Ferro- and antiferromagnetism in oxychalcogenides LnCrOX2 (Ln = La or Nd and X = S or Se)

Synthesis, crystal structure, and magnetic properties of layered SmCrS2−xSexO solid solutions

Layered SmCrS_2−xSe_xO (x = 0–2) solid solutions were synthesized which show typical antiferromagnetic orderings.

Synthesis, Crystal Structure, and Physical Properties of Layered LnCrSe2O (Ln = Ce-Nd)

The layered oxyselenides with the formula LnCrSe₂O (Ln = Ce-Nd) were synthesized via molten salt methods. The isostructural compounds crystallize in the monoclinic space group of C2/m. The crystal structures feature _∞²[CrSe₂O]^3- motifs stacked along the a axis, which are separated by Ln³⁺ ions. The _∞²[CrSe₂O]^3- layers are composed of [Cr1Se₆]^9- and [Cr2Se₄O₂]^9- octahedra via corner and edge sharing. Powder X-ray diffraction results confirm the phase purities of the as-synthesized compounds. LnCrSe₂O (Ln = Ce-Nd) show typical antiferromagnetic ordering with T_N = 125, 120, and 118 K, respectively. Heat capacity measurement for NdCrSe₂O indicates that the Debye temperature is 278.4 K. Similar metal-to-semiconductor phase transitions were observed for LnCrSe₂O (Ln = Ce-Nd) plates with transition temperatures of 115, 109, and 95 K, respectively. NdCrSe₂O also possesses a magnetoresistance effect at low temperature (<25 K) with a significant positive magnetoresistance ∼ 16% at 2 K and 1 T.

Flux synthesis, crystal structures, and physical properties of new lanthanum vanadium oxyselenides

The new lanthanum vanadium oxyselenides LaVSe₂O, La₅V₃Se₆O₇, La₅V₃Se₇O₅, La₇VSe₅O₇, and La₁₃V₇Se₁₆O₁₅ were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined using single-crystal and powder X-ray diffraction experiments. LaVSe₂O and La₅V₃Se₆O₇ adopt known structure types, whereas La₅V₃Se₇O₅, La₇VSe₅O₇, and La₁₃V₇Se₁₆O₁₅ crystallize in hitherto unknown structure types. The main building blocks of these compounds are chains of edge-sharing VSe₆, VSe₅O, and/or VSe₄O₂ octahedra, linked together by edge-sharing OLa₄ and/or OLa₃V tetrahedra forming fluorite-like ribbons. LaVSe₂O, La₅V₃Se₇O₅, and La₇VSe₅O₇ contain only V(iii) ions, whereby La₅V₃Se₆O₇ and La₁₃V₇Se₁₆O₁₅ contain mixtures of either V(iii)/V(iv) or V(iii)/V(v) cations. Magnetic measurements indicate Curie-Weiss paramagnetism and magnetic ordering of the vanadium moments at low temperatures. More precisely, we observe antiferromagnetism for La₅V₃Se₆O₇, metamagnetism for La₅V₃Se₇O₅, ferromagnetism for La₇VSe₅O₇ and a complex magnetic structure for La₁₃V₇Se₁₆O₁₅.

Flux Synthesis, Crystal Structures, and Magnetic Ordering of the Rare-Earth Chromium(II) Oxyselenides RE2CrSe2O2 (RE = La-Nd)

The rare-earth chromium(II) oxyselenides RE₂CrSe₂O₂ (RE = La-Nd) were synthesized in eutectic NaI/KI fluxes, and their crystal structures were determined by single-crystal and powder X-ray diffraction (Pb₂HgCl₂O₂-type, C2/m, Z = 2). The magnetic structure of La₂CrSe₂O₂ was solved and refined from neutron powder diffraction data. Main building blocks are chains of edge-sharing CrSe₄O₂ octahedra linked together by two edge-sharing ORE₃Cr tetrahedra forming infinite ribbons. The Jahn-Teller instability of divalent Cr²⁺ (d⁴) leads to structural phase transitions at 200 and 130 K in La₂CrSe₂O₂ and Ce₂CrSe₂O₂, respectively. RE₂CrSe₂O₂ are Curie-Weiss paramagnetic above T_N ≈ 14-17 K. Neutron powder diffraction reveals anti-ferromagnetic ordering of the Cr²⁺ moments in La₂CrSe₂O₂ below T_N = 12.7(3) K with an average ordered moment of 3.40(4) μ_B/Cr²⁺ at 4 K, which was confirmed by muon spin rotation experiments.

The magnetic and electronic properties of oxyselenides-influence of transition metal ions and lanthanides

Magnetic oxyselenides have been a topic of research for several decades, firstly in the context of photoconductivity and thermoelectricity owing to their intrinsic semiconducting properties and ability to tune the energy gap through metal ion substitution. More recently, interest in the oxyselenides has experienced a resurgence owing to the possible relation to strongly correlated phenomena given the fact that many oxyselenides share a similar structure to unconventional superconducting pnictides and chalcogenides. The two dimensional nature of many oxyselenide systems also draws an analogy to cuprate physics where a strong interplay between unconventional electronic phases and localised magnetism has been studied for several decades. It is therefore timely to review the physics of the oxyselenides in the context of the broader field of strongly correlated magnetism and electronic phenomena. Here we review the current status and progress in this area of research with the focus on the influence of lanthanides and transition metal ions on the intertwined magnetic and electronic properties of oxyselenides. The emphasis of the review is on the magnetic properties and comparisons are made with iron based pnictide and chalcogenide systems.

Synthesis and Characterization of Ba[CoSO]: Magnetic Complexity in the Presence of Chalcogen Ordering

Barium thio-oxocobaltate(II), Ba[CoS2/2 O2/2 ], was synthesized by the reaction of equimolar amounts of BaO, Co, and S in closed silica ampoules. The title compound (Cmcm, a=3.98808(3), b=12.75518(9), c=6.10697(4) Å) is isostructural to Ba[ZnSO]. The use of soft X-ray absorption spectroscopy confirmed that cobalt is in the oxidation state +2 and tetrahedrally coordinated. Its coordination consists of two sulfur and two oxygen atoms in an ordered fashion. High-temperature magnetic susceptibility data indicate strong low-dimensional spin-spin interactions, which are suggested to be closely related to the layer-type crystal structure and perhaps the ordered distribution of sulfur and oxygen. Antiferromagnetic ordering below TN =222 K is observed as an anomaly in the specific heat, coinciding with a significant lowering of the magnetic susceptibility. Density functional theory calculations within a generalized-gradient approximation (GGA)+U approach identify an antiferromagnetic ground state within the square-like two-dimensional layers of Co, and antiferromagnetic correlations for nearest and next nearest neighbors along bonds mediated by oxygen or sulfur. However, this magnetic state is subject to frustration by relatively strong interlayer couplings.