We fabricated GaAs-based spin-LED (light emitting diode) structures using half-metallic Fe3O4 as spin injectors and measured the circular polarization of the electroluminescence (EL). The circular polarization of the EL due to the spin injection was improved by the low temperature growth of the ferromagnetic layer, compared to the room temperature growth. We also studied the excitation wavelength dependence of the photoluminescence (PL) spectra and the variation of the EL spectra with increasing current. The excess carrier dependence of the EL peaks was found to be different from that of the PL peaks, which was explained by the carrier injection into the buffer layer. (C) 2012 Elsevier B.V. All rights reserved.