μSR studies on S = 1/2 stacked Ising kagome antiferromagnet Na5Co15.5Te6O36

Na5Co15.5Te6O36 (NCTO) with S=1/2 is reported to exhibit stacked Ising-kagome antiferromagnets below 50 K. The single crystal study by one of us shows three successive magnetic transitions at T1 = 45.2 K, T2 = 35.4 K, and T3 ∼ 20 K. When the magnetic field is applied along the Ising c-axis, a strikingly anomalous initial magnetization lying outside the hysteresis loop is observed below T3. The transitions at T1 and T3 are supposed to be associated with the Co1 sublattice, while the transition at T2 is likely related to Co2-Co3 chains. The observed experimental phenomena below T3, including the FC-ZFC bifurcation, suggest a partially disordered antiferromagnetic (PDA) state below 45 K and frozen PDA (FPDA) below 20 K with AFM ordering at then intermediate temperature range. We have performed EMU express on the powder sample of Na5Co15.5Te6O36 and have found two transitions, at 30 K and 60 K in the zero-field relaxation rate. Further, longitudinal field (LF) at 60 K up to 4000 G shows that much higher value of LF will be needed to investigate the field dependence of relaxation rate. We therefore propose to carry out detailed ZF and LF muon-spin-rotation (μSR) measurements on NCTO on HiFi up to 4 Tesla to microscopically understand the magnetic behaviors.