Metamagnetic behavior of NdBaCo$_2$O$_{5+\delta}$, $\delta\approx0.5$, layered cobaltite

NdBaCo$_2$O$_{5+\delta}$, $\delta\approx0.5$, layered cobaltite is a metamagnet, which at a relatively low magnetic field transforms below $T\sim 20$ K from the antiferromagnetic phase to the mixed ferromagnetic state. Above $T\sim 20$ K, it is a mixture of exchange-coupled ferromagnetic and antiferromagnetic phases. The transition from the quasimetallic state to the state with a low electrical conductivity is accompanied by the spin-state transition in Co$^{3+}$ ions from the HS/LS state to the IS/LS one.