Exchange coupling in ferromagnetic/antiferromagnetic systems.

摘要

Spin arrangement at interfaces in a layered magnetic material often has an important effect on the properties of the material. In exchange-biased ferromagnetic/antiferromagnetic systems, the interfacial spin arrangement is believed to play an important role in appearance of exchange bias. Due to the interfacial exchange coupling, the spin arrangement at the interface can strongly affect the spin configuration in the ferromagnetic layer. As part of this thesis, investigations have been performed on domain wall nucleation and behavior during magnetization reversal in a series of exchange-biased ferromagnetic/antiferromagnetic bilayers with in-plane and out-of-plane anisotropies using magnetometry and magnetic force microscopy. From these investigations, useful information has been obtained on the interfacial arrangement and its effect on the magnetization reversal in the exchange- biased ferromagnetic layer.; Interlayer exchange coupling is a general feature that exists in ferromagnetic/nonmagnetic metallic (insulating) spacer/ferromagnetic systems with in-plane anisotropy. The coupling oscillates between antiferromagnetic and ferromagnetic as a function of thickness of metallic spacers, but decays monotonically as a function of thickness of insulating spacers. Interlayer exchange coupling also exists in ferromagnetic/nonmagnetic metallic spacer/ferromagnetic systems with perpendicular anisotropy. However, for insulating spacers, observation of out-of-plane interlayer exchange coupling is scarce. In this thesis, out-of-plane interlayer exchange coupling has been investigated in two Pt/Co multilayers with perpendicular anisotropy separated by NiO spacers. Strong antiferromagnetic coupling has been observed when the NiO spacer is very thin, and the coupling oscillates between antiferromagnetic and ferromagnetic as a function of the NiO thickness. This oscillatory behavior has been ascribed to the antiferromagnetic ordering of NiO spacers. Oscillatory behavior has also been observed as a function of the Pt thickness.