  Effect of Ge substitution on first order ferrimagnetic (FRI) -
antiferromagnetic (AFM) transition in Mn$_2$Sb has been studied. It shows that
transition temperature (T$_t$) can be tuned between 119~K - 271~K by
substituting 2.5-10\% Ge at Sb site in Mn$_2$Sb. The variation of density of
state at Fermi level N(E$_f$) with Ge substitution shows that dN(E)/dE is
positive at E$_f$ in the AFM state. With the application of magnetic field
T$_t$ shifts to low temperature, which results in a giant negative
magnetoresistance (MR) reaching a value of 70\% for 2.5\% substitution. Our
results show that FRI to AFM transformation during cooling stops around 35 K,
even though it remains incomplete. It along with non-monotonic variation of
lower critical field, open loop in isothermal MR and increasing difference in
zero field cooled warming (ZFCW) and field cooled warming (FCW) resistivity
with increasing magnetic field shows that FRI to AFM transition is kinetically
arrested in the case of 2.5\% Ge substitution.
