  Magneto-structural phase transition in FeRh epitaxial layers was studied
optically. It is shown that the transition between the low-temperature
antiferromagnetic phase and the high-temperature ferromagnetic phase is
accompanied by a rather large change of the optical response in the visible and
near infrared spectral ranges. This phenomenon was used to measure the phase
transition temperature in FeRh films with thicknesses from 6 to 100 nm and it
was observed that the hysteretic transition region broadens significantly in
the thinner films.
