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

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-raymagnetic 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.