Antiferromagnetic Heusler Ru$_{2}$ MnGe Epitaxial Thin Films Showing Néel Temperatures up to 353 K

Structural and electrical transport properties were investigated for Heusler-type alloy Ru
$_{2}$
MnGe thin films. Ru
$_{2}$
MnGe films on MgO substrate were subjected to an in-plane compressive strain due to their small lattice mismatch
$({-}0.7\hbox{\%})$
, and exhibited enhanced antiferromagnetic transition temperature
$(T_{\rm N})$
up to 353 K, which is much higher than that of the bulk material (
$T_{\rm N}= 316$
K). In contrast, the films on MgAl
$_{2}$
O
$_{4}$
were almost in a relaxed-strain state, and showed
$T_{\rm N}$
close to the bulk value (304 K). It was also found that the
$T_{\rm N}$
of Ru
$_{2}$
MnGe thin films on MgO exhibited oscillating behavior depending on
$c/a$
ratio. We argued that the next-nearest neighbor magnetic interactions
$(J_{2})$
of Mn-Mn atoms has oscillated depending on the degree of strain in Ru
$_{2}$
MnGe, which contribute to the oscillating behavior of
$T_{\rm N}$
against
$c/a$
.