Interface magnetism in complex oxides heterostructures and manufactured magnetoelectric coupling

Novel electronic and magnetic properties can be achieved in materials engineered at nanometer length scales. Examples include conducting or magnetic interfaces between materials that are neither conducting nor magnetic. With an understanding of interface structure, electronic and magnetic degrees of freedom may be controlled, ideally at room temperature, to achieve magnetoelectric coupling in a nanocomposite or possibly to control spin textures in topological materials.

In this talk, the origin of a novel form of magnetism in BiFeO₃ (BFO) when sandwiched between La_0.7Sr_0.3MnO₃ (LSMO) layers is discussed [1]. Our results exclude charge transfer, intermixing, strain and octahedral rotations/tilts as dominating mechanisms for the large uncompensated magnetization we see in thin BFO layers. We show that ultrathin BFO is simultaneously ferrimagnetic and ferroelectric up to 200 K.

A second example illustrates the use of ionic liquids (IL) to switch reversibly the ferroelectric (FE) polarization of large area PbZr_0.2Ti_0.8O₃ (PZT) films [2]. Control of the polarization enabled us to show that hole accumulation and depletion induced by the FE polarization leads to a reduction or an enhancement, respectively, of the interface magnetism. IL-assisted FE gating may enable new applications of magnetoelectric coupled multiferroics—ones that operate at room temperature.
[1] Er-Jia Guo, et al., Advanced Materials, 29, 1700790 (2017).
[2] A. Herklotz, et al., NanoLetters, 17, 1665 (2017).