In magnetic insulators, transport of charge is prohibited due to the large bandgap. Spin can still be transported however by spin waves (magnons), the excitations of magnetic systems. The field that studies the properties of spin waves in magnetic insulators is known as magnon spintronics . In the past years, research in the field has been focused on dipolar magnons, which are low-energy spin waves. We have shown  that magnons with energy comparable to the thermal energy (exchange magnons) can also transport spin over long distances, characterized by a spin diffusion length λ ≈ 9.5 μm. We have developed a non-local measurement scheme in which exchange magnons are excited and detected making use of the spin Hall- and inverse spin Hall-effect, respectively. This enables the conversion from electronic charge, to electron spin current, to magnonic spin current and vice-versa, using DC electronic signals. This provides a direct interface with conventional electronics and opens up new magnonic device functionalities. Additionally, it allows us to gain insight in the transport of magnons by studying the non-local signal as a function of various parameters, such as an external magnetic field  or sample temperature. Finally, studying the long-distance transport of thermal magnons can increase our understanding of the spin Seebeck effect in both the longitudinal and the non-local geometry.
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