Probing strain-induced ferromagnetism in epitaxial SrMnO3 films

Abstract

The development of multiferroic materials with strong magnetoelectric coupling would allow creating low energy consumption devices where the magnetic response could be controllable by an electric field. The coexistence between magnetism and polar order — driven by the off-centering of the magnetic Mn4+ cation (d3) — has been observed in SrMnO3 perovskite compounds. As the same cation is responsible for both the polar and magnetic orders, strong magnetoelectric coupling is expected. While in bulk SrMnO3 the Mn — O — Mn superexchange magnetic interaction stabilizes the G type antiferromagnetic (AF) order, first-principles calculations suggest that different magnetic ground states may be accessible in SrMnO3 epitaxial films by tuning the biaxial strain exerted by the substrate. For tensile stress, a rich phase diagram is inferred, in which a progressive increase in the strain magnitude induces a gradual transition from different types of AF orders to eventually a ferromagnetic (FM) order. Here, we study three fully strained 10 nm-thick SrMnO3 epitaxial films grown on (La,Sr)(Al,Ta)O3 (LSAT), SrTiO3 (STO), and DyScO3 (DSO) single-crystal substrates with mismatch values of +1.68%, +2.63%, and 3.78%, respectively, in order to determine the strain-oxygen vacancies magnetic phase diagram. Synchrotron-based X-ray linear dichroism (XLD), X-ray magnetic circular dichroism (XMCD), and element-specific magnetic hysteresis loops, were performed in all samples around the L2,3 -Mn edges at low temperature and high magnetic field. Preliminary results show sizeable XMCD signals and a slight opening of the hysteresis loops in the case of the DSO and LSAT, suggesting the emergence of FM order in these strained systems (see Figure 1). Besides, the comparison of the experimental data with calculated reference spectra is also in progress to determine the evolution of the Mn3+/Mn4+ ratio as a function of the strain and its effect on both the local magnetic moment and the resulting magnetic order.