Understanding the effect of foreign atoms occupation on the metamagnetic behaviors in MnCoSi-based alloys: taking Pt-doping as an example.

Present research on TiNiSi-type MnCoSi-based alloys focuses on finding a suitable doping element to effectively reduce the critical magnetic field ( μ 0 H cri ) required to induce a metamagnetic transition. This paper provides a guide to achieve this goal through an experimental investigation of Mn 1- x Pt x CoSi and MnCo 1- x Pt x Si alloys. In Mn 1- x Pt x CoSi, as x increases, μ 0 H cri at room temperature decreases, while in MnCo 1- x Pt x Si, it increases. This phenomenon can be attributed to the fact that larger Pt atoms prefer Co sites over Mn sites, as predicted by our density-functional theory. Consequently, in Mn 1- x Pt x CoSi, larger Co atoms are extruded into the Mn atoms chain, increasing the nearest Mn-Mn distance and resulting in a reduced μ 0 H cri . This finding suggests that transition-metal atoms with more valence electrons preferably occupy the Co site, while those with fewer valence electrons preferably occupy the Mn site. Adhering to this rule, one can easily obtain a low μ 0 H cri and large magnetostrain under a low magnetic field by selecting a suitable foreign element and chemical formula, as demonstrated by the Mn 1- x Pt x CoSi alloy.