メカニカルアロイング法によるＣｏ２０Ｃｕ８０合金の熱処理と磁気抵抗

Abstract

Magnetoresistance (MR) was investigated in Co20Cu80 alloys prepared by the mechanical alloying (MA) method.The crystal structure and magnetic properties of the asmilled and annealed samples were examined for various milling times. After hot pressing at 300°C for 1 h, the MR ratios of samples annealed at 400°C, 430°C, and 450°C for 1 h increased with the milling time. The compact of Co20Cu80 mixture milled for 50 h had an MR ratio of 6.4% when subjected to a field of 15 kOe at room temperature, after annealing at 450°C for 1 h. The annealing time giving the maximum MR ratio became shorter with an increase in the annealing temperature from 400°C to 500°C. The MR ratio of the sample annealed at 450°C for 3 h was 6.7% at room temperature, and did not saturate in a magnetic field of 15 kOe. The content of substituted Co atoms in the fcc Cu lattice phase increased with the milling time. The content of Cu atoms in the hcp Co phase also increased with the milling time, and the hcp phase disappeared after milling times of more than 5 h. The magnetization of the Co20Cu80 mixture decreased with the milling time. Phase separation occurred in both the fcc Cu(Co) phase and the hcp Co(Cu) phase, and the magnetization increased on annling.