Bulk ferromagnetism in cleavable van der Waals telluride NbFeTe2.

A van der Waals telluride, NbFeTe2, has been synthesized using chemical vapor transport reactions. The optimized synthetic conditions yield high-quality single crystals with a novel monoclinic crystal structure. Monoclinic NbFeTe2 demonstrates a (100) cleavage plane, bulk ferromagnetism below 87 K, and a metallic ground state-the necessary prerequisites for needed spintronics technologies.

Cleavable crystals, crystal structure, and magnetic properties of the NbFe1+xTe3 layered van der Waals telluride.

Transition metal-based two-dimensional nanomaterials with competing magnetic states are at the cutting edge of spintronic and low-power memory devices. In this paper, we present a Fe-rich NbFe1+xTe3 layered telluride (x ≈ 0.5), which shows an interplay of spin-glass and antiferromagnetic states below the Néel temperature of 179 K. The compound has a layered crystal structure, where the NbFeTe3 layers are terminated by the Te atoms and van der Waals gaps. Bulk single crystals grown by chemical vapor transport reactions possess the (1̄01) cleavage plane suitable for the exfoliation of two-dimensional nanomaterials. Combination of high-resolution transmission electron microscopy and powder X-ray diffraction reveals the zigzag ladders of Fe atoms inside the structural layers, as well as complementary zigzag chains of the partially occupied Fe positions in the interstitial region. Fe atoms carry large effective magnetic moment of 4.85(3)µB per atom in the paramagnetic state yielding intriguing magnetic properties of NbFe1+xTe3. They include frozen spin-glass state at low temperatures and spin-flop transition in high magnetic fields indicating promising flexibility of the magnetic system and its potential control by magnetic field or gate tuning in the spintronic devices and heterostructures.

Mummified Wood of Juniperus (Cupressaceae) from the Late Miocene of Taman Peninsula, South Russia.

Juniperus L. is the second-largest genus of conifers, having the widest distribution of all conifer genera. Its phytogeographic history is, however, obscure due to its very poor fossil record. We described a wood of Juniperus sp. from the lower Maeotian sediments of the Popov Kamen section, Taman Peninsula, South Russia, in order to clarify its taxonomic position shedding light on the phytogeographic history of the genus. This fossil wood was well-preserved by mummification, which allowed for it to be studied by the same methods as used for the anatomical examination of modern woods. The wood from the Popov Kamen section shows the greatest similarity to the extant Mediterranean species J. excelsa, belonging to the section Sabina. This is the first reliable macrofossil evidence of the sect. Sabina from Eurasia convincingly dated to the Miocene. The age of the mummified wood from the Popov Kamen section is consistent with molecular dating of diversification of the lineage comprising juniper species of the sect. Sabina from Europe, Asia and eastern Africa. The wood of Juniperus sp. has not been buried in situ, as it was found in the relatively deep-water marine sediments. The available coeval pollen series and macrofossils of Cupressaceae from the surrounding regions suggest that this wood was likely transferred by sea current from the northwestern side of the Black Sea, which was a part of the Eastern Paratethys.

Fe-Rich Ferromagnetic Cleavable Van der Waals Telluride Fe5AsTe2.

Transition metal-based layered compounds with van der Waals gaps between the structural layers are a rich source of magnetic materials for spintronic applications. Bulk crystals can be cleaved, providing high-quality two-dimensional nanomaterials, which are promising for the manipulation of spins in spintronic devices and low power quantum logic interfaces. The layered van der Waals telluride Fe5AsTe2 can be synthesized by the high-temperature reaction of elements. In the crystal structure, Fe-rich structural layers with the composition of Fe4.58(4)AsTe2 are separated by the van der Waals gaps with no atoms in the interstitial region. Crystal growth employing chemical vapor transport reactions yields bulk cleavable crystals, which exhibit weak inherent ferromagnetism below the Curie temperature of TC = 48 K. In the ordered state, the magnetization shows a dual-slope behavior in low magnetic fields, indicating the compensated or canted nature of magnetism. Magnetic susceptibility and magnetization measurements reveal perpendicular magnetic anisotropy. The large Rhodes-Wohlfarth ratio of 4.6 indicates the itinerant nature of ferromagnetism in Fe5AsTe2.

Araucarioid wood from the late Oligocene-early Miocene of Hainan Island: first fossil evidence for the genus Agathis in the Northern Hemisphere.

Although many fossil and molecular data suggest migrations from Malesia and Asia to Australia appear to dominate floristic exchange between Australian and Asian rainforests, evidence is emerging that demonstrate dispersal of plant groups from Australia to Asia. In this paper, a new species Agathis ledongensis sp. nov. is described on the basis of silicified wood from the late Oligocene-early Miocene of the Qiutangling Formation in Ledong, Hainan Island, South China. It is the first fossil record of Agathis in the Northern Hemisphere, and the only known fossil evidence of its dispersal outside of Gondwana. The close affinity of the fossil wood from Ledong with the genus Agathis was confirmed by comparing quantitative traits in 31 wood samples of 20 species representing all three extant genera of the Araucariaceae. The percentage of tracheids with uniseriate pitting on radial walls is shown as an additional diagnostic trait for separating Agathis and Wollemia from Araucaria. The wood of Agathis ledongensis provides evidence for the dispersal of this important plant group from Australia, or another Gondwanan terrane, to eastern Asia based on reliable fossil data. It records the occurrence of this genus in Hainan Island by the early Miocene, i.e. at the beginning of the formation of the island chains between Australia and the South-East Asia and thus the provision of a land migration route. As the land routes between these continents were restricted at that time, the migration of Agathis to Malesia and Asia was presumably facilitated by long-distance dispersal of its winged seeds by wind.