Effect of sintering time on the structural and magnetocaloric properties of Mn-Fe-P-Si-Ge-B alloys prepared by spark plasma sintering

Abstract

Spark plasma sintering (SPS) has some advantages for preparing multifunctional materials, such as fast heating rate, short sintering time, and high compactness of products. In this work, we reported the effect of sintering time on the structural and magnetocaloric properties of Mn1.15Fe0.85P0.65Si0.13Ge0.2B0.02 prepared by SPS. The crystalline structure, microstructure and composition were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The results indicated that all the alloys crystallized in the hexagonal structure with a space group of P6 − 2m. A secondary phase of (Mn,Fe)3(Si,Ge) was not found in SEM but in TEM measurement. Transition temperature and isothermal entropy change were determined from thermal magnetization data measured in different constant magnetic fields. The results showed that the alloys undergo first-order phase transitions at transition temperatures between 248.8 K and 281.9 K. The maximum isothermal entropy change was found in the alloy sintered for 15 min, being 15.6 J ⋅ kg−1 ⋅ K−1 for a magnetic field change of 3 T. It indicated that no less than 15 min sintering time was required to prepare the alloy with good homogeneousness and large magnetocaloric effect. Consequently, SPS is an effective method for synthesizing the Fe2P-type alloys and the resultant alloys are promising magnetocaloric materials for magnetic refrigeration near room temperature.