Investigations on the interlayer coupling in Co/Pt multilayers with perpendicular anisotropy via the extraordinary Hall effect

The interlayer coupling in Co/Pt multilayers has been investigated via the measurements of extraordinary Hall effect. In the conventional [Co/Pt]_n multilayer, the coercivity H_C has been observed to increase exponentially for n < 6 and almost linearly for n > 6 with the decrease of temperature. Surprisingly, H_C for n = 1 shows the fastest increase at low temperatures, and becomes the largest one at T < 40 K. As a function of the repetition number n, the almost temperature-independent oscillation of H_C has been observed, being indicative of the Ruderman-Kittel-Kasuya-Yosida type ferromagnetic interlayer coupling in the [Co/Pt]_n multilayer. However, the antiferromagnetic interlayer coupling can be realized via the spin-valve configuration of the Co/Pt multilayer. In the Co/Pt/[Co/Pt]_n multilayer, the antiferromagnetic-to-ferromagnetic transition of the interlayer coupling has been observed at low temperatures. These observed phenomena are strongly related to the temperature-dependent polarization in the Co/Pt multilayers.