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24 May 2010

Volume 96, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 96, 213701 (2010); http://dx.doi.org/10.1063/1.3431628 (3 pages)

Satish Rao, Saurabh Raj, Stefan Balint, Carlota Bardina Fons, Susana Campoy, Montserrat Llagostera, and Dmitri Petrov
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Bulk and interfacial scatterings in current-perpendicular-to-plane giant magnetoresistance with Co2Fe(Al0.5Si0.5) Heusler alloy layers and Ag spacer

T. M. Nakatani, T. Furubayashi, S. Kasai, H. Sukegawa, Y. K. Takahashi, S. Mitani, and K. Hono

Appl. Phys. Lett. 96, 212501 (2010); http://dx.doi.org/10.1063/1.3432070 (3 pages) | Cited 30 times

Online Publication Date: 24 May 2010

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We report the transport properties of a current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) device with Co2Fe(Al0.5Si0.5) (CFAS) Heusler alloy ferromagnetic layers and a Ag spacer layer. The CPP-GMR devices showed relatively high ΔRA values and MR ratios up to 17 m Ω μm2 and 80% at 14 K, and 8 m Ω μm2 and 34% at 290 K. The spin diffusion length ∼ 3 nm and the bulk spin asymmetry ∼ 0.77 for the CFAS alloy at 14 K were estimated by the Valet–Fert model, indicating a large contribution of the interfacial scattering.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Defect-enhanced ferromagnetism in Gd- and Si-coimplanted GaN

R. P. Davies, B. P. Gila, C. R. Abernathy, S. J. Pearton, and C. J. Stanton

Appl. Phys. Lett. 96, 212502 (2010); http://dx.doi.org/10.1063/1.3437085 (3 pages) | Cited 8 times

Online Publication Date: 25 May 2010

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GaN grown by metal-organic chemical vapor deposition was coimplanted with Gd+ ions with energy of 155 keV and dose of 2.75×1010 cm−2 and Si4+ ions with energies of 5 and 40 keV and corresponding doses of 8×1011 and 3.6×1012 cm−2. The implanted samples were not annealed before characterization. X-ray diffraction measurements revealed that the implanted GaN exhibited no secondary phase formation or clustering effects attributable to Gd. Superconducting quantum interference device magnetometer measurements indicated that Gd- and Si-coimplanted GaN exhibited about a 400% higher magnetic moment than a Gd-implanted GaN thin film. This emphasizes the role of defects in producing large saturation magnetization in Gd-doped GaN. Both types of films displayed ferromagnetic ordering and Curie temperatures above room temperature. The higher magnetic moment was displayed when the magnetic field was applied perpendicular to the sample surface (parallel to the c-axis of the sample), suggesting the polarization field in wurtzite GaN plays a crucial role.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.55.Eq III-V semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Electric-field effects on thickness dependent magnetic anisotropy of sputtered MgO/Co40Fe40B20/Ta structures

M. Endo, S. Kanai, S. Ikeda, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 96, 212503 (2010); http://dx.doi.org/10.1063/1.3429592 (3 pages) | Cited 53 times

Online Publication Date: 27 May 2010

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We have investigated the effect of applied electric field EG on thickness dependent magnetic anisotropy of sputtered Co40Fe40B20 sandwiched with MgO and Ta. The range of CoFeB thickness explored is 2 nm and below. As the thickness is reduced, the easy axis of magnetization becomes perpendicular from in-plane. We show that perpendicular magnetic anisotropy of in-plane samples and coercivity of perpendicular samples can be modified by applying EG at room temperature. Furthermore, superparamagnetic behavior is observed for CoFeB layers with further reduced thickness below ≈0.9 nm, where electric-field effect is also observed below their blocking temperature.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.85.+t Magnetoelectric effects, multiferroics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Perpendicular spin-torque switching with a synthetic antiferromagnetic reference layer

Ioan Tudosa, J. A. Katine, S. Mangin, and Eric E. Fullerton

Appl. Phys. Lett. 96, 212504 (2010); http://dx.doi.org/10.1063/1.3441402 (3 pages) | Cited 10 times

Online Publication Date: 27 May 2010

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Spin-torque switching of perpendicular anisotropy nanopillar spin valve devices with synthetic antiferromagnetic reference layers is presented. The use of composite reference layer reduces the dipolar interaction with the free layer yielding two remanent states. We derive a complete current-field phase diagram including minor loops of the free layer where we determine the relative dipolar fields and effective spin polarization of the reference layer in both the parallel and antiparallel configurations. We find the magnetic response of the reference layer relatively insensitive to the spin polarized current which may prove advantageous for spin-torque applications.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.30.Wx Spin crossover
75.75.Jn Dynamics of magnetic nanoparticles
75.78.Jp Ultrafast magnetization dynamics and switching
75.76.+j Spin transport effects
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Tunnel magnetoresistance with improved bias voltage dependence in lattice-matched Fe/spinel MgAl2O4/Fe(001) junctions

Hiroaki Sukegawa, Huixin Xiu, Tadakatsu Ohkubo, Takao Furubayashi, Tomohiko Niizeki, Wenhong Wang, Shinya Kasai, Seiji Mitani, Koichiro Inomata, and Kazuhiro Hono

Appl. Phys. Lett. 96, 212505 (2010); http://dx.doi.org/10.1063/1.3441409 (3 pages) | Cited 8 times

Online Publication Date: 27 May 2010

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We fabricated fully epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions using plasma oxidation of an Mg/Al bilayer. The MgAl2O4 showed a (001)-oriented spinel-type structure, and there were few misfit dislocations at the interfaces between the MgAl2O4 and the two Fe layers due to a small lattice mismatch ( ∼ 1%). Tunnel magnetoresistance (TMR) ratios up to 117% (165%) were obtained at room temperature (15 K). The bias voltage for one-half of the zero-bias TMR ratio (Vhalf) was relatively large, ranging from 1.0 to 1.3 V at room temperature, which is attributed to the small misfit dislocation density.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
61.72.Bb Theories and models of crystal defects

A differential dual spin valve with high pinning stability

G. C. Han, J. J. Qiu, C. C. Wang, V. Ko, and Z. B. Guo

Appl. Phys. Lett. 96, 212506 (2010); http://dx.doi.org/10.1063/1.3441412 (3 pages) | Cited 6 times

Online Publication Date: 27 May 2010

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A differential dual spin valve (DDSV) is very promising for ultrahigh linear density recording. The antiparallel magnetization configuration of two reference layers in a DDSV has been realized by using a double synthetic antiferromagnetic coupling structure (SAF) in one spin valve and a single SAF in the other. A high pinning field has been obtained using a double SAF with a magnetically balanced structure. The observed resistance transitions at low fields can be ascribed to the inconsistent switching of two free layers. By forming a strong ferromagnetic coupling between two free layers, a consistent switching is achieved.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Nonuniformity of a planar polarizer for spin-transfer-induced vortex oscillations at zero field

A. V. Khvalkovskiy, J. Grollier, N. Locatelli, Ya. V. Gorbunov, K. A. Zvezdin, and V. Cros

Appl. Phys. Lett. 96, 212507 (2010); http://dx.doi.org/10.1063/1.3441405 (3 pages) | Cited 17 times

Online Publication Date: 28 May 2010

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We discuss a possible mechanism of the spin-transfer-induced oscillations of a vortex in the free layer of spin-valve nanostructures, in which the polarizer layer has a planar magnetization. We demonstrate that if such planar polarizer is essentially nonuniform, steady gyrotropic vortex motion with large amplitude can be excited. The best excitation efficiency is obtained for a circular magnetization distribution in the polarizer. In this configuration, the conditions for the onset of the oscillations depend on the vortex chirality but not on the direction of its core.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Synthesis, anisotropy, and superconducting properties of LiFeAs single crystal

Yoo Jang Song, Jin Soo Ghim, Byeong Hun Min, Yong Seung Kwon, Myung Hwa Jung, and Jong-Soo Rhyee

Appl. Phys. Lett. 96, 212508 (2010); http://dx.doi.org/10.1063/1.3435472 (3 pages) | Cited 12 times

Online Publication Date: 28 May 2010

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A LiFeAs single crystal with Tconset ∼ 19.7 K was grown in a sealed tungsten crucible using the Bridgeman method. The electrical resistivity experiments revealed a ratio of room temperature to residual resistivity of approximately 46 and 18 for the in-plane and out-of plane directions, respectively. The estimated anisotropic resistivity, γρ = ρc/ρab, was approximately 3.3 at Tconset. The upper critical fields had large Hc2∥ab and Hc2∥c values of 83.4 T and 72.5 T, respectively, and an anisotropy ratio is γH = Hc2∥ab/Hc2∥c ∼ 1.15. The high upper critical field value and small anisotropy highlight the potential use of LiFeAs in a variety of applications. The calculated critical current density (Jc) from the M-H loop is approximately 103 A/cm2
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81.10.Fq Growth from melts; zone melting and refining
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Sv Critical currents
74.81.-g Inhomogeneous superconductors and superconducting systems, including electronic inhomogeneities
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