The effect of spacer layer thickness on the exchange bias between NiFe and polycrystalline IrMn: experiment and micromagnetic simulations

Abstract By inserting a non-magnetic Cu layer between permalloy (NiFe) and polycrystalline iridium manganese (IrMn) thin films with (111) and a mixture of (002) textures, the dependence of exchange bias, coercive field and magnetic reversal mechanism on the spacer layer thickness has been investigated both experimentally and by micromagnetic simulation technique in the temperature range of 10–300 K. Magnetic force microscopy measurements display a surface magnetic domain structure with random orientations in (002) texture regions and uniform orientations in (111) textured regions consistent with the polycrystalline structure of IrMn. Magnetization measurements reveal that the exchange bias, coercive fields, switching field values exhibit an exponential decline with increasing thickness of the Cu spacer layer. Suggesting that the observed decrease is solely attributable to the weakening of the interaction between Py and IrMn rather than any proximity effects due to the presence of a Cu spacer. Additionally, the magnetic coupling strength between Py and IrMn along the Cu spacer layer is temperature dependent such that at 100 K the exchange bias exhibits long-range characteristics, while above this temperature it displays short-range characteristics. The decay of exchange bias with increasing the spacer layer thickness was modelled to determine the temperature dependence of the characteristic decay length. Finally, detailed micromagnetic simulations were able to reproduce the low temperature experimental hysteresis curves in agreement with phenomenological models using coherent rotation of magnetization.