Magnetic circular dichroism spectroscopy in epitaxial La_0.7Sr_0.3MnO₃ thin films

Magneto-optic measurements are a very powerful tool for investigating the polarization of a conduction band as a function of temperature and are used here to study the polarization of the mobile electrons in 500 Å La_0.7Sr_0.3MnO₃ strained thin films grown epitaxially on single crystalline (001) LaAlO₃ (LAO) and (001) La_0.3Sr_0.7Al_0.65Ta_0.35O₉ substrates. The magnetic circular dichroism (MCD) has been investigated in magnetic fields up to 0.5 T and over a temperature range (10–450 K). The MCD spectra of both the films show a peak at the band gap at around 3 eV and the peak is found to be shifted toward lower energy side with the increase in temperature. A separate polaron peak (well known in insulating samples) appears at lower energy (∼1.8 eV) with the increase in temperature in all these metallic films. The rapid decrease in conduction band polarization in the film on LAO has strong implications for the use of these manganites in room temperature spintronics.