Structural, magnetic, and dielectric properties of charge-order phases in manganite La(Ca0.8Sr0.2)2Mn2O7

Abstract

Charge-ordered layered manganites ReA2Mn2O7 (Re = rare-earth species and A = Ca, Sr, Ba, etc.) are believed to offer a number of fascinating electronic and magnetic properties, including the long-time claimed but not yet confirmed ferroelectricity associated with charge-ordering. Experimental observations of the charge-order induced transport and electrically polar behaviors have been insufficient. In this work, we synthesize the La(Ca0.8Sr0.2)2Mn2O7 (LCSMO) single crystal and investigate its structural, magnetic, and dielectric properties. It is revealed that LCSMO undergoes two consecutive charge-ordering transitions upon decreasing temperature T before entering an antiferromagnetic state in the low-T range. The first charge-order transition occurs at temperature TCO1 ∼ 314 K from the high-T paramagnetic state. This charge-order state (CO1 state) is transferred into another charge-order state (CO2 state) by a sequence starting from ∼290 K, and the resultant CO2 state is dynamic and polar-like. The dynamic behaviors of this polar-like CO2 state is confirmed by the remarkable dielectric relaxation associated with this state. The present work provides a connection between the charge-ordering and electrically polar response in LCSMO, while ferroelectricity remains yet to be an issue.