Magnetic excitations localized near the interface between two ferromagnets

We present the solution of the full magnetic problem arising from a system consisting on two different Heisenberg ferromagnetic media magnetized in the same direction coupled by an interface. The calculation concerns in particular the spin fluctuation dynamics on a magnetic interface and employs a closed form of the spin-wave Green function and the matching technique procedure in the random phase approximation. Only the nearest neighbours exchange interactions are considered between the spins in the model. The theoretical approach determines the bulk and evanescent spin fluctuation fields in the two-dimensional plane normal to the interface. The results are used to calculate the localized modes of magnons associated with the interface. Numerical examples of the modes are given and they are found to exhibit various effects due to the interplay between the bulk and interface modes. It is shown that there may be interface spin waves that decay in amplitude with distance into each medium and the bulk spin fluctuations field as well as the magnons localized at the interface depend on the nature of the bulk–interface coupling exchange.