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14 Dec 2009

Volume 95, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 95, 242102 (2009); http://dx.doi.org/10.1063/1.3272858 (3 pages)

W. H. Lim, F. A. Zwanenburg, H. Huebl, M. Möttönen, K. W. Chan, A. Morello, and A. S. Dzurak
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In-situ characterization of rapid crystallization of amorphous CoFeB electrodes in CoFeB/MgO/CoFeB junctions during thermal annealing

W. G. Wang, J. Jordan-sweet, G. X. Miao, C. Ni, A. K. Rumaiz, L. R. Shah, X. Fan, P. Parsons, R. Stearrett, E. R. Nowak, J. S. Moodera, and J. Q. Xiao

Appl. Phys. Lett. 95, 242501 (2009); http://dx.doi.org/10.1063/1.3273397 (3 pages) | Cited 15 times

Online Publication Date: 14 December 2009

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We report the crystallization study of CoFeB/MgO/CoFeB magnetic tunnel junctions using in-situ, time-resolved synchrotron-based x-ray diffraction and transmission electron microscopy. It was found that the crystallization of amorphous CoFeB electrodes occurs on a time scale of seconds during the postgrowth high temperature annealing. The crystallization can be well fit by the Johnson–Mehl–Avrami model and the effective activation energy of the process was determined to be 150 kJ/mol. The solid-state epitaxy mode of CoFeB was found to involve separate crystallization at different locations followed by subsequent merging of small grains, instead of layer-by-layer growth of CoFeB film along the MgO template.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Kj Amorphous and quasicrystalline magnetic materials

Magnetization reorientation in antiferromagnetically coupled Co films and (Co/Pd) multilayers

Rachid Sbiaa, S. N. Piramanayagam, and Randall Law

Appl. Phys. Lett. 95, 242502 (2009); http://dx.doi.org/10.1063/1.3273856 (3 pages) | Cited 5 times

Online Publication Date: 15 December 2009

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Magnetization reversal of antiferromagnetically coupled (AFC) Co thin film and (Co/Pd) multilayers has been investigated. For 5 Å thick Co layer, a high exchange coupling field (Hex) of 7.8 kOe at room temperature and 8.5 kOe at 5 K was measured from the shift in the hysteresis loop. This high value of Hex was accompanied by a magnetization reorientation from in-plane to out-of-plane of the thin Co. When Co thickness increases, the magnetization reorientation was not possible. This unusual high Hex can be used to stabilize AFC structures when the patterning to nanoscale size is needed.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Ee Antiferromagnetics
75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

GaMnAs-based magnetic tunnel junctions with an AlMnAs barrier

Shinobu Ohya, Iriya Muneta, Pham Nam Hai, and Masaaki Tanaka

Appl. Phys. Lett. 95, 242503 (2009); http://dx.doi.org/10.1063/1.3254218 (3 pages) | Cited 5 times

Online Publication Date: 16 December 2009

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We investigate the spin-dependent transport of GaMnAs-based magnetic tunnel junctions (MTJs) containing a paramagnetic AlMnAs barrier with various thicknesses. The barrier height of AlMnAs with respect to the Fermi level of GaMnAs is estimated to be 110 meV. We observe tunneling magnetoresistance (TMR) ratios up to 175% (at 2.6 K), which is higher than those of the GaMnAs-based MTJs with other barrier materials in the same temperature region. These high TMR ratios can be mainly attributed to the relatively high crystal quality of AlMnAs and the suppression of the tunneling probability at the in-plane wave vector k∥ ∼ 0.
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75.47.Pq Other materials
72.25.Dc Spin polarized transport in semiconductors
73.20.At Surface states, band structure, electron density of states
75.50.Pp Magnetic semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects

Thermal stability and spin-transfer switchings in MgO-based magnetic tunnel junctions with ferromagnetically and antiferromagnetically coupled synthetic free layers

Satoshi Yakata, Hitoshi Kubota, Toru Sugano, Takayuki Seki, Kay Yakushiji, Akio Fukushima, Shinji Yuasa, and Koji Ando

Appl. Phys. Lett. 95, 242504 (2009); http://dx.doi.org/10.1063/1.3275753 (3 pages) | Cited 8 times

Online Publication Date: 16 December 2009

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We prepared MgO-based magnetic tunnel junctions having a CoFeB/Ru/CoFeB synthetic free layer in which magnetizations of the CoFeB layers were ferromagnetically coupled (F-coupled Sy) or antiferromagnetically coupled (AF-coupled Sy). We studied spin-transfer switchings to evaluate their thermal stability (Δ0 = KV/kBT) and intrinsic switching current density (JC0). Although the free layers of two types showed nearly equal JC0, the Δ0 of F-coupled Sy was observed to be twice that of AF-coupled Sy. This difference is attributable to the shape magnetic anisotropy of the free-layer cells. Results show that F-coupled Sy is superior to AF-coupled Sy for memory applications.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.30.Sg Magnetocaloric effect, magnetic cooling

Magnetic properties and atomic structure of La2/3Ca1/3MnO3–YBa2Cu3O7 heterointerfaces

Z. L. Zhang, U. Kaiser, S. Soltan, H.-U. Habermeier, and B. Keimer

Appl. Phys. Lett. 95, 242505 (2009); http://dx.doi.org/10.1063/1.3274044 (3 pages) | Cited 1 time

Online Publication Date: 16 December 2009

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A heterostructure comprised of a 2.7 nm (7 unit cell) thick layer of the metallic ferromagnet La2/3Ca1/3MnO3 and two 50 nm thick layers of the high-temperature superconductor YBa2Cu3O7 epitaxially grown on (100) SrTiO3 by pulsed-laser deposition was characterized by magnetization measurements and spherical-aberration-corrected high-resolution transmission electron microscopy (HRTEM). The saturation magnetization is about half of that in bulk La2/3Ca1/3MnO3. A massive reduction in the magnetization previously inferred from sputter-deposited La2/3Ca1/3MnO3–YBa2Cu3O7 heterostructures can be ruled out. HRTEM image analysis, combined with image simulation and a focus series reconstruction, revealed atomically sharp epitaxial structures with stacking sequences –(La,Ca)O–CuO2– and –BaO–MnO– at the top and bottom interface.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
74.78.Fk Multilayers, superlattices, heterostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.15.Fg Pulsed laser ablation deposition
75.50.Dd Nonmetallic ferromagnetic materials
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