Single Molecule Magnets on Surfaces: achievements and challenges

Single Molecule Magnets on Surfaces: achievements and challenges

06/11/2012
Single Molecule Magnets on Surfaces:
achievements and challenges
Roberta Sessoli
Department of Cheistry & INSTM, University of Florence, Italy
FUNMOL - October 2012 - Bonn
Single Molecule Magnets
MnIV
S=3/2
MnIII(S=2)
∆E=
DS2
τ=τ0exp(∆E/kBT)
Stot=10
D≈-0.7 K
τ0≈10-7s
∆E/kB≈65 K
Sessoli et al. Nature 1993
Christou et al. MRS Bull. 2000
1
06/11/2012
Why magnetic molecule @ surfaces ?
STM
Electric field can be much more “local”
SMM
Address individual molecules
Scanning Probe Microscopies
Molecules in nano-junctions
Source
Drain
Gate
e-
Vb
Vg
Spacer
Spacer
Linker
Beyond SMMs
Switchable SMM
STM
Spin cross-over
UV
Cornia, Sessoli
Dalton 2012
Miyamachi et al. Nat.
Commun. 2012
Valence Tautomerism
hν, T, P, E
hν, T, P
A.Dei,
G. Poneti
E
SQ rad - CoII
Cathecol - CoIII
Sanvito
PRL,2011
2
06/11/2012
SP-STM Detection of Magnetic Bistability
Science, 2012
STM
SMM
Fen
@
Cu2N
@
Cu(100)
The sunset of Mn12 for Spintronics
Challenges
Chemical stability on surfaces
3
06/11/2012
The sunset
of Mn12 for Spintronics
TbPc
2: a robust single ion SMM
Tb3+
L=3
S=3
J=6
Thermally Evaporable
Flat
Large magnetic moment
Large anisotropy
High TB
1.4 K
3.0 K
5.0 K
10.0 K
15.0 K
27.0 K
4
M (µB)
2
0
-2
-4
-30
et al.Lett.
2009
KernKomeda
et al., Nano
2008
Hietschol et al. JACS 2011
-20
-10
0
10
20
30
H (kOe)
The sunset
of Mn single
for Spintronics
TbPc
ion SMM
2: a robust 12
Tb3+
L=3
S=3
Ishikawa et al.,
J. Am. Chem. Soc., 2003,
125, 8694-8695.
J=6
Thermally Evaporable
Flat
Large magnetic moment
Large anisotropy
High TB
∆E
∼
700 K
4
06/11/2012
The sunset
of Mn12 for Spintronics
Spintronics
architectures
based on TbPc2
a) Komeda et al. Nature Commun. 2011/ Vincent et al. Nature 2012
b) Candini et al. Nanoletters 2011
c) Urdampilleta et al. Nature Materials 2011
The sunset of Mn12 for Spintronics
Challenges
Chemical stability on surfaces
Robustness of SMM behavior
5
06/11/2012
The sunset
Mn12 for Spintronics
SMM behavior
is of
sensitive
to nanostructure
TbPc2
Terbium bisphthalocyaninato
Monolayer
@ Au(111)
thick film
ID8@
TheImplanted
sunset of Mn
12 for Spintronics
probes
(8Li+, µ+)
Muon: S=1/2
Muon decay (life time 2.2 µs)
µ+
Low energy muons
e+ + νµ + νe
Positrons are preferentially
emitted along muon spin
In collaboration with Zaher Salman @ PSI
6
06/11/2012
sunset
of Mn
12 for Spintronics
TbPc2 The
SMM
films:
implanted
muons studies
Gradual increase of the relaxation time on increasing the 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
The sunset of Mn&
Spintronics hysteresis
12 for
TbPc2 : disappearing
reappearing
Microcrystals
TbPc2
Powder in the
crucible before
T (K)
1.4
3
5
10
15
27
39 K
0.04
v=0.6T/m
Magnetization
Evaporated
Thick Film
TbPc2
deposition of the film
0.00
2K
-0.04
-3
-2
-1
0
B (T)
1
2
3
-3
-2
-1
0
B (T)
1
2
3
-3
-2
-1
0
1
2
3
B (T)
7
06/11/2012
The sunsetTbPc
of Mn12 &
forYPc
Spintronics
v = 0 .6 T /m
Magnetization
2
T (K )
1 .4
3
5
10
15
27
39 K
0 .0 4
2
0 .0 0
Pristine
TbPc2
-0 .0 4
-3
-2
-1
0
1
2
3
B (T )
Heated
TbPc2
2 K
-3
-2
-1
0
1
2
3
B (T )
Evaporated
Thick Film
TbPc2
-3
-2
-1
0
1
2
No correlation with
Intermolecular exchange
interactions
3
B (T )
The sunset
of Mn12 for
TbPc
& Spintronics
Hysteresis
2: Tunneling
0.04
v=0.6T/m
60 50
40
30
20
1000
100
0.00
10
-0.04
-3
-2
-1
0
1
2
3
B (T)
τ (ms)
Magnetization
T (K)
T (K)
1.4
3
5
10
15
27
39 K
Pristine
1
0.1
Heated
0.01
0.02
0.03
heated, Hdc=5kOe
heated, Hdc=0 Oe
pristine, Hdc=5kOe
pristine, Hdc=0 Oe
0.04
0.05
0.06
1/T
(K-1)
τ0 (s)
2K
-3
-2
-1
0
1
2
3
TbPc2⋅CH2Cl2
pristine
TbPc2⋅CH2Cl2
heated
∆ (K)
Γqt (s-1)
1.85(5)×
×10-6
965(20)
42
1.5(1)×
×10-6
856(20)
3660
B (T)
8
06/11/2012
Lanthanides: a source of magnetic anisotropy
Record Blocking Temperature in a RE SMM
[{[(Me3Si)2N]2Dy(THF)}2(µ
µ-N2)]Tb
N23- S=1/2
J(R-Gd) = 27 cm-1
Anti-Ferromagnetic
Stot=13/2
9
06/11/2012
RE in high symmetry environment
Ishikawa et al.
Gao et al.
Coronado et al.
DyDOTA: a quasi-tetragonal SMM
♦Quasi tetragonal coordination sphere
in Na[Dy(DOTA)(H2O)]⋅⋅4H2O (≈
≈ DOTAREM MRI contrast agent)
Two processes of relaxation
∼ C4 symmetry
τ (ms)
10
4
10
2
10
0
10
H4DOTA
Car et al. Chem. Commun. 2011
100%
50%
20%
-2
0.0
0.02
0.1
0.4
1.0
4.0
H (kOe)
10
06/11/2012
χT / emu K mol
-1
Single Crystal Investigations of DyDOTA
calc.
rot X
rot Y
rot Z
20
EXP
z
y
y
z
-z
-x
-y
10
0
-90
x
x
0
90
Seff = ½
g1
g2
θ/°
180
270
Giuseppe
Cucinotta
Na+
Dy3+
g3
17.0(1) 4.8(1) 3.4(1)
Easy axis anisotropy but
not along the pseudo-tetragonal axis
Ab-initio calculations of magnetic anisotropy
♦ Post Hartree-Fock Calculations
using CASSCF methods as
implemented in the code MOLCAS
Javier
Luzon
THEOR
EXP
Na+
Dy3+
11
06/11/2012
Beyond simple Magneto-Structural correlations
Th. Eeasy
Axis
Rotation 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
H2O
♦ Ab initio calculations show that
the easy axis of magnetization is
not related to the first
coordinations sphere but to the
position of the hydrogen atoms
of the apical water molecule
Na+
Dy3+
G. Cucinotta et al.
Magnetic Anisotropy of the LnDOTA series
Tb
Dy
Ho
Er
58°
6° 48°
Tm
Yb
THEOR
EXP
85° 86°
84° 78°
12° 7°
12
06/11/2012
Magnetic Anisotropy of Lanthanide ions
|mJ|=J states are stabilized (easy axis anisotropy) by a
axial ligand
equatorial ligand
oblate ion
prolate ion
Tb
Dy
Ho
Er
Tm
Yb
Rinehart & Long, Chemical Science 2011
Magnetic Anisotropy of LnDOTA series
Tb
85°86°
THEOR
EXP
Dy
Ho
Er
Yb
84°78°
58°
6°48°
12° 7°
DOTA4- ligand is of equatorial type
but four-fold symmetry is broken at a larger scale
and all lanthanides have an easy axis of
magnetization
Boulon et al. submitted
13
06/11/2012
Spin parity effect in LnDOTA series
Tb
Yb
Dy
Ho
Er
Tm
18.06
0.9
0.2
6.17
3.29
1.28
10.9
2.8
1.8
?
?
?
6.83
1.04
0.09
f8
f9
f10
f11
f12
f13
NO
SMM
∆E =
61 K
NO
SMM
NO
SMM
∆E =
29 K
g1= 12.69
g2= 2.1
g3= 0.5
∆E =
39 K
Fe4: a high symmetry and robust SMM
ST=3x5/2-5/2=5
Lower TB than Mn12
Fe(III) hs S=5/2
O
C
14
06/11/2012
Functionalization of Fe4 clusters
O
O
O
S
O
Fe4
O
O
O
S
O
Fe4C9SAc
By Andrea Cornia, University of Modena , Italy
X-ray Magnetic Circular Dichroism at low temperature
French End-Station
(TBT)
setup by
J.-P. Kappler
(IPCMS, Strasbourg)
&
Ph. Sainctavit
(IMPMC. Paris)
•UHV, bakeable
•3He-4He dilution refrigerator:
T ≈ 500 mK
•Superconducting coil :
-7 T < B < +7 T
15
06/11/2012
Magnetic hysteresis of Fe4 wired to a gold surface
0.01
0.00
-0.01
-0.02
b T = 0.70 K
0.01
0.00
-0.01
-0.02
-1.5 -1.0 -0.5
0.0
µ0H (T)
0.5
1.0
1.5
c T = 0.50
0.02K
0.02
XMCD (a.u)
0.02
XMCD (a.u)
a T = 1.0 K
XMCD (a.u)
XMCD (a.u)
0.02
-1.5 -1.0 -0.5
0.01
0.00
c T = 0.50 K
0.01
0.00
-0.01
-0.02
-0.01
0.0
0.5
1.0
1.5
-1.5
µ0H (T)
-0.02
-1.0 -0.5
0.0
0.5
1.0
1.5
µ0H (T)
Monolayer
-1.5 -1.0 -0.5
0.0
0.5
1.0
1.5
µ0H (T)
Bulk
Mannini et al. Nature Mat 2009: doi:10.1038/NMAT2374
Engineering the orientation of Fe4 SMMs
DFT calculations by
Federico Totti
16
06/11/2012
Angular Dependence of the Magnetic Hysteresis
θH
30
20
% XMCD
10
θH=0°
θH=45°
T=650 mK
θH=60°
0
-10
-20
-30
-10
0
Mannini et al. Nature 2010, 468, 417
10
H (kOe)
Simulation of the Magnetic Hysteresis
T=650 mK
30
% XMCD
10
0
θH=0°
θH=45°
Energy (K)
20
θH=60°
0
-10
-8
-16
-20
Exp.
0
-30
0
Calc.
θD=35°
-10
0
Magnetic Field (kOe)
10
-5
-10
10
Magnetization (µB)
5
5
Magnetic Field (kOe)
10
-12.36
-12.38
-12.40
-12.42
6.05
6.10
6.15
∆EQT ∼ 10 mK
17
06/11/2012
UHV-Preparation & characterization facilities
XPS,UPS,LEIS
Surface treatment
(sputterng, annealing)
Evaporation of metal
& molecules
Variable temperature (20 K)
STM & AFM
STM image of Fe4Ph evaporated on Au(111)
Au(111)
Fe4Ph is weakly
bound to Au but
does not form
multilayer
aggregates
10
nm
Malavolti et al.in preparation
18
06/11/2012
XMCD of Fe4Ph evaporated on Au(111)
Fe4@Au; Fe L2edge
θ
θ
-40
= 0°
=45°
XMCD (%)
-20
0
θ
20
T=650 mK
40
-2
-1
0
1
2
B (T)
angular dependent hysteresis
preferential orientation on the surface
Integrating SMMs in Spintronic Devices
Lanthanium-Strontium-Manganite
LSMO= Conducting &
Ferromagnetic
An evaporable Fe4 derivative
La3+, Sr2+
Mn3+, Mn4+
O2-
La1-xSrxMnO3
V. A. Dediu
@ ISMN-CNR
Bologna
19
06/11/2012
Parallel evaporation of Fe4Ph on Au & LSMO
Au/mica
LSMO 40 nm @NGO
Fe@Fe4/LSMO
Mn@Fe4/LSMO
XAS (a.u.)
Fe@Fe4/Au
% XMCD
Deposition
of intact
Fe4 SMMs
0
10
-20
-10
0
-20
-30
-40
700
710
720
730
700
710
720
Energy (eV)
730
630
640
650
660
670
Monolayer of Fe4 on a magnetic substrate
Hysteresis Mn Edge
0.4
XMCD
0.2
T=650 mK
θ = 45°
θ = 0°
Hysteresis Fe Edge
0.0
0.4
-0.2
-2.0 -1.5 -1.0 -0.5 0.0
0.5
1.0
1.5
2.0
B (T)
0.6
0.4
Hysteresis Fe Edge
XMCD
0.2
LSMO
-0.4
θ=0°
0.0
Fe4@LSMO
-0.2
θ=0°
θ=45°
-0.4
XMCD
0.2
-2.0 -1.5 -1.0 -0.5 0.0
0.0
0.5
1.0
1.5
2.0
Field (T)
-0.2
Fe4@Au
-0.4
-2.0 -1.5 -1.0 -0.5 0.0
0.5
1.0
1.5
2.0
B (T)
20
06/11/2012
Monolayer of Fe4 on a magnetic substrate
Hysteresis Mn Edge
0.4
0.2
XMCD
T=650 mK
θ = 45°
θ = 0°
Hysteresis Fe L-Edge
0.0
0.4
-0.2
-2.0 -1.5 -1.0 -0.5 0.0
0.5
1.0
1.5
2.0
B (T)
Hysteresis Fe Edge
0.6
0.0
-0.2
θ=0°
θ=45°
0.4
XMCD
0.2
LSMO
-0.4
Fe4 @ LSMO
Fe4 @ Au
-0.4
-1.5
-1.0
-0.5
0.0
0.0
0.5
1.0
1.5
B (T)
-0.2
Fe4@Au
-0.4
-2.0 -1.5 -1.0 -0.5 0.0
0.5
1.0
1.5
2.0
B (T)
Temperature dependence of hysteresis
Fe4@Au
Fe4@LSMO
-60
-40
-40
640mK
750mK
840mK
-30
-20
-10
0
T=840 mK
20
% XMCD
% XMCD
-20
640mK
750 mK
840 mK
0
10
20
40
30
-60
60
40
-40
-30
-40
-20
-10
T=750 mK
0
20
% XMCD
% XMCD
-20
0
10
20
40
30
-60
60
40
-40
-30
-40
-20
-20
-10
0
T=640 mK
20
% XMCD
% XMCD
XMCD
0.2
0
10
20
30
40
40
60
-2
-1
0
1
Magneti Field (T)
2
-2
-1
0
1
2
Magnetic Field (T)
No increase of TB due to the magnetic substrate
21
06/11/2012
Through-space or through-bond interactions?
Hypotheses:
Distribution of
dipolar fields at
Fe4 sites spreads
H=0 quantum
resonance
☺ Exchange
interactions
quench the
tunneling
Termination layer of LSMO
XPS
Few Å
hν
ν
He+
LEIS
First layer
e- He+
Lorenzo
Poggini
22
06/11/2012
Termination layer of LSMO
XPS
Few Å
hν
ν
He+
LEIS
First layer
e- He+
1400
10 nm
40 nm
O
1200
2500
A.U.
A.U.
1000
2000
800
1500
600
1000
400
Sr
Mn
Sr
O
La
500
200
0
0
200
200
400
400
600
600
K.E.
(eV)
K.E.
(eV)
800
800
1000
1000
Fe4 on LSMO: A new proximity effect ?
Hysteresis Fe L-Edge
0.4
Fe4 @ LSMO
Fe4 @ Au
XMCD
0.2
0.0
-0.2
-0.4
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
Energy
Field (T)
Further experimental work
(XMCD @ mK ) is needed
to confirm this hypotesis !
Resonant QTM is suppressed
23
06/11/2012
What to take home?
• SMMs continue to represent a school of physics, now for
investigation of magnetism and transport at the single
molecule scale
• Identification of robust candidates by theoretical screening
would help to identify promising candidate ( structural,
electronic and magnetic robustness)
• Lanthanides (Actinides) are promising but control of their
anisotropy is very demanding
Contributions
• Hybrid nanostructures based on molecular & more
traditional magnetic materials deserve to be further
explored
University of Florence (Italy)
•Surface Science
Dr. Matteo Mannini, Ludovica Margheriti, Francesco Pineider,
Luigi Malavolti, Lorenzo Poggini, Brunetto Cortigiani
•Lanthanide based SMM
Marie-Emmanuelle Boulon,Giuseppe Cucinotta, Mauro Perfetti
•Theory
Dr. Federico Totti, S. Ninova, Dr. Javier Luzon (now in Zaragoza)
•Synthesis
Pasquale Totaro
University of Modena (Italy)
Prof. Andrea Cornia & coworkers
University of Parana (Brazil)
Prof. Jaisa F. Soares & coworkers
•LSMO
CNR-Bologna (Italy)
Dr. V. a. Dediu & coworkers
•XAS/XMCD
University Pierre et Marie Curie, Paris (France)
Prof. Philippe Sainctavit
24
Acknowledgements
06/11/2012
(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
…and
for grants
MAGMANet (NMP3-CT-2005-515767);
EC - Integrating Activity on Synchrotron and Free Electron Laser Science;
Italian MIUR (FIRB, FISR); Italian CNR
European Research Council
Programme IDEAS - AdGrant
25