06/11/2012
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Single Molecule Magnets on Surfaces: achievements and challenges
Roberta SessoliDepartment of Cheistry & INSTM, University of Floren ce, Italy
FUNMOL - October 2012 - Bonn
D≈-0.7 K
MnIII(S=2)MnIV
S=3/2
τ0≈10-7s∆E/kB≈65 K
Sessoli et al. Nature 1993Christou et al. MRS Bull. 2000
Single Molecule Magnets
Stot=10
∆∆∆∆E=DS2
τ=τ0exp(∆E/kBT)
06/11/2012
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Why magnetic molecule @ surfaces ?
STM
SMMElectric field can be much more “local”
Address individual molecules
Spacer
Linker
Spacer
e-
Scanning Probe Microscopies
Gate
Source
VbVg
Drain
Molecules in nano-junctions
Switchable SMM
Cornia, SessoliDalton 2012
Beyond SMMs
STM Spin cross-over
Miyamachi et al. Nat. Commun. 2012
Valence Tautomerism
hν, T, P, E
SQ rad - Co II Cathecol - Co III
hν, T, P A.Dei,G. Pone ti
E SanvitoPRL,2011
UV
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SP-STM Detection of Magnetic Bistability
STM
SMM
Fen@Cu2N@Cu(100)
Science, 2012
The sunset of Mn12 for SpintronicsChallenges
Chemical stability on surfaces
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The sunset of Mn12 for SpintronicsTbPc2: a robust single ion SMM
Tb3+
L=3S=3
J=6
� Thermally Evaporable� Flat� Large magnetic moment� Large anisotropy� High T B
Kern et al., Nano Lett. 2008Hietschol et al. JACS 2011
Komeda et al. 2009 -30 -20 -10 0 10 20 30
-4
-2
0
2
4
M (
µ B)
H (kOe)
1.4 K3.0 K5.0 K10.0 K15.0 K27.0 K
The sunset of Mn12 for SpintronicsTbPc2: a robust single ion SMM
Tb3+
L=3S=3
J=6
� Thermally Evaporable� Flat� Large magnetic moment� Large anisotropy� High T B
Ishikawa et al., J. Am. Chem. Soc., 2003, 125, 8694-8695.
∆∆∆∆E∼∼∼∼
700 K
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The sunset of Mn12 for SpintronicsSpintronics architectures based on TbPc 2
a) Komeda et al. Nature Commun. 2011/ Vincent et al. Nature 2012b) Candini et al. Nanoletters 2011c) Urdampilleta et al. Nature Materials 2011
The sunset of Mn12 for SpintronicsChallenges
Chemical stability on surfaces
Robustness of SMM behavior
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The sunset of Mn12 for SpintronicsSMM behavior is sensitive to nanostructureTbPc 2
Terbium bis-phthalocyaninato
Monolayer@ Au(111)thick film
ID8@
The sunset of Mn12 for SpintronicsImplanted probes ( 8Li+, µµµµ+)
Muon decay (life time 2.2 µs)
Muon: S=1/2
Positrons are preferentially emitted along muon spin
µ+ e+ + νµ + νe
In collaboration with Zaher Salman @ PSI
Low energy muons
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The sunset of Mn12 for SpintronicsTbPc2 SMM films: implanted muons studiesGradual increase of the relaxation time on increasing th e distance
from the Au substrate
Molecular packing is more important than electronic interaction with the substrate
Hofmann & al ACS Nano in press:doi:10.1021/nn3031673 L. Malavolti
-3 -2 -1 0 1 2 3-0.04
0.00
0.04
Mag
netiz
atio
n
B (T)
T (K)
v=0.6T/m
1.43510152739 K
-3 -2 -1 0 1 2 3
2 K
B (T)
The sunset of Mn12 for SpintronicsTbPc2 : disappearing & reappearing hysteresis
EvaporatedThick Film
TbPc 2
MicrocrystalsTbPc 2
Powder in the crucible beforedeposition of the film
-3 -2 -1 0 1 2 3
B (T)
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-3 -2 -1 0 1 2 3
B (T )
-3 -2 -1 0 1 2 3-0 .0 4
0 .0 0
0 .0 4M
agne
tizat
ion
B (T )
T (K )
v = 0 .6 T /m
1 .4351 01 52 73 9 K
-3 -2 -1 0 1 2 3
2 K
B (T )
The sunset of Mn12 for SpintronicsTbPc2 & YPc2
EvaporatedThick Film
TbPc 2
PristineTbPc 2
HeatedTbPc 2
No correlation withIntermolecular exchangeinteractions
The sunset of Mn12 for SpintronicsTbPc2: Tunneling & Hysteresis
0.02 0.03 0.04 0.05 0.06
heated, Hdc=5kOeheated, Hdc=0 Oepristine, Hdc=5kOepristine, Hdc=0 Oe
1/T (K-1)
0.01
0.1
1
10
100
1000
60 50 40 30 20T (K)
τ (m
s)
-3 -2 -1 0 1 2 3-0.04
0.00
0.04
Mag
netiz
atio
n
B (T)
T (K)
v=0.6T/m
1.43510152739 K
-3 -2 -1 0 1 2 3
2 K
B (T)
Pristine
Heated
ττττ0 (s) ∆∆∆∆ (K) Γ Γ Γ Γqt (s-1)
TbPc2⋅⋅⋅⋅CH2Cl2 pristine
1.85(5)××××10-6 965(20) 42
TbPc2⋅⋅⋅⋅CH2Cl2 heated
1.5(1)××××10-6 856(20) 3660
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Lanthanides: a source of magnetic anisotropy
Record Blocking Temperature in a RE SMM
[{[(Me 3Si)2N]2Dy(THF)} 2(µµµµ-N2)]-
N23- S=1/2
J(R-Gd) = 27 cm -1
Anti-FerromagneticStot=13/2
Tb
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RE in high symmetry environment
Ishikawa et al. Coronado et al. Gao et al.
DyDOTA: a quasi-tetragonal SMM
Car et al. Chem. Commun. 2011
Two processes of relaxation
100
104
102
10-2
1.00.02 0.1
20%50%
0.0 4.0
H (kOe)0.4
100%τ (m
s)∼∼∼∼ C4 symmetry
H4DOTA
♦Quasi tetragonal coordination spherein Na[Dy(DOTA)(H 2O)] ⋅⋅⋅⋅4H2O (≈≈≈≈ DOTAREM MRI contrast agent)
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GiuseppeCucinotta-90 0 90 180 270
0
10
20
-x
y
x
-z
x
z
-y
z
calc. rot X rot Y rot Z
χT /
emu
K m
ol-1
θ / °
y
Single Crystal Investigations of DyDOTA
Na+
Dy3+
EXP
g1 g2 g3
17.0(1) 4.8(1) 3.4(1)
Easy axis anisotropy butnot along the pseudo-tetragonal axis
Seff = ½
♦ Post Hartree-Fock Calculationsusing CASSCF methods asimplemented in the code MOLCAS
Na+
Dy3+
EXPTHEOR
Ab-initio calculations of magnetic anisotropy
Javier Luzon
06/11/2012
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Na+
Dy3+
Th. EeasyAxis
H2ORotation of
g1 g2 g3 ∆1/cm -1
exp 17.0(1) 4.8(1) 3.4(1) 53(8) [a]
Mod. A 18.6 0.9 0.2 64
Mod. A’ 18.3 1.5 0.44 13
♦ Ab initio calculations show thatthe easy axis of magnetization isnot related to the first coordinations sphere but to the position of the hydrogen atomsof the apical water molecule
Beyond simple Magneto-Structural correlations
G. Cucinotta et al.
Tb
85° 86°
Dy
84° 78°
Ho
58°
Er
6° 48°
Tm Yb
12° 7°
Magnetic Anisotropy of the LnDOTA series
EXPTHEOR
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Tb Dy Er YbHo
Magnetic Anisotropy of Lanthanide ions
Rinehart & Long, Chemical Science 2011
|mJ|=J states are stabilized ( easy axis anisotropy ) by a axial ligand equatorial ligandoblate ion prolate ion
Tm
Tb Dy ErHo85°86° 84°78° 6°48°58° 12° 7°
Magnetic Anisotropy of LnDOTA series
EXPTHEOR
DOTA4- ligand is of equatorial typebut four-fold symmetry is broken at a larger scale
and all lanthanides have an easy axis ofmagnetization
Boulon et al. submitted
Yb
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Tb Dy Er YbHo
f8
NOSMM
NOSMM
∆∆∆∆E =61 K
∆∆∆∆E =39 K
∆∆∆∆E =29 K
Spin parity effect in LnDOTA series
f9 f10 f11 f13
g1= 12.69
g2= 2.1
g3= 0.5
18.06
0.9
0.2
6.17
3.29
1.28
10.9
2.8
1.8
6.83
1.04
0.09
Tm?
?
?
NOSMM
f12
Fe4: a high symmetry and robust SMM
ST=3x5/2-5/2=5�
Lower TB than Mn12
Fe(III) hs S=5/2OC
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Functionalization of Fe 4 clusters
By Andrea Cornia, University of Modena , Italy
S
O
O
O
O
Fe4 S
O
O
O
O
Fe4C9SAc
X-ray Magnetic Circular Dichroism at low temperature
•UHV, bakeable
•3He-4He dilution refrigerator:
T ≈ 500 mK
•Superconducting coil :-7 T < B < +7 T
French End-Station (TBT)
setup by J.-P. Kappler
(IPCMS, Strasbourg)&
Ph. Sainctavit(IMPMC. Paris)
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-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-0.02
-0.01
0.00
0.01
0.02
c
XM
CD
(a.
u)
µ0H (T)
T = 0.50 K
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-0.02
-0.01
0.00
0.01
0.02 b
XM
CD
(a.
u)
µ0H (T)
T = 0.70 K
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-0.02
-0.01
0.00
0.01
0.02
XM
CD
(a.
u)
µ0H (T)
a T = 1.0 K
Magnetic hysteresis of Fe 4 wired to a gold surface
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-0.02
-0.01
0.00
0.01
0.02
c
XM
CD
(a.
u)
µ0H (T)
T = 0.50 K
Monolayer
Bulk
Mannini et al. Nature Mat 2009: doi:10.1038/NMAT2374
DFT calculations byFederico Totti
Engineering the orientation of Fe4 SMMs
06/11/2012
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-10 0 10-30
-20
-10
0
10
20
30
θH=0°
θH=45°
θH=60°
% X
MC
D
H (kOe)
Angular Dependence of the Magnetic Hysteresis
T=650 mK
Mannini et al. Nature 2010, 468, 417
θθθθH
0 5 10
-16
-8
0
Ene
rgy
(K)
Magnetic Field (kOe)
Simulation of the Magnetic Hysteresis
-30
-20
-10
0
10
20
30
θH=0°
θH=45°
θH=60°
% X
MC
D
-10 0 10
-10
-5
0
5
10
Magnetization (µ
B )
Magnetic Field (kOe)
6.05 6.10 6.15-12.42
-12.40
-12.38
-12.36
Exp.
Calc.θθθθD=35°
∆∆∆∆EQT ∼∼∼∼ 10 mK
T=650 mK
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UHV-Preparation & characterization facilities
XPS,UPS,LEIS
Variable temperature (20 K)STM & AFM
Evaporation of metal & molecules
Surface treatment (sputterng, annealing)
STM image of Fe 4Ph evaporated on Au(111)
Au(111)
10nm
Fe4Ph is weaklybound to Au butdoes not formmultilayeraggregates
Malavolti et al.in preparation
06/11/2012
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XMCD of Fe4Ph evaporated on Au(111)
Fe4@Au; Fe L 2edge
angular dependent hysteresis
preferential orientation on the surface
θθθθ
-2 -1 0 1 2
40
20
0
-20
-40 θ = 0°
θ =45°
XM
CD
(%
)
B (T)
T=650 mK
La1-xSrxMnO3
Integrating SMMs in Spintronic Devices
Lanthanium-Strontium-ManganiteLSMO= Conducting &
Ferromagnetic
V. A. Dediu@ ISMN-CNRBologna
An evaporable Fe 4 derivative
La3+, Sr2+
Mn3+, Mn4+
O2-
06/11/2012
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Parallel evaporation of Fe 4Ph on Au & LSMO
Au/mica
LSMO 40 nm @NGO
700 710 720 730700 710 720 730
-40
-20
0
630 640 650 660 670
-30
-20
-10
0
10
% X
MC
D
Energy (eV)
Fe@Fe4/Au Fe@Fe4/LSMO
XA
S (
a.u.
)
Mn@Fe4/LSMO
Depositionof intactFe4 SMMs
Monolayer of Fe 4 on a magnetic substrate
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
-0.4
-0.2
0.0
0.2
0.4
0.6
XM
CD
B (T)
θ=0° θ=45°
Hysteresis Fe Edge
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
-0.4
-0.2
0.0
0.2
0.4
XM
CD
B (T)
θ = 45°
θ = 0°
Hysteresis Mn Edge
Fe4@Au
LSMO
T=650 mK
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
-0.4
-0.2
0.0
0.2
0.4
θ=0°
Hysteresis Fe Edge
Field (T)
XM
CD
Fe4@LSMO
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Monolayer of Fe 4 on a magnetic substrate
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
-0.4
-0.2
0.0
0.2
0.4
0.6
XM
CD
B (T)
θ=0° θ=45°
Hysteresis Fe Edge
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
-0.4
-0.2
0.0
0.2
0.4
XM
CD
B (T)
θ = 45°
θ = 0°
Hysteresis Mn Edge
Fe4@Au
LSMO
T=650 mK
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-0.4
-0.2
0.0
0.2
0.4
Fe4 @ LSMO Fe4 @ Au
Hysteresis Fe L-Edge
B (T)
XM
CD
Temperature dependence of hysteresis
60
40
20
0
-20
-40
-60
60
40
20
0
-20
-40
-60
-2 -1 0 1 260
40
20
0
-20
-40
-60
% X
MC
D
640mK 750mK 840mK
% X
MC
D%
XM
CD
Magneti Field (T)-2 -1 0 1 2
40
30
20
10
0
-10
-20
-30
-4040
30
20
10
0
-10
-20
-30
-4040
30
20
10
0
-10
-20
-30
-40
% X
MC
D
Magnetic Field (T)
% X
MC
D
640mK 750 mK 840 mK
% X
MC
D
Fe4@Au Fe4@LSMO
T=840 mK
T=750 mK
T=640 mK
No increase of T B due to the magnetic substrate
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Through-space or through-bond interactions?
Hypotheses:
���� Distribution ofdipolar fields at Fe4 sites spreadsH=0 quantum resonance
☺☺☺☺ Exchange interactionsquench the tunneling
Termination layer of LSMO
XPSLEIS
Few Å First layerhννννe-He+
He+
Lorenzo Poggini
06/11/2012
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Termination layer of LSMO
XPSLEIS
Few Å First layerhννννe-He+
He+
Mn
200 400 600 800 1000
0
500
1000
1500
2000
2500
A.U
.
K.E. (eV)
Sr
La
O
40 nmO
200 400 600 800 10000
200
400
600
800
1000
1200
1400
A.U
.
K.E. (eV)
Sr
10 nm
Fe4 on LSMO: A new proximity effect ?
Energy
Resonant QTM is suppressed
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-0.4
-0.2
0.0
0.2
0.4
Fe4 @ LSMO Fe4 @ Au
Hysteresis Fe L-Edge
Field (T)
XM
CD
Further experimental work (XMCD @ mK ) is neededto confirm this hypotesis !
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What to take home?What to take home?
• SMMs continue to represent a school of physics, now forinvestigation of magnetism and transport at the single molecule scale
• Identification of robust candidates by theoretical screen ing would help to identify promising candidate ( structural , electronic and magnetic robustness)
• Lanthanides (Actinides) are promising but control of the iranisotropy is very demanding
• Hybrid nanostructures based on molecular & more traditional magnetic materials deserve to be furtherexplored
Con
trib
utio
nsC
ontr
ibut
ions
University of Florence (Italy)•Surface Science
Dr. Matteo Mannini , Ludovica Margheriti, Francesco Pineider, Luigi Malavolti, Lorenzo Poggini, Brunetto Cortigian i
•Lanthanide based SMMMarie-Emmanuelle Boulon,Giuseppe Cucinotta, Mauro Pe rfetti
•TheoryDr. Federico Totti, S. Ninova, Dr. Javier Luzon (no w in Zaragoza)
•SynthesisPasquale Totaro
University of Modena (Italy)Prof. Andrea Cornia & coworkersUniversity of Parana (Brazil)Prof. Jaisa F. Soares & coworkers
•LSMOCNR-Bologna (Italy)Dr. V. a. Dediu & coworkers
•XAS/XMCDUniversity Pierre et Marie Curie, Paris (France)Prof. Philippe Sainctavit
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Ack
now
ledg
emen
tsA
ckno
wle
dgem
ents
…and for grants
MAGMANet (NMP3-CT-2005-515767);EC - Integrating Activity on Synchrotron and Free El ectron Laser Science;Italian MIUR (FIRB, FISR); Italian CNR
European Research CouncilProgramme IDEAS - AdGrant
(SIM- X11MA) Beamline@ SLS-PSI, Villigen (Switzerland)Frithjof Nolting, Loïc Joly, Arantxa Fraile-Rodríguez & SLS staff
ID8 Beamline @ ESRF, Grenoble (France)Julio C. Cezar & ESRF staff
Deimos Beamline @ Soleil, Paris (France)Edwige Otero & Philippe Ohresser
