China
Africa
Explore chapters and articles related to this topic
Quasi-two-dimensional magnets with triangular motifs in the structure
Published in A.N. Vasiliev, O.S. Volkova, E.A. Zvereva, M.M. Markina, Low-Dimensional Magnetism, 2019
A.N. Vasiliev, O.S. Volkova, E.A. Zvereva, M.M. Markina
Another candidate for the realization of the quantum spin liquid state was the mineral vésiginité BaCu3V2O8(OH)2 structurally related to herbertsmithite, which, however, shows a very different type of magnetic behaviour [321, 338–343]. This compound crystallizes into a monoclinic C2/m layer structure, with Cu2+ ions in a distorted octahedral coordination forming a kagome lattice, as shown in Fig. 7.5a [343]. Unlike from herbertsmithite, vésiginité shows the establishment of a long-range magnetic order of the Néel type (q = 0) with TN = 9 K. In this case, the dependence χ(T) shown in Fig. 7.5b, has a sharp maximum. It is established that the copper ions form a non-collinear 120° spin configuration, and magnetism is determined by the dominant antiferromagnetic exchange between the nearest neighbors J = 53 K. Investigations by the NMR method [342, 343] have shown the essential role of the Dzyaloshinsky–Moriya anisotropy for the clarification of which the EPSR method was used [321]. Analysis of the temperature dependences of the main EPSR parameters, as shown by the solid lines in Fig. 7.6, made it possible to estimate the contribution of the Dzyaloshinsky–Moriya interaction. It is established that a large intrasplane anisotropy effectively suppresses quantum spin fluctuations in BaCu3V2O8(OH)2, which leads to stabilization of the long-range magnetic order in this compound, unlike herbertsmithite [321].
Optical control of layered nanomaterial generation by pulsed-laser ablation in liquids
Published in Journal of Modern Optics, 2020
Likewise, we were able to generate layered metastable basic zinc(II)-containing nanocrystals by pulsed-laser ablation in liquids (14). They were layered hydroxide double salts that are also known as anionic clays (35). Relative stabilities of these hydroxy-hydrated zinc minerals are pH dependent; all are soluble in strongly acidic solution (36). The most stable zinc hydroxide chloride hydrate polymorphs at room temperature are β-Zn(OH)Cl, ZnO·ZnCl2·2H2O, and 4Zn(OH)2·ZnCl2·H2O (= Zn5(OH)8Cl2·H2O, simonkolleite) (37), all of which convert into ZnO and ZnCl2 upon heating (35). We observed solely generation of layered crystalline nanosimonkolleite of stiochiometry Zn5(OH)8Cl2·H2O during pulsed-laser ablation of zinc metal in aqueous ZnCl2 + NH4OH solution (14), although very high electron temperatures of ca. (8,400 ± 1,300) K were reached during preparation (Figure 4); we added NH4OH to the aqueous ZnCl2 ablation liquid to raise the pH to neutral and be able to obtain a non-dissolved solid material. We also laser-prepared the nitrate analogue, the layered anionic clay zinc hydroxide nitrate hydrate of the stoichiometry Zn5(OH)8(NO3)2·2H2O (14). Zinc hydroxide nitrate hydrate is monoclinic, exhibits a layered structure that is closely related to that of zinc hydroxide chloride hydrate (38), and decomposes above 300°C via an anhydrous zinc nitrate phase to ZnO (39). Despite the high temperatures in the laser synthesis we did not observe any ZnO or Zn(NO3)2 in the generated nanomaterial; instead we obtained phase-pure crystalline zinc hydroxide nitrate hydrate. Further, we used pulsed-laser ablation in liquids to generate a mixed-metal phase of stoichiometry Cu3(Cu, Zn)Cl2(OH)6 (14), called zincian paratacamite, which occurs in nature as herbertsmithite (40, 41); the material has been extensively studied as a structurally perfect S = 1/2 kagome antiferromagnet in search of a quantum spin liquid (42, 43).