Reversed exchange-bias effect associated with magnetization reversal in the weak ferrimagnet LuFe0.5Cr0.5O3

The exchange-bias (EB) effect with sign reversalwas found in LuFe0.5Cr0.5O3 ferrite-chromite, which is a weak ferrimagnet below T-N = 265K, 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 similar to 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 Fe3+ and Cr3+ ions.