Magnetocrystalline anisotropy inUMn2Ge2and related Mn-based actinide ferromagnets

Abstract

We present magnetization isotherms in pulsed magnetic fields up to 62 Tesla, supported by first principles calculations, demonstrating a huge uniaxial magnetocrystalline anisotropy energy -approximately 20 MJ/m 3 -in UMn 2 Ge 2 . This large anisotropy results from the extremely strong spin-orbit coupling affecting the uranium 5 f electrons, which in the calculations exhibit a substantial orbital moment exceeding 2 Bohr magnetons. We also find from theoretical calculations that a number of isostructural Mn-actinide compounds are expected to have similarly large anisotropy.Introduction. Uranium-3d transition metal compounds present a wide range of behaviors, ranging from superconductivity in U 6 Mn and U 6 Fe 1 , ferromagnetism with T c above room temperature in UMn 2 Ge 2 2 , antiferromagnetism and heavy-fermion behavior in UNi 4 B, 3 , and the unexpected paramagnetism 4 in UMn 2 . All these materials appear to present an interplay across energy scales, in particular in which the uranium spin-orbit coupling rivals and sometimes exceeds typical energy scales such as the crystal field splitting and electronic band width.

Competing magnetic ground states and their coupling to the crystal lattice in CuFe2Ge2

“…What we study here is the coupling of the moments to the crystalline structure, or effectively the magnetic anisotropy. As is well known, this anisotropy derives from spin-orbit coupling, which is expected to be weak here as all elements are relatively light (one recalls the effective Z 4 dependence 16 of spin-orbit coupling). Hence these energy differences are expected to be very small.…”

Tuning the Magnetic Properties and Structural Stabilities of the 2-17-3 MagnetsSm2Fe17X3(Pandey1, Du2, Parker3 2018Phys. Rev. AppliedSelf Cite

“…Positive (negative) K corresponds to uniaxial (planar) anisotropy. Although the calculation of MAE from firstprinciples methods is somewhat difficult, as shown in some recent studies [22,[41][42][43][44][45] precise calculations often produce MAE in good agreement with experiments. To ensure the accuracy of MAE, its convergence with respect to number of k-point was carefully checked.…”

Imaging the magnetic states in an actinide ferromagnet UMn2Ge2

“…Magnetization, neutron scattering, and Kerr effect experiments indicate that the Mn ordering temperature T M n c ≈ 380 K, while the uranium atoms order below T U c ≈ 150 K [9][10][11]. Furthermore, recent magnetization measurements under pulsed magnetic fields up to 62 T reveal a strong uniaxial anisotropy with a second order anisotropy constant larger than that of the first order [12]. To date, however, a local and spatially resolved study on the magnetic properties of this compound is still lacking.…”