  Electrical and magnetic properties of four series of manganates LnxCa1-xMnO3
(Ln=La, Nd, Gd and Y) have been studied in the electron doped regime
(x=0.02-0.25) in order to investigate the various inter-dependent phenomena
such as ferromagnetism, phase separation and charge ordering. The general
behavior of all the four series of manganates is similar, with some of the
properties showing dependence on the average radius of the A-site cations, <rA>
and cation size disorder. Thus, all the compositions show increase in
magnetization at 100-120 K (TM) for x<xmax, the magnetization increasing with
increasing x. The value of xmax increases with decreasing <rA>, probably due to
the increased phase separation induced by site disorder. This is also reflected
in the larger width of the hysteresis loops at T<TM for small x or <rA>. In
this regime, the electrical resistivity decreases with increasing x, but
remains low and nearly constant T>TM. The percolative nature of the conduction
mechanism at T<TM is substantiated by the fit of the conductivity data to the
scaling law, s \mu |xc-x|p where p is in the 2-4 range. When x>xmax, the
materials become antiferromagnetic and charge-ordered at a temperature TCA,
accompanied by a marked increase in resistivity. The value of TCA increases
with increase in <rA> and x (upto x=0.3). Thus, all the four series of
manganates are characterized by a phase-separated regime between x=0.02 and
0.1-0.15 and an antiferromagnetic charge-ordered regime at x>0.1-0.15.
