Role of inter-site exchange and hybrid interactions in itinerant ferromagnetism

Abstract

In this work, we study the magnetic properties of itinerant electron systems using the Hubbard-like tight binding Hamiltonian along with inter-site exchange and hybrid interactions. We have used the mean-field approximation to deal with the exchange and hybrid interactions. It is found that hybrid interaction is more effective than exchange interaction for the on-set of ferromagnetic state. We have studied the effect of hybrid interaction on various physical quantities at different temperatures. The effective mass ( m*/ m) of up spin electrons increases slowly as the temperature decreases but below the critical temperature ( T c), it decreases rapidly. For down spin electrons effective mass increases slowly as the temperature decreases and below T c, it increases more rapidly. Spectral weight ( n/ m*) for up spin electrons decreases slowly upto T c and below T c, it increases rapidly. For down spin electrons spectral weight decreases slowly upto T c and below T c, it decreases rapidly. Our results for both the effective mass and spectral weight are in good agreement with recently observed experimental behaviour in itinerant ferromagnet Ga 1− x Mn x As [Phys. Rev. Lett. 89 (2002) 097203]. We have also studied variation of the spectral weight and optical absorption with temperature in presence of magnetic field. We found that these two quantities for up spin electrons increase as applied magnetic field increases at all temperatures (∼4 T c). For down spin electrons these two quantities decrease as applied magnetic field increases.