CrCl3 is a layered insulator that undergoes a crystallographic phase transition below room temperature and orders antiferromagnetically at low temperature. Weak van der Waals bonding between the layers and ferromagnetic in-plane magnetic order make it a promising material for obtaining atomically thin magnets and creating van der Waals heterostructures. In this work we have grown crystals of CrCl3, revisited the structural and thermodynamic properties of the bulk material, and explored mechanical exfoliation of the crystals. We find two distinct anomalies in the heat capacity at 14 and 17 K confirming that the magnetic order develops in two stages on cooling, with ferromagnetic correlations forming before long range antiferromagnetic order develops between them. This scenario is supported by magnetization data. A magnetic phase diagram is constructed from the heat capacity and magnetization results. We also find an anomaly in the magnetic susceptibility at the crystallographic phase transition, indicating some coupling between the magnetism and the lattice. First principles calculations accounting for van der Waals interactions also indicate spin-lattice coupling, and find multiple nearly degenerate crystallographic and magnetic structures consistent with the experimental observations. Finally, we demonstrate that monolayer and few-layer CrCl3 specimens can be produced from the bulk crystals by exfoliation, providing a path for the study of heterostructures and magnetism in ultrathin crystals down to the monolayer limit.

The ability to synthesize new complex oxide materials that belong to any of the large number of known oxide structural families relies typically on a general understanding of the relationship between the specific structure type and the chemical composition of its members. However, before one can create such a structure-composition relationship that enables the synthesis of new members, one needs structural information about a sizable number of existing compositions belonging to this structural family, somewhat of a ''chicken or the egg'' problem. In this Highlight we will use one family of oxides, specifically oxides related to the hexagonal perovskite structure, to illustrate how exploratory crystal growth methods have been used successfully to synthesize enough diverse compositions to enable the formulation of a general structural description. Furthermore, by now it appears that enough members with different compositions have been synthesized so that one can attempt to create a structurecomposition relationship that has predictive powers.

A series of seven compounds, Sr2Mn(OH)6, Ba2Mn(OH)6, Sr2Co(OH)6, Ba2Co(OH)6, Sr2Ni(OH)6, Ba2Ni(OH)6, and Ba2Cu(OH)6, were synthesized using a low-melting hydroflux, a hybrid approach between aqueous hydrothermal and molten hydroxide flux techniques. Crystals of the hexahydroxometallates were obtained by dissolving appropriate amounts of alkaline-earth nitrates or hydroxides and transition-metal oxides, acetates, or chlorides in the hydroflux and reacting at 180-230 °C. The isostructural compounds all crystallize in the monoclinic space group P2(1/n). The monoclinic structure consists of isolated transition-metal octahedra within a three-dimensional framework of corner- and edge-shared eight-coordinate, alkaline-earth polyhedra. Magnetic susceptibility data show that all compounds are simple paramagnets. Thermogravimetric analysis indicates that these hydroxides lose water between 215 and 350 °C and transform into oxide products, the identity of which depends on the metal cations present in the parent hexahydroxometallates.

Crystallographic structure information, magnetic agreement indices, neutron diffraction patterns and magnetic data plots, ICSD and CCDC numbers (PDF) Data for BaFe 4 O 7 (CIF) Data for Ba 0.89 K 0.22 Fe 4 O 7 (CIF)

For iron-sulfide (FeS), we investigate the correlation between the structural details, including its dimensionality and composition, with its magnetic and superconducting properties. We compare, theoretically and experimentally, the two-dimensional (2D) layered tetragonal ("t-FeS") phase with the 3D hexagonal ("h-FeS") phase. X-ray diffraction reveals iron-deficient chemical compositions of t-Fe 0.93(1) S and h-Fe 0.84(1) S that show no low-temperature structural transitions. First-principles calculations reveal a high sensitivity of the 2D structure to the electronic and magnetic properties, predicting marginal antiferromagnetic instability for our compound (sulfur height of z S = 0.252) with an ordering energy of about 11 meV/Fe, while the 3D phase is magnetically stable. Experimentally, h-Fe 0.84 S orders magnetically well above room temperature, while t-Fe 0.93 S shows coexistence of antiferromagnetism at T N = 116 and filamentary superconductivity below T c = 4 K. Low temperature neutron diffraction data reveals antiferromagnetic commensurate ordering with wave vector k m = (0.25,0.25,0) and 0.46(2) μ B /Fe. Additionally, neutron scattering measurements were used to find the particle size and iron vacancy arrangement of t-FeS and h-FeS. The structure of iron sulfide has a delicate relationship with the superconducting transition; while our sample with a =3.6772(7) Å is a filamentary superconductor coexisting with an antiferromagnetic phase, previously reported samples with a > 3.68 Å are bulk superconductors with no magnetism, and those with a ≈ 3.674 Å show magnetic properties.

We reported the utilization of a series of heterobimetallic diblock copolymers to prepare different iron–cobalt/carbon and iron–cobalt phosphide/carbon magnetic materials. Through the control of compositions of ferrocene- and cobaltocenium-containing blocks, a transition of final inorganic materials from metal phosphide to metal alloy was observed. These metal elements were embedded on amorphous carbon films or encapsulated in crystallized multiwalled carbon nanotubes. Detailed magnetic characterization showed that all these inorganic materials were ferromagnetic under room temperature with great difference in their magnetic susceptibilities. The saturated magnetization was related with the weight fraction of phosphorus and cobalt, indicating the ability to control the magnetization of these inorganic materials via polymer compositions.

The composition of Sr2Fe1.5Mo0.5O6−δ, a SOFC electrode material, is investigated by neutron diffraction in both highly oxidizing and reducing conditions, and correlated with measured physical properties.

Single crystals of Na 5 RE 4 IJOH)ijSiO 4 ] 4 (RE = Pr, Nd, Sm, Eu, Tb-Yb, Y) were grown using the hydroflux synthetic method. All compositions adopt the tetragonal I4 space group with lattice parameter ranges of a = 11.5275IJ4)-12.0588IJ3) Å and c = 5.3951IJ4)-5.4846IJ13) Å. Intense photoluminescent properties were observed for Na 5 Eu 4 IJOH)ijSiO 4 ] 4 , Na 5 Gd 4 IJOH)ijSiO 4 ] 4 , and Na 5 Tb 4 IJOH)ijSiO 4 ] 4 . The magnetic susceptibility was measured for the magnetic rare earth containing compositions, where the terbium analogue displayed antiferromagnetic order at T = 2.8 K. Among the many different classes of structures explored for use in solid state lighting, alkali metal containing silicate and germanate structures such as Na 3 have been studied extensively. A similar structural family, A 5 RE 4 XijTO 4 ] 4 , [A = alkali metal, RE = rare earth, T = tetragen] contains several known compounds in closely related structure types, and includes Na 5 Nd 4 IJOH)ijSiO 4 ] 4 , 24 Na 5 Y 4 FijSiO 4 ] 4 , 25 K 5 La 4 FijSiO 4 ] 4 , 26 Na 5 Nd 4 Ge 4 O 16 IJOH), 27 and IJNa 0.63IJ2) Nd 0.37IJ2) )IJNaSiO 4 ) 4 IJO 0.52 F 0.48 ). 28 As most rare earths can be accommodated in this tetragen based structure type, it represents an attractive host material for new, rare earth based, luminescent materials.Herein, we report the synthesis of alkali metal containing silicates Na 5 RE 4 IJOH)IJSiO 4 ) 4 (RE = Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y) using the hydroflux technique. The CrystEngComm, 2015, 17, 4691-4698 | 4691This journal is