Abstract
The non-stoichiometric system Li0.8Ni0.6Sb0.4O2 is a Li-deficient derivative of the zigzag honeycomb antiferromagnet Li3Ni2SbO6. Structural and magnetic properties of Li0.8Ni0.6Sb0.4O2 were studied by means of X-ray diffraction, magnetic susceptibility, specific heat, and nuclear magnetic resonance measurements. Powder X-ray diffraction data shows the formation of a new phase, which is Sb-enriched and Li-deficient with respect to the structurally honeycomb-ordered Li3Ni2SbO6. This structural modification manifests in a drastic change of the magnetic properties in comparison to the stoichiometric partner. Bulk static (dc) magnetic susceptibility measurements show an overall antiferromagnetic interaction (Θ = −4 K) between Ni2+ spins (S = 1), while dynamic (ac) susceptibility reveals a transition into a spin glass state at a freezing temperature TSG ~ 8 K. These results were supported by the absence of the λ-anomaly in the specific heat Cp(T) down to 2 K. Moreover, combination of the bulk static susceptibility, heat capacity and 7Li NMR studies indicates a complicated temperature transformation of the magnetic system. We observe a development of a cluster spin glass, where the Ising-like Ni2+ magnetic moments demonstrate a 2D correlated slow short-range dynamics already at 12 K, whereas the formation of 3D short range static ordered clusters occurs far below the spin-glass freezing temperature at T ~ 4 K as it can be seen from the 7Li NMR spectrum.
Highlights
A rich variety of chemical and physical properties of honeycomb systems due to their crystal structure and peculiarities of electronic bonds has attracted an active interest of researchers in recent years
Even though the honeycomb lattice is not magnetically frustrated for nearest spins, the competition of exchange interaction may occur due to significant contribution of next-nearest and next-next-nearest exchange couplings
The nuclear magnetic resonance (NMR) spectra were obtained at a fixed frequency by stepby-step sweeping the field and integrating the solid-echo signal at each field point. 7Li longitudinal relaxation rate T1−1 was measured using a stimulated echo pulse sequence and 7Li transverse relaxation rate T2−1 was obtained by measuring the solid-echo integral as a function of τ, where τ is time between two π/2 pulses
Summary
A rich variety of chemical and physical properties of honeycomb systems due to their crystal structure and peculiarities of electronic bonds has attracted an active interest of researchers in recent years. The clusters with local magnetic ordering are observed experimentally [9,17,18,19] and predicted by Monte-Carlo calculations [20] at some conditions Such a combination of the properties of 3D spin glasses, 2D AFM ordering, 2D fluctuating magnetic states in in layered frustrated magnets with triangle, honeycomb and kagome geometry is often referred to as an unconventional spin glass [17,19,21,22]. This motivated us to study a two-dimensional honeycomb S = 1 magnet with an intermediate, in the mentioned above sense, number of defects using a combination of bulk and local experimental techniques This combination has proven to be effective for investigating unconventional spin glasses [17,23,24,25].
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