In-plane Dielectric and Magnetoelectric Studies of BiFeO3

TL;DR

This study investigates the dielectric and magnetoelectric properties of BiFeO3 thin films, revealing multiple phase transitions near 180-550 K and analyzing skin layer effects and relaxor behavior through experimental and theoretical approaches.

Contribution

It provides new insights into the in-plane dielectric behavior and magnetoelectric coupling of BiFeO3 thin films, including temperature-dependent phase transitions and skin layer effects.

Findings

Identified dielectric anomalies near 180 K, 201 K, 450 K, and 550 K.

Observed relaxor-like phase transition following a Vogel-Fulcher relation.

Developed a theoretical model for in-plane magnetoelectric coefficients.

Abstract

In-plane temperature dependent dielectric behavior of BiFeO3 (BFO) as-grown thin films show diffuse but prominent phase transitions near 450 (+/-10) K and 550 K with dielectric loss temperature dependences that suggest skin layer effects. The 450 K anomalies are near the "transition" first reported by Polomska et al. [Phys. Stat. Sol. 23, 567 (1974)]. The 550 K anomalies coincide with the surface phase transition recently reported [Xavi et al. PRL 106, 236101 (2011)]. In addition, anomalies are found at low temperatures: After several experimental cycles the dielectric loss shows a clear relaxor-like phase transition near what was previously suggested to be a spin reorientation transition (SRT) temperature (~ 201 K) for frequencies 1 kHz < f < 1MHz which follow a nonlinear Vogel-Fulcher (V-F) relation; an additional sharp anomaly is observed near ~180 K at frequencies below 1 kHz. As emphasized recently by Cowley et al. [Adv. Phys. 60, 229 (2011)], skin effects are expected for all relaxor ferroelectrics. Using the interdigital electrodes, experimental data and a theoretical model for in-plane longitudinal and transverse direct magnetoelectric (ME) coefficient are presented.