Effects of dilution on magnetic and transport properties of La0.7Ca0.3Mn1-xMx′O3

Magnetic and transport properties of La(0.7)Ca(0.3)Mn(1-x)M(x)(')O(3) (M(')=Al,Ti) are studied. The dilution of the Mn network results in a weakening of the ferromagnetism, a deterioration of the metallic conductivity, and a strong enhancement of the magnetoresistance. Although T(c) linearly decreases with x in the low substitution ranges for both M(') series, the scaling behavior T(c)(n(p)) previously observed for La(0.7)Sr(0.3)Mn(1-x)M(x)(')O(3) [D. N. H. Nam , Phys. Rev. B 73, 184430 (2006)] is no longer obtained. Extrapolations of the T(c)(n(p)) linear curves to T(c)=0 K give n(p) values much smaller than one. These results suggest that, according to a molecular-field approximation, antiferromagnetic superexchange between Mn ions is significant in La(0.7)Ca(0.3)MnO(3), in contrast to what was observed in La(0.7)Sr(0.3)MnO(3). Additionally, the structural data of the Al-substituted samples suggest that variations of the e(g)-electron bandwidth W cannot explain the decrease in T(c) in magnetically diluted manganites.