By Georgia Barrington-Smith
Amidst the ongoing global energy crisis, industries such as power, manufacturing, and transportation are significant contributors to energy consumption. These sectors produce substantial amounts of unwanted heat as a byproduct, typically released into the environment through exhaust systems, heated surfaces, or cooling mechanisms. This thermal energy, often considered waste, represents a largely underutilised resource.
Fortunately, innovative technologies are emerging to capture and transform this excess heat into usable energy. By harnessing this thermal energy, industries can reduce their overall energy consumption and hence lower their consumption of fossil fuels.
Advancing energy efficiency through breakthrough materials
Thermoelectric materials are a promising technology for capturing this wasted heat. These materials convert heat into electrical energy through the Seebeck effect, in which temperature differences cause the movement of charge carriers.
Recent advancements have shown that incorporating magnetic nanoparticles into these thermoelectric materials can significantly enhance their performance and energy efficiency.
Kyle Portwin, an AINSE PGRA scholar, along with collaborators at ANSTO and the University of Wollongong, has investigated the interactions between magnetic nanoparticles and tin selenide, a promising thermoelectric material, to assist in the development of higher performing energy-efficient materials.
Inside magnetic thermoelectric materials
Magnetic thermoelectric materials are highly complex systems due to the interplay of three types of (quasi)particles:
- Electrons, which carry electric charge,
- Phonons, the vibrations of the atomic lattice that transport heat, and
- Magnons, related to the spin structure of electrons.
Electrons interact with both phonons and magnons, while phonons and magnons can also influence each other independently. Understanding these interactions is crucial for designing advanced thermoelectric materials with enhanced energy efficiency.
To study these interactions, Kyle used inelastic neutron scattering (INS) techniques at ANSTO’s Australian Centre for Neutron Scattering (ACNS) facility, and computational techniques such as density functional theory (DFT), molecular dynamics and linear spin wave theory, to model the dynamics of electrons, atoms and spins in materials.
Specifically, Kyle used Time-of-Flight inelastic neutron scattering, a technique that allows the observer to “see” how particles like phonons and magnons behave inside a material, providing information about its thermoelectric performance.
Using this technique, Kyle was able to analyse some key properties of thermoelectric materials, including quasiparticle broadening (the spread of particle energy), softening (a reduction in energy), and group velocity (the speed at which disturbances travel through the material), to gain deeper insights into the microscopic interactions that govern thermoelectric efficiency.
Why are these properties important?
- Quasiparticle broadening: The width of phonon/magnon modes is linked to their lifetime within the material. The broader a mode becomes, the shorter the lifetime (and the greater the scattering rate), which is of particular importance since it directly relates to spin/thermal transport behaviour.
- Softening: This property is related to the anharmonicity (state in which the atom or molecule is stretched, oscillated, and bent) of phonon/magnon modes, and generally appears as a temperature dependent reduction in energy.
- Group velocity: governs the thermal and spin transport in materials. The lower the group velocity, the lower the thermal conductivity.
Understanding thermoelectric materials using inelastic neutron scattering
Kyle focused his research on one particular thermoelectric material: tin selenide (SnSe), known for its exceptional thermoelectric performance due to its ultralow thermal conductivity, and moderate electrical conductivity.
Using Time-of-Flight INS and DFT calculations, Kyle investigated how SnSe behaves when heated from 100 K – 500 K. The analysis revealed significant broadening of phonon modes, where the vibrations within the material become less well-defined. Normally, phonons have a sharp, clear energy signature, similar to a well-tuned musical note. However, broadening causes this energy range to become fuzzy, like a musical note that’s blurred by nearby vibrations, losing its sharpness and clarity. Additionally, a softening effect was observed where phonon modes shifted to lower energies. This indicating that atomic bonds had become weaker, and the system’s vibrations more anharmonic.
As optical modes broadened and softened to lower energies, the acoustic modes became confined to a smaller region of phase space. This caused the vibrations in the material to lose energy and spread out, leading to a decrease in phonon group velocity. Consequently, the speed at which heat travels through the material slowed down. Since these vibrations typically carry heat, their limited movement reduces heat conduction through SnSe, greatly improving thermoelectric performance.
Using magnetic nanoparticles to boost thermoelectric materials
Magnetite (Fe₃O₄) nanoparticles are promising candidates for integration with thermoelectric materials because they are strongly magnetic (high magnetic moment), retain their magnetism well (high coercivity), and remain magnetic even at elevated temperatures (high Curie temperature)—a crucial feature for thermal energy applications.
When these nanoparticles become sufficiently small, they enter a special state called superparamagnetism, where each tiny particle acts like a miniature magnet that can easily flip its direction. This unique behaviour can influence how heat and electricity move through a material, potentially improving its energy performance.
To explore how magnetic nanoparticles affect thermoelectric materials, Kyle embedded Fe₃O₄ nanoparticles into a SnSe matrix. Using Time-of-Flight INS, he discovered that the vibrations in the SnSe became significantly broader—especially at higher energy levels—when combined with Fe₃O₄. This effect went beyond a simple combination of the two materials’ behaviours, indicating the possible formation of new, hybrid phonon-magnon modes inside the composite material.
These hybrid modes may influence both electrical conductivity and thermal transport by introducing new pathways for energy transfer, an area that will be further explored in the final stages of Kyle’s PhD research.
Kyle’s research lights the way for next-gen energy conversion technologies
By merging magnetism with thermoelectric materials, Kyle’s research points to a bold new direction for turning waste heat into usable energy.
Kyle’s ongoing research into the interactions of electrons, phonons, and magnons seeks to inform the development of advanced materials for improved energy conversion and long-term sustainability. Such advancements have important applications in sustainable power generation and electronic cooling.
AINSE are proud to spotlight Kyle for his pioneering work!
If you, like Kyle, want to become part of the next generation of researchers addressing global energy challenges, learn how AINSE scholarships can support your research journey at ainse.edu.au/scholarships.
To keep exploring AINSE’s research spotlights head to ainse.edu.au/research-spotlights/.
As we end Magnetic May charged up on curiosity, we transition into a new month exploring the wonders of space for Lunar June!
Keep connected as we share our first spotlight showcasing the fascinating work of Larissa Lopes Cavalcante, an AINSE PGRA scholar, examining the chemical complexity of Titan, Saturn’s largest moon!
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