Finite-size versus Surface effects in nanoparticles

We study the finite-size and surface effects on the thermal and spatial behaviors of the magnetisation of a small magnetic particle. We consider two systems: 1) A box-shaped isotropic particle of simple cubic structure with either periodic or free boundary conditions. This case is treated analytically using the isotropic model of D-component spin vectors in the limit $D\to \infty$, including the magnetic field. 2) A more realistic particle ($\gamma$-Fe$_{2}$O$_{3}$) of ellipsoidal (or spherical) shape with open boundaries. The magnetic state in this particle is described by the anisotropic classical Dirac-Heisenberg model including exchange and dipolar interactions, and bulk and surface anisotropy. This case is dealt with by the classical Monte Carlo technique. It is shown that in both systems finite-size effects yield a positive contribution to the magnetisation while surface effects render a larger and negative contribution, leading to a net decrease of the magnetisation of the small particle with respect to the bulk system. In the system 2) the difference between the two contributions is enhanced by surface anisotropy. The latter also leads to non saturation of the magnetisation at low temperatures, showing that the magnetic order in the core of the particle is perturbed by the magnetic disorder on the surface. This is confirmed by the profile of the magnetisation.Comment: 6 pages of RevTex including 4 Figures, invited paper to 3rd EuroConference on Magnetic Properties of Fine Nanoparticles, Barcelona, October 9

Three-dimensional rotation of even-even triaxial nuclei

With the self-consistent three-dimensional cranked Hartree-Fock-Bogoliubov (3d-cranked HFB) method, various types of rotational motion near the yrast line are investigated in an even-even nucleus in the $A\simeq 130$ mass region ($^{134}_{58}$Ce$_{76}$). The possibilities of chiral rotations, tilted-rotations, and dynamical aspects of these rotations are discussed through the analysis of the 3d-cranked HFB solutions. Although a stable planar solution of the chiral rotation is obtained, an aplanar chiral configuration is found to be unstable when triaxial deformation is treated self-consistently.Comment: 4 pages, 3 figures; accepted for publication in Phys. Lett.

Summer Preview of the 2007 Annual Meeting October 24-27, 2007

Summer Preview of the Annual Meetin

MWERA 2007 Highlights

Annual Meeting Highlight

Mid-Western Educational Research Association 2007 Annual Meeting, October 24-27, 2007

Call for Proposal

Contemporary Treatment of Reliability and Validity in Educational Assessment

MWERA 2009 Presidential Addres