パーマロイ薄膜の保磁力と磁気抵抗効果に及ぼす蒸着時真空度の影響

Abstract

The effects of vacuum pressure on the coercivity and magnetoresistivity of thin permalloy films during the deposition process were investigated. Samples of permalloy films ranging in thickness between 15 and 300 nm were deposited on a glass substrate by the electron beam method under a 10−4-10−6 Pa vacuum. The substrate temperature was 573 K, and the composition of the permalloy films was Ni-19 mass%Fe with near-zero magnetostriction. The average electrical resistivity (ρa) of permalloy films during deposition decreases, as vacuum pressure is decreased and film thickness is increased. However, since the change in magnetoresistivity (Δρ) is independent of vacuum pressure and film thickness, the magnetoresistivity ratio (Δρ⁄ρa) increases, as pressure is decreased and thickness is increased. On the other hand, the coercivity (Hc) and the magnetic anisotropy field (Hk) increase, as vacuum pressure is decreased. Moreover, the Hc and Hk peak at a thickness of nearly 70 nm. Through transmission electron microscopy, it is observed that the grain size in permalloy films increases as vacuum pressure is decreased. Auger analysis indicates that the concentration of oxygen in permalloy films decreases as vacuum pressure is decreased. These results suggest that the decrease in ρa and the increase in Hc under high vacuum are attributed to the decrease in oxygen and the grain growth in permalloy films.