Magnetika Chování magnetů v nehomogenním magnetickém poli   DIPÓL V HOMOGENNÍM POLI 0M B   0výsl iF F  DIPÓL V NEHOMOGENNÍM POLI BsIFB   dd DIPÓL V NEHOMOGENNÍM POLI zyxzyx BF ,,,, grad  + DIPÓL V NEHOMOGENNÍM POLI zyxzyx BF ,,,, grad  - Dielektrika Rozložení elektronů elektrický dipól Magnetika Pohyb elektronů magnetický dipól B B   moment dipólovýmagnetický NIS moment síly působící na dipól potenciální energie dipólu BM    BEp  . Pole v látce I PE E = E0 – P/0 MB0 B B = B0 + 0 M B0 M B spin elektronů orbitální moment hybnosti elektronů Magnetické dipóly v látce: „Smyčkový model“ orb IS  2 e ev I T r   2 S r 2 e rv L mr v  orb 2 e L m    orb 2m L mrv e   orb 2 e L m    kvantováno Bohrův magneton orbitální dipólový magnetický moment orbitální moment hybnosti elektronu Skutečnost 1 L  34 foton , 0,54 10 J sE       kvantováno , spin elektronu S 2 kvantováno spinový dipólový magnetický moment Skutečnost 2 kvantováno S m e spin  2  Einsteinův - de Haasův jev Otto Stern and Walther Gerlach, Frankfurt, Germany, 1922 Sternův – Gerlachův experiment (1922) Magnetismus a elektrony a protony Magnetické dipóly v látce orbitální a spinové magnetické momenty elektronů se skládají magnetický moment atomu/látky klasifikace látek (magnetik) DIA PARA FERO MAGNETIKUM Diamagnetism is a kind of magnetism characteristic of materials that partly expel from their interior the magnetic field in which they are placed. First observed by S. J. Brugmans (1778) in bismuth and antimony; diamagnetism was named and studied by Michael Faraday (beginning in 1845). He and subsequent experimenters found that some elements and most compounds exhibit this "negative" magnetism. Indeed, all substances are diamagnetic: the strong external magnetic field speeds up or slows down the electrons orbiting in atoms in such a way as to oppose the action of the external field in accordance with Lenz's law. The diamagnetism of some materials, however, is masked either by a weak magnetic attraction (paramagnetism) or a very strong attraction (ferromagnetism). Diamagnetism is observable in substances with symmetric electronic structure (as ionic crystals and rare gases) and no permanent magnetic moment. Diamagnetism is not affected by changes in temperature. For diamagnetic materials the value of the susceptibility (a measure of the relative amount of induced magnetism) is always negative and typically near negative one-millionth. DIAMAGNETIKA B B BE E -  -  Paramagnetism is a kind of magnetism characteristic of materials weakly attracted by a strong magnet, named and extensively investigated by the British scientist Michael Faraday beginning in 1845. Most elements and some compounds are paramagnetic. Strong paramagnetism (not to be confused with the ferromagnetism of the elements iron, cobalt, nickel, and other alloys) is exhibited by compounds containing iron, palladium, platinum, and the rare-earth elements (lanthanides and actinides). In such compounds atoms of these elements have some inner electron shells that are incomplete. Their unpaired electrons’ spin and orbital magnetic moments make the atoms a permanent magnet tending to align with and hence strengthen an applied magnetic field. Strong paramagnetism decreases with rising temperature because of the re-alignment produced by the greater random motion of the atomic magnets. Weak paramagnetism is found in many metallic elements in the solid state, such as sodium and the other alkali metals, because an applied magnetic field affects the spin of some of the loosely bound conduction electrons. The value of susceptibility (a measure of the relative amount of induced magnetism) for paramagnetic materials is always positive and at room temperature is typically about 1/100,000 to 1/10,000 for weakly paramagnetic substances and about 1/10,000 to 1/100 for strongly paramagnetic substances. eV039.0 2 1  TkE Bk meV17.02  BEp  PARAMAGNETIKA BB 39 meV 0.17 meV J/T10 23 B 1,5 T 300 KkB = 1.38.10-23 J/K (síran chromito-draselný) FEROMAGNETIKA B magnetické domény hystereze l SN L 2 0  d S C 0  r r Pole v látce II UQC  IL  EdU  BS rEE 0 0BB r  1r 1r1r Chování magnetik v nehomogenním magnetickém poli Proč ? Chování magnetik v nehomogenním magnetickém poli DIAMAGNETICKÁ LÁTKA PARAMAGNETICKÁ LÁTKA je vytlačována z pole ven je vtahována do pole FEROMAGNETICKÁ LÁTKA DIELEKTRIKUM je vtahováno do pole Fyzika v akci Pole v látce III Pole na rozhraní dvou prostředí 1r 2r 2r1r 21 tt EE  2211 nrnr EE   2211 rtrt BB   21 nn BB    S SB 0d.  B1n = B2n Toroid s jádrem a vzduchovou mezerou R NI B r   2 0 Na závěr… atomové jádro a magnetismus Jaderná magnetická rezonance h B f z2  1,41.10-26 J/T 1,80 T 6,63.10-34 J.s MHz6,76 … a na začátek nového