Study of magnetic anisotropy by Magnetic Circular X-ray Dichroism

The technique of Magnetic Circular X-ray Dichroism (MCXD) has been investigated and developed. This has included measurements in the collinear geometries, and in the recently-developed transverse geometry, as well as hysteresis measurements. The depth sensitivity of the technique was tested, and it was found that a 100 A thick cap of Pt was insufficient to completely stop the dichroism signal from a Co layer. A reliable correction for distortion of the spectra by other elements was developed, whereby the sum spectra for different samples are normalised to each other. The transverse geometry was tested using Co/Pt multilayers with different anisotropies. The TMCXD signal was found to show the direction of the easy axis in these samples, however the calculated anisotropy energies were an order of magnitude larger than expected from torque magnetometry measurements. Measurements on epitaxial Co samples showed that the TMCXD signal followed the net easy axis and not the crystalline anisotropy axis. The TMCXD signal was noted to be field-dependent, and this effect was investigated. It was found that the orbital anisotropy signal did not change with field, although the spin anisotropy signal did. This shows that TMCXD is a good measure of orbital anisotropy. It is proposed that the measured orbital anisotropy is affected by shape or strain effects in the sample, and therefore reflects the net anisotropy in the sample. (author)Available from British Library Document Supply Centre-DSC:DXN032622 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo