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1 Jul 2007

Volume 102, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 102, 011301 (2007); http://dx.doi.org/10.1063/1.2750414 (22 pages)

S. N. Piramanayagam
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Spin lifetime in silicon in the presence of parasitic electronic effects

Biqin Huang, Douwe J. Monsma, and Ian Appelbaum

J. Appl. Phys. 102, 013901 (2007); http://dx.doi.org/10.1063/1.2750411 (4 pages) | Cited 14 times

Online Publication Date: 3 July 2007

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A hybrid ferromagnet/semiconductor device is used to determine a lower bound on the spin lifetime for conduction electrons in silicon. We use spin precession to self-consistently measure the drift velocity versus drift field of spin-polarized electrons, and use this electronic control to change the transit time between electron injection and detection. A measurement of normalized magnetocurrent as a function of drift velocity is used with a simple exponential-decay model to argue that the value obtained ( ≈ 2 ns) is artificially lowered by electronic effects and could potentially be orders of magnitude higher.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
85.30.-z Semiconductor devices

Perpendicular magnetic anisotropy in TbFeCo films studied by magnetic Compton scattering

H. Sakurai, M. Ota, X. Liu, A. Morisako, Y. Sakurai, M. Itou, T. Nagao, and A. Koizumi

J. Appl. Phys. 102, 013902 (2007); http://dx.doi.org/10.1063/1.2751080 (5 pages) | Cited 6 times

Online Publication Date: 3 July 2007

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Magnetic Compton profiles (MCPs) of TbFeCo amorphous films have been measured from a viewpoint of perpendicular magnetic anisotropy (PMA). Analysis of anisotropies of the MCPs has shown that anisotropies of wave functions are small in both a PMA film and an isotropic magnetization (IM) film. Element selective analysis of the MCPs has shown that a Tb magnetic moment and a magnetic moment of 3d transition metal (TM) are coupled antiparallel in the PMA film. In the case the IM film, the magnetic moment of 3d TM tends to align toward the magnetic field but the Tb magnetic moment distributed to random orientations. The PMA natures reflect the magnetic structures of the Tb magnetic moment and the 3d TM magnetic moment in the TbFeCo films.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
78.70.-g Interactions of particles and radiation with matter

Identification of switching fields in magnetic nanostructures by partial first order reversal curves

L. Clime, T. Veres, and A. Yelon

J. Appl. Phys. 102, 013903 (2007); http://dx.doi.org/10.1063/1.2751115 (5 pages) | Cited 2 times

Online Publication Date: 3 July 2007

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A nonparametric approach to the identification of magnetic anisotropies in ferromagnetic nanostructures is described in this article. By an adequate choice of convenient measurement points on the first order reversal curves (FORC), essential information about either switching fields or symmetry of FORC diagrams are obtained from sets of five-point reversal curves only. Numerical simulations performed on assemblies of particles with known switching field distributions indicate that this method presents a high degree of accuracy and can successfully be used in order to characterize individual entities in magnetic nanostructures.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.-d Domain effects, magnetization curves, and hysteresis
75.30.Gw Magnetic anisotropy

Volumetric negative-refractive-index medium exhibiting broadband negative permeability

Scott M. Rudolph and Anthony Grbic

J. Appl. Phys. 102, 013904 (2007); http://dx.doi.org/10.1063/1.2751490 (6 pages) | Cited 7 times

Online Publication Date: 3 July 2007

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In this article, a broadband, volumetric, negative-refractive-index metamaterial is presented and its operation is explained. The structure achieves a negative permeability bandwidth of 60% using a periodic cage of backward-wave transmission lines. The permeability is negative over a broad bandwidth due to contradirectional coupling between a backward wave guided by a transmission line and a forward, free-space wave. Negative permittivity is realized using an array of inductively loaded wires. Propagation within the infinite negative-refractive-index (NRI) medium as well as transmission through finite slabs of the NRI medium is presented. The results demonstrate that the proposed NRI medium exhibits a refractive index equal to −1 at 2.45 GHz and is well matched to free space throughout the NRI bandwidth.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)

Ordering promotion and intergrain decoupling in FePt thin films by Ta and Ta/Bi buffer layers

L. J. Zhang, J. W. Cai, and H. Y. Pan

J. Appl. Phys. 102, 013905 (2007); http://dx.doi.org/10.1063/1.2752546 (5 pages) | Cited 2 times

Online Publication Date: 5 July 2007

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The magnetic properties and microstructure of annealed near-equiatomic FePt thin films with Ta and Ta/Bi buffer layers have been investigated. While Ta buffer layer effectively enhances the coercivity of FePt thin films, the insertion of a thin Bi layer between FePt and Ta layers further boosts the coercivity multifold. Most representatively, the 12 nm Fe48Pt52 films without buffer and with Ta (6 nm), and Ta (6 nm)/Bi (2 nm) buffer layers after annealing at 400 °C have coercivity of 0.95, 2.7, and 9.2 kOe, respectively, indicating greatly promoted L10 ordering of FePt films through a buffer layer of Ta, especially Ta/Bi. Moreover, the intergrain exchange interaction is appreciably reduced for the annealed Ta/FePt film and almost decoupled for the Ta/Bi/FePt film after annealing. The structural and chemical analyses reveal that Pt atoms transfer from FePt layer into the Ta layer while Ta atoms migrate into the grain boundaries of the FePt layer, and the thin Bi insertion layer reinforces the migration of Ta and Pt due to the outdiffusion of Bi during annealing, which results in the improvement of the ordering as well as the weakening of the intergrain exchange coupling for Ta/FePt, especially for Ta/Bi/FePt.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Magnetostructural transformation, microstructure, and magnetocaloric effect in Ni-Mn-Ga Heusler alloys

Babita Ingale, R. Gopalan, M. Manivel Raja, V. Chandrasekaran, and S. Ram

J. Appl. Phys. 102, 013906 (2007); http://dx.doi.org/10.1063/1.2751489 (5 pages) | Cited 8 times

Online Publication Date: 5 July 2007

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Magnetostructural transformation and the associated magnetic entropy change were investigated in Ni-rich ferromagnetic Heusler alloys. A direct transformation from the ferromagnetic martensite phase to the paramagnetic austenite phase was observed in selected Ni54.8Mn20.3Ga24.9 and Ni55Mn18.9Ga26.1 two-alloy compositions. The magnetic and martensitic transformations were incurred at nearly the same temperature (351 K) in the Ni54.8Mn20.3Ga24.9 alloy. Such a typical composition involves a change of the magnetic entropy ΔSM as large as −7.0 J/kg K at 332 K in an applied magnetic field of 1.2 T.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations

Substitution effects of barium and calcium on magnetic properties of AxSr1−x(Fe0.5Ru0.5)O3 double perovskites (x = 0.05, A = Ba,Ca)

K. Nomura, R. Zboril, J. Tucek, W. Kosaka, S. Ohkoshi, and I. Felner

J. Appl. Phys. 102, 013907 (2007); http://dx.doi.org/10.1063/1.2751101 (11 pages) | Cited 2 times

Online Publication Date: 6 July 2007

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AxSr1−x(Fe0.5Ru0.5)O3 double perovskites (x = 0.05 and A = Ba,Ca) were prepared by a sol-gel method and an effect of the cation substitution at the A site of the crystal structure of SrFe0.5Ru0.5O3 on their magnetic properties was monitored by x-ray diffraction (XRD), magnetic measurements, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and temperature-dependent and in-field 57Fe Mössbauer spectroscopy. Both Ca- and Ba-substituted samples reveal the orthorhombic structure similar to the undoped perovskite; however, the cell volume changes with the substituting ion radius. TEM and SEM micrographs manifest agglomerated nanocrystalline samples with particle sizes of about 20–60, 15–50, and 40–70 nm for the undoped, Ba-doped, and Ca-doped perovskites, respectively. Generally, the magnetic regime of both substituted and undoped perovskites can be described by a spin-glass behavior caused by a spin frustration. Among other factors, this is manifested by a nonsaturation of the hysteresis loops even at a high field of 50 kOe, by a low-temperature divergence of the zero-field-cooled and field-cooled magnetization curves, and by a cusp in the zero-field-cooled magnetization curve. The low-temperature spin-glass state is also supported by the in-field Mössbauer spectra, recorded on these systems. The isomer shift parameters, extracted from the Mössbauer spectra, confirm a high-spin iron(III) state with S = 5/2. In contrast to the undoped and Ba-doped samples, the narrower distribution of the hyperfine magnetic fields, observed in the Ca-doped perovskite can be ascribed to the larger particles. Compared to the undoped sample, the field of maximum probability is higher in the Ca-substituted perovskite while it is reduced in the Ba-doped sample because of the effects of the chemical compression and expansion, respectively. In addition, the Ca-doped sample exhibits more negative Weiss temperature (Θ = −105 K) than that found for the Ba-substituted perovskite (Θ = −49 K), implying that doping with Ca at Sr sites of SrFe0.5Ru0.5O3 perovskite structure provokes strengthening of antiferromagnetic interactions at the expense of the other ones. Furthermore, both substituted samples reveal significantly reduced coercive fields in the hysteresis loops recorded at 5 K, probably as a result of decreasing magnetocrystalline anisotropy. This is an indirect evidence of the essential influence of the substitution on the crystal growth of the synthesized particles. The role of SrRuO3 and SrFeO3 compounds, which have been detected in magnetic and Mössbauer measurements as admixtures, is discussed.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.-s Critical-point effects, specific heats, short-range order
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
76.80.+y Mössbauer effect; other γ-ray spectroscopy
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
61.66.Fn Inorganic compounds

Magnetocaloric effect in Mn-containing Hitperm-type alloys

V. Franco, C. F. Conde, J. S. Blázquez, M. Millán, and A. Conde

J. Appl. Phys. 102, 013908 (2007); http://dx.doi.org/10.1063/1.2751407 (4 pages) | Cited 6 times

Online Publication Date: 6 July 2007

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The magnetocaloric effect of Fe60−xMnxCo18Nb6B16 (x = 0,2,4) is studied. Mn addition decreases the Curie temperature of the alloys but also reduces the peak entropy change and the refrigerant capacity of the material. The estimated adiabatic temperature change, for a maximum applied field of 15 kOe, is 1.3 K. Obtained values are comparable to those of some Nanoperm-type alloys. The magnetic entropy change, ΔSM, of the studied samples follows a master curve, which is the same for all of them. The exponent controlling the field dependence of ΔSM scales with reduced temperature in the same way as the master curve does.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys
65.40.G- Other thermodynamical quantities

The study of low-field positive and negative magnetic entropy changes in Ni43Mn46−xCuxSn11 alloys

D. H. Wang, C. L. Zhang, H. C. Xuan, Z. D. Han, J. R. Zhang, S. L. Tang, B. X. Gu, and Y. W. Du

J. Appl. Phys. 102, 013909 (2007); http://dx.doi.org/10.1063/1.2752140 (4 pages) | Cited 19 times

Online Publication Date: 6 July 2007

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A series of Ni43Mn46−xCuxSn11 (x = 1, 2, and 3) alloys was prepared by the arc melting method. The martensitic transition shifts to a higher temperature with increasing Cu concentration. The isothermal magnetization curves around the martensitic transition temperature show a typical metamagnetic behavior. Under a low applied magnetic field of 10 kOe, positive values of magnetic entropy change around the martensitic transition temperature are 14.1, 18.0, and 15.8 J/kg K for x = 1, 2, and 3, respectively. While in the vicinity of the Curie temperature of the austenitic phase, these negative values are 1.1, 1.0, and 0.9 J/kg K for x = 1, 2, and 3, respectively. The origin of the large entropy changes and the potential application for Ni43Mn46−xCuxSn11 alloys as a working substance for magnetic refrigeration are discussed.
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75.30.Sg Magnetocaloric effect, magnetic cooling
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys

Manipulation of magnetic nanoparticles by the strayfield of magnetically patterned ferromagnetic layers

I. Ennen, V. Höink, A. Weddemann, A. Hütten, J. Schmalhorst, G. Reiss, C. Waltenberg, P. Jutzi, T. Weis, D. Engel, and A. Ehresmann

J. Appl. Phys. 102, 013910 (2007); http://dx.doi.org/10.1063/1.2752146 (4 pages) | Cited 4 times

Online Publication Date: 6 July 2007

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The manipulation of magnetic particles at the nanometer scale is of great interest for applications in biotechnology. In this work the self-assembly of 12 nm Co nanocrystallites under the influence of magnetic strayfields originating from a magnetically patterned 3 nm thick CoFe layer has been investigated. The magnetic patterning has been carried out by bombardment with 10 keV He ions in an external magnetic field. A controllable accumulation of magnetic nanoparticles has been found at areas of the sample with a head to head orientation of the local magnetization. The force generated by the strayfield of Néel walls without head to head orientation of the magnetization is about ten times weaker and turned out to be just strong enough to attract a relatively small number of nanocrystals. Furthermore, it has been shown that the choice of the procedure to bring the particle solution onto the magnetically patterned sample determines the successful generation of particle arrangements and can be used to tune the number of particles and their coordination within the strayfield.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
68.37.Ps Atomic force microscopy (AFM)

Micromagnetic reversal behavior of multiscale permalloy elements

B. R. Craig, S. McVitie, J. N. Chapman, D. O. O’Donnell, and A. B. Johnston

J. Appl. Phys. 102, 013911 (2007); http://dx.doi.org/10.1063/1.2752151 (5 pages) | Cited 3 times

Online Publication Date: 6 July 2007

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Lorentz microscopy has been used to study the micromagnetic processes occurring during the reversal of multiscale permalloy elements. The elements, which have similar dimensions to write heads used in magnetic recording, typically have length scales varying from 10 μm in the element “core” down to 100 nm in the element “tip.” A discussion of the effect of varying the geometry and critical dimensions of the elements on the reversal behavior and switching fields is presented. While the magnetization processes in the core tend to be similar to what is observed in the absence of a tip, the presence of the core strongly influences the tip reversal, even for tips with widths of 100 nm. The results demonstrate clearly the role played by shape anisotropy in complex shaped elements fabricated from an isotropic magnetic film.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films

Magnetic anisotropies in ultrathin iron films grown on the surface-reconstructed GaAs substrate

B. Aktaş, B. Heinrich, G. Woltersdorf, R. Urban, L. R. Tagirov, F. Yıldız, K. Özdoğan, M. Özdemir, O. Yalçin, and B. Z. Rameev

J. Appl. Phys. 102, 013912 (2007); http://dx.doi.org/10.1063/1.2749469 (8 pages) | Cited 10 times

Online Publication Date: 11 July 2007

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Magnetic anisotropies of epitaxial ultrathin iron films grown on the surface-reconstructed GaAs substrate were studied. Ferromagnetic resonance technique was exploited to determine magnetic parameters of the films in the temperature range of 4–300 K. Extraordinary angular dependence of the FMR spectra was explained by the presence of fourfold and twofold in-plane anisotropies. A strong in-plane uniaxial anisotropy with magnetic hard axis along the [1math0] crystallographic direction is present at the GaAs/Fe(001) interface while a weak in-plane uniaxial anisotropy for the Fe grown on Au has its easy axis oriented along [1math0]. A linear dependence of the magnetic anisotropies as a function of temperature suggests that the strength of the in-plane uniaxial anisotropy is affected by the magnetoelastic anisotropies and differential thermal expansion of contacting materials.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.80.+q Magnetomechanical effects, magnetostriction
65.40.G- Other thermodynamical quantities

Microstructures of SiC nanoparticle-doped MgB2/Fe tapes

Y. Zhu, A. Matsumoto, B. J. Senkowicz, H. Kumakura, H. Kitaguchi, M. C. Jewell, E. E. Hellstrom, D. C. Larbalestier, and P. M. Voyles

J. Appl. Phys. 102, 013913 (2007); http://dx.doi.org/10.1063/1.2750409 (9 pages) | Cited 22 times

Online Publication Date: 11 July 2007

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We have studied bulk MgB2 synthesized by reaction of MgH2 and B with and without SiC nanoparticles and at a range of reaction temperatures. All of the samples showed enhanced upper critical fields compared to most bulk MgB2, including the sample with 10 at. % SiC reacted at 600 °C, which showed Hc2(0 K)>42 T. Extensive transmission electron microscopy (TEM) and STEM observations show that using MgH2 instead of pure Mg reduces the concentration of oxide second phases in the tapes, but that adding SiC reintroduces nanoscale grains of MgO, SiO2, and SiOxCy, and larger grains of Mg2Si. SiC causes some C doping of the MgB2, but electron energy loss spectroscopy and x-ray diffraction measurements show that the C concentration is similar to other bulk C-doped MgB2. In all the samples with and without SiC, the grain size is very small, 10–60 nm. Electron scattering from the high density of grains and second-phase boundaries is responsible for the enhanced Hc2 of these samples. However, the Hc2 properties are somewhat compromised by very broad transitions that may have their origin in the local variations of nanostructure.
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74.25.Op Mixed states, critical fields, and surface sheaths
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
68.37.Lp Transmission electron microscopy (TEM)
74.62.Dh Effects of crystal defects, doping and substitution

Enhancement of the critical current density and the irreversibility field in maleic anhydride doped MgB2 based tapes

Zhaoshun Gao, Yanwei Ma, Xianping Zhang, Dongliang Wang, Zhengguang Yu, Huan Yang, Haihu Wen, and E. Mossang

J. Appl. Phys. 102, 013914 (2007); http://dx.doi.org/10.1063/1.2748711 (4 pages) | Cited 17 times

Online Publication Date: 11 July 2007

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A significant enhancement of Jc, Hirr, and Hc2 in MgB2 tapes has been achieved by using maleic anhydride (C4H2O3) as dopants. MgB2 tape samples with 0 up to 30 wt % C4H2O3 added were prepared by an in situ processed powder-in-tube method. Compared to the pure tapes, Jc for the 10 wt % C4H2O3 doped samples was improved by more than an order of magnitude in high fields up to 18 T. At 4.2 K, the transport Jc for the 10 wt % doped samples reached 1.08×104, 5.42×103, and 2.18×103 A/cm2 at 12, 14, and 16 T, respectively, and were better than those of the best MgB2/Fe tapes reported by far. Furthermore, the Hirr for the 10 wt % doped sample reached 9.6 T at 20 K, which was comparable to that of NbTi at 4.2 K. The improvement of the superconducting properties in doped tapes can be attributed to the increase of Hc2 and the grain size refinement by C4H2O3 doping.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Sv Critical currents
74.25.F- Transport properties

Dynamic and temperature effects in toggle magnetic random access memory

Dorin Cimpoesu, Alexandru Stancu, and Leonard Spinu

J. Appl. Phys. 102, 013915 (2007); http://dx.doi.org/10.1063/1.2752138 (7 pages) | Cited 10 times

Online Publication Date: 11 July 2007

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In this paper we have studied the dynamic switching in magnetic random access memory (MRAM) and its dependence on thermal effects due to a finite temperature. The model is based on the Landau-Lifshitz-Gilbert equation and the stochastic Landau-Lifshitz-Gilbert equation which are numerically integrated. The magnetic layers are assumed to be ellipsoid shaped with each magnetic layer single domain. In addition, we have taken into account the uniaxial intrinsic anisotropy. Simulations were performed for both balanced and nonbalanced synthetic antiferromagnetic elements. The switching properties are discussed as a function of applied field pulses’ length and shape. In this paper we present how the thermal fluctuations affect the switching behavior, the reliability, and the writing speed of MRAM devices.
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84.30.Sk Pulse and digital circuits
85.70.Ay Magnetic device characterization, design, and modeling

Electrical and magnetic properties of chemically derived nanocrystalline cobalt ferrite

N. Sivakumar, A. Narayanasamy, K. Shinoda, C. N. Chinnasamy, B. Jeyadevan, and J.-M. Greneche

J. Appl. Phys. 102, 013916 (2007); http://dx.doi.org/10.1063/1.2752098 (8 pages) | Cited 20 times

Online Publication Date: 12 July 2007

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Nanocrystalline cobalt ferrite particles of 8 nm grain size were synthesized by coprecipitation technique and subsequently suitably heat treated to obtain higher grain sizes. The experimentally observed changes in the dc electrical conductivity and Curie temperature with heat treatment have been attributed to the changes in the cation distributions as obtained from the Mössbauer and extended x-ray absorption fine structure (EXAFS) measurements and to the grain size. The activation energies for conduction as determined from the Arrhenius plots suggest that the conductivity is due to hopping of both electrons and holes. The observed decrease in conductivity when the grain size is increased from 8 to 92 nm is clearly due to the predominant effect of migration of some of the Fe3+ ions from octahedral to tetrahedral sites, as is evident from in-field Mössbauer and EXAFS measurements. But the higher conductivity of the 102 and 123 nm particles compared to that of the 92 nm particles is attributed to the higher grain size, since the cation distribution is found to be the same for all these three samples. The Néel temperature increases from 709 K for the as-prepared particles (8 nm) to 809 K for the 92 nm particles because of the change in the cation distribution and it remains almost the same for the higher grain sizes as there is no further change in the cation distribution.
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73.63.Bd Nanocrystalline materials
72.20.Ee Mobility edges; hopping transport
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
81.40.Rs Electrical and magnetic properties related to treatment conditions

Inverse tunnel magnetoresistance in magnetic tunnel junctions with an Fe4N electrode

Kazuyuki Sunaga, Masakiyo Tsunoda, Kojiro Komagaki, Yuji Uehara, and Migaku Takahashi

J. Appl. Phys. 102, 013917 (2007); http://dx.doi.org/10.1063/1.2753576 (4 pages) | Cited 16 times

Online Publication Date: 13 July 2007

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The magnetotransport properties of Fe4N/MgO/CoFeB and Fe/MgO/CoFeB magnetic tunnel junctions (MTJs) were investigated at room temperature. In the Fe/MgO/CoFeB-MTJ, normal tunnel magnetoresistance (TMR) effect and roughly symmetric bias voltage (VB) dependence were observed, similar to the MTJs exhibiting coherent tunneling such as Fe/MgO/Fe. On the other hand, the inverse TMR effect, showing higher tunnel resistance for parallel magnetization configuration than for antiparallel configuration, and strong asymmetric VB dependence of TMR ratio were observed in the Fe4N/MgO/CoFeB-MTJ. The maximum TMR magnitude of 18.5% was obtained at VB = −200 mV, where the current flows from Fe4N to CoFeB. The enhancement of the inverse TMR ratio around VB = −200 mV is due to the broad peak of tunnel conductance in antiparallel configuration of Fe4N and CoFeB magnetizations. A large peak of the density of state at +300 meV from the Fermi level for minority spin electrons of bulk Fe4N might be an origin of this phenomenon.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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