Evidence of reduction in spin disorder by Ho³⁺doping in La_0.7Ca_0.3MnO

We have shown in a recent study that substitution of Ho3+ ions (4f10; magnetic momen μB) in La0.7Ca0.3MnO3 causes significant reduction in electrical resistivity compared with Y3+ (4d0; non-magnetic) ion substitution. This reduction in resistivity was attributed to the reduced spin disorder scattering in La0.7Ca0.3MnO3 samples containing magnetic Ho3+. We have estimated the Mn-spin canting angles in Ho3+ - and Y3+-doped La0.7Ca0.3MnO3 compounds from the resistivity data using the magnetic localization model. We find that the canting angles of the Mn spins in the Ho3+ doped compounds are smaller than those obtained for the Y3+-doped compounds for all compositions and at all applied magnetic fields, showing clearly a reduction in the spin disorder in the former. The difference between the T C values for Ho3+ - and Y3+-doped compounds for all compositions may be attributed to the presence of an internal field due to Ho3+ doping. This internal field may be responsible for the decrease in spin disorder in the Ho3+-doped compounds. The increase in the canting angles with increase in Ho3+ and Y3+ content could be attributed to the decrease in the strength of the ferromagnetic exchange interactions. A strong ferromagnetic coupling (as discussed recently by the present authors and co-workers) of Ho3+ moments with the Mn moments is responsible for the observed behaviour.