Grain-boundary capacitance ofLa0.7Ca0.3MnO3films

Abstract

The capacitance of grain boundaries formed at step edges in ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ films was measured using impedance spectroscopy. The grain-boundary capacitance decreases with temperature and vanishes in the paramagnetic phase. The grain-boundary region is modeled as an abrupt metal-semiconductor contact inducing a depletion layer; the built in voltage is expected to be caused by chemical potential shifts due to differences in the ferromagnetic order in the grains and the grain boundaries. This model indicates that the capacitance vanishes with the second power of the difference between grain and grain-boundary magnetization; the data indicate that the capacitance follows more closely the grain-boundary magnetization as determined from the magnetoresistance.