Field-induced Polar Order at the N\'eel Temperature of Chromium in Rare-earth Orthochromites: Interplay of Rare-earth and Cr Magnetism

TL;DR

This study reveals that magnetic rare-earth ions in RCrO3 induce switchable polarization below the Ne9el temperature of chromium, driven by weak ferromagnetism and magnetic field effects, suggesting a magnetoelectric coupling mechanism.

Contribution

It demonstrates the emergence of field-induced polar order in RCrO3 due to the interplay of rare-earth and chromium magnetism, highlighting the role of weak ferromagnetism.

Findings

Polarization appears only with magnetic R ions.

Polarization vanishes at the spin reorientation transition.

Magnetic field significantly influences the polarization.

Abstract

We report field-induced switchable polarization (P = 0.2 ~ 0.8 microC/cm2) below the N\'eel temperature of chromium (TN Cr) in weakly ferromagnetic rareearth orthochromites, RCrO3 (R=rareearth) but only when the rareearth ion is magnetic. Intriguingly, the polarization in ErCrO3 (TC ~ 133 K) disappears at a spin reorientation (Morin) transition (TSR ~ 22 K) below which the weak ferromagnetism associated with the Cr sublattice also disappears, demonstrating the crucial role of weak ferromagnetism in inducing the polar order. Further, the polarization (P) is strongly influenced by applied magnetic field, indicating a strong magneto electric effect. We suggest that the polar order occurs in RCrO3, due to the combined effect of poling field that breaks the symmetry and the exchange field on R ion from Cr sublattice stabilizes the polar state. We propose that a similar mechanism could work in the isostructural rareearth orthoferrites, RFeO3 as well.