Assoc. Prof. Glen Stewart Associate Professor, Discipline Coordinator - Physics & Oceanography BSc, PhD, DipEd. Monash, FAIP School of Physical, Environmental and Mathematical Sciences UNSW @ ADFA Canberra   ACT   2600 AUSTRALIA Phone: +61 2 6268 8786 Fax: +61 2 6268 8017 Email: g.stewart@adfa.edu.au Location:PEMS Sth, Room G21

Research Interests:

Advanced Materials

Background

Glen Stewart’s background is in hyperfine interaction techniques and his current research is directed primarily at rare earth compounds that exhibit interesting bulk behaviour and/or potential for technological application. These properties are often influenced by the local crystal field and magnetic exchange interactions at the rare earth site. The key technique employed at UNSW@ADFA is that of ¹⁶⁹Tm Mössbauer spectroscopy. The crystal field is characterized via the temperature-dependent quadrupole interaction that it induces at the ¹⁶⁹Tm nucleus.

Other rare earth Mössbauer resonances (including ¹⁵⁵Gd, ¹⁶⁶Er and ¹⁷⁰Yb) are available via international collaborations and the Mössbauer spectroscopy investigations are complemented by inelastic neutron scattering, magnetic susceptibility and specific heat measurements. Materials currently under investigation include multi-ferroic and colossal magnetoresistance rare earth manganites, the intermetallic silicides RT₂Si₂ (R = rare earth, T = Cu, Ni, Co, Fe, Mn, Cr) and, in collaboration with Wayne Hutchison, the intermetallic series RNiAl₄ which exhibits intriguing magnetic properties.

A concerted effort has also been directed at the application of ⁵⁷Fe-Mössbauer spectroscopy as a tool for monitoring ore refining processes. Although many analysis techniques provide precise quantitative information on the relative amounts of elements, they cannot provide the chemical form in which these elements are present. This is where a phase analysis technique such as ⁵⁷Fe- Mössbauer spectroscopy comes into its own, especially in sectors of the mining industry where iron-rich ores are involved.

Research

Mössbauer spectroscopy as a tool for monitoring ore refining processes
Assoc. Prof. Glen Stewart & Banchachit Saensunon with Dr Randolph Pax & Dr Stephen Harker

Work in collaboration with Dr Randolph Pax of Roche Mineral Technologies has recently demonstrated the advantages of ⁵⁷Fe-Mössbauer spectroscopy as a phase analysis tool for monitoring the reduction stage in the production of synthetic rutile from mineral sands. The majority of this work was conducted by Banchachit Saensunon during his honours project. A separate investigation looked at the processing of local porphyry Cu/Au deposits with the assistance of Visiting Fellow Stephen Harker. This work revealed that what appeared to be bornite grains under a low magnification optical microscope were predominantly chalcopyrite grains laced with small quantities of bornite and pyrite. This was important because bornite is universally recognised as a useful “indicator” of the presence of richer gold-bearing deposits.

Mössbauer study of a potential biomagnetic material
Assoc. Prof. Glen Stewart with Assoc. Prof. Tim White

Hydroxyapatite is a natural mineral that is also found in the teeth and bones of all vertebrate animals. Because of this, iron-substituted hydroxyapatite nanoparticles offer considerable potential as a magnetic biomaterial for biomedical applications. A new mini-collaboration with Tim White at Singapore’s Nanyang Technical University looks at where the substituted iron atoms sit in the hydroxyapatite crystal structure and investigates how this is influenced by the conditions of specimen preparation.

Nature and influence of the crystal field interaction at the rare earth site in intermetallic compounds
Assoc. Prof. Glen Stewart, Banchachit Saensunon & Dr Wayne Hutchison with Dr Paul Gubbens, Assoc. Prof. Hiko Nishimura & Prof. Dominic Ryan

Banchachit Saensunon’s thesis work is directed at the influence of the crystal field interaction in rare earth intermetallic compounds. The first part of this project extends a systematic investigation of the crystal field interaction for the isostructural series RT₂Si₂ (R = rare earth, T = Cu, Ni, Co, Fe) to include T = Mn and Cr. The nature of the crystal field interaction in intermetallic compounds is complicated by the presence of itinerant electrons and the purpose of his investigation is to compare how the methods of Mössbauer spectroscopy and inelastic neutron scattering cope with this. The second part of the thesis project is being conducted in collaboration with Wayne Hutchison and Hiko Nishimura and looks at the crystal field origins of intriguing magnetic behaviour of the intermetallic series RNiAl₄.

Radar absorbing properties of doped barium hexaferrite
Assoc. Prof. Glen Stewart & Dr Wayne Hutchison

A series of student projects was directed at the radar absorbing properties of barium hexaferrite when its trivalent iron content was substituted with increasing concentrations of different tetravalent-divalent transition metal pairs. The microwave network analyser measurements were performed at DSTO’s Maribyrnong site.

Structural and magnetic properties of rare earth multiferroic manganites
Assoc. Prof. Glen Stewart & Hazar Salama with Prof. Hugh O’Neill, Assoc. Prof. Hiko Nishimura & Prof. Dominic Ryan

So-called multi-ferroic compounds are of interest to researchers because they exhibit both ferroelectric order (spontaneous electric polarization accompanied by structural distortion) and antiferromagnetism (an ordered magnet structure with zero net magnetization). The interplay between the two effects could possibly be exploited in future magnetic storage devices. As part of her PhD project, Hazar Salama has used ⁵⁷Fe- and ¹⁷⁰Yb-Mössbauer spectroscopy to investigate the local magnetic moments and crystal field interactions in both the hexagonal and orthorhombic phases of ytterbium manganite (YbMnO₃). In the case of orthorhombic YbMnO₃, an intriguing hysteresis effect has been observed in the temperature region immediately below its antiferromagnetic transition. This work will next be extended to the two phases of TmMnO₃ employing ¹⁶⁹Tm-Mössbauer spectroscopy.

Assoc. Prof. Glen Stewart, Nakorn Suwuntanasarn (Wayne’s PhD student) &
Dr Wayne Hutchison in front of one of the Advanced Materials group’s two
³He-⁴He dilution refrigerators, with a base operating temperature of 6 millikelvin.

Collaborators

• Dr Paul Gubbens (T. U. Delft, The Netherlands)
• Dr Stephen Harker (Visiting Fellow, PEMS, UNSW@ADFA)
• Assoc. Prof. Hiko Nishimura (University of Toyama, Japan)
• Prof. Hugh O’Neil (RSES, ANU)
• Dr Randolph Pax (Downer EDI, Mineral Technologies, Queensland)
• Prof. Dominic Ryan (McGill University, Canada)
• Banchachit Saensunon (PEMS, UNSW@ADFA)
• Hazar Salama (PEMS, UNSW@ADFA)
• Assoc. Prof. Tim White (Nanyang Technological University, Singapore)
• Dr Wayne Hutchison (PEMS, UNSW@ADFA)

PhD Opportunities and Scholarships

Phase analysis investigations of selected ore-refining processes
A separate PhD scholarship will shortly be announced for research in the area of phase analysis investigations of selected orerefining processes.
Contact: Associate Professor Glen Stewart, g.stewart@adfa.edu.au.

More information for future postgraduate research students to UNSW@ADFA is available at: http://www.unsw.adfa.edu.au/student/future/research.html

Recent Publications

Journal - refereed

Saensunon, B., Stewart, G. A. & Pax, R., 2008, A combined ⁵⁷Fe-Mössbauer and x-ray diffraction study of the ilmenite reduction process in a commercial rotary kiln, International Journal of Mineral Processing, 86, 26-32.

Journal - Letter or note

Stewart, G. A., 2007, Conference report – Wagga 2007, Australian Physics, 44(1), 11.

Conference - Full paper refereed

Hutchison, W. D., Saensunon B. & Stewart, G. A., in press, Magnetic ordering temperatures across the RNiAl₄series, Proceedings of the 32nd Annual ANZIP Condensed Matter and Materials Meeting, Wagga Wagga 2008, submitted.

Hutchison, W. D., Goossens, D. J., Saensunon, B., Stewart, G. A., Avdeev, M. & Nishimura, K., 2007, Magnetic order studies of ErNiAl₄, Proceedings of the 31st Annual Condensed Matter and Materials Meeting, Wagga Wagga, 6-9 February 2007, pp. 42-44. Available at: www.aip. org.au/wagga2007/2007_10.pdf

Saensunon, B., Nishimura, K. & Stewart, G. A., 2007, The magnetic environment of the rare earth site in RT₂Si₂ compounds (R = rare earth, T = Cr & Mn), Proceedings of the 31st Annual Condensed Matter and Materials Meeting, Wagga Wagga, Australia. 6-9 February 2007, pp. 75-77. Available at: http://www.aip.org.au/ wagga2007/2007_21.pdf

Salama, H. A., Scott, D., Taboada, J. B., Strickland, N., O’Neill, H. S. & Stewart, G. A., 2007, Preparation of orthorhombic phase YbMnO₃ and Yb_2/3Ca_1/3MnO₃, Proceedings of the 31st Annual Condensed Matter and Materials Meeting, Wagga Wagga, Australia, Available at: http://www.aip. org.au/wagga2007/2007_22.pdf

Conference abstract

Saensunon, B., Stewart, G. A., Gubbens, P. C. M., Hutchison, W. D. & Buchsteiner, A., 2007, The crystal field parameters for Er³⁺ in ErNiAl₄, Sixth AINSE/ ANBUG Neutron Scattering Symposium, December 2007.

Hutchison, W. D., Goossens, D. J., Saensunon, B., Stewart, G. A., Avdeev, M. & Nishimura K., 2006, Magnetic studies of RNiAl₄, Fifth AINSE/ANBUG Neutron Scattering Symposium (AANSS2006), Lucas Heights, 11-13 December, 2006.

Saensunon, B., Stewart, G. A., Gubbens, P. C. M. Hutchison, W. D. & Buchsteiner, A., 2006, The crystal field scheme for Er³⁺ in ErNiAl₄, Fifth AINSE/ANBUG Neutron Scattering Symposium (AANSS2006), Lucas Heights, 11-13 December, 2006.

Saensunon, B., Stewart, G. A. & Pax, R., 2006, Ilmenite reduction process, Thirtieth Annual Condensed Matter & Materials Meeting, Wagga Wagga, 7-10 February, 2006.

Saensunon, B., Stewart, G. A. & Pax, R., 2006, Ilmenite reduction process, Fifth AINSE/ANBUG Neutron Scattering Symposium (AANSS2006), Lucas Heights 11-13 December, 2006.

Tucker, D., Stewart, G. A., Amiet, A. & Edge, V. J., 2006, Microwave absorption properties of Ni-Ti doped barium hexaferrite, Thirtieth Annual Condensed Matter & Materials Meeting, Wagga Wagga, 7-10 February, 2006.

Recent Grants

G. A. Stewart, The crystal field at the rare earth site in thulium manganese silicide, AINSE Grant, 2007: $2,578.

G. A. Stewart, Magnetic and crystal field interactions at the rare earth site in thulium chromium silicide, AINSE Grant, 2006: $999.

G. A. Stewart, W. D. Hutchison & P. C. M. Gubbens, Application for access to NEAT time-of-flight spectrometer, Crystal field interaction for the intermetallic series RNiAl₄ (R = rare earth) Berlin Neutron Scattering Centre, 2006, 10 days beam time awarded.