Relaxation dynamics of ferromagnetic FePt thin films in a Broad Frequency Range

GABRIELA ALEJANDRO; NADIA ÁLVAREZ; JAVIER GÓMEZ; ETIENNE GOOVAERTS; A. BUTERA

Buenos Aires

Conferencia; X Latin American Workshop on Magnetism, Magnetic Materials and Their Applications, Buenos Aires, April 8-12, 2013. (Charla Invitada).; 2013

FePt thin films in the chemically disordered FCC phase present a rich variety of magnetic phenomena due to the competition between demagnetization, magnetocrystalline and stress anisotropies. The shape anisotropy tends to align the magnetization in the film plane, while the other two sources of anisotropy favor an out of plane alignment. For films thicker than a critical thickness, dcr ~ 30 nm, a transition from planar magnetic domains to a structure of stripes with an out of plane component of the magnetization has been observed. The dynamic behavior of these films has been studied using Ferromagnetic Resonance spectroscopy in a broad range of frequencies, from 1 to 100 GHZ. A set of samples with thicknesses between 10 nm and 100 nm was investigated at room temperature in order to analyze the frequency response and the behavior of the magnetic anisotropy. As expected, the increase in frequency is accompanied by larger resonance fields and linewidths. These two quantities also display an anisotropic response when the applied external field is rotated from the in-plane to the out of plane direction. We have also observed that the linewidth is different for fields applied parallel or perpendicular to the film plane which, in principle, should not occur in homogeneous ferromagnetic films. This behavior could be understood by the presence of a frequency independent anisotropic inhomogeneous broadening, in addition to the Gilbert damping term which gives a linear frequency dependence. We have also analyzed the possible contribution of additional damping mechanisms, such as two magnon scattering which can give an anisotropic contribution to the linewidth and has a distinguishable square root dependence with frequency.