Anisotropy determination in epitaxial Sm–Co/Fe exchange springs

Abstract

We report in-plane anisotropy in epitaxial Sm–Co(x)/Fe(y) bilayers as determined by ferromagnetic resonance (FMR). Four samples, (x,y)=(35,30) and (20, 20) nm each on MgO (110) and (100) substrates, have been prepared via magnetron sputtering. The two substrate orientations result in twofold and fourfold Sm–Co symmetry respectively, with the Sm–Co c-axis in-plane. Magnetization curves indicate elastic exchange spring Fe behavior in reversing fields up to the Sm–Co switching fields (6 and 8 kG at room temperature in the (35, 30) and (20, 20) nm films, respectively). 35 GHz in-plane FMR measurements were made in order to map the crystalline anisotropy of the Fe layer as well as the induced anisotropy from the exchange coupling to the Sm–Co layer. The twofold Sm–Co samples exhibit a clear superposition of the near fourfold Fe crystal field anisotropy (530 Oe) and the unidirectional exchange-bias anisotropy (≈650 Oe) arising from the Fe/Sm–Co interface. The crystalline Fe anisotropy in the fourfold Sm–Co samples is less well defined, presumably due to poorer epitaxy of the Fe layer for this orientation.