磁性材料简介磁性材料种类与其形成机制

1、磁性材料简介磁性材料种类与其形成机制磁阻效應磁阻效應 磁阻 (H) 是被定義為樣品在磁場中電阻之改變量，即(H) = (H) - (H = 0)，此處 (H) 是在磁場H 下樣品之電阻率。 材料有不同之磁阻,其原因可來自;電荷受羅倫茲力之作用而改變甚行進路徑造成電荷與晶格間散射機率增加, 此時 (H) 0 ; 受磁矩在磁場下電子自旋與磁矩間間散射狀態改變的影響, 若樣品是鐵磁性材料, 其磁矩對電荷自旋之散射機率會因為外加磁場之增加而減小, 此時 (H) 0 。其他物理原因。XZYABHJXZHYJ(a) (b)AB樣品置於外加磁場H 之中, 若將電流 J 通於樣品, 此樣品在磁場下產生磁阻效應

2、。(a)為縱向磁阻效應 (H H 之之方向方向平行於J J之方向之方向);(b)為橫向磁阻效應(H H之方向垂直於J J之方向)Nd,SrMnOb (5.46 )c (7.7 )a (5.47 )氧化物氧化物 Nd1-XSrXMnO3 巨磁阻材料中巨磁阻材料中NdNd, Sr, Mn 和和O原子之排列情形，原子之排列情形， 此化合物之居禮溫度約在此化合物之居禮溫度約在 230 K。0100200300Temperature (K)0100200300400M (emu/cm3 )The La0.7Ca0.3MnO3 thin filmThickness = 1900H = 1000 Gauss

3、0100200300T (K)10203040M (emu/cm3)100150200T (K)041/Tc = 222 KNd0.7Sr0.3MnO3H = 100 GNSMO and LCMO films show the Curie temperature at 222 K and 250 K respectively. The pattern for resistivity and Hall measurementsV = V3-V2ResistanceVh = V2-V1Hall coefficient050100150200250300350T (K)0.000.020.040.0

4、6xx (ohm -cm )0.00000.00010.00020.0003xx (ohm -cm )YBCONSMO0 T3 T7 T0 T3 T5 TTemperature dependence of the longitudinal resistivity xx for YBa2Cu3Oy (YBCO) (1500 and NSMO (2100 ) films.(b)Nd1-XSrXMnO3薄膜在薄膜在 (a)不同磁場下電阻與溫度的相依行為不同磁場下電阻與溫度的相依行為; (b)磁阻比與溫度磁阻比與溫度的相依行為的相依行為巨磁阻薄膜在溫度為30 K的電阻對角度B相依行為，B為磁場與基座法

5、線之夾角。由上而下的圖形外加磁場值分別為600 G，2500 G，4500 G，5500 G，12.5 kG，20 kG 及 60 kG。Diamagnetism ParamagnetismFerromagnetismAntiferromagnetismOthers磁性磁性 DiamagnetismDiamagnetism is a form of magnetism which is only exhibited by a substance in the presence of an externally applied magnetic field. It is the result o

6、f changes in the orbital motion of electrons due to the application of an externally applied magnetic field. Applying a magnetic field creates a magnetic force on a moving electron in the form of F=qv x B. This force changes the centripetal force on the electron, causing it to either speed up or slo

7、w down in its orbital motion. This changed electron speed modifies the magnetic moment of the orbital in a direction against the external field.1. The spin with which electrons are associated;Paramagnetic contribution to the magnetizationDiamagnetic contribution to the magnetization2.2. Their orbita

8、l angular momentum about the nucleus;3. The change in the orbital moment induced by an applied magnetic field.Note: Atoms with filled electron shells have zero spin and zero orbital moment. The moments of atoms are associated with electrons in unfilled shells. 1.e-e-NucleonH3.INucleon PARAMAGNETISM

9、PARAMAGNETISM Paramagnetism is the tendency of the atomic magnetic dipoles to align with an external magnetic field. This effect occurs due to quantum-mechanical spin as well as electron orbital angular momentum. Paramagnetic materials exhibit magnetisation according to Curies Law: where M is the re

10、sulting magnetisation; B is the magnetic flux density of the applied field, measured in tesla; T is absolute temperature, measured in kelvins and C is a material-specific Curie constant. TkNB32, if B Tc FERROMAGNETIC ORDERVibrating Sample Magnetometer (VSM)SQUID MagnetometerEnergy product 0 superpar

11、amagneticsmall soft magnetic material large hard magnetic materialSaturated MagnetizationMagnetic Hysteresis Curve FERROMAGNETIC ORDER FERROMAGNETIC ORDERTemperature Dependence of the Saturation MagnetizationIf we omit the applied magnetic field and replace B by the molecular field BE = M, thenFor s

12、pin , M = N tanh(B/kBT) M = N tanh(M /kBT) FERROMAGNETIC ORDER ANTIFERROMAGNETIC ORDER= M/BaM = Magnetic moment per unit volume, Ba = applied magnetic field. FERROMAGNETIC DOMAINSEnergy is relatively high FERROMAGNETIC DOMAINSDomain Wall10200 nm FERROMAGNETIC DOMAINS FERROMAGNETIC DOMAINSThe directions of magnetization of different domains need not be parallel.An arrangement of domains is tend to approximately zero resultant magnetic moment.Domains form also in antiferromagnetics, ferroelectrics, anti-ferroelectrics, and superconductors etc. SING