Toward the Mott state with magnetic cluster formation in heavily Cu-doped
- Northwestern Univ., Evanston, IL (United States)
- Rice Univ., Houston, TX (United States); Univ. of California, Berkeley, CA (United States)
- 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)
- Grant/Contract Number:
- FG02-05ER46248; FG02-05ER46202; SC0012311
- OSTI ID:
- 1506097
- Alternate ID(s):
- OSTI ID: 1505669
- Journal Information:
- Physical Review B, Vol. 99, Issue 15; ISSN 2469-9950
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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