ИСТИНА

The problem of the disorder in the frustrated magnets attracts a lot of interest both due to fundamental aspects and because the real samples always contain the defects. Of particular interest, in our opinion, is the situation where the level of disorder, on the one hand, is high enough to destroy the long-range homo- geneity, and, on the other hand, not enough to destroy the two-dimensionality of the magnetic structure,so the homogeneity survives on the short-range scale. In such compounds, the combination of two-dimensionality, frustrations and a short-range scale of interactions give rise to a nontrivial phase diagram and unusual states. For investigation of this problem we have chosen the complex transition metal oxide compound Li0.8Ni0.6Sb0.4O2. It is a Li-deficient derivative of zig-zag antiferromagnet Li3Ni2SbO6, which has 2D structural order of magnetic Ni2+ (S = 1) ions on a honeycomb lattice with non-magnetic Sb in the middle, while honeycomb layers being separated by Li ions. Using a combination of bulk and local experimental techniques, we studied non-trivial magnetic proper- ties of Li0.8Ni0.6Sb0.4O2, in particular, a nonconventional cluster spin-glass state. ̇ This work was supported by grants 14-03-01122 (I.S. and V.N.) and 18-02- 00664 (T.S. and M.I.) from the Russian Foundation for Basic Research. E.V. would like to thank financial support from the government assignment for FRC Kazan scientific Center of RAS.