Thermal expansion and thermodynamic characterization of antiferromagnetic phase transition in elementalα-Mn

Abstract

High‐resolution measurements of thermal expansion and specific heat have been performed on α‐Mn. An analysis of these thermodynamic properties, with particular emphasis on their behavior in the temperature region near the Néel temperature, TN = 101.4(2) K, suggests that the antiferromagnetic phase transition is continuous (second order within the Ehrenfest classification scheme). The thermal expansion for T≲TN is negative, which is probably related to the volume dependence of the magnetic exchange interactions. This is manifested in the negative pressure derivative normaldTN/normaldP and may also be related to the anomalously low reported values of the bulk modulus for α‐Mn. Large, negative values of the bulk Grüneisen function, γG, for T< 75 K are comparable to those of antiferromagnetic Cr. In each case, the magnetic contribution to γG dominates for T≤TN.

Strong effects of uniaxial pressure and short-range correlations in Cr2Ge2Te6

“…While the c axis shows a nearly prefect scaling from 200 K to 80 K and good scaling below 64 K, minor deviations can be seen for the ab-plane, especially between 70 K and 130 K. The effective magnetic Grüneisen parameter for the c axis is γ c,mag,eff = 1.6 • 10 −6 mol/J and γ ab,mag,eff varies from −6 • 10 −7 mol/J to −1.1 • 10 −6 mol/J between 120 K and 30 K. With κ = 0.071/GPa as before this yields large magnetic Grüneisen factors γ c,mag = 21 and γ ab,mag = 12...23. These values are of the same magnitude as other magnetic Grüneisen factors, e.g., γ mag ≈ −18 for α−Mn [36]. A part of the deviations around T C stems from the fact that the specific heat was measured by a relaxation method and thus averages over a temperature range, whereas the thermal expansion data is measured closer to thermal equilibrium, with a warming rate of 0.3 K/min.…”

On the third-generation Calphad databases: An updated description of Mn

“…u D , K method [12] 410 heat capacity measurements [13] 343.5 [14] 348 [15] 417 [16] 392 [20] 415 [17] 409 [43] 350 thermal expansion measurements [22] 380 AE 20 [26] 485 elastic moduli measurements [31] 438, T > 95 K neutron diffraction studies 536, T < 95 K [44] 370 thermal expansion and heat capacity measurement temperature of a-Mn was selected equal to 460 K as the initial value for this optimization, as proposed by Weiss and Tauer [8].…”