Influence of magnetic dopants on the metal-insulator transition in semiconductors.

InSb:Mn and InSb:Ge reveal differences in their resistivity near the metal-insulator transition although both are acceptors of comparable depth. InSb:Ge shows the commonly observed behavior whereas InSb:Mn exhibits a strong enhancement of the resistivity below 10 K and pronounced negative magnetoresistance effects at 1.6 K. Both effects increase by applying hydrostatic pressure. The different behavior arises from the differences in the filling of the 3d shell, half filled 3d;{5} for Mn with a total spin of S=5/2 and entirely filled 3d;{10} for Ge with total angular momentum of J=0. The exchange interaction between the hole spin of the Mn acceptor and the S=5/2 spin of its 3d;{5} shell is the dominant correlation effect leading to the formation of an antiferromagnetic alignment of the Mn 3d;{5} spins along the percolation path which inhibits hopping of holes between neighboring Mn sites.