Stripe Antiferromagnetism and Disorder in the Mott Insulator NaFe${}_{1-x}$Cu${}_x$As ($x\lesssim 0.5$)

Abstract

Neutron scattering measurements have demonstrated that the heavily Cu-doped NaFe${}_{1-x}$Cu${}_x$As compound behaves like a Mott insulator exhibiting both real space Fe-Cu stripes, as well as antiferromagnetism below a Néel temperature for $x\lesssim 0.5$. We have investigated evolution of structural and magnetic ordering using ${}^{23}$Na and ${}^{75}$As NMR for single crystals ($x$ = 0.39 and 0.48), confirming antiferromagnetism in the form of magnetic stripes. We show that end-chain defects in these stripes are the principal source of magnetic disorder and are responsible for cluster spin-glass transitions in both compounds, in the latter case coexistent with antiferromagnetism. Aided by our numerical simulation of the ${}^{75}$As spectra, we show that a staggered magnetization at the Fe sites is induced by non-magnetic Cu dopants.

8 pages, 11 figures