The influence of layer thickness and post annealing on magnetism of pulsed laser deposited ZnO/Co multilayers

• The as-deposited and annealed ZnO/Co multilayers with different layers present various magnetic behaviors for their different structure.
• The FM–AFM coupling also was found in the annealed ZnO/Co multilayers.
• The number of layer has great relations with the phase transformation during annealing, resulting in different magnetic behavior.

ZnO/Co multilayers with different layers have been deposited on silicate (100) substrate by the pulsed laser deposition method. The as-deposited multilayers present the structure of amorphous phase and a narrow hysteresis loop with high saturation magnetization and low coercivity, showing the typical soft magnetic behavior. The post annealing at the elevated temperature causes the transformation from as-deposited amorphous phase to crystalline metallic cobalt and ZnO phase, as well as the interdiffusion of different layer forming CoO and ZnCo2O4 phases. The presence of crystalline metallic cobalt phase with ferromagnetic (FM) and cobalt oxide (CoO) phase with antiferromagnetic (AFM) is beneficial to the FM–AFM coupling, resulting in the shift of widening of the hysteresis loop. But an excessively high annealing temperatures leads to the formation of large amount of simple or complex oxides with paramagnetic, antiferromagnetic properties, inducing the decrease of magnetic properties significantly.