Thermal Expansion and Elastic Properties of Mn–Ge–Fe Alloys

Abstract

Young’s modulus, the thermal expansion and the magnetization at 120–700 K and the crystal structure at room temperature were investigated for annealed Mn–Ge–Fe alloys with various crystal structures such as β+γ, γ, γ+ε and ε phases. Young’s modulus vs temperature curves of the ternary alloys consisting of β+γ and γ phases show a reversible change at a heating and cooling speed of about 27.8×10⁻³ K/s, and have distinct minima and maxima, corresponding to the Néel point of the γ phase T_N(γ) and the β\ ightleftarrowsγ reversible phase transformation point T_t below about 10 at% iron, and the alloys containing iron more than 10 at% show only the T_N(γ). The Elinvar characteristic appears around the temperature which corresponds to a minimum or a maximum of Young’s modulus vs temperature curves. However, the Young’s modulus of the ternary alloys consisting of the γ+ε and ε phases shows a minimum point of T_N(ε) or T_N(γ), and the Elinvar characteristic around these points becomes rapidly less pronounced with increasing iron content.
The composition range of the Mn–Ge–Fe alloys whose temperature coefficients of Young’s modulus are about zero or −20×10⁻⁵ is relatively narrow with iron concentration, and it widens mostly at the composition of Fe-70 at%Mn. This composition range has no relation to that of the Fe–Mn–Ge ternary alloys reported previously.