The capacitance of grain boundaries formed at step edges in La0.7Ca0.3MnO3 films was measured by using impedance spectroscopy. The grain-boundary capacitance decreased with temperature and vanishes in the paramagnetic phase. The grain-boundary region was modeled as an abrupt metal-semiconductor contact inducing a depletion layer; the built in voltage was expected to be caused by chemical potential shifts due to differences in the ferromagnetic order in the grains and the grain boundaries. This model indicated that the capacitance vanishes with the second power of the difference between grain and grain-boundary magnetization; the data indicated that the capacitance follows more closely the grain-boundary magnetization as determined from the magnetoresistance.

Grain-Boundary Capacitance of La0.7Ca0.3MnO3 Films. A.Glaser, M.Ziese: Physical Review B, 2002, 66[9], 094422 (5pp)