Charge density modulation and defect ordering in the $$Na_xMnBi_y$$ magnetic semimetal
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, $$q_1 = \left( \frac{2}{3}, 0, 1 \right)$$ and $$q_2 = \left( \frac{2}{3}, \frac{1}{3}, \frac {1}{2} \right)$$. This constitutes a superlattice transition ($$T_s$$) that lowers the symmetry from the high-temperature centrosymmetric $P4/nmm$ to the noncentrosymmetric $$P\overline{4}m2$$. In crystals with a large MR, a close to room temperature $$T_s$$ is observed with $$q_1$$ appearing first, followed by $$q_2$$. In crystals with low MR, however, $$T_s$$ is much lower and only $$q_1$$ is observed. Finally, the charge modulation and spin fluctuations may both contribute to the enhancement of MR.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- AC05-00OR22725; FG02-01ER45927
- OSTI ID:
- 1724452
- Journal Information:
- Physical Review B, Vol. 102, Issue 2; ISSN 2469-9950
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Similar Records
Defect-driven extreme magnetoresistance in an I-Mn-V semiconductor
Centrosymmetric [N(CH{sub 3}){sub 4}]{sub 2}TiF{sub 6} vs. noncentrosymmetric polar [C(NH{sub 2}){sub 3}]{sub 2}TiF{sub 6}: A hydrogen-bonding effect on the out-of-center distortion of TiF{sub 6} octahedra