropy. In samples treated at high temperatures, this growth-induced anistropy is overshadowed by the elastic anisotropy resulting from the substantial stresses in the films of giant magnetostrictive material. Domain patterns of different kinds of anisotropy were also monitored using a magnetic force microscope. The consequences of the growth-induced and elastomagnetic anisotropies to possible applications to microactuation are discussed.

Su, Q.; Teter, J. P.; Wen, Y.; Cullen, J. R.; Wuttig, M.

1997-04-01

117

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

118

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

119

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

PubMed Central

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

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

2014-01-01

120

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

121

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

122

Anisotropy of the magnetic susceptibility of gallium  

USGS Publications Warehouse

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

Pankey, T., Jr.

1960-01-01

123

Effect of Anisotropy in Two-dimensional Dimer model of magnetic ferrofluids  

NASA Astrophysics Data System (ADS)

The magnetization and the Initial susceptibility have been calculated using statistical mechanics for two-dimensional structured dilute ferro-fluid taking the effect of the magnetic anisotropy and inter-particle interaction. We assumed the assembly consists of N/2 non-interacting systems. Each system is composed of 2 interacting single domain fine magnetic spherical particles. We referred to this model as a Dimer-model. We found that when the easy axis is fixed with respect to the external magnetic field, the ordering temperature depend on the anisotropy constant K in both parallel and perpendicular cases.

Obeidat, Abdalla; Al-Sharo, Wesam

2009-03-01

124

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

125

Anisotropy of magnetic and transport properties in actinide intermetallics  

SciTech Connect

The authors have studied the giant magnetic anisotropy, which is a characteristic feature of actinide intermetallics, for uranium ternary intermetallics crystallizing in various structure types. It is shown that the easy magnetization direction is in general oriented perpendicular to the directions of the presumed strongest U-U bonding. Moreover, the coupling of magnetic moments is usually strong and ferromagnetic along this direction(s), whereas in directions perpendicular to it, the authors observe weaker ferro or antiferromagnetic coupling. This situation can be explained supposing the mechanism of the hybridization-induced exchange interaction and the related magnetic anisotropy.

Havela, L.; Sechovsky, V. [Charles Univ., Prague (Czech Republic). Dept. of Metal Physics] [Charles Univ., Prague (Czech Republic). Dept. of Metal Physics; Nakotte, H.; Brueck, E.; Boer, F.R. de [Univ. of Amsterdam (Netherlands). Van der Waals-Zeeman Lab.] [Univ. of Amsterdam (Netherlands). Van der Waals-Zeeman Lab.

1994-03-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

127

Local stress engineering of magnetic anisotropy in soft magnetic thin films  

SciTech Connect

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

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

2009-02-09

128

Estimation of Magnetic Susceptibility Anisotropy of Carbon Nanotubes Using  

E-print Network

excitation (PLE) spectrum of such samples showed peaks assigned20 to specific nano- tube species (chiralitiesEstimation of Magnetic Susceptibility Anisotropy of Carbon Nanotubes Using Magnetophotoluminescence a magnetophotoluminescence excitation spectroscopy study on micelle-suspended single-walled carbon nanotubes in high magnetic

Kono, Junichiro

129

Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films  

SciTech Connect

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

Hellman, Frances

1998-10-03

130

Underscreened Kondo effect in S=1 magnetic quantum dots: Exchange, anisotropy, and temperature effects  

NASA Astrophysics Data System (ADS)

We present a theoretical analysis of the effects of uniaxial magnetic anisotropy and contact-induced exchange field on the underscreened Kondo effect in S=1 magnetic quantum dots coupled to ferromagnetic leads. First, by using the second-order perturbation theory we show that the coupling to spin-polarized electrode results in an effective exchange field Beff and an effective magnetic anisotropy Deff. Second, we confirm these findings by using the numerical renormalization group method, which is employed to study the dependence of the quantum-dot spectral functions, as well as quantum-dot spin, on various parameters of the system. We show that the underscreened Kondo effect is generally suppressed due to the presence of effective exchange field and can be restored by tuning the anisotropy constant, when |Deff|=|Beff|. The Kondo effect can also be restored by sweeping an external magnetic field, and the restoration occurs twice in a single sweep. From the distance between the restored Kondo resonances one can extract the information about both the exchange field and the effective anisotropy. Finally, we calculate the temperature dependence of linear conductance for the parameters where the Kondo effect is restored and show that the restored Kondo resonances display a universal scaling of S=1/2 Kondo effect.

Misiorny, Maciej; Weymann, Ireneusz; Barna?, Józef

2012-12-01

131

Critical Field Anisotropy in an Organic Superconductor ?-(BEDT-TTF)2I3  

NASA Astrophysics Data System (ADS)

A measurement of the anisotropy of the upper critical field Hc2 in an organic superconductor ?-(BEDT-TTF)2I3 is reported. A large anisotropy is observed with high critical fields when the magnetic field is applied in the crystallographic a-b plane and a low critical field in the perpendicular direction. (Hc2a{=}9.7 kOe, Hc2b'{=}9.3 kOe, Hc2c*{=}460 Oe at 0.5 K) The result is expressed in terms of the anisotropic coherence lengths and transfer integrals, winch corroborate the two dimensional character of the electronic structure in this organic superconducting material.

Tokumoto, Madoka; Bando, Hiroshi; Anzai, Hiroyuki; Saito, Gunzi; Murata, Keizo; Kajimura, Koji; Ishiguro, Takehiko

1985-03-01

132

Tuning magnetic anisotropy in Fe/Pt multilayers on Pt(001) by surface charging  

NASA Astrophysics Data System (ADS)

Magnetic anisotropy of nanoscale systems has recently received considerable attention from both experimentally and theoretically perspectives. Diverse ways of manipulating the anisotropy have been sought and found. Those include alloying, external electric field exposure and electrolyte charging. However, the hunt for a system that would exhibit a large anisotropy and be easy to manipulate at the same time is still on. By using density functional theory tools, we study the magnetic anisotropy of Fe/Pt multilayers on Pt(001). Our fully relativistic ab initio calculations demostrate that the value of magnetic anisotropy energy (MAE) strongly depends on the composition of Fe/Pt multilayers, achieving remarkable large values for systems featuring Fe layers capped with Pt. For instance, positive charging of a Fe slab capped with Pt enhances significantly the MAE. More intriguing is the behavior of Fe bilayers, for which surface charging does not only change the value of the anisotropy but can also lead in the switching of the easy axis. To understand the physics underlying this behavior of MAE, we analyze the electronic structure of the system by means of the second-order perturbation theory linking MAE to the local density of electronic states near the Fermi level.

Ruiz-Diaz, Pedro; Stepanyuk, Valeri

2013-03-01

133

Extracting anisotropy energy barrier distributions of nanomagnetic systems from magnetization/susceptibility measurements  

NASA Astrophysics Data System (ADS)

Anisotropy barrier distributions of single domain particle systems are an important issue in the nanomagnetism and its applications. Different methods to extract the distribution from temperature, field, or time-dependent magnetization/susceptibility are reviewed and compared. A single domain particle system is measured to test the methods.

Zheng, Rongkun; Gu, Hongwei; Zhang, Bei; Liu, Hui; Zhang, Xixiang; Ringer, Simon P.

2009-05-01

134

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

135

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

136

Magnetization reversal mechanism of Nd-Fe-B films with perpendicular magnetic anisotropy  

SciTech Connect

The microstructure and magnetic properties of Nd-Fe-B films with thicknesses from 100 nm to 3 nm have been investigated. All the films show excellent perpendicular magnetic anisotropy with a squareness ratio of 1 in the perpendicular direction and almost zero coercivity in the in-plane direction. Of particular interest is that the initial magnetization curves sensitively depended on the film thickness. Films thicker than 15 nm show steep initial magnetization curve. Although the films have coercivities larger than 21 kOe, the films can be fully magnetized from the thermally demagnetized state with a field as small as 5 kOe. With the decrease of film thickness to 5 nm, the initial magnetization curve becomes flat. The evolution of initial magnetization curves with film thickness can be understood by the microstructure of the films. Films with thickness of 15 nm show close-packed grains without any intergranular phases. Such microstructures lead to steep initial magnetization curves. On the other hand, when the film thickness decreased to 3 nm, the film thickness became nonuniform. Such microstructure leads to flat initial magnetization curves.

Liu Xiaoxi; Ishida, Go; Morisako, Akimitsu [Department of Information Engineering, Shinshu University, 4-17-1 wakasato, Nagano 380-8553 (Japan)

2011-04-01

137

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

138

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

139

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

140

Magnetic fields in astrophysics  

Microsoft Academic Search

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

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

1983-01-01

141

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

142

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

143

Anisotropy of magnetic properties of Fe1+yTe.  

PubMed

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. 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

144

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

145

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

146

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

147

Magnetic field sensor  

NASA Astrophysics Data System (ADS)

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

Silva, Nicolas

2012-09-01

148

Studies of HTSC crystal magnetization features using indicator magnetooptic films with in-plane anisotropy  

Microsoft Academic Search

Indicator ferrimagnetic films with in-plane anisotropy are applied for studying the magnetic flux distribution in high-Tc YBaCuO (YBa2Cu3O7) single crystals. Induction gradients are measured to estimate the critical current density Jc. Temperature dependences of Jc are found to be different for different field directions. For the field along the orthorhombic c-axis Jc||ab exhibits an exponential temperature decay. In the case

L. A. Dorosinskii; M. V. Indenbom; V. I. Nikitenko; Yu. A. Ossip'yan; A. A. Polyanskii; V. K. Vlasko-Vlasov

1992-01-01

149

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

150

Control of single-spin magnetic anisotropy by exchange coupling  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

151

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

152

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.

153

Role of magnetic anisotropy in spin-filter junctions  

SciTech Connect

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

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

2011-01-10

154

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

155

Anisotropy-induced Feshbach resonances in a quantum dipolar gas of highly magnetic atoms.  

PubMed

We explore the anisotropic nature of Feshbach resonances in the collision between ultracold highly magnetic submerged-shell dysprosium atoms in their energetically lowest magnetic sublevel, which can only occur due to couplings to rotating bound states. This is in contrast to well-studied alkali-metal atom collisions, where broadest (strongest) Feshbach resonances are hyperfine induced and due to rotationless bound states. Our first-principle coupled-channel calculation of the collisions between these spin-polarized bosonic dysprosium atoms reveals a strong interplay between the anisotropies in the dispersion and magnetic dipole-dipole interaction. The former anisotropy is absent in alkali-metal and chromium collisions. We show that both types of anisotropy significantly affect the Feshbach spectrum as a function of an external magnetic field. Effects of the electrostatic quadrupole-quadrupole interaction are small. Over a 20 mT magnetic field range, we predict about 10 Feshbach resonances and show that the resonance locations depend on the dysprosium isotope. PMID:23005285

Petrov, Alexander; Tiesinga, Eite; Kotochigova, Svetlana

2012-09-01

156

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

157

Magnetic fields of galaxies  

Microsoft Academic Search

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

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

1988-01-01

158

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

159

Synthesis of cobalt nanoparticles in polymeric membrane and their magnetic anisotropy  

NASA Astrophysics Data System (ADS)

We systematically synthesized cobalt nanoparticles in the perfluorinated sulfo-cation membrane (MF-4SK) in aqua solution using ion-exchange method. The average radius of cobalt nanoparticles in the polymer film is determined to be 3.5±1.0 nm by TEM. FMR measurements show that the angle dependence of resonance field ( Hr) follows the characteristics of flat-plate magnetic film and the easy axis lies along the surface of the polymer film. The experimental results suggest that the magnetic anisotropy comes from magnetized polymer film containing Co nanoparticles.

Park, I.-W.; Yoon, M.; Kim, Y. M.; Kim, Y.; Kim, J. H.; Kim, S.; Volkov, V.

2004-05-01

160

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

161

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, Frederic; Shiota, Yoichi; Miwa, Shinji; Suzuki, Yoshishige

2014-01-01

162

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

163

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

SciTech Connect

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

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

2008-02-21

164

Facility Measures Magnetic Fields  

NASA Technical Reports Server (NTRS)

Partly automated facility measures and computes steady near magnetic field produced by object. Designed to determine magnetic fields of equipment to be installed on spacecraft including sensitive magnetometers, with view toward application of compensating fields to reduce interfernece with spacecraft-magnetometer readings. Because of its convenient operating features and sensitivity of its measurements, facility serves as prototype for similar facilities devoted to magnetic characterization of medical equipment, magnets for high-energy particle accelerators, and magnetic materials.

Honess, Shawn B.; Narvaez, Pablo; Mcauley, James M.

1991-01-01

165

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

166

Earths magnetic field  

Microsoft Academic Search

Recent studies of the Paleosecular Variation of lavas (PSVL) by the authors and others, shows that the variability of Earth's magnetic field over the last several million years is less than the variability of the present Earth's magnetic field. The present magnetic field is asymmetric between the northern and southern hemispheres. The dispersion in the southern hemisphere being much greater

N. Opdyke; V. Mejia

2003-01-01

167

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

168

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

169

Effect of lattice relaxation on magnetic anisotropy: Zr-doped Sm2Co17  

NASA Astrophysics Data System (ADS)

The magnetic anisotropy energy (MAE) in rare-earth/transition-metal hard magnets originates from the onsite anisotropy of the rare-earth element with additional contribution from the transition-metal sublattice. While SmCo5 can be transformed to Sm2Co17 by partial substitution of Sm by Co2 dumbbells, the MAE in Sm2Co17 is noticeably smaller compared to that in SmCo5. However, small dopings of nonmagnetic Zr significantly increase the MAE in Sm2Co17. We show that the changes to the MAE in Sm2Co17 can be traced down to the reduction of the crystal field at the Sm site due to the Co sublattice relaxation upon Sm?Co2 substitution which is subsequently restored upon substitution of Co2?Zr.

Larson, P.; Mazin, I. I.

2004-01-01

170

Giant Uniaxial Anisotropy in the Magnetic and Transport Properties of CePd5Al2  

NASA Astrophysics Data System (ADS)

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

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

2008-07-01

171

The Magnetic Field  

NSDL National Science Digital Library

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

Barker, Jeffrey

172

Magnetic Fields Analogous to electric field, a magnet  

E-print Network

Magnetic Fields Analogous to electric field, a magnet produces a magnetic field, B Set up a B field two ways: Moving electrically charged particles Current in a wire Intrinsic magnetic field Basic characteristic of elementary particles such as an electron #12;Magnetic Fields Magnetic field lines Direction

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

173

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

174

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

NASA Astrophysics Data System (ADS)

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

Shikama, T.; Kitaoka, H.; Hasuo, M.

2014-07-01

175

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

176

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

177

Perpendicular magnetic anisotropy and the magnetization process in CoFeB/Pd multilayer films  

NASA Astrophysics Data System (ADS)

The perpendicular magnetic anisotropy (PMA) and dynamic magnetization-reversal process in [CoFeB t nm/Pd 1.0 nm]n(t = 0.4, 0.6, 0.8, 1.0 and 1.2 nm n = 2 ? 20) multilayer films have been studied by means of magnetic hysteresis and Kerr effect measurements. Strong and controllable PMA with an effective uniaxial anisotropy up to 7.7 × 106 Jm?3 and a saturation magnetization as low as 200 emu cm?3 are achieved. The surface/interfacial anisotropy of the CoFeB/Pd interfaces—the main contribution to the PMA—is separated from the effective uniaxial anisotropy of the films and appears to increase with the number of CoFeB/Pd bilayers. Observation of the magnetic domains during a magnetization-reversal process, using polar magneto-optical Kerr microscopy, reveals the detailed behavior of the nucleation and displacement of the domain walls.

Ngo, Duc-The; Quach, Duy-Truong; Tran, Quang-Hung; Møhave, Kristian; Phan, The-Long; Kim, Dong-Hyun

2014-11-01

178

The role of coercivity and dislocations for films with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Understanding and controlling macroscopic quantities directly associated with a random field, such as the coercive field Hc and dislocations in magnetic materials, is important for many applications that include films with perpendicular magnetic anisotropy. Here, using a model system with perpendicular magnetic anisotropy, Cu/Ni/Cu, we show that Hc in double 4 nm thick Ni films is about 0.65 times the value obtained for the single Ni film, a fact that can be understood if the propagation of misfit dislocations is not transmitted to the second magnetic block, implying that its statistical distribution remains unchanged whereas the magnetic driving force increases with the nickel thickness. This interpretation is based on the direct measurement of the in-plane and out-of-plane lattice parameters of the Ni blocks by the extended x-ray absorption fine structure method, a chemically selective technique tuned to probe exclusively the environment of the Ni atoms. With this finding and applying the rigid domain walls model, the Hc ratio between double and single Ni films is calculated, yielding a value of 0.71.

Corredor, E. C.; Coffey, D.; Arnaudas, J. I.; Proietti, M. G.; Ciria, M.

2014-10-01

179

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

NASA Astrophysics Data System (ADS)

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

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

1999-04-01

180

Static and dynamic order-disorder transition of a vortex lattice in YBaCuO crystals: The effect of point defects, anisotropy, temperature, and magnetic field  

NASA Astrophysics Data System (ADS)

This paper presents the results of measurements of the field dependence Fp(H) and angle dependence Fp(?) of the pinning force in an YBa2Cu3O7-? crystal that contains various concentrations of point defects. A comparison of the Fp(H ) and Fp(?) dependences gives decisive reasons for assuming that, when the vortices travel at low velocities ?, the minimum on the Fp(?) dependence corresponds to the order-disorder transition in the vortex lattice (VL). It is shown that the minimum on the Fp(?) dependence shifts toward larger angles ? at large velocities ?, and this is caused by the partial dynamic ordering of the disordered VL.

Petrusenko, Yu. T.

2010-01-01

181

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

E-print Network

We investigate the spectral shape, the anisotropy of the wave vector distributions and the anisotropy of the amplitudes of the magnetic fluctuations in the Earth's magnetosheath within a broad range of frequencies. We present the first observations of a Kolmogorov-like inertial range of Alfvenic fluctuations in the magnetosheath flanks, below fci. In the vicinity of fci, a spectral break is observed, like in solar wind turbulence. Above the break, the energy of compressive and Alfvenic fluctuations generally follow a power law with a spectral index between -3 and -2. Concerning the anisotropy of the wave vector distribution, we observe a change in its nature in the vicinity of ion characteristic scales: if at MHD scales there is no evidence for a dominance of a slab (k||>kperp) or 2D (kperp>k||) turbulence, above the spectral break, (f>fci, kc/wpi>1) the 2D turbulence dominates. This 2D turbulence is observed in six selected one-hour intervals among which the average proton beta varies from 0.8 to 9. It is observed for both the transverse and compressive magnetic fluctuations, independently on the presence of linearly unstable modes at low frequencies or Alfven vortices at the spectral break. We then analyse the anisotropy of the magnetic fluctuations in a time dependent reference frame based on the field B and the flow velocity V directions. Within the range of the 2D turbulence, at scales [1,30]kc/wpi, and for any beta we find that the magnetic fluctuations at a given frequency in the plane perpendicular to B have more energy along the BxV direction. This non-gyrotropy of the fluctuations is consistent with gyrotropic fluctuations at a given wave vector, with kperp>k||, which suffer a different Doppler shift along and perpendicular to V in the plane perpendicular to B.

Olga Alexandrova; Catherine Lacombe; Andre Mangeney

2008-10-03

182

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.

183

The Magnetic Field  

NSDL National Science Digital Library

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

184

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

PubMed

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

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

2011-10-25

185

Magnetic Field Example 1  

NSDL National Science Digital Library

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

Christian, Wolfgang; Belloni, Mario

2008-02-19

186

Alignment of magnetic uniaxial particles in a magnetic field: Simulation  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

187

Dynamic converse magnetoelectric effect in ferromagnetic nanostructures with electric-field-dependent interfacial anisotropy  

NASA Astrophysics Data System (ADS)

Magnetization oscillations excited by microwave voltages in ferromagnetic nanostructures having electric-field-dependent interfacial anisotropy are described theoretically. By calculating frequency dependencies of complex susceptibilities we show that this dynamic magnetoelectric effect acquires anomalous characteristics near thickness-induced spin reorientation transitions (SRTs) in nanolayers of cubic ferromagnets. Most importantly, the peak magnetoelectric susceptibilities may reach giant values exceeding 10-6 s/m, and the tunability of the resonance frequency of the magnetization precession by a dc voltage increases drastically near the critical thickness or voltage inducing an SRT.

Viaud, G.; Pertsev, N. A.

2014-08-01

188

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

NASA Astrophysics Data System (ADS)

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

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

189

Magnetically enhanced bicelles delivering switchable anisotropy in optical gels.  

PubMed

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

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

2014-01-22

190

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

191

Switching distributions in Co-Ni nanopillars with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

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

Gopman, Daniel Bernard

192

Anisotropy of the field-induced kinetic energy density in Bi2212  

NASA Astrophysics Data System (ADS)

We present an experimental study of the in-field kinetic energy density in two Bi2Sr2CaCu2O8+? single crystals. The kinetic energy density is determined from magnetization measurements performed above the irreversibility line. Anisotropy effects are observed when an external magnetic field is applied in the direction perpendicular or parallel to the superconducting Cu-O2 planes. When the field is applied parallel to the c-axis, the most relevant contribution to the kinetic energy comes from the Abrikosov vortices. At low fields, an additional term related to granularity is also observed. A kink in the kinetic energy density associated to the decoupling of the superconducting layers is identified when the field is applied parallel to the ab planes.

Peña, J. P.; da Silva, R. R.; Pureur, P.

2014-01-01

193

Statistical anisotropy of the curvature perturbation from vector field perturbations  

SciTech Connect

The {delta}N formula for the primordial curvature perturbation {zeta} is extended to include vector as well as scalar fields. Formulas for the tree-level contributions to the spectrum and bispectrum of {zeta} are given, exhibiting statistical anisotropy. The one-loop contribution to the spectrum of {zeta} is also worked out. We then consider the generation of vector field perturbations from the vacuum, including the longitudinal component that will be present if there is no gauge invariance. Finally, the {delta}N formula is applied to the vector curvaton and vector inflation models with the tensor perturbation also evaluated in the latter case.

Dimopoulos, Konstantinos; Karciauskas, Mindaugas; Lyth, David H. [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom)] [Department of Physics, Lancaster University, Lancaster LA1 4YB (United Kingdom); Rodriguez, Yeinzon, E-mail: k.dimopoulos1@lancaster.ac.uk, E-mail: m.karciauskas@lancaster.ac.uk, E-mail: d.lyth@lancaster.ac.uk, E-mail: yeinzon.rodriguez@uan.edu.co [Centro de Investigaciones, Universidad Antonio Narino, Cra 3 Este 47A-15, Bogota D.C. (Colombia)] [Centro de Investigaciones, Universidad Antonio Narino, Cra 3 Este 47A-15, Bogota D.C. (Colombia)

2009-05-15

194

Switching current reduction using perpendicular anisotropy in CoFeB-MgO magnetic tunnel junctions  

Microsoft Academic Search

We present in-plane CoFeB-MgO magnetic tunnel junctions with perpendicular magnetic anisotropy in the free layer to reduce the spin transfer induced switching current. The tunneling magnetoresistance ratio, resistance-area product, and switching current densities are compared in magnetic tunnel junctions with different CoFeB compositions. The effects of CoFeB free layer thickness on its magnetic anisotropy and current-induced switching characteristics are studied

P. Khalili Amiri; Z. M. Zeng; J. Langer; H. Zhao; G. Rowlands; Y.-J. Chen; I. N. Krivorotov; J.-P. Wang; H. W. Jiang; J. A. Katine; Y. Huai; K. Galatsis; K. L. Wang

2011-01-01

195

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

196

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

197

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

Microsoft Academic Search

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

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

2012-01-01

198

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

SciTech Connect

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

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

2013-06-15

199

Abstract: Quasistatic magnetic fields  

Microsoft Academic Search

A prototype switching system has been developed which can switch 20 kA at 230 V for short periods of time through inductive loads. High power silicon controlled rectifiers are used to switch the National Magnet Laboratory dc generators on and off into a liquid N2 cooled, low impedance high field magnet so that high fields can be generated for a

H. C. Praddaude; S. Foner

1979-01-01

200

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

201

Magnetic Fields in Galaxies  

NASA Astrophysics Data System (ADS)

Magnetic fields are a major agent in the interstellar medium. They contribute significantly to the total pressure which balances the gas disk against gravitation. They affect the gas flows in spiral arms (Gómez and Cox, 2002). The effective sound speed of the gas is increased by the presence of strong fields which reduce the shock strength. The interstellar fields are closely connected to gas clouds. They affect the dynamics of the gas clouds (Elmegreen, 1981; de Avillez and Breitschwerdt, 2004). The stability and evolution of gas clouds are also influenced by magnetic fields, but it is not understood how (Crutcher, 1999; see Chap. 7). Magnetic fields are essential for the onset of star formation as they enable the removal of angular momentum from the protostellar cloud during its collapse (magnetic braking, Mouschovias, 1990). Strong fields may shift the stellar mass spectrum towards the more massive stars (Mestel, 1990). MHD turbulence distributes energy from supernova explosions within the ISM (Subramanian, 1998) and regenerates the field via the dynamo process (Wielebinski, R., Krause, 1993, Beck et al., 1996; Sect. 6). Magnetic reconnection is a possible heating source for the ISM and halo gas (Birk et al., 1998). Magnetic fields also control the density and distribution of cosmic rays in the ISM. A realistic model for any process in the ISM needs basic information about the magnetic field which has to be provided by observations.

Beck, Rainer

202

Influence of topological transitions in a quantizing magnetic field and anisotropy of current carrier scattering by acoustic phonons on the longitudinal electrical conductivity of layered crystals with open fermi surfaces  

NASA Astrophysics Data System (ADS)

It is demonstrated that the dependence of Fermi's energy on the magnetic field causes a set of the Shubnikov - de Haas (SDH) oscillation frequencies to change, and their relative contribution to the total longitudinal conductivity of layered crystals depends on whether the scattering of current carriers is isotropic or anisotropic. Owing to the topological transition in a strong magnetic field, Fermi's surface (FS) is transformed from open into closed one and is compressed in the magnetic field direction. Therefore, in an ultraquantum limit, disregarding the Dingle factor, the longitudinal electrical conductivity of the layered crystal tends to zero as a reciprocal square of the magnetic field for the isotropic scattering and as a reciprocal cube of the magnetic field for the anisotropic scattering. All calculations are performed in the approximation of relaxation time considered to be constant versus the quantum numbers for the isotropic scattering and proportional to the longitudinal velocity of current carriers for the anisotropic scattering.

Gorskii, P. V.

2011-03-01

203

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

204

Anisotropy in transport and magnetic properties of K0.64Fe1.44Se2  

NASA Astrophysics Data System (ADS)

We report a study of the anisotropy in transport and magnetic properties of K0.64Fe1.44Se2.00 single crystals. The anisotropy in resistivity is up by one order of magnitude between 1.8 and 300 K. The magnetic susceptibility exhibits weak temperature dependence in the normal state with no significant anomalies with decreasing temperature. The lower critical fields Hc1 of K0.64Fe1.44Se2.00 are only about 3 Oe and the anisotropy of Hc1,c/Hc1,ab is about 1. The critical currents for H?ab and H?c are about 10-103 A/cm2, which is smaller than in iron pnictides and in FeTe1-xSex, and nearly isotropic.

Lei, Hechang; Petrovic, C.

2011-05-01

205

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

206

Long-range orientational order, local-field anisotropy, and mean molecular polarizability in liquid crystals  

Microsoft Academic Search

The problems on the relation of the mean effective molecular polarizability bar gamma to the long-range orientational order of molecules (the optical anisotropy of the medium) in uniaxial and biaxial liquid crystals, the local anisotropy on mesoscopic scales, and the anisotropy of the Lorentz tensor L and the local-field tensor f are formulated and solved. It is demonstrated that the

E. M. Aver'yanov

2009-01-01

207

Long-range orientational order, local-field anisotropy, and mean molecular polarizability in liquid crystals  

Microsoft Academic Search

The problems on the relation of the mean effective molecular polarizability -bar to the long-range orientational order of molecules (the optical anisotropy of the medium) in uniaxial and biaxial liquid crystals, the local anisotropy on mesoscopic scales, and the anisotropy of the Lorentz tensor L and the local-field tensor f are formulated and solved. It is demonstrated that the presence

Averyanov

2009-01-01

208

Radiation from sub-Larmor scale magnetic fields  

Microsoft Academic Search

Spontaneous rapid growth of strong magnetic fields is ubiquitous in high-energy density environments ranging from astrophysical sources and relativistic shocks, to reconnection, to laser-plasma interaction laboratory experiments, where they are produced by kinetic streaming instabilities of the Weibel type. Relativistic electrons propagating through these sub-Larmor-scale magnetic fields radiate in the jitter regime, in which the anisotropy of the magnetic fields

M. V. Medvedev; J. T. Frederiksen; T. Haugbølle; Å. Nordlund

2010-01-01

209

Imaging the magnetization reversal of step-induced uniaxial magnetic anisotropy in vicinal epitaxial La0.7Sr0.3MnO3 films  

NASA Astrophysics Data System (ADS)

The magnetization reversal of La0.7Sr0.3MnO3 (LSMO) epitaxial films deposited on 10° vicinal SrTiO3(001) substrates has been investigated at room temperature by using longitudinal magneto-optical Kerr microscopy. In the case when the magnetic field is applied parallel to the substrate steps, magnetization reversal proceeds first by the nucleation of magnetic domains with well-defined magnetic domain walls (DWs) oriented parallel to the step direction and then by DW propagation. No magnetic domains are found in the case when the magnetic field is applied perpendicular to the steps, in which case magnetization reversal proceeds by coherent rotation. Our results provide a direct visualization of the step-induced uniaxial magnetic anisotropy in half-metallic systems and for LSMO thickness up to 70 nm.

Perna, P.; Méchin, L.; Saïb, M.; Camarero, J.; Flament, S.

2010-10-01

210

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

SciTech Connect

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

Asahi, Y. [Graduate University for Advanced Studies, Oroshi-cho, 322-6, Toki-shi 509-5292 (Japan); Suzuki, Y.; Watanabe, K. Y. [Graduate University for Advanced Studies, Oroshi-cho, 322-6, Toki-shi 509-5292 (Japan); National Institute for Fusion Science, Oroshi-cho, 322-6, Toki-shi 509-5292 (Japan); Cooper, W. A. [Ecole Polytechnique Federale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association Euratom-Confederation Suisse, CH1015 Lausanne (Switzerland)

2013-02-15

211

Giant conductance anisotropy in magnetically coupled Ferromagnet-Superconductor-Ferromagnet structures  

Microsoft Academic Search

We demonstrate the evolution of the anisotropic conductivity in the superconductor that is magnetically coupled with two adjacent ferromagnetic layers. Stripe magnetic domain structure in the ferromagnetic layers results in directional superconducting order parameter in the superconducting layer. The conductance anisotropy strongly depends on the period of the magnetic domains and the strength of the local magnetization. The anisotropic conductivity

A. Belkin; V. Novosad; M. Iavarone; R. Divan; J. Hiller; T. Proslier; J. E. Pearson; G. Karapetrov

2010-01-01

212

Symmetry breaking effect of dc bias current on magnetoimpedance in microwire with helical anisotropy: Application to magnetic sensors  

NASA Astrophysics Data System (ADS)

We have investigated the effect of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwire with helical anisotropy and experimentally demonstrated that, by changing the dc current IB, it is possible to considerably affect the MI dependence. We propose to use this effect in developing a longitudinal MI sensor that overcomes the drawbacks usually associated with the longitudinal MI—namely the impossibility to determine the direction of an external axial magnetic field HE and the low sensitivity near the zero-field point. We demonstrate that a set of two measurements of longitudinal wire impedance with properly selected bias current IB allows determination of both the magnitude and direction of the magnetic field HE over an extended range, much higher than the sample anisotropy field. Additional features of the proposed method are the increased sensitivity and the detection of exceeding the operating range.

Ipatov, M.; Zhukova, V.; Gonzalez, J.; Zhukov, A.

2011-10-01

213

Magnetic Bar Field Model  

NSDL National Science Digital Library

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

Christian, Wolfgang; Franciscouembre; Cox, Anne

2009-09-18

214

Magnetic Anisotropy in the High Transition Temperature Superconductor Yttrium BARIUM(2) COPPER(3) OXYGEN(7-DELTA)  

NASA Astrophysics Data System (ADS)

The strong anisotropy found in the electronic structure of YBa_2Cu_3 O_{7-delta} resulting from the existence of both the CuO_2 planes within the a,b plane and the CuO chains along the b axis has brought strong interest regarding the effect of the electronic structure anisotropy on the superconducting properties in this material. Such superconducting properties include both the intrinsic type (such as H _{c1}, H_ {c2}, H_{ c}, lambda,xi ...) and the non-intrinsic type (such as flux pinning and j_{c} ). The availability of twinned and more recently, untwinned single crystals of YBa_2Cu _3O_{7-delta } has made it possible for such anisotropic properties to be investigated. Magnetization critical currents (j_{c}) were measured for H//c and H//a,b in order to investigate the characteristics of flux pinning. The temperature dependence of j_{c} was measured up to 77 K, to determine the viability of the material for application use at such high temperatures. Irradiation of the single crystals with high energy neutrons is also done to investigate the possibility of using such a method for increasing j_{c} . Intrinsic superconducting parameters are investigated by measuring the magnitude and anisotropy of the lower critical field H_{c1} and comparing it to the measurements of the upper critical field H_{c2} . From these values the magnitude and anisotropy of the other characteristic values such as lambda, kappa and H_{c} are estimated using an anisotropic Ginzburg -Landau model. The temperature dependence of H _{c1} was found to give unusual results, which differed with the direct temperature dependent measurements of the magnetic penetration depth lambda. The lower critical field was measured on an untwinned single crystal of YBa _2Cu_3O_ {7-delta}, to investigate both the a-b anisotropy and the effects of the twin boundaries on the measurements of H_{c1 }.

Umezawa, Ado

1991-05-01

215

Temperature and bias voltage dependence of Co/Pd multilayer-based magnetic tunnel junctions with perpendicular magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Temperature- and bias voltage-dependent transport measurements of magnetic tunnel junctions (MTJs) with perpendicularly magnetized Co/Pd electrodes are presented. Magnetization measurements of the Co/Pd multilayers are performed to characterize the electrodes. The effects of the Co layer thickness in the Co/Pd bilayers, the annealing temperature, the Co thickness at the MgO barrier interface, and the number of bilayers on the tunneling magneto resistance (TMR) effect are investigated. TMR-ratios of about 11% at room temperature and 18.5% at 13 K are measured and two well-defined switching fields are observed. The results are compared to measurements of MTJs with Co-Fe-B electrodes and in-plane anisotropy.

Kugler, Zoë; Drewello, Volker; Schäfers, Markus; Schmalhorst, Jan; Reiss, Günter; Thomas, Andy

2011-01-01

216

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

NASA Astrophysics Data System (ADS)

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 64nm thick are irradiated with 80keV 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 patterns and CoL3 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.

2006-02-01

217

Evidence of high-spin Ru and universal magnetic anisotropy in SrRuO3 thin films  

NASA Astrophysics Data System (ADS)

We have investigated the origins of enhanced saturated magnetic moment and strong strain-dependent magnetic anisotropy in epitaxial films of the transition-metal oxide SrRuO3. We find evidence for an enhancement of the carrier concentration and the stabilization of high-spin Ru4+. Through x-ray magnetic circular dichroism measurements, we also observe a strain-dependent enhancement of the out-of-plane orbital magnetic moment. Such an enhancement is consistent with the universal out-of-plane anisotropy axis shown to occur in films in a variety of different crystallographic orientations. We explain all these effects in terms of an anisotropic reduction in the crystal field resulting from anisotropically reduced orbital overlap in distorted films.

Grutter, A. J.; Wong, F. J.; Arenholz, E.; Vailionis, A.; Suzuki, Y.

2012-04-01

218

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

E-print Network

Using first-principles calculations, we investigated the impact of chromium (Cr) and vanadium (V) impurities on the magnetic anisotropy and spin polarization in Fe/MgO magnetic tunnel junctions. It is demonstrated using layer resolved anisotropy calculation technique, that while the impurity near the interface has a drastic effect in decreasing the perpendicular magnetic anisotropy (PMA), its position within the bulk allows maintaining high surface PMA. Moreover, the effective magnetic anisotropy has a strong tendency to go from in-plane to out-of-plane character as a function of Cr and V concentration favoring out-of-plane magnetization direction for ~1.5 nm thick Fe layers at impurity concentrations above 20 %. At the same time, spin polarization is not affected and even enhanced in most situations favoring an increase of tunnel magnetoresistance (TMR) values.

Hallal, A; Chshiev, M

2014-01-01

219

Role of magnetic anisotropy on the magnetic properties of Ni nanoclusters embedded in a ZnO matrix  

NASA Astrophysics Data System (ADS)

We have investigated the magnetic properties of Ni nanoaggregates produced by ion implantation in ZnO single crystals. Several deviations from classical models usually adopted to describe the magnetic properties of nanoparticle systems were found. The strain between host and Ni nanoaggregates induces a magnetic anisotropy with a preferred direction. We show that these anisotropy effects can be misinterpreted as a ferromagnetic or antiferromagnetic coupling among the nanoaggregates similar to that of an oriented, interacting nanocrystal ensemble.

Nunes, W. C.; Borges, R. P.; Cruz, M. M.; da Silva, R. C.; Wahl, U.; Cuchillo, A.; Vargas, P.; Magen, C.; Godinho, M.

2014-07-01

220

AMORPHOUS AND SPIN GLASSES. Random magnetic anisotropy in amorphous alloys containing rare earth  

E-print Network

AMORPHOUS AND SPIN GLASSES. Random magnetic anisotropy in amorphous alloys containing rare earth anisotropy in amorphous alloys containing non 5-state rare earth ions is analysed in detail. Magnetisation of amorphous rare-earth-transition metal/noble metal alloys is reasonably described by dense random packing

Paris-Sud XI, Université de

221

Magnetic Fields, Flares & Forecasts  

Microsoft Academic Search

A 2D wavelet transform modulus maxima (WTMM) method is used to characterise the complexity of the distribution of the photospheric magnetic field of active regions. The WTMM method offers increased accuracy and reliability over previous fractal and multifractal methods. The multifractal spectrum of both quiet Sun and active region magnetic features are presented. It is shown that the multifractal nature

Paul A. Conlon; P. Kestener; R. McAteer; P. Gallagher

2009-01-01

222

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

223

The First Magnetic Fields  

E-print Network

We demonstrate that the Biermann battery mechanism for the creation of large scale magnetic fields can arise in a simple model protogalaxy. Analytic calculations and numerical simulations follow explicitly the generation of vorticity (and hence magnetic field) at the outward-moving shock that develops as the protogalactic perturbation collapses. Shear angular momentum then distorts this field into a dipole-like configuration. The magnitude of the field created in the fully formed disk galaxy is estimated to be 10^(-17) Gauss, approximately what is needed as a seed for the galactic dynamo.

George Davies; Lawrence M. Widrow

1999-12-14

224

Solar Wind Magnetic Fields  

NASA Technical Reports Server (NTRS)

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

Smith, E. J.

1995-01-01

225

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

226

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

227

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

228

Magnetic hysteresis in young mid-ocean ridge basalts: Dominant cubic anisotropy?  

Microsoft Academic Search

Magnetic hysteresis data from young mid-ocean ridge basalts include samples with saturation remanence to saturation magnetization (Mrs\\/Ms) ratios greater than 0.5, the theoretical limit for an assemblage of single domain grains with uniaxial anisotropy. Under the usual assumption of dominant uniaxial anisotropy, the narrow single domain grain size implied by the high Mrs\\/Ms values is difficult to reconcile with petrographic

Jeff Gee; Dennis V. Kent

1995-01-01

229

A study of magnetic anisotropy energy in CuMn spin glass  

E-print Network

(Member) Robert E. Tribble (Head of Department) August 1986 ABSTRACT A Study of Magnetic Anisotropy Energy in CuMn Spin Glass. (August 1986) Christine Adele Allen, B. S. , Sam Houston State University Chairman of Advisory Committee: Dr. Thomas W... (Member) Robert E. Tribble (Head of Department) August 1986 ABSTRACT A Study of Magnetic Anisotropy Energy in CuMn Spin Glass. (August 1986) Christine Adele Allen, B. S. , Sam Houston State University Chairman of Advisory Committee: Dr. Thomas W...

Allen, Christine Adele

2012-06-07

230

Planetary magnetic fields  

Microsoft Academic Search

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

David J. Stevenson

2003-01-01

231

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

232

Perpendicular magnetic anisotropy in ion beam sputtered Co/Ni multilayers  

E-print Network

Co/Ni multilayers display perpendicular magnetic anisotropy and have applications in magnetic devices that could lead to a large increase in the density of magnetic storage. Co/Ni 10-(2 Å Co/ 8Å Ni) and 10-(2 Å Co/ 4 Å Ni) ...

Rasin, Boris

2009-01-01

233

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

234

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

235

Engineering Magnetic Anisotropy in Nanostructured 3d and 4f Ferromagnets  

NASA Astrophysics Data System (ADS)

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

Hsu, Chin-Jui

236

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

237

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

238

Graphene Magnetic Field Sensors  

Microsoft Academic Search

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

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

2010-01-01

239

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

240

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

NASA Astrophysics Data System (ADS)

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

Beaujour, Jean-Marc

2010-03-01

241

Switching current reduction using perpendicular anisotropy in CoFeB-MgO magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

We present in-plane CoFeB-MgO magnetic tunnel junctions with perpendicular magnetic anisotropy in the free layer to reduce the spin transfer induced switching current. The tunneling magnetoresistance ratio, resistance-area product, and switching current densities are compared in magnetic tunnel junctions with different CoFeB compositions. The effects of CoFeB free layer thickness on its magnetic anisotropy and current-induced switching characteristics are studied by vibrating sample magnetometry and electrical transport measurements on patterned elliptical nanopillar devices. Switching current densities ˜4 MA/cm2 are obtained at 10 ns write times.

Khalili Amiri, P.; Zeng, Z. M.; Langer, J.; Zhao, H.; Rowlands, G.; Chen, Y.-J.; Krivorotov, I. N.; Wang, J.-P.; Jiang, H. W.; Katine, J. A.; Huai, Y.; Galatsis, K.; Wang, K. L.

2011-03-01

242

Magnetic Field and Life  

NSDL National Science Digital Library

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

243

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

244

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

245

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

246

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

247

Long-range orientational order, local-field anisotropy, and mean molecular polarizability in liquid crystals  

Microsoft Academic Search

The problems on the relation of the mean effective molecular polarizability $$\\u000a\\\\bar \\\\gamma\\u000a$$\\u000a to the long-range orientational order of molecules (the optical anisotropy of the medium) in uniaxial and biaxial liquid crystals,\\u000a the local anisotropy on mesoscopic scales, and the anisotropy of the Lorentz tensor L and the local-field tensor f are formulated and solved. It is demonstrated

E. M. Aver’yanov

2009-01-01

248

Voltage Control of Domain Wall Motion in Perpendicular Magnetic Anisotropy Materials  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

249

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

250

Magnetic moments and anisotropies in smooth and rough surfaces and interfaces  

NASA Astrophysics Data System (ADS)

The relation between the magnetic surface and step moments and anisotropies in free and Pd-covered Fe(110) surfaces is studied experimentally by torsion oscillation magnetometry (TOM) of ultrathin Fe(110) films on W(110) in situ in UHV before, during and after Pd coverage. As a result of Pd coverage, the excess surface moment is enhanced by 0.70? B per surface atom. The enhancement is restricted to the first monolayer of Pd. Near [001] steps, the additional excess step moment is reduced by 0.65? B by Pd. The surface anisotropies of both free and Pd-covered Fe(110) surfaces support perpendicular magnetization. Near [001] steps, they are enhanced by additional step anisotropies, of equal sign and order of magnitude, if expressed by anisotropy energy per atom.

Gradmann, U.; Dürkop, T.; Elmers, H. J.

1997-01-01

251

Magnetic moments and anisotropies in smooth and rough surfaces and interfaces  

NASA Astrophysics Data System (ADS)

The relation between the magnetic surface and step moments and anisotropies in free and Pd-covered Fe(110) surfaces is studied experimentally by torsion oscillation magnetometry (TOM) of ultrathin Fe(110) films on W(110) in situ in UHV before, during and after Pd coverage. As a result of Pd coverage, the excess surface moment is enhanced by 0.70? B per surface atom. The enhancement is restricted to the first monolayer of Pd. Near [001] steps, the additional excess step moment is reduced by 0.65? B by Pd. The surface anisotropies of both free and Pd-covered Fe(110) surfaces support perpendicular magnetization. Near [001] steps, they are enhanced by additional step anisotropies, of equal sign and order of magnitude, if expressed by anisotropy energy per atom.

Gradmann, U.; Dürkop, T.; Elmers, H. J.

252

On magnetic field ``reconstruction''  

NASA Astrophysics Data System (ADS)

Context: Solanki and colleagues have presented intriguing 3D “reconstructions” of magnetic fields from the vector polarimetry of the He I 1083 nm multiplet. Aims: In this Research Note I re-examine the reconstruction technique used. Methods: Using a simple dipole field, I examine the reconstruction technique as applied to the theoretical fields. I assume that the He line forms in two locations, (1) along the magnetic loops and (2) in a horizontal plane. Results: The planar interpretation can account for all aspects of the data, but the loop interpretation has geometrical and physical problems. Conclusions: The data by themselves are not sufficient to determine which picture is more applicable. Nevertheless I argue that the planar interpretation makes more physical sense and that the early reconstructions lead to spurious results. I suggest additional tests that might help constrain the problem further.

Judge, P. G.

2009-01-01

253

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

254

Modeling of Magnetic Anisotropy of SrRuO3 Thin Films Using Tensors  

Microsoft Academic Search

Spintronic devices and magnetic tunneling devices have been a major topic of research in recent years. One of the most promising heterostructures are SrRuO3\\/SiTiO3 heterostructures. Anisotropy induced magnetic properties of SrRuO3 become complicated in SrRuO3\\/SrTiO3 heterostructure because of distorted interfacial symmetry coming from orthorhombic nature of SrRuO3 and cubic SrRuO3. Although the magnetic anisotropy is known to be related with

M. Haji-Sheikh; Y. Z. Yoo; O. Chmaissem; S. Kolesnik; A. Ullah

2006-01-01

255

Structural Control of Magnetic Anisotropy in a Multiferroic EuTiO3 Thin Film  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

256

Substrate-induced magnetic anisotropy in La epitaxial thin films grown onto  

E-print Network

-based oxides [1, 2], as well as in metal systems [3] and in diluted semiconductors [4]. The competition betweenSubstrate-induced magnetic anisotropy in La 0.7 Sr 0.3 MnO 3 epitaxial thin films grown onto (110 Author manuscript, published in "JEMS 2010 (Joint European Magnetic Symposia), Kracovie : Poland (2010

Paris-Sud XI, Université de

257

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.

258

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

259

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

260

The Heliospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

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

Balogh, André; Erdõs, Géza

2013-06-01

261

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

SciTech Connect

A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm{sup 2} coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO{sub 2} dot arrays formed on a Si wafer. At first, arrays of the SiO{sub 2} dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO{sub 2} dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO{sub 2} dots are about 24, 43, and 17 nm, respectively. Then (Co(0.4 nm)/Pt(0.08 nm)){sub 8} MLs with a 3 nm Pt buffer layer is deposited onto the SiO{sub 2} dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO{sub 2} substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner-Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array.

Rahman, M. Tofizur; Shams, Nazmun N.; Lai, C.-H. [Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (China)

2009-04-01

262

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

SciTech Connect

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

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

2010-11-15

263

Magnetic anisotropies and spin reorientations of R/sub 2/Fe/sub 14/B-type compounds  

SciTech Connect

Magnetic anisotropy of R/sub 2/T/sub 14/B (R = rare earth and T = transition metals such as Fe and Co) and partly substituted derivatives thereof are studied over a range of temperatures. The salient features are axial anisotropy for Y/sub 2/Fe/sub 14/B versus planar anisotropy for Y/sub 2/Co/sub 14/B. Only R with negative second-order Stevens' factor (such as Nd) will show axial anisotropy contributions near room temperature. However, even in this case nonaxial contributions compete at cryogenic temperature, leading to a spin reorientation for R = Nd and Ho with T/sup R//sub s/ = 140 and 62 K, respectively, for the Fe-based compounds. The symbol R is used to amplify the point that the spin reorientation is primarily triggered by an internal competition of R in question. The origin of this anisotropy competition is further illuminated by studies on partly R substituted materials, such as (Nd/sub 1-//sub x/R/sub x/)/sub 2/Fe/sub 14/B. Several contributions to the complex situation are considered including: (a) different site contributions (4f, 4g), (b) different order crystal-field terms, such as V/sup 0//sub 2/, V/sup 2//sub 2/, and V/sup 0//sub 4/ on 4f and 4g, (c) relative magnitude of exchange and crystal field, and (d) the trend for smaller R to preferentially occupy the 4f site. Another type of spin reorientation is observed when R and T sublattice anisotropies compete. An example is Er/sub 2/Fe/sub 14/B with T/sup R//sup -//sup T//sub s/ = 326 K. More complex mixed cases are either observed or predicted.

Abache, C.; Oesterreicher, J.

1986-11-15

264

Radiation Signatures of Sub-Larmor Scale Magnetic Fields  

Microsoft Academic Search

Spontaneous rapid growth of strong magnetic fields is rather ubiquitous in high-energy density environments ranging from astrophysical sources (e.g., gamma-ray bursts and relativistic shocks), to reconnection, to laser-plasma interaction laboratory experiments, where they are produced by kinetic streaming instabilities of the Weibel type. Relativistic electrons propagating through these sub-Larmor-scale magnetic fields radiate in the jitter regime, in which the anisotropy

Mikhail V. Medvedev; Jacob Trier Frederiksen; Troels Haugboelle; Åke Nordlund

2011-01-01

265

Magnetic Fields, Flares & Forecasts  

NASA Astrophysics Data System (ADS)

A 2D wavelet transform modulus maxima (WTMM) method is used to characterise the complexity of the distribution of the photospheric magnetic field of active regions. The WTMM method offers increased accuracy and reliability over previous fractal and multifractal methods. The multifractal spectrum of both quiet Sun and active region magnetic features are presented. It is shown that the multifractal nature of the quiet Sun is significantly different from that of an active region. As such, a method is proposed to seperate the information corresponding to the multifractal spectrum of an active region from the surrounding quite Sun texture. The WTMM method and segmentation procedure are shown to detect the internal restructuring of active region magnetic features prior to flaring. We detect two thresholds (Haussdorf dimension > 1.2 and Holder Exponent > -0.7) as possible indicators for conditions favourable to flaring.

Conlon, Paul A.; Kestener, P.; McAteer, R.; Gallagher, P.

2009-05-01

266

Field dependence of the superconducting basal plane anisotropy of TmNi2B2C  

SciTech Connect

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

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

2012-10-01

267

Magnetic field annealing dependent magnetic properties of Co90Pt10 nanowire arrays  

NASA Astrophysics Data System (ADS)

Co90Pt10 alloy and elemental Co nanowires (NWs) are fabricated by electrodeposition in the self-assembled anodic alumina templates. The fabricated NWs are subjected to magnetic field (MF) annealing under 1000 Oe applied magnetic field in a direction parallel to the nanowire axis at 265 °C. The corresponding changes in the saturation magnetization, coercivity, remanent squareness, the shape of hysteresis loops and crystal structure of NWs before and after MF annealing have been investigated. The enhanced magnetic anisotropy has been observed in Co90Pt10 alloy NWs by MF annealing. The elemental Co NWs have not been affected by MF annealing. The stress relief between the domains and diffusional pair ordering of unlike atoms along the direction of external applied field are thought to be the causes of enhanced anisotropy. Re-annealing of the samples in the absence of magnetic field at 600 °C does not completely remove the enhanced anisotropy. The shape of the NWs is concluded to play major role in persistence of enhanced magnetic anisotropy after high temperature reannealing.

Shamaila, S.; Sharif, R.; Chen, J. Y.; Liu, H. R.; Han, X. F.

2009-12-01

268

Magnetic fields and cancer  

SciTech Connect

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

Jones, T.L.

1993-10-01

269

Magnetic Field of the Earth  

NSDL National Science Digital Library

Students can learn about how the magnetic field of the earth is similar to magnets. Go to the following link: Magnetic Field of the Earth 1. What makes the earth like a magnet? 2. How do we measure magnetism? Be sure to check out the fun games and activities on this web site too!! Now click on the following link and listen to a 2 minute presentation about magnetism: Pulse Planet Next go to ...

Merritt, Mrs.

2005-10-18

270

Mapping Magnetic Susceptibility Anisotropies of White Matter in vivo in the Human Brain at 7 Tesla  

PubMed Central

High-resolution magnetic resonance phase- or frequency- shift images acquired at high field show contrast related to magnetic susceptibility differences between tissues. Such contrast varies with the orientation of the organ in the field, but the development of quantitative susceptibility mapping (QSM) has made it possible to reproducibly image the intrinsic tissue susceptibility contrast. However, recent studies indicate that magnetic susceptibility is anisotropic in brain white matter and, as such, needs to be described by a symmetric second-rank tensor (?¯¯). To fully determine the elements of this tensor, it would be necessary to acquire frequency data at six or more orientations. Assuming cylindrical symmetry of the susceptibility tensor in myelinated white matter fibers, we propose a simplified method to reconstruct the susceptibility tensor in terms of a mean magnetic susceptibility, MMS = (?? + 2??)/3 and a magnetic susceptibility anisotropy, MSA = ?? ? ??, where ?? and ?? are susceptibility parallel and perpendicular to the white matter fiber direction, respectively. Computer simulations show that with a practical head rotation angle of around 20°–30°, four head orientations suffice to reproducibly reconstruct the tensor with good accuracy. We tested this approach on whole brain 1×1×1 mm3 frequency data acquired from five healthy subjects at 7 T. The frequency information from phase images collected at four head orientations was combined with the fiber direction information extracted from diffusion tensor imaging (DTI) to map the white matter susceptibility tensor. The MMS and MSA were quantified for regions in several large white matter fiber structures, including the corona radiata, posterior thalamic radiation and corpus callosum. MMS ranged from ?0.037 to ?0.053 ppm (referenced to CSF being about zero). MSA values could be quantified without the need for a reference and ranged between 0.004 and 0.029 ppm, in line with the expectation that the susceptibility perpendicular to the fiber is more diamagnetic than the one parallel to it. PMID:22561358

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

2012-01-01

271

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

272

Birefringence of silica hydrogels prepared under high magnetic fields reinvestigated  

E-print Network

Birefringence is an indicator of structural anisotropy of materials. We measured the birefringence of Pb(II)-doped silica hydrogels prepared under a high magnetic field of various strengths. Because the silica is diamagnetic, one does not expect the structural anisotropy induced by a magnetic field. In previous work [Mori A, Kaito T, Furukawa H 2008 Mater. Lett. 62 3459-3461], we prepared samples in cylindrical cells made of borosilicate glass and obtained a preliminary result indicating a negative birefringence for samples prepared at 5T with the direction of the magnetic field being the optic axis. We have measured the birefringence of Pn(II)-doped silica hydrogels prepared in square cross-sectional cells made of quartz and reverted the previous conclusion. Interestingly, the magnetic-influenced silica hydrogels measured have been classified into four classes: two positive birefringent ones, no birefringent one, and negative birefringent one. Proportionality between birefringence and the strength of magneti...

Mori, Atsushi; Furukawa, Hidemitsu; Yamato, Masafumi; Takahashi, Kohki

2014-01-01

273

Structural anisotropy of magnetically aligned single wall carbon nanotube films  

SciTech Connect

Thick films of aligned single wall carbon nanotubes and ropes have been produced by filtration/deposition from suspension in strong magnetic fields. We measured mosaic distributions of rope orientations in the film plane, for samples of different thicknesses. For an {approx}1 {mu}m film the full width at half maximum (FWHM) derived from electron diffraction is 25 degree sign -28 degree sign . The FWHM of a thicker film ({approx}7 {mu}m) measured by x-ray diffraction is slightly broader, 35{+-}3 degree sign . Aligned films are denser than ordinary filter-deposited ones, and much denser than as-grown material. Optimization of the process is expected to yield smaller FWHMs and higher densities. (c) 2000 American Institute of Physics.

Smith, B. W. [Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)] [Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Benes, Z. [Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)] [Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Luzzi, D. E. [Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)] [Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Fischer, J. E. [Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)] [Department of Materials Science and Engineering and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States); Walters, D. A. [Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77259 (United States)] [Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77259 (United States); Casavant, M. J. [Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77259 (United States)] [Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77259 (United States); Schmidt, J. [Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77259 (United States)] [Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77259 (United States); Smalley, R. E. [Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77259 (United States)] [Center for Nanoscale Science and Technology, Rice University, Houston, Texas 77259 (United States)

2000-07-31

274

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

SciTech Connect

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

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

2009-09-21

275

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

276

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

277

Magnetic anisotropy observed at surface of amorphous silicate and its implications for the mechanism of dust alignment  

NASA Astrophysics Data System (ADS)

Amorphous silicate is considered to be one of the major dust-forming material, however its possibility of magnetic alignment by magnetic anisotropy has not been considered as yet. This is because the anisotropy of an amorphous material is generally considered to be negligibly small. In the present study, depth profile of paramagnetic anisotropy ??para was experimentally obtained for the first time on an amorphous silicate sample, namely moldavite, with a spatial resolution of 0.5 mm. For the above purpose, ??para of square plate (2 mm×2 mm×0.5 mm), separated from a quadrangular prism (2 mm×2 mm×10 mm), were measured one by one; the prism was cut from the amorphous sample with its long axis directed normal to the surface. In order to realize the above measurement, a new experimental device was adopted which could detect ??para of a sub-mm sized sample by measuring its field-induced rotational oscillation in an ?G area. The observed magnetic unstable axis of the plate was always normal to surface plane. The magnitude of ??para at the surface was at a level of 10-6 emu/g, which was comparable to the value previously obtained for of olivine and pyroxene, which are major dust components in the proto-planetary disk region. Accordingly, most of the dust forming materials in the above region is expected to possess finite amount of ?? to cause partial dust alignment.

Yokoi, M.; Katsura, M.; Hisayoshi, K.; Uyeda, C.

2014-10-01

278

Perpendicular magnetic anisotropy in FePt/AlN layered structure  

NASA Astrophysics Data System (ADS)

FePt/AlN layered structures were deposited onto fused quartz substrate by magnetron sputtering method and found to show in-plane anisotropy. However, annealing of the films leads to a transition of magnetic anisotropy from in-plane to perpendicular direction, and the perpendicular anisotropy gets stronger as the annealing temperature increases. Structural analysis shows that the FePt and AlN layers are textured with (111) and (002) orientations, respectively, along the film normal, and no ordering transformation is found for FePt alloy. To study the origin of the developed anisotropy, stress condition was analyzed with an equal biaxial stress model using X-ray diffraction 2 ?- ? scan method and interface quality was evaluated by X-ray reflectivity measurement and transmission electron microscopy observation. The results reveal that perpendicular magnetic anisotropy of the annealed FePt/AlN layered structure can be attributed to the enhanced interface anisotropy, which is due to flattening of the interfaces through annealing.

Zhang, Cong; Sannomiya, Takumi; Muraishi, Shinji; Shi, Ji; Nakamura, Yoshio

2014-09-01

279

AC Magnetic Field Survey Report  

E-print Network

AC Magnetic Field Survey Report of Literature Building - 3000 University of California San Diego:..........................................................................................................2 ELF OR AC MAGNETIC FIELD CHARACTERISTICS:...............................................2 UNITS of California San Diego La Jolla, California PROJECT: AC Magnetic Field Survey SCOPE: The scope of this project

Krstic, Miroslav

280

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

281

Magnetic Field Topology in Jets  

NASA Technical Reports Server (NTRS)

We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.

Gardiner, T. A.; Frank, A.

2000-01-01

282

Low field magnetic resonance imaging  

DOEpatents

A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.

Pines, Alexander (Berkeley, CA); Sakellariou, Dimitrios (Billancourt, FR); Meriles, Carlos A. (Fort Lee, NJ); Trabesinger, Andreas H. (London, GB)

2010-07-13

283

Single-ion anisotropy in Mn-doped diluted magnetic semiconductors  

NASA Astrophysics Data System (ADS)

Motivated by recent developments in spintronics, we propose an explanation of the single-ion anisotropy of Mn-doped diluted magnetic semiconductors using as an example high-quality ZnO:Mn thin films for which X -band electron-paramagnetic-resonance studies were performed. We derive an analytic formula for the axial parameter D and we prove its validity by the exact diagonalization method. We demonstrate a quantitative agreement between the experimental data and our model. These results bring insights into a long-standing problem of single-ion anisotropy in magnetic solids.

Savoyant, A.; Stepanov, A.; Kuzian, R.; Deparis, C.; Morhain, C.; Grasza, K.

2009-09-01

284

Chemically manipulated anomalous Hall effect and perpendicular magnetic anisotropy in Co/Pt multilayers  

NASA Astrophysics Data System (ADS)

Chemically manipulated anomalous Hall effect (AHE) and perpendicular magnetic anisotropy (PMA) have been studied in MgO/[Co/Pt]3/MgO multilayers by introducing a Mg metal layer between the Co layer and the top MgO layer. It is shown that the saturation anomalous Hall resistivity (?AH) and effective magnetic anisotropy (Keff) are 125% and 26% larger than those in the multilayers without Mg insertion, respectively. The X-ray photoelectron spectroscopy (XPS) analysis shows that the enhancement of AHE and PMA is primarily ascribed to effective control of chemical states at the Co/MgO interface.

Jiang, Shao-Long; Chen, Xi; Zhang, Jing-Yan; Yang, Guang; Teng, Jiao; Li, Xu-Jing; Cao, Yi; Zhao, Zhi-Duo; Yang, Kang; Liu, Yang; Yu, Guang-Hua

2014-11-01

285

Visualization of nonuniform magnetic fields by gadolinium-cobalt amorphous films  

Microsoft Academic Search

Configurations of magnetic domain structure of gadolinium-cobalt amorphous films with a perpendicular anisotropy under the effect of spatially nonuniform magnetic stray fields produced by various miniature sources have been studied. The domain structure of the amorphous films has been shown to qualitatively and quantitatively reflect the symmetry and magnitude of the normal component of the nonuniform magnetic fields and, similar

V. E. Ivanov

2008-01-01

286

TOPICAL REVIEW: Texturing by cooling a metallic melt in a magnetic field  

Microsoft Academic Search

Processing in a magnetic field leads to the texturing of materials along an easy-magnetization axis when a minimum anisotropy energy exists at the processing temperature; the magnetic field can be applied to a particle assembly embedded into a liquid, or to a solid at a high diffusion temperature close to the melting temperature or between the liquidus and the solidus

Robert F. Tournier; Eric Beaugnon

2009-01-01

287

Diamagnetic Orientation of Polymerized Molecules under High Magnetic Field  

Microsoft Academic Search

Diamagnetic alignment of polymerized organic molecules is discussed both from the theoretical and experimental points of view. When a number of molecules aggregate with their diamagnetic principal axes along the same direction, the resultant diamagnetic anisotropy energy becomes comparable to the thermal energy and the aggregated molecule can align under a conventional magnetic field, even at room temperatures. Polymerization of

Akio Yamagishi; Tetsuya Takeuchi; Terumasa Higashi; Muneyuki Date

1989-01-01

288

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

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

289

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

NASA Astrophysics Data System (ADS)

We investigated the dependencies of both the magnetization characteristics and the perpendicular magnetic anisotropy of CoxFe3-xO4(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 Ku are strongly dependent on the reactive gas (O2) 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 CoxFe3-xO4 epitaxial films are governed by the oxidation state and the film structure at the vicinity of the interface.

Yanagihara, H.; Utsumi, Y.; Niizeki, T.; Inoue, J.; Kita, Eiji

2014-05-01

290

Primordial magnetic seed field amplification by gravitational waves  

SciTech Connect

Using second-order gauge-invariant perturbation theory, a self-consistent framework describing the nonlinear coupling between gravitational waves and a large-scale homogeneous magnetic field is presented. It is shown how this coupling may be used to amplify seed magnetic fields to strengths needed to support the galactic dynamo. In situations where the gravitational wave background is described by an 'almost' Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmology we find that the magnitude of the original magnetic field is amplified by an amount proportional to the magnitude of the gravitational wave induced shear anisotropy and the square of the field's initial comoving scale. We apply this mechanism to the case where the seed field and gravitational wave background are produced during inflation and find that the magnitude of the gravitational boost depends significantly on the manner in which the estimate of the shear anisotropy at the end of inflation is calculated. Assuming a seed field of 10{sup -34} G spanning a comoving scale of about 10 kpc today, the shear anisotropy at the end of inflation must be at least as large as 10{sup -40} in order to obtain a generated magnetic field of the same order of magnitude as the original seed. Moreover, contrasting the weak-field approximation to our gauge-invariant approach, we find that while both methods agree in the limit of high conductivity, their corresponding solutions are otherwise only compatible in the limit of infinitely long-wavelength gravitational waves.

Betschart, Gerold; Zunckel, Caroline [Department of Mathematics and Applied Mathematics, University of Cape Town, 7701 Rondebosch (South Africa); Dunsby, Peter K.S. [Department of Mathematics and Applied Mathematics, University of Cape Town, 7701 Rondebosch (South Africa); South African Astronomical Observatory, Observatory 7925, Cape Town (South Africa); Marklund, Mattias [Department of Physics, Umeaa University, SE-901 87 Umeaa (Sweden)

2005-12-15

291

Tunable magnetic anisotropy in permalloy thin films grown on holographic relief gratings  

NASA Astrophysics Data System (ADS)

The aim of the present work is to show a simple method that combines conventional laser interferometry and standard thin film deposition techniques to fabricate modulated magnetic nanostructures with lateral periodicity, and to tailor the magnetic properties by varying geometrical parameters. Well defined Ni80Fe20 magnetic thin films with sinusoidal grating profiles were obtained with a periodicity of 1.2 ?m and different grating depths. Magnetic studies via ferromagnetic resonance and magneto optical Kerr effect demonstrate the tunability of the induced in-plane magnetic anisotropy with depth profile.

Berendt, J.; Teixeira, J. M.; García-García, A.; Raposo, M.; Ribeiro, P. A.; Dubowik, J.; Kakazei, G. N.; Schmool, D. S.

2014-02-01

292

NMR at low magnetic fields  

NASA Astrophysics Data System (ADS)

NMR provides outstanding information in chemistry and in medicine. But the equipment is expensive as high-field magnets are employed. Low-field NMR works with inexpensive permanent magnets. Until recently these did not provide fields sufficiently homogeneous for spectroscopy and were mostly used for relaxation measurements. Relaxation can also be measured outside the magnet, and small mobile NMR devices have been developed for non-destructive testing of large objects. Today small stray-field magnets and small magnets with homogeneous fields are available for relaxation analysis, imaging, and spectroscopy. Their availability is believed to be essential for shifting NMR analysis from a specialist's tool to a convenience tool.

Blümich, Bernhard; Casanova, Federico; Appelt, Stephan

2009-08-01

293

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

294

Non-volatile electrically-driven repeatable magnetization reversal with no applied magnetic field  

NASA Astrophysics Data System (ADS)

Repeatable magnetization reversal under purely electrical control remains the outstanding goal in magnetoelectrics. Here we use magnetic force microscopy to study a commercially manufactured multilayer capacitor that displays strain-mediated coupling between magnetostrictive Ni electrodes and piezoelectric BaTiO3-based dielectric layers. In an electrode exposed by polishing approximately normal to the layers, we find a perpendicularly magnetized feature that exhibits non-volatile electrically driven repeatable magnetization reversal with no applied magnetic field. Using micromagnetic modelling, we interpret this nominally full magnetization reversal in terms of a dynamic precession that is triggered by strain from voltage-driven ferroelectric switching that is fast and reversible. The anisotropy field responsible for the perpendicular magnetization is reversed by the electrically driven magnetic switching, which is, therefore, repeatable. Our demonstration of non-volatile magnetic switching via volatile ferroelectric switching may inspire the design of fatigue-free devices for electric-write magnetic-read data storage.

Ghidini, M.; Pellicelli, R.; Prieto, J. L.; Moya, X.; Soussi, J.; Briscoe, J.; Dunn, S.; Mathur, N. D.

2013-02-01

295

Magnetic Fields in Irregular Galaxies  

E-print Network

Magnetic fields are an important component of the interstellar medium, especially in low-mass galaxies like irregulars where the magnetic pressure may be significant. However, few irregular galaxies have observed magnetic field structures. Using the VLA, the GBT, and the ATCA, we have observed several irregular galaxies in the radio continuum to determine their magnetic field structures. Here we report on our results for the galaxies NGC 4214 and NGC 1569.

Amanda A. Kepley; Stefanie Muehle; Eric M. Wilcots; John Everett; Ellen Zweibel; Timothy Robishaw; Carl Heiles

2007-08-24

296

Magnetoelastic coupling induced magnetic anisotropy in Co2(Fe/Mn)Si thin films  

NASA Astrophysics Data System (ADS)

We report the influence of in-plane strain on uniaxial magnetic anisotropy of Co2(Fe/Mn)Si [CF(M)S] films grown on SrTiO3 (STO) and MgO by varying film thickness. The analysis of magnetic free energy functional for the films on STO showed the presence of magnetoelastic anisotropy with magnetostriction constant of 12.22 × 10-6 for CFS and 2.02 × 10-6 for CMS in addition to intrinsic magnetocrystalline anisotropy. Single-domain phase diagram reveals a gradual transition from in-plane to canted state with decreasing film thickness due to strain-induced tetragonal distortion. A maximum canting angle of 41.5° with respect to film plane is predicted for CFS (12 nm)/STO film.

Pandey, Himanshu; Rout, P. K.; Anupam; Joshi, P. C.; Hossain, Z.; Budhani, R. C.

2014-01-01

297

FIELD EVALUATION OF DIPOLE METHOD TO MEASURE AQUIFER ANISOTROPY  

EPA Science Inventory

The ultimate size of a three-dimensional groundwater circulation cell surrounding a vertical circulation well (VCW) is a strong function of the aquifer hydraulic anisotropy, the ratio of the hydraulic conductivity in the horizontal direction to that in the vertical direction. In ...

298

Magnetic Fields in Protostellar Disks  

E-print Network

· Shear in disc may wind up field or drive MRI · Equipartition field in the minimum solar nebula to the shear in the disc? ­ which form of diffusion is dominant? logn/nH (s-1) M+ C+ m+ e He+ H+ H3 instability (MRI) ­ disc-driven winds Magnetic fields · Magnetic fields play an important role during star

Wardle, Mark

299

S-Z power spectrum produced by primordial magnetic fields  

E-print Network

Primordial magnetic fields generated in the very early universe are one of the candidates for the origin of magnetic fields observed in galaxy clusters. After recombination, the Lorentz force acts on the residual ions and electrons to generate density fluctuations of baryons. Accordingly these fluctuations induce the early formation of dark halos which cause the Sunyaev-Zel'dovich (S-Z) effect in cosmic microwave background radiation. This additional S-Z effect due to primordial magnetic fields amplifies the angular power spectrum of cosmic microwave temperature anisotropies on small scales. This amplification depends on the comoving amplitude and the power law index of the primordial magnetic fields spectrum. Comparing with the small scale CMB observations, we obtained the constraints on the primordial magnetic fields, i.e., Bmagnetic fields at 1 Mpc and n is the power law index. These constraints are tighter than t...

Tashiro, Hiroyuki

2009-01-01

300

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

301

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

302

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

303

Mathematical model of voltage–current characteristics of Bi(2223)\\/Ag magnets under an external magnetic field  

Microsoft Academic Search

We have developed a mathematical model, which enables us to predict the voltage–current V(I) characteristics of a solenoidal high-temperature superconductor (HTS) magnet subjected to an external magnetic field parallel to the magnet axis. The model takes into account the anisotropy in the critical current–magnetic field (Ic(B)) characteristic and the n-value of Bi(2223)Ag multifilamentary tape at 20 K. From the power

J Pitel; A Korpela; J Lehtonen; P Kovác

2002-01-01

304

Magnetic Fields: Visible and Permanent.  

ERIC Educational Resources Information Center

Children will be able to see the concept of a magnetic field translated into a visible reality using the simple method outlined. Standard shelf paper, magnets, iron filings, and paint in a spray can are used to prepare a permanent and well-detailed picture of the magnetic field. (Author/JN)

Winkeljohn, Dorothy R.; Earl, Robert D.

1983-01-01

305

Flow directions in dikes from anisotropy of magnetic susceptibility data: The bootstrap way  

Microsoft Academic Search

One of the first applications of anisotropy of magnetic susceptibility (AMS) was an attempt to determine flow directions from mafic dikes [Khan, 1962]. Since the seminal work of Knight and Walker [1988] defining the expected behavior of AMS in response to magma flow, there has been increasing interest in using AMS for this purpose. Here we present a quantitative method

L. Tauxe; J. S. Gee; H. Staudigel

1998-01-01

306

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

307

A dinuclear cobalt(II) complex of calix[8]arenes exibiting strong magnetic anisotropy.  

PubMed

The solvothermal reaction of cobalt(II) acetate with p-tert-butylcalix[8]arene (calix) and triethylamine affords the compound (Et3NH)2 [CoII2(calix)2] (.2Et3NH) that shows a hydrogen bond bridged dinuclear complex [CoII2(calix)2]2- () with cobalt(II) ions in a tetrahedral geometry. The compound crystallises in the monoclinic, space group P2(1)/n with cell parameters a=14.89(1) A, b=20.90(2) A, c=30.87(4) A, beta=102.57(7) degrees, V=9376(16) A3, Z=2. The magnetic studies together with ab initio calculations are evidence of an important role of the geometry of the second coordination sphere of carbon and hydrogen atoms around the CoO4 core in quantifying the zero field splitting on cobalt sites. This results in strong magnetic anisotropies with a negative axial component on the cobalt fragments. PMID:17928916

Petit, Sarah; Pilet, Guillaume; Luneau, Dominique; Chibotaru, Liviu F; Ungur, Liviu

2007-10-28

308

27-DAY Variations of the GCR Intensity and Anisotropy in Different Epochs of Solar Magnetic Activity  

NASA Astrophysics Data System (ADS)

We study 27-day (27d) variations of the galactic cosmic ray (GCR) intensity (I) and the ecliptic anisotropy (A) based on analyses of neutron monitors and ground muon telescopes data for different epochs of solar magnetic activity. Generally, there can be distinguish three scenarios: (1) when the 27d variations are revealed in changes of the both, I and A; (2) 27d variation is observed in changes of I, but not in A; and (3) 27d variation is observed in changes of A, but not in I. We suppose that these phenomena are related with the distinguished mechanisms of creation of the 27d variations in changes of I and A. Among them more decipherable should be: (1) a distinction in sizes of vicinity of heliosphere where 27d variations of I and A are created, (2) propagation of the processes of heliolongitudinal asymmetry (corotating interaction regions) from the Sun to inner and to further distances of heliosphere, (3) preferential roles of spiral interplanetary magnetic field (IMF) in changes of A. Especially, it is inestimable in minimum and near minimum epochs of solar activity, when, even under absence of any heliolongitudinal asymmetries in parameters of solar wind and solar activity a recognizable 27d variation in A is observed due to drift of GCR particles in well established sector structure of the IMF. For all three scenarios we have recognized several distinctions in the rigidity dependences of the amplitudes of the (27d) variations of the I and A.

Alania, Michael; Modzelewska, Renata; Gil, Agnieszka; Wawrzynczak-Szaban, Anna

309

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

310

Induced magnetic anisotropy in Fe80B20 metallic glass by mechanical milling  

Microsoft Academic Search

By means of transmission Mo¨ssbauer spectroscopy, the effect of mechanical milling on the magnetic anisotropy of Fe80B20 metallic glass has been studied. On the basis of variation of the areal ratio R21 of the second to the first Mo¨ssbauer line with milling time, it was found that a rotation of the average magnetic-moment directions from the in-plane to an out-of-plane

G. J. Fan; M. X. Quan; Z. Q. Hu

1996-01-01

311

Magnetic anisotropy in the excited states of low symmetry lanthanide complexes.  

PubMed

Ab initio investigation of multiplet spectrum of lanthanides in archetypal coordination geometries shows an unexpected regular structure consisting of (i) mirror symmetry of anisotropic magnetic properties of doublet states, (ii) high magnetic axiality of low-lying and high-lying doublets, comparable to complexes with ideal axial symmetry, and (iii) the strong rotation of the anisotropy axes of individual doublets. The obtained high axiality of the ground doublet states explains the SMM behaviour of low-symmetry lanthanide complexes. PMID:22027865

Ungur, Liviu; Chibotaru, Liviu F

2011-12-01

312

(version 6/26/06) Magnetic Fields  

E-print Network

where the magnetic fields of the Earth and the bar magnet sum to zero. INTRODUCTION A magnetic field(version 6/26/06) Magnetic Fields GOALS (1) To visualize the magnetic fields produced by several to trace out the magnetic field lines of a single bar magnet on a large sheet of paper. (3) To calculate

Collins, Gary S.

313

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

314

NATIONAL HIGH MAGNETIC FIELD LABORATORY  

E-print Network

and testing areas, magnet experiment cells, and laser laboratory areas. The laboratory is used 24 hours perNATIONAL HIGH MAGNETIC FIELD LABORATORY NHMFL FLORIDA STATE UNIVERSITY SAFETY PROCEDURE SP-3 TITLE Dalton ______________________________________________________ ASSISTANT DIRECTOR, ENVIRONMENTAL, HEALTH

Weston, Ken

315

Growth induced magnetic anisotropy in crystalline and amorphous thin films  

SciTech Connect

The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and Ni-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials. A brief summary of work done in each area is given.

Hellman, F.

1998-07-20

316

Understanding the Chromospheric Magnetic Field  

NASA Astrophysics Data System (ADS)

The chromospheric magnetic field is an important and essential component for understanding solar atmospheric fields. Due to the problems of polarization radiation transfer in the chromosphere and the low detective sensitivity of chromospheric spectrum lines, observations of chromospheric magnetic fields are very difficult, so studies of chromospheric fields are infrequent. However, the understanding of chromospheric fields is evolving. In this report, we summarize our current empirical knowledge and basic physical understanding of chromospheric fields. We concentrate on the comparison of magnetic fields in the photosphere and chromosphere, and then display their difference.

Jin, C. L.; Harvey, J. W.; Pietarila, A.

2014-10-01

317

Magnetic Susceptibility Anisotropy, Molecular Quadrupole Moment, and the Sign of the Electric Dipole Moment in OCCCS: A High-Resolution Microwave Fourier Transform Study Combined with IGLO Calculations  

Microsoft Academic Search

The molecular Zeeman effects of 16O12C12C12C32S and 16O12C12C12C34S have been observed by microwave Fourier transform spectroscopy in magnetic fields up to 20 000 G. The magnetic susceptibility anisotropy of the OCCCS molecule is xi-xi? = -18.740(6) 10-6 erg G-2 mol-1. The molecular g? values for the two isotopomers obtained from the J = 3 --> J = 2 transitions are

F. Holland; U. Fleischer; A. Klesing; D. H. Sutter

1993-01-01

318

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

319

Reconnection of Magnetic Fields  

NASA Astrophysics Data System (ADS)

Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.

Birn, J.; Priest, E. R.

2007-01-01

320

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

321

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

322

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

323

The Galileo magnetic field investigation  

Microsoft Academic Search

The Galileo Orbiter carries a complement of fields and particles instruments designed to provide data needed to shed light on the structure and dynamical variations of the Jovian magnetosphere. Many questions remain regarding the temporal and spatial properties of the magnetospheric magnetic field, how the magnetic field maintains corotation of the embedded plasma and the circumstances under which corotation breaks

M. G. Kivelson; K. K. Khurana; J. D. Means; C. T. Russell; R. C. Snare

1992-01-01

324

Mars Observer magnetic fields investigation  

NASA Technical Reports Server (NTRS)

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 wind interaction, the mapping of crustal magnetic fields, and studies of the Martian ionosphere, which are activities included in the Mars Observer mission objectives. Attention is also given to the flight software incorporated in the on-board data processor, and the procedures of data processing and analysis.

Acuna, M. H.; Connerney, J. E. P.; Wasilewski, P.; Lin, R. P.; Anderson, K. A.; Carlson, C. W.; Mcfadden, J.; Curtis, D. W.; Reme, H.; Cros, A.

1992-01-01

325

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

326

High coercive force and large remanent moment magnetic films with special anisotropies (invited)  

NASA Astrophysics Data System (ADS)

Special sputtering methods have been used to synthesize magnetic films that exhibit high intrinsic coercive forces iHc, large remanent moments, and special anisotropies. By special anisotropies we mean that the easy direction of magnetization in various films can be made to be either in or out of the film plane or in a particular direction within the film plane. To achieve high coercive forces in the films it has been necessary to synthesize the films from high iHc rare-earth transition metal systems such as SmCo5, Nd2Fe14B, and several new compounds in the Sm-Ti-Fe system. Films have been synthesized with different crystal textures by varying the sputtering parameters. The magnetic properties observed have been found to be strongly dependent on the film texture. Several possible film scale geometries for electronic applications have been considered.

Cadieu, F. J.

1987-04-01

327

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

328

Tailoring perpendicular magnetic anisotropy in ultrathin Co/Pt multilayers coupled to NiO  

NASA Astrophysics Data System (ADS)

The nanomagnetism of ultrathin Co/Pt multilayer films is set largely by the microstructure and composition of the interface. To examine these finite-size effects on the Co/Pt magnetism, we have made different Co thickness multilayer films using an ion-beam deposition method with controlled ion energies via an End-Hall voltage (VEH) , and deposited a layer of NiO to examine the nature of the magnetic anisotropy by way of studying the in-plane and perpendicular magnetism. Examining different Co/Pt multilayers made using different VEH (ion energies), we have ascertained that 1.2 nm of Co is the minimum thickness required to establish perpendicular magnetic anisotropy (PMA) and that no intermixing of Co and Pt at their interface is necessary for PMA to occur. First-principles calculations, consistent with the analysis of electron-energy-loss spectrometry with near atomic resolution, indicate that PMA is due to hybridization of Co and Pt at the interface which results in a perpendicular magnetization axis being set in the Co layer due to a significant lowering of the interfacial anisotropy energy. These results point toward an interesting way to tune PMA in ultrathin Co/Pt multilayers.

Ouyang, H.; Han, Y.-H.; Lo, S.-C.; Su, C.-H.; Shiu, Y.-R.; Lin, K.-W.; Desautels, R. D.; van Lierop, J.

2010-06-01

329

Trend of the magnetic anisotropy for individual Mn dopants near the (1?1?0) GaAs surface  

NASA Astrophysics Data System (ADS)

Using a microscopic finite-cluster tight-binding model, we investigate the trend of the magnetic anisotropy energy as a function of the cluster size for an individual Mn impurity positioned in the vicinity of the (1?1?0) GaAs surface. We present results of calculations for large cluster sizes containing approximately 104 atoms, which have not been investigated so far. Our calculations demonstrate that the anisotropy energy of a Mn dopant in bulk GaAs, found to be non-zero in previous tight-binding calculations, is purely a finite size effect that vanishes with inverse cluster size. In contrast to this, we find that the splitting of the three in-gap Mn acceptor energy levels converges to a finite value in the limit of the infinite cluster size. For a Mn in bulk GaAs this feature is related to the nature of the mean-field treatment of the coupling between the impurity and its nearest neighbor atoms. We also calculate the trend of the anisotropy energy in the sublayers as the Mn dopant is moved away from the surface towards the center of the cluster. Here the use of large cluster sizes allows us to position the impurity in deeper sublayers below the surface, compared to previous calculations. In particular, we show that the anisotropy energy increases up to the fifth sublayer and then decreases as the impurity is moved further away from the surface, approaching its bulk value. The present study provides important insights for experimental control and manipulation of the electronic and magnetic properties of individual Mn dopants at the semiconductor surface by means of advanced scanning tunneling microscopy techniques.

Mahani, M. R.; Pertsova, A.; Canali, C. M.

2014-10-01

330

(Revised December 30, 2013) Magnetic Fields  

E-print Network

of the points where the magnetic fields of the Earth and the bar magnet sum to zero. INTRODUCTION A magnetic(Revised December 30, 2013) Magnetic Fields GOALS (1) To visualize the magnetic fields produced compasses to trace out the magnetic field lines of a single bar magnet on a large sheet of paper. (3

Collins, Gary S.

331

Anisotropic physical properties of SC15 epoxy reinforced with magnetic nanofillers under uniform magnetic field  

Microsoft Academic Search

The mechanical properties of SC-15 epoxy can be significantly enhanced when reinforced with nanofillers. In this study, SC-15\\u000a epoxy is loaded with iron oxide nanoparticles and chemically functionalized single-wall carbon nanotubes and cured in a modest\\u000a magnetic field. Magnetic analysis shows that the iron oxide nanoparticles flocculate to form chains and create a structural\\u000a anisotropy in the system. Measurements of

O. Malkina; H. Mahfuz; K. D. Sorge; V. K. Rangari

2011-01-01

332

The Nature of Crustal Seismic Anisotropy: Constraints From Field and Rock Physics Observations  

NASA Astrophysics Data System (ADS)

Compared with mantle seismic anisotropy studies, which have been active for almost five decades, anisotropy of the crystalline crust has been only rarely studied. Seismic anisotropy within continental tectonic provinces is however important because it provides earth scientists with a powerful tool for measuring and quantifying deformation within the crust. Preferred mineral alignment observed in metamorphic terranes produced during metamorphism by recrystallization is associated with planar structures such as slaty cleavage, schistosity, and gneissic layering. These structures are often pervasive for tens to hundreds of kilometers in major collision zones and produce significant compressional wave seismic anisotropy as well as shear wave splitting. Observations of crustal anisotropy within (1) slates of the chlorite subzone of the Haast schist terrane of South Island, New Zealand, (2) prehnite-pumpellite to lower greenschist facies slates and phyllites of the Taiwan Slate Belt, (3) greenschist faces phyllites and metagraywackes of the Valdez Group Chugach terrane in southern Alaska, and (4) amphibolite facies quartzofeldspathic gneisses, approaching granulite grade, within the Nanga Parbat-Haramosh massif demonstrate that crustal anisotropy is not limited to rocks of any particular metamorphic grade and thus can be present at all crustal levels. Laboratory studies of compressional and shear wave velocities provide important constraints on the magnitudes and symmetries of anisotropies at various crustal levels within these orogenic zones. Although compositional layering can produce anisotropy, preferred mineral orientation of highly anisotropic single crystals, resulting from metamorphic recrystallization, is the major contributor. Most metamorphic rocks show significant compressional and shear wave anisotropy. Anisotropy is a particularly important parameter in low grade pelitic rocks such as phyllite and slate and can be as high as 20%. For the medium grade metamorphic rocks tonalitic gneiss, quartz mica schist and amphibolite anisotropy is also high. High grade mafic granulite and crustal eclogite are relatively low in anisotropy, however lower crustal restites are highly anisotropic. Symmetries of these rocks are often treated to a first approximation as hexagonal, although most are actually of orthorhombic or lower symmetry due to lineations present on foliation surfaces. Thus a complete understanding of wave propagation in anisotropic crustal rocks often requires laboratory measurements of nine or more independent elastic constants. At present only a few crustal rocks have been studied in this detail. These measurements will become increasingly critical in the interpretations of future crustal anisotropy field investigations

Christensen, N. I.; Okaya, D.; Meltzer, A.

2006-12-01

333

Magnetic field modulation of chirooptical effects in magnetoplasmonic structures  

NASA Astrophysics Data System (ADS)

In this work we analyse the magnetic field effects on the chirooptical properties of magnetoplasmonic chiral structures. The structures consist of two-dimensional arrays of Au gammadions in which thin layers of Co have been inserted. Due to the magnetic properties of the Au/Co interface the structures have perpendicular magnetic anisotropy which favours magnetic saturation along the surface normal, allowing magnetic field modulation of the chirooptical response with moderate magnetic fields. These structures have two main resonances. The resonance at 850 nm has a larger chirooptical response than the resonance at 650 nm, which, on the other hand, exhibits a larger magnetic field modulation of its chirooptical response. This dissimilar behaviour is due to the different physical origin of the chirooptical and magneto-optical responses. Whereas the chirooptical effects are due to the geometry of the structures, the magneto-optical response is related to the intensity of the electromagnetic field in the magnetic (Co) layers. We also show that the optical chirality can be modulated by the applied magnetic field, which suggests that magnetoplasmonic chiral structures could be used to develop new strategies for chirooptical sensing.In this work we analyse the magnetic field effects on the chirooptical properties of magnetoplasmonic chiral structures. The structures consist of two-dimensional arrays of Au gammadions in which thin layers of Co have been inserted. Due to the magnetic properties of the Au/Co interface the structures have perpendicular magnetic anisotropy which favours magnetic saturation along the surface normal, allowing magnetic field modulation of the chirooptical response with moderate magnetic fields. These structures have two main resonances. The resonance at 850 nm has a larger chirooptical response than the resonance at 650 nm, which, on the other hand, exhibits a larger magnetic field modulation of its chirooptical response. This dissimilar behaviour is due to the different physical origin of the chirooptical and magneto-optical responses. Whereas the chirooptical effects are due to the geometry of the structures, the magneto-optical response is related to the intensity of the electromagnetic field in the magnetic (Co) layers. We also show that the optical chirality can be modulated by the applied magnetic field, which suggests that magnetoplasmonic chiral structures could be used to develop new strategies for chirooptical sensing. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr05889a

Armelles, Gaspar; Caballero, Blanca; Prieto, Patricia; García, Fernando; Cebollada, Alfonso; González, Maria Ujué; García-Martin, Antonio

2014-03-01

334

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

335

Magnetic response to applied electrostatic field in external magnetic field  

NASA Astrophysics Data System (ADS)

We show, within QED and other possible nonlinear theories, that a static charge localized in a finite domain of space becomes a magnetic dipole, if it is placed in an external (constant and homogeneous) magnetic field in the vacuum. The magnetic moment is quadratic in the charge, depends on its size and is parallel to the external field, provided the charge distribution is at least cylindrically symmetric. This magneto-electric effect is a nonlinear response of the magnetized vacuum to an applied electrostatic field. Referring to the simple example of a spherically symmetric applied field, the nonlinearly induced current and its magnetic field are found explicitly throughout the space; the pattern of the lines of force is depicted, both inside and outside the charge, which resembles that of a standard solenoid of classical magnetostatics.

Adorno, T. C.; Gitman, D. M.; Shabad, A. E.

2014-04-01

336

MHD Simulation Heliospheric Magnetic Fields and Turbulence  

NASA Technical Reports Server (NTRS)

This talk will present a summary of our results on simulations of heliospheric structure and dynamics. We use a three-dimensional MHD code in spherical coordinates to produce a solar wind containing a rotating, tilted heliospheric current sheet, fast-slow stream and microstream shear layers, waves, 2-D turbulence, and pressure balanced structures that are input to the inner (superAlfvenic) boundary. The evolution of various combinations of these has led to a deeper understanding of sector structure, magnetic holes, fluctuation anisotropies, and general turbulent evolution. We show how the sectors are likely to be connected, how spiral fields can arise, and how field line diffusion can be caused by waves with transverse structure and microstream shears.

Roberts, D. Aaron

2005-01-01

337

Investigations on the stability of HTSC used to high magnetic fields at 4.2K and 77K  

SciTech Connect

Bi-based oxide superconductors show high critical current density even in very high magnetic fields. This means that they could be used to high field superconducting magnets. In this paper, the flux-jump stability of HTSC superconducting magnets was studied. A critical state model is proposed for HTSC which shows anisotropy and weak-link, the effects of anisotropy and weak-link on the stability are discussed. The mechanical stability was also considered.

Xiao, L.Y.; Han, S.; Lin, L.Z. [Institute of Electrical Engineering, Beijing (China)

1994-12-31

338

Theory of fossil magnetic field  

E-print Network

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

2014-01-01

339

Characterizing local anisotropy of coercive force in motor laminations with the moving magnet hysteresis comparator  

NASA Astrophysics Data System (ADS)

Non oriented silicon steels are widely used within rotating electrical machines and are assumed to have no anisotropy. There exists a need to detect the anisotropic magnetic properties and to evaluate the local changes in magnetic material properties due to manufacturing cutting processes. In this paper, the so called moving magnet hyteresis comparator is applied to non destructively detect directional variations in coercive force in a variety of local regions of rotor and stator laminations of two materials commonly used to construct induction motors cores. Maximum to minimum coercive force ratios were assessed, varying from 1.4 to 1.7.

Garshelis, I. J.; Crevecoeur, G.

2014-05-01

340

Resolving the physics of anisotropy, flow and chaotic fields  

E-print Network

in a helical magnetic container · Host development of advanced plasma measurement systems · Contribute diagnostics Improve plasma production/reliability/cleanliness Improving opportunities for collaboration

Hudson, Stuart

341

Origin of cosmic magnetic fields.  

PubMed

We calculate, in the free Maxwell theory, the renormalized quantum vacuum expectation value of the two-point magnetic correlation function in de Sitter inflation. We find that quantum magnetic fluctuations remain constant during inflation instead of being washed out adiabatically, as usually assumed in the literature. The quantum-to-classical transition of super-Hubble magnetic modes during inflation allow us to treat the magnetic field classically after reheating, when it is coupled to the primeval plasma. The actual magnetic field is scale independent and has an intensity of few×10(-12)??G if the energy scale of inflation is few×10(16)??GeV. Such a field accounts for galactic and galaxy cluster magnetic fields. PMID:23971556

Campanelli, Leonardo

2013-08-01

342

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

343

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

344

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

345

NATIONAL HIGH MAGNETIC FIELD LABORATORY  

E-print Network

NATIONAL HIGH MAGNETIC FIELD LABORATORY SUPPORTED BY: THE NATIONAL SCIENCE FOUNDATION and THE STATE OF FLORIDA OPERATED BY: FLORIDA STATE UNIVERSITY · UNIVERSITY OF FLORIDA · LOS ALAMOS NATIONAL LABORATORY Page 15 2005 ANNUAL REPORT #12;2005 ANNUAL REPORT National High magnetic Field Laboratory 2005 NHMFL

Weston, Ken

346

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

347

Electric field assisted switching in magnetic tunnel junctions  

NASA Astrophysics Data System (ADS)

It is of great interest to acquire large effects of electric field on magnetic properties, partly driven by the premise that voltage-controlled magnetization reversal would be far more energy efficient and be compatible with the ubiquitous voltage-controlled semiconductor devices. Normally the effect of electric field in metallic systems is negligible because the electric field can only penetrate into the materials by a few monolayers due to screening by the free electrons. Here we report the pronounced effects of electric field in magnetic tunnel junctions (MTJs) with very thin CoFeB electrodes, where the magnetic anisotropy originates solely from the CoFeB/MgO interfaces. The MTJs have the key structure of Co40Fe40B20(1.2-1.3nm)/MgO(1.2-2nm)/Co40Fe40B20(1.6nm) and the tunneling magnetoresistance in all junctions is in excess of 100%. Due to the redistribution of electrons among the different 3d orbitals of Fe and Co, the perpendicular magnetic anisotropy of the CoFeB electrodes can be significantly modified by an applied electric field. As a result, the coercivity, the magnetic configuration, and the tunneling magnetoresistance of the MTJs can be manipulated by voltage pulses, such that the high and low resistance states of the MTJ can be reversibly controlled by voltages less than 1.5 V in magnitude and with much smaller current densities.

Wang, Weigang; Li, Mingen; Hagemen, Stephen; Chien, C. L.

2012-02-01

348

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.

349

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

350

Magnetic Field Measurements in Beam Guiding Magnets  

E-print Network

Electromagnets used as beam guiding elements in particle accelerators and colliders require very tight tole-rances on their magnetic fields and on their alignment along the particle path. This article describes the methods and equipment used for magnetic measurements in beam transport magnets. Descriptions are given of magnetic resonance techniques, various induction coil methods, Hall generator measurements, the fluxgate magnetometer as well as the recently developed method of beam based alignment. References of historical nature as well as citations of recent work are given. The present commercial availability of the different sensors and asso-ciated equipment is indicated. Finally we shall try to analyze possible future needs for developments in those fields.

Henrichsen, K N

1998-01-01

351

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

352

Determination of the magnetic anisotropy constant of nanoparticles using measurements of the low-temperature heat capacity  

NASA Astrophysics Data System (ADS)

At low temperatures, the anisotropy energy can significantly affect heat capacity of a superparamagnetic “ideal gas”. At sufficiently low temperatures, when the anisotropy energy of uniaxial magnetic nanoparticles exceeds the energy of thermal fluctuations, the anisotropy energy can be expressed as a sum of the energies of two thermodynamic subsystems (two potential wells). One of these subsystems is composed of magnetic nanoparticles oriented predominantly along the axis of anisotropy, and the other - of particles of opposite orientation. There is a similarity between the considered anisotropy energy and the two-level quantum system. Therefore, the temperature dependence of the magnetic part of the heat capacity (similar to Schottky anomaly) will have a sharp peak. At low temperatures, on the curve of the temperature dependence of the heat capacity, besides a usual T3 background, a portion with a pronounced maximum is monitored. The relation between the maximum heat capacity and the magnetic anisotropy constant is derived. Using this relation and measuring the maximum heat capacity at a given temperature, the numerical value of the magnetic anisotropy constant can be obtained.

Ugulava, A.; Chkhaidze, S.; Kekutia, Sh.; Verulashvili, M.

2014-12-01

353

Influence of crystal structure on the perpendicular magnetic anisotropy of an epitaxial CoPt alloy  

E-print Network

Influence of crystal structure on the perpendicular magnetic anisotropy of an epitaxial CoPt alloy epitaxy CoPt1.1 alloys were simultaneously prepared on Mo seeding layers on Al2O3(11­20), 1­102 , and 1­100 substrates, respectively. Distinct crystal structures and chemical ordering of the CoPt1.1 alloys were

Huang, Jung-Chun

354

Magnetic anisotropy of the rhombohedral antiferromagntic crystals with S-ions. A quantitative estimation  

Microsoft Academic Search

The method to investigate the “single-ion” exchange anisotropy (as predicted by pair model) is treated by means of exploration of several isostructural diamagnetic crystals containing magnetic impurities sufficient to pair spectrum of the electron spin resonance (ESR). The ESR spectra were observed for ferric borate isostructural crystals MBO3+Fe3+(M=Ga, In, Lu, Sc). The experimental dependences of the spin-Hamiltonian axial constants of

V. V. Men'shikov; S. G. Ovchinnikov; V. V. Rudenko; A. N. Sudakov; V. I. Tugarinov; A. M. Vorotynov

2003-01-01

355

Magnetic anisotropy of the rhombohedral antiferromagntic crystals with S-ions. A quantitative estimation  

Microsoft Academic Search

The method to investigate the ``single-ion'' exchange anisotropy (as predicted by pair model) is treated by means of exploration of several isostructural diamagnetic crystals containing magnetic impurities sufficient to pair spectrum of the electron spin resonance (ESR). The ESR spectra were observed for ferric borate isostructural crystals MBO3+Fe3+(M=Ga, In, Lu, Sc). The experimental dependences of the spin-Hamiltonian axial constants of

V. V. Men'shikov; S. G. Ovchinnikov; V. V. Rudenko; A. N. Sudakov; V. I. Tugarinov; A. M. Vorotynov

2003-01-01

356

Magnetic anisotropy quantitative estimation for the rhombohedral antiferromagnetic crystals containing S -state ions  

Microsoft Academic Search

The method to investigate ``single-ion'' exchange anisotropy (as predicted by the pair model) is treated by exploration of several isostructural diamagnetic crystals containing magnetic impurities. The electron paramagnetic resonance (EPR) spectra were observed for ferric borate isostructural crystals MBO3:Fe3+ (M=Ga,In,Lu,Sc) . The experimental dependences of the spin-Hamiltonian axial parameters of the second-order DS and fourth-order (a-F)cS versus total pair spin

V. V. Men'Shikov; S. G. Ovchinnikov; V. V. Rudenko; A. N. Sudakov; V. I. Tugarinov; A. M. Vorotynov

2005-01-01

357

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

358

Matrix isolation ESR spectroscopy and magnetic anisotropy of D{sub 3h} symmetric septet trinitrenes  

SciTech Connect

The fine-structure (FS) parameters D of a series of D{sub 3h} symmetric septet trinitrenes were analyzed theoretically using density functional theory (DFT) calculations and compared with the experimental D values derived from ESR spectra. ESR studies show that D{sub 3h} symmetric septet 1,3,5-trichloro-2,4,6-trinitrenobenzene with D=-0.0957 cm{sup -1} and E= 0 cm{sup -1} is the major paramagnetic product of the photolysis of 1,3,5-triazido-2,4,6-trichlorobenzene in solid argon matrices at 15 K. Trinitrenes of this type display in the powder X-band ESR spectra intense Z{sub 1}-transition at very low magnetic fields, the position of which allows one to precisely calculate the parameter D of such molecules. Thus, our revision of the FS parameters of well-known 1,3,5-tricyano-2,4,6-trinitrenobenzene [E. Wasserman, K. Schueller, and W. A. Yager, Chem. Phys. Lett. 2, 259 (1968)] shows that this trinitrene has Double-Vertical-Line D Double-Vertical-Line = 0.092 cm{sup -1} and E= 0 cm{sup -1}. DFT calculations reveal that, unlike C{sub 2v} symmetric septet trinitrenes, D{sub 3h} symmetric trinitrenes have the same orientations of the spin-spin coupling tensor D-caret{sub SS} and the spin-orbit coupling tensor D-caret{sub SOC} and, as a result, have negative signs for both the D{sub SS} and D{sub SOC} values. The negative magnetic anisotropy of septet 2,4,6-trinitrenobenzenes is considerably strengthened on introduction of heavy atoms in the molecules, owing to an increase in contributions of various excitation states to the D{sub SOC} term.

Misochko, Eugenii Ya.; Akimov, Alexander V.; Masitov, Artem A.; Korchagin, Denis V.; Aldoshin, Sergei M.; Chapyshev, Sergei V. [Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow Region 142432 (Russian Federation)

2013-05-28

359

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

360

Electric-field control of magnetic domain wall motion and local magnetization reversal.  

PubMed

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-BaTiO(3) 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

361

The Link between Magnetic Fields and Cloud/Star Formation  

E-print Network

The question whether magnetic fields play an important role in the processes of molecular cloud and star formation has been debated for decades. Recent observations have revealed a simple picture that may help illuminate these questions: magnetic fields have a tendency to preserve their orientation at all scales that have been probed - from 100-pc scale inter-cloud media down to sub-pc scale cloud cores. This ordered morphology has implications for the way in which self-gravity and turbulence interact with magnetic fields: both gravitational contraction and turbulent velocities should be anisotropic, due to the influence of dynamically important magnetic fields. Such anisotropy is now observed. Here we review these recent observations and discuss how they can improve our understanding of cloud/star formation.

Li, Hua-bai; Sridharan, T K; Houde, Martin; Li, Zhi-Yun; Novak, Giles; Tang, Kwok Sun

2014-01-01

362

Magnetic anisotropy energy and effective exchange interactions in Co intercalated graphene on Ir(1?1?1).  

PubMed

The electronic structure, magnetic moments, effective exchange interaction parameter and the magnetic anisotropy energy of [monolayer Co]/Ir(1?1?1) and Co intercalated graphene on Ir(1?1?1) are studied making use of the first-principles density functional theory calculations. A large positive magnetic anisotropy of 1.24 meV/Co is found for [monolayer Co]/Ir(1?1?1), and a high Curie temperature of 1190 K is estimated. These findings show the Co/Ir(1?1?1) system is a promising candidate for perpendicular ultra-high density magnetic recording applications. The magnetic moments, exchange interactions and the magnetic anisotropy are strongly affected by graphene. Reduction of the magnetic anisotropy and the Curie temperature are found for graphene/[monolayer Co]/Ir(1?1?1). It is shown that for graphene placed in the hollow-hexagonal positions over the monolayer Co, the magnetic anisotropy remains positive, while for the placements with one of the C atoms on the top of Co it becomes negative. These findings may be important for assessing the use of graphene for magnetic recording and magnetoelectronic applications. PMID:25351898

Shick, A B; Hong, S C; Maca, F; Lichtenstein, A I

2014-11-26

363

Magnetic anisotropy energy and effective exchange interactions in Co intercalated graphene on Ir(1?1?1)  

NASA Astrophysics Data System (ADS)

The electronic structure, magnetic moments, effective exchange interaction parameter and the magnetic anisotropy energy of [monolayer Co]/Ir(1?1?1) and Co intercalated graphene on Ir(1?1?1) are studied making use of the first-principles density functional theory calculations. A large positive magnetic anisotropy of 1.24 meV/Co is found for [monolayer Co]/Ir(1?1?1), and a high Curie temperature of 1190 K is estimated. These findings show the Co/Ir(1?1?1) system is a promising candidate for perpendicular ultra-high density magnetic recording applications. The magnetic moments, exchange interactions and the magnetic anisotropy are strongly affected by graphene. Reduction of the magnetic anisotropy and the Curie temperature are found for graphene/[monolayer Co]/Ir(1?1?1). It is shown that for graphene placed in the hollow-hexagonal positions over the monolayer Co, the magnetic anisotropy remains positive, while for the placements with one of the C atoms on the top of Co it becomes negative. These findings may be important for assessing the use of graphene for magnetic recording and magnetoelectronic applications.

Shick, A. B.; Hong, S. C.; Maca, F.; Lichtenstein, A. I.

2014-11-01

364

Large magnetic exchange anisotropy at a heterointerface composed of nanostructured BiFeO3 and NiO  

NASA Astrophysics Data System (ADS)

Magnetic interfaces created by the formation of a nanocomposite of ferromagnetic BiFeO3 nanoparticles of mean size 11 nm and antiferromagnetic network-like nanostructured NiO are studied. The effective radius of the ferromagnetic region is smaller than the actual nanoparticle size, thus confirming the involvement of a large fraction of surface spins in the interfacial magnetism. The exchange coupling between the BiFeO3 nanoparticles and the network-like nanostructured NiO leads to an interfacial blocking phase having an average blocking temperature of about 80 K. The temperature dependent saturation magnetization follows the Bloch law at high (150-300 K) temperature and exponential behaviour in intermediate (25-150 K) and low (5-25 K) temperature regimes. Exchange bias appears below the irreversible temperature of about 300 K, well below the Néel temperature of NiO. The composition dependences of the exchange bias field (HEB) and the coercivity (HC) reveal maximum values of HEB = 1550 Oe and HC = 1730 Oe at 5 K and a cooling field of 50 kOe for a BiFeO3?:?NiO :: 50?:?50 concentration ratio. The exchange bias field decreases exponentially with increase of the temperature. Strong interfacial coupling due to uncompensated surface spins leads to a remarkable enhancement of the magnetic anisotropy at the BiFeO3/NiO interface.

Chakrabarti, Kaushik; Dalal, Biswajit; Ashok, Vishal Dev; Das, Kajari; Sinha Chaudhuri, Sheli; De, S. K.

2014-08-01

365

Preflare magnetic and velocity fields  

NASA Technical Reports Server (NTRS)

A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

1986-01-01

366

Frustrated square lattice with spatial anisotropy: Crystal structure and magnetic properties of PbZnVO(PO4)2  

NASA Astrophysics Data System (ADS)

Crystal structure and magnetic properties of the layered vanadium phosphate PbZnVO(PO4)2 are studied using x-ray powder diffraction, magnetization and specific-heat measurements, as well as band-structure calculations. The compound resembles AA'VO(PO4)2 vanadium phosphates and fits to the extended frustrated square-lattice model with the couplings J1,J1' between nearest neighbors and J2,J2' between next-nearest neighbors. The temperature dependence of the magnetization yields estimates of averaged nearest-neighbor and next-nearest-neighbor couplings, J¯1?-5.2K and J¯2?10.0K , respectively. The effective frustration ratio ?=J¯2/J¯1 amounts to -1.9 and suggests columnar antiferromagnetic ordering in PbZnVO(PO4)2 . Specific-heat data support the estimates of J¯1 and J¯2 and indicate a likely magnetic ordering transition at 3.9 K. However, the averaged couplings underestimate the saturation field, thus pointing to the spatial anisotropy of the nearest-neighbor interactions. Band-structure calculations confirm the identification of ferromagnetic J1,J1' and antiferromagnetic J2,J2' in PbZnVO(PO4)2 and yield (J1'-J1)?1.1K in excellent agreement with the experimental value of 1.1 K, deduced from the difference between the expected and experimentally measured saturation fields. Based on the comparison of layered vanadium phosphates with different metal cations, we show that a moderate spatial anisotropy of the frustrated square lattice has minor influence on the thermodynamic properties of the model. We discuss relevant geometrical parameters, controlling the exchange interactions in these compounds and propose a strategy for further design of strongly frustrated square-lattice materials.

Tsirlin, Alexander A.; Nath, Ramesh; Abakumov, Artem M.; Shpanchenko, Roman V.; Geibel, Christoph; Rosner, Helge

2010-05-01

367

CoNi Films with Perpendicular Magnetic Anisotropy Prepared by Alternate Monoatomic Layer Deposition  

NASA Astrophysics Data System (ADS)

We investigate the magnetic properties of CoNi and CoPt films prepared by an alternate monoatomic layer deposition and discuss the possible existence of a metastable superlattice structure. We find that, as has been reported for the CoPt and CoPd films, the CoNi film also exhibits a perpendicular magnetic anisotropy when the monoatomic Co and Ni layers are stacked alternately, suggesting the possible formation of superlattice structure. Since the CoNi film contains neither noble nor rare-earth metals, it should be an attractive material system for applications.

Fukami, Shunsuke; Sato, Hideo; Yamanouchi, Michihiko; Ikeda, Shoji; Ohno, Hideo

2013-07-01

368

A high anisotropy barrier in a sulfur-bridged organodysprosium single-molecule magnet.  

PubMed

The sulfur-bridged dimers [{Cp'(2)Ln(?-SSiPh(3))}(2)] (Ln=Gd (1), Dy (2); Cp'=?(5)-C(5)H(4)Me) were synthesized by the transmetalation reactions between [Cp'(3)Ln] and Ph(3)SiSLi. Compound 2 is a single-molecule magnet with slow relaxation of magnetization up to 40 K and an anisotropy barrier of U(eff) =133 cm(-1). Insight into the SMM properties of 2 and closely related SMMs has been obtained using ab initio calculations. PMID:22684888

Tuna, Floriana; Smith, Charlene A; Bodensteiner, Michael; Ungur, Liviu; Chibotaru, Liviu F; McInnes, Eric J L; Winpenny, Richard E P; Collison, David; Layfield, Richard A

2012-07-01

369

Ion irradiation induced enhancement of out-of-plane magnetic anisotropy in ultrathin Co films  

SciTech Connect

Ga{sup +} or He{sup +} irradiated MBE grown ultrathin films of sapphire/Pt/Co(d{sub Co})/Pt(d{sub Pt}) were studied using polar Kerr effect in wide ranges of both cobalt d{sub Co} and platinum d{sub Pt} thicknesses as well as ion fluences F. Two branches of increased magnetic anisotropy and enhanced Kerr rotation angle induced by Ga{sup +} or He{sup +} irradiation are clearly visible in two-dimensional (d{sub Co}, LogF) diagrams. Only Ga{sup +} irradiation induces two branches of out-of-plane magnetization state.

Mazalski, P.; Kurant, Z.; Maziewski, A. [Faculty of Physics, University of Bialystok, Bialystok (Poland); Liedke, M. O.; Fassbender, J. [Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany); Baczewski, L. T.; Wawro, A. [Institute of Physics, Polish Academy of Science, Warszawa (Poland)

2013-05-07

370

Relief and generation of frustration in pyrochlore magnets by single-ion anisotropy  

NASA Astrophysics Data System (ADS)

We show that a strongly anisotropic classical Heisenberg magnet on the pyrochlore lattice can be mapped onto an Ising model with an exchange constant of the opposite sign. This mapping can be applied to the recently discovered ``spin ice'' Ho2Ti2O7 [Harris et al., Phys. Rev. Lett. 79, 2554 (1997)], a pyrochlore ferromagnet which-counterintuitively-is frustrated. We describe the implications of this mapping for the ordering properties of the magnets at low temperatures. Finally, we extend this discussion to the ordering properties of Heisenberg pyrochlore antiferromagnets of any anisotropy strength.

Moessner, R.

1998-03-01

371

Radiation from sub-Larmor scale magnetic fields  

Microsoft Academic Search

Spontaneous rapid growth of strong magnetic fields is rather ubiquitous in\\u000ahigh-energy density environments ranging from astrophysical sources (e.g.,\\u000agamma-ray bursts and relativistic shocks), to reconnection, to laser-plasma\\u000ainteraction laboratory experiments, where they are produced by kinetic\\u000astreaming instabilities of the Weibel type. Relativistic electrons propagating\\u000athrough these sub-Larmor-scale magnetic fields radiate in the jitter regime, in\\u000awhich the anisotropy

Mikhail V. Medvedev; Jacob Trier Frederiksen; Troels Haugboelle; Aake Nordlund

2010-01-01

372

Structure, magnetism, and theoretical study of a mixed-valence Co(II)3Co(III)4 heptanuclear wheel: lack of SMM behavior despite negative magnetic anisotropy.  

PubMed

A mixed-valence Co(II)/Co(III) heptanuclear wheel [Co(II)3Co(III)4(L)6(MeO)6] (LH2 = 1,1,1-trifluoro-7-hydroxy-4-methyl-5-aza-hept-3-en-2-one) has been synthesized and its crystal structure determined using single-crystal X-ray diffraction. The valence state of each cobalt ion was established by bond valence sum calculations. Studies of the temperature dependence of the magnetic susceptibility and the field dependence of the magnetization evidence ferromagnetic interactions within the compound. In order to understand the magnetic properties of this Co7 wheel, we performed ab initio calculations for each cobalt fragment at the CASSCF/CASPT2 level, including spin-orbit coupling effects within the SO-RASSI approach. The four Co(III) ions were found to be diamagnetic and to give a significant temperature-independent paramagnetic contribution to the susceptibility. The spin-orbit coupling on the three Co(II) sites leads to separations of approximately 200 cm(-1) between the ground and excited Kramers doublets, placing the Co7 wheel into a weak-exchange limit in which the lowest electronic states are adequately described by the anisotropic exchange interaction between the lowest Kramers doublets on Co(II) sites. Simulation of the exchange interaction was done within the Lines model, keeping the fully ab initio treatment of magnetic anisotropy effects on individual cobalt fragments using a recently developed methodology. A good description of the susceptibility and magnetization was obtained for nearest-neighbor (J1) and next-nearest-neighbor (J2) exchange parameters (1.5 and 5.5 cm(-1), respectively). The strong ferromagnetic interaction between distant cobalt ions arises as a result of low electron-promotion energies in the exchange bridges containing Co(III) ions. The calculations showed a large value of the magnetization along the main magnetic axis (10.1 mu(B)), which is a combined effect of the ferromagnetic exchange interaction and negative magnetic anisotropy on the two marginal Co(II) sites. The lack of single-molecule magnet behavior in [Co(II)3Co(III)4(L)6(MeO)6] is explained by relatively large matrix elements of transverse magnetic moments between states of maximal magnetization of the ground Kramers doublet, evidenced by ab initio calculations, and the associated large tunneling rates between these states in the presence of dipolar transverse magnetic fields in the crystal. PMID:18717564

Chibotaru, Liviu F; Ungur, Liviu; Aronica, Christophe; Elmoll, Hani; Pilet, Guillaume; Luneau, Dominique

2008-09-17

373

Spin glass or random anisotropy?: The origin of magnetically glassy behavior in nanostructured GdAl{sub 2}  

SciTech Connect

Initially crystalline GdAl{sub 2} was mechanically milled for long times to produce a highly chemically disordered phase with approximately 8-nm grains. Analysis of dc magnetization measurements using an Arrott plot and the approach to saturation suggest the presence of significant random anisotropy. ac susceptibility measurements showed that the shift in the peak temperature with frequency usually seen in magnetically glassy and superparamagnetic systems was virtually undetectable in the 10-1000-Hz frequency range. Based on these results, we believe that this material represents an interacting system with random anisotropy, where the anisotropy is the result of surface and interface asymmetries.

Shand, P.M.; Stark, C.C.; Williams, D.; Morales, M.A.; Pekarek, T.M.; Leslie-Pelecky, D.L. [Department of Physics, University of Northern Iowa, 205 Physics Building, Cedar Falls, Iowa 50614 (United States); Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0111 (United States); Department of Chemistry and Physics, University of North Florida, 4567 St. John's Bluff Road South, Jacksonville, Florida 32224 (United States); Department of Physics and Astronomy and Center for Materials Research and Analysis, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0111 (United States)

2005-05-15

374

Streamer propagation in magnetic field  

E-print Network

The propagation of a streamer near an insulating surface under the influence of a transverse magnetic field is theoretically investigated. In the weak magnetic field limit it is shown that the trajectory of the streamer has a circular form with a radius that is much larger than the cyclotron radius of an electron. The charge distribution within the streamer head is strongly polarized by the Lorentz force exerted perpendicualr to the streamer velocity. A critical magnetic field for the branching of a streamer is estimated. Our results are in good agreement with available experimental data.

Zhuravlev, V N; Vagner, I D; Wyder, P

1997-01-01

375

AC photovoltaic module magnetic fields  

SciTech Connect

Implementation of alternating current (AC) photovoltaic (PV) modules, particularly for distributed applications such as PV rooftops and facades, may be slowed by public concern about electric and magnetic fields (EMF). This paper documents magnetic field measurements on an AC PV module, complementing EMF research on direct-current PV modules conducted by PG and E in 1993. Although not comprehensive, the PV EMF data indicate that 60 Hz magnetic fields (the EMF type of greatest public concern) from PV modules are comparable to, or significantly less than, those from household appliances. Given the present EMF research knowledge, AC PV module EMF may not merit considerable concern.

Jennings, C.; Chang, G.J. [Pacific Gas and Electric Co., San Francisco, CA (United States); Reyes, A.B.; Whitaker, C.M. [Endecon Engineering, San Ramon, CA (United States)

1997-12-31

376

Investigating Magnetic Force Fields  

NSDL National Science Digital Library

In this classroom activity, the students will investigate the magnetic pull of a bar magnet at varying distances with the use of paper clips. Students will hypothesize, conduct the experiment, collect the data, and draw conclusions that support their data. Each student will record the experiment and their findings in their science journals. As a class, students will compare each groups' data and their interpretation of the results.

Daryl ("Tish") Monjeau, Bancroft Elementary School, Minneapolis, MN

2012-03-18

377

Magnetic field modulation of chirooptical effects in magnetoplasmonic structures.  

PubMed

In this work we analyse the magnetic field effects on the chirooptical properties of magnetoplasmonic chiral structures. The structures consist of two-dimensional arrays of Au gammadions in which thin layers of Co have been inserted. Due to the magnetic properties of the Au/Co interface the structures have perpendicular magnetic anisotropy which favours magnetic saturation along the surface normal, allowing magnetic field modulation of the chirooptical response with moderate magnetic fields. These structures have two main resonances. The resonance at 850 nm has a larger chirooptical response than the resonance at 650 nm, which, on the other hand, exhibits a larger magnetic field modulation of its chirooptical response. This dissimilar behaviour is due to the different physical origin of the chirooptical and magneto-optical responses. Whereas the chirooptical effects are due to the geometry of the structures, the magneto-optical response is related to the intensity of the electromagnetic field in the magnetic (Co) layers. We also show that the optical chirality can be modulated by the applied magnetic field, which suggests that magnetoplasmonic chiral structures could be used to develop new strategies for chirooptical sensing. PMID:24569696

Armelles, Gaspar; Caballero, Blanca; Prieto, Patricia; García, Fernando; Cebollada, Alfonso; González, Maria Ujué; García-Martin, Antonio

2014-04-01

378

Impurities, anisotropy and the magnetic penetration depth in YBCO  

NASA Astrophysics Data System (ADS)

We examine the effect of impurities on the critical temperature and the magnetic penetration depth for one and two band model systems of YBCO. In the two band system, one of which represents the planes and the other the chains, we find that a high level of impurities in the chain layer only suppresses Tc by a small amount. This is consistent with two experimental observations. First that Ni, which preferentially goes into the chains(David J. Payne, Meera Chandrasekhar, H.R. Chandrasekhar, Solid State Comm. 98), 971 (1996)., suppresses Tc much less that Zn, which goes into the planes and second, the change in the b-axis penetration depth when YBCO is over doped(D.N. Basov, R. Liang, D.A. Bonn, W.N. Hardy, B. Dabrowski, M. Quijada, D.B. Tanner, J.P. Rice, D.M. Ginsberg and T. Timusk, Phys. Rev. Lett. 74), 598 (1995). which suggests that the oxygen deficiency is in the chains since it has little or no effect on the a- and c-axis penetration depths nor on the critical temperature, T_c.

O'Donovan, C.; Carbotte, J. P.

1998-03-01

379

Neutron scattering in magnetic fields  

SciTech Connect

The use of magnetic fields in neutron scattering experimentation is reviewed briefly. Two general areas of application can be distinguished. In one the field acts to change the properties of the scattering sample; in the second the field acts on the neutron itself. Several examples are discussed. Precautions necessary for high precision polarized beam measurements are reviewed. 33 references.

Koehler, W.C.

1984-01-01

380

Evolution of magnetic fields in the IGM: kinetic MHD turbulence  

Microsoft Academic Search

In this work, we present 3D MHD simulations of non-helical, forced turbulence, with an anisotropic thermal pressure with respect to the orientation of the local magnetic field. Such anisotropy arises when the plasma is weakly collisional, i.e., when the Larmor frequency is much greater than the ion-ion collision frequency. In this Kinetic MHD regime (KMHD), there are instabilities that give

Reinaldo S. de Lima; A. Lazarian; D. Falceta-Gonçalves

2009-01-01

381

Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeability.  

PubMed

We report on the synthesis, microstructure and mass transport properties of a colloidal hydrogel self-assembled from a mixture of colloidal silica and nontronite clay plates at different particle concentrations. The gel-structure had uniaxial long-range anisotropy caused by alignment of the clay particles in a strong external magnetic field. After gelation the colloidal silica covered the clay particle network, fixing the orientation of the clay plates. Comparing gels with a clay concentration between 0 and 0.7 vol%, the magnetically oriented gels had a maximum water permeability and self-diffusion coefficient at 0.3 and 0.7 vol% clay, respectively. Hence the specific clay concentration resulting in the highest liquid flux was pressure dependent. This study gives new insight into the effect of anisotropy, particle concentration and bound water on mass transport properties in nano/microporous materials. Such findings merit consideration when designing porous composite materials for use in for example fuel cell, chromatography and membrane technology. PMID:24803339

Abrahamsson, Christoffer; Nordstierna, Lars; Bergenholtz, Johan; Altskär, Annika; Nydén, Magnus

2014-06-28

382

N-flationary magnetic fields  

NASA Astrophysics Data System (ADS)

There is increasing interest in the role played by pseudo Nambu Goldstone bosons (pNGBs) in the construction of string-inspired models of inflation. In these models the inflaton is expected to be coupled to gauge fields, and will lead to the generation of magnetic fields that can be of cosmological interest. We study the production of such fields mainly focusing on the model of N-flation, where the collective effect of several pNGBs drives inflation. Because the fields produced are maximally helical, inverse cascade processes in the primordial plasma significantly increase their coherence length. We discuss under what conditions inflation driven by pNGBs can account for the cosmological magnetic fields observed. A constraint on the parameters of this class of inflationary scenarios is also derived by requiring that the magnetic field does not backreact on the inflating background.

Anber, Mohamed M.; Sorbo, Lorenzo

2006-10-01

383

Field of the Magnetic Monopole  

E-print Network

This paper shows that based upon the Helmholtz decomposition theorem the field of a stationary magnetic monopole, assuming it exists, cannot be represented by a vector potential. Persisting to use vector potential in monopole representation violates fundamentals of mathematics. The importance of this finding is that the vector potential representation was crucial to the original prediction of the quantized value for a magnetic charge.

A. R. Hadjesfandiari

2007-01-19

384

Neutron in Strong Magnetic Fields  

E-print Network

Relativistic world-line Hamiltonian for strongly interacting 3q systems in magnetic field is derived from the path integral for the corresponding Green's function. The neutral baryon Hamiltonian in magnetic field obeys the pseudomomentum conservation and allows a factorization of the c.m. and internal motion. The resulting expression for the baryon mass in magnetic field is written explicitly with the account of hyperfine, OPE and OGE (color Coulomb) interaction. The neutron mass is fast decreasing with magnetic field, losing 1/2 of its value at eB~0.25 GeV^2 and is nearly zero at eB~0.5 GeV^2. Possible physical consequences of the calculated mass trajectory of the neutron, M_n(B), are presented and discussed.

M. A. Andreichikov; B. O. Kerbikov; V. D. Orlovsky; Yu. A. Simonov

2013-12-08

385

Spin dynamics and magnetic anisotropies at the Fe/GaAs(001) interface  

SciTech Connect

20Au/(d)Fe/GaAs(001) structures were deposited using molecular beam epitaxy, where Fe thickness d = (5...90) atomic layers. Interface anisotropies were investigated using the in-plane angular dependence of ferromagnetic resonance (FMR). Intrinsic and extrinsic contributions to magnetic damping were investigated using FMR linewidth ({Delta}H) measurements at 9, 24, 36, and 72 GHz (in-plane configuration) and 9, 24, and 36 GHz (perpendicular configuration). The in-plane cubic and uniaxial perpendicular anisotropies were well described by the bulk and interface contributions indicating that the Fe films have a high lattice coherence and high critical Curie temperature T{sub c}. The in-plane uniaxial anisotropy is more complex and will be discussed in detail. The frequency dependence of {Delta}H(f) was analyzed using the Gilbert damping, two magnon scattering, and long range magnetic inhomogeneity contributions. The thickness dependence of the Gilbert damping parameter {alpha} was found to be well described by the bulk and interface terms.

Kardasz, B.; Montoya, E. A.; Eyrich, C.; Girt, E.; Heinrich, B. [Physics Department, Simon Fraser University, 8888 University Drive, Burnaby, British Columbia, V5A 1S6 (Canada)

2011-04-01

386

Fe3O4 nanoparticles and nanocomposites with potential application in biomedicine and in communication technologies: Nanoparticle aggregation, interaction, and effective magnetic anisotropy  

NASA Astrophysics Data System (ADS)

Magnetite nanoparticles with a size of 5-6 nm with potential impact on biomedicine and information/communication technologies were synthesized by thermal decomposition of Fe(acac)3 and subsequently coated with a silica shell exploiting a water-in-oil synthetic procedure. The as-produced powders (comprised of either Fe3O4 or Fe3O4@silica nanoparticles) were mixed with a photocurable resin obtaining two magnetic nanocomposites with the same nominal amount of magnetic material. The static magnetic properties of the two nanopowders and the corresponding nanocomposites were measured in the 10 K-300 K temperature range. Magnetic measurements are shown here to be able to give unambiguous information on single-particle properties such as particle size and magnetic anisotropy as well as on nanoparticle aggregation and interparticle interaction. A comparison between the size distribution functions obtained from magnetic measurements and from TEM images shows that figures estimated from properly analyzed magnetic measurements are very close to the actual values. In addition, the present analysis allows us to determine the value of the effective magnetic anisotropy and to estimate the anisotropy contribution from the surface. The Field-cooled/zero field cooled curves reveal a high degree of particle aggregation in the Fe3O4 nanopowder, which is partially reduced by silica coating and strongly decreased by dissolution in the host polymer. In all considered materials, the nanoparticles are magnetically interacting, the interaction strength being a function of nanoparticle environment and being the lowest in the nanocomposite containing bare, well-separate Fe3O4 particles. All samples behave as interacting superparamagnetic materials instead of ideal superparamagnets and follow the corresponding scaling law.

Allia, P.; Barrera, G.; Tiberto, P.; Nardi, T.; Leterrier, Y.; Sangermano, M.

2014-09-01

387

SEISMIC ANISOTROPY IN TIGHT GAS SANDSTONES, RULISON FIELD, PICEANCE BASIN, COLORADO  

E-print Network

parameters have been estimated using P-wave VSP inversion and ultrasonic core plugs measurements. For VTI system at Rulison Field. P-wave NMO azimuthal anisotropy indicated a high eccentricity area on the west coal layer. Orientation of the fractures within this area shows anN70ºW to N85ºW preference direction

388

Anisotropy of the magnetic susceptibility of CeCu6-xAux near the quantum phase transition  

NASA Astrophysics Data System (ADS)

We report on the low-temperature dc magnetic susceptibility of CeCu6-xAux(x=0.1) in very small fields B=100 ?T and 1 mT. For x=0.1, i.e. for the quantum critical concentration, we confirm the anomalous exponent ? of the susceptibility along the easy c-direction, ?c-1??+T? with ?=0.8 observed previously in moderate fields B=100 mT (see, A. Schröder, et al., Nature 407 (2000) 351). However, below 240 mK we see a clear additional contribution to ?c. At the lowest measuring temperature T=40 mK, the ratio ?c:?a:?b=4:1.5:1 of the susceptibility anisotropy is weaker than at higher T where the ratio is 10:2:1. This is caused by a steeper increase of ?a and ?b as compared to ?c.

Tomanic, T.; Hamann, A.; Löhneysen, H. v.

2008-04-01

389

Review of magnetic field observations  

NASA Technical Reports Server (NTRS)

Recent observations of magnetic fields in the magnetosphere are reviewed, and critical experiments and data are identified for theoretical analysis and interpretation. Quantitative studies of the solar wind interaction with the earth's magnetic field, regional measurements near the earth's equator at R = 2-8 R sub E, the polar cusp region of the geomagnetosphere, and structural models of the neutral sheet region in the geomagnetic tail are considered.

Ness, N. F.

1971-01-01

390

Magnetic anisotropy of (Ga,Mn)As formed by Mn ion implantation and pulsed-laser melting  

NASA Astrophysics Data System (ADS)

We report on the magnetic anisotropy of (Ga,Mn)As formed by Mn ion implantation followed by pulsed-laser melting. Three specimens with different Mn doses have been systematically studied by SQUID magnetometry, magnetotransport and ferromagnetic resonance. The sample corresponding to the lowest Mn dose does not show any measurable magnetic anisotropy. With increasing Mn doses, however, complex magnetic anisotropy behavior clearly emerges. In particular, the high-Mn-dose samples show unambiguous in-plane uniaxial and cubic anisotropy, similar to that observed in (Ga,Mn)As layers grown by LT-MBE. As these samples were produced by a different processing method, this result lends credence to the hypothesis that the in-plane cubic symmetry breaking is intrinsic to the dilute (Ga,Mn)As phase. Furthermore, in contrast to LT-MBE grown (Ga,Mn)As, these specimens show small perpendicular uniaxial anisotropy, which can be interpreted by a small built-in compressive strain due to the absence of Mn interstitials characteristic of these specimens. Finally, we also observe that a super-paramagnetic phase with distinct perpendicular magnetic anisotropy exists in these specimens. An investigation into the origin of this second magnetic phase is in progress.

Cho, Y. J.; Ge, Z.; Zhou, Y. Y.; Liu, X.; Dobrowolska, M.; Furdyna, J. K.; Scarpulla, M. A.; Dubon, O. D.

2006-03-01

391

Birefringence of silica hydrogels prepared under high magnetic fields reinvestigated  

E-print Network

Birefringence is an indicator of structural anisotropy of materials. We measured the birefringence of Pb(II)-doped silica hydrogels prepared under a high magnetic field of various strengths. Because the silica is diamagnetic, one does not expect the structural anisotropy induced by a magnetic field. In previous work [Mori A, Kaito T, Furukawa H 2008 Mater. Lett. 62 3459-3461], we prepared samples in cylindrical cells made of borosilicate glass and obtained a preliminary result indicating a negative birefringence for samples prepared at 5T with the direction of the magnetic field being the optic axis. We have measured the birefringence of Pn(II)-doped silica hydrogels prepared in square cross-sectional cells made of quartz and reverted the previous conclusion. Interestingly, the magnetic-influenced silica hydrogels measured have been classified into four classes: two positive birefringent ones, no birefringent one, and negative birefringent one. Proportionality between birefringence and the strength of magnetic field is seen for the former two.

Atsushi Mori; Takamasa Kaito; Hidemitsu Furukawa; Masafumi Yamato; Kohki Takahashi

2014-09-17

392

Chiral transition with magnetic fields  

E-print Network

We study the nature of the chiral transition for an effective theory with spontaneous breaking of symmetry, where charged bosons and fermions are subject to the effects of a constant external magnetic field. The problem is studied in terms of the relative intensity of the magnetic field with respect to the mass and the temperature. When the former is the smallest of the scales, we present a suitable method to obtain magnetic and thermal corrections up to ring order at high temperature. By these means, we solve the problem of the instability in the boson sector for these theories, where the squared masses, taken as functions of the order parameter, can vanish and even become negative. The solution is found by considering the screening properties of the plasma, encoded in the resummation of the ring diagrams at high temperature. We also study the case where the magnetic field is the intermediate of the three scales and explore the nature of the chiral transition as we vary the field strength, the coupling constants and the number of fermions. We show that the critical temperature for the restoration of chiral symmetry monotonically increases from small to intermediate values of the magnetic fields and that this temperature is always above the critical temperature for the case when the magnetic field is absent.

Alejandro Ayala; Luis Alberto Hernandez; Ana Julia Mizher; Juan Cristobal Rojas; Cristian Villavicencio

2014-04-25

393

Optical sensor of magnetic fields  

DOEpatents

An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

Butler, M.A.; Martin, S.J.

1986-03-25

394

Interplay of Magnetic and Structural Anisotropy in Co|Ni Multilayer Thin Films  

NASA Astrophysics Data System (ADS)

Interfacial perpendicular magnetic anisotropy (PMA) is important for spin transfer devices and has been predicted to overcome dipolar shape anisotropy for [t Co|2t Ni] multilayers with thicknesses, t, of 4 A or less [1]. layered between Cu, however, thickness dependent PMA (t=1, 2, 3, 4 and 6 A) is not sufficiently strong to produce perpendicular magnetization. Anomalous diffraction reveals that the Co and Ni are expansively strained by the Cu within the sample plane. As calculated in reference 2 this trigonal strain would be sufficient to overcome the PMA. Ferromagnetic resonance measurements [3] indicate that the net Lande g-factors are enhanced above bulk for all thicknesses, and increase further with decreasing layer thickness. By applying element-specific x-ray magnetic circular dichroism (XMCD) we have been able to study the Co and Ni individually. Both elements show increasing spin to orbit ratios with decreasing thickness magnetized either in-plane or along sample normal. In all cases the spin to orbit ratio is enhanced along the sample normal compared with the in-plane direction. [1] Phys. Rev. Lett. 68, 682 (1992) [2] Phys. Rev. B 69, 104426 (2004) [3] Eur. Phys. J. B 59, 475 (2007)

Dvorak, Joseph; Krycka, Kathryn; Beaujour, Jean-Marc; Chen, Wenyu; Kent, Andrew; Kao, Chi-Chang

2008-03-01

395

Magnetic field induced dynamical chaos  

SciTech Connect

In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x–y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra, E-mail: bidhanchandra.bag@visva-bharati.ac.in [Department of Chemistry, Visva-Bharati, Santiniketan 731 235 (India)

2013-12-15

396

The Effects of Inhomogeneities and Anisotropies on Electrocardiographic Fields  

E-print Network

], the study of bioelectric fields from the heart [5], [6], and design and optimization of implantable defibrillators [7]. As the cost of high­speed processing and computer memory has decreased, it has become

Utah, University of

397

Magnetic fields in protoplanetary disks  

E-print Network

Magnetic fields likely play a key role in the dynamics and evolution of protoplanetary discs. They have the potential to efficiently transport angular momentum by MHD turbulence or via the magnetocentrifugal acceleration of outflows from the disk surface, and magnetically-driven mixing has implications for disk chemistry and evolution of the grain population. However, the weak ionisation of protoplanetary discs means that magnetic fields may not be able to effectively couple to the matter. I present calculations of the ionisation equilibrium and magnetic diffusivity as a function of height from the disk midplane at radii of 1 and 5 AU. Dust grains tend to suppress magnetic coupling by soaking up electrons and ions from the gas phase and reducing the conductivity of the gas by many orders of magnitude. However, once grains have grown to a few microns in size their effect starts to wane and magnetic fields can begin to couple to the gas even at the disk midplane. Because ions are generally decoupled from the magnetic field by neutral collisions while electrons are not, the Hall effect tends to dominate the diffusion of the magnetic field when it is able to partially couple to the gas. For a standard population of 0.1 micron grains the active surface layers have a combined column of about 2 g/cm^2 at 1 AU; by the time grains have aggregated to 3 microns the active surface density is 80 g/cm^2. In the absence of grains, x-rays maintain magnetic coupling to 10% of the disk material at 1 AU (150 g/cm^2). At 5 AU the entire disk thickness becomes active once grains have aggregated to 1 micron in size.

Mark Wardle

2007-04-07

398

Active Region Magnetic Fields. I. Plage Fields  

Microsoft Academic Search

We present observations taken with the Advanced Stokes Polarimeter (ASP) in active-region plages and study the frequency distribution of the magnetic field strength (B), inclination with respect to vertical ( gamma ), azimuthal orientation ( chi ), and filling factor (f). The most common values at disk center are B = 1400 G, gamma < 10 deg, no preferred east-west

V. Martinez Pillet; B. W. Lites; A. Skumanich

1997-01-01

399

Origin of perpendicular magnetic anisotropy in Co/Ni multilayers on Ti layer  

NASA Astrophysics Data System (ADS)

Magnetic materials in which their magnetic moment direction is oriented perpendicular to the plane of the magnetic layers in thin film heterostructures have been much studied for their potential application to spintronic devices. In particular, theories of current induced excitation, via the phenomenon of spin torque transfer, show that perpendicularly magnetized layers can be more easily excited or their magnetization direction switched than in-plane magnetized layers. In particular, Co/Ni multilayers are promising due to high spin polarization and small Gilbert damping compared to Co/Pt or Fe/Pt. However, their perpendicular magnetic anisotropy (PMA) is highly sensitive to the underlayer that is critical in device performance because, for instance, the current shunting can substantially reduce the spin transfer torque in magnetic racetrack memory. We observed an excellent PMA in annealed Co/Ni on Ti underlayer whose resistance is significantly greater than those of Co/Ni, thereby minimizing the current shunting. It is found that the PMA does not simply originate from magneto-crystalline effect (spin-orbit interaction) but mainly from magnetoelastic effect caused by compressive strain along (111) direction. We will present systematic results and quantitative analyses.

Yang, See-Hun; Thoms, Kuei-Hung; Thomas, Luc; Parkin, Stuart

2012-02-01

400

Magnetic-field-induced phases in anisotropic triangular antiferromagnets: Application to CuCrO2  

NASA Astrophysics Data System (ADS)

We introduce a minimal spin model for describing the magnetic properties of CuCrO2. Our Monte Carlo simulations of this model reveal a rich magnetic-field-induced phase diagram, which explains the measured field dependence of the electric polarization. The sequence of phase transitions between different multiferroic states arises from a subtle interplay between spatial and spin anisotropy, magnetic frustration, and thermal fluctuations. Our calculations are compared to new measurements up to 92 T.

Lin, Shi-Zeng; Barros, Kipton; Mun, Eundeok; Kim, Jae-Wook; Frontzek, Matthias; Barilo, S.; Shiryaev, S. V.; Zapf, Vivien S.; Batista, Cristian D.

2014-06-01

401

Visualization of nonuniform magnetic fields by gadolinium-cobalt amorphous films  

Microsoft Academic Search

Configurations of magnetic domain structure of gadolinium-cobalt amorphous films with a perpendicular anisotropy under the\\u000a effect of spatially nonuniform magnetic stray fields produced by various miniature sources have been studied. The domain structure\\u000a of the amorphous films has been shown to qualitatively and quantitatively reflect the symmetry and magnitude of the normal\\u000a component of the nonuniform magnetic fields and, similar

V. E. Ivanov

2008-01-01

402

Magnetic fields in O stars  

NASA Astrophysics Data System (ADS)

During the last decade, large-scale, organized (generally dipolar) magnetic fields with strengths between 0.1 and 20 kG have been detected in dozens of OB stars. This contribution reviews the impact of such fields on the stellar winds of O-type stars, with emphasis on variability and X-ray emission.

Nazé, Y.

2014-11-01

403

Magnetization and rotation of MTG HTSC ring in magnetic field  

Microsoft Academic Search

The magnetization of a melt-texture growth (MTG) HTSC ring has been studied. It is shown that the magnetic field inside the ring is larger than the external field under a certain range of external magnetic fields. We have also investigated the magnetic field dependence of the response of a detective coil near a rotating superconducting ring. The responses of the

E. V. Postrekhin; L. W. Zhou; K. J. Huang; C. B. Cai; S. M. Gong; Y. X. Fu

1996-01-01

404

The Effects of Inhomogeneities and Anisotropies on Electrocardiographic Fields  

E-print Network

epicardial fatpads, cardiac chambers, major arteries and veins, ster­ num, ribs, spine and clavicles on computed body surface potential maps (BSPMs) from a large­scale model of the human thorax. Methods Problem Formulation The electric fields produced in the human thorax can be mathematically described by Maxwell

Utah, University of

405

On the role of crystal and stress anisotropy in magnetic Barkhausen noise  

NASA Astrophysics Data System (ADS)

The article describes the micromagnetic behavior of non- and pre-plastically deformed high strength steel samples under applied stress using different magnetic nondestructive methods such as magnetic Barkhausen noise analysis and hysteresis measurements. It was found that the maximum amplitude of Barkhausen noise (MMAX) increases with applied stress up to a certain point and then decreases again (so-called MMAX(?)-curve). Changes of magnetostriction, hysteresis curves and magnetic domain structures have been measured and have been further investigated to find out the reasons with respect to macro- and microscopic material behavior. The results obtained are mainly discussed on the basis of the Villari effect and the relation between applied stress and the Barkhausen noise parameters is described. It is concluded that the interaction between crystal and stress anisotropy is the main reason of the specific MMAX(?)-curve observed.

Sheikh Amiri, Meisam; Thielen, Matthias; Rabung, Madalina; Marx, Michael; Szielasko, Klaus; Boller, Christian

2014-12-01

406

Synthesis, Magnetic Anisotropy and Optical Properties of Preferred Oriented Zinc Ferrite Nanowire Arrays  

PubMed Central

Preferred oriented ZnFe2O4 nanowire arrays with an average diameter of 16 nm were fabricated by post-annealing of ZnFe2 nanowires within anodic aluminum oxide templates in atmosphere. Selected area electron diffraction and X-ray diffraction exhibit that the nanowires are in cubic spinel-type structure with a [110] preferred crystallite orientation. Magnetic measurement indicates that the as-prepared ZnFe2O4 nanowire arrays reveal uniaxial magnetic anisotropy, and the easy magnetization direction is parallel to the axis of nanowire. The optical properties show the ZnFe2O4 nanowire arrays give out 370–520 nm blue-violet light, and their UV absorption edge is around 700 nm. The estimated values of direct and indirect band gaps for the nanowires are 2.23 and 1.73 eV, respectively. PMID:20676211

2010-01-01

407

Confined dissipative droplet solitons in spin-valve nanowires with perpendicular magnetic anisotropy.  

PubMed

Magnetic dissipative droplets are localized, strongly nonlinear dynamical modes excited in nanocontact spin valves with perpendicular magnetic anisotropy. These modes find potential application in nanoscale structures for magnetic storage and computation, but dissipative droplet studies have so far been limited to extended thin films. Here, numerical and asymptotic analyses are used to demonstrate the existence and properties of novel solitons in confined structures. As a nanowire's width is decreased with a nanocontact of fixed size at its center, the observed modes undergo transitions from a fully localized two-dimensional droplet into a two-dimensional droplet edge mode and then a pulsating one-dimensional droplet. These solitons are interpreted as dissipative versions of classical, conservative solitons, allowing for an analytical description of the modes and the mechanisms of bifurcation. The presented results open up new possibilities for the study of low-dimensional solitons and droplet applications in nanostructures. PMID:24580485

Iacocca, Ezio; Dumas, Randy K; Bookman, Lake; Mohseni, Majid; Chung, Sunjae; Hoefer, Mark A; Akerman, Johan

2014-01-31

408

Magnetic field investigations on low cost missions  

Microsoft Academic Search

Magnetic fields pervade all of space and provide important diagnostic information on the nature of processes occurring within and around solar system objects. Thus magnetic investigations are frequently included on planetary missions. Since spacecraft subsystems can generate magnetic fields that may interfere with the measurement of the ambient field, magnetic cleanliness programs are usually instituted to minimize such extraneous magnetic

R. C. Snare; C.T. Russell

1995-01-01

409

Biaxial anisotropy driven asymmetric kinked magnetization reversal in exchange-biased IrMn/NiFe bilayers  

NASA Astrophysics Data System (ADS)

The significant biaxial anisotropy contribution below 50 K is evidenced and identified as a cause of asymmetric "kinked" magnetization reversal behaviour and strong single cycle training effect in ion-beam sputtered IrMn/NiFe bilayers. The minor loop measurement clearly suggests that the magnetization reversal along the descending branch of the hysteresis loop takes place in two distinct steps comprising initial magnetization rotation followed by irreversible domain processes. Our experimental observations of characteristic magnetoresistance and minor loop measurements unambiguously endorse the recent theoretical prediction of Hoffmann suggesting the critical role of the symmetry of antiferromagnetic anisotropy on the reversal asymmetry and training effect.

Fulara, Himanshu; Chaudhary, Sujeet; Kashyap, Subhash C.

2013-07-01

410

Lanthanides in molecular magnetism: old tools in a new field.  

PubMed

In this tutorial review we discuss some basic aspects concerning the magnetic properties of rare-earth ions, which are currently the subject of a renovated interest in the field of molecular magnetism, after the discovery that slow relaxation of the magnetization at liquid nitrogen temperature can occur in mononuclear complexes of these ions. Focusing on Dy(III) derivatives a tutorial discussion is given of the relation of the crystal field parameters, which determine the anisotropy of these systems and consequently their interesting magnetic properties, with the geometry of the coordination sphere around the lanthanide centre and with the pattern of f orbitals. The problem of systems of low point symmetry is also addressed by showing how detailed single crystal investigation, coupled to more sophisticated calculation procedures, is an absolute necessity to obtain meaningful structure-property relationships in these systems. PMID:21390351

Sorace, Lorenzo; Benelli, Cristiano; Gatteschi, Dante

2011-06-01

411

Indoor localization using magnetic fields  

NASA Astrophysics Data System (ADS)

Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing hallways with different kinds of pillars, doors and elevators. All in all, this dissertation contributes the following: 1) provides a framework for understanding the presence of ambient magnetic fields indoors and utilizing them to solve the indoor localization problem; 2) develops an application that is independent of the user and the smart phones and 3) requires no other infrastructure since it is deployed on a device that encapsulates the sensing, computing and inferring functionalities, thereby making it a novel contribution to the mobile and pervasive computing domain.

Pathapati Subbu, Kalyan Sasidhar

412

Magnetic anisotropy in ultrathin Fe films on GaAs, ZnSe, and Ge (001) substrates  

NASA Astrophysics Data System (ADS)

We discuss magnetic anisotropy parameters of ferromagnetic body-centered cubic (bcc) Fe films grown by molecular beam epitaxy (MBE) on (001) substrates of face-centered cubic (fcc) GaAs, ZnSe, and Ge. High-quality MBE growth of these metal/semiconductor combinations is made possible by the fortuitous atomic relationship between the bcc Fe and the underlying fcc semiconductor surfaces, resulting in excellent lattice match. Magnetization measurements by superconducting quantum interference device (SQUID) indicate that the Fe films grown on (001) GaAs surfaces are characterized by a very strong uniaxial in-plane anisotropy; those grown on (001) Ge surfaces have a fully cubic anisotropy; and Fe films grown on ZnSe represent an intermediate case between the preceding two combinations. Ferromagnetic resonance measurements carried out on these three systems provide a strikingly clear quantitative picture of the anisotropy parameters, in excellent agreement with the SQUID results. Based on these results, we propose that the observed anisotropy of cubic Fe films grown in this way results from the surface reconstruction of the specific semiconductor substrate on which the Fe film is deposited. These results suggest that, by controlling surface reconstruction of the substrate during the MBE growth, one may be able to engineer the magnetic anisotropy in Fe, and possibly also in other MBE-grown ferromagnetic films.

Tivakornsasithorn, K.; Liu, X.; Li, X.; Dobrowolska, M.; Furdyna, J. K.

2014-07-01

413

Dynamic self-organization of magnetic domains in amorphous films with perpendicular anisotropy  

Microsoft Academic Search

Dynamic self-organization of magnetic domains is observed in amorphous gadolinium-cobalt films in narrow temperature intervals\\u000a on both sides of the magnetic compensation point. Spiral dynamic domains form in a limited range of ac magnetic field amplitudes\\u000a and frequencies.

G. S. Kandaurova; V. E. Ivanov

1997-01-01

414

Mars Crustal Magnetic Field Remnants  

NASA Technical Reports Server (NTRS)

The radial magnetic field measured is color coded on a global perspective view that shows measurements derived from spacecraft tracks below 200 km overlain on a monochrome shaded relief map of the topography.

This image shows especially strong Martian magnetic fields in the southern highlands near the Terra Cimmeria and Terra Sirenum regions, centered around 180 degrees longitude from the equator to the pole. It is where magnetic stripes possibly resulting from crustal movement are most prominent. The bands are oriented approximately east - west and are about 100 miles wide and 600 miles long, although the longest band stretches more than 1200 miles.

The false blue and red colors represent invisible magnetic fields in the Martian crust that point in opposite directions. The magnetic fields appear to be organized in bands, with adjacent bands pointing in opposite directions, giving these stripes a striking similarity to patterns seen in the Earth's crust at the mid-oceanic ridges.

These data were compiled by the MGS Magnetometer Team led by Mario Acuna at the Goddard Space Flight Center in Greenbelt, MD.

2001-01-01