Optical magnetoelectric effect of patterned oxide superlattices with ferromagnetic interfaces

Abstract

Format

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Abstract

Recent development of pulsed laser deposition technique makes it possible to build up different kinds of perovskite oxides and to create new electric and magnetic properties of heterointerfaces, which can neither be realized in bulk properties of the constitute oxides and nor be treated as the simple combination of them. The extraction of unique properties of interfaces thus crucially relies on the development of a new method to selectively detect their electronic properties accompanied with magnetism. Here we show a new approach with use of the optical magnetoelectric (ME) effect to address the unique properties of ferromagnetic oxide superlattices (SLs). The ME effect, that is, the control of the polarization P by a magnetic field H or inversely the control of the magnetization M by an electric field E, can be considered as a typical manifestation of cross-correlation phenomena in solids. Even at optical frequencies, such a cross-correlation response coming from the ME effect is known to show up in materials with a lack of both space-inversion and time-reversal symmetries. This is referred to as the optical ME effect. The optical ME response emerges as a change of reflection and transmission when the wavevector k of light is set to parallel or antiparallel to the toroidal moment T defined as P X M, which in turn enables us to control the intensity of light by changing the directions of E and/or H. In this work, we fabricated SLs composed of LaMnO3, SrMnO3, and LaAlO3 and exploited the use of their unique properties of heterointerfaces as a medium for optical ME effect. Such 'tricolor' SLs are expected to artificially break both space-inversion and time-reversal symmetries, which are induced by asymmetric stacking sequences of three different oxides and by the charge-transfer-induced magnetism at LaMnO3/SrMnO3 interfaces, respectively. We patterned the grating structure with a period of 4 ìm on SLs and employed the Bragg diffraction geometry to sensitively detect the optical ME effect. The optical ME effect was clearly observed when the diffracted light was used as a probe. The optical ME response depending on PABC X Minterface is a direct consequence of the symmetry breaking at interfaces. Its magnitude per interface was thus estimated to be tilde operator = varies with = similar to 0.01% in H of 2 kOe, which are relatively large as compared to previously reported values in bulk materials showing the optical ME effect. Our data provide that the present method would be used as a tool for the study of oxide heterointerfaces.