Far-infrared optical properties of antiferromagnetic SmTiO3

The polarized reflectance of nominally stoichiometric SmTiO3 has been measu red in the far-infrared at temperatures above and below the antiferromagnet ic Neel temperature T-N of 50 K. The appearance of a feature near 120 cm(-1 ) when the electric field vector is polarized along the b axis correlates w ith the onset of magnetic ordering in the Ti and Sm sublattices, suggesting it is likely due to a magnetic transition. Its large linewidth and relativ ely high-energy scale point to a two-magnon process. Because the RTiO3 fami ly of compounds (where R is a rare earth or Y) is susceptible to doping by vacancies on the R site, the nominally stoichiometric sample examined has a small, but finite background conductivity of the order 20 Omega(-1)cm(-1) at low frequencies. This background conductivity, like that along the semic onducting c axis in underdoped cuprate superconductors. appears to be of an incoherent nature with a magnitude below Mott's minimum metallic conductiv ity. At temperatures below T-N there is evidence that the continuum interac ts strongly with a nearby allowed phonon mode causing considerable asymmetr y. The correlation between the onset of magnetic ordering and the appearanc e of asymmetry in the allowed phonon mode suggests that this continuum, to which the mode appears to be strongly coupled, may be of magnetic origin. [ S0163-1829(99)09209-7].