Spin Seebeck effect in Fe3O4 heterostructures

Fe₃O₄ epitaxial thin films with different thickness were deposited on a magnesium oxide substrate by means of pulsed laser deposition (PLD) in an ultrahigh-vacuum chamber. Anomalous Nernst effect (ANE) and SSE measurements were performed to careful study the characteristic dependence of thermomagnetic signal on the thickness of the magnetite. The experimental data is in agreement with reported models [1, 2] where the bulk spin current is calculated macroscopically with the Boltzmann equation for the magnon flow. Following this model the estimation of the magnon diffusion length in magnetite thin films is 17 ± 3 nm at 300 K.

SSE has also been investigated in highly crystalline magnetic multilayer Fe₃O₄/Pt films. Voltage as well as power generated by the SSE were found to be significantly enhanced with increasing the number of layers [3]. This voltage enhancement defies the simple understanding of the SSE and suggests that spin current flowing between the magnetic layers in the thickness direction plays an important role in multilayer SSE systems and the observed voltage enhancement.

 

References

[1] S. M. Rezende et al., Magnon spin-current theory for the longitudinal Spin Seebeck effect, Phys. Rev. B 89, 014416 (2014).

[2] Steven S.-L. Zhang and Shufeng Zhang, Magnon mediated electric current drag across a ferromagnetic insulator layer, Phys. Rev. Lett. 109, 096603 (2012).

[3] R. Ramos et al., Unconventional scaling and significant enhancement of the spin Seebeck effect in multilayers, Phys. Rev. B 92 220407 (2015).