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7 May 2013

Volume 113, Issue 17, Articles (17xxxx)

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J. Appl. Phys. 113, 174302 (2013); http://dx.doi.org/10.1063/1.4798262 (4 pages)

Yuichiro Kurokawa, Takehiko Hihara, and Ikuo Ichinose
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back to top Half-Metallic Materials

The zero-magnetization Heusler ferrimagnet

M. Hakimi, M. Venkatesan, K. Rode, K. Ackland, and J. M. D. Coey

J. Appl. Phys. 113, 17B101 (2013); http://dx.doi.org/10.1063/1.4794744 (3 pages)

Online Publication Date: 12 March 2013

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An unusual zero-moment half-metallic state has been predicted in stoichiometric Heusler compounds with 24 valence electrons, where, unlike an antiferromagnet, the two sublattices are chemically or crystallographically inequivalent. We have examined the following candidate materials: Cr2FeGe, Cr2CoGa, Fe2VGa, and Mn3Ga with various annealing and milling treatments. The Fe2VGa compound is identified as a weak itinerant ferromagnet, but both cubic Mn3Ga and perfectly ordered Cr2CoGa are potential zero-magnetization ferrimagnets.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics

Structure and magnetic properties of low-temperature annealed Ni-Mn-Al alloys

Yongdeok Kim, Seung Jae Lee, Won Bae Han, Hee-Soo Kim, Hyeun Hwan An, and Chong Seung Yoon

J. Appl. Phys. 113, 17B102 (2013); http://dx.doi.org/10.1063/1.4795323 (3 pages)

Online Publication Date: 19 March 2013

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Off-stoichiometric Ni2Mn2−xAlx (x = 0.5–1.2) and Ni2+y(Mn1.3Al0.7)1−y/2, (y = 0.04–0.12) alloys were prepared to locate the composition range which is likely to form the ferromagnetic ordered L21 phase through low-temperature thermal annealing. In the Ni2Mn2−xAlx (x = 0.5–1.2) series, the alloy partially transformed to the ferromagnetic phase in the narrow composition range of x = 0.8–1.1. For the Ni-enriched composition series, Ni2+y(Mn1.3Al0.7)1−y/2, (y = 0.04–0.12), magnetic ordering was not observed and the magnetic susceptibility proportionally decreased with the Ni concentration. It was concluded that moving away from stoichiometric composition would likely increase the disordering of Mn and Al site occupation and is not conducive to achieving ferromagnetism in Ni2MnAl.
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61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
81.40.Gh Other heat and thermomechanical treatments
61.66.Bi Elemental solids

Three-dimensional mapping of the anisotropic magnetoresistance in Fe3O4 single crystal thin films

Z. Ding, J. X. Li, J. Zhu, T. P. Ma, C. Won, and Y. Z. Wu

J. Appl. Phys. 113, 17B103 (2013); http://dx.doi.org/10.1063/1.4796178 (3 pages)

Online Publication Date: 25 March 2013

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The anisotropic magnetoresistance (AMR) effect with a magnetic field along arbitrary directions in single crystalline (001)-oriented Fe3O4 films was studied. A cubic symmetry term, an in-plane uniaxial term, and an out-of-plane uniaxial term could be quantitatively separated. The cubic term is independent of the current direction, and decreases with increasing temperature, but both in-plane and out-of-plane uniaxial terms are found to be strongly dependent on the current orientation. This three-dimensional magnetoresistance measurement provides a quantitative method for identifying the different contributions to the AMR effect.
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75.70.Ak Magnetic properties of monolayers and thin films
61.66.Fn Inorganic compounds
68.55.-a Thin film structure and morphology

Magnetotransport properties in epitaxial Fe3O4(001) thin films with current perpendicular to the plane geometry

H. Yanagihara, K. Shimada, T. Niizeki, E. Kita, J. Inoue, A. Fukushima, and S. Yuasa

J. Appl. Phys. 113, 17B104 (2013); http://dx.doi.org/10.1063/1.4795842 (3 pages)

Online Publication Date: 29 March 2013

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We investigated the fundamental transport properties of epitaxial magnetite (Fe3O4) films with applied current perpendicular to the plane geometry. The devices with a junction area of 36 μm2 were fabricated with TiN/Fe3O4/ TM (TM: Ti and Fe) stacking. Both the temperature dependence and the magnetic field dependence of the junction resistance were measured. Most of the resistance properties were independent of whether the electrode was magnetic (Fe) or nonmagnetic (Ti). Below the Verwey point, the junction resistance abruptly increased with decreasing temperature, and the resistance reached maximum at approximately 30 K. The magnetoresistance showed a peak of ∼ 27% at T ≈ 55 K. The observed resistance behavior was consistent with a hopping conduction mechanism with a Coulomb interaction.
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75.47.Pq Other materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
71.30.+h Metal-insulator transitions and other electronic transitions

Effect of three dimensional interface in determination of spin polarization using Andreev reflection spectroscopy

J. A. Gifford, C. N. Snider, J. Martinez, and T. Y. Chen

J. Appl. Phys. 113, 17B105 (2013); http://dx.doi.org/10.1063/1.4798624 (3 pages)

Online Publication Date: 9 April 2013

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A theoretical study of a three-dimensional (3D) normal metal/superconductor interface with arbitrary spin polarization and interface geometry is presented. The interface geometry can drastically affect the Andreev spectrum due to the 3D injection. The 3D effect can be attributed to a larger interfacial scattering factor in the 1D model, yielding the same intrinsic spin polarization and superconducting gap as the 3D model. This demonstrates that the 1D model can be utilized to extract the intrinsic spin polarization and the superconducting gap values for a 3D interface as long as the interfacial scattering factor is not concerned.
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72.25.-b Spin polarized transport
74.25.Gz Optical properties
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.20.Pq Electronic structure calculations
74.25.F- Transport properties

Ab initio studies of disorder in the full Heusler alloy Co2FexMn1−xSi

P. J. Hasnip, J. H. Smith, and V. K. Lazarov

J. Appl. Phys. 113, 17B106 (2013); http://dx.doi.org/10.1063/1.4801745 (3 pages)

Online Publication Date: 15 April 2013

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Co-based full Heusler alloys have been predicted to be half-metals, with 100% spin polarisation at the Fermi level, yet this has yet to be realised in practice. Heusler thin-films often exhibit a degree of atomic disorder, and this is believed to be one cause of the low magnetoresistance in Heusler-based spin valves' devices. We present an ab initio density functional theory + U investigation into the effect of disorder on the electronic properties of Co2Fe0.5Mn0.5Si. It is found that the half-metallicity depends strongly on the kind of disorder present, with low or even reversed spin-polarisation when the Co sublattice mixes with either the Fe/Mn or Si sublattice, but keeps the high spin polarisation when the Mn/Fe and Si sublattices are mixed. Calculations of the formation energy show that this latter kind of disorder is by far the most likely to occur, an encouraging result which means that it may not be necessary to produce perfectly ordered Heusler alloys in order to achieve 100% spin polarisation.
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71.20.Gj Other metals and alloys
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Magnetism and magnetotransport in symmetry matched spinels: Fe3O4/MgAl2O4

D. Gilks, L. Lari, Z. Cai, O. Cespedes, A. Gerber, S. Thompson, K. Ziemer, and V. K. Lazarov

J. Appl. Phys. 113, 17B107 (2013); http://dx.doi.org/10.1063/1.4800690 (3 pages)

Online Publication Date: 15 April 2013

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In this work, we show that Fe3O4 films grown by oxygen plasma assisted molecular beam epitaxy have anomalous magnetic properties such as negative magnetoresistance and high saturation magnetic fields. The film substrate mismatch of 3% is relieved by the formation of misfit dislocations at the interface. Transmission electron microscopy results show that misfit dislocations are not the cause of antiphase domain boundary (APB). This suggests that in this system APB formation is a property of the three dimensional Fe3O4 growth.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.at Other materials
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