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471.
The electronic structure and magnetism of Fe3/Crn(1 1 0) (n=1, 3, 5) superlattices (SL) with varying layer thickness have been studied using the full-potential linearized augmented plane-wave (FLAPW) method within the first-principle formalism. The results show that the ferromagnetic state is the preferable phase in the ground state. The magnetic moments of the Fe layers are slightly modified by the presence of the Cr layers. The Cr magnetic moments alternate direction from layer to layer, and an antiferromagnetic coupling between Fe and Cr at the interfacial layer is seen. The magnetic moments of the Cr layers are suppressed because there is a strong hybridization between d-states of both Fe and Cr atoms. Only a small moment is found in the Cr layer. The Cr moment alignment is determined by a delicate balance between the different magnetic interaction. 相似文献
472.
A. Cuchillo P. Vargas P. Levy R.D. Snchez J. Curiale A.G. Leyva H.E. Troiani 《Journal of magnetism and magnetic materials》2008,320(14):e331-e334
Magnetic properties of a single nanotube whose walls are constituted by nanograins of La2/3Sr1/3MnO3 are studied by means of Monte Carlo (MC) simulation. The system is considered as composed by ferromagnetic grains which couple via dipolar interaction. The grain size distribution is obtained from experimental measurements and the inter-grain distance distribution is obtained from a study of distance distribution among magnetic particles distributed in the tube walls. We show the magnetization behavior for a tube of 700 nm of diameter and 3.5 μm length. We discuss the simulation for different temperatures and external fields. As a main result, we show that the distribution of inter-granular distances has a unique behavior for tubular structures of similar diameter/length aspect ratio, independent of their sizes. This scaling relation allows us to perform the simulations using a tube of smaller dimensions. We succeed in explaining the magnetization curves, finding that dipolar interaction is necessary to explain the experimental behavior and that the grains behave as having magnetic dead layers. 相似文献
473.
V. Srinivas S.K. Barik Bhaskarjyoti Bodo Debjani Karmakar T.V. Chandrasekhar Rao 《Journal of magnetism and magnetic materials》2008
Fine nickel fibers have been synthesized by chemical reduction of nickel ions in aqueous medium with sodium borohydride. The thermal stability and relevant properties of these fibers, as-prepared as well as air-annealed, have been investigated by structural, magnetic and electrical measurements. As-prepared samples appear to have a novel crystal structure due to the presence of interstitial oxygen. Upon annealing in air, the fcc-Ni phase emerges out initially and develops into a nanocomposite subsequently by retaining its fiber-like structure in nano phase. The as-prepared sample is observed to be weakly magnetic at room temperature, but attains surprisingly high magnetization values at low temperatures. This is attributed to the modified spin structure, presumably due to the presence of interstitial oxygen in the lattice. Development of a weakly ferromagnetic and electrically conducting phase upon annealing in air is attributed to the formation of the fcc-Ni phase. The structural phase transformations corroborate well with magnetic and electrical measurements. 相似文献
474.
Single-phased polycrystalline Y3Fe5−2xAlxCrxO12 garnet samples (x=0, 0.2, 0.4 and 0.6) have been prepared by the conventional ceramic technique. Rietveld refinement of X-ray diffraction patterns of the samples shows them to crystallize in the Ia3d space group and the corresponding lattice constant to decrease with increasing Al3+ and Cr3+ contents (x). Mössbauer results indicate that Cr3+ substitutes for Fe3+ at the octahedral sites whilst Al3+ essentially replaces Fe3+ at the tetrahedral sites. This result indicates that co-doping of Y3Fe5O12 does not affect the preferential site occupancy for separate individual substitution of either Cr3+ or Al3+. The magnetization measurements reveal that the Curie temperature (Tc) monotonically decreases with increasing x while the magnetic moment per unit formula decreases up to x=0.4 and then slightly increases for x=0.6. This reflects a progressive weakening of the ferrimagnetic exchange interaction between the Fe3+ ions at octahedral and tetrahedral sites due to co-substitution. The magnetic moment was calculated using the cations distribution inferred from the Mössbauer data and the collinear ferrimagnetic model, and was found to agree reasonably with the experimentally measured value. The phenomenological amplitude crossover, characterized by the temperature T*, has also been observed in the doped YIG and briefly discussed. 相似文献
475.
Two series of elpasolite perovskites Ln2CoMnO6 and Ln2NiMnO6 (Ln=La, Pr, Nd, Sm, Gd) have been prepared. The electronic band gap and magnetic Curie temperature vary systematically as a function of the rare earth cation size within both series. Here we used Raman scattering spectroscopy along with the results of previous structural studies to show that there is little change in octahedral distortion but significant changes in the octahedral tilting angle upon decreasing lanthanide ionic radius. The data indicate differences in the orbital overlap and bond strengths between the two series of materials that allow us to understand variations in the magnetic and electrical properties within and between the two perovskite series. 相似文献
476.
Irena Stein Manfred Speldrich Helmut Schilder Heiko Lueken Prof. Dr. Uwe Ruschewitz Prof. Dr. 《无机化学与普通化学杂志》2007,633(9):1382-1390
with MII = Fe, Co, Ni (n = 2) and MII = Cu (n = 1): Four New Coordination Polymers with Acetylenedicarboxylate (ADC2?) as Bridging Ligand By slow diffusion of pyridine (Py) into an aqueous solution of a respective metal salt and acetylenedicarboxylic acid (H2ADC) single crystals of new coordination polymers of composition (M = Fe, Co, Ni; C2/c, Z = 4) ( 1 – 3 ) and (P212121, Z = 4) ( 4 ) were obtained. In compounds 1 – 3 octahedral MIIO4N2 units are connected via acetylenedicarboxylate anions to form chain‐like polymers. In compound 4 square pyramidal CuIIO3N2 units are found, which are also connected to chains by acetylenedicarboxylates. Thermoanalytical investigations on 3 show an abrupt mass loss of approx. 40 % above 130 °C, which points to a release of both pyridine ligands (calc.: 43 %). Thereafter, the sample decomposes continuously, which is confirmed by XRPD measurements, as an amorphous residue is found. Magnetic susceptibility measurements of 1 – 3 display paramagnetic behaviour in the temperature range 2‐300 K. While μeff of 3 (d8 configuration) with orbital singlet ground state is nearly temperature‐independent, 1 (d6) and 2 (d7) exhibit complicated μeff?T behaviour on account of a ligand‐field ground state derived from the cubic states 5T2 and 4T1, respectively. On the basis of a tetragonal ligand‐field model excellent adaptations are obtained with reasonable ligand‐field parameters. Exchange interactions between the magnetic ions are detected in no case. 相似文献
477.
478.
479.
Alina Bieńko Julia Kłak Jerzy Mroziński Sławomir Domagała Bohdan Korybut-Daszkiewicz Krzysztof Woźniak 《Polyhedron》2007
The syntheses, crystal structures and magnetic properties of the new bimetallic compounds {CuLα[Ni(NCS)4(H2O)2]} (1) and {CuLα[Mn(NCS)4(H2O)2]} (2), where L = N-dl-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene, are reported. Both structures consist of well-separated and magnetically equivalent layers which are composed of thiocyanate-bridged Cu(II)–Mn(II) or Cu(II)–Ni(II) binuclear units and create infinite polymeric zig-zag-like chains in the crystal lattices. The [Ni(NCS)4(H2O)2] and [Mn(NCS)4(H2O)2] molecular fragments have a distorted octahedral symmetry. The geometry of the Cu(II) unit is octahedral with the apical positions occupied by bridging thiocyanate ligands and the basal ones by four nitrogen atoms from the macrocyclic ring. The shortest intramolecular M–M distances are: 6.342 Å (Cu–Ni) and 6.421 Å (Cu–Mn). Magnetic susceptibility and magnetization measurements for the examined compounds have been carried out over the range 1.8–300 K. The data suggest antiferromagnetic interactions through the thiocyanate bridge. Finally, the magnitudes of the Cu(II)–M(II) interactions (M = Ni and Mn) have been compared and qualitatively rationalised. 相似文献
480.
Syntheses of complexes of the type [ML(NO3)2], where M = Co(II), Ni(II), and Cu(II), L = N-(2-pyridylethyl)pyridine-2-carbaldimine, a tridentate ligand, are described. They were characterized by elemental analysis, spectral, magnetic, thermal studies, and X-ray crystallography. In the cobalt (1), nickel (2), and copper (3) complexes, the bivalent metal ion is coordinated by the three nitrogen atoms of the tridentate L with two pyridine-N groups occupying trans positions. Amongst the two nitrates one coordinates in a bidentate fashion while the other adopts a monodentate fashion. The X-band EPR spectra of 1, 2, and 3 in the polycrystalline state and in acetonitrile solution at 77 K are reported. Room temperature vibrating sample magnetometer data of 1, 2, and 3 afforded μeff values respectively of 3.928, 3.897, and 1.952 BM. The thermal stability order is 1 > 2 > 3, showing a reverse Irving-Williams trend. 相似文献