固体磁性第二章.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,第二章,无磁序固体材料磁性,电子轨道运动受磁场作用，产生一附加电流以抵消磁 通量的变化，于是就产生了抗磁性磁矩,1,朗之万,(,Langevin,),抗磁理论,2-1-1,局域电子抗磁性,.,2-1,抗磁性,(DM),磁场引起附加进动，产生附加角动量,2,量子力学计算,在磁场中电子系统哈密顿量,用微扰法求体系能量，微扰哈密顿量：,若考虑系统有,N,个原子,定性结论：,1),抗磁性为一切物质所具有，是物质的共性,2),抗磁磁化率为负,3),若,不受热运动影响，则,d,与温度无关,4),d,随原子中电子数及原子序数增加而增加，且正比于各原子的轨道半径平方,2-1-2,传导电子抗磁性,来源于传导电子在外磁场下进行回旋运动的量子效应,.,所有金属均存在,.,经典理论无法给出传导电子的宏观抗磁性,.,经典回旋运动不改变电子动能,.,在磁场中传导电子的哈密顿量为：,3,德哈斯,范阿尔芬效应,在低温下某些金属抗磁（顺磁）磁化率随磁场改编成周期性震荡,。,德哈斯,-,范阿尔芬效应可提供关于费米面的信息,.,Landau levels.,有效质量,.,Free Electron.Approx.,by F-D statistics,考虑到晶格的周期静电势,弱的温度依赖性,.,Bi:,Strong DM of CE明显的温度依赖性,!,在半导体和半金属材料中，电子浓度低,当满足,E,m,or,E,F,kT,时，,费米统计转化为玻尔兹曼统计,朗之万经典理论,设单位体积中有,N,个原子，每个原子具有磁矩为 ，磁矩间无相互作用,外磁场中，磁矩位能,2-2,顺磁性,(PM),2-2-1,取向顺磁性,每个磁矩态和：,高温时,低温强场下,实验室普通条件,2,量子化修正,磁矩在磁场方向投影非连续分布，只能取,在实验室普通条件,2-2-2 Van,Vleck,PM,来源于磁场与磁矩作用的二级微扰,激发态混入（电子云形变）,.,Localized electrons,vv,may exists when,J,=0 or,J,0 at ground state.,vv,在能带电子中同样存在,.,一般情况,vv,与,温度,T,无关,.,2-2-3,传导电子顺磁性，,Pauli PM,外加磁场导致正负自旋能带错开，从而使得电子重新分布，导致正负自旋电子数量不一致，导致了磁化,单位体积中,，,(2),传导电子间的交换作用及库仑相关,.,增强泡利顺磁磁化率,1.,小结,:,2.,pi,:,局域电子顺磁磁化率，来源于具有固有磁矩的,原子、离子及金属中的原子实。,取向顺磁性，磁场取向与热运动之间的竞争。,居里及居里,-,外斯定律,1.,di,:,局域电子抗磁磁化率，来源于,原子、离子及金属中的原子实,di,10-6,。随原子中电子数及原子序数增加而增加，且正比于各原子的轨道半径平方；一般不依赖温度,.,3.,vv,:,范弗莱克顺磁性，磁场导致的电子云形变,.,vv,0-10,-4,.,其数值与电子云的对称性（形状）有关。,与温度无关。,4.,de,:,传导电子抗磁性，,来源于传导电子在外磁场下进行回旋运动的量子效应,.,de,10,-6,一般与温度无关,.,5.,pe,:,传导电子顺磁性，,外加磁场导致正负自旋能带错开从而导致正负自旋电子数量不一致,.,交换增强效应,.,2-3,无磁序磁性材料,多种磁性作用共存于固体材料中，它们之间的相互竞争导致了材料最终的磁性能,.,金属及半导体,=,di,+,pi,+pe,+,de,.,非金属,=,di,+,pi,.,2-3-1,周期表中元素的磁性,Table 1.Data of atomic magnetic susceptibility of metallic elements in periodic table at room temperature.,A,II,A,2,3,4,5,6,7,Li,3,25.2,Be,4,-9.02,Na,11,15.6,Mg,12,6,K,19,21.5,Ca,20,44,Rb,37,19.2,Sr,38,92,Cs,55,29.9,Fr,87,Ba,56,20,Ra,88,Sc,21,315,Y,39,191,La,57,140,Ac,89,(90-103),Ti,22,150,Zr,40,120,Hf,58,70,Ku,104,V,23,230,Nb,41,120,Ta,59,145,Ha,105,Cr,24,160,Mo,42,54,W,60,40,Mn,25,527,Tc,43,Re,61,68.7,Fe,26,-,Ru,44,44,Os,62,7.6,From left to right:weak PM-strong PM with FM,AF&FIM-DM.,B,B,2,3,4,5,6,7,Co,27,Rh,45,113,Ir,77,25,Ni,28,Pd,46,580,Pt,78,200,Cu,29,-5.4,Ag,47,-21.56,Au,79,-29.6,Zn,30,-10.3,Cd,48,-19.6,Hg,80,-33.8,Ga,31,-16.8,In,49,-12.6,-Tl,81,-44.0,Ge,32,-8.9,-Sn,50*,4.4,As,33,-5.5,Pb,82,-24.9,Sb,51,-107,Bi,83,-285,Se,34,-26.5,Te,52,-40.8,Po,84,B,5,-6.7,Al,13,16.7,C,6,-42,Si,14,P,15,*,-Sn,A,=-31.510,-6,PM Simple metals,Group IA and IIA,except Be(,A,=,-10,10,-6,),Theoretical and experimental values are shown in,Table 2-2,2.Diamagnetic metals,Group IB,IIB,IIIA,IVA,VA except Al(PM)are diamagnetic.,Cu,Ag,Au,Cu Ag Au,A,-5.4 -21.56 -29.59 measured,ion,-18.0 -31.0 -45.08 determined indirectly,Ae,12.6 9.44 16.21,A,-,ion,Ape,18.9 14.16 24.3,di,is determined by indirect method from data of salts(13)or semi-theoretical method.(13),pe,can be determined directly by CESR.,pe,intansify,indirectly by NMR from knight,K,pe,or indirectly by(,e,-,di,),3/2,as in the above table.,(2)Bi,Sb,etc.,with nearly fully filled band,m*small.,pe,-,de,.,Diamagnetic non-metals and gases.,Elements in IIIA-VIIIA,Covalent solid,molecules,and inert gases,All diamagnetic with some exceptions,C:diamond,A,=-5.9,Graphite:,A,=2.2510,6,Sn,:(-37,3.1),4 Transition metals,*,29TMs:3FM,2AFM,19PM.,10,-5,-10,-4,*All PM,strong PM TM:Pd,V,Sc,Pt.,*,T,varying,(1),Normal T dependence:T,with large,and Max.,N,(,E,F,).,(2)Abnormal T dependence:T,for small,and,Min.,N,(,E,F,).,=,di,+,vv,+,de,(,d,)+,pe,(,d,)+,de,(,s,)+,pe,(,s,),5 RE metals 4f electrons provide main magnetism,=,d i,+,p,+,vv,+,CE,Mostly,mag,.order at low T.,Strong PM at high T,Ac period,Complicated,T-dependence of,Independent on T,increasing or decreasing.,习题,*1.,为什么传导电子有时表现顺磁性,有时为抗磁性,?,*2.,范,-,弗莱克磁化率,vv,的表现及机理,.,*3.,在材料中共有哪些顺磁性及抗磁性,?,并描述每种磁化率与温度的依赖关系,.,