Recent results of the Department of Nuclear Physics KFKI Research Institute for Particle and Nuclear Physics, Budapest, Hungary Compiled by D.L. Nagy, 2 May 2004 Nuclear Solid State Physics and Nuclear Materials Science

Objectives  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 interest  Formation and structure of metallic and semiconductor thin films  Basic processes of ion implantation  Thin-film magnetism, nanomagnetism  Structure of porous materials

Experimental methods  Ion-beam analysis  Mössbauer spectroscopy including nuclear resonant scattering of synchrotron radiation  Positron annihilation  Neutron reflectometry  MOKE magnetometry

On-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 machine  MECA 2000 metallic MBE  Maximum sample size: 2”  2 e-guns of 4 crucibles each  3 effusion cells, one of them for 57 Fe  Co-evaporation from all source combinations  UHV suitcase for sample transportation

Load-lock Annealing chamber Evaporation chamber UHV suitcase Main parts of the MBE system

Experimental 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 generator

Research staff Bottyán, László, CScMolnár, Béla, MSc Deák, László, PhDNagy, Dénes Lajos, DSc Dézsi, István, DScNémeth, Attila, CSc Fetzer, Csaba, PhDPászti, Ferenc, CSc Kajcsos, Zsolt, DScSajti, Szilárd, PhD Kostka, Pál, MScSzilágyi, Edit, CSc Kótai, Endre, CScSzűcs, Imre, PhD Liszkay, László, PhDTanczikó, Ferenc, MSc Major, Márton, MScTunyogi, Árpád, MSc Manuaba, Asrama, MScVarga, László, CSc

Examples 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 porous Si after ion implantation Columnar-type porous Si implanted by 4-MeV 14 N + ions suffers densification and its pore walls get tilted: width of the 16 O( ,  ) 16 O resonance peak in backscattering vs. sample tilt angle Densification Tilting

Densification and pore-wall tilting of porous Si after ion implantation Transmission electron microscopy evidence of densification and pore-wall tilting in porous Si Densified layer

Morphology and magnetic structure of 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.

In-plane spin flop in an antiferromagnetic multilayer - conversion electron Mössbauer polarimetry (CEMP) H hf k With an unpolarised source, the Mössbauer spectrum line intensity depends only on the angle between k and H hf. In-plane alignments of the magnetisation are difficult to distinguish. H hf pol k H hf With a source in a polarised magnetic matrix, the line intensities depend on the angles (k,H hf ) and (k,H hf pol ). In-plane alignments of the magnetisation are easy to distinguish.  Conversion electron Mössbauer polarimetry (CEMP).

In-plane spin flop in an AF-coupled Fe/Cr multilayer - an application of CEMP Easy direction: Bulk spin flop, H SF =15 mT : domain-wall motion

Hard direction: Surface spin flop, H SF =75 mT : domain rotation In-plane spin flop in an AF-coupled Fe/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 multilayers 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 Mössbauer reflectometry (SMR) ESRF ID18 Correlation length:  = 1/  Q x   0.8  m   2.6  m MgO(001)[ 57 Fe(26Å)/Cr(13Å)] 20 2 AF reflection, hard axis The 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 annihilation lifetime studies in in polyvinyl ophthalmic lens a) free volume radius R b) the relative fractional volume FFV, normalised to the pure MMA monomers c) 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).