Beneficial Effects of ${\rm Si}_{3}{\rm N}_{4}$ Buffer/Spacer Layers on the Magnetic Properties of Exchange-Coupled PtFe/Fe Composite Films

Exchange-coupled PtFe/Fe composite films have been prepared with Si₃N₄ as spacer layer and buffer layer. The coercivity generally decreases with increasing thickness of the Fe layer at fixed thickness of the Si₃N₄ spacer layer. At fixed thickness of Fe the layer, the coercivity shows a maximum and then declines with increasing thickness of the Si₃N₄ spacer layer because Si₃N₄ layer is too thin to play a role of separation. However, the magnetic properties are significantly enhanced by a Si₃N₄ buffer layer, which is proposed to be due to effective prevention of diffusion between Mo and PtFe phase, as indicated by microstructure images. Fine grain sizes estimated to be about 30 nm, an enhanced coercivity and better remanence ratio indicate the beneficial effects of Si₃N₄ buffer layer on the magnetic properties and on the exchange-coupling of PtFe/Fe composite films.