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21 Aug 2000

Volume 77, Issue 8, pp. 1071-1232

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Enhanced blocking temperature in NiO spin valves: Role of cubic spinel ferrite layer between pinned layer and NiO

R. F. C. Farrow, M. J. Carey, R. F. Marks, P. M. Rice, and David J. Smith

Appl. Phys. Lett. 77, 1191 (2000); http://dx.doi.org/10.1063/1.1289660 (3 pages) | Cited 4 times

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We compare the blocking temperature for simple permalloy (80% Ni)/Au/permalloy/NiO spin valves with and without an interfacial, oxidized Fe layer (Fe layer 12 Å thick) inserted at the permalloy/NiO interface. We find a significantly increased blocking temperature and pinning field for spin valves with the interfacial Fe-oxide layer, as a result of moderate (230 °C/1 h) annealing of the Au/permalloy/Fe-oxide/NiO part of the spin valve. High resolution transmission electron microscopy and electron energy loss microanalysis reveal that the Fe-oxide layer is converted to a cubic spinel ferrite (Ni0.8Fe2.2O4) layer by solid state reaction with the NiO. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Gg Ferrimagnetics

Magnetic properties of CoII mesoclusters

Michi Sato, Syozo Takada, Shigemi Kohiki, Tomohiro Babasaki, Hiroyuki Deguchi, Masaoki Oku, and Masanori Mitome

Appl. Phys. Lett. 77, 1194 (2000); http://dx.doi.org/10.1063/1.1289654 (3 pages) | Cited 4 times

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Clusters of cobalt (II) ions dispersed in a mesoporous silicate, prepared by calcination of the MCM-41 molecular sieve soaked in CoCl2 0.01 mol/l aqueous solution, showed no x-ray diffraction peaks except one from the molecular sieve. X-ray photoelectron spectroscopy and ultraviolet-visible diffuse reflectance spectroscopy revealed that the mesoclusters consisted of CoII ions in tetrahedral coordination. We have observed temperature and frequency dependences of the alternating current susceptibility, and no divergent peaks of the nonlinear susceptibility due to superparamagnetism. Spins derived from the field dependent magnetization above the blocking temperature with the Langevin equation fairly agree with those at the cluster surface estimated from the ionic radii of Co2+ and O2−. © 2000 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Ee Antiferromagnetics
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Procedure for preparing epitaxial Tl-2201 films on single crystal LaAlO3

H. Q. Chen, L.-G. Johansson, and Z. G. Ivanov

Appl. Phys. Lett. 77, 1197 (2000); http://dx.doi.org/10.1063/1.1289065 (3 pages) | Cited 3 times

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Epitaxial Tl-2201 films are prepared by treating precursor films deposited on single crystal LaAlO3 by laser ablation with Tl2O vapor at high temperature. Here, a procedure is described that includes thallization in two separate steps. The first thallization at 720 °C resulted in good epitaxy as well as in smooth morphology. The second thallization at 820 °C resulted in an improvement of the superconducting properties and in film crystallinity without affecting epitaxy or morphology. The films were characterized by x-ray diffraction (ϕ scan, Ω scan, θ–θ scan), and by resistance and susceptibility measurements. The films are tetragonal. In a typical film, the full width at half maximum of the Ω scan of the (0,0,10) reflection was 0.27°. A 5 μm wide bridge patterned in one film had a Tc of 84 K. The critical current density reached 1.4×106 A/cm2 at 77 K and 1.4×107 A/cm2 at 4.2 K. © 2000 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.10.+v Occurrence, potential candidates
74.25.Sv Critical currents
87.64.Bx Electron, neutron and x-ray diffraction and scattering
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.F- Transport properties
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