We have investigated the magnetic and magnetoelasticproperties of a series of Cr-substituted cobaltferriteCoCrxFe2−xO4 (x=0.0-0.79) samples. Substitution of Cr for some of the Fe in cobaltferrite reduced the Curie temperature, and the effect is more pronounced than that observed in Mn-substituted cobaltferrite samples. Cr substitution also caused the maximum magnetostriction to decrease at a greater rate than substitution of the same amount of Mn. The maximum of the strain derivative, dλ/dH, was reached for x=0.38. The behavior of the Curie temperature of Cr-substituted and Mn-substituted cobaltferrites has been analyzed using the Néel molecular field model and compared with recent Mössbauer spectroscopy results. We have investigated the magnetic and magnetoelastic properties of a series of Cr-substituted cobalt ferrite CoCr x Fe 2−x O 4 ͑x = 0.0-0.79͒ samples. Substitution of Cr for some of the Fe in cobalt ferrite reduced the Curie temperature, and the effect is more pronounced than that observed in Mn-substituted cobalt ferrite samples. Cr substitution also caused the maximum magnetostriction to decrease at a greater rate than substitution of the same amount of Mn. The maximum of the strain derivative, d / dH, was reached for x = 0.38. The behavior of the Curie temperature of Cr-substituted and Mn-substituted cobalt ferrites has been analyzed using the Néel molecular field model and compared with recent Mössbauer spectroscopy results.
Magnetic and magnetoelasticproperties of a series of Ga-substituted cobaltferrites,CoGaxFe2−xO4 (x=0.0-0.8), have been investigated. The Curie temperatureTCand hysteresis properties were found to vary with gallium content (x), which indicates that exchange and anisotropy energies changed as a result of substitution of Ga for Fe. The maximum magnitude of magnetostriction decreased monotonically with increasing gallium content over the range x=0.0-0.8. The rate of change of magnetostriction with applied magnetic field (dλ/dH) showed a maximum value of 3.2×10−9A−1m for x=0.2. This is the highest value among recently reported cobaltferrite based materials. It was found that the dependence of magnetic and magnetoelasticproperties on the amount of substituent (x) was different for Mn, Cr, and Ga. This is considered to be due to the differences in cation site occupancy preferences of the elements within the spinel crystal structure: Mn3+ and Cr3+ prefer the octahedral (B) sites, whereas Ga3+ prefers the tetrahedral (A) sites. KeywordsAmes Laboratory, CNDE, Cobalt, Ferrites, Magnetostriction, Magnetic anisotropy, Curie point Disciplines Materials Science and Engineering CommentsThe following appeared in Journal of Applied Physics 101 ( Magnetic and magnetoelastic properties of a series of Ga-substituted cobalt ferrites, CoGa x Fe 2−x O 4 ͑x = 0.0-0.8͒, have been investigated. The Curie temperature T C and hysteresis properties were found to vary with gallium content ͑x͒, which indicates that exchange and anisotropy energies changed as a result of substitution of Ga for Fe. The maximum magnitude of magnetostriction decreased monotonically with increasing gallium content over the range x = 0.0-0.8. The rate of change of magnetostriction with applied magnetic field ͑d / dH͒ showed a maximum value of 3.2ϫ 10 −9 A −1 m for x = 0.2. This is the highest value among recently reported cobalt ferrite based materials. It was found that the dependence of magnetic and magnetoelastic properties on the amount of substituent ͑x͒ was different for Mn, Cr, and Ga. This is considered to be due to the differences in cation site occupancy preferences of the elements within the spinel crystal structure: Mn 3+ and Cr 3+ prefer the octahedral ͑B͒ sites, whereas Ga 3+ prefers the tetrahedral ͑A͒ sites.
The conductivity tensors of single crystals and polycrystals of RFe 2 (RϭGd,Tb,Ho,Lu) and GdCo 2 were determined in the visible and near UV ranges. The magneto-optical Kerr effect ͑MOKE͒ was studied at different temperatures and magnetic fields. The single-crystal data show more features and larger magnitudes in the MOKE spectrum than the polycrystalline data under the same experimental conditions. The theoretical optical conductivity tensors for these compounds were calculated using the tight-binding linear-muffin-tin orbital ͑TB-LMTO͒ method in the local spin-density approximation. The agreement between theory and experiment was poor except for LuFe 2 , in which the 4 f shell is completely closed.
A micromagnetic model has been developed for investigating the effect of stress on the magnetic properties of thin films. This effect has been implemented by including the magnetoelastic energy term into the Landau-Lifshitz-Gilbert equation. Magnetization curves of a nickelfilm were calculated under both tensile and compressive stresses of various magnitudes applied along the field direction. The modeling results show that coercivity increased with increasing compressive stress while remanence decreased with increasing tensile stress. The results are in agreement with the experimental data in the literature and can be interpreted in terms of the effects of the applied stress on the irreversible rotation of magnetic moments during magnetization reversal under an applied field. KeywordsAmes Laboratory, CNDE, Magnetic films, Coercive force, Magnetic moments, Magnetization reversals, Metallic thin films Disciplines Electromagnetics and Photonics CommentsThe following article appeared in Journal of Applied Physics 89 (2001) A micromagnetic model has been developed for investigating the effect of stress on the magnetic properties of thin films. This effect has been implemented by including the magnetoelastic energy term into the Landau-Lifshitz-Gilbert equation. Magnetization curves of a nickel film were calculated under both tensile and compressive stresses of various magnitudes applied along the field direction. The modeling results show that coercivity increased with increasing compressive stress while remanence decreased with increasing tensile stress. The results are in agreement with the experimental data in the literature and can be interpreted in terms of the effects of the applied stress on the irreversible rotation of magnetic moments during magnetization reversal under an applied field.
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