Charge density modulation and defect ordering in the NaxMnBiy magnetic semimetal

A. Wegner, D. Louca, K. M. Taddei, J. Neuefeind

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Abstract

The I-Mn-V antiferromagnet, NaMnBi, develops a very large positive magnetoresistance (MR) up to 10 000% at 2 K and 9 T in crystals showing a semiconductor-to-metal transition (SMT). In the absence of an SMT, a modest (20%) MR is achieved. Here, we show that upon cooling below the magnetic transition, a spatial modulation appears giving rise to new Bragg peaks due to charge and defect ordering in a checkerboard pattern, with two kinds of modulation vectors, q1=(23,0,1) and q2=(23,13,12). This constitutes a superlattice transition (Ts) that lowers the symmetry from the high-temperature centrosymmetric P4/nmm to the noncentrosymmetric P4¯m2. In crystals with a large MR, a close to room temperature Ts is observed with q1 appearing first, followed by q2. In crystals with low MR, however, Ts is much lower and only q1 is observed. The charge modulation and spin fluctuations may both contribute to the enhancement of MR.

Original languageEnglish
Article number020403
JournalPhysical Review B
Volume102
Issue number2
DOIs
StatePublished - Jul 1 2020

Funding

The authors would like to thank C. dela Cruz and M. Tucker for their assistance with the neutron experiments. They would also like to acknowledge support from the Department of Energy, Grant No. DE-FG02-01ER45927. A portion of this research used resources at the High Flux Isotope Reactor and the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.

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