Spin ordering and dynamics in the frustrated antiferromagnet YBaCo4O7.1

The stoichiometric 114-layered material YBaCo4O7 exhibits long-range antiferromagnetic order below a Neel temperature of 106 K. Nonstoichiometric YBaCo4O7.1, which contains a relatively small amount (1.4%) of interstitial oxygen, has recently been shown to have drastically modified magnetic properties compared to the parent compound. The present experiments have used magnetization, ac susceptibility, and zero applied field NMR to study the spin configuration and spin dynamics in a single crystal of YBaCo4O7.1 as a function of temperature below 100 K. Evidence has been obtained for a magnetic transition at 80 K corresponding to some form of spin freeze-out. Based on previous results for the stoichiometric material, it is likely that the freezing process involves spins in the triangular layers in this frustrated antiferromagnet. At lower temperatures, dynamic effects persist and below 50 K a fraction of the spins, located primarily in the kagome layers, constitute what may be termed a viscous spin liquid component. ForT < 10 K, a disordered or glasslike spin structure, with a large distribution of spin correlation times, emerges as the low-temperature state of the spin system.