Random dilution effects in the frustrated spin chain β − CaCr 2 − x Sc x O 4
Résumé
Random dilution effects in the magnetic zigzag ladder (J1−J2 chain) β−CaCr2−xScxO4 have been investigated combining magnetic susceptibility, specific heat measurements, and neutron scattering. The pseudogapped magnetic excitations observed above TN in β−CaCr2O4 (x=0) persist up to x=0.3 with an increasing characteristic frequency E0 but vanish for x=0.5 for which a quasielastic signal extending up to 8meV becomes the characteristic feature of the magnetic spectrum. Magnetic ordering is seen up to x=0.3 with decreased ordering temperature TN 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 J2 in propagating magnetic excitations. For an average chain length l smaller than ∼16 magnetic atoms, the system breaks apart into a set of disconnected units with the dynamical properties of a spin glass.