Metal-insulator transition in antiferromagnetic $Ba_{1-x}K_xMn_2As_2$ $(0\le x\le0.4)$ single crystals studied by $^{55}$Mn and $^{75}$As NMR

摘要

The magnetic structure and metal-insulator transition in antiferromagnetic(AFM) BaMn2As2 and Ba1-xKxMn2As2 single crystals have been investigated by 55Mnand 75As nuclear magnetic resonance (NMR) measurements. In the parent AFMinsulator BaMn2As2 with a Neel temperature TN = 625 K, we observed a 55Mnzero-field NMR (ZFNMR) spectrum and confirmed the G-type AFM structure from thefield dependence of the 55Mn spectra and 75As-NMR spectra below TN. Inhole-doped crystals with x > 0.01, similar 55Mn ZFNMR spectra were observed andthe AFM state was revealed to be robust up to x = 0.4 with the ordered momentnearly independent of x. The nuclear spin-lattice relaxation rates (1/T1) forboth nuclei in the doped samples follow the Korringa relation T1T = const.,indicating a metallic state. This confirms the coexistence of AFM orderedlocalized 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 thistransition is caused by vanishing of the hole concentration as the transitionis approached from the metallic side.