Anisotropy determination in epitaxial Sm-Co/Fe exchange springs

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 (approximate to 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. (C) 2000 American Institute of Physics. [S0021-8979(00)88008-1].