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Magnetic And Properties And Magnetocaloric Effects Mn(FeCo)GeB_y Compounds

Posted on:2012-03-05Degree:MasterType:Thesis
Country:ChinaCandidate:Y H WangFull Text:PDF
GTID:2120330335974718Subject:Condensed matter physics
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It needs a plenty of refrigeration technology that is much more convenient in the modern world. It's main technology is conventional vapor compression refrigeration. but the efficiency of gasfication and liquefaction in this technology is low, Freon produced by conventional vapor compression refrigeration destroys ozonosphere and imperil our environment.Recnrtly, magnetic refrigeration through magnetism thermal reaction has a prosperous development, which is regarded as magnetic refrigeration for room-temperature application. a series of compound formed by Mn (FeCo) Ge are the latest and potential magnetic refrigeration material. The study on manufacture technics, magnetic property magnetism. thermal reaction,structure phase. Is a fat lot.The magnetic properties and magnetocaloric effect of MnFe1.2Co0.8GeBy (y= 0.00,0.05,0.10,0.15,0.20), and MnFe,.2Co0.8GeBx (x=0.00,0.03,0.05, 0.07,0.10,) were separately investigated. The study on manufacture technics, magnetic property magnetism thermal reaction,structure phase.The Mn(FeCo)GeBx series compounds are a potential magnetic-refrigeration material in recent years. In First chapter, We study the development of magnetic refrigerators. In Second chapter, We study the theoretical aspects. In third chapter, We study the Experimental techniques. In fourth chapter,fifth chapter of the paper, the manufacture technics, the magnetic properties and magnetocaloric effect of MnFe1.2Co0.8GeBy (y= 0.00,0.05,0.10, 0.15,0.20), and MnFe1.2Co0.8GeBx (x=0.00,0.03,0.05,0.07,0.10,) and MnCoGeBo.o.3 were separately investigated.In the fourth chapter,we use planetary machine to make Mn (Fe0.2Co08) GeBy(y=0,0.05,0.1,0.15,0.2) under Ar gas atmosphere of 100-200 mbar, and the ampoules undergo a heat treatment process in order to obtain the expected crystalline microstructure and properties,which is simple and convenient. The also has disadvantage. it will have sample bonding and be difficult to take down sample in the ball-milling instrument,which will affect the stability of sample..we actualize adjustability of curie temperature of Mn (Fe0.2Co0.8) GeBy by adding a few interstitial atoms B. with adding the interstitial atoms B, curie temperature increased from256k to 298k, which decreased the magnetic-entropy change from 1.47J/kgK to1.32J/kgK. The thermal hysteresis of Mn (Fe0.2Co0.8) GeBy(y=0,0.05,0.1,0.15,0.2) is quite little with overlooking the magnetic measure error,which is fit to reversible thermal circulation without thermal hysteresis. In the fifth chapter,we achieved the a series of MnFe0.2Co0.8GeBx (x=0,0.03,0.05,0.07,0.1) using Metallurgy. At same time, we added 5% more atoms of Mn to recuperate its lose to ensure the accordance between academic matching and experimental results. The series of MnFeo.2Coo.8GeBx (x=0,0.03,0.05,0.07,0.1) have two different phases which are main hexagonal Ni2In-type phase and subsidiary orthorhombic TiNiSi-type phase. The crystal lattice a and c,crystal volume and crystal aberrant degree will decrease with the adding the atoms B. the curie temperature of a series of MnFe0.2Co0.8GeBx (x=0,0.03,0.05,0.07,0.1) will increase from 288k to 302k,which could achieve the most magnetic-entropy change with 3.46J/KGK at Tc=298K and also actualized the modulation of curie temperature under room temperature. Thermal hysteresis of second-order phase transition material of MnFe0.2Co0.8GeBx (x=0,0.03,0.05,0.07,0.1) is nearly zero,which is most fit to reversible thermal circulation on magnetic refrigeration.
Keywords/Search Tags:Planetary mill, transition-metal compound, magnetic-entropy change, magnetocaloric effect
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