Magnetic-Field-Dependent Carrier Injection at La2/3Sr1/3MnO3/ and Organic Semiconductors Interfaces

We have fabricated organic diodes utilizing several $\pi$-conjugated organic semiconductors (OSEC) as spacer layers between ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_3$ (LSMO) and various metallic electrodes, and measured their magnetoresistance (MR) and magnetoelectroluminescence (MEL) responses. The devices exhibit large negative high-field MR responses that resemble the MR response of the LSMO electrode, but amplified by $\sim 3$ orders in the resistance, and accompanied by a positive high-field MEL effect. These magnetic-field effects result from enhanced carrier injection at the LSMO-OSEC interface that is attributed to the anomalous field-dependent Fermi level shift in LSMO.