Recent results of the Department of Nuclear Physics KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary Compiled by D.L. Nagy,

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).