Metal-insulator transition in antiferromagnetic Ba1−xKxMn2As2(0≤x≤0.4) single crystals studied by55Mn and75As NMR

Abstract

The magnetic structure and metal-insulator transition in antiferromagnetic (AFM) BaMn${}_{2}$As${}_{2}$ and Ba${}_{1\ensuremath{-}x}$K${}_{x}$Mn${}_{2}$As${}_{2}$ single crystals have been investigated by ${}^{55}\phantom{\rule{0.16em}{0ex}}$Mn and ${}^{75}$As nuclear magnetic resonance (NMR) measurements. In the parent AFM insulator BaMn${}_{2}$As${}_{2}$ with a N\'eel temperature ${T}_{\mathrm{N}}=625$ K, we observed a ${}^{55}\phantom{\rule{0.16em}{0ex}}$Mn zero-field NMR (ZFNMR) spectrum and confirmed the G-type AFM structure from the field dependence of the ${}^{55}\phantom{\rule{0.16em}{0ex}}$Mn spectra and ${}^{75}$As NMR spectra below ${T}_{\mathrm{N}}$. In hole-doped crystals with $x>0.01$, similar ${}^{55}\phantom{\rule{0.16em}{0ex}}$Mn ZFNMR spectra were observed and the AFM state was revealed to be robust up to $x=0.4$ with the ordered moment nearly independent of $x$. The nuclear spin-lattice relaxation rates ($1/{T}_{1}$) for both nuclei in the doped samples follow the Korringa relation ${T}_{1}T=\text{const}$, indicating a metallic state. This confirms the coexistence of AFM ordered localized Mn spins and conduction carriers from a microscopic point of view. From the $x$ dependence of ${({T}_{1}T)}^{\ensuremath{-}1/2}$ for both nuclei, we conclude that this transition is caused by vanishing of the hole concentration as the transition is approached from the metallic side.