Enhanced magnon transport through an amorphous magnetic insulator and the orbital moment in Fe3O4

Speaker: Dr Stuart Cavill (University of York)

https://www.york.ac.uk/physics/people/cavill/

Title: Enhanced magnon transport through an amorphous magnetic insulator and the orbital moment in Fe₃O₄

Abstract: Magnonics research is focused on the transport of spin information via spin-wave, ormagnon, excitations in magnetic materials. Due to its exceptionally low damping, even in thin films, the magnetic insulator Yttrium Iron Garnet (YIG) is considered the most prominent material in this field being widely used in spin transport experiments. New research has been stimulated by a report of the observation of exceptionally long µm magnon diffusion lengths in amorphous YIG (a-YIG) where there is no significant long range structural orferrimagnetic order (M ≈ 0) [1]. Spin transport through disordered magnetic insulators is suggested to be mediated by short range spin correlations and is highly dependent on the relative size of the correlation length to grain size [2]. Similar nonlocal experiments have failed to observe long range spin transport through a-YIG [3] and FMR spin-pumping in Permalloy/a-YIG/Pt trilayers provides a much lower (3.6nm) magnon diffusion length for a-YIG [4], or fails to observe magnon transport at all [5].

In this seminar I will report on the magnon diffusion length in YIG (45nm)/a-YIG(t)/Pt (5nm) trilayer structures fabricated on Gadolinium Gallium Garnet (GGG) substrates by pulsed laser deposition (PLD). In-plane VNA-FMR spectroscopy was performed to obtain the damping of the YIG in the trilayer, as a function of a-YIG thickness (t), and extract the magnon diffusion length. The experimental data shows a large change in damping with the addition of either Pt, or a-YIG plus Pt; indicating spin-pumping through the a-YIG spacer into the Pt. As the thickness of the a-YIG layer is increased the additional damping due to spin pumping into the Pt is reduced. The relationship between damping and a-YIG thickness is described, tentatively, by diffusive transport. However, a significantly longer “magnon diffusion length” for a-YIG is observed: approximately an order of magnitude larger than found in previous spin-pumping studies [4, 5].

Secondly, and if time permits, I will briefly show some new results that will help clarify another well-known debate in the field of magnetic oxides – the size of the orbital moment in Fe₃O₄.

References:

[1] D. Wesenberg et al. NPhys 13, 987 (2017).

[2] H. Ochoa et al. Phys. Rev. B 98, 054424 (2018).

[3] J. Gomez-Perez et al. Appl. Phys. Lett.116, 032401 (2020). 

[4] H. Wang et al. Phys. Rev. B. 91, 220410 (2015).

[5] L. Yang et al. Phys. Rev. B. 104, 144415 (2021).