Magnetic Characteristics of Laves Phases Containing Lanthanide Metals Combined with Nickel

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Abstract
Studies have been made of the series of compounds represented by the formula ANi2, in which A is Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. These compounds are all isostructural, possessing the MgCu2 structure. Nine of the compounds exhibit magnetic ordering at temperatures ranging from 8°K (for PrNi2) to 90°K (for GdNi2). The Y, Ce, and Lu ramain paramagnetic down to liquid helium temperatures. YNi2 and LuNi2 exhibit Pauli paramagnetism from 4° to 300°K suggesting that nickel has a filled 3d shell and is not carrying a moment in these phases. CeNi2 likewise exhibits Pauli paramagnetism, which implies that Ce has been ionized to the quadripositive state. The measured saturation moment extrapolated to 0°K is in good agreement with the value expected if nickel is nonmagnetic and the lanthanide component carries the moment of the free tripositive ion in the case of GdNi2 but is in poor agreement for the eight other compounds which order magnetically. For all except SmNi2, which appears to be a special case, the observed moment is less than that of the free ion, the discrepancy ranging from 78% for PrNi2 to 28% for HoNi2. The low moment is attributed to the quenching effect of the crystal field, but the possibility cannot be excluded that these are not simple ferromagnets. The moment for SmNi2 is 6.3 μB, as compared with 0.71 μB for the ground state free tripositive ion (L‐S coupling). The origin of the high moment for this compound is not understood. Its magnitude can be rationalized in terms of a change to L+S coupling.