Nano-cap Structure Of Ferromagnetic / Antiferromagnetic Bilayers, The Exchange Bias

The magnetic properties of nano-structured exchange bias systems are closely related to their lateral size,aspect ratio or shape.Due to the complicated system parameters, it is still hard to give a general description of the size effects of exchange bias nanostructures.We chose the sphere cap-shaped ferromagnetic/antiferromagnetic(FM/AFM) nanomagnets arrays as the study system,investigated the influence of nanostructure morphology in Exchange Bias effect.Close-packed 2 dimensional(2D) Polystyrene(Ps) beads arrays were used as the templates to fabricate the nanocap Exchange Bias Cu/FeNi/FeMn/Cu structures. Scanning Electron Microscope(SEM) gives us direct view of the nanocap structure. Vibrating sample magnetometer(VSM) are used to collect the magnetic information of the samples.Pronounce asymmetry evolution of the hysteresis loops was observed through tailoring the thickness ratio of AFM to FM in nanocap EB structures.The hysteresis loop shift of nanocap structures is smaller than that of continuous films with the same composition,whereas the exchange bias field(H_E) evolution trends depending on AFM thickness are different for the two kinds of samples.The nanocap structures can cont??te to either a reduction or an enhancement of the coercivity (H_c),depending on the AFM layer thickness.H_E of both nanocap structures and the continuous films samples follows the 1/t_FM law with different slopes.Tne effects different from those of continuous films are ascribed to the influences of nanocap morphology.