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16 Jul 2012

Volume 101, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 101, 033301 (2012); http://dx.doi.org/10.1063/1.4734240 (5 pages)

Ting-Gang Chen, Bo-Yu Huang, En-Chen Chen, Peichen Yu, and Hsin-Fei Meng
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Variation of magnetic domain structure during martensite variants rearrangement in ferromagnetic shape memory alloys

Xingzhe Wang and Fang Li

Appl. Phys. Lett. 101, 032401 (2012); http://dx.doi.org/10.1063/1.4737172 (4 pages)

Online Publication Date: 16 July 2012

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Studies of magnetic domain and anisotropy in ferromagnetic shape memory alloys (FSMAs) are crucial for both understanding their ferromagnetism and engineering in applications. The experimental measurements showed that magnetization rotations and domain-wall motions exhibit distinct characteristics in the field-preferred variants and stress-preferred variants of FSMAs [Y. W. Lai, N. Scheerbaum, D. Hinz, O. Gutfleisch, R. Schäfer, L. Schultz, and J. McCord, Appl. Phys. Lett. 90, 192504 (2007)]. Aiming at characterization of formation and variation of the complex magnetic microstructure in FSMAs, we present an analytical approach based on the energy minimization theory and Boltzmann relation on magnetic domains. The magnetic domain behavior during the martensite variants rearrangement is captured to show a good agreement with the experimental observations.
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81.05.Bx Metals, semimetals, and alloys
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetoresistance effect in L10-MnGa/MgO/CoFeB perpendicular magnetic tunnel junctions with Co interlayer

Q. L. Ma, T. Kubota, S. Mizukami, X. M. Zhang, H. Naganuma, M. Oogane, Y. Ando, and T. Miyazaki

Appl. Phys. Lett. 101, 032402 (2012); http://dx.doi.org/10.1063/1.4737000 (4 pages) | Cited 3 times

Online Publication Date: 16 July 2012

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The fully perpendicular magnetic tunnel junctions (p-MTJs) based on L10-MnGa and thin CoFeB electrodes with MgO barrier were reported in this letter. A thin Co layer was introduced between the MnGa layer and the MgO barrier layer to investigate interfacial effect on the device’s magnetic and transport properties. The magnetoresistance ratio improved significantly due to the Co insertion, and reached 40% at room temperature (80% at 5 K) when the Co thickness was 1.5 nm. Moreover, the junctions with Co interlayer exhibited four low-resistance states in one full cycle rather than two in normal MTJs. The physical origin was discussed by considering the coupling between MnGa and Co layers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.47.Pq Other materials

Precessional reversal in orthogonal spin transfer magnetic random access memory devices

H. Liu, D. Bedau, D. Backes, J. A. Katine, and A. D. Kent

Appl. Phys. Lett. 101, 032403 (2012); http://dx.doi.org/10.1063/1.4737010 (4 pages) | Cited 2 times

Online Publication Date: 18 July 2012

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Single-shot time-resolved resistance measurements have been used to determine the magnetization reversal mechanisms of orthogonal spin transfer magnetic random access memory (OST-MRAM) devices at nanosecond time scales. There is a strong asymmetry between antiparallel (AP) to parallel (P) and P to AP transitions under the same pulse conditions. P to AP transitions are shown to occur by precession of the free layer magnetization, while the AP to P transition is typically direct, occurring in less than 200 ps. We associate the asymmetry with spin torques perpendicular to the plane of the free layer, an important characteristic of OST-MRAM bit cells that can be used to optimize device performance.
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85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Electrical characterization of all-epitaxial Fe/GaN(0001) Schottky tunnel contacts

Sergio Fernández-Garrido, Kai U. Ubben, Jens Herfort, Cunxu Gao, and Oliver Brandt

Appl. Phys. Lett. 101, 032404 (2012); http://dx.doi.org/10.1063/1.4737905 (4 pages)

Online Publication Date: 19 July 2012

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We analyze the properties of Fe Schottky contacts prepared in situ on n-type GaN(0001) by molecular beam epitaxy. In particular, we investigate the suitability of these epitaxial Fe layers for electrical spin injection. Current-voltage-temperature measurements demonstrate pure field emission for Fe/GaN:Si Schottky diodes with [Si] = 5×1018 cm−3. The Schottky barrier height of the clean, epitaxial Fe/GaN interface is determined by both current-voltage-temperature and capacitance-voltage techniques to be (1.47±0.09)eV.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Controllable spin-glass behavior and large magnetocaloric effect in Gd-Ni-Al bulk metallic glasses

Fang Yuan, Juan Du, and Baolong Shen

Appl. Phys. Lett. 101, 032405 (2012); http://dx.doi.org/10.1063/1.4738778 (4 pages) | Cited 1 time

Online Publication Date: 20 July 2012

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Glass-forming ability, spin-glass (SG) behavior, and magnetocaloric effect in Gd55NixAl45-x (x = 15, 20, 25, 30) metallic alloys were investigated. A ferromagnetic SG behavior was observed for glassy ribbons with compositions of x = 15, 20, and 25, but it disappeared for that of x = 30. Furthermore, the maximum magnetic entropy change (−ΔSmmax) increased with the increasing Ni/Al-ratio while the decrease of full width at half −ΔSmmax was almost negligible. Accordingly, −ΔSmmax of 9.25 J kg−1 K−1, adiabatic temperature change of 4.3 K and refrigeration capacity of 851 J kg−1 under 50 kOe were obtained for Gd55Ni30Al15 glassy alloy.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
75.50.Lk Spin glasses and other random magnets
64.70.pe Metallic glasses
61.43.Fs Glasses
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
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