Seminar "Characterization of spin-current propagation in antiferromagnetic insulator" by Dr. Hiroto Sakimura, Tokyo Insititute of Technology

Title: Characterization of spin-current propagation in antiferromagnetic insulator

Speaker: Dr. Hiroto Sakimura, School of Materials and Chemical TEchnology, Tokyo Institute of Technology

Venue: C016, Lab1

Day and time: Feb 17, 14:00-15:00

Abstract:

An experimental evaluation of the spin decay length, which is a parameter characterizing the spin propagation property of each material, in an antiferromagnetic insulator (AFI) is presented. In general, there are two major measurement methods to evaluate the spin decay length, spin-pumping and non-local methods. The former is more standard and frequently-used, whose sample configuration is ferromagnet (FM)/AFI/heavy-metal trilayer structures, where the ferromagnet and heavy-metal act as spin-current injector and detector, respectively. This method is simpler, but the values of spin decay length measured by this method are relatively smaller (~few tens of nm) than that measured by the latter (~µm) [1-4]. In this study, we focused on the FM/AFI interface to fill this discrepancy and found that a spin current generated by spin pumping is strongly suppressed by two-magnon scattering enhanced by position-dependent fluctuation of microscopic exchange bias, which is inevitable at FM/AFI junctions. By eliminating the two-magnon contribution from the spin transmission signal, we discovered that the characteristic length of spin decay in polycrystalline NiO, a prototypical AFI, was around 100 nm, which is an order of magnitude longer than that previously believed [5]. Our result provides a new perspective in the emerging field of antiferromagnetic spintronics, especially for the fundamental understanding of spin transport physics in insulators.

[1] H. Wang et al., Phys. Rev. Lett. 113, 097202 (2014)

[2] C. Hahn et al., Europhys. Lett. 108, 57005 (2014)

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

[4] R. Lebrun et al., Nature 561, 222 (2018)

[5] H. Sakimura et al., Phys. Rev. Research 1, 013013 (2019)