Direct observation of the alignment of ferromagnetic spins by antiferromagnetic spins

The arrangement of spins at interfaces in a layered magnetic material often has an important effect on the properties of the material. One example of this is the directional coupling between the spins in an antiferromagnet an d those in an adjacent ferromagnet, an effect first discovered(1) in 1956 a nd referred to as exchange bias. Because of its technological importance fo r the development of advanced devices such as magnetic read heads(2) and ma gnetic memory cells(3), this phenomenon has received much attention(4,5). D espite extensive studies, however, exchange bias is still poorly understood , largely due to the lack of techniques capable of providing detailed infor mation about the arrangement of magnetic moments near interfaces. Here we p resent polarization-dependent X-ray magnetic dichroism spectro-microscopy t hat reveals the micromagnetic structure on both sides of a ferromagnetic-an tiferromagnetic interface. Images of thin ferromagnetic Co films grown on a ntiferromagnetic LaFeO3 show a direct link between the arrangement of spins in each material. Remanent hysteresis loops, recorded for individual ferro magnetic domains, show a local exchange bias. Our results imply that the al ignment of the ferromagnetic spins is determined, domain by domain, by the spin directions in the underlying antiferromagnetic layer.