Intrinsic exchange bias effect in a charge-ordered manganite

Pr$_{1/3}$Ca$_{2/3}$MnO$_{3}$ is a charge-ordered (CO) and antiferromagnetic (AFM) manganite, with a N\'{e}el temperature $T_{N}\sim 160$K. However, for temperatures below $T_{N}$ the magnetization vs. field ($M$-$H$) loops exhibit hysteresis and a shift towards a negative field ($-H_{E}$) when the sample is cooled in a positive field. Both the exchange bias field ($H_{E} $) and the width of the hysteresis loop present a strong dependence on the value of the cooling field ($H_{cool}$). The observed dependence is successfully described in terms of nanometer-sized ferromagnetic (FM) inclusions, interacting via exchange coupling with a disordered shell at the interface with the CO/AFM matrix. The existence of a disordered spin layer around the FM bubbles is also consistent with the observed training effect of the exchange bias. The calculated size of the FM domains, $D\sim 1.9$nm, is similar to that found by neutron scattering in other electron doped manganites. We acknowledge useful discussions with Chris Leighton.