Tuning magnetocaloric effect by carbon interstitial phase in RE15Si9Cx (RE = Er, Ho) compounds for hydrogen liquefaction

Abstract

The manipulation of the magnetocaloric effect in rare-earth-based compounds through interstitial doping has attracted extensive research interest. While interstitials are known to regulate magnetic transition temperatures, their role in enhancing the magnetocaloric effect remains scarcely reported. Here, we demonstrate that interstitial carbon in RE15Si9Cx (RE = Er, Ho; x = 1, 2) compounds drives a transition from antiferromagnetic to ferromagnetic states, accompanied by a significant enhancement of the magnetocaloric effect. This improvement positions these compounds as promising candidates for hydrogen liquefaction applications. Theoretical calculations reveal that the interstitial carbon modifies both the exchange interactions and crystal field effects between adjacent magnetic ions, thereby inducing the observed magnetic transitions.