MAGNETIC GRUNEISEN PARAMETERS OF CRITICAL FLUCTUATIONS IN SPIN-DENSITY WAVE METALS CR, MNSI AND MN3SI

Critical fluctuations in the paramagnetic phase of Cr are considerably more volume dependent than the long range magnetic order, the Grüneisen parameter, Γ+ = -155, above the Néel temperature TN being about a factor 4 larger than the value, Γ- = -40, below TN. The available thermophysical data for MnSi and Mn3Si are analysed to show that in these two spin-density wave metals the magnitude of Γ+, corresponding to the logarithmic volume dependence of the critical fluctuations, is about a factor 2 smaller than Γ- in the ordered state. The giant Grüneisen parameter in the paramagnetic phase relative to the ordered phase thus seems to be a peculiarity of pure Cr, which also is not observed in dilute Cr(V) alloys. © 1989.