Coexistence of magnetic and dielectric glassy states in alternating kagome and triangular lattice LuBaCo$_4$O$_7$ cobaltite

Abstract

To date, the alternating kagome and triangular lattice cobaltites, RBaCo$_4$O$_7$ (R = Ca, Y, and rare earth elements), have been well studied for their large structural distortions, anisotropic exchange interactions, chiral spin liquid states, and giant multiferroic properties. Here, we report the co-existence of magnetic and dielectric glassy states in LuBaCo$_4$O$_7$ below 50 K. AC magnetization studies show an absence of conventional spin-freezing behavior. The cooling and heating in unequal fields (CHUF), thermal cycling, and time-dependent magnetization measurements at low temperature ($T$) show the presence of magnetic glassy state. The $T$-dependent dielectric constant $\epsilon'$ measurements exhibit a strong frequency-independent response at the first-order structural phase transition $T = 160$ K (trigonal $P31c$ to monoclinic $Cc$) and also significant features at the $T = 110$ K (monoclinic $Cc$ to orthorhombic $Pbn2_1$) phase transition. Further, $\epsilon'$ shows a frequency-independent peak at 43 K ($Pbn2_1$) and also dipolar glassy features below 20 K ($Cc$). The non-equilibrium magnetic glassy dynamics and dipolar glassy state at low-$T$ arises from the kinetic arrest of $Cc$ and $Pbn2_1$ phases. From the dielectric probe, we are able to clearly distinguish the kinetically arrested phases at low-$T$ , whereas the bulk magnetization studies are unable to do so as the arrested phases have low magnetic moments.