THE FORMATION OF LOCALISED MAGNETIC STATES IN ITINERANT ANTIFERROMAGNETS

Abstract

The properties of dilute antiferromagnetic alloys are investigated in the light of Anderson's model for localised magnetic states. The host metal is described by a two-band model for itinerant antiferromagnets (Cr in particular) due to Lomer. The one-electron Green's functions for this model are obtained by the equation of motion method and a self-consistent Hartree-Fock factorisation scheme. Analytic expressions are derived for the magnitude of the localised magneticimoment, the spin polarisation near the impurity site and the initial change in Nee1 temperature with impurity concentration. The ground state of antiferromagnetic chromium is a linear spin density wave (SDW) state with a single magnetic super-lattice vector Q. The super-lattice is incommensurate with the crystal lattice and the SDW is polarised longitudinally for temperatures T 2 , (2) A:(A,) creates (destroys) an electron of spin o in a localised impurity state. The Hartree-Fock analysis yields a set of self-consistent equations relating A , and AQ. In the limit of dilute impurity concentration and zero temperature A , is given by the integral equation : A, = (1 I' J ~ ( A ~ ) , A,))-' x where x 1' rcr J~(A;') , (3)