Compositional Dependence of g-Factor and Damping Constant of GdFeCo Amorphous Alloy Films

Abstract

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Time-domain magnetization dynamics of sputtered GdFeCo (30 nm) amorphous alloy films was measured by pump-probe method using high-power ultra-short pulse fiber laser. The effective <emphasis emphasistype="italic">g</emphasis>-factor <emphasis emphasistype="italic">g</emphasis><formula formulatype="inline"><tex Notation="TeX">$_{\rm eff}$</tex></formula> and effective damping constant <formula formulatype="inline"> <tex Notation="TeX">$\alpha_{\rm eff}$</tex></formula> of the GdFeCo films were estimated by using a numerical calculation of Landau–Lifshitz–Gilbert equation. The precessional frequency took a maximum near the magnetization compensation composition <formula formulatype="inline"><tex Notation="TeX">$C_{\rm M}$</tex></formula> of the GdFeCo, while the estimated <emphasis emphasistype="italic">g</emphasis><formula formulatype="inline"><tex Notation="TeX">$_{\rm eff}$</tex></formula> and <formula formulatype="inline"><tex Notation="TeX">$\alpha_{\rm eff}$</tex></formula> increased around the angular momentum compensation composition <formula formulatype="inline"> <tex Notation="TeX">$C_{\rm A}$</tex></formula>. The compositional dependences of <emphasis emphasistype="italic">g</emphasis><formula formulatype="inline"> <tex Notation="TeX">$_{\rm eff}$</tex></formula> and <formula formulatype="inline"> <tex Notation="TeX">$\alpha_{\rm eff}$</tex></formula> were roughly described by a mean-field model. The <emphasis emphasistype="italic">g</emphasis><formula formulatype="inline"><tex Notation="TeX">$_{\rm eff}$</tex></formula> and <formula formulatype="inline"><tex Notation="TeX">$\alpha_{\rm eff}$</tex></formula> were also estimated from the ferromagnetic resonance (FMR) spectra, and the data from the FMR spectra agreed well with those from the pump-probe measurement except for the composition near <formula formulatype="inline"><tex Notation="TeX">$C_{\rm M}$</tex></formula>. The FMR method was unable to excite the magnetization near <formula formulatype="inline"><tex Notation="TeX">$C_{\rm M}$</tex></formula> because of the small net magnetization. </para>