Effective pair exchange interactions between Mn atoms in III-V and group-IV diluted magnetic semiconductors are determined from a two-step first-principles procedure. In the first step, the self-consistent electronic structure of a system is calculated for a collinear spin structure at zero temperature with the substitutional disorder treated within the framework of the coherent-potential approximation. The effective exchange pair interactions are then obtained in a second step by mapping the total energies associated with rotations of magnetic moments onto an effective classical Heisenberg Hamiltonian using the magnetic force theorem and one-electron Green functions. The formalism is applied to ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ alloys with and without As antisites, and to ${\mathrm{Ge}}_{1-x}{\mathrm{Mn}}_x$ alloys recently studied experimentally. A detailed study of the behavior of pair exchange interactions as a function of the distance between magnetic atoms as well as a function of the concentrations of the magnetic atoms and compensating defects is presented. We have found that due to disorder and the half-metallic character of the system the pair exchange interactions are exponentially damped with increasing distance between the Mn atoms. The exchange interactions between Mn atoms are ferromagnetic for distances larger than the ones corresponding to the averaged nearest-neighbor Mn-Mn distance. The pair exchange interactions are also reduced with increasing concentrations of the Mn atoms and As antisites. As a simple application of the calculated exchange interactions we present mean-field estimates of Curie temperatures.

Recent studies have demonstrated the potential of antiferromagnets as the active component in spintronic devices. This is in contrast to their current passive role as pinning layers in hard disk read heads and magnetic memories. Here we report the epitaxial growth of a new high-temperature antiferromagnetic material, tetragonal CuMnAs, which exhibits excellent crystal quality, chemical order and compatibility with existing semiconductor technologies. We demonstrate its growth on the III–V semiconductors GaAs and GaP, and show that the structure is also lattice matched to Si. Neutron diffraction shows collinear antiferromagnetic order with a high Néel temperature. Combined with our demonstration of room-temperature-exchange coupling in a CuMnAs/Fe bilayer, we conclude that tetragonal CuMnAs films are suitable candidate materials for antiferromagnetic spintronics.

We present an ab initio study of the magnetism induced in $\mathrm{Zr}{\mathrm{O}}_2$ dioxide by substitution of the cation by an impurity from the groups $1A$ or $2A$ of the Periodic Table (K and Ca). It is demonstrated that the K impurity leads to a robust induced magnetic moment on the surrounding O atoms in the cubic $\mathrm{Zr}{\mathrm{O}}_2$ host whilst Ca impurity leads to a nonmagnetic groundstate. The estimated Curie temperature is above room temperature.

By using spin-polarized full potential linearized augmented plane wave method we obtained the electronic structure of (Ga,Mn)As crystals with Mn in substitutional, interstitial, and both positions. It is shown that the interstitial Mn acts as a double donor and compensates the holes created by two Mn atoms in substitutional positions. This explains why the number of holes in ${\mathrm{Ga}}_{1-x}{\mathrm{Mn}}_x\mathrm{As}$ is usually much smaller than x. The effective Mn doping efficiency is simply related to the proportion of substitutional and interstitial Mn and does not depend on x provided that the proportion is fixed. The calculated local electronic structure of the substitutional and interstitial Mn differ appreciably, so that the x-ray L emission spectra can be used to distinguish the two positions of Mn.

We propose to replace Ga in (Ga,Mn)As with Li and Zn as a route to high Curie temperature, carrier mediated ferromagnetism in a dilute moment $n$-type semiconductor. Superior material characteristics, rendering Li(Zn,Mn)As a realistic candidate for such a system, include high solubility of the isovalent substitutional Mn impurity and carrier concentration controlled independently of Mn doping by adjusting Li-(Zn,Mn) stoichiometry. Our predictions are anchored by ab initio calculations and comparisons with the familiar and directly related (Ga,Mn)As, by the physical picture we provide for the exchange interaction between Mn local moments and electrons in the conduction band, and by analysis of prospects for the controlled growth of Li(Zn,Mn)As materials.