Possible origin of magnetic transition ordering in La2/3A1/3MnO3 oxides

Magnetic phase transition behaviors of perovskite-like La2/3A1/3MnO3 (A=Ca, Sr and Ba) oxides at Curie temperature (Tc) are explored through a systematic study on their structural, magnetic, and thermal properties. It is found that the ferromagnetic transition changes from first order to second order as the ionic radius of doped alkaline earth element increases. In the first order magnetic transition of La2/3Ca1/3MnO3 oxide, polarons transit discontinuously to itinerant electrons, but continuously in the second order transitions of both La2/3Sr1/3MnO3 and La2/3Ba1/3MnO3 oxides. The distortion of the MnO6 octahedra of the oxides, which is dominated by the lattice structures, may play an important role in the order of magnetic transitions through controlling the polaron delocalization.