Correlations between interface structures and magnetic properties of Co/Cu multilayers sputter-grown on Ta buffers

Photon Factory, High Energy Accelarator Reserch Organization
â—‹Kotaro Ishiji Hiroo Hashizume

Interface structures are a crucial factor influencing the magnetic properties of metal multilayers. For magnetic applications, large magnetoresistance (MR) ratio and low saturation field are desirable. To investigate the correlation between interface structures and magnetic properties, we prepared five Co/Cu multilayers on Ta buffer of varying thickness tTa =30-500 nm by a magnetron sputtering. As tTa grows, the buffer surface becomes rough, which is duplicated onto the Co/Cu interface. We thus controlled the roughness, σCo/Cu, from 0.6 to 1.0 nm in rms values. With increasing σCo/Cu, the peak MR ratio decreases, but the rate of decrease is not uniform (Fig. 1). AFM images of the buffer surfaces show that the abrupt decrease of the peak MR ratio and coupling energy J in the 0.7-0.9 nm range of σCo/Cu is concomitant with the growth of large grains of 80-100 nm in in-plane size. It is considered that superparamagnetic particles and the orange peel effect are produced by the presence of the grain.