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

The spin-wave stiffness constant
D
and the Curie temperature
T
_C
for series of
L
2
₁
phase in Co
₂
CrGa, Co
₂
MnGa, Co
₂
Mn(Al
_1-
x
Si
x
) , Co
₂
Fe(Al
_1-
x
Si
x
), and Co
₂
Fe(Ga
_1-
x
Si
x
) Heusler alloys were evaluated from the thermomagnetization measurements. For the Co
₂
CrGa, Co
₂
MnGa, and Co
₂
Mn(Al
_1-
x
Si
x
) alloys, there was a linear relation between
D
and
T
_C
. The tendency between
D
and
T
_C
was different from that for Co
₂
Fe(Al
_1-
x
Si
x
) and Co
₂
Fe(Ga
_1-
x
Si
x
) 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 ·nm
²
for
x
=1 (Co
₂
FeSi) to 5.24 meV ·nm
²
for
x
=0 (Co
₂
FeGa) in the case of Co
₂
Fe(Ga
_1-
x
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.