Exploring the microscopic origin of exchange bias with photoelectron emission microscopy (invited)

It is well known that magnetic exchange coupling across the ferromagnet-ant iferromagnet interface results in an unidirectional magnetic anisotropy of the ferromagnetic layer, called exchange bias. Despite large experimental a nd theoretical efforts, the origin of exchange bias is still controversial, mainly because detection of the interfacial magnetic structure is difficul t. We have applied photoelectron emission microscopy (PEEM) on several ferr omagnet-antiferromagnet thin-film structures and microscopically imaged the ferromagnetic and the antiferromagnetic structure with high spatial resolu tion. Taking advantage of the surface sensitivity and elemental specificity of PEEM, the magnetic configuration and critical properties such as the Ne el temperature were determined on LaFeO3 and NiO thin films and single crys tals. On samples coated with a ferromagnetic layer, we microscopically obse rve exchange coupling across the interface, causing a clear correspondence of the domain structures in the adjacent ferromagnet and antiferromagnet. F ield dependent measurements reveal a strong uniaxial anisotropy in individu al ferromagnetic domains. A local exchange bias was observed even in not ex plicitly field-annealed samples, caused by interfacial uncompensated magnet ic spins. These experiments provide highly desired information on the relat ive orientation of electron spins at the interface between ferromagnets and antiferromagnets. (C) 2001 American Institute of Physics.