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We examine the relationship between the transport and magnetic properties of digital ferromagnetic heterostructure superlattices in which 0.5 monolayer MnAs planes alternate with undoped GaAs spacer layers. The data show that as the thickness t of the GaAs spacers increases, charge transport and the Curie temperature both approach their independent-layer limits at comparable values of t. An increase in the per-layer conductivity with decreasing t accompanies a rise in TC. This behavior is consistent with an enhancement of interlayer ferromagnetic interactions by charge coupling across the spacers.

We report that adsorption of monolayers of organic molecules onto ferromagnetic semiconductor heterostructures can produce large changes in magnetic properties [1]. The digital-alloy heterostructures studied have 1/2 monolayer MnAs planes embedded in GaAs. We investigate effects on magnetic properties of self-assembly of various organic molecules onto the heterostructure surface. Depending on the molecular structure, the monolayers can either strengthen or suppress ferromagnetism. We attribute this chemical modulation of magnetic properties to electronic changes brought about by molecular binding to the semiconductor surface.