  Thermodynamic properties of cubic Heisenberg ferromagnets with competing
exchange interactions are considered near the frustration point where the
coefficient $D$ in the spin-wave spectrum $E_{\mathbf{k}}\sim D k^{2}$
vanishes. Within the Dyson-Maleev formalism it is found that at low
temperatures thermal fluctuations stabilize ferromagnetism by increasing the
value of $D$. For not too strong frustration this leads to an unusual "concave"
shape of the temperature dependence of magnetization, which is in agreement
with experimental data on the europium chalcogenides. The phase diagram is
constructed by means of Monte Carlo simulation, and suppression of
magnetization and Curie temperature is found in comparison with the results of
the spin-wave theory. This effect is explained by the the presence of
non-analytical corrections to the spin-wave spectrum which are represented in
the lowest order by the term $\sim (T/S)^{2} k^{2}\log{k}$.
