X-ray magnetic circular dichroism studies of magnetic alloys and multilayers (invited) (abstract)

Abstract

X-ray magnetic circular dichroism (XMCD) is a newly developed technique that measures local magnetic properties with element specificity. The element specificity makes it possible to probe both the magnetic and the ‘‘nonmagnetic’’ elements in alloys and multilayers. When XMCD is combined with a suitable electron or x-ray microscopy technique, it can be used on multidomain samples without any external magnetic field and the samples can be studied with high spatial resolution. We have carried out a series of XMCD studies on magnetic thin films and multilayers that clearly demonstrated all of these aspects. Large XMCD signals have been observed near the Co L3 and L2 edges in pure Co thin film, Co0.2Pd0.8 alloy and Co/Pd multilayers. Application of a recently proposed sum rule to our data indicates that the orbital magnetic moments at the Co site in both the alloy and multilayer samples are greatly enhanced compared to pure Co metal. This gives strong support to recent theoretical predictions and has implications for the strong perpendicular anisotropy observed in the alloy and multilayer samples. XMCD results near the Pd L3 and L2 edges on Co/Pd multilayers showed that Pd atoms near the interface have nonvanishing magnetic moments with its direction parallel to that of Co atom. We have also used the XMCD technique along with an electrostatic imaging lens system to examine a CoPtCr magnetic recording disk which had been patterned with a recording signal. The magnetic contrast arises from the fact that x-ray absorption depends on the relative orientation of the photon spin and the local magnetization direction. We have obtained images with good contrast (up to 20%) and a spatial resolution of 1 μm. With improved electron optics and x-ray source, this new microscopy technique should provide a much higher spatial resolution. It appears particularly valuable for the investigation of magnetism at interfaces and in complex materials where the magnetic contribution from different elements needs to be distinguished.