Oxygen isotope effect on the AFM-FM phase transition of the layered cobaltite HoBaCo2O5.47

Zero-field muon spin rotation (ZF-muSR) and DC magnetization investigations have been performed on the antiferromagnetic-ferromagnetic (AFM-FM) and the ferromagnetic-paramagnetic (FM-PM) transitions of two oxygen isotope (16O or 18O) substituted HoBaCo2O5.47 powders. While the FM-PM phase transition shows nearly no isotope effect, a small but clear shift of 1.5K on the transition temperature is observed for the AFM-FM transition. Together with the recent observation of an isotope effect on the metal-insulator transition on the same sample [E. Pomjakushina, et al., Phys. Rev. B 73 (2006) 113105.], our observations clearly show the coupling of electronic, magnetic and structural degrees of freedom in this system.