Phase transitions in Sr2YRuO6investigated by Mössbauer spectroscopy, magnetization, and thermodynamic measurements

Abstract

Recent specific-heat data measured in Sr${}_{2}$YRuO${}_{6}$ have revealed two transition features at $\ensuremath{\sim}$26 and $\ensuremath{\sim}$30 K, where only one transition could be inferred before from magnetic susceptibility and transport measurements. We have investigated this temperature region using ${}^{99}$Ru M\"ossbauer spectroscopy, magnetization, and thermodynamic measurements in order to elucidate the unusual properties in this temperature region. Below 25 K, fits to the M\"ossbauer spectra show that there is a unique value of the hyperfine magnetic field at each Ru site indicating static long-range magnetic order. Beyond 25 K, this static long-range magnetic order rapidly deteriorates. We have found that the temperature dependence of the M\"ossbauer spectra between $\ensuremath{\sim}$25 and $\ensuremath{\sim}$28 K can be described as due to either motional narrowing or to a temperature-dependent distribution of hyperfine magnetic fields. The M\"ossbauer spectra collapse to a single peak in this narrow temperature interval so that there is no evidence of static magnetic order by $\ensuremath{\sim}$30 K. As a result, no evidence of the transition at 30 K is seen in the M\"ossbauer spectra.