Transcript Slide 1

Bulk and Interface Properties of
Winter season
Multilayer Systems
Edson Passamani Caetano
530 km
Universidade Federal do Espírito Santo
Physics Departament/Espírito Santo/Vitória/Brazil
Outline
Introduction
• Thin films/Multilayers
• Relevant discorverings in multilayers
Studied problems
• Non-collinear magnetic coupling
• Exchange bias effect
Sample preparations
• Fe/Mn/Fe trilayers (MBE)
• FeNi/FeMn/FeNi trilayers (Sputtering)
Mössbauer results
• Fe/Mn/Fe trilayers
• FeNi/FeMn/FeNi trilayers
General Remarks
Thin films/Multilayers
System with one of its dimension in nanometer scale
If the effusion cells
can be independently controlled
material A
materials A+B
substrate
substrate
substrate
Relevant Discoverings in Multilayers
From especial issue of J3M (1999)
~1400
Exchange bias
+ Spin-Valves
RKKY
GMR
AFM
Coupling
Studied Systems
Influence of interfacial roughness/alloy on the:
(i) Non-collinear coupling of Fe/Mn/Fe trilayers
(ii) EB effect in FeNi/FeMn/FeNi trilayers
Fe
How do Fe layers interact in the
simplest multilayer system?
AFM
Fe
Wegded-sample: Fe(10nm)/Cr(xnm)/Fe(10nm)
FM
90o
AFM
90o
FM
AFM
90o
FM
M1 upper Fe
M2 lower Fe
Pictures from Grunberg´s group
Yan et al. have found non-collinear coupling
in Fe/Mn/Fe (PRB 59 (1999))
Fe (5nm)
Mn
0.5 nm
0.9 nm
Fe(5nm)
1.4 nm
Sample preparation : MBE (KULeuven)
Vacuum during the deposition 6x10-11 mbar
57Fe
(1nm) deposited in both
interfaces with 0.07 Å/s
4 up to 9 nm – natFe
Rate of 0.16 Å/s
(lower layer)
or
MgO(001)
Ag(100nm)
MgO(001)
Substrate temperature (Ts) = 50-175 ºC
Si – 8 nm
natFe
4 nm
Mn (x nm) deposited with 0.04 Å/s
MgO (001)
Experimental Characterization Methods
Structural characterization
• Reflection High Energy Electron Diffraction (RHEED) – [KULeuven]
• Rutherford Back-Scaterring (RBS) – [KULeuven]
•X-ray Diffraction (low and high angles) – [KULeuven]
Magnetic Characterization
• VSM and PPMS – [KULeuven and UFES/Brazil]
• X-ray Magnetic Circular Dicroism (XMCD) – [LNLS/Brazil]
• Ferromagnetic Ressonance (FMR) – [UFG/Brazil]
Hyperfine Characterization
• Conversion Electron Mössbauer Spectroscopy (CEMS) – [KU Leuven
and UFES/Brazil]
Mössbauer Spectroscopy
M
L
K
10% 14.4 keV
100% 14.4 keV
90%
+3/2
+1/2
-1/2
-3/2
+1/2
-1/2
e80% 7.3 keV
57Fe
nucleus
Mn
γ-rays direction
Ideal interface
Transmission mode
Contagem (u.a.)
(a.u.)
Relative transmission
57Fe
1,0

0,5
-10
-8
-6
-4
-2
0
2
4
6
8
10
Energia = f(v) (mm/s)
V(mm/s)
Interface Bhf
1,35
57Fe
Emission mode
5
2
1,30
6
Relative emission
1
Emissão Relativa
1,25
Bhfbulk (natFe layer)
57
Fe
1,20
1,15
4
3
1,10
1,05
1,00
-8
MgO(001)
-6
-4
-2
0
2
V
(mm/s)
Velocidade
mm/s
4
6
8
MgO/Fe(5nm)/Mn(0.5nm)/Fe(5nm) prepared at different Ts
Trilayers ((a);(b);(c))
Trilayers ((a);(b);(c))
0
T =1500C
TSS=1500C
40
Trilayers ((a);(b);(c))
2%
2%
2%
TS=150 C
Si(8nm)
Si(8nm)
Si(8nm)
nat
nat
natFe(4nm)
Fe(4nm)
Fe(4nm)Si
35
nat
nat
nat
Fe(4nm)
Fe(4nm)
P(B
)
P(B
P(B
hf ))
hf
hf
30
0
TS=50
=500C
C
T
S
0
25
MgO(001)
MgO(001)
Bilayer
((d))
MgO(001)
Bilayer ((d))
Si(8nm)
Si(8nm)
57Fe
20
0
TS=500C
0
nat
TS=50 C
S
1%
1%1%
Relative intensity
Relative
intensity
intensity
bulkRelative
Fe fraction
(%)
0
TS=100
=1000C
C
T
S
Mn
Si
Fe(4nm)
nat
nat
Fe(4nm)
MgO(001)
15
-8 40-6
-4
-8
-8
-4
-4
-6
-6
0
2
4
6
8
0
60-2
80
100
120
o
-2V (mm/s)
0
2Growth
4 temperature
6
8
(0 C)
-2
0
V
V (mm/s)
(mm/s)
2
4
6
8
0
8
16
14024
32
8
8
B (T)24
16
16 hf 24
32
32
Bhf(T)
(T)
B
hf
160
MgO(001)
MgO(001)
57
Mn(tMn=0.5nm)
Fe(1nm)
MgO(001)
Mn(tMn=0.5nm)
=0.5nm)
Mn(t
Mn
57
57
Fe(1nm)
Fe(1nm)
TS=150 C
TS=175 C
0,0
MgO/Ag/(100nm)/Fe(10nm)/Mn(x nm)/Fe(5nm)
-0,5
1.0 nm direction
ETx==EField
anistopry + EZeeman + Eexchange
(b)
-1,0
-1,0
M/Ms
1,0
x=1.0 nm
0,0
0,5
-0,5
TT
=150 C0
S S=50 C
0,5
1,0
-0,2
Coupling energy
0
-0,5
-1,0
-0.3
-0,10
0.3
-
-0,05
0,2
0
TS=50 C
Eexch C  C (   )
0,0
(e)
1.4 nm 0,1
-0,1 x =0,0
2
M/MS
M/Ms
Magnetometry:
Field Applied // to the Film Plane
0,5
 C

(c)
C  C
0,00 0,05 0,10
0
0.3
0
μoH(T)
0.3
2
(f)
-0,10
-0.1 -0,05 0,00
0
0H(T)
Applied magnetic
field (T)
botton Fe layer
top Fe layer
0,05
0,10
0.1
MgO/Ag(100nm) substrate
(TS = 50o C)
x=1.0 nm
Upper Fe layer
Lower Fe layer
P(Bhf)
Relative intensity
θ=470
x=1.4 nm
θ~900
-8
-6
-4
-2
0
V(mm/s)
2
4
6
8
10
20
Bhf(T)
30
40
MgO/Ag(100nm)/Fe(10nm)/Mn(1nm)/Fe(5nm)
TS=50oC
Relative intensity
38% of bulk α-Fe
-8
 =47o
-6
-4
-2
0
2
4
6
8
Velocity(mm/s)
MgO/Fe(5nm)/Mn(1nm)/Fe(5nm)
17 % of bulk α-Fe
 =72o
TS=150oC
2nd problem to be shown
EB effect
EB effect Shifting of the
M(H) curve along
field axis
Hc1
Hc2
Heb= [HC1–HC2]/2
Meiklejohn and Bean
JAP 33 (1962) 1328
Sample preparation: Sputtering (CBPF)
Py=Ni80Fe20
WTi (10nm)
Py (10nm)
FeMn (15 nm)
Py (30 nm)
WTi (10nm)
FM
AFM
FM
Deposition conditions:
Vacuum: 5 x 10-8 Torr
Argon working pressure (PW):
2, 5 and 10 mTorr;
Applied field during
deposition ( 460 Oe)
TS: 20 oC
Si (100)
Samples: A2, A5 and A10
PW= 2, 5 and 10 mTorr
Interfacial effect/EB system
Heb values increase with roughness
[Uyama et al., J. Magn. Soc. Jpn. 21 (1997) 911]
Heb values reduce with roughness
[Nogués et al., PRB 59 (1999) 6984]
Samples: A2, A5 and A10
PW= 2, 5 and 10 mTorr
Relative intensity (a.u.)
X-ray Reflectivity data
1000000
100000
10000
1000
100
10
1
0,1
A10
1000000
100000
10000
1000
100
10
1
0,1
A5
1000000
100000
10000
1000
100
10
1
0,1
0,01
A2
0
1
2
3
4
2 (degree)
5
6
7
8
Si/WTi/Py(30)/FeMn(15)/Py(10)/WTi
PW= 2, 5 and 10 mTorr (A2, A5 and A10)
X-ray Reflectivity results
Sample
Thickness and roughness (nm) from the fits
A2
Py(30.5)/0.3/FeMn(13.6)/0.7/Py(10.1)
A5
Py(30.6)/0.8/FeMn(13.8)/1.1/Py(10.3)
A10
Py(30.2)/1.0/FeMn(13.1)/2.7/Py(10.1)
Py
Upper Interface
FeMn
Py
Lower interface
Samples: A2 and A10
PW= 2 and 10 mTorr
800
Heb1
600
A2
3
M (emu/cm )
400
A10
200
0
-200
-400
Heb2
-600
-800
-200
-100
0
H (Oe)
100
200
Si/WTi/Py(30)/FeMn(15)/Py(10)/WTi
PW= 2, 5 and 10 mTorr (A2, A5 and A10)
Magnetometry
Sample
Heb1 (Oe)
HC1(Oe)
Heb2(Oe)
HC2(Oe)
A2
41.4
3.1
116.1
8.4
A5
25.7
3.7
101.6
11.2
A10
29.0
5.5
62.4
20
Heb values decrease while
Hc values increase with roughness
Si/WTi(10)/Py(30)/FeMn(15)/Py(10)/WTi(10)
PW= 2, 5 and 10 mTorr (A2, A5 and A10)
A5
22 24 26 28 30 32 34
Bhf (T)
-6
2
4
6
8
0
2
4
6
8
0
2
4
6
8
P (Bhf)
P (Bhf)
A2
22 24 26 28 30 32 34
-9
0
P (Bhf)
P (Bhf)
Relative emission
22 24 26 28 30 32 34
0.2 %
P (Bhf)
P (Bhf)
A10
Bhf (T)
-3
0
V (mm/s)
3
6
9
Hyperfine parameters
Calculated fraction
Fe50Mn50 48%
Ni80Fe20 52%
Components
Ni80Fe20 (Py)
FeMn +
AFM and/or
PM interface
phases
FM interfacial
alloy
Hyperfine
parameters
Samples
A2
A5
A10
Bhf (T)
29  2
29  1
28  2
 (mm/s)
0.04  0.05
0.05  0.01
-0.02  0.09
A%
44
39
35
A%
56
57
58
Bhf (T)
-
16.6  0.1
16.2  0.4
 (mm/s)
-
-0.08  0.01
-0.06  0.01
A%
-
4
7
“chemical roughness (alloy) ” exceeds the interfacial roughness
Proposal model
Transversal view
NiFe
WTi (10nm)
Py (10nm)
FeMn (15 nm)
Rich- Fe – phase
from the NiFe
(sextet)
Ni
Fe
Mn
Roughness and/or alloy
Py (30 nm)
FeMn
WTi (10nm)
AFM
(FeMn +
(NiFe)xMny)
FM phase at
the interface
Si (100)
Fase PM
At the
interface
NiFe
General Remarks
• Bulk magnetic properties of multilayer systems are intrinsically
associated with their interface properties.
• In trilayer systems, the upper interface is usually rougher than the lower
one. In addition, the “chemical roughness (alloy)” is in general larger than
the interfacial/surface roughness.
• The magnetic coupling angles in Fe/Mn/Fe trilayers are related to their
interfacial roughnesses and therefore it is not due to the quasi-helicoidal
AFM state of Mn layer in the trilayer.
• The Py/FeMn/Py trilayers Heb  1/roughness and HC  roughness.
Theirs values are intrinsically related to the fraction of each Mössbauer
component.
UFES
KULeuven
CBPF
IF - UFG
Prof. Dr. André Vantomme (KULeuven-Belgium)
Prof. Dr. Elisa Baggio-Saitovitch (CBPF/Brazil)
Prof. Dr. Fernando Pelegrini (IFG/Brazil)
Dr. Bart de Groot (KULeuven-Belgium)
Dr. Bart Croonenborghs (KULeuven-Belgium)
Dr. Valberto Pedruzi Nascimento (CBPF/Brazil)
MSc. Breno Segatto (UFES/Brazil)
MSc. Francisco Almeida (KULeuven-Belgium)
Sponsors:
Thank you!
Magnetic structure model
Spins FM planar
Ni(+)FeMn
H direction
during
deposition
Spins AFM planares
FeMn
Spins AFM planar
NiFeMn
Spins FM
perpendicular
NiFe
Spins non-colinear
NiFe
phase FM
x
Frustation
PM clusters
x
x
x
phase PM and AFM
(FeMn and NiFeMn)