Spin-density-wave effects on the elasticity of Cr - Ga alloy single crystals

Abstract

Measurements are reported of the temperature dependence of the elastic constants, ultrasonic attenuation and thermal expansion of dilute Cr - Ga alloy single crystals containing 0.16, 0.42 and 0.88 at.% Ga. Well defined magnetic anomalies were observed in all of these physical properties at the Néel temperature , at the incommensurate - commensurate (I - C) spin-density-wave (SDW) transition temperature and at the spin-flip transition temperature . The complete magnetic phase diagram of the alloy system has been determined for x < 1 at.% Ga from the temperatures of these anomalies. The magnetovolume and the magnetic component to the bulk modulus were both found to vary as , as predicted by theory, in the ISDW phases of all three of the crystals. Values of the pressure derivatives of for the crystals containing 0.16 at.% Ga and 0.42 at.% Ga were calculated from the results for and calculated for the Cr + 0.16 at.% Ga crystal compares very well with the value obtained from direct high-pressure measurements. High-pressure measurements have not been made on the Cr + 0.42 at.% Ga crystal for a comparison. The value calculated from and for Cr + 0.88 at.% Ga does not compare well with obtained from direct high-pressure measurements. This may point to inadequacies in the thermodynamic model used for the calculations. Predictions of microscopic theories for the temperature dependence of the ultrasonic attenuation, magnetovolume and the magnetic components of the elastic constants close to do not fit the present measurements.