Effect of the kinds of ferromagnetic layers on exchange coupling strength in IrMn/FM films

Abstract

Antiferromagnet (AFM)/ferromagnet (FM) exchange coupling in polycrystalline IrMn/FM films with the saturation magnetization Ms=200–1910 emu/cm3 has been investigated through observation of both exchange-bias field and coercivity increase. It was found that there is some critical Ms below which the exchange coupling effect becomes almost zero. A critical FM thickness has also been found for the exchange coupling effect to appear, below which FM layers exhibit M-H curves characteristic of superparamagnetism, which increases exponentially with decreasing Ms. It suggests that frustrated FM spins caused by the exchange coupling with the AFM layer are responsible for these phenomena.