On the origins of Mn-dependent magnetic properties of LaFe11.5-xMnxSi1.5 compounds

Mn-doped La(Fe,Si)13 compounds have been demonstrated as excellent candidates for magnetic refrigeration applications. However, the origins of Mn-dependent magnetic properties are still unclear. Here, by employing density functional theory calculations and Monte Carlo simulations, the changes in magnetic moment, total magnetic exchange coupling constant Jtotal, atomic local environment, and Curie temperature TC of Mn-doped La(Fe,Si)13 compounds were investigated. Mn atoms were found to prefer 96i sites and anti-parallelly couple with Fe atoms. The reduction of total magnetic moments during Mn substitution originates from the decreasing magnetic moments of Fe and anti-ferromagnetic coupling between Mn and Fe. Moreover, Mn dopants lead to the decrease in Jtotal and TC, and the analysis of atomic local environment indicates that the weakening of Jtotal can be mainly attributed to the shrinkage of the intra-icosahedral bond between Fe-I and Fe-II. This work offers a theoretical comprehension of the fundamental magnetic properties of Mn-doped La(Fe,Si)13 compounds.