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. N eutron diffraction experiments were also performed on the two Cr-Ru cr ystals. Well defined anomalies were observed in all the elastic consta nts as well as in the integrated neutron intensities at the magnetic p hase 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 t emperature dependence of the magnetic contributions (DELTAB) to the bu lk modulus (B) reasonably well, but fails to give the observed relatio nship between DELTAB and the magnetization.