Epitaxial-Strain-Induced Spontaneous Magnetization in Polar Mn₂Mo₃O₈

Mn2Mo3O8 simultaneously exhibits ferroelectric polarization and unique magnetic properties, such as strong magnetoelectric coupling and magnetic-field-induced collinear-to-noncollinear spin structure transitions. However, practical applications of multiferroic Mn2Mo3O8 are hindered by low spontaneous magnetization (0.01 μB/f.u. at 2 K) owing to the collinear spin order. Herein, we report the emergence of large spontaneous magnetization of 0.35 μB/f.u. by applying 0.5% tensile strain to c-axis-oriented Mn2Mo3O8 epitaxial films. The Mn and Mo valence states were divalent and tetravalent, respectively. The enhanced spontaneous magnetization was directed in the in-plane direction, in contrast to that in the case of the bulk. These results suggest that the film has a noncollinear spin structure with tilted Mn2+ magnetic moments from the c-axis probably due to the tensile strain. We also performed first-principles calculations and demonstrated that the direction of the Mn2+ magnetic moment is sensitive to tensile strain.