Nonlinear Magneto-Optical Probing of Ultrathin Magnetic Layer Interfaces: CoNi/Pt and Co/Cu

Abstract

The recently developed technique of Magnetization induced Second Harmonic Generation (MSHG) has been shown to be an ideal tool for the investigation of ultrathin magnetic multilayers [1] due to its extreme interface sensitivity with very large magneto-optical effects. We have used MSHG in combination with XRD, AFM, MR, and VSM techniques on CoNi/Pt (magnetic data storage) and Co/Cu (sensors and MRAM) multilayers to study their dependence on preparation condition and thermal stability: (a) The crystallographic contribution of the nonlinear magneto optical response from CoNi/Pt interfaces appears to scale linearly with increasing interface roughness as determined by small angle X-ray scattering and Atomic Force Microscopy. From the MSHG magnetic contribution it follows that the increased interface roughness causes the interface moment to turn out of plane while the bulk of the film has an in-plane magnetization. (b) The long-term thermal stability of giant magneto resistance and tunnel magneto resistance sensors found in magnetic multilayers with a hard artificial antiferromagnetic (AAF) subsystem has been investigated at 300°C. The annealing is found to cause a stabilizing increase in the transport signal, the saturation field of the antiferromagnetic coupling and the Co layer coercivity respectively and a decrease in the Co magnetization. The MSHG shows that the Co/Cu crystallographic and magnetic interface characteristics also display a similar behavior upon heating. The results indicate that relaxation of the film structure is responsible for the sudden change, while demixing of Co/Cu and granularization of the Co layer are taking place.