Neutron diffraction experiments have been performed on a TbMn2 single crystal and on Tb(Mn0.96Fe0.04)2 powder samples. The magnetic structure of TbMn2 is metastable poised between two structures, S1 with propagation vector (2/3 2/3 0) and S2 with propagation vector (1/2 1/2 1/2). A transition from S1 to S2 can be induced either by an applied field of 4.5 T at 25 K or by chemical pressure induced by substitution of Mn by Fe. The S2 structure has been studied in Tb(Mn0.96Fe0.04)2. The transition to this structure is accompanied by a huge rhombohedral distortion and the structure itself is notable for the coexistence of magnetic and non-magnetic manganese atoms. This peculiar feature is attributed to instability of the Mn moment combined with frustration of the Mn itinerant antiferromagnetism.

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UFe 6 Ga 6 polycrystalline samples were prepared by arc-melting, and single crystals were grown by the Czochralski method. This compound crystallizes in the orthorhombic ScFe 6 Ga 6-type structure (space group Immm, aZ5.0560(4), bZ8.5484(7) and cZ8.6914(7) Å), an ordered variant of the ThMn 12-type structure. A ferromagnetic-type transition at T C Z530(5) K is seen in the magnetization and A.C.-susceptibility measurements, and no other magnetic anomaly is observed down to 5 K. Single crystal magnetization measurements along the three different crystallographic axes indicated a as the easy direction, with a spontaneous magnetization M S Z12.3 m B /f.u. at 5 K. The analysis of the 57 Fe Mössbauer spectroscopy data indicated magnetic hyperfine fields, B hf , significantly lower on 4f sites than on 8k sites, in agreement with the trend already observed on UFe x Al 12Kx , where the average B hf were found to increase with the iron-iron interatomic distances.