MAGNETOELASTICITY OF A CR-PERCENT AL-ALLOY SINGLE-CRYSTAL(2.2 AT)

The temperature dependences of the elastic constants and thermal expan sion of a Cr-Al-alloy single crystal containing 2.2 at.% Al are report ed. This is a critical concentration, being simultaneously close to th e very steep incommensurate-commensurate spin-density wave transition line on the magnetic phase diagram as well as to the triple point, whe re the incommensurate and commensurate spin-density wave states coexis t with the paramagnetic state. Very large magnetic contributions at 0 K of up to 28% for c(L) = 1/2(c11 + c12 + 2c44), 24% for c11 and 48% f or the adiabatic bulk modulus, B, were observed, while the magnetic co ntributions to the shear elastic constants, c44 and 1/2 (C11 - C12), a mount to less than 1% at 0 K. The magnetovolume, the longitudinal elas tic constants as well as B vary linearly with temperature over a large temperature range. This cannot be explained by existing theories. The absolute value of the zero-temperature magnetic Gruneisen parameter i s exceptionally large, reflecting the much larger magnetic contributio n to B than to the volume of the crystal at 0 K.