Influence of the thicknesses of Cr interlayer on the transition of magnetoresistance effect of Gd/FeCo thin films

As one of the most representative features to characterize the spin valve structure, magnetoresistance is an important method to study the interlayer coupling in multilayers. Considering the induced magnetism of rare earth at room temperature due to the coupling and magnetic proximity effect in the structure of rare earth/magnetic transition metal, an intermediate nonmagnetic metal can be inserted to form the spin valve structure to regulate the interlayer coupling, which expands the application of rare earth in spintronics. In this paper, the interlayer exchange coupling and interfacial effects of Gd(4 nm)/Cr(t_Cr)/FeCo(5 nm) trilayers with different Cr layer thicknesses (t_Cr) are studied by means of in plane magnetoresistance. Compared with FeCo film, more obvious anisotropic magnetoresistance is obtained in Gd/FeCo film. While the magnetoresistance obtained with the configuration of I⊥H shows a minimum value at the peak with the inserting of Cr layer, and this minimum value becomes more obvious with the increase of t_Cr. When t_Cr=3 nm, the negative spin valve effect almost totally overcome the anisotropic-magnetoresistance effect. Different spin asymmetry of scattering is formed of FeCo layer and Cr/Gd layers that produce the negative spin valve magnetoresistance, in which the resistance becomes smaller near the coercive, while the resistance becomes larger at high field (parallel alignment of magnetic moments). The oscillation of magnetoresistance with t_Cr at I//H and the hysteresis loops at 5 K further confirm the existence of interlayer coupling both at room temperature and 5 K.