Magnetocrystalline anisotropy in UMn2Ge2 and related Mn-based actinide ferromagnets

We present magnetization isotherms in pulsed magnetic fields up to 62 T, supported by first-principles calculations, demonstrating a huge uniaxial magnetocrystalline anisotropy energy - approximately 20 MJ/m3 - in UMn2Ge2. This large anisotropy results from the extremely strong spin-orbit coupling affecting the uranium 5f electrons, which in the calculations exhibit a substantial orbital moment exceeding 2μB. We also find from theoretical calculations that a number of isostructural Mn actinide compounds are expected to have similarly large anisotropy.