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

TL;DR

This study investigates the magnetic moment evolution in (Mn,Fe)2(P,Si,B) compounds during the ferromagnetic phase transition, using X-ray magnetic circular dichroism to test predictions of electronic reconstruction effects.

Contribution

It provides experimental evidence on the magnetic moments of Mn and Fe, challenging previous predictions of strong Fe moment quenching in giant magnetocaloric materials.

Findings

Fe moments are less quenched than predicted

Mn and Fe moments show similar evolution during transition

Metamagnetic behavior observed in spectra

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 Fe2Pbased 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 element specific in the vicinity of the first-order ferromagnetic transition. The experimental spectra are compared with first-principle calculations and charge-transfer multiplet simulations in order to derive the magnetic moments. Even though signatures of a metamagnetic behaviour 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.