Multiscale study of complex magnetic structure of ultrathin Fe/Ir(001) films

Laszlo Szunyogh

Budapest University of Technology and Economics, Institute of Physics, Department of Theoretical Physics, Budapest, Hungary

We study the ground state magnetic structure of iron thin films on the surface of fcc-Ir(001) by using the recently developed spin-cluster expansion method to parametrize the adiabatic grand potential surface. We go beyond the usual second-order expansion of the spin-Hamiltonian and include isotropic biquadratic terms as well. We then look for the ground state of the system by performing Landau-Lifshitz-Gilbert spin-dynamics simulations.

For the case of a single iron layer on Ir(001) we found that layer relaxations drastically rearrange the interaction landscape, leading to the appearance of complex noncollinear spin structures. Spin-dynamics simulations show that including biquadratic interactions to the spin model significantly alters the ground state spin configuration. To compare with experimental results we also study thin films of iron consisting of two and four monolayers. While the bilayer system still produces a single-q spin spin-spiral as ground state, in the quadrilayer system there is a nonzero net magnetization superimposed by a cycloidal spin structure. This finding is consistent with the experimental results showing a ferromagnetic signal in magneto-optic Kerr effect measurements above four monolayers of Fe.

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