Doping-Dependent Magnetism and Exchange Bias in CaMn1-xRexO3

Magnetic and structural properties of CaMn1-xRexO3 (0.02 <= x <= 0.1) have been investigated. Substitution of Re5+ ion for the Mn4+ site of CaMnO3 generates Mn3+ ions according to the chemical formula CaMn1-2x4+ Mnx3+Rex5+O3, accompanied by an increase of lattice parameters and unit-cell volume with increasing x. With increasing doping level x, the magnetic ground state evolves from an antiferromagnetic (AFM) with a weak ferromagnetic (FM) component, for x = 0.02 - 0.06, to the charge ordered C-type AFM state at x = 0.1. Spontaneous magnetization at T = 10 K increases quickly with increasing x, approaches the maximum value of 3.5 emu/g for x = 0.04, and then decreases rapidly to 0.2 emu/g for x = 0.1. Anomalous negative magnetization (NM) for x = 0.02 has been observed in the zero-field-cooled and field-cooled (FC) magnetization below the magnetic transition temperature. Exchange bias (EB) effect, manifested by horizontal shift in the hysteresis loops of FC samples, has also been observed. This effect is very small for x = 0.02, almost zeroes for 0.04, and monotonously increases with increasing x. The EB appears due to low-temperature phase separation into FM clusters and charge-ordered AFM phases. The effect of hydrostatic pressure for all samples revealed a significant increase of the FM phase volume under pressure, linked to both suppression of NM in x = 0.02 sample and reduction of the EB effect in all samples