Temperature dependence of magnetic anisotropy of Ga-substituted cobalt ferrite

Abstract

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. KeywordsMagenetic anisotropy, Cobalt, Ferrites, Anisotropy, Materials properties Disciplines Electromagnetics and Photonics | Materials Science and Engineering CommentsThe following article appeared in Journal of Applied Physics 103 (2008) The temperature dependence of magnetization, magnetic anisotropy, and coercive field of gallium-substituted cobalt ferrite was investigated for a series of compositions of CoGa x Fe 2−x O 4 ͑0 ഛ x ഛ 0.8͒. Hysteresis loops were measured for each sample over the range of −5 T ഛ 0 H ഛ 5 T for selected temperatures between 10 and 400 K. The magnetization at 5 T and low temperatures was found to increase for the lower Ga contents ͑x = 0.2 and 0.4͒ compared to pure CoFe 2 O 4 , indicating that at least initially, Ga 3+ 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 K 1 was calculated from curve fitting to these data. It was found that K 1 decreased with increasing Ga content at all temperatures. Both anisotropy and coercivity increased substantially as temperature decreased. Below 150 K, for certain compositions ͑x = 0, 0.2, 0.4͒, the maximum applied field of 0 H = 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 method can lead to calculated values of K 1 which are lower than the correct value.

Investigation of Ga substitution in cobalt ferrite (CoGaxFe2−xO4) using Mossbauer spectroscopy

“…They show that at least for the smaller amounts of substituted Ga 3+ , the overall magnetization increases relative to pure cobalt ferrite upon substitution of Ga 3+ for Fe 3+ . 12 Since Ga 3+ is nonmagnetic, and the A-site and B-site moments couple antiparallel ͑and remembering that there are twice as many B sites as A sites͒, this supports the idea that Ga 3+ substitutes preferentially into the A sites. Further support is provided by the observation that substitution of Ga 3+ for Fe 3+ in cobalt ferrite has been observed to decrease the Curie temperature at a faster rate than of Mn 3+ or Cr 3+ ͑see discussion in Ref.…”

Dependence of magnetomechanical performance of CoGaxFe2−xO4 on temperature variation

“…This can be explained in terms of the effect of increase in temperature on anisotropy and coercive field. A previous study 12 shows that increase in temperature results in lower anisotropy and coercive field which was expected to lead to less magnetostrictive hysteresis as observed.…”

Physical, electrical and magnetic properties of nano-sized Co-Cr substituted magnesium ferrites

“…The first-order cubic anisotropy constant (K 1 ) of the samples were determined using the Law of Approach to saturation. 9 The Law of Approach is said to be valid in the range 0.97M S < M M S . 10 Therefore, the high field region of the magnetization curve corresponding to this range was used to determine anisotropy constant, K 1 .…”