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This is NOT the question
or not ?
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Everything is magnetic
How ?
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macroscopic world
atomic or molecular world
 wonder  world
meter
nano meter
1 / 1 000 000 000 10-9 10-9
mole
molecule
1
1023
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macroscopic world
atomic or molecular world
 wonder  world
Lewis Carroll, Through the looking-glass, Penguin
Books, London, 1998 Illustrations by John Tenniel
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macroscopic world
atomic or molecular world
 wonder  world
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macroscopic world  traditional, classical 
magnets
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macroscopic world
A pioneering experiment by M. Faraday  Farady
lines of forces  about magnetic flux
Courtesy Prof. Peter Day, the RI See also
The Philosophers Tree,The Institute of Physics
Publishing, Bristol, 1999)
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Courtesy Prof. Frank James, the RI
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M. Faradays magnetic laboratory
Courtesy Prof. Frank James, the RI
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M. Faraday in his laboratory
Courtesy Prof. Frank James, the RI
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macroscopic world  traditional  magnets
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macroscopic world  traditional  magnets
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macroscopic world looking closer to the magnetic
domains
many sets of domains
many sets of
?
?
?
?
atomic magnetic moments
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Physics Macroscopic Mesoscopic
Nanoscopic
permanent magnets micron particles nanoparticles clusters molecular clusters individual spins
Wolfgang Wernsdorfer, Grenoble
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No ! no ! The adventures first said the Gryphon
in an impatient tone explanations take such a
dreadful time.
Lewis Carroll, Alices Adventures in Wonderland,
Penguin Books, London, 1998 Illustrations by
John Tenniel
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Everyday life is full of useful magnets
which traditionally take the form of
three-dimensional solids, oxides, metals and
alloys
Magnets Domains Curie Temperature
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The magnetic moments order at Curie temperature
A set of molecules / atoms
Magnetic Order Temperature or Curie
Temperature
kT ltlt J
kT gtgt J
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Magnetic Order ferro-, antiferro- and
ferri-magnetism
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Magnetization of nanoparticles of Prussian Blue
analogues,
MicroSQUID, 4 K
(A. Bleuzen, W. Werndorfer)
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Magnetization of nanoparticles of Prussian Blue
analogues,
MicroSQUID, 4 K
(A. Bleuzen, W. Werndorfer)
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 He seemed to give off a radiance,
an inner fire,
and I coulnt resist this magnetism
Fernande Olivier, Loving Picasso, H.N. Abrams
Publishers, New York, 2001, p.139
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How magnetism comes to molecules ?
the different faces of the electron
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Origin of Magnetism
the electron
I am an electron
rest mass me, charge e-, magnetic moment
µB
everything, tiny, elementary
but do not forget nuclear magnetism !
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Origin of Magnetism
 Orbital  magnetic moment
 Intrinsic  magnetic moment
due to the spin
µorbital
s 1/2
µspin
e-
µspin gs x µB x s µB
µtotal µorbital µspin
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Origin of Magnetism
in molecules
electrons in atoms in molecules
forgetting the nuclear magnetism
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Dirac Equation
The Principles of Quantum Mechanics, 1930
Nobel Prize 1933
1928
1905
http//www-history.mcs.st-and.ac.uk/history/PictDi
splay/Dirac.html
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Representations, Models, Analogies
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.
Lewis Carroll, Through the Looking-Glass, Penguin
Books, London, 1998 Illustrations by John Tenniel
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Electron corpuscle and wave
Wave function or  orbital  ?n, l, ml
l 0 1 2 3
s
p
d
angular representation
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Electron also an energy level
Orbitals
Vacant
Singly occupied
Doubly occupied
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Electron also a spin !
Up
Singly occupied
Doubly occupied
Down
 Paramagnetic  S 1/2
 Diamagnetic  S 0
Nitrogen Monoxyde NO
Nitronylnitroxyde
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Analogy Spin and Arrow
Paul Klee, Théorie de lart, Denoël, Paris
An Isolated Spin
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Spin in Maya World ?
Uxmal, Palacio del Gobernador, Mayab, Yucatan,
July 2004
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Molecules are most often regarded as
isolated, non magnetic, creatures
Dihydrogen
diamagnetic Spin S 0
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the dioxygen that we continuously breathe
is a magnetic molecule
orthogonal p molecular orbitals
paramagnetic, spin S 1
Two of its electrons have parallel magnetic
moments that shapes aerobic life and allows our
existence as human beings
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when dioxygen is in an excited state it can
becomes a singlet (spin S0) and strange
reactivity appears sometines useful (glow-worm
)
Paramagnetic O2 Luminol Light
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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)
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Transition Elements
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Mononuclear complex ML6
Splitting of the energy levels
E
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How large is the splitting ?
Weak Field
Strong Field
Intermediate Field Temperature Dependent Spin
Cross-Over
High spin
Low spin
L H2O C2O42-
L CN-
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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
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story of jumping electrons and moving spins
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two blue solutions
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KCN Methylene Blue
CoII(H2O)62 Methylene Blue
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one yellow solution
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blue blue yellow !
CoIII(CN)63- Methylene Reduced Colorless
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FeII(H2O)62 pale green
FeII(o-Phen)32 bright red
S0
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Low spin, chiral, FeII(bipyridine)32
?
?
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Playing with ligands, the chemist is able to
control the spin state
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Review by Philipp Gütlich et al. Mainz
University Angewandte Chemie 1994
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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
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Curie Law
?MT Constant
?MT n (n2) /8
if n 4, ?MT 3 !
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Spin Cross-Over
Bistability Domain
Room Temperature
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Red
0
The system  remembers  its thermal past !
O. Kahn, C. Jay and ICMC Bordeaux
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Hysteresis allows bistability of the system
and use in display, memories
Spin and colour changes
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Spin Cross-over
Display Device
Joule and Peltier Elements
Compound in Low spin state (Thin Layer)
Display
O. Kahn, J. Kröber, C. Jay Adv. Mater. 1992, 718
Kahn O., La Recherche, 1994, 163
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From the molecule to the material and to the
device
O. Kahn, C. Jay and ICMC Bordeaux
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Red
White
From J.F. Letard, ICMC Bordeaux
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O. Kahn, Y. Garcia, Patent
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May we go further and dream of molecular
magnets  i.e. low density, biocompatible
transparent or colourful magnets ?