Enhancement of Magnetoresistance by Co Substitution in Pr0.6Sr0.4Mn1−xCoxO3

We investigate the effect of Co substitution on magnetism, electrical resistivity, and magnetoresistance (MR) in Pr
_0.6
Sr
_0.4
Mn
_1-x
Co
_x
O
₃
(x = 0-0.2). The parent compound Pr
_0.6
Sr
_0.4
MnO
₃
is a double exchange (DE) ferromagnet with a ferromagnetic (FM) transition at T
_C
= 305 K. The long-range FM order persists for x = 0.05 with a radical downshift in T
_C
(260 K). A decrease in magnetization as well as a drastic increase in electrical resistivity (ρ ~ 0.02 Ω · cm for x = 0 to ~ 10
⁷
Ω · cm for x = 0.2 at 10 K) with Co doping indicates the weakening of DE interaction and the evolution of glassy magnetic ground state. For both x = 0 and 0.05, ρ shows a prominent peak at their respective T , whereas such a feature is absent for x ≥ 0.1. A large enhancement in MR at low temperatures occurs with increasing Co doping (from -45% for x = 0 to -85% for x = 0.2 at 10 K at 7 T magnetic field). The occurrence of such a huge MR at low temperatures for Co-doped compounds could be either due to spin-dependent tunneling between FM clusters with the spin-glass-like interface within grains or suppression of spin fluctuations.