Metal-insulator transition in antiferromagnetic Ba sub(1-x) K sub(x) Mn sub(2) As sub(2) (0 [< or =] x [< or =] 0.4) single crystals studied by super(55)Mn and super(7)5As NMR

The magnetic structure and metal-insulator transition in antiferromagnetic (AFM) BaMn sub(2) As sub(2) and Ba sub(1-x) K sub(x) Mn sub(2) As sub(2) single crystals have been investigated by super(55)Mn and super(75)As nuclear magnetic resonance (NMR) measurements. In the parent AFM insulator BaMn sub(2) As sub(2) with a Neel temperature T sub(N) = 625 K, we observed a super(55)Mn zero-field NMR (ZFNMR) spectrum and confirmed the G-type AFM structure from the field dependence of the super(55)Mn spectra and super(75)As NMR spectra below T sub(N). In hole-doped crystals with x > 0.01, similar super(55)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 sub(1)) for both nuclei in the doped samples follow the Korringa relation T sub(1)T, 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 sub(1)T) super(-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.