Search

We prepared an organically templated magnet, (enH2)0.5VPO4OH (enH2 = diprotonated ethylenediamine), hydrothermally and characterized its crystal structure by powder X-ray diffraction and Fourier-transform infrared spectroscopy, and its physical properties by magnetization, specific heat and nuclear magnetic resonance measurements and density functional theory calculations. (enH2)0.5VPO4OH consists of uniform chains of V3+ (d2, S = 1) ions and exhibits Haldane magnetism with spin gap Δ = 59.3 K from the magnetic susceptibility χ(T) at μ0H = 0.1 T, which is reduced to 48.4 K at μ0H = 9 T according to the 31P shift. The NMR data evidence the formation of a spin-glass state of unpaired S = 1/2 spins at TS–G ≈ 3 K and indicate that the Haldane S = 1 spin chain segments are much longer in the organically templated magnet (enH2)0.5VPO4OH than in the ammonium counterpart NH4VPO4OH. The single-ion anisotropy D and the interchain exchange J′ in (enH2)0.5VPO4OH and NH4VPO4OH were estimated in density functional calculations to find them very weak compared to the intrachain exchange J. [ABSTRACT FROM AUTHOR]

Pyridinium cesium cobalt nitrate, (PyH)CsCo2(NO3)6, obtained from a nitric acid solution crystallizes in the orthorhombic space group Pnma with unit cell parameters a = 8.6905(14) Å, b = 11.9599(18) Å, c = 18.386(3) Å, V = 1911.0(5) Å3, and Z = 4. It consists of [Co(NO3)3]− layers, in which each Co2+ ion is connected with four monodentate bridging NO3-groups and one bidentate terminal NO3-group, forming a corrugated rectangular net. Magnetization and specific heat measurements show that (PyH)CsCo2(NO3)6 undergoes a long-range canted antiferromagnetic ordering in two steps at TC1 = 5.0 K and TC2 = 2.6 K. The temperature dependence of the magnetic susceptibility and the field dependence of the magnetization measured for (PyH)CsCo2(NO3)6 show that it is an Ising antiferromagnet. In support of these observations, our DFT + U + SOC calculations show that the Co2+ ions of (PyH)CsCo2(NO3)6 have an easy-axis magnetic anisotropy with preferred spin orientation along the b-axis. To a first approximation, the spin lattice of (PyH)CsCo2(NO3)6 is a weakly alternating Ising antiferromagnetic chain (J1/J2 ∼ 0.85), and these chains interact weakly (J3/J2 ∼ 0.07) to form a rectangular Ising antiferromagnetic lattice. In agreement with the prediction for a rectangular Ising antiferromagnet by Onsager, (PyH)CsCo2(NO3)6 undergoes a long-range antiferromagnetic ordering. [ABSTRACT FROM AUTHOR]

We prepared a new compound, Co3(SeO3)(SeO4)(OH)2, having layers in a kagomé-like arrangement of Co2+ (spin S = 3/2) ions. This phase crystallizes in the orthorhombic space group Pnma (62) with unit cell parameters a = 11.225(9) Å, b = 6.466(7) Å and c = 11.530(20) Å. Its layers, parallel to the ab-plane, are made up of Co1O5 square pyramids and Co2O6 and Co3O6 octahedra. As the temperature is lowered, Co3(SeO3)(SeO4)(OH)2 undergoes three successive magnetic transitions at 27.5, 19.4 and 8.1 K, and the magnetization of Co3(SeO3)(SeO4)(OH)2 measured at 2.4 K exhibits a 1/3-magnetization plateau between 7.8 and 19.9 T. The H–T magnetic phase diagram constructed for Co3(SeO3)(SeO4)(OH)2 from ac and dc magnetic susceptibility, specific heat and magnetization measurements contains three magnetic phases I, II and III. Phase I is antiferromagnetic, while phases II and III are ferrimagnetic and responsible for the 1/3-magnetization plateau. To interpret these complex magnetic properties, we identified the correct spin lattice for Co3(SeO3)(SeO4)(OH)2 by evaluating its intralayer and interlayer spin exchanges based on spin-polarized DFT+U calculations. [ABSTRACT FROM AUTHOR]

A mixed-valence compound Pb2Cu10O4(SeO3)4Cl7 has a complex structure consisting of one nonmagnetic Cu+ (S = 0) ion and four nonequivalent magnetic Cu2+ (S = 1/2) ions. It exhibits antiferromagnetic ordering at TN = 10.2 K. At a temperature below TN, a sequence of spin-flop transition at Bspin-flop = 1.3 T and 1/3 plateau formation at Bspin-flip = 4.4 K is observed in the magnetization curve M(B). The 1/3 magnetization plateau persists at least up to 53.5 T. The spin exchanges of Pb2Cu10O4(SeO3)4Cl7 evaluated by performing energy-mapping analysis based on DFT+U calculations show that the magnetic properties of Pb2Cu10O4(SeO3)4Cl7 are described by the (Cu2+)7 cluster of corner-sharing (Cu2+)4 tetrahedra, and that each (Cu2+)7 cluster has a S = 3/2 spin arrangement in the ground state. The 1/3 magnetization plateau observed for Pb2Cu10O4(SeO3)4Cl7 is explained by the field-induced flip of every second (Cu2+)7 cluster within a unit cell. [ABSTRACT FROM AUTHOR]

Describes ligand field splitting in terms of density functional theory. Association of split levels with the subterms of 4f[sup n-1]6s[sup 2] (n=3-14) configurations of lanthanide monofluorides; Relationship between multiplet splitting and single-determinant energies; Factors attributing the efficacy of ligand potential.

Investigates the formulated method to calculate split levels of spectroscopic subterms of lanthanide irons under the weak field coupling scheme. Application of the density functional theory and ligand field theory; Removal of the 4f-electron contribution from the potential; Introduction of pseudopotentials.