  We report the superconducting properties of the
Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$/Cu/Ni/Cu/Pb spin-valve structure which magnetic
part comprises the Heusler alloy layer HA = Co$_2$Cr$_{1-x}$Fe$_x$Al$_y$ with a
high degree of spin polarization (DSP) of the conduction band and the Ni layer
of variable thickness. We obtained that the separation between the
superconducting transition curves measured for the parallel ($\alpha =
0^\circ$) and perpendicular ($\alpha = 90^\circ$) orientation of the
magnetizations of the HA and Ni layers reaches up to 0.5 K ($\alpha$ is an
angle between the magnetization of two ferromagnetic layers). For all studied
samples the dependence of the superconducting transition temperature $T_c$ on
$\alpha$ demonstrates a deep minimum in the vicinity of the perpendicular
configuration of magnetizations. This suggests that the observed minimum and
the corresponding full switching effect of the spin valve is caused by the
long-range triplet component of the superconducting condensate in the
multilayer. Such a large effect can be attributed to a half-metallic nature of
the HA layer which in the orthogonal configuration efficiently draws off the
spin-polarized Cooper pairs from the space between the HA and Ni layers. Our
results indicate a significant potential of the concept of the superconducting
spin-valve multilayer comprising a half-metallic ferromagnet recently proposed
by A. Singh et al., Phys. Rev. X 5, 021019 (2015) in achieving large values of
the switching effect.
