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Sample records for magnetic anisotropy field

  1. Anisotropy in MHD turbulence due to a mean magnetic field

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

  2. Studying the Interstellar Magnetic Field from Anisotropies in Velocity Channels

    NASA Astrophysics Data System (ADS)

    Esquivel, A.; Lazarian, A.; Pogosyan, D.

    2015-11-01

    Turbulence in the interstellar medium is anisotropic due to the ubiquitous magnetic fields. This anisotropy depends on the strength of the magnetic field and leaves an imprint on observations of spectral line maps. We use a grid of ideal magnetohydrodynamic simulations of driven turbulence and produce synthetic position–position–velocity maps to study the turbulence anisotropy in velocity channels of various resolutions. We found that the average structure function of velocity channels is aligned with the projection of the magnetic field on the plane of the sky. We also found that the degree of such anisotropy increases with the magnitude of the magnetic field. For thick velocity channels (low velocity resolution), the anisotropy is dominated by density, and the degree of anisotropy in these maps allows one to distinguish sub-Alfvénic and super-Alfvénic turbulence regimes, but it also depends strongly on the sonic Mach number. For thin channels (high velocity resolution), we find that the anisotropy depends less on the sonic Mach number. An important limitation of this technique is that it only gives a lower limit on the magnetic field strength because the anisotropy is related only to the magnetic field component on the plane of the sky. It can, and should, be used in combination with other techniques to estimate the magnetic field, such as the Fermi-Chandrasekhar method, anisotropies in centroids, Faraday rotation measurements, or direct line-of-sight determinations of the field from Zeeman effect observations.

  3. Anisotropy of photon production: initial eccentricity or magnetic field.

    PubMed

    Bzdak, Adam; Skokov, Vladimir

    2013-05-10

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

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

    E-print Network

    Qin, Lu-Chang

    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

  5. Anisotropies in magnetic field evolution and local Lyapunov exponents

    SciTech Connect

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

    2000-01-13

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

  6. Current helicity and magnetic field anisotropy in solar active regions

    NASA Astrophysics Data System (ADS)

    Xu, H.; Stepanov, R.; Kuzanyan, K.; Sokoloff, D.; Zhang, H.; Gao, Y.

    2015-12-01

    The electric current helicity density ? =< ? _{ijk}b_i{partial b_k/partial x_j}rangle contains six terms, where bi are components of the magnetic field. Due to the observational limitations, only four of the above six terms can be inferred from solar photospheric vector magnetograms. By comparing the results for simulation we distinguished the statistical difference of above six terms for isotropic and anisotropic cases. We estimated the relative degree of anisotropy for three typical active regions and found that it is of order 0.8 which means the assumption of local isotropy for the observable current helicity density terms is generally not satisfied for solar active regions. Upon studies of the statistical properties of the anisotropy of magnetic field of solar active regions with latitudes and with evolution in the solar cycle, we conclude that the consistency of that assumption of local homogeneity and isotropy requires further analysis in the light of our findings.

  7. Current helicity and magnetic field anisotropy in solar active regions

    E-print Network

    Xu, H; Kuzanyan, K; Sokoloff, D; Zhang, H; Gao, Y

    2015-01-01

    The electric current helicity density $\\displaystyle \\chi=\\langle\\epsilon_{ijk}b_i\\frac{\\partial b_k}{\\partial x_j}\\rangle$ contains six terms, where $b_i$ are components of the magnetic field. Due to the observational limitations, only four of the above six terms can be inferred from solar photospheric vector magnetograms. By comparing the results for simulation we distinguished the statistical difference of above six terms for isotropic and anisotropic cases. We estimated the relative degree of anisotropy for three typical active regions and found that it is of order 0.8 which means the assumption of local isotropy for the observable current helicity density terms is generally not satisfied for solar active regions. Upon studies of the statistical properties of the anisotropy of magnetic field of solar active regions with latitudes and with evolution in the solar cycle, we conclude that the consistency of that assumption of local homogeneity and isotropy requires further analysis in the light of our finding...

  8. Electric field modulation of magnetic anisotropy in perpendicularly magnetized Pt/Co structure with a Pd top layer

    NASA Astrophysics Data System (ADS)

    Hibino, Yuki; Koyama, Tomohiro; Obinata, Aya; Miwa, Kazumoto; Ono, Shimpei; Chiba, Daichi

    2015-11-01

    We investigated the electric field effect on magnetic anisotropy in a perpendicularly magnetized Pt/Co system with a top ultrathin layer of nonmagnetic Pd. By applying an electric field to the surface of the ferromagnetic Pd layer, we observed a clear modulation of the perpendicular magnetic anisotropy of the system. This result shows that the magnetic anisotropy can be modulated by an electric field even when nonmagnetic Pd is inserted at the interface formed by the magnetic layer and insulator. The electric field effect of the proximity-induced moment in Pd might contribute to the anisotropy modulation.

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

    SciTech Connect

    Chen, J. P.; Xie, Y. L.; Chu, P.; Wang, Y. L.; Wang, Z. Q.; Gao, X. S.; Liu, J.-M.

    2014-06-28

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

  10. Field dependent magnetic anisotropy of Fe1-xZnx thin films

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

  11. Field dependent magnetic anisotropy of Ga0.2Fe0.8 thin films

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

    Using longitudinal MOKE in combination with a variable strength rotating magnetic field, called the rotational MOKE (ROTMOKE) method, we show that the magnetic anisotropy for a Ga0.2Fe0.8 single crystal film with a thickness of 17 nm, grown on GaAs (001) with a thick ZnSe buffer layer, depends linearly on the strength of the applied magnetic field. The torque moment curves generated using ROTMOKE are well fit with a model that accounts for the uniaxial, cubic, or fourfold anisotropy, as well as additional terms with a linear dependence on the applied magnetic field. The uniaxial and cubic anisotropy fields, taken from both the hard and the easy axis scans, are seen to remain field independent. The field dependent terms are evidence of a large affect of the magnetostriction and its contribution to the effective magnetic anisotropy in GaxFe1-x thin films.

  12. Correlation between proton anisotropy and magnetic field direction in the distant geotail

    NASA Technical Reports Server (NTRS)

    Klecker, B.; Scholer, M.; Hovestadt, D.; Gloeckler, G.; Ipavich, F. M.; Smith, E. J.; Tsurutani, B. T.

    1984-01-01

    A statistical analysis has been conducted of the anisotropy of suprathermal protons and the polarity of the magnetic field during April 10-16, 1983. At this time, ISEE-3 was at lunar distances in the geomagnetic tail of the earth, and well within the nominal magnetopause. The first-order anisotropy is presently correlated with the latitude angle and the z-component of the magnetic field. The anisotropy direction's frequency distribution is strongly peaked in the earthward and tailward direction, indicating fast earthward and tailward flows. For large anisotropies, and within 5 earth radii of the nominal neutral sheet position, a strong correlation is found between the earthward-streaming suprathermal protons and the northward polarity of the magnetic field; large tailward anisotropies are generally correlated with southward magnetic field polarity. This correlation is most simply interpreted in terms of a neutral line or reconnection model.

  13. Alignment of Iron Nanoparticles in a Magnetic Field Due to Shape Anisotropy

    DOE PAGESBeta

    Radhakrishnan, Balasubramaniam; Nicholson, Don M; Eisenbach, Markus; Ludtka, Gerard Michael; Rios, Orlando; Parish, Chad M

    2015-07-09

    During high magnetic field processing there is evidence for alignment of non-spherical metallic particles above the Curie temperature in alloys with negligible magneto-crystalline anisotropy. The main driving force for alignment is the magnetic shape anisotropy. Current understanding of the phenomenon is not adequate to quantify the effect of particle size, aspect ratio, temperature and the magnetic field on particle alignment. We demonstrate a Monte Carlo approach coupled with size scaling to show the conditions under which alignment is possible.

  14. Magnetic field-dependent shape anisotropy in small patterned films studied using rotating magnetoresistance.

    PubMed

    Fan, Xiaolong; Zhou, Hengan; Rao, Jinwei; Zhao, Xiaobing; Zhao, Jing; Zhang, Fengzhen; Xue, Desheng

    2015-01-01

    Based on the electric rotating magnetoresistance method, the shape anisotropy of a Co microstrip has been systematically investigated. We find that the shape anisotropy is dependent not only on the shape itself, but also on the magnetization distribution controlled by an applied magnetic field. Together with micro-magnetic simulations, we present a visualized picture of how non-uniform magnetization affects the values and polarities of the anisotropy constants and . From the perspective of potential appliantions, our results are useful in designing and understanding the performance of micro- and nano-scale patterned ferromagnetic units and the related device properties. PMID:26563520

  15. Magnetic field-dependent shape anisotropy in small patterned films studied using rotating magnetoresistance

    PubMed Central

    Fan, Xiaolong; Zhou, Hengan; Rao, Jinwei; Zhao, Xiaobing; Zhao, Jing; Zhang, Fengzhen; Xue, Desheng

    2015-01-01

    Based on the electric rotating magnetoresistance method, the shape anisotropy of a Co microstrip has been systematically investigated. We find that the shape anisotropy is dependent not only on the shape itself, but also on the magnetization distribution controlled by an applied magnetic field. Together with micro-magnetic simulations, we present a visualized picture of how non-uniform magnetization affects the values and polarities of the anisotropy constants and . From the perspective of potential appliantions, our results are useful in designing and understanding the performance of micro- and nano-scale patterned ferromagnetic units and the related device properties. PMID:26563520

  16. Magnetic field-dependent shape anisotropy in small patterned films studied using rotating magnetoresistance

    NASA Astrophysics Data System (ADS)

    Fan, Xiaolong; Zhou, Hengan; Rao, Jinwei; Zhao, Xiaobing; Zhao, Jing; Zhang, Fengzhen; Xue, Desheng

    2015-11-01

    Based on the electric rotating magnetoresistance method, the shape anisotropy of a Co microstrip has been systematically investigated. We find that the shape anisotropy is dependent not only on the shape itself, but also on the magnetization distribution controlled by an applied magnetic field. Together with micro-magnetic simulations, we present a visualized picture of how non-uniform magnetization affects the values and polarities of the anisotropy constants and . From the perspective of potential appliantions, our results are useful in designing and understanding the performance of micro- and nano-scale patterned ferromagnetic units and the related device properties.

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

    SciTech Connect

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

    2014-01-20

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

  18. Spin-orbit field switching of magnetization in ferromagnetic films with perpendicular anisotropy

    NASA Astrophysics Data System (ADS)

    Wang, D.

    2012-05-01

    As an alternative to conventional magnetic field, the effective spin-orbit field in transition metals, derived from the Rashba field experienced by itinerant electrons confined in a spatial inversion asymmetric plane through the s-d exchange interaction, is proposed for the manipulation of magnetization. Magnetization switching in ferromagnetic thin films with perpendicular magnetocrystalline anisotropy can be achieved by current induced spin-orbit field, with small in-plane applied magnetic field. Spin-orbit field induced by current pulses as short as 10 ps can initiate ultrafast magnetization switching effectively, with experimentally achievable current densities. The whole switching process completes in about 100 ps.

  19. Field-impressed anisotropies of magnetic susceptibility and remanence in minerals

    SciTech Connect

    Potter, D.K.; Stephenson, A. )

    1990-09-10

    The application of alternating (AF) or direct (DF) magnetic fields to samples containing dispersed particles of magnetite, titanomagnetite, or maghemite has been found to alter significantly the measured low-field susceptibility anisotropy even though the particle orientation is unchanged. The acquisition of isothermal remanent magnetization (IRM) is also strongly dependent on the previous AF treatment given to the samples. A method of quantifying the changes brought about by application of the fields is described. The samples studied were intrinsically isotropic or only weakly anisotropic, and the computed impressed susceptibility or IRM ellipsoids produced by the applied fields were ellipsoids of revolution with the unique axis aligned with the applied field axis. The size and shape of the field-impressed ellipsoids were strongly dependent upon particle size. These effects might thus form the basis of a rapid, nondestructive means of estimating particle size in rocks. The results also have important implications for magnetic fabric analysis and the static AF demagnetization of rocks. In particular, to ensure that the intrinsic magnetic fabric is measured without any field-impressed component of anisotropy, samples should not be subjected to static AF demagnetization prior to the determination of either low field susceptibility anisotropy or IRM anisotropy. Samples should also not carry a significant remanence (such as an IRM acquired in a field greater than about 5 mT) prior to low field susceptibility anisotropy analysis.

  20. Anisotropy in the Cosmic Microwave background As a Probe for early Universe magnetic field

    NASA Astrophysics Data System (ADS)

    Duorah, H. L.

    2015-08-01

    The cosmic background radiation is the remnant of the Big Bang stretched into the microwave region characterized by a temperature of 2.725K. The fluctuation in the background produces anisotropies and it is detected with amplitude of ?T/T?10-5 . Various effects like the Sachs-Wolfe effect, Sunyaev-Zel’ dovich effect are imprinted in this background. The effect of a primordial magnetic field in the plasma at the last scattering surface is examined here. The high magnetic field generated during the phase transition in the early universe is found to be too small to produce the observed anisotropy. However it can be surmised that the magnetic field being ubiquitous can be found in the plasma at the last scattering surface to contribute to the anisotropy. A magnetic field of about 10-2G may produce the desired effect.

  1. Field-dependent perpendicular magnetic anisotropy in CoFeB thin films

    SciTech Connect

    Barsukov, I. Krivorotov, I. N.; Fu, Yu; Gonçalves, A. M.; Sampaio, L. C.; Spasova, M.; Farle, M.; Arias, R. E.

    2014-10-13

    We report ferromagnetic resonance measurements of perpendicular magnetic anisotropy in thin films of Ta/Co{sub 20}Fe{sub 60}B{sub 20}/MgO as a function of the Co{sub 20}Fe{sub 60}B{sub 20} layer thickness. The first and second order anisotropy terms show unexpectedly strong dependence on the external magnetic field applied to the system during the measurements. We propose strong interfacial spin pinning as a possible origin of the field-dependent anisotropy. Our results imply that high-field anisotropy measurements cannot be directly used for quantitative evaluation of zero-field performance parameters of CoFeB-based devices such as spin torque memory.

  2. Effects of anisotropies in turbulent magnetic diffusion in mean-field solar dynamo models

    SciTech Connect

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

    2014-04-10

    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.

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

    E-print Network

    Oughton, Sean

    Scaling anisotropy of the power in parallel and perpendicular components of the solar wind magnetic of the Power in Parallel and Perpendicular Components of the Solar Wind Magnetic Field Miriam A. Forman1 ZLWK GLVWDQFH IURP WKH 6XQ 7KLV GDWD LQFOXGHV WKH VRlar wind whose total power (Pxx + Pyy + Pzz#12; LQ

  4. Development of magnetic system with high-anisotropy localized magnetic field for terahertz time-domain spectroscopy

    NASA Astrophysics Data System (ADS)

    Azbite, Solveyga E.; Denisultanov, Alaudi K.; Khodzitsky, Mikhail K.

    2015-08-01

    In this paper magnetic system with a localized high-intensity magnetic field due to giant magnetic anisotropy magnets was proposed for THz time-domain spectroscopy. The magnetic system consists of two hemispheres which are made from two types of magnets. The both hemispheres will be used for an improvement of THz generation and one hemisphere will be used for investigation of spectral and optical properties of an object at strong magnetic field. The proposed magnetic system was numerically calculated in COMSOL MultiPhysics using AC/DC Module. These results may be used for development of real magnetic THz time-domain spectroscopy system.

  5. Measuring remanence anisotropy of hematite in red beds: anisotropy of high-field isothermal remanence magnetization (hf-AIR)

    NASA Astrophysics Data System (ADS)

    Bilardello, Dario; Kodama, Kenneth P.

    2009-09-01

    The potential of using high-field anisotropy of isothermal remanence magnetization (hf-AIR) measurements for determining the origin of natural remanent magnetization in red beds and for identifying and correcting possible red-bed inclination shallowing was investigated for specimens of the Carboniferous Shepody Formation of New Brunswick and Nova Scotia, Canada. The technique makes it possible for a typical paleomagnetic laboratory to measure the remanence anisotropy of high-coercivity hematite. High-field (hf) AIR was used in conjunction with 100 mT alternating field (af) and 120°C thermal demagnetization to separate the contribution of hematite to the remanence anisotropy from that of magnetite/maghemite and goethite, respectively. A 5-T impulse DC magnetic field was used for the hf-AIR to reset the magnetic moment of high-coercivity hematite so that demagnetization between AIR orientations was not necessary. The ability of a 5-T field to reset the magnetization was tested by generating an isothermal remanent magnetization acquisition curve for hematite by using impulse DC magnetic fields up to 5 T in one orientation and followed by applying a field in the opposite direction at each step. Each field application was treated by 120°C heating and 100 mT af demagnetization before measurement. At 5 T, the difference between the magnetizations applied in opposite directions disappeared indicating that no magnetic memory persisted at this field strength. We performed a validity and reproducibility test of our hf-AIR measurement technique by measuring three specimens multiple times along two orthogonal coordinate systems. The method yielded highly reproducible results and, on rotating the specimen's coordinates, the fabric rotated by 90° as expected, showing that it is not an artifact of the technique. We also measured hf-AIR on samples that had previously been chemically demagnetized in 3N HCl to remove the secondary, chemically grown pigmentary hematite. The hf-AIR fabric of leached samples is similar to that of untreated samples, but shows a better-defined magnetic lineation and imbrication. We interpret the fabric observed for the Shepody Formation to be a compactional fabric that has been reoriented by strain during folding following a flexural-slip model.

  6. Magnetic-field-induced quantum criticality in a planar ferromagnet with single-ion anisotropy

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    We analyze the effects induced by single-ion anisotropy on quantum criticality in a d-dimensional spin-3/2 planar ferromagnet. To tackle this problem we employ the two-time Green's function method, using the Tyablikov decoupling for exchange interactions and the Anderson-Callen decoupling for single-ion anisotropy. In our analysis the role of non-thermal control parameter which drives the quantum phase transition is played by a longitudinal external magnetic field. We find that the single-ion anisotropy has substantial effects on the structure of the phase diagram close to the quantum critical point.

  7. Magnetic anisotropy of chloritoid

    NASA Astrophysics Data System (ADS)

    Haerinck, Tom; Debacker, Timothy; Sintubin, Manuel

    2013-04-01

    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.

  8. Electric field controlled reversible magnetic anisotropy switching studied by spin rectification

    SciTech Connect

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

    2014-03-10

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

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

    SciTech Connect

    Qu, Xiao-bo; Zhang, Yi; Liu, Cheng; Hu, Hong-bo; Xue, Liang

    2012-05-01

    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.

  10. Tuning of the nucleation field in nanowires with perpendicular magnetic anisotropy

    SciTech Connect

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

    2013-04-28

    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.

  11. Magnetic Fields and Cosmic-Ray Anisotropies at TeV Energies

    NASA Astrophysics Data System (ADS)

    Battaner, Eduardo; Castellano, Joaquín; Masip, Manuel

    2015-02-01

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

  12. Anisotropy of the solar network magnetic field around the average supergranule

    NASA Astrophysics Data System (ADS)

    Langfellner, J.; Gizon, L.; Birch, A. C.

    2015-07-01

    Supergranules in the quiet Sun are outlined by a web-like structure of enhanced magnetic field strength, the so-called magnetic network. We aim to map the magnetic network field around the average supergranule near disk center. We use observations of the line-of-sight component of the magnetic field from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The average supergranule is constructed by coaligning and averaging over 3000 individual supergranules. We determine the positions of the supergranules with an image segmentation algorithm that we apply to maps of the horizontal flow divergence measured using time-distance helioseismology. In the center of the average supergranule, the magnetic (intranetwork) field is weaker by about 2.2 Gauss than the background value (3.5 Gauss), whereas it is enhanced in the surrounding ring of horizontal inflows (by about 0.6 Gauss on average). We find that this network field is significantly stronger west (prograde) of the average supergranule than in the east (by about 0.3 Gauss). With time-distance helioseismology, we find a similar anisotropy. The observed anisotropy of the magnetic field adds to the mysterious dynamical properties of solar supergranulation.

  13. Alignment of iron nanoparticles in a magnetic field due to shape anisotropy

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, B.; Nicholson, D. M.; Eisenbach, M.; Parish, C.; Ludtka, G. M.; Rios, O.

    2015-11-01

    During high magnetic field solidification processing there is evidence for the alignment of nanoscale metallic particles with elongated morphologies that nucleate from a liquid metal. Such alignment occurs well above the Curie temperature of the particle where the magneto-crystalline anisotropy energy and exchange energy contributions are negligible. The main driving force for alignment is the magnetic shape anisotropy. Current understanding of the phenomenon is not adequate to quantify the effect of particle size, aspect ratio, temperature and the magnetic field on particle alignment. We demonstrate a Monte Carlo approach coupled with a scaling law for the dipole-dipole interaction energy as a function of the particle size to identify the conditions under which such alignment is possible.

  14. Modification of the classical Heisenberg helimagnet by weak uniaxial anisotropy and magnetic field

    SciTech Connect

    Zaliznyak, I.A.; Zhitomirsky, M.E.

    1995-09-01

    A classical ground state of the isotropic Heisenberg spin Hamiltonian on a primitive Bravais lattice is known to be a single-Q plane helix. Additional uniaxial anisotropy and external magnetic field can greatly distort this structure by generating higher-order (at the wave vectors nQ) Fourier harmonics in the spatial spin configuration. These features are not captured within the usual formalism based on the Luttinger-Tisza theorem, when the classical ground state energy is minimized under the {open_quotes}weak{close_quotes} condition on the lengths of the spins. We discuss why the correct solution is lost in that approach and present another microscopic treatment of the problem. For easy-axis and easy-plane quadratic uniaxial anisotropy it allows one to find the classical ground state for general Q and for any orientation of the magnetic field considering the effect of anisotropy (but not the field) as a perturbation of the exchange structure. As a result, the classical ground state energy, the uniform magnetization, and the magnetic Bragg peak intensities that are measured in the experiments are calculated. 21 refs., 1 fig.

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

    NASA Technical Reports Server (NTRS)

    Venters, T. M.; Pavlidou, V.

    2013-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Venters, T. M.; Pavlidou, V.

    2012-01-01

    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.

  17. Origin of anomalously high exchange field in antiferromagnetically coupled magnetic structures: Spin reorientation versus interface anisotropy

    NASA Astrophysics Data System (ADS)

    Ranjbar, M.; Piramanayagam, S. N.; Wong, S. K.; Sbiaa, R.; Song, W.; Tan, H. K.; Gonzaga, L.; Chong, T. C.

    2011-11-01

    Magnetization reorientation from in-plane to perpendicular direction, observed in Co thin film coupled antiferromagnetically to high perpendicular magnetic anisotropy (Co/Pd) multilayers, is studied systematically for Co thickness ranging from 0 to 2.4 nm. The sample with 0.75 nm thick Co showed an exchange coupling field (Hex) exceeding 15 kOe at room temperature and 17.2 kOe at 5 K. With an increase of Co thickness, Hex decreased as expected and beyond certain thickness, magnetization reorientation was not observed. Indeed, three regions were observed in the thickness dependence of magnetization of the thin layer; one in which the thin layer (in the thickness range up to 0.8 nm) had a perpendicular magnetic anisotropy due to interface effects and antiferromagnetic coupling, another in which the thin layer (0.9-1.2 nm) magnetization had no interface or crystallographic anisotropy but was reoriented in the perpendicular direction due to antiferromagnetic coupling, and the third (above 1.2 nm) in which the magnetization was in-plane. In addition, Hall effect measurements were carried out to observe the anomalous and planar Hall voltages and to quantify the perpendicular and in-plane components of magnetization. The sample with thicker Co layer (2.4 nm) showed an in-plane component of magnetization, whereas the sample with 0.75 nm Co showed no in-plane component. The high value of Hex observed in 0.75 nm Co samples can have important implications in spintronics and bit patterned media.

  18. Magnetic multilayer interface anisotropy

    SciTech Connect

    Pechan, M.J.

    1992-01-01

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

  19. Magnetic multilayer interface anisotropy

    SciTech Connect

    Pechan, M.J.

    1991-01-01

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

  20. Magnetic multilayer interface anisotropy

    SciTech Connect

    Pechan, M.J.

    1990-01-01

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

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

    E-print Network

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

    2011-01-01

    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 ...

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

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

    NASA Technical Reports Server (NTRS)

    Ghosh, Sanjoy; Roberts, D. Aaron

    2010-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  6. Anisotropy of magnetic susceptibility in diamagnetic limestones reveals deflection of the strain field near the Dead Sea Fault, northern Israel

    NASA Astrophysics Data System (ADS)

    Issachar, R.; Levi, T.; Marco, S.; Weinberger, R.

    2015-08-01

    To exploit the potential of anisotropy of magnetic susceptibility (AMS) as a tool to estimate the strain field around major faults, we measured the AMS of calcite-bearing diamagnetic rocks that crop out next to the Dead Sea Fault (DSF) in northern Israel. Through integrated magnetic and geochemical methods we found that the rocks are almost pure calcite rocks and therefore the magnetic fabric is primarily controlled by preferred crystallographic orientation (PCO) with the minimum principal AMS axes (k3) parallel to calcite c-axes. We applied a separation procedure in several samples with high Fe content in order to calculate the AMS anisotropy parameters and compare them to pure diamagnetic rocks. AARM, thermo-susceptibility curves and IRM were used to characterize the magnetic phases. We found that for Fe content below 500 ppm the AMS is mostly controlled by the diamagnetic phase and showed that differences in the degree of anisotropy P' up to 3% (P' = 1.005 to 1.023) and in anisotropy difference ?k (up to ~ 0.25 × 10- 6 SI) in diamagnetic rocks are related to differences of strain magnitudes. The spatial distribution of the magnetic fabrics indicates ~ N-S maximum shortening parallel to the strike of the Hula Western Border fault (HWBF), one of the main strands of the DSF in northern Israel. The anisotropy parameters suggest that the strain magnitudes increase eastward with the proximity to the HWBF. These results suggest that the strain field near the HWBF is locally deflected as a consequence of the DSF activity. In light of the "fault weakness" model and geological setting of the study area, we suggest that the area accommodates dominant transtension during the Pleistocene. The present study demonstrates the useful application of AMS measurements in "iron-free" limestones as recorders of the strain field near plate boundaries.

  7. Primordial magnetic field constrained from CMB anisotropies,and its generation and evolution before, during and after the BBN

    E-print Network

    Yamazaki, D G; Kajino, T; Mathews, G J; Yamazaki, Dai G.; Ichiki, Kiyotomo; Kajino, Toshitaka; Mathews, Grant J.

    2006-01-01

    The primordial magnetic field (PMF) can strongly affect the cosmic microwave background (CMB) power spectrum and the formation of large scale structure. In this presentation, we calculate the CMB temperature anisotropies generated by including a power-law magnetic field at the photon last scattering surface (PLSS). We then deduce an upper limit on the primordial magnetic field based upon our theoretical analysis of the power excess on small angular scales. We have taken into account several important effects such as the modified matter sound speed in the presence of a magnetic field. An upper limit to the field strength of $|B_\\lambda|\\lesssim$ 4.7 nG at the present scale of 1 Mpc is deduced. This is obtained by comparing the calculated theoretical result including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the small scale CMB anisotropies from the Wilkinson Microwave Anisotropy Probe (WMAP), the Cosmic Background Imager (CBI) and the Arcminute Cosmology Bolometer Array Receiver (ACBAR). W...

  8. Primordial magnetic field constrained from CMB anisotropies,and its generation and evolution before, during and after the BBN

    E-print Network

    Dai G. Yamazaki; Kiyotomo Ichiki; Toshitaka Kajino; Grant J. Mathews

    2006-10-09

    The primordial magnetic field (PMF) can strongly affect the cosmic microwave background (CMB) power spectrum and the formation of large scale structure. In this presentation, we calculate the CMB temperature anisotropies generated by including a power-law magnetic field at the photon last scattering surface (PLSS). We then deduce an upper limit on the primordial magnetic field based upon our theoretical analysis of the power excess on small angular scales. We have taken into account several important effects such as the modified matter sound speed in the presence of a magnetic field. An upper limit to the field strength of $|B_\\lambda|\\lesssim$ 4.7 nG at the present scale of 1 Mpc is deduced. This is obtained by comparing the calculated theoretical result including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the small scale CMB anisotropies from the Wilkinson Microwave Anisotropy Probe (WMAP), the Cosmic Background Imager (CBI) and the Arcminute Cosmology Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for the generation and evolution of the PMF before, during and after the BBN.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Matczak, Micha?; Szyma?ski, Bogdan; Ku?wik, Piotr; Urbaniak, Maciej; Stobiecki, Feliks; Kurant, Zbigniew; Maziewski, Andrzej; Lengemann, Daniel; Ehresmann, Arno

    2014-08-01

    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.

  11. Magnetic-field-induced quantum criticality in a spin-1 planar ferromagnet with single-ion anisotropy

    NASA Astrophysics Data System (ADS)

    Mercaldo, Maria Teresa; Rabuffo, Ileana; Decesare, Luigi; Caramicod'Auria, Alvaro

    2014-03-01

    The effects of single-ion anisotropy on field-induced quantum criticality in spin-1 planar ferromagnet is explored by means of the two-time Green's function method. We work at the Tyablikov decoupling level for exchange interactions and the Anderson-Callen decoupling level for single-ion anisotropy. In our analysis a longitudinal external magnetic field is used as the non-thermal control parameter and the phase diagram and the quantum critical properties are established for suitable values of the single-ion anisotropy parameter. We find that the single-ion anisotropy has sensible effects on the structure of the phase diagram close to the quantum critical point. Indeed, for values of the uniaxial crystal-field parameter above a positive threshold a re-entrant behavior appears for the critical line, while above this value the conventional magnetic-field-induced quantum critical scenario remains unchanged. M. T. Mercaldo, I. Rabuffo, L. De Cesare, A. Caramico D'Auria, Eur. Phys. J. B 86, 340 (2013)

  12. Constraints on the Evolution of the Primordial Magnetic Field from the Small-Scale Cosmic Microwave Background Angular Anisotropy

    E-print Network

    D. Yamazaki; K. Ichiki; T. Kajino; G. J. Mathews

    2009-02-19

    Recent observations of the cosmic microwave background (CMB) have extended the measured power spectrum to higher multipoles $l\\gtrsim$1000, and there appears to be possible evidence for excess power on small angular scales. The primordial magnetic field (PMF) can strongly affect the CMB power spectrum and the formation of large scale structure. In this paper, we calculate the CMB temperature anisotropies generated by including a power-law magnetic field at the photon last-scattering surface (PLSS). We then deduce an upper limit on the PMF based on our theoretical analysis of the power excess on small angular scales. We have taken into account several important effects such as the modified matter sound speed in the presence of a magnetic field. An upper limit to the field strength of $|B_\\lambda|\\lesssim$ 4.7 nG at the present scale of 1 Mpc is deduced. This is obtained by comparing the calculated theoretical result including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the small-scale CMB anisotropies from the $Wilkinson Microwave Anisotropy Probe$ (WMAP), the Cosmic Background Imager (CBI), and the Arcminute Cosmology Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for the generation and evolution of the PMF.

  13. Direct measurement of the magnetic anisotropy field in Mn-Ga and Mn-Co-Ga Heusler films

    NASA Astrophysics Data System (ADS)

    Fowley, Ciarán; Ouardi, Siham; Kubota, Takahide; Yildirim, Oguz; Neudert, Andreas; Lenz, Kilian; Sluka, Volker; Lindner, Jürgen; Law, Joseph M.; Mizukami, Shigemi; Fecher, Gerhard H.; Felser, Claudia; Deac, Alina M.

    2015-04-01

    The static and dynamic magnetic properties of tetragonally distorted Mn-Ga based alloys were investigated. Static properties are determined in magnetic fields up to 6.5 T using SQUID magnetometry. For the pure Mn1.6Ga film, the saturation magnetisation is 0.36 MA m-1 and the coercivity is 0.29 T. Partial substitution of Mn by Co results in Mn2.6Co0.3Ga1.1. The saturation magnetisation of those films drops to 0.2 MA m-1 and the coercivity is increased to 1 T. The time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe the high-frequency dynamics of Mn-Ga. The ferromagnetic resonance frequency extrapolated to zero-field is found to be 125 GHz with a Gilbert damping, ?, of 0.019. The anisotropy field is determined from both SQUID and TR-MOKE to be 4.5 T, corresponding to an effective anisotropy density of 0.81 MJ m-3. Given the large anisotropy field of the Mn2.6Co0.3Ga1.1 film, pulsed magnetic fields up to 60 T are used to determine the field strength required to saturate the film in the plane. For this, the extraordinary Hall effect was employed as a probe of the local magnetisation. By integrating the reconstructed in-plane magnetisation curve, the effective anisotropy energy density for Mn2.6Co0.3Ga1.1 is determined to be 1.23 MJ m-3.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    SciTech Connect

    Dziatkowski, K.; Liu, X.; Furdyna, J. K.; Twardowski, A.

    2011-04-01

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

  16. Magnetic Anisotropy of a Three-Dimensional Honeycomb Iridate

    NASA Astrophysics Data System (ADS)

    Modic, Kimberly; McDonald, Ross; Shekter, Arkady; Analytis, James; Ramshaw, Brad

    2015-03-01

    We present the magnetic anisotropy of a 3-dimensional honeycomb iridate, where the large spin-orbit coupling of iridium provides the possibility for exotic magnetic ground states. A complete angular dependence of magnetic torque provides evidence for highly spin-anisotropic exchange interactions at low temperature. An extension of these measurements to high magnetic fields shows that the magnetic anisotropy switches sign at 50 T and becomes five times larger than the anisotropy at low fields. The anisotropy continues to increase up to the largest applied fields suggesting the presence of new magnetically ordered states.

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

    SciTech Connect

    Jedamzik, Karsten; Abel, Tom E-mail: tabel@slac.stanford.edu

    2013-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Jedamzik, Karsten; Abel, Tom

    2013-10-01

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

  19. CMB temperature anisotropy at large scales induced by a causal primordial magnetic field

    SciTech Connect

    Bonvin, Camille; Caprini, Chiara E-mail: camille.bonvin@cea.fr

    2010-05-01

    We present an analytical derivation of the Sachs Wolfe effect sourced by a primordial magnetic field. In order to consistently specify the initial conditions, we assume that the magnetic field is generated by a causal process, namely a first order phase transition in the early universe. As for the topological defects case, we apply the general relativistic junction conditions to match the perturbation variables before and after the phase transition which generates the magnetic field, in such a way that the total energy momentum tensor is conserved across the transition and Einstein's equations are satisfied. We further solve the evolution equations for the metric and fluid perturbations at large scales analytically including neutrinos, and derive the magnetic Sachs Wolfe effect. We find that the relevant contribution to the magnetic Sachs Wolfe effect comes from the metric perturbations at next-to-leading order in the large scale limit. The leading order term is in fact strongly suppressed due to the presence of free-streaming neutrinos. We derive the neutrino compensation effect dynamically and confirm that the magnetic Sachs Wolfe spectrum from a causal magnetic field behaves as l(l+1) C{sup B}{sub l}?l{sup 2} as found in the latest numerical analyses.

  20. Anisotropy of the solar network magnetic field around the average supergranule

    E-print Network

    Langfellner, J; Birch, A C

    2015-01-01

    Supergranules in the quiet Sun are outlined by a web-like structure of enhanced magnetic field strength, the so-called magnetic network. We aim to map the magnetic network field around the average supergranule near disk center. We use observations of the line-of-sight component of the magnetic field from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The average supergranule is constructed by coaligning and averaging over 3000 individual supergranules. We determine the positions of the supergranules with an image segmentation algorithm that we apply on maps of the horizontal flow divergence measured using time-distance helioseismology. In the center of the average supergranule the magnetic (intranetwork) field is weaker by about 2.2 Gauss than the background value (3.5 Gauss), whereas it is enhanced in the surrounding ring of horizontal inflows (by about 0.6 Gauss on average). We find that this network field is significantly stronger west (prograde) of the average sup...

  1. SWAP operation in the two-qubit Heisenberg XXZ model: Effects of anisotropy and magnetic field

    SciTech Connect

    Zhou Yue; Yang Fuhua; Feng Songlin; Zhang Guofeng

    2007-06-15

    In this paper we study the SWAP operation in a two-qubit anisotropic XXZ model in the presence of an inhomogeneous magnetic field. We establish the range of anisotropic parameter {lambda} within which the SWAP operation is feasible. The SWAP errors caused by the inhomogeneous field are evaluated.

  2. Competing magnetic anisotropies in obliquely deposited thin permalloy film

    NASA Astrophysics Data System (ADS)

    Belyaev, B. A.; Izotov, A. V.; Solovev, P. N.

    2016-01-01

    Distribution of the magnetic anisotropy in thin film prepared by thermal vacuum oblique deposition of permalloy with small off-normal angle of incident in the presence of an external magnetic field has been studied by ferromagnetic resonance technique. On local area of the sample, a mutual compensation of near orthogonal in-plane uniaxial magnetic anisotropies induced by oblique deposition and by applied magnetic field has been found. Moreover, in addition to the uniaxial (twofold) magnetic anisotropy, fourfold and sixfold magnetic anisotropies have been observed in the sample. To explain the obtained high-order anisotropies, we assumed that the sample has exchange coupled adjacent regions or phases with different parameters of magnetic anisotropy. The results of the micromagnetic analysis of a two-layer model of the sample confirm the hypothesis.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Takami, Hajime; Inoue, Susumu; Yamamoto, Tokonatsu

    2012-07-01

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

  5. Micromagnetics of shape anisotropy based permanent magnets

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  6. Magnetic anisotropy of strained epitaxial manganite films

    SciTech Connect

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

    2011-05-15

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

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

    E-print Network

    Dasso, Sergio

    Anisotropy of the Taylor scale and the correlation scale in plasma sheet and solar wind magnetic and C. Mouikis4 Received 23 September 2008; revised 2 April 2009; accepted 13 April 2009; published 14 and the solar wind are employed to determine the correlation scale and the magnetic Taylor microscale from

  8. Critical Current Anisotropy of Zr Doped MOCVD Coated Conductor in Magnetic Fields up to 8T

    NASA Astrophysics Data System (ADS)

    Mineev, N. A.; Baskakov, A. O.; Rudnev, I. A.

    The critical current angular distributions in the magnetic field range from 0 up to 8 T have been measured for Zr doped MOCVD (metalorganic chemical vapor deposition) tape produced by Super Power Inc. The vortex path model was used to fit these distributions to specify a tilted peak near c-axis that corresponds to the presence of BaZrO3 columnar defects in the tape. The orientation of such defects was found to be 10.3o with respect to the c-axis direction. Peak in the ab direction was observed in the whole field range and it could be interpreted as pinning on spacer layers between CuO planes. The appearance of gauss distribution was found in high fields that confirms chosen model.

  9. Tailored magnetic anisotropy in an amorphous trilayer

    SciTech Connect

    Fu Yu; Barsukov, I.; Spasova, M.; Lindner, J.; Meckenstock, R.; Farle, M.; Raanaei, H.; Hjoervarsson, B.

    2011-06-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  11. Magnetic anisotropy data of CH2NCl

    NASA Astrophysics Data System (ADS)

    Kumar, M.; Gupta, R.

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

  12. Advanced magnetic anisotropy determination through isothermal remanent magnetization of nanoparticles

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

  13. The influence of magnetic aftereffects on the magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Mashukov, A.; Mashukova, A.

    2012-04-01

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

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

    SciTech Connect

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

    2011-12-10

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

  15. PHYSICAL REVIEW B 88, 205203 (2013) Magnetic anisotropy of single Mn acceptors in GaAs in an external magnetic field

    E-print Network

    Flatte, Michael E.

    2013-01-01

    PHYSICAL REVIEW B 88, 205203 (2013) Magnetic anisotropy of single Mn acceptors in Ga properties in spintronic devices. The most commonly investigated material as a magnetic semiconductor is Ga will refer to as the Mn core from now on. On the other hand, for applications in spintronic devices

  16. Anisotropy of MHD Turbulence at Low Magnetic Reynolds Number

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

  17. Magnetic patterning using ion irradiation for highly ordered CoPt alloys with perpendicular anisotropy

    SciTech Connect

    Abes, M.; Venuat, J.; Muller, D.; Carvalho, A.; Schmerber, G.; Beaurepaire, E.; Dinia, A.; Pierron-Bohnes, V.

    2004-12-15

    We used a combination of ion irradiation and e-beam lithography to magnetically pattern an ordered CoPt alloy with strong perpendicular magnetic anisotropy. Ion irradiation disorders the alloy and strongly reduces the magnetic anisotropy. Magnetic force microscopy showed a regular array of 1 {mu}m{sup 2} square dots with perpendicular anisotropy separated by 1 {mu}m large ranges with in-plane anisotropy. This is further confirmed by magnetic measurements, which showed that arrays protected by a 200 nm Pt layer present the same coercive field and the same perpendicular anisotropy as before irradiation. This is promising for applications in magnetic recording technologies.

  18. Electric-field-induced angular dependence of magnetic anisotropy in a FeCo/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Yang, Chengcheng; Wang, Fenglong; Dong, Chunhui; Sui, Wenbo; Jiang, Changjun; Xue, Desheng

    2015-04-01

    To understand the distribution of the in-plane magnetic anisotropy under a dc electric field, FeCo films deposited onto Pb(Mg1/3Nb2/3)O3-PbTiO3 (011)-orientated substrates by RF-magnetron sputtering were investigated. Vibrating sample magnetometer was performed and the occurrence of switching was demonstrated of the magnetization easy axis in FeCo films upon applying solely a dc electric field. A theoretical calculation was performed to provide a simplified account of the magnetoelastic contribution to the magnetic anisotropy. Quantification of the angular distribution of the magnetic anisotropy field under various electric fields was obtained, which can contribute to realizing low-loss electric-field-turning devices.

  19. Carrier-dependent magnetic anisotropy of cobalt doped titanium dioxide

    PubMed Central

    Shao, Bin; Feng, Min; Zuo, Xu

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-03-01

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

  1. Three-dimensional mapping of single-atom magnetic anisotropy.

    PubMed

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

    2015-03-11

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

  2. IEEE TRANSACTIONS ON MAGNETICS, VOL. 40, NO. 4, JULY 2004 2697 Induced Anisotropy in FeCo-Based Nanocrystalline

    E-print Network

    Laughlin, David E.

    , the ac power loss and relative permeability are im- portant figures of merit for soft ferromagnets the magnetic anisotropy in FeCo-base nanocrystalline soft ferro- magnetic alloys. Alloys of composition Fe44 5 anisotropy. Index Terms--FeCo alloys, field annealing, magnetic anisotropy, nanocrystals, soft magnetic

  3. Single-ion anisotropy and magnetic field response in the spin-ice materials Ho2Ti2O7 and Dy2Ti2O7

    NASA Astrophysics Data System (ADS)

    Tomasello, Bruno; Castelnovo, Claudio; Moessner, Roderich; Quintanilla, Jorge

    2015-10-01

    Motivated by its role as a central pillar of current theories of the dynamics of spin ice in and out of equilibrium, we study the single-ion dynamics of the magnetic rare-earth ions in their local environments, subject to the effective fields set up by the magnetic moments with which they interact. This effective field has a transverse component with respect to the local easy axis of the crystal electric field, which can induce quantum tunneling. We go beyond the projective spin-1/2 picture and use instead the full crystal-field Hamiltonian. We find that the Kramers versus non-Kramers nature, as well as the symmetries of the crystal-field Hamiltonian, result in different perturbative behavior at small fields (?1 T ), with transverse field effects being more pronounced in Ho2Ti2O7 than in Dy2Ti2O7 . Remarkably, the energy splitting range we find is consistent with time scales extracted from experiments. We also present a study of the static magnetic response, which highlights the anisotropy of the system in the form of an off-diagonal g tensor, and we investigate the effects of thermal fluctuations in the temperature regime of relevance to experiments. We show that there is a narrow but accessible window of experimental parameters where the anisotropic response can be observed.

  4. Magnetic nanoparticle array with perpendicular crystal magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Haginoya, Chiseki; Heike, Seiji; Ishibashi, Masayoshi; Nakamura, Kimio; Koike, Kazuyuki; Yoshimura, Toshiyuki; Yamamoto, Jiro; Hirayama, Yoshiyuki

    1999-06-01

    By using electron beam lithography, a continuous CoCrPt film with a perpendicular crystal magnetic anisotropy has been patterned into a magnetic nanoparticle array of 29 Gdot/in.2 with a 150 nm period, an 80 nm diameter, and a 44 nm height. Studies of magnetic properties using a magnetic force microscope and a vibrating sample magnetometer show that this patterning increases the remanent-to-saturation magnetization ratio from 0.2 of the continuous film to 1 of the particles, and that each particle has a single magnetic domain with perpendicular anisotropy. The application of this array to future high density magnetic recording media is discussed.

  5. Voltage controlled magnetic anisotropy in magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Wang, Weigang

    2013-03-01

    Recently, voltage controlled magnetic anisotropy (VCMA) in 3d transitional ferromagnets (FM) has attracted a great deal of attentions. VCMA has traditionally been explored in multiferroic materials and diluted magnetic semiconductors, but not in metals because of the anticipated negligible effects since the electric field would be screened within 1-2 Å at the metal surface. However, a voltage may exert marked effects if the magnetic properties of ultrathin films are dominated by interfacial magnetic anisotropy. Here we demonstrate a large VCMA effect in perpendicular MgO magnetic tunnel junctions (p-MTJs) with very thin CoFeB layers. The p-MTJs have the key structure of Co40Fe40B20(1.2-1.3nm)/MgO(1.2-2nm)/Co40Fe40B20(1.6nm) exhibiting at room temperature tunneling magnetoresistance in excess of 100%. The perpendicular magnetic anisotropy (PMA) in this system is believed to be stabilized by hybridization between the out-of-plane 3d orbitals of the FM and oxygen 2p orbitals. We show that both the magnitude and the direction of the electric field can systematically alter the PMA of the thin CoFeB layers interfaced with the MgO barrier. Furthermore, under a given electric field, the two CoFeB layers on either side of the MgO barrier respond in the opposite manner as expected. By exploiting the combined effect of spin transfer torque and VCMA in CoFeB/MgO/CoFeB nanopillars, we have accomplished voltage controlled spintronic devices, where the MTJ can be manipulated by a unipolar switching process using consecutive negative voltages less than 1.5 V in magnitude. In this manner, voltage can access the high resistance or the low resistance state of an MTJ with very small current densities. Wang, W.-G., Li, M., Hageman, S. & Chien, C. L. Electric-field-assisted switching in magnetic tunnel junctions. Nature Materials 11, 64 (2012). This work is done in collaboration with Mingen Li, Stephen Hageman and C. L. Chien. Research is supported by the NSF grant DMR 05-20491.

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

    PubMed

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

    2015-02-11

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

  7. Efficient enhancement of magnetic anisotropy by optimizing the ligand-field in a typically tetranuclear dysprosium cluster.

    PubMed

    Liu, Jiang; Chen, Yan-Cong; Jiang, Zhong-Xia; Liu, Jun-Liang; Jia, Jian-Hua; Wang, Long-Fei; Li, Quan-Wen; Tong, Ming-Liang

    2015-05-01

    The perturbation to the ligand field around the lanthanide ion may significantly contribute to the magnetic dynamics of single molecule magnets. This can be demonstrated by two typical Dy4 cluster-based single molecular magnets (SMMs), [Dy4X2(?3-OH)2(?-OH)2(2,2-bpt)4(H2O)4]X2·2H2O·4EtOH (X = Cl and Br for and , respectively), which were constructed by using 3,5-bis(pyridin-2-yl)-1,2,4-triazole (2,2-bptH) as the polynuclear-chelating ligand. Alternating-current (ac) magnetic susceptibility measurements show that the energy barriers in complexes and were immensely enhanced by comparing with our previous work due to the optimization of the ligand field around Dy(III) ions. Remarkably, their high thermal active barriers at 190 K () and 197 K () under a zero applied external dc magnetic field are also among the highest within the reported tetranuclear lanthanide-based SMMs. PMID:25837027

  8. Magnetic alignment of block copolymer microdomains by intrinsic chain anisotropy

    E-print Network

    Yekaterina Rokhlenko; Kai Zhang; Manesh Gopinadhan; Steve R. Larson; Pawel W. Majewski; Kevin G. Yager; Padma Gopalan; Corey S. O'Hern; Chinedum O. Osuji

    2015-09-03

    We examine the role of intrinsic chain susceptibility anisotropy in magnetic field directed self-assembly of a block copolymer using \\textit{in situ} X-ray scattering. Alignment of a lamellar mesophase is observed on cooling across the disorder-order transition with the resulting orientational order inversely proportional to the cooling rate. We discuss the origin of the susceptibility anisotropy, $\\Delta\\chi$, that drives alignment, and calculate its magnitude using coarse-grained molecular dynamics to sample conformations of surface-tethered chains, finding $\\Delta\\chi\\approx 2\\times10^{-8}$. From field-dependent scattering data we estimate grains of $\\approx1.2$ $\\mu$m are present during alignment. These results demonstrate that intrinsic anisotropy is sufficient to support strong field-induced mesophase alignment and suggest a versatile strategy for field control of orientational order in block copolymers.

  9. Magnetic Fields

    E-print Network

    Schöller, Markus

    2015-01-01

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

  10. Magnetic Anisotropy in UMn2Ge2

    NASA Astrophysics Data System (ADS)

    Berg, Morgann; de Lozanne, Alex; Baumbach, Ryan; Kim, Jeehoon; Bauer, Eric; Thompson, Joe; Ronning, Filip

    2015-03-01

    UMn2Ge2, a permanent magnet, is a ternary intermetallic compound with a tetragonal crystal structure of type ThCr2Si2 and with space group I4/mmm. Local U and Mn moments in UMn2Ge2 order on their respective sublattices at temperatures near 100 and 380 K, respectively. Previous x-ray diffraction, Kerr rotation angle, and SQUID magnetometry data support the commonly accepted notion that U moments order at low temperature and align Mn moments along the c-axis, introducing anisotropy. Previous results obtained using a multi-mode atomic force microscope in magnetic force microscopy (MFM) mode indeed confirmed that UMn2Ge2 displays uniaxial anisotropy with an easy axis coinciding with the c-axis of the material. However, the branching domains in UMn2Ge2 consistent with uniaxial anisotropy were observed all the way up to room temperature by MFM. This indicates that the effect of uranium moments on the magnetic microstructure of UMn2Ge2 is not limited to low temperatures near the ordering temperature of the uranium sublattice. We further investigate closure domains in the surface of UMn2Ge2 and report on characteristics and signatures of anisotropy revealed by the orientation and periodic structures of closure domains. Supported by NSF Grant DMR-0810119.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  12. Anisotropy-Tuned Magnetic Order in Pyrochlore Iridates

    NASA Astrophysics Data System (ADS)

    Lefrançois, E.; Simonet, V.; Ballou, R.; Lhotel, E.; Hadj-Azzem, A.; Kodjikian, S.; Lejay, P.; Manuel, P.; Khalyavin, D.; Chapon, L. C.

    2015-06-01

    The magnetic behavior of polycrystalline samples of Er2Ir2O7 and Tb2Ir2O7 pyrochlores is studied by magnetization measurements and neutron diffraction. Both compounds undergo a magnetic transition at 140 and 130 K, respectively, associated with an ordering of the Ir sublattice, signaled by thermomagnetic hysteresis. In Tb2Ir2O7 , we show that the Ir molecular field leads the Tb magnetic moments to order below 40 K in the all-in-all-out magnetic arrangement. No sign of magnetic long-range order on the Er sublattice is evidenced in Er2Ir2O7 down to 0.6 K where a spin freezing is detected. These contrasting behaviors result from the competition between the Ir molecular field and the different single-ion anisotropy of the rare-earth elements on which it is acting. Additionally, this strongly supports the all-in-all-out iridium magnetic order.

  13. The anisotropy of magnetic susceptibility in biotite, muscovite and chlorite single crystals

    E-print Network

    Utrecht, Universiteit

    of the magnetic anisotropy properties for these common rock-forming minerals. The low-field AMS and the high of the magnetic anisotropy where it reflects mineral fabrics and deformation of rocks. D 2003 Elsevier Science B susceptibility (AMS) 1. Introduction Phyllosilicates, and in particular micas, are com- mon rock-forming minerals

  14. Magnetic anisotropy of transition-metal thin films: Convergence properties

    NASA Astrophysics Data System (ADS)

    Pick, Št.?pán; Dorantes-Dávila, J.; Pastor, G. M.; Dreyssé, Hugues

    1994-07-01

    On the basis of extended recursion-scheme calculations and general analysis we show that the instabilities and oscillations of the magnetic anisotropy energy (MAE) curve result from numerical inaccuracies. We explain how to obtain quickly convergent results within the tight-binding recursion method. For an Fe(001) monolayer we find a negligible MAE, for a Co(111) monolayer the in-plane anisotropy is preferred whereas for a Co(111) bilayer the result is sensitive to the choice of parameters. Crystal-field effects are also discussed.

  15. Scale-dependent Normalized Amplitude and Weak Spectral Anisotropy of Magnetic Field Fluctuations in the Solar Wind Turbulence

    NASA Astrophysics Data System (ADS)

    Wang, Xin; Tu, Chuanyi; Marsch, Eckart; He, Jiansen; Wang, Linghua

    2016-01-01

    Turbulence in the solar wind was recently reported to be anisotropic, with the average power spectral index close to -2 when sampling parallel to the local mean magnetic field B0 and close to -5/3 when sampling perpendicular to the local B0. This result was widely considered to be observational evidence for the critical balance theory (CBT), which is derived by making the assumption that the turbulence strength is close to one. However, this basic assumption has not yet been checked carefully with observational data. Here we present for the first time the scale-dependent magnetic-field fluctuation amplitude, which is normalized by the local B0 and evaluated for both parallel and perpendicular sampling directions, using two 30-day intervals of Ulysses data. From our results, the turbulence strength is evaluated as much less than one at small scales in the parallel direction. An even stricter criterion is imposed when selecting the wavelet coefficients for a given sampling direction, so that the time stationarity of the local B0 is better ensured during the local sampling interval. The spectral index for the parallel direction is then found to be -1.75, whereas the spectral index in the perpendicular direction remains close to -1.65. These two new results, namely that the value of the turbulence strength is much less than one in the parallel direction and that the angle dependence of the spectral index is weak, cannot be explained by existing turbulence theories, like CBT, and thus will require new theoretical considerations and promote further observations of solar-wind turbulence.

  16. Magnetic anisotropy data of C3H2NCl

    NASA Astrophysics Data System (ADS)

    Kumar, M.; Gupta, R.

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

  17. High Magnetic Anisotropy Materials Takao Suzuki

    E-print Network

    Carver, Jeffrey C.

    High Magnetic Anisotropy Materials Takao Suzuki MINT Center MINT Seminar (2/6/2015) 1 #12;Contents. m-DO19 (Co-Ni)3Pt 6. m-DO19 Fe3Pt 7. Low Temperature Phase (LTP) MnBi 8. Summary MINT Seminar (2-CoFeSiB K (erg/cc) 102~3 106 107~8 H M HC Magnetic Materials MINT Seminar (2/6/2015) 3 a-TbFeCo, CoCrPt, Fe

  18. Magnetostriction and magnetic anisotropy of Fe35Co 65

    NASA Astrophysics Data System (ADS)

    Ren, Tong

    2011-12-01

    A Fe35Co65 single crystal has been prepared by a long time anneal at temperature close to its fcc-bcc phase boundary. Its magnetostriction constant lambda100 and magnetocrystalline anisotropy constant K1 was measured using a strain gauge rosette and magnetization and torque magnetometer curves. The magnetostriction constant lambda 100 is as high as 200 ppm. The value of the anisotropy constant K 1 and the value of the susceptibility were small and influenced by the magnetoelastic energy. The symmetry of the torque curves changes from 2-fold to 4-fold with increasing external field which indicates the existence of a second uniaxial phase. This result can be interpreted by the alignment of the magnetization of an epitaxial fcc precipitate in the bcc host by external field.

  19. Magnetic domains in ferromagnetic particles with perpendicular anisotropy

    NASA Astrophysics Data System (ADS)

    Komineas, Stavros; Moutafis, Christoforos; Bland, Tony

    2006-03-01

    We derive a Derrick-like virial theorem for static states in a disc-shaped ferromagnetic particle with an axially symmetric magnetic configuration. This is applied to elementary magnetic states such as a single domain and a vortex. We calculate the vortex state in a disc-shaped particle with no anisotropy and study the very thin and very thick limits. In the very thin limit the virial relation effectively gives the vortex core radius. We also consider a particle with significant perpendicular anisotropy and show that a vortex is a static state for sufficiently thin particles. For thicker particles the vortex core expands to become comparable to the particle lateral size while the magnetization at the periphery of the particle tilts out of plane opposite to the vortex core region. In sufficiently thick particles, the magnetic state takes the form of a magnetic ``bubble'' (well-known in films) viewed here as a bidomain state. The signature of a bubble is its magnetostatic field which consists of two concentric regions of opposite sign above the particle top surface. Higher order states of multiple concentric domains of opposite magnetization are found in larger particles. We finally study the effect of an external field on magnetic bubble states.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  1. Strong uniaxial magnetic anisotropy in CoFe films on obliquely sputtered Ru underlayer

    SciTech Connect

    Fukuma, Y.; Lu, Z.; Fujiwara, H.; Mankey, G. J.; Butler, W. H.; Matsunuma, S.

    2009-10-01

    Co{sub 90}Fe{sub 10} films with an in-plane uniaxial magnetic anisotropy have been grown on an obliquely sputtered thin Ru underlayer. The anisotropy field can be increased up to 200 Oe. The hysteresis curves show a very high squareness in the easy axis direction and almost no hysteresis in the hard axis direction, suggesting that the induced uniaxial anisotropy is uniform throughout the films. The switching characteristics of the nanoelements fabricated from the films by e-beam lithography are also investigated. There is no degradation of the magnetic anisotropy after the annealing and lithographical process.

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

    PubMed Central

    2014-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  4. Inkjet printed superparamagnetic polymer composite hemispheres with programmed magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    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

    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

  5. Single-crystal magnetic anisotropies of rock-forming minerals

    NASA Astrophysics Data System (ADS)

    Biedermann, Andrea Regina; Hirt, Ann Marie; Pettke, Thomas

    2013-04-01

    Anisotropy of magnetic susceptibility (AMS) is often used as an indicator of mineral fabric in rocks. For a quantitative estimate of mineral fabric, it is necessary to know and understand the intrinsic magnetic anisotropy of each mineral in the rock. Susceptibility, and thus AMS, is a superposition of paramagnetic and ferromagnetic components. In general, the paramagnetic contribution can be related to silicates, whereas the ferromagnetic component arises from iron oxide inclusions. We determined single-crystal AMS in both low and high magnetic fields for a series of olivine, amphibole, clinopyroxene and orthopyroxene compositions. Analysis of high-field data allows for separation of ferromagnetic and paramagnetic contributions to the magnetic anisotropy. Acquisition of isothermal remanent magnetization (IRM) was measured in order to further characterize the ferromagnetic inclusions. Often, the iron oxides grow epitaxially on the silicate structure and have specific orientations with respect to the silicate. The ferromagnetic component of the AMS can provide information on the orientation or shape of the inclusions. The paramagnetic AMS in a single crystal is related to the distribution of cations with a strong magnetic moment, e.g. ferric and ferrous iron, in the lattice structure. Relationships between the anisotropy, e.g. the anisotropy degree (delta k) or principal susceptibility directions, and iron content were thus established for each mineral group. For example, the orientation of the intermediate and minimum susceptibility axes in olivine depends on the iron content - the minimum susceptibility is parallel to the crystallographic a-axis for 3-5 wt.% FeO and parallel to b for 7-9 wt.% FeO at room temperature; and for amphiboles, the degree of AMS increases linearly with increasing iron content. AMS in a rock depends on the single-crystal properties, which are influenced by lattice structure and composition, as well as the crystallographic preferred orientation of crystals. Information on single crystal AMS can thus be used to predict bulk AMS of ultrabasic rocks, when the orientation distribution function of the constituent minerals is known.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  7. Manipulating magnetic anisotropy and ultrafast spin dynamics of magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Cheng, Zhao-Hua; He, Wei; Zhang, Xiang-Qun; Sun, Da-Li; Du, Hai-Feng; Wu, Qiong; Ye, Jun; Fang, Ya-Peng; Liu, Hao-Liang

    2015-07-01

    We present our extensive research into magnetic anisotropy. We tuned the terrace width of Si(111) substrate by a novel method: varying the direction of heating current and consequently manipulating the magnetic anisotropy of magnetic structures on the stepped substrate by decorating its atomic steps. Laser-induced ultrafast demagnetization of a CoFeB/MgO/CoFeB magnetic tunneling junction was explored by the time-resolved magneto-optical Kerr effect (TR-MOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electron tunneling current. This opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions. Furthermore, an all-optical TR-MOKE technique provides the flexibility for exploring the nonlinear magnetization dynamics in ferromagnetic materials, especially with metallic materials. Project supported by the National Basic Research Program of China (Grant Nos. 2015CB921403, 2011CB921801, and 2012CB933101) and the National Natural Science Foundation of China (Grant Nos. 51427801, 11374350, 51201179, and 11274361).

  8. Experimental investigation of magnetic anisotropy in spin vortex discs

    SciTech Connect

    Garraud, N. Arnold, D. P.

    2014-05-07

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

  9. Configurational anisotropy and thermally activated switching in magnetic nanosquares

    NASA Astrophysics Data System (ADS)

    Torres, L.; Lopez-Diaz, L.; Martínez, E.; Iñiguez, J.

    2001-12-01

    Switching processes in magnetic nanosquares of size 10 lex< a<64 lex and thickness t=1.5 lex have been systematically analyzed for different applied field angles. The effect of configurational anisotropy in all the cases is discussed. Thermally activated switching is studied in nanosquares of a=20 lex and 40 lex with t=1.5 lex by solving the stochastic Landau-Lifschitz-Gilbert equation. The dependence of the relaxation time on applied field and temperature is investigated. Superparamagnetic effects are found to be significant for a=20 lex.

  10. Collective Magnetic Behavior of Geometrically Frustrated Arrays with Perpendicular Anisotropy

    NASA Astrophysics Data System (ADS)

    Pan, Y.; Kohli, K. K.; Fraleigh, R.; Balk, A. L.; Finkel, D.; Zhang, S.; Li, J.; Gilbert, I.; Lammert, P. E.; Misra, R.; Crespi, V. H.; Schiffer, P.; Samarth, N.; Erickson, M.; Leighton, C.

    2012-02-01

    We use the magneto-optical Kerr effect (MOKE) to study the global and local magnetic behavior of geometrically frustrated arrays of single domain ferromagnetic islands with perpendicular anisotropy. MOKE measurements over macroscopic length scales probe the global properties of arrays with different lattice geometries and island spacings. The variation of switching field as a function of island spacing gives us insight into the influence of local frustration on the collective magnetic response of the arrays. The experimental results are compared with mean field calculations. Finally, we use spatially resolved Kerr microscopy to probe nucleation and domain propagation in the magnetization reversal process. Supported by U.S. Department of Energy Award DE-SC0005313. Lithography performed with the support of the National Nanotechnology Infrastructure Network

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

    PubMed

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

    2009-06-01

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

  12. Magnetic anisotropy of epitaxial Cu/Ni/Cu nanolines

    NASA Astrophysics Data System (ADS)

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

    2004-06-01

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

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

    SciTech Connect

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

    2011-06-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  15. Interplay between magnetic anisotropy and vibron-assisted tunneling in a single-molecule magnet transistor

    NASA Astrophysics Data System (ADS)

    Park, Kyungwha; McCaskey, Alexander; Yamamoto, Yoh; Warnock, Michael; Burzuri, Enrique; van der Zant, Herre

    2015-03-01

    Molecules trapped in single-molecule devices vibrate with discrete frequencies characteristic to the molecules, and the molecular vibrations can couple to electronic charge and/or spin degrees of freedom. For a significant electron-vibron coupling, electrons may tunnel via the vibrational excitations unique to the molecules. Recently, electron transport via individual anisotropic magnetic molecules (referred to as single-molecule magnets) has been observed in single-molecule transistors. A single-molecule magnet has a large spin moment and a large magnetic anisotropy barrier. So far, studies of electron-vibron coupling effects in single-molecule devices, are mainly for isotropic molecules. Here we investigate how the electron-vibron coupling influences electron transport via a single-molecule magnet Fe4, by using a model Hamiltonian with parameter values obtained from density-functional theory (arXiv:1411.2677). We show that the magnetic anisotropy of the Fe4 induces new features in vibrational conductance peaks and creates vibrational satellite peaks. The main and satellite peak heights have a strong, unusual dependence on the direction and magnitude of applied magnetic field, because the magnetic anisotropy barrier is comparable to vibrational energies. Funding from NSF DMR-1206354, EU FP7 program project 618082 ACMOL, advanced ERC grant (Mols@Mols). Computer resources from SDSC Trestles under DMR060009N and VT ARC.

  16. Grain size dependence of coercivity in magnetic metal-insulator nanogranular films with uniaxial magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Yao, Dongsheng; Ge, Shihui; Zhou, Xueyun; Zuo, Huaping

    2010-04-01

    Excellent soft magnetic properties and appropriate uniaxial magnetic anisotropy field have been achieved in a wide metal volume fraction (x) range for as-deposited (Fe65Co35)x(SiO2)1-x granular films fabricated by magnetron sputtering. With decreasing x from 0.86 to 0.53, the coercive force of easy axis Hce decreases clearly and shows the minimum value (Hce=0.85 Oe) at x =0.53. More importantly, not only nanoscale grain-size D contributing to small coercivity is proved, but also a D3 dependence of Hce is observed in the range of 0.53anisotropy model of Suzuki and Herzer, the grain-size D dependence of coercivity Hce in our metal-insulator granular film system was analyzed. Analyze results indicate that strong coherent uniaxial anisotropy which dominates over the random anisotropy ?K1? of magnetic grains obtained by the random anisotropy model can be responsible for the D3 dependence of the coercivity Hce. In addition, in the range of 0.42

  17. Tuning the Magnetic Anisotropy at a Molecule-Metal Interface

    NASA Astrophysics Data System (ADS)

    Bairagi, K.; Bellec, A.; Repain, V.; Chacon, C.; Girard, Y.; Garreau, Y.; Lagoute, J.; Rousset, S.; Breitwieser, R.; Hu, Yu-Cheng; Chao, Yen Cheng; Pai, Woei Wu; Li, D.; Smogunov, A.; Barreteau, C.

    2015-06-01

    We demonstrate that a C60 overlayer enhances the perpendicular magnetic anisotropy of a Co thin film, inducing an inverse spin reorientation transition from in plane to out of plane. The driving force is the C60/Co interfacial magnetic anisotropy that we have measured quantitatively in situ as a function of the C60 coverage. Comparison with state-of-the-art ab initio calculations show that this interfacial anisotropy mainly arises from the local hybridization between C60 pz and Co dz2 orbitals. By generalizing these arguments, we also demonstrate that the hybridization of C60 with a Fe(110) surface decreases the perpendicular magnetic anisotropy. These results open the way to tailor the interfacial magnetic anisotropy in organic-material-ferromagnet systems.

  18. Anisotropy-Tuned Magnetic Order in Pyrochlore Iridates.

    PubMed

    Lefrançois, E; Simonet, V; Ballou, R; Lhotel, E; Hadj-Azzem, A; Kodjikian, S; Lejay, P; Manuel, P; Khalyavin, D; Chapon, L C

    2015-06-19

    The magnetic behavior of polycrystalline samples of Er(2)Ir(2)O(7) and Tb(2)Ir(2)O(7) pyrochlores is studied by magnetization measurements and neutron diffraction. Both compounds undergo a magnetic transition at 140 and 130 K, respectively, associated with an ordering of the Ir sublattice, signaled by thermomagnetic hysteresis. In Tb(2)Ir(2)O(7), we show that the Ir molecular field leads the Tb magnetic moments to order below 40 K in the all-in-all-out magnetic arrangement. No sign of magnetic long-range order on the Er sublattice is evidenced in Er(2)Ir(2)O(7) down to 0.6 K where a spin freezing is detected. These contrasting behaviors result from the competition between the Ir molecular field and the different single-ion anisotropy of the rare-earth elements on which it is acting. Additionally, this strongly supports the all-in-all-out iridium magnetic order. PMID:26197002

  19. Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion.

    PubMed

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

    2014-01-01

    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

  20. Quasi-Long-Range Order in Random-Anisotropy Magnets

    NASA Astrophysics Data System (ADS)

    Fisch, Ronald

    1998-03-01

    Monte Carlo simulations have been used to study a discretized Heisenberg ferromagnet (FM) with random anisotropy on simple cubic lattices. The spin variable on each site is chosen from the twelve [110] directions. The random anisotropy has infinite strength and a random direction on a fraction x of the sites of the lattice, and is zero on the remaining sites. In most respects, the behavior of this model is qualitatively similar to that of the corresponding random-field model,(R. Fisch, Phys. Rev. B 57, XXX (Jan. 1, 1998).) except that one needs a substantially larger value of x to get a comparable result for the random anisotropy, as compared to the random field. Due to the discretization, for small x at low temperature there is a [110] FM phase. For x>0 there is an intermediate phase between the paramagnet and the ferromagnet, which is characterized by a |k|-3 divergence of the magnetic structure factor S(k) for small k, but no true FM order. At the transition between the paramagnetic and quasi-long-range ordered phases S(k) diverges as |k|-2. For x close to 1 the low temperature form of S(k) can be fit by a Lorentzian with a correlation length estimated to be 11 ± 1 at x=1.0 and 25 ± 5 at x=0.75.

  1. Tuning the magnetic anisotropy in single-layer crystal structures

    NASA Astrophysics Data System (ADS)

    Torun, E.; Sahin, H.; Bacaksiz, C.; Senger, R. T.; Peeters, F. M.

    2015-09-01

    The effect of an applied electric field and the effect of charging are investigated on the magnetic anisotropy (MA) of various stable two-dimensional (2D) crystals such as graphene, FeCl2, graphone, fluorographene, and MoTe2 using first-principles calculations. We found that the magnetocrystalline anisotropy energy of Co-on-graphene and Os-doped-MoTe2 systems change linearly with electric field, opening the possibility of electric field tuning MA of these compounds. In addition, charging can rotate the easy-axis direction of Co-on-graphene and Os-doped-MoTe2 systems from the out-of-plane (in-plane) to in-plane (out-of-plane) direction. The tunable MA of the studied materials is crucial for nanoscale electronic technologies such as data storage and spintronics devices. Our results show that controlling the MA of the mentioned 2D crystal structures can be realized in various ways, and this can lead to the emergence of a wide range of potential applications where the tuning and switching of magnetic functionalities are important.

  2. Perpendicular magnetic anisotropy in Co-Pt granular multilayers

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

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

    PubMed Central

    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

    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

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

    PubMed

    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

    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

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  6. Step-induced magnetic-hysteresis anisotropy in ferromagnetic thin films D. Zhao, Feng Liu,a)

    E-print Network

    Simons, Jack

    Step-induced magnetic-hysteresis anisotropy in ferromagnetic thin films D. Zhao, Feng Liu,a) D. L; accepted for publication 15 November 2001 We investigate the quasistatic magnetic hysteresis. The simulated hysteresis loops show a strong anisotropy: the coercive field is the largest when the external

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

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  8. Magnetic anisotropy of small clusters and very thin transition-metal films

    NASA Astrophysics Data System (ADS)

    Dreysse, H.; Dorantes-Davila, J.; Pick, S.; Pastor, G. M.

    1994-11-01

    The magnetic anisotropy of 3d-transiton metal (TM) clusters is studied in the framework of a d-electron tight-binding Hamiltonian including hopping, Coulomb, and spin-orbit interactions on the same electronic level. Results for the magnetic anisotropy energy and spin-polarized density of states (DOS) are given as a function of the bond length for the Fe6 cluster. In particular it is shown that the magnetic anisotropy energy (MAE) may be qualitatively related to the projections of the orbital moment along the magnetization directions, and that the 'in-plane' anisotropy can be of the same order of magnitude as the 'perpendicular' anisotropy. Using the same Hamiltonian, the problem of the convergence of the magnetic anisotropy energy of very thin films is revisited. By the choice of a basis which mixed spherical harmonics, it is shown that the irregular oscillations of the MAE versus the band filling disappear. For Co(111) excellent stability of the in-plane anisotropy as observed experimentally was found. Finally, the crystal-field effects are also discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2009-02-01

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

  10. Anisotropic Magnetism in Field-Structured Composites

    SciTech Connect

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

    1999-06-24

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

  11. Colossal anisotropy of the magnetic properties of doped lithium nitrodometalates

    SciTech Connect

    Antropov, Vladimir P; Antonov, Victor N

    2014-09-01

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

  12. Anisotropy of the magnetic susceptibility of gallium

    USGS Publications Warehouse

    Pankey, T., Jr.

    1960-01-01

    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.

  13. Magnetic anisotropy and structural properties of ferromagnet/MgO/ferromagnet system.

    E-print Network

    Kisiel, Zbigniew

    for magnetic field applied in-plane for two perpendicular directions MgO Co Co Co Co Mo #12;Magnetic anisotropy and structural properties of ferromagnet/MgO/ferromagnet system. L. Gladczuk, P Academy of Sciences, 02 668 Warsaw, Poland. RHEED patterns obtained for layers of Co/MgO/Co structure

  14. Three tetracoordinate Co(II) complexes [Co(biq)X2] (X = Cl, Br, I) with easy-plane magnetic anisotropy as field-induced single-molecule magnets.

    PubMed

    Smolko, L; ?ernák, J; Dušek, M; Miklovi?, J; Titiš, J; Bo?a, R

    2015-10-28

    Three mononuclear complexes [Co(biq)X2] (biq = 2,2'-biquinoline; X = Cl, Br, I) were prepared by a solvothermal method and characterized by single-crystal X-ray diffraction. In all three complexes the Co(ii) atom is tetrahedrally coordinated by one biq ligand bonded in a chelate manner and two halogenido ligands. Hydrogen bonding interactions (C-HX) along with the ?-? interactions contribute to the stability of the formed packing. Magnetic measurements as well as ab initio calculations revealed that the complexes possess a sizable easy-plane magnetic anisotropy (D > 0). They display a superparamagnetic behaviour in an applied external field that culminates between BDC = 0.2-0.3 T. Two relaxation processes are observed; the faster can be analysed in terms of the direct and Orbach processes yielding U/kB = 42.6 K and ?0 = 1.9 × 10(-10) s for X = Cl, U/kB = 39.6 K and ?0 = 1.2 × 10(-10) s for X = Br and U/kB = 57.0 K and ?0 = 3.2 × 10(-13) s for X = I at BDC = 0.2 T. PMID:26391615

  15. Magnetic anisotropy of mesoscale-twinned Ni-Mn-Ga thin films

    NASA Astrophysics Data System (ADS)

    Chernenko, V. A.; Lvov, V. A.; Golub, V.; Aseguinolaza, I. R.; Barandiarán, J. M.

    2011-08-01

    The ferromagnetic resonance data obtained for the twinned orthorhombic martensitic phase of Ni-Mn-Ga film epitaxially grown on MgO(100) substrate are presented. The reported data prove that the mesoscale twinning reduces the value of in-plane magnetic anisotropy field of the Ni-Mn-Ga film by an order of magnitude. The reduced magnetic anisotropy field corresponds to the tetragonal symmetry, while the unit cells of the film are orthorhombic. The experimentally observed change of the in-plane magnetic anisotropy is explained in the framework of the magnetoelastic model of martensite, and the second-order and fourth-order magnetic anisotropy constants are evaluated. The perpendicular magnetic anisotropy constant proved to be negative and small in the absolute value. Therefore the estimated value of the magnetic domain wall width is comparable with the widths of mesoscale twins observed in the investigated film. This confirms an idea that the magnetic vectors of twin components are strongly coupled by the exchange interaction.

  16. Enhanced magnetic anisotropy in cobalt-carbide nanoparticles

    SciTech Connect

    El-Gendy, AA; Qian, MC; Huba, ZJ; Khanna, SN; Carpenter, EE

    2014-01-13

    An outstanding problem in nano-magnetism is to stabilize the magnetic order in nanoparticles at room temperatures. For ordinary ferromagnetic materials, reduction in size leads to a decrease in the magnetic anisotropy resulting in superparamagnetic relaxations at nanoscopic sizes. In this work, we demonstrate that using wet chemical synthesis, it is possible to stabilize cobalt carbide nanoparticles which have blocking temperatures exceeding 570 K even for particles with magnetic domains of 8 nm. First principles theoretical investigations show that the observed behavior is rooted in the giant magnetocrystalline anisotropies due to controlled mixing between C p- and Co d-states. (C) 2014 AIP Publishing LLC.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

  18. PUBLISHED ONLINE: 6 OCTOBER 2013 | DOI: 10.1038/NPHYS2766 Spintronic magnetic anisotropy

    E-print Network

    Loss, Daniel

    ARTICLES PUBLISHED ONLINE: 6 OCTOBER 2013 | DOI: 10.1038/NPHYS2766 Spintronic magnetic anisotropy to ferromagnets, a quadrupolar spintronic exchange field is generated locally. It is observable by means. Analogously to the spintronic dipolar exchange field, giving rise to a local spin torque, the effect

  19. Magnetic anisotropy in "scorpionate" first-row transition-metal complexes: a theoretical investigation.

    PubMed

    Peri?, Marko; García-Fuente, Amador; Zlatar, Matija; Daul, Claude; Stepanovi?, Stepan; García-Fernández, Pablo; Gruden-Pavlovi?, Maja

    2015-02-23

    In this work we have analyzed in detail the magnetic anisotropy in a series of hydrotris(pyrazolyl)borate (Tp(-)) metal complexes, namely [VTpCl](+), [CrTpCl](+), [MnTpCl](+), [FeTpCl], [CoTpCl], and [NiTpCl], and their substituted methyl and tert-butyl analogues with the goal of observing the effect of the ligand field on the magnetic properties. In the [VTpCl](+), [CrTpCl](+), [CoTpCl], and [NiTpCl] complexes, the magnetic anisotropy arises as a consequence of out-of-state spin-orbit coupling, and covalent changes induced by the substitution of hydrogen atoms on the pyrazolyl rings does not lead to drastic changes in the magnetic anisotropy. On the other hand, much larger magnetic anisotropies were predicted in complexes displaying a degenerate ground state, namely [MnTpCl](+) and [FeTpCl], due to in-state spin-orbit coupling. The anisotropy in these systems was shown to be very sensitive to perturbations, for example, chemical substitution and distortions due to the Jahn-Teller effect. We found that by substituting the hydrogen atoms in [MnTpCl](+) and [FeTpCl] by methyl and tert-butyl groups, certain covalent contributions to the magnetic anisotropy energy (MAE) could be controlled, thereby achieving higher values. Moreover, we showed that the selection of ion has important consequences for the symmetry of the ground spin-orbit term, opening the possibility of achieving zero magnetic tunneling even in non-Kramers ions. We have also shown that substitution may also contribute to a quenching of the Jahn-Teller effect, which could significantly reduce the magnetic anisotropy of the complexes studied. PMID:25591004

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

    NASA Astrophysics Data System (ADS)

    Yamamoto, Yoh; Park, Kyungwha

    2013-07-01

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

  1. Exchange coupling in hybrid anisotropy magnetic multilayers quantified by vector magnetometry

    SciTech Connect

    Morrison, C. Miles, J. J.; Thomson, T.; Anh Nguyen, T. N.; Fang, Y.; Dumas, R. K.; Åkerman, J.

    2015-05-07

    Hybrid anisotropy thin film heterostructures, where layers with perpendicular and in-plane anisotropy are separated by a thin spacer, are novel materials for zero/low field spin torque oscillators and bit patterned media. Here, we report on magnetization reversal and exchange coupling in a archetypal Co/Pd (perpendicular)-NiFe (in-plane) hybrid anisotropy system studied using vector vibrating sample magnetometry. This technique allows us to quantify the magnetization reversal in each individual magnetic layer, and measure of the interlayer exchange as a function of non-magnetic spacer thickness. At large (>1?nm) spacer thicknesses Ruderman-Kittel-Kasuya-Yosida-like exchange dominates, with orange-peel coupling providing a significant contribution only for sub-nm spacer thickness.

  2. Magnetic nanoparticle motion in external magnetic field

    NASA Astrophysics Data System (ADS)

    Usov, N. A.; Liubimov, B. Ya

    2015-07-01

    A set of equations describing the motion of a free magnetic nanoparticle in an external magnetic field in a vacuum, or in a medium with negligibly small friction forces is postulated. The conservation of the total particle momentum, i.e. the sum of the mechanical and the total spin momentum of the nanoparticle is taken into account explicitly. It is shown that for the motion of a nanoparticle in uniform magnetic field there are three different modes of precession of the unit magnetization vector and the director that is parallel the particle easy anisotropy axis. These modes differ significantly in the precession frequency. For the high-frequency mode the director points approximately along the external magnetic field, whereas the frequency and the characteristic relaxation time of the precession of the unit magnetization vector are close to the corresponding values for conventional ferromagnetic resonance. On the other hand, for the low-frequency modes the unit magnetization vector and the director are nearly parallel and rotate in unison around the external magnetic field. The characteristic relaxation time for the low-frequency modes is remarkably long. This means that in a rare assembly of magnetic nanoparticles there is a possibility of additional resonant absorption of the energy of alternating magnetic field at a frequency that is much smaller compared to conventional ferromagnetic resonance frequency. The scattering of a beam of magnetic nanoparticles in a vacuum in a non-uniform external magnetic field is also considered taking into account the precession of the unit magnetization vector and director.

  3. Correlations, spin-charge separation, and magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Skomski, Ralph; Manchanda, Priyanka

    2015-03-01

    Much of the physics of condensed matter reflects electron-electron correlations. On an independent-electron level, correlations are described by a single Slater determinant with broken spin symmetry. This approach includes Hund's rule correlations as well the LSDA and LSDA+U approximations to density-functional theory (DFT). However, from Kondo and heavy-fermion systems it is known that the independent-electron approach fails to describe spin-charge separation in strongly correlated systems, necessitating the use of two or more Slater determinants. Using first-principle and model calculations, we show that spin-charge separation strongly affects the leading rare-earth anisotropy contribution in top-end permanent magnet materials such as Nd2Fe14B and SmCo5. Explicit correlation results are obtained for two limiting cases. First, we derive the density functional for tripositive rare-earth ions in a Bethe-type crystal field. The potential looks very different from the LSDA(+U) potentials, including gradient corrections. Second, we use a simple model to show that Kondo-type spin-charge separation yield a rare-earth anisotropy contribution absent in the independent-electron approach. This research is supported by DOE (DE-FG02-04ER46152).

  4. Static magnetic fields enhance turbulence

    E-print Network

    Pothérat, Alban

    2015-01-01

    More often than not, turbulence occurs under the influence of external fields, mostly rotation and magnetic fields generated either by planets, stellar objects or by an industrial environment. Their effect on the anisotropy and the dissipative behaviour of turbulence is recognised but complex, and it is still difficult to even tell whether they enhance or dampen turbulence. For example, externally imposed magnetic fields suppress free turbulence in electrically conducting fluids (Moffatt 1967), and make it two-dimensional (2D) (Sommeria & Moreau 1982); but their effect on the intensity of forced turbulence, as in pipes, convective flows or otherwise, is not clear. We shall prove that since two-dimensionalisation preferentially affects larger scales, these undergo much less dissipation and sustain intense turbulent fluctuations. When higher magnetic fields are imposed, quasi-2D structures retain more kinetic energy, so that rather than suppressing forced turbulence, external magnetic fields indirectly enha...

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

    SciTech Connect

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

    2014-02-25

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

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

    PubMed Central

    Pertsev, Nikolay A.

    2013-01-01

    Spin-polarized currents represent an efficient tool for manipulating ferromagnetic nanostructures but the critical current density necessary for the magnetization switching is usually too high for applications. Here we show theoretically that, in magnetic tunnel junctions having electric-field-dependent interfacial anisotropy, the critical density may reduce down to a very low level (~104?A cm?2) when the junction combines small conductance with the proximity of free layer to a size-driven spin reorientation transition. The theory explains easy magnetization switching recently discovered in CoFeB/MgO/CoFeB tunnel junctions, surprisingly showing that it happens when the spin-transfer torque is relatively small, and provides a recipe for the fabrication of magnetic tunnel junctions suitable for industrial memory applications. PMID:24067783

  7. Influence of magnetic surface anisotropy on spin wave reflection from the edge of ferromagnetic film

    NASA Astrophysics Data System (ADS)

    Gruszecki, P.; Dadoenkova, Yu. S.; Dadoenkova, N. N.; Lyubchanskii, I. L.; Romero-Vivas, J.; Guslienko, K. Y.; Krawczyk, M.

    2015-08-01

    We study propagation of the Gaussian beam of spin waves and its reflection from the edge of thin yttrium-iron-garnet film with in-plane magnetization perpendicular to this edge. We have performed micromagnetic simulations supported by analytical calculations to investigate the influence of the surface magnetic anisotropy present at the film edge on the reflection, especially in the context of the Goos-Hänchen effect. We have shown the appearance of a negative lateral shift between reflected and incident spin wave beams' spots. This shift is particularly sensitive to the surface magnetic anisotropy value and is a result of the Goos-Hänchen shift which is sensitive to the magnitude of the anisotropy and of the bending of the spin wave beam. We have demonstrated that the demagnetizing field provided a graded increase of the refractive index for spin waves, which is responsible for the bending.

  8. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films

    PubMed Central

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H. B.; Wang, J.; Ma, B.; Jin, Q. Y.

    2015-01-01

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3?nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0?kOe can be achieved at PO2?=?12% for the sample of tCFAO?=?2.1?nm or at PO2?=?7% for tCFAO?=?2.8?nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices. PMID:26190066

  9. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films.

    PubMed

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H B; Wang, J; Ma, B; Jin, Q Y

    2015-01-01

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3 nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0 kOe can be achieved at PO2 = 12% for the sample of tCFAO = 2.1 nm or at PO2 = 7% for tCFAO?= 2.8 nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices. PMID:26190066

  10. Perpendicular magnetic anisotropy and magnetization dynamics in oxidized CoFeAl films

    NASA Astrophysics Data System (ADS)

    Wu, Di; Zhang, Zhe; Li, Le; Zhang, Zongzhi; Zhao, H. B.; Wang, J.; Ma, B.; Jin, Q. Y.

    2015-07-01

    Half-metallic Co-based full-Heusler alloys with perpendicular magnetic anisotropy (PMA), such as Co2FeAl in contact with MgO, are receiving increased attention recently due to its full spin polarization for high density memory applications. However, the PMA induced by MgO interface can only be realized for very thin magnetic layers (usually below 1.3?nm), which would have strong adverse effects on the material properties of spin polarization, Gilbert damping parameter, and magnetic stability. In order to solve this issue, we fabricated oxidized Co50Fe25Al25 (CFAO) films with proper thicknesses without employing the MgO layer. The samples show controllable PMA by tuning the oxygen pressure (PO2) and CFAO thickness (tCFAO), large perpendicular anisotropy field of ~8.0?kOe can be achieved at PO2?=?12% for the sample of tCFAO?=?2.1?nm or at PO2?=?7% for tCFAO?=?2.8?nm. The loss of PMA at thick tCFAO or high PO2 results mainly from the formation of large amount of CoFe oxides, which are superparamagnetic at room temperature but become hard magnetic at low temperatures. The magnetic CFAO films, with strong PMA in a relatively wide thickness range and small intrinsic damping parameter below 0.028, would find great applications in developing advanced spintronic devices.

  11. Role of the substrate on the magnetic anisotropy of magnetite thin films grown by ion-assisted deposition

    NASA Astrophysics Data System (ADS)

    Prieto, Pilar; Prieto, José Emilio; Gargallo-Caballero, Raquel; Marco, José Francisco; de la Figuera, Juan

    2015-12-01

    Magnetite (Fe3O4) thin films were deposited on MgO (0 0 1), SrTiO3 (0 0 1), LaAlO3 (0 0 1) single crystal substrates as well on as silicon and amorphous glass in order to study the effect of the substrate on their magnetic properties, mainly the magnetic anisotropy. We have performed a structural, morphological and compositional characterization by X-ray diffraction, atomic force microscopy and Rutherford backscattering ion channeling in oxygen resonance mode. The magnetic anisotropy has been investigated by vectorial magneto-optical Kerr effect. The results indicate that the magnetic anisotropy is especially influenced by the substrate-induced microstructure. In-plane isotropy and uniaxial anisotropy behavior have been observed on silicon and glass substrates, respectively. The transition between both behaviors depends on grain size. For LaAlO3 substrates, in which the lattice mismatch between the Fe3O4 films and the substrate is significant, a weak in-plane fourfold magnetic anisotropy is induced. However when magnetite is deposited on MgO (0 0 1) and SrTiO3 (0 0 1) substrates, a well-defined fourfold in-plane magnetic anisotropy is observed with easy axes along [1 0 0] and [0 1 0] directions. The magnetic properties on these two latter substrates are similar in terms of magnetic anisotropy and coercive fields.

  12. Edge-modulated perpendicular magnetic anisotropy in [Co/Pd]n and L10-FePt thin film wires

    NASA Astrophysics Data System (ADS)

    Zhang, Jinshuo; Ho, Pin; Currivan-Incorvia, Jean Anne; Siddiqui, Saima A.; Baldo, Marc A.; Ross, Caroline A.

    2015-11-01

    Thickness modulation at the edges of nanostructured magnetic thin films is shown to have important effects on their perpendicular magnetic anisotropy. Thin film wires with tapered edges were made from [Co/Pd]20 multilayers or L10-FePt films using liftoff with a double-layer resist. The effect of edge taper on the reversal process was studied using magnetic force microscopy and micromagnetic modeling. In [Co/Pd]20, the anisotropy was lower in the tapered edge regions which switched at a lower reverse field compared to the center of the wire. The L10-FePt wires showed opposite behavior with the tapered regions exhibiting higher anisotropy.

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

    SciTech Connect

    Shaw, Justin M.; Nembach, Hans T.; Silva, T. J.

    2014-08-11

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

  14. Spin-orbit coupling, magnetic anisotropy and hard magnetism in Sr3NiIrO6

    NASA Astrophysics Data System (ADS)

    Zapf, Vivien

    2015-03-01

    Strong spin-orbit coupling is a pre-requisite for hard magnetism with high coercive magnetic fields. Magnetic oxides containing 5d ions such as Ir4+ should show significant spin-orbit coupling due to the high Z value. Furthermore, in 5d ions, the comparable energy scales of crystal-electric field splitting, Coulomb repulsion and spin-orbit interactions create unusual electronic ground states that can entangle spins and orbits, mix t2g and eg levels and drive magnetic exchange anisotropy. Another set of interesting electronic ground states can arise when 5d orbitals overlap 3d orbitals. In the compound Sr3NiIrO6, electronic structure calculations predict that the 3d orbitals of the Ni2+ ion directly overlap 5d orbitals of the Ir4+ ion. In addition to a ``Jeff = 1/2'' Ir4+ ground state that mixes t2g and eg levels, the Ni2+ should show strong single-ion anisotropy [1-3]. We present magnetization measurements of Sr3NiIrO6 to high magnetic fields. We demonstrate magnetic hysteresis with a record 55 Tesla coercive magnetic field and long stability over time in some crystals. More generally, the A3BB'O6 family of compounds shows hard magnetism as B' ion goes from 3d to 4d to 5d. Further complexities to do with evolving magnetic order and magnetic frustration also present in this family.

  15. Magnetic anisotropy in strained manganite films and bicrystal junctions

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  16. Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO.

    PubMed

    Baumann, S; Donati, F; Stepanow, S; Rusponi, S; Paul, W; Gangopadhyay, S; Rau, I G; Pacchioni, G E; Gragnaniello, L; Pivetta, M; Dreiser, J; Piamonteze, C; Lutz, C P; Macfarlane, R M; Jones, B A; Gambardella, P; Heinrich, A J; Brune, H

    2015-12-01

    We report on the magnetic properties of individual Fe atoms deposited on MgO(100) thin films probed by x-ray magnetic circular dichroism and scanning tunneling spectroscopy. We show that the Fe atoms have strong perpendicular magnetic anisotropy with a zero-field splitting of 14.0±0.3??meV/atom. This is a factor of 10 larger than the interface anisotropy of epitaxial Fe layers on MgO and the largest value reported for Fe atoms adsorbed on surfaces. The interplay between the ligand field at the O adsorption sites and spin-orbit coupling is analyzed by density functional theory and multiplet calculations, providing a comprehensive model of the magnetic properties of Fe atoms in a low-symmetry bonding environment. PMID:26684139

  17. Control of magnetism by electric fields

    NASA Astrophysics Data System (ADS)

    Matsukura, Fumihiro; Tokura, Yoshinori; Ohno, Hideo

    2015-03-01

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

  18. Magnetic field effect on hemin

    NASA Astrophysics Data System (ADS)

    Bartoszek, Mariola; Balanda, Maria; Skrzypek, Danuta; Drzazga, Zofia

    2001-12-01

    Magnetic behaviour of hemin has been investigated by means of magnetostatic methods, AC-susceptibility measurements and EPR spectroscopy. The measurements were made using polycrystalline and oriented samples of hemin in the temperature range 2.3-292 K and in magnetic fields up to 6 T. In the paramagnetic region, the susceptibility obeys the Curie-Weiss law with positive Curie-Weiss temperature. At low temperature, a rapid increase of the susceptibility is noticed but up to 2 K no long-range correlations are observed. The studies show that the iron ion in hemin exists in two spin states ( S= {5}/{2} and {1}/{2}). The applied magnetic field increases the occupation of the low-spin state. Hemin shows high-field-induced magnetic anisotropy which, similar to the susceptibility, increases with decreasing temperature.

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

    SciTech Connect

    Jaafar, M.; Sanz, R.; McCord, J.; Jensen, J.; Schaefer, R.; Vazquez, M.; Asenjo, A.

    2011-03-01

    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.

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

    SciTech Connect

    You, Chun-Yeol

    2014-01-28

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

  1. Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes.

    PubMed

    Prado, Yoann; Daffé, Niéli; Michel, Aude; Georgelin, Thomas; Yaacoub, Nader; Grenèche, Jean-Marc; Choueikani, Fadi; Otero, Edwige; Ohresser, Philippe; Arrio, Marie-Anne; Cartier-Dit-Moulin, Christophe; Sainctavit, Philippe; Fleury, Benoit; Dupuis, Vincent; Lisnard, Laurent; Fresnais, Jérôme

    2015-01-01

    Superparamagnetic nanoparticles are promising objects for data storage or medical applications. In the smallest-and more attractive-systems, the properties are governed by the magnetic anisotropy. Here we report a molecule-based synthetic strategy to enhance this anisotropy in sub-10-nm nanoparticles. It consists of the fabrication of composite materials where anisotropic molecular complexes are coordinated to the surface of the nanoparticles. Reacting 5?nm ?-Fe2O3 nanoparticles with the [Co(II)(TPMA)Cl2] complex (TPMA: tris(2-pyridylmethyl)amine) leads to the desired composite materials and the characterization of the functionalized nanoparticles evidences the successful coordination-without nanoparticle aggregation and without complex dissociation-of the molecular complexes to the nanoparticles surface. Magnetic measurements indicate the significant enhancement of the anisotropy in the final objects. Indeed, the functionalized nanoparticles show a threefold increase of the blocking temperature and a coercive field increased by one order of magnitude. PMID:26634987

  2. Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes

    PubMed Central

    Prado, Yoann; Daffé, Niéli; Michel, Aude; Georgelin, Thomas; Yaacoub, Nader; Grenèche, Jean-Marc; Choueikani, Fadi; Otero, Edwige; Ohresser, Philippe; Arrio, Marie-Anne; Cartier-dit-Moulin, Christophe; Sainctavit, Philippe; Fleury, Benoit; Dupuis, Vincent; Lisnard, Laurent; Fresnais, Jérôme

    2015-01-01

    Superparamagnetic nanoparticles are promising objects for data storage or medical applications. In the smallest—and more attractive—systems, the properties are governed by the magnetic anisotropy. Here we report a molecule-based synthetic strategy to enhance this anisotropy in sub-10-nm nanoparticles. It consists of the fabrication of composite materials where anisotropic molecular complexes are coordinated to the surface of the nanoparticles. Reacting 5?nm ?-Fe2O3 nanoparticles with the [CoII(TPMA)Cl2] complex (TPMA: tris(2-pyridylmethyl)amine) leads to the desired composite materials and the characterization of the functionalized nanoparticles evidences the successful coordination—without nanoparticle aggregation and without complex dissociation—of the molecular complexes to the nanoparticles surface. Magnetic measurements indicate the significant enhancement of the anisotropy in the final objects. Indeed, the functionalized nanoparticles show a threefold increase of the blocking temperature and a coercive field increased by one order of magnitude. PMID:26634987

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  4. Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La1.875Ba0.125CuO4

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Utz, Y.; Hücker, M.; Gu, G. D.; Büchner, B.; Grafe, H.-J.

    2015-10-01

    We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal?low-temperature orthorhombic?low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T1-1 sharply upturns at the charge-ordering temperature TCO=54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T1-1 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ?[001 ] , which are completely suppressed for large fields along the CuO2 planes. Our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.

  5. Controlling magnetic anisotropy in epitaxial FePt(001) films

    SciTech Connect

    Lu Zhihong; Walock, M. J.; LeClair, P.; Butler, W. H.; Mankey, G. J.

    2009-07-15

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

  6. Statistical study of effective anisotropy field in ordered ferromagnetic nanowire arrays.

    PubMed

    Zhao, S; Clime, L; Chan, K; Normandin, F; Roberge, H; Yelon, A; Cochrane, R W; Veres, T

    2007-01-01

    Soft ferromagnetic nanowire arrays were obtained by electrodeposition of Co-Fe-P alloy into the pores of high quality home-made anodized aluminum oxide (AAO) templates. Bath acidity and current density were the two parameters used in order to tailor the orientation of local anisotropy axes in individual nanowires. In order to quantify the influence of the induced anisotropies on the magnetization processes in individual nanowires, the in-plane magnetization loops of the arrays are modeled as log-normal distributions of Stoner-Wohlfarth transverse magnetization processes. Using the lognormal mean parameter as an approximation for the saturation applied field of the array, we compute the effective anisotropy of the nanowires, which is found to increase with the pH of the electrodeposition bath. PMID:17455508

  7. Application of Magnetic Reorientation Phase Transition in the Study of Exchange Anisotropy

    NASA Astrophysics Data System (ADS)

    Chen, Youjun; Lottis, D. K.; Dahlberg, E. Dan

    A Magnetic Reorientation Phase Transition (MRPT) was discovered in 1981 in Molecular-Beam-Epitaxially (MBE) grown thin iron (Fe) films on (110) GaAs substrates. The reorientation transition was characterized by the sudden switching of the in-plane magnetization in the Fe films. Subsequent to this work it was discovered that at low temperatures, the natural oxide on these films becomes antiferromagnetic and provides an exchange anisotropy field. In a ferromagnetic material such as Fe, because of the anisotropic magnetoresistance effect the resistance depends on the angle between the current and the magnetization which is in turn determined by the magnetic energy expression. This paper reviews the application of the MRPT in the study of exchange anisotropy in both the experimental and theoretical aspects.

  8. Electronic configurations and magnetic anisotropy in organometallic metallocenes

    NASA Astrophysics Data System (ADS)

    Nawa, Kenji; Kitaoka, Yukie; Nakamura, Kohji; Akiyama, Toru; Ito, Tomonori

    2015-05-01

    Electronic configurations and magnetic anisotropy of organometallic metallocenes (MCp2s) were investigated by means of first principles calculations based on the constraint density functional theory. The results predict that the ground states for M = Cr, Mn, Fe, Co, and Ni are the 3E2 g, 2E2 g, 1A1 g, 2E1 g, and 3A2 g states, respectively. The magnetizations of the CoCp2 and NiCp2 energetically favor highly orienting along the perpendicular and parallel directions to the cyclopentadienyl (Cp) plane, respectively, and the others show almost no preference for the magnetic easy axis.

  9. Ion-beam induced magnetic anisotropies in iron films

    NASA Astrophysics Data System (ADS)

    Neubauer, M.; Reinecke, N.; Uhrmacher, M.; Lieb, K. P.; Münzenberg, M.; Felsch, W.

    1998-04-01

    100-300 nm thin Fe layers evaporated onto crystalline and amorphous Si or SiO 2 substrates were irradiated, at 77 K, with 10 14-10 16 Xe +-ions/cm 2 at 450 keV beam energy. The magnetizations in the films were measured by means of Perturbed Angular Correlation (PAC) spectroscopy with implanted 111In tracer ions, or the Magneto-Optic Kerr Effect (MOKE). Upon ion implantation, dramatic changes of the magnetic anisotropy were observed which are attributed to ion-beam enhanced lateral grain growth. Very little influence of the deposition parameters (type and cristallinity of substrate, evaporation rate) on the anisotropic magnetization was found.

  10. Easy-plane anisotropy stabilizes skyrmions in 2D chiral magnets

    NASA Astrophysics Data System (ADS)

    Rowland, James; Banerjee, Sumilan; Randeria, Mohit

    2014-03-01

    Experiments on two-dimensional (2D) chiral magnetic materials, like thin films of non-centrosymmetric helimagnets and metallic magnetic layers, have revealed interesting spatially modulated spin textures such as spirals and skyrmions. Motivated by this we study the ground-state phase diagram for a 2D chiral magnet in a magnetic field using a Ginzburg-Landau model, with Dzyaloshinskii-Moriya (DM) term, anisotropic exchange and single-ion anisotropy. The easy-axis anisotropy region of the phase diagram has been well-studied, whereas the easy-plane region has not been discussed. In the easy-plane region, we find an unexpectedly large stable skyrmion crystal (SkX) phase in a perpendicular magnetic field. We find re-entrant transitions between ferromagnetic and SkX phases, and intriguing internal structure of the skyrmion core with two-length scales. We argue that such an easy-plane anisotropy arises naturally from the compass terms induced by spin-orbit coupling that is also responsible for the DM term, as proposed recently in the context of oxide interfaces. We also discuss the phase diagram in a tilted field configuration, relevant for torque magnetometry experiments. JR and MR supported by NSF MRSEC DMR-0820414 and SB by DOE-BES DE-SC0005035.

  11. Primordial Statistical Anisotropies: The Effective Field Theory Approach

    E-print Network

    Abolhasani, Ali Akbar; Emami, Razieh; Firouzjahi, Hassan

    2015-01-01

    In this work we present the effective field theory of primordial statistical anisotropies generated during anisotropic inflation involving a background $U(1)$ gauge field. Besides the usual Goldstone boson associated with the breaking of time diffeomorphism we have two additional Goldstone bosons associated with the breaking of spatial diffeomorphisms. We further identify these two new Goldstone bosons with the expected two transverse degrees of the $U(1)$ gauge field fluctuations. Upon defining the appropriate unitary gauge, we present the most general quadratic action which respects the remnant symmetry in the unitary gauge. The interactions between various Goldstone bosons leads to statistical anisotropy in curvature perturbation power spectrum. Calculating the general results for power spectrum anisotropy, we recover the previously known results in specific models of anisotropic inflation. In addition, we present novel results for statistical anisotropy in models with non-trivial sound speed for inflaton ...

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

    SciTech Connect

    Skalicky; Fidler; Groessinger; Kirchmayr

    1986-01-01

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

  13. Primordial Statistical Anisotropies: The Effective Field Theory Approach

    E-print Network

    Ali Akbar Abolhasani; Mohammad Akhshik; Razieh Emami; Hassan Firouzjahi

    2015-11-10

    In this work we present the effective field theory of primordial statistical anisotropies generated during anisotropic inflation involving a background $U(1)$ gauge field. Besides the usual Goldstone boson associated with the breaking of time diffeomorphism we have two additional Goldstone bosons associated with the breaking of spatial diffeomorphisms. We further identify these two new Goldstone bosons with the expected two transverse degrees of the $U(1)$ gauge field fluctuations. Upon defining the appropriate unitary gauge, we present the most general quadratic action which respects the remnant symmetry in the unitary gauge. The interactions between various Goldstone bosons leads to statistical anisotropy in curvature perturbation power spectrum. Calculating the general results for power spectrum anisotropy, we recover the previously known results in specific models of anisotropic inflation. In addition, we present novel results for statistical anisotropy in models with non-trivial sound speed for inflaton fluctuations. Also we identify the interaction which leads to birefringence-like effects in anisotropic power spectrum in which the speed of gauge field fluctuations depends on the direction of the mode propagation and the two polarization of gauge field fluctuations contribute differently in statistical anisotropy. As another interesting application, our EFT approach naturally captures interactions generating parity violating statistical anisotropies.

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

    SciTech Connect

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

    2014-09-08

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

  15. Phase diagram of an ideal three-dimensional antiferromagnet with random magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Borisov, Pavel; Perez, Felio A.; Johnson, Trent A.; Stanescu, Tudor D.; Lederman, David; Fitzsimmons, Michael R.; Aczel, Adam A.; Hong, Tao

    2014-03-01

    The magnetic phase diagram of three-dimensional (3D) antiferromagnets with random magnetic anisotropy (RMA) is not well understood because systems studied experimentally to date have complicated magnetic structures with competing two-dimensional and three-dimensional exchange interactions. The properties of epitaxial thin films of the 3D RMA antiferromagnet FexNi1-xF2 thin films grown on (110) MgF2 substrates were investigated by magnetometry and neutron scattering. FexNi1-xF2 is an ideal 3D antiferromagnet with which to study this problem due to the single-ion anisotropy energies of the transition metal site which tend to order Ni2+ and Fe2+ spins perpendicular to each other. The magnetic phase diagram determined from these measurements was analyzed using mean field theory. Regions with uniaxial, oblique and easy plane anisotropy were identified. An anisotropy glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs. Supported by the NSF (grant 0903861), the WVHEPC (Research Challenge Grant HEPC.dsr.12.29), the WVU Shared Research Facilities, and the DOE BES.

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

    SciTech Connect

    Fu, Yu E-mail: cangcangzhulin@gmail.com; Meckenstock, R.; Farle, M.; Barsukov, I.; Lindner, J.; Raanaei, H.; Hjörvarsson, B.

    2014-02-17

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

  17. Full 180° Magnetization Reversal with Electric Fields

    PubMed Central

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

    2014-01-01

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

  18. Temperature-dependent magnetic anisotropies in epitaxial Fe/CoO/MgO(001) system studied by the planar Hall effect

    NASA Astrophysics Data System (ADS)

    Cao, W. N.; Li, J.; Chen, G.; Zhu, J.; Hu, C. R.; Wu, Y. Z.

    2011-06-01

    Exchange-induced in-plane magnetic anisotropies in a single-crystalline Fe/CoO/MgO(001) system were quantitatively investigated using the planar Hall effect as a function of temperature. Field cooling can induce a strong uniaxial anisotropy in Fe film with the easy axis along the CoO<110> directions close to the cooling field direction. The exchange coupling also induces a 4-fold anisotropy with the easy axis along the CoO<100> directions. Our results prove that the strong magneto-crystalline anisotropy of CoO antiferromagnetic spin plays a significant role in exchange-induced anisotropy.

  19. Artificially engineered Heusler ferrimagnetic superlattice exhibiting perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

  1. Spin-orbit effect and magnetic anisotropy in Pt clusters

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  2. Role of magnetic anisotropy in spin-filter junctions

    SciTech Connect

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

    2011-01-10

    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.

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

    SciTech Connect

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

    2014-05-07

    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.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  5. Giant voltage modulation of magnetic anisotropy in strained heavy metal/magnet/insulator heterostructures

    NASA Astrophysics Data System (ADS)

    Ong, P. V.; Kioussis, Nicholas; Odkhuu, D.; Khalili Amiri, P.; Wang, K. L.; Carman, Gregory P.

    2015-07-01

    Ab initio electronic structure calculations reveal that epitaxial strain has a dramatic effect on the voltage-controlled magnetic anisotropy (VCMA) in Ta/FeCo/MgO junctions. Strain can give rise to a wide range of novel VCMA behaviors where the MA can change from a ?- to a ?-shape electric-field dependence with giant VCMA coefficients which are asymmetric under voltage reversal. The underlying mechanism is the interplay of the strain- and electric-field-induced changes in the spin-orbit coupled d states at the interfaces and the strain-induced modification of the dielectric constant of MgO. These findings demonstrate the feasibility of highly sensitive VCMA through strain engineering, which may provide a viable avenue for tailoring magnetoelectric properties for spintronic applications.

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

    SciTech Connect

    Davydenko, A. V. Kozlov, A. G.; Chebotkevich, L. A.

    2014-10-14

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

  7. Stress induced anisotropy in CoFeMn soft magnetic nanocomposites

    SciTech Connect

    Leary, AM; Keylin, V; Ohodnicki, PR; McHenry, ME

    2015-05-07

    The use of processing techniques to create magnetic anisotropy in soft magnetic materials is a well-known method to control permeability and losses. In nanocomposite materials, field annealing below the Curie temperature results in uniaxial anisotropy energies up to similar to 2 kJ/m(3). Higher anisotropies up to similar to 10 kJ/m(3) result after annealing Fe-Si compositions under stress due to residual stress in the amorphous matrix acting on body centered cubic crystals. This work describes near zero magnetostriction Co80-x-yFexMnyNb4B14Si2 soft magnetic nanocomposites, where x and y < 8 at. % with close packed crystalline grains that show stress induced anisotropies up to similar to 50 kJ/m(3) and improved mechanical properties with respect to Fe-Si compositions. Difference patterns measured using transmission X-ray diffraction show evidence of affine strain with respect to the stress axis. (C) 2015 AIP Publishing LLC.

  8. Stress induced anisotropy in CoFeMn soft magnetic nanocomposites

    SciTech Connect

    Leary, A. M. Keylin, V.; McHenry, M. E.; Ohodnicki, P. R.

    2015-05-07

    The use of processing techniques to create magnetic anisotropy in soft magnetic materials is a well-known method to control permeability and losses. In nanocomposite materials, field annealing below the Curie temperature results in uniaxial anisotropy energies up to ?2?kJ/m{sup 3}. Higher anisotropies up to ?10?kJ/m{sup 3} result after annealing Fe-Si compositions under stress due to residual stress in the amorphous matrix acting on body centered cubic crystals. This work describes near zero magnetostriction Co{sub 80?x?y}Fe{sub x}Mn{sub y}Nb{sub 4}B{sub 14}Si{sub 2} soft magnetic nanocomposites, where x and y?anisotropies up to ?50?kJ/m{sup 3} and improved mechanical properties with respect to Fe-Si compositions. Difference patterns measured using transmission X-ray diffraction show evidence of affine strain with respect to the stress axis.

  9. Enhancement of Magnetic Anisotropy in Ultrathin Epitaxial La0.67Sr0.33MnO3 Thin Films via Nanostructure Engineering

    NASA Astrophysics Data System (ADS)

    Rajapitamahuni, Anil; Zhang, Le; Burton, John; Singh, Vijay; Tsymbal, Evgeny; Hong, Xia

    2015-03-01

    We report a more than ten-fold enhancement of magnetic anisotropy in nanostructured La0.67Sr0.33MnO3 (LSMO) thin films grown epitaxially on (001) SrTiO3 substrates. We have etched periodic linear trenches in 6 nm LSMO films, and investigated magnetic anisotropy in these nanostructured thin films via the planar Hall effect (PHE). These trenches have depth of 2 nm and periodicities of 200 - 400 nm. The PHE resistance of the un-patterned LSMO films exhibits sinusoidal angular dependence in an in-plane magnetic field, and shows four-fold sharp resistance switching below a critical magnetic field of 400 Oe, corresponding to a biaxial magnetic anisotropy of ~ 1x105 erg/cm3 along <110>directions. In the nanostructured samples, we observe an additional two-fold resistance switching feature, which persists in magnetic fields higher than 4000 Oe, corresponding to a uniaxial magnetic anisotropy >1x106 erg/cm3 along one of the biaxial magnetic easy axes. This significant enhancement of magnetic anisotropy cannot be accounted for by shape anisotropy or a uniform strain modulation. We also discuss the effects of the orientation and periodicity of the nano-trenches on the anisotropy enhancement.

  10. Magnetic field mapper

    NASA Technical Reports Server (NTRS)

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

    1969-01-01

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

  11. Dynamical skyrmion state in a spin current nano-oscillator with perpendicular magnetic anisotropy.

    PubMed

    Liu, R H; Lim, W L; Urazhdin, S

    2015-04-01

    We study the spectral characteristics of spin current nano-oscillators based on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy. By varying the applied magnetic field and current, both localized and propagating spin wave modes of the oscillation are achieved. At small fields, we observe an abrupt onset of the modulation sidebands. We use micromagnetic simulations to identify this state as a dynamical magnetic skyrmion stabilized in the active device region by spin current injection, whose current-induced dynamics is accompanied by the gyrotropic motion of the core due to the skew deflection. Our results demonstrate a practical route for controllable skyrmion manipulation by spin current in magnetic thin films. PMID:25884135

  12. Advanced MHD models of anisotropy, flow and chaotic fields

    E-print Network

    Hudson, Stuart

    Advanced MHD models of anisotropy, flow and chaotic fields M. J. Hole1, M. Fitzgerald1, G. Dennis1 pinches Highlight some recent progress Future directions · Conclusions #12;· Pressure different parallel, pressure" #12;· Pressure different parallel and perpendicular to field due mainly to directed neutral beam

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

    SciTech Connect

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

    2014-03-21

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

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

    NASA Astrophysics Data System (ADS)

    Pan, Y.; Li, J.

    2012-12-01

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

  15. Magnetic Fields Analogous to electric field, a magnet

    E-print Network

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

    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

  16. Electronic configurations and magnetic anisotropy in organometallic metallocenes

    SciTech Connect

    Nawa, Kenji Kitaoka, Yukie; Nakamura, Kohji; Akiyama, Toru; Ito, Tomonori

    2015-05-07

    Electronic configurations and magnetic anisotropy of organometallic metallocenes (MCp{sub 2}s) were investigated by means of first principles calculations based on the constraint density functional theory. The results predict that the ground states for M?=?Cr, Mn, Fe, Co, and Ni are the {sup 3}E{sub 2g}, {sup 2}E{sub 2g}, {sup 1}A{sub 1g}, {sup 2}E{sub 1g}, and {sup 3}A{sub 2g} states, respectively. The magnetizations of the CoCp{sub 2} and NiCp{sub 2} energetically favor highly orienting along the perpendicular and parallel directions to the cyclopentadienyl (Cp) plane, respectively, and the others show almost no preference for the magnetic easy axis.

  17. Quantum engineering of spin and anisotropy in magnetic molecular junctions

    PubMed Central

    Jacobson, Peter; Herden, Tobias; Muenks, Matthias; Laskin, Gennadii; Brovko, Oleg; Stepanyuk, Valeri; Ternes, Markus; Kern, Klaus

    2015-01-01

    Single molecule magnets and single spin centres can be individually addressed when coupled to contacts forming an electrical junction. To control and engineer the magnetism of quantum devices, it is necessary to quantify how the structural and chemical environment of the junction affects the spin centre. Metrics such as coordination number or symmetry provide a simple method to quantify the local environment, but neglect the many-body interactions of an impurity spin coupled to contacts. Here, we utilize a highly corrugated hexagonal boron nitride monolayer to mediate the coupling between a cobalt spin in CoHx (x=1,2) complexes and the metal contact. While hydrogen controls the total effective spin, the corrugation smoothly tunes the Kondo exchange interaction between the spin and the underlying metal. Using scanning tunnelling microscopy and spectroscopy together with numerical simulations, we quantitatively demonstrate how the Kondo exchange interaction mimics chemical tailoring and changes the magnetic anisotropy. PMID:26456084

  18. Quantum engineering of spin and anisotropy in magnetic molecular junctions

    NASA Astrophysics Data System (ADS)

    Jacobson, Peter; Herden, Tobias; Muenks, Matthias; Laskin, Gennadii; Brovko, Oleg; Stepanyuk, Valeri; Ternes, Markus; Kern, Klaus

    2015-10-01

    Single molecule magnets and single spin centres can be individually addressed when coupled to contacts forming an electrical junction. To control and engineer the magnetism of quantum devices, it is necessary to quantify how the structural and chemical environment of the junction affects the spin centre. Metrics such as coordination number or symmetry provide a simple method to quantify the local environment, but neglect the many-body interactions of an impurity spin coupled to contacts. Here, we utilize a highly corrugated hexagonal boron nitride monolayer to mediate the coupling between a cobalt spin in CoHx (x=1,2) complexes and the metal contact. While hydrogen controls the total effective spin, the corrugation smoothly tunes the Kondo exchange interaction between the spin and the underlying metal. Using scanning tunnelling microscopy and spectroscopy together with numerical simulations, we quantitatively demonstrate how the Kondo exchange interaction mimics chemical tailoring and changes the magnetic anisotropy.

  19. Quantum engineering of spin and anisotropy in magnetic molecular junctions.

    PubMed

    Jacobson, Peter; Herden, Tobias; Muenks, Matthias; Laskin, Gennadii; Brovko, Oleg; Stepanyuk, Valeri; Ternes, Markus; Kern, Klaus

    2015-01-01

    Single molecule magnets and single spin centres can be individually addressed when coupled to contacts forming an electrical junction. To control and engineer the magnetism of quantum devices, it is necessary to quantify how the structural and chemical environment of the junction affects the spin centre. Metrics such as coordination number or symmetry provide a simple method to quantify the local environment, but neglect the many-body interactions of an impurity spin coupled to contacts. Here, we utilize a highly corrugated hexagonal boron nitride monolayer to mediate the coupling between a cobalt spin in CoHx (x=1,2) complexes and the metal contact. While hydrogen controls the total effective spin, the corrugation smoothly tunes the Kondo exchange interaction between the spin and the underlying metal. Using scanning tunnelling microscopy and spectroscopy together with numerical simulations, we quantitatively demonstrate how the Kondo exchange interaction mimics chemical tailoring and changes the magnetic anisotropy. PMID:26456084

  20. Perpendicular-magnetic-anisotropy CoFeB racetrack memory

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Cheng, Xuemei M.

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

  2. Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Ueno, Tetsuro; Sinha, Jaivardhan; Inami, Nobuhito; Takeichi, Yasuo; Mitani, Seiji; Ono, Kanta; Hayashi, Masamitsu

    2015-10-01

    We have studied the magnetic layer thickness dependence of the orbital magnetic moment in magnetic heterostructures to identify contributions from interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlOx and Pt/Co/Pt, which possess significant interface contribution to the perpendicular magnetic anisotropy, are studied as model systems. X-ray magnetic circular dichroism spectroscopy is used to evaluate the relative orbital moment, i.e. the ratio of the orbital to spin moments, of the magnetic elements constituting the heterostructures. We find that the relative orbital moment of Co in Pt/Co/Pt remains constant against its thickness whereas the moment increases with decreasing Co layer thickness for Pt/Co/AlOx, suggesting that a non-zero interface orbital moment exists for the latter system. For Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray absorption spectra shows that a particular oxidized Co state in Pt/Co/AlOx, absent in other heterosturctures, may give rise to the interface orbital moment in this system. These results show element specific contributions to the interface orbital magnetic moments in ultrathin magnetic heterostructures.

  3. Enhanced orbital magnetic moments in magnetic heterostructures with interface perpendicular magnetic anisotropy

    PubMed Central

    Ueno, Tetsuro; Sinha, Jaivardhan; Inami, Nobuhito; Takeichi, Yasuo; Mitani, Seiji; Ono, Kanta; Hayashi, Masamitsu

    2015-01-01

    We have studied the magnetic layer thickness dependence of the orbital magnetic moment in magnetic heterostructures to identify contributions from interfaces. Three different heterostructures, Ta/CoFeB/MgO, Pt/Co/AlOx and Pt/Co/Pt, which possess significant interface contribution to the perpendicular magnetic anisotropy, are studied as model systems. X-ray magnetic circular dichroism spectroscopy is used to evaluate the relative orbital moment, i.e. the ratio of the orbital to spin moments, of the magnetic elements constituting the heterostructures. We find that the relative orbital moment of Co in Pt/Co/Pt remains constant against its thickness whereas the moment increases with decreasing Co layer thickness for Pt/Co/AlOx, suggesting that a non-zero interface orbital moment exists for the latter system. For Ta/CoFeB/MgO, a non-zero interface orbital moment is found only for Fe. X-ray absorption spectra shows that a particular oxidized Co state in Pt/Co/AlOx, absent in other heterosturctures, may give rise to the interface orbital moment in this system. These results show element specific contributions to the interface orbital magnetic moments in ultrathin magnetic heterostructures. PMID:26456454

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

    SciTech Connect

    Borisov, A. B.; Kishine, Jun-ichiro; Bostrem, I. G.; Ovchinnikov, A. S.

    2009-04-01

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

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

    SciTech Connect

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

    2014-07-15

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  7. Giant magnetic anisotropy in Li3-xFexN permanent magnets

    NASA Astrophysics Data System (ADS)

    Jesche, Anton; Thimmaiah, Srinivasa; Bud'Ko, Sergey; Canfield, Paul

    2013-03-01

    Single crystals of Li2(Li1-xFex)N were successfully grown out of Li-flux. Fe-concentrations and lattice parameters were determined by means of single crystal and powder diffraction which also confirmed the substitution of Fe on only one of the Li sites resulting in Li1-xFex layers separated by Li2N layers. Magnetization measurements revealed a ferromagnetically ordered ground state with Curie temperatures of ~ 60 K for Fe concentrations of x ~ 20 %. Large saturation moments of up to 5 ?B per Fe atom were found along the hexagonal crystallographic c-axis. These values exceed the spin-only contribution of Fe and are also reflected in correspondingly large effective moments at room temperature. The anisotropy field at T = 2 K, defined as intersection of the magnetization for M ? c and M ? c , can be estimated to lie well beyond 100 Tesla. Electrical resistivity measurements show insulating behavior and raise questions about the nature of the underlying magnetic exchange mechanism. This work is supported by the US DOE, Basic Energy Sciences under Contract No. DE-AC02-07CH11358.

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

    SciTech Connect

    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

    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.

  9. Magnetic Fields and Plasmas

    SciTech Connect

    Schep, T.J.

    2004-03-15

    Plasmas and magnetic fields are inseparably related in numerous physical circumstances. This is not only the case in natural occurring plasmas like the solar corona and the earth magnetic tail, but also in laboratory plasmas like tokamaks and stellarators.

  10. Solar wind turbulence: anisotropy, anisotropy, anisotropy!

    NASA Astrophysics Data System (ADS)

    Wicks, R.; Forman, M. A.; Summerlin, E. J.; Roberts, D. A.; Salem, C. S.

    2014-12-01

    Turbulence heats the solar wind as it expands away from the Sun, but where and how does heating of ions and electrons occur? In order to understand this we must first look at the fluctuations making up the cascade, the properties and anisotropies of which will determine whether ions or electrons are heated and whether field-parallel or -perpendicular heating will occur, all of which amounts to a lot of different anisotropies! With this in mind, we present a review of recent advances in the observation of plasma turbulence in the solar wind and comparison with simulations; which features of solar wind turbulence are well reproduced and which need to be captured better? The first anisotropy is that of the fluctuations making up the turbulent cascade itself, fluctuations are known to be highly transverse, meaning that the perpendicular magnetic field components are dominant over the field-parallel component. The second anisotropy is that of the scaling of amplitude towards smaller scales with steeper spectra parallel to the local magnetic field direction. Observations of the anisotropy of the full power spectral tensor will be discussed, in particular with reference to Alfvenic and pseudo-Alfvenic fluctuations (effectively two different polarizations of Alfven waves), the next step beyond the traditional "slab + 2D" approach to incompressible MHD turbulence. The third anisotropy is that of the ion and electron distributions. Both sets of charged particles frequently show non-Maxwellian distributions with higher temperatures found either perpendicular to or parallel to the magnetic field direction. Proton distributions often show beams and the heavier alpha particles are often hotter than the protons. Localized structures such as current sheets and magnetic discontinuities are shown to be sites of intense and anisotropic heating. Small scale fluctuations filling the space between such discontinuities may also dissipate energy into ions and electrons, either through electric fields intrinsic to the modes generated by the turbulence or through resonant or stochastic processes. Observations show that kinetic Alfven waves are the dominant mode.

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

    SciTech Connect

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

    2014-05-14

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

  12. Bifurcation of magnetic anisotropy caused by small addition of Sm in (Nd1-xSmxDy)(FeCo)B magnetic alloy

    NASA Astrophysics Data System (ADS)

    Kablov, E. N.; Ospennikova, O. G.; Kablov, D. E.; Piskorskii, V. P.; Kunitsyna, E. I.; Dmitriev, A. I.; Valeev, R. A.; Korolev, D. V.; Rezchikova, I. I.; Talantsev, A. D.; Morgunov, R. B.

    2015-06-01

    In sintered (Nd1-xSmxDy)(FeCo)B magnets, the contributions of "soft" (Nd1-xSmxDy)2(FeCo)2B and "hard" (Nd1-xSmxDy)2(FeCo)14B phases to the temperature and field dependences of magnetization have been distinguished. The increase in Sm concentration up to 3% provides stronger interlattice RE-TM (RE—rare-earth metals, TM—transition metals) exchange interaction. Contributions of the NdDy and Sm to magnetic anisotropy have been determined. The competition between the positive contribution of Nd and Dy and the negative contribution of Sm ions results in non-monotonous temperature and Sm concentration dependencies of anisotropy field. Anisotropy of the studied alloys is intermediate between "easy axis" and "easy plane" symmetry.

  13. Perpendicular magnetic fields in cantilever beam magnetometry

    NASA Astrophysics Data System (ADS)

    Koch, R.; Das, A. K.; Yamaguchi, H.; Pampuch, C.; Ney, A.

    2004-09-01

    Cantilever beam magnetometry is a common technique to determine the magnetoelastic (ME) coupling constants of thin films by measuring the stress that develops when the film magnetization is changed. In cantilever beam experiments performed so far the film magnetization was mainly rotated within the film plane. Here we discuss the measurement of the ME coupling constants, when the magnetizing field is chosen so that it rotates the film magnetization out of the film plane. A major stress contribution, which arises additionally to the ME stress, originates in the torque that magnetic dipoles experience in a magnetic field. In order to separate torque effects from ME contributions in cantilever beam experiments a general method is proposed. With this method the ME coupling constants can be quantitatively determined and furthermore the film magnetization as well as its perpendicular anisotropy constant are obtained quantitatively.

  14. Full 180u Magnetization Reversal with Electric Fields

    E-print Network

    Chen, Long-Qing

    or is assisted by a magnetic field or spin transfer torque5 . Alternatively, Iwasaki25 proposed an interesting-driven magnetization reversal in magnetostrictive films, which required epitaxial or highly textured magnetic films to keep the four-fold symmetric magnetocrystalline anisotropy of magnetostrictive crystals. Recently, Roy

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

    NASA Astrophysics Data System (ADS)

    Tournus, F.; Bonet, E.

    2011-05-01

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

  16. Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface

    NASA Astrophysics Data System (ADS)

    Oyarzún, Simón; Tamion, Alexandre; Tournus, Florent; Dupuis, Véronique; Hillenkamp, Matthias

    2015-10-01

    Strong size-dependent variations of the magnetic anisotropy of embedded cobalt clusters are evidenced quantitatively by combining magnetic experiments and advanced data treatment. The obtained values are discussed in the frame of two theoretical models that demonstrate the decisive role of the shape in larger nanoparticles and the predominant role of the surface anisotropy in clusters below 3?nm diameter.

  17. Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface.

    PubMed

    Oyarzún, Simón; Tamion, Alexandre; Tournus, Florent; Dupuis, Véronique; Hillenkamp, Matthias

    2015-01-01

    Strong size-dependent variations of the magnetic anisotropy of embedded cobalt clusters are evidenced quantitatively by combining magnetic experiments and advanced data treatment. The obtained values are discussed in the frame of two theoretical models that demonstrate the decisive role of the shape in larger nanoparticles and the predominant role of the surface anisotropy in clusters below 3?nm diameter. PMID:26439626

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

    E-print Network

    Utrecht, Universiteit

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

  19. Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface

    PubMed Central

    Oyarzún, Simón; Tamion, Alexandre; Tournus, Florent; Dupuis, Véronique; Hillenkamp, Matthias

    2015-01-01

    Strong size-dependent variations of the magnetic anisotropy of embedded cobalt clusters are evidenced quantitatively by combining magnetic experiments and advanced data treatment. The obtained values are discussed in the frame of two theoretical models that demonstrate the decisive role of the shape in larger nanoparticles and the predominant role of the surface anisotropy in clusters below 3?nm diameter. PMID:26439626

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

    E-print Network

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

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

    PubMed Central

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

    2015-01-01

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

  2. Heavy quarkonia in strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Bonati, Claudio; D'Elia, Massimo; Rucci, Andrea

    2015-09-01

    We investigate the influence of a homogeneous and constant strong external magnetic field on the heavy-meson spectrum. Quarkonium states c c ¯ and b b ¯ are described within a nonrelativistic framework and by means of a suitable potential model based on the Cornell parametrization. In particular, in this work we propose a model which takes into account the possible anisotropies emerging at the level of the static quark-antiquark potential, as observed in recent lattice studies. The investigation is performed both with and without taking into account the anisotropy of the static potential, in order to better clarify its effects.

  3. Giant reversible rotating cryomagnetocaloric effect in KEr (MoO4)2 induced by a crystal-field anisotropy

    NASA Astrophysics Data System (ADS)

    Tká?, V.; Orendá?ová, A.; ?ižmár, E.; Orendá?, M.; Feher, A.; Anders, A. G.

    2015-07-01

    Magnetocaloric properties of KEr(MoO4)2 single crystals were investigated using magnetization and specific heat measurements in the magnetic field applied along the easy and hard axis. Large conventional magnetocaloric effect was found around 10 K (-? Smax =14 J/kg K for 5 T) in the field applied along the easy axis. What is more, a huge magnetic anisotropy in the a b plane leads to a large anisotropy of magnetocaloric effect, -? SR ,max =10 and 13 J/kg K obtained by a simple rotating of the single crystal within the a b plane in the constant magnetic field 2 and 5 T, respectively. Large ? SR values with no hysteresis losses and rather wide working temperature spans imply that KEr(MoO4)2 may serve as a promising candidate for the implementation of a compact rotary magnetic cryorefrigerator.

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

    PubMed Central

    2012-01-01

    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

  5. Electronic structure and magnetic anisotropy of Sm2Fe17Nx

    NASA Astrophysics Data System (ADS)

    Akai, Hisazumi; Ogura, Masako

    2014-03-01

    Electronic structure and magnetic properties of Sm2Fe17Nx are studies on the basis of the first-principles electronic structure calculation in the framework of the density functional theory within the local density and coherent potential approximations. The magnetic anisotropy of the system as a function of nitrogen concentration x is discussed by taking account not only of the crystal field effects but also of the effects of the f-electron transfer from Sm to the neighboring sites. Also discussed is the magnetic transition temperature that is estimated by mapping the system into a Heisenberg model. The results show the crystalline magnetic anisotropy changes its direction from in-plane to uniaxial ones as x increases. It takes the maximum value near x ~ 2 . 8 and then decreases slightly towards x = 3 . The mechanism for these behaviors is discussed in the light of the results of detailed calculations on the bonding properties between Sm and its neighboring N. This work was partly supported by Elements Strategy Initiative Center for Magnetic Materials Project, the Ministry of Education, Culture, Sports, Science and Technology, Japan.

  6. Magnetic field generator

    DOEpatents

    Krienin, Frank (Shoreham, NY)

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Yang, Z.; Liu, J. L.; Biasini, M.; Beyermann, W. P.

    2008-01-01

    Well-above room temperature and electron concentration dependent ferromagnetism was observed in n-type ZnO:Mn films, indicating long-range ferromagnetic order. Magnetic anisotropy was also observed in these ZnO:Mn films, which is another indication for intrinsic ferromagnetism. The electron-mediated ferromagnetism in n-type ZnO:Mn contradicts the existing theory that the magnetic exchange in ZnO:Mn materials is mediated by holes.

  8. Fast magnetization in counterstreaming plasmas with temperature anisotropies

    E-print Network

    M. Lazar

    2007-11-15

    Counterstreaming plasmas exhibits an electromagnetic unstable mode of filamentation type, which is responsible for the magnetization of plasma system. It is shown that filamentation instability becomes significantly faster when plasma is hotter in the streaming direction. This is relevant for astrophysical sources, where strong magnetic fields are expected to exist and explain the nothermal emission observed.

  9. Electric-field guiding of magnetic skyrmions

    NASA Astrophysics Data System (ADS)

    Upadhyaya, Pramey; Yu, Guoqiang; Amiri, Pedram Khalili; Wang, Kang L.

    2015-10-01

    We theoretically study equilibrium and dynamic properties of nanosized magnetic skyrmions in thin magnetic films with broken inversion symmetry, where an electric field couples to magnetization via spin-orbit coupling. Based on a symmetry-based phenomenology and micromagnetic simulations we show that this electric-field coupling, via renormalizing the micromagnetic energy, modifies the equilibrium properties of the skyrmion. This change, in turn, results in a significant alteration of the current-induced skyrmion motion. Particularly, the speed and direction of the skyrmion can be manipulated by designing a desired energy landscape electrically, which we describe within Thiele's analytical model and demonstrate in micromagnetic simulations including electric-field-controlled magnetic anisotropy. We additionally use this electric-field control to construct gates for controlling skyrmion motion exhibiting a transistorlike and multiplexerlike function. The proposed electric-field effect can thus provide a low-energy electrical knob to extend the reach of information processing with skyrmions.

  10. Magnetic Field & Right Hand Rule

    E-print Network

    Heller, Barbara

    Magnetic Field & Right Hand Rule Academic Resource Center #12;Magnetic Fields And Right Hand Rules By: Anthony Ruth #12;Magnetic Fields vs Electric Fields · Magnetic fields are similar to electric charges and stationary charges. · In addition, magnetic fields create a force only on moving charges

  11. Measuring temperature and field profiles in heat assisted magnetic recording

    NASA Astrophysics Data System (ADS)

    Hohlfeld, J.; Zheng, X.; Benakli, M.

    2015-08-01

    We introduce a theoretical and experimental framework that enables quantitative measurements of the temperature and magnetic field profiles governing the thermo-magnetic write process in heat assisted magnetic recording. Since our approach allows the identification of the correct temperature dependence of the magneto-crystalline anisotropy field in the vicinity of the Curie point as well, it provides an unprecedented experimental foundation to assess our understanding of heat assisted magnetic recording.

  12. IrMn as exchange-biasing material in systems with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    van Dijken, Sebastiaan; Besnier, Magali; Moritz, Jerome; Coey, J. M. D.

    2005-05-01

    Contact between a Co /Pt multilayer and an IrMn film leads to perpendicular exchange bias. The exchange bias field does not depend on the degree of (111) film texture and for Co /Pt multilayers with IrMn at the bottom it can be enhanced by magnetic field annealing. The perpendicular exchange bias of the Co /Pt-IrMn system is limited by a misalignment between the Co spins and the film normal, which is due to a negative magnetic anisotropy contribution from the Co /IrMn interface (KSCo /IrMn=-0.09mJ/m2). The insertion of a 3Å thick Pt layer at the Co /IrMn interface maximizes the perpendicular exchange-bias field.

  13. Magnetic Fields in Galaxies

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    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.

  14. Influence of shape and dimension on magnetic anisotropies and magnetization reversal of Py, Fe, and Co nano-objects with four-fold symmetry

    NASA Astrophysics Data System (ADS)

    Ehrmann, Andrea; Blachowicz, Tomasz

    2015-09-01

    Different magnetic anisotropies and magnetization reversal mechanisms were identified in magnetic nano-objects of four-fold symmetry, using micromagnetic simulations. Nano-particles with lateral dimensions between 50 nm and 400 nm, simulated with typical properties of permalloy, iron and cobalt, were tested in dependence of the angular orientation with respect to the externally applied magnetic field. All nano-objects exhibited steps on the sides of the hysteresis loops, which can be correlated with stable intermediate states at remanence, for some angular regions. Coercive fields were found to show an irregular and unpredictable angular dependence in case of cobalt nano-particles, while this material depicted the largest number of steps in general. Comparing the angular dependence of the coercive fields with previous calculations, it was shown that usual descriptions of fourfold anisotropies are no longer valid in most of the nano-objects under examination.

  15. THE ROLE OF PRESSURE ANISOTROPY ON PARTICLE ACCELERATION DURING MAGNETIC RECONNECTION

    SciTech Connect

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

    2013-02-20

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

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

    SciTech Connect

    Rushforth, A. W.

    2014-04-21

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

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

    NASA Astrophysics Data System (ADS)

    Rushforth, A. W.

    2014-04-01

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

  18. Magnetic anisotropy, unusual hysteresis and putative "up-up-down" magnetic structure in EuTAl4Si2 (T = Rh and Ir).

    PubMed

    Maurya, Arvind; Thamizhavel, A; Dhar, S K; Bonville, P

    2015-01-01

    We present detailed investigations on single crystals of quaternary EuRhAl4Si2 and EuIrAl4Si2. The two compounds order antiferromagnetically at TN1?=?11.7 and 14.7?K, respectively, each undergoing two magnetic transitions. The magnetic properties in the ordered state present a large anisotropy despite Eu(2+)being an S-state ion for which the single-ion anisotropy is expected to be weak. Two features in the magnetization measured along the c-axis are prominent. At 1.8?K, a ferromagnetic-like jump occurs at very low field to a value one third of the saturation magnetization (1/3?M0) followed by a wide plateau up to 2 T for Rh and 4 T for Ir-compound. At this field value, a sharp hysteretic spin-flop transition occurs to a fully saturated state (M0). Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet. Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis. This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an "up-up-down" magnetic structure in zero field. PMID:26156410

  19. Magnetic anisotropy, unusual hysteresis and putative “up-up-down” magnetic structure in EuTAl4Si2 (T = Rh and Ir)

    PubMed Central

    Maurya, Arvind; Thamizhavel, A.; Dhar, S. K.; Bonville, P.

    2015-01-01

    We present detailed investigations on single crystals of quaternary EuRhAl4Si2 and EuIrAl4Si2. The two compounds order antiferromagnetically at TN1?=?11.7 and 14.7?K, respectively, each undergoing two magnetic transitions. The magnetic properties in the ordered state present a large anisotropy despite Eu2+being an S-state ion for which the single-ion anisotropy is expected to be weak. Two features in the magnetization measured along the c-axis are prominent. At 1.8?K, a ferromagnetic-like jump occurs at very low field to a value one third of the saturation magnetization (1/3?M0) followed by a wide plateau up to 2 T for Rh and 4 T for Ir-compound. At this field value, a sharp hysteretic spin-flop transition occurs to a fully saturated state (M0). Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet. Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis. This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an “up-up-down” magnetic structure in zero field. PMID:26156410

  20. Magnetic anisotropy, unusual hysteresis and putative “up-up-down” magnetic structure in EuTAl4Si2 (T = Rh and Ir)

    NASA Astrophysics Data System (ADS)

    Maurya, Arvind; Thamizhavel, A.; Dhar, S. K.; Bonville, P.

    2015-07-01

    We present detailed investigations on single crystals of quaternary EuRhAl4Si2 and EuIrAl4Si2. The two compounds order antiferromagnetically at TN1?=?11.7 and 14.7?K, respectively, each undergoing two magnetic transitions. The magnetic properties in the ordered state present a large anisotropy despite Eu2+being an S-state ion for which the single-ion anisotropy is expected to be weak. Two features in the magnetization measured along the c-axis are prominent. At 1.8?K, a ferromagnetic-like jump occurs at very low field to a value one third of the saturation magnetization (1/3?M0) followed by a wide plateau up to 2 T for Rh and 4 T for Ir-compound. At this field value, a sharp hysteretic spin-flop transition occurs to a fully saturated state (M0). Surprisingly, the magnetization does not return to origin when the field is reduced to zero in the return cycle, as expected in an antiferromagnet. Instead, a remnant magnetization 1/3 M0 is observed and the magnetic loop around the origin shows hysteresis. This suggests that the zero field magnetic structure has a ferromagnetic component, and we present a model with up to third neighbor exchange and dipolar interaction which reproduces the magnetization curves and hints to an “up-up-down” magnetic structure in zero field.

  1. Perpendicular magnetic anisotropy and complex magnetotransport behavior of cobalt nanoparticles in silver matrix

    NASA Astrophysics Data System (ADS)

    Kumar, Dinesh; Chaudhary, Sujeet; Pandya, Dinesh K.

    2015-05-01

    A cobalt concentration dependent transition from usual magnetoresistance (MR) to complex MR behavior is reported in the co-sputtered Co-Ag thin films containing cobalt nanoparticles. At 20 K, the MR behavior of 32.6% film consists of three contributions superparamagnetic (SPM), ferromagnetic (FM), and perpendicular magnetic anisotropy (PMA), which are, respectively, operative at high, intermediate, and low fields. Magnetic force microscopy (MFM) provides the supporting evidence for the existence of a magnetic microstructure with magnetization perpendicular to the film plane for a threshold of 32.6% cobalt concentration. MFM images show the presence of regions with perpendicular magnetization having sizes much larger than the particle size. In addition, the magnetization measurements also substantiate the presence of PMA in films above 25.2% cobalt. The observed complex magnetotransport behavior and associated PMA are interpreted in terms of inter-particle (FM-SPM-FM) interactions in which local magnetic fields of the nearby FM particles align the SPM particles out of film plane.

  2. Magnetic fields in the early Universe

    NASA Astrophysics Data System (ADS)

    Grasso, D.; Rubinstein, H. R.

    2001-07-01

    This review concerns the origin and the possible effects of magnetic fields in the early Universe. We start by providing the reader with a short overview of the current state of the art of observations of cosmic magnetic fields. We then illustrate the arguments in favor of a primordial origin of magnetic fields in the galaxies and in the clusters of galaxies. We argue that the most promising way to test this hypothesis is to look for possible imprints of magnetic fields on the temperature and polarization anisotropies of the cosmic microwave background radiation (CMBR). With this purpose in mind, we provide a review of the most relevant effects of magnetic fields on the CMBR. A long chapter of this review is dedicated to particle-physics-inspired models which predict the generation of magnetic fields during the early Universe evolution. Although it is still unclear if any of these models can really explain the origin of galactic and intergalactic magnetic fields, we show that interesting effects may arise anyhow. Among these effects, we discuss the consequences of strong magnetic fields on the big-bang nucleosynthesis, on the masses and couplings of the matter constituents, on the electroweak phase transition, and on the baryon and lepton number violating sphaleron processes. Several intriguing common aspects, and possible interplay, of magnetogenesis and baryogenesis are also discussed.

  3. Temperature dependence of magnetization and anisotropy in uniaxial NiFe?O? nanomagnets: Deviation from the Callen-Callen power law

    SciTech Connect

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

    2014-10-21

    The thermal variation of magnetic anisotropy (K) and saturation magnetization (M{sub S}) for uniaxial nickel ferrite (NiFe?O?) nanomagnets are investigated. Major magnetic hysteresis loops are measured for the sample at temperatures over the range 5–280?K using a vibrating sample magnetometer. The high-field regimes of the hysteresis loops are modeled using the law of approach to saturation, based on the assumption that at sufficiently high field only direct rotation of spin-moment take place, with an additional forced magnetization term that is linear with applied field. The uniaxial anisotropy constant K is calculated from the fitting of the data to the theoretical equation. As temperature increases from 5?K to 280?K, a 49% reduction of K, accompanied by an 85% diminution of M{sub S} is observed. Remarkably, K is linearly proportional to M{sub S}?.? in the whole temperature range violating the existing theoretical model by Callen and Callen. The unusual power-law behavior for the NiFe?O? 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.

  4. Magnetic anisotropy of embedded Co nanoparticles: Influence of the surrounding matrix

    NASA Astrophysics Data System (ADS)

    Tamion, Alexandre; Raufast, Cécile; Hillenkamp, Matthias; Bonet, Edgar; Jouanguy, J.; Canut, Bruno; Bernstein, Estella; Boisron, Olivier; Wernsdorfer, Wolfgang; Dupuis, Véronique

    2010-04-01

    We report on the magnetic properties of Co clusters embedded in four different matrices (Ag, Au, Si, and amorphous carbon). The recently developed “triple fit” method for treating conventional magnetometry data allows, together with micro-superconducting quantum interference device ( ? -SQUID) investigations, the detailed study of the influence of the surrounding matrix on the magnetic volume and the magnetic anisotropy of Co nanoparticles. While interdiffusion between matrix and Co atoms cannot be excluded in Si and amorphous C matrices, the structure of clusters embedded in the metallic matrices remains intact. Ag and Au matrices increase significantly the magnetic anisotropy energy of the Co clusters. ? -SQUID experiments indicate that the magnetic anisotropy of embedded clusters is not affected by a magnetically dead layer and that an anisotropy dispersion must be taken into account for size-selected nanoparticles.

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

    SciTech Connect

    Inoue, Jun-ichiro; Yanagihara, Hideto; Kita, Eiji; Niizeki, Tomohiko; AIMR, Tohoku University, Sendai 980-8577 ; Itoh, Hiroyoshi

    2014-02-15

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

  6. Coercivity and magnetic anisotropy of sintered Sm{sub 2}Co{sub 17}-type permanent magnets

    SciTech Connect

    Tellez-Blanco, J.C.; Kou, X.C.; Groessinger, R.; Estevez-Rams, E.; Fidler, J.; Ma, B.M.

    1997-10-01

    Anisotropic and isotropic Sm{sub 2}Co{sub 17}-type permanent magnets have been prepared by using the conventional sintering technique. Transmission electron microscopy was used to characterize the cellular structure within the Sm{sub 2}(Fe,Co){sub 17} grains. Hysteresis loops (M{approximately}H) were measured in the temperature range from 4.2 to about 1000 K by using a pulsed-field magnetometer with a maximum field strength up to 24 MA/m. The magnetocrystalline anisotropy field H{sub A} has been measured up to 1000 K by using the singular point detection technique on anisotropic samples with external fields applied perpendicular to the magnetic alignment direction. The saturation magnetization M{sub s} has been measured on anisotropic samples with external fields applied parallel to the magnetic alignment direction. From studies of the coercivity mechanism by using a micromagnetic analysis of the temperature dependence of the coercivity field, it follows that the coercivity of Sm(Co,Fe,Cu,Zr){sub z} is controlled at elevated temperature (above 520 K) by a nucleation process of reversal domains. {copyright} {ital 1997 American Institute of Physics.}

  7. Thermally activated domain wall motion in [Co/Ni](111) superlattices with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Le Gall, S.; Vernier, N.; Montaigne, F.; Gottwald, M.; Lacour, D.; Hehn, M.; Ravelosona, D.; Mangin, S.; Andrieu, S.; Hauet, T.

    2015-02-01

    Field-induced magnetization dynamics in a [Co/Ni] superlattice exhibiting strong perpendicular magnetic anisotropy is studied using Kerr microscopy. We report domain wall velocity over 8 decades within thermally activated, transitory, and flow dynamical regimes. At low field, the thermally activated regime is characterized by dendritic domain growth that differs from the creep mechanism usually observed for the interaction of domains wall with a 2D random pinning potential for layers grown by sputtering. This result is explained by the epitaxial nature of the [Co/Ni] superlattices involving a single-type defect. The transition from the thermally activated to the flow regime is characterized by a reduction of the density of non-reversed domains which exists after domain wall displacement.

  8. Magnetic anisotropy and magnetic domain structure in C-doped Mn5Ge3

    NASA Astrophysics Data System (ADS)

    Michez, L.-A.; Virot, F.; Petit, M.; Hayn, R.; Notin, L.; Fruchart, O.; Heresanu, V.; Jamet, M.; Le Thanh, V.

    2015-07-01

    Magnetic properties of Mn5Ge3C0.7 thin films grown by molecular beam epitaxy have been studied. SQUID-VSM measurements and magnetic force microscopy have been used to probe the magnetic state and determine the relevant magnetic parameters. The results are supported by a combination of improved Saito's and Kittel's models. The moderate perpendicular magnetic anisotropy ( Qe x p=2/Ku ?0MSa t 2 ?0.2 ) leads to a stripe domain structure for film thicknesses above 28 nm. For thinner films, the magnetization lies in-plane. The uniaxial magnetocrystalline constant has been found to be much weaker than in Mn5Ge3 and is assigned to hybridization effect between the Mn and C atoms.

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

    SciTech Connect

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

    2013-02-15

    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.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  11. Evaluation of Microcracks orientation at Stromboli volcano using a Magnetic Ferrofluid and the Method of Anisotropy of Magnetic Susceptibility

    NASA Astrophysics Data System (ADS)

    Lewis, O.; Benson, P. M.; Vinciguerra, S.; Meredith, P. G.

    2005-12-01

    Most crustal rocks are anisotropic. In volcanic areas, anisotropy primarily results due to preferred directions of microcracks as magma cools. This effect is, in turn, enhanced due to local stress fields during deposition. The combined effects of these processes may thus give rise to a complex anisotropic fabric. Such fabrics can play crucial roles when enhancing the formation of slip surfaces which can lead to sector collapses of volcanic edifices, as is the case of Stromboli volcano (Italy) which experienced 4 sector collapses in the past 13ka. However, the rapid analysis of anisotropic microcrack fabrics (in terms of magnitude and principal direction) remains non-trivial. Current methods range from time consuming microcrack analysis of thin sections to the preparation of oriented cores for elastic-wave velocity measurement. To further our understanding of how microcrack fabrics influence the bulk properties of volcanic basalt, we employ a novel method which rapidly evaluates the 3-D microcrack orientation using technique of Anisotropy of Magnetic Susceptibility (AMS). First, we determine the rock matrix AMS (mAMS) using standard methods (via a Agico KLY-4 Kappabridge). Samples are then saturated with a magnetic ferrofluid, filling the microcrack network with a magnetically susceptible suspension of microscopic (10nm) magnetite particles. The AMS is then re-measured, with the matrix susceptibility values subtracted from these readings to yield the average 3-D pore space shape, size and orientation (pAMS). We describe the use of this method using basalt from Stromboli and comparing to a granite (Takidani) from the Japanese Alps in order to verify the technique and to investigate the relationship between the basalt microcrack geometry and field scale observation. For Takidani granite we find the structural anisotropy formed by the void space, as measured by pAMS, is well described by elastic wave velocity measurement; exhibiting anisotropy values of 19.1% and 7.6% for P-waves and S-waves respectively. Stromboli basalt possesses a weaker anisotropy of 4.7% and 3.0% (P-wave and S-wave velocity). We relate our pore space AMS measurements to the layering observed in Stromboli basalt on the flanks of the volcanic edifice; and infer that the microcrack network is both formed by this deposition and active tectonics as well as providing a key control on its physical properties. Such data has crucial significance upon the accurate assessment of flank stability, with consequences to hazard assessment for the surrounding area.

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

    SciTech Connect

    Pechan, M.J.

    1992-12-01

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

  13. Pressure-Induced Enhanced Magnetic Anisotropy in Mn(N(CN)2)2

    SciTech Connect

    Quintero, P. A.; Rajan, D.; Peprah, M. K.; Brinzari, T. V.; Fishman, Randy Scott; Talham, Daniel R.; Meisel, Mark W.

    2015-01-01

    Using DC and AC magnetometry, the pressure dependence of the magnetization of the threedimensional antiferromagnetic coordination polymer Mn(N(CN)2)2 was studied up to 12 kbar and down to 8 K. The magnetic transition temperature, Tc, increases dramatically with applied pressure (P), where a change from Tc(P = ambient) = 16:0 K to Tc(P = 12:1 kbar) = 23:5 K was observed. In addition, a marked difference in the magnetic behavior is observed above and below 7.1 kbar. Specifically, for P < 7:1 kbar, the differences between the field-cooled and zero-field-cooled (fc-zfc) magnetizations, the coercive field, and the remanent magnetization decrease with increasing pressure. However, for P > 7:1 kbar, the behavior is inverted. Additionally, for P > 8:6 kbar, minor hysteresis loops are observed. All of these effects are evidence of the increase of the superexchange interaction and the appearance of an enhanced exchange anisotropy with applied pressure.

  14. Magnetic field dosimeter development

    SciTech Connect

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

    1980-09-01

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

  15. Magnetosheath magnetic field variability

    NASA Technical Reports Server (NTRS)

    Sibeck, D. G.

    1994-01-01

    A case study using simulations IRM and CCE observations demonstrates that transient magnetospheric events correspond to pressure pulses in the magnetosheath, inward bow shock motion, and magnetopause compression. Statistical surveys indicate that the magnetosheath magnetic field orientation rarely remains constant during periods of magnetopause and bow shock motion (both characterized by periods of 1 to 10 min). There is no tendency for bow shock motion to occur for southward interplanetary magnetic field (IMF) orientations.

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

    PubMed

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

    2001-05-01

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

  17. Competing magnetic anisotropies in an AFM-FM-AFM trilayer

    SciTech Connect

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

    2009-08-01

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

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

    E-print Network

    California at Berkeley, University of

    Magnetic fluctuation power near proton temperature anisotropy instability thresholds in the solar wind S. D. Bale, J. C. Kasper, G. G. Howes, E. Quataert,§ C. Salem,¶ and D. Sundkvist¶ (Dated: August 10, 2009) The proton temperature anisotropy in the solar wind is known to be constrained by the theo

  19. Magnetic anisotropy of C and N doped bulk FeCo alloy: A first principles study

    NASA Astrophysics Data System (ADS)

    Khan, Imran; Hong, Jisang

    2015-08-01

    Using the full potential linearized augmented plane wave (FLAPW) method, we investigated the magnetocrystalline anisotropy of carbon and nitrogen doped FeCo in the interstitial site. Here, we have considered 3.125% impurity doping concentration. The impurity doping induces a tetragonal distortion in the FeCo lattice, and both carbon and nitrogen impurities play a similar role for lattice distortion. The local magnetic moment of Fe atom around the impurity site was greatly reduced, whereas the Co had rather robust magnetic moment. We found a uniaxial magnetocrystalline anisotropy constant of 0.65 and 0.58 MJ/m3 for C and N doped bulk FeCo, and this was mainly due to the tetragonal distortion induced by C and N impurity, not from the hybridization effect with Fe or Co. Additionally, the estimated maximum energy product and coercive field were 81.4, 72.5 MGOe and 600, 530 kA m-1 for C and N doped bulk FeCo, respectively. These results may imply that the interstitial C or N doped FeCo can be used for potential rare earth free permanent magnet although those values are likely to be suppressed in real samples due to micromagnetic factors such as structural defects, geometrical effect, or grain boundary effect.

  20. Effect of deposition technique of Ni on the perpendicular magnetic anisotropy in Co/Ni multilayers

    NASA Astrophysics Data System (ADS)

    Akbulut, S.; Akbulut, A.; Özdemir, M.; Yildiz, F.

    2015-09-01

    The perpendicular magnetic anisotropy (PMA) of Si/Pt 3.5/(Co 0.3/Ni 0.6)n /Co 0.3/ Pt 3 (all thicknesses are nm) multilayers were investigated for two different sample sets by using ferromagnetic resonance (FMR) and magnetooptic Kerr effect (MOKE) techniques. In the first sample set all layers (buffer, cap, Co and Ni) were grown by magnetron sputtering technique while in the second sample set Ni sub-layers were grown by molecular beam epitaxy (MBE) at high vacuum. Apart from deposition technique of Ni, all other parameters like thicknesses and growth rates of each layers are same for both sample sets. Multilayers in these two sample sets display PMA in the as grown state until a certain value of bilayer repetition (n) and the strength of PMA decreases with increasing n. Magnetic easy axis's of the multilayered samples switched from film normal to the film plane when n is 9 and 5 for the first and second sample sets, respectively. The reason for that, PMA was decreased due to increasing roughness with increasing n. This was confirmed by X Ray Reflectivity (XRR) measurements for both sample sets. Moreover, in the first sample set coercive field values are smaller than the second sample set, which means magnetic anisotropy is lower than the latter one. This stronger PMA is arising due to existence of stronger Pt (111) and Co/Ni (111) textures in the second sample set.

  1. Kondo model with magnetic anisotropy terms for magnetic impurities on surfaces

    E-print Network

    ?itko, Rok

    (Cu) with a decoupling layer (CuN) behave as high-spin Kondo impurities with strong magnetic - S2 y) using the numerical renormalization group technique [6, 7]. Axial anisotropy only (D = 0, E -3 10 -2 TK /W S=1/2 XXZ anisotropic model Jz =0.1 Dynamic properties (D = 0, E = 0) 0,2 0,4 0,6 0

  2. Solar Wind Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Smith, E. J.

    1995-01-01

    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.

  3. Molecules in Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Berdyugina, Svetlana

    2015-08-01

    Molecules probe cool matter in the Universe and various astrophysical objects. Their ability to sense magnetic fields provides new insights into magnetic properties of these objects. During the past fifteen years we have carried out a theoretical study of molecular magnetic effects such as the Zeeman, Paschen-Back and Hanle effects and their applications for inferring magnetic structures and spatial inhomogeneities on the Sun, cool stars, brown dwarfs, and exoplanets from molecular spectro-polarimetry (e.g., Berdyugina 2011). Here, we present an overview of this study and compare our theoretical predictions with recent laboratory measurements of magnetic properties of some molecules. We present also a new web-based tool to compute molecular magnetic effects and polarized spectra which is supported by the ERC Advanced Grant HotMol.

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

    PubMed Central

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

    2015-01-01

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

  5. Magnetic anisotropy and spin-glass behavior in single crystalline U2PdSi3.

    PubMed

    Li, D X; Kimura, A; Haga, Y; Nimori, S; Shikama, T

    2011-02-23

    We present the magnetic and transport properties of single crystalline U(2)PdSi(3) measured with the magnetic field (H) (or measuring current, I) applied along two typical crystallographic directions, i.e. H ? c-axis and H c-axis (or I ? c-axis and I c-axis). For both directions, a spin-glass state is confirmed to form at low temperature with the same spin freezing temperature T(f) (=11.5 K), initial frequency shift ?T(f) (=0.023) and activation energy E(a)/k(B) (=90.15 K) in zero dc field. Strong anisotropy in magnetic and transport behavior is found to be a significant feature of U(2)PdSi(3). The unusual ferromagnetic-like anomaly in ac susceptibility and dc magnetization curves around T(m)=71 K is observed in the case of H c-axis but not in the cases of H ? c-axis. The characteristic temperature T(ir), below which evident irreversible magnetism originated from random spin freezing can be observed, shows much stronger field dependence for H ? c-axis than for H c-axis. Moreover, an unusual finding is that the electrical resistivity measurements indicate the formation of magnetic Brillouin-zone boundary gaps and much larger magnetic scattering for I ? c-axis, while the coherent-Kondo-effect-like behavior is obvious for I c-axis. We also emphasize that no resistivity minimum can be detected down to 2.5 K for either direction. The observed magnetic and transport behaviors are compared with those in polycrystalline U(2)PdSi(3) and other 2:1:3 intermetallic compounds. PMID:21411890

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

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

    E-print Network

    Bi, Lei

    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 ...

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

    NASA Astrophysics Data System (ADS)

    Karmakar, S.

    1985-08-01

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

  9. Magnetic Field Solver

    NASA Technical Reports Server (NTRS)

    Ilin, Andrew V.

    2006-01-01

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

  10. Magnetic Field Measurement System

    SciTech Connect

    Kulesza, Joe; Johnson, Eric; Lyndaker, Aaron; Deyhim, Alex; Waterman, Dave; Blomqvist, K. Ingvar; Dunn, Jonathan Hunter

    2007-01-19

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

  11. Determination of magnetic anisotropy constants and domain wall pinning energy of Fe/MgO(001) ultrathin film by anisotropic magnetoresistance.

    PubMed

    Hu, Bo; He, Wei; Ye, Jun; Tang, Jin; Zhang, Yong-Sheng; Ahmad, Syed Sheraz; Zhang, Xiang-Qun; Cheng, Zhao-Hua

    2015-01-01

    It is challenging to determine domain wall pinning energy and magnetic anisotropy since both coherent rotation and domain wall displacement coexist during magnetization switching process. Here, angular dependence anisotropic magnetoresistance (AMR) measurements at different magnetic fields were employed to determine magnetic anisotropy constants and domain wall pinning energy of Fe/MgO(001) ultrathin film. The AMR curves at magnetic fields which are high enough to ensure the coherent rotation of magnetization indicate a smooth behavior without hysteresis between clockwise (CW) and counter-clockwise (CCW) rotations. By analyzing magnetic torque, the magnetic anisotropy constants can be obtained. On the other hand, the AMR curves at low fields show abrupt transitions with hysteresis between CW and CCW rotations, suggesting the presence of multi-domain structures. The domain wall pinning energy can be obtained by analyzing different behaviors of AMR. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of magnetic anisotropy and domain wall pinning energy, which is still a critical issue for spintronics. PMID:26369572

  12. Determination of magnetic anisotropy constants and domain wall pinning energy of Fe/MgO(001) ultrathin film by anisotropic magnetoresistance

    PubMed Central

    Hu, Bo; He, Wei; Ye, Jun; Tang, Jin; Zhang, Yong-Sheng; Ahmad, Syed Sheraz; Zhang, Xiang-Qun; Cheng, Zhao-Hua

    2015-01-01

    It is challenging to determine domain wall pinning energy and magnetic anisotropy since both coherent rotation and domain wall displacement coexist during magnetization switching process. Here, angular dependence anisotropic magnetoresistance (AMR) measurements at different magnetic fields were employed to determine magnetic anisotropy constants and domain wall pinning energy of Fe/MgO(001) ultrathin film. The AMR curves at magnetic fields which are high enough to ensure the coherent rotation of magnetization indicate a smooth behavior without hysteresis between clockwise (CW) and counter-clockwise (CCW) rotations. By analyzing magnetic torque, the magnetic anisotropy constants can be obtained. On the other hand, the AMR curves at low fields show abrupt transitions with hysteresis between CW and CCW rotations, suggesting the presence of multi-domain structures. The domain wall pinning energy can be obtained by analyzing different behaviors of AMR. Our work suggests that AMR measurements can be employed to figure out precisely the contributions of magnetic anisotropy and domain wall pinning energy, which is still a critical issue for spintronics. PMID:26369572

  13. Perpendicular magnetic anisotropy of amorphous [CoSiB/Pt]{sub N} thin films

    SciTech Connect

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

    2015-05-07

    Materials with perpendicular magnetic anisotropy (PMA) have been intensively studied for high-density nonvolatile memory such as spin-transfer-torque magnetic random access memory with low switching current density and high thermal stability. Compared with crystalline PMA multilayers, considerable works have been done on amorphous PMA multilayers because the amorphous materials are expected to have lower pinning site density as well as smaller domain wall width. This study is an overview of the PMA properties of amorphous [CoSiB/Pt]{sub N} multilayers with varying N, where the energy contribution is changed from domain wall energy to magnetostatic energy around N?=?6. By measuring the field-induced domain wall motion, we obtain the creep exponent of ??=?1/4. These results in the amorphous PMA multilayers of [CoSiB/Pt]{sub N} demonstrate possible potential as a free layer for PMA-based memory devices.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    SciTech Connect

    Silva, V.C.; Meunier, G.; Foggia, A.

    1995-05-01

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

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

    PubMed

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

    2014-11-26

    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

  17. Supercritical dynamics of domain walls in magnetic films with in-plane anisotropy

    NASA Astrophysics Data System (ADS)

    Korzunin, L. G.; Filippov, B. N.; Zverev, V. V.

    2015-08-01

    Based on the numerical solution of Landau-Lifshitz equations, the nonlinear dynamic behavior of vortex-like domain walls in films with in-plane anisotropy has been investigated in external magnetic fields H significantly exceeding critical fields H c , above which the stationary motion of domain walls is replaced by nonstationary (periodic or aperiodic) motion. A method has been proposed for the detection of complex aperiodic dynamics of structural rearrangements of domain walls, which is based on the construction of diagrams of the dependences of the tilt angle of the magnetization M with respect to the plane of the domain wall in some of its points on the corresponding angle in other points. It has been found that these diagrams significantly change with variations in the external magnetic field applied along the easy axis of magnetization in the range H > H c . It has been shown that the pattern of these changes is similar to the scenario of the Feigenbaum transition to dynamic chaos.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  19. Enhanced perpendicular magnetic anisotropy in Fe/Mn bilayers by incorporating ultrathin ferromagnetic underlayer through

    E-print Network

    Lin, Minn-Tsong

    for reasonable power consumption becomes important issues. Utilizing the perpen- dicular magnetic anisotropy (PMA ordering of the AFM Mn layer characterized by the magnetic ordering temperature (TOrdering). For the bulk in perpendicular-based magnetic devices, it is important to search for an approach that can enhance the TOrdering

  20. Accurate determination of the magnetic anisotropy in cluster-assembled nanostructures

    NASA Astrophysics Data System (ADS)

    Tamion, Alexandre; Hillenkamp, Matthias; Tournus, Florent; Bonet, Edgar; Dupuis, Véronique

    2009-08-01

    The simultaneous triple adjustment of experimental magnetization curves under different conditions is shown to allow the unambiguous and consistent determination of both the magnetic particle size distribution and anisotropy for granular nanostructures of Co clusters embedded in protective matrices. The importance of interface effects resulting in magnetically dead layers is demonstrated.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

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

    SciTech Connect

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

    2014-08-04

    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.

  3. Magnetic fields at uranus.

    PubMed

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

    1986-07-01

    The magnetic field experiment on the Voyager 2 spacecraft revealed a strong planetary magnetic field of Uranus and an associated magnetosphere and fully developed bipolar masnetic tail. The detached bow shock wave in the solar wind supersonic flow was observed upstream at 23.7 Uranus radii (1 R(U) = 25,600 km) and the magnetopause boundary at 18.0 R(U), near the planet-sun line. A miaximum magnetic field of 413 nanotesla was observed at 4.19 R(U ), just before closest approach. Initial analyses reveal that the planetary magnetic field is well represented by that of a dipole offset from the center of the planet by 0.3 R(U). The angle between Uranus' angular momentum vector and the dipole moment vector has the surprisingly large value of 60 degrees. Thus, in an astrophysical context, the field of Uranus may be described as that of an oblique rotator. The dipole moment of 0.23 gauss R(3)(U), combined with the large spatial offset, leads to minimum and maximum magnetic fields on the surface of the planet of approximately 0.1 and 1.1 gauss, respectively. The rotation period of the magnetic field and hence that of the interior of the planet is estimated to be 17.29+/- 0.10 hours; the magnetotail rotates about the planet-sun line with the same period. Thelarge offset and tilt lead to auroral zones far from the planetary rotation axis poles. The rings and the moons are embedded deep within the magnetosphere, and, because of the large dipole tilt, they will have a profound and diurnally varying influence as absorbers of the trapped radiation belt particles. PMID:17812894

  4. High-purity cobalt thin films with perpendicular magnetic anisotropy prepared by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Ootera, Yasuaki; Shimada, Takuya; Kado, Masaki; Quinsat, Michael; Morise, Hirofumi; Nakamura, Shiho; Kondo, Tsuyoshi

    2015-11-01

    A study of the chemical vapor deposition (CVD) of high-purity cobalt thin films is described. The Co layer prepared by a thermal CVD technique with a Pt/Ta underlayer and a Pt cap layer shows a saturation magnetization (Ms) of ?1.8 T and perpendicular magnetic anisotropy (PMA) with an anisotropy energy (Ku) of ?105 J/m3. The cobalt thickness dependence of Ku reveals that the interfacial anisotropy at the Pt/Co interface is most likely the origin of the obtained PMA.

  5. Mercury's Magnetic Field

    NASA Astrophysics Data System (ADS)

    Johnson, C. L.

    2014-12-01

    Mercury is the only inner solar system body other than Earth to possess an active core dynamo-driven magnetic field and the only planet with a small, highly dynamic magnetosphere. Measurements made by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have provided a wealth of data on Mercury's magnetic field environment. Mercury's weak magnetic field was discovered 40 years ago by the Mariner 10 spacecraft, but its large-scale geometry, strength and origin could not be definitively established. MESSENGER data have shown that the field is dynamo-generated and can be described as an offset axisymmetric dipole field (hereafter OAD): the magnetic equator lies ~0.2 RM (RM = 2440 km) north of the geographic equator and the dipole moment is 2.8 x1019 Am2 (~0.03% that of Earth's). The weak internal field and the high, but variable, solar wind ram pressure drive vigorous magnetospheric dynamics and result in an average distance from the planet center to the sub-solar magnetopause of only 1.42 RM. Magnetospheric models developed with MESSENGER data have allowed re-analysis of the Mariner 10 observations, establishing that there has been no measureable secular variation in the internal field over 40 years. Together with spatial power spectra for the OAD, this provides critical constraints for viable dynamo models. Time-varying magnetopause fields induce secondary core fields, the magnitudes of which confirm the core radius estimated from MESSENGER gravity and Earth-based radar data. After accounting for large-scale magnetospheric fields, residual signatures are dominated by additional external fields that are organized in the local time frame and that vary with magnetospheric activity. Birkeland currents have been identified, which likely close in the planetary interior at depths below the base of the crust. Near-periapsis magnetic field measurements at altitudes greater than 200 km have tantalizing hints of crustal fields, but crustal sources cannot be distinguished from core fields, nor cleanly separated from external fields. I will report on recent data acquired at altitudes as low as 25 km that have the potential to resolve these issues. The presence of remanent crustal fields would have profound implications for Mercury's thermal and dynamical histories.

  6. The induced magnetic field.

    PubMed

    Islas, Rafael; Heine, Thomas; Merino, Gabriel

    2012-02-21

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

  7. Probing boundary magnetization through exchange bias in heterostructures with competing anisotropy

    NASA Astrophysics Data System (ADS)

    Wang, Yi; Binek, Christian

    2013-03-01

    Cr2O3 (chromia) is a magnetoelectric antiferromagnet with a bulk TN of 307 K. It has been utilized for electrically controlled exchange bias (EB) by taking advantage of voltage-controllable boundary magnetization (BM) occurring as a generic property in magnetoelectric single domain antiferromagnets.[2] In the perpendicular Cr2O3(0001)/CoPd EB system the EB-field shows an order parameter type T-dependence close to TN reflecting the T-dependence of the BM. At about 150 K a decrease of the EB-field sets in with decreasing temperature suggesting canting of the BM. To evidence this mechanism we use EB as a probe. Specifically, we investigate EB in Permalloy(5nm)/Cr2O3 (0001)(100nm) with Permalloy and chromia having competing anisotropies. We measure easy axis magnetic hysteresis loops via longitudinal magneto-optical Kerr effect for various temperatures after perpendicular and in-plane magnetic field-cooling. The T-dependence of the EB field supports the canting mechanism. In addition to the all thin film EB system, we explore a Permalloy(10nm)/Cr2O3(0001 single crystal) heterostructure where magnetoelectric annealing allows selecting Cr2O3 single domain states. Here the effect of T-dependent canting of the BM is compared with findings in the complementary perpendicular EB system. Financial support by NSF through MRSEC and the Nanoelectronic Research Initiative.

  8. Evolution of magnetic anisotropy and thermal stability during nanocrystal-chain growth

    NASA Astrophysics Data System (ADS)

    Charilaou, M.; Sahu, K. K.; Faivre, D.; Fischer, A.; García-Rubio, I.; Gehring, A. U.

    2011-10-01

    We compare measurements and simulations of ferromagnetic resonance spectra of magnetite nanocrystal-chains at different growth-stages. By fitting the spectra, we extracted the cubic magnetocrystalline anisotropy field and the uniaxial dipole field at each stage. During the growth of the nanoparticle-chain assembly, the magnetocrystalline anisotropy grows linearly with increasing particle diameter. Above a threshold average diameter of D ? 23 nm, a dipole field is generated, which then increases with particle size and the ensemble becomes thermally stable. These findings demonstrate the anisotropy evolution on going from nano to mesoscopic scales and the dominance of dipole fields over crystalline fields in one-dimensional assemblies.

  9. HMI Magnetic Field Products

    NASA Astrophysics Data System (ADS)

    Hoeksema, Jon T.; HMI Magnetic Field Team

    2013-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

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

    SciTech Connect

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

    2007-07-01

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

  12. Large and negative magnetic anisotropy in pentacoordinate mononuclear Ni(ii) Schiff base complexes.

    PubMed

    Nemec, Ivan; Herchel, Radovan; Svoboda, Ingrid; Bo?a, Roman; Trávní?ek, Zden?k

    2015-05-28

    A series of pentacoordinate Ni(ii) complexes of the general formula [Ni(L5)] () with various pentadentate Schiff base ligands H2L5 (originating in a condensation of aromatic ortho-hydroxy-aldehydes and aliphatic triamines) was synthesized and characterized by X-ray structure analysis and magnetometry. The alternations of substituents on the H2L parent ligand resulted in the complexes with the geometry varying between the square-pyramid and trigonal-bipyramid. In the compounds whose chromophore geometry is closer to a trigonal-bipyramid, a large and negative uniaxial anisotropy (D = -64 cm(-1)) was identified. Moreover, the simple linear expression for the axial zero-field splitting (ZFS) parameter, D/cm(-1) = 32.7(4.8) - 151(10)?, was proposed, where ? (in degrees) stands for the Addison parameter. The results of magnetic analysis were also supported by ab initio CASSCF/NEVPT2 calculations of the ZFS splitting parameters D and E, and g tensors. Despite large and negative D-values of the reported compounds, slow relaxation of magnetization was not observed either in zero or non-zero static magnetic field, thus no single-molecule magnetic behaviour was detected. PMID:25919125

  13. Biological Magnetometry: Torque on Superparamagnetic Beads in Magnetic Fields

    NASA Astrophysics Data System (ADS)

    van Oene, Maarten M.; Dickinson, Laura E.; Pedaci, Francesco; Köber, Mariana; Dulin, David; Lipfert, Jan; Dekker, Nynke H.

    2015-05-01

    Superparamagnetic beads are widely used in biochemistry and single-molecule biophysics, but the nature of the anisotropy that enables the application of torques remains controversial. To quantitatively investigate the torques experienced by superparamagnetic particles, we use a biological motor to rotate beads in a magnetic field and demonstrate that the underlying potential is ? periodic. In addition, we tether a bead to a single DNA molecule and show that the angular trap stiffness increases nonlinearly with magnetic field strength. Our results indicate that the superparamagnetic beads' anisotropy derives from a nonuniform intrabead distribution of superparamagnetic nanoparticles.

  14. Effects of magnetocrystalline anisotropy and magnetization saturation on the mechanically induced switching in nanomagnets

    NASA Astrophysics Data System (ADS)

    Yi, Min; Xu, Bai-Xiang; Shen, Zhigang

    2015-03-01

    The effects of magnetocrystalline anisotropy (Ku) and magnetization saturation (Ms) on the mechanically induced switching in nanomagnets are studied using a constraint-free phase field model, which allows explicit magneto-mechanical coupling and strictly constant magnetization magnitude. The effects of Ku and Ms on the transition boundary between the coherent and incoherent switching modes are presented in terms of the nanomagnet geometry. It is found that Ms rather than Ku can affect the transition boundary between the two switching modes. In the coherent mode, there exists a critical strain ( ?c ) to induce a deterministic 90° switching. By using the dynamic nature and overrun behavior of the magnetization, a deterministic 180° switching can occur if the mechanical strain is removed once the magnetization rotates to the largest achievable angle ( ?1m ). For 90° switching, increasing Ku can enhance both ?c and ?1m , whereas Ms incurs no noticeable changes. For 180° switching, the switching time (ts) increases with Ms linearly, but initially decreases with increasing Ku and then saturates. The results for ts suggest that moderate Ku and Ms are advisable to simultaneously obtain relatively low ?c , quick switching, high storage density, and high magnetization-state stability in nanomagnets. This work provides insight on tuning mechanically assisted nanomagnet-based logic and memory devices through Ms and Ku.

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

    SciTech Connect

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

    2012-03-29

    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

  16. High field superconducting magnets

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  17. Ultra Low Energy Switching of Ferromagnet with Perpendicular Anisotropy on Topological Insulator by Voltage Controlled Magnetic Anisotropy

    NASA Astrophysics Data System (ADS)

    Ghosh, Bahniman; Pramanik, Tanmoy; Dey, Rik; Roy, Urmimala; Register, Leonard; Banerjee, Sanjay

    2015-03-01

    We propose and demonstrate, through simulation, an ultra low energy memory device on a topological insulator thin film. The device consists of a thin layer of Fe deposited on the surface of a topological insulator, Bi2Se3. The top surface of Fe is covered with MgO so that the ferromagnetic layer has perpendicular anisotropy. Current is passed on the surface of the topological insulator which switches the magnetization of the Fe ferromagnet through strong exchange interaction, between electrons contributing to the surface current on the Bi2Se3 and the d electrons in the ferromagnet, and spin transfer torque due to shunting of current through the ferromagnet. Voltage controlled magnetic anisotropy enables ultra low energy switching. Our micromagnetic simulations, predict switching time of the order of 2.4 ns and switching energy of the order of 0.16 fJ for a ferromagnetic bit with thermal stability of 90 kBT. The proposed structure combines the advantages of both large spin torque from topological insulators and those of perpendicular anisotropy materials. This work is supported by NRI SWAN and NSF NASCENT Center.

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

    SciTech Connect

    Pirogov, A. N. Bogdanov, S. G.; Rosenfeld, E. V.; Park, J.-G.; Choi, Y. N.; Lee, Seongsu; Prokes, K.; Golosova, N. O.; Sashin, I. L.; Kudrevatykh, N. V.; Skryabin, Yu. N.; Vokhmyanin, A. P.

    2012-11-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  20. ROTMOKE study of step-induced magnetic anisotropy in vicinal Cu/Py/Ni/Cu(001)

    NASA Astrophysics Data System (ADS)

    Deng, J. X.; Ma, Song; Tan, A.; Li, J.; Zhang, Z. D.; Hwang, C.; Qiu, Z. Q.

    2015-03-01

    Py/Ni films were epitaxially grown on a 6o vicinal Cu(001) substrate with steps parallel to the [110] axis. The addition of Py film increases the Ni film spin reorientation transition (SRT) thickness to permit a study of the step-induced in-plane magnetic anisotropy in a wider Ni thickness range. Rotation MOKE (ROTMOKE) was applied to determine the step-induced magnetic anisotropy in the vicinal Cu/Py/Ni/Cu(001) as a function of both the Py and Ni film thicknesses. We found that the atomic steps from the vicinal Cu(001) induce an in-plane uniaxial magnetic anisotropy that favors both Py and Ni magnetizations perpendicular to the steps. In addition, thickness-dependent ROTMOKE measurement allows a separation of the Py and Ni volume-type step-induced magnetic anisotropies. We show that Ni films exhibit different step-induced magnetic anisotropies below and above ~ 5-6ML Ni thickness. visiting scholar at University of California at Berkeley.

  1. Correlated oscillations of the magnetic anisotropy energy and orbital moment anisotropy in thin films: The role of quantum well states

    NASA Astrophysics Data System (ADS)

    Sandratskii, L. M.

    2015-10-01

    We report the first-principles study of the correlated behavior of the magnetic anisotropy energy (MAE) and orbital moment anisotropy (OMA) as the functions of the thickness N of the Fe film. The work is motivated by recent experimental studies combining photoemission, x-ray magnetic circular dichroism, and magnetic anisotropy measurements. In agreement with experiment, the correlated oscillations of MAE (N ) and OMA (N ) are obtained that have their origin in the formation of the 3d quantum well states (QWS) confined in the films. The main contribution to the oscillation amplitude comes from the surface layer. This is an interesting feature of the phenomenon consisting in the peculiar dependence of the physical quantities on the thickness of the film. We demonstrate that the band structure of the bulk Fe does not reflect adequately the properties of the 3d QWS in thin films and, therefore, does not provide the basis for understanding the oscillations of MAE (N ) and OMA (N ) . A detailed point-by-point analysis in the two-dimensional (2D) Brillouin zone (BZ) of the film shows that the contribution of the ? point, contrary to a rather common expectation, does not play an important role in the formation of the oscillations. Instead, the most important contributions come from a broad region of the 2D BZ distant from the center of the BZ. Combining symmetry arguments and direct calculations we show that orbital moments of the electronic states possess nonzero transverse components orthogonal to the direction of the spin magnetization. The account for this feature is crucial in the point-by-point analysis of the OMA. On the basis of the calculations for noncollinear spin configurations we suggest interpretations of two interesting experimental findings: fast temperature decay of the oscillation amplitude in MAE (N ) and unexpectedly strong spin mixing of the initial states of the photoemission process.

  2. Transport Properties of Equilibrium Argon Plasma in a Magnetic Field

    SciTech Connect

    Bruno, D.; Laricchiuta, A.; Chikhaoui, A.; Kustova, E. V.; Giordano, D.

    2005-05-16

    Electron electrical conductivity coefficients of equilibrium Argon plasma in a magnetic field are calculated up to the 12th Chapman-Enskog approximation at pressure of 1 atm and 0.1 atm for temperatures 500K-20000K; the magnetic Hall parameter spans from 0.01 to 100. The collision integrals used in the calculations are discussed. The convergence properties of the different approximations are assessed. The degree of anisotropy introduced by the presence of the magnetic field is evaluated. Differences with the isotropic case can be very substantial. The biggest effects are visible at high ionization degrees, i.e. high temperatures, and at strong magnetic fields.

  3. Magnetic fields at Uranus

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  4. Magnetic fields at Uranus

    NASA Astrophysics Data System (ADS)

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

    1986-07-01

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

  5. Interfacial magnetic anisotropy of Co90Zr10 on Pt layer.

    PubMed

    Kil, Joon Pyo; Bae, Gi Yeol; Suh, Dong Ik; Choi, Won Joon; Noh, Jae Sung; Park, Wanjun

    2014-11-01

    Spin Transfer Torque (STT) is of great interest in data writing scheme for the Magneto-resistive Random Access Memory (MRAM) using Magnetic Tunnel Junction (MTJ). Scalability for high density memory requires ferromagnetic electrodes having the perpendicular magnetic easy axis. We investigated CoZr as the ferromagnetic electrode. It is observed that interfacial magnetic anisotropy is preferred perpendicular to the plane with thickness dependence on the interfaces with Pt layer. The anisotropy energy (K(u)) with thickness dependence shows a change of magnetic-easy-axis direction from perpendicular to in-plane around 1.2 nm of CoZr. The interfacial anisotropy (K(i)) as the directly related parameters to switching and thermal stability, are estimated as 1.64 erg/cm2 from CoZr/Pt multilayered system. PMID:25958513

  6. Tuning Magnetic Anisotropy in Metallic Multilayers by Surface Charging: An Ab Initio Study

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

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

  7. Temperature dependence of magnetic anisotropy constant in manganese ferrite nanoparticles at low temperature

    E-print Network

    Krishnan, Kannan M.

    Temperature dependence of magnetic anisotropy constant in manganese ferrite nanoparticles at low temperature Sunghyun Yoon1,a) and Kannan M. Krishnan2 1 Department of Physics, Gunsan National University December 2010; published online 7 April 2011) The temperature dependence of the effective magnetic

  8. The Role of Numerical Precision in Calculating the Magnetic Anisotropy Energy in Density Functional Theory

    E-print Network

    Jansen, Henri J. F.

    the magnetic moments reside locally on atoms. Itinerant electron behavior and quenched orbital momentum dueThe Role of Numerical Precision in Calculating the Magnetic Anisotropy Energy in Density Functional Theory G. Schneider \\Lambda and H.J.F. Jansen Department of Physics, Oregon State University, Corvallis

  9. Effects of auroral-particle anisotropies and mirror forces on high-latitude electric fields

    NASA Technical Reports Server (NTRS)

    Chiu, Y. T.; Schulz, M.; Cornwall, J. M.

    1981-01-01

    It is noted that, for most of the mechanisms for the strong electric fields that characterize the narrow regions in which there is acceleration and precipitation of ring current and/or plasma-sheet plasma, certain effects must be taken into account in simulations of auroral electric fields. The effects are those of auroral particle anisotropy, of mirror forces due to the inhomogeneous geomagnetic field, of auroral electron backscatter by the atmosphere, and of electron trapping by the combination of magnetic mirroring and electrostatic forces. What is more, the effects of the very strong perpendicular electric field must also be taken into account in a kinetic description of the Poisson equation in order to achieve a unified theory of the auroral electrostatic structure. Progress in these areas during the past few years is reviewed. It is shown that particle anisotropies and mirror forces can account for some basic electrostatic features of the quiet arc, while additional effects may be occurring in strong events in which the parallel potential drop is more than about 10 kV.

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

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

    SciTech Connect

    Landa, Romina A.; Soledad Antonel, Paula; Ruiz, Mariano M.; Negri, R. Martín; Perez, Oscar E.; Butera, Alejandro; Jorge, Guillermo; Oliveira, Cristiano L. P.

    2013-12-07

    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.

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

    SciTech Connect

    Rahman, M. Tofizur; Shams, Nazmun N.; Lai, C.-H.

    2009-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Rahman, M. Tofizur; Shams, Nazmun N.; Lai, Chih-Huang

    2009-04-01

    A simple method is demonstrated to fabricate 25 nm magnetic nanodot arrays with perpendicular anisotropy over 10 cm2 coverage area. The nanodot arrays are fabricated by depositing Co/Pt multilayers (MLs) onto the SiO2 dot arrays formed on a Si wafer. At first, arrays of the SiO2 dots are fabricated on a Si wafer by anodizing a thin Al film deposited on it. The SiO2 dots are formed at the base of the anodized alumina (AAO) pores due to the selective oxidation of the Si through the AAO pores during over anodization of the Al film. The average diameter, periodicity, and height of the SiO2 dots are about 24, 43, and 17 nm, respectively. Then {Co(0.4 nm)/Pt(0.08 nm)}8 MLs with a 3 nm Pt buffer layer is deposited onto the SiO2 dot arrays by sputtering. The average diameter and periodicity of the Co/Pt nanodot arrays are 25.4 and 43 nm, respectively, with narrow distribution. The nanodot arrays exhibit strong perpendicular anisotropy with a squareness ratio of unity and negative nucleation fields. The coercivity of the nanodot arrays is about one order higher than that of the continuous film, i.e., the same structure deposited on the SiO2 substrate. The magnetization reversal of the continuous film is governed by domain-wall motion, while the magnetization reversal of the nanodot arrays is dominated by the Stoner-Wohlfarth-like rotation. These results indicate that the fabricated structure can be considered as an isolated nanodot array.

  14. Growth of perpendicularly magnetized thin films on a polymer buffer and voltage-induced change of magnetic anisotropy at the MgO|CoFeB interface

    NASA Astrophysics Data System (ADS)

    Lam, D. D.; Bonell, F.; Shiota, Y.; Miwa, S.; Nozaki, T.; Tamura, E.; Mizuochi, N.; Shinjo, T.; Suzuki, Y.; Yuasa, S.

    2015-06-01

    We show that perpendicularly magnetized thin films can be grown onto polyimide, a potentially flexible substrate. With polar Kerr magnetometry, we demonstrate that the coercive field of CoFeB thin film can be modulated by applying a back gate voltage. Our proposed multi-layered structure is suitable for surface-sensitive measurements of the voltage-induced change in anisotropy, and could be used to realize flexible spintronics devices.

  15. Reionization constraints on primordial magnetic fields

    NASA Astrophysics Data System (ADS)

    Pandey, Kanhaiya L.; Choudhury, T. Roy; Sethi, Shiv K.; Ferrara, Andrea

    2015-08-01

    We study the impact of the extra density fluctuations induced by primordial magnetic fields on the reionization history in the redshift range: 6 < z < 10. We perform a comprehensive Markov chain Monte Carlo (MCMC) physical analysis allowing the variation of parameters related to primordial magnetic fields (strength, B0, and power-spectrum index n_{B}), reionization and ? cold dark matter cosmological model. We find that magnetic field strengths in the range: B0 ? 0.05-0.3 nG (for nearly scale-free power spectra) can significantly alter the reionization history in the above redshift range and can relieve the tension between the Wilkinson Microwave Anisotropy Probe and quasar absorption spectra data. Our analysis puts upper limits on the magnetic field strength B0 < 0.358, 0.120 and 0.059 nG (95 per cent c.l.) for n_{B} = -2.95, -2.9 and -2.85, respectively. These represent the strongest magnetic field constraints among those available from other cosmological observables.

  16. Asymptotic dependence of the relaxation time of the magnetization of a ferromagnetic particle on the anisotropy of the particle

    NASA Astrophysics Data System (ADS)

    Scully, C. N.; Cregg, P. J.; Crothers, D. S. F.

    1992-01-01

    It is known that the direction of the magnetization vector of very fine single-domain ferromagnetic particles fluctuates under the influence of thermal agitation. Perturbation theory is applied rigorously to a singular integral equation to derive an asymptotic formula for the relaxation time of the magnetization, for the case of uniaxial anisotropy and an applied magnetic field. The result agrees with that of Brown [Phys. Rev. 130, 1677 (1963)] as described succinctly by Aharoni [Phys. Rev. 177, 793 (1969)]. It should be emphasized that both Gilbert's equation and the earlier Landau-Lifshitz equation are merely phenomenological equations, which are used to explain the time decay of the average magnetization. Brown suggested that the Gilbert equation should be augmented by a white-noise driving term in order to explain the effect of thermal fluctuations of the surroundings on the magnetization.

  17. Nonmonotonic effects of perpendicular magnetic anisotropy on current-driven vortex wall motions in magnetic nanostripes

    NASA Astrophysics Data System (ADS)

    Su, Yuan-Chang; Lei, Hai-Yang; Hu, Jing-Guo

    2015-09-01

    In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy (PMA) on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations. The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current. Project supported by the National Natural Science Foundation of China (Grant Nos. 11247026 and 11374253).

  18. Radial magnetic field in magnetic confinement device

    NASA Astrophysics Data System (ADS)

    Xiong, Hao; Liu, Ming-Hai; Chen, Ming; Rao, Bo; Chen, Jie; Chen, Zhao-Quan; Xiao, Jin-Shui; Hu, Xi-Wei

    2015-09-01

    The intrinsic radial magnetic field (Br) in a tokamak is explored by the solution of the Grad-Shafranov equation in axisymmetric configurations through an expansion of the four terms of the magnetic surfaces. It can be inferred from the simulation results that at the core of the device, the tokamak should possess a three-dimensional magnetic field configuration, which could be reduced to a two-dimensional one when the radial position is greater than 0.6a. The radial magnetic field and the amzimuthal magnetic field have the same order of magnitude at the core of the device. These results can offer a reference for the analysis of the plasma instability, the property of the core plasma, and the magnetic field measurement. Project supported by the Special Domestic Program of ITER, China (Grant No. 2009GB105003).

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

    NASA Astrophysics Data System (ADS)

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

    2011-10-01

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

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

    E-print Network

    Chen, Long-Qing

    - plings in magnetic/ferroelectric FE artificial multiferroic heterostructures.2 This indirect electricPhase-field simulation of strain-induced domain switching in magnetic thin films Jia-Mian Hu, G of the Bloch point in a magnetic film with strong uniaxial magnetic anisotropy Low Temp. Phys. 37, 690 (2011

  1. Coronal Magnetic Field Models

    NASA Astrophysics Data System (ADS)

    Wiegelmann, Thomas; Petrie, Gordon J. D.; Riley, Pete

    2015-07-01

    Coronal magnetic field models use photospheric field measurements as boundary condition to model the solar corona. We review in this paper the most common model assumptions, starting from MHD-models, magnetohydrostatics, force-free and finally potential field models. Each model in this list is somewhat less complex than the previous one and makes more restrictive assumptions by neglecting physical effects. The magnetohydrostatic approach neglects time-dependent phenomena and plasma flows, the force-free approach neglects additionally the gradient of the plasma pressure and the gravity force. This leads to the assumption of a vanishing Lorentz force and electric currents are parallel (or anti-parallel) to the magnetic field lines. Finally, the potential field approach neglects also these currents. We outline the main assumptions, benefits and limitations of these models both from a theoretical (how realistic are the models?) and a practical viewpoint (which computer resources to we need?). Finally we address the important problem of noisy and inconsistent photospheric boundary conditions and the possibility of using chromospheric and coronal observations to improve the models.

  2. Experimental evidence of skyrmion-like configurations in bilayer nanodisks with perpendicular magnetic anisotropy

    SciTech Connect

    Stebliy, Maxim E. Kolesnikov, Alexander G.; Davydenko, Alexander V.; Ognev, Alexey V.; Samardak, Alexander S.; Chebotkevich, Ludmila A.

    2015-05-07

    Formation and existence of magnetic skyrmion-like configurations in bilayer nanodisks (Ta(3?nm)/[Co(0.37?nm)/Ni(0.58?nm)]{sub 10}){sub 2} with perpendicular magnetic anisotropy are shown experimentally at room temperature. Magnetization reversal through the skyrmion state is studied using magnetic hysteresis measurements. An evolution of skyrmion configurations in the nanodisk structure is analyzed. Experimental methods and micromagnetic simulations help to understand the magnetization reversal processes occurring through the stable skyrmion-like configurations. Formation of the intermediate C-states during magnetization reversal is demonstrated. The skyrmion number for all possible spin configurations is calculated.

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

    PubMed Central

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

    2012-01-01

    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

  4. Low field magnetic resonance imaging

    DOEpatents

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

    2010-07-13

    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.

  5. Tuning magnetic anisotropies of Fe films on Si(111) substrate via direction variation of heating current

    PubMed Central

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

    2013-01-01

    We adopted a novel method to tune the terrace width of Si(111) substrate by varying the direction of heating current. It was observed that the uniaxial magnetic anisotropy (UMA) of Fe films grown on the Si(111) substrate enhanced with decreasing the terrace width and superimposed on the weak six-fold magnetocrystalline anisotropy. Furthermore, on the basis of the scanning tunneling microscopy (STM) images, self-correlation function calculations confirmed that the UMA was attributed mainly from the long-range dipolar interaction between the spins on the surface. Our work opens a new avenue to manipulate the magnetic anisotropy of magnetic structures on the stepped substrate by the decoration of its atomic steps. PMID:23529097

  6. Influence of controlled surface oxidation on the magnetic anisotropy of Co ultrathin films

    NASA Astrophysics Data System (ADS)

    Di, N.; Kubal, J.; Zeng, Z.; Greeley, J.; Maroun, F.; Allongue, P.

    2015-03-01

    We studied the influence of controlled surface-limited oxidation of electrodeposited epitaxial Co(0001)/Au(111) films on their magnetic anisotropy energy using real time in situ magneto optical Kerr effect and density functional theory (DFT) calculations. We investigated the Co first electrochemical oxidation step which we demonstrate to be completely reversible and determined the structure of this oxide layer. We show that the interface magnetic anisotropy of the Co film increases by 0.36 erg/cm2 upon Co surface oxidation. We performed DFT calculations to determine the different surface structures in a wide potential range as well as the charge transfer at the Co surface. Our results suggest that the magnetic anisotropy change is correlated with a positive charge increase of 0.54 e- for the Co surface atom upon oxidation.

  7. Micromagnetic simulation of CNT-MFM probes under magnetic field

    NASA Astrophysics Data System (ADS)

    Manago, Takashi; Asada, Hironori; Kuramochi, Hiromi

    2013-06-01

    On the ferromagnetic-film-coated carbon nanotube for a magnetic force microscope (CNT-MFM) probe, the stability of the magnetic structure in an external magnetic field was investigated using a three-dimensional micromagnetic simulation. When a magnetic field was applied along the longitudinal direction, in the direction opposite that of the magnetization of the probe, the direction of the magnetic moments of the probe remained the same up to -200 mT and then reversed all at once. When a magnetic field was applied along horizontal direction, the direction of the magnetic moments gradually tilts with increasing field. MFM observations seem to be possible for magnetic fields up to 100 ˜ 150 mT, judging from the magnetic structure of the probe. In contrast, the magnetic structures of pyramidal probes show vortex-like magnetic structure and low tolerance to an external magnetic field. The CNT-MFM probe is relatively robust under an external magnetic field due to the strong shape anisotropy attributed to its cylindrical shape.

  8. Magnetic anisotropy investigations of (Ga,Mn)As with a large epitaxial strain

    NASA Astrophysics Data System (ADS)

    Juszy?ski, P.; Gryglas-Borysiewicz, M.; Szczytko, J.; Tokarczyk, M.; Kowalski, G.; Sadowski, J.; Wasik, D.

    2015-12-01

    Magnetic properties of 20 nm thick (Ga,Mn)As layer deposited on (Ga,In)As buffer with very large epitaxial tensile strain are investigated. Ga1-xInxAs buffer with x=30% provides a 2% lattice mismatch, which is an important extension of the mismatch range studied so far (up to 0.5%). Evolution of magnetic anisotropy as a function of temperature is determined by magnetotransport measurements. Additionally, results of direct measurements of magnetization are shown.

  9. The Galactic Magnetic Field

    NASA Astrophysics Data System (ADS)

    Jansson, Ronnie; Farrar, Glennys R.

    2012-12-01

    With this Letter, we complete our model of the Galactic magnetic field (GMF), by using the WMAP7 22 GHz total synchrotron intensity map and our earlier results to obtain a 13-parameter model of the Galactic random field, and to determine the strength of the striated random field. In combination with our 22-parameter description of the regular GMF, we obtain a very good fit to more than 40,000 extragalactic Faraday rotation measures and the WMAP7 22 GHz polarized and total intensity synchrotron emission maps. The data call for a striated component to the random field whose orientation is aligned with the regular field, having zero mean and rms strength ?20% larger than the regular field. A noteworthy feature of the new model is that the regular field has a significant out-of-plane component, which had not been considered earlier. The new GMF model gives a much better description of the totality of data than previous models in the literature.

  10. A large scale coherent magnetic field: interactions with free streaming particles and limits from the CMB

    SciTech Connect

    Adamek, Julian; Durrer, Ruth; Fenu, Elisa; Vonlanthen, Marc E-mail: ruth.durrer@unige.ch E-mail: marc.vonlanthen@unige.ch

    2011-06-01

    We study a homogeneous and nearly-isotropic Universe permeated by a homogeneous magnetic field. Together with an isotropic fluid, the homogeneous magnetic field, which is the primary source of anisotropy, leads to a plane-symmetric Bianchi I model of the Universe. However, when free-streaming relativistic particles are present, they generate an anisotropic pressure which counteracts the one from the magnetic field such that the Universe becomes isotropized. We show that due to this effect, the CMB temperature anisotropy from a homogeneous magnetic field is significantly suppressed if the neutrino masses are smaller than 0.3 eV.

  11. Electric and magnetic fields

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.; Robinson, R. S.; Etters, R. D.

    1982-01-01

    A number of energy momentum anomalies are described that result from the use of Abraham-Lorentz electromagnetic theory. These anomalies have in common the motion of charged bodies or current carrying conductors relative to the observer. The anomalies can be avoided by using the nonflow approach, based on internal energy of the electromagnetic field. The anomalies can also be avoided by using the flow approach, if all contributions to flow work are included. The general objective of this research is a fundamental physical understanding of electric and magnetic fields which, in turn, might promote the development of new concepts in electric space propulsion. The approach taken is to investigate quantum representations of these fields.

  12. Primordial magnetic seed field amplification by gravitational waves

    SciTech Connect

    Betschart, Gerold; Zunckel, Caroline; Dunsby, Peter K.S.; Marklund, Mattias

    2005-12-15

    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.

  13. Single-ion anisotropy in Mn-doped diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

    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.

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

    PubMed Central

    Boujraf, Saïd

    2014-01-01

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

  15. Director Field of Disclination Line in Uniaxial Nematic Liquid Crystal in the Presence of Magnetic Field

    NASA Astrophysics Data System (ADS)

    Kadivar, Erfan

    Using the Oseen-Zöcher-Frank theory, in the steady state, I study the distortion energy of a disclination line in nematic liquid crystal in the presence of an external magnetic field. The director field around a disclination line is exactly calculated by minimizing the total free energy. The behavior of total free energy as a function of magnetic field for two kinds of nematic material (positive and negative magnetic anisotropy) are discussed. In the short distance limit, the total free energy per unit length is calculated. In this case, the magnetic dependence of total free energy is discussed.

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

    SciTech Connect

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

    2014-05-07

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

  17. Tuning the magnetic anisotropy of CoFeB grown on flexible substrates

    NASA Astrophysics Data System (ADS)

    Zhang, Hao; Li, Yuan-Yuan; Yang, Mei-Yin; Zhang, Bao; Yang, Guang; Wang, Shou-Guo; Wang, Kai-You

    2015-07-01

    The magnetic properties of CoFeB thin films grown on flexible polyimide substrates were investigated using a magneto-optical Kerr effect magnetometer. In-plane uniaxial magnetic anisotropy was observed in the virgin state. The strain induced by bending the flexible substrate was applied on the sample to change the magnetic properties of CoFeB. The strain induced uniaxial magnetic anisotropy changed linearly with the deformation by about 8.41 × 1041 erg/cm3 at 1% of deformation. Our results prove the magnetic properties of CoFeB grown on flexible polyimide substrate can be tuned effectively by bending, which could be important for future flexible spintronics. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB922201 and 2015CB921401) and the National Natural Science Foundation of China (Grant Nos. 11174272, 11474272, 11274371, 51431009, and 61225021).

  18. Influence of perpendicular magnetic anisotropy on spin-transfer switching current in CoFeB /MgO/CoFeB magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Yakata, S.; Kubota, H.; Suzuki, Y.; Yakushiji, K.; Fukushima, A.; Yuasa, S.; Ando, K.

    2009-04-01

    We investigated the spin-torque diode effect in submicron-scale Co60Fe20B20/MgO/(CoxFe1-x)80B20 (0?x?0.9) magnetic tunnel junctions (MTJs) under perpendicular magnetic fields Hext up to 10kOe. A single peak was clearly observed in every spin-torque diode spectrum and the dependence of resonant frequency fres on Hext was well explained by using Kittel's formula. It was found that effective demagnetizing fields in the perpendicular-to-plane direction of the Fe-rich CoFeB free layers obtained from the spectra were considerably smaller than those expected from the magnetizations of the free layers. This suggested that the Fe-rich CoFeB free layers exhibited a perpendicular magnetic anisotropy, which agreed well with the reduced switching current density in the MTJs.

  19. Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO3

    NASA Astrophysics Data System (ADS)

    Lahtinen, Tuomas H. E.; Shirahata, Yasuhiro; Yao, Lide; Franke, Kévin J. A.; Venkataiah, Gorige; Taniyama, Tomoyasu; van Dijken, Sebastiaan

    2012-12-01

    We report on domain formation and magnetization reversal in epitaxial Fe films on ferroelectric BaTiO3 substrates with ferroelastic a-c stripe domains. The Fe films exhibit biaxial magnetic anisotropy on top of c domains with out-of-plane polarization, whereas the in-plane lattice elongation of a domains induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The strong modulation of magnetic anisotropy symmetry results in full imprinting of the a-c domain pattern in the Fe films. Exchange and magnetostatic interactions between neighboring magnetic stripes further influence magnetization reversal and pattern formation within the a and c domains.

  20. CoxC nanorod magnets: Highly magnetocrystalline anisotropy with lower Curie temperature for potential applications

    SciTech Connect

    El-Gendy, AA; Almugaiteeb, T; Carpenter, EE

    2013-12-01

    Magnetic CoxC nanorods with larger magnetocrystalline anisotropy of 5 x 10(5) J/m(3) as well as larger coercivity and lower Curie temperature are introduced. The particles have an average diameter of 8 nm and shows three different magnetic behaviors. The sample shows ferromagnetism up to 400 K, superparamagnetism at temperature > 400 K and magnets, magnetic sensors and contract agent for magnetic resonance imaging. (c) 2013 Elsevier B.V. All rights reserved.

  1. Planetary magnetic fields

    NASA Astrophysics Data System (ADS)

    Stevenson, David J.

    2003-03-01

    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 radial extent. The relevant electrical conductivities range from metallic values to values that may be only about 1% or less that of a typical metal, appropriate to ionic fluids and semiconductors. In all planets, the Coriolis force is dynamically important, but slow rotation may be more favorable for a dynamo than fast rotation. The maintenance and persistence of convection appears to be easy in gas giants and ice-rich giants, but is not assured in terrestrial planets because the quite high electrical conductivity of iron-rich cores guarantees a high thermal conductivity (through the Wiedemann-Franz law), which allows for a large core heat flow by conduction alone. In this sense, high electrical conductivity is unfavorable for a dynamo in a metallic core. Planetary dynamos mostly appear to operate with an internal field ˜(2 ??/ ?) 1/2 where ? is the fluid density, ? is the planetary rotation rate and ? is the conductivity (SI units). Earth, Ganymede, Jupiter, Saturn, Uranus, Neptune, and maybe Mercury have dynamos, Mars has large remanent magnetism from an ancient dynamo, and the Moon might also require an ancient dynamo. Venus is devoid of a detectable global field but may have had a dynamo in the past. The presence or absence of a dynamo in a terrestrial body (including Ganymede) appears to depend mainly on the thermal histories and energy sources of these bodies, especially the convective state of the silicate mantle and the existence and history of a growing inner solid core. Induced fields observed in Europa and Callisto indicate the strong likelihood of water oceans in these bodies.

  2. Ferroelectric-domain-controlled magnetic anisotropy in Co40Fe40B20/YMnO3 multiferroic heterostructure

    NASA Astrophysics Data System (ADS)

    Wang, J. W.; Zhao, Y. G.; Fan, C.; Sun, X. F.; Rizwan, S.; Zhang, S.; Li, P. S.; Lin, Z.; Yang, Y. J.; Yan, W. S.; Luo, Z. L.; Zou, L. K.; Liu, H. L.; Chen, Q. P.; Zhang, X.; Zhu, M. H.; Zhang, H. Y.; Cai, J. W.; Han, X. F.; Cheng, Z. H.; Gao, C.; Xie, D.; Ren, T. L.

    2013-03-01

    We report on the magnetic properties of Co40Fe40B20/YMnO3 multiferroic heterostructures in which Co40Fe40B20 shows an in-plane uniaxial magnetic anisotropy with the magnetic easy axis along the ferroelectric polarization direction of YMnO3. The coercive field (Hc) of Co40Fe40B20 shows an interesting non-monotonic change from the easy axis to hard axis with a maximum at a certain angle. It was demonstrated that the magnetic property of Co40Fe40B20 was dominated by the FE domain induced strain and the angular dependence of Hc can be understood by the two phase model. This work is helpful for understanding the coupling between ferromagnetic and ferroelectric materials.

  3. Origin of `in-plane' and `out-of-plane' magnetic anisotropies in as-deposited and annealed CoFeB ferromagnetic thin films

    NASA Astrophysics Data System (ADS)

    Swamy, G. Venkat; Rakshit, R. K.; Pant, R. P.; Basheed, G. A.

    2015-05-01

    A detailed comparative Ferromagnetic resonance study of pulsed laser deposited Co40Fe40B20 thin films, before and after annealing, was under taken. The dependence of resonance field (Hres) and peak-to-peak linewidth (?Hpp) on film thickness, annealing temperature, and magnetic field orientation is examined. `In-plane' (IP) and `out-of-plane' (OP) angular dependence of the resonance fields, (IP:Hres(?); OP:Hres(?)), were measured at T = 150 and 295 K for the as deposited (as-) to annealed (an-) thin film samples to determine IP ( HK ? ) and OP ( HK ? ) uniaxial anisotropy fields. Variation of Hres(?) and Hres(?) on sample geometry demonstrate that the uniaxial magnetic anisotropy is present in as- and an-thin films of Co40Fe40B20. The effective magnetic anisotropy ( Ku e f f ) increases after nanocrystallization in CoFeB films indicates that the exchange interactions are unable to average out the local-magnetocrystalline anisotropy of the nanocrystalline grains and thereby lead to magnetic hardening in the early stages of crystallization.

  4. Fabrication and characterization of perpendicular magnetic anisotropy thin-film CoCrPt grown on a Ti underlayer

    E-print Network

    Kane, Margaret Marie

    2015-01-01

    CoCrPt has potential applications as a memory storage technology because of its perpendicular magnetic anisotropy (PMA) characteristics. An underlayer can be used to ensure the out-of-plane magnetization required for PMA ...

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

    NASA Astrophysics Data System (ADS)

    Bauer, U.; D?browski, M.; Przybylski, M.; Kirschner, J.

    2011-10-01

    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 anisotropy is found to oscillate as a function of Co thickness with a period of 2.3 atomic layers, modulated exactly as theoretically predicted by L. Szunyogh [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.56.14036 56, 14036 (1997)] and independently by M. Cinal [J. Phys. Condens. MatterJCOMEL0953-898410.1088/0953-8984/15/2/304 15, 29 (2003)] and M. Cinal and A. Umerski [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.73.184423 73, 184423 (2006)]. Sub-monolayer Au coverage was used to fine-tune magnetic anisotropy and to provide convenient experimental access to anisotropy oscillations. The anisotropy oscillations, which are present up to room temperature, are attributed to quantum well states in the minority d band at the Fermi level of Co.

  6. Pulse electrodeposition and electrochemical quartz crystal microbalance techniques for high perpendicular magnetic anisotropy cobalt nanowire arrays

    SciTech Connect

    Ursache, Andrei; Goldbach, James T.; Russell, Thomas P.; Tuominen, Mark T.

    2005-05-15

    This research is focused on the development of pulse electrodeposition techniques to fabricate a high-density array of vertically oriented, high-magnetic anisotropy cobalt nanowires using a porous polymer film template. This type of array is a competitive candidate for future perpendicular magnetic media capable of storage densities exceeding 1 Terabit/in.{sup 2} The polymer template, derived from a self-assembling P(S-b-MMA) diblock copolymer film, provides precise control over the nanowire diameter (15 nm) and interwire spacing (24 nm), whereas nanowire length (typically 50 to 1000 nm) is controlled accurately with the aid of real-time electrochemical quartz crystal monitoring. Pulse and pulse-reversed electrodeposition techniques, as compared to dc, are shown to significantly enhance the perpendicular magnetic anisotropy of the magnetic nanowire array and ultimately result in coercivity as large as 2.7 kOe at 300 K. Magnetic and structural characterizations suggest that these properties arise from an improved degree of magnetocrystalline anisotropy (due to c-axis oriented crystal growth and improvements in crystal quality) that strongly supplements the basic shape anisotropy of the nanowires. Low temperature magnetometry is used to investigate exchange bias effects due to the incorporation of CoO antiferromagnetic impurities during the electrodeposition process and subsequent Co oxidation in air.

  7. Correlation between perpendicular exchange bias and magnetic anisotropy in IrMn /[Co/Pt]n and [Pt/Co]n/IrMn multilayers

    NASA Astrophysics Data System (ADS)

    van Dijken, Sebastiaan; Moritz, Jerome; Coey, J. M. D.

    2005-03-01

    Perpendicular exchange bias has been observed for IrMn /[Co/Pt]n and [Pt/Co]n/IrMn multilayers in the as-deposited state. The exchange bias field is largest when the IrMn film is grown on magnetically saturated Co /Pt multilayers (8.12mT for n =3), whereas it is considerably smaller when domain formation in the IrMn film occurs before Co /Pt deposition (3.30mT for n =3). After annealing at 220°C in an out-of-plane magnetic field the perpendicular exchange bias field and magnetic anisotropy are considerably larger for the Co /Pt multilayers with an IrMn film at the bottom. The apparent correlation between bias and anisotropy is explained by the dependence of the perpendicular exchange bias field on the orientation of the Co spins near the Co /IrMn interface.

  8. Van der Waals torque induced by external magnetic fields

    SciTech Connect

    Esquivel-Sirvent, R.; Cocoletzi, G. H.; Palomino-Ovando, M.

    2010-01-01

    We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III–IV semiconductors such as InSb, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of InSb. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of InSb increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropicmaterials when the magnetic fields is close to 1 T.

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

    NASA Astrophysics Data System (ADS)

    Hariri, Samer H.

    The Beaver River Diabase (BRD) is a series of mafic dikes and sills within the Beaver Bay Complex (BBC) of northern Minnesota, which formed during the development of the ~1.1 Ga Midcontinent Rift (MCR). The BRD is one of the youngest and most extensive intrusive phases of the BBC. The BRD dikes and sills were emplaced into the medial levels of the 6-10 kilometer-thick North Shore Volcanic Group and occur over an arcuate area extending 120 by 20 kilometers. The BRD is composed of fine- to medium-grained ophitic olivine gabbro and does not display obvious foliation or lineation features and rarely displays modal layering. Without obvious magmatic internal structures, it is difficult to determine emplacement properties such as flow direction using standard geologic mapping or petrographic techniques. For this reason, we measured the anisotropy of magnetic susceptibility (AMS), in conjunction with other rock magnetic properties, to better understand the BRD's emplacement and deformation history in the context of the MCR. AMS measures the directional dependence of low-field magnetic susceptibility, and is used to infer a shape-preferred orientation of magnetic minerals within a rock, which can be related to specific emplacement mechanisms (e.g. directional flow or settling). Preliminary analysis of AMS at 20 sites within the southern half of the BRD (with 4-7 samples per site) shows maximum susceptibility values between 4.48 x 10-6 and 2.22 x 10-4 m 3/kg (1165 and 65400 ?SI). Most specimens display nearly isotropic AMS ellipsoids (Pj < 1.15) with minor degrees of prolateness and oblateness. However, about 20% of specimens have higher anisotropies (Pj between 1.15 and 1.67) and higher degrees of oblateness and prolateness. Variations in AMS properties may reflect differences in concentration and composition of magnetic minerals, as well as emplacement mechanisms. Measurements of susceptibility as a function of temperature yield Curie points between 470 and 570 °C, indicating the presence of low-titanium titanomagnetite. Major hysteresis loops show coercivities between 1 and 25 mT, consistent with titanomagnetite as the dominant remanence carrier.

  10. Magnetic Fields: Visible and Permanent.

    ERIC Educational Resources Information Center

    Winkeljohn, Dorothy R.; Earl, Robert D.

    1983-01-01

    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)

  11. Magnetic field therapy: a review.

    PubMed

    Markov, Marko S

    2007-01-01

    There is increasing interest in using permanent magnets for therapeutic purposes encouraged by basic science publications and clinical reports. Magnetotherapy provides a non invasive, safe, and easy method to directly treat the site of injury, the source of pain and inflammation, and other types of disease. The physiological bases for the use of magnetic fields for tissue repair as well as physical principles of dosimetry and application of various magnetic fields are subjects of this review. Analysis of the magnetic and electromagnetic stimulation is followed by a discussion of the advantage of magnetic field stimulation compared with electric current and electric field stimulation. PMID:17454079

  12. Magnetic anisotropy in Ta/CoFeB/MgO investigated by x-ray magnetic circular dichroism and first-principles calculation

    SciTech Connect

    Kanai, Shun; Tsujikawa, Masahito; Shirai, Masafumi; Miura, Yoshio; Matsukura, Fumihiro Ohno, Hideo

    2014-12-01

    We study the spin and orbital magnetic moments in Ta/Co{sub 0.4}Fe{sub 0.4}B{sub 0.2}/MgO by x-ray magnetic circular dichroism measurements as well as first-principles calculations, in order to clarify the origin of the perpendicular magnetic anisotropy. Both experimental and theoretical results show that orbital magnetic moment of Fe is more anisotropic than that of Co with respect to the magnetization direction. The anisotropy is larger for thinner CoFeB, indicating that Fe atoms at the interface with MgO contribute more than Co to the observed perpendicular magnetic anisotropy.

  13. What Are Electric and Magnetic Fields? (EMF)

    MedlinePLUS

    ... Print this page Share What are Electric and Magnetic Fields? (EMF) Electric and Magnetic Fields Electricity is an essential part of our ... we take for granted. What are electric and magnetic fields? Electric and magnetic fields (EMF) are invisible ...

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

    SciTech Connect

    Staa, F. von; Hempel, K.A.; Artz, H.

    1995-11-01

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

  15. Photonic Magnetic Field Sensor

    NASA Astrophysics Data System (ADS)

    Wyntjes, Geert

    2002-02-01

    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.

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

    SciTech Connect

    Antropov, Vladimir; Ke, Liqin; Aberg, Daniel

    2014-07-11

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

  17. Structural controlled magnetic anisotropy in Heusler L1{sub 0}-MnGa epitaxial thin films

    SciTech Connect

    Wang Kangkang; Lu Erdong; Smith, Arthur R.; Knepper, Jacob W.; Yang Fengyuan

    2011-04-18

    Ferromagnetic L1{sub 0}-MnGa thin films have been epitaxially grown on GaN, sapphire, and MgO substrates using molecular beam epitaxy. Using diffraction techniques, the epitaxial relationships are determined. It is found that the crystalline orientation of the films differ due to the influence of the substrate. By comparing the magnetic anisotropy to the structural properties, a clear correlation could be established indicating that the in-plane and out-of-plane anisotropy is directly determined by the crystal orientation of the film and could be controlled via selection of the substrates. This result could be helpful in tailoring magnetic anisotropy in thin films for spintronic applications.

  18. Interface effect on the magnetic anisotropy of CoPt clusters

    NASA Astrophysics Data System (ADS)

    Rohart, S.; Raufast, C.; Favre, L.; Bernstein, E.; Bonet, E.; Wernsdorfer, W.; Dupuis, V.

    2007-09-01

    We study the magnetic anisotropy of CoPt clusters produced by condensation of a stoichiometric vapor with an inert gas (helium) and co-deposited with various matrices. From electron transmission microscopy we show that the clusters have a mean diameter of about 2 nm with a narrow size distribution and present the FCC A1 disordered phase. At high temperature, the clusters display a superparamagnetic behavior. The transition to the blocked state enables us to determine the clusters magnetic anisotropy energy (MAE). From a careful analysis, we show in the one hand that CoPt clusters present a higher volume and intrinsic surface MAE than pure Co ones. In the other hand, the presence of platinum at the interface in CoPt clusters decreases the strong interfacial exchange anisotropy observed for Co clusters embedded in MgO.

  19. Magnetic Propeller for Uniform Magnetic Field Levitation

    E-print Network

    Krinker, Mark

    2008-01-01

    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.

  20. Magnetic Propeller for Uniform Magnetic Field Levitation

    E-print Network

    Mark Krinker; Alexander Bolonkin

    2008-07-12

    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.

  1. Anisotropy and microstructure of Sm2(Co,Fe,Cu,Zr)17 magnetic materials. Final report, January 1982-January 1983

    SciTech Connect

    Fidler, J.; Grossinger, R.; Kirchmayr, H.; Skalicky, P.

    1983-05-01

    The present report is divided into two parts, the anisotropy measurements and the microstructural investigations of Sm2(Co,Fe,Cu,Zr)17 magnetic materials. Section I shows that the pulsed field technique is a versatile extension of a static magnetometer. Beside the possibility of generating fields up to 280 k theta e it can be used an an instrument with specific possibilities. An example for this is the SPD-technique which delivers even for polycrystalline samples - a value for the anisotropy field Ha. Up to now no clear correlation between the magnetic parameters like coercivity or energy product and the absolute value of Ha is possible. However, the knowledge of Ha allows the application of models which may help to understand the occurrence of these parameters. The temperature dependence of Ha should be mainly determined by the temperature dependence of the magnetization of the Sm sublattice. If this is known the validity of the One Ion Model can be tested. The role of the partly substituted Co sublattice is not so clear. More accurate M(T) measurements should be done. The influence of the inter-atomic distance on Ha(T), which should exist according to to an extended One Ion model, necessitates the knowledge of the thermal expansion.

  2. Magnetic phase diagram of the triangular lattice antiferromagnet ABX 3 under high magnetic field

    NASA Astrophysics Data System (ADS)

    Asano, Takayuki; Ajiro, Yoshitami; Mekata, Mamoru; Aruga Katori, Hiroko; Goto, Tsuneaki

    1994-07-01

    Our recent experimental study on the magnetic phase diagrams of stacked triangular lattice antiferromagnets (TAL-AF) is summarized. The precise magnetization measurements in the temperature range between 1.4 and 20 K under static magnetic fields up to 12 T have revealed that the magnetic field versus temperature phase diagrams of the ABX 3 compounds are classified into two types depending on the difference in their magnetic anisotropies in agreement with the theoretical prediction. In the case of the XY TAL-AF, CsMnBr 3 and RbMnBr 3 with an easy plane anisotropy, only a single transition is observed at zero field but it splits into two successive transitions under finite fields in the basal plane. On the other hand, in the case of the Ising-like TAL-AF, CsNiBr 3 and CsMnI 3 with an easy axis anisotropy, two successive transitions are observed at zero field and these are merged into a single transition at the multicritical point under finite fields parallel to the c-axis and a line of the spin-flop transition also meets this point.

  3. Surface magnetic anisotropy in nearly zero magnetostrictive CAW and GCAW by FMR measurements

    NASA Astrophysics Data System (ADS)

    Chiriac, Horia; Lupu, Nicoleta; Fecioru, Alin-Mihai; Óvári, Tibor-Adrian

    2005-04-01

    The surface anisotropy distribution in conventional amorphous wires (CAW) and glass-coated microwires (GCAW) with nearly zero magnetostriction and nominal composition Co 68.15Fe 4.35Si 12.5B 15 is analyzed by ferromagnetic resonance (FMR) measurements. The derivative resonance spectrum changes with applied tensile stress and torque. The surface anisotropy fields were calculated for both type wires. The experimental results are explained considering the coupling between magnetostriction and applied stress.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  5. Magnetic phase diagram and anisotropy of pseudoternary (Er/sub x/Dy/sub 1-//sub x/)/sub 2/Fe/sub 14/B compounds

    SciTech Connect

    Ibarra, M.R.; Algarabel, P.A.; Marquina, C.; Arnaudas, J.I.; del Moral, A.; Pareti, L.; Moze, O.; Marusi, G.; Solzi, M.

    1989-04-01

    A complete study of the magnetic phase diagram and magnetic anisotropy of pseudoternary (Er/sub x/Dy/sub 1-//sub x/)/sub 2/Fe/sub 14/B compounds has been carried out by the use of low-field ac magnetic susceptibility, magnetization, and singular-point detection measurements on magnetically aligned samples. A cone magnetic structure has been observed in compounds with 0.6less than or equal tox<0.9, even at low temperatures, and the thermal dependence of the cone angle for each concentration has been determined. Substitution of Er by Dy gives rise to a significant modification of the magnitude and temperature dependence of the anisotropy field H/sub A//sup '/ (i.e., the field on the basal plane), a linear dependence being observed with Dy concentration at 293 K. The present data have been interpreted in terms of a crystalline-electric-field--mean-field model. The inclusion of only second- and fourth-order crystal-field terms is enough to account for the phase diagram and the cone magnetic structure. The fourth-order terms should necessarily be included into the Hamiltonian in order to account for the variation of angle of the cone magnetic structure, both with temperature and concentration.

  6. Leptogenesis and primordial magnetic fields

    SciTech Connect

    Long, Andrew J.; Sabancilar, Eray; Vachaspati, Tanmay E-mail: eray.sabancilar@asu.edu

    2014-02-01

    The anomalous conversion of leptons into baryons during leptogenesis is shown to produce a right-handed helical magnetic field; in contrast, the magnetic field produced during electroweak baryogenesis is known to be left-handed. If the cosmological medium is turbulent, the magnetic field evolves to have a present day coherence scale ? 10 pc and field strength ? 10{sup ?18} Gauss. This result is insensitive to the energy scale at which leptogenesis took place. Observations of the amplitude, coherence scale, and helicity of the intergalactic magnetic field promise to provide a powerful probe of physics beyond the Standard Model and the very early universe.

  7. Fast superconducting magnetic field switch

    DOEpatents

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

    1996-01-01

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

  8. Fast superconducting magnetic field switch

    DOEpatents

    Goren, Y.; Mahale, N.K.

    1996-08-06

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

  9. Martian external magnetic field proxies

    NASA Astrophysics Data System (ADS)

    Langlais, Benoit; Civet, Francois

    2015-04-01

    Mars possesses no dynamic magnetic field of internal origin as it is the case for the Earth or for Mercury. Instead Mars is characterized by an intense and localized magnetic field of crustal origin. This field is the result of past magnetization and demagnetization processes, and reflects its evolution. The Interplanetary Magnetic Field (IMF) interacts with Mars' ionized environment to create an external magnetic field. This external field is weak compared to lithospheric one but very dynamic, and may hamper the detailed analysis of the internal magnetic field at some places or times. Because there are currently no magnetic field measurements made at Mars' surface, it is not possible to directly monitor the external field temporal variability as it is done in Earth's ground magnetic observatories. In this study we examine to indirect ways of quantifying this external field. First we use the Advanced Composition Explorer (ACE) mission which measures the solar wind about one hour upstream of the bow-shock resulting from the interaction between the solar wind and the Earth's internal magnetic field. These measurements are extrapolated to Mars' position taking into account the orbital configurations of the Mars-Earth system and the velocity of particles carrying the IMF. Second we directly use Mars Global Surveyor magnetic field measurements to quantify the level of variability of the external field. We subtract from the measurements the internal field which is otherwise modeled, and bin the residuals first on a spatial and then on a temporal mesh. This allows to compute daily or semi daily index. We present a comparison of these two proxies and demonstrate their complementarity. We also illustrate our analysis by comparing our Martian external field proxies to terrestrial index at epochs of known strong activity. These proxies will especially be useful for upcoming magnetic field measurements made around or at the surface of Mars.

  10. Magnetic field modification of optical magnetic dipoles.

    PubMed

    Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David

    2015-03-11

    Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate. PMID:25646869

  11. Spin Hall switching of the magnetization in Ta/TbFeCo structures with bulk perpendicular anisotropy

    SciTech Connect

    Zhao, Zhengyang; Jamali, Mahdi; Smith, Angeline K.; Wang, Jian-Ping

    2015-03-30

    Spin-orbit torques are studied in Ta/TbFeCo/MgO patterned structures, where the ferrimagnetic material TbFeCo provides a strong bulk perpendicular magnetic anisotropy (bulk-PMA) independent of the interfaces. The current-induced magnetization switching in TbFeCo is investigated in the presence of a perpendicular, longitudinal, or transverse field. An unexpected partial-switching phenomenon is observed in the presence of a transverse field unique to our bulk-PMA material. It is found that the anti-damping torque related with spin Hall effect is very strong, and a spin Hall angle is determined to be 0.12. The field-like torque related with Rashba effect is unobservable, suggesting that the interface play a significant role in Rashba-like torque.

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

    SciTech Connect

    Kozio?-Rachwa?, A.; ?l?zak, T.; Przewo?nik, J.; Skowro?ski, W.; Stobiecki, T.; Wilgocka-?l?zak, D.; Qin, Q. H.; Dijken, S. van; Korecki, J.

    2013-12-14

    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}.

  13. Stress-induced magnetic anisotropy in Xe-ion-irradiated Ni thin films

    NASA Astrophysics Data System (ADS)

    Zhang, Kun

    2006-01-01

    Samples consisting of 75 nm Ni films deposited on Si substrates were bent mechanically and irradiated with 200 keV Xe-ions at a dose of 4 × 1014 ions/cm2. Magneto-optical Kerr effect, Rutherford backscattering spectrometry and X-ray diffraction were used to investigate the changes in the magnetic and microstructural properties. Perfect uniaxial magnetic anisotropy was found in the Ni films after irradiation and removal of the samples from the target holder. The magnetic behavior is shown to be very sensitive to the external stress produced in the films. With increasing curvature of the bent samples (?2 m-1), the easy axis of the magnetic anisotropy rotated in the direction perpendicular to the bending axis, indicating a compressive stress in the films after irradiation and relaxation.

  14. Volume191,number6 CHEMICALPHYSICSLETTERS 17April 1992 The magnetic hyperpolarizability anisotropy of the neon atom

    E-print Network

    Helgaker, Trygve

    Volume191,number6 CHEMICALPHYSICSLETTERS 17April 1992 The magnetic hyperpolarizability anisotropy rightsreserved. 599 #12;Volume 19l, number 6 CHEMICAL PHYSICS LETTERS 17 April 1992 consistently discuss the q be obtained as mC=2nNAAq/27, ( 1 ) where NA is Avogadro's constant. For comparison with other works, 1 au of q

  15. Evolution of twisted magnetic fields

    SciTech Connect

    Zweibel, E.G.; Boozer, A.H.

    1985-02-01

    The magnetic field of the solar corona evolves quasistatically in response to slowly changing photospheric boundary conditions. The magnetic topology is preserved by the low resistivity of the solar atmosphere. We show that a magnetic flux coordinate system simplifies the problem of calculating field evolution with invariant topology. As an example, we calculate the equilibrium of a thin magnetic flux tube with small twist per unit length.

  16. Oscillatory interlayer exchange coupling in MgO tunnel junctions with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Nistor, Lavinia E.; Rodmacq, Bernard; Auffret, Stéphane; Schuhl, Alain; Chshiev, Mairbek; Dieny, Bernard

    2010-06-01

    The influence of magnetic layer thickness on the interlayer coupling through a tunnel barrier is investigated in Co/MgO/Co structures with perpendicular anisotropy. Despite the rather large MgO thickness, a clear antiferromagnetic coupling is observed. It oscillates with increasing magnetic layer thickness, in agreement with theories on indirect coupling through insulating spacers. Although the average interlayer coupling strength decreases with increasing annealing temperature, constant period and amplitude of these oscillations are observed for all annealing temperatures.

  17. Exposure guidelines for magnetic fields

    SciTech Connect

    Miller, G.

    1987-12-01

    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.

  18. Magnetic-field-dosimetry system

    DOEpatents

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

    1981-01-21

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  20. Electric Field Effect on Magnetism in Metallic Ultra-thin Films

    NASA Astrophysics Data System (ADS)

    Chiba, Daichi

    2015-10-01

    Recent experimental developments on the electric field effect on magnetism in metallic magnetic materials are reviewed. The change in the electron density at the surface of metallic ultra-thin magnets by the application of an electric field results in modulations of the Curie temperature, magnetic moment, magnetic anisotropy, and domain wall velocity. The study focused on this paper is the electric field effect on the Curie temperature (magnetic phase transition) in Pt/Co ultra-thin film systems. Electric field modifications of the magnetic moment induced by ferromagnetic proximity effects in Pd, which is usually a nonmagnetic element, are also discussed.

  1. The formation of linear aggregates in magnetic hyperthermia: implications on specific absorption rate and magnetic anisotropy.

    PubMed

    Saville, Steven L; Qi, Bin; Baker, Jonathon; Stone, Roland; Camley, Robert E; Livesey, Karen L; Ye, Longfei; Crawford, Thomas M; Mefford, O Thompson

    2014-06-15

    The design and application of magnetic nanoparticles for use as magnetic hyperthermia agents has garnered increasing interest over the past several years. When designing these systems, the fundamentals of particle design play a key role in the observed specific absorption rate (SAR). This includes the particle's core size, polymer brush length, and colloidal arrangement. While the role of particle core size on the observed SAR has been significantly reported, the role of the polymer brush length has not attracted as much attention. It has recently been reported that for some suspensions linear aggregates form in the presence of an applied external magnetic field, i.e. chains of magnetic particles. The formation of these chains may have the potential for a dramatic impact on the biomedical application of these materials, specifically the efficiency of the particles to transfer magnetic energy to the surrounding cells. In this study we demonstrate the dependence of SAR on magnetite nanoparticle core size and brush length as well as observe the formation of magnetically induced colloidal arrangements. Colloidally stable magnetic nanoparticles were demonstrated to form linear aggregates in an alternating magnetic field. The length and distribution of the aggregates were dependent upon the stabilizing polymer molecular weight. As the molecular weight of the stabilizing layer increased, the magnetic interparticle interactions decreased therefore limiting chain formation. In addition, theoretical calculations demonstrated that interparticle spacing has a significant impact on the magnetic behavior of these materials. This work has several implications for the design of nanoparticle and magnetic hyperthermia systems, while improving understanding of how colloidal arrangement affects SAR. PMID:24767510

  2. Pulsed field probe of real time magnetization dynamics in magnetic nanoparticle systems

    NASA Astrophysics Data System (ADS)

    Foulkes, T.; Syed, M.; Taplin, T.

    2015-05-01

    Magnetic nanoparticles (MNPs) are extensively used in biotechnology. These applications rely on magnetic properties that are a keen function of MNP size, distribution, and shape. Various magneto-optical techniques, including Faraday Rotation (FR), Cotton-Mouton Effect, etc., have been employed to characterize magnetic properties of MNPs. Generally, these measurements employ AC or DC fields. In this work, we describe the results from a FR setup that uses pulsed magnetic fields and an analysis technique that makes use of the entire pulse shape to investigate size distribution and shape anisotropy. The setup employs a light source, polarizing components, and a detector that are used to measure the rotation of light from a sample that is subjected to a pulsed magnetic field. This magnetic field "snapshot" is recorded alongside the intensity pulse of the sample's response. This side by side comparison yields useful information about the real time magnetization dynamics of the system being probed. The setup is highly flexible with variable control of pulse length and peak magnitude. Examining the raw data for the response of bare Fe3O4 and hybrid Au and Fe3O4 nanorods reveals interesting information about Brownian relaxation and the hydrodynamic size of these nanorods. This analysis exploits the self-referencing nature of this measurement to highlight the impact of an applied field on creating a field induced transparency for a longitudinal measurement. Possible sources for this behavior include shape anisotropy and field assisted aggregate formation.

  3. Seismic anisotropy and anisotropy of magnetic susceptibility (AMS) in the Pelona-Orocopia-Rand schist in the Mojave region of southern California

    NASA Astrophysics Data System (ADS)

    Brownlee, S. J.; Hacker, B. R.; Feinberg, J. M.; Chapman, A. D.; Saleeby, J.; Seward, G. G.

    2013-12-01

    Our current interpretation of the composition and elastic properties of the middle and lower crust depends strongly on seismic observations. Advances in seismic methods are leading to more studies focused on seismic anisotropy in the lower crust. With increasing observations of lower crustal anisotropy, the need for a more comprehensive characterization of the seismic properties of candidate lower crustal materials is growing. In addition, links between seismic anisotropy and other geophysical parameters need to be investigated. This work combines measurements of anisotropy of magnetic susceptibility (AMS) and electron backscatter diffraction (EBSD)-based calculations of seismic anisotropy in samples of the Pelona-Orocopia-Rand (POR) schist from the Mojave region of southern California. The POR schist is thought to comprise much of the lower crust of southern California, and is one of the archetypes for understanding shallow slab subduction and subduction erosion. The goals of this study are to characterize the: 1) seismic anisotropy of the POR schist and its relationship to observed crustal anisotropy in the region, and 2) relationship between seismic anisotropy and AMS. Velocity anisotropy in individual samples of the POR schist ranges from ~2-11% in VP and ~3-15% in VS, which is consistent with results of Porter et al. (2011) for lower crustal anisotropy in southern California from analysis of receiver functions. When all schist samples are averaged together to approximate the bulk schist, the velocity anisotropy is significantly reduced to ~6% in Vs and ~8% in Vs, lower than the average values inferred by Porter et al. (2011). AMS results indicate that the directions of maximum and minimum susceptibility are subparallel to Vp-max and Vp-min, respectively (Figure 1). The magnitude of anisotropy in AMS does not show as strong a correlation with magnitude of seismic anisotropy, and may have a stronger dependence on magnetic mineralogy. These results indicate that AMS measurements may provide a proxy for maximum and minimum Vp directions. Figure 1. Maximum and minimum AMS directions (filled symbols) correlate with directions of maximum and minimum Vp (open symbols). Both properties have maxima within the foliation, ~parallel to lineation, and minima perpendicular to foliation. Equal area, lower hemisphere projection.

  4. Stress-mediated magnetic anisotropy and magnetoelastic coupling in epitaxial multiferroic PbTiO3-CoFe2O4 nanostructures

    NASA Astrophysics Data System (ADS)

    Tsai, C. Y.; Chen, H. R.; Chang, F. C.; Tsai, W. C.; Cheng, H. M.; Chu, Y. H.; Lai, C. H.; Hsieh, W. F.

    2013-04-01

    This study reports a self-assembled multiferroic nanostructure, composed of PbTiO3 (PTO) pillars embedded in a CoFe2O4 (CFO) matrix, deposited on MgO(001) by pulsed laser deposition. The epitaxial relationship in the PTO-CFO nanostructure is (100)[101]PTO?(001)[101]CFO?(001)[101]MgO, confirming the in-plane aligned polarization of PTO. The perpendicular magnetic anisotropy of this thin film results from the magnetoelastic anisotropy that exceeds the shape anisotropy. The increased frequency and the enhanced intensity of the tetrahedral (T-) site phonon modes by increasing the magnetic field indicate strong magnetoelastic coupling through magnetostriction in this multiferroic nanostructure. The anisotropic Raman strength enhancement of the T-site phonon along different directions suggests the magnetoelastic coupling is most efficient in the in-plane direction.

  5. Magnetic anisotropy induced by crystal distortion in Ge1-xMnxTe/PbTe//KCl (001) ferromagnetic semiconductor layers

    NASA Astrophysics Data System (ADS)

    Knoff, W.; ?usakowski, A.; Domaga?a, J. Z.; Minikayev, R.; Taliashvili, B.; ?usakowska, E.; PieniÄ ?ek, A.; Szczerbakow, A.; Story, T.

    2015-09-01

    Ferromagnetic resonance (FMR) study of magnetic anisotropy is presented for thin layers of IV-VI diluted magnetic semiconductor Ge1-xMnxTe with x = 0.14 grown by molecular beam epitaxy on KCl (001) substrate with a thin PbTe buffer. Analysis of the angular dependence of the FMR resonant field reveals that an easy magnetization axis is located near to the normal to the layer plane and is controlled by two crystal distortions present in these rhombohedral Ge1-xMnxTe layers: the ferroelectric distortion with the relative shift of cation and anion sub-lattices along the [111] crystal direction and the biaxial in-plane, compressive strain due to thermal mismatch.

  6. Magnetic field depression within electron holes

    NASA Astrophysics Data System (ADS)

    Vasko, I. Y.; Agapitov, O. V.; Mozer, F.; Artemyev, A. V.; Jovanovic, D.

    2015-04-01

    We analyze electron holes that are spikes of the electrostatic field (up to 500 mV/m) observed by Van Allen Probes in the outer radiation belt. The unexpected feature is the magnetic field depression of about several tens of picotesla within many of the spikes. The earlier observations showed amplification or negligible perturbations of the magnetic field within the electron holes. We suggest that the observed magnetic field depression is due to the diamagnetic current of hot and highly anisotropic population of electrons trapped within the electron holes. The required trapped population should have a density up to 65% of the background plasma density, a temperature up to several keV, and a temperature anisotropy T?/T?˜2. We argue that the observed electron holes could be generated due to injections of highly anisotropic plasma sheet electrons into the outer radiation belt. These electron holes may present a source of the seed population due to transport of trapped electrons to higher latitudes and can be potentially used for distant probing of plasma properties in their source region.

  7. Spin-fluctuation mechanism of anomalous temperature dependence of magnetocrystalline anisotropy in itinerant magnets

    SciTech Connect

    Zhuravlev, I. A.; Antropov, V. P.; Belashchenko, K. D.

    2015-11-16

    The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe1–xCox)2B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit “hot spots” by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization. This peculiar electronic mechanisms is in stark contrast to the assumptions of the existing models.

  8. Pressure anisotropy generation in a magnetized plasma configuration with a shear flow velocity

    E-print Network

    De Camillis, S; Califano, F; Pegoraro, F

    2015-01-01

    The nonlinear evolution of the Kelvin Helmholtz instability in a magnetized plasma with a perpendicular flow close to, or in, the supermagnetosonic regime can produce a significant parallel-to-perpendicular pressure anisotropy. This anisotropy, localized inside the flow shear region, can make the configuration unstable either to the mirror or to the firehose instability and, in general, can affect the development of the KHI. The interface between the solar wind and the Earth's magnetospheric plasma at the magnetospheric equatorial flanks provides a relevant setting for the development of this complex nonlinear dynamics.

  9. Magnetic anisotropy engineering: Single-crystalline Fe films on ion eroded ripple surfaces

    SciTech Connect

    Liedke, M. O.; Koerner, M.; Lenz, K.; Grossmann, F.; Facsko, S.; Fassbender, J.

    2012-06-11

    We present a method to preselect the direction of an induced in-plane uniaxial magnetic anisotropy (UMA) in thin single-crystalline Fe films on MgO(001). Ion beam irradiation is used to modulate the MgO(001) surface with periodic ripples on the nanoscale. The ripple direction determines the orientation of the UMA, whereas the intrinsic cubic anisotropy of the Fe film is not affected. Thus, it is possible to superimpose an in-plane UMA with a precision of a few degrees - a level of control not reported so far that can be relevant for example in spintronics.

  10. Spin-fluctuation mechanism of anomalous temperature dependence of magnetocrystalline anisotropy in itinerant magnets

    DOE PAGESBeta

    Zhuravlev, I. A.; Antropov, V. P.; Belashchenko, K. D.

    2015-11-16

    The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe1–xCox)2B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit “hot spots” by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization. This peculiar electronic mechanisms is in stark contrast to the assumptions of the existing models.

  11. Spin-Fluctuation Mechanism of Anomalous Temperature Dependence of Magnetocrystalline Anisotropy in Itinerant Magnets

    NASA Astrophysics Data System (ADS)

    Zhuravlev, I. A.; Antropov, V. P.; Belashchenko, K. D.

    2015-11-01

    The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe1 -xCox )2B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit "hot spots" by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization due to these peculiar electronic mechanisms, which contrast starkly with those assumed in existing models.

  12. Spin-Fluctuation Mechanism of Anomalous Temperature Dependence of Magnetocrystalline Anisotropy in Itinerant Magnets.

    PubMed

    Zhuravlev, I A; Antropov, V P; Belashchenko, K D

    2015-11-20

    The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe_{1-x}Co_{x})_{2}B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit "hot spots" by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization due to these peculiar electronic mechanisms, which contrast starkly with those assumed in existing models. PMID:26636868

  13. Vestibular stimulation by magnetic fields.

    PubMed

    Ward, Bryan K; Roberts, Dale C; Della Santina, Charles C; Carey, John P; Zee, David S

    2015-04-01

    Individuals working next to strong static magnetic fields occasionally report disorientation and vertigo. With the increasing strength of magnetic fields used for magnetic resonance imaging studies, these reports have become more common. It was recently learned that humans, mice, and zebrafish all demonstrate behaviors consistent with constant peripheral vestibular stimulation while inside a strong, static magnetic field. The proposed mechanism for this effect involves a Lorentz force resulting from the interaction of a strong static magnetic field with naturally occurring ionic currents flowing through the inner ear endolymph into vestibular hair cells. The resulting force within the endolymph is strong enough to displace the lateral semicircular canal cupula, inducing vertigo and the horizontal nystagmus seen in normal mice and in humans. This review explores the evidence for interactions of magnetic fields with the vestibular system. PMID:25735662

  14. Magnetic fields around evolved stars

    NASA Astrophysics Data System (ADS)

    Leal-Ferreira, M.; Vlemmings, W.; Kemball, A.; Amiri, N.; Maercker, M.; Ramstedt, S.; Olofsson, G.

    2014-04-01

    A number of mechanisms, such as magnetic fields, (binary) companions and circumstellar disks have been suggested to be the cause of non-spherical PNe and in particular collimated outflows. This work investigates one of these mechanisms: the magnetic fields. While MHD simulations show that the fields can indeed be important, few observations of magnetic fields have been done so far. We used the VLBA to observe five evolved stars, with the goal of detecting the magnetic field by means of water maser polarization. The sample consists in four AGB stars (IK Tau, RT Vir, IRC+60370 and AP Lyn) and one pPN (OH231.8+4.2). In four of the five sources, several strong maser features were detected allowing us to measure the linear and/or circular polarization. Based on the circular polarization detections, we infer the strength of the component of the field along the line of sight to be between ~30 mG and ~330 mG in the water maser regions of these four sources. When extrapolated to the surface of the stars, the magnetic field strength would be between a few hundred mG and a few Gauss when assuming a toroidal field geometry and higher when assuming more complex magnetic fields. We conclude that the magnetic energy we derived in the water maser regions is higher than the thermal and kinetic energy, leading to the conclusion that, indeed, magnetic fields probably play an important role in shaping Planetary Nebulae.

  15. Modification of structure and magnetic anisotropy of epitaxial CoFe?O? films by hydrogen reduction

    SciTech Connect

    Chen, Aiping; Poudyal, Narayan; Xiong, Jie; Liu, J. Ping; Jia, Quanxi

    2015-03-16

    Heteroepitaxial CoFe?O? (CFO) thin films with different thicknesses were deposited on MgO (001) substrates. The as-deposited CFO films show a clear switching of magnetic anisotropy with increasing film thickness. The thinner films (<100 nm) show a perpendicular magnetic anisotropy due to the out-of-plane compressive strain. The thicker films exhibit an in-plane easy axis owing to the dominating shape anisotropy effect. The magnetostriction coefficient of CFO films is estimated to be ?[001] =-188 × 10??. Metallic CoFe? films were obtained by annealing the as-deposited CFO films in forming gas (Ar 93% + H? 7%) at 450 °C. XRD shows that CoFe? films are textured out-of-plane and aligned in-plane, owing to lattice matching between CoFe? and MgO substrate. TEM results indicate that as-deposited films are continuous while the annealed films exhibit a nanopore mushroom structure. The magnetic anisotropy of CoFe? films is dominated by the shape effect. The results demonstrate that hydrogen reduction can be effectively used to modify microstructures and physical properties of complex metal oxide materials.

  16. Magnetic anisotropy in Shiba bound states across a quantum phase transition.

    PubMed

    Hatter, Nino; Heinrich, Benjamin W; Ruby, Michael; Pascual, Jose I; Franke, Katharina J

    2015-01-01

    The exchange coupling between magnetic adsorbates and a superconducting substrate leads to Shiba states inside the superconducting energy gap and a Kondo resonance outside the gap. The exchange coupling strength determines whether the quantum many-body ground state is a Kondo singlet or a singlet of the paired superconducting quasiparticles. Here we use scanning tunnelling spectroscopy to identify the different quantum ground states of manganese phthalocyanine on Pb(111). We observe Shiba states, which are split into triplets by magnetocrystalline anisotropy. Their characteristic spectral weight yields an unambiguous proof of the nature of the quantum ground state. Our results provide experimental insights into the phase diagram of a magnetic impurity on a superconducting host and shine light on the effects induced by magnetic anisotropy on many-body interactions. PMID:26603561

  17. Magnetic anisotropy in Shiba bound states across a quantum phase transition

    PubMed Central

    Hatter, Nino; Heinrich, Benjamin W.; Ruby, Michael; Pascual, Jose I.; Franke, Katharina J.

    2015-01-01

    The exchange coupling between magnetic adsorbates and a superconducting substrate leads to Shiba states inside the superconducting energy gap and a Kondo resonance outside the gap. The exchange coupling strength determines whether the quantum many-body ground state is a Kondo singlet or a singlet of the paired superconducting quasiparticles. Here we use scanning tunnelling spectroscopy to identify the different quantum ground states of manganese phthalocyanine on Pb(111). We observe Shiba states, which are split into triplets by magnetocrystalline anisotropy. Their characteristic spectral weight yields an unambiguous proof of the nature of the quantum ground state. Our results provide experimental insights into the phase diagram of a magnetic impurity on a superconducting host and shine light on the effects induced by magnetic anisotropy on many-body interactions. PMID:26603561

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  19. Cosmic Magnetic Fields - An Overview

    NASA Astrophysics Data System (ADS)

    Wielebinski, Richard; Beck, Rainer

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

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

    PubMed

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

    2014-10-01

    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 10(4) 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. PMID:25212432

  1. 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 ...

  2. Origin of cosmic magnetic fields.

    PubMed

    Campanelli, Leonardo

    2013-08-01

    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

  3. Measurements of magnetic field alignment

    SciTech Connect

    Kuchnir, M.; Schmidt, E.E.

    1987-11-06

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

  4. In-plane current induced domain wall nucleation and its stochasticity in perpendicular magnetic anisotropy Hall cross structures

    NASA Astrophysics Data System (ADS)

    Sethi, P.; Murapaka, C.; Lim, G. J.; Lew, W. S.

    2015-11-01

    Hall cross structures in magnetic nanowires are commonly used for electrical detection of magnetization reversal in which a domain wall (DW) is conventionally nucleated by a local Oersted field. In this letter, we demonstrate DW nucleation in Co/Ni perpendicular magnetic anisotropy nanowire at the magnetic Hall cross junction. The DWs are nucleated by applying an in-plane pulsed current through the nanowire without the need of a local Oersted field. The change in Hall resistance, detected using anomalous Hall effect, is governed by the magnetic volume switched at the Hall junction, which can be tuned by varying the magnitude of the applied current density and pulse width. The nucleated DWs are driven simultaneously under the spin transfer torque effect when the applied current density is above a threshold. The possibility of multiple DW generation and variation in magnetic volume switched makes nucleation process stochastic in nature. The in-plane current induced stochastic nature of DW generation may find applications in random number generation.

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

    NASA Astrophysics Data System (ADS)

    Garshelis, I. J.; Crevecoeur, G.

    2014-05-01

    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.

  6. The MAVEN Magnetic Field Investigation

    NASA Astrophysics Data System (ADS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2015-12-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a resolution of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05 %. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers—multiple rotations about the spacecraft x and z axes—to characterize spacecraft fields and/or instrument offsets in flight.

  7. The MAVEN Magnetic Field Investigation

    NASA Astrophysics Data System (ADS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2015-06-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a resolution of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05 %. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers—multiple rotations about the spacecraft x and z axes—to characterize spacecraft fields and/or instrument offsets in flight.

  8. The MAVEN Magnetic Field Investigation

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2014-01-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a quantization uncertainty of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05%. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers - multiple rotations about the spacecraft x and z axes - to characterize spacecraft fields and/or instrument offsets in flight.

  9. Fast magnetization switching in GaMnAs induced by electrical fields

    NASA Astrophysics Data System (ADS)

    Balestrière, P.; Devolder, T.; Kim, Joo-Von; Lecoeur, P.; Wunderlich, J.; Novák, V.; Jungwirth, T.; Chappert, C.

    2011-12-01

    We study the electrical field induced magnetization reversal in a GaMnAs thin film magnet at the nanosecond scale. Quasi-static electrical fields deplete partially the magnetic material, reducing its magneto-crystalline cubic anisotropy and affecting its transport properties. We demonstrate that electrical field pulses can trigger the nucleation of domains with reversed magnetization. Pulse durations of 2.5 ns are enough to induce the nucleation, indicating precessional effects in the dynamical magnetic response. Full reversal can be obtained with 10 ns and 3 V and the assistance of magnetic fields substantially lower than the coercivity of the material in the absence of gate voltage.

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

    NASA Astrophysics Data System (ADS)

    Kota, Yohei; Sakuma, Akimasa

    2012-08-01

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

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

    PubMed Central

    Lahtinen, Tuomas H. E.; Franke, Kévin J. A.; van Dijken, Sebastiaan

    2012-01-01

    Spintronic devices currently rely on magnetic switching or controlled motion of domain walls by an external magnetic field or spin-polarized current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including enhanced functionality and low power consumption. Here we report on an approach to electrically control local magnetic properties, including the writing and erasure of regular ferromagnetic domain patterns and the motion of magnetic domain walls, in CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer from ferroelastic domains in ferroelectric media to continuous magnetostrictive films with negligible magnetocrystalline anisotropy. Optical polarization microscopy of both ferromagnetic and ferroelectric domain structures reveals that domain correlations and strong inter-ferroic domain wall pinning persist in an applied electric field. This leads to an unprecedented electric controllability over the ferromagnetic microstructure, an accomplishment that produces giant magnetoelectric coupling effects and opens the way to electric-field driven spintronics. PMID:22355770

  12. Magnetic Field Control of the Quantum Chaotic Dynamics of Hydrogen Analogs in an Anisotropic Crystal Field

    SciTech Connect

    Zhou Weihang; Chen Zhanghai; Zhang Bo; Yu, C. H.; Lu Wei; Shen, S. C.

    2010-07-09

    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. The 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.

  13. Magnetic Field Control of the Quantum Chaotic Dynamics of Hydrogen Analogues in an Anisotropic Crystal Field

    E-print Network

    Weihang Zhou; Zhanghai Chen; Bo Zhang; C. H. Yu; Wei Lu; S. C. Shen

    2010-03-09

    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.

  14. Magnetic anisotropy and permeability in sputtered iron aluminum nitride thin-film materials

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Kuang

    Significant improvement in magnetic properties of FeXN (X = Al, Zr, Ta...) thin films deposited on the sloping surfaces, especially at 60°, was achieved by using various interlayer materials or proper sputtering conditions. The oblique incidence problems in permalloy and CoZrRe thin films were also greatly improved. Test heads fabricated using these materials showed improved permeability. Significant improvement of the thermal stability in FeXN thin films was also achieved. Sputtered at the reduced target-substrate spacing of 38 mm, 200 nm thick thermally stable FeXN thin films were obtained. They had hard axis coercivity ?0.1--2.0 Oe, easy axis coercivity ?1.5--3.0 Oe, Hk = 8--16 Oe and Bs = 19--20 kG. Results from transverse field annealing experiments in a uniform field of 700 Oe show no significant change of magnetic properties at 150°C for 3 hours. At 150°C for 24 hours, Hk decreased by 2--4 Oe. Their easy/hard axes did not rotate and the coercivity remained almost unchanged. This superior thermal stability of FeXN films is promising for high moment write heads. The effects of N doping on the magnetic and structural properties of a series of 100 nm FeAlN films sputtered in the presence of N partial pressures were investigated. Increasing N doping increased film resistivity but decreased MS. Extended x-ray absorption fine structure spectra of the short-range atomic order in the Fe(Al) lattices directly indicated that the N went into octahedral sites of bcc Fe and fcc Fe in alpha-Fe and gamma'-Fe 4N phases, respectively, and triggered the order-disorder phase transition observed in x-ray 0--20 diffraction spectra. Mild N doping decreased the grain size and reduced Hc. It also increased the local atomic disorder, which coincided with the maximal value of Ku and the in-plane anisotropic behaviors in the as-deposited films. The roles of N doping in FeXN film optimization processes and its effects on magnetic and structural properties, especially the uniaxial anisotropy and its thermal stability, were investigated. The locations/distributions of N incorporation in the films are being investigated and compared with the film properties.

  15. Characterization of the log lithology of cores LB-07A and LB-08A of the Bosumtwi impact structure by using the anisotropy of magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Schell, Christina; Schleifer, Norbert; Elbra, Tiiu

    Petrophysical data are commonly used for the discrimination of different lithologies, as the variation in mineralogy, texture, and porosity is accompanied by varying physical properties. A special field of investigation is the analysis of the directional dependence (anisotropy) of the petrophysical properties, which can provide further information on the characteristics of the lithologies, due to the fact that this parameter is different in the various rock-forming and rockchanging processes, e.g., deformation or sedimentation. To characterize the rocks in drill cores LB-07A and LB-08A, which were drilled into the deep crater moat and central uplift of the Bosumtwi impact structure, Ghana, samples were taken for the study of petrophysical properties. In the present work the magnetic properties of these samples were determined in the laboratory. The results are discussed in relation to the various lithologies represented by this sample suite. The shape and degree of magnetic anisotropy, in combination with the magnetic susceptibility, proved useful in distinguishing between the different lithologies present in the drill cores (polymict lithic breccia, suevite, shale component, and meta-graywacke). It was possible to correlate layers of high (shale component), ntermediate (graywacke, polymict lithic breccia), and low (suevite) anisotropy degree with the lithostratigraphic sequences determined for cores LB-07A and LB-08A. The shape of the anisotropy showed that foliation is most dominant within the shale component, whereas lineation is more pronounced in the meta-graywacke and polymict lithic breccia. An overall increase of the anisotropy degree was observed from core LB-07A towards core LB-08A. Thus magnetic anisotropy data provide a useful contribution towards an improved petrophysical characterization of the lithostratigraphic sequences in drillcores from the Bosumtwi impact structure.

  16. Sputtering of cobalt film with perpendicular magnetic anisotropy on disorder-free graphene

    SciTech Connect

    Jamali, Mahdi; Lv, Yang; Zhao, Zhengyang; Wang, Jian-Ping

    2014-10-15

    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.

  17. Modification of structure and magnetic anisotropy of epitaxial CoFe?O? films by hydrogen reduction

    DOE PAGESBeta

    Chen, Aiping; Poudyal, Narayan; Xiong, Jie; Liu, J. Ping; Jia, Quanxi

    2015-03-16

    Heteroepitaxial CoFe?O? (CFO) thin films with different thicknesses were deposited on MgO (001) substrates. The as-deposited CFO films show a clear switching of magnetic anisotropy with increasing film thickness. The thinner films (more »films are textured out-of-plane and aligned in-plane, owing to lattice matching between CoFe? and MgO substrate. TEM results indicate that as-deposited films are continuous while the annealed films exhibit a nanopore mushroom structure. The magnetic anisotropy of CoFe? films is dominated by the shape effect. The results demonstrate that hydrogen reduction can be effectively used to modify microstructures and physical properties of complex metal oxide materials.« less

  18. Magnons in ultrathin ferromagnetic films with a large perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Qin, H. J.; Zakeri, Kh.; Ernst, A.; Chuang, T.-H.; Chen, Y.-J.; Meng, Y.; Kirschner, J.

    2013-07-01

    We report on an experimental observation of high-energy magnon excitations in ultrathin ferromagnetic films with a perpendicular easy axis. We demonstrate that a transversally spin-polarized beam can be used to excite and probe the high-energy magnons within spin-polarized electron energy-loss spectroscopy experiments. The magnon dispersion relation and lifetime are probed over the entire surface Brillouin zone for a set of body-centered tetragonal FeCo films with a large perpendicular magnetic anisotropy. First-principles calculations reveal that in addition to the tetragonal distortion, which is the origin of the large perpendicular magnetic anisotropy, the interfacial electronic hybridization also has a considerable impact on the properties of magnons.

  19. Magnetic field dependence of critical currents in superconducting polycrystals

    SciTech Connect

    Kugel, K.I.; Lisovskaya, T.Y. ); Mints, R.G. )

    1992-02-10

    The authors study the dependence of critical current j{sub c} on magnetic field H in superconducting polycrystals which are considered as system of superconducting crystallites (isotropic or anisotropic) with Josephson contacts between them. Isotropy or anisotropy of contacts depends on the orientation of their crystallographic axes relatively to edges of contact planes. In this paper it is shown that for a system of randomly oriented isotropic contacts, the dependence j{sub c}(H) in a relatively wide field range has the asymptotic form j{sub c} {approximately} (InH)/H{sup 2}. This differs drastically from j{sub c}(H) for single contacts. Anisotropy effects due to large differences in London penetration depth {lambda} values corresponding to external magnetic field directed along different axes are analyzed in detail. It is shown that for uniaxal crystals with {lambda}{sub 1} = {lambda}{sub 2} {lt} {lambda}{sub 3}, this anisotropy leads to the relation j{sub c} {approximately} {radical}{lambda}{sub 3}/{lambda}{sub 1} for chaotic orientation of crystallites. The form of j{sub c}(H) curves for two different orientations of the magnetic field relatively to the transport current through the sample is found.

  20. Magnetization reversal in antiferromagnetically coupled [Pt/CoFeB]N1/Ru/[CoFeB/Pt]N2 structures with perpendicular anisotropy

    NASA Astrophysics Data System (ADS)

    Xiao, Yili; Chen, Shaohai; Zhang, Zongzhi; Ma, Bin; Jin, Q. Y.

    2013-05-01

    Magnetic interlayer coupling and magnetization switching characteristics have been investigated in synthetic antiferromagnetically coupled [Pt/CoFeB]N1/Ru/[CoFeB/Pt]N2 structures with perpendicular anisotropy. We observe an oscillatory behavior of the antiferromagnetic coupling with a period of 0.7 nm and a maximum coupling strength of 0.09 erg/cm2. The coupling field is shown to decrease rapidly with the increase of repetition number and measurement temperature. Depending on the repetition numbers of the two multilayers, magnetic hysteresis loops may or may not display a reversal feature of the net magnetic moment. Samples with large N have a bow-tie loop shape due to the formation of multi-domains. The analysis of magnetic moments and exchange coupling fields show that there exists a ˜0.4 nm thick magnetic dead layer mostly at the CoFeB/Ru interface.

  1. Interfacial oxygen migration and its effect on the magnetic anisotropy in Pt/Co/MgO/Pt films

    SciTech Connect

    Chen, Xi; Feng, Chun E-mail: ghyu@mater.ustb.edu.cn; Liu, Yang; Jiang, Shaolong; Hua Li, Ming; Hua Yu, Guang E-mail: ghyu@mater.ustb.edu.cn; Long Wu, Zheng; Yang, Feng

    2014-02-03

    This paper reports the interfacial oxygen migration effect and its induced magnetic anisotropy evolution in Pt/Co/MgO/Pt films. During depositing the MgO layer, oxygen atoms from the MgO combine with the neighboring Co atoms, leading to the formation of CoO at the Co/MgO interface. Meanwhile, the films show in-plane magnetic anisotropy (IMA). After annealing, most of the oxygen atoms in CoO migrate back to the MgO layer, resulting in obvious improvement of Co/MgO interface and the enhancement of effective Co-O orbital hybridization. These favor the evolution of magnetic anisotropy from IMA to perpendicular magnetic anisotropy (PMA). The oxygen migration effect is achieved by the redox reaction at the Co/MgO interface. On the contrary, the transfer from IMA to PMA cannot be observed in Pt/Co/Pt films due to the lack of interfacial oxygen migration.

  2. Anisotropy of the Magnetic Susceptibility of the Alnö alkaline and carbonatite igneous complex

    NASA Astrophysics Data System (ADS)

    Andersson, M.; Almqvist, B.; Malehmir, A.; Troll, V. R.; Snowball, I.; Lougheed, B.

    2013-12-01

    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.

  3. Self-Assembled Epitaxial Core-Shell Nanocrystals with Tunable Magnetic Anisotropy.

    PubMed

    Liao, Sheng-Chieh; Chen, Yong-Lun; Kuo, Wei-Cheng; Cheung, Jeffrey; Wang, Wei-Cheng; Cheng, Xuan; Chin, Yi-Ying; Chen, Yu-Ze; Liu, Heng-Jui; Lin, Hong-Ji; Chen, Chien-Te; Juang, Jeng-Yih; Chueh, Yu-Lun; Nagarajan, Valanoor; Chu, Ying-Hao; Lai, Chih-Huang

    2015-09-01

    Epitaxial core-shell CoO-CoFe2 O4 nanocrystals are fabricated by using pulsed laser deposition with the aid of melted material (Bi2 O3 ) addition and suitable lattice mismatch provided by substrates (SrTiO3 ). Well aligned orientations among nanocrystals and reversible core-shell sequence reveal tunable magnetic anisotropy. The interfacial coupling between core and shell further engineers the nanocrystal functionality. PMID:26034015

  4. Real-space presentation of the magnetic anisotropy of metallic ferromagnets

    SciTech Connect

    Inoue, Jun-ichiro; Yoshioka, Takuya; Tsuchiura, Hiroki

    2015-05-07

    A real-space representation of the uniaxial magnetic anisotropy (MA) of metallic ferromagnets is formulated using the full-orbital tight-binding model. By adopting a second-order perturbation for the spin-orbit interaction, numerical calculations of the uniaxial MA are performed for the L1{sub 0} FePt and Y{sub 2}Fe{sub 14}B compounds to evaluate the validity and applicability of the present method.

  5. Magnetic field modulation of chirooptical effects in magnetoplasmonic structures.

    PubMed

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

    2014-04-01

    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

  6. Magnetic Exchange Coupling and Anisotropy of 3d Transition Metal Nanowires on Graphyne

    PubMed Central

    He, Junjie; Zhou, Pan; Jiao, N.; Ma, S. Y.; Zhang, K. W.; Wang, R. Z.; Sun, L. Z.

    2014-01-01

    Applying two-dimensional monolayer materials in nanoelectronics and spintronics is hindered by a lack of ordered and separately distributed spin structures. We investigate the electronic and magnetic properties of one-dimensional zigzag and armchair 3d transition metal (TM) nanowires on graphyne (GY), using density functional theory plus Hubbard U (DFT + U). The 3d TM nanowires are formed on graphyne (GY) surfaces. TM atoms separately and regularly embed within GY, achieving long-range magnetic spin ordering. TM exchange coupling of the zigzag and armchair nanowires is mediated by sp-hybridized carbon, and results in long-range magnetic order and magnetic anisotropy. The magnetic coupling mechanism is explained by competition between through-bond and through-space interactions derived from superexchange. These results aid the realization of GY in spintronics. PMID:24510164

  7. Lorentz transmission electron microscopy on nanometric magnetic bubbles and skyrmions in bilayered manganites La1.2Sr1.8(Mn1-yRuy)2O7 with controlled magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Morikawa, D.; Yu, X. Z.; Kaneko, Y.; Tokunaga, Y.; Nagai, T.; Kimoto, K.; Arima, T.; Tokura, Y.

    2015-11-01

    We have investigated nanometric magnetic textures in thin (<150 nm) plates of Ru-doped bilayered manganites La1.2Sr1.8(Mn1-yRuy)2O7. Ru substitution for Mn site changes the magnetic anisotropy from in-plane to out-of-plane easy axis type without any significant change of global magnetic and crystal structures. The combination of conventional and Lorentz transmission electron microscopy observations confirms the emergence of magnetic bubbles and skyrmions in the absence of magnetic field. With the changing Ru concentration, systematic changes in the type of magnetic bubbles are observed. A tiny residual magnetic field also affects the generation and the type-change of magnetic bubbles.

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

    SciTech Connect

    Misochko, Eugenii Ya.; Akimov, Alexander V.; Masitov, Artem A.; Korchagin, Denis V.; Aldoshin, Sergei M.; Chapyshev, Sergei V.

    2013-05-28

    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.

  9. Effects of eddy current and dispersion of magnetic anisotropy on the high-frequency permeability of Fe-based nanocomposites

    NASA Astrophysics Data System (ADS)

    Han, M.; Rozanov, K. N.; Zezyulina, P. A.; Wu, Yan-Hui

    2015-06-01

    Fe-Cu-Nb-Si-B microflakes have been prepared by ball milling. The structural, magnetostatic and microwave permeability of the flakes and flake-filled composites have been studied. Two ferromagnetic phases, nanograins and amorphous matrix, are found in the flakes. The Mössbauer study shows that the nanograins are ?-Fe3(Si) with D03 superlattice structure. High resolution transmission electron microscopy shows that the nanograins are well dispersed in the matrix. The microwave permeability of composites containing the flakes has been measured. The comparison of the intrinsic permeability of the flakes obtained from the permeability measurements and from the anisotropy field distribution reveals a disagreement in the magnetic loss peak location. It is concluded that the low-frequency loss in the composites is not due to the effect of eddy currents. The low-frequency loss may be attributed to other sources, such as domain wall motion or peculiarities of the magnetic structure of the flakes in the composite.

  10. Interfacial perpendicular magnetic anisotropy and damping parameter in ultra thin Co{sub 2}FeAl films

    SciTech Connect

    Cui, Yishen; Khodadadi, Behrouz; Schaefer, Sebastian; Mewes, Tim; Lu, Jiwei; Wolf, Stuart A.; Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904

    2013-04-22

    B2-ordered Co{sub 2}FeAl films were synthesized using an ion beam deposition tool. A high degree of chemical ordering {approx}81.2% with a low damping parameter ({alpha}) less than 0.004 was obtained in a 50 nm thick film via rapid thermal annealing at 600 Degree-Sign C. The perpendicular magnetic anisotropy (PMA) was optimized in ultra thin Co{sub 2}FeAl films annealed at 350 Degree-Sign C without an external magnetic field. The reduced thickness and annealing temperature to achieve PMA introduced extrinsic factors thus increasing {alpha} significantly. However, the observed damping of Co{sub 2}FeAl films was still lower than that of Co{sub 60}Fe{sub 20}B{sub 20} films prepared at the same thickness and annealing temperature.

  11. AC photovoltaic module magnetic fields

    SciTech Connect

    Jennings, C.; Chang, G.J.; Reyes, A.B.; Whitaker, C.M.

    1997-12-31

    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.

  12. Magnetoconvection in sheared magnetic fields

    SciTech Connect

    Bian, N. H.; Garcia, O. E.

    2008-10-15

    The development of magnetoconvection in a sheared magnetic field is investigated. The equilibrium magnetic field B{sub 0} is horizontal and its orientation varies linearly along the vertical axis. Preliminary consideration of the transition from the inertial to the viscous regime of the gravitational resistive interchange instability, reveals that the latter is characterized by the existence of viscoresistive boundary layers of vertical width which scales as Q{sup -1/6}, where Q is the Chandrasekhar number. The situation is analogous to the one encountered in magnetically confined laboratory plasmas, where convective flows are constrained by the magnetic shear to develop in boundary layers located around resonant magnetic surfaces in order to fulfill the 'interchange condition'k{center_dot}B{sub 0}=0, where k is the wave vector of the magnetic perturbation. It follows that when the effect of thermal diffusion is taken into account in the process, convection can only occur above a certain critical value of the Rayleigh number which scales as Q{sup 2/3} for large Q. At the onset, the convection pattern is a superposition of identically thin convective rolls everywhere aligned with the local magnetic field lines and which therefore adopt the magnetic field geometry, a situation also reminiscent of the penumbra of sunspots. Using this degeneracy, equations describing the weakly nonlinear state are obtained and discussed. A reduced magnetohydrodynamic description of magnetoconvection is introduced. Since it is valid for arbitrary magnetic field configurations, it allows a simple extension to the case where there exists an inclination between the direction of gravity and the plane spanned by the equilibrium magnetic field. These reduced magnetohydrodynamic equations are proposed as a powerful tool for further investigations of magnetoconvection in more complex field line geometries.

  13. Magneto-structural properties and magnetic anisotropy of small transition-metal clusters: a first-principles study.

    PubMed

    B?o?ski, Piotr; Hafner, Jürgen

    2011-04-01

    Ab initio density-functional calculations including spin-orbit coupling (SOC) have been performed for Ni and Pd clusters with three to six atoms and for 13-atom clusters of Ni, Pd, and Pt, extending earlier calculations for Pt clusters with up to six atoms (2011 J. Chem. Phys. 134 034107). The geometric and magnetic structures have been optimized for different orientations of the magnetization with respect to the crystallographic axes of the cluster. The magnetic anisotropy energies (MAE) and the anisotropies of spin and orbital moments have been determined. Particular attention has been paid to the correlation between the geometric and magnetic structures. The magnetic point group symmetry of the clusters varies with the direction of the magnetization. Even for a 3d metal such as Ni, the change in the magnetic symmetry leads to small geometric distortions of the cluster structure, which are even more pronounced for the 4d metal Pd. For a 5d metal the SOC is strong enough to change the energetic ordering of the structural isomers. SOC leads to a mixing of the spin states corresponding to the low-energy spin isomers identified in the scalar-relativistic calculations. Spin moments are isotropic only for Ni clusters, but anisotropic for Pd and Pt clusters, orbital moments are anisotropic for the clusters of all three elements. The magnetic anisotropy energies have been calculated. The comparison between MAE and orbital anisotropy invalidates a perturbation analysis of magnetic anisotropy for these small clusters. PMID:21403235

  14. Magnetic field dependent transport through a Mn4 single-molecule magnet

    NASA Astrophysics Data System (ADS)

    Haque, F.; Langhirt, M.; del Barco, E.; Taguchi, T.; Christou, G.

    2011-04-01

    We present a preliminary study of the single-electron transport response of a Mn4 single-molecule magnet in which pyridyl-alkoxide groups have been added to electrically protect the magnetic core and to increase the stability of the molecule during the experiments. Three-terminal single-electron transistors with nanogapped gold electrodes formed by electromigration and a naturally oxidized aluminum backgate were used to perform experiments at temperatures down to 240 mK in the presence of arbitrarily oriented magnetic fields. Coulomb blockade and electronic excitations that curve with the magnetic field and present zero-field splitting represent evidence of magnetic anisotropy. Level anticrossings and large excitation slopes are associated with the behavior of molecular states with high-spin values (S ˜ 9), as expected from Mn4.

  15. Magnetic Field Generation in Stars

    NASA Astrophysics Data System (ADS)

    Ferrario, Lilia; Melatos, Andrew; Zrake, Jonathan

    2015-10-01

    Enormous progress has been made on observing stellar magnetism in stars from the main sequence (particularly thanks to the MiMeS, MAGORI and BOB surveys) through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence, in the generation and stability of neutron star fields.

  16. Neutron scattering in magnetic fields

    SciTech Connect

    Koehler, W.C.

    1984-01-01

    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.

  17. The effect of magnetic anisotropy on the spin configurations of patterned La0.7Sr0.3MnO3 elements

    NASA Astrophysics Data System (ADS)

    Wohlhüter, P.; Rhensius, J.; Vaz, C. A. F.; Heidler, J.; Körner, H. S.; Bisig, A.; Foerster, M.; Méchin, L.; Gaucher, F.; Locatelli, A.; Niño, M. A.; El Moussaoui, S.; Nolting, F.; Goering, E.; Heyderman, L. J.; Kläui, M.

    2013-05-01

    We study the effect of magnetocrystalline anisotropy on the magnetic configurations of La0.7Sr0.3MnO3 bar and triangle elements using photoemission electron microscopy imaging. The dominant remanent state is a low energy flux-closure state for both thin (15 nm) and thick (50 nm) elements. The magnetocrystalline anisotropy, which competes with the dipolar energy, causes a strong modification of the spin configuration in the thin elements, depending on the shape, size and orientation of the structures. We investigate the magnetic switching processes and observe in triangular shaped elements a displacement of the vortex core along the easy axis for an external magnetic field applied close to the hard axis, which is well reproduced by micromagnetic simulations.

  18. Magnetic anisotropy of CoxPt1-x clusters embedded in a matrix: Influences of the cluster chemical composition and the matrix nature

    NASA Astrophysics Data System (ADS)

    Rohart, S.; Raufast, C.; Favre, L.; Bernstein, E.; Bonet, E.; Dupuis, V.

    2006-09-01

    We report on the magnetic properties of CoxPt1-x clusters embedded in various matrices. Using a careful analysis of magnetization curves and zero field cooled susceptibility measurements, we determine the clusters magnetic anisotropy energy (MAE) and separate the surface and volume contributions. By comparing different chemical compositions, we show that a small amount of Pt (15%) induces an important increase in the volume anisotropy with respect to pure Co clusters, even in chemically disordered fcc clusters. Comparing the measurements of clusters embedded in Nb and MgO matrices, we show that the oxide matrix induces an important increase of the surface MAE attributed to the formation of an antiferromagnetic CoO shell around the clusters.

  19. Reconnection of stressed magnetic fields

    NASA Technical Reports Server (NTRS)

    Hassam, A. B.

    1992-01-01

    It is shown that magnetized plasma configurations under magnetic stress relax irreversibly to the state of minimum stress at a rate that is essentially Alfvenic provided a magnetic null is present. The relaxation is effected by the reconnection at the field null and proceeds at a rate proportional to the absolute value of ln(eta) exp-1, where eta is the resistivity. An analytic calculation in the linear regime is presented.

  20. Magnetic-field-induced periodic deformations in planar nematic layers.

    PubMed

    Krzyza?ski, D; Derfel, G

    2000-06-01

    Periodic deformations of strongly anchored planar nematic layers subjected to magnetic fields were studied numerically. Two magnetic-field configurations, giving rise to the so-called periodic splay-twist and periodic twist-splay patterns, were taken into account. The stationary director distribution was calculated for various values of elastic anisotropy and magnetic-field strength. Some alternative conclusions that shed light on the properties of the periodic deformations were drawn: (i) the transition from the periodically deformed structure to the homogeneously deformed one, which occurs in high field, is due to the divergence of the spatial period of the deformations to infinity; (ii) the spatial dependence of the angles determining the high-field director distribution strongly deviates from the theoretically predicted functions of sinusoidal form. The diagrams showing the ranges of parameters, for which the periodic deformations can realize, were built. The stable wave-number bands were determined numerically. PMID:11088358

  1. Alternating magnetic anisotropy of Li 2 ( Li 1 - x T x ) N ( T = Mn , Fe , Co , and Ni )

    DOE PAGESBeta

    Jesche, A.; Ke, L.; Jacobs, J. L.; Harmon, B.; Houk, R. S.; Canfield, P. C.

    2015-05-01

    Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li?(Li1-xTx)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy plane?easy axis?easy plane?easy axis when progressing from T = Mn ? Fe ? Co ? Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model.more »The calculated magnetic anisotropies show surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.« less

  2. Alternating magnetic anisotropy of Li2(Li1–xTx)N(T=Mn,Fe,Co,andNi)

    DOE PAGESBeta

    Jesche, A.; Ke, L.; Jacobs, J. L.; Harmon, B.; Houk, R. S.; Canfield, P. C.

    2015-05-11

    Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li2(Li1–xTx)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy plane?easy axis?easy plane?easy axis when progressing from T = Mn ? Fe ? Co ? Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model.more »As a result, the calculated magnetic anisotropies show surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.« less

  3. Alternating magnetic anisotropy of Li2(Li1–xTx)N (T = Mn, Fe, Co, and Ni)

    DOE PAGESBeta

    Jesche, A.; Ke, L.; Jacobs, J. L.; Harmon, B.; Houk, R. S.; Canfield, P. C.

    2015-05-11

    Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li2(Li1–xTx)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy plane?easy axis?easy plane?easy axis when progressing from T = Mn ? Fe ? Co ? Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model.more »As a result, the calculated magnetic anisotropies show surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.« less

  4. Alternating magnetic anisotropy of Li2(Li1 -xTx )N (T =Mn ,Fe ,Co ,andNi )

    NASA Astrophysics Data System (ADS)

    Jesche, A.; Ke, L.; Jacobs, J. L.; Harmon, B.; Houk, R. S.; Canfield, P. C.

    2015-05-01

    Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li2(Li1 -xTx)N . Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy plane?easy axis?easy plane?easy axis when progressing from T =Mn ?Fe ?Co ?Ni . This behavior can be understood based on a perturbation approach in an analytical, single-ion model. The calculated magnetic anisotropies show surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.

  5. Tunable giant magnetic anisotropy in amorphous SmCo thin films

    SciTech Connect

    Magnus, F.; Moubah, R.; Roos, A. H.; Kapaklis, V.; Hjoervarsson, B.; Andersson, G.; Kruk, A.; Hase, T.

    2013-04-22

    SmCo thin films have been grown by magnetron sputtering at room temperature with a composition of 2-35 at. % Sm. Films with 5 at. % or higher Sm are amorphous and smooth. A giant tunable uniaxial in-plane magnetic anisotropy is induced in the films which peaks in the composition range 11-22 at. % Sm. This cross-over behavior is not due to changes in the atomic moments but rather the local configuration changes. The excellent layer perfection combined with highly tunable magnetic properties make these films important for spintronics applications.

  6. Crystal anisotropy induced temperature dependent magnetization in cobalt nanowires electrodeposited within alumina template

    NASA Astrophysics Data System (ADS)

    Srivastav, Ajeet K.; Shekhar, Rajiv

    2014-01-01

    Cobalt nanowires were deposited within nanoporous alumina template by direct current electrodeposition. The effect of pH on temperature dependent hysteresis behavior and magnetic properties of Co nanowires has been analyzed and discussed in detail. The easy axis of magnetization was observed to change uniformly from parallel to perpendicular direction to the wire axis with decrease of temperature from 400 K to 5 K. The effect could be attributed to increased magnetocrystalline anisotropy at lower temperatures (e.g. 5 K). Strong pH dependence of cross-over temperature that changes from 300 K to 50 K was observed and the change was delayed with increase of pH.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    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.

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

    SciTech Connect

    Mazalski, P.; Kurant, Z.; Maziewski, A.; Liedke, M. O.; Fassbender, J.; Baczewski, L. T.; Wawro, A.

    2013-05-07

    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.

  9. Measuring Earth's Magnetic Field Simply.

    ERIC Educational Resources Information Center

    Stewart, Gay B.

    2000-01-01

    Describes a method for measuring the earth's magnetic field using an empty toilet paper tube, copper wire, clear tape, a battery, a linear variable resistor, a small compass, cardboard, a protractor, and an ammeter. (WRM)

  10. Enhancement of rotatable anisotropy in ferrite doped FeNi thin film with oblique sputtering

    NASA Astrophysics Data System (ADS)

    Zhou, Cai; Jiang, Changjun; Zhao, Zhong

    2015-07-01

    Rotatable anisotropy of stripe domain (SD) was investigated in a ferrite doped FeNi thin film with different oblique angles. Rotation of SD under an in-plane magnetic field was observed by magnetic force microscopy, suggesting the existence of rotatable anisotropy. A rotatable anisotropy field Hrot was derived from the fitting curves of the in-plane resonance field versus the angle between the orientation of easy axis and applied field. As the oblique angle increases, an increase of Hrot from 305 Oe to 468 Oe was observed and the perpendicular anisotropy increased as well, indicating a correlation between rotatable anisotropy and perpendicular anisotropy.

  11. Black Holes and Magnetic Fields

    E-print Network

    Filip Hejda; Ji?í Bi?ák

    2015-10-01

    We briefly summarise the basic properties of spacetimes representing rotating, charged black holes in strong axisymmetric magnetic fields. We concentrate on extremal cases, for which the horizon surface gravity vanishes. We investigate their properties by finding simpler spacetimes that exhibit their geometries near degenerate horizons. Employing the simpler geometries obtained by near-horizon limiting description we analyse the Meissner effect of magnetic field expulsion from extremal black holes.

  12. 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)

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

    2014-09-01

    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.

  13. Magnetic fields on the Sun

    NASA Technical Reports Server (NTRS)

    Howard, R.

    1981-01-01

    Synoptic observations of solar magnetic fields are discussed. Seen in long-term averages, the magnetic fields of the Sun show distinctive behavior. The active-region latitudes are characterized by magnetic fields of preceding polarity. The flow of following polarity fields to make up the polar fields is episodic, not continuous. This field motion is a directed poleward flow and is not due to diffusion. The total magnetic flux on the solar surface, which is related linearly to the calcium emission in integrated sunlight, varies from activity minimum to maximum by a factor of 2 or 3. Nearly all this flux is seen at active-region latitudes-only about 1% is at the poles. The total flux of the Sun disappears from the surface at a very rapid rate and is replaced by new flux. All the field and flux patterns that we see originate in active-region latitudes. The polar magnetic fields of the Sun were observed to change polarity recently. The variations of the full-disk solar flux are shown to lead to the proper rotation rate of the Sun, but the phase of the variations is constant for only a year or two at most.

  14. Optical sensor of magnetic fields

    DOEpatents

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

    1986-03-25

    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.

  15. Unidirectional Spin-Dependent Molecule-Ferromagnet Hybridized States Anisotropy in Cobalt Phthalocyanine Based Magnetic Tunnel Junctions.

    PubMed

    Barraud, Clément; Bouzehouane, Karim; Deranlot, Cyrile; Fusil, Stéphane; Jabbar, Hashim; Arabski, Jacek; Rakshit, Rajib; Kim, Dong-Jik; Kieber, Christophe; Boukari, Samy; Bowen, Martin; Beaurepaire, Eric; Seneor, Pierre; Mattana, Richard; Petroff, Frédéric

    2015-05-22

    Organic or molecular spintronics is a rising field of research at the frontier between condensed matter physics and chemistry. It aims to mix spin physics and the richness of chemistry towards designing new properties for spin electronics devices through engineering at the molecular scale. Beyond the expectation of a long spin lifetime, molecules can be also used to tailor the spin polarization of the injected current through the spin-dependent hybridization between molecules and ferromagnetic electrodes. In this Letter, we provide direct evidence of a hybrid interface spin polarization reversal due to the differing hybridization between phthalocyanine molecules and each cobalt electrode in Co/CoPc/Co magnetic tunnel junctions. Tunnel magnetoresistance and anisotropic tunnel magnetoresistance experiments show that interfacial hybridized electronic states have a unidirectional anisotropy that can be controlled by an electric field and that spin hybridization at the bottom and top interfaces differ, leading to an inverse tunnel magnetoresistance. PMID:26047247

  16. Magnetic field induced dynamical chaos

    SciTech Connect

    Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra

    2013-12-15

    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.

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

    NASA Astrophysics Data System (ADS)

    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

    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.

  18. Varied magnetic field, multiple-pulse, and magic-angle spinning proton nuclear magnetic resonance study of muscle water.

    PubMed Central

    Fung, B M; Ryan, L M; Gerstein, B C

    1980-01-01

    The nuclear magnetic resonance linewidth of 1H in water of frog muscle was studied as a function of magnetic field strength and angle of orientation. The results suggest that the observed spectra are dominated by demagnetization field anisotropy and dispersion, but a small static dipolar interaction of the order of a few hertz man be present. Data from line-narrowing, multiple-pulse experiments also indicate the presence of a small dipolar broadening. PMID:6266526

  19. Electric-field-induced modification in magnetocrystalline anisotropy, exchange interaction, and Curie temperature of transition-metal thin films

    NASA Astrophysics Data System (ADS)

    Nakamura, K.; Oba, M.; Akiyama, T.; Ito, T.; Weinert, M.; Freeman, A. J.

    2014-03-01

    Magnetism induced by an external electric field (E-field) has received much attention as a potential approach for controlling magnetism at the nano-scale with the promise of ultra-low energy power consumption. For magnetocrystalline anisotropy (MCA) in transition-metal thin films, it is agreed that a change in the screening charge density due to an E-field, which causes a small change in band structures around Fermi energy, gives rise to a modification of the MCA energy.[2] Here, we extend our first-principles investigation to Curie temperature of an Fe monolayer in an E-field. Calculations were carried out using film-FLAPW method that treats spin-spiral structures in an E-field. Results predict that when the E-field is introduced, calculated magnon (spin-spiral formation) energy is modified, by a few tens of meV, compared to that in zero field. The exchange parameters within the classical Heisenberg model, by making the back Fourier transformation of the magnon energy, suggest the E-field-induced modification of Curie temperature. Taking a large MCA energy of the monolayer into account, the modification of Curie temperature by the E-field was demonstrated by Monte Carlo simulations. Supported by DOE (DE-FG02-05ER45372)

  20. Magnetic fields in quiescent prominences

    NASA Technical Reports Server (NTRS)

    Van Ballegooijen, A. A.; Martens, P. C. H.

    1990-01-01

    The origin of the axial fields in high-latitude quiescent prominences is considered. The fact that almost all quiescent prominences obey the same hemisphere-dependent rule strongly suggests that the solar differential rotation plays an important role in producing the axial fields. However, the observations are inconsistent with the hypothesis that the axial fields are produced by differential rotation acting on an existing coronal magnetic field. Several possible explanations for this discrepancy are considered. The possibility that the sign of the axial field depends on the topology of the magnetic field in which the prominence is embedded is examined, as is the possibility that the neutral line is tilted with respect to the east-west direction, so that differential rotation causes the neutral line also to rotate with time. The possibility that the axial fields of quiescent prominences have their origin below the solar surface is also considered.

  1. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures.

    PubMed

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L; Zhang, Qianfan; Zhao, Weisheng

    2015-01-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM. PMID:26656721

  2. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

    PubMed Central

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L.; Zhang, Qianfan; Zhao, Weisheng

    2015-01-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM. PMID:26656721

  3. The magnetic field of Uranus

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Acuna, Mario H.; Ness, Norman F.

    1987-01-01

    Aspherical harmonic model of the planetary magnetic field of Uranus is obtained from the Voyager 2 encounter observations using generalized inverse techniques which allow partial solutions to complex (underdetermined) problems. The Goddard Space Flight Center 'Q3' model is characterized by a large dipole tilt (58.6 deg) relative to the rotation axis, a dipole moment of 0.228 G R(Uranus radii cubed) and an unusually large quadrupole moment. Characteristics of this complex model magnetic field are illustrated using contour maps of the field on the planet's surface and discussed in the context of possible dynamo generation in the relatively poorly conducting 'ice' mantle.

  4. Influence of structural disorder on magnetic domain formation in perpendicular anisotropy thin films

    NASA Astrophysics Data System (ADS)

    Pierce, M. S.; Davies, J. E.; Turner, J. J.; Chesnel, K.; Fullerton, E. E.; Nam, J.; Hailstone, R.; Kevan, S. D.; Kortright, J. B.; Liu, Kai; Sorensen, L. B.; York, B. R.; Hellwig, O.

    2013-05-01

    Using a combination of resonant soft x-ray scattering, magnetometry, x-ray reflectivity, and microscopy techniques we have investigated the magnetic properties and microstructure of a series of perpendicular anisotropy Co/Pt multilayer films with respect to structural disorder tuned by varying the sputtering deposition pressure. The observed magnetic changes in domain size, shape, and correlation length originate from structural and chemical variations in the samples, such as chemical segregation and grain formation as well as roughness at the surface and interfaces, which are all impacted by the deposition pressure. All samples exhibited short-range “liquid-like” positional ordering over significant portions of their major hysteresis loops, while only the lowest disorder samples showed evidence of a random “gas-like” distribution of magnetic domains, present just after nucleation as well as prior to saturation. The structural and chemical disorder induced by the higher deposition pressure first leads to an increase in the number of magnetic point defects that limit free domain wall propagation. Then, as the sputtering pressure is further increased, the domain wall energy density is lowered due to the formation of local regions with reduced magnetic moment, and finally magnetically void regions appear that confine the magnetic domains and clusters, similar to segregated granular magnetic recording media.

  5. Aging of anisotropy of solar wind magnetic fluctuations in the inner heliosphere

    E-print Network

    Dasso, Sergio

    property of an MHD system with a mean magnetic field (B0). Understanding the nature and origin with respect to the mean magnetic field B0. This was originally demonstrated in laboratory experiments field B0. We analyze a set of 1065 24hour long intervals (covering full missions). For each interval, we

  6. Heavy atom effect on magnetic anisotropy of matrix-isolated monobromine substituted septet trinitrene.

    PubMed

    Misochko, Eugenii Ya; Masitov, Artem A; Akimov, Alexander V; Korchagin, Denis V; Chapyshev, Sergei V

    2015-03-19

    The heavy atom effect on the magnetic anisotropy of septet trinitrenes is reported. Septet 1-bromo-3,5-dichloro-2,4,6-trinitrenobenzene (S-1) was generated in a solid argon matrix by ultraviolet irradiation of 1,3,5-triazido-2-bromo-4,6-dichlorobenzene. This trinitrene displays an electron spin resonance (ESR) spectrum that drastically differs from ESR spectra of all previously studied septet trinitrenes. The zero-field splitting (ZFS) parameters, derived from the experimental spectrum, show the parameter |D| = 0.1237 cm(-1) and the unprecedentedly large ratio of E/D = 0.262 that is close to the rhombic limit E/D = 1/3 for high-spin molecules. The CASCI (based on state-averaged CASSCF) and DFT methods were applied to calculate the ZFS tensor focusing on the heavy (bromine) atom effects on the spin-orbit term. These calculations show that the multiconfigurational ab initio formalism and the CASCI method are the most successful for accurate predictions of the spin-orbit term in the ZFS tensor of high-spin nitrenes containing heavy bromine atoms. Due to the presence of the bromine atom in S-1, the contribution of the spin-orbit term to the total parameter D is dominant and responsible for the unusual orientation of the easy Z-axis lying in the molecular plane perpendicular to the C-Br bond. As a result, the principal values D(XX), D(YY), and D(ZZ) of the total tensor D?(Tot) have such magnitudes and signs for which the ratio E/D is close to the rhombic limit, and the total parameter D is large in magnitude and positive in sign. PMID:25350487

  7. Influence of shape, size and internal structure on magnetic properties of core-edge nanodots with perpendicular anisotropy

    SciTech Connect

    Mili?ska, E. Wawro, A.

    2014-11-21

    The properties of perpendicularly magnetized isolated nanodots different in shape, size, and internal structure are simulated by micromagnetic calculations. Investigated dots are magnetically uniform, or they are composed of a core and an edge characterized by different anisotropy—stronger or weaker than that of the core. Based on calculated hysteresis loops, we discuss in details the magnetization reversal processes, stability of magnetic structures, and spin configurations in the dots.

  8. Magnetic anisotropy and X-ray magnetic circular dichroism of MnNi surface alloy: Ab initio studies

    NASA Astrophysics Data System (ADS)

    Hong, Jisang

    2007-06-01

    The magnetic properties of MnNi surface alloy grown on fcc Co(0 0 1) surface have been explored through the full potential linearized augmented plane wave (FLAPW) method. It has been found that one monolayer (ML) of Mn 0.5Ni 0.5 alloy on Co(0 0 1) surface has a ferromagnetic (FM) ground state. We suggest that the direct exchange coupling between Mn and Ni plays an essential role for the ferromagnetism. The vertical position of Mn is higher by 0.26 Å than that of Ni, i.e., the surface has a buckling geometry. In contrast to pure fcc Co(0 0 1) film which has in-plane magnetization, we have obtained that the magnetocrystalline anisotropy of MnNi/Co(0 0 1) due to spin-orbit interaction is perpendicular to the film surface and the magnetic anisotropy energy is 146 ?eV/cell. In addition, the theoretically calculated X-ray magnetic circular dichroism (XMCD) is presented.

  9. Tailoring the magnetic anisotropy of Py/Ni bilayer films using well aligned atomic steps on Cu(001)

    PubMed Central

    Ma, S.; Tan, A.; Deng, J. X.; Li, J.; Zhang, Z. D.; Hwang, C.; Qiu, Z. Q.

    2015-01-01

    Tailoring the spin orientation at the atomic scale has been a key task in spintronics technology. While controlling the out-of-plane to in-plane spin orientation has been achieved by a precise control of the perpendicular magnetic anisotropy at atomic layer thickness level, a design and control of the in-plane magnetic anisotropy has not yet been well developed. On well aligned atomic steps of a 6° vicinal Cu(001) surface with steps parallel to the [110] axis, we grow Py/Ni overlayer films epitaxially to permit a systematic exploration of the step-induced in-plane magnetic anisotropy as a function of both the Py and the Ni film thicknesses. We found that the atomic steps from the vicinal Cu(001) induce an in-plane uniaxial magnetic anisotropy that favors both Py and Ni magnetizations perpendicular to the steps, opposite to the behavior of Co on vicinal Cu(001). In addition, thickness-dependent study shows that the Ni films exhibit different magnetic anisotropy below and above ~6?ML Ni thickness. PMID:26067408

  10. Theory of magnetic fluid heating with an alternating magnetic field with temperature dependent materials properties for self-regulated heating

    NASA Astrophysics Data System (ADS)

    Ondeck, C. L.; Habib, A. H.; Ohodnicki, P.; Miller, K.; Sawyer, C. A.; Chaudhary, P.; McHenry, M. E.

    2009-04-01

    Magnetic nanoparticles (MNP) offer promise for local hyperthermia, thermoablative cancer therapy and microwave curing of polymers. Rosensweig's theory predicts that particle size dependence on RF magnetic heating of ferrofluids is chiefly determined by magnetic moment, magnetic anisotropy, and the viscosity of the fluid. Since relaxation times are thermally activated and material parameters can have strong T dependences, heating rates peak at a certain temperature. We extend the model to include the T dependence of the magnetization and anisotropy using mean field theory and literature reported T dependences of selected fluids considered for biomedical applications. We model materials with Curie temperatures near room temperature for which the magnetic properties are strongly T dependent to address the problem of self-regulated heating of ferrofluids.

  11. Magnetic field fluctuations during substorms

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.

    1971-01-01

    Before a magnetospheric substorm and during its early phases the magnetic field magnitude in the geomagnetic tail increases and field lines in the nighttime hemisphere assume a more tail-like configuration. Before the substorm onset a minimum amount of magnetic flux is observed to cross the neutral sheet which means that the neutral sheet currents attain their most earthward locations and their greatest current densities. This configuration apparently results from an increased transport of magnetic flux to the tail caused by a southward interplanetary magnetic field. The field begins relaxing toward a more dipolar configuration at the time of a substorm onset with the recovery probably occurring first between 6 and 10 R sub E. This recovery must be associated with magnetospheric convection which restores magnetic flux to the dayside hemisphere. Field aligned currents appear to be required to connect magnetospheric currents to the auroral electrojets, implying that a net current flows in a limited range of longitudes. Space measurements supporting current systems are limited. More evidence exists for the occurrence of double current sheets which do not involve net current at a given longitude.

  12. Effects of magnetic fields on dissolution of arthritis causing crystals

    NASA Astrophysics Data System (ADS)

    Takeuchi, Y.; Iwasaka, M.

    2015-05-01

    The number of gout patients has rapidly increased because of excess alcohol and salt intake. The agent responsible for gout is the monosodium urate (MSU) crystal. MSU crystals are found in blood and consist of uric acid and sodium. As a substitute for drug dosing or excessive water intake, physical stimulation by magnetic fields represents a new medical treatment for gout. In this study, we investigated the effects of a magnetic field on the dissolution of a MSU crystal suspension. The white MSU crystal suspension was dissolved in an alkaline solution. We measured the light transmission of the MSU crystal suspension by a transmitted light measuring system. The magnetic field was generated by a horizontal electromagnet (maximum field strength was 500 mT). The MSU crystal suspension that dissolved during the application of a magnetic field of 500 mT clearly had a higher dissolution rate when compared with the control sample. We postulate that the alkali solution promoted penetration upon diamagnetic rotation and this magnetic field orienting is because of the pronounced diamagnetic susceptibility anisotropy of the MSU crystal. The results indicate that magnetic fields represent an effective gout treatment approach.

  13. Tuning magnetic anisotropy and the damping constant using substrate-induced strain in a FeCo/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

    NASA Astrophysics Data System (ADS)

    Yang, Chengcheng; Wang, Fenglong; Zhang, Chao; Zhou, Cai; Jiang, Changjun

    2015-11-01

    To investigate how substrate-induced strain affects the magnetic anisotropy and damping constant, FeCo films were deposited onto Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) (0?1?1)-orientated substrates by RF-magnetron sputtering. Interestingly, as the strain, which is controlled by an applied electric field, increases, the magnetic anisotropy is enhanced while the damping constant decreases sharply. The angular dependence of coercive force and magnetoelastic energy were obtained to analyze the mechanism of magnetization reversal under strain modulation. The nonvolatile strain-modulation was demonstrated by the application of different pulsed electric fields. The reversible magnetization processes and low magnetic damping constant can be modulated by the substrate-induced strain, which can contribute to the realization of low-loss strain-mediated spin-transfer-torque based magnetic devices.

  14. Transformation volume effect on the magnetic anisotropy of Ni-Mn-Ga thin films

    NASA Astrophysics Data System (ADS)

    L'vov, V. A.; Golub, V.; Salyuk, O.; Barandiarán, J. M.; Chernenko, V. A.

    2015-01-01

    Ni-Mn-Ga ferromagnetic shape memory films with similar thickness and chemical composition, deposited onto cold (with a subsequent annealing) and hot MgO(001) substrates exhibit different internal stress and structure giving rise to a different orientation of the magnetic easy axes. A quantitative theoretical analysis of the crystallographic and ferromagnetic resonance (FMR) data shows that the different anisotropies can be caused by the difference in sign between the transformation volume changes in these films, as influenced by the internal stresses. To explain FMR data, the magnetoelastic coupling term of fourth-order in the magnetic vector and linear in the strain tensor components, appearing in the Landau expansion for the free energy, is taken into account. The coefficient of the term, which couples the magnetic vector components with the volume change of the Ni-Mn-Ga alloy, was estimated to be equal to about 10 7 erg cm - 3 .

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

    PubMed Central

    2010-01-01

    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

  16. Universal scaling of the magnetic anisotropy in two-dimensional rare-earth layers

    NASA Astrophysics Data System (ADS)

    Benito, L.; Ward, R. C. C.

    2015-07-01

    Unraveling the influence that low dimensionality has upon the spin's stability in two-dimensional (2D) systems is instrumental for the efficient engineering of energy barriers in ultrathin magnetic layers. Taking rare-earth-based ultrathin multilayered nanostructures as a model system, we have investigated the dissimilar impact that low dimensionality and finite-size effects have upon the magnetic anisotropy energy (MAE) at the nanoscale. We conclusively show that the reduced dimensionality of the spin's system in 2D ferromagnetic layers imprints on the MAE constants a universal temperature decay as a quadratic power law of the reduced magnetization. This result is in agreement with predictions, although in marked contrast to the rank-dependent, thereby faster, decay of the MAE constants observed in three-dimensional nanostructures.

  17. Satellite to study earth's magnetic field

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The Magnetic Field Satellite (Magsat) designed to measure the near earth magnetic field and crustal anomalies is briefly described. A scalar magnetometer to measure the magnitude of the earth's crustal magnetic field and a vector magnetometer to measure magnetic field direction as well as magnitude are included. The mission and its objectives are summarized along with the data collection and processing system.

  18. Indoor localization using magnetic fields

    NASA Astrophysics Data System (ADS)

    Pathapati Subbu, Kalyan Sasidhar

    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.

  19. High-frequency electromagnetic properties of soft magnetic Y2Fe17Nx particles with easy-plane anisotropy

    NASA Astrophysics Data System (ADS)

    Tan, Guoguo; Zhang, Yongbo; Qiao, Liang; Wang, Tao; Wang, Jianbo; Li, Fashen

    2015-11-01

    The microwave magnetic properties of the soft magnetic Y2Fe17Nx (x?3) particles with easy-plane anisotropy were reported. The high MS and out-of-plane anisotropy result in the high permeability in GHz frequency band. The complex permeability of the Y2Fe17Nx particles/paraffin composite was further enhanced by inducing the easy magnetization planes of the particles to be parallel to each other through a rotational orientation. The calculated reflection loss (RL) properties of the orientated Y2Fe17Nx composite revealed that this composite can be used as high-performance absorber in S band.

  20. Anisotropic magnetohydrodynamic turbulence in a strong external magnetic field

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Turner, L.

    1981-01-01

    A strong external dc magnetic field introduces a basic anisotropy into incompressible magnetohydrodynamic turbulence. The modifications that this is likely to produce in the properties of the turbulence are explored for the high Reynolds number case. The conclusion is reached that the turbulent spectrum splits into two parts: an essentially two dimensional spectrum with both the velocity field and magnetic fluctuations perpendicular to the dc magnetic field, and a generally weaker and more nearly isotropic spectrum of Alfven waves. A minimal characterization of the spectral density tensors is given. Similarities to measurements from the Culham-Harwell Zeta pinch device and the UCLA Macrotor Tokamak are remarked upon, as are certain implications for the Belcher and Davis measurements of magnetohydrodynamic turbulence in the solar wind.

  1. Parallel heat transport in integrable and chaotic magnetic fields

    SciTech Connect

    Castillo-Negrete, D. del; Chacon, L.

    2012-05-15

    The study of transport in magnetized plasmas is a problem of fundamental interest in controlled fusion, space plasmas, and astrophysics research. Three issues make this problem particularly challenging: (i) The extreme anisotropy between the parallel (i.e., along the magnetic field), {chi}{sub ||} , and the perpendicular, {chi}{sub Up-Tack }, conductivities ({chi}{sub ||} /{chi}{sub Up-Tack} may exceed 10{sup 10} in fusion plasmas); (ii) Nonlocal parallel transport in the limit of small collisionality; and (iii) Magnetic field lines chaos which in general complicates (and may preclude) the construction of magnetic field line coordinates. Motivated by these issues, we present a Lagrangian Green's function method to solve the local and non-local parallel transport equation applicable to integrable and chaotic magnetic fields in arbitrary geometry. The method avoids by construction the numerical pollution issues of grid-based algorithms. The potential of the approach is demonstrated with nontrivial applications to integrable (magnetic island), weakly chaotic (Devil's staircase), and fully chaotic magnetic field configurations. For the latter, numerical solutions of the parallel heat transport equation show that the effective radial transport, with local and non-local parallel closures, is non-diffusive, thus casting doubts on the applicability of quasilinear diffusion descriptions. General conditions for the existence of non-diffusive, multivalued flux-gradient relations in the temperature evolution are derived.

  2. Effect of structure on the magnetic anisotropy of L 10 FePt nanoparticles

    NASA Astrophysics Data System (ADS)

    Kabir, Alamgir; Hu, Jun; Turkowski, Volodymyr; Wu, Ruqian; Camley, Robert; Rahman, Talat S.

    2015-08-01

    We carry out a systematic theoretical investigation of magnetocrystalline anisotropy (MCA) of L 10 FePt clusters with alternating Fe and Pt planes along the (001) direction. The clusters studied contain 30-484 atoms. We calculate the structural relaxation and magnetic moment of each cluster by using ab initio spin-polarized density functional theory, and the MCA with both the self-consistent direct method and the torque method. We find the two methods give equivalent results for all the structures examined. We find that bipyramidal clusters whose central layer is Pt have higher MCA than their same-sized counterparts whose central layer is Fe. This results from the fact that the Pt atoms in such configurations are coordinated with more Fe atoms than in the latter. By thus participating in more instances of hybridization, they contribute higher orbital moments to the overall MCA of the unit. Our findings suggest that by properly tailoring the structure one can avoid encapsulating the FePt L 10 nanoparticles, as has been proposed earlier, to protect a high and stable magnetic anisotropy. Additionally, using a simple model to capture the thermal behavior, we predict that a five-layered nanoparticle with approximately 700 atoms can be expected to be useful in magnetic recording applications at room temperature.

  3. Advanced MHD models of anisotropy, flow and chaotic fields M. J. Hole1

    E-print Network

    Hudson, Stuart

    Advanced MHD models of anisotropy, flow and chaotic fields M. J. Hole1 , M. Fitzgerald1 , G. R, USA e-mail address of submitting author: matthew.hole@anu.edu.au Large scale neutral beam heating to the toroidal current density are treated iteratively. The parallel heat flow approximation chosen for the model

  4. Capping layer-tailored interface magnetic anisotropy in ultrathin Co{sub 2}FeAl films

    SciTech Connect

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

    2015-01-14

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

  5. Palaeomagnetism and magnetic anisotropy of Carboniferous red beds from the Maritime Provinces of Canada: evidence for shallow palaeomagnetic inclinations and implications for North American apparent polar wander

    NASA Astrophysics Data System (ADS)

    Bilardello, Dario; Kodama, Kenneth P.

    2010-03-01

    A palaeomagnetic and magnetic anisotropy study was conducted on the lower-middle Carboniferous Maringouin and Shepody red bed formations of the Maritime Provinces of Canada to detect and correct inclination shallowing. Because of the shallow inclinations commonly observed in red beds and the strong dependence of North America's Palaeo-Mesozoic apparent polar wander (APW) on red beds, inclination shallowing may substantially affect large portions of North America's APW path. Hematite is the primary magnetic mineral carrier in these red beds, accompanied by secondary magnetite, maghemite, goethite and pigmentary hematite. Thermal and chemical demagnetization of the Shepody Fm. successfully isolated characteristic remanence directions of D = 177°, I = 20.4°, ?95 = 6.5°, N = 19 and D = 177.8° I = 17.7°, ?95 = 6.9°, N = 16, respectively. Thermal demagnetization of the Maringouin Fm. isolated a characteristic remanence direction of D = 178.7°, I = 24.9°, ?95 = 14.5°, N = 9. High field anisotropy of isothermal remanence followed by alternating field and thermal cleaning on leached samples was used to isolate the fabric of hematite. Individual particle anisotropy was measured directly from magnetic separates using a new technique. Hematite's magnetic fabric and particle anisotropy were used to apply an inclination correction. Our inclination corrections indicate up to 10° of inclination shallowing, corresponding to corrected palaeopole positions of 27.2°N, 118.3°E, A95 = 6.2° and 27.4°N, 117.2°E, A95 = 13.1° for the Shepody and Maringouin formations, respectively. This correction corresponds to a ~ 6° increase in colatitude for Carboniferous North America, which translates into approximately a 650 km change in North America's palaeogeographic position. The proposed position of North America supports a Pangea B-type reconstruction.

  6. Polarization bispectrum for measuring primordial magnetic fields

    NASA Astrophysics Data System (ADS)

    Shiraishi, Maresuke

    2013-11-01

    We examine the potential of polarization bispectra of the cosmic microwave background (CMB) to constrain primordial magnetic fields (PMFs). We compute all possible bispectra between temperature and polarization anisotropies sourced by PMFs and show that they are weakly correlated with well-known local-type and secondary ISW-lensing bispectra. From a Fisher analysis it is found that, owing to E-mode bispectra, in a cosmic-variance-limited experiment the expected uncertainty in the amplitude of magnetized bispectra is 80% improved in comparison with an analysis in terms of temperature auto-bispectrum alone. In the Planck or the proposed PRISM experiment cases, we will be able to measure PMFs with strength 2.6 or 2.2 nG. PMFs also generate bispectra involving B-mode polarization, due to tensor-mode dependence. We also find that the B-mode bispectrum can reduce the uncertainty more drastically and hence PMFs comparable to or less than 1 nG may be measured in a PRISM-like experiment.

  7. Polarized neutron reflection study of the unidirectional magnetic anisotropy of permalloy on Ni{sub 0.5}Co{sub 0.5}O

    SciTech Connect

    Felcher, G.P.; Huang, Y.Y.; Carey, M.; Berkowitz, A.

    1992-08-01

    Couples of ferromagnetic permalloy/antiferromagnetic metal oxide exhibit unidirectional magnetic anisotropy along a magnetic field applied during cooling. Polarized neutron reflection has been used to check if the effect is due to a bias of the antiferromagnetic configuration in the oxide, where the layer immediately adjacent to the permalloy is polarized parallel to the easy direction of magnetization. The measurements were made on a sample consisting of permalloy/500{Angstrom} Ni{sub 0.05}Co{sub 0.5}O. The polarized neutron reflectivities taken at the four corners of the magnetic hysteresis loop at 20K. A faint magnetic signal consistent with the unidirectional bias of the F/AF structure is also observed. This behavior is discussed in the light of the current theories.

  8. Polarized neutron reflection study of the unidirectional magnetic anisotropy of permalloy on Ni[sub 0. 5]Co[sub 0. 5]O

    SciTech Connect

    Felcher, G.P.; Huang, Y.Y. ); Carey, M.; Berkowitz, A. . Center for Magnetic Recording Research)

    1992-08-01

    Couples of ferromagnetic permalloy/antiferromagnetic metal oxide exhibit unidirectional magnetic anisotropy along a magnetic field applied during cooling. Polarized neutron reflection has been used to check if the effect is due to a bias of the antiferromagnetic configuration in the oxide, where the layer immediately adjacent to the permalloy is polarized parallel to the easy direction of magnetization. The measurements were made on a sample consisting of permalloy/500[Angstrom] Ni[sub 0.05]Co[sub 0.5]O. The polarized neutron reflectivities taken at the four corners of the magnetic hysteresis loop at 20K. A faint magnetic signal consistent with the unidirectional bias of the F/AF structure is also observed. This behavior is discussed in the light of the current theories.

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

    SciTech Connect

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

    2014-07-28

    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.

  10. Magnetic Field Issues in Magnetic Resonance Imaging.

    NASA Astrophysics Data System (ADS)

    Petropoulos, Labros Spiridon

    Advances in Magnetic Resonance Imaging depend on the capability of the available hardware. Specifically, for the main magnet configuration, using derivative constraints, we can create a static magnetic field with reduced levels of inhomogeneity over a prescribed imaging volume. In the gradient coil, the entire design for the axial elliptical coil, and the mathematical foundation for the transverse elliptical coil have been presented. Also, the design of a self-shielded cylindrical gradient coil with a restricted length has been presented. In order to generate gradient coils adequate for head imaging without including the human shoulders in the design, asymmetric cylindrical coils in which the gradient center is shifted axially towards the end of a finite cylinder have been introduced and theoretical as well as experimental results have been presented. In order to eliminate eddy current effects in the design of the non-shielded asymmetric gradient coils, the self-shielded asymmetric cylindrical gradient coil geometry has been introduced. Continuing the development of novel geometries for the gradient coils, the complete set of self-shielded cylindrical gradient coils, which are designed such that the x component of the magnetic field varies linearly along the three traditional gradient axes, has been presented. In order to understand the behavior of the rf field inside a dielectric object, a mathematical model is briefly presented. Although specific methods can provide an indication of the rf behavior inside a loosely dielectric object, finite element methodology is the ultimate approach for modeling the human torso and generating an accurate picture for the shape of the rf field inside this dielectric object. For this purpose we have developed a 3D finite element model, using the Coulomb gauge condition as a constraint. Agreement with the heterogeneous multilayer planar model has been established, while agreement with theoretical results from the spherical model and experimental results from the cylindrical model at 170 M H z is very good and provides an encouraging sign for using this finite element approach for modeling the rf inside the human body. (Abstract shortened by UMI.).

  11. Photospheric and coronal magnetic fields

    SciTech Connect

    Sheeley, N.R., Jr. )

    1991-01-01

    Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

  12. Cosmic microwave background polarization signals from tangled magnetic fields.

    PubMed

    Seshadri, T R; Subramanian, K

    2001-09-01

    Tangled, primordial cosmic magnetic fields create small rotational velocity perturbations on the last scattering surface of the cosmic microwave background radiation. For fields which redshift to a present value of B0 = 3 x 10(-9) G, these vector modes are shown to generate polarization anisotropies of order 0.1-4 microK on small angular scales (500

  13. Magnetic fields around black holes

    NASA Astrophysics Data System (ADS)

    Garofalo, David A. G.

    Active Galactic Nuclei are the most powerful long-lived objects in the universe. They are thought to harbor supermassive black holes that range from 1 million solar masses to 1000 times that value and possibly greater. Theory and observation are converging on a model for these objects that involves the conversion of gravitational potential energy of accreting gas to radiation as well as Poynting flux produced by the interaction of the rotating spacetime and the electromagnetic fields originating in the ionized accretion flow. The presence of black holes in astrophysics is taking center stage, with the output from AGN in various forms such as winds and jets influencing the formation and evolution of the host galaxy. This dissertation addresses some of the basic unanswered questions that plague our current understanding of how rotating black holes interact with their surrounding magnetized accretion disks to produce the enormous observed energy. Two magnetic configurations are examined. The first involves magnetic fields connecting the black hole with the inner accretion disk and the other involves large scale magnetic fields threading the disk and the hole. We study the effects of the former type by establishing the consequences that magnetic torques between the black hole and the inner accretion disk have on the energy dissipation profile. We attempt a plausible explanation to the observed "Deep Minimum" state in the Seyfert galaxy MCG-6- 30-15. For the latter type of magnetic geometry, we study the effects of the strength of the magnetic field threading the black hole within the context of the cherished Blandford & Znajek mechanism for black hole spin energy extraction. We begin by addressing the problem in the non-relativistic regime where we find that the black hole-threading magnetic field is stronger for greater disk thickness, larger magnetic Prandtl number, and for a larger accretion disk. We then study the problem in full relativity where we show that our Newtonian results are excellent approximations for slowly spinning black holes. We proceed to address the issue of the spin dependence of the Blandford & Znajek power. The result we choose to highlight is our finding that given the validity of our assumption for the dynamical behavior of the so-called plunge region in black hole accretors, rotating black holes produce maximum Poynting flux via the Blandford & Znajek process for a black hole spin parameter of about a [approximate] 0.8. This is contrary to the conventional claim that the maximum electromagnetic flux is achieved for highest black hole spin.

  14. Enhanced interface perpendicular magnetic anisotropy in Ta|CoFeB|MgO using nitrogen doped Ta underlayers

    NASA Astrophysics Data System (ADS)

    Sinha, Jaivardhan; Hayashi, Masamitsu; Kellock, Andrew J.; Fukami, Shunsuke; Yamanouchi, Michihiko; Sato, Hideo; Ikeda, Shoji; Mitani, Seiji; Yang, See-hun; Parkin, Stuart S. P.; Ohno, Hideo

    2013-06-01

    We show that the magnetic characteristics of Ta|CoFeB|MgO magnetic heterostructures are strongly influenced by doping the Ta underlayer with nitrogen. In particular, the saturation magnetization drops upon doping the Ta underlayer, suggesting that the doped underlayer acts as a boron diffusion barrier. In addition, the thickness of the magnetic dead layer decreases with increasing nitrogen doping. Surprisingly, the interface magnetic anisotropy increases to ˜1.8 erg/cm2 when an optimum amount of nitrogen is introduced into the Ta underlayer. These results show that nitrogen doped Ta serves as a good underlayer for spintronic applications including magnetic tunnel junctions and domain wall devices.

  15. Supplementary Notes: 1. Simulated magnetic field pattern

    E-print Network

    Cai, Long

    magnetic field B0 and the MNP- labeled cell's magnetization vector: || = = ! "# $ !% & '. (3 here, under a 400 G magnetizing field B0) uniformly distributed on a 15-µm diameter spherical cell with the applied bias magnetic field B0 to create a characteristic 2-lobed shape common to all labeled cells

  16. Modification of interface magnetic anisotropy by ion irradiation on epitaxial Cu/Ni/Cu(002)/ Si(100) films

    NASA Astrophysics Data System (ADS)

    Lee, J.-S.; Lee, K.-B.; Park, Y. J.; Kim, T. G.; Song, J. H.; Chae, K. H.; Lee, J.; Whang, C. N.; Jeong, K.; Kim, D.-H.; Shin, S.-C.

    2004-05-01

    Various x-ray scattering and magnetic measurements were employed to reveal changes in intrinsic structural and magnetic properties on epitaxial Cu/Ni(t)/Cu(002)/Si(100) thin films (t=20, 30, 60, and 90 Å) before and after 1 MeV C+ ion irradiation. Torque magnetometer and grazing incidence x-ray diffraction measurements were carried out to understand relation between magnetic and structural properties, respectively. X-ray reflectivity measurements were performed to characterize interface roughness and intermixing. It is observed that effective magnetic anisotropy values of ion-irradiated films are negative over the entire nickel thickness range and the dominant factor of the reorientation of magnetic easy axis from surface normal to surface parallel is reduction of the interface magnetic anisotropy coefficient in spite of decreased interface mixing after ion irradiation.

  17. Crystal field and magnetic properties

    NASA Technical Reports Server (NTRS)

    Flood, D. J.

    1977-01-01

    Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at theta = 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) x 10 to the -6th Weber m/kg Tesla. The saturation moment is 3.84 + or - 1 - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is on the order of 160 to 180 K.

  18. Transverse Magnetic Field Propellant Isolator

    NASA Technical Reports Server (NTRS)

    Foster, John E.

    2000-01-01

    An alternative high voltage isolator for electric propulsion and ground-based ion source applications has been designed and tested. This design employs a transverse magnetic field that increases the breakdown voltage. The design can greatly enhance the operating range of laboratory isolators used for high voltage applications.

  19. Heliospheric Electric and Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Popescu, Adrian Sabin

    2007-09-01

    From the Maxwell equations in the local Minkowski spacetime chart (derived from the DEUS topology) we obtain the relations to be particularized for a solar type star and a massive star, and later to be used for a 3D representation of the electric and magnetic field topology (in heliosphere or in a stellar atmosphere) and of its evolution with the cosmological time.

  20. Temperature dependence of magnetic anisotropy constant in CoFe2O4 nanoparticles examined by Mössbauer spectroscopy

    NASA Astrophysics Data System (ADS)

    Yoon, Sunghyun

    2015-04-01

    The temperature dependence of the effective magnetic anisotropy constant of CoFe2O4 nanoparticles is determined based on the measurements of SQUID magnetometry and Mössbauer spectroscopy. Under an intuitive assumption that the superparamagnetic fraction of the cumulative area in the particle size distribution at a temperature is equal to the doublet fraction in the Mössbauer spectra at that temperature, we are able to get a relation between r and T B, from which the temperature dependence of the effective magnetic anisotropy constant is determined. The resultant magnetic anisotropy constant increases markedly with decreasing temperature from 2.0 ×105 J/m 3 at 300 K to 8.3 ×106 J/m 3 at 125 K.