Friday, 21 March 2025 11:00am – 12:00pm

This seminar will be delivered in Chemistry Lecture Theatre 4

Speaker: Siobhan Tobin

Host: Prof. Brendan Kennedy

Title: Her Dark Materials: exploration of magnetic phenomena in quantum materials with neutron scattering

Abstract
In this talk I will present experimental investigations of two different quantum materials, each of which showcases the strongly correlated magnetism of 3d transition metal ions. I will also discuss the Wombat neutron diffractometer and future developments for this instrument.

The topological semimetal candidate and thermoelectric material YbMnSb2 has a high magnetic ordering temperature and strongly anisotropic charge transport characteristics, with low resistivity in the plane of the Sb square net. Our neutron triple-axis spectroscopy study revealed the out-of-plane exchange perpendicular to the Sb square net is surprisingly large [1], an interaction that may be mediated by topological quasiparticles [2]. Our magnetic model of YbMnSb2 is consistent with this compound being a gapped Dirac semimetal [3].

The rare earth iron garnets are of prime interest for spintronic applications due to their very coherent, spin-polarised magnons. I will talk about my experimental work on the novel cobalt-doped rare earth iron garnet Lu3Co0.5Si0.5Fe4O12 (LuCoSiIG). Introducing cobalt generates a high degree of magnetocrystalline anisotropy in the system at low temperatures, comparable with the magnetic rare earths. However, at room temperature, LuCoSiIG is a soft magnet, similar to YIG and LuIG. I will discuss the effects on the spin wave spectrum and ramifications for spin current generation in this material.

[1] S. M. Tobin et al. Phys. Rev. B 107 (2023) 195146

[2] X. Hu et al. Phys. Rev. B 107 (2023) L201117

[3] J-R Soh, S. M. Tobin et al. Phys. Rev. B 104 (2021) L161103

Bio
Siobhan Tobin is an instrument scientist at Wombat, ANSTO’s high intensity neutron diffractometer. Her main research interests lie in magnetic materials, topological materials and other strongly correlated electronic systems, as well as sample environment development for neutron scattering experiments. In 2024, she completed her PhD in condensed matter physics supervised by Andrew Boothroyd at the University of Oxford on a Rhodes Scholarship. Prior to that, Siobhan worked at ANSTO as part of the graduate program 2017 – 2019, completing rotations in neutron scattering sample environment, radionuclide metrology and computational reactor physics. She is enthusiastic about science education, having worked in the Oxford Physics Teaching Laboratory 2020 – 2024, tutored at Oxford and the ANU, and taught with the Australian Science Olympiads physics program 2013 – 2019. Siobhan looks forward to developing collaborations with local neutron beam users and introducing more scientists to the wonders of Wombat.