Study On The Magnetism,Magnetocaloric Properties And Magnetocrystalline Anisotropy Of Fe₂P-Based Compounds

It is known that the binary Fe₂P compound has a hexagonal crystal structure?space group P-62m?.P atoms occupy 1b and 2c two different crystal sites,and Fe atoms occupy two different crystal sites,namely 3g high magnetic moment site and 3f low magnetic moment site,respectively.It exhibits large magnetocrystalline anisotropy,and an easy axis of the c-axis.Binary Fe₂P compound has been considered as one of the candidates of permanent magnet materials.However,its Curie temperature is too low?about 217 K?to practical application.In this thesis,the synthesis,crystal structure,magnetic properties,magnetocaloric and magnetocrystalline anisotropy properties were studied for Fe_1.90(P_1-xSi_x)?x=0.10,0.20,0.25,0.27?ternary series compounds,Mn_xFe_2-xP_0.5Si_0.5?x=0.1,0.3,0.5,0.7,0.9,1.0?and Mn_xFe_2-xP_0.73Ge_0.27?x=0.1,0.3,0.5,0.7,1.0?quaternary series of compounds.The innovation of this work is that:series of polycrystalline compounds have been synthesized by using mechanical alloying technique.The compounds could meet the requirements of:the high magnetic moment and large magnetocaloric effects as for magnetic refrigerant;the high Curie temperature and strong magnetocrystalline anisotropy as for hard magnetic materials.Moreover,the magnetocrystalline anisotropy of polycrystalline compound has been studied by using orientation bonding technology.The high Curie temperature allows to achieve the orientation bonding at room temperature.It makes it easier to study the magnetocrystalline anisotropy by comparing the X-ray diffraction pattern and magnetic hysteresis loops before and after magnetic orientation.The article content could be divided into the following sections:The first chapter introduces the research background and basic principles of magnetic refrigeration,the overview of Fe₂P-based magnetic refrigerant and their magnetocrystalline anisotropy properties.At the same time,it introduces the ideas of topic selection and research contents,purpose and significance.The second chapter introduces the experimental instruments and experimental methods used in this thesis.The third chapter studies the magnetism,magnetocaloric effect and magnetocrystalline anisotropy of the ternary compounds of Fe_1.90(P_1-xSi_x)?x=0.10,0.20,0.25,0.27?.The results show that the substitution of Si for P has little effect on the magnetocaloric effect of the compound,but can increase the Curie temperature to 514 K for the compound with x=0.27,and meanwhile,maintain strong magnetocrystalline anisotropy.The XRD pattern showed that the structure of the compound is of Fe₂P-type hexagonal structure,with a space group of P-62m.As for the magnetic field orientated compound,the 002 peak intensity is enhanced,indicates the easy axis of the compound is the c-axis.It can be seen from the magnetization curve that compounds are easier to reach saturation magnetization when magnetizing along easy axis.Comparing with Fe₂P,the compound with small amount of Si doping not only show an increased Curie temperature,but also appropriate amounts of remanence and coercivity.In chapter 4,quaternary compounds of Mn_xFe_1.9-x.9-x P_0.5Si_0.5?x=0.1,0.3,0.5,0.7,0.9,1.0?and Mn_xFe_2-xP_0.73Ge_0.27?x=0.1,0.3,0.5,0.7,1.0?have been synthesized.All the two series of compounds crystallize in Fe₂P-type hexagonal structure,with a space group of P-62m.The studies show that after magnetic field orientation,the easy axis canted from a-b plane to c axis with decreasing of Mn content for all the Mn_x Fe_1.9-xP_0.5Si_0.5?x=0.1,0.3,0.5,0.7,0.9,1.0?and Mn_xFe_2-xP_0.73Ge_0.27?x=0.1,0.3,0.5,0.7,1.0?compounds.The hysteresis loop shows that the magnetocrystalline anisotropy is stronger when the easy axis is along the c-axis.Meanwhile,the maximum magnetic entropy of Mn_1.0Fe_0.9P_0.5Si_0.5compound at 3 T is about 23.6 J/?kg·K?.All these features indicate important reference value for studying the application of that the Mn-Fe-P-Si/Ge compounds are promising candidates for both magnetic refrigeration and permanent magnet applications.