Zener versus de Gennes ferromagnetism inLa1−xSrxMnO3

Measurement of the transport properties of single-crystal ${\mathrm{La}}_{0.86}{\mathrm{Sr}}_{0.14}{\mathrm{MnO}}_3$ as a function of temperature under different hydrostatic pressures $P<~18\mathrm{kbars}$ has revealed a discontinuous change in the ferromagnetic Curie temperature $T_c$ at $P\approx 3\mathrm{kbars}$ where it crosses the first-order orbital-ordering transition, and at $P_c\approx 11\mathrm{kbars}$ 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 $P_c\approx 11\mathrm{kbars}.$ The distinction between Zener and de Gennes ferromagnetism in this system and the role of orbital ordering are clarified.