Abstract

We have shown in a recent study that substitution of Ho 3+ ions in La 0.7 Ca 0.3 MnO 3 causes significant reduction in electrical resistivity compared with Y 3+ ion substitution. This reduction in resistivity was attributed to the reduced spin disorder scattering in La 0.7 Ca 0.3 MnO 3 samples containing magnetic Ho 3+ . We have estimated the Mn-spin canting angles in Ho 3+ - and Y 3+ -doped La 0.7 Ca 0.3 MnO 3 compounds from the resistivity data using the magnetic localization model. We find that the canting angles of the Mn spins in the Ho 3+ doped compounds are smaller than those obtained for the Y 3+ -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 Ho 3+ - and Y 3+ -doped compounds for all compositions may be attributed to the presence of an internal field due to Ho 3+ doping. This internal field may be responsible for the decrease in spin disorder in the Ho 3+ -doped compounds. The increase in the canting angles with increase in Ho 3+ and Y 3+ content could be attributed to the decrease in the strength of the ferromagnetic exchange interactions. A strong ferromagnetic coupling of Ho 3+ moments with the Mn moments is responsible for the observed behaviour