IAEA CRP: Ion Beam Modification of Insulators RCM, Dec , 2007, FNRC, Uni. Chiang Mai, Thailand Study of the formation of ferro-, para- and superpara- magnetic nano clusters by ion implantation itno suitable insulators Principal investigators : Prof. K. Bharuth-Ram, University of KwaZulu-Natal, Durban and iThemba LABS, Faure. S. Africa and iThemba LABS, Faure. S. Africa Prof. Dr. Hans Hofsaess, Universitaet Goettingen, Germany Prof. Dr. Hans Hofsaess, Universitaet Goettingen, Germany + Carsten Ronning, Peter Schaaf, Michael Uhrmacher, Uni-Goettingen. + Carsten Ronning, Peter Schaaf, Michael Uhrmacher, Uni-Goettingen. Terry Doyle, Cebo …, iThemba LABS, South Africa. Terry Doyle, Cebo …, iThemba LABS, South Africa. + Uli Wahl: Emission channeling + Uli Wahl: Emission channeling Gerd Weyer et al., MS following Mn57 implantation Gerd Weyer et al., MS following Mn57 implantation

Introduction Nanoclusters of Fm atoms have high proportion of surface atoms increase spin magnetic moment towards high spin limit reduction in effective quenching of the orbital magnetic moment. + quantum size effects + modified valence electron screening  Novel properties: magnetic moments enhanced by up to 35% superparamagnetic behaviour in clusters below a critical size magnetic behaviour in non-FM transition metals Applications in ultra-high recording magnetic recording media, information and telecommunications technology. Achieved already by ion implantation at doses of cm due to accumulation at extended lattice sites? or diffusion and agglomeration of implanted ions?

Objective: Investigate the implantation parameters required to achieve magnetic nano-clusters, i.e. energy and dose, sample temperature and annealing characteristics, Methods include Temperature dependent Moessbauer spectroscopy and magnetization measurements, to determine the size of clusters and their magnetic properties. RBS and Raman Spectrometry, MOKE, UV-VIS Transmission Spectrometry -- to determine implantation profile and complex formation in the host matrix.

Reported on in June 2006: Implant of 57 Fe at E = 60 keV, at Uni-Goettingen to a dose of 5 x cm -2. Substrates: 3C-SiC, CVD diamond, graphite Moessbauer spectroscopy (at UKZN) at RT and LN2 on 3C-SiC sample: as-implanted sample, and after annealing at 400 C. Moessbauer spectroscopy (at Uni-Goettingen) after annealing at 600 C VSM on as-implanted and after annealing at 600 C on 3C-SiC sample MOKE and Raman Spectroscopy on as- implanted and after annealing at 400 C and 600 C: CVD and 3C-SiC samples

Results: Mossbauer Measurements Mossbauer measurements were made with a approx. 8 mCi source (30 mCi in May 2003). Each spectrum at RT, has > 10 million events, accumulated over 4 weeks. At LN2, longer measurement time was required.

MOKE Measurements (Magneto-Optical Kerr Effect) a) As implanted b) T A = 900 K

VSM Measurements (TB Doyle, UKZN) SiC(Fe) sample, Virgin SiC, Holder VSM measurements only possible after acquisition of a bipolar power supply for magnet, obtained in 2005 as donation from the Alexander von Humboldt Stiftung. Plot shows average of data collected during many measurements over several months (TB Doyle). We are at the limit of resolution of the device, but a small ferromagnetic effect is noticeable.

Raman Spectroscopy a) CVD diamond as-Implanted b) CVD diamond annealed at 900 K c) 3C-SiC sample annealed at 900K

There is evidence of ferromagnetic and paramagnetic ordering, but data with better statistics is required. So, Plans for 2007 included: i) obtaining new, stronger Moessbauer Sources (50 mCi) ii) Increasing the concentration of Fe in the samples, iii) investigating implantation induced magnetization effects in other substrates. Early in 2007, enriched 57 Fe pellets were purchased, and implantation into 3C-SiC, CVD diamond, ZnO, SiO2 and graphite were undertaken at 60 and 80 keV energy, and up to a fluence of 1 x /cm 2 (at Goettingen). Two 50mCi MS sources ordered, eventually delivered in Oct Measurements from end October : CEMS, TMS.

SubstrateFluence (x10 16 /cm 2 ) Temp (K) MOKE RBSRaman UV-VISMOSS VSM CVD RT 600C RT Y YYYY YYYY 3C-SiC RT 400C RT 300C Y Graphite ZnO RT 325C Y YYYY SiO RT YY

SAIP 2007 Hyperfine Interactions and Measurables 1. Isomer Shift 2. Magnetic interaction E mag = - . B E mag = m I. g  N. B z  = k (  abs –  ref )( – ), lattice site, charge state 3. Electric Quadrupole Interaction

RBS Measurements 2 MeV 4 He+ Grazing angle =  10 O

UV-VIS Transmission 1.3C-SiC: virgin and implanted region i) as implanted, ii) Annealed at 350C. 2. ZnO: Implanted regions i) as implanted ii) Annealed at 350 C.

3C-SiC 1 x /cm 2

SiO 2

ZnO as Impl. T A = 350 C

Moessbauer Measurements 1.CVD Diamond:

Magnetization measurements ??? -- merger of UDW and UN  UKZN - School of Physics (and Fac. of Science) to Westville campus VSM equipment dismantled – and still in boxes!!!

Moessbauer Studies following 57 Mn implantation 57 Mn 57 Co EC  137 keV 14.4 keV, 98 ns 0 CE 57 Fe 5/2  3/2  ½½ Co source: 30 mCi + Typical dose: 5 x Fe  t m ~ 14 days lattice damage 2. In-beam MS CE and recoil implant 57 Fe* t m ~ 24 –36 hrs Dose < cm-2. t eff =  Mn* implantation Dose < cm-2.  decay  57Fe* E recoil = 40 keV t m ~ 10 min. At ISOLDE, CERN Mass separated 57 Mn* accelerated to 60 keV, and implanted into sample held at temp T (+  E) keV gammas detected in PPAC, mounted directly on to MDU.

Production of radioactive ion beams at ISOLDE, CERN.

3C-SiC

Graphite

Components: S1 : Single line D1: defect doublet Sx1 : sharp FM sextet Sx2 & Sx3: Broad sextets with Eq interaction. Effect is reversible.  due Fe-V-O complex??

Conclusions 1. The lighter mass substrates ( SiC, SiO 2 ) hold greater promise. 2. After implantation to a fluence of 1 x / cm 2  indications of magnetically split components in Moessbauer spectra  this fluence gives Moessbauer spectra with acceptable statistics  higher dose implantation with Fe-56 other fm species (Mn, Co) non-fm species (Na, C)

ACKNOWLEDGEMENTS 1.IAEA – Wulf Rosenberg and Francoise Mullhauser 2.Hans Hofsaess, Uli wahl and colleagues in Goettingen 3.Yu Liangden and FNRC, Chiang Mai University 4.The Group generally. Thank You