Effects of the Mn/Bi ratio on the magnetic properties of MnBi thin films grown by magnetron co-sputtering

摘要

This paper presents the preparation of MnBi thin films with different Mn/Bi atomic ratios by magnetron co-sputtering and analyzes the effect of the Mn/Bi ratio on their magnetic properties. Variations in the Mn/Bi ratio of the thin films are demonstrated to affect their magnetic behavior, including changes in the easy magnetization axis direction and the observance of the spontaneous exchange bias phenomenon. The axis of easy magnetization transforms from in-plane to out-of-plane directions as the Mn/Bi ratio increases. The spontaneous exchange bias phenomenon is observed only within a specific range of Mn/Bi ratios, and a maximum exchange bias field about 1032 Oe is obtained at room temperature for the optimal ratio. This is the largest exchange bias magnitude thus far reported for MnBi materials at room temperature. These effects of the Mn/Bi ratio are evaluated according to the results of structural, chemical, and morphological analyses. (C) 2020 Elsevier B.V. All rights reserved.