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25 Feb 2008

Volume 92, Issue 8, Articles (08xxxx)

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Appl. Phys. Lett. 92, 081101 (2008); http://dx.doi.org/10.1063/1.2883874 (3 pages)

Marcel W. Pruessner, Todd H. Stievater, and William S. Rabinovich
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Soft-magnetic materials characterized using a superconducting solenoid as magnetic source

Giovanni Mastrogiacomo, Jörg F. Löffler, and Neil R. Dilley

Appl. Phys. Lett. 92, 082501 (2008); http://dx.doi.org/10.1063/1.2838733 (3 pages) | Cited 1 time

Online Publication Date: 25 February 2008

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Magnetization measurements of soft-magnetic materials can be affected if they are characterized using a superconducting solenoid. Recording hysteresis loops while stepping the magnetic field can cause an apparently inverted hysteresis, if due to the pinned remanent flux in the magnet the field at the sample location exceeds the sample’s coercive field. Hysteresis loops recorded while sweeping the field can also be affected by ramping rate. The sweeping-rate dependence is caused by leakage currents resulting from the persistent switch and synchronization issues regarding collection of magnetic moment and field data. The resulting errors can be estimated by measuring paramagnetic dysprosium oxide.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities

Photoemission and x-ray absorption studies of valence states in (Ni,Zn,Fe,Ti)3O4 thin films exhibiting photoinduced magnetization

M. Kobayashi, Y. Ooki, M. Takizawa, G. S. Song, A. Fujimori, Y. Takeda, K. Terai, T. Okane, S.-I. Fujimori, Y. Saitoh, H. Yamagami, M. Seki, T. Kawai, and H. Tabata

Appl. Phys. Lett. 92, 082502 (2008); http://dx.doi.org/10.1063/1.2885080 (3 pages) | Cited 1 time

Online Publication Date: 25 February 2008

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By means of photoemission and x-ray absorption spectroscopy, we have studied the electronic structure of (Ni,Zn,Fe,Ti)3O4 thin films, which exhibits a cluster glass behavior with a spin-freezing temperature Tf of ∼ 230 K and photoinduced magnetization (PIM) below Tf. The Ni and Zn ions were found to be in the divalent states. Most of the Fe and Ti ions in the thin films were trivalent (Fe3+) and tetravalent (Ti4+), respectively. While Ti doping did not affect the valence states of the Ni and Zn ions, a small amount of Fe2+ ions increased with Ti concentration, consistent with the proposed charge-transfer mechanism of PIM.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
75.50.Lk Spin glasses and other random magnets
79.60.Dp Adsorbed layers and thin films
78.70.Dm X-ray absorption spectra

Origin of uniaxial magnetic anisotropy in epitaxial MnAs film on GaAs(001) substrate

Kwang-Su Ryu, JinBae Kim, YoungPak Lee, Hiro Akinaga, Takashi Manago, Ravindranath Viswan, and Sung-Chul Shin

Appl. Phys. Lett. 92, 082503 (2008); http://dx.doi.org/10.1063/1.2844856 (3 pages) | Cited 9 times

Online Publication Date: 25 February 2008

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We investigate the origin of in-plane uniaxial magnetic anisotropy of epitaxial ferromagnetic MnAs film on GaAs(001). Interestingly, as temperature increases, the in-plane uniaxial magnetic anisotropy along the MnAs[11math0] direction changes and then disappears. Direct microscopic domain observations show that the type of domain structure changes from a simple domain to a closure one with increasing temperature. From these results, the temperature-dependent change of the in-plane magnetic anisotropy is ascribed to a decrease in the shape anisotropy induced by the decrease in the width of the ferromagnetic α-stripe.
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75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Minimizing the linewidth of the flux-flow oscillator

Andrey L. Pankratov

Appl. Phys. Lett. 92, 082504 (2008); http://dx.doi.org/10.1063/1.2839605 (3 pages) | Cited 5 times

Online Publication Date: 26 February 2008

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The linewidth of the flux-flow oscillator has been calculated by direct computer simulation of the sine-Gordon equation with noise. Good agreement of the numerical results with the formula derived in Phys. Rev. B 65, 054504 (2002) has been achieved. Depending on the length of the unbiased tail, the power may be maximized and the linewidth may be minimized in a broad range of bias currents. The linewidth can be decreased further by 1.5 times by proper load matching.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Gz Optical properties
74.50.+r Tunneling phenomena; Josephson effects

Control of epitaxy-induced magnetocrystalline anisotropy in a molecular beam epitaxy–grown Co/MgO/Fe/MgO(100) pseudo-spin-valve

J.-B. Laloë, A. Ionescu, T. J. Hayward, J. Llandro, J. A. C. Bland, and M. E. Vickers

Appl. Phys. Lett. 92, 082505 (2008); http://dx.doi.org/10.1063/1.2887907 (3 pages) | Cited 1 time

Online Publication Date: 27 February 2008

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We show that by obtaining a crystalline structure in a Co/MgO/Fe tunnel junction, we are able to control the magnetic anisotropies in the spin valve and therefore, induce independent switching of the two magnetic layers. In situ and ex situ structural characterization confirms that the multilayer is fully epitaxial, with smooth interfaces throughout. In confirmation of the high quality of the insulating barrier, we also present a layer-selective measurement of the magnetization of the top electrode using current-in-plane transport measurements.
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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
61.66.Fn Inorganic compounds
75.45.+j Macroscopic quantum phenomena in magnetic systems

Current-driven magnetization reversal at extremely low threshold current density in (Ga,Mn)As-based double-barrier magnetic tunnel junctions

Maya Watanabe, Jun Okabayashi, Hiroshi Toyao, Takeshi Yamaguchi, and Junji Yoshino

Appl. Phys. Lett. 92, 082506 (2008); http://dx.doi.org/10.1063/1.2841703 (3 pages) | Cited 11 times

Online Publication Date: 28 February 2008

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Current-driven magnetic orientation reversal at an extremely low threshold current density, as low as 2.0×104 A/cm2, has been achieved in (Ga,Mn)As-based double-barrier magnetic tunneling junctions (MTJs) sandwiched between top and bottom MTJs. The middle magnetic free layer thickness dependence clearly demonstrates that the low threshold current density is owing not only to the small magnetization of the magnetic free layer but also the enhancement of the spin torque caused by a spin-polarized current through the top and bottom MTJs.
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75.60.Jk Magnetization reversal mechanisms
75.50.Pp Magnetic semiconductors
72.25.Dc Spin polarized transport in semiconductors
75.47.Pq Other materials

Flux pinning in YBa2Cu3O7−δ thin film samples linked to stacking fault density

J. Wang, J. H. Kwon, J. Yoon, H. Wang, T. J. Haugan, F. J. Baca, N. A. Pierce, and P. N. Barnes

Appl. Phys. Lett. 92, 082507 (2008); http://dx.doi.org/10.1063/1.2888749 (3 pages) | Cited 15 times

Online Publication Date: 28 February 2008

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In this paper, we report a strong correlation between the stacking fault (SF) density and the critical current density of YBa2Cu3O7−δ (YBCO) thin films in applied field (Jcin-field). We found that the Jcin-field (H∥c) increases as a clear linear dependence of the density of SF identified in the as-grown samples deposited on both SrTiO3 (STO) and LaAlO3 substrates. Detailed microstructural studies including cross-section transmission electron microscopy (TEM) and high resolution TEM were conducted for all the films deposited on STO substrates. This work suggests that the YBCO SF density plays an important role in the YBCO in-field transport performance.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects

Room temperature ferromagnetism in ZnO films due to defects

Qingyu Xu, Heidemarie Schmidt, Shengqiang Zhou, Kay Potzger, Manfred Helm, Holger Hochmuth, Michael Lorenz, Annette Setzer, Pablo Esquinazi, Christoph Meinecke, and Marius Grundmann

Appl. Phys. Lett. 92, 082508 (2008); http://dx.doi.org/10.1063/1.2885730 (3 pages) | Cited 115 times

Online Publication Date: 29 February 2008

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ZnO films were prepared by pulsed laser deposition on a-plane sapphire substrates under N2 atmosphere. Ferromagnetic loops were obtained with the superconducting quantum interference device at room temperature, which indicate a Curie temperature much above room temperature. No clear ferromagnetism was observed in intentionally Cu-doped ZnO films. This excludes that Cu doping into ZnO plays a key role in tuning the ferromagnetism in ZnO. 8.8% negative magnetoresistance probed at 5 K at 60 kOe on ferromagnetic ZnO proves the lack of s-d exchange interaction. Anomalous Hall effect (AHE) was observed in ferromagnetic ZnO as well as in nonferromagnetic Cu-doped ZnO films, indicating that AHE does not uniquely prove ferromagnetism. The observed ferromagnetism in ZnO is attributed to intrinsic defects.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.47.Pq Other materials
75.30.Et Exchange and superexchange interactions
75.50.Pp Magnetic semiconductors
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