SPIN-DENSITY-WAVE EFFECTS ON THE ELASTICITY OF CR-GA ALLOY SINGLE-CRYSTALS

Measurements are reported of the temperature dependence of the elastic constants, ultrasonic attenuation and thermal expansion of dilute Cr- Cla alloy single crystals containing 0.16, 0.42 and 0.88 at.% Ga. Well defined magnetic anomalies were observed in all of these physical pro perties at the Neel temperature (T-N), at the incommensurate-commensur ate (I-C) spin-density-wave (SDW) transition temperature (T-IC) and at the spin-hip transition temperature (T-sf). The complete magnetic pha se diagram of the Cr1-xGax alloy system has been determined for x < 1 at.% Ga from the temperatures of these anomalies. The magnetovolume (D elta omega) and the magnetic component (Delta B) to the bulk modulus w ere both found to vary as a + bT(2) + cT(4), as predicted by theory, i n the ISDW phases of all three of the crystals. Values of the pressure derivatives of T-N for the crystals containing 0.16 at.% Ga and 0.42 at.% Ga were calculated from the results for Delta B and Delta omega. dT(N)/d omega = (0.09 +/- 0.02) x 10(5) K calculated for the Cr + 0.16 at.% Ga crystal compares very well with the value dT(N)/d omega = (0. 108 +/- 0.006) x 10(5) K obtained from direct high-pressure measuremen ts. High-pressure measurements have not been made on the Cr + 0.42 at. % Ga crystal for a comparison. The value dT(IC)/d omega = (0.59 +/- 0. 03) x 10(5) K calculated from Delta omega and Delta B for Cr + 0.88 at .% Ga does not compare well with dT(IC)/d omega = (0.17 +/- 0.07) x 10 (5) K 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 T-N do not fit the present measureme nts.