Magnetic phase diagram and possible Kitaev-like behavior of honeycomb-lattice antimonate Na3Co2SbO6

Recent theoretical studies have suggested that Kitaev physics and such effects as formation of a mysterious spin-liquid state can be expected not only in RuCl3 and iridates, but also in conventional $3d$ transition metal compounds. Using DC and AC magnetometry, thermodynamic and $^{23}$Na nuclear magnetic resonance measurements (NMR) we studied such a candidate material Na3Co2SbO6 . A full phase diagram of Na3Co2SbO6 in a wide range of magnetic fields and temperatures is presented. The results demonstrate transformation of the magnetic structure realized at low-temperature and suppression of the AFM order under the external field, the gradual development of the saturation phase, as well as evidence of gapped spin-liquid-like behavior in certain parts of the phase diagram

Static and resonant properties of decorated square kagome lattice compound KCu7_7(TeO4_4)(SO4_4)5_5Cl

The magnetic subsystem of nabokoite, KCu$_7$(TeO$_4$)(SO$_4$)$_5$Cl, is constituted by buckled square kagome lattice of copper decorated by quasi-isolated Cu$^{2+}$ ions. This combination determines peculiar physical properties of this compound evidenced in electron spin resonance (ESR) spectroscopy, dielectric permittivity $\varepsilon$, magnetization $M$ and specific heat $C_p$ measurements. At lowering temperature, the magnetic susceptibility $\chi = M/H$ passes through broad hump at about 150 K inherent for low-dimensional magnetic systems and evidences sharp peak at antiferromagnetic phase transition at $T_N = 3.2$K. The $C_p(T)$ curve also exhibits sharp peak at $T_N$ readily suppressed by magnetic field and additional peak-like anomaly at $T_\textrm{peak}= 5.7$ K robust to magnetic field. The latter can be ascribed to low-lying singlet excitations filling the singlet-triplet gap in magnetic excitation spectrum of the square kagome lattice [J.Richter, O.Derzhko and J.Schnack, Phys. Rev. B 105, 144427 (2022)]. According to position of $T_\textrm{peak}$, the leading exchange interaction parameter $J$ in nabokoite is estimated to be about 60K. ESR spectroscopy provides indications that antiferromagnetic structure below $T_N$ is non-collinear. These complex thermodynamic and resonant properties signal the presence of two weakly coupled magnetic subsystems in nabokoite, namely spin-liquid with large singlet-triplet gap and antiferromagnet represented by decorating ions. Separate issue is the observation of antiferroelectric-type behavior in $\varepsilon$ at low temperatures, which tentatively reduces the symmetry and partially lifts frustration of magnetic interactions of decorating copper ions with buckled square kagome lattice.Comment: 13 pages, 13 figure

Magnetic Properties of A2Ni2TeO6 (A = K, Li): Zigzag Order in the Honeycomb Layers of Ni2+ Ions Induced by First and Third Nearest-Neighbor Spin Exchanges

The static and dynamic magnetic properties and the specific heat of K2Ni2TeO6 and Li2Ni2TeO6 were examined and it was found that they undergo a long-range ordering at TN = 22.8 and 24.4 K, respectively, but exhibit a strong short-range order. At high temperature, the magnetic susceptibilities of K2Ni2TeO6 and Li2Ni2TeO6 are described by a Curie–Weiss law, with Curie-Weiss temperatures Θ of approximately −13 and −20 K, respectively, leading to the effective magnetic moment of about 4.46 ± 0.01 µB per formula unit, as expected for Ni2+ (S = 1) ions. In the paramagnetic region, the ESR spectra of K2Ni2TeO6 and Li2Ni2TeO6 show a single Lorentzianshaped line characterized by the isotropic effective g-factor, g = 2.19 ± 0.01. The energy-mapping analysis shows that the honeycomb layers of A2Ni2TeO6 (A = K, Li) and Li3Ni2SbO6 adopt a zigzag order, in which zigzag ferromagnetic chains are antiferromagnetically coupled, because the third nearest-neighbor spin exchanges are strongly antiferromagnetic while the first nearest-neighbor spin exchanges are strongly ferromagnetic, and that adjacent zigzag-ordered honeycomb layers prefer to be ferromagnetically coupled. The short-range order of the zigzag-ordered honeycomb lattices of K2Ni2TeO6 and Li2Ni2TeO6 is equivalent to that of an antiferromagnetic uniform chain, and is related to the short-range order of the ferromagnetic chains along the direction perpendicular to the chains. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Russian Foundation for Basic Research, РФФИ; Ministry of Education, MOE: 2020R1A6A1A03048004; National Research Foundation of Korea, NRF; Russian Science Foundation, RSF: 22-42-08002; Government Council on Grants, Russian Federation: 075-15-2021-604Funding: This work was supported by the grant 14-03-01122 from the Russian Foundation for Basic Research (VBN), by the Russian Scientific Foundation through Grant No. 22-42-08002, and by the Mega-grant program of the Government of Russian Federation through the project 075-15-2021-604. The work at KHU was financially supported by the Basic Science Research Program through the National Research Foundation (NRF) of Korea, which was funded by the Ministry of Education (2020R1A6A1A03048004)

Synthesis and Characterization of Sodium-Iron Antimonate Na2FeSbO5: One-Dimensional Antiferromagnetic Chain Compound with a Spin-Glass Ground State

A new oxide, sodium-iron antimonate, Na2FeSbO5, was synthesized and structurally characterized, and its static and dynamic magnetic properties were comprehensively studied both experimentally by dc and ac magnetic susceptibility, magnetization, specific heat, electron spin resonance (ESR) and Mössbauer measurements, and theoretically by density functional calculations. The resulting single-crystal structure (a = 15.6991(9) Å b = 5.3323 (4) Å c = 10.8875(6) Å S.G. Pbna) consists of edge-shared SbO6 octahedral chains, which alternate with vertex-linked, magnetically active FeO4 tetrahedral chains. The 57Fe Mössbauer spectra confirmed the presence of high-spin Fe3+ (3d5) ions in a distorted tetrahedral oxygen coordination. The magnetic susceptibility and specific heat data show the absence of a long-range magnetic ordering in Na2FeSbO5 down to 2 K, but ac magnetic susceptibility unambigously demonstrates spin-glass-type behavior with a unique two-step freezing at Tf1 ≈ 80 K and Tf2 ≈ 35 K. Magnetic hyperfine splitting of 57Fe Mössbauer spectra was observed below T∗ ≈ 104 K (Tf1 < T*). The spectra just below T∗ (Tf1 < T < T*) exhibit a relaxation behavior caused by critical spin fluctuations, indicating the existence of short-range correlations. The stochastic model of ionic spin relaxation was used to account for the shape of the Mössbauer spectra below the freezing temperature. A complex slow dynamics is further supported by ESR data revealing two different absorption modes presumably related to ordered and disordered segments of spin chains. The data imply a spin-cluster ground state for Na2FeSbO5. © 2019 American Chemical Society

Peculiarities of magnetic ordering in the S=5/2 two-dimensional square-lattice antimonate NaMnSb O4

© 2020 American Physical Society. An orthorhombic compound, NaMnSbO4, represents a square net of magnetic Mn2+ ions residing in vertex-shared oxygen octahedra. Its static and dynamic magnetic properties were studied using magnetic susceptibility, specific heat, magnetization, electron spin resonance (ESR), nuclear magnetic resonance (NMR), and density-functional calculations. Thermodynamic data indicate an establishment of the long-range magnetic order with TN∼44K, which is preceded by a short-range one at about 55 K. In addition, a nontrivial wasp-waisted hysteresis loop of the magnetization was observed, indicating that the ground state is most probably canted antiferromagnetic. Temperature dependence of the magnetic susceptibility is described reasonably well in the framework of two-dimensional square-lattice model with the main exchange parameter J=-5.3K, which is in good agreement with density-functional analysis, NMR, and ESR data