《E物質的磁性》PPT課件.ppt

Chapter 10 Magnetism of matter,1 Magnetic medium and its classification,2 Magnetization Magnetic field intensity,3 Ferromagnetic substance,4 Example,1 Magnetic medium and its classification,1 Magnetic medium,Magnetic medium 磁介質 在磁場作用下發(fā)生變化，并能反過來影響磁場的物質,(2) The Magnetization of magnetic medium :磁介質的磁化 磁介質在磁場作用下的變化稱為磁化,2 The classification of magnetic medium,Relative permeability 相對磁導率,In medium:,各種物質都具有一定的磁性，都能對磁場產生影響，因此一切物質都可以認為是磁介質。,(2) Paramagnetic medium 順磁質 manganese、chrome、oxygen etc.,The B in medium is larger than in vacuum.,(3) Ferromagnetic medium 鐵磁質 iron、cobalt、nickel etc.,The B in medium is more lareger than in vacuum.,Diamagnetic medium 抗磁質 copper、plumbum、hydrogen etc.,The B in medium is less than in vacuum.,Typically r differs from unity by only a few parts in 105,2 Magnetization 磁化強度 Magnetic field intensity 磁場強度,1 The Magnetization of magnetic medium,The motion of electron spin: 電子自旋運動： spin magnetic moment自旋磁矩 ； The motion of electron orbit:電子繞核運動： orbit magnetic moment 軌道磁矩；,Molecular magnetic moment 分子磁矩,固有磁矩： 所有電子的軌道磁矩和自旋磁矩的矢量和。,Molecular current：分子電流 分子磁矩用等效的圓電流表示。,(1) Molecular magnetic moment 分子磁矩,(2) Additional magnetic moment 附加磁矩,In an external magnetic induction, the every electron of molecule experiences force which is called Lorentz force. 電子的運動狀態(tài)發(fā)生改變。這時，每個電子的運動，除了自旋運動和繞核運動之外，還要附加一個以外磁場為軸線的轉動，稱為電子的進動 the precessional motion of electron.,無外磁場時，分子磁矩的排列雜亂無章； In an external magnetic induction, molecular magnetic moment experiences torques It shows that the magnetic moment tends to orient itself parallel to the field 分子磁矩沿外磁場方向排列-順磁性 paramagnetism,其方向總是與外磁場相反抗磁性 diamagnetism, 用電磁感應現象可以說明附加磁矩方向與外磁場方向相反： If the flux through a circuit changes, an electromotive force is induced around it. The polarity of the induced emf is such as to oppose the change that caused it. The induced current always flows to create a magnetic field that opposite the change in flux through the circuit. Using the Lorentz force of electron experienced the diamagnetism can be explained too: 根據電子受力方向判斷電子進動形成的電流流向，從而確定對應的附加磁矩的方向,The motion of electron forms additional magnetic moment 電子的進動，形成附加磁矩,2 Magnetization and Magnetization current,單位體積內分子磁矩或附加磁矩的矢量和。,表征介質的磁化程度,Paramagnetic medium：,分子磁矩起主要作用,Diamagnetic medium：,附加磁矩起作用,(1) Magnetization,(2) Magnetization current 磁化電流,由于磁化而在磁介質的邊緣形成的環(huán)形電流,The relationship between magnetization current and magnetization,3 Gausss law in medium,The total magnetic flux through a close surface is equal to zero.,4 Ampere circuital theorem in medium,Magnetization current,Conducting current,The line integral of magnetization along with random closed path is equal to the sum of magnetization current through L.,The line integral of magnetic field intensity along a closed path L is equal to the sum of conducting current through L.,Magnetic field intensity has nothing to do with magnetization current.,magnetic field intensity 磁場強度,Ampere circuital theorem in medium:,5 The relationship between B and H,Experiment show：,Paramagnetic medium：,Diamagnetic medium：,In vacuum：,In medium：,3 Ferromagnetic substance 鐵磁質,Experiments express: The characteristics of ferromagnetics as follows:,（1） r1 For high-permeability substance, r can be as high as 106,Pure iron 純鐵：,（2）,非線性關系,r is not a constant.,（3）the phenomenon of hysteresis 磁滯現象 B的變化落后H的變化,（4）Curie point 居里點 鐵磁質轉化為順磁質,B is not a single-valued function of H.,1 鐵磁質的磁化規(guī)律Hysteresis loop 磁滯回線,接測量儀表,在待測的磁性材料做成的圓環(huán)樣品上均勻地繞滿漆包導線，作為初級線圈，再在其上繞若干圓漆包導線作為次級線圈，接在回路中。,Hysteresis loop,Hc：coercive force 矯頑力,Br：remanent magnetic induction 剩余磁感應強度 剩磁,2 The classification of ferromagnetic substance,According to coercive force ferromagnetic substance can be classified as two kinds:,(1)Soft magnetic materials 軟磁材料： a smaller coercive force 矯頑力小 矯頑力小，意味著磁滯回線狹長，它所包圍的面積小，磁滯損耗小，適合于在交變磁場中應用：變壓器，鐵芯,(2) Hard magnetic materials 硬磁材料： a larger coercive force 矯頑力大 矯頑力大，意味著磁化后剩余磁感應強度很大，稱為永磁鐵permanent magnet 或永磁體 permanent magnet material ：磁化后撤去外磁場而仍能長期保持較久磁性的物質，電表，揚聲器和錄音機等都離不開永磁體。 碳鋼，鎢鋼，鉻鋼等各種合金,3 Magnetization mechanism of ferromagnetics 鐵磁質的磁化機理,鐵磁質的磁性來源于電子的自旋磁矩。無外磁場時，鐵磁質中電子的自旋磁矩可以在小范圍內自發(fā)地排列起來，形成一個個小的自發(fā)磁化區(qū)Magnetic domain磁疇。由于熱運動，各磁疇的磁化方向不同，因而在宏觀上對外不顯磁性。 當鐵磁質受到外磁場作用時，它將通過以下兩種方式實現磁化：外場較弱時，磁化方向與外場相近或相同的那些磁疇的體積將逐漸增大（疇壁位移）；外場較強時，每個磁疇的自發(fā)磁化方向將作為一個整體，在不同程度上轉向外磁場方向；當所有磁疇都沿外磁場方向排列時，磁化達到飽和。,Magnetic domain 磁疇,Ex 1 如圖所示，相對磁導率(relative permeability)為r1的無限長磁介質圓柱，半徑為R1，其中通以電流I，且電流沿橫截面均勻分布。在磁介質圓柱的外面有半徑為R2的無限長同軸圓柱面，該圓柱面上通有大小也為I但方向相反的電流。在圓柱面和圓柱體之間充滿相對磁導率為r2( r1) 的均勻磁介質，圓柱面外為真空。試求B和H的分布。,（1）rR1：,（2）R1 rR2：,（3）rR2：,