Recent results of the Department of Nuclear Physics KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary Compiled by D.L. Nagy,
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Recent results of theDepartment of Nuclear Physics
KFKI Research Institute forParticle and Nuclear Physics,Budapest, Hungary
Compiled by D.L. Nagy, 2 May 2004Compiled by D.L. Nagy, 2 May 2004
Nuclear Solid State Physics andNuclear Solid State Physics andNuclear Materials ScienceNuclear Materials Science
ObjectivesObjectives
Fundamental research on condensed-matter systems of potential technological application utilising nuclear methods.
Methodological development of nuclear methods for solid-state physics and materials sciences.
Materials and phenomena of interestMaterials and phenomena of interest
Formation and structure of metallic and semiconductor thin films
Basic processes of ion implantation
Thin-film magnetism, nanomagnetism
Structure of porous materials
Experimental methodsExperimental methods
Ion-beam analysis
Mössbauer spectroscopy including nuclear resonant scattering of synchrotron radiation
Positron annihilation
Neutron reflectometry
MOKE magnetometry
On-site sample-preparation facilitiesOn-site sample-preparation facilities
Molecular-beam epitaxy (MBE) machine
500-kV heavy-ion implanter
Electrolytic cells with in-situ Mössbauer emission spectroscopy
Photo: Miklós Mocsári
MBE machineMBE machine
MECA 2000 metallic MBE
Maximum sample size: 2”
2 e-guns of 4 crucibles each
3 effusion cells, one of them for 57Fe
Co-evaporation from all source combinations
UHV suitcase for sample transportation
Load-lock
Annealing chamber
Evaporation chamber
UHV suitcase
Main parts of the MBE systemMain parts of the MBE system
Experimental facilitiesExperimental facilities
5-MV Van de Graaff ion accelerator with scattering chambers for RBS, PIXE, channeling and NRA
Mössbauer spectrometers with versatile sample environment and detection systems
Positron annihilation spectrometers, slow-positron source
Access to European synchrotron-radiation and neutron sources, ion accelerators and slow-positron generators
The EG-2R Van de Graaff generatorThe EG-2R Van de Graaff generator
Research staffResearch staffBottyán, László, CSc Molnár, Béla, MSc
Deák, László, PhD Nagy, Dénes Lajos, DSc
Dézsi, István, DSc Németh, Attila, CSc
Fetzer, Csaba, PhD Pászti, Ferenc, CSc
Kajcsos, Zsolt, DSc Sajti, Szilárd, PhD
Kostka, Pál, MSc Szilágyi, Edit, CSc
Kótai, Endre, CSc Szűcs, Imre, PhD
Liszkay, László, PhD Tanczikó, Ferenc, MSc
Major, Márton, MSc Tunyogi, Árpád, MSc
Manuaba, Asrama, MSc Varga, László, CSc
Examples of recent resultsExamples of recent results
Densification and pore-wall tilting of porous Si after ion implantation
Morphology and magnetic structure of Fe thin films on Ag
Spin flop in a coupled Fe/Cr multilayer
Ripening of antiferromagnetic domains in a Fe/Cr multilayer
Free volume in polymers
Densification and pore-wall tilting of Densification and pore-wall tilting of porous Si after ion implantationporous Si after ion implantation
Columnar-type porous Si implanted by 4-MeV 14N+ ions suffers densification and its pore walls get tilted: width of the 16O(,)16O resonance peak in backscattering vs. sample tilt angle
Densification
Tilting
Densification and pore-wall tilting of Densification and pore-wall tilting of porous Si after ion implantationporous Si after ion implantation
Transmission electron microscopy evidence of densification and pore-wall tilting in porous Si
1m
Surface
Densified layer
Morphology and magnetic structure Morphology and magnetic structure of Fe thin films on Agof Fe thin films on Ag
Conversion electron Mössbauer spectroscopy
(CEMS)
At small Ag thickness no magnetic interaction but a distribution of the quadrupole interaction. Magnetism appears at high Ag thickness.
Spin-reorientation is observed with increasing Ag thickness.
The primary Ag clusters form continuous layers of two different Fe environments at high Ag thickness.
-1 0 1
-6 -4 -2 0 2 4 6
E 7.5 ML
C 6 ML
P(Q
S)
QS
B 2 MLP(Q
S)
QS
A 0.5 MLP(Q
S)
QS
D6 ML
0.0 0.5 1.0
inte
nsi
ty
0.0 0.5 1.0
0.0 0.5 1.0
0 10 20 30
velocity (mm/s)
F
100 K
10 MLP(H
)
H
In-plane spin flop in an In-plane spin flop in an antiferromagnetic multilayer - antiferromagnetic multilayer -
conversion conversion electron Mössbauer electron Mössbauer polarimetry (CEMP)polarimetry (CEMP)
Hhf
k
With an unpolarised source, the Mössbauer spectrum line intensity depends only on the angle between k and Hhf . In-plane alignments of the magnetisation are difficult to distinguish.
Hhfpol
k
Hhf
With a source in a polarised magnetic matrix, the line intensities depend on the angles (k,Hhf) and (k,Hhf
pol ). In-plane alignments of the magnetisation are easy to distinguish. Conversion electron Mössbauer polarimetry (CEMP).
In-plane spin flop in an AF-coupled In-plane spin flop in an AF-coupled Fe/Cr multilayer - an application of CEMPFe/Cr multilayer - an application of CEMP
0 10 20 30 40 50
20
30
40
50
60
70
80
90
45oH Hpol
easy
easy
field up field down
Pe
rpe
nd
icu
lar
Inte
nsi
ty (
%)
H (mT)
Easy direction: Bulk spin flop, HSF=15 mT : domain-wall motion
Hard direction: Surface spin flop, HSF=75 mT : domain rotation
0 50 100 150 200 250 30020
25
30
35
40
45
50
55
3o3o
45o
hard
hard
H Hpol
field up field down
Pe
rpe
nd
icu
lar
Inte
nsi
ty (
%)
H (mT)
In-plane spin flop in an AF-coupled In-plane spin flop in an AF-coupled Fe/Cr multilayer - an application of CEMPFe/Cr multilayer - an application of CEMP
Layer magnetisations:
The ‘magnetic field lines’ are shortcut by the AF structure stray field is reduced ‘patch’ domains form.
Patch domains in AF-coupled Patch domains in AF-coupled multilayersmultilayers
The domain-size-dependent magnetoresistance noise may be as high as to limit GMR applications domain studies and domain ‘tailoring’ required
Domain ripening: off-specular synchrotron Domain ripening: off-specular synchrotron Mössbauer reflectometry (SMR)Mössbauer reflectometry (SMR)
ESRFID18
Correlation length: = 1/Qx
0.8 m 2.6 m
MgO(001)[MgO(001)[5757Fe(26Å)/Cr(13Å)]Fe(26Å)/Cr(13Å)]2020
22@ @ AF reflection, hard axisAF reflection, hard axisThe size of the antiferromagnetic domains is spontaneously and irreversibly increasing and their shape (i.e., the magnetisation autocorrelation function) is changing with decreasing magnetic field.
Free volume in polymers: positron Free volume in polymers: positron annihilation lifetime studies in annihilation lifetime studies in in polyvinyl in polyvinyl
ophthalmic lensophthalmic lensa) free volume radius Rb) the relative fractional volume FFV, normalised to the pure MMA monomersc) the drug diffusion coefficient D
for MMA- () and BMA- () based co-polymers with increasing percentage of EHA.
The monomers were methyl methacrylate (MMA), ethyl-hexyl acrylate (EHA), butyl methacrylate (BMA), and ethylene glycol dimethacrylate (EGDMA), as cross-linker).
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