Alannah Hallas

Assistant Professor

Research Classification

Research Interests

quantum phenomena
magnetism
Materials design and discovery
Quantum materials

Relevant Thesis-Based Degree Programs

Affiliations to Research Centres, Institutes & Clusters

 
 

Research Methodology

Crystal growth
neutron scattering
Muon spin relaxation

Recruitment

Master's students
Doctoral students
Postdoctoral Fellows
Any time / year round

Materials innovations have sparked most of the major technological advances across the millennia – from the stone, bronze, and iron ages through to the current silicon age. Science now stands on the precipice of a new era: the age of quantum materials – materials with extraordinary electronic and magnetic properties that rely on quantum mechanical effects. In the Hallas group, we use state-of-the-art crystal growth techniques to discover new quantum materials that could unlock these future technologies. 

 

Crystal growth of new materials

Our group uses a wide range of synthetic methods to grow samples of the materials we study. Conventional solid state methods (shake-and-bake) and flux crystal growth are ideally suited to exploratory synthesis in the pursuit of exciting new materials. The optical floating zone image furnace is a powerful tool that allows us to grow pristine large single crystals. High pressure methods allow us to capture metastable phases that cannot be grown under ambient pressure conditions, an excellent route to finding new structural phases with the potential for exotic new properties. By using this diverse set of synthetic techniques, we are able to explore the periodic table in an unconstrained way, applying the most favourable method for the material we seek to grow.

 

Structure and the role of disorder

Understanding the crystallography of our new material provides the foundation upon which all other characterizations rest. First and foremost, the crystal symmetry and the connectivity of our lattice informs which theoretical models may be applicable to our material. Furthermore, it is often the materials with the most interesting ground states that exhibit the most profound sensitivity to disorder. Thus, it is crucial to determine what types of disorder are present, and attempt to modify the crystal growth recipe to obtain the highest quality samples. To accomplish these structural characterizations, our starting point is always x-ray diffraction. From there on, we can expand to other tools such as neutron diffraction and electron microscopy.

 

Magnetic and electronic phenomena

Quantum materials can have remarkable magnetic and electronic states, ranging from superconductors to spin liquids to topological semimetals. These states often emerge under extreme conditions, very low temperatures and high magnetic fields. We have the ability to measure a wide range of physical properties, including magnetic susceptibility, heat capacity, and electrical resistivity, down to 0.05 K (1/20th of a degree above absolute zero!) and magnetic fields up to 14 T. 

 

Seeing deeper with neutrons and muons

While we can perform many measurements in our very own lab, some experimental techniques require us to travel to beam lines at large user facilities. We are lucky that Canada's only muon source, TRIUMF, is conveniently located on UBC campus. We can use muon spin relaxation experiments to understand whether our magnetic material is frozen or dynamic or to determine the penetration depth in our superconductor. To access neutron beams we have to travel further; Canada does not currently have a major neutron source. Neutron scattering experiments can tell us the arrangement of magnetic moments in a magnetically ordered material or to map out the the spin excitations. Muon and neutron experiments provide critical insights into the behaviors of quantum materials, that in some cases cannot be accomplished with any other experimental probe. 

I am open to hosting Visiting International Research Students (non-degree, up to 12 months).
I am interested in hiring Co-op students for research placements.

Complete these steps before you reach out to a faculty member!

Check requirements
  • Familiarize yourself with program requirements. You want to learn as much as possible from the information available to you before you reach out to a faculty member. Be sure to visit the graduate degree program listing and program-specific websites.
  • Check whether the program requires you to seek commitment from a supervisor prior to submitting an application. For some programs this is an essential step while others match successful applicants with faculty members within the first year of study. This is either indicated in the program profile under "Admission Information & Requirements" - "Prepare Application" - "Supervision" or on the program website.
Focus your search
  • Identify specific faculty members who are conducting research in your specific area of interest.
  • Establish that your research interests align with the faculty member’s research interests.
    • Read up on the faculty members in the program and the research being conducted in the department.
    • Familiarize yourself with their work, read their recent publications and past theses/dissertations that they supervised. Be certain that their research is indeed what you are hoping to study.
Make a good impression
  • Compose an error-free and grammatically correct email addressed to your specifically targeted faculty member, and remember to use their correct titles.
    • Do not send non-specific, mass emails to everyone in the department hoping for a match.
    • Address the faculty members by name. Your contact should be genuine rather than generic.
  • Include a brief outline of your academic background, why you are interested in working with the faculty member, and what experience you could bring to the department. The supervision enquiry form guides you with targeted questions. Ensure to craft compelling answers to these questions.
  • Highlight your achievements and why you are a top student. Faculty members receive dozens of requests from prospective students and you may have less than 30 seconds to pique someone’s interest.
  • Demonstrate that you are familiar with their research:
    • Convey the specific ways you are a good fit for the program.
    • Convey the specific ways the program/lab/faculty member is a good fit for the research you are interested in/already conducting.
  • Be enthusiastic, but don’t overdo it.
Attend an information session

G+PS regularly provides virtual sessions that focus on admission requirements and procedures and tips how to improve your application.

 

ADVICE AND INSIGHTS FROM UBC FACULTY ON REACHING OUT TO SUPERVISORS

These videos contain some general advice from faculty across UBC on finding and reaching out to a potential thesis supervisor.

Postdoctoral Fellows

Graduate Student Supervision

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Probing itinerant magnetism in ZrZn₂ via μSR (2023)

Considerably more experimental and theoretical progress has been made in studying localmoment magnets compared to itinerant magnets, systems where magnetic moment carriersare delocalized throughout the crystal lattice. Progress is hindered by the small number ofknown itinerant magnets, difficulties in synthesis, and small moment sizes. In this thesis,we study itinerant magnetism in the intermetallic compound ZrZn₂. Presumed to order ferromagnetically, recent evidence from the local probes of muon spin relaxation (μSR) andtime dependent perturbed angular correlation (TDPAC) suggests ZrZn₂’s ordered phase isa more complex magnetic ordering. We find that polycrystalline ZrZn₂ is best synthesizedthrough solid state reaction at reaction temperatures below 700 °C. Impurity phase percentages are found to increase with temperature, with ZrZn₃ being the dominant impurity above800 °C. Bulk magnetization measurements reveal ZrZn₂ is an unsaturated magnet up to 7T,with a saturated moment size 0.18 μB/f.u. We find saturated moment sizes at 2K, in externalfields, are only 10% of free moment sizes obtained from Curie-Weiss like fits to the magnetic susceptibility. Furthermore, Knight shift measurements show the zero field orderedmoment corresponding to simple ferromagnetic ordering is only 4% of the free moment.As this is suggestive of geometric moment cancellations in the ordered phase of ZrZn₂,we employ μSR to probe its magnetic ordering in zero field (ZF) and dynamical processescontributing to this ordering in longitudinal field (LF). ZF μSR spectra displays oscillationsin the ordered phase (below 15.5K) that are more damped than the only previous report inliterature, hinting at inhomogeneities in the measured sample. In the LF geometry, we findnon-zero residual relaxation rates in ZrZn₂ persist up to 2K, which is atypical of simpleferromagnets. We conclude that while the temperature dependence of LF relaxation ratesabove 15.5K and inverse magnetic susceptibility in the paramagnetic regime agrees with theself consistent renormalization theory (SCR) for itinerant ferromagnets, a large differencein ordered and free moment size and non-zero LF relaxation rates up to 2K are suggestiveof magnetic ordering more complex than simple ferromagnetism in ZrZn₂.

View record

Investigating the synthesis and properties of transition-metal medium & high entropy oxides (2021)

High entropy oxides (HEOs) are compounds defined as having a crystallographically ordered structure with substantial configurational entropy from having up to five elements occupying a site equivalent sublattice. In certain HEOs, the disorder functions as the driving force behind the stabilization of the crystal structure. Therefore, HEOs are capable of providing host to hitherto unexplored combinations of elements, particularly rare earth and 3d/4d transition metals, regardless of atomic mass, radii, charge, and magnetic character. The applications of these materials include reversible energy storage, components for electronic devices, and improved optical coatings. In this thesis I present two of my contributions to the domain of entropy materials from their exploratory synthesis to a robust characterization of their magnetic and physical properties. The first topic is focused on the magnetic properties of spinel-type HEO (MnCrFeCoNi)₃O₄ and a novel series of magnetic dilutions through the imposition of gallium onto the magnetic sublattice. Using SQUID magnetometry and neutron diffraction we confirm the presence of long-range antiferromagnetic order persistent throughout the parent and magnetically diluted samples. Moreover, magnetization as a function of field data reveals that replacing magnetic transition metals with gallium remarkably enhances the saturation and retentivity of the bulk magnetic moment. Shifting perspectives, we also explored a novel four component medium entropy oxide, (TiHfZrSn)O₂. The purpose of this investigation was to exploit the high tolerance for a wide dispersion in atomic mass among entropy materials in order to convolute the phonon scattering and recover enhanced thermal insulating properties. After fitting our measurements of heat capacity to a Debye model, we calculate the Debye temperature TD = 415.03 +/- 0.25 K. This is considerably lower than TD for the individual oxides and motivates further study of the phonon scattering with direct methods. Through further investigation into the αPbO₂ structure of (TiHfZrSn)O₂, we suspect that entropy stabilization plays a role in the structure formation for this compound. This is based on an investigation in the literature for a similar compound, (TiZr)O₄ in αPbO₂, where the entropy stabilized structure was realized almost two decades prior to the first reported entropy stabilized HEO.

View record

News Releases

This list shows a selection of news releases by UBC Media Relations over the last 5 years.
 
 

If this is your researcher profile you can log in to the Faculty & Staff portal to update your details and provide recruitment preferences.

 
 

Read tips on applying, reference letters, statement of interest, reaching out to prospective supervisors, interviews and more in our Application Guide!