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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Effects of magnetic layer thickness and of head-to-medium spacing on noise in advanced particulate recording media

Tim Mercer, Philip R. Bissell, Paul Ardeleanu, Laurentiu Stoleriu, and Alexandru Stancu

J. Appl. Phys. 93, 6334 (2003); http://dx.doi.org/10.1063/1.1566088 (10 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The effects of magnetic layer thickness on the noise characteristics of advanced metal particle tape have been observed using a dc demagnetization process generated with a uniform in-plane magnetizer. The three-dimensional (3D) surface maps of spectral noise power plotted as a function of remanent magnetization state showed a change in behavior as the recording layer became thinner. The thickest magnetic coating of 310 nm showed “trough-like” characteristics associated with conventional thick particulate media. The thinnest sample with a 165 nm magnetic coating showed a “peak-like” response that is observed in continuous thin-film media, with a graduated trend from one to the other for the two intermediate samples. A simulation of these results has been made with an 8000 spherical particle micromagnetic model of the media remanent states and a simulated magnetoresistive read head. Noise maps produced from the simulation compared well with experiment. Spatial isolation of the noise contributions was achieved by dividing the modeled magnetic layer into sublayers. This revealed that particles at the surface were the source of the “peak-like” response, and their contributions became more dominant as the magnetic coating got thinner. Further model investigations showed an association of the different sublayer characteristics with a change in the mean magnetostatic interaction field. The interaction field of particles at the surface had characteristics similar to those of 2D granular thin films and hence generated “thin film-like” noise. A further effect was associated with the spacing between the head and various regions of particles. As this was increased, not only was the amplitude of the noise reduced, but the increased region of integration meant that longer range correlations were incorporated into the observed characteristics, resulting in noise maps more like those of conventional thick particulate media. © 2003 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ss Magnetic recording materials

Simple technique to determine the drain temperature in GaAs metal semiconductor field effect transistor

Mohamed Kameche and Mohamed Feham

J. Appl. Phys. 93, 6344 (2003); http://dx.doi.org/10.1063/1.1566475 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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The effects of the operating temperature T and the drain voltage on the drain temperature in GaAs metal semiconductor field effect transistor (MESFET) are a serious problem, which do not receive enough attention in the scientific literature in the last years. This article presents a simple technique to determine the drain temperature by setting the equality between the field-dependent diffusivity-to-mobility ratio (nonlinear relation) and the constant ratio linear modeling. So, we investigate the impact of the high-field electron diffusivity model in GaAs on the characteristics of MESFETs. Two dimensional numerical simulation is used to describe significant physics in the characteristics for 0.5 μm MESFET GaAs. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Lateral current density fronts in asymmetric double-barrier resonant-tunneling structures

Pavel Rodin and Eckehard Schöll

J. Appl. Phys. 93, 6347 (2003); http://dx.doi.org/10.1063/1.1568529 (7 pages) | Cited 9 times

Online Publication Date: 9 May 2003

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We present a theoretical analysis and numerical simulations of lateral current density fronts in bistable resonant-tunneling diodes with Z-shaped current–voltage characteristics. The bistability is due to the charge accumulation in the quantum well of the double-barrier structure. We focus on asymmetric structures in the regime of sequential incoherent tunneling and study the dependence of the bistability range, the front velocity, and the front width on the structure parameters. We propose a sectional design of a structure that is suitable for experimental observation of front propagation and discuss potential problems of such measurements in view of our theoretical findings. We point out the possibility to use sectional resonant-tunneling structures as controllable three-terminal switches. © 2003 American Institute of Physics.
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85.30.Kk Junction diodes
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.30.De Semiconductor-device characterization, design, and modeling

Low-field transverse magnetovoltage in manganite films

V. Moshnyaga, B. Damaschke, R. Tidecks, and K. Samwer

J. Appl. Phys. 93, 6354 (2003); http://dx.doi.org/10.1063/1.1567036 (7 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The temperature and in plane magnetic field dependences of the transverse voltage, VY, were studied in patterned epitaxial films of La0.7Ca0.3MnO3(LCMO)/MgO and La0.7(Ca0.5Sr0.5)0.3MnO3(LSCMO)/MgO. Above the Curie temperature, TC, VY(T) shows the same insulating behavior as the longitudinal voltage, VX(T). With the onset of long range ferromagnetic order near TC, an additional contribution to VY appears, exhibiting a sin(2α) dependence on the angle α between the current and the magnetic field, H. An hysteretic VY(H) behavior with two minimums at the coercive field, ±HC, due to the magnetization reversal, was found in the ferromagnetic regime. A magneto voltage, ΔVY(0.5 kOe)/VY(0)=400%, and a low-field sensitivity of 20%/Oe (50 μV/Oe) for Hext=10–20 Oe in a LSCMO film were observed at room temperature. The results are explained as an anisotropic magnetoresistance (AMR) effect, which becomes maximal slightly below TC. The maximal AMR ratios, 1.7% and 1.5–2.3%, were obtained for LCMO and LSCMO films, respectively. © 2003 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.47.Lx Magnetic oxides
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Jk Magnetization reversal mechanisms
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