Lecture1磁性物理和磁学基本概念

1、磁性材料：原理、工艺与应用磁性材料：原理、工艺与应用Magnetic Materials: Basic theory, Processing and ApplicationsLecture 1 磁学基本概念与磁性物理基础磁学基本概念与磁性物理基础磁性材料：原理、工艺与应用2OutlinenIntroduction to this coursenOrigin of MagnetismnVarious types of magnetismnVarious magnetic materialsnSummary磁性材料：原理、工艺与应用3Before start, some questionsnWha

2、t metals are magnetic?nSince Fe are magnetic metal, why does it not attract a small piece of iron?nPure iron is magnetic and some steel is not, Why?nFe, W, Mo, V, Nb are all b.c.c structured and have unpaired electrons, why is only Fe magnetic?nWhy do NdFeB magnets packed with Fe foil when posted?磁性

3、材料：原理、工艺与应用4A SurveyHave you ever studied -nFerromagnetism铁磁学?nMagnetism磁学?nElectromagnetism电磁学?nSolid Physics固体物理?nMaterials Physics材料物理?nGeneral Physics普通物理（大学物理）?磁性材料：原理、工艺与应用5About This CourseIt is not -nElectromagnetism电磁学!nMagnetism磁学!nMagnetic Physics磁性物理！It is nMagnetic Materials！We emphasiz

4、e theory, processing and application!磁性材料：原理、工艺与应用6Course Structure共32学时，含：n论文报告4学时n学术报告4学时n讨论2学时n讲授24学时内容： 磁性基础、软磁材料、硬磁材料、磁记录、磁致伸缩材料、磁性-物性相互作用、巨磁阻材料、吸波材料、磁性薄膜、磁性纳米结构、磁性材料最新进展磁性材料：原理、工艺与应用7What is your opinion about this course?nWhat do you want to learn?nHow to teach?Let me know by email!磁性材料：原理、工艺

5、与应用8All About Examn论文报告，70%；平时，30%。Topics for your report: Recent progress in advanced - 1. Nanocomposite Rare-earth permanent magnetic materials; 2. Nanocomposite soft magnetic materials; 3. perpendicular magnetic recording; 4. Magnetoelectric materials; 5. Magnetic thin films for microwave absorbe

6、r; 6. GMR materials; 7. One-dimension magnetic nanostructures; 8. Spintronics; 9. Magnetocaloric materials; 10. Magnetostriction materials.You can write your report in Chinese though use of English is encouraged !Note1)In formal journal paper style;2)Recent progress;3)No plagiarism allowed.磁性材料：原理、工

7、艺与应用9nTerm Magnet comes from the ancient Greek city of Magnesia, at which many natural magnets were found. nPliny the Elder (23-79 AD Roman) wrote of a hill near the river Indus that was made entirely of a stone that attracted iron.nKnown in China and Europe -800 BCLodestoneLets get start: A story 磁

8、性材料：原理、工艺与应用10LODESTONEnNow, we refer to these natural magnets as lodestones (also spelled loadstone; lode means to lead or to attract) which contain magnetite, a natural magnetic material Fe3O4.nWhen lightning strikes the earth it could create a magnetic field large enough to saturate the magnetiza

9、tion of lodestone .Typical current 1,000,000 Amp.Once in 1 10 million years磁性材料：原理、工艺与应用11Historyn Chinese as early as 121 AD knew that an iron rod which had been brought near one of these natural magnets would acquire and retain the magnetic propertyand that such a rod when suspended from a string

10、would align itself in a north-south direction.n Use of magnets to aid in navigation can be traced back to at least the 11th century.Basically, we knew the phenomenon existed andwe learned useful applications for it. We did not understand it.司南司南磁性材料：原理、工艺与应用12Electrified Amber attracts small objects

11、Lodestone attracts iron A Connection ?Hans Christian rsted ( 1777 1851) Oersteds Experimentn Danish scientist Hans Christian Oersted observed that a compass needle in the vicinity of a wire carrying electrical current was deflected!n a connection between electrical and magnetic phenomena shown.Oerst

12、eds experiment (1820)磁性材料：原理、工艺与应用13A quantitative relationship between a changing magnetic field and the electric field created by the changeMichael Faraday(1791-1867) Faraday: Effect of a changing magnetic fieldnIn 1831, Faraday discovered that a momentary current existed in a circuit, when the cu

13、rrent in a nearby circuit was started or stopped. nShortly thereafter, he discovered that motion of a magnet toward or away from a circuit could produce the same effect.磁性材料：原理、工艺与应用14Henrys work: a lesson!Joseph Henry (1797-1878)nJoseph Henry failed to publish what he had discovered 6-12 months bef

14、ore FaradaynHenry was always slow in publishing his results, and he was unaware of Faradays work. nToday Faraday is recognized as the discoverer of mutual inductance (the basis of transformers), while Henry is credited with the discovery of self-inductance.磁性材料：原理、工艺与应用15The connection is madeSUMMAR

15、Y: Oersted showed that magnetic effects could be produced by moving electrical charges; Faraday and Henry showed that electric currents could be produced by moving magnetsAll magnetic phenomena result from forces between electric charges in motion.磁性材料：原理、工艺与应用16Ampere: Molecular CurrentsAmpere firs

16、t suggested in 1820 that magnetic properties of matter were due to tiny atomic currents:nExistence of small molecular currents nEach atom/molecule would behave as a small permanent magnetnWould align in the presence of a magnetic fieldAndre Marie Ampere(1775-1836) 磁性材料：原理、工艺与应用17The magnetic field i

17、n space around an electric current is proportional to the electric current which serves as its source. Amperes LawFor any closed loop path, the sum of the length elements times the magnetic field in the direction of the length element is equal to the permeability times the electric current enclosed

18、in the loop.磁性材料：原理、工艺与应用18Do not forget themnrsted showed that magnetic effects could be produced by moving electrical charges; nFaraday and Henry showed that electric currents could be produced by moving magnets. All magnetic phenomena result from forces between electric charges in motion.nAmpere

19、first suggested in 1820 that magnetic properties of matter were due to tiny atomic currents.磁性材料：原理、工艺与应用19Top ten list: what we should have known about magnetism？1. There are North Poles and South Poles. 2. Like poles repel, unlike poles attract. 3. Magnetic forces attract only magnetic materials.

20、4. Magnetic forces act at a distance. 5. While magnetized, temporary magnets act like permanent magnets. 6. A coil of wire with an electric current flowing through it becomes a magnet. 7. Putting iron inside a current-carrying coil increases the strength of the electromagnet. 8. A changing magnetic

21、field induces an electric current in a conductor.9. A charged particle experiences no magnetic force when moving parallel to a magnetic field, but when it is moving perpendicular to the field it experiences a force perpendicular to both the field and the direction of motion. 10. A current-carrying w

22、ire in a perpendicular magnetic field experiences a force in a direction perpendicular to both the wire and the field.磁性材料：原理、工艺与应用20Origin of Magnetism of MatternAmpere: molecular currentsnModern physics: magnetic moments in atoms （“磁矩学说磁矩学说”或或“磁偶极矩学说磁偶极矩学说”） 1) unpaired electron spins mainly 2) th

23、e orbital motion of electrons within the material to a lesser extent磁性材料：原理、工艺与应用21n物理学原理：任何带电体的运动都必然在周围的空间产生磁场。n电动力学定律：一个环形电流具有一定的磁矩，它在磁场中行为像个磁性偶极子。设环形电流的强度为I（A），它所包围的面积为A（m2）,则该环流的磁矩为：m=I*A （A m2）n玻尔（Bohr）原子模型：原子内的电子在固定的轨道上绕原子核作旋转运动，同时还绕自身的轴线作自旋运动。前一种运动产生“轨道磁矩”，后一种运动产生“自旋磁矩”。n物质磁性来源的同一性：尽管宏观物质的磁性是

24、多种多样的，但这些磁性都来源于电子的运动。A(m2)I(A)mOrigin of Magnetism of Matter磁性材料：原理、工艺与应用22原子磁矩Macroscopic properties are the result of electron magnetic moments。Moments come from 2 sources: Orbital motion around a nucleus（轨道磁矩）与Spinning around an axis（自旋磁矩）。原子核磁矩比电子磁矩小3个数量级，一般情况下忽略不计。因此，原子磁矩主要来源于原子核外电子的。n 原子中的电子成对

25、地存在。这些成对电子的自旋磁矩和轨道磁矩方向相反而互相抵消，使原子中的电子总磁矩为零。 非磁原子。n 原子中的电子磁矩没有完全抵消使原子中电子的总磁矩（有时叫净磁矩，剩余磁矩）不为零。磁性原子。磁性材料：原理、工艺与应用23原子的总磁矩应是按照原子结构和量子原子的总磁矩应是按照原子结构和量子力学规律将原子中各个电子的轨道磁矩力学规律将原子中各个电子的轨道磁矩和自旋磁矩相加起来的合磁矩。和自旋磁矩相加起来的合磁矩。原子磁矩nThe net magnetic moment for an atom is the sum of the magnetic moments of constituent e

26、lectronsn Atoms with completely filled electron shells are incapable permanent magnetizationn All materials exhibit some form of magnetization.n Three types of response; ferro, dia and paramagnetic.磁性材料：原理、工艺与应用24原子的磁矩n电子和原子核均有磁矩，但原子核的磁矩仅有电子磁矩的1/1836.5。n电子轨道磁矩： l：轨道角量子数，0, 1, 2, 3, 4n-1 (s, p, d, f,

27、电子态)；n: 主量子数；波尔磁子B=9.273210-24 A/m2 轨道磁矩在外磁场方向的投影: l,H=mlB ml: 角动量方向量子数或磁量子数=0,1, 2, ln电子自旋磁矩： s：自旋量子数， s=1/2 自旋磁矩在外磁场方向的投影: s,H=2msB ms: 自旋角动量方向量子数= 1/2Blll) 1( Bsss) 1(2磁性材料：原理、工艺与应用25原子的磁矩n原子磁矩=电子轨道磁矩+自旋磁矩n对于3d过渡族和4f稀土金属及合金，原子磁矩： 式中: 称为郎德因子。J：原子总角量子数；L：原子总轨道角量子数；S：原子总自旋量子数；波尔磁子B=9.273210-24 A/m2n

28、量子力学证明，原子磁矩在外磁场方向的投影也是量子化的 J,H=gJmJB mJ: 原子角动量方向量子数或原子磁量子数=0,1, 2, JnIf J, L and S are known, J and J,H can be calculated.BJJJJg) 1() 1(2) 1() 1() 1(1JJLLSSJJgJ磁性材料：原理、工艺与应用26n 在一个填满的电子壳层中，电子的轨道磁矩和自旋磁矩为零。n 对于次电子层（等）未填满电子的原子，在基态下，其总角量子数J、总轨道量子数L和总自旋量子数S存在如下关系： （1）在未填满电子的那些次电子层内，在Pauli原理允许的条件下S和L均取最大值

29、；（2）次电子层未填满一半时， J=L-S；（3）次电子层填满一半或一半以上时， J=L+SHund规则J,H=gJmJBmJ=0,1, 2, J磁性材料：原理、工艺与应用27原子磁矩尽管上述计算方法有其深奥的量子力学来源，但与实验值之间的符合并不十分好。对铁磁和反铁磁材料，有时也使用更简化的方程：= g s 或者干脆将g作为可调参数以与实验结果吻合。磁性材料：原理、工艺与应用28众所周知，电子轨道运动是量子化的，因而只有分立的轨道存在，换言之、角动量是量子化的，并由下式给出Pl 普郎克(Planck)常数：玻尔磁子 (Bohr magneton)(10055. 1234JSxh电子的轨道磁矩

30、220022e reMr 2Pm r电子的角动量是：电子的轨道磁矩：PMLeiv电子的轨道磁矩Pmel20WbmmeB29010165. 12llmeBl20磁性材料：原理、工艺与应用29与自旋相联系的角动量的大小是/2，因而自旋角动量可写为：sP S是自旋角动量量子数21自旋磁矩自旋磁矩PmeS0通常磁矩和P之间的关系由下式给出：PmegS20这里g因子( g-factor)对自旋运动是自旋运动是2，而对轨道运动是轨道运动是1。ssmexBs2220lMlmexMBL210不论是自旋磁矩，还是轨道磁矩，都是玻尔磁子 B的整数倍。P se电子的自旋磁矩磁性材料：原理、工艺与应用30The Un

31、iversality: MagnetismnAll matter are magnetic 物质磁性无处不在 （1）物质的各种形态，无论是固态、液态、气态、等离子态、超高密度态和反物质态都具有磁性； （2）物质的各个层次，无论是原子、原子核、基本粒子和基础粒子等都会具有磁性。 （3）无限广袤的宇宙，无论是天体，还是星际空间都存在着或强或弱的磁场。地球磁场强度：240A/m，太阳的磁场强度80A/m，中子星磁场强度高达1013-1014A/m。n物质的磁性与其他属性之间存在着广泛的联系，并构成多种多样的耦合效应和双重（多重）效应（如磁电效应、磁光效应、和磁热效应等）。这些效应是了解物质结构和性能

32、关系的重要途径，又是发展各种应用技术和功能器件（如磁光存储技术、磁记录技术和霍尔器件等）的基础。磁性材料：原理、工艺与应用31Magnetic Poles (磁极磁极)nthe external magnetic field is strongest at the polesnThe two types of magnetic poles cannot exist separately always coupled together as a dipole. Isolated magnetic monopoles have not yet been detected.n表示磁极强弱的物理量称为

33、“磁极强度” 。两个强弱相同的磁极，在真空中相距1厘米时，如果它们之间相互作用力为1达因，则每个磁极的强度就规定为一个电磁系单位制的磁极强度单位。n磁极强度（Wb or emu）为m1、m2的磁极间相互作用力：F=km1m2/r2k=1/40, 0=410-7 H/m磁性材料：原理、工艺与应用32A magnetic dipole （磁偶极子）l A loop of electric current generates a magnetic dipole fieldl Field lines run from the North pole to the South polel Field li

34、nes indicate the direction of force that would be experienced by a North magnetic monopole磁性材料：原理、工艺与应用33Magnetic Moment （磁矩）n电流在其四周产生环绕的磁场。如果把通电导线圈成一个半径为r的圆环，其周围的铁屑则展示了其产生的磁场的形态。这个磁场等效于一个磁矩为M的磁铁产生的磁场。n由电流i产生的磁场，其强度和圆环的面积相关（圆环越大，磁矩就越大），即M = ir2。由n个圆环产生的总磁矩是由这些单一圆环产生的磁矩的迭加，即：M=nir2 因此，磁矩M的单位为Am2。n环电流

35、磁矩：M=IA 棒状磁铁磁矩：M=mllmAI磁性材料：原理、工艺与应用34Magnetic Field（磁场）, HnA magnetic field H is generated whenever there is electric charge in motion (electric currents). This can be due to macroscopic currents in a conductor, or microscopic currents associated with electrons in atomic orbits, or be produced by a

36、 permanent magnet. nH is measured in A/m or Oe (SI system or cgs system). 1 A/m = 0.01257 Oe For a solenoid:H=NI/L磁性材料：原理、工艺与应用35Magnetic Field（磁场）, Hn电流能够产生磁场，因此可以借助于电场来定义由其产生的磁场。当导线通以电流时，根据右手法则，右手的大拇指指向电流方向（即正方向，与电子流动方向相反），其它成环状的四指则指示了相应的磁场方向。n磁场H同时垂直于电流方向和径向单位矢量r，其强度与电流强度成正比。磁场强度H可以由安培定律给出： 因此，磁场

37、强度H的单位为A/m。磁性材料：原理、工艺与应用36Magnetic Field, HnA force field similar to the gravitational and electrical field, detected by a probe. nA magnetic field exerts a torque which orients dipoles with the field.nDirection of magnetic field at any point is defined as the direction of motion of a charged partic

38、le on which the magnetic field would not exert a force. nMagnetic field lines describe the structure of magnetic fields in three dimensions.For a magnet: H=F/m1=k m1/r2F=km1m2/r2磁性材料：原理、工艺与应用37Flux density （磁通密度）（磁通密度）, Bn磁通量（磁通量（Magnetic flux， ）磁场是一个矢量场，在任何一点它都由方向和强度共同定义。其方向由磁力线箭头确定，而其强度则由磁力线的密度确定。

39、磁力线即为磁通量，其密度可用来衡量磁场的强度（即磁感应强度B）。nDensity of flux (or field) lines determines forces on magnetic polesnDirection of flux indicates direction of force on a North polenHigher flux density exerts more force on magnetic polesB A磁性材料：原理、工艺与应用38Flux density BB depends onnGeometry and current in solenoidnMa

40、gnetic properties of the materialnGeometry of material磁性材料：原理、工艺与应用39Magnetic Induction（磁感应强度）（磁感应强度）, BnThe magnetic induction B, also known as the flux density, measured in Tesla (SI) or Gauss (cgs), is the response of a medium to the presence of a magnetic field. 1T=10000GsnH field creates magnet

41、ic inductionnB is the magnetic induction; the magnitude of the internal field within a substance磁性材料：原理、工艺与应用40Magnetic Permeability（磁导率）, B= Hn is the permeability （磁导率）（磁导率） of the medium (Henries per meter)B0 = 0Hn 0 is the permeability of a vacuum r= / 0n r is the relative permeability磁性材料：原理、工艺

42、与应用41Magnetization (磁化强度磁化强度), MnWe define magnetization as the total magnetic dipole moment (magnetic moment) per unit volume within the materialnIt is measured in A/m (SI) or emu/cm3 (cgs).VolumeMNii1磁性材料：原理、工艺与应用42Magnetization depends on.nNumber density of magnetic dipole moments within material

43、nMagnitude of the magnetic dipole moments within the materialnThe arrangement of the magnetic dipoles within the material磁性材料：原理、工艺与应用43Polarization（磁极化强度）, JnThe magnetic polarisation J, measured in Tesla, is given by J= oM, where o (=1.23664 10-6 H/m) is the permeability of free space. nM increase

44、s as more electronic magnetic moments are aligned. nWhen all magnetic moments are aligned in the same direction, the saturation magnetisation (polarisation) Ms (Js) is achieved.磁性材料：原理、工艺与应用44How does M respond to H?nThere is a variety of ways that M responds to HnResponse depends on type of materia

45、lnResponse depends on temperaturenResponse can sometimes depend on the previous history of magnetic field strengths and directions applied to the material磁性材料：原理、工艺与应用45Non-linear responsesnGenerally, the response of M to H is non-linearnOnly at small values of H or high temperatures is response som

46、etimes linearnM tends to saturate at high fields and low temperatures磁性材料：原理、工艺与应用46B, H, M, J RelationshipsnB (in T) consists of two contributions: one from magnetic field H (A/m), the other from magnetisation M (A/m). This leads to one of the most important relations in magnetism:JHMHB00)(n If the

47、re is no magnetization M .B0H磁性材料：原理、工艺与应用47Magnetic Susceptibility（磁化率）（磁化率）, nB = 0 ( H + M ) nReplace B= H H = 0 ( H + M ) r 0 H = 0 ( H + M ) 0 M = 0 ( r -1) H M = ( r -1) H Magnetic SusceptibilityM=H =r1n, Susceptibility, measures the material response relative to a vacuum (Dimensionless)磁性材料：原

48、理、工艺与应用48Various MagnetismBased on n抗磁性（Diamagnetism）n顺磁性（Paramagnetism）n铁磁性（Ferromagnetism）n亚铁磁性（Ferrimagnetism）n反铁磁性（Antiferromagnetism） 0, typically 10-3-10-5 1, typically 50-104 1, typically 50-104) show large, intrinsic magnetic moments, and can behave as if they were spontaneously magnetised.

49、Various types of magnetic moment ordering have been observed: (1) Ferromagnetic; (2) Ferrimagnetic; (3) Antiferromagnetic.磁性材料：原理、工艺与应用50Various Magnetism磁性材料：原理、工艺与应用51Diamagnetism （抗磁性）（抗磁性）nDiamagnets have no net magnetic moment on their atoms, because the electrons are all paired with antiparall

50、el spins.n拉莫尔进动 When a magnetic field H is applied, the orbits of the electrons change in accordance with Lenzs law, and they set up an orbital magnetic moment which opposes the field, and therefore gives very small negative susceptibility (磁化率0，数值很小，约为10-3-10-6。顺磁性也可以分为三类： 1、郎之万（Langevin）顺磁性 包括O2和N

51、2气体、三价Pt和Pd、稀土元素，许多金属盐以及居里温度以上的铁磁性和亚铁磁性物质。原子磁矩可自由地进行热振动，值与温度有关，服从居里（Curie）定律： =C/T 或居里-外斯（Curie-Weiss）定律： =C/（T+） 式中：C居里常数（K）， T绝对温度（K）， 外斯常数（K）1/T(K)斜率C居里（Curie）定律居里-外斯（Curie-Weiss）Paramagnetism (顺磁性顺磁性)磁性材料：原理、工艺与应用56 2、 泡利（Pauli）顺磁性 典型代表物为碱金属，它们的磁化率相对较前一种为低，并且其值几乎不随温度变化。 3、 超顺磁性 在常态下为铁磁性的物质，当呈现为极

52、微细的粒子时则表现为超顺磁性。此时粒子的自发极化本身作热运动，产生郎之万磁性行为，初始磁化率随温度降低而升高。Paramagnetism (顺磁性顺磁性)磁性材料：原理、工艺与应用57n M is proportional to the applied field Hn = Lim H 0 M / Hn = C / TCURIES LAWPIERRE CURIEnNormal paramagnetic substances obey the Curie Law nExamples : Aluminum, platinum, manganese, chromium =C/T1/ =T/C 1/

53、T in KParamagnetism (顺磁性顺磁性): Curies Law磁性材料：原理、工艺与应用58强磁性强磁性(Magnetic ordering materials)n在强磁性物质中，原子间的交换作用使得原子磁矩保持有秩序地排列，即产生所谓自发磁化。nMagnetic domain: 原子磁矩方向排列规律一致的自发磁化区域叫做磁畴。n存在饱和磁化强度Ms。n强磁性物质的磁化率值是很大的正值，并且易于在外磁场作用下达到饱和磁化。强磁性可以分为如下三种类型：铁磁性、亚铁磁性、弱铁磁性。磁性材料：原理、工艺与应用59where q is the angle between spins

54、and Jex is the exchange integral. For Jex0, ferromagnetic order results in an energy minimum; for Jex 0，交换作用使得相邻原子磁矩平行排列，产生铁磁性（Ferromagnetism）。 ii）Jex 0, r 1DIAmagneticn 0 , r 0, r 1磁性材料：原理、工艺与应用74Magnetic domainsApplying a field changes domain structure; Domains with magnetization in direction of f

55、ield grow; Other domains shrinkApplying very strong fields can saturate magnetization by creating single domainFerromagnetic materials tend to form magnetic domains; Each domain is magnetized in a different direction; Domain structure minimizes energy due to stray fields磁性材料：原理、工艺与应用75Magnetic domai

56、nsnRemoving the field does not necessarily return domain structure to original statenHence results in magnetic hysteresis磁性材料：原理、工艺与应用76Magnetic hysteresisnM depends on previous state of magnetizationnRemanent magnetization Mr remains when applied field is removednNeed to apply a field (coercive fie

57、ld) in opposite direction to reduce M to zero.磁性材料：原理、工艺与应用77nHeating a magnetized material generally decreases its magnetization.nRemnant magnetization is reduced to zero above Curie temperature TcnHeating a sample above its Curie temperature is a way of demagnetizing itnThermal demagnetizationEffe

58、ct of temperature on remanent magnetization磁性材料：原理、工艺与应用78Generating a uniform magnetic field in the laboratorynAn electric current run through a conducting coil (solenoid) generates a uniform flux density within the coil 磁性材料：原理、工艺与应用79Inserting a specimen into the coilnGenerally, the orbital and s

59、pin magnetic moments within atoms respond to an applied magnetic fieldnFlux lines are perturbed by specimen磁性材料：原理、工艺与应用80Specimen in magnetic fieldnIf specimen has no magnetic response, flux lines are not perturbed磁性材料：原理、工艺与应用81“Magnetic” materialsn“magnetic” materials tend to concentrate flux lin

60、esnExamples: materials containing high concentrations of magnetic atoms such as iron, cobalt磁性材料：原理、工艺与应用82Diamagnetic materialsnDiamagnetic materials tend to repel flux lines weaklynExamples: water, protein, fat磁性材料：原理、工艺与应用83Magnetic MaterialsROOM TEMPERATURE磁性材料：原理、工艺与应用84n 对于磁学单位，考虑强度为p1, p2的磁极，