Bulk and Interface Properties of Multilayer Systems Edson Passamani Caetano Universidade Federal do...
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Transcript of Bulk and Interface Properties of Multilayer Systems Edson Passamani Caetano Universidade Federal do...
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
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
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
From especial issue of J3M (1999)~1400
AFM Coupling
GMR
RKKY
Relevant Discoverings in Multilayers
Exchange bias+ Spin-Valves
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
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
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
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
• 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
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)
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)
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
MgO/Ag(100nm) substrate (TS = 50o C)
Upper Fe layer
Lower Fe layer
θ=470
θ~900
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
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
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
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]
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
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)
-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
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
Si/WTi(10)/Py(30)/FeMn(15)/Py(10)/WTi(10)
PW= 2, 5 and 10 mTorr (A2, A5 and A10)
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
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)
• 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.
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!
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