Spin Wave-Stiffness Constants of Half-Metallic Ferromagnets ${\rm Co}_{2}YZ$ ( $Y={\rm Cr}$ , M

The spin-wave stiffness constant D and the Curie temperature T_C for series of L2₁ phase in Co₂CrGa, Co₂MnGa, Co₂Mn(Al_1-xSix) , Co₂Fe(Al_1-xSix), and Co₂Fe(Ga_1-xSix) Heusler alloys were evaluated from the thermomagnetization measurements. For the Co₂CrGa, Co₂MnGa, and Co₂Mn(Al_1-xSix) alloys, there was a linear relation between D and T_C . The tendency between D and T_C was different from that for Co₂Fe(Al_1-xSix) and Co₂Fe(Ga_1-xSix) alloys, that is, T_C was in the temperature region from 1040 to 1100 K indicating weak concentration dependence, whereas D was sensitive to the composition. For example, D changed from 2.28 meV ·nm² for x=1 (Co₂FeSi) to 5.24 meV ·nm² for x=0 (Co₂FeGa) in the case of Co₂Fe(Ga_1-xSix) 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.