Finite-sized Heisenberg chains and magnetism of one-dimensional metal systems

We present a combined experimental and theoretical study of the magnetization of one-dimensional atomic cobalt chains deposited on a platinum surface. We discuss the intrinsic magnetization parameters derived by X-ray magnetic circular dichroism measurements and the observation of ferromagnetic order in one dimension in connection with the presence of strong, dimensionality-dependent anisotropy energy barriers of magnetocrystalline origin. An explicit transfer matrix formalism is developed to treat atomic chains of finite length within the anisotropic Heisenberg model. This model allows us to fit the experimental magnetization curves of cobalt monatomic chains, measured parallel to the easy and hard axes, and provides values of the exchange coupling parameter and the magnetic anisotropy energy consistent with those reported in the literature. The analysis of the spin–spin correlation as a function of temperature provides further insight into the tendency to magnetic order in finite-sized one-dimensional systems. PACS 57.10.Pq; 75.30.-m; 75.30.Gw; 78.70.Dm     

(2‐Acetyl­pyridine‐κN 4‐phenyl­thio­semicarbazonato‐κ2N1,S)­halogeno‐trans‐di­methyl­tin(IV) (halogeno = chloro and bromo)

A thio­semicarbazone derivative, 2‐acetyl­pyridine 4‐phenyl­thio­semicarbazone, was prepared and complexed to Lewis acids, Sn(CH₃)₂X₂, X = Cl and Br. The products, [SnX(C₁₄H₁₃N₄S)(CH₃)₂], were characterized by single‐crystal X‐ray diffraction, and IR, NMR and Mössbauer spectroscopies. They are isomorphous and crystallize in the monoclinic space group P2₁/n. The structure determination revealed discrete neutral complexes with the Sn^IV atom in a distorted octahedral coordination geometry, with the halogeno ligand and the thio­semicarbazone derivative in the equatorial plane and the methyl groups in axial positions.     

21α‐Fluoro‐7‐norvouacapane‐17β,21α‐lactone

The crystal structure of 21α‐fluoro‐7‐norvouacapane‐17β,21α‐lactone, C₂₀H₂₅FO₃, a new synthetic derivative of the diterpenoid 6α,7β‐di­hydroxy­vouacapan‐17β‐oic acid isolated from Pterodon polygalaeflorus Benth fruits, is described.     

Magnetic field behavior of resonant current steps in one dimensional arrays of Josephson tunnel junctions

We study the magnetic field behavior of the resonant current steps appearing in one dimensional arrays of Josephson tunnel junctions. The analysis is carried out in the framework of the Kulik theory of resonances in small Josephson junctions, and the theoretical maximum current amplitude of the Fiske steps is computed as a function of the applied magnetic field. Preliminary measurements of the Fiske step current modulations induced by varying the magnetic field is also reported and discussed.