Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe₄₀Ni₄₀B₂₀ and Fe₄₀Ni₃₈Mo₄B₁₈ metallic glass ribbons. 90 MeV ¹²⁷I beam was used for the irradiations. Irradiation doses were 5×10¹³ and 7.5×10¹³ ions/cm². The relative intensity ratios D ₂₃ of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.     

Synthetic magnetic opals

We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there exists no report in literature on any BiNi compound which is magnetic.     

Magnetization curves for general cylindrical samples in a transverse field

Using the recent results for the surface current density on cylindrical surfaces of arbitrary cross-section producing uniform interior magnetic field we propose a method for obtaining solutions of Bean’s critical state model for general cylindrical samples. The method uses the technique of conformal mapping to express the sample surface and the flux-fronts in terms of a set of coefficients that depend on a parameter. The flux-fronts are to be determined by solving a system of nonlinear ordinary differential equations for the coefficients. Retaining only a certain finite number of leading coefficients we get an approximate solution. The procedure is illustrated by considering two cyclindrical samples — one with an elliptical cross-section and the other with a non-elliptical cross-section. The virgin curve and small and large magnetization hysteresis loops for the two samples are obtained.     

Low-field vortex dynamics in various high-T c thin films

We present a novel ac susceptibility technique for the study of vortex creep in superconducting thin films. With this technique we study the dynamics of dilute vortices in c-axis oriented Y-123, Hg-1212, and Tl-1212 thin films, as well as a axis oriented Hg-1212 thin films. Results on the Hg-1212 and Tl-1212 thin films indicate that dislocation-mediated plastic flux creep of single vortices dominates at low temperatures and fields. As the temperature (or the field) is increased, the increasing vortex-vortex interactions promote a collective behavior, which can be characterized by elastic creep with a non-zero μ exponent. Also, in some of these samples effects of thermally assisted quantum creep are visible up to 45 K in some of these samples. In Y-123 thin films, creep is found to be collective down to the lowest temperatures and fields investigated, while the quantum creep persists only up to 10–11 K.     

A New Abietane Diterpenoid from Plectranthus bishopianus Benth.

Chemical examination of the MeOH extract of Plectranthus bishopianus Benth ., a rare and endangered plant, resulted in isolation of a new abietane diterpene, 6β‐hydroxy‐7α‐methoxyroyleanone ( 1 ), along with two more diterpenoids, 6,7‐dehydroroyleanone, and 6β,7α‐dihydroxyroyleanone, a triterpene oleanolic acid, and two sterols, β‐sistosterol and stigmasterol. The structures of the isolated compounds were elucidated on the basis of spectroscopic data and also by comparison with authentic samples.     

Chalcones as inorganic analytical reagents

1·0–6·0 p.p.m. of germanium could be estimated spectrophoto-metrically with 2′, 3′, 4′-trihydroxy chalcone as reagent at pH 5·8–6·0. The complex was shown to contain three gram-moles of the reagent to one gram-atom of germanium both by Job’s method of continuous variations and the slope ratio method of Harvey and Manning. The instability constant was determined by the method of Edmonds and Birnbaum and found to be 1·670×10^?11 at 28° C. It is concluded that complex formation involved only the two ortho hydroxyls in each molecule of the reagent and the carbonyl group played no part.     

Electrospray ionization studies of transition-metal complexes of 2-acetylbenzimidazolethiosemicarbazone using collision-induced dissociation and ion-molecule reactions

The complexes of transition-metal ions (M2+, where M = Fe, Co, Ni, Cu, Zn, Cd, and Hg) with 2-acetylbenzimidazolethiosemicarbazone (L) are studied under electrospray ionization (ESI) conditions. The ESI mass spectra of Fe and Co complexes showed the complex ions corresponding to [M+2L-2H]+, and those of Ni and Zn complexes showed [M+2L-H]+ ions, wherein the metal/ligand ratio is 1:2 and the oxidation state of the central metal ion is +3 in the case of Fe and Co and +2 in the case of Ni and Zn. The Cd and Cu complexes showed preferentially 1:1 complex ions, i.e., [M+L-H]+ or [M+L+Cl]+, whereas Hg formed both 1:1 and 1:2 complex ions. During formation of the above complex ions one or two ligands are deprotonated after keto-enol tautomerism, depending on the nature and oxidation state of central metal ion. The structures and coordination numbers of the metal ions in the complex ions were studied by their collision-induced dissociation spectra and ion-molecule reactions with acetonitrile or propylamine in the collision cell. Based on these results it is concluded that Fe, Co, Ni and Zn form stable octahedral complexes, whereas tetrahedral or square planar complexes are formed preferentially for other metals. In addition, the Cu complex showed a [2L+2Cu-3H]+ ion with a Cu-Cu bond.     

Magnetization curves for non-elliptic cylindrical samples in a transverse field

Using recent results for the surface current density on cylindrical surfaces of arbitrary cross-section producing uniform interior magnetic field and an assumed set of flux-fronts, solutions of Bean’s critical state model for cylindrical samples with non-elliptic cross-section are presented. Magnetization hysteresis loops for two cross-sections with different aspect ratios are obtained. A comparison with some exact results shows the limitations of this approach.