Strategy of preparing SmCo based films with high coercivity and remanence ratio achieved by temperature and chemical optimization

Abstract

SmCo based films with excellent intrinsic magnetic properties have promising applications in micro-electro-mechanical system (MEMS). However, due to the complexity of phase composition and uncontrollable crystallization degree of SmCo hard magnetic phase in the film, both the coercivity (Hc) and remanence (Mr) of films are difficult to enhance simultaneously. In this paper, SmCo based films were deposited with a Cr underlayer and capping layer on single crystal Si substrates via magnetron sputtering process. The effects of annealing parameters and Sm/Co atomic ratio on the phase structure and coercivity of films are discussed. By adjusting the Sm/Co atomic ratio from 1:5 to 1:4, Co soft magnetic phase disappears and the single phase SmCo5 is obtained, leading to the increase of coercivity of the films from 30 to 34 kOe. The influence of deposition temperature and Cu doping on magnetic properties of SmCo based films was investigated. When the deposition temperature increases from room temperature to 250 °C, the coercivity will further increase from 34 to 51 kOe. However, a severe kink is observed in the demagnetization curves due to the poor exchanged coupling. An analysis of transmission electron microscopy (TEM) confirms that the average size of non-hard magnetic amorphous phase exceeds the effective exchanged coupling length of SmCo5, which contributes to the decoupling and low remanence ratio. Therefore, doping Cu and applying a post-annealing process can significantly improve the crystallization degree of the films. Both the coercivity and the remanence ratio of the demagnetization curves are greatly enhanced. We propose a plausible strategy to prepare the SmCo based films with high coercivity and remanence ratio by temperature and chemical optimization, which can be utilized in high performed MEMS devices.