Evidence of reduction in spin disorder by Ho3+ doping in La0.7Ca0.3MnO

We have shown in a recent study that substitution of Ho³⁺ ions (4f¹⁰; magnetic momen _μB) in La_0.7Ca_0.3MnO₃ 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 La_0.7Ca_0.3MnO₃ samples containing magnetic Ho³⁺. We have estimated the Mn-spin canting angles in Ho³⁺ - and Y³⁺-doped La_0.7Ca_0.3MnO₃ 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.