Two ferromagnetic phases in ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ $(x\sim 1/8)$

It was discovered in ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ $(x\sim 1/8)$ that a field-induced phase transition occurs from a ferromagnetic metal (FM) phase to a ferromagnetic insulator (FI) phase. The magnetization shows a sharp jump at the transition field accompanied by a remarkable increase of magnetoresistance. Striction measurements clarified that this transition is associated with the structural change from a Jahn-Teller (JT) distorted orthorhombic phase to a pseudocubic phase. These results evidently show that the FI phase with a pseudocubic symmetry is more stable in high fields than the FM phase due to the double-exchange interaction. The driving force of this transition is explained by the enhancement of the ferromagnetic superexchange interaction induced by an antiferromagnetic-type orbital ordering in the pseudocubic phase, which was recently found in the anomalous x-ray scattering experiments.