Influence of Cr interlayer with different thickness on transition of magnetoresistance effect of Gd/FeCo thin films

Abstract

As one of the most representative features characterizing 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 scope of applications of rare earth in spintronics. In this work, the interlayer exchange coupling and interfacial effects of Gd (4 nm)/Cr (<i>t</i><sub>Cr</sub>)/FeCo (5 nm) trilayers with different Cr layer thickness (<i>t</i><sub>Cr</sub>) are studied by means of in plane magnetoresistance. Compared with FeCo film, Gd/FeCo film obtains more obvious anisotropic magnetoresistance. While the magnetoresistance value obtained for the configuration of <i>I</i>⊥<i>H</i> shows a minimum value at the peak due to the insertion of Cr layer, and this minimum value becomes more pronounced with the increase of <i>t</i><sub>Cr</sub>. When<i> t</i><sub>Cr</sub> = 3 nm, the negative spin valve effect almost totally overcomes the anisotropic-magnetoresistance effect. Different spin asymmetries of scattering that are formed in FeCo layer and Cr/Gd layers are mainly responsible for creating the negative spin valve magnetoresistance, in which the resistance becomes smaller near the coercive, while the resistance becomes larger at high field parallel to magnetic moment. The oscillation of magnetoresistance with <i>t</i><sub>Cr</sub> at <i>I</i> // <i>H</i> and the hysteresis loops at 5 K further confirm the existence of interlayer coupling both at room temperature and 5 K.