The magnetism in 12.5% and 25% Mn delta-doped cubic GaN has been investigated using the density-functional theory calculations. The results show that the single-layer delta-doping and half-delta-doping structures show robust ground state half-metallic ferromagnetism (HMF), and the double-layer delta-doping structure shows robust ground state antiferromagnetism (AFM) with large spin-flip energy of 479.0 meV per Mn-Mn pair. The delta-doping structures show enhanced two-dimensional magnetism. We discuss the origin of the HMF using a simple crystal field model. Finally, we discuss the antiferromagnet/ferromagnet heterostructure based on Mn doped GaN.
Using the first-principles density-functional theory plan-wave pseudopotential method, we investigate the structure and magnetism in 25% Mn substitutive and interstitial doped monoclinic, tetragonal and cubic ZrO2 systematically. Our studies show that the introduction of Mn impurities into ZrO2 not only stabilizes the high temperature phase, but also endows ZrO2 with magnetism. Based on the simple crystal field theory (CFT), we discuss the origination of magnetism in Mn doped ZrO2. Moreover, we discuss the effect of electron donor on magnetic semiconductors, and the possibility as electronic structure modulator.
The magnetic properties of the intermetallic compound FeAl are investigated using exact exchange density functional theory. This is implemented within a state of the art all-electron full potential method. We find that FeAl is magnetic with a moment of 0.70 $mu_B$, close to the LSDA result of 0.69 $mu_B$. A comparison with the non-magnetic density of states with experimental negative binding energy result shows a much better agreement than any previous calculations. We attribute this to the fine details of the exchange field, in particular its asymmetry, which is captured very well with the orbital dependent exchange potential.
We study the electronic structure and magnetism of 25% Mn substituted cubic Zirconia (ZrO2) with several homogeneous and heterogeneous doping profiles using density-functional theory calculations. We find that all doping profiles show half-metallic ferromagnetism (HMF), and delta-doping is most energy favorable while homogeneous doping has largest ferromagnetic stabilization energy. Using crystal field theory, we discuss the formation scheme of HMF. Finally, we speculate the potential spintronics applications for Mn doped ZrO2, especially as spin direction controllment.
By means of ab initio calculations within the density functional theory, we have found that B80 fullerenes can condense to form stable face-centered-cubic fcc solids. It is shown that when forming a crystal, B80 cages are geometrically distorted, the Ih symmetry is lowered to Th, and four boron-boron chemical bonds are formed between every two nearest neighbor B80 cages. The cohesive energy of B80 fcc solid is 0.23 eV/atom with respect to the isolated B80 fullerene. The calculated electronic structure reveals that the fcc B80 solid is a metal. The predicted solid phase would constitute a form of pure boron and might have diverse implications. In addition, a simple electron counting rule is proposed, which could explain the stability of B80 fullerene and the recently predicted stable boron sheet.
We study 1 or 2 neighboring Mn impurities, as well as complexes of 1 Mn and 1 or 2 Mg ions in a 64 atoms supercell of GaN by means of density functional calculations. Taking into account the electron correlation in the local spin density approximation with explicit correction of the Hubbard term (the LSDA+U method) and full lattice relaxation we determine the nearest neighbor exchange J for a pair of Mn impurities. We find J to be ferromagnetic and of the order of about 18 meV in the Hamiltonian H=-2*J1*J2. That J is only weakly influenced by the U parameter (varying between 2 and 8 eV) and by the lattice relaxation. From a detailed analysis of the magnetization density distribution we get hints for a ferromagnetic super-exchange mechanism. Also the Mn valence was found to be 3+ without any doubt in the absence of co-doping with Mg. Co-doping with Mg leads to a valence change to 4+ for 1 Mg and to 5+ for 2 Mg. We show that the valence change can already be concluded from a careful analysis of the density of states of GaN doped with Mn without any Mg.