Study of the oxygen vacancy influence on magnetic properties of Fe- and Co-doped SnO2 diluted alloys

Transition-metal (TM)-doped diluted magnetic oxides (DMOs) have attracted attention from both experimental and theoretical points of view due to their potential use in spintronics towards new nanostructured devices and new technologies. In the present work, we study the magnetic properties of Sn_0.96TM_0.04O₂ and Sn_0.96TM_0.04O_1.98(V_O)_0.02, where TM = Fe and Co, focusing in particular in the role played by the presence of O vacancies nearby the TM. The calculated total energy as a function of the total magnetic moment per cell shows a magnetic metastability, corresponding to a ground state, respectively, with 2 and 1 μ_B/cell, for Fe and Co. Two metastable states, with 0 and 4 μ_B/cell were found for Fe, and a single value, 3 μ_B/cell, for Co. The spin-crossover energies (E_S) were calculated. The values are E_S^0/2 = 107 meV and E_S^4/2 = 25 meV for Fe. For Co, E_S^3/1 = 36 meV. By creating O vacancies close to the TM site, we show that the metastablity and E_S change. For iron, a new state appears, and the state with zero magnetic moment disappears. The ground state is 4 μ_B/cell instead of 2 μ_B/cell, and the energy E_S^2/4 is 30 meV. For cobalt, the ground state is then found with 3 μ_B/cell and the metastable state with 1 μ_B/cell. The spin-crossover energy E_S^1/3 is 21 meV. Our results suggest that these materials may be used in devices for spintronic applications that require different magnetization states.