Abstract
In a recently published paper [Phys. Rev. B 62, 5313 (2000)], Yuan et al. studied the magnetoresistance (MR) and electron paramagnetic resonance (EPR) of ceramic samples of $({\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}{)}_{1/3}{\mathrm{Ca}}_{2/3}{\mathrm{MnO}}_{3}$ $(x=0.15,0.20).$ They argue that the EPR linewidth and the MR exhibit similar temperature dependences in the range ${T}_{C}<~T<~{T}_{\mathrm{onset}},$ and conclude that the same mechanism underlies both effects. In our opinion, they made a mistake in analyzing the origin of EPR line broadening below ${T}_{\mathrm{onset}}.$ Similar experiments carried out in single crystals showed that while the peak of MR around ${T}_{C}$ is intrinsic to these manganites, the observed line broadening is not. This effect has been previously related to the presence of pores between grains in polycrystalline samples and surface irregularities in single crystals, and is common to other magnetic materials that do not show colossal magnetoresistance.
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