Electrical and magnetic properties ofFe3−zAl

Abstract

Electrical resistivity and magnetization measurements have been carried out on synthetic single crystals of Fe 3Ϫz Al z O 4 in the range 0рzϽ0.06. 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.

Magnetic properties of subaerial basalts at low temperatures

“…First, it is quite likely that titanomagnetites in these samples occur in a continuous range of compositions starting from nearly pure magnetite. Second, other minor impurities, most notably Mg and Al, tend to lower the Curie point, while their effect on the Verwey temperature is much smaller than that of Ti (Koz lowski et al, 1996a;Brabers et al, 1998). Most probably, both mechanisms play a role in the behavior of the samples used in the present study.…”

The effect of doping on global lattice properties of magnetite Fe3−xMexO4 (Me=Zn, Ti and Al)

“…The actual composition and sample uniformity were checked using a microprobe electron [14][15][16] showing the characteristic break, differentiating first and second order Verwey transition. Note that this break is probably absent for Al and that Al effect on T V is lower (that results in x Al /1.7 scaling [17]). Stars show composition dependence of monoclinic angle b (the result of the presented studies), scaled to match T V dependence.…”

“…Already even very small substitution for iron lowers the transition temperature and the nature of the Verwey transition is changed from first order to the continuous one. Moreover, in case of Zn and Ti (and also nonstoichiometry parameter 3d in Fe 3(1À d) O 4 ) the T V vs. x23d relation is universal [14][15][16]; the influence of Al on the transition is lower and the relation T V vs. x Al /1.7 holds better [17], (see Fig. 2).…”

“…Stars show composition dependence of monoclinic angle b (the result of the presented studies), scaled to match T V dependence. Table 1 Dopants content, the site they enter the lattice [16,17,26] and their respective ionic radii [23], together with the Verwey transition temperature T V (determined by AC magnetic susceptibility vs. T relation) of all studies samples. Italic symbols refer to samples measured exclusively by spectroscopic method.…”

Low temperature magnetic properties of the Late Archean Boolgeeda iron formation (Hamersley Group, Western Australia): environmental implications

“…Titanomagnetite (Fe 3−x Ti x O 4 ) is detected in these layers but always with a broad range of titanium content, clustering around x = 0.6. Such high titanium concentration is quite enough to totally suppress the Verwey transition (Kakol et al, 1992;Kozłowski et al, 1996a). The high titanium content and very localized layers where these iron oxides are observed make this phase a poor candidate for the low T v .…”