Superexchange and spin-glass formation in semimagnetic semiconductors

The Mn-Mn superexchange interaction in semimagnetic semiconductors A(1-x)Mn(x)B (where A=Zn, Cd and B=S, Se, Te) is studied within the three-level model of the band structure. We focus on the dependence of the interaction on the interion distance J(dd)(r) = J(0)f(r). In the present work, the function f(r) is obtained analytically. This, only weakly material-dependent function is found to decrease with Mn-Mn distance much slower than its Gaussian approximation derived previously. The exact form of the decay of the superexchange can be approximated by a power law J(0)r(-8.5). This is close to an experimental result, J(0)r(-6.8), determined on the basis of the spin-glass transition temperature on the composition.