The Electron and Magnon Spectra of Ferrimagnetic Semiconductors

Abstract

AbstractA calculation of the magnon spectrum is carried out for a degenerate ferrimagnetic semiconductor. The spin‐polarized conduction electrons indirectly effect the exchange between the local magnetic moments. As a result, in the case of antiferromagnetic direct exchange, the acoustic branch becomes harder with increase in the carrier concentration, whereas the optical branch becomes softer, if the signs of the s‐d exchange integrals are the same in both sublattices. With a certain concentration reached, the initial ferromagnetic ordering becomes absolutely unstable with respect to the long‐wave optical magnons. Also a study is made of the electron spectrum at the Néel point. In spite of the absence of the long‐range order, the short‐range order in the paramagnetic proximity still remains. Therefore, the conduction electrons move in such a manner that their spin follows the direction of the local magnetic moment slowly changing in space. This enables the electron to obtain a considerable gain in energy. It follows that a gigantic conduction band edge shift should also occur above the Néel point.