Reconstruction of an effective magnon mean free path distribution from spin Seebeck measurements in thin films

Abstract

A thorough understanding of the mean-free-path (MFP) distribution of the energy carriers is crucial to engineer and tune the transport properties of materials. In this context, a significant body of work has investigated the phonon and electron MFP distribution, however, similar studies of the magnon MFP distribution have not been carried out so far. In this work, we used thickness-dependence measurements of the longitudinal spin Seebeck (LSSE) effect of yttrium iron garnet films to reconstruct the cumulative distribution of a SSE related effective magnon MFP. By using the experimental data reported by (Guo et al 2016 Phys. Rev. X 6 031012), we adapted the phonon MFP reconstruction algorithm proposed by (Minnich 2012 Phys. Rev. Lett. 109 205901) and apply it to magnons. The reconstruction showed that magnons with different MFP contribute in different manner to the total LSSE and the effective magnon MFP distribution spreads far beyond their typical averaged values.

Determining phonon mean free path spectrum by ballistic phonon resistance within a nanoslot-patterned thin film

“…Some restrictions are imposed to this convex optimization: The accumulated phonon MFP distribution 𝐹 should be smooth and increase monotonically from 𝐹(0) = 0 to 𝐹(∞) = 1. Detailed discussions of the convex optimization can be found in other studies, 13,24,[57][58][59] in which a MATLAB-based package CVX was used for this purpose. 24, 56…”

Modulation of magnon spin transport in a magnetic gate transistor

“…When M Py and M YIG are oriented parallel to each other, the transmission of magnons from the YIG film into the Py strip and spin-flip scattering at the interface is maximized. Considering a shorter magnon mean free path in Py as compared to YIG [11,12], the transmission of magnons into the Py would lead to a decrease in the non-equilibrium magnon density in the YIG channel. This will result in the modulation of the non-local magnon spin signal measured by the Pt detector as a function of the relative orientation between M Py and M YIG .…”

Impact of the Regularization Parameter in the Mean Free Path Reconstruction Method: Nanoscale Heat Transport and Beyond

“…The desired F acc will be strongly affected by the “shape” of the selected SF. Therefore the choice of a different SF will lead to a different MFP distribution [11].…”

“…As we showed in the supporting information, for the case of temperature dependence measurements of the Spin Seebeck coefficient, the optimal μ -value varies among the measurements (See Figure S2). This effect comes from the differences in the spread of the experimental data in each temperature regime and the importance of carriers with longer MFPs as the temperature decreases [11].…”

“…The relation between the transport coefficient α nano ( d ) and the suppression function was originally derived for thermal conductivity [4,10], and more recently has been used to determine the MFP of magnons and the spin diffusion length distribution [11]. This relation can be expressed by means of a cumulative MFP distribution asα=αnano(d)αbulk=−∫0∞Facc(Λbulk)dS(χ)dχdχdΛbulkdΛbulkwhere S ( χ ) is the suppression function, χ is the Knudsen number χ = Λ bulk / d , Λ bulk is the bulk MFP and d the characteristic length of the sample and F acc is the accumulation function given byFacc=1αbulk∫0ΛcαΛ(Λbulk)dΛbulkwhere α Λ is the contribution to the total transport property of carriers with a mean free path Λ.…”