  We report detailed structural, electrical, magnetic and specific heat studies
on La0.7Ca0.3Mn1-xCrxO3 manganites. Rietveld analysis of fitted and observed
XRD patterns exhibited the single-phase nature of all the studied materials,
which crystallize in Pbnm space group. Successive substitution of Cr at Mn site
in La0.7Ca0.3Mn1-xCrxO3 manganites increases the electrical resistivity and
decrease the characteristic insulator-metal transition temperature (TIM) of the
parent compound along with a hump like feature for higher Cr-content samples.
The hump structure basically signifies the onset of anti-ferromagnetic (AFM)
interactions as inferred by both the magnetic and infra-red (IR) spectroscopy
studies. The systematic suppression of FM state results in a spin glass (SG)
like behavior. IR studies revealed that the vibration mode at 413 cm-1 being
associated with internal bending of MnO6 octehedra, becomes softer, indicating
an increase in distortion and hence the possible spin glass behavior. The
critical exponents alpha, beta and gama are calculated from the heat capacity
(CP) data near the TIM/TFM. The same exhibited variations of their values with
doping. In particular the value of beta increases from 0.37 to 0.43, clearly
indicating the coexistence of both long and short range magnetic orders i.e.
tendency towards SG state for Cr doped samples. On the basis of present
results, it is suggested that Cr dilutes double-exchange (DE) based FM and
rather promotes the AFM based super exchange interactions (SE) via Cr3+/Mn4+
ions. Substitution of Cr systematically destroys both the metallic state and
long range ferromagnetic (FM) order.
