We report resonant ultrasound spectroscopy (RUS), dilatometry/ magnetostriction, magnetotransport, magnetization, specific-heat, and S 119 n Mössbauer spectroscopy measurements on SnTe and Sn0.995 Cr 0.005 Te. Hall measurements at T=77K indicate that our Bridgman-grown single crystals have a p -type carrier concentration of 3.4× 1019 cm -3 and that our Cr-doped crystals have an n -type concentration of 5.8× 1022 cm-3. Although our SnTe crystals are diamagnetic over the temperature range 2≤T≤1100K, the Cr-doped crystals are room-temperature ferromagnets with a Curie temperature of 294 K. For each sample type, three-terminal capacitive dilatometry measurements detect a subtle 0.5μm distortion at Tc ≈ 85K. Whereas our RUS measurements on SnTe show elastic hardening near the structural transition, pointing to co-elastic behavior, similar measurements on Sn0.995 Cr 0.005 Te show a pronounced softening, pointing to ferroelastic behavior. Effective Debye temperature, θD, values of SnTe obtained from S 119 n Mössbauer studies show a hardening of phonons in the range 60-115 K (θD =162K) as compared with the 100-300 K range (θD =150K). In addition, a precursor softening extending over approximately 100 K anticipates this collapse at the critical temperature and quantitative analysis over three decades of its reduced modulus finds Δ C44 / C44 =A |( T-T0 )/T0 | -κ with κ=0.50±0.02, a value indicating a three-dimensional softening of phonon branches at a temperature T0 ∼75K, considerably below Tc. We suggest that the differences in these two types of elastic behaviors lie in the absence of elastic domain-wall motion in the one case and their nucleation in the other.
|Physical Review B - Condensed Matter and Materials Physics
|Published - 18 Nov 2010