FIRB “Microsistemi e Nanomateriali Magnetici”
Tematica T4 “Films e Multistrati”
Nanocompositi Magnetici Multistrato
Laboratorio “Superfici”
M. Carbucicchio, M. Rateo, M. Prezioso, F. Zini
Dipartimento di Fisica – Università di Parma
Collaborazioni:
G. Asti, M. Ghidini, M. Solzi
Laboratorio “Magnetometria”
Dip. Fisica, Università, Parma
A. Paoluzi, G. Turilli
Laboratorio IMEM
CNR, Parma
Steve Bennett
Department of Synchrotron Radiation
Daresbury Laboratory
Warrington, UK
Frank J. Berry
Department of Chemistry
The Open University
Milton Keyness, UK
Michel Labrune
Laboratoire PMTM-CNRS
Université Paris-13
Villetaneuse, France
Ultra-High Vacuum Growth by Electron Beams
Vacuum: Starting10-8 Pa
Operating 10-6 Pa
Deposition Rate:
0.5 ÷ 0.8 nm/min
Substrates: Amorphous Quartz
Si(100), Si(111) no native oxide removal
Materials:
1. Model System
Co/Fe + Co Multilayers
Fe
Co: 5.0 ÷ 15.0 nm
0.5 ÷ 45.0 nm
2. RE-TM Systems
Co/NdFeB/Co + Mo
Nd2Fe14B arc evaporated
5[SmCo/Fe] + SmCo + Au
SmCo5 arc evaporated
3[SmCo/Co]
Co/SmCo5/Co
SmCo5 from 10[Sm0.3/Co0.5]
SmCo5 co-evaporated
Characterization:
Auger Electron Spectroscopy
Layer Thickness, Very Low Contamination
Grazing Incidence X-Ray Diffraction (SRS Daresbury, UK)
Crystallographic Structure, Textures, Grain Sizes
Grazing Incidence X-Ray Reflection (SRS Daresbury, UK)
Thickness, Density, Interface Roughness
Atomic Force Microscopy
Morphology of Surfaces
Transmission Electron Microscopy (Erlangen, DE)
Morphology of Multilayers and Interfaces
Conversion Electron Mössbauer Spectroscopy
Composition and Dimensions of Interfaces
Direction of Magnetization
Magnetic Force Microscopy
Magnetic Domains
Model System: simple materials
soft/hard ratio = 3
In-plane AGFM Hysteresis Loops (IMEM)
Interaction-based deviation parameter
MR = saturation remanence
IIRM(H) = isothermal remanence
IDCD(H) = dc demagnetization remanence
M > 0  positive exchange coupling
(ferromagnetic interaction)
Interface Analysis: CEMS
120
120
Co Concentration %
100
100
Co
80
80
60
60
40
40
20
20
0
0
0
1
2
3
4
5
6
7
8
9
10 11 12
Fe Concentration %
Pure Iron
Interfaces
Co
Fe
 Hhf distribution:
- main peak (35 T)
narrow linewidth  similar sublattices
 sharp Fe concentration gradient
- small peak (32 T)
broad linewidth  a few Fe into Co Depth (nm)
Magnetic Anisotropy
AGFM Hysteresis Loops (IMEM)
Magnetization (emu)
1e-3
Co5nm/Fe2nm
5e-4
0
-5e-4
-1e-3
-100
-50
0
50
100
Applied Magnetic Field (Oe)
For Fe layer thickness up to 24 nm
Strong Uniaxial Magnetic Anisotropy
Hard Axis  Low Hysteresis (Mr/Ms  0)
Easy Axis  High Squareness (Mr/Ms  1)
Remanence ratio Mr/Ms vs the in-plane applied magnetic field angle
180° periodicity with |sin| behaviour
Anisotropy constant K1  (1.77  7.63)  104 erg/cm3
CEMS
MFM
out-of-plane angle  (deg)
Fe layer thickness:
< 5 nm
 in-plane magnetization No stray fields
 Stretched domains
5  24 nm
 out-of-plane ~10°
 Stripe domains
> 24 nm
 out-of-plane ~40°
40
30
20
10
0
0
5
10
15
20
Fe layer thickness (nm)
25
30
First Endeavors: RE-TM Hard Layer
AGFM Hysteresis Loop (IMEM)
60
M (emu/g)
40
Co/NdFeB/Co
20
0
-20
-40
-60
-100
-80
-60
-40
-20
0
20
H (Oe)
Problems: - Uncoupled Phases
- Low Coercive Field
- Composition
40
60
80
100
AGFM Hysteresis Loop (IMEM)
1.0
5[SmCo/Fe]+SmCo+Au
M/Ms
0.5
0.0
-0.5
-1.0
-1000
-500
0
500
H (Oe)
Single Phase Magnetic Behaviour
CEMS for 5[SmCo/Fe] + SmCo + Au
Problems: - Stoichiometry
- Reproducibility
- Interdiffusion (GIXRR, CEMS)
1000
AGFM Hysteresis Loop (IMEM)
1.0
Co/SmCo5/Co co-evaporated
M/Ms
0.5
0.0
-0.5
-1.0
-400
-200
0
200
400
H (Oe)
Synchrotron Radiation GIXRD Pattern
Count rate (cps)
2000
Co/SmCo5/Co co-evaporated
1500
1000
500
0
20
30
40
50
60
70
80
2 Angle (deg)
Single Phase Magnetic Behaviour
Low Coercive Field: Nanostructuration
SmCo5 Stoichiometry
90
Future Activities
Ultra-High Vacuum Electron Beam Deposition of
- RE-TM Films with High Coercive Fields
- RE-TM/Fe Bilayers and Multilayers
AFM and MFM observations
- Morphology
- Magnetic Domains
CEMS
- Composition and Dimensions of Interfaces
- Direction of Magnetization
Synchrotron Radiation GIXRD
- Phase Composition
- Grain Size, Textures
- Kind and Intensities of Stresses
- Depth-profiling: different X-ray incidence angles
TEM and HEED Analyses both in plane and in cross-section
- Morphology, Defectivity
- Continuity, Thickness of layers
- Grain Sizes, Crystallographic textures
- Phase Composition Mapping
- Roughness, Interdiffusion, Dimensions of Interfaces