Effects of cooling field strength on exchange anisotropy at permalloy/CoO interfaces

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Abstract
We have studied exchange anisotropy at ferromagnet/antiferromagnet (FM‐AFM) interfaces as a function of cooling field in Ni80Fe20 (permalloy) films deposited on bulk single‐crystal CoO substrates. Hysteresis loops measured after cooling through the antiferromagnetic ordering temperature in different magnetic fields show that the exchange bias has little dependence on cooling field. Large cooling fields produced hysteresis loops with larger remanent magnetization and larger coercivity. These trends can be explained using a model that assumes that the FM anisotropy axis directions can be influenced by the magnetic history of the AFM. Large cooling fields also led to larger CoO susceptibility, which implies rotation of the CoO spin axes. The simultaneous rotation of the FM anisotropy axes and the AFM spin axes suggests perpendicular coupling at the FM‐AFM interface.