Recent theories of the anisotropy and magnetostriction due to the presence of Co2+ in spinel ferrites are reviewed and new work on the effects of Fe2+ is presented. The effects of these ions are great because the orbital angular momentum is not fully quenched by the crystal field. In the case of Co2+, the orbital moment of the ground state is coupled strongly to the trigonal axis of the crystal field. The very large anisotropy and magnetostriction arise from spin-orbit coupling in first order. The theory is found to account for many of the effects of cobalt-iron ferrite and cobalt-manganese ferrite at higher temperatures. The contribution of Fe2+ to these effects is less extreme but still striking. Here the orbital moment is more nearly quenched but the spin is still coupled strongly to the trigonal axis. The coupling gives rise to cubic anisotropy in second order approximation. This term appears to account for the large compositional dependence of anisotropy in manganese-rich manganese-iron ferrite. A cr...

Anisotropy and Magnetostriction in Magnetic Oxides

Synthesis and characterizations of manganese ferrites for hyperthermia applications

Water-based ferrofluids of substituted ferrites Fe1−xMnxFe2O4 (0⩽x⩽1) have been prepared by the co-precipitation method and characterized. Particles are superparamagnetic with an average particle size of about 10–12nm. The specific absorption rate (SAR) was measured by calorimetric measurement at a frequency of 300kHz and a field of 10–45kA∕m. The variation of SAR and magnetization of Fe1−xMnxFe2O4 with Mn concentration shows similar dependence. Innocuousness studies of MnFe2O4 ferrofluids to the living cells have been carried out with BHK-21 cells. In vitro studies showed that threshold biocompatible concentration is dependent on the nature of ferrites and coating.

Preparation and investigation of potentiality of different soft ferrites for hyperthermia applications

Study of hyperthermia temperature of manganese-substituted cobalt nano ferrites prepared by chemical co-precipitation method for biomedical application

The phenomenology and atomic origins of magnetocrystalline anisotropy are reviewed, and the experimental data are summarized for the spinel ferrites, garnets, metals of the 3d and 4f transition series, and some selected rare earth compounds. Only intrinsic magnetocrystalline anisotropy is covered, and attention is principally confined to single-crystal results. Antiferromagnetic materials have been omitted.

Magnetocrystalline anisotropy of ferro- and ferrimagnetics

The magnetic anisotropy energy is measured as a function of temperature in eleven single crystal compositions corresponding to MnxFe3−xO4, where x is varied from 0.00 to 1.90. The interesting features observed are as follows.(1) Small manganese concentrations in magnetite (x=0) are shown to decrease the temperature of the “isotropy point” known to exist in magnetite at low temperatures.(2) An unexpected variation in the temperature dependence and magnitude of the anisotropy energy in the x=0.4 to 1.0 composition region is shown.(3) The anisotropy energy in the composition region between x=1.0 and 1.8 is semiquantitatively shown to be related to cubic crystalline field splitting of the energy levels of ferric ions.(4) A large planar anisotropy is measured in a crystal composition given by x = 1.90 and is discussed in terms of the expected tetragonal nature of trivalent manganese.(5) Finally, a minute magnetic annealing effect at a temperature of 370°K has been shown to exist in a crystal composition corres...

M. W. Shafer

Papers

On the Magnetic Anisotropy in Manganese‐Iron Spinels