3d-Metal Induced Magnetic Ordering on U(IV) Atoms as a Route toward U(IV) Magnetic Materials

Uranium(IV) 5f ² magnetism is dominated by a transition from a triplet to a singlet ground state at low temperatures. For the first time, we achieved magnetic ordering of U(IV) atoms in a complex fluoride through the incorporation of 3d transition metal cations. This new route allowed us to obtain an unprecedented series of U(IV) ferrimagnetic materials of the new composition Cs ₂ MU ₃ F ₁₆ (M = Mn ²⁺ , Co ²⁺ , and Ni ²⁺ ), which were comprehensively characterized with respect to their structural and magnetic properties. Magnetic susceptibility measurements revealed ferromagnetic-like phase transitions at temperatures of â 14.0, 3.5, and 4.8 K for M = Mn ²⁺ , Co ²⁺ , and Ni ²⁺ , respectively. The transition is not observed when the magnetic M cations are replaced by a diamagnetic cation, Zn ²⁺ . Neutron diffraction measurements revealed the magnetic moments of 0.91(6)-1.97(3) μ _B on the U atoms, which are only partially compensated by antiparallel moments of 1.53(14)-3.26(5) μ _B on the 3d cations. This arrangement promotes suppression of the transition to a diamagnetic ground state characteristic of U(IV), and in doing so, induces magnetic ordering on uranium via 3d-5f exchange coupling.