Chapter10Magnetismofmatter§1Magneticmediumanditsclassification§2MagnetizationMagneticfieldintensity§3Ferromagneticsubstance§4Example§1Magneticmediumanditsclassification1Magneticmedium

Magneticmedium

磁介質(zhì)在磁場(chǎng)作用下發(fā)生變化，并能反過(guò)來(lái)影響磁場(chǎng)的物質(zhì)(2)TheMagnetizationofmagneticmedium:磁介質(zhì)的磁化磁介質(zhì)在磁場(chǎng)作用下的變化稱為磁化2TheclassificationofmagneticmediumRelativepermeability相對(duì)磁導(dǎo)率Inmedium:各種物質(zhì)都具有一定的磁性，都能對(duì)磁場(chǎng)產(chǎn)生影響，因此一切物質(zhì)都可以認(rèn)為是磁介質(zhì)。(2)Paramagneticmedium順磁質(zhì)

manganese、chrome、oxygenetc.TheBinmediumislargerthaninvacuum.(3)Ferromagneticmedium鐵磁質(zhì)iron、cobalt、nickeletc.TheBinmediumismorelaregerthaninvacuum.

Diamagneticmedium抗磁質(zhì)copper、plumbum、hydrogenetc.TheBinmediumislessthaninvacuum.Typicallyrdiffersfromunitybyonlyafewpartsin105(2)Additionalmagneticmoment附加磁矩Inanexternalmagneticinduction,theeveryelectronofmoleculeexperiencesforcewhichiscalledLorentzforce.電子的運(yùn)動(dòng)狀態(tài)發(fā)生改變。這時(shí)，每個(gè)電子的運(yùn)動(dòng)，除了自旋運(yùn)動(dòng)和繞核運(yùn)動(dòng)之外，還要附加一個(gè)以外磁場(chǎng)為軸線的轉(zhuǎn)動(dòng)，稱為電子的進(jìn)動(dòng)—theprecessionalmotionofelectron.無(wú)外磁場(chǎng)時(shí)，分子磁矩的排列雜亂無(wú)章；Inanexternalmagneticinduction,molecularmagneticmomentexperiencestorquesItshowsthatthemagneticmomenttendstoorientitselfparalleltothefield分子磁矩沿外磁場(chǎng)方向排列------順磁性paramagnetism其方向總是與外磁場(chǎng)相反—抗磁性diamagnetism用電磁感應(yīng)現(xiàn)象可以說(shuō)明附加磁矩方向與外磁場(chǎng)方向相反：Ifthefluxthroughacircuitchanges,anelectromotiveforceisinducedaroundit.Thepolarityoftheinducedemfissuchastoopposethechangethatcausedit.Theinducedcurrentalwaysflowstocreateamagneticfieldthatoppositethechangeinfluxthroughthecircuit.UsingtheLorentzforceofelectronexperiencedthediamagnetismcanbeexplainedtoo:根據(jù)電子受力方向判斷電子進(jìn)動(dòng)形成的電流流向，從而確定對(duì)應(yīng)的附加磁矩的方向Themotionofelectronformsadditionalmagneticmoment電子的進(jìn)動(dòng)，形成附加磁矩2MagnetizationandMagnetizationcurrent單位體積內(nèi)分子磁矩或附加磁矩的矢量和。表征介質(zhì)的磁化程度Paramagneticmedium：分子磁矩起主要作用Diamagneticmedium：附加磁矩起作用(1)Magnetization

(2)Magnetizationcurrent磁化電流由于磁化而在磁介質(zhì)的邊緣形成的環(huán)形電流Longsolenoid：TherelationshipbetweenmagnetizationcurrentandmagnetizationThelineintegralofmagneticfieldintensityalongaclosedpathLisequaltothesumofconductingcurrentthroughL.Magneticfieldintensityhasnothingtodowithmagnetizationcurrent.magneticfieldintensity磁場(chǎng)強(qiáng)度Amperecircuitaltheoreminmedium:5TherelationshipbetweenBandHExperimentshow：Paramagneticmedium：Diamagneticmedium：Invacuum：Inmedium：§3Ferromagneticsubstance鐵磁質(zhì)Experimentsexpress:Thecharacteristicsofferromagneticsasfollows:（1）

r>>1Forhigh-permeabilitysubstance,r

canbeashighas106Pureiron純鐵：（2）非線性關(guān)系r

isnotaconstant.（3）thephenomenonofhysteresis磁滯現(xiàn)象

B的變化落后H的變化（4）Curiepoint居里點(diǎn)鐵磁質(zhì)轉(zhuǎn)化為順磁質(zhì)B

isnotasingle-valuedfunctionofH.2TheclassificationofferromagneticsubstanceAccordingtocoerciveforceferromagneticsubstancecanbeclassifiedastwokinds:(1)Softmagneticmaterials軟磁材料：asmallercoerciveforce矯頑力小矯頑力小，意味著磁滯回線狹長(zhǎng)，它所包圍的面積小，磁滯損耗小，適合于在交變磁場(chǎng)中應(yīng)用：變壓器，鐵芯(2)Hardmagneticmaterials硬磁材料：alargercoerciveforce矯頑力大矯頑力大，意味著磁化后剩余磁感應(yīng)強(qiáng)度很大，稱為永磁鐵permanentmagnet或永磁體permanentmagnetmaterial：磁化后撤去外磁場(chǎng)而仍能長(zhǎng)期保持較久磁性的物質(zhì)，電表，揚(yáng)聲器和錄音機(jī)等都離不開(kāi)永磁體。碳鋼，鎢鋼，鉻鋼等各種合金3Magnetizationmechanismofferromagnetics鐵磁質(zhì)的磁化機(jī)理鐵磁質(zhì)的磁性來(lái)源于電子的自旋磁矩。無(wú)外磁場(chǎng)時(shí)，鐵磁質(zhì)中電子的自旋磁矩可以在小范圍內(nèi)自發(fā)地排列起來(lái)，形成一個(gè)個(gè)小的自發(fā)磁化區(qū)—Magneticdomain磁疇。由于熱運(yùn)動(dòng)，各磁疇的磁化方向不同，因而在宏觀上對(duì)外不顯磁性。當(dāng)鐵磁質(zhì)受到外磁場(chǎng)作用時(shí)，它將通過(guò)以下兩種方式實(shí)現(xiàn)磁化：外場(chǎng)較弱時(shí)，磁化方向與外場(chǎng)相近或相同的那些磁疇的體積將逐漸增大（疇壁位移）；外場(chǎng)較強(qiáng)時(shí)，每個(gè)磁疇的自發(fā)磁化方向?qū)⒆鳛橐粋€(gè)整體，在不同程度上轉(zhuǎn)向外磁場(chǎng)方向；當(dāng)所有磁疇都沿外磁場(chǎng)方向排列時(shí)，磁化達(dá)到飽和。Magneticdomain磁疇Ex1如圖所示，相對(duì)磁導(dǎo)率(relativepermeability)為r1的無(wú)限長(zhǎng)磁介質(zhì)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(zhì)圓柱的外面有半徑為R2的無(wú)限長(zhǎng)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(duì)磁導(dǎo)率為r2(>r1)的均勻磁介質(zhì)，圓柱面外為真空。試求B和H的分布。（1）r<R1：（2）R