Perpendicular anisotropy and damping of MgO/Fe/Au trilayers with broken inversion symmetry

Author / Creator

MMM 2020 (2020)

Conferences

MMM 2020 A3: Magnetization Dynamics and Damping I: Damping and Ferromagnetic Resonance (2020)

Available as

Online

Summary

Insulator / 3d ferromagnet / 5d metal trilayers with broken inversion symmetry along the film normal direction is of great interest, since the broken symmetry is known to contribute to the perpendi...

Insulator / 3d ferromagnet / 5d metal trilayers with broken inversion symmetry along the film normal direction is of great interest, since the broken symmetry is known to contribute to the perpendicular magnetic anisotropy (PMA) and the conversion of in-plane charge current to perpendicular spin current through the Rashba spin-orbit coupling [1, 2]. Here, we report on the PMA and magnetization dynamics of the MgO/Fe/Au trilayer with the Fe layer thickness from 0.4 nm to 1.2 nm, and compare the results with the Au/Fe/Au system with a symmetric structure along the film normal. These trilayers were grown on MgO(001) substrate by molecular beam epitaxy method. The PMA and dynamics were investigated by the time-resolved magneto-optical Kerr effect (TRMOKE) measurements. Figure 1 shows Fe thickness dependence of (a) effective anisotropy field Hkeff, (b) g-factor, (c) anisotropy distribution ΔHkeff, and (d) damping constant α of MgO/Fe/Au and Au/Fe/Au trilayers. Both MgO/Fe/Au and Au/Fe/Au showed an increase of Hkeff with decreasing the Fe thickness, and MgO/Fe/Au was confirmed to exhibit slightly larger Hkeff than Au/Fe/Au due to the Rashba effect. The g-factor of both trilayers decreased from the bulk value with decreasing the Fe thickness. ΔHkeff increased at Fe thickness of 0.8 nm for both trilayers which is considered to be due to the relaxation of lattice mismatch around the Fe thickness of 1 nm. The damping constant α of both trilayers increased with decreasing the Fe thickness from 0.8 nm to 0.4 nm due to the effect of spin pumping. The reduction of α at Fe thickness of 0.8 nm is explained by the effect of two-magnon scattering which is enhanced by the increase of ΔHkeff. Interestingly, MgO/Fe/Au trilayers show larger damping constant than Au/Fe/Au with the same Fe thickness, which may reflect the Rashba spin-orbit coupling and/or the variation in the density of states at the Fermi level.References: [1] S. E. Barnes et. al., Sci. Rep. 4, 4105 (2014). [2] I. M. Miron et al., Nat. Mater. 9, 230 (2010).

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