Competing Magnetic Anisotropies in the Antiferromagnet Thin Film Alloy Ni­_1-xMn_xF_2­

NiF₂ and MnF₂ both have a rutile crystal structure and antiferromagnetic (AF) order at low temperature, but NiF₂ has an easy-plane plane anisotropy with an effective Dzyaloshinskii-Moriya interaction, while MnF₂ is an easy axis uniaxial anisotropy. Bulk NiF₂ orders at 73 K and prefers to orient the AF spins along the [100] or [010] directions, while bulk MnF₂ orders at 67 K with an easy axis anisotropy that orients the spins along the [001] direction. The close structural similarity and relatively small lattice mismatch between the NiF₂ and MnF₂ crystals makes them good candidates for a mixed thin film alloy system with competing AF anisotropies. I will present our work growing and characterizing thin film Ni­_1-xMn_xF_2­ alloys, a system which to date has not been studied. These alloys represent a system with competing single-ion AF anisotropies without frustration due to the exchange interaction. Thin films of varying stoichiometries were grown via MBE and characterized with x ray diffraction (XRD), which showed that the alloys grow epitaxially and single phase along the [110] direction. XRD measurements also show a smooth change of the lattice constants as the stoichiometry is changed and strain due to epitaxial growth on the MgF₂ (110) substrate. The magnetic moment of these samples was measured and used to determine the magnetic anisotropy of the alloys, demonstrating that the easy axis flips near x = 0.7, and the effect of strain on transition temperature.