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

Uranium­(IV) 5f2 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 Cs2MU3F16 (M = Mn2+, Co2+, and Ni2+), which were comprehensively characterized with respect to their structural and magnetic properties. Magnetic susceptibility measurements revealed ferromagnetic-like phase transitions at temperatures of ∼14.0, 3.5, and 4.8 K for M = Mn2+, Co2+, and Ni2+, respectively. The transition is not observed when the magnetic M cations are replaced by a diamagnetic cation, Zn2+. Neutron diffraction measurements revealed the magnetic moments of 0.91(6)–1.97(3) μB on the U atoms, which are only partially compensated by antiparallel moments of 1.53(14)–3.26(5) μB 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.四价铀（Uranium(IV)）的5f²电子构型磁性主要由低温下三重态向单重态基态的转变主导。本研究首次通过引入3d过渡金属阳离子，在复合氟化物体系中实现了U(IV)原子的磁有序。这一全新合成策略使我们获得了组成为Cs₂MU₃F₁₆（M = Mn²+、Co²+和Ni²+）的U(IV)基亚铁磁材料系列，该系列此前从未被报道过。研究团队针对其结构与磁学性质开展了全面表征：磁化率测试结果显示，当M分别为Mn²+、Co²+和Ni²+时，材料分别在~14.0 K、3.5 K和4.8 K处出现类铁磁相变；而当将磁性过渡金属阳离子替换为抗磁性的Zn²+时，则未观测到该相变。中子衍射表征表明，铀原子的磁矩介于0.91(6)~1.97(3) μB（玻尔磁子）之间，其仅被3d金属阳离子上1.53(14)~3.26(5) μB的反平行磁矩部分抵消。这种磁矩排布抑制了U(IV)所特有的抗磁性基态转变，并通过3d-5f交换耦合诱导铀原子产生磁有序。