In-situ study of exchange-bias in interlayer coupled Co/CoO/Co trilayer structure

Abstract

Exchange bias (EB) properties of Co/CoO/Co trilayer structure with increasing top Co layer thickness has been studied in-situ using magneto-optic Kerr effect (MOKE) and reflection high energy electron diffraction (RHEED). Intermediate native oxide layer (CoO) was prepared by thermal oxidation of the bottom Co layer (Cobot), whereas the trilayer structure was formed by subsequent deposition of another Co layer (Cotop) on top. Two step magnetization reversal of trilayer at room temperature (RT) is observed due to the different coercive field (Hc) contribution of Cobot and Cotop layers. Individual contribution of magnetization reversal of both Co layers at RT as well as field cooled (FC) conditions is separated out by fitting the magnetic hysteresis loops using an adequate mathematical function. Increasing thickness of Cotop on Cobot/CoO bilayer is found to affect EB and Hc of the Cobot layer significantly. With an addition of 4 nm thick Cotop layer, EB corresponding to a Cobot layer is reduced by about 20% when FC to 153 K. Whereas, a further increase in Cotop layer thickness is found to be responsible for the relatively slow reduction in EB. Unusual asymmetric magnetization reversal with single step coherent rotation in descending branch and two step reversal in ascending branch of the loop after field cooling below Néel temperature (TN) was understood in terms of the combined effect of interface induced EB and interlayer coupling (IC) between Cotop and Cobot layers. The present study, where all the measurements are performed in-situ just after each step of deposition on the same film, provided genuine information about the EB in interlayer coupled spin valve like Co, CoO based trilayer structure.