Electrical and magnetic properties of ${\mathrm{Fe}}_{3\mathrm{-}\mathit{z}}$${\mathrm{Al}}_{\mathit{z}}$${\mathrm{O}}_4$ (z<0.06)

Electrical resistivity and magnetization measurements have been carried out on synthetic single crystals of ${\mathrm{Fe}}_{3\mathrm{-}\mathit{z}}$${\mathrm{Al}}_{\mathit{z}}$${\mathrm{O}}_4$ in the range 0≤z<0.06. The samples were annealed to achieve the ideal 3:4 ratio of cations to anions. As has been previously reported for nonstoichiometric magnetite and for Zn- and Ti-doped magnetite, there is a change in the nature of the Verwey transition: with increasing z the transformation shifts from first to higher order and then disappears. Saturation magnetization measurements have been used to determine the possible distribution of divalent and trivalent iron and of trivalent aluminum among the tetrahedrally and octahedrally coordinated interstices. Differences in the present findings from those in Zn- and Ti-doped magnetite are pointed out and their implications are discussed. © 1996 The American Physical Society.