bulk and interface properties of multilayer systems edson passamani caetano universidade federal do...
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Bulk and Interface Properties of Bulk and Interface Properties of Multilayer SystemsMultilayer Systems
Edson Passamani Caetano
Universidade Federal do Espírito Santo Physics Departament/Espírito Santo/Vitória/Brazil
530 km
Winter season
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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
Introduction• Thin films/Multilayers
• Relevant discorverings in multilayers
Outline
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Thin films/Multilayers
If the effusion cells
can be independently controlled
substrate
materials A+B
substrate
material A
substrate
System with one of its dimension in nanometer scale
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From especial issue of J3M (1999)~1400
AFM Coupling
GMR
RKKY
Relevant Discoverings in Multilayers
Exchange bias+ Spin-Valves
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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
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AFM
FM
90o
FM90oAFM
90o
FM
M1 upper Fe
M2 lower Fe
Wegded-sample: Fe(10nm)/Cr(xnm)/Fe(10nm)
Pictures from Grunberg´s group
How do Fe layers interact in the simplest multilayer system?
Fe
Fe
AFM
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Yan et al. have found non-collinear coupling in Fe/Mn/Fe (PRB 59 (1999))
Fe (5nm)Mn
Fe(5nm)0.5 nm 0.9 nm 1.4 nm
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Sample preparation : MBE (KULeuven)Vacuum during the deposition 6x10-11 mbar
Substrate temperature (Ts) = 50-175 ºC
MgO(001)
4 up to 9 nm – natFe Rate of 0.16 Å/s(lower layer)
57Fe (1nm) deposited in both interfaces with 0.07 Å/s
MgO (001)
Mn (x nm) deposited with 0.04 Å/s
natFe 4 nm
Si – 8 nm
MgO(001)
Ag(100nm)or
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• Reflection High Energy Electron Diffraction (RHEED) – [KULeuven]
• Rutherford Back-Scaterring (RBS) – [KULeuven]
•X-ray Diffraction (low and high angles) – [KULeuven]
Structural characterization
• VSM and PPMS – [KULeuven and UFES/Brazil]
• X-ray Magnetic Circular Dicroism (XMCD) – [LNLS/Brazil]
• Ferromagnetic Ressonance (FMR) – [UFG/Brazil]
Magnetic Characterization
Hyperfine Characterization
• Conversion Electron Mössbauer Spectroscopy (CEMS) – [KU Leuven and UFES/Brazil]
Experimental Characterization Methods
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57Fe Mössbauer Spectroscopy
+1/2
+3/2
-3/2
-1/2
+1/2-1/2
57Fe nucleus
γ-rays direction Mn
57Fe
MgO(001)
Ideal interface
Interface Bhf
Bhfbulk (natFe layer)
-10 -8 -6 -4 -2 0 2 4 6 8 10
0,5
1,0
Con
tage
m (
u.a.
)
Energia = f(v) (mm/s)
Rel
ativ
e tr
ansm
issi
on (
a.u.
)
V(mm/s)
Transmission mode
MLK 10% 14.4 keV
e-
80% 7.3 keV
90%100% 14.4 keV
Rel
ativ
e em
issi
on
Emission mode
V (mm/s)
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MgO/Fe(5nm)/Mn(0.5nm)/Fe(5nm) prepared at different Ts
0.4 nm Fe bulk
0.6 nm Fe bulk 57Fe Mn
Si
MgO(001)
Si
MgO(001)
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Field direction
MgO/Ag/(100nm)/Fe(10nm)/Mn(x nm)/Fe(5nm)
x = 1.4 nm
-0.1 0.10
TS=500C
-0.3 0 0.3
M/M
S
x=1.0 nm
0H(T)
Magnetometry: Field Applied // to the Film PlaneMagnetometry: Field Applied // to the Film Plane
0.30-0.3
M/M
s
μoH(T)
x = 1.0 nmET= Eanistopry + EZeeman + Eexchange
2 2( )E C C
C
C C
Coupling energy
exch
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MgO/Ag(100nm) substrate (TS = 50o C)
Upper Fe layer
Lower Fe layer
θ=470
θ~900
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MgO/Fe(5nm)/Mn(1nm)/Fe(5nm) TS=150oC
MgO/Ag(100nm)/Fe(10nm)/Mn(1nm)/Fe(5nm) TS=50oC
17 % of bulk α-Fe
38% of bulk α-Fe
=47o
=72o
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EB effect
2nd problem to be shown
Meiklejohn and BeanJAP 33 (1962) 1328
EB effect - Shifting of the
M(H) curve along field axis
Hc1
Hc2
Heb= [HC1–HC2]/2
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Py (30 nm)
Py (10nm)FeMn (15 nm)
WTi (10nm)
WTi (10nm)
Si (100)
Deposition conditions:
Vacuum: 5 x 10-8 TorrArgon working pressure (PW): 2, 5 and 10 mTorr;Applied field during deposition ( 460 Oe)TS: 20 oC
Sample preparation: Sputtering (CBPF)
Py=Ni80Fe20
AFM
FM
FM
Samples: A2, A5 and A10 PW= 2, 5 and 10 mTorr
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Interfacial effect/EB system
Heb values reduce with roughness
[Nogués et al., PRB 59 (1999) 6984]
Heb values increase with roughness
[Uyama et al., J. Magn. Soc. Jpn. 21 (1997) 911]
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Samples: A2, A5 and A10 PW= 2, 5 and 10 mTorr
X-ray Reflectivity data
0 1 2 3 4 5 6 7 80,010,1
110
1001000
10000100000
1000000
2 (degree)
A2
0,11
10100
100010000
1000001000000
A5
Rel
ativ
e in
tens
ity (
a.u.
)
0,11
10100
100010000
1000001000000
A10
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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
Py
FeMnUpper Interface
Lower interface
Si/WTi/Py(30)/FeMn(15)/Py(10)/WTiPW= 2, 5 and 10 mTorr (A2, A5 and A10)
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-200 -100 0 100 200-800
-600
-400
-200
0
200
400
600
800
Heb2
M
(e
mu
/cm
3 )
H (Oe)
A2 A10
Heb1
A2 A10
Samples: A2 and A10 PW= 2 and 10 mTorr
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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
Magnetometry
Si/WTi/Py(30)/FeMn(15)/Py(10)/WTiPW= 2, 5 and 10 mTorr (A2, A5 and
A10)
Heb values decrease while
Hc values increase with roughness
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Si/WTi(10)/Py(30)/FeMn(15)/Py(10)/WTi(10)
PW= 2, 5 and 10 mTorr (A2, A5 and A10)
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ComponentsHyperfine
parametersSamples
A2 A5 A10
Ni80Fe20 (Py)
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
FeMn +AFM and/or PM interface
phases
A % 56 57 58
FM interfacialalloy
Bhf (T) - 16.6 0.1 16.2 0.4
(mm/s) - -0.08 0.01-0.06
0.01
A % - 4 7
Hyperfine parameters
“chemical roughness (alloy) ” exceeds the interfacial roughness
Ni80Fe20 52%
Fe50Mn50 48%
Calculated fraction
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Proposal model Transversal view
Ni
Fe
Roughness and/or alloy
FM phase at the interface
AFM (FeMn + (NiFe)xMny)
Mn
Fase PMAt the interface
Rich- Fe – phase from the NiFe
(sextet)
NiFe
NiFe
FeMn
Py (30 nm)
Py (10nm)FeMn (15 nm)
WTi (10nm)
WTi (10nm)
Si (100)
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• 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.
• Bulk magnetic properties of multilayer systems are intrinsically associated with their interface properties.
General Remarks
• The Py/FeMn/Py trilayers Heb 1/roughness and HC roughness. Theirs values are intrinsically related to the fraction of each Mössbauer component.
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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)
UFES KULeuven IF - UFGCBPF
Sponsors:
Thank you!
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NiFe
NiFe
phase FM
H direction during deposition
Spins FM planar
Spins AFM planaresFeMn
Spins non-colinear
x Frustation
phase PM and AFM (FeMn and NiFeMn)
Ni(+)FeMn
PM clusters
Spins AFM planarNiFeMn
x
x
x
Spins FMperpendicular
Magnetic structure model