Magnetostriction in Nickel Ferrite and Cobalt—Nickel Ferrite

Abstract

The magnetostriction constants λ₁₀₀ and λ₁₁₁ for nickel ferrite have been measured using a ferromagnetic resonance technique which also permits measurements of linewidth, g factor, and anisotropy on the same sample. Our measurements show that all of these parameters are essentially temperature independent from 4° to 300°K in contrast to the behavior of other ferrites. The magnetostriction results are: λ₁₀₀=−46×10⁻⁶, λ₁₁₁=−22×10⁻⁶ at room temperature with less than a 20% variation from these values down to 4°K. The temperature independence of the linewidth and its magnitude (∼20 Oe) both indicate an absence of the ferrous ions which have complicated measurements by some other investigators. Measurements have also been made of the magnetostriction of Co_0.05Ni_0.95Fe₂O₄ over the range ∼100° to 300°K. At room temperature both λ₁₀₀ and λ₁₁₁ have approximately the same values as in NiFe₂O₄, but at lower temperatures the cobalt contribution causes |λ₁₁₁| to increase sharply while |λ₁₀₀| is relatively unaffected. This behavior is qualitatively in agreement with a theory by Slonczewski for the similar problem of Co²⁺ in magnetite. The sign of λ₁₁₁, however, is different in the two materials. Linewidth in the three principal directions in Co_0.05Ni_0.95Fe₂O₄ has also been measured.