Structure and magnetic properties of high-entropy honeycomb-layered A3Q2SbO6 (A = Li or Na; Q = Co1/5Ni1/5Cu1/5Mg1/5Zn1/5)

Abstract

Monoclinic layered Li₃(CoNiCuMgZn)_0.4SbO₆ and Na₃(CoNiCuMgZn)_0.4SbO₆ (A₃Q₂SbO₆ for short) were prepared by solid-state reactions. The X-ray Rietveld refinement of both materials confirms their structural analogy with their monocation counterparts (space group C2/m), random mixing of the five cations and their honeycomb ordering with Sb(5+). The Li compound shows considerable Li/Q site inversion, much larger than that in Li₃Cu₂SbO₆. Static (DC) and dynamic (AC) magnetic susceptibility and specific heat measurements indicate the absence of any magnetic order down to 2 K in Na₃Q₂SbO₆, while Li₃Q₂SbO₆ demonstrates spin-cluster glass behaviour below 5 K. The Mydosh parameter (K) characterizing the frequency (f) shift of the freezing temperature amounts to 0.05. Within the critical slowing down model, a glassy freezing temperature (T_g) of 4.1 K (at f → 0), a microscopic spin flipping time (τ₀) of 10⁻¹⁰ s and a critical exponent (zν) of 10 were obtained.