Study On The Performance Of Rare Earth-transition Metal-based And MnCoGe-base Magnetocaloric Materials

As the pivotal part of magnetic refrigeration technology,magnetocaloric materials have been the cutting-edge research topic in multidiscipline including materials science,condensed matter physics and solid-state chemistry during the recent decades.In this dissertation,multiple aspects concerning the exploration of novel magnetocaloric materials have been covered,ranging from theoretical interpretations of structure-property relationship of a magnetocaloric compound and exploration of exotic normal and rotating magnetocaloric effects in intermetallic compounds to fabrication of composite magnetocaloric materials with outstanding comprehensive performances.HoNiGa,as an antiferromagnetically ordered intermetallic compound,is revealed to exhibit a large normal magnetocaloric effect due to a field-induced antiferromagnetic-ferromagnetic metamagnetic transition.The maximum of magnetic entropy change is calculated to be 22 J/kg K with a magnetic field change of 5 T.The magnetic transition of HoNiGa is found to be reversible,which will beneficial to practical application.Textured Tb3NiGe2 material shows an exotic rotating magnetocaloric effect.The rotating magnetic entropy change and adiabatic temperature change are 2.91 J/kg K and 1.6 K with a magnetic field of 2 T.The mathematical equivalence of diverse calculation methods is also proved.Fabricating magnetocaloric composite materials will pave the way for a commercialized magnetic refrigerator as most of the promising magnetocaloric compounds are intrinsically brittle and can not be used directly as magnetic refrigerants.The In-bonded La(Fe,Si),3 composite materials prepared in this dissertation display combined merits of large magnetic entropy change and adiabatic temperature change,ultrahigh thermal conductivity and stable performance after refrigeration cycles.Stemming from theoretical elucidations of crystal structure and chemical bondings in hexagonal MnCoGe,an experimental method to stabilize hexagonal MnCoGe structure is proposed by tuning valance electron counts and proved by experimental results.The method also leads to the discovery of a new intermetallic compound MnCoGe2/3As1/3.