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

Abstract

Present research on TiNiSi-type MnCoSi-based alloys focuses on finding a suitable doping element to effectively reduce the critical magnetic field (μ0Hcri) required to induce a metamagnetic transition. This paper provides a guide to achieve this goal through an experimental investigation of Mn1-xPtxCoSi and MnCo1-xPtxSi alloys. In Mn1-xPtxCoSi, as x increases, μ0Hcri at room temperature decreases, while in MnCo1-xPtxSi, 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 Mn1-xPtxCoSi, larger Co atoms are extruded into the Mn atoms chain, increasing the nearest Mn-Mn distance and resulting in a reduced μ0Hcri. 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 μ0Hcri and large magnetostrain under a low magnetic field by selecting a suitable foreign element and chemical formula, as demonstrated by the Mn1-xPtxCoSi alloy.