Uncompensated antiferromagnetic spins at the interface in Mn-Ir based exchange biased bilayers

The microscopic origin of the uncompensated antiferromagnetic (AFM) spins was investigated by means of the x-ray magnetic circular dichroism (XMCD) spectroscopy with transmission mode for Mn-Ir/ferromagnetic (FM) bilayers. As the AFM layer thickness increases, resonant absorption magnitude of Mn L edge naturally increases, but the XMCD magnitude does not change so much. When the FM layer material is modified, the XMCD signal of Mn L edge drastically changes not only in its magnitude but also in its sign. The XMCD signal vanishes without the FM layer. These facts clearly mean that the uncompensated Mn components are induced through the exchange interaction between the FM and the AFM layers and are localized at the very interface. Micromagnetic simulation within the framework of the classical Heisenberg model well supported the above conclusion.