Heusler alloys are one of several promising materials currently being investigated for their potential use in ‘spintronic’ devices. The interest arises from the fact that some Heusler alloy compositions are predicted to be half-metallic ferromagnets due to a band gap in the minority-spin states, and thus have 100% spin-polarisation at the Fermi level. Evidence of this high spin-polarisation has been seen indirectly via magneto-transport effects such as tunnelling magnetoresistance (TMR). Here I will discuss how the element-specific sensitivity of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) can be exploited to probe the half-metallic properties of cobalt based Heusler alloys. In particular I will review our recent results on local moment formation and how this relates to the origin of the half-metallic behaviour. I will also discuss the effects of site disorder and the temperature dependence of the magnetism in these materials.
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