Dominic Ryan's home page, Physics/McGill

Dominic Ryan

The Centre for the Physics of Materials (CPM), (RQMP), and Department of Physics

SHIPPING ADDRESS:

Room 108,

Rutherford Physics Building,

McGill University,

3600 University St.,

Montreal (Quebec)

H3A 2T8, Canada

PHONE: (514) 398-6534

FAX: (514) 398-8434

E-MAIL: dominic AT physics DOT mcgill DOT ca

Meet former members of the group here...

Research Interests

I use nuclear methods to study a wide variety of problems in magnetism.
My research interests are centred on magnetic materials which contain frustrated or competing interactions that lead to exotic magnetic ordering behaviour.
Some typical materials of recent interest include:

a-Fe_xZr_100-x and a-Fe_90-xRu_xZr₁₀, are amorphous Fe-based alloys that exhibit varying degrees of exchange frustration due to random exchange bonds between the iron moments. At high frustration levels, these materials are spin glasses, while alloys with lower amounts of frustration exhibit ferromagnetic ordering at T_c, followed by transverse spin freezing at T_xy.

a-(Fe_1-xMn_x)₇₈Si₈B₁₄ is a site-frustrated metallic glass that exhibits behaviour that appears superficially similar to that of the a-Fe-Zr alloys but is quite different.
We have also studied the effects of bond and site frustration using Monte Carlo simulations.
RFe₆Ge₆ (R=Y, La-Lu) where a cancellation in the R-Fe exchange leads to a two orders of magnitude difference in the rare-earth and Fe sub-lattice ordering temperatures.

Many RMn₆Sn₆ compounds undergo spin reorientations between the c-axis and ab-plane which can be driven either thermally or by externally applied fields. We have been exploiting these clean 90^o reorientations to study the nature of the hyperfine field transfer process between the magnetic ions (R, Mn) and our non-magnetic probes (¹¹⁹Sn).

R₃T₄X₄ (R=Y, La-Lu; T=Cu,Ag; X=Si,Ge,Sn) This large family of intermetallic compounds exhibits some remarkably complex magnetic ordering behaviour. The rare earth atoms occupy two crystallographically distinct sites, and in many of the compounds (e.g. Er₃Cu₄X₄) the two sites order at different temperatures. In another (Tb₃Ag₄Sn₄) there is a coupled first-order magneto-structural transition.

The R₅X₄ (where R=Y, La-Lu; X=Si,Ge,Sn) family of giant magnetocaloric compounds are of both fundamental and practical interest. We have used ¹¹⁹Sn Mössbauer spectroscopy to study the magnetostructural transition in Gd₅Sn₄ and ¹⁷⁰Yb Mössbauer spectroscopy to investigate valence and magnetic ordering in Yb₅Si_xGe_4-x.

Neutron diffraction on 'impossible' materials. Several elements, notably B, Cd, Sm, Eu and Gd, have very large absorption cross-sections for thermal neutrons and are therefore generally avoided. We developed a large-area flat-plate mounting technique which has allowed us to study a wide variety of highly absorbing compounds.

Research Techniques
My primary in-house research tool is Mössbauer spectroscopy, using a wide variety of resonances.
We also use magnetisation and ac-susceptibility for bulk characterisation.
In 2012 we built a fully digital time-differential perturbed angular correlation (TDPAC) spectrometer which currently works with ¹¹¹In and ¹⁸¹Hf. This is being used to extend our ability to study magnetic ordering in systems that lack a Mössbauer-active element.
Results from these measurements are complemented by neutron diffraction work at the CNBC located at Chalk River, Ontario and µSR at TRIUMF in Vancouver, BC.

In-house facilities include:

Transmission Mössbauer Spectroscopy
We have a variety of furnaces, cryostats and magnets that permit measurements at temperatures between 1.5 K and 1100 K in fields of up to 7 Tesla, with both transverse and longitudinal access.
Current research projects involve the following Mössbauer resonances:

⁵⁷Fe
¹¹⁹Sn
¹⁵¹Eu
¹⁵³Eu
¹⁵⁵Gd
¹⁶⁶Er
¹⁶⁹Tm
¹⁷⁰Yb
¹⁹⁷Au

Conversion Electron Mössbauer Spectroscopy (CEMS)
from room temperature down to 50 K. The system is being used to study the interplay between magnetic order and layer morphology in a variety of Fe-TM multilayer systems.

Selective Excitation Double Mössbauer spectroscopy (SEDM)
as an experimental technique for the study of magnetic relaxation phenomena in random alloys (such as Invar), spin-glasses (such as amorphous Fe-Sc), and fine particle systems (such as ferrofluids). Our systems can be operated between 20K and 500K.

Off-site facilities include:

The Canadian Neutron Beam Centre (CNBC)
used to provide user-access to a state-of-the-art neutron scattering facility based around the 120MW NRU research reactor.
Unfortunately, NRU ceased operations permanently on March 31^st 2018 with no plans for a replacement facility.
Despite being one of the first countries to invest in neutron beam research, Canada no longer has a major domestic neutron source.
Users had access to powder diffraction, reflectometry and triple-axis spectrometers with both polarised and unpolarised beams.
There was also an extensive array of sample environments available.
Access to the facilty was entirely free and was managed through a peer-review process operated by the
Canadian Institute for Neutron Scattering (CINS)

Muon spin relaxation (µSR) at (TRIUMF)
This user facility is based around the 500MeV cyclotron at TRIUMF and delivers beams of surface muons to several experimental stations with access to a wide range of experimental environments.
Our µSR work has centred on the frustrated a-Fe-Zr and a-Fe-Mn metallic glasses.

Some Links

Recent publications

Updated: 25-June-2023 by Dominic Ryan, ERP 425, (514) 398-6534