Single-domain Transition Research Articles

Size dependent magnetic and magneto-optical properties of Ni0.2Zn0.8Fe2O4 nanoparticles

Ni0.2Zn0.8Fe2O4 spinel nanoparticles have been synthesized by combustion method. Average particles size varies from 15.5 to 50.0nm depending on annealing temperature. Correlations between particles size and magnetic and magneto-optical properties are investigated. Magnetization dependences on temperature and external magnetic field correspond to the sum of paramagnetic and superparamagnetic response. Critical size of single-domain transition is found to be 15.9nm. Magnetic circular dichroism (MCD) studies of nickel zinc spinel are presented here for the first time. The features in magnetic circular dichroism spectrum are assigned to the one-ion d–d transitions in Fe3+ and Ni2+ ions, as well to the intersublattice and intervalence charge transfer transitions. The MCD spectrum rearrangement was revealed with the change of the nanoparticles size.

The lattice parameter of nanocrystalline Ni as function of crystallite size

An anomalous dependence on crystallite size of the lattice parameter of nanocrystalline Ni as occurring in ultrathin Ni films and in ball-milled Ni powder was observed: lattice contraction followed by lattice expansion with decrease in crystallite size. These data were determined by application of detailed in-situ X-ray diffraction measurements during annealing treatments. To this end, the lattice parameter of Ni was accurately determined by correcting for influences of residual stress and stacking faults in the thin films and the ball-milled Ni powders, respectively. The non-monotonic variation of the lattice constant was discussed in terms of competing mechanisms: interface stress induced contraction versus magnetic multidomain to single-domain transition occurring at about the crystallite size value where a minimum value for the lattice parameter is observed.

Rock-magnetic properties confirm the eolian origin of Miocene sequences from the west of the Chinese Loess Plateau

Diagnostic rock-magnetic characteristics of Miocene sequences from the western part of the Chinese Loess Plateau are used to confirm the eolian nature of sections the origin of which has been a matter of recent dispute (Alonso-Zarza et al., 2009, 2010; Guo et al. 2010). The key magnetic properties include (i) detailed correlation of both the orbitally timed and supra-orbital variations in magnetic properties between widely separated sections, (ii) the bi-modal distribution of magnetic properties with respect to particle size, reflecting in situ neoformation alongside the deposition of detrital minerals derived from the source areas, (iii) the consistent presence, in the clay fractions, of fine ferrimagnetic grains close to the superparamagnetic/stable single domain transition, all within the size range characteristic of those formed by weathering and pedogenesis under at least partially aerobic conditions, and (iv) absence of evidence for lacustrine indicators such as bacterial magnetosome assemblages, sub-oxic diagenesis or greigite formation.

Observation of double- to single-domain transition on the Eu/Si(1 0 0) surface by LEED and STM

The orientational phase diagram and morphology of the Eu-adsorbed Si(1 0 0) surface miscut by 0.4° have been studied by low-energy electron diffraction and scanning tunneling microscopy. We demonstrate that the original double-domain configuration with single-layer steps on the Si(1 0 0) substrate can be drastically broken at 0.4 monolayer (ML) of Eu. At this coverage, the ordered domain pattern formed by topographically non-equivalent terraces with Eu-induced 2 × 3 and “2 × 1” (so-called “wavy” structure) reconstructions is found, while no orthogonal 3 × 2 and “1 × 2” domains are observed. A model of the single-domain surface is proposed. The origin of the double- to single-domain transition found for the Eu/Si(1 0 0) system is discussed.

Evolution of step and terrace structure on [formula omitted]- and [formula omitted]-miscut Si(1 1 1) surfaces upon formation of triple- and single-domain Yb-induced 3 × 2 reconstruction

Evolution of step and terrace structures on vicinal Si(1 1 1) surfaces miscut 4° in the [ 1 ̄ 1 ̄ 2] and [1 1 2 ̄ ] directions after the 3 × 2-Yb formation and subsequent annealing in the temperature range of 500–790 °C has been investigated by room temperature scanning tunneling microscopy and low-energy electron diffraction. On the [ 1 ̄ 1 ̄ 2] -miscut surface, steps favor the nucleation of Yb-induced 3 × 2 domains oriented along step edges and depress the other domain orientations after properly chosen annealing temperature. Simultaneously with the triple- to single-domain transition, the single- and triple-layer step structure observed for the Si(1 1 1)-7 × 7 and 3 × 2-Yb triple-domain surface is converted into the mixture of step heights where double-layer steps dominate. Contrary to the case of [ 1 ̄ 1 ̄ 2] -miscut surface, no 3 × 2-Yb triple- to single-domain transition is observed after annealing cycles on the [1 1 2 ̄ ] -miscut surface. However, the step bunch splitting and the more unified 3 × 2-Yb domains are revealed after annealing at 750 °C.

Correlations Between X-Ray Microstructures and Magnetic Properties of CoCrTa Alloy thin Films

AbstractThin film structures determined by X-ray reflection and transmission diffractometer methods has been used to co rrelate with th e magnetic p roperties of CoCrTa thin films. Well-crystallized CoCrTa alloy particles with strong h.c.p. c-axis preferred oriented normal to the film surfaces were found to be mainly responsible for the perpendicular magnetic anisotropy observed in specimens IL and 8L, whereas poorly crystallized CoCrTa particles in the 150Å thick magnetic layers of a third specimen 33L have led to an observed longitudinal magnetization. Microstrains generated by the crystalline - amorphous interface stresses induced an enhanced perpendicular magnetic anisotropy in specimen 8L. Values of crystallite size D determined from the Warren-Averbach analysis were correlated with the coercivities He. Analysis of the He vs. D curve indicated th a t the critical particle size for a magnetic multi- to single-domain transition was 270± 25Å. The retention in coercivity (Hc=175 Oe) at a small particle size (D=75Å) in specimen 8L suggested that strong interparticle interactions existed among the wellcrystallized CoCrTa particles. A much smaller retention in coercivity (Hc=90 Oe) at D=70Å of specimen 33L indicated the inter particle interactions in poorly crystallized CoCrTa layers were relatively weak.