Spin Wave-Stiffness Constants of Half-Metallic Ferromagnets ${rm Co}_{2}YZ$ ($Y={rm Cr}$, Mn, and Fe, $Z={rm Ga}$, Al, and Si) Heusler Alloys

摘要

The spin-wave stiffness constant $D$ and the Curie temperature $T_{rm C}$ for series of $L2_{1}$ phase in ${rm Co}_{2}{rm CrGa}$, ${rm Co}_{2}{rm MnGa}$, ${rm Co}_{2}{rm Mn}({rm Al}_{1-x}{rm Si}_{x})$ , ${rm Co}_{2}{rm Fe}({rm Al}_{1-x}{rm Si}_{x})$, and ${rm Co}_{2}{rm Fe}({rm Ga}_{1-x}{rm Si}_{x})$ Heusler alloys were evaluated from the thermomagnetization measurements. For the ${rm Co}_{2}{rm CrGa}$, ${rm Co}_{2}{rm MnGa}$, and ${rm Co}_{2}{rm Mn}({rm Al}_{1-x}{rm Si}_{x})$ alloys, there was a linear relation between $D$ and $T_{rm C}$ . The tendency between $D$ and $T_{rm C}$ was different from that for ${rm Co}_{2}{rm Fe}({rm Al}_{1-x}{rm Si}_{x})$ and ${rm Co}_{2}{rm Fe}({rm Ga}_{1-x}{rm Si}_{x})$ alloys, that is, $T_{rm C}$ was in the temperature r-n-negion from 1040 to 1100 K indicating weak concentration dependence, whereas $D$ was sensitive to the composition. For example, $D$ changed from 2.28 ${rm meV} cdot {rm nm}^{2}$ for $x=1$ $({rm Co}_{2}{rm FeSi})$ to 5.24 $ {rm meV} cdot {rm nm}^{2}$ for $x=0$ $({rm Co}_{2}{rm FeGa})$ in the case of ${rm Co}_{2}{rm Fe}({rm Ga}_{1-x}{rm Si}_{x})$ alloys. It was suggested that magnetic stability against the temperature of the Co-based Heusler alloys containing Fe element was governed not only by the spin-wave excitation but also by the other kinds of excitation.