We have explored the possibility of double-exchange interaction between ions of different elements by studying a series of ${\mathrm{LaMn}}_{1-x}{\mathrm{Cr}}_x{\mathrm{O}}_3$ $(0.1\mathrm{}<~x<~0.7)$ perovskites, with the measurements of magnetization, resistivity, magnetoresistance, infrared spectra, and electron-spin resonance (ESR). It was found that the doping of Cr in ${\mathrm{LaMnO}}_3$ introduces ferromagnetism and cluster glass behaviors. Moreover, a close correlation between magnetic state and transport behavior as well as a large magnetoresistance were observed when $x\sim \mathrm{0.3.}$ These results suggest that a ferromagnetic exchange interaction similar to double exchange could occur between Mn and Cr. Nevertheless, the variation of the Mn-O-Cr bond angle and length due to the mismatch of ion radii between Cr and Mn, as evidenced by infrared phonon spectra, is not so favorable for electronic transfer as that in ${\mathrm{Mn}}^{3+}-\mathrm{O}-{\mathrm{Mn}}^{4+}.$ Besides, the ESR signals show that the competing antiferromgantic component increases with Cr doping. Therefore the double exchange in ${\mathrm{LaMn}}_{1-x}{\mathrm{Cr}}_x{\mathrm{O}}_3$ is somewhat weakened and consequently leads to the absence of a metallic state in the ferromagnetic phase.

• Received 13 December 2000

DOI:https://doi.org/10.1103/PhysRevB.63.174438