  The tuning of magnetic phase, chemical potential, and structure is crucial to
observe diverse exotic topological quantum states in $MnBi_2Te_4(Bi_2Te_3)_m$
(m = 0, 1, 2, & 3). Here we show a ferromagnetic (FM) phase with a chiral
crystal structure in $Mn(Bi_{1-x}Sb_x)_4Te_7$, obtained via tuning the growth
conditions and Sb concentration. Unlike previously reported
$Mn(Bi_{1-x}Sb_x)_4Te_7$, which exhibits FM transitions only at high Sb doping
levels, our samples show FM transitions ($T_C$ = 13.5 K) at 15%-27% doping
levels. Furthermore, our single crystal x-ray diffraction structure refinements
find Sb doping leads to a chiral structure with the space group of P3,
contrasted with the centrosymmetric P-3m1 crystal structure of the parent
compound $MnBi_4Te_7$. Through ARPES measurements, we also demonstrated that
the non-trivial band topology is preserved in the Sb-doped FM samples. Given
that the non-trivial band topology of this system remains robust for low Sb
doping levels, our success in making FM $Mn(Bi_{1-x}Sb_x)_4Te_7$ with $x$ =
0.15, 0.175, 0.2 & 0.27 paves the way for realizing the predicted topological
quantum states such as axion insulator and Weyl semimetals. Additionally, we
also observed magnetic glassy behavior in both antiferromagnetic $MnBi_4Te_7$
and FM $Mn(Bi_{1-x}Sb_x)_4Te_7$ samples, which we believe originates from
cluster spin glass phases coexisting with long-range AFM/FM orders. We have
also discussed how the antisite Mn ions impact the interlayer magnetic coupling
and how FM interlayer coupling is stabilized in this system.
