DCMPMS Seminars

The structural and magnetic properties of new potential quantum spin liquid systems: Sr3CuM2O9 [M = Sb, Nb] and Y2CuTiO6

by Mr. Susanta Kundu (Research Associate, Indian Institute of Technology Bombay)

Friday, January 4, 2019 from to (Asia/Kolkata)
at AG80
Description
The compounds with geometric frustration, which might then lead to a spin liquid behaviour, continue to evoke interest in the scientific community. Motivated by the recent findings in the Ba3CuSb2O9 system, we have investigated Sr3CuM2O9 [M = Sb, Nb] for possible spin liquid behavior. Due to the different ionic size of Sr2+ compared to Ba2+, the Sr-based systems crystallize in a different structure than that of the Ba system. Sr3CuSb2O9 (SCSbO) and Sr3CuNb2O9 (SCNO) both crystallize in the tetragonal I4/mcm space group. We found the evidence of 1:2 cations ordering at the B-site which forms an edge-shared triangular lattice network of magnetic Cu2+ ions. Bulk susceptibility reveals no magnetic ordering down to 1.8 K and a high θCW = - 143 K for SCSbO (- 38 K for SCNO) suggesting AFM correlations among Cu2+ ions. Our specific heat data show no anomalies down to 0.35 K and a power law behavior of the magnetic heat capacity is observed. The 121Sb and 93Nb NMR data also do not show any evidence of LRO. These results point towards the quantum spin liquid (QSL) behaviour. 

The system Y2CuTiO6 crystallizes in the non-centrosymmetric hexagonal P63cm space group. It contains geometrically frustrated edge-shared triangular planes where the vertices are occupied by magnetic Cu and nonmagnetic Ti atoms in equal proportion. In spite of the large dilution of the triangular magnetic lattice, We observed no magnetic ordering down to 0.5 K in the dc susceptibility χ(T) data and even no bifurcation between ZFC-FC data at H = 50 Oe. The Curie-Weiss (CW) temperature θCW = -134 K suggests antiferromagnetic correlations among the Cu2+ ions. The specific heat shows no anomalies down to 0.35 K and follows a power law (Cm = γTα) with T suggesting gapless excitations from the ground state. Our 89Y NMR results also do not show any signs ordering, suggesting a QSL ground state. 

I will present the results of our bulk and local probe (NMR) measurements on the above systems.