Magnetization statics and dynamics in Ir/Co/Pt multilayers with Dzyaloshinskii-Moriya interaction

Abstract

Magnetic multilayers of Ir/Co/Pt with interfacial Dzyaloshinskii-Moriya interaction (IDMI) [1] were deposited by magnetron sputtering with Co thickness d=1.8nm and repetitions N=6. Ferromagnetic resonance spectroscopy was applied to determine the values of effective magnetic uniaxial anisotropy, Hu = -0.45 T. Exploiting magneto-optical Kerr effect in longitudinal mode microscopy, magnetic force microscopy and vibrating sample magnetometery the magnetic field driven evolution of domain structures and hysteresis loops have been studied. Existence of weak stripe domains structure was deduced – large micrometer size domains with in-plane "core" magnetization modulated by small nano-domains with out-of-plane magnetization. Quantitative evaluation of IDMI was carried out using Brillouin light scattering (BLS) spectroscopy [2,3] from the difference between Stokes and anti-Stokes peak frequencies Δf. Due to the additive nature of IDMI, the asymmetric combination of Ir and Pt covers led to large values of surface DMI energy density Ds. Fig. 1 shows Stokes and anti-Stokes peaks for magnon scattering. It was found that Stokes and anti-Stokes frequencies as well as Δf, measured as a function of in-plane applied magnetic field, show hysteresis. These results are explained under the consideration of the influence of IDMI on the dynamics of in-plane magnetized “core” with weak stripe domains. In order to understand the spatial magnetization distribution and magnetization process, the micro-magnetic simulations were performed. Our findings leverage the impact of IDMI on domain structure. Large values of Ds can be useful for the stabilization of skyrmions [1] and studying the dynamical behavior of magnetic skyrmions in the in-plane magnetized sample [4].  Fig. 1. BLS spectrum for d=1.8 nm where Stokes and anti-Stokes peaks are shown. Measurement was done for wavevector k=11.81 μm-1 and applied in-plane magnetic field µ0H=72.8 mT. Experimental data (black line) and its mirror curve (red line, for easy comparison) determine the frequency difference Δf ≈1.5 GHz.