Electronic And Magnetic Properties Of Phosphorus Across The First-Order Ferromagnetic Transition Of (Mn,Fe)(2)(P,Si,B) Giant Magnetocaloric Materials

To study the evolution of the electronic states and magnetism of the metallic and metalloid atoms across the first-order ferromagnetic transition of (Mn,Fe)(2)(P,Si,B) compounds, x-ray absorption (XAS) and magnetic circular dichroism (XMCD) spectra were recorded at the K edges of P, Mn, and Fe. Surprisingly, while the Fe and Mn XAS spectra do not show pronounced changes, the K-edge XAS of P is strongly modified across the ferromagnetic transition and is a fingerprint of electronic structure changes at the phase transition. The evolution of the 3p electronic states of phosphorus is linked to changes in metal-metalloid bonding. The amplitude of this effect is correlated to the discontinuity in interatomic distances at the transition and progressively disappears with boron substitution. Moreover, it is found that the P atoms carry a finite magnetic moment in the ferromagnetic state in accordance with the results of band-structure calculations.