Spin polarization of charge carriers and Andreev reflection in (LaCa)MnO/superconductor point contacts

Abstract

Spin polarization of charge carriers in La0.65Ca0.35MnO3 (LCMO) is studied using point-contact Andreev spectroscopy. Pb and MgB2 are used to make superconducting electrodes. In all cases, the transport spin polarization obtained from the conductivity of LCMO/superconductor point contacts does not exceed 80–85%. Different models of the current flow through the superconductor-ferromagnetic metal contact and possible reasons for noncomplete spin polarization of a current in manganites are explored. The level of spin polarization observed in Sharvin contacts (contact area ∼104 A2) is most naturally explained in terms of a model that suggests separation of the crystal into nanosized magnetic phases, only one of which is a ferromagnetic metal with full spin polarization of charge carriers.