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6 Mar 2006

Volume 88, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 88, 103107 (2006); http://dx.doi.org/10.1063/1.2182096 (3 pages)

A. B. Djurišić, Y. H. Leung, K. H. Tam, L. Ding, W. K. Ge, H. Y. Chen, and S. Gwo
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Pinning in c-axis oriented YBa2Cu3O7−δ films studied with angular dependent magnetoresistivity

M. Abdelhadi, K. H. Chow, J. Jung, E. K. Hollmann, and A. V. Tumarkin

Appl. Phys. Lett. 88, 102501 (2006); http://dx.doi.org/10.1063/1.2181652 (3 pages) | Cited 2 times

Online Publication Date: 6 March 2006

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We report measurements of the angular dependence of the magnetoresistivity in c-axis oriented YBa2Cu3O7−δ films near their superconducting transition temperature. The behavior of the samples falls into two categories. In some films, a local minimum in the resistivity is observed when the magnetic field is applied along the c axis, indicating that strong pinning of vortices is taking place. In other samples, no such minimum exists. The correlations between this behavior and the physical properties of the film are discussed, and possible candidates for the pinning centers presented.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena

Exchange bias-like phenomenon in SrRuO3

Li Pi, Shixiong Zhang, Shun Tan, and Yuheng Zhang

Appl. Phys. Lett. 88, 102502 (2006); http://dx.doi.org/10.1063/1.2182015 (3 pages) | Cited 14 times

Online Publication Date: 6 March 2006

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Exchange bias-like phenomenon is observed in the SrRuO3 polycrystalline. After the sample is cooled down to 4 K in a magnetic field, the magnetic hysteresis loop shifts in the opposite direction to the applied biasing field. The shift decreases as the sweeping range of the measuring field increases. This phenomenon may arise from the spin glass property of SrRuO3. Since SrRuO3 is widely used in spintronics devices, the observation of exchange bias-like shift in SrRuO3 itself suggests that the application of SrRuO3 should be more carefully considered.
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75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Lk Spin glasses and other random magnets

Temperature dependence of magnetocrystalline anisotropy constants in the single variant state of L10-type FePt bulk single crystal

K. Inoue, H. Shima, A. Fujita, K. Ishida, K. Oikawa, and K. Fukamichi

Appl. Phys. Lett. 88, 102503 (2006); http://dx.doi.org/10.1063/1.2177355 (3 pages) | Cited 17 times

Online Publication Date: 7 March 2006

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The temperature dependence of magnetocrystalline anisotropy constants and the saturation magnetization in a single variant state have been investigated for L10-type Fe60Pt40 bulk single crystal prepared under compressive stress. The uniaxial magnetocrystalline anisotropy constant Ku evaluated from the magnetization curve is 6.9×107 erg cm−3 at 5 K. The values of the second- and fourth-order magnetocrystalline anisotropy constants K1 and K2 at 5 K determined by the Sucksmith–Thompson method are 7.4 and 0.13×107 erg cm−3, respectively. Both the values of Ku and K1 decrease with increasing temperature T, while K2 is almost independent of T. The difference between the power law of the Callen and Callen model is described by the dimensionality and the thermal variation of the axial ratio c/a due to the thermal expansion.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
65.40.De Thermal expansion; thermomechanical effects

Influence of bicrystal microstructural defects on high-transition-temperature direct-current superconducting quantum interference device

C. H. Wu, U. C. Sou, J. C. Chen, K. L. Chen, H. C. Yang, M. H. Hsu, T. S. Lai, J. T. Jeng, Y. S. Tsai, and H. E. Horng

Appl. Phys. Lett. 88, 102504 (2006); http://dx.doi.org/10.1063/1.2182066 (3 pages) | Cited 10 times

Online Publication Date: 8 March 2006

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Using atomic force microscopy and scanning electron microscopy (SEM), we investigate the correlations between the microstructural defects and the electrical characteristics of the bicrystal grain-boundary Josephson junctions and dc superconducting quantum inference devices (SQUIDs). The structural defects are shown to correlate qualitatively with the characteristics of grain-boundary Josephson junctions patterned on the YBa2Cu3O7−x film. SEM images show that these defects grown on the grain boundary were a few submicron depth of the groove. The low flux noise characteristics were observed when the groove depth was smaller than 18 nm in the junctions of the SQUID. The existence of these defects is expected to affect the supercurrent and the motion of the magnetic flux in the films, which dominate the excess noise in the SQUID with bicrystal junctions.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
61.72.Mm Grain and twin boundaries
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures

Tuning of magnetocaloric effect in a La0.69Ca0.31MnO3 single crystal by pressure

Young Sun, J. Kamarad, Z. Arnold, Zhi-qi Kou, and Zhao-hua Cheng

Appl. Phys. Lett. 88, 102505 (2006); http://dx.doi.org/10.1063/1.2183824 (3 pages) | Cited 11 times

Online Publication Date: 8 March 2006

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We report a study of the effect of hydrostatic pressure on the magnetocaloric effect in a La0.69Ca0.31MnO3 single crystal. The single crystal exhibits a much larger magnetic entropy change (ΔSm) than the corresponding polycrystalline samples, reaching 5.2 J/kg K and 8.5 J/kg K for a magnetic field variation of 1 T and 5 T, respectively. Under hydrostatic pressure, the peak position of ΔSm significantly moves to higher temperatures due to the shift of the magnetic phase transition, from 213.5 K under ambient pressure up to 236.5 K under a pressure of 1.1 GPa, while the maximum value of ΔSm remains nearly the same. These exceptional results demonstrate that the magnetocaloric effect in magnetic materials with strong spin-lattice coupling can be effectively tuned by pressure.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
65.40.G- Other thermodynamical quantities

Microscopic interfacial structures and magnetic properties of ultrathin Co/Si(111) films

J. S. Tsay, T. Y. Fu, M. H. Lin, C. S. Yang, and Y. D. Yao

Appl. Phys. Lett. 88, 102506 (2006); http://dx.doi.org/10.1063/1.2185259 (3 pages) | Cited 16 times

Online Publication Date: 9 March 2006

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The relation between magnetic properties and microscopic structure for a metal/semiconductor system is described. Cobalt films on a CoSi interface possess an in-plane easy axis of magnetization as the result of magnetocrystalline anisotropy of the Co/CoSi interface. On a Si(111)-7×7 surface, direct evidence for the formation of CoSi2 compounds at the interface was found by the appearance of doubled spot defects in scanning tunneling microscopic images. The interfacial effects cause the easy axis of magnetization of a Co/Si interface to be canted out of plane.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
68.35.Ct Interface structure and roughness

Nature of the transient BaF2-related phases in the “BaF2” processing of Ba2YCu3O7−x superconductors

W. Wong-Ng, I. Levin, L. P. Cook, and R. Feenstra

Appl. Phys. Lett. 88, 102507 (2006); http://dx.doi.org/10.1063/1.2184757 (3 pages) | Cited 6 times

Online Publication Date: 10 March 2006

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Transient BaF2-based oxyfluoride phases are thought to play a critical role in the formation of the c-textured Ba2YCu3O7−x layers of coated conductors. In situ high-temperature x-ray diffraction from the precursor films containing pure BaF2 as well as pseudobinary BaF2–Y, BaF2–Cu, and Y–Cu mixtures and heat treated in water vapor under reduced conditions revealed that the transient BaF2-based superstructures, similar to those observed during formation of Ba2Cu3O7−x, develop even from the pure BaF2 precursor. These superstructures results from the dissolution of oxygen in BaF2 leading to formation of the oxyfluoride phase, Ba(F2−2x◻x)Ox, with an ordered arrangement of O, F, and F vacancies.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
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