Effect of Cu Layer on Exchange Bias in FeMn

One of the most important puzzles related to the mechanism of exchange bias is the origin and role of uncompensated magnetization in the antiferromagnet. We study effects of a Cu layer on the uncompensated magnetization and exchange bias in FeMn, the material with a high potential for applications in magnetic recording. The multilayers of Ta(50 {\AA})/[FeMn(50 {\AA} -- 150 {\AA})/Cu(50 {\AA})]$_{10}$/Ta(50 {\AA}) are deposited by UHV DC magnetron sputtering on top of Si/SiO$_{x}$ 3 mm x5 mm substrates. Samples with a single layer of FeMn of the same thickness, Ta(50 {\AA})/FeMn(50 {\AA} -- 150 {\AA})/Ta(50 {\AA}) are used as control samples. The samples are cooled in a field of 7 T and their magnetization is measured using a SQUID magnetometer. All the samples have uncompensated magnetization that exhibits a hysteresis at 10 K. The hysteresis loops for FeMn/Cu multilayers are exchange bias shifted, while FeMn without Cu exhibits no exchange bias. Dependence of coercive field (H$_{c})$, exchange bias (H$_{e})$, and saturated magnetization (M$_{s})$ on the FeMn thickness and on temperature will be discussed. Work is supported by Texas A{\&}M University, TAMU-CONACYT Collaborative Research Program, and by NSF (USF).