Structural, transport, and magnetic properties of narrow bandwidth Nd$_{1-x}$Ca$_{x}$CoO$_{3-\delta}$ and comparisons to Pr$_{1-x}$Ca$_{x}$CoO$_{3-\delta}$

Pr$_{1-x}$Ca$_x$CoO$_{3-\delta}$ (PCCO), has drawn attention due to a 1st-order insulator-metal transition (IMT) that appears on cooling at x=0.5, connected to a shift in electron occupancy between Pr and Co sites. Furthermore, the evolution of the magnetic/transport properties in low-bandwidth (LB) cobaltites is of interest due to anticipated enhancement of magneto-electronic phase separation by suppressed bandwidth. We discuss the structural, magnetic, and transport properties of a second series, Nd$_{1-x}$Ca$_x$CoO$_{3-\delta}$ (NCCO, 0$\leq x\leq0.4$), which, devoid of the unique Pr-O bonding in PCCO, serves as a control for assessing the intrinsic physics of LB cobaltites. Using small-angle neutron scattering, neutron diffraction, and AC/DC magnetometry, a magnetic phase diagram is developed. Common to both systems is development of a metallic ferromagnetic (FM) state with low T$_c$ ($<$ $\sim$60 K for NCCO) upon hole substitution, while at higher temperatures ($\sim$270 K for NCCO), short-range FM is stabilized, likely around O vacancies. Phase separation leads to exchange-spring behavior around $T_c$. Unique to NCCO is ferrimagnetic ordering ($<$ $\sim$14 K) involving Nd. Absence of a 1st-order IMT in NCCO affirms the influence of Pr-O bonding on the IMT in PCCO.