Perpendicular Exchange Bias Effect in Tb/FeCo Multilayer Films

Two kinds of Glass/Cu(60 nm)/Tb(tTb=1.5, 3.0 nm)/FeCo(1.5 nm)₅/Ta(10 nm) multilayer films were fabricated by magnetron sputtering method. The crystal structure, magnetic domain structure and room temperature (RT) magnetic properties of the samples were characterized with X-ray diffraction, atomic force and magnetic force microscopy, and vibrating sample magne-mtoeter. The perpendicular magnetic anisotropy and perpendicular exchange bias effects of the multilayer films were studied. X-ray diffraction analysis show that the Tb/FeCo interfaces in the multilayer films are mainly in amorphous or nanocrystalline structure. The magnetic force microscope images exhibit a disordered labyrinthine stripe domain structure for all of the as-deposited films. The magnetic measurements at RT show that all the samples exhibit out-of-plane anisotropy with the perpendicular coercive fields of 122 and 351 kA/m for the Glass/Cu(60 nm)/Tb(tTb)/FeCo(1.5 nm)₅/Ta(10 nm) multilayers with t_Tb=1.5 and 3.0 nm, respectively. A robust perpendicular exchange bias (P-EB) effect with an exchange bias field of 20 kA/m is observed in a prototypical soft/hard exchange coupled spin valve structure consisting of Glass/Cu(60 nm)/Tb(1.5 nm)/FeCo(1.5 nm)₂/Tb(3.0 nm)/FeCo(1.5 nm)₅/Ta(10 nm) multilayers. Such a robust P-EB effect obtained in Tb/FeCo based multilayer films may be of crucial importance for applications in modern ultrafast storage media.