Exchange bias and magnetic structure in modulation-doped manganite superlattices

Superlattices of antiferromagnetic (AF) La13Ca23MnO3 and ferromagnetic (F) La23Ca13MnO3 were grown using sputtering technique. The AF layer thickness ranged between 3.9 nm≤tAF≤15.6 nm while the F layer thickness was kept constant (7.8 nm). Hysteresis measurements after field cooling, show an exchange bias up to a temperature of ~100 K. Surprisingly, the saturation magnetization increases with antiferromagnetic layer thickness and can exceed the expected bulk value for the La23Ca13MnO3 composition, whereas the interface coupling energy between the AF and F layers derived from the exchange bias is constant. This suggests that magnetization depth profile extends beyond the chemical doping interface.