Superexchange Interactions and Magnetic Lattices of the Rhombohedral Sesquioxides of the Transition Elements and Their Solid Solutions
1956; American Institute of Physics; Volume: 102; Issue: 4 Linguagem: Inglês
10.1103/physrev.102.1015
ISSN1536-6065
Autores Tópico(s)Advanced Condensed Matter Physics
ResumoA semiempirical analysis of the superexchange interactions responsible for the formation of the magnetic lattices in ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$ and $\ensuremath{\alpha}$-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ is given. The difference between the two magnetic lattices is attributed to the fact that ${\mathrm{Cr}}^{+3}$ has a less-than-half-full $d$-shell and ${\mathrm{Fe}}^{+3}$ a half-filled $d$-shell. We predict that the ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$-type magnetic lattice should be found in ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$, ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$, and TiFe${\mathrm{O}}_{3}$. One of the superchange interactions in the sesquioxides is compared with the $A\ensuremath{-}B$ interaction in magnetic spinels. The magnetic phase diagrams of the systems ${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$---${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$ and TiFe${\mathrm{O}}_{3}$---${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ are tentatively outlined from theoretical considerations. A ferrimagnetic structure is proposed for the crystals of the composition ${\mathrm{Ti}}_{\frac{2}{3}}{\mathrm{Fe}}_{\frac{4}{3}}{\mathrm{O}}_{3}$ which are found in nature and are conspicuously related to certain problems in rock-magnetism. The predictions derived from our semiempirical analysis should be tested by neutron diffraction experiments and magnetic measurements. The experiments of Forestier and of Pouillard on the ${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$---${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$ system are discussed.
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