Magnetic properties tailored by inserting ultrathin Cr layer in Gd/Ni80Fe20 film

The magnetic properties of Gd(4 nm)/Cr(t(Cr))/Ni80Fe20(12 nm) films with different thicknesses of Cr layer prepared by magnetron sputtering were investigated. X-ray diffraction proves the coexistence of hexagonal closed-packed (hcp) (002) and face-centred cubic (fcc) (111) peaks in the Gd layer. Magnetic measurements show a modulation akin to RKKY coupling in the saturation magnetization (M-s) as a result of the coupling sign between Gd and Py layers oscillating with t(Cr). The strained hcp phase and, in particular, the fcc phase lead to poor magnetic moments and strongly reduced saturation of Gd, which can also be affected by the possible magnetically dead layers, the intermixing at interfaces and a presumably more gradual transition to adjacent phases. Theoretical fittings of the relationship between the ferromagnetic resonance field (H-r) and the microwave frequency yield the effective magnetization (4 pi M-eff) and perpendicular anisotropy constant (K-perpendicular to), which are all enhanced by introducing Gd and Cr layers as a result of the increased interfaces. Interestingly, with the increasing thickness of Cr spacer layer, an obvious decrease in the magnetic damping coefficient (alpha(eff)) is observed, from which we infer that both the spin-orbit interaction due to the interlayer couplings and the electron density of states (DOS) at the Fermi energy n(E-F) resulting from the intermixing at the interfaces of Gd/Cr/Ni80Fe20 film are the major origins. In addition, all magnetic parameters are approaching to those of a Py film with t(Cr) increasing to 3 nm.