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Heisenberg exchange in magnetic monoxides | | Walter A. Harrison
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18 Jan 2007 | | Subject: | Materials Science | | Abstract: | The superexchange intertacion in transition-metal oxides, proposed initially by Anderson in 1950, is treated using contemporary tight-binding theory and existing parameters. We find also a direct exchange for nearest-neighbor metal ions, larger by a factor of order five than the superexchange. This direct exchange arises from Vddm coupling, rather than overlap of atomic charge densities, a small overlap exchange contribution which we also estimate. For FeO and CoO there is also an important negative contribution from the partially filled minority-spin band which broadens when ionic spins are aligned. The corresponding J1 and J2 parameters are obtained for MnO, FeO, CoO, and NiO, and give good predictions of the Neel and of the Curie-Weiss temperatures and a reasonable account of their volume dependences. For MnO the predicted value for the magnetic susceptibility at the Neel temperature and the crystal distortion arising from the antiferromagnetic transition were also reasonably well given. An Appendix gives exact treatment of a model of two correlated electrons in a pair of coupled states, and of four electrons in two pairs of coupled states, surprisingly different, providing the basis upon which the superexchange, direct exchange, and minority-spin-band exchange calculations were formulated. | | Source: | arXiv, cond-mat/0701423 | | Services: | Forum | Review | PDF | Favorites | |
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