Unusual Co moment reduction in the NiCoO/Co exchange bias system

To answer the question on how the explicit mechanism of coupling in the antiferromagnetic alloy NiCoO is established when in close contact to a ferromagnetic Co layer, X-ray magnetic circular dichroism (XMCD) measurements have been performed. Precise XMCD spectra at the L_{2, 3}-edge of Ni as well as Co have been obtained at room temperature and at 80 K by measuring total electron yield X-ray absorption spectra. The Ni XMCD clearly shows the existence of free, rotatable magnetic Ni moments in the antiferromagnet. As for the Co, XMCD at room temperature shows an average magnetic moment comparable to bulk values. Cooling the sample to 80 K decreases the average Co moment by 10 %. This decrease is explained by a reduction of ferromagnetic cobalt moments related to antiferromagnetic coupling or pinning close to the interface.