Reversed exchange-bias effect associated with magnetization reversal in the weak ferrimagnet LuFe_(0.5)Cr_(0.5)O_3

摘要

The exchange-bias (EB) effect with sign reversal was found in LuFe_(0.5)Cr_(0.5)O_3 ferrite-chromite, which is a weak ferrimagnet below T_N = 265 K, exhibiting antiparallel orientation of the ferromagnetic (FM) moments of the Fe and Cr sublattices due to opposite sign of the Fe-Cr Dzyaloshinskii vector, as compared to that of the Fe-Fe and Cr-Cr. The weak FM moments of the studied compound compensate each other at temperature T_(comp) = 230 K, leading to the net magnetic moment reversal and to observed negative magnetization, at moderate applied fields, below T_(comp). Both vertical and horizontal shifts from the origin were gotten in the field-cooled magnetization hysteresis loops. The EB sign was found to be positive below T_(comp) and negative above T_(comp), with nonmonotonic dependence on cooling field H_(cool). It sharply increases at small values of magnetic fields up to H_(cool) ~ 1 kOe, then remains almost unchanged in the range 1-30 kOe and strongly decreases with further increase of H_(cool). This unusual behavior results from the competition of various Dzyaloshinskii-Moriya interactions between Fe~(3+) and Cr~(3+) ions.