Temperature- and field-induced valence transitions of EuNi2(Si1-xGex)(2)

The magnetic properties of the EuNi2(Si1-xGex)(2) system were studied in which an intermediate-valence state of Eu is realized at around x = 0.75. It was found that the compounds with 0.70 less than or equal to x less than or equal to 0.82 show a temperature-induced valence transition below room temperature, while those with x greater than or equal to 0.85 are antiferromagnetic with a stable Eu2+ state. A first-order valence transition induced by high magnetic field was observed for 0.75 less than or equal to x less than or equal to 0.82. Such valence transitions against temperature or field are discussed on the basis of the interconfigurational fluctuation (ICF) model. It is shown that the observed linear relation between the transition field and the transition temperature is explained by the present model.