《E物质的磁性》PPT课件.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 磁介质 在磁场作用下发生变化，并能反过来影响磁场的物质,(2) The Magnetization of magnetic medium :磁介质的磁化 磁介质在磁场作用下的变化称为磁化,2 The classification of magnetic medium,Relative permeability 相对磁导率,In medium:,各种物质都具有一定的磁性，都能对磁场产生影响，因此一切物质都可以认为是磁介质。,(2) Paramagnetic medium 顺磁质 manganese、chrome、oxygen etc.,The B in medium is larger than in vacuum.,(3) Ferromagnetic medium 铁磁质 iron、cobalt、nickel etc.,The B in medium is more lareger than in vacuum.,Diamagnetic medium 抗磁质 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 磁化强度 Magnetic field intensity 磁场强度,1 The Magnetization of magnetic medium,The motion of electron spin: 电子自旋运动： spin magnetic moment自旋磁矩 ； The motion of electron orbit:电子绕核运动： orbit magnetic moment 轨道磁矩；,Molecular magnetic moment 分子磁矩,固有磁矩： 所有电子的轨道磁矩和自旋磁矩的矢量和。,Molecular current：分子电流 分子磁矩用等效的圆电流表示。,(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. 电子的运动状态发生改变。这时，每个电子的运动，除了自旋运动和绕核运动之外，还要附加一个以外磁场为轴线的转动，称为电子的进动 the precessional motion of electron.,无外磁场时，分子磁矩的排列杂乱无章； In an external magnetic induction, molecular magnetic moment experiences torques It shows that the magnetic moment tends to orient itself parallel to the field 分子磁矩沿外磁场方向排列-顺磁性 paramagnetism,其方向总是与外磁场相反抗磁性 diamagnetism, 用电磁感应现象可以说明附加磁矩方向与外磁场方向相反： 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: 根据电子受力方向判断电子进动形成的电流流向，从而确定对应的附加磁矩的方向,The motion of electron forms additional magnetic moment 电子的进动，形成附加磁矩,2 Magnetization and Magnetization current,单位体积内分子磁矩或附加磁矩的矢量和。,表征介质的磁化程度,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 磁化电流,由于磁化而在磁介质的边缘形成的环形电流,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 磁场强度,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 铁磁质,Experiments express: The characteristics of ferromagnetics as follows:,（1） r1 For high-permeability substance, r can be as high as 106,Pure iron 纯铁：,（2）,非线性关系,r is not a constant.,（3）the phenomenon of hysteresis 磁滞现象 B的变化落后H的变化,（4）Curie point 居里点 铁磁质转化为顺磁质,B is not a single-valued function of H.,1 铁磁质的磁化规律Hysteresis loop 磁滞回线,接测量仪表,在待测的磁性材料做成的圆环样品上均匀地绕满漆包导线，作为初级线圈，再在其上绕若干圆漆包导线作为次级线圈，接在回路中。,Hysteresis loop,Hc：coercive force 矫顽力,Br：remanent magnetic induction 剩余磁感应强度 剩磁,2 The classification of ferromagnetic substance,According to coercive force ferromagnetic substance can be classified as two kinds:,(1)Soft magnetic materials 软磁材料： a smaller coercive force 矫顽力小 矫顽力小，意味着磁滞回线狭长，它所包围的面积小，磁滞损耗小，适合于在交变磁场中应用：变压器，铁芯,(2) Hard magnetic materials 硬磁材料： a larger coercive force 矫顽力大 矫顽力大，意味着磁化后剩余磁感应强度很大，称为永磁铁permanent magnet 或永磁体 permanent magnet material ：磁化后撤去外磁场而仍能长期保持较久磁性的物质，电表，扬声器和录音机等都离不开永磁体。 碳钢，钨钢，铬钢等各种合金,3 Magnetization mechanism of ferromagnetics 铁磁质的磁化机理,铁磁质的磁性来源于电子的自旋磁矩。无外磁场时，铁磁质中电子的自旋磁矩可以在小范围内自发地排列起来，形成一个个小的自发磁化区Magnetic domain磁畴。由于热运动，各磁畴的磁化方向不同，因而在宏观上对外不显磁性。 当铁磁质受到外磁场作用时，它将通过以下两种方式实现磁化：外场较弱时，磁化方向与外场相近或相同的那些磁畴的体积将逐渐增大（畴壁位移）；外场较强时，每个磁畴的自发磁化方向将作为一个整体，在不同程度上转向外磁场方向；当所有磁畴都沿外磁场方向排列时，磁化达到饱和。,Magnetic domain 磁畴,Ex 1 如图所示，相对磁导率(relative permeability)为r1的无限长磁介质圆柱，半径为R1，其中通以电流I，且电流沿横截面均匀分布。在磁介质圆柱的外面有半径为R2的无限长同轴圆柱面，该圆柱面上通有大小也为I但方向相反的电流。在圆柱面和圆柱体之间充满相对磁导率为r2( r1) 的均匀磁介质，圆柱面外为真空。试求B和H的分布。,（1）rR1：,（2）R1 rR2：,（3）rR2：,