Exchange bias and enhanced coercivity in phase separated La _0.45Sr _0.55MnO ₃ and Pr _0.55(Ca _0.65S _0.35) _0.45MnO ₃ films

An epitaxial La _0.45Sr _0.55MnO ₃ (LSMO) film, which has a paramagnetic-to-ferromagnetic transition at ∼260 K and a partial ferromagnetic-to-antiferromagnetic transition at ∼150 K upon cooling, was synthesized on (001) (La _0.18Sr _0.82)(Al _0.59Ta _0.41)O ₃ with pulsed laser deposition. The x-ray diffraction pattern showed interference fringes around the (002) LSMO peak, indicating a successful growth of a high quality and smooth film. When the LSMO film was cooled down in a magnetic field of 5 kOe, it exhibited a large exchange bias (H _EX) of ∼490 Oe and an enhanced coercivity (H _C) of ∼800 at 10 K, respectively. The observed exchange bias effect, which is associated with phase coexistence of the ferromagnetic (FM) and antiferromagnetic (AF) phases, displayed a distinctive training effect, which is probably due to a competing spin order at the boundary between the FM and AF phases. Similarly, we also observed a large exchange bias and enhanced coercivity in a phase separated Pr _0.55(Ca _0.65S _0.35) _0.45MnO ₃ film, which had simultaneous FM and AF transitions at ∼150 K. Our results show that the exchange bias effect can be induced even in single layer films with a magnetic phase coexistence state of FM and AF phases, which may be exploited as a very simple structure for spin-valve devices.