Magnetotransport studies and mechanism ofHo- andY-dopedLa0.7Ca0.3MnO3

Abstract

Transport properties of mixed-valence manganites of the type $({\mathrm{La}}_{0.7\ensuremath{-}x}{R}_{x}){\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ where $R=\mathrm{Ho}$ (magnetic) and Y (nonmagnetic) have been investigated above the ferromagnetic transition temperature ${(T}_{C}).$ It is interesting to see that the Ho-doped compounds have less resistivity compared to the Y-doped compounds, although Ho and Y ions have almost the same ionic radii and hence lattice strain effect would be the same in both the cases. The internal magnetic field of Ho $({\ensuremath{\mu}}_{\mathrm{eff}}^{\mathrm{Ho}}=10.5{\ensuremath{\mu}}_{B})$ is found to be responsible for this decrease in resistivity in Ho-doped compounds. Coupling of Ho magnetic moment to that of Mn has been confirmed by magnetization measurements. The resistivity data above ${T}_{C}$ fit well to the magnetic localization model proposed by Viret et al. [Phys. Rev. B 55, 8067 (1997); Phys. Rev. Lett. 75, 3910 (1995)] and the localization lengths thus obtained are reasonable. The localization lengths of the Ho-doped compounds are greater than that of Y-doped compounds of the same composition indicating that the coupling of the Ho moment with that of the Mn moments is responsible for this effect.