Electronic and Magnetic Properties of Ba$_{1-x}$K$_{x}$Mn$_{2}$As$_{2}$ Studied by $^{55}$Mn and $^{75}$As-NMR

BaMn$_{2}$As$_{2}$ (Mn$^{2+}$; S = 5/2) is a G-type antiferromagnetic (AF) semiconductor with N\'{e}el temperature $T_{N} \sim $ 625 K and a small band gap of $\sim $ 27 meV. Hole doping by substitution of Ba with K drives BaMn$_{2}$As$_{2}$ into a metallic state while maintaining the same AF spin structure with similar high $T_{N}$. In order to investigate hole doping effects on electronic and magnetic properties in Ba$_{1-x}$K$_{x}$Mn$_{2}$As$_{2 }$from a microscopic point of view, we have conducted $^{55}$Mn and $^{75}$As-NMR spectra and spin-lattice relaxation measurements on single crystals of Ba$_{1-x}$K$_{x}$Mn$_{2}$As$_{2}$ ($x$ = 0, 0.04, 0.4). The temperature ($T)$ dependence of 1/$T_{1}$ for $^{55}$Mn and $^{75}$As for the $x$=0 compound shows 1/$T_{1} \quad \sim \quad T ^{3}$ dependence for both nuclei, suggesting that 1/$T_{1}$ of the nuclei arises from interactions with magnon excitations in the local-moment AF state. On the other hand, the 1/$T_{1}$ of both nuclei is found to be proportional to $T$ (Korringa relation) in K-doped materials below $T_{N}$, which corresponds to the AF metallic state in Ba$_{1-x}$K$_{x}$Mn$_{2}$As$_{2}$.