Thermodynamic Studies and Magnetic Ordering of Ni-Cr Alloys Close to the Critical Composition

Abstract

We report measurements of the specific heat capacity and the thermal expansion for Ni-Cr alloys in the vicinity of the magnetic ordering temperature TM and at lower temperatures. No evidence of a contribution due to the magnetic ordering is found in the specific heat capacity and only the indication of a small contribution in the thermal expansion near to T M for an Ni 11 at. % Cr alloy.A significant contribution of magnetic origin is seen for both quantities at lower temperatures.Values for the magnetic Grlineisen parameter yi, are derived from the specific heat capacity and thermal expansion data and compared with values of dIn TM/d In V obtained from direct measurements of dTM/dP. Both yi, and -d In TM/d In V are large and negative for weakly ferromagnetic alloys but differ numerically, whereas for paramagnetic alloys yi, is large and positive.

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“…For metals and alloys, c v includes an electronic contribution proportional to temperature T which is relatively significant only at low temperatures. For Ni 1−x Cr x alloys with x = 0.09 to 0.15, and hence a Curie temperature T c below 20 K, the experimental measurements have verified the proportionality of α to c v (Simpson and Smith 1982, Kaiser and Smith 1989, Smith et al 1991. In equation ( 1), B and γ usually vary only weakly with temperature.…”

“…On the basis of these studies, we estimate T c 400 K (100 K) for x 0.05 (0.1), so the hightemperature comparisons made here for the alloys are well above T c . Simpson and Smith (1982) have measured α for Ni 1−x Cr x for x = 9, 9.8, 11, 12, 13, 14 and 15% so as to bracket the paramagnetic-to-ferromagnetic transition for x c 12%. These measurements carried out below 20 K (since T c for these materials is low) show that for x > x c , the paramagnetic alloys have values of α higher than that for ferromagnetic alloys for x < x c .…”