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Cs2Cu3(SeO3)4·2H2O is a ferrimagnet and exhibits a highly anisotropic 1/3-magnetization plateau. The necessary requirements for observing magnetic plateaus were explored by analyzing the topology of magnetic bonding.

A mixed-valence compound Pb2Cu10O4(SeO3)4Cl7 has a complex structure consisting of one nonmagnetic Cu+ (S = 0) ion and four nonequivalent magnetic Cu2+ (S = 1/2) ions.

The review is devoted to compounds and materials demonstrating extremely high magnetic hardness. The recent advances in the synthesis of modern materials for permanent magnets are considered, and a range of exotic compounds interesting for fundamental research is described. The key details of chemical composition, crystal structure and magnetic microstructure responsible for the appearance of high magnetic anisotropy and giant coercivity are analyzed. The challenges of developing the title materials are noted and strategies for their solution are discussed. The bibliography includes 389 references.

We prepared Cs

Single-domain particles of SrFe8Al4O19 were prepared by thermal treatment of porous products of citrate–nitrate autocombustion at 1200 °C, and the effect of synthesis time on the particle morphology and magnetic properties was estimated. The procedure allows one to obtain SrFe8Al4O19 particles with mean diameters of 100–460 nm and coercivity ranges from 14.5 to 18.4 kOe, while ferromagnetic resonance frequencies vary from 149 to 164 GHz.

Single-domain Sr1−x/12Cax/12Fe12−xAlxO19 (x = 4–6) particles are synthesized by a simple citrate auto-combustion method. The room temperature coercivity of the materials rises with aluminum content from 21.3 kOe (x = 4) to a maximum of 36 kOe (x = 5.5). This value is the highest among ferrite materials to date. Moreover, the magnetic alignment of the particles leads to further coercivity improvement up to 40 kOe. Due to large magnetic anisotropy the samples demonstrate sub-terahertz electromagnetic wave absorption by natural (zero-field) ferromagnetic resonance (NFMR). The absorption lines shift with aluminum substitution from 160 GHz (x = 4) to 250 GHz (x = 5.5), which is the record NFMR frequency known for a magnetic material. This research paves the way for development low-cost materials with extremely high coercivity and sub-terahertz NFMR.

Uniform quasi-one-dimensional integer spin compounds are of interest as a potential realization of the Haldane conjecture of a gapped spin liquid. This phase, however, has to compete with magnetic anisotropy and long-range ordered phases, the implementation of which depends on the ratio of interchain J′ and intrachain J exchange interactions and both uniaxial D and rhombic E single-ion anisotropies. Strontium nickel selenite chloride, Sr2Ni(SeO3)2Cl2, is a spin-1 chain system which passes through a correlations regime at Tmax ~ 12 K to long-range order at TN = 6 K. under external magnetic field it experiences the sequence of spin-flop at Bc1 = 9.0 T and spin-flip transitions Bc2 = 23.7 T prior to full saturation at Bsat = 31.0 T. Density functional theory provides values of the main exchange interactions and uniaxial anisotropy which corroborate the experimental findings. The values of J′/J = 0.083 and D/J = 0.357 place this compound into a hitherto unoccupied sector of the Sakai-Takahashi phase diagram. © 2021, The Author(s). Support by the P220 program of Government of Russia through the project 075-15-2021-604 is acknowledged. ANV acknowledges support by the RFBR Grant 19-02-00015. Work at Heidelberg was supported by BMBF via the project SpinFun (13XP5088) and by Deutsche Forschungsgemeinschaft (DFG) under Germany’s Excellence Strategy EXC2181/1-390900948 (the Heidelberg STRUCTURES Excellence Cluster) and through project KL 1824/13-1. We acknowledge the support of the HLD-HZDR, member of the European Magnetic Field Laboratory (EMFL). Theoretical calculations using density functional theory were supported by the Russian Science Foundation via project 20-62-46047. Experimental research was supported by the Russian Science Foundation via project 19-42-02010.

Magnetically hard ferrites attract considerable interest due to their ability to maintain a high coercivity of nanosized particles and therefore show promising applications as nanomagnets ranging from magnetic recording to biomedicine. Herein, we report an approach to prepare nonsintered single-domain nanoparticles of chromium-substituted hexaferrite via crystallization of glass in the system SrO–Fe2O3–Cr2O3–B2O3. We have observed a formation of plate-like hexaferrite nanoparticles with diameters changing from 20 to 190 nm depending on the annealing temperature. We demonstrated that chromium substitution led to a significant improvement of the coercivity, which varied from 334 to 732 kA m−1 for the smallest and the largest particles, respectively. The results provide a new strategy for producing high-coercivity ferrite nanomagnets.

In this study, we demonstrate the synthesis and the investigation of magnetostatic and magnetodynamic properties of epsilon iron oxide (e-Fe2O3) nanoparticles of various sizes. Silica gels were obtained by rapid hydrolysis of tetraethoxysilane in an aqueous–alcoholic solution of iron(III) nitrate and then dried to form xerogels. The annealing of the xerogels at temperatures of 1000–1250 °C led to the formation of e-Fe2O3 particles with average sizes of 7–38 nm, respectively. With an increase in the annealing temperature, the coercivity of the samples increased and reached 21 kOe for 1200 °C, while the frequency of the natural ferromagnetic resonance increased from 161 to 170 GHz followed by narrowing of the absorption lines from 40 to 2 GHz. It was shown for the first time that the parameters of the natural ferromagnetic resonance line of epsilon iron oxide can be varied by controlling the size of e-Fe2O3 particles. It was also demonstrated that the duration of e-Fe2O3 synthesis can be considerably reduced by increasing the rate of tetraethoxysilane hydrolysis, while the magnetic properties of the target material do not degrade.

Considerable attention has been paid recently to $\mathrm{Fe}{\mathrm{Te}}_{2}{\mathrm{O}}_{5}\mathrm{Cl}$ due to reduced dimensionality and frustration in the magnetic subsystem, succession of phase transitions, and multiferroicity. The efforts to grow its selenite sibling resulted in the mixed halide compound $\mathrm{Fe}({\mathrm{Te}}_{1.5}{\mathrm{Se}}_{0.5}){\mathrm{O}}_{5}\mathrm{Cl}$, which was found crystallizing in a different structural type and possessing properties drastically different from those of a parent system. Its magnetic subsystem features weakly coupled ${\mathrm{Fe}}^{3+}\ensuremath{-}{\mathrm{Fe}}^{3+}$ dimers showing the regime of short-range correlations at ${T}_{\mathrm{M}}\ensuremath{\sim}70\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and long-range order at ${T}_{\mathrm{N}}=22\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. In a magnetically ordered state, sizable spin-orbital interactions lead to a small canting of ${\mathrm{Fe}}^{3+}$ moments. Magnetic dipole-dipole interactions contribute significantly to the experimentally observed orientation of magnetization easy axis in the $ac$ plane. The first principles calculations of leading exchange interactions were found in agreement with measurements of thermodynamic properties and Raman spectroscopy.

Chloromenite, Cu9O2(SeO3)4Cl6, is the product of volcanic activity. To conduct various physical studies both natural and synthetic samples of chloromenite were used which resulted in a long-standing controversy regarding its crystal structure. We carried out the temperature dependent single crystal X-ray diffraction study in the range 100 – 370 K and established that the reflection conditions are consistent with a primitive monoclinic cell with the only possible P21/n space group. Raman scattering evidences a complex interplay of crystal lattice and spin degrees of freedom. The observation of a sequence of short range fluctuation effects points to the existence of competing interactions or nearly degenerate energy scales. To gain microscopic understanding of the magnetic properties of Cu9O2(SeO3)4Cl6 the first principles density functional theory calculations have been performed. Basing on the new data on magnetization and the hierarchy of exchange interaction parameters a model of Cu9O2(SeO3)4Cl6 magnetic structure is suggested.

We report the results of magnetization and specific heat measurements, a 57Fe Mossbauer study of hyperfine interactions and density functional theory calculations in TlFe(MoO4)2 demonstrating two m...

Our study of FeSe 1 − x Te x crystals with x d − d exchange in the iron plane in the framework of the basic phenomenological description such as the Bethe–Slater curve. With this approach, when the distance between iron atoms is close to the value at which the sign of the magnetic exchange for some d orbitals changes, structural and electronic instability can occur. Anomalies in the crystal field near the point of charge neutrality can also be a significant component of this instability.

We report studies of the Seebeck coefficient $S$ of the quasi-one-dimensional compound $\mathrm{Nb}{\mathrm{S}}_{3}$, together with the temperature dependence of its specific conductivity ${\ensuremath{\sigma}}_{\mathrm{s}}$ and heat capacity ${c}_{p}$. The monoclinic phase $(\mathrm{Nb}{\mathrm{S}}_{3}$-II) is studied over the temperature range $T=80--400$ K, which covers two charge density wave (CDW) transitions at ${T}_{\mathrm{P}1}=360$ K (CDW-1) and ${T}_{\mathrm{P}2}=150$ K (CDW-2). The $S(T)$ curves show features in the vicinities of both CDW transitions and appear to be correlated with the value of ${\ensuremath{\sigma}}_{\mathrm{s}}(300\phantom{\rule{0.28em}{0ex}}\mathrm{K})$: The increase of $S$ below ${T}_{\mathrm{P}1}$ in the high-Ohmic samples reveals a complete dielectrization of the electronic spectrum, while in the low-Ohmic samples $S$ decreases below ${T}_{\mathrm{P}1}$ and even becomes negative below ${T}_{\mathrm{P}2}$. The magnitude of $S$ in low-Ohmic samples at $Tl{T}_{\mathrm{P}2}$ is well below ${k}_{\mathrm{B}}/e\ensuremath{\approx}86\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{V}/\mathrm{K},{k}_{B}$ being the Boltzmann constant and $e$ the elementary charge, which is surprisingly low for a usual CDW semiconducting state. Our results suggest that at ${T}_{\mathrm{P}1}$ the main electronic band with $p$-type carriers becomes gapped, while some $n$-type carriers can remain in a separate band with low density of states. These carriers, whose concentration is defined by the compositional doping, are gapped at ${T}_{\mathrm{P}2}$. We also report $S$ for the triclinic dielectric phase of $\mathrm{Nb}{\mathrm{S}}_{3}\phantom{\rule{4pt}{0ex}}(\mathrm{Nb}{\mathrm{S}}_{3}\text{\ensuremath{-}}\mathrm{I})$. Its low absolute value, $\ensuremath{\sim}{k}_{\mathrm{B}}/e$, and the anomalous temperature dependence demonstrate that $\mathrm{Nb}{\mathrm{S}}_{3}\text{\ensuremath{-}}\mathrm{I}$ is neither a semiconductor nor a CDW conductor in the usual sense.

${\mathrm{Fe}}^{3+} S=5/2$ ions form saw-tooth-like chains along the $a$ axis of the oxoselenite ${\mathrm{Fe}}_{2}\mathrm{O}{({\mathrm{SeO}}_{3})}_{2}$ and an onset of long-range magnetic order is observed for temperatures below ${T}_{C}=105$ K. This order leads to distinct fingerprints in phonon mode linewidths and energies as resolved by Raman scattering. In addition, new excitations with small linewidths emerge below $T=150$ K, and are assigned to two-magnon scattering processes with the participation of flat-band and high energy magnon branches. From this a set of exchange coupling constants is estimated. The specific ratio of the saw-tooth spine-spine and spine-vertex interactions may explain the instability of the dimer quantum ground state against an incommensurate 3D magnetic order.

The iron oxoselenite Fe2O(SeO3)2 hosts unique tilted saw-tooth chains of vertex-sharing iron triangles. It experiences long-range magnetic order below TN ≈ 105 K characterized by a sharp dichotomy in zero-field-cooled and field-cooled behavior (T ≈ 0.31), which results from a spin-wave treatment. The mean-field analysis of the temperature evolution of the fields Bhf,Fei(T) allowed evaluation of exchange interactions between different iron sublattices. A spin relaxation behavior of Fe2O(SeO3)2 in the temperature range T*

We demonstrate that the simultaneous substitution of calcium and aluminum for strontium and iron in strontium hexaferrite results in a significant increase of coercivity up to a record high of 21.3 kOe. We propose that the effect is originated from a crystal structure distortion causing an increase of the magnetocrystalline anisotropy.

We report on the magnetic and transport properties of the ternary Fe 1+ δ Te 1− x Se x crystals with nominal Fe excess δ = 0.03–0.04 and x = 0.1, 0.2, 0.28, 0.4, 0.45. The peculiarity of these crystals is the coexistence of superconductivity and magnetism. Susceptibility of all samples follows the Curie–Weiss law at temperatures above approximately 100 K. The values of effective magnetic moment are close to 4 Bohr magnetons for all compositions. Superconducting transition temperature ranges from 12 to 14.5 K with a maximum at around x = 0.3–0.4. For almost all samples the μ 0 H c ( T ) curves have positive curvature regions near T c when the field is parallel to the c axis.