We use combine high resolution neutron diffraction (HRPD) with density functional theory (DFT) to investigate the exchange striction at the Curie temperature (TC) of Fe2P and to examine the effect of boron and carbon doping on the P site. We find a s
ignificant contraction of the basal plane on heating through TC with a simultaneous increase of the c-axis that results in a small overall volume change of ~0.01%. At the magnetic transition the FeI-FeI distance drops significantly and becomes shorter than FeI-FeII . The shortest metal-metalloid (FeI-PI) distance also decreases sharply. Our DFT model reveals the importance of the latter as this structural change causes a redistribution of the FeI moment along the c-axis (Fe-P chain). We are able to understand the site preference of the dopants, the effect of which can be linked to the increased moment on the FeI-site, brought about by strong magneto-elasticity and changes in the electronic band structure.
We here show by first principles theory that it is possible to achieve a structural and magnetic phase transition in common steel alloys like Fe$_{85}$Cr$_{15}$, by alloying with Ni or Mn. The predicted phase transition is from the ferromagnetic body
centered cubic (bcc) phase to the paramagnetic face centered cubic (fcc) phase. The relatively high average magnetic moment of $sim1.4mu_{B}$/atom predicted at the transition suggests that stainless steel potentially can present a magnetocaloric effect strong enough to make these alloys good candidates for refrigeration applications operating at and around room temperature.
