2. or not ? This is NOT the question

3. Everything is magnetic … How ?

4. macroscopic world atomic or molecular world « wonder » world meter …nano meter … mole …molecule … 1 / 1 000 000 000 = 10 -9 10 -9 110 +23

5. macroscopic world atomic or molecular world « wonder » world Lewis Carroll, Through the looking-glass, Penguin Books, London, 1998 Illustrations by John Tenniel

6. macroscopic world atomic or molecular world « wonder » world quantum macro

7. N S macroscopic world « traditional, classical » magnets macro

8. A pioneering experiment by M. Faraday « Farady lines of forces » about magnetic flux N S macroscopic world macro Courtesy Prof. Peter Day, the RI ; See also : The Philosopher ’ s Tree,The Institute of Physics Publishing, Bristol, 1999)

9. Courtesy Prof. Frank James, the RI

10. M. Faraday’s magnetic laboratory Courtesy Prof. Frank James, the RI

11. M. Faraday in his laboratory Courtesy Prof. Frank James, the RI

12. macroscopic world « traditional » magnets N S N S attraction N S N S macro

13. macroscopic world « traditional » magnets N S repulsion N S N S N S macro

14. macroscopic world looking closer to the magnetic domains S N many sets of domains   many sets of  atomic magnetic moments macro quantum

15. permanent magnets micron particles nanoparticlesclusters molecular clusters individual spins Physics : Macroscopic Mesoscopic Nanoscopic multi - domain nucleation, propagation and annihilation of domain walls single - domain uniform rotation curling magnetic moment quantum tunneling, quantization quantum interference Wolfgang Wernsdorfer, Grenoble macro quantum

16. Lewis Carroll, Alice’s Adventures in Wonderland, Penguin Books, London, 1998 Illustrations by John Tenniel “No ! no ! The adventures first” said the Gryphon in an impatient tone : “explanations take such a dreadful time.”

17. Everyday life is full of useful magnets which traditionally take the form of three-dimensional solids, oxides, metals and alloys macro Magnets Domains Curie Temperature

18. The magnetic moments order at Curie temperature … Paramagnetic solid : thermal agitation (kT) larger than the interaction (J) between molecules Solid, Magnetically Ordered thermal agitation (kT) weaker than the interaction (J) between molecules A set of molecules / atoms : kT << JkT >> J T C kT ≈ J Magnetic Order Temperature or Curie Temperature

19. Magnetic Order : ferro-, antiferro- and ferri-magnetism + = Ferromagnetism : Magnetic moments are identical and parallel + = 0 Antiferromagnetism : Magnetic moments are identical and anti parallel + = Ferrimagnetism (Néel) : Magnetic moments are different and anti parallel

20. Magnetization of nanoparticles of Prussian Blue analogues, (A. Bleuzen, W. Werndorfer) MicroSQUID, 4 K

21. Magnetization of nanoparticles of Prussian Blue analogues, (A. Bleuzen, W. Werndorfer) MicroSQUID, 4 K Remnant magnetization Coercive Field

22. Fernande Olivier, Loving Picasso, H.N. Abrams Publishers, New York, 2001, p.139 « He seemed to give off a radiance, an inner fire, and I couln’t resist this magnetism

23. How magnetism comes to molecules ? … the different faces of the electron

24. Origin of Magnetism … the electron * I am an electron rest mass m e, charge e -, magnetic moment µ B everything, tiny, elementary quantum * but do not forget nuclear magnetism !

25. Origin of Magnetism e-e- « Orbital » magnetic moment« Intrinsic » magnetic moment due to the spin quantum µ spin = g s x µ B x s ≈ µ B s = ± 1/2 µ orbital = g l x µ B x µ total = µ orbital + µ spin µ orbital µ spin

26. Origin of Magnetism … in molecules quantum electrons * in atoms in molecules * forgetting the nuclear magnetism

27. Dirac Equation http://www-history.mcs.st-and.ac.uk/history/PictDisplay/Dirac.html 19281905 Nobel Prize 1933 The Principles of Quantum Mechanics, 1930

28. Lewis Carroll, Through the Looking-Glass, Penguin Books, London, 1998 Illustrations by John Tenniel “When I use a word”, Humpty Dumpty said, … “it just means what I choose it to mean – neither more nor less “ “The question is”, said Alice, whether you can make words mean so different things” “The question is”, said Humpty Dumpty, “which is to be master – that's all.” Representations, Models, Analogies …

29. l = 0123 s p d angular representation Electron : corpuscle and wave Wave function or « orbital »  n, l, m l …

30. Vacant Doubly occupied Orbitals Energy Diagramme Singly occupied Electron : also an energy level

31. Singly occupied Nitrogen Monoxyde NO Nitronylnitroxyde Electron : also a spin ! Up Down Doubly occupied « Paramagnetic » S = ± 1/2 « Diamagnetic » S = 0

32. Paul Klee, Th é orie de l ’ art, Deno ë l, Paris An Isolated Spin Analogy : Analogy : Spin and Arrow

33. Spin in Maya World ? Uxmal, Palacio del Gobernador, Mayab, Yucatan, July 2004

34. Molecules are most often regarded as isolated, non magnetic, creatures Dihydrogen diamagnetic Spin S = 0

35. the dioxygen that we continuously breathe is a magnetic molecule paramagnetic, spin S =1 Two of its electrons have parallel magnetic moments that shapes aerobic life and allows our existence as human beings orthogonal π molecular orbitals

36. macro when dioxygen is in an excited state it can becomes a singlet (spin S=0) and strange reactivity appears sometines useful (glow-worm …) Paramagnetic O 2 Luminol Light

37. More complex molecular frameworks called metal complexes built from transition metal and molecules are able to bear up to five or seven electrons with aligned magnetic moments (spins)

39. Transition Elements quantum

40. Mononuclear complex ML 6 E Splitting of the energy levels

41. How large is the splitting ? High spin L = H 2 O [C 2 O 4 ] 2- Low spin L = CN- Weak FieldStrong FieldIntermediate Field Temperature Dependent Spin Cross-Over

42. macro The complexes of transition metal present often delicate and beautiful colours depending mostly on the splitting of the d orbitals Colours in water Geometry changes Spin changes h

43. story of jumping electrons and moving spins …

44. two blue solutions

45. [Co II (H 2 O) 6 ] 2+ + Methylene Blue KCN + Methylene Blue

47. one yellow solution

48. blue + blue = yellow ! [Co III (CN) 6 ] 3- + Methylene Reduced Colorless

49. [Fe II (H 2 O) 6 ] 2+ pale green Fe II (o-Phen) 3 ] 2+ bright red S=0 S=2

50. Low spin, chiral, Fe II (bipyridine) 3 ] 2+  

51. Playing with ligands, the chemist is able to control the spin state

52. Review by Philipp Gütlich et al. Mainz University Angewandte Chemie 1994

53. Spin Cross-Over A Fe(II) « Chain » with spin cross-over Triazole substituted Ligand (R) ; insulated by counter-anions Many groups : Leiden, Mainz, Kojima, O. Kahn, C. Jay, Y. Garcia, ICMC Bordeaux 4+

54. Curie Law  M T = Constant  M T ≈ n (n+2) /8 … if n = 4,  M T ≈ 3 !

55. Spin Cross-Over Bistability Domain The system « remembers » its thermal past ! Room Temperature O. Kahn, C. Jay and ICMC Bordeaux Red 3 0

56. macro Hysteresis allows bistability of the system and use in display, memories … Spin and colour changes

57. Spin Cross-over Display Device (1)(2) (3) Display Connections O. Kahn, J. Kröber, C. Jay Adv. Mater. 1992, 718 Kahn O., La Recherche, 1994, 163 Joule and Peltier Elements Compound in Low spin state (Thin Layer)

58. O. Kahn, C. Jay and ICMC Bordeaux From the molecule to the material and to the device …

59. From J.F. Letard, ICMC Bordeaux Red White

60. O. Kahn, Y. Garcia, Patent

61. May we go further and dream of molecular magnets i.e. low density, biocompatible transparent or colourful magnets ?