Atomic-scale control of exchange bias at BaTiO3 - La0.67Sr0.33MnO3 interface for new multi-state memory

Abstract

The atomic-scale interfaces of 3D transition-metals oxides are the fascinating playground for several atomic-scale interactions of spins. Novel physical phenomena such as magnetoelectric coupling, unconventional exchange bias (EB) coupling, etc. which originate at such interfaces have huge potential for next-generation nanoscale spintronic devices. Among them, EB is the most studied due to its importance for device applications such as high-density memory and sensor. Here, we demonstrate EB coupling (EB shift, HEB~40 Oe at 2 K) at the interface of epitaxially grown ferromagnetic (FM) La0.67Sr0.33MnO3 (LSMO) – ferroelectric (FE) BaTiO3 (BTO) bilayer thin films on SrTiO3 (STO) single crystal substrates in absence of any conventional antiferromagnetic (AFM) material. Such EB is only observed when the thickness of LSMO is only a few unit cells (<10nm). Importantly, we find that the EB coupling follows training effect, bias field dependency, and temperature dependency. By X-ray magnetic circular dichroism (XMCD) measurement, it is observed that in such epitaxial heterostructure Ti of BTO poses magnetisation at 2K and can reversibly switch between two distinct magnetization states by switching external applied magnetic field. A remanent magnetization (MR) in Ti is also observed. The magnetization of Ti as well the EB vanishes at high temperature (300K) which confirms the EB coupling between Ti of BTO and Mn of LSMO at low temperature. This is an important step towards creating EB coupling between FM and FE materials without conventional AFM materials, which may enable a new class of multi-state memory devices by switching magnetization, FE polarisation and EB coupling in the same device.