Racial stereotyping: survey of psychiatrists in the United Kingdom

No abstracts available

Magnetization reversal of NiFe films exchange-biased by IrMn and FeMn

We have used the transmission electron microscope to study how the magnetization reversal mechanism of thin NiFe layers exchange-biased by IrMn and FeMn varies over a wide temperature range, The reversal behaviour was qualitatively similar for layers biased by both types of antiferromagnet, At room temperature and below the most striking feature was the scale of the domain structures observed. Very high density domain structures with micron (or sub-micron) wall separations developed. By contrast at elevated temperatures, the reversal mechanism simplified. This is consistent with there being a strong local variation of the pinning strength between the NiFe and the antiferromagnetic layer, The overall temperature variation of the pinning changes much more rapidly than the magnetic properties of an isolated NiFe layer over a similar temperature range

Compositional, structural, and electrical characterization of plasma oxidized thin aluminum layers for spin-tunnel junctions

In this paper we present results on how the plasma oxidation of a thin (1.5 nm) Al layer proceeds. Transmission electron microscopy of a Co/Al-oxide multilayer was used to determine the thickness of the oxides and Rutherford backscattering spectrometry and elastic recoil detection were utilized in order to determine the oxygen content. The oxide was also characterized via ac impedance measurements. These measurements indicated that the oxidation of Al on Co occurs in three discrete steps

Structure and soft magnetic properties of sputter deposited MnZn-ferrite films

In this paper we report the soft magnetic properties of thin films of sputtered MnZn ferrite deposited on thermally oxidized Si substrates. A high deposition temperature, 600¿°C, together with the addition of water vapor to the sputtering gas was found to improve the initial ac permeability, µ. The highest value obtained was approximately 30. For MnZn-ferrite films with much larger grain sizes, as obtained by deposition on a polycrystalline Zn-ferrite substrate, a µ of 100 was obtained. The results are discussed in terms of the so-called nonmagnetic grain boundary model

Direct observation of magnetization reversal processes in micron-sized elements of spin-valve material

Simple calculations suggest that when continuous films of spin-valvematerial are patterned into micron-sized elements the magnetic properties should change markedly, depending on the element shape and size. We have used the differential phase contrast imaging mode of transmission electron microscopy to study directly the magnetization distributions supported by such elements in zero field and when subjected to an applied field in the pinning direction. For elements whose long axis is parallel to the pinning direction a parallel alignment of the free and pinned layers is favored. When subjected to a field a complex domain structure evolves and different irreversible paths are followed as the element is taken from negative to positive saturation and back again. By contrast, when the pinning direction is parallel to the short axis an antiparallel arrangement, where the magnetostatic contribution to the energy is effectively suppressed, can be preferred and simpler reversal mechanisms, with a higher degree of reversibility, are frequently seen

Asymmetric bias voltage dependence of the magnetoresistance of Co/Al2O3/Co magnetic tunnel junctions: Variation with the barrier oxidation time

Recently it has been observed that the magnetoresistance (MR) of plasma oxidized exchange biased Co/Al2O3/Co tunnel junctions can have a strongly asymmetric bias voltage (Vbias) dependence. In this article we report on the dependence of this phenomenon on barrier oxidation time tox. For junctions based on 1.5 nm Al, tox was varied from 20 to 120 s. For tox = 20 s, for which the MR is approximately 20% at Vbias = 0, and for tox = 90 s symmetric MR(Vbias) curves are found, with the MR decreasing monotonically with |Vbias|. A strong asymmetric bias voltage dependence was observed for intermediate oxidation times, which correspond to essentially full oxidation of the Al layer, but almost no formation of stoichiometric CoO at the bottom electrode. Samples with tox = 60 s show even an asymmetric double peak in MR(Vbias). Due to its strength, it has an important consequence for device applications: for a series of junctions with variable tox the maximum signal voltage (at a fixed current) is not necessarily obtained for junctions which have the largest MR ratio at Vbias = 0. ©2001 American Institute of Physics

The optimum oxidation state for plasma-oxidised tunnel junctions

In this paper we present results on how both the resistance and the magnetoresistance of magnetic spin-tunnel junctions depend on the oxidation time used to form the AlOx barrier. The bias voltage dependence of junctions with barriers created with different oxidation times is measured and found to be optimal when the oxidation time is chosen to give sufficient oxygen for the barrier to be stoichiometric Al2O3. The oxygen content of the barrier was determined by Rutherford backscattering spectrometry and elastic recoil detection