Abstract
The metal-insulator - phase transitions relevant to charge ordering (CO) have been investigated for perovskite-type crystals, in which the one-electron bandwidth is systematically controlled by varying the averaged ionic radius of the site and by application of quasihydrostatic pressure . Competition between the ferromagnetic double exchange and the antiferromagnetic CO interactions give rise to complex phase diagrams with temperature and and/or as the parameters. The phase boundaries are associated with critically - and -dependent hystereses, which result in unique appearance of the metastable state. We have demonstrated the pressure-induced phase transition from the metastable ferromagnetic metal to the thermodynamically stable charge-ordered insulator for the =0.875 crystal locating near the critical phase boundary. With decrease of , the CO instability accompanying the antiferromagnetic spin correlations subsists even above the ferromagnetic transition temperature and enhances the electron-lattice coupling. Consequently, the lattice-coupled first-order transition is observed at in the small- region of . It was found that application of magnetic field also induces the phase transition from the insulator with antiferromagnetic spin correlations to the ferromagnetic metal, which is accompanied by lattice-structural change.
- Received 2 May 1997
DOI:https://doi.org/10.1103/PhysRevB.56.9386
©1997 American Physical Society