Metal-insulator transition in antiferromagnetic $B{a}_{1-x}{K}_{x}M{n}_{2}A{s}_2$ $(0\le x\le 0.4)$ single crystals studied by ${}^{55}$Mn and ${}^{75}$As NMR

Abstract

The magnetic structure and metal-insulator transition in antiferromagnetic (AFM) BaMn2As2 and Ba1-xKxMn2As2 single crystals have been investigated by 55Mn and 75As nuclear magnetic resonance (NMR) measurements. In the parent AFM insulator BaMn2As2 with a Neel temperature TN = 625 K, we observed a 55Mn zero-field NMR (ZFNMR) spectrum and confirmed the G-type AFM structure from the field dependence of the 55Mn spectra and 75As-NMR spectra below TN. In hole-doped crystals with x > 0.01, similar 55Mn 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/T1) for both nuclei in the doped samples follow the Korringa relation T1T = 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 (T1T)^(-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.

arXiv comment5 pages, 4 figures, submitted to Phys. Rev. B

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