title: Tensile strain-induced softening of iron at high temperature.
abstract: In weakly ferromagnetic materials, already small changes in the atomic configuration triggered by temperature or chemistry can alter the magnetic interactions responsible for the non-random atomic-spin orientation. Different magnetic states, in turn, can give rise to substantially different macroscopic properties. A classical example is iron, which exhibits a great variety of properties as one gradually removes the magnetic long-range order by raising the temperature towards its Curie point of  TC°= 1043 K. Using first-principles theory, here we demonstrate that uniaxial tensile strain can also destabilise the magnetic order in iron and eventually lead to a ferromagnetic to paramagnetic transition at temperatures far below TC°. In consequence, the intrinsic strength of the ideal single-crystal body-centred cubic iron dramatically weakens above a critical temperature of ~500 K. The discovered strain-induced magneto-mechanical softening provides a plausible atomic-level mechanism behind the observed drop of the measured strength of Fe whiskers around 300-500 K. Alloying additions which have the capability to partially restore the magnetic order in the strained Fe lattice, push the critical temperature for the strength-softening scenario towards the magnetic transition temperature of the undeformed lattice. This can result in a surprisingly large alloying-driven strengthening effect at high temperature as illustrated here in the case of Fe-Co alloy.
authors.affiliation: Department of Materials Science and Engineering, KTH - Royal Institute of Technology, 10044, Stockholm, Sweden.
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Materials Science and Engineering, KTH - Royal Institute of Technology, 10044, Stockholm, Sweden.
authors.forename: Stephan
authors.initials: S
authors.lastname: Schönecker
authors.affiliation: Department of Theoretical Physics, Budapest University of Technology and Economics, Budafoki út 8., HU-1111, Budapest, Hungary.
authors.forename: Eszter
authors.initials: E
authors.lastname: Simon
authors.affiliation: Department of Materials and Nano Physics, KTH Royal Institute of Technology, Electrum 229, SE-16440, Kista, Sweden.
authors.forename: Lars
authors.initials: L
authors.lastname: Bergqvist
authors.affiliation: Department of Materials Science and Engineering, KTH - Royal Institute of Technology, 10044, Stockholm, Sweden.|Center of Microstructure Science, Frontier Institute of Science and Technology, Xi'an Jiaotong University, 710054, Xi'an, China.
authors.forename: Hualei
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Theoretical Physics, Budapest University of Technology and Economics, Budafoki út 8., HU-1111, Budapest, Hungary.|MTA-BME Condensed Matter Research Group, Budafoki út 8., HU-1111, Budapest, Hungary.
authors.forename: László
authors.initials: L
authors.lastname: Szunyogh
authors.affiliation: Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Dalian University of Technology), Ministry of Education, 116024, Dalian, China.
authors.forename: Jijun
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Department of Materials Science and Engineering, KTH - Royal Institute of Technology, 10044, Stockholm, Sweden.|Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, SE-75120, Uppsala, Sweden.
authors.forename: Börje
authors.initials: B
authors.lastname: Johansson
authors.affiliation: Department of Materials Science and Engineering, KTH - Royal Institute of Technology, 10044, Stockholm, Sweden.|Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, SE-75120, Uppsala, Sweden.|Research Institute for Solid State Physics and Optics, Wigner Research Center for Physics, P.O. Box 49, HU-1525, Budapest, Hungary.
authors.forename: Levente
authors.initials: L
authors.lastname: Vitos