Interfacial Dzyaloshinskii-Moriya Interaction in Pt/CoFeB Films: Effect of the Heavy-Metal Thickness

Dzyaloshinskii-Moriya interaction (DMI), i.e., the antisymmetric exchange interaction, is the subject of intense research due to its capability to induce the formation of chiral spin textures, such as magnetic Skyrmion lattices and spin spirals. In ultrathin ferromagnetic (FM) films in contact with a nonmagnetic heavy metal (HM), a noticeable interfacial DMI can arise due to the large spin-orbit coupling in the presence of the broken inversion symmetry at the FM/HM interface, leading to an asymmetric spin-wave dispersion. Here, we study the influence of the heavy-metal thickness on the interfacial DMI, performing Brillouin Light Scattering measurements on ultrathin CoFeB films in contact with a Pt layer with variable thickness. The experimental results are explained by analytical calculations based on the three-site indirect exchange mechanism that predicts a Dzyaloshinskii-Moriya interaction at the interface between a ferromagnetic thin layer and a heavy metal. The strength of the interfacial DMI was found to increase with Pt thickness, reaching a saturation value of 0.45 mJ/m2 for Pt thickness larger than a few nanometers. This result opens up a way to control and optimize chiral effects in ferromagnetic thin films through the thickness of the heavy-metal layer.


Measured (points) and calculated (curves) frequency asymmetry as a function of the wave vector k for different Pt thicknesses.





(a) Spin-wave frequency asymmetry in CoFeB/Pt films as a function of the Pt thickness at kmax=2.04×107 rad/m. The inset shows the in-plane angular dependence of Δf and its corresponding fit curve for a Pt thickness of 5 nm at a wave vector k =1.35×107 rad/m.

(b) Evolution of the DMI strength as a function of the Pt thickness.





Pubblication and authors:

S. Tacchi, R. E. Troncoso, M. Ahlberg, G. Gubbiotti, M. Madami, J. Åkerman, and P. Landeros "Interfacial Dzyaloshinskii-Moriya interaction in Pt/CoFeB films: effect of the heavy-metal thickness" , Phys Rev. Lett. 118, 147201  (2017). DOI: