Resistivity extrema in double-exchange ferromagnetic nondegenerate semiconductors

A version of the magnetoimpurity theory of the colossal magnetoresistance materials suitable for the double-exchange ferromagnetic nondegenerate semiconductors is presented. It provides an explanation of the nonmonotonic temperature dependence for the charge-carrier density in them when it displays first a maximum and then a minimum, on increase in temperature. Respectively, the resistivity displays first a minimum and then a maximum. The theory is based on the relation between the charge-carrier activation energy and the change in the magnon free energy caused by the ionization of an impurity. This is tantamount to the relation between the charge-carrier density and the so-called giant red shift of the optical absorption edge.