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15 Nov 2004

Volume 85, Issue 20, pp. 4561-4807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4768 (2004); http://dx.doi.org/10.1063/1.1818331 (3 pages)

G. Walter, N. Holonyak, M. Feng, and R. Chan
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Tunable field imbalance and spin precession in magnetic double layers

Y. Au, R. Sooryakumar, and K. Bussmann

Appl. Phys. Lett. 85, 4675 (2004); http://dx.doi.org/10.1063/1.1818725 (3 pages) | Cited 1 time

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We report on the manipulation of spin-wave mode profiles by a field imbalance in magnetic double layers produced by the combination of an external field (Hext) and an in-plane spacer layer current-induced Amperian field (Hcur). The magnetizations between layers are tuned from antiparallel to parallel alignment and the associated oscillation amplitudes monitored by Brillouin light scattering. While the results are well accounted for by Maxwell and Landau–Lifshitz equations, a mechanical coupled pendulum analog in a variable unbalanced gravitational acceleration (Δg) provides insight into the underlying physics. It is pointed out that the application of magnetic field pulses of specific strength and duration will lead to direct cross-communication between spin-wave normal modes, a feature unique to the tunable local imbalanced field.

Doping of low-temperature GaAs and GaMnAs with carbon

G. M. Schott, C. Rüster, K. Brunner, C. Gould, G. Schmidt, L. W. Molenkamp, M. Sawicki, R. Jakiela, A. Barcz, and G. Karczewski

Appl. Phys. Lett. 85, 4678 (2004); http://dx.doi.org/10.1063/1.1819522 (3 pages) | Cited 5 times

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The incorporation of carbon in low-temperature (LT) GaAs and GaMnAs layers deposited by molecular-beam epitaxy under various growth conditions has been investigated. The lattice parameter depends on Mn content, C content, and the growth conditions which strongly affect Mn, C, and point defect incorporation. We found optimum growth conditions (Tsub=270 °C, the beam equivalent pressure ratio is 5, growth rate is 0.1 nm∕s) at which high-quality GaMnAs layers with moderate Mn content as well as LT-GaAs layers were deposited, which were efficiently p-doped by carbon. LT GaAs:C revealed the same electrical activation of carbon of about 50% at a high doping level p=5×1019 cm−3 as observed in high-temperature GaAs:C. The Curie temperature as well as the saturation magnetization of GaMnAs decreases with C doping. This suggests a reduced amount of Mn contributing to the ferromagnetic phase in GaMnAs:C.

Thermal effects on the magnetic-field dependence of spin-transfer-induced magnetization reversal

D. Lacour, J. A. Katine, N. Smith, M. J. Carey, and J. R. Childress

Appl. Phys. Lett. 85, 4681 (2004); http://dx.doi.org/10.1063/1.1819516 (3 pages) | Cited 36 times

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We have developed a self-aligned, high-yield process to fabricate current-perpendicular-to-plane giant magnetoresistance (GMR) spin-valve sensors of sub-100-nm dimensions. A pinned synthetic antiferromagnet is used as the reference layer which minimizes dipole coupling to the free layer and field-induced rotation of the reference layer. We find that the critical currents for spin-transfer-induced magnetization reversal of the free layer vary dramatically with relatively small changes in the in-plane magnetic field, in contrast to theoretical predictions based on stability analysis of the Gilbert equations of magnetization dynamics, including Slonczewski-type spin-torque terms. The discrepancy is believed due to thermal fluctuations over the time scale of the measurements. Once thermal fluctuations are taken into account, we find good quantitative agreement between our experimental results and numerical simulations.

Phase separation and magnetic properties of half-metal-type Co2Cr1−xFexAl alloys

K. Kobayashi, R. Y. Umetsu, R. Kainuma, K. Ishida, T. Oyamada, A. Fujita, and K. Fukamichi

Appl. Phys. Lett. 85, 4684 (2004); http://dx.doi.org/10.1063/1.1821654 (3 pages) | Cited 41 times

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The phase stability and magnetic properties of the half-metal-type Co2Cr1−xFexAl alloy system were investigated. It was found that the occurrence of two-phase separation is unavoidable in a concentration range of less than x=0.4, leading to deviation of the saturation magnetic moments from the generalized Slater–Pauling line. The L21-type phase becomes stable in a concentration range of more than x=0.7, where no half-metallic behaviors are present. Consequently, it is concluded that the most favorable concentration for applications to spintronic devices is located around x=0.4 in Co2Cr1−xFexAl alloys having the B2-type phase.

Stress/strain dependence of ac loss and critical current of Bi2Sr2Ca2Cu3O10 reinforced tape

Guo Min Zhang, Justin Schwartz, P. V. P. S. S. Sastry, Liang Zhen Lin, Li Ye Xiao, and Yun Jia Yu

Appl. Phys. Lett. 85, 4687 (2004); http://dx.doi.org/10.1063/1.1819995 (3 pages) | Cited 2 times

Online Publication Date: 16 November 2004

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The critical current and ac loss of a stainless steel reinforced Bi2Sr2Ca2Cu3O10 composite superconducting tape were measured under tensile stress/strain at 77 K. By use of the definition of irreversible strain, a formula describing the variation of the critical current with strain was proposed. A relationship between ac loss and tensile strain was developed from Norris’ formula and the critical current–strain relation. It is shown that the experimental results agree well with the values calculated from our formulas.
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84.71.Mn Superconducting wires, fibers, and tapes
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Applied field Mössbauer study of shape anisotropy in Fe nanowire arrays

Qing-feng Zhan, Wei He, Xiao Ma, Ya-qiong Liang, Zhi-qi Kou, Nai-li Di, and Zhao-hua Cheng

Appl. Phys. Lett. 85, 4690 (2004); http://dx.doi.org/10.1063/1.1827330 (3 pages) | Cited 11 times

Online Publication Date: 16 November 2004

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In order to investigate the magnetic anisotropy of Fe nanowire arrays from microscopic point of view, 57Fe Mössbauer spectra were measured at various magnetic fields along and perpendicular to the nanowire axis, respectively. On the basis of the absorption intensities of the second and the fifth lines of sextet, the orientation of Fe magnetic moments can be detected. It was found that the shape anisotropy dominates the overall magnetic anisotropy in the Fe nanowires. Furthermore, the longitudinal and transverse demagnetizing fields of Fe nanowire, respectively, were deduced from the effective hyperfine field at 57Fe nuclei as a function of applied field. The chain-of-spheres model in conjunction with symmetric fanning mechanism was adopted to interpret the domain structure and the parallel coercivity of magnetic nanowire arrays.
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75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure

Characterization of single magnetic particles with InAs quantum-well Hall devices

G. Landry, M. M. Miller, B. R. Bennett, M. Johnson, and V. Smolyaninova

Appl. Phys. Lett. 85, 4693 (2004); http://dx.doi.org/10.1063/1.1827328 (3 pages) | Cited 15 times

Online Publication Date: 16 November 2004

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We have measured the magnetic dipolar field from individual micron-sized spherical ferromagnetic particles. The particles were positioned using an atomic force microscope and measured using submicron Hall sensors fabricated from an InAs single-quantum-well heterostructure with lateral dimensions of 0.5–2.5 μm. The magnetic moment of individual particles has been measured, verifying their dipolar moment. We also demonstrate a scaling rule for the detection of individual particles which is relevant to the design of biosensors.
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85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Tt Fine-particle systems; nanocrystalline materials
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