Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Magnetism of nanoparticles: non magnetic metals, core shell, exchange bias
M. A. Garcia
Instituto de Cerámica y Vidrio
CSIC
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
many thanks to….. Antonio Hernando Jesus Gonzalez Puer to Morales Sabino Veintemillas Mar Garcia-Hernández Axel Hoffman Jesus Chaboy Jose Luis Vicent Lucas Perez Julio Camarero Ivan Schuller Davide Cozzoli Teresa Pellegrino Cesar de Julian Hari Srikanth German Castro Jose Costa Pietro Gambardella
Adrian Quesada Jose de la Venta Virginia Bouzas Sandra Martinez Bustos Aida Serrano Esther Enriquez Alvaro Muñoz Fernando Galvez Ana Espinosa Enrique Fernandez Pinel
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Outline I. Nanoscale effects in magnetic materials -Monodomain regime -Superparamagnetism Proximity effects :Exchange bias
II: Nanoscale induced magnetism -Size effects -Proximity polarization -Surface induced magnetism
III. Measurement of nanoscale magnetism -Traditional magnetometry -XMCD & Neutrons (brief)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
I. Nanoscale effects in magnetic materials
…size matters……
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Size effects
NPs has similar size to relavant parameters of physical processes
Macroscopic systems (size>>> typical) periodic conditions
NP: Boundary Conditions(size typical)
HY=E Y
…… ……
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Surface effects
Surface atoms are different to volume ones
0 100 200 300 400 5001E-3
0.01
0.1
1
Ato
mos
. sup/A
tom
os
volu
men
R (nm)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
FM NM
M
FM FM
Interaction is of the order of few nanometers
For nanoparticles this region be a significant part of the
whole material
Proximity effects
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Monodomain regime
Domains decrease the magnetostatic energy
Domains are separated by domain walls
Domain wall width (exchange correlation
length) is few nanometers
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Monodomain regime
Domains walls have a certain energy
- Eexchange
- Eanisotropy
For small nanoparticles is more favourable to have no domains walls
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Monodomain regime
Two different mechanisms for
magnetization rotation
Coherent spin rotation
H
Domain wall motion H
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Moodomine regime
In monodomain nanoparticles there is no domain walls
Increase of the Coercive force
Hc
Particle size
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Superparamagnetism
Energy Barrier = KV
Thermal Energy= KBT
Relaxation Tk
VK
Be·
·
0· =
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Superparamagnetism
Time
M
Time
M
H=0 H0
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Superparamagnetismo
Hc
Particle size
If relaxation time is measuring time
Coercitivity drops (Big problem for data storage)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Fingerprints of superparamagnetism
KV≈25 KBT
L(x)=coth(x)-1/x
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Exchange bias
FM AFM
Junction of FM & AFM
TC>TN
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
H TC
TN
Cooling with field
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
M
H
Magnetization curve
FM FM+AFM
Increase of coercivity
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Exchange bias was discovered by W. H. Meiklejohn in 1957
EB is not fully understood
It has been observed in FM/AFM FM/FiM FiM/AFM FiM/FiM FM/disordered layer
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Exchange bias in core-shell nanoparticles
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
EB in Co/CoO nanoparticles
Co
EB in Fe3O4/Fe2O3
Co
Fe3O4
Naturally oxidized EB
EB depends critically on the shell thickness
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
…some reviews……..
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
II. Nanoscale induced magnetism
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Proximity polarization
FM NM
Interface region of the NM will exhibit some magnetic polarization
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Materials “close to be ferromagnetic”?
Magnetic nanoparticles
Close to satisfy Stoner criterion
EF
To change the spin of one electron:
Increase of orbital energy E=1/N(EF)
Energy balance: E=1/N(EF)-I<0
N(EF)·I>1 (Stoner criterion)
N(EF)
1
Decrease of Exchange energy: I
(Stoner parameter)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Pd (FCC) is a paramagnetic metal
2.4 nm Pd NP exhibit ferromagnetism
Ferromagnetism in Pd nanoparticles
-2000 -1000 0 1000 2000
-0,04
-0,02
0,00
0,02
0,04
M (
em
u/g
)
H (Oe)
M (
em
u/g
)*10
-3
H (Oe)
T = 100K
T = 200K
T = 275K
-100 -50 0 50 100
-5,0
-2,5
0,0
2,5
5,0
5K
100K
200K
275K
B. Sampedro et al, PRL 91 (2003) 237203 0 50 100 150 200
0,00
0,01
0,02
0,03
0,04
0,05 Pd NP ( 2.4 nm)
Pd bulk
T (K)
M (
em
u/g
)*10
-3
M (
em
u/g
)
T (K)
0 50 100 150 200
6,0
6,5
7,0
7,5
Blocking T is over 300 K
N(EF)·I=0.87<1 (non ferromagnetic behaviour)
N(EF)=1.23 eV-1 spin-1atom -1
I =0.71 eV
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
HREM studies found a large number of twin boundaries
Ferromagnetism in Pd nanoparticles
Twin boundaries reduce the energy of the NP
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
FCC metals present:
-Highly anisotropic Surface Energy
- Low formation energy for twin boundaries
Ferromagnetism in Pd nanoparticles
Es
Es
Es Es
Es
Es Es
Es
The presence of twin boundaries reduce ESurface
The increase of Evolume is low
Total energy decreases with twin boundaries
Es Es
Es Es
Es Es
Es
Es
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Ferromagnetism in Pd nanoparticles
Only atoms close to the TB contributes to ferromagnetism Low MS (10-3 B atom-1)
Cubic symmetry splits d levels
At the twin boundaries there is a lack of symmetry No splitting of the 4d level
t2g
Local enhancement of N(EF)
Stoner criterion is satisfied !!
Lack of symmetry at the TB blocks the angular momentum
L S
Pd exhibits large spin-orbit couplingLarge K TB >300 K
4d
eg
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Ferromagnetism in Pt nanoparticles
Pt is similar to Pd: - FCC metal
- N (EF)=0.9 eV-1
- I=0.85 eV atom-1
Stoner criterion almost satisfied
2-5 nm Pt NP exhibit FM
-8000 -6000 -4000 -2000 0 2000 4000 6000 8000
-1,0x10-2
-5,0x10-3
0,0
5,0x10-3
1,0x10-2
5K
50 K
300K
M (
em
u/g
Pt)
H (Oe)
Blocking T is over 300 K
0 50 100 150 200 250 300
8,5x10-3
9,0x10-3
9,5x10-3
1,0x10-2
M (
em
u/g
Pt)
T (K)
M. A. Garcia et al, Nanotech. to be publish
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Ferromagnetism in Pt nanoparticles
(c)
(d)
5 nm
(b)
[101]
0.23 nm
111
111
(a)
(c)
(d)
5 nm
(b) (c)(c)
(d)(d)
5 nm
(b)
5 nm5 nm
(b)
[101]
0.23 nm
[101][101][101]
0.23 nm
111
111
(a)
111
111
111
111
(a)Pt NP also exhibit:
- a large density of twin boundaries - low MS.
The same mechanism than Pd
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Effects in diamagnetic materials?
What we need for ferromagnetic behaviour?
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
L
S
For a single atom
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
In a solid……..Magnetocrystalline anisotropy
L
S
E
2 0
For an atom
KV~ eV
KBT~meV
Energy barrier= KV
Thermal energy= KBT
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
To observe FM we need to increase energy barriers
Exchange: Interaction between magnetic moments tending to keep them aligned
E
2 0
Barrier: E
E
2 0
Barrier n·E
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
We should need huge anisotropy to observe FM in single atoms
Co atom
Pt (111)
Gambardella, Rusponi et al Science 300 (2003) 1130
Co-Pt bond blocks Co L
Spin-orbit copling blocks S
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Anisotropy is always increased in surfaces: Symmetry broken
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Magnetic moments can be induced by bonds
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Gold Nanoparticles
Holes in 5d orbital via thiol bonding
Very large spin-orbit coupling
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Two set of samples:
Au-SR sample: Gold NPs capped with thiol groups
(dodecane alkyl chain)
Strong interaction with Au at surface
Au-NR sample: Gold NPs stabilized by a surfactant
(tetraoctyl ammonium bromide).
Weak interaction with Au at surface of the NP
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
0 1 2 3 4 50
5
10
15
20
25
30
Dm=1.4 nm
% P
art
icle
s
D (nm)
0 1 2 3 4 5 6 70
10
20
30
40
% P
artic
les
D (nm)
D=1.5-5 nm
100nm0 10 20 30 40 50 60
0
0.5
1
1.5
2
2.5
3
3.5
X[nm]
Z[n
m]
Au-NR
Au-SR
AFM Dispersed NP
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
-10000 -5000 0 5000 10000
-1,0
-0,5
0,0
0,5
1,0
-10000 -5000 0 5000 10000
-0,006
-0,004
-0,002
0,000
0,002
0,004
0,006
T=300K
T=5K
Au-SR
M (
em
u/g
Au
)
H(Oe)
T=5K
T=300K Au-NR
M (
em
u/g
)
H(Oe)
SR samples present ferromagnetic-like behaviour up
to 300 K
-10000 -5000 0 5000 10000
-1,0
-0,5
0,0
0,5
1,0
-10000 -5000 0 5000 10000
-0,006
-0,004
-0,002
0,000
0,002
0,004
0,006
b)
T=300K
T=5K
Au-SR
M (
em
u/g
Au
)
H(Oe)
a)
T=5K
T=300K Au-NR
M (
em
u/g
)
H(Oe)
NR Samples are diamagnetic (as bulk gold)
Magnetic properties
The capping molecule determines the magnetic behaviour of the NP
P. Crespo et al, PRL 93 (2004) 087204
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Au L3 XANES Spectra
There is charge transfer from Au(5d) to S(2p).
Increase of d holes density at the surface Au atoms.
S Au
-10 0 10 20 30 400,0
0,4
0,8
1,2 Au-foil
Au-surfactant
Au-thiol
Norm
alized y
ield
(a.
u.)
E-E0
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
ZnO Nanoparticles
TOPO
Tryoctylphosphine
THIOL
Dodecanethiol
AMINE
Tryoctylamine
NPs capped with different molecules
-O -N -S
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Crystallographic structure does not depend on the molecule
ZnO wurtzite structure
10 nm
30 40 50 600
1
2
3
4
5
TOPO
THIOL
(103)
(110)
(102)
(101)
(002)
Inte
nsity (
arb
.un
.)
2
(100)
AMINE
(a)
7 nm
(b)
0.25 nm
(c)
101
(d)1017 nm
(b)
0.25 nm
(c)
101
(d)1017 nm
7 nm
(b)
0.25 nm
(c)
101
(d)101
101
(d)101101
30 40 50 600
1
2
3
4
5
TOPO
THIOL
(103)
(110)
(102)
(101)
(002)
Inte
nsity (
arb
.un
.)
2
(100)
AMINE
(a)
7 nm
(b)
0.25 nm
(c)
101
(d)1017 nm
7 nm
(b)
0.25 nm
(c)
101
(d)101
101
(d)1011017 nm
7 nm
(b)
0.25 nm
(c)
101
(d)101
101
(d)1011017 nm
7 nm
(b)
0.25 nm
(c)
101
(d)101101
101
(d)101101
XRD TEM
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XANES spectra
(Zn K-edge)
-20 0 20 40 60 80 100 1200,0
0,5
1,0
Norm
alise
d Y
ield
(a.u
)
E-Eo (eV)
THIOL
AMINE
TOPO
-20 0 20 40 60 80 100 1200,0
0,5
1,0
Norm
alise
d Y
ield
(a.u
)
E-Eo (eV)
THIOL
AMINE
TOPO
Different degree of occupation of the Zn outer orbitals depending on the molecule.
Different charge transfer for each molecule !!
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Photoluminescence
The energy levels are altered by the molecule
500 550 600 6500
2
4
6
8
10
12
THIOL
AMINE
PL
In
ten
stity
(a
rb.
un
.)
Wavelength (nm)
TOPO
(3.4 eV) (2.3 eV)
(a)
(b)
500 550 600 6500
2
4
6
8
10
12
THIOL
AMINE
PL
In
ten
stity
(a
rb.
un
.)
Wavelength (nm)
TOPO
(3.4 eV) (2.3 eV)
(a)
(b)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
M. A. Garcia et al, Nano Letters 7 (2007) 1489.
Magnetic Properties
-10000 -5000 0 5000 10000
-0,003
-0,002
-0,001
0,000
0,001
0,002
0,003
300 K
THIOL
AMINE
TOPO
M (
em
u/g
)
H (Oe)
(a) (b)
(c) (d)
-10000 -5000 0 5000 10000
-0,003
-0,002
-0,001
0,000
0,001
0,002
0,003 THIOL
AMINE
TOPO
5 K
M (
em
u/g
)
H (Oe)
-10000 -5000 0 5000 10000-0,006
-0,003
0,000
0,003
0,006
THIOL
AMINE
TOPO
5 K
M (
em
u/g
)
H(Oe)
-10000 -5000 0 5000 10000-0,006
-0,003
0,000
0,003
0,006
THIOL
AMINE
TOPO
M (
em
u/g
)
H (Oe)
300 K
0 100 200 300
M
T (K)
-10000 -5000 0 5000 10000
-0,003
-0,002
-0,001
0,000
0,001
0,002
0,003
300 K
THIOL
AMINE
TOPO
M (
em
u/g
)
H (Oe)
(a) (b)
(c) (d)
-10000 -5000 0 5000 10000
-0,003
-0,002
-0,001
0,000
0,001
0,002
0,003 THIOL
AMINE
TOPO
5 K
M (
em
u/g
)
H (Oe)
-10000 -5000 0 5000 10000-0,006
-0,003
0,000
0,003
0,006
THIOL
AMINE
TOPO
5 K
M (
em
u/g
)
H(Oe)
-10000 -5000 0 5000 10000-0,006
-0,003
0,000
0,003
0,006
THIOL
AMINE
TOPO
M (
em
u/g
)
H (Oe)
300 K
0 100 200 300
M
T (K)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Correlation between structure and magnetism
500 550 600 6500
2
4
6
8
10
12
THIOL
AMINE
PL
In
ten
stity
(a
rb.
un
.)
Wavelength (nm)
TOPO
(3.4 eV) (2.3 eV)
(a)
(b)
500 550 600 6500
2
4
6
8
10
12
THIOL
AMINE
PL
In
ten
stity
(a
rb.
un
.)
Wavelength (nm)
TOPO
(3.4 eV) (2.3 eV)
(a)
(b)
-20 0 20 40 60 80 100 1200,0
0,5
1,0
Nor
mal
ised
Yie
ld (a
.u)
E-Eo (eV)
THIOL
AMINE
TOPO
-20 0 20 40 60 80 100 1200,0
0,5
1,0
Nor
mal
ised
Yie
ld (a
.u)
E-Eo (eV)
THIOL
AMINE
TOPO
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Reproducibility?
25 nm ZnO NPs
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Reproducibility
-60 -40 -20 0 20 40 60-30
-20
-10
0
10
20
30
M (
mem
u/g
)
H (KOe)
THIOL
AMINE
TOPO
5K
a
-60 -40 -20 0 20 40 60-4
-3
-2
-1
0
1
2
3
M (
mem
u/g
)
H (KOe)
THIOL
AMINE
TOPO
5 K
b
0 50 100 150 200 250 300
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
M (
mem
u/g
)
T (K)
THIOL
AMINE
TOPO
H=1000 Oe
c
-60 -40 -20 0 20 40 60-15
-10
-5
0
5
10
15
M (
me
mu
/g)
H (KOe)
THIOL
AMINE
TOPO
5K
d
-60 -40 -20 0 20 40 60-30
-20
-10
0
10
20
30
M (
mem
u/g
)
H (KOe)
THIOL
AMINE
TOPO
5K
a
-60 -40 -20 0 20 40 60-4
-3
-2
-1
0
1
2
3
M (
mem
u/g
)
H (KOe)
THIOL
AMINE
TOPO
5 K
b
0 50 100 150 200 250 300
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
M (
mem
u/g
)
T (K)
THIOL
AMINE
TOPO
H=1000 Oe
c
-60 -40 -20 0 20 40 60-15
-10
-5
0
5
10
15
M (
me
mu
/g)
H (KOe)
THIOL
AMINE
TOPO
5K
d
Different dependence on the molecule
Same correlation electronic structure -magnetism
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Origin of the magnetism
Magnetism in ZnO (and other 3d oxides) is explained as due to unbalanced 3d holes with
some exchange interactions
1s
2s
2p
3s
3p
4s
3d
Zn Zn O
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XMCD
XMCD ZnO L3 edge (2p→3d)
APS
XMCD ZnO K edge (1s→4p)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XMCD
Magnetism is at the 4p -> CONDUCTION BAND
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
III. Measurement of nanoscale magnetism
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Magnetic measurements with lab magnetometers
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Los sistemas de magnetometría SQUID, VSM miden por VSM& SQUID detect ALL the magnetic flux across the coil
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Valores de Imanación: Fe: 220 emu/g
Co: 160 emu/g
Fe3O4: 83 emu/g
10-5 emu=5·10-8 g de Fe !!!
A 15 μm particle could account for this signal
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Kapton tape
-10 -5 0 5 10-6
-4
-2
0
2
4
6
M (
e
mu
/cm
)
H (kOe)-10 -5 0 5 10
-40
-20
0
20
40
M (
e
mu
/cm
)
H (kOe)
(a) (b)
(d)(c)
-10 -5 0 5 10
-15
-10
-5
0
5
10
15
m (
e
mu
)
H (kOe)
-20 -10 0 10 20
-10
0
10
5K
300 K
m (
e
mu
)
H (kOe)
-10 -5 0 5 10-6
-4
-2
0
2
4
6
M (
e
mu
/cm
)
H (kOe)-10 -5 0 5 10
-40
-20
0
20
40
M (
e
mu
/cm
)
H (kOe)
(a) (b)
(d)(c)
-10 -5 0 5 10
-15
-10
-5
0
5
10
15
m (
e
mu
)
H (kOe)
-20 -10 0 10 20
-10
0
10
5K
300 K
m (
e
mu
)
H (kOe)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Kapton tape
-10 -5 0 5 10-6
-4
-2
0
2
4
6
M (
e
mu
/cm
)
H (kOe)-10 -5 0 5 10
-40
-20
0
20
40
M (
e
mu
/cm
)
H (kOe)
(a) (b)
(d)(c)
-10 -5 0 5 10
-15
-10
-5
0
5
10
15
m (
e
mu
)
H (kOe)
-20 -10 0 10 20
-10
0
10
5K
300 K
m (
e
mu
)
H (kOe)
-10 -5 0 5 10-6
-4
-2
0
2
4
6
M (
e
mu
/cm
)
H (kOe)-10 -5 0 5 10
-40
-20
0
20
40
M (
e
mu
/cm
)
H (kOe)
(a) (b)
(d)(c)
-10 -5 0 5 10
-15
-10
-5
0
5
10
15
m (
e
mu
)
H (kOe)
-20 -10 0 10 20
-10
0
10
5K
300 K
m (
e
mu
)
H (kOe)
Cinta Kapton sin bolsa: m>2μemu ~60-70%
Cinta Kapton en bolsa hermética: m>2μemu ~10-20%
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Kapton tape
-10 -5 0 5 10-6
-4
-2
0
2
4
6 As received
30 min exposed to air
M
(e
mu
/cm
)
H (kOe)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Kapton tape
-10 -5 0 5 10
-15
-10
-5
0
5
10
15 Stored in air
Removing edges
m (
e
mu
)
H (kOe)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Metallic twizzers
(a)(b)
-10 -5 0 5 10-200
-100
0
100
200
Clean
Iron tweezers pressed
m (
e
mu
)
H (kOe)
-10 -5 0 5 10
-100
-50
0
50
100
m (
e
mu
)
H(kOe)
(a)(b)
-10 -5 0 5 10-200
-100
0
100
200
Clean
Iron tweezers pressed
m (
e
mu
)
H (kOe)
-10 -5 0 5 10
-100
-50
0
50
100
m (
e
mu
)
H(kOe)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Metallic twizeers
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
-10 -5 0 5 10-3
-2
-1
0
1
2
3
Nylon sieve
Iron sieve
H (kOe)
M (
me
mu
/g)
2.5 m
KeV
Co
un
ts
KeV
Co
un
ts
(a)
(c) (d)
(b)
-10 -5 0 5 10-3
-2
-1
0
1
2
3
Nylon sieve
Iron sieve
H (kOe)
M (
me
mu
/g)
2.5 m
KeV
Co
un
ts
KeV
Co
un
ts
(a)
(c) (d)
(b)
Metallic twizzers
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Cotton
-20 -10 0 10 20-8
-4
0
4
8
-0.2
-0.1
0.0
0.1
0.2
M (
em
u/g
)
m
(m
em
u)
H (KOe)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Silver paint
-8 -4 0 4 8-1.0
-0.5
0.0
0.5
1.0
M(e
mu
/g)
H (KOe)
Tintas de rotulador (roja !!!) ~4 x 10-5 emu
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Plastic sampleholders
-10 -5 0 5 10
-4
-2
0
2
4
New straw
Deformed straw
m (
e
mu
)
H (KOe)
300K
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Sample position
dR
m
0.0 0.2 0.4 0.6 0.8 1.0
1.0
1.5
2.0
2.5
3.0
Ma
gn
etic f
lux (
arb
. u
nits)
d/R
(b)(a)
dR
m
0.0 0.2 0.4 0.6 0.8 1.0
1.0
1.5
2.0
2.5
3.0
Ma
gn
etic f
lux (
arb
. u
nits)
d/R
(b)(a)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Sample position: Anisotropy?
-10 -5 0 5 10
-100
-50
0
50
100
H perpendicular
H parallel
M (
e
mu
)
H (kOe)-10 -5 0 5 10
-200
-100
0
100
200 H perpendicular
H parallel
M (
e
mu
)H (kOe)
(a)
(b)
-10 -5 0 5 10
-100
-50
0
50
100
H perpendicular
H parallel
M (
e
mu
)
H (kOe)-10 -5 0 5 10
-200
-100
0
100
200 H perpendicular
H parallel
M (
e
mu
)H (kOe)
(a)
(b)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
Element specific techniques are required for confirmation -XMCD .Neutrons
For reliability
For a better understanding
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XMCD in Au Nanoparticles
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XMCD in Au Nanoparticles
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XMCD & Neutrons in Au Nanoparticles
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XMCD in Au Nanoparticles
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XMCD in ZnO nanoparticles
XMCD ZnO L3 edge (2p→3d)
APS
XMCD ZnO K edge (1s→4p)
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
XMCD
Magnetism is at the 4p -> CONDUCTION BAND
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
….in summary……
Magnetic materials modify their properties at the nanoscale
New magnetic effects appear at the nanoscale
Experimental measurement of nanomagnetism requires
specific techniques and protocols.
Novel Frontiers of Magnetism
Benasque 10-14 February , 2014 M. A. Garcia
APS + IPNS
http://www.bonsai-project.eu
EU 6th FP- Proyecto BONSAI …and money came from….
…..and user programs of:
Proyecto FIS-2008-469
Proyecto PIF
2007-50I015
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