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19 Mar 2001

Volume 78, Issue 12, pp. 1649-1795

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Interface reaction of NiO/NiFe and its influence on magnetic properties

G. H. Yu, C. L. Chai, F. W. Zhu, J. M. Xiao, and W. Y. Lai

Appl. Phys. Lett. 78, 1706 (2001); http://dx.doi.org/10.1063/1.1343474 (3 pages) | Cited 35 times

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Ta/NiO/NiFe/Ta multilayers were prepared by rf reactive and dc magnetron sputtering. The exchange coupling field between NiO and NiFe reached 120 Oe. The composition and chemical states at the interface region of NiO/NiFe were studied using the x-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there are two thermodynamically favorable reactions at NiO/NiFe interface: NiO+Fe=Ni+FeO and 3NiO+2Fe=3Ni+Fe2O3. The thickness of the chemical reaction as estimated by angle-resolved XPS was about 1–1.5 nm. These interface reaction products are magnetic defects, and we believe that the exchange coupling field Hex and the coercivity Hc of NiO/NiFe are affected by these defects. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Ct Interface structure and roughness
75.30.Et Exchange and superexchange interactions
79.60.Jv Interfaces; heterostructures; nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.65.Ac Multilayers

Cobaltous oxide infiltrated yttrium iron garnet thin films as high-coercivity media for data storage

A. C. Rastogi, V. N. Moorthy, and Sandip Dhara

Appl. Phys. Lett. 78, 1709 (2001); http://dx.doi.org/10.1063/1.1355671 (3 pages)

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Significant enhancement in the saturation magnetization Ms and coercivity Hc of yttrium iron garnet (YIG) films has been obtained by a simple method of surface infiltration of CoO. Deposition of a CoO overlayer under specific conditions by a low-pressure chemical-vapor deposition process over the crystallized YIG film has been observed to show high out-of-plane Hc and Ms values of 282.7 and 85.7 kA/m, respectively. The effect of the CoO deposition rate, temperature dependence of coercivity Hc, and annealing studies have been described that indicate CoO infiltration during the growth, resulting in a Co-rich YIG layer, and generation of interfacial stress are responsible for this unusual effect. Delineation of the interface by ion-beam etching in conjunction with magnetic studies has led to the understanding of the nature of the Co-rich YIG interfacial layer. Enhanced Hc and Ms values without the usual method of Ce4+ compensation of Co-doped YIG films described in this letter are of considerable use for application in high-density magneto-optic recording media. © 2001 American Institute of Physics.
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75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.60.Bs Mechanical and acoustical properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
75.50.Ss Magnetic recording materials
42.79.Vb Optical storage systems, optical disks
81.40.Rs Electrical and magnetic properties related to treatment conditions

Photoinduced insulator–metal transition in La0.81MnO3/Al2O3/Nb tunnel junctions

A. Gilabert, A. Plecenik, K. Fröhlich, Š. Gaži, M. Pripko, Ž. Mozolová, D. Machajdík, Š. Beňačka, M. G. Medici, M. Grajcar, and P. Kúš

Appl. Phys. Lett. 78, 1712 (2001); http://dx.doi.org/10.1063/1.1354163 (3 pages) | Cited 12 times

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We report the effect of illumination by ultraviolet and visible light on the resistance versus temperature and current versus voltage characteristics of La0.81MnO3/Al2O3/Nb tunnel junctions. Under illumination, the resistance of tunnel junctions follows the resistance in darkness at high temperatures but at temperatures lower than 95 K, the illumination induces a colossal decrease of the resistance. This is a transient effect because the changes are reversible when the light is switched on and off. Changes of the electrical properties under illumination were seen for the tunnel junctions only and not in the epitaxial La0.81MnO3 electrode which shows a classical insulator–metal transition at temperature Tc = 285 K. We explain this effect by a photoinduced insulator–metal transition of the oxygen depleted manganite interface close to the tunnel barrier which changes dramatically the width of the barrier. © 2001 American Institute of Physics.
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71.30.+h Metal-insulator transitions and other electronic transitions
72.40.+w Photoconduction and photovoltaic effects
75.47.Gk Colossal magnetoresistance
73.40.Rw Metal-insulator-metal structures

Direct detection of the magnetic flux noise from moving vortices in wide YBa2Cu3O7−δ grain boundary junctions

S. Hirano, H. Oyama, S. Kuriki, T. Morooka, and S. Nakayama

Appl. Phys. Lett. 78, 1715 (2001); http://dx.doi.org/10.1063/1.1355669 (3 pages) | Cited 4 times

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We measured the flux of a wide bicrystal grain boundary of YBa2Cu3O7−δ film, cooled to 77 K in a field of 10 μT, using a superconducting thin-film coil and Nb-based superconducting quantum interference device (SQUID). When the applied field was changed to, and above, a small threshold value, the sample showed random switching noises with a sharp increase in low-frequency noise power. The results suggested that there was long-distance movement of vortices over 20–500 μm within the grain boundary, driven by the shielding current. The vortex movement was suppressed to lengths of less than 1 μm in a slotted grain boundary by making an array of SQUIDs that can hold vortices stably. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
85.25.Dq Superconducting quantum interference devices (SQUIDs)
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