Spin Wave-Stiffness Constants of Half-Metallic Ferromagnets Co₂YZ (Y= Cr, Mn, and Fe, Z= Ga, Al, and Si) Heusler Alloys

The spin-wave stiffness constantDand the Curie temperatureTCfor series ofL21phase in Co2CrGa, Co2MnGa, Co2Mn(Al1-xSix) , Co2Fe(Al1-xSix), and Co2Fe(Ga1-xSix) Heusler alloys were evaluated from the thermomagnetization measurements. For the Co2CrGa, Co2MnGa, and Co2Mn(Al1-xSix) alloys, there was a linear relation betweenDandTC. The tendency betweenDandTCwas different from that for Co2Fe(Al1-xSix) and Co2Fe(Ga1-xSix) alloys, that is,TCwas in the temperature region from 1040 to 1100 K indicating weak concentration dependence, whereasDwas sensitive to the composition. For example,Dchanged from 2.28 meV ·nm2forx=1 (Co2FeSi) to 5.24 meV ·nm2forx=0 (Co2FeGa) in the case of Co2Fe(Ga1-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.