Preparation of High-Coercivity Magnetic Powder via Heat Treatment of a Rapidly Quenched Amorphous Starting Compound with a ThMn₁₂ Structure

Abstract

Amorphous (Sm_0.8Zr_0.2)_1.1(Fe_0.9Co_0.1)_11.3Ti_0.7 samples prepared by the rapid-quenching method were annealed under various conditions (848–1223 K and 1–60 min) in a pure Ar atmosphere (PO₂ < 10⁻² Pa). The powders obtained at low annealing temperatures (<1073 K) were predominantly composed of the 1-9 phase (SmFe₉), whereas those obtained at high annealing temperatures (>1123 K), were mostly composed of the 1-12 phase (ThMn₁₂). However, the highest coercivity (H_c) of more than 400 kAm⁻¹ (5 kOe) was observed for samples containing a mixture of the 1-9 and 1-12 phases, which were obtained by annealing at intermediate temperatures of 1123–1173 K for 10–30 min. Domain structure observations revealed that the sample with the highest H_c (magnetic anisotropy field (H_a) of approximately 6 MAm⁻¹) was composed of single-domain particles. Moreover, H_c was decreased to approximately 160 kAm⁻¹ (2 kOe) by the formation of a domain structure (approximately 500 nm in width) in samples of the 1-12 mono-phase, despite high H_a of approximately 9 MAm⁻¹. A mechanism for these coercivity variations is proposed.

Fig. 5 Variation of H_c for the samples subjected to heat treatment under various conditions.