Ellipsometric studies of magnetic phase transitions of Fe-Rh alloys

Spectroscopic ellipsometric measurements of the dielectric functions for Fe-Rh alloys with 48, 50, 52, and 54 at. % Fe concentrations were performed between 25 and 125 \ifmmode^\circ\else\textdegree\fi{}C in the 1\char21{}3-eV range. Results show that the band structure of Fe-Rh is not drastically affected as the antiferromagnetic-ferromagnetic phase transition occurs and is less affected than band-structure calculations indicate. Therefore, the large change in the linear term of the electronic specific heat between the antiferromagnetic and ferromagnetic phases can be attributed primarily to a magnetic contribution rather than to a change in the density of electronic states at the Fermi surface.