Possible double-exchange interaction between manganese and chromium in LaMn1-xCrxO3

We have explored the possibility of double-exchange interaction between ions of different elements by studying a series of LaMn_1-xCr_xO₃ (0.1<=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 LaMnO₃ 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~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 Mn³⁺-O-Mn⁴⁺. Besides, the ESR signals show that the competing antiferromgantic component increases with Cr doping. Therefore the double exchange in LaMn_1-xCr_xO₃ is somewhat weakened and consequently leads to the absence of a metallic state in the ferromagnetic phase.