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We have synthesized magnesium cage compounds $R$Ni$_{2}$Mg$_{20}$ ($R$ = Pr and Nd). We report the measurements of electrical resistivity $\rho$, magnetic susceptibility $\chi$, isothermal magnetization $M$, and specific heat $C$. Polycrystalline samples with $R$ = Pr and Nd were obtained by annealing, while the counterparts for $R$ = La, Ce, and Y were found to be absent. The ${\rho}(T)$ data for $R$ = Pr and Nd monotonically decrease on cooling from 300 K to 40 K and exhibit shoulders at around 13 K and 15 K, respectively. The Curie-Weiss behaviors of the ${\chi}(T)$ data indicate the trivalent states of both the Pr and Nd ions. For $R$ = Pr, the maximum in $C(T)$ at around 7 K is reproduced by a doublet-triplet two-level model with an energy gap of 14 K. The peak in $C(T)$ at 0.7 K is attributed to a short-range order of quadrupolar degrees of freedom in the non-Kramers ground doublet. On the other hand, for $R$ = Nd, a maximum in $C(T)$ at around 9 K is explained by thermal excitation from a ground state doublet to an excited quartet separated by 23 K. Upon further cooling, $C(T)$ shows a lambda-shaped peak at 1.5 K. By applying magnetic fields up to 2 T, the peak becomes broad and shifts to higher temperatures, which is a characteristic of a ferromagnetic order., Comment: 7 pages, 10 figures

We have studied the pressure effect on the rattling of tetrahedrite Cu$_{10}$Zn$_{2}$Sb$_{4}$S$_{13\,}$(CZSS) and type-I clathrate Ba$_{8}$Ga$_{16}$Sn$_{30\,}$(BGS) by specific heat and x-ray diffraction measurements. By applying pressure $P$, the rattling energy for CZSS initially decreases and steeply increases for $P$ $\textgreater$ $1$ GPa. By contrast, the energy for BGS increases monotonically with $P$ up to 6.5 GPa. An analysis of the pressure dependent specific heat and x-ray diffraction indicates that the out-of-plane rattling of the Cu atoms in the S$_{3}$ triangle of CZSS originates from the chemical pressure, unlike the rattling of the Ba ions among off-center sites in an oversized cage of BGS. The rattling in CZSS ceases upon further increasing $P$ above 2 GPa, suggesting that Cu atoms escape away from the S$_{3}$ triangle plane., Comment: 16 pages, 3 figures, 1 table

Superconductivity in PrIr$_{2}$Zn$_{20}$ appears at $T_{\rm c} = 0.05$ K in the presence of an antiferroquadrupolar order below $T_{\rm Q} = 0.11$ K. We have studied pressure dependences of $T_{\rm c}$, $T_{\rm Q}$, and non-Fermi liquid behaviors in the resistivity $\rho (T)$ by using two pressure transmitting media: argon maintaining highly hydrostatic pressure, and glycerol, which solidifies above 5 GPa producing nonhydrostatic pressure. Upon applying $P$ with argon up to 10.6 GPa, $T_{\rm c}$ hardly changes, while $T_{\rm Q}$ monotonically increases from 0.11 to 0.23 K. With glycerol, however, $T_{\rm Q}$ and $T_{\rm c}$ simultaneously fall below 0.04 K at 6.3 GPa. The contrasting results indicate that onsite quadrupolar fluctuations induce superconductivity in this compound., Comment: 15 pages, 4 figures

Structural, transport and magnetic properties of single-crystalline samples of a praseodymium-based cubic compound PrMgNi4 were studied. The single-crystal X-ray structural analysis revealed that Mg atoms are substituted for the Pr atoms at the 4a site by 4.5%. The chi(T) data follow the Curie-Weiss law with an effective moment for the Pr3+ ion. The magnetic specific heat divided by temperature, Cm/T, shows a broad maximum at around 3 K, which is reproduced by a two-level model with a ground state doublet. On cooling below 1 K, Cm/T approaches a constant value, which behavior is reproduced by a random two-level model. The twofold degeneracy of the ground state is lifted by symmetry lowering due to the substituted Mg atoms for the Pr atoms or strong hybridizations between the 4f2 electron states and conduction bands, which hinders the long-range quadrupole order.

We report the effects of electron doping on the ground state of a diamagnetic semiconductor FeGa$_{3}$ with a band gap of 0.5 eV. By means of electrical resistivity, magnetization and specific heat measurements we have found that gradual substitution of Ge for Ga in FeGa$_{3-y}$Ge$_{y}$ yields metallic conduction at a very small level of $y = 0.006$, then induces weak ferromagnetic (FM) order at $y = 0.13$ with a spontaneous moment of 0.1 $\mu_{B}$/Fe and a Curie temperature $T_{C}= 3.3$ K, which continues increasing to $T_{C} = 75$ K as doping reaches $y = 0.41$. The emergence of the FM state is accompanied by quantum critical behavior as observed in the specific heat, $C/T \propto -$ln$T$, and in the magnetic susceptibility, $M/B \propto T^{-4/3}$. At $y= 0.09$, the specific heat divided by temperature $C/T$ reaches a large value of 70 mJ/K$^{2}$molFe, twice as large as that reported on FeSi$_{1-x}$Ge$_{x}$ for $x_{c}= 0.37$ and Fe$_{1-x}$Co$_{x}$Sb$_{2}$ for $x_{c}=0.3$ at their respective FM quantum critical points. The critical concentration $y_{c}=0.13$ in FeGa$_{3-y}$Ge$_{y}$ is quite small, despite the fact that its band gap is one order of magnitude larger than those in FeSi and FeSb$_{2}$. In contrast, no FM state emerges by substituting Co for Fe in Fe$_{1-x}$Co$_{x}$Ga$_{3}$ in the whole range $0 \leq x \leq 1$, although both types of substitution should dope electrons into FeGa$_{3}$. The FM instability found in FeGa$_{3-y}$Ge$_{y}$ indicates that strong electron correlations are induced by the disturbance of the Fe 3d - Ga 4p hybridization., Comment: 21 pages, 11 figures, accepted for publication in Phys. Rev. B

Electrical resistivity rho, magnetic susceptibility chi, magnetization M and specific heat measurements are reported on a singlecrystalline sample of CePd5Al2, showing successive antiferromagnetic orderings at T_N1=4.1 K and T_N2=2.9 K. The temperature dependence of T_N1 shows a Kondo metal behavior with large anisotropy, rho_c/rho_a=3.2 at 20 K, and opening of a superzone gap along the tetragona c-direction below T_N1. Both T_N1 and T_N2 gradually increase with applying pressure up to 2.5 GPa. The data of chi(T) and M(B) in the paramagnetic state were analyzed using a crystalline electric field (CEF) model. It led to a Kramers doublet ground state with wave functions consisting primarily of |+-5/2>, whose energy level is isolated from the excited states by 230 and 300 K. This CEF effect gives rise to the large anisotropy in the paramagnetic state. In the ordered state, the uniaxial magnetic anisotropy is manifested as M_c/M_a=20 in B=5 T and at 1.9 K, and chi_c/chi_a=25 in B=0.1 T and at 4 K. This huge uniaxial magnetic anisotropy in the antiferromagnetic states can be interpreted in terms of isotropic magnetic interaction among the Ce^{3+} moments governed by the strong CEF. In powder neutron diffraction experiments, magnetic reflections were observed owing to the antiferromagnetic ordered states below T_N1, however, no additional reflection was found below T_N2., Comment: 8 pages, 8 figures, submitted to J. Phys. Soc. Jpn