Magnetocrystalline anisotropy in cobalt-substituted magnetite single crystals

Abstract

The growth of single crystals corresponding to x=0 (high-purity magnetite), x -0 0 1 and x -0 0 4 in the composition series Co x Fe3_^O4 is described. First-and second-order anisotropy constants of these crystals are determined by the torque method over the temperature range 120-450° K. The substitution of small amounts of cobalt for iron is found to add a positive contribution to K\ and a negative contribution to Kt. At low cobalt concentrations the magnitude of this contribution is a linear function of the amount of cobalt added. It is suggested that the effect of cobalt on the anisotropy is enhanced by the presence of divalent iron in magnetite, and it is concluded that the change in sign of AT in magnetite at about 130°K is not caused by the presence of cobalt or any other foreign impurity.LIST OF SYMBOLS W A = Magnetocrystalline anisotropy energy per unit volume, erg/cm 3 . Ki -First-order anisotropy constant, erg/cm 3 . K 2 = Second-order anisotropy constant, erg/cm 3 . K' = Uniaxial anisotropy constant, erg/cm 3 . <*i > a 2> a 3 -Direction cosines of magnetization with respect to cubic crystal axes, [hkl] = Crystallographic direction designated by Miller indices h, k and 1. (hkl) = Crystallographic plane whose normal is designated by Miller indices h, k and 1. x = Mol fraction of cobalt ferrite in solid solution with magnetite.

Temperature dependence of the structural, magnetic, and magnetostrictive properties of zinc-substituted cobalt ferrite

“…6, it can be seen that magnetic susceptibility is inversely related to magnetocrystalline anisotropy, as expected. The K 1 values obtained in this study at 300 K for all compositions are comparable to those obtained from theoretical calculations and experimental studies on un-substituted cobalt ferrite at 300 K. [21][22][23] This is because, the concentration of Zn in the samples studied here is low and consequently, a moderate variation of K 1 with composition is obtained.…”

Low-temperature viscous magnetization of multidomain magnetite: Evidence for disaccommodation contribution

“…Below T V disaccommodation is attributed to various re-ordering and tunnelling processes, and depends strongly on the stoichiometry of the magnetite, e.g., near-stoichiometric magnetite displays a strong disaccommodation peak at 300 K, which is reduced in stoichiometric magnetite [18]. In addition, below T V there is large increase in the intensity of the magnetocrystallographic anisotropy and a change in its symmetry [19,20]. There are also corresponding changes in many other magnetic properties [17,21].…”

Low-temperature susceptibility and hysteresis of magnetite

“…The first cubic magnetocrystalline anisotropy constant changes sign on passing through an isotropic point (T k ) at 130 K [5]. A few degrees below T k the crystal structure changes from cubic to monoclinic at the Verwey transition, 120-124 K, T v [6], and there are anomalies in most of the controlling magnetic energies, most notably in the magnetocrystalline anisotropy energy, where there is a very large increase in its magnitude and a reduction in its symmetry [7].…”