Surface anisotropy of permalloy in NM/NiFe/NM multilayers

We measure surface anisotropy in permalloy (Py) deposited, between two layers of normal metal (NM = Ag, Cu, or Ta) by measuring the total perpendicular anisotropy with the angular dependence of the ferromagnetic resonance (FMR) field in a resonant cavity. Comparisons are made with the frequency dependence of a broadband FMR technique and vibrating sample magnetometry, and neither match the sensitivity and range of the cavity technique. We see there is a difference between the surface anisotropy at the interfaces: Py-Ta has a surface anisotropy of (0.078 +/- 0.009) mJ/m(2) and the Py-Ag and Py-Cu interfaces have surface anisotropies of (0.10 +/- 0.007) mJ/m(2).