Magnetic behavior of rare-earth iron-rich intermetallic compounds

The thermal variation of lattice parameters of rare earth-transition metal intermetallic compounds rich in Fe, Co or Ni in the temperature range of 25-900°K is studied. For the Fe compounds, negative thermal expansion is observed below their magnetic ordering temperatures regardless of the nature of substitutional ordering. For Co and Ni compounds, the thermal expansion behavior is normal. It is then concluded that for the Fe compounds, the magnetic properties are mainly determined by the Fe-Fe interatomic distances and the number of Fe nearest neighbors, whereas for Co and Ni compounds the magnetic properties are determined by the conduction electron transfer from the rare earth to the band of Co or Ni, The anomalous thermal expansion of Fe compounds and the metamagnetic transition of the Lu compound is explained in terms of the distance dependence of the interaction energy as proposed by Néel.