A large magnetoresistance (MR) effect was observed in the layered compounds NdCoAsO and SmCoAsO, in which ferromagnetically ordered itinerant-electrons of Co are sandwiched by localized 4$f$-electrons of $Ln^{ 3+}$, below ferromagnetic-antiferromagnetic transition (FAFT) temperature $T_\mathrm{ N}$ as observed in other FAFT compounds. In SmCoAsO, the large MR effect is also observed up to the Curie temperature $T_\mathrm{ C}$, and it is found to be originating in the presence of another antiferromagnetic phase in the low-magnetic field region of the ferromagnetic phase.
Categories: cond-mat.str-el