Stripe disorder and dynamics in the hole-doped antiferromagnetic insulator La${}_{5/3}$Sr${}_{1/3}$CoO${}_4$

We investigate the magnetic ordering and dynamics of the stripe phase of La${}_{5/3}$Sr${}_{1/3}$CoO${}_4$, a material shown to have an hourglass magnetic excitation spectrum. A combination of muon-spin relaxation, nuclear magnetic resonance, and magnetic susceptibility measurements strongly suggest that the physics is determined by a partially disordered configuration of charge and spin stripes whose frustrated magnetic degrees of freedom are dynamic at high temperature and which undergo an ordering transition around 35 K with coexisting dynamics that freeze out in a glassy manner as the temperature is further reduced.

Figure 1

(a) Perfect stripe order in the CoO${}_2$ planes. (Circles represent nonmagnetic Co${}^{3+}$, and arrows represent $S=3/2$ Co${}^{2+}$ spins.) (b) Disordering the charges leads to unfavorable exchange interactions between spins (shaded). (c) and (d) Magnetic susceptibility as a function of temperature for field-cooled and zero-field-cooled protocols for two crystal orientations.

Figure 2

(a) Example zero-field ${\mu }^{+}$SR spectra measured at ISIS. (b) ISIS relaxation rate $\lambda$ with a fit to an activated behavior at high temperatures (see main text). Inset: Initial muon polarization $P\left(0\right)$. (c) Data measured at S$\mu$S showing oscillations at early times. (d) The larger of the two precession frequencies as a function of temperature. (e) Evolution of longitudinal relaxation rates $1/T_1$. (f) Amplitudes of the transverse and longitudinal components.

Figure 3

Top: Frequency-swept (a) ${}^{59}$Co and (b) ${}^{139}$La NMR spectra in $B_{\mathrm{app}}=8$ T at three selected temperatures. Insets: Field-swept spectra at 5 K. Bottom: Shifts of (c) the central line of ${}^{59}$Co, and (d) the central doublet of ${}^{139}$La as a function of temperature.

Figure 4

(a) Evolution of spin-spin relaxation rates $T_2^{-1}$ with $T$ for ${}^{59}$Co (circles), ${}^{139}$La (triangles), and muon relaxation rates $\lambda$ (crosses). (b) Integrated spectral amplitudes, corrected for $T_2^{-1}$ relaxation, as a function of temperature.