Magnetic properties of frustrated spin-$\frac{1}{2}$ capped-kagome antiferromagnet (CsBr)Cu${}_5$V${}_2$O${}_{10}$

Abstract

The structural and magnetic properties of a spin-$\frac{1}{2}$ averievite (CsBr)Cu${}_5$V${}_2$O${}_{10}$ are investigated by means of temperature-dependent x-ray diffraction, magnetization, heat capacity, and ${}^{51}$V nuclear magnetic resonance (NMR) measurements. The crystal structure (trigonal, $P\bar{3}$) features a frustrated capped-kagome lattice of the magnetic Cu${}^{2+}$ ions. Magnetic susceptibility analysis indicates a large Curie-Weiss temperature of ${\theta }_{\mathrm{CW}}\simeq -175$ K. Heat capacity signals the onset of a magnetic long-range-order (LRO) at $T_{\mathrm{N}}\simeq 21.5$ K at zero magnetic field due to the presence of significant inter-planer coupling in this system. The magnetic LRO below 27 K is further evident from the drastic change in the ${}^{51}$V NMR signal intensity and rapid enhancement in the ${}^{51}$V spin-lattice relaxation rate in a magnetic field of 6.3 T. The frustration index $f=|{\theta }_{\mathrm{CW}}|/T_{\mathrm{N}}\simeq 8$ ascertains strong magnetic frustration in this compound. From the high-temperature value of the ${}^{51}$V NMR spin-lattice relaxation rate, the leading antiferromagnetic exchange interaction between the Cu${}^{2+}$ ions is calculated to be $J/k_{\mathrm{B}}\simeq 136$ K.

11 pages, 8 figures, Phys. Rev. B (Accepted)