Nanostructural evidence at the phase boundary of A-and C-type antiferromagnetic phases in Nd_1-xSr_xMnO₃ crystals

A weak ferromagnetic phase appears around the phase boundary between the A-type and C-type antiferromagnetic phases in overdoped Nd_1-xSr _xMnO₃ crystals (0.6≤x≤0.7). We investigated the crystal structure and the magnetic domain structure around the phase boundary, by powder synchrotron x-ray diffractometry and transmission electron microscopy. The phase boundary exists between x = 0.62 in the phase separation region where the A-type and C-type antiferromagnetic phases coexist and x = 0.625 in the C-type antiferromagnetic phase. By transmission electron microscopy, the orbital-disordered nanodomains in the C-type antiferromagnetic matrix phase were only observed in the vicinity of the phase boundary in the C-type antiferromagnetic phase. This is a nanoscale inhomogeneity but is not a conventional phase separation for manganites. We also successfully observed magnetic domain structures in the weak ferromagnetic phase by Lorentz electron microscopy. Moreover, we found that the ferromagnetic correlation becomes a short-range correlation when the orbital-disordered nanodomains appear. We consider that the orbital-disordered nanodomains interfere with the long-range ferromagnetic correlation.