TY - JOUR
T1 - Superexchange in dilute magnetic dielectrics
T2 - Application to (Ti,Co) O2
AU - Kikoin, K.
AU - Fleurov, V.
PY - 2006
Y1 - 2006
N2 - We extend the model of ferromagnetic superexchange in dilute magnetic semiconductors to the ferromagnetically ordered highly insulating compounds (dilute magnetic dielectrics). The intrinsic ferromagnetism without free carriers is observed in oxygen-deficient films of anatase TiO2 doped with transition-metal impurities in cation sublattice. We suppose that ferromagnetic order arises due to superexchange between complexes (oxygen vacancies + magnetic impurities), which are stabilized by charge transfer from vacancies to impurities. The Hund rule controls the superexchange via empty vacancy related levels so that it becomes possible only for the parallel orientation of impurity magnetic moments. The percolation threshold for magnetic ordering is determined by the radius of vacancy levels, but the exchange mechanism does not require free carriers. The crucial role of the nonstoichiometry in formation of the ferromagnetism makes the Curie temperatures extremely sensitive to the methods of sample preparation.
AB - We extend the model of ferromagnetic superexchange in dilute magnetic semiconductors to the ferromagnetically ordered highly insulating compounds (dilute magnetic dielectrics). The intrinsic ferromagnetism without free carriers is observed in oxygen-deficient films of anatase TiO2 doped with transition-metal impurities in cation sublattice. We suppose that ferromagnetic order arises due to superexchange between complexes (oxygen vacancies + magnetic impurities), which are stabilized by charge transfer from vacancies to impurities. The Hund rule controls the superexchange via empty vacancy related levels so that it becomes possible only for the parallel orientation of impurity magnetic moments. The percolation threshold for magnetic ordering is determined by the radius of vacancy levels, but the exchange mechanism does not require free carriers. The crucial role of the nonstoichiometry in formation of the ferromagnetism makes the Curie temperatures extremely sensitive to the methods of sample preparation.
UR - http://www.scopus.com/inward/record.url?scp=33750729895&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.74.174407
DO - 10.1103/PhysRevB.74.174407
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AN - SCOPUS:33750729895
SN - 1098-0121
VL - 74
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 17
M1 - 174407
ER -