Soft magnetic properties and high frequency permeability in [CoAlO/oxide] multilayer films

Abstract

A CoAlO thin film was found to have good soft magnetic properties and gigahertz frequency response when it had a thickness of tens of nanometres. Increasing the thickness by more than 100 nm rapidly increased the coercivity and seriously degraded the high frequency response. A multilayering technique (laminating the magnetic layer with oxide spacers) was exploited to improve the magnetic properties in thick films. AlOx and SiOx were used as the oxide spacing layers in this experiment. For the 105 nm CoAlO films, the easy and hard axis coercivities were reduced by more than 8 times by introducing 2 nm AlOx or 5 nm SiOx spacers. With our optimum lamination [CoAlO (52.5 nm)/AlOx (2 nm)]7, good soft magnetic properties (easy and hard axis coercivities: 21 and 14 Oe and effective anisotropy field: 54 Oe) and high frequency response (real permeability: >200 up to ∼2 GHz) were successfully obtained in a multilayer film at a thickness of 380 nm. The changes in the microstructures and film stress with the introduction of the oxide spacers are discussed in this paper.