Temperature dependence of magnetic anisotropy in Mn-substituted cobalt ferrite

Abstract

The temperature variation of magnetic anisotropy and coercive field of magnetoelastic manganese-substituted cobaltferrites (CoMnxFe2−xO4 with 0⩽x⩽0.6) was investigated. Major magnetic hysteresis loops were measured for each sample at temperatures over the range 10-400 K, using a superconducting quantum interference device magnetometer. The high-field regimes of the hysteresis loops were modeled using the law of approach to saturation equation, based on the assumption that at sufficiently high field only rotational processes remain, with an additional forced magnetization term that was linear with applied field. The cubic anisotropy constant K1 was calculated from the fitting of the data to the theoretical equation. It was found that anisotropy increases substantially with decreasing temperature from 400 to 150 K, and decreases with increasing Mn content. Below 150 K, it appears that even under a maximum applied field of 5 T, the anisotropy of CoFe2O4 and CoMn0.2Fe1.8O4 is so high as to prevent complete approach to saturation, thereby making the use of the law of approach questionable in these cases. The temperature variation of magnetic anisotropy and coercive field of magnetoelastic manganese-substituted cobalt ferrites ͑CoMn x Fe 2−x O 4 with 0 ഛ x ഛ 0.6͒ was investigated. Major magnetic hysteresis loops were measured for each sample at temperatures over the range 10-400 K, using a superconducting quantum interference device magnetometer. The high-field regimes of the hysteresis loops were modeled using the law of approach to saturation equation, based on the assumption that at sufficiently high field only rotational processes remain, with an additional forced magnetization term that was linear with applied field. The cubic anisotropy constant K 1 was calculated from the fitting of the data to the theoretical equation. It was found that anisotropy increases substantially with decreasing temperature from 400 to 150 K, and decreases with increasing Mn content. Below 150 K, it appears that even under a maximum applied field of 5 T, the anisotropy of CoFe 2 O 4 and CoMn 0.2 Fe 1.8 O 4 is so high as to prevent complete approach to saturation, thereby making the use of the law of approach questionable in these cases.

Magnetic and magnetoelastic properties of Ga-substituted cobalt ferrite

“…Promising results were obtained, showing that Curie temperature and magnetic anisotropy could be decreased, and d / dH increased without causing much loss of magnetostriction. [5][6][7][8] Mössbauer spectroscopy investigations confirmed that the Mn 3+ ions and the Cr 3+ ions substitute preferentially into the octahedral sites in cobalt ferrite. 9,10 In the present study, a family of Gasubstituted cobalt ferrite CoGa x Fe 2−x O 4 samples has been investigated.…”

“…Likewise, we have observed this experimentally for Mn-substituted and Cr-substituted cobalt ferrites. 7,8 So with T C decreasing as a function of x even more strongly with Ga substitution than it does for Cr or Mn substitution, the anisotropy energy at 300 K is expected to decrease, even more than for Cr or Mn substitution for the same value of x.…”

Magnetic and magnetoelastic properties of Cr-substituted cobalt ferrite

“…Recently cobalt ferrite based composites have received attention because of their high magnetostriction, high sensitivity of magnetic induction to applied stress, chemical stability and low cost. [9][10][11][12] These make the materials attractive for use in magnetoelastic sensors, 1 and as the magnetoelastic component in oxidebased "multiferroic" composites.…”

Effect of Ho3+substitution on the cation distribution, crystal structure and magnetocrystalline anisotropy of nanocrystalline cobalt ferrite

“…This magnetocrystalline anisotropy is a very important parameter for the characterisation of the magnetic materials, which decides whether the magnetic material is magnetically soft or hard material and, it can be tuned by replacing A site and/or B site by different transition and non-transition elements. The recent investigations of the substitution at the Fe sites of CoFe 2 O 4 by various cations like Ga, Mn, Al, Cr, etc., have revealed the change in atomic level magnetic interaction, which has modified the K 1 and magnetic properties [15][16][17][18].…”