v nehomogenním magnetickém poli

Transcription

1 Magnetika

2 Chování magnetů v nehomogenním magnetickém poli µ µ

3 DIPÓL V HOMOGENNÍM POLI r M r F výsl r r = µ B r = F = i 0 0

4 DIPÓL V NEHOMOGENNÍM POLI r r r d = I ds B F B

5 DIPÓL V NEHOMOGENNÍM POLI F = r µ grad B x, y, z x, y, z

6 DIPÓL V NEHOMOGENNÍM POLI F = r µ grad B x, y, z x, y, z

7 Dielektrikum?

8 Dielektrika Rozložení elektronů elektrický dipól

9 Magnetikum?

10 Magnetika Pohyb elektronů magnetický dipól B B

11 magnetický dipólový moment r µ µ = NIS moment síly působící na dipól potenciální energie dipólu r r M = r µ B r r E p = µ. B

12 Pole v látce I E P B B 0 M E = E 0 P/ε 0 B = B 0 + µ 0 M B M B 0

13 Magnetické dipóly v látce: orbitální moment hybnosti elektronů spin elektronů

14 Smyčkový model µ = orb IS = e rv 2 e ev I = = S = π r T 2π r r r r L = mr v 2m L = mrv = orb e µ r e r µ = orb m L 2m 2

15 , Skutečnost 1 orbitální moment hybnosti elektronu r L r kvantováno ( 34 E ) foton = hω, h 0,54 10 J s orbitální dipólový magnetický moment r e r µ = L orb 2m kvantováno Bohrův magneton

16 Skutečnost 2 spin elektronu r S r kvantováno spinový dipólový magnetický moment r e r µ 2 spin = S 2m kvantováno

17 Einsteinův - de Haasův jev

18 Otto Stern and Walther Gerlach, Otto Stern and Walther Gerlach, Frankfurt, Germany, 1922

19 Sternův Gerlachův experiment (1922)

20 Magnetismus a elektrony a protony

21 Magnetické dipóly v látce orbitální a spinové magnetické momenty elektronů se skládají magnetický moment atomu/látky klasifikace látek (magnetik) DIA PARA FERO MAGNETIKUM

22 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.

23 DIAMAGNETIKA B B - µ E B µ - E

24 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 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.

25 PARAMAGNETIKA B (síran chromito-draselný) µ J/T 1,5 T µ B E p = 2 µ B = 0.17 mev E 1 = k BT 2 k = = 0.039eV mev k B = J/K 300 K

26 FEROMAGNETIKA magnetické domény B hystereze

27 Pole v látce II ε ε C = r 0 S d L = µ r µ 0 l N 2 S C = Q U L = Φ I U = Ed Φ = BS E = E ε B = µ 0 r r B 0

28 µ =1 + χ r µ µ < 1 µ r >1 µ r

29 Měření magnetizace B0 = µ 0 n I P B = B 0 + BM

30 Chování magnetik v nehomogenním magnetickém poli Proč?

31 DIPÓL V HOMOGENNÍM POLI r M r F výsl r r = µ B r = F = i 0 0

32 DIPÓL V NEHOMOGENNÍM POLI

33 Chování magnetik v nehomogenním magnetickém poli DIAMAGNETICKÁ LÁTKA je vytlačována z pole ven PARAMAGNETICKÁ LÁTKA FEROMAGNETICKÁ LÁTKA je vtahována do pole

34 DIELEKTRIKUM je vtahováno do pole

35 Fyzika v akci

36 Pole v látce III Pole na rozhraní dvou prostředí ε ε r1 r 2 ε µ µ µ r1 µ r2 E = E B µ = B µ t1 r1 t2 r2 E t1 t2 ε E = ε E r1 n1 r2 n2 B = B n1 n2

37 Toroid s jádrem a vzduchovou mezerou B µ µ = 0 r NI 2πRπ R B 1n = B 2n.dS = S r r B 0

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40 Na závěr atomové jádro a magnetismus Jaderná magnetická rezonance 1, J/T 1,80 T 2µ z f = zb = h = = 76,6 MHz 6, J.s

41 a na začátek nového