The spontaneous exchange bias effect in La2-xCaxCoMnO6 series

TL;DR

This study investigates the structural, electronic, and magnetic properties of La2-xCaxCoMnO6 compounds, revealing a spontaneous exchange bias effect that strengthens with Ca doping due to increased antiferromagnetic interactions.

Contribution

It demonstrates the emergence and enhancement of the spontaneous exchange bias effect in La2-xCaxCoMnO6 due to Ca doping, linking magnetic behavior to structural and compositional changes.

Findings

All samples have orthorhombic structure with decreasing unit cell size with Ca doping.

Two ferromagnetic transitions are observed, related to different Co-Mn couplings.

Spontaneous exchange bias effect appears in Ca-doped samples, increasing with Ca content.

Abstract

Structural, electronic and magnetic properties of polycrystalline La2-xCaxCoMnO6 (0 $\leq$ x $\leq$ 0.75) compounds are investigated by x-ray diffraction and magnetometry. All the samples have an orthorhombic structure and show a slight decrease in the unit cell with Ca-doping. Temperature-dependent magnetization measurements reveal a complex magnetic behavior with two ferromagnetic transitions. These transitions are ascribed to Co2+--Mn4+ and Co3+--Mn3+ couplings and suggest the presence of additional antiferromagnetic couplings in these disordered compounds. Field-dependent magnetization curves, measured after cooling the samples in a zero external magnetic field, reveal the spontaneous exchange bias (SEB) effect for the Ca-doped samples. The strengthening of the uncompensated magnetic coupling at the interfaces, caused by the increased antiferromagnetic phase, explains the increase of SEB with increasing the Ca-content.