Incommensurate and commensurate antiferromagnetic states in CaMn2As2 and SrMn2As2 revealed by 75As NMR
Date
2021-12-09
Authors
Ding, Q.-P.
Sangeetha, N.S.
Pandey, Abhishek
Johnston, D.C.
Furukawa, Y.
Major Professor
Advisor
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Iowa State University Digital Repository, Ames IA (United States)
Abstract
We carried out As-75 nuclear magnetic resonance (NMR) measurements on the trigonal CaMn2As2 and SrMn2As2 insulators exhibiting antiferromagnetic (AFM) ordered states below Neel temperatures T-N = 62 and 120 K, respectively. In the paramagnetic state above T-N, typical quadrupolar-split As-75 NMR spectra were observed for both systems. The As-75 quadrupolar frequency nu(Q) for CaMn2As2 decreases with decreasing temperature, while nu(Q) for SrMn2As2 increases, showing an opposite temperature dependence. In the AFM state, the relatively sharp and distinct As-75 NMR lines were observed in SrMn2As2 and the NMR spectra were shifted to lower fields for both magnetic fields H parallel to c axis and H parallel to ab plane, suggesting that the internal fields B-int at the As site produced by the Mn ordered moments are nearly perpendicular to the external magnetic field direction. No obvious distribution of B-int was observed in SrMn2As2, which clearly indicates a commensurate AFM state. In sharp contrast to SrMn2As2, broad and complex NMR spectra were observed in CaMn2As2 in the AFM state, which clearly shows a distribution of B-int at the As site, indicating an incommensurate state. From the analysis of the characteristic shape of the observed spectra, the AFM state of CaMn2As2 was determined to be a two-dimensional incommensurate state where Mn ordered moments are aligned in the ab plane. A possible origin for the different AFM states in the systems was discussed. Both CaMn2As2 and SrMn2As2 show very large anisotropy in the nuclear spin-lattice relaxation rate 1/T-i in the paramagnetic state. 1/T-i for H parallel to ab is much larger than that for H parallel to c, indicating strong anisotropic AFM spin fluctuations in both compounds.
Series Number
Journal Issue
Is Version Of
Versions
Series
IS-J 10674
Academic or Administrative Unit
Type
article
Comments
This article is published as Ding, Q-P., N. S. Sangeetha, Abhishek Pandey, D. C. Johnston, and Y. Furukawa. "Incommensurate and commensurate antiferromagnetic states in Ca Mn 2 As 2 and Sr Mn 2 As 2 revealed by As 75 NMR." Physical Review B 104, no. 22 (2021): 224413.
DOI: 10.1103/PhysRevB.104.224413.
Copyright 2021 American Physical Society.
DOE Contract Number(s): AC02-07CH11358.
Posted with permission.