Moment evolution across the ferromagnetic phase transition of giant magnetocaloric (Mn,Fe)2(P,Si,B) compounds

Abstract

A strong electronic reconstruction resulting in a quenching of the Fe magnetic moments has recently been predicted to be at the origin of the giant magnetocaloric effect displayed by Fe2P-based materials. To verify this scenario, x-ray magnetic circular dichroism experiments have been carried out at the L edges of Mn and Fe for two typical compositions of the (Mn,Fe)2(P,Si,B) system. The dichroic absorption spectra of Mn and Fe have been measured in the vicinity of the first-order ferromagnetic transition. The experimental spectra are compared with first-principles calculations and charge-transfer multiplet simulations in order to derive the magnetic moments. Even though signatures of a metamagnetic behavior are observed either as a function of the temperature or the magnetic field, the similarity of the Mn and Fe moment evolution suggests that the quenching of the Fe moment is weaker than previously predicted.