Doping of the (Sr,Ba)10(PO4)6(OH)2 apatite ceramics with a small quantity of Dy2O3 was studied. Formation of the Dy3+ containing high-energy single-ion magnet (SIM) in the apatite structure was confirmed. Partial replacement of Ba for Sr in the structure resulted in a regular increase of the remagnetization energy barrier Ueff from 1043 to 1119 cm-1, while the solubility of Dy3+ in the compound dropped drastically. Ueff followed simple relations with the alkaline-earth metal cation size and the compound composition, highlighting predictability of SIM parameters.

Synthetic conditions for cobalt-doped chalcopyrites Cu1 – x/2In1 – x/2CoxSe2 were modified by adding a stage of fast temperature quenching from 1000 °C to cause significant ferromagnetism. Ferromagnetism persisted even at room temperature, and it was characterized by coercivity up to 140 Oe.

Two series of cobalt-doped CuGa1 – xCoxSe2 and Cu1 – x/2Ga1 – x/2CoxSe2 chalcopyrites were prepared. Cobalt in part entered the chalcopyrite structure to ensure the appearance of paramagnetic properties, while in part it remained involved in cobalt selenide admixtures. High-temperature quenching forced almost all of the cobalt to enter the crystal structure in the Cu1 – x/2Ga1 – x/2CoxSe2 samples. Significant ferromagnetism appears in the Cu0.9Ga0.9Co0.2Se2 sample, which had the highest cobalt concentration, in particular at room temperature.

New complexes of manganese(II) hexafluoroacetylacetonate [Mn(hfac)2] with 2-(1-R-3-pyrazol-4-yl)-4,4,5,5-tetramethyl-2-imidazoline-3-oxide-1-oxyl (R = CHF2, CH2CH2F, CH2CHF2 or CH2CF3) were synthesised and characterised structurally and magnetically. All complexes were prepared under similar conditions. Nonetheless, their crystal structures were considerably different. Depending on the structure of fluorinated alkyl substituent R, the complexation reaction led to complexes of three types: chain-polymeric complexes with the head-to-head or head-to-tail motif and complexes of molecular structure. All complexes show strong antiferromagnetic behaviour in a high-temperature region (150–300 K) and weak ferro- or antiferromagnetic exchange interactions at low temperatures. The stronger antiferromagnetic exchange, −101.7 ± 1.5 or −136 ± 10 cm−1, −82.3 ± 1.3 cm−1 and −87.4 ± 1.3 cm−1, was attributed to the magnetic interaction in three- or two-spin clusters: {>N∸O–Mn2+–O∸N<} or {>N∸O–Mn2+}, respectively. The weaker antiferromagnetic interaction, −0.005, between three-spin clusters or ferromagnetic interactions, 0.18–0.81 cm−1, between two-spin clusters are realised through the pyrazole ring or intermolecular contacts.

Two series of cobalt-doped CuGa1 – xCoxSe2 and Cu1 – x/2Ga1 – x/2CoxSe2 chalcopyrites were prepared. Cobalt in part entered the chalcopyrite structure to ensure the appearance of paramagnetic properties, while in part it remained involved in cobalt selenide admixtures. High-temperature quenching forced almost all of the cobalt to enter the crystal structure in the Cu1 – x/2Ga1 – x/2CoxSe2 samples. Significant ferromagnetism appears in the Cu0.9Ga0.9Co0.2Se2 sample, which had the highest cobalt concentration, in particular at room temperature.

Two series of samples of the composition CuIn1−XCoXSe2 (m-series) and Cu1−X/2In1−X/2CoXSe2 (d-series) were prepared by solid-state synthesis and their magnetic properties were investigated. It was shown that cobalt is much better incorporated into the chalcopyrite matrix of the d-series samples, thus providing the onset of paramagnetic properties. Quenching allows the concentration of the incorporated cobalt to increase, which leads to the onset of weak ferromagnetism.

The first instance of a rare-earth single-ion magnet in a robust extended solid has been found, which possesses a crystal structure different from apatite. The compound exhibits slow relaxation of magnetization in a zero field revealing simultaneously two energy barriers for magnetization reversal.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Two series of manganese-doped chalcopyrite CuGaSe2 samples have been prepared by solid-state reactions. Because of its low solubility, the manganese is distributed between chalcopyrite lattice sites, ensuring paramagnetic properties, and manganese-containing antiferromagnetic impurity phases. Quenching the samples from 1000°C has made it possible to considerably increase the ferromagnetic response, which begins to rise starting at a certain doping level.

Two series of manganese-doped chalcopyrites Cu 1 – x /2 Ga 1 – x /2 Mn x Se 2 and CuGa 1 – x Mn x Se 2 have been prepared by solid-phase synthesis. Manganese-containing impurities have been found in all samples because of low solubility of manganese in chalcopyrite CuGaSe 2 . Nevertheless, manganese is incorporated into the chalcopyrite structure in a noticeable amount. All manganese-containing chalcopyrites have mainly paramagnetic properties; however, a ferromagnetic contribution has been found for all samples.

Manganese-doped semiconductors CuGa 1 – x Mn x Se 2 ( x = 0.02–0.20) with a chalcopyrite structure have been studied by EPR spectroscopy. For all samples, a singlet signal with g factor equal to ~2.00 is observed, the width of which decreases with an increase in the manganese concentration from 22.5 to 16.2 mT. For the most diluted sample with x = 0.02, a fine and hyperfine structure of the spectrum of the Mn 2+ ion is observed in the high-frequency W-range (93 GHz). The hyperfine splitting parameter A has been estimated and the longitudinal and transverse relaxation times at 10 K have been determined by the electron spin echo method.

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.

Tb-diluted and Tb-rich apatite-type silicates with compositions Y7.75Tb0.25Ca2(SiO4)6O2 and Tb8Ca2(SiO4)6O2, respectively, exhibit field induced multiple slow relaxation of magnetization. The former reveals two slow relaxation paths, the latter only one with a longer relaxation time of several seconds. The relaxation features of the Tb-diluted one are comparable with those of analogue compounds, where Tb is replaced by Dy, as well as with those of a Tb-doped calcium phosphate apatite. The relaxation parameters of the Tb-rich compound virtually match those of the Dy-based analogue Dy8Ca2(SiO4)6O2. The latter represents the first instance of independence of magnetization relaxation on the nature of a paramagnetic rare-earth metal ion in single ion magnet like materials.

Manganese-doped semiconductors CuGa1 – xMnxSe2 (x = 0.02–0.20) with a chalcopyrite structure have been studied by EPR spectroscopy. For all samples, a singlet signal with g factor equal to ~2.00 is observed, the width of which decreases with an increase in the manganese concentration from 22.5 to 16.2 mT. For the most diluted sample with x = 0.02, a fine and hyperfine structure of the spectrum of the Mn2+ ion is observed in the high-frequency W-range (93 GHz). The hyperfine splitting parameter A has been estimated and the longitudinal and transverse relaxation times at 10 K have been determined by the electron spin echo method.

The compound reveals dual magnetization relaxation with largely varying contributions from fast and slow relaxation paths controlled by field and temperature. The relaxation times retain values of a few seconds up to 40 K.

Apatite-type silicates Y7.75Dy0.25Ca2(SiO4)6O2 and Dy8Ca2(SiO4)6O2 were prepared by high-temperature solid state synthesis. In the crystal lattice, Dy3+ partially substitutes Ca2+, preferably at the 6h Ca2-site, and forms a short bond of 2.2 Å with the intra-channel O2-. The imposed strong ligand field anisotropy provides large magnetic anisotropy, which manifests itself as slow relaxation of magnetization at low temperatures. The magnetic dynamics is characterized by three or two characteristic values of relaxation time, respectively, which may be attributed to a single Dy3+ center. A phenomenological model is proposed which explains this response in terms of single paramagnetic center multiple relaxation.

All-inorganic single-ion magnets representing paramagnetic ions incorporated in a crystalline diamagnetic matrix are reviewed. Key results and advantages of this approach in comparison with the common strategy based on molecular metal-organic complexes are considered, and some unsolved problems and future perspectives are discussed.