Effect of thickness and temperature on interfacial interaction between Cr and Ni nanolayers: An exchange bias study

The phenomenon of negative exchange bias is typically observed in ferromagnetic and antiferromagnetic materials following a field cooling protocol. However, the occurrence of positive exchange bias is hardly found. The majority of models show positive exchange bias after undergoing field cooling or zero-field-cooling process. In this work, we achieved a novel positive exchange bias effect for Cr/Ni bilayer after gradually increasing the temperature from low temperature (5 K) to high temperature (up to RT) in the absence of magnetic field. The M-H loops at different temperatures reveal not only temperature dependent exchange bias but also thickness dependent exchange bias for Cr/Ni layer. A systematic investigation was conducted to analyse the influence of the exchange bias field on the thickness of the ferromagnetic layer. Significantly, our experimental observations also reveal a notable room temperature exchange bias field measuring 320 Oe for the optimum bilayer. Moreover, to obtain a detailed understanding of coercivity in the Cr/Ni bilayer, Kerr hysteresis was also recorded at room temperature in longitudinal geometry (L-MOKE). Hence, the discovery of our work not only suggests a novel methodology to achieve positive exchange bias in ferromagnetic and antiferromagnetic bilayers but also the oscillatory behavior of HEB with respect to increase in temperature is observed for polycrystalline Cr (AFM) layer.