Spin-polarized scanning tunneling spectroscopic (SP-STS) studies of the intrinsic electronic heterogeneity in ferromagnetic (FM) cobaltites and manganites

The perovskite manganites Ln$_{1-x}$A$_{x}$MnO$_{3}$ and cobaltites Ln$_{1-x}$A$_{x}$CoO$_{3}$ (Ln: trivalent rare earth ions; A: divalent alkaline earth ions) exhibit interesting magnetotransport properties in their FM state: the former show colossal magnetoresistance (CMR) and the latter display giant anomalous Hall effect (AHE), where the AHE coefficient peaks near the Curie temperature ($T_{C})$. These novel phenomena are associated with the intrinsic electronic heterogeneity resulting from strongly correlated multi-valence multi-spin electronic configurations. We perform SP-STS studies on epitaxial films of La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ and La$_{1-x}$A$_{x}$CoO$_{3}$ (A = Sr, Ca; 0.4 $\le $ x $\le $ 0.6). In the manganites electronic heterogeneity on the scale of $\sim $10$^{2}$ nm is found to develop below $T_{C}$ and diminish with increasing magnetic field. A surface FM insulating phase is manifested by the spin filtering effect and is attributed to the MnO$_{2}$ surface layer. Similar studies are conducted on the cobaltites to reveal possible correlation between magnetic clustering effects and the Berry phase.