Structure And Magnetic Properties Of （Mn,Fe）₂（P,X）（X=Si,Ge） Compounds By Transition Metal Doping

Refrigeration technology is an indispensable technology in industrial production and people’s life,which provides great convenience for daily life.With the rapid development of society,people’s awareness of environmental protection is increasing,and science is also developing towards the direction of energy conservation and environmental protection.The refrigerant used in traditional gas compression refrigeration will produce pollutants and seriously destroy the earth’s ozone layer,which is one of the main causes of the greenhouse effect.Magnetic refrigeration technology because of its high efficiency and energy saving,no environmental pollution,stability and reliability,no noise and no vibration and other characteristics,has become an important direction of refrigeration technology development in the future.In this paper,the structure and magnetic properties of Mn_1.28Fe_0.67P_0.44Si_0.56 compounds and Mn Fe_1-xZ_xP_0.77Ge_0.23（Z=V,Cr,Ru）compounds were studied.1.The Mn_1.28Fe_0.67P_0.44Si_0.56 compound was prepared by high-energy ball milling and two heat treatment processes,quenching and natural cooling.X ray diffraction results show that the quenched and naturally cooled samples have formed Fe₂P-type hexagonal structure,and the space group is P-62m.Magnetic measurements show that the Curie temperatures of the quenched and naturally cooled samples are about 270K and 303K,respectively.And the maximum isothermal magnetic entropy changes are9.34J·kg^-1K^-1and 9.24J·kg^-1K^-1,respectively.The X-ray absorption fine structure analysis results of the Mn and Fe K edges are in agreement with the X ray diffraction results within the error range.The analysis of temperature variable X ray absorption spectroscopy shows that with the increase of temperature,the Fe-Fe distances atoms on the ab plane undergoes obvious changes.When the temperature is beyond the Curie temperature the first nearest neighbor distances between Fe atoms will change from 2.73（?）to 2.66（?）.The second nearest neighbor distances between Fe atoms will change from 4.07（?）to 4.04（?）.It shows that the magneto elastic change occurs near the Curie temperature.2.Mn Fe_1-xZ_xP_0.77Ge_0.23（x=0.05,0.06,0.08,0.10,0.15;Z=V,Cr）compounds were prepared by high-energy ball milling.X ray diffraction results show that the samples have formed Fe₂P-type hexagonal structure,and the space group is P-62m.Magnetic measurements show that the Curie temperature and the maximum isothermal magnetic entropy of compounds decreased with the increasing of the dopant V,Cr elements.The Curie temperature of the Mn Fe_0.95V_0.5P_0.77Ge_0.23 and Mn Fe_0.95Cr_0.5P_0.77Ge_0.23compound is 296 K and 332 K,respectively.And the maximum isothermal magnetic entropy change is 11J·kg^-1K^-1and 4.5J·kg^-1K^-1,respectively.The X ray absorption fine structure analysis of the Mn,Fe and Ge K edges shows that Mn atoms occupy 3g site,Fe atoms occupy 3f site,and Ge atoms occupy 2c site.The results are in agreement with the X ray diffraction results within the error range.3.Mn Fe_1-xRu_xP_0.77Ge_0.23（x=0.15,0.20,0.25,0.30,0.35）compounds were prepared by high-energy ball milling and two heat treatment processes,quenching and natural cooling.X ray diffraction results show that the samples have formed Fe₂P-type hexagonal structure,and the space group is P-62m.The scanning electron microscope results show that compounds formed uniform and stable phase and the doped elements were evenly distributed throughout the phase.Magnetic measurements showed that the Curie temperature and the maximum isothermal magnetic entropy of compounds decreased with the increasing of the dopant Ru element.The Curie temperatures of the naturally cooled and quenched Mn Fe_0.85Ru_0.15P_0.77Ge_0.23 compounds are 330K and 323K,respectively and the maximum isothermal magnetic entropy changes are 9.59J·kg^-1K^-1 and12.35J·kg^-1K^-1,respectively.Quenching will reduce the Curie temperature of the compound and increase the isothermal magnetic entropy change.