Determination of the exchange constant of Tb0.3Dy0.7Fe2 by broadband ferromagnetic resonance spectroscopy.

We present measurements of the exchange stiffness D and the exchange constant A of a sputtered 80 nm Tb0.3Dy0.7Fe2 film. Using a broadband ferromagnetic resonance setup in a wide frequency range from 10 GHz to 50 GHz, multiple perpendicular standing spin-wave resonances were observed with the external static magnetic field applied in-plane. The field corresponding to the strongest resonance peak at each frequency is used to determine the effective magnetization, the g-factor and the Gilbert damping. Furthermore, the dependence of spin-wave mode on field-position is observed for several frequencies. The analysis of spin-wave resonance spectra at multiple frequencies allows precise determination of the exchange stiffness D = (2.79 ± 0.02) × 10-17 T · m2 for an 80 nm thick film. From this value, we calculated the exchange constant A = (9.1 ± 0.1) pJ · m-1.