Toward the Mott state with magnetic cluster formation in heavily Cu-doped ${\mathrm{NaFe}}_{1-x}{\mathrm{Cu}}_x\mathrm{As}$

Journal Article · 08 April 2019 · Physical Review B

DOI: https://doi.org/10.1103/PhysRevB.99.155114 · OSTI ID:1506097

Xin, Yizhou ^[1]; Stolt, Ingrid ^[2]; Lee, Jeongseop A. ^[2]; Song, Yu ^[3]; Dai, Pengcheng ^[4]; Halperin, W. P. ^[2]

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1. Northwestern Univ., Evanston, IL (United States); Northwestern University
2. Northwestern Univ., Evanston, IL (United States)
3. Rice Univ., Houston, TX (United States); Univ. of California, Berkeley, CA (United States)
4. Rice Univ., Houston, TX (United States)

Recent neutron scattering measurements imply that NaFe$$_{1-x}$$Cu$$_{x}$$As forms an antiferromagnetic stripe phase near $$x\approx 0.5$$ in a Mott insulating state. This copper concentration is well in excess of that required for superconductivity, $x < 0.04$. We have investigated the development of magnetism in this compound using $$^{23}$$Na nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation measurements performed on single crystals ($$x$$ = 0.13, 0.18, 0.24, and 0.39). We find multiple inequivalent Na sites, each of which is associated with a different number of nearest neighbor Fe sites occupied by a Cu dopant. We show that the distribution of Cu substituted for Fe is random in-plane for low concentrations ($x = 0.13$ and 0.18), but deviates from this with increasing Cu doping. As is characteristic of many pnictide compounds, there is a spin pseudo gap that increases in magnitude with dopant concentration. This is correlated with a corresponding increase in orbital NMR frequency shift indicating a change in valence from Cu$$^{2+}$$ to a Cu$$^{1+}$$ state as $$x$$ exceeds 0.18, concomitant with the change of Fe$$^{2+}$$ to Fe$$^{3+}$$ resulting in the formation of magnetic clusters. Yet, for $$x\leq 0.39$$ there is no evidence of long-range static magnetic order.

• Research Organization: Northwestern Univ., Evanston, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
• Grant/Contract Number: FG02-05ER46248
• OSTI ID: 1506097
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 15 Vol. 99; ISSN 2469-9950; ISSN PRBMDO
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English