ULTRASONIC PHONON VELOCITIES IN Cd_l-xMn_xTe BETWEEN 1.5 AND 96 K : ANOMALIES NEAR THE MAGNETIC TRANSITION

Abstract
Transit times of 30 MHz ultrasonic waves have been measured from 1.5 K to 96 K for Cd_l-xMn_xTe samples with 0.05 ≤ x ≤ 0.65. Below 60 K the velocities for higher concentrations exhibit anomalous features which depend on x and are stronger for shear modes than for longitudinal modes. The shear mode anomalies are flattening of the temperature dependence for x = 0.20 and 0.35 at low temperatures and a wide minimum centered around 22 K for samples with x ≥ 0.55. The location of each minimum indicates that it is connected with a transition to the spin glass or antiferromagnetic state. The depth of the minimum is much greater than the elastic constant depression observed in transition metal alloy spin glasses (TMASG). This may be due to electrons (or holes) in large orbits around shallow-level impurities affecting the Mn magnetic moments.