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1 Oct 2001

Volume 90, Issue 7, pp. 3135-3665

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Role of thermal energy on the magnetic properties of laminated antiferromagnetically coupled recording media

S. N. Piramanayagam, C. H. Hee, and J. P. Wang

J. Appl. Phys. 90, 3442 (2001); http://dx.doi.org/10.1063/1.1399030 (8 pages) | Cited 14 times

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The effect of thermal energy (kBT), which has been found to play some important roles in the magnetic properties of recently developed antiferromagnetically coupled media, is described. It was observed that the thermal energy helps to obtain an antiparallel configuration of moments at remanence. Therefore, a reduction in the remnant moment–thickness product (Mrδ) is observed, even for smaller values of J (interface coupling constant) than those used in simulations that do not consider thermal energy. The magnetic viscosity measurement helps to distinguish the magnetization decay behavior of the top and bottom layers. The magnetic moments of top and bottom layers show maximum decay at different fields and the decay rates approximately scale with their thickness. Viscosity results also point out that the magnetization reversal of the bottom layer should occur in the first quadrant, in order to obtain a low noise and thermally stable media. Micromagnetic simulation was performed by including thermal effects. In that case, Mrδ reduction could be obtained for smaller values of J than in the case where thermal energy is not included in the simulation. © 2001 American Institute of Physics.
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75.50.Ee Antiferromagnetics
75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.60.Dv Thermal stability; thermal effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Lr Magnetic aftereffects
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Transport properties of submicron YBa2Cu3O7−δ step-edge Josephson junctions

Peter Larsson, Alexander Ya. Tzalenchuk, and Zdravko G. Ivanov

J. Appl. Phys. 90, 3450 (2001); http://dx.doi.org/10.1063/1.1400098 (5 pages) | Cited 2 times

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Submicron step-edge Josephson junctions in YBa2Cu3O7−δ (YBCO) thin films were fabricated and studied. All measured junctions fall into three categories: low critical current resistively shunted Josephson junctions, intrinsic Josephson junctions, and quasiparticle tunnel junctions. The transport in the junctions is correlated with the microstructure of YBCO films grown on the step edge. We argue that the properties of conventional step-edge junctions can be understood as a superposition of those types. © 2001 American Institute of Physics.
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85.25.Cp Josephson devices
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
74.25.F- Transport properties

Magnetic response of hard superconductors subjected to parallel rotating magnetic fields

A. F. Carballo-Sánchez, F. Pérez-Rodríguez, and A. Pérez-González

J. Appl. Phys. 90, 3455 (2001); http://dx.doi.org/10.1063/1.1400094 (7 pages) | Cited 6 times

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The manifestation of flux-line cutting in the magnetic behavior of a type-II superconductor, either (i) subjected to a rotating magnetic field, or (ii) undergoing slow oscillations in a static magnetic field, is investigated theoretically. We have applied both the generalized double critical-state model and the two-velocity hydrodynamic one to interpret available experimental results for oscillating disks of Nb. The hydrodynamic model generates only closed hysteresis loops, after the first full oscillation, in accordance with the experimental hysteresis loops observed at a relatively small amplitude of oscillation, θmax=45°. However, at larger amplitudes of oscillation, several measured loops are evidently open. This behavior as well as their asymmetric form could be reproduced only by the generalized double critical-state model. The limits of applicability of both models are discussed. © 2001 American Institute of Physics.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Dynamic permeability in soft magnetic composite materials

A. Chevalier and M. Le Floc’h

J. Appl. Phys. 90, 3462 (2001); http://dx.doi.org/10.1063/1.1389520 (4 pages) | Cited 16 times

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This article reports on an isotropic model of the magnetic susceptibility based on an average field theory and proposes to predict the dynamic behaviors of powder magnetic materials. It was essentially built around a so-called effective demagnetizing factor capable of taking the particle shapes into account. So, for a population of randomly distributed particles of anisotropic shapes like, for instance, needles or flakes, we show that the effective demagnetizing factor of this population of particles can be significantly lowered with regard to the well known value of 1/3 classically used to represent the isotropy state. This phenomenon is interpreted as the natural tendency of particles to form clusters to which a moving demagnetizing factor must be assigned. Taking then the aggregation process of particles into account, the ability of the model to predict the dynamic properties of many composite magnetic materials is successfully demonstrated. Our development is illustrated by experimental results concerning a nickel–zinc ferrimagnetic (Ni0.7Zn0.3Fe2O4) powder. © 2001 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Dd Nonmetallic ferromagnetic materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Tt Fine-particle systems; nanocrystalline materials

Giant magnetoimpedance of chemically thinned and polished magnetic amorphous ribbons

F. Amalou and M. A. M. Gijs

J. Appl. Phys. 90, 3466 (2001); http://dx.doi.org/10.1063/1.1398072 (5 pages) | Cited 8 times

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We have measured the giant magnetoimpedance (GMI) of microstructured Co-based Metglas® 2714a amorphous magnetic ribbons. Before micropatterning, the amorphous ribbons were chemically thinned or polished, to study the influence of sample thickness and surface state on the GMI effect. The magnetic domain structure of polished foils near saturation is observed using the bitter fluid technique. The well-defined geometry of the samples allows a quantitative comparison of the GMI effect with a simple skin depth model, from which we obtain the frequency-dependent permeability of the material. We have measured the GMI effect for magnetic fields parallel and transverse to the long axis of the sample. We compare the different measurement geometries and film preparation methods and, typically, find a room-temperature GMI ratio of about 35%–90% in fields of a few mT and at frequencies of 10–40 MHz. © 2001 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Cc Other ferromagnetic metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
81.65.Ps Polishing, grinding, surface finishing
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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