We report the effects of Mn substitution, corresponding to hole doping, on the
electronic properties of the narrow gap semiconductor, FeSb2, using single crystals of
Fe1‒xMnxSb2 grown by the Sb flux method. The orthorhombic Pnnm structure was confirmed
by powder X-ray diffraction (XRD) for the pure and Mn-substituted samples. Their crystal
structure parameters were refined using the Rietveld method. The chemical composition was
investigated by wavelength-dispersive X-ray spectroscopy (WDX). The solubility limit of Mn
in FeSb2 is xmax ~ 0.05 and the lattice constants change monotonically with increasing the
actual Mn concentration. A drastic change from semiconducting to metallic electronic
transports was found at very low Mn concentration at x ~ 0.01. Our experimental results and
analysis indicate that the substitution of a small amount of Mn changes drastically the
electronic state in FeSb2 as well as the Co-substitution does: closing of the narrow gap and
emergence of the density of states (DOS) at the Fermi level.