Paper EM+SS+TF-ThA12
Single Crystal Study of Layered U_nRhIn_3n+2 Materials: Case of the Novel U₂RhIn₈ Compound

Thursday, November 10, 2016, 6:00 pm, Room 102A

Materials of reduced dimensionality appear in many contemporary fields of research and technology, because they encompass a wide variety of interesting electronic phenomena. For instance carbon can be prepared in 3D (diamond), quasi-2D (graphite), 2D (graphene) or 1D (carbon nanotubes). All of these structures have distinct electronics. Diamond is an insulator. Graphene is semimetal. However, when the dimensionality is increased by putting several graphene layers together (eventually making graphite), the resulting band structure moves to that of a more trivial metal. Another example is high temperature superconductors being quasi-2D materials as well.

The role of dimensionality in f-electron systems has been mainly discussed in the context of quantum phase transitions and related phenomena. The series Ce_nT_mIn_{3n+2m (}n = 1, 2; m = 0, 1, 2; T = transition metal) of layered compounds has been extensively investigated. CeIn₃ is cubic (3D) and orders antiferromagnetically (AFM) at T_N = 10.2 K. Under hydrostatic pressure superconductivity appears with highest T_c = 0.3 K at p = 2.5 GPa. In CeRhIn₅, the anisotropic crystal structure leads to a quasi-2D electronic and magnetic structure. The AFM order is reduced (T_N = 3.8 K) while superconductivity is supported, T_c increases to 1.9 K at p = 1.77 GPa.

We report on the properties of the novel U₂RhIn₈ compound studied the single crystal form in the context of parent URhIn₅ and UIn₃ systems [1]. The compounds were prepared by In self-flux method. U₂RhIn₈ adopts the Ho₂CoGa₈-type structure with lattice parameters a = 4.6056(6) Å and c = 11.9911(15) Å. The behavior of U₂RhIn₈ strongly resembles features of related URhIn₅ and UIn₃ with respect to magnetization, specific heat, and resistivity, except for magnetocrystalline anisotropy developing with lowering dimensionality in the series UIn₃ vs. U₂RhIn₈ and URhIn₅. U₂RhIn₈ orders AFM below T_N = 117 K and exhibits slightly enhanced Sommerfeld coefficient γ = 47 mJ.mol^-1.K^-2. Magnetic field leaves the value of Néel temperature for both URhIn₅ and U₂RhIn₈ unaffected up to 9 T. On the other hand, T_N increases with applying hydrostatic pressure up to 3.2 GPa. Results of thermal expansion measurement will be discussed in the framework of Ehrenfest relations. The character of uranium 5f electron states of U₂RhIn₈ was studied by first principles calculations based on the density functional theory combined with the Hubbard model. The overall phase diagram of U₂RhIn₈ is discussed in the context of magnetism in related UTX₅ and UX₃ (T = transition metal, X = In, Ga) compounds.