Neutron Scattering Studies of Some Spinels

Abstract

The magnetic structures of a number of single and mixed spinel ferrites have been determined using the polarised neutron diffraction technique. It is shown that this method is applicable even when the structure is noncollinear. The experimental magnetization curves in MgFe2O4 have been fitted to a molecular field expression to derive the dominant exchange interactions as JAB = — 22 °K and JAA = — 4 °K. From paramagnetic neutron Scattering, the only dominant exchange interactions in ZnFe2O4 and ZnCr2O4 have been determined as JBB (Fe3+-Fe3+) = 1.04 °K and JBB (Cr3+-Cr3+) = 2.38 °K. In MnAl2O4 (9 % inverted) JAA (Mn2+-Mn2+) = — 0.21 °K, JAB (Mn2+-Mn2+) = — 16 °K

Thermodynamic Assessment of the Fe-Mn-O System

“…Other authors found a very low degree of inversion. [118,119] Faller and Birchenall [120] showed that in some cases even rapid quenching is not sufficient to retain the equilibrium distribution of cations corresponding to the annealing temperature. Therefore, the experimental data on the degree of inversion (fraction of Mn ions in octahedral sites) from Jirák and Vratislav was used to evaluate the cation distribution in MnFe 2 O 4 .…”

About the electromagnetic properties of the thin films of zinc metaferrites in microwave range

“…The metaferrite films were deposited onto a GaAs substrate (devices using these films can be monolithically integrated with GaAs circuits [3], [4]). The S -parameters determined with the HFSS 13.0 were used to calculate the quantities of interest.…”

“…Average size of the film nanograins is of 4 -20 nm [8], [10] (no grater than the film thickness when it is the case). Each nanocrystal has a tetragonal ferrite structure, with a 0 = b 0 = 8.389 Å, c 0 = 8.488 Å [3]. The structure is of spinels (figure 1) and presents the exchange interactions between Fe 3+ -Fe 3+ ions.…”