Reversed exchange-bias effect associated with magnetization reversal in the weak ferrimagnet LuF e0.5 C r0.5 O3

Abstract

The exchange-bias (EB) effect with sign reversal was found in LuFe0.5Cr0.5O3 ferrite-chromite, which is a weak ferrimagnet below TN=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 Tcomp=230K, leading to the net magnetic moment reversal and to observed negative magnetization, at moderate applied fields, below Tcomp. 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 Tcomp and negative above Tcomp, with nonmonotonic dependence on cooling field Hcool. It sharply increases at small values of magnetic fields up to Hcool∼1kOe, then remains almost unchanged in the range 1-30 kOe and strongly decreases with further increase of Hcool. This unusual behavior results from the competition of various Dzyaloshinskii-Moriya interactions between Fe3+ and Cr3+ ions.