Muon spin relaxation study of spin dynamics in the extended kagome systems YBaCo4O7+delta (delta=0,0.1)

Abstract

We present muon spin relaxation (mu SR) measurements of the extended kagome systems YBaCo4O7+delta (delta = 0,0.1), comprising two interpenetrating kagome sublattice of Co(I)(3+) (S = 3/2) and a triangle sublattice of Co(II)(2+) (S = 2). The zero-and longitudinal-field mu SR spectra of the stoichiometric compound YBaCo4O7 unveil that the triangular subsystem orders at T-N = 101 K. In contrast, the muon spin relaxation rate pertaining to the kagome subsystem shows persistent spin dynamics down to T = 20 K and then a sublinear decrease lambda(T) similar to T-0.66(5) on cooling towards T = 4 K. In addition, the introduction of interstitial oxygen (delta = 0.1) is found to drastically affect the magnetism. For the fast-cooling experiment (> 10 K/min), YBaCo4O7.1 enters a regime characterized by persistent spin dynamics below 90 K. For the slow-cooling experiment (1 K/min), evidence is obtained for the phase separation into interstitial oxygen-poor and oxygen-rich regions with distinct correlation times. The observed temperature, cooling rate, and oxygen content dependencies of spin dynamics are discussed in terms of a broad range of spin-spin correlation times, relying on a different degree of frustration between the kagome and triangle sublattices as well as of oxygen migration.