Negative Thermal Expansion of Ni-Doped MnCoGe at Room-Temperature Magnetic Tuning

Compounds that exhibit the unique behavior of negative thermal expansion (NTE) - the physical property of contraction of the lattice parameters on warming - can be applied widely in modern technologies. Consequently, the search for and design of an NTE material with operational and controllable qualities at room temperature are important topics in both physics and materials science. In this work, we demonstrate a new route to achieve magnetic manipulation of a giant NTE in (Mn 0.95 Ni 0.05 )CoGe via strong magnetostructural (MS) coupling around room temperature (∼275 to ∼345 K). The MS coupling is realized through the weak bonding between the nonmagnetic CoGe-network and the magnetic Mn-sublattice. Application of a magnetic field changes the NTE in (Mn 0.95 Ni 0.05 )CoGe significantly: in particular, a change of ΔL/L along the a axis of absolute value 15290(60) x 10 -6 - equivalent to a -31% reduction in NTE - is obtained at 295 K in response to a magnetic field of 8 T.