Search

This study computationally demonstrates that room-temperature ferromagnetism, which has been experimentally observed in Eu-doped GaN, is induced by holes in N 2p states (i.e., Zener's double exchange interaction) that arise on the assumption that Ga vacancies appear as a result of the introduction of Eu ions (i.e., volume compensation). The calculated Curie temperature (TC) suddenly increases over a certain range of Ga-vacancy concentrations and gradually increases with an increasing concentration of Eu ions. High TC above room temperature is dominated by Zener's double exchange mechanism in partially occupied N 2p hole-states, which itinerate throughout the whole crystals, and low TC is dominated by Zener's p-f exchange mechanism in Eu 4f and N 2p hybridization. We can reasonably explain the surprising experimental data of 4000 μB per Gd atom in Gd-doped GaN reported by Dhar et al. [Phys. Rev. Lett. 94, 037205 (2005)]. [ABSTRACT FROM AUTHOR]

A possibility of half-metallic ferromagnetism for the homogeneous phase in the half-Heusler alloy-based DMS CoTi1− xFe xSb is predicted. A phase diagram of the spinodal and binodal decomposition is constructed through the evaluation of the mixing free energies. By applying the Monte Carlo simulation method to the Ising model with realistic chemical pair interactions between Fe magnetic impurities, we simulate the spinodal decomposition and nanoscale separation in this alloy. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of XYSi (X = Ni, Pd, Pt; Y = Mn and Cr) are investigated through the ab initio calculation of the electronic structure, equilibrium lattice constant, magnetic exchange interaction and Curie temperature. The role of X and Y elements in the opening of the minority spin gap is discussed. The Fermi level lies closer to the conduction band for slighter X or Y. XYSi is half-metallic ferromagnets at equilibrium lattice constant, except PdMnSi. The Curie temperature of 1076, 785 and 634 K has been predicted by Monte Carlo simulations for NiMnSi, PtMnSi and NiCrSi, respectively. [ABSTRACT FROM AUTHOR]

We present a first principle study of the half-metallicity and ferromagnetism in half-heusler alloys XYSi (X = Ni, Pd and Pt; Y = Cr and Mn). The equilibrium lattice constants are predicted by means of the ultrasoft pseudo-potential method. The electronic structure and magnetic exchange interaction of various alloys are investigated within KKR-LSDA. The Curie temperature is predicted by using the Monte Carlo simulation, the random phase and mean field approximations, as well. The role of elements X, Y components and influence of the lattice parameters in stabilizing half-metallicity and ferromagnetism are discussed. Except PdMnSi, alloys are half-metallic at equilibrium lattice constant. The Curie temperatures of 634 K, 785 K, and 1076 K for NiCrSi, PtMnSi and NiMnSi, respectively, are predicted by Monte Carlo simulation. The structural stability of C1b is also considered. [ABSTRACT FROM AUTHOR]

Abstract: Material designs based on the first principle calculations of electronic structures are proposed for α-quartz SiO2-based dilute magnetic semiconductors. The incorporation of transition metals (TMs) into Si sites and of the non-TM atoms into O sites are treated for various concentrations. At temperatures higher than room temperature, most of the TM-doped SiO2 have no magnetism, yet Si1−x Mn x O2 might achieve the ferromagnetism. The substitution of O by non-TM atoms as C or N also induces the magnetism in the host. However, while the N''s substitution induces the ferromagnetism, C''s substitution causes an anti-ferromagnetic behavior in the host material SiO2. [Copyright &y& Elsevier]

We propose new-type ferromagnetic semiconductors based on CaO and K2S without any transition metal elements. These materials show transparent and half-metallic ferromagnetism if the deep-impurity-band width ( W) induced by doping of C, N, Si, or Ge impurities, and the electron-correlation energy ( U) satisfy the Stoner’s condition of highly correlated electron system ( U> W). Based on our first-principles calculations, we demonstrate that these materials satisfy the Stoner’s condition, and could be new candidates for transparent and half-metallic DMSs. [ABSTRACT FROM AUTHOR]

Abstract: We present a first-principles study of the magnetic properties of N-doped MgO, CaO and SrO, which have been proposed to constitute a new class of dilute magnetic semiconductors (DMSs) with no magnetic elements. In this study, it was found that under a homogeneously distributed condition, Curie temperatures could reach room temperature at sufficient N concentrations in the range of 20–30at.%; however, an inhomogeneous N distribution in these DMSs is the favored configuration, which indicates that spinodal decomposition leads to a room-temperature blocking temperature at smaller N concentrations than those estimated for room-temperature ferromagnetism in the homogeneous distribution condition. [Copyright &y& Elsevier]