  We have investigated the influence of B - site doping on the crystal and
magnetic structure in $La_{0.5}Ca_{0.5}Mn_{1-x}B_{x}O_{3}$ (B= Fe, Ru, Al and
Ga) compounds using neutron diffraction, SANS, magnetization and resistivity
techniques. The B - site doped samples are isostructural and possess an
orthorhombic structure in \textit{Pnma} space group at 300K. A structural
transition from orthorhombic to monoclinic is found to precede the magnetic
transition to CE - type antiferromagnetic state in few of these samples. On
doping with Fe, charge and orbitally ordered CE - type antiferromagnetic state
is suppressed, followed by the growth in ferromagnetic insulating phase in
$0.02\leq x\leq0.06$ compounds. At higher Fe doping in $x>0.06$, the
ferromagnetic state is also suppressed and no evidence of long range magnetic
ordering is observed. In Ru doped samples $(0.01\leq x\leq0.05)$, the
ferromagnetic metallic state is favored at $T{}_{C}\approx200K$ and
$T_{MI}\approx125K$ and no significant change in $T_{C}$ and $T_{MI}$ as a
function of Ru doping is found. In contrast, with non magnetic Al substitution
for $0.01\leq x\leq0.03$, the charge ordered CE - type antiferromagnetic state
coexists with the ferromagnetic metallic phase. With further increase in Al
doping $(0.05\leq x\leq0.07)$, both CE - type antiferromagnetic and
ferromagnetic phases are gradually suppressed. This behavior is accompanied by
the evolution of A - type antiferromagnetic insulating state. Eventually, at
higher Al doping $(0.10\leq x\leq0.13)$, this phase is also suppressed and
signature of spin glass like transition are evident in M(T). Likewise,
substitution with Ga is observed to induce similar effects as described for Al
doped samples. The presence of short ranged ferromagnetic ordering has been
further explored using SANS measurements in few of the selected samples.
