Magnetic properties of micro-structured exchange coupled bilayers

The purpose of this study is to fabricate 3 dimensionally micro-structured exchange coupled bilayers，and to clarify a responsible mechanism for the exchange coupling field in relation to formation of the antiferromagnetic domains and walls.Amongst transition metal alloys and oxides，Cr-Al or NiO was chosen as an antiferromagnet and Fe I D 220个D 2 Ni I D 280个D 2 permalloy was chosen as a ferromagnet.After the structural analyses on the grain size and crystallographic orientations between the ferromagnetic layers with using X-ray diffractometer，atomic force microscope and electron microscope，submicron sized exchange coupled bilayers were fabricated by means of electron-bean lithography。The magnetic domain structure as well as magneto-transport properties were then carefully examined with magnetic force microscope and 4terminal methods.For the first time，the magnetization reversal processes occurring in the sub-micron region was obtained by analyzing the anisotropy magnetoresistance and the planar Hall effects.The results were compared with the demagnetization curves calculated by micromagnetic simulation.It was found that the exchange coupling field varies proportional to the inverse of the coupling area.Furthermore the slope of the variation was found to reflect the degree of roughness at the interface which determines the strength of the net exchange coupling due to the random exchange field.From this experimental study，the exchange coupling field was shown to be controlled by adjusting the coupling area in submicron scale，which determines the antiferromagnetic domain size。

The purpose of this study is to fabricate 3 dimensionally micro-structured exchange coupled bilayers, and to clarify a responsible mechanism for the exchange coupling field in relation to formation of the antiferromagnetic domains and walls. Amongst transition metal alloys and oxides, Cr-Al or NiO was chosen as an antiferromagnet and FeィイD220ィエD2NiィイD280ィエD2 permalloy was chosen as a ferromagnet. After the structural analyses on the grain size and crystallographic orientations between the ferromagnetic and antiferromagnetic layers with using X-ray diffractometer, atomic force microscope and electron microscope, submicron sized exchange coupled bilayers were fabricated by means of electron-bean lithography. The magnetic domain structure as well as magneto-transport properties were then carefully examined with magnetic force microscope and 4 terminal methods. For the first time, the magnetization reversal processes occurring in the sub-micron region was obtained by analyzing the anisotropy magnetoresistance and the planar Hall effects. The results were compared with the demagnetization curves calculated by micromagnetic simulation. It was found that the exchange coupling field varies proportional to the inverse of the coupling area. Furthermore the slope of the variation was found to reflect the degree of roughness at the interface which determines the strength of the net exchange coupling due to the random exchange field.From this experimental study, the exchange coupling field was shown to be controlled by adjusting the coupling area in submicron scale, which determines the antiferromagnetic domain size.