Magnetic hysteresis loops of the 10-nm-thick Fe film measured at various temperatures from 2 to 300 K. The sample was initially cooled in a positive 20 kOe field down to 2 K. Hysteresis loops were obtained on increasing temperature. At , the loop shift is opposite to the field cooling direction indicating a negative exchange bias. On the contrary, at , the loop shift has switched to the same direction as the cooling field indicating a positive exchange bias.
Exchange-bias loop shift (a) and coercivity (b) as a function of temperature for the 10-nm-thick Fe film. Sample was initially cooled in a positive 20 kOe field down to 2 K. Hysteresis loops were obtained on increasing temperature. The solid lines are guides to the eye.
The exchange-bias field vs the inverse of the Fe thickness . The hysteresis loops were measured at 2 K after 20 kOe field cooling from room temperature.
Schematic illustration of the spin configuration at (a) and (b) in our simple model. is the surface-spin-glass transition temperature. is the Fe layer spins, whereas and are the surface and interior spins for Fe oxide nanoparticles at the interface (see text).
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