LiZn${}_2$V${}_3$O${}_8$: A new geometrically frustrated cluster spin-glass

Abstract

We have investigated the structural and magnetic properties of a new cubic spinel LiZn${}_2$V${}_3$O${}_8$ (LZVO) through x-ray diffraction, dc and ac susceptibility, magnetic relaxation, aging, memory effect, heat capacity and ${}^7$Li nuclear magnetic resonance (NMR) measurements. A Curie-Weiss fit of the dc susceptibility ${\chi }_{\mathrm{dc}}$($T$) yields a Curie-Weiss temperature ${\theta }_{\mathrm{CW}}$ = -185 K. This suggests strong antiferromagnetic (AFM) interactions among the magnetic vanadium ions. The dc and ac susceptibility data indicate the spin-glass behavior below a freezing temperature $T_f$ $\simeq$ 3 K. The frequency dependence of the $T_f$ is characterized by the Vogel-Fulcher law and critical dynamic scaling behavior or power law. From both fitting, we obtained the value of the characteristic angular frequency ${\omega }_0$ $\approx$ 3.56$\times$10${}^6$ Hz, the dynamic exponent $zv$ $\approx$ 2.65, and the critical time constant ${\tau }_0$ $\approx$ 1.82$\times$10${}^{-6}$ s, which falls in the conventional range for typical cluster spin-glass (CSG) systems. The value of relative shift in freezing temperature $\delta T_f$ $\simeq$ 0.039 supports a CSG ground states. We also found aging phenomena and memory effects in LZVO. The asymmetric response of the magnetic relaxation below $T_f$ supports the hierarchical model. Heat capacity data show no long-range or short-range ordering down to 2 K. Only about 25% magnetic entropy change $(\Delta S_{\mathrm{m}})$ signifies the presence of strong frustration in the system. The ${}^7$Li NMR spectra show a shift and broadening with decreasing temperature. The spin-lattice and spin-spin relaxation rates show anomalies due to spin freezing around 3 K as the bulk magnetization.

12 pages, 17 figures, 2 tables