Vladimir Golub

The synthesis of core–shell iron@gold nanoparticles and their characterization

Au-coated magnetic Fe nanoparticles have been successfully synthesized by partial replacement reaction in a polar aprotic solvent with about 11 nm core of Fe and about 2.5 nm shell of Au. In this work, a combination of TEM (transmission electron microscopy), XRD (X-ray powder diffractometry), EDS (energy disperse X-ray spectroscopy), SQUID (superconducting quantum interference device), TGA (thermograviometric analysis) and UV–visible absorption spectroscopy were employed to characterize the morphology, structure, composition and magnetic properties of the products. HRTEM images show clear core–shell structure with different crystal lattices from Fe and Au. SQUID magnetometry reveals that particle magnetic properties are not significantly affected by the overlayer of a moderately thick Au shell. The Au-coated particles exhibit a surface plasmon resonance peak that red-shifts from 520 to 680 nm. And all the above characterizations show that in this sample there are no iron oxides inside the particle.

A building block approach to the synthesis of organic–inorganic oxide materials: the hydrothermal synthesis and network structure of [{Ni4(tpypyz)3}{Mo5O15(O3PCH2CH2PO3)}2]·23H2O (tpypyz = tetra-2-pyridylpyrazine)

The hydrothermal reaction of MoO3, [Ni(CH3CO2)2] x 4H2O, tpypyz, ethylenediphosphonic acid and water yields the 2D material [[Ni4(tpypyz)3][Mo5O15(O3PCH2CH2PO3)]2] x 23H2O (1 x 23H2O), constructed from [Mo5O15(O3PCH2CH2PO3)]4- clusters linked in one-dimension through the ethylene tethers of the diphosphonate component; these molybdodiphosphonate chains are in turn linked into a 2D network through the tetranuclear secondary metal-ligand subunit [Ni4(tpypyz)3]8+.

Anomalous magnetoresistance in NiMnGa thin films

The origin of anomalous negative magnetoresistance and its temperature dependence in polycrystalline Ni–Mn–Ga films prepared by pulse laser deposition was studied. The investigation of structural, transports, magnetic, and ferromagnetic resonance properties of the films suggests contributions of different mechanisms in magnetotransport. At low magnetic fields the main contribution to magnetoresistance is due to the transport between the areas with different orientation of magnetic moments, while at high fields it is an electron scattering of in spin-disordered areas.

Anion influences on the construction of one-dimensional structures of the Cu(II)–bisterpy family (bisterpy=2,2′:4′,4″:2″,2‴-quarterpyridyl, 6′,6″-di-2-pyridiine)

The hydrothermal reactions of M(II) salts with 2,2′:4′,4″:2″,2‴-quaterpyridyl, 6′,6″-di-2-pyridine (bisterpy) in the presence of a variety of anionic subunits have been investigated. The compounds [Cu 2 (bisterpy)(H 2 O) 2 Cl 2 ]Cl 2 ( 1 ), [Cu 2 (bisterpy)Br 4 ] ( 2 ), and [Cu 2 (bisterpy) (NO 3 ) 4 ]·2H 2 O ( 3 ·2H 2 O) are molecular. In contrast, [Cu 2 (bisterpy)Cl 2 (PF 6 )] ( 4 ), [Mn 2 (bisterpy)(SO 4 ) 2 ] ( 5 ), [Zn 2 (bisterpy)(SO 4 ) 2 ] ( 6 ), [Cu 2 (phbisterpy)(SO 4 ) 2 ]·2H 2 O ( 7 ·2H 2 O), [Cu 2 (bisterpy)(MoO 4 ) 2 ] ( 8 ), [Zn 2 (bisterpy)(MoO 4 ) 2 ] ( 9 ), [Cu 2 (bisterpy)(H 2 O) 2 (SO 4 )] [Mo 4 O 13 ]·1.25H 2 O ( 10 ·1.25H 2 O) and [Cu 2 (bisterpy)Mo 8 O 26 ]·2H 2 O ( 11 ·2H 2 O) are one-dimensional materials. The structural evolution of the molybdate series 8 , 10 , and 11 illustrates the profound influence of hydrothermal reaction conditions on product identity and architecture. The (PF 6 ) − bridged solid 4 is mixed valence Cu(I)/Cu(II), a feature consistent with the magnetic properties of this material.

Solid state coordination chemistry: structural consequences of variations in tether length in the oxovanadium–copper–bisterpy–{O3P(CH2)nPO3}4− system, n= 1–6 (bisterpy = 2,2′:4′,4″:2″,2‴-quarterpyridyl-6′,6″-di-2-pyridine)

Hydrothermal reactions of Na3VO4, an appropriate Cu(II) source, bisterpy and an organodiphosphonate, H2O3P(CH2)nPO3H2 (n = 1-6) yielded a family of materials of the type [Cu2(bisterpy)]4+/VxOy(n-)/[O3P(CH2)nPO3]4-. This family of bimetallic oxides is characterized by an unusual structural diversity. The oxides [[Cu2(bisterpy)]V2O4[O3PCH2PO3H]2] (1), [[Cu2(bisterpy)(H2O)]VO2[O3P(CH2)3PO3][HO3P(CH2)3PO3H2]] (4) and [[Cu2(bisterpy)]V2O4[O3P(CH2)6PO3H]2].2H2O (7.2H2O) are one-dimensional, while [[Cu2(bisterpy)(H2O)2]V2O4[O3P(CH2)2PO3][HO3P(CH2)2PO3H]2] (2), [[Cu2(bisterpy)]V4O8[O3P(CH23PO3]2].4H2O (3.4H2O) and [[Cu2(bisterpy)]V2O4(OH)2[O3P(CH2)4PO3]].4H2O (5.4H2O) are two-dimensional. The V(IV) oxide [[Cu2(bisterpy)]V4O4[O3P(CH2)5PO3H]4].7.3H2O (6.7.3H2O) provides a relatively unusual example of a three-dimensional bimetallic oxide phosphonate. The structures reveal a variety of V/P/O substructures as building blocks.

Preparation, structural characterization, and dynamic properties investigation of permalloy antidot arrays

Regular nanosized structures are considered to be promising materials for magnetic information storage media with high density of information. Recently attention was paid to static and dynamic magnetic properties arising from dimensional confinement in such nanostructures. Here we present an investigation of permalloy antidot arrays of different thicknesses. Thin permalloy films of thickness ranging from 10to500nm were deposited on nanoporous Al2O3 membranes with a pore size of 100nm. It was found that additional ferromagnetic resonance peaks appear for film thicknesses below 100nm, while films with larger thicknesses show resonance properties similar to continuous films. A comparison between the films deposited onto Si wafers and porous media was done. An evolution of the domain structures observed in MFM experiments was confirmed by micromagnetic calculations.

Hydrothermal synthesis and characterization of a novel bimetallic polyoxocation, [Cu6(dtbbpy)6Mo7O26]2+ (dtbbpy=4,4′-ditertbutyl-2,2′-biyridine)

Abstract The hydrothermal reaction of CuSO4·5H2O, MoO3, 4,4′-ditertbutyl-2,2′-biyridine and H2O in the mole ratio 2:1.5:1:2500 yields [ Cu 6 ( dtbbpy ) 6 Mo 7 O 26 ] 2 [ Mo 8 O 26 ]·26 H 2 O ( 1 ·26 H 2 O ) . The structure of 1 ·26 H 2 O consists of discrete α-[Mo8O26]4− anions and [Cu6(dtbbpy)6Mo7O26]2+ cations. The polyoxocation is constructed of an equatorial ring of three edge-sharing {MoO6} octahedra, capped on one face by a {Mo3Cu3O6} ring of corner-sharing molybdenum tetrahedra and copper square pyramids, and on the second face by a {Cu3MoO4} unit.

Ferromagnetic Resonance Properties and Anisotropy of Ni-Mn-Ga Thin Films of Different Thicknesses Deposited on Si Substrate

Ni-Mn-Ga films of different thicknesses were deposited onto Si(100) substrates by magnetron sputtering and annealed at 1073 K for 1 h in high vacuum. X-ray diffraction analysis showed the formation of 220 fiber texture perpendicular to the film plane. Magnetic properties of thin films were investigated at room temperature using ferromagnetic resonance (FMR) technique. The dependencies of both the FMR absorption maximum position and resonance linewidth on the direction of the external magnetic field with respect to the film normal were studied. The data analysis showed that the direction of magnetocrystalline anisotropy easy axis in the films makes 45° angle with the film normal. The modeling allowed evaluation of the uniaxial anisotropy constant, which is found to increase with thickness of Ni-Mn-Ga films. Uniaxial anisotropy constants were found to be ∼2.8×105 erg/cm3 for 0.1 and 0.5 μm film thickness, ∼4.2×105 erg/cm3 for 1 μm film, and ∼5.1×105 erg/cm3 for 3 μm film.

GMR multilayers on a new embossed surface

It has been shown that the deposition of magnetoresistive multilayers on stepped, corrugated or V-grooved surfaces can increase the magnitude of giant magnetoresistance (GMR). The primary reason for this enhancement of GMR is that the in-the-substrate-plane current crosses multiple magnetic layers which results in the mixed current-in-plane and current perpendicular to plane modes called current at an angle to the plane mode. In our studies, we use a novel substrate consisting of nano-hemispheres organized in a regular hexagonal array. The substrate was produced by anodization of Al and subsequent etching of alumina membrane. Scanning electron microscopy was used to investigate larger areas and cross-sectional images of the embossed surface, whereas detailed analysis of the surface structure was made by high resolution atomic force microscopy. We deposited uncoupled Co/Cu multilayers on the alumina substrate with an 8-nm-thick Fe buffer using magnetron sputtering. Our preliminary studies of the magnetotransport using a physical property measurement system (quantum design) demonstrated that the samples on the new substrate have an enhanced GMR effect compared to the samples with similar composition deposited on smooth (100) Si wafers. Because of the inexpensive method of fabrication of the embossed substrate, the GMR structures deposited on this substrate have a potential for use in magnetic sensors.

Magnetic and structural properties of nonstoichiometric Ni2MnGa alloys with Ni and Ga excess

The influence of nickel and gallium excess on local structure and magnetic properties of Ni–Mn–Ga alloys has been studied. Nuclear magnetic resonance experiments showed that excessive Ni occupies Mn and Ga positions. This leads to the appearance of low-frequency line from the nearest Mn55 nuclei and generation of fractional nuclear echo signals due to the increase of electrical field gradients on these nuclei. Magnetic measurements revealed the difference of Curie temperature determined from ac susceptibility and extrapolated from high-temperature magnetization behavior. The most probable explanation of this fact is the reduction of manganese–manganese indirect exchange via the faults in Mn–Ga layers interchange caused by excessive Ga.