PRESSURE-DEPENDENCE OF THE ELASTIC-CONSTANTS OF CR+0.3 ATMOSPHERIC-PERCENT RU NEAR THE COMMENSURATE-INCOMMENSURATE SPIN-DENSITY WAVE TRANSITION

The hydrostatic pressure dependences of the elastic stiffnesses c11 and c(L) = (c11 + c12 + 2c44)/2 for a Cr + 0.3 at.% Ru alloy have been determined in the pressure range up to 1.5 kbar and at several fixed temperatures between 248 K and 298 K. This temperature region spans the antiferromagnetic incommensurate (I)-commensurate (C) spin density wave (SDW) transition. At room temperature both c11 and c(L) soften under pressure in a similar manner to that seen in the ferromagnetic Invar material Fe72Pt28. By contrast, for a Cr + 5 at.% V alloy, which remains paramagnetic at all temperatures, the elastic constants are found to increase slightly with pressure. Below room temperature, (partial-derivative-c11/partial-derivative-p) and (partial-derivative-c(L)/partial-derivative-p) for the Cr + 0.3 at.% Ru alloy exhibit rapid increases over a narrow pressure range together with hysteresis behaviour. Such features are characteristic of a first-order CSDW-ISDW transition at T(IC). The observations suggest that Cr + 0.3 at.% Ru is an antiferromagnetic Invar material.