Isotropic Γ₆ Ground State in Caged Cubic Compound NdRu₂Zn₂₀

Abstract

The magnetic susceptibility χ, the magnetization M, and the specific heat C were measured for the caged cubic compound NdRu 2 Zn 20 at temperatures down to 0.5 K in the magnetic field H along the three crystallographic principal axes, [100], [110], and [111]. The ferromagnetic phase transition was observed at the Curie temperature T C = 1.9 K in both the temperature dependence of χ(T ) and C(T ). Below T C , the magnetization curves M(H) show very weak magnetic anisotropy, and the C(T ) curves in the fields along the three principal axes show no magnetic anisotropy both below and above T C . The easy direction of magnetization at 0.5 K changes from the [111] direction in 0 T to the [110] diretion in 7 T. We analyzed these characteristic behaviors theoretically taking into account the crystalline-electric-field energy, the magnetic exchange interaction, and the Zeeman energy. It was found that these features are originated from the isotropic Γ 6 ground state mixing with the magnetic Γ (1 [2][3][4] YbT 2 Zn 20 (T = Fe, Co, Ru, Rh, Os, Ir) are heavy-electron compounds with large local-moment degeneracy. 5) DyFe 2 Zn 20 is a ferromagnetic compound with a strong coupling between the Dy and Fe ions. 6, 7) These compounds are crystallized in the cubic CeCr 2 Al 20 -type structure (space group is Fd3m). 8) R element seizes in the cubic-symmetry site (the point symmetry is T h ). Characteristic features in this type of compounds are (1) the weak magnetic coupling due to the dilute content of R elements, and (2) the weak magnetic anisotropy due to the highly symmetrical environment around R ions. 8) PrRu 2 Zn 20 remains in a normal state down to 0.04 K, showing no magnetic order nor quadrupolar order but a structural transition at 138 K, according to Onimaru et al.2) The energy scheme due to the crystalline electric field (CEF) is speculated to be a singlet ground state and a singlet excited state situated at 8 K above the ground state based on the low-temperature specific-heat experiment. 2) Very recently, Iwasa et al. 9) determined the energy scheme and the CEF parameters x and W of PrRu 2 Zn 20 by the inelastic neutron scattering experiment. Their ground state and excited state are Γ 3 (0 K)-Γ 5 (36.7 K), which is contradictory to the energy scheme inferred from the specific-heat experiment.We have studied the magnetic and the thermal properties of NdRu 2 Zn 20 to observe the competition between the exchange interaction and the CEF effect. In this Letter, we present the experimental results of NdRu 2 Zn 20 at temperatures down to 0.5 K. NdRu 2 Zn 20 is a ferromagnet with the Curie temperature T C = 1.9 K. Present experimental results could be analyzed numerically very well by taking into account the exchange interaction between the Nd ions, the CEF effect, and the Zeeman energy. The CEF parameter of NdRu 2 Zn 20 was derived by a sophisticated method based on the CEF parameters of PrRu 2 Zn 20 . 9) Theoretical calculations reveal that the isotropic properties of NdRu 2 Zn 20 are caused by the isotropic Γ 6 ground state ...

Transport and magnetic properties in the Nd diluted system Y$_{1-x}$Nd$_{x}$Co$_{2}$Zn$_{20}$

“…Here, it is noted that relatively large c− f hybridization is needed to exhibit the two-channel Kondo effect in the 4 f 3 systems. Among NdTr 2 X 20 , the c− f hybridization in NdCo 2 Zn 20 is expected to be larger than the other NdTr 2 X 20 compounds, because the lattice parameter is the smallest and the magnetic transition temperature T N = 0.53 K is the lowest [8][9][10][11][12][13]. In fact, the ρ(T ) data of NdCo 2 Zn 20 decrease with an upward convex curvature on cooling from 4 K to T N , which is expressed by the theoretical form derived from the two-channel Anderson lattice model [8].…”

Magnetic structure of an antiferromagnet NdRh2Zn20 investigated by powder neutron diffraction

“…Nd-based compounds NdTr 2 X 20 exhibit ferromagnetic or antiferromagnetic transitions below 2 K [17,18,19,20,21,22,23]. The crystalline electric field (CEF) ground states of the Nd ion are mostly the Γ 6 doublets.…”

Synthesis and study of transport and magnetic properties of magnesium cage compounds $R$Ni$_{2}$Mg$_{20}$ ($R$ = Pr and Nd)

“…Furthermore, the NFL behaviors in the diluted Pr system Y(Pr)Ir 2 Zn 20 [18,19] indicate manifestation of the quadrupole Kondo effect [20,21]. On the other hand, in isostructural Nd-based compounds NdT 2 X 20 with the 4 f 3 configuration, the crystalline electric field (CEF) ground states are mostly the magnetic Γ 6 doublets [22,23,24,25,26,27]. NdT 2 X 20 exhibit either ferromagnetic (FM) or antiferromagnetic (AFM) transitions.…”