Field-induced polar order at the Néel temperature of chromium in rare-earth orthochromites: Interplay of rare-earth and Cr magnetism

Abstract

We report field-induced switchable polarization ( P ∼ 0.2–0.8 μC/cm 2 ) below the Néel temperature of chromium ( T N Cr ) in weakly ferromagnetic rare-earth orthochromites, R CrO 3 ( R = rare earth) but only when the rare-earth ion is magnetic. Intriguingly, the polarization in ErCrO 3 ( T C = 133 K) disappears at a spin-reorientation (Morin) transition ( T S R ∼ 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 an applied magnetic field, indicating a strong magnetoelectric effect. We suggest that the polar order occurs in R CrO 3 , due to the combined effect of the poling field that breaks the symmetry and the exchange field on the R ion from the Cr sublattice that stabilizes the polar state. We propose that a similar mechanism could work in the isostructural rare-earth orthoferrites R FeO 3 as well.