Volume 89, Issue 11, 01 June 2001
Index of content:
- EXCHANGE BIASING: DOMAINS AND AE STRUCTURE
89(2001); http://dx.doi.org/10.1063/1.1358828View Description Hide Description
It is well known that magnetic exchange coupling across the ferromagnet–antiferromagnet interface results in an unidirectional magnetic anisotropy of the ferromagnetic layer, called exchange bias. Despite large experimental and theoretical efforts, the origin of exchange bias is still controversial, mainly because detection of the interfacial magnetic structure is difficult. We have applied photoelectron emission microscopy(PEEM) on several ferromagnet–antiferromagnet thin-filmstructures and microscopically imaged the ferromagnetic and the antiferromagneticstructure with high spatial resolution. Taking advantage of the surface sensitivity and elemental specificity of PEEM, the magnetic configuration and critical properties such as the Néel temperature were determined on and NiO thin films and single crystals. On samples coated with a ferromagnetic layer, we microscopically observe exchange coupling across the interface, causing a clear correspondence of the domain structures in the adjacent ferromagnet and antiferromagnet. Field dependent measurements reveal a strong uniaxial anisotropy in individual ferromagnetic domains. A local exchange bias was observed even in not explicitly field-annealed samples, caused by interfacial uncompensated magnetic spins. These experiments provide highly desired information on the relative orientation of electron spins at the interface between ferromagnets and antiferromagnets.
89(2001); http://dx.doi.org/10.1063/1.1358829View Description Hide Description
Monte Carlo simulations of a system consisting of a ferromagnetic layer exchange coupled to a diluted antiferromagnetic layer described by a classical spin model show a strong dependence of the exchange bias on the degree of dilution in agreement with recent experimental observations on Co/CoO bilayers. These simulations reveal that diluting the antiferromagnet leads to the formation of domains in the volume of the antiferromagnet carrying a remanent surplus magnetization which causes and controls exchange bias. To further support this domain state model for exchange bias we study, in the present article, the dependence of the bias field on the thickness of the antiferromagnetic layer. It is shown that the bias field strongly increases with increasing film thickness and eventually goes over a maximum before it levels out for large thicknesses. These findings are in full agreement with experiments.
89(2001); http://dx.doi.org/10.1063/1.1358830View Description Hide Description
By incorporating a random interfacial exchange interaction into the Landau–Lifshitz–Gilbert equation, a unified picture of exchange bias for single crystals, textured crystals, twin structures, and polycrystals of antiferromagnets is presented. It is found that the lateral interaction in the antiferromagnet is a key element governing the exchange bias and magnetization reversal of the ferromagnet.