  The effects of strain on a film of mulitferroic GdMnO3 are investigated using
both magnetometry and magneto-optic spectroscopy. Optical spectra, in the
energy range 1.5eV - 3.5eV, were taken in Faraday geometry in an applied
magnetic field and also at remanence. This yielded rich information on the
effects of strain on the spin ordering in these films. Epitaxial films of
GdMnO3 were grown on SrTiO3 and LaAlO3 substrates. The LaAlO3 was twinned and
so produced a highly strained film whereas the strain was less for the film
grown on SrTiO3. The Ne\'el temperatures and coercive fields were measured
using zero field data and hysteresis loops obtained using a SQUID magnetometer.
Optical absorption data agreed with earlier work on bulk materials. The two
well known features in the optical spectrum, the charge transfer transition
between Mn d states at ~2eV and the band edge transition from the oxygen p band
to the d states at ~3eV are observed in the magnetic circular dichroism;
however they behaved very differently both as a function of magnetic field and
temperature. This is interpreted in terms of the magnetic ordering of the Mn
spins.
