FIRST-ORDER PHASE TRANSITION IN EUROPIUM METAL

We have used Mössbauer-effect measurements of the hyperfine (hf) interaction in Eu metal to study the behavior of its sublattice magnetization in the vicinity of the magnetic ordering temperature. At 88.6°K, the hf field falls from 0.4 of the saturation value to zero. This results from the existence of a first-order transition coincident with the magnetic ordering. The possible causes of the transition are discussed. The temperature dependence of the hyperfine field just below the transition is analyzed in terms of criticalpoint theory. The results of thermal-expansion measurements are also presented and discussed. © 1969 The American Physical Society.