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 t han or equal to 18 kbars has revealed a discontinuous change in the ferroma gnetic Curie temperature T-c at P approximate to 3 kbars where it crosses t he first-order orbital-ordering transition, and at P-c approximate to 11 kb ars where it crosses a first-order transition from vibronic to metallic (Ze ner 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 i ncreases with pressure to P=P-c; the first-order low-temperature insulator- metal transition is contiguous with the first-order vibronic-metallic trans ition occurring at P(c)approximate to 11 kbars. The distinction between Zen er and de Gennes ferromagnetism in this system and the role of orbital orde ring are clarified.