We investigated non-reciprocal spin wave (SW) dispersion relations by using Brillouin Light Scattering (BLS) in inversion symmetry breaking heterostructures. The non-reciprocal SW dispersion relation is a fingerprint of the existence of asymmetric exchange coupling, Dzyaloshinskii-Moriya Interaction (DMI). The quantification of DMI is important, because it is an essential ingredient of the domain wall motion and skyrmion based logic devices. We obtained DMI energy densities of various NM1/ferromagnetic(Co, CoFeB)/NM2 structures, where NM1,2 are non-magnetic heavy metals (Pt, Ir, Ta) or insulators (MgO, AlOx). We revealed that DMI is proportional to the inverse of ferromagnetic layer thickness, which strong evidence of interface nature of DMI in the heterostructure. In order to exclude the possible source of non-reciprocal SW dispersions, we carefully examined DMI with three independent measurement methods, field strength dependence, SW wave vector magnitude dependence, and SW propagating angle dependences, and found all three measurements gave the same results. It implies our measurement results are more reliable compared with other methods. We also found that sign and strength are sensitive function of materials, interface qualities, layer orders, and annealing conditions. Since the strong spin-orbit coupling (SOC) between ferromagnetic and the heavy metal layers is a source DMI, we also investigated SOC related quantities such as perpendicular magnetic anisotropy, magneto-optical Kerr effect, and spin pumpings. And we found that the relation between SOC and DMI is not the same with other SOC-related physical quantities.
Chun-Yeol You, "Determination of the Dzyaloshinskii Moriya interaction for various hetero-structure
(Conference Presentation)," Proc. SPIE 9931, Spintronics IX, 99313S (Presented at SPIE Nanoscience + Engineering: September 01, 2016; Published: 4 November 2016); https://doi.org/10.1117/12.2237109.5167075284001.
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