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10 Jan 2005

Volume 86, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 86, 021101 (2005); http://dx.doi.org/10.1063/1.1849439 (3 pages)

H. W. Choi, C. W. Jeon, C. Liu, I. M. Watson, M. D. Dawson, P. R. Edwards, R. W. Martin, S. Tripathy, and S. J. Chua
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Microscopic simulation of the percolation of manganites

Shuai Dong, Han Zhu, X. Wu, and J.-M. Liu

Appl. Phys. Lett. 86, 022501 (2005); http://dx.doi.org/10.1063/1.1848184 (3 pages) | Cited 8 times

Online Publication Date: 30 December 2004

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The one-orbital double exchange model is studied using the METROPOLIS Monte Carlo method and the microscopic resistor network. The phase competition and percolation are displayed microscopically. As far as the resistivity is concerned, the metal–insulator transition is described by the competition between a fraction p of metallic resistors and a fraction 1−p of insulating resistors. p can be obtained as a function of temperature T, doping percentage x, and external field H. In the present model, systems with different x, T, and H can be unified into a single class of percolation, which is different from the standard picture.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
64.60.A- Specific approaches applied to studies of phase transitions
71.30.+h Metal-insulator transitions and other electronic transitions
72.80.Ga Transition-metal compounds
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

The effect of oxygenation on the superconducting properties of MgB2 thin films

K. A. Yates, Z. Lockman, A. Kursumovic, G. Burnell, N. A. Stelmashenko, J. L. MacManus Driscoll, and M. G. Blamire

Appl. Phys. Lett. 86, 022502 (2005); http://dx.doi.org/10.1063/1.1849837 (3 pages) | Cited 8 times

Online Publication Date: 3 January 2005

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The effects of oxygen on the superconducting properties of thin films of MgB2 have been studied. It is found that after annealing for short times in flowing O2 at 400 °C, complex oxides of Mgx(ByO)z are formed that cause a “two-step” behavior in the resistively determined superconducting transition. These oxides are not stable at room temperature and decay into MgO and B2O3 precipitates. As the complex oxides decay so the original Tc behavior of the films is restored to its preoxygenation level.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.62.Dh Effects of crystal defects, doping and substitution
74.25.F- Transport properties
81.40.Gh Other heat and thermomechanical treatments

Enhancing domain wall motion in magnetic wires by ion irradiation

F. Cayssol, J. L. Menéndez, D. Ravelosona, C. Chappert, J.-P. Jamet, J. Ferré, and H. Bernas

Appl. Phys. Lett. 86, 022503 (2005); http://dx.doi.org/10.1063/1.1846935 (3 pages) | Cited 6 times

Online Publication Date: 3 January 2005

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The influence of low-energy He ion irradiation on the dynamics of a single Bloch domain wall was studied in magnetic wires based on Pt∕Co∕Pt trilayers exhibiting perpendicular anisotropy. The domain wall velocity is highly enhanced (up to three orders of magnitude) after irradiation at moderate fluence. A study in the thermally activated regime shows that this is consistent with a reduction of the density of pinning centers and of the pinning force. Uniform ion irradiation significantly improves domain wall motion, as required for future magnetic devices.
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78.20.Ls Magneto-optical effects
85.60.-q Optoelectronic devices

Vortex avalanche phenomena in MgB2 superconducting film studied by current noise measurements

R. Eggenhöffner, E. Celasco, V. Ferrando, and M. Celasco

Appl. Phys. Lett. 86, 022504 (2005); http://dx.doi.org/10.1063/1.1848182 (3 pages) | Cited 7 times

Online Publication Date: 3 January 2005

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Vortex avalanche phenomenon enhanced by thermomagnetic instabilities suppresses critical current in MgB2 films. This effect is investigated at 4.2 K by spectral noise power measurements up to 1 kHz with a dc superconducting quantum interference device apparatus. 1/fγ behavior is shown at low frequencies in magnetic fields and feeding currents below jc. γ increases from 1 to 2 at increasing magnetic field, typical of fluxon avalanche processes. A peak in the power spectrum frequency behavior, observed only in magnetic field, is attributed to vortex–antivortex annihilations. Thermal instabilities disappear when an efficient thermal link to the He bath is attained and no vortex avalanche extra-noise is observed.
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74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.F- Transport properties
74.40.-n Fluctuation phenomena
74.25.Sv Critical currents

Analytical investigation of spin-transfer dynamics using a perpendicular-to-plane polarizer

K. J. Lee, O. Redon, and B. Dieny

Appl. Phys. Lett. 86, 022505 (2005); http://dx.doi.org/10.1063/1.1852081 (3 pages) | Cited 13 times

Online Publication Date: 6 January 2005

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We studied current-induced magnetic switching and excitations in structures comprising a free layer with in-plane magnetization traversed by a current with perpendicular-to-plane spin polarization. We derived analytical solutions from the Landau–Lifshitz–Gilbert equation including the spin-torque term, and compared them to numerical simulations within the single domain assumption. Taking into account the criterion of thermal stability, the magnetization switching in nanostructures of typical size below 100 nm comprising a perpendicular polarizer is found to require larger current density but to be much faster than with a longitudinal polarizer. Furthermore, a steady precession of magnetization can be generated in this geometry; those frequencies can be tuned from about 1 to 20 GHz by only changing the current without applying any external field. This opens a promising application as microwave sources.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Gw Magnetic anisotropy

Magnetic shape memory effect in an antiferromagnetic γ‐Mn‐Fe(Cu) alloy

J. H. Zhang, W. Y. Peng, Shipu Chen, and T. Y. Hsu (Xu Zaoyao)

Appl. Phys. Lett. 86, 022506 (2005); http://dx.doi.org/10.1063/1.1850613 (3 pages) | Cited 6 times

Online Publication Date: 6 January 2005

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A magnetic shape memory effect occurring in a polycrystalline antiferromagnetic Mn85.5Fe9.5Cu5.0 (at. %) alloy is reported. The results show that because of a strong coupling between the antiferromagnetic transition and the fcc→fct martensitic transformation with (101) twinning in the alloy, its martensitic transformation start temperature (MS) and reverse transformation temperature (Af) are close to each other and almost coincide with the antiferromagnetic transition temperature (TN). Being driven by an applied magnetic field of ∼ 10 kOe, the recoverable magnetic-field-induced strains reach to −4.8×10−4 (ε‖) and +3.0×10−4 (ε⊥) in the directions parallel and transverse to the field, respectively, indicating a type of magnetic shape memory material, based on a Mn-rich Mn-Fe composition, which is different from existing ferromagnetic alloys.
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75.50.Ee Antiferromagnetics
81.30.Kf Martensitic transformations
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Lm Deformation, plasticity, and creep
61.72.Mm Grain and twin boundaries
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
64.70.K- Solid-solid transitions
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
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