ULTRASONIC AND NEUTRON-DIFFRACTION STUDIES OF DILUTE CR-RE AND CR-RU ALLOY SINGLE-CRYSTALS

Measurements are reported on the temperature dependence of the elastic constants of dilute Cr-Ru and Cr-Re alloy single crystals, containing respectively 0.3 at.% Ru, 0.5 at.% Ru, 0.3 at.% Re and 0.5 at.% Re. Neutron diffraction experiments were also performed on the two Cr-Ru crystals. Well defined anomalies were observed in all the elastic constants as well as in the integrated neutron intensities at the magnetic phase transitions of the alloys. The commensurate (c) spin density wave (SDW) to paramagnetic (p) and incommensurate (I) SDW to P transitions are second-order phase transitions, while the ISDW-CSDW and CSDW-ISDW transitions are of first order. A thermodynamic model describes the temperature dependence of the magnetic contributions (DELTAB) to the bulk modulus (B) reasonably well, but fails to give the observed relationship between DELTAB and the magnetization.