Random dilution effects in the frustrated spin chainβ−CaCr2−xScxO4

Random dilution effects in the magnetic zigzag ladder (${J}_{1}\ensuremath{-}{J}_{2}$ chain) $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{CaC}{\mathrm{r}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{c}}_{x}{\mathrm{O}}_{4}$ have been investigated combining magnetic susceptibility, specific heat measurements, and neutron scattering. The pseudogapped magnetic excitations observed above ${T}_{\mathrm{N}}$ in $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{CaC}{\mathrm{r}}_{2}{\mathrm{O}}_{4} (x=0)$ persist up to $x=0.3$ with an increasing characteristic frequency ${E}_{0}$ but vanish for $x=0.5$ for which a quasielastic signal extending up to $8\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ becomes the characteristic feature of the magnetic spectrum. Magnetic ordering is seen up to $x=0.3$ with decreased ordering temperature ${T}_{\mathrm{N}}$ and correlation length. The results are interpreted in terms of the progressive confinement of one-dimensional excitations within shorter chains as $x$ increases and emphasize the crucial role of ${J}_{2}$ in propagating magnetic excitations. For an average chain length $l$ smaller than \ensuremath{\sim}16 magnetic atoms, the system breaks apart into a set of disconnected units with the dynamical properties of a spin glass.