Observation of room-temperature ferromagnetism in Cu:ZnO films part I; soft X-ray Magnetic Circular Dichroism

We report direct evidence of room-temperature ferromagnetic ordering in O-deficient Cu:ZnO films by using soft x-ray magnetic circular dichroism and x-ray absorption [1]. Our measurements have revealed unambiguously two distinct features of Cu atoms associated with (i) magnetically ordered Cu ions present only in the oxygen-deficient samples and (ii) magnetically disordered regular Cu$^{2+}$ ions present in all the samples. We find that a sufficient amount of both oxygen vacancies and Cu impurities is essential to the observed ferromagnetism, and a non-negligible portion of Cu impurities is uninvolved in the magnetic order.\\[4pt] [1] T.S. Herng et al, Phys. Rev. Lett. {\bf 105}, 207201 (2010)