First Observation of a Magnetic-Exchange Induced Valence Transition

A magnetic-exchange induced valence transition has been observed for the first time for different compositions x of Tm1-xEuxSe. This new effect is explained in terms of an exchange splitting 2E of the 5d conduction band which leads to a crossing of the lower 5d band edge with the Tm2 4f13 state at a certain temperature. The polar magneto-optical Kerr effect of the Eu2+ 4f7 4f65d transition is used to study E as a function of temperature via the magnetic red shift. Volume changes of more than 1% have been observed which correspond to an exchange-induced valence change of the Tm ions by 0.15. © 1985 The American Physical Society.