Volume 92, Issue 2, 15 July 2002
Index of content:
- MAGNETISM AND SUPERCONDUCTIVITY (PACS 74-76)
92(2002); http://dx.doi.org/10.1063/1.1486020View Description Hide Description
A generalized Meiklejohn–Bean model in which the exchange coupling includes bilinear (direct exchange) and biquadratic (spin–flop) terms is proposed to study the exchange bias in ferromagnetic (FM)/antiferromagnetic (AFM) bilayers. For the strong antiferromagneticanisotropy, an explicit formula for the exchange bias is derived and used to discuss the thickness and angular dependencies, and a lot of recent experimental results can thus be illustrated. The results show that both the critical thickness of the antiferromagnetic layer displaying the exchange bias and the saturation value of the exchange bias depend on the exchange coupling constants, the angle between the FM easy axis and AFM easy axis, as well as the orientation of an applied field. The bilinear and biquadratic terms will provide competitive contributions to the exchange bias, while the angular variation of the applied field can tune the exchange bias.
92(2002); http://dx.doi.org/10.1063/1.1485108View Description Hide Description
We have combined magnetic force microscopy in the presence of an external magnetic field with in situmagnetoresistance measurements. This provides the unique opportunity of studying the interplay between the domain structure and the magnetoresistance of mesoscopic ferromagneticthin film structures. We examined 2 μm wide Co zigzag wires because of their pronounced shape induced anisotropyeffects. By combining zigzag wires in a Wheatstone bridge geometry, the hysteresis behavior for zigzag wires parallel and perpendicular to the magnetic field can be compared directly. The magnetoresistance measurements provide quantitative information about the difference in resistivity between the two configurations due to the anisotropic magnetoresistanceeffect and the different domain structure.
92(2002); http://dx.doi.org/10.1063/1.1484223View Description Hide Description
The switching fields of nickel cylinders with dimensions have been compared to the predictions of a numerical micromagnetic model. The switching field decreases with increasing diameter and decreasing aspect ratio, and there is a good agreement between the measured and calculated values. The samples have a strong 〈111〉 preferred crystal orientation, and the large increase in switching field and switching field distribution with decreasing temperature can be explained by the large increase in magnetocrystalline anisotropy at low temperatures.
92(2002); http://dx.doi.org/10.1063/1.1486025View Description Hide Description
multilayers have been deposited by magnetron sputtering onto different seed layers with simultaneous gradients in both thickness and composition x. These gradients make it possible to perform magnetic and structural measurements for different thicknesses and compositions on one single wafer. Hence, the depositions are not sensitive to variations in background conditions such as temperature, pressure, or contaminants that could otherwise vary between runs. The study concluded that the maximum for the coercivity of the multilayers is, in this case, dependent on the microstructure, namely the degree of c-axis orientation in the films. Specifically, the coercivity maximum coincides with the maximum of the x-ray diffraction peak full-width at-half-maximum for the two separate cases shown.
92(2002); http://dx.doi.org/10.1063/1.1487908View Description Hide Description
Nanocomposite permanent ferrites have been prepared by the sol-gel method and their structure and magnetic properties have been analyzed by x-ray diffraction,transmission electron microscopy, and vibrating sample magnetometer. When thermal treatment temperature is below 800 °C, the samples pressed into a flake exhibit exchange-coupling interaction between the two nanostructured phases of and The flake sample treated at 800 °C produces an isotropic nanocomposite with a intrinsic coercivity of 6015 Oe, a maximum magnetization of 75.6 emu/g and a maximum energy product of 1.87 MGOe as compared with the powder sample of 6400 Oe, 75.9 emu/g, and 1.52 MGOe, respectively. The exchange-coupling interaction and the enhancement of isotropic in nanocomposite permanent ferrites have been discussed.