The examination of surface anisotropy in ferromagnetic resonance measurement

Abstract

Abstract— We examined the uniform and first spin wave mode of permalloy thin films Ni79Fe21 (Py). Surface anisotropies in ferromagnetic thin films might be estimated through spin-wave resonance (SWR). It is apparent from results that (surface anisotropy) Ks = 0.12 mJ/ m2 for Py/Cu, by using difference of exchange field in normal and parallel measurement of FMR.

In this study, the samples with the structure “Si/SiO2 /Ta(5nm)/ Cu(5nm)/ FM(t)/ Cu(5nm)/ Ta(5nm)” (FM = Ni79Fe21 (Py)) were deposited by UHV magnetron sputtering with a base pressure of 5×10−9 Torr. The samples were magnetic characterized by field-swept, variable frequency FMR over 2-26 GHz using a coplanar waveguide with biasing field HB applied normal to the sample surface (n.c.) and parallel to film plane (p.c.). We measured uniform and first (p = 0, 1) perpendicular standing spin-wave mode (PSSW) in films. There were differences between uniform and PSSW resonance mode, which are exchange fields Hex. And Hex was decreasing depend on thickness.

The most common method to find surface anisotropy is uniform mode FMR measurement of Meff and 1/t to fitting [4]. It can be seen from the Figure-1 that Meff reduces when t decreases for each geometry conditions of FMR. Therefore, there is perpendicular surface anisotropy (Ks>0). Due to this fitting type, we find that normal condition is Ks=0.14 mJ/ m2 and parallel condition is Ks=0.12 mJ/ m2.