FMR Line Splitting in Fe/Cr Multilayers

Abstract

Measurements of the magnetization curves and ferromagnetic resonance (FMR) were made on a series of samples of multilayers [Fe(13 A)/Cr(t Cr )] 12 , with 7 A < t Cr < 40 A, deposited by the method of molecular-beam epitaxy on a sapphire substrate with the Fe buffer layer of 40 A thickness. The effective demagnetizing field 4πM s - H' u was estimated for all samples from the angular dependence of an FMR resonant field 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 small spacer thickness (t Cr < 16 A). Its intensity was equal to that of a main line under the condition of t Cr t Fe 12 A, decreasing down to zero both at reduction, and at the increase of t Cr , The FMR lineshape in a field parallel to the surface was simulated by a superposition of two curves, possessing in view of the magnetization curve approximately Lorentzian shape with different effective field values H' u . The possible reason of the features observed can he the formation of regions with different effective anisotropy field values in a sample plane during the deposition. For all samples investigated at longitudinal excitation, an FMR signal which corresponds to an optical mode was not observed.