Temperature dependence of magnetic anisotropy of Ga-substituted cobalt ferrite

The temperature dependence of magnetization, magnetic anisotropy, and coercive field of gallium-substituted cobaltferrite was investigated for a series of compositions of CoGaxFe2−xO4 (0⩽x⩽0.8). Hysteresis loops were measured for each sample over the range of −5T⩽μ0H⩽5T for selected temperatures between 10 and 400K. The magnetization at 5T and low temperatures was found to increase for the lower Ga contents (x=0.2 and 0.4) compared to pure CoFe2O4, indicating that at least initially, Ga3+substitutes predominantly into the tetrahedral sites of the spinel structure. The high field regions of these loops were modeled using the law of approach to saturation, which represents the rotational process, together with an additional linear forced magnetization term. The first order cubic magnetocrystalline anisotropy coefficient K1 was calculated from curve fitting to these data. It was found that K1 decreased with increasing Ga content at all temperatures. Both anisotropy and coercivity increased substantially as temperature decreased. Below 150K, for certain compositions (x=0, 0.2, 0.4), the maximum applied field of μ0H=5T was less than the anisotropy field and, therefore, insufficient to saturate the magnetization. In these cases, the use of the law of approach method can lead to calculated values of K1 which are lower than the correct value

Dependence of magnetomechanical performance of CoGaxFe2-xO4 on temperature variation

The temperature dependence of the magnetoelastic properties of the CoGaxFe2−xO4 system (for x = 0.0, 0.2, and 0.4) has been studied. It has been shown that increase in temperature resulted in reduced magnetostrictive hysteresis. For both CoGa0.2Fe1.8O4 and CoGa0.4Fe1.6O4, the measured magnetostriction amplitudes were higher at 250 K than at 150 K. It was also shown that the temperature stability of magnetostriction in CoGa0.2Fe1.8O4 is higher than that of the other compositions studiedwhich is important for sensor applications. The highest strain sensitivity was obtained for CoGa0.2Fe1.8O4 at 250 K. Results demonstrate the possibility of tailoring magnetomechanical properties of the material to suit intended applications under varying temperature conditions

Temperature dependence of magnetic anisotropy of germanium/cobalt cosubstituted cobalt ferrite

The variations in magnetization and magnetic anisotropy of Ge4+/Co2+ cosubstituted cobalt ferrite with temperature were investigated for a series of compositions Co1+xGexFe2−2xO4 (0 ≤ x ≤ 0.4). The magnetization at 5 T and low temperature were observed to increase for all Ge/Co cosubstituted samples compared to pure CoFe2O4. Hysteresis loops were measured for each sample over the magnetic field range of −5 T to +5 T for temperatures in the range of 10–400 K. The high field regions of these loops were modeled using Law of Approach to saturation, which represents the rotational and forced magnetization processes. The first order cubic magnetocrystalline anisotropy coefficient K1 was calculated from these fits. K1 decreased with increasing Ge content at all temperatures. Anisotropy increased substantially as temperature decreased. Below 150 K, for certain compositions (x = 0, 0.1, 0.2, and 0.3), the maximum applied field of μ0H = 5 T was less than the anisotropy field and therefore insufficient to saturate the magnetization. In these cases, the use of the Law of Approach model can give values of K1 that are lower than the correct values and this method cannot be used to estimate anisotropy accurately under these conditions