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[1] The influence of carbon impurities on the properties of iron phases (bcc, hcp, dhcp, fcc) has been studied using the first-principles projector augmented-wave (PAW) method for a wide pressure range. It is shown that the presence of $6 at. % of interstitial carbon has a little effect on the calculated structural sequence of the iron phases under high pressure. The bcc ! hcp transition both for pure iron and iron containing carbon takes place around 9 GPa. According to the enthalpies comparison, the solubility of carbon into the iron solid is decreased by high pressure. The coexistence of iron carbide (Fe 3 C) + pure hcp Fe is most stable phase at high pressure compared with other phases. Based on the analysis of the pressure-density dependences for Fe 3 C and hcp Fe, we suggest that there might be some fraction of iron carbide present in the core. Citation: Huang, L., N. V.

The magnetic and electronic properties of the transition metal (TM) (V, Cr, Mn, Fe, Co, Ni, Cu) doped In2O3 have been theoretically studied by using the density functional theory. When two TM ions are placed close to each other (TM-TM distance of about 3.4 Å), the ferromagnetic ordering is found to be the lowest-energy configuration. The only exception is Fe, which possesses a half-filled 3d band. However, for further separation distance of about 7.2 Å, only Co, Ni and Cu ions (having more than half-filled 3d band) still prefer the ferromagnetic orientation, while V, Cr, or Mn ions (having less than half-filled 3d band) prefer antiferromagnetic ordering. The energies of the 3d band for TM ions show a decrease with increasing TM atomic number. For V, Cr and Mn, the 3d bands are merged with the conduction band, and show less hybridization with the host valence band; while for Co, Ni and Cu, the 3d bands show strong hybridization with the host valence band mainly formed by the oxygen 2p state. In this situation, polarized holes are formed on the oxygen sites close to the TM ions. Moreover, V-doped In2O3 is found to meet the requirements for a strong donor-mediated ferromagnetism.

Diluted magnetic semiconductors (DMSs), with the Curie temperature at room temperature, are of technological and fundamental importance. Defect engineering has been an effective way to introduce magnetic moments in various non-magnetic systems. Here we show firstly, InN film directly grown on (0001)-oriented Al2O3 substrate with In deficiency is ferromagnetic with its Curie temperature as high as 297K. The undesirable large lattice mismatch between the film and substrate leads to a peculiar surface structure that the film separates into distinct In-rich and In-poor regions. Our first-principles calculations suggest the defect of In-vacancy is responsible for the magnetism. A local magnetic moment of 2.5μB is found, in agreement with experimental results. Our findings demonstrate that room-temperature ferromagnetism can also be induced in narrow band gap semiconductors through defect engineering, which remains largely unexplored so far.

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