Zener versus de Gennes ferromagnetism in La1-xSrxMnO3

Measurement of the transport properties of single-crystal La0.86Sr0.14MnO3 as a function of temperature under different hydrostatic pressures P less than or equal to 18 kbars has revealed a discontinuous change in the ferromagnetic Curie temperature T-c at P approximate to 3 kbars where it crosses the first-order orbital-ordering transition, and at P-c approximate to 11 kbars where it crosses a first-order transition from vibronic to metallic (Zener to de Gennes) ferromagnetism. On cooling below T-c within the vibronic phase, a second-order vibronic-insulator transition occurs at a T-00 that increases with pressure to P=P-c; the first-order low-temperature insulator-metal transition is contiguous with the first-order vibronic-metallic transition occurring at P(c)approximate to 11 kbars. The distinction between Zener and de Gennes ferromagnetism in this system and the role of orbital ordering are clarified.