Effects of electric and magnetic fields on phase-separated La 0.7 Sr 0.3 MnO 3- d thin films

We perform field-effect experiments on side-gate devices made of underdoped La0.7Sr0.3MnO3-d epitaxial thin films. The resistance modulation is small due to the high carrier concentration in this compound; however, it is significantly enhanced by an external magnetic field. We discuss our results in the framework of a double-exchange mechanism and phase separation and suggest that our experimental data together with other complementary data of the literature are a straightforward consequence of the percolative nature of transport in the phase-separation regime of manganites. We demonstrate the possibility of driving the percolation process by field effect.