Electronic states of magnetic refrigerator materials Mn _0.9Fe_1.1P_0.55As_0.45 using soft x-ray magnetic circular dichroism

The system of MnFeP_1-xAs_x is a candidate of a magnetic refrigerator material. We have investigated the temperature (T)- and magnetic field (H)-dependence of the magnetic properties of the Mn and Fe ions for Mn_0.9Fe_1.1P_0.55As_0.45 using a soft X-ray magnetic circular dichroism (XMCD) in the regions of the Mn and Fe L_2,3 absorption edges. In the ferromagnetic states, the magnetic moments of the Mn and Fe ions turn to the same direction. It is considered that the Mn ions are close to divalent (Mn²⁺) states and that the Fe ions are a mixture of trivalent (Fe³⁺) and divalent (Fe²⁺) states. However, we deduce that the ferromagnetic properties of the Fe ions are mainly derived from the Fe²⁺ states. Using the XMCD sum rules, we have found that the magnitude of the magnetic moment of the Mn ions is larger than that of the Fe ions. The paramagnetic to ferromagnetic transitions are clearly observed by the T- and H- dependent XMCD measurements. Scince the shapes of the spectra don't change in all experiment conditions, the electronic configurations of the Mn and Fe ions are not changed by the PM-FM transition.