Large and antiferromagnetic negative thermal expansion over a wide temperature zone in MnNiGe1-xPbx (0.04 ≤ x ≤ 0.2) alloys

MnM'X-based alloys, a typical type of magnetocaloric materials, recently start to attract new interest because of giant negative thermal expansion (NTE). However, the NTE is usually tied with strong ferromagnetism in those alloys, which limits their applications particularly in a magnetic environment. Here we report the tunable giant NTE behavior in MnNiGe(1-x)pb(x) alloys that exhibit weak magnetism. With increasing x, the NTE performance is firstly improved and then degraded, and optimized at x = 0.08 with an average coefficient of linear thermal expansion of -97 ppm/K between 170 K and 270 K. Because Pb substitution enlarges the Mn-Mn distance, the antiferromagnetic state is stabilized for 0.04 <= x <= 0.2. Consequently, the current alloys show a much lower magnetostriction than that of FM MnM'X-based counterparts, suggesting their potential applications in magnetic fields. (C) 2019 Elsevier B.V. All rights reserved.