Evolution of magnetic properties of CaMn1−xNbxO3 with Nb-doping

Abstract

Magnetic and structural properties of Nb-doped CaMnO3 have been studied and the effect of doping with 0.02 ⩽ x ⩽ 0.1 has been investigated. Substitution of Nb5+ ion for the Mn4+ site of the parent matrix causes one-electron doping with the chemical formula , accompanied by a monotonous increase of the lattice parameters, unit-cell volume, average Mn–O bond distance and a decrease in Mn–O–Mn bond angle, with increasing x. Low temperature magnetic ground state of CaMn1−xNbxO3 has been found to be dependent on niobium doping level. The ground magnetic state evolves from mostly antiferromagnetic, with a weak ferromagnetic component for x = 0.02–0.08, to charge ordered C-type antiferromagnetic state at x = 0.1. Spontaneous magnetization increases sharply with increasing doping level, approaches a maximal value of 4.1 emu g−1 at T = 10 K for x = 0.08, and then decreases rapidly to reach a very small value of 0.2 emu g−1 for x = 0.1. Anomalous negative magnetization behavior below the magnetic transition temperature has been observed for the compound with x = 0.04 in the field cooled magnetization and remanent dc magnetization measurements. Vertical and horizontal shifts of the hysteresis loop of the field cooled sample have been observed for CaMn0.9Nb0.1O3 as possible signatures of the exchange bias effect. The effect of hydrostatic pressure on dc magnetization for the sample with x > 0.02 revealed a significant increase of the ferromagnetic phase volume under pressure, linked to progressive suppression of a negative magnetization in x = 0.04 sample.