  Large magnetoresistive materials are of immense interest for a number of
spintronic applications by developing high density magnetic memory devices,
magnetic sensors and magnetic switches. Colossal magnetoresistance, for which
resistivity changes several order of magnitude (${\sim10^4 \%}$) in an external
magnetic field, occurs mainly in phase separated oxide materials, namely
manganites, due to the phase competition between the ferromagnetic metallic and
the antiferromagnetic insulating regions. Can one further enhance the
magnetoresistance by tuning the volume fraction of the two phases? In this
work, we report a huge colossal magnetoresistance along with the ultra-sharp
metamagnetic transition in half doped ${Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3}$
manganite compound by suitably tuning the volume fraction of the competing
phases. The obtained magnetoresistance value at 10 K is as large as
$\sim10^{13}\%$ in a 30 kOe external magnetic field and $\sim10^{15}\%$ in 90
kOe external magnetic field and is several orders of magnitude higher than any
other observed magnetoresistance value reported so far. Using model Hamiltonian
calculations we have shown that the inhomogeneous disorder, deduced from
tunneling electron microscopy, suppresses the CE-type phase and seeds the
ferromagnetic metal in an external magnetic field.
