Anomalous temperature dependence of the giant magnetoresistance in Ni/Cu, Ni95Co5/Cu and Ni95Fe5/Cu multilayer films

In this paper we examine the temperature dependence of the giant magnetoresistance (GMR) of Ni/Cu, Ni95Co5/Cu and Ni95Fe5/Cu multilayers in the temperature range 4.2-350 K. The samples were prepared by magnetron sputtering on glass substrates. In all the multilayers examined, oscillations of the MR ratio as a function of the Cu thickness were observed at room temperature. However, in the Ni/Cu multilayers around the first peak the MR ratio exhibited a clear maximum near room temperature and decreased with decreasing temperature, The magnetic hysteresis curves were also measured between 77 and 350 K. The remanent magnetization and coercive field increased with decreasing temperature, Such behavior was also observed for Ni95Co5/Cu and Ni95Fe5/Cu multilayers around the first peak. We explain these anomalous temperature dependences of the magnetoresistance and magnetization curve by taking account of the rapid increase in the magnetic anisotropy with decreasing temperature.