International audienceThis review summarizes recent first-principles investigations of the electronic structure and magnetism of dilute magnetic semiconductors (DMSs), which are interesting for applications in spintronics. Details of the electronic structure of transition-metal-doped III-V and II-VI semiconductors are described, especially how the electronic structure couples to the magnetic properties of an impurity. In addition, the underlying mechanism of the ferromagnetism in DMSs is investigated from the electronic structure point of view in order to establish a unified picture that explains the chemical trend of the magnetism in DMSs. Recent efforts to fabricate high-TC DMSs require accurate materials design and reliable TC predictions for the DMSs. In this connection, a hybrid method (ab initio calculations of effective exchange interactions coupled to Monte Carlo simulations for the thermal properties) is discussed as a practical method for calculating the Curie temperature of DMSs. The calculated ordering temperatures for various DMS systems are discussed, and the usefulness of the method is demonstrated. Moreover, in order to include all the complexity in the fabrication process of DMSs into advanced materials design, spinodal decomposition in DMSs is simulated and we try to assess the effect of inhomogeneity in them. Finally, recent works on first-principles theory of transport properties of DMSs are reviewed. The discussion is mainly based on electronic structure theory within the local-density approximation to density-functional theory

No abstract

The bistability of ordered spin states in ferromagnets (FMs) provides the magnetic memory functionality. Traditionally, the macroscopic moment of ordered spins in FMs is utilized to write information on magnetic media by a weak external magnetic field, and the FM stray field is used for reading. However, the latest generation of magnetic random access memories demonstrates a new efficient approach in which magnetic fields are replaced by electrical means for reading and writing. This concept may eventually leave the sensitivity of FMs to magnetic fields as a mere weakness for retention and the FM stray fields as a mere obstacle for high-density memory integration. In this paper we report a room-temperature bistable antiferromagnetic (AFM) memory which produces negligible stray fields and is inert in strong magnetic fields. We use a resistor made of an FeRh AFM whose transition to a FM order 100 degrees above room-temperature, allows us to magnetically set different collective directions of Fe moments. Upon cooling to room-temperature, the AFM order sets in with the direction the AFM moments pre-determined by the field and moment direction in the high temperature FM state. For electrical reading, we use an antiferromagnetic analogue of the anisotropic magnetoresistance (AMR). We report microscopic theory modeling which confirms that this archetypical spintronic effect discovered more than 150 years ago in FMs, can be equally present in AFMs. Our work demonstrates the feasibility to realize room-temperature spintronic memories with AFMs which greatly expands the magnetic materials base for these devices and offers properties which are unparalleled in FMs

We have calculated Heisenberg exchange parameters for bcc-Fe, fcc-Co, and fcc-Ni using the non-relativistic spin-polarized Green function technique within the tight-binding linear muffin-tin orbital method and by employing the magnetic force theorem to calculate total energy changes associated with a local rotation of magnetization directions. We have also determined spinwave stiffness constants and found the dispersion curves for metals in question employing the Fourier transform of calculated Heisenberg exchange parameters. Detailed analysis of convergence properties of the underlying lattice sums was carried out and a regularization procedure for calculation of the spin-wave stiffness constant was suggested. Curie temperatures were calculated both in the mean-field approximation and within the Green function random phase approximation. The latter results were found to be in a better agreement with available experimental data.PACS numbers: 71.15.-m, 75.10.-b, 75.30.Ds of the relevant physical quantities such as spin-wave stiffness, Curie temperature T C , etc., for comparison with experimental data.It is therefore of a great importance to develop an ab initio, parameter-free, scheme for the description of ferromagnetic metals at T > 0 K. Such an approach must be able to go beyond the ground state and to take into account excited states, in particular the magnetic excitations responsible for the decrease of the magnetization with temperature and for the phase transition at T = T C . Although density functional theory can be formally extended to non-zero temperature, there exists at present no practical scheme allowing to implement it. One therefore has to rely on approximate approaches. The approximations to be performed must be chosen on the basis of physical arguments.In itinerant ferromagnets, it is well known that magnetic excitations are basically of two different types: (i) Stoner excitations, in which an electron is excited from an occupied state of the majority-spin band to an empty state of the minority-spin band and creates an electron-hole pair of triplet spin. They are associated with longitudinal fluctuations of the magnetization; (ii) the spin-waves or magnons, which correspond to collective transverse fluctuations of the direction of the magnetization. Near the bottom of the excitation spectrum, the density of states of magnons is considerably larger than that of corresponding Stoner excitations, so that the thermodynamics in the low-temperature regime is completely dominated by magnons and Stoner excitations can be neglected. Therefore it seems reasonable to extend this approximation up to the Curie temperature, and to estimate the latter by neglecting Stoner excitations. This is a good approximation for ferromagnets with a large exchange splitting such as Fe and Co, but it is less justified for Ni which has a small exchange splitting.The purpose of the present paper is to describe the spin-wave properties of transition metal itinerant ferromagnets at ab initio level. With thermodynamic propertie...