Effect of Hetrovalent substitution at Mn site on the Magnetic and Transport Properties of La${}_{0.67}$Sr${}_{0.33}$MnO${}_3$

Magnetic and transport properties of Ti substituted La${}_{0.67}$Sr${}_{0.33}$MnO${}_3$ are drastically affected with a change in preparation conditions. Low temperature infra-red absorption measurements reveal that this is perhaps due to inhomogeniety in substitution of Ti${}^{4+}$ on Mn sites. It is found that, in the high temperature annealed samples, the substitution of Ti supresses the double exchange interaction due to the formation of Mn${}^{3+}$-O-Ti${}^{4+}$ chains. While in the low temperature annealed case substitution of Ti causes formation of isolated ferromagnetic clusters linked to each other by a variable range hopping polaron.