We demonstrate the stabilization of a magnetic ground state in epitaxial NiMn2O4 (NMO) thin films not observed in their bulk counterpart. Bulk NMO exhibits a magnetic transition from a paramagnetic phase to a collinear ferrimagnetic moment configuration below 110 K and to a canted moment configuration below 70 K. By contrast, as-grown NMO films exhibit a single magnetic transition at 60 K and annealed films exhibit the magnetic behavior found in bulk. Cation inversion and epitaxial strain are ruled out as possible causes for the new magnetic ground state in the asgrown films. However a decrease in the octahedral Mn 4+ :Mn 3+ concentration is observed and likely disrupts the double exchange that produces the magnetic state at intermediate temperatures. Xray magnetic circular dichroism and bulk magnetometry indicate a canted ferrimagnetic state in all samples at low T. Together these results suggest that the collinear ferrimagnetic state observed in bulk NMO at intermediate temperatures is suppressed in the as grown NMO thin films due to a decrease in octahedral Mn 4+ , while the canted moment ferrimagnetic ordering is preserved below 60 K.

We report the synthesis of epitaxial spinel CuCr 2 O 4 thin films that display enhanced magnetization in excess of 200% of the bulk values when grown on single-crystal (110) MgAl 2 O 4 substrates. Bulk CuCr 2 O 4 is a ferrimagnetic insulator with a net magnetic moment of 0.5μ B due to its distorted tetragonal unit cell (c/a= 1.29) and frustrated triangular moment configuration. We show that through epitaxial growth and substrate-induced strain, it is possible to tune the magnetic functionality of our films by reducing the tetragonal distortion of the unit cell which effectively decreases the frustration of the magnetic moments allowing for an overall greater net moment.