Large spontaneous magnetostrictive softening below the Curie temperature of Fe3C Invar particles

Abstract

Fe 3 C incorporates only Fe as a metallic element and is an Invar material with valence electron concentration 8.67. We have studied the equation of state up to 20GPa of Fe3C particles (d∼40nm) below and above the Curie temperature (room temperature and 550K, respectively) to search for a softening associated with a magnetovolume instabilities characteristic of Invar-type material. The isothermal bulk modulus of Fe3C particles at room temperature was found to be about 13% smaller than that of the value at 550K. This difference is comparable with the relative difference in the bulk modulus of Fe65Ni35 Invar in a similar temperature range around the Curie temperature.