Measurements are reponed on tbe temperature dependence of the elastic mnsmts of dilute Cr-Ru and Cr-Re alloy single crystals, wnta$ing respectively 0.3 at% Ru, 0.5 at.% Ru. 0.3 al. % Re and 0.5 at.% Re. Neutron diffraction experiments were also performed on lhe two Cr-Ru cryslals. Well defined anomalies were observed in all the elastic constants as well as in the integrated neutron intensities at the magnetic phase vansitions of the alloys.The commensurate (C) spin density wave (SDW) to paramagnetic (P) and incommensurate ( I ) SDW 10 P vansitions are spond-order phase bansitions, while fhe I S D W ~D W and CSDW-tSDW vansitions are of fin1 order. A thermodynamic model describes the tempenlure dependence of the magnetic mntributions (AB) to the bulk modulus ( 8 ) reasonably well, but fails to give Lhe observed relationship between A 8 and tbe magnetization

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