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13 Jun 2005

Volume 86, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 86, 241913 (2005); http://dx.doi.org/10.1063/1.1946181 (3 pages)

E. Placidi, F. Arciprete, V. Sessi, M. Fanfoni, F. Patella, and A. Balzarotti
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Improved current densities in MgB2 by liquid-assisted sintering

S. K. Chen, Z. Lockman, M. Wei, B. A. Glowacki, and J. L. MacManus-Driscoll

Appl. Phys. Lett. 86, 242501 (2005); http://dx.doi.org/10.1063/1.1947374 (3 pages) | Cited 5 times

Online Publication Date: 6 June 2005

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Polycrystalline MgB2 samples with GaN additions were prepared by reaction of Mg, B, and GaN powders. The presence of Ga leads to a low melting eutectic phase which allowed liquid phase sintering and produces platelike grains. For low-level GaN additions ( ⩽ 5 at. %), the critical transition temperature, Tc, remained unchanged and in 1 T magnetic field, the critical current density, Jc was enhanced by a factor of 2 and 10, for temperatures of ∼ 5 K and 20 K, respectively. The values obtained are approaching those of hot isostatically pressed samples.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.Sv Critical currents
74.10.+v Occurrence, potential candidates

Impact of Ru doping in bilayered manganese oxide La1.2Sr1.8Mn2O7

Y. Onose, J. P. He, Y. Kaneko, T. Arima, and Y. Tokura

Appl. Phys. Lett. 86, 242502 (2005); http://dx.doi.org/10.1063/1.1947900 (3 pages) | Cited 9 times

Online Publication Date: 6 June 2005

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The Ru doping effect on the bilayered manganese oxide La1.2Sr1.8(Mn1−yRuy)2O7 has been investigated in the range of 0 ⩽ y ⩽ 0.2. The ferromagnetic transition temperature (TC) increases, while the saturated magnetization decreases, with Ru doping. These indicate that in addition to the doping-induced suppression of charge-orbital correlation, the antiferromagnetic coupling between the Ru and the Mn moments is relevant to the enhancement of TC. The axis of easy magnetization changes from within the in plane to along the c axis with Ru doping, owing to the strong magnetic anisotropy of Ru spins.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.up Other materials
75.47.Lx Magnetic oxides
75.30.Gw Magnetic anisotropy
75.30.Cr Saturation moments and magnetic susceptibilities

Flux-flow critical-state susceptibility of superconductors

D.-X. Chen, E. Pardo, and A. Sanchez

Appl. Phys. Lett. 86, 242503 (2005); http://dx.doi.org/10.1063/1.1947370 (3 pages) | Cited 5 times

Online Publication Date: 8 June 2005

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The field-amplitude Hm and circular frequency ω dependent ac susceptibility, χ = χ′−jχ″, of a hard superconducting cylinder with flux-flow type current-voltage characteristic is calculated. A remarkable feature of the resultant χ(Hm,ω) is that both the maximum χ″, χm″, and d lg Hm(χm″)/d lg ω increase with increasing ω. This behavior is observed in actual Bi-2223/Ag tapes and YBa2Cu3O7−δ-coated conductors. Our result provides a useful tool to study the intergranular critical state in high-temperature superconductors.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Op Mixed states, critical fields, and surface sheaths
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.F- Transport properties
74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes

Tunneling spectroscopy studies of treated aluminum oxide tunnel barrier layers

P. G. Mather, A. C. Perrella, E. Tan, J. C. Read, and R. A. Buhrman

Appl. Phys. Lett. 86, 242504 (2005); http://dx.doi.org/10.1063/1.1948532 (3 pages) | Cited 7 times

Online Publication Date: 8 June 2005

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We report scanning tunneling microscopy and ballistic electron emission microscopy studies of the electronic states of the uncovered and chemisorbed-oxygen covered surface of AlOx tunnel barrier layers. These states change when chemisorbed oxygen ions are moved into the oxide by either flood gun electron bombardment or by thermal annealing. While untreated samples exhibit band tails extending to zero bias, the former, if sufficiently energetic, results in locally well defined conduction band onsets at ∼ 1 V, while the latter results in a progressively higher local conduction band onset, exceeding 2.3 V for 500 and 600 °C thermal anneals.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.40.Gh Other heat and thermomechanical treatments
68.37.Vj Field emission and field-ion microscopy
68.43.Mn Adsorption kinetics
71.20.Ps Other inorganic compounds

Laser ablated Ni-doped HfO2 thin films: Room temperature ferromagnets

Nguyen Hoa Hong, Joe Sakai, Nathalie Poirot, and Antoine Ruyter

Appl. Phys. Lett. 86, 242505 (2005); http://dx.doi.org/10.1063/1.1949723 (3 pages) | Cited 15 times

Online Publication Date: 9 June 2005

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Laser ablated Ni-doped HfO2 thin films fabricated under a wide range of growth conditions all showed ferromagnetism above room temperature. However, the films deposited at 800 °C under an oxygen partial pressure of 10−6 Torr have the largest magnetic moment of 2.7μB/Ni. Ni-doped HfO2 films also well demonstrate a large anisotropy. Magnetic force microscopy measurements confirmed that Ni-doped HfO2 films are real room temperature ferromagnets with a domain structure, and that the size of magnetic domains is larger than 10 μm.
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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
68.37.Rt Magnetic force microscopy (MFM)
75.30.Cr Saturation moments and magnetic susceptibilities
81.15.Fg Pulsed laser ablation deposition

Distinctive current-induced magnetization switching in a current-perpendicular-to-plane giant-magnetoresistance nanopillar with a synthetic antiferromagnet free layer

T. Ochiai, Y. Jiang, A. Hirohata, N. Tezuka, S. Sugimoto, and K. Inomata

Appl. Phys. Lett. 86, 242506 (2005); http://dx.doi.org/10.1063/1.1949709 (3 pages) | Cited 12 times

Online Publication Date: 9 June 2005

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We investigated current-induced magnetization switching (CIMS) in two types of pseudo-spin-valve nanopillars with current-perpendicular-to-plane giant magnetoresistance (CPP-GMR); Co90Fe10(10 nm)/Cu(10 nm)/Co90Fe10(2.5 nm) (conventional type) and Co90Fe10(10 nm)/Cu(10 nm)/Co90Fe10(1.5 nm)/Ru(0.45 nm)/Co90Fe10(2.5 nm) (synthetic antiferromagnet; SyAF type). We observed the CIMS in the both CPP-GMR structures at room temperature. In particular for the SyAF type nanopillars, the CIMS was observed only in a negative current regime. We also discovered that the applied magnetic field dependence of the CIMS shows absolutely different behavior from that of the conventional type. These peculiar CIMS behaviors with the SyAF free layer are attributed to majority electron spin transfer torque from the thick to the thin Co90Fe10 layers, enhanced by the presence of a Ru layer.
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75.47.Np Metals and alloys
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.De Giant magnetoresistance
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Effect of current processing on the transport property of the La0.67Ca0.33MnO3 film

J. R. Sun, G. J. Liu, S. Y. Zhang, H. W. Zhang, X. F. Han, and B. G. Shen

Appl. Phys. Lett. 86, 242507 (2005); http://dx.doi.org/10.1063/1.1944894 (3 pages) | Cited 13 times

Online Publication Date: 10 June 2005

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Current effect on the transport property of the La0.67Ca0.33MnO3 film has been studied as a function of temperature and magnetic field. The two-lead resistance of the sample shows a strongly asymmetric behavior with respect to current direction after a treatment under a current of the density of ∼ 1.6×105 A/cm2, and the resistance is much lower in forward direction, the direction of the processing current, than in backward direction. A definite change in current–voltage slope at small but finite forward voltages is observed when alternating the electric field from backward to forward, which is indicative of the presence of two different resistive states corresponding to the two current directions and an energy barrier between these states. The magnetoresistance effect of the two resistive states is significantly different, and it is much stronger for the backward current than for the forward one. This has been proved a combined effect of the inclining of the current–voltage slope and the depression of intermediate energy barrier under magnetic field. The present work suggests a possibility to get a different magnetoresistance via interfacial engineering.
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75.47.Lx Magnetic oxides
72.20.My Galvanomagnetic and other magnetotransport effects
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