Direct evidence of imprinted vortices in exchange-biased patterned bilayer nanomagnets

We investigate the magnetic domain structure in lithographically patterned nanomagnet arrays using element-sensitive circularly polarized XPEEM imaging. ZFC Py/IrMn (FM/AFM) bilayer nanodot (0.5 um -- 4um dia.) arrays imaged across the Fe and Ni L edges clearly demonstrate spontaneous formation of vortex states. Magnetic contrast at the Mn L edge resonance indicates that the vortex state is transferred into the underlying AFM layer. The exchange-bias, measured through magneto-optical hysteresis measurements, verifies the AFM nature of the underlying IrMn, suggesting that the imprinted vortex state is confined to the interface by local interactions of the uncompensated interfacial Mn spins with the FM Py layer.