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1 Apr 2012

Volume 111, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 111, 071101 (2012); http://dx.doi.org/10.1063/1.3694674 (23 pages)

Shunfeng Li and Andreas Waag
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back to top New Magnetic Materials, Instrumentation, and Measurement Techniques

1s2p resonant inelastic x-ray scattering-magnetic circular dichroism: A sensitive probe of 3d magnetic moments using hard x-ray photons

M. Sikora, A. Juhin, G. Simon, M. Zając, K. Biernacka, Cz. Kapusta, L. Morellon, M. R. Ibarra, and P. Glatzel

J. Appl. Phys. 111, 07E301 (2012); http://dx.doi.org/10.1063/1.3670064 (3 pages)

Online Publication Date: 7 February 2012

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We investigated the magnetic properties of thin magnetite and iron films grown on MgO(001) by means of hard x-ray photon-in photon-out probe, namely, 1s2p resonant inelastic x-ray scattering-magnetic circular dichroism (RIXS-MCD). A comparison of the spectra acquired from bulk and thin layer magnetite samples reveals their nearly identical shape. Hysteresis loops measured with RIXS-MCD also show a close similarity to the vibrating sample magnetometer profiles supporting the conclusion that the technique can be applied for the quantitative analysis of element and site specific magnetization in buried films containing transition metal elements. We show that Fe 1s2p RIXS-MCD is insensitive to the magnetic signal of iron impurities naturally dispersed in monocrystalline MgO substrates. The latter, combined with a unique feature of resonant inelastic x-ray scattering, namely the ability to tune incident and emitted photon (transfer) energy, allows us to separate the dichroic signal of metal layers from that of ferrite and, thus, to independently probe the magnetization of metal and oxide layers in multilayer systems.
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75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.Ck X-ray scattering
75.30.Cr Saturation moments and magnetic susceptibilities
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Magnetic characteristics of a new cubic defect spinel Li0.5Mg0.5MnO3

V. Singh, M. S. Seehra, A. Manivannan, and P. N. Kumta

J. Appl. Phys. 111, 07E302 (2012); http://dx.doi.org/10.1063/1.3670504 (3 pages)

Online Publication Date: 7 February 2012

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Magnetic properties of Li0.5Mg0.5MnO3−δ nanoparticles (size ≃ 20 nm) synthesized by the Pechini method are investigated using temperature dependence of its magnetization (M) and electron magnetic resonance (EMR) spectra at 9.286 GHz. Analysis of the x-ray diffraction spectra yields its structure to be a cubic defect spinel with the formula 4(Li0.5Mg0.5MnO2.75) = 3{[Li2/3Mg1/3][Mn4/3Mg1/3□1/3]O11/3]} so that Mn occupies the octahedral B-sites only. The data of M versus T yields a blocking temperature TB ≃ 9 K above which the Curie–Weiss law variation with θ = 13 K and μ = 3.96μB characteristic of Mn4+ ions is established. For T < 9 K, temperature dependent coercivity and remanence are observed. The observed temperature dependence of the EMR parameters (linewidth ΔH, resonance field Hr, and intensity Io) for T < 30 K is interpreted in terms of TB (EMR) ≃ 30 K. Formation of ferromagnetic Mn4+ clusters, resulting from the co-presence of non-magnetic Mg2+ and vacancies on the B-sites, is inferred.
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75.75.Cd Fabrication of magnetic nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.jd Vacancies

Spin reorientation transition and hard magnetic properties of MnBi intermetallic compound

K. Suzuki, X. Wu, V. Ly, T. Shoji, A. Kato, and A. Manabe

J. Appl. Phys. 111, 07E303 (2012); http://dx.doi.org/10.1063/1.3670505 (3 pages)

Online Publication Date: 8 February 2012

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The effects of mechanical grinding (MG) on the crystallite size, the spin reorientation transition temperature (TSR) and the hard magnetic properties in melt-spun low temperature phase (LTP) MnBi have been investigated in order to understand the origin of magnetic hardening induced by MG. The room-temperature coercive field (μ0Hcj) is enhanced dramatically from 0.08 T before MG to 1.5 T after MG for 43.2 ks while TSR is concurrently suppressed from 110 to 38 K. The coercive force exhibits positive temperature dependence approximately 50–60 K above TSR and the lowered TSR after MG could result in magnetic hardening at room temperature. The room-temperature coercive force of LTP-MnBi is highly dependent on the crystallite size (D) and is found to be described phenomenologically by the following relationship: μ0Hcj = μ0Ha(δ/D)n, where μ0Ha is ∼ 4 T, the Bloch wall width δ is 7 nm, and the exponent n is approximately 0.7. Our results suggest that the grain refinement is the primary origin of the hardening effect induced by MG with a possible minor hardening effect due to the suppression of the spin reorientation transition temperature.
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75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ww Permanent magnets
75.60.Ch Domain walls and domain structure
75.50.Vv High coercivity materials

Spin-dependent synchrotron x-ray excitations studied by scanning tunneling microscopy

V. Rose, T. Y. Chien, J. W. Freeland, D. Rosenmann, J. Hiller, and V. Metlushko

J. Appl. Phys. 111, 07E304 (2012); http://dx.doi.org/10.1063/1.3670968 (3 pages) | Cited 2 times

Online Publication Date: 9 February 2012

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The ability to position a sharp probe in close proximity to a sample while the surface is illuminated by synchrotron x-rays opens a path to localized spectroscopy and imaging with chemical and magnetic contrast. We have employed a scanning tunneling microscope for the local study of synchrotron x-ray magnetic circular dichroism of micron-sized NiFe rings. Spectra have been obtained by an insulator-coated tip positioned about 200 nm over the sample surface. A negative sample bias is required in order to enhance the dichroism signal at the tip.
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78.20.Ls Magneto-optical effects

Study on rare-earth–doped type-I germanium clathrates

Xiaohui Zhu, Ning Chen, Lihua Liu, and Yang Li

J. Appl. Phys. 111, 07E305 (2012); http://dx.doi.org/10.1063/1.3671396 (3 pages)

Online Publication Date: 13 February 2012

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The synthesis of rare-earth clathrates RExBa8−xGa16Ge30 is a challenging task. The Group IV clathrates with rare-earth doping are hardly to be experimentally prepared, except Eu clathrate. In the current study, the first-principle method based on the density functional theory was implemented. The effects of the various RE elements doping on the binding energy and chemical reaction drive energy were studied by optimizing the phase structure. The energy calculations suggest that it is difficult to synthesize RE clathrates without Ga doping. The function of Ga doping is to effectively increase the drive chemical reaction in order to synthesize the clathrates. The simulation shows that, besides Eu, other rare-earth elements, such as Sm, Nd, and Yb can also enter cage lattice in the considering of drive energy, thus making it possible to synthesize the (RE,Ba)8Ge30Ga16 clathrates.
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61.72.up Other materials
71.15.-m Methods of electronic structure calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Magnetic properties and crystal structure of melt-spun Sm(Co, M)7 (M = Al and Si) ribbons

C. C. Hsieh, C. W. Shih, Z. Liu, W. C. Chang, H. W. Chang, A. C. Sun, and C. C. Shaw

J. Appl. Phys. 111, 07E306 (2012); http://dx.doi.org/10.1063/1.3671429 (3 pages) | Cited 1 time

Online Publication Date: 14 February 2012

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Effect of Si and Al contents on the magnetic properties and crystal structure of melt-spun SmCo7-xMx (M = Al and Si) ribbons have been investigated. The Rietveld refinement results show that Al and Si prefer to occupy the 3g site in the TbCu7-type structure. The changes in both the magnetocrystalline anisotropy field and the microstructure with Si or Al substitution may account for the variation of magnetic properties. The coercivity of SmCo7−xSix ribbons is enhanced from 1.9 kOe for SmCo7 to 4.7 kOe for SmCo6.5Si0.5 and 2.6 kOe for SmCo6.95Al0.05, which is mainly because of the enhancement of magnetic anisotropy field by the Si and Al substitution for Co in 3g sites. Furthermore, in melt-spun SmCo7−xMx ribbons system, with increasing x, the grain size is slightly reduced for M = Si, but increased for M = Al. In addition, with further increasing x, the enhancement of coercivity is attributed to both the third element substitution for Co in 3g sites and grain refinement.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
61.66.Dk Alloys
75.30.Gw Magnetic anisotropy
75.50.Ww Permanent magnets
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Theoretical investigation on the magnetic phase stability of Fe-doped Bi tellurides

Miyoung Kim and Jung-Hwan Song

J. Appl. Phys. 111, 07E307 (2012); http://dx.doi.org/10.1063/1.3671777 (3 pages) | Cited 2 times

Online Publication Date: 14 February 2012

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The structural properties and magnetic phase stability of Fe-doped Bi2Te3 are studied in first principles by means of the highly precise full-potential linearized augmented plane-wave method within the generalized gradient approximation. Two different types of Fe doping, which are substitutional and interstitial, are examined, assuming about 8% of the Fe doping level, where the atomic structures are fully optimized by atomic force calculations. Our results show that: (i) ferromagnetic phases are energetically more stable over paramagnetic phases for both substitutional and interstitial Fe dopings, (ii) the substitutional Fe doping indicates a high magnetic phase with a largely enhanced Fe magnetic moment of 3.40 μB while the interstitial Fe doping shows the magnetic moment similar to the Fe bulk value, and (iii) the structural optimization reduces the Fe magnetic moments for both doping types while the overall effects on the total moment exhibit different results for different doping types.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
61.72.jj Interstitials
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Field-induced magnetic transition in cobalt-ferrite

Martin Kriegisch, Weijun Ren, Reiko Sato-Turtelli, Herbert Müller, Roland Grössinger, and Zhidong Zhang

J. Appl. Phys. 111, 07E308 (2012); http://dx.doi.org/10.1063/1.3671778 (3 pages) | Cited 3 times

Online Publication Date: 15 February 2012

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We present magnetostriction and magnetization measurements of a cobalt ferrite (Co0.8Fe2.2O4) single crystal. We observe unusual behavior in the magnetic hard axis of the single crystal which manifests in a jump of the magnetization curve at a critical field. This first order magnetization process (FOMP), which is explained as an anisotropy-driven transition, is visible at temperatures lower than 150 K. By analyzing the anisotropy constants, we found that the higher order anisotropy constant K2 dominates the anisotropy energy. In the magnetostriction measurements, the FOMP is clearly visible as a huge jump in the [111] direction, which can be explained by means of a geometric model.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy

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

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

J. Appl. Phys. 111, 07E309 (2012); http://dx.doi.org/10.1063/1.3671785 (3 pages) | Cited 2 times

Online Publication Date: 15 February 2012

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

Instability of the ferromagnetic ground state in Lu2Fe17−XMnX [x = 0.5, 0.7]

Z. Arnold, A. Kuchin, and J. Kamarad

J. Appl. Phys. 111, 07E310 (2012); http://dx.doi.org/10.1063/1.3672072 (3 pages) | Cited 1 time

Online Publication Date: 22 February 2012

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The magnetic properties of polycrystalline Lu2Fe16.5Mn0.5 and Lu2Fe16.3Mn0.7 compounds have been studied under hydrostatic pressure up to 10 kbar in the temperature range of 5–300 K and at magnetic fields up to 5 T. The Lu2Fe16.3Mn0.7 compound is in the ferromagnetic (FM) state, and the Lu2Fe16.5Mn0.5 is in the FM state at low temperatures and in the antiferromagnetic state at high temperatures at ambient pressure. We have revealed that the FM state is very sensitive to volume changes and even moderate pressure is sufficient to complete its suppression. The critical pressures are 4 kbar for Lu2Fe16.5Mn0.5 and 7 kbar for Lu2Fe16.3Mn0.7. The suppression of the FM ground state is observed at practically the same volume of the elementary cell. The pressure induced Néel temperature, TN, of both compounds decreases with increasing pressure, dTN/dp = −2.5 K/kbar and dTN/dp = −3.4 K/kbar, for Lu2Fe16.5Mn0.5 and Lu2Fe16.3Mn0.7, respectively. The remarkable strengthening of the FM ground state by the Mn substitution and its total suppression by external pressure can mainly be attributed to a subtle competition of positive and negative local direct exchange interactions between Fe atoms located at inequivalent structural sites. These interactions are strongly dependent on the interatomic Fe-Fe distances.
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75.30.Et Exchange and superexchange interactions
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.Ee Antiferromagnetics
75.50.Bb Fe and its alloys

Domain wall propagation in micrometric wires: Limits of single domain wall regime

V. Zhukova, J. M. Blanco, V. Rodionova, M. Ipatov, and A. Zhukov

J. Appl. Phys. 111, 07E311 (2012); http://dx.doi.org/10.1063/1.3672076 (3 pages) | Cited 3 times

Online Publication Date: 22 February 2012

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We measured magnetic domain propagation and local domain wall(DW) nucleation in Fe-Co-rich amorphous microwires with metallic nucleus diameters from 2.8 to 18 μm. We found that manipulation of magnetoelastic energy through application of applied stresses, changing of magnetostriction constant, and variation of internal stresses through changing the microwires geometry affects DW velocity. We observed uniform or uniformly accelerated DW propagation along the microwire. The abrupt increasing of DW velocity on v(H) dependencies correlates with the location of the nucleation place of the new domain wall.
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75.60.Ch Domain walls and domain structure
75.78.Fg Dynamics of domain structures
75.80.+q Magnetomechanical effects, magnetostriction

Preparation and magnetic properties of MnBi

Y. B. Yang, X. G. Chen, R. Wu, J. Z. Wei, X. B. Ma, J. Z. Han, H. L. Du, S. Q. Liu, C. S. Wang, Y. C. Yang, Y. Zhang, and J. B. Yang

J. Appl. Phys. 111, 07E312 (2012); http://dx.doi.org/10.1063/1.3672086 (3 pages) | Cited 3 times

Online Publication Date: 23 February 2012

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MnBi with low temperature phase was fabricated by melt-spinning and subsequently annealing. The influence of quenching speeds, compositions and annealing conditions on the formation of low temperature phase MnBi was systematically investigated. It was found the amorphous MnBi ribbons could transform into low temperature phase by heat treatment in a temperature range of 533–593 K. The coercivity of MnBi was greatly improved by porphyrization, and exhibited a positive temperature coefficient. The maximum energy product BHmax of the anisotropic bonded magnet is 7.1 MGOe (56 kJ/m3) and 4.0 MGOe (32 kJ/m3) at room temperature and 400 K.
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75.75.Cd Fabrication of magnetic nanostructures
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.40.Gh Other heat and thermomechanical treatments

Impacts of enhanced electronic correlation in anion p-orbitals on electronic structure and magnetic properties of nitrogen or carbon doped zinc oxide

Yao-fang Zhang, Hong Liu, Jian Wu, and Xu Zuo

J. Appl. Phys. 111, 07E313 (2012); http://dx.doi.org/10.1063/1.3672090 (3 pages)

Online Publication Date: 23 February 2012

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The electronic structure and magnetic properties of nitrogen or carbon doped zinc oxide are studied by using ab initio calculation, where the electronic correlation in anion p-orbitals are enhanced by adding the on-site Coulomb repulsion. The calculation shows that the enhanced electronic correlation can result in an insulating density of state and negligible exchange coupling beyond the next nearest neighbor, both of which question the possibility of hole-induced ferromagnetism in these materials.
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71.20.Nr Semiconductor compounds
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.70.Gm Exchange interactions
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities

Effects of nitrogen deficiency on the magnetostructural properties of antiperovskite manganese nitrides

D. Kasugai, A. Ozawa, T. Inagaki, and K. Takenaka

J. Appl. Phys. 111, 07E314 (2012); http://dx.doi.org/10.1063/1.3672243 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2012

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Giant negative thermal expansion in antiperovskite manganese nitrides Mn3AN (A = Zn, Ga, etc.) is achieved by substituting Ge for A as a “relaxant” to the sharp volume change associated with the magnetic transition. We have studied the effects of nitrogen deficiency on the broadening of volume change. Although the broadening increases with decreasing nitrogen content for Mn3Cu0.5Ge0.5N1-δ, the sharp volume change is robust against nitrogen deficiency in Ge-free Mn3GaN1-δ. Nitrogen deficiency probably does not broaden the volume change by itself; rather it probably assists the broadening in conjunction with the Ge dopant. The origin of the broadening is discussed in terms of local lattice distortion of the Mn6N octahedra.
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65.40.De Thermal expansion; thermomechanical effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.sd Impurity concentration

New magnetic configuration in paramagnetic phase of HoCo2

C. M. Bonilla, I. Calvo, J. Herrero-Albillos, A. I. Figueroa, C. Castan-Guerrero, J. Bartolomé, J. A. Rodriguez-Velamazan, D. Schmitz, E. Weschke, D. Paudyal, V. K. Pecharsky, K. A. Gschneidner, Jr., F. Bartolomé, and L. M. García

J. Appl. Phys. 111, 07E315 (2012); http://dx.doi.org/10.1063/1.3672258 (3 pages) | Cited 1 time

Online Publication Date: 23 February 2012

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X-ray magnetic circular dichroism (XMCD) measurements on HoCo2 reveal the inversion of Co moment at temperatures higher than the critical temperature, Tc, showing that the net magnetization under a field of the Ho and Co sublattices remain antiparallel even above Tc. The Ho moment also changes its orientation to align antiparallel to the applied field at high temperature giving rise to a new magnetic configuration in the paramagnetic regime. Transverse susceptibility (TS) and small angle neutron scattering (SANS) measurements performed above Tc indicate the existence of sizable magnetic short-range correlated regions in HoCo2. First principles calculations based on spin polarized local-density approximation, LSDA+U havebeen performed to obtain insights on the origin of the short-range correlated volume.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
78.20.Ls Magneto-optical effects
75.20.En Metals and alloys

A wavelet approach for the identification of surface cracks using current injection perturbation

A. A. Adly and S. K. Abd-El-Hafiz

J. Appl. Phys. 111, 07E316 (2012); http://dx.doi.org/10.1063/1.3672401 (3 pages)

Online Publication Date: 23 February 2012

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The non-destructive identification of surface cracks in steel parts has always been an issue of great industrial interest. Among the non-destructive crack inspection approaches proposed in the past is field measurement resulting from impressed current crack perturbation. Obviously, crack detection becomes more challenging as the active sensor dimensions and/or surface clearance become large in comparison to the crack itself. In this paper, the wavelets approach is utilized in crack volume and location detection using impressed current differential measurements involving relatively large sensing elements. Detailed methodology and results demonstrating the advantages of the proposed approach are given in the paper.
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89.20.Kk Engineering
02.30.Rz Integral equations
46.50.+a Fracture mechanics, fatigue and cracks
81.70.-q Methods of materials testing and analysis

Delayed switching applied to memristor neural networks

Frank Z. Wang, Na Helian, Sining Wu, Xiao Yang, Yike Guo, Guan Lim, and Md Mamunur Rashid

J. Appl. Phys. 111, 07E317 (2012); http://dx.doi.org/10.1063/1.3672409 (3 pages) | Cited 1 time

Online Publication Date: 24 February 2012

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Magnetic flux and electric charge are linked in a memristor. We reported recently that a memristor has a peculiar effect in which the switching takes place with a time delay because a memristor possesses a certain inertia. This effect was named the “delayed switching effect.” In this work, we elaborate on the importance of delayed switching in a brain-like computer using memristor neural networks. The effect is used to control the switching of a memristor synapse between two neurons that fire together (the Hebbian rule). A theoretical formula is found, and the design is verified by a simulation. We have also built an experimental setup consisting of electronic memristive synapses and electronic neurons.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
84.35.+i Neural networks

Six-input lookup table circuit with 62% fewer transistors using nonvolatile logic-in-memory architecture with series/parallel-connected magnetic tunnel junctions

D. Suzuki, M. Natsui, T. Endoh, H. Ohno, and T. Hanyu

J. Appl. Phys. 111, 07E318 (2012); http://dx.doi.org/10.1063/1.3672411 (3 pages)

Online Publication Date: 24 February 2012

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A compact 6-input lookup table (LUT) circuit using nonvolatile logic-in-memory (LIM) architecture with series/parallel-connected magnetic tunnel junction (MTJ) devices is proposed for a standby-power-free field-programmable gate array. Series/parallel connections of MTJ devices make it possible not only to reduce the effect of resistance variation, but also to enhance the programmability of resistance values, which achieves a sufficient sensing margin even when process variation is serious in the recent nanometer-scaled VLSI. Moreover, the additional MTJ devices do not increase the effective chip area because the configuration circuit using MTJ devices is simplified and these devices are stacked over the CMOS plane. As a result, the transistor counts of the proposed circuit are reduced by 62% in comparison with those of a conventional nonvolatile LUT circuit where CMOS-only-based volatile static random access memory cell circuits are replaced by MTJ-based nonvolatile ones.
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84.30.Sk Pulse and digital circuits
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.70.-w Magnetic devices

Thermoelectric efficiency of topological insulators in a magnetic field

O. A. Tretiakov, Ar. Abanov, and Jairo Sinova

J. Appl. Phys. 111, 07E319 (2012); http://dx.doi.org/10.1063/1.3672847 (3 pages) | Cited 2 times

Online Publication Date: 24 February 2012

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We study the thermoelectric properties of three-dimensional topological insulators in magnetic fields with many holes (or pores) in the bulk. We find that at a high density of these holes in the transport direction the thermoelectric figure of merit, ZT, can be large due to the contribution of the topologically protected conducting surfaces and the suppressed phonon thermal conductivity. By applying an external magnetic field, a subgap can be induced in the surface states’ spectrum. We show that the thermoelectric efficiency can be controlled by this tunable subgap leading to values of ZT much greater than 1. Such high values of ZT for reasonable system parameters and its tunability by a magnetic field make this system a strong candidate for applications in the heat management of nanodevices, especially at low temperatures.
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72.20.Pa Thermoelectric and thermomagnetic effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Measurement of the two-dimensional magnetostriction and the vector magnetic property for a non-oriented electrical steel sheet under stress

Y. Kai, Y. Tsuchida, T. Todaka, and M. Enokizono

J. Appl. Phys. 111, 07E320 (2012); http://dx.doi.org/10.1063/1.3673807 (3 pages)

Online Publication Date: 28 February 2012

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This paper presents the influence of mechanical stress on the two-dimensional (2-D) magnetostriction and the vector magnetic property for a non-oriented electrical steel sheet. A six-axial strain gauge is developed in order to measure the in-plane mechanical stress and the magnetostriction of the non-oriented electrical steel sheet. The vector magnetic property and 2-D magnetostriction under tensile and compressive stress are also measured. From the results, the difference in the vector magnetic property and 2-D magnetostriction due to the applied mechanical stress is obtained.
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75.80.+q Magnetomechanical effects, magnetostriction
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.05.Bx Metals, semimetals, and alloys

Stochastic limits in synchronous imaging of sub-micron magnetization dynamics using scanning transmission x-ray microscopy

Cheng Cheng, Konstantine Kaznatcheev, and William E. Bailey

J. Appl. Phys. 111, 07E321 (2012); http://dx.doi.org/10.1063/1.3673825 (3 pages) | Cited 1 time

Online Publication Date: 28 February 2012

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We demonstrate a synchronous (lock-in) technique for imaging thin-film magnetization dynamics using scanning transmission x-ray microscopy (STXM). Gated photon counting synchronized with magnetic field modulation allows image acquisition with differential contrast for high and low magnetization. We have applied this technique to 5 × 12 μm2 Ni81Fe19 ellipses with well-defined closure domains at remanence. The stochastic nature of the domain wall motion and nucleation is apparent in images recorded during cycling along successive major hysteresis loops. Synchronous imaging shows the clearest enhancement of contrast for small-amplitude domain wall motion, with a less obvious benefit at higher fields/displacements. The technique shows promise for the contrast enhancement of magnetization in dynamics in STXM.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Yz X-ray microscopy

Structures and magnetic properties of Sm5Fe17 melt-spun ribbon

Tetsuji Saito, Hiroya Miyoshi, and Daisuke Nishio-Hamane

J. Appl. Phys. 111, 07E322 (2012); http://dx.doi.org/10.1063/1.3675148 (3 pages)

Online Publication Date: 29 February 2012

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The crystallization behavior of amorphous Sm5Fe17 melt-spun ribbon was studied. The crystallized phases in annealed specimens were deeply dependent on both the annealing temperature and the heating rate. The optimally annealed Sm5Fe17 melt-spun ribbon consisted of Sm5Fe17 grains of around 50–100 nm in diameter and exhibited a remanence of 50 emu/g with a high coercivity of 40 kOe.
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61.66.Dk Alloys
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High field (14 T) magneto transport of Sm/PrFeAsO

R. S. Meena, Shiva Kumar Singh, Anand Pal, Anuj Kumar, R. Jha, K. V. R. Rao, Y. Du, X. L. Wang, and V. P. S Awana

J. Appl. Phys. 111, 07E323 (2012); http://dx.doi.org/10.1063/1.3675156 (3 pages) | Cited 1 time

Online Publication Date: 29 February 2012

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We report high field magneto transport of Sm/PrFeAsO. Below spin density wave transition (TSDW), the magneto-resistance (MR) of Sm/PrFeAsO is positive and increasing with decreasing temperature. The MR of SmFeAsO is found to be 16%, whereas it is 21.5% in the case of PrFeAsO, at 2.5 K under applied magnetic field of 14 Tesla (T). In the case of SmFeAsO, the variation of isothermal MR with field below 20 K is nonlinear at lower magnetic fields (<2 T) and it is linear at moderately higher magnetic fields (H ≥ 3.5 T). On the other hand, PrFeAsO shows almost linear MR at all temperatures below 20 K. The anomalous behavior of MR being exhibited in PrFeAsO is originated from Dirac cone states. The stronger interplay of Fe and Pr ordered moments is responsible for this distinct behavior. PrFeAsO also shows a hump in resistivity (R-T) with a possible conduction band (FeAs) mediated ordering of Pr moments at around 12 K. However, the same is absent in SmFeAsO even down to 2 K. Our results of high field magneto-transport of up to 14 T brings about clear distinction between ground states of SmFeAsO and PrFeAsO.
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75.47.Pq Other materials
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Ds Spin waves

Development of microscopic magnetometer with reflective objective using magneto-optical Kerr effect

Y. Kondo, Y. Nakamura, K. Yamakawa, S. Ishio, and J. Ariake

J. Appl. Phys. 111, 07E324 (2012); http://dx.doi.org/10.1063/1.3675176 (3 pages)

Online Publication Date: 29 February 2012

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A microscopic magnetometer using magneto-optical Kerr effect (MOKE) was developed to characterize the magnetic properties of hard magnetic nano-structures such as a bit-patterned medium and a magnetoresistive random access memory. Our new type magnetometer has a unique feature that adopts the reflective objective instead of the generally used refractive lens to reduce the unnecessary rotation of polarization axis of the light by the lens with Verdet constant in a magnetic field. A Schwarzschild-type objective consisting of two spherical mirrors was applied as the reflective objective in our magnetometer. The objective was designed specifically for our magnetometer. An actual focusing spot diameter at the sample surface was estimated to be 4.7 μm by the knife-edge measurement. Furthermore, a magnetization curve was measured by MOKE for the Co80Pt20 thin-film line with a width of 75 μm, and demonstrated that our magnetometer can reduce the unnecessary rotation of polarization axis compared with the one measured by the magnetometer with a refractive lens.
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78.20.Ls Magneto-optical effects
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
42.79.Bh Lenses, prisms and mirrors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Extended frequency analysis of magnetic losses under rotating induction in soft magnetic composites

O. de la Barrière, C. Appino, F. Fiorillo, C. Ragusa, M. Lecrivain, L. Rocchino, H. Ben Ahmed, M. Gabsi, F. Mazaleyrat, and M. LoBue

J. Appl. Phys. 111, 07E325 (2012); http://dx.doi.org/10.1063/1.3675177 (3 pages)

Online Publication Date: 29 February 2012

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We present novel results on magnetic losses in soft magnetic composites (SMCs) excited with rotating field. Soft composites are very promising in electrical engineering applications, where new topologies of electrical machines with two- and three-dimensional induction loci are increasingly found. An experimental characterization of industrial SMC products has, therefore, been carried out, up to the kilohertz range, under alternating and circular flux loci, making use of a specifically designed and optimized loss measuring setup. The obtained results have been analyzed for all kinds of excitation, according to the loss separation concept, with the emphasis being placed on the relationship between the rotational and the alternating loss components. In particular, it is found that the ratio between the rotational and the alternating losses is, for any given peak induction, independent of frequency.
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75.60.-d Domain effects, magnetization curves, and hysteresis
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