FMR line splitting in Fe/Cr multilayers

Measurements of the magnetization curves and ferromagnetic resonance (FMR) were made on a series of samples of multilayers [Fe(13 Angstrom)/Cr(t(Cr))] (12), with 7 Angstrom < t(Cr) < 40 Angstrom, deposited by the method of mol ecular-beam epitaxy on a sapphire substrate with the Fe buffer layer of 40 Angstrom thickness. The effective demagnetizing field 4 pi M-s, - H'(u) was estimated for all samples from the angular dependence of an FMR resonant f ield and linewidth for the uniform mode at the transverse excitation, where M-s is the saturation magnetization of the Fe layer, H'(u) is the uniaxial anisotropy field. An additional FMR line was observed for samples with sma ll spacer thickness (t(Cr) < 16 Angstrom). Its intensity was equal to that of a main line under the condition of t(Cr) approximate to t(Fe) approximat e to 12 Angstrom, decreasing down to zero both at reduction, and at the inc rease of t(Cr). The FMR lineshape in a field parallel to the surface was si mulated by a superposition of two curves, possessing in view of the magneti zation curve approximately Lorentzian shape with different effective field values H'(u). The possible reason of the features observed can be the forma tion of regions with different effective anisotropy field values in a sampl e plane during the deposition. For all samples investigated at longitudinal excitation, an FMR signal which corresponds to an optical mode was not obs erved.