Magnetostriction in aluminium‐substituted titanomagnetites¹

Using the strain gauge technique, the magnetostriction constants λ_S have been measured on sintered polycrystalline specimens of titanomagnetites with Fe_2.4‐δ Ti_0.6 A𝓁_δ O₄ compositions (0.05 ≤ δ ≤ 0.20) in the temperature range between 25°C and T_c. The cell‐edge, saturation magnetization, and Curie temperature decrease with increasing aluminium concentration. The room‐temperature λ_S values are 95.7, 70.6, 52.9 and 25.2×10⁻⁶ for δ=0.05, 0.10, 0.15 and 0.20 respectively. A linear relationship is found between the magnetostriction constant and the aluminium content at room temperature. The constant λ_S(T) is proportional to approximately the third power of the saturation magnetization M_S(T). The values of the index n in λ_S (T) ∼ M_S ⁿ(T) are 2.72, 3.16, 3.35 and 3.60 for δ=0.05, 0.10, 0.15 and 0.2 respectively. This if the first reported measurement of λ_S(T) at elevated temperatures for A𝓁‐substituted titanomagnetites. Such data are urgently needed in theoretical and experimental magnetic domain structure studies in rock magnetism.