Strongly frustrated magnetism of the metallic pyrochlore oxide Pr2Ir2O7 has been revealed by single crystal study. While Pr 4f moments have an antiferromagnetic RKKY interaction energy scale of /T*/ = 20 K mediated by Ir 5d-conduction electrons, no magnetic long-range order is found except for partial spin freezing at 120 mK. Instead, the Kondo effect, including a lnT dependence in the resistivity, emerges and leads to a partial screening of the moments below /T*/. Our results indicate that the underscreened moments show spin-liquid behavior below a renormalized correlation scale of 1.7 K.

A polycrystalline sample of FeSe, which adopts the tetragonal PbO-type structure (P 4 /nmm) at room temperature, has been prepared using solid state reaction. We have investigated pressure-induced structural changes in tetragonal FeSe at varying hydrostatic pressures up to 0.6 GPa in the orthorhombic (T = 50 K) and tetragonal (T = 190 K) phases using high resolution neutron powder diffraction. We report that the structure is quite compressible with a bulk modulus ≈ 31 GPa to 33 GPa and that the pressure response is anisotropic with a larger compressibility along the c-axis. Key bond angles of the SeFe 4 pyramids and FeSe 4 tetrahedra are also determined as a function of pressure.

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Single crystals of Ce 2 PdGa 12 have been synthesized in Ga flux and characterized by X-ray diffraction. This compound crystallizes in the tetragonal P4=nbm space group, Z ¼ 2 with lattice parameters of a ¼ 6:1040ð2ÞÅ and c ¼ 15:5490ð6ÞÅ. It shows strongly anisotropic magnetism and orders antiferromagnetically at T N $11 K. A field-induced metamagnetic transition to the ferromagnetic state is observed below T N . Structure-property relationships with the related heavy-fermion antiferromagnet CePdGa 6 are discussed.