Grain engineered polar-axis-oriented epitaxial Mn2Mo3O8 films with enhanced magnetic transition temperature

Abstract

Mn₂Mo₃O₈ is a layered multiferroic material that exhibits unique properties such as two-dimensional magnetism, room-temperature ferroelectric order, and strong magnetoelectric coupling. However, it has a low magnetic transition temperature (T_N) of 41 K. Therefore, in this study, we grain engineered polar-axis-oriented Mn₂Mo₃O₈ epitaxial films to enhance the T_N. Mn₂Mo₃O₈ films were grown on yttria-stabilized zirconia (111) substrates. These films consisted of two types of hexagonal grains (G1 and G2) that were oriented at an angle of 30° with respect to each other while maintaining the ferroelectric polar axis of the film along the out-of-plane direction. Such a dual grain system is a result of the layered structure of Mn₂Mo₃O₈, in which the Mn and Mo layers are alternately stacked along the polar axis. The volume fraction of G2 was significantly affected by the film thickness and varied widely in the range 2–48%. Importantly, T_N of the grain engineered Mn₂Mo₃O₈ films increased to 163 K with increasing the volume fraction. We speculate that this increase in T_N is due to the formation of a three-dimensional magnetic network at the grain boundaries.