Fig. 2

Characteristic hysteresis loop of the multi-layered heterostructure obtained with the help of magneto-optical microscopy. The magneto-optical signal I is proportional to the out-of-plane component of the magnetization of the iron sublattice in the entire heterostructure. a Characteristic hysteresis loop of the entire heterostructure, constructed by averaging the pixel intensities of magneto-optical images recorded at varying strengths of the out-of-plane bias magnetic field H_B. b Typical raw magneto-optical images, measured with H_B = 0, and the inset value corresponds to the average pixel intensity of the associated image. The four shaded levels of the hysteresis loop correspond to the four stable magnetic states that can be obtained, with the left (right) arrow indicating the orientation of the magnetization of gadolinium within the top (bottom) layer of GdFeCo