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α-Fe 6 Ga 5 was synthesized from the elements as a polycrystalline powder. Its crystal structure was redetermined by high-resolution powder X-ray diffraction, which showed a complex monoclinic structure of the Fe 6 Ge 5 type. The determined lattice parameters ( a = 10.08380(6) Å, b = 7.97071(5) Å, c = 7.70489(5) Å, and β = 108.3062(2)°) differ notably from the previous reports. Despite possessing the same structure type as Fe 6 Ge 5 , α-Fe 6 Ga 5 displays several distinctive features, such as short Ga-Ga bonds and distorted Fe layers. According to magnetization measurements, α-Fe 6 Ga 5 is a soft ferromagnet with a high Curie temperature of 760 K, which is in stark contrast to the antiferromagnetic behavior of Fe 6 Ge 5 reported in the literature. The electronic structure of α-Fe 6 Ga 5 was studied theoretically using density functional theory-calculations, which showed the pronouncedly covalent character of the short Fe-Ga and Ga-Ga bonds. Similar calculations were performed for Fe 6 Ge 5 , which revealed stronger Fe-Ge interactions, which preclude the formation of short Ge-Ge bonds. In both cases, the theoretical calculations showed ferromagnetic instability, which leads to ferromagnetic ordering only in the case of α-Fe 6 Ga 5 , likely due to the different nature of Fe-Ga-Fe and Fe-Ge-Fe superexchange interactions.

A van der Waals telluride, NbFeTe 2 , has been synthesized using chemical vapor transport reactions. The optimized synthetic conditions yield high-quality single crystals with a novel monoclinic crystal structure. Monoclinic NbFeTe 2 demonstrates a (100) cleavage plane, bulk ferromagnetism below 87 K, and a metallic ground state-the necessary prerequisites for needed spintronics technologies.

Layered chalcogenides containing 3d transition metals are promising for the development of two-dimensional nanomaterials with interesting magnetic properties. Both mechanical and solution-based exfoliation of atomically thin layers is possible due to the low-energy van der Waals bonds. In this paper, we present the synthesis and crystal structures of the Mn 2 Ga 2 S 5 and Mn 2 Al 2 Se 5 layered chalcogenides. For Mn 2 Ga 2 S 5 , we report magnetic properties, as well as the exfoliation of nanofilms and nanoscrolls. The synthesis of both polycrystalline phases and single crystals is described, and their chemical stability in air is studied. Crystal structures are probed via powder X-ray diffraction and high-resolution transmission electron microscopy. The new compound Mn 2 Al 2 Se 5 is isomorphous with Mn 2 Ga 2 S 5 crystallizing in the Mg 2 Al 2 Se 5 structure type. The crystal structure is built by the ABCBCA sequence of hexagonal close-packing layers of chalcogen atoms, where Mn 2+ and Al 3+ /Ga 3+ species preferentially occupy octahedral and tetrahedral voids, respectively. Mn 2 Ga 2 S 5 exhibits an antiferromagnetic-like transition at 13 K accompanied by the ferromagnetic hysteresis of magnetization. Significant frustration of the magnetic system may yield spin-glass behavior at low temperatures. The exfoliation of Mn 2 Ga 2 S 5 layers was performed in a non-polar solvent. Nanolayers and nanoscrolls were observed using high-resolution transmission electron microscopy. Fragments of micron-sized crystallites with a thickness of 70-100 nanometers were deposited on a glass surface, as evidenced by atomic force microscopy.

Single crystals of two new intermetallic phases Sm 2 Mn 1- x Ga 6- y Ge y ( x = 0.1-0.3, y = 0.6-1.0) and Sm 4 MnGa 12- y Ge y ( y = 3.0-3.5) were grown using a self-flux technique. According to single crystal X-ray diffraction data, Sm 4 MnGa 12- y Ge y is characterised by the Y 4 PdGa 12 structure type ( a ∼ 8.65 Å; Im 3̄ m ), while Sm 2 Mn 1- x Ga 6- y Ge y formally adopts the K 2 PtCl 6 structure type ( a ∼ 8.71 Å; Fm 3̄ m ). The general features of both compounds with rather similar crystal structures are represented by the alternation of empty and Mn-filled p-element octahedra, the order of which is determined by the Mn concentration. The diffraction data for Sm 2 Mn 1- x Ga 6- y Ge y reveal a large concentration of Mn vacancies ( x ∼ 0.3), which affects adjacent Ga/Ge atoms leading to their shift towards the vacancy. Both compounds demonstrate two ferromagnetic-like transitions and the presence of two interacting Mn and Sm magnetic sublattices. The Mn sublattice orders at T C1 of 143 K and 318 K, while the Sm one orders at lower temperatures at T C2 of 50 K and 280 K for Sm 4 MnGa 8.6 Ge 3.4 and Sm 2 Mn 0.74 Ga 5.1 Ge 0.9 , respectively. The increase in Mn content not only increases the ordering temperatures, but also dramatically decreases the coercivity μ 0 H C from 230 mT to just 6.5 mT at 2 K. Despite the presence of two magnetically active sublattices in Sm 2 Mn 0.74 Ga 5.1 Ge 0.9 , the magnetic entropy change is quite low and only reaches 0.3 J kg -1 K -1 at T = 300 K and μ 0 H = 5 T, while the estimated relative cooling power (RCP) is about 36 J kg -1 at 5 T.