Long- and short-range magnetic interactions in nanocrystalline lightly Cr-doped manganites

This work investigated the effect of lightly Cr3+-doped ions on the structural, magnetic, and critical behavior of the nominal composition La0.7Ca0.3Mn1-xCrxO3 (0 <= x <= 0.09). Our compounds adopted a single phase with a rhombohedral structure (space group R (3) over barc). Furthermore, a comparative study of the crystallite sizes of compounds by X-ray powder diffraction, XRD, is reported. Individual contributions of the crystallite sizes and lattice microstrains were examined through the Williamson-Hall (W-H) analysis, the size-strain plot (SSP), and Halder-Wagner (H-W) methods. Greater accuracy was noted with W-H, where points were more likely to contact the fitting line than those using other methods. From magnetic data analyzed, a second-order paramagnetic-ferromagnetic phase transition appears at Curie temperatures, T-c, between 212 and 261K. A deviation from the Curie Weiss law is due to the presence of local inhomogeneities in our samples for T >= T-c characteristic of a Griffiths Phase. The critical coefficient values obtained for beta, gamma, and delta from different methods are fairly close to the theoretical prediction of the tricritical mean-field model for x = 0.0 and 0.03 and which are in accordance with those predicted by the 3D Ising model for x = 0.06. The values found for beta, gamma, and delta are close to those expected for the mean field x = 0.09. In our samples, we found that two types of interactions exist, long-range exchange interactions for x = 0.0, 0.03 and 0.06 and short-range exchange interactions for x = 0.09.

Automated summary

This work investigates the effect of lightly Cr3+-doped ions on the structural, magnetic, and critical behavior of La0.7Ca0.3Mn1-xCrxO3 compounds. The compounds adopt a single phase rhombohedral structure. XRD analysis is used to compare crystallite sizes, and various methods are employed to examine the contributions of crystallite sizes and lattice microstrains. The magnetic data shows a second-order paramagnetic-ferromagnetic phase transition and the presence of a Griffiths Phase.