Thickness dependence of the exchange bias in epitaxial manganite bilayers

Exchange bias has been studied in a series of La_2/3Ca _1/3MnO₃/La_1/3Ca_2/3MnO₃ bilayers grown on (001) SrTiO₃ substrates by ozone-assisted molecular-beam epitaxy. The high crystalline quality of the samples and interfaces has been verified using high-resolution x-ray diffractometry and Z-contrast scanning transmission electron microscopy with electron-energy-loss spectroscopy. The dependence of exchange bias on the thickness of the antiferromagnetic layer has been investigated. A critical value for the onset of the hysteresis loop shift has been determined. An antiferromagnetic anisotropy constant has been obtained by fitting the results to the generalized Meiklejohn-Bean model.