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Spin Caloritronics with Unconventional and Quantum Magnetic Materials

As we reach the end of Moore’s law, the search for a potential successor to CMOS technology has begun. Spintronics (utilizing electron spin in electronic devices) has been identified as one potential candidate to serve this purpose. A new direction has recently emerged within this community: examining the intersection between spin transport and heat transport. This new area, known as spin caloritronics, is centered on generating and manipulating currents of spin through the application of currents of heat. We will explore this using the spin Seebeck effect to generate spin currents in new magnetic material systems, with a focus on using unconventional spin excitations. Many new types of magnetic systems beyond ferromagnets have been shown to generate large spin currents from thermal spin transport such as paramagnets, antiferromagnets, and geometrically frustrated magnetic systems. Thermal spin current generation is possible in insulating magnetic systems that rely on spin excitations beyond the conventional ferromagnetic magnon. Taking advantage of this fact allows for us to use the spin Seebeck effect as a diagnostic tool to identify otherwise hidden spin excitations in systems such as in the low temperature and high magnetic field regime of Gd 3 Ga 5 O 12 (gadolinium gallium garnet), a canonical frustrated antiferromagnet and classical spin liquid material. Signatures in the spin Seebeck response exhibit a one-to-one correlation with magnetic field induced ordering in gadolinium gallium garnet, identified using neutron scattering techniques, and hint at further undiscovered spin excitations at higher magnetic fields. Future prospects in other unconventional magnetic systems such as quantum spin liquid candidates and 2D materials will be discussed.