High-magnetic-field study of magnetic and transport properties of hole-doped NdBaCo2O5+δ

Abstract

Magnetic and transport properties of the NdBaCo${}_{2}$O${}_{5+\ensuremath{\delta}}$ system are studied in the less investigated hole-doped region (0.52 \ensuremath{\delta} 0.72) and in pulsed magnetic fields up to 47 T. The conductance in zero-magnetic field and $T$ 130 K is described by a two-gap expression completed by the term of variable range hopping (VRH). The thermoelectric power $S$($T$ ) measurements confirm the magnetic phase diagram found by magnetic and electric transport investigations. It has been shown that ferromagnetic behavior of NdBaCo${}_{2}$O${}_{5+\ensuremath{\delta}}$ (0.52 \ensuremath{\delta} 0.72) is stabilized and spans in lower temperatures by increasing the external magnetic field in agreement with structural and magnetic phase diagrams found on the NdBaCo${}_{2}$O${}_{5.75}$ and GdBaCo${}_{2}$O${}_{5+\ensuremath{\delta}}$ systems. Variable range hopping mode gives good approximation in zero- and high-magnetic field 47 T. The isothermal magnetoconductance ($G$ ) of hole-doped polycrystalline NdBaCo${}_{2}$O${}_{5.72}$ is well fitted by $G$($H$, $T$ )/$G$(0) $=$ ${G}_{0}$exp($H$/${H}_{0}$) dependence at 55 K $T$ 138 K (the region where FM state appears) instead of simple linear dependence found for manganites La${}_{0.7}$Sr${}_{0.3}$MnO${}_{3}$. The parameter ${H}_{0}$ is considered as the magnetic field of full spin sublattices' reorientation and $MR$ saturation. The magnetoconductance is possibly realized through the $a$-oriented grains due to the strong decrease of resistivity \ensuremath{\Delta}${\ensuremath{\rho}}_{c}$/${\ensuremath{\rho}}_{c}$ in magnetic field along the $a$ axis. The deduced reason for observed behavior is the specific origin of the antiferromagnetic (AFM)-ferromagnetic (FM) transition in layered cobaltites.