Abstract The study of ferromagnetic nanoparticles is of broad scientific interest, crossing the t... more Abstract The study of ferromagnetic nanoparticles is of broad scientific interest, crossing the traditional boundaries between physics, chemistry, and biology. Indeed, recent research can be found on magnetic nanoparticle assemblies in all of these fields. While we do not aim to provide an exhaustive study on the science of magnetic nanoparticles, we will aim to give a brief introduction to the physics of this class of material. In particular, we will outline some of the recent scientific research on these systems including both theoretical and experimental aspects. After providing a broad and general overview to theoretical aspects to the study of magnetic nanoparticle assemblies, including both equilibrium and dynamical considerations, we will discuss some of the principal experimental techniques which have been employed in the study of their collective magnetic properties. We pay particular attention to the interplay between the intrinsic properties of the material and the size, shape, temperature, and dipolar interactions, which define the global state of the nanoparticle array. We further introduce and discuss experimental methods used to characterize magnetic nanoparticle assemblies, providing a brief overview of the methodology and select some representative results to demonstrate the type of information that can be obtained with each technique under varying experimental conditions.
We present a microscopic model for nanoparticles, of the maghemite (γ their magnetic properties. ... more We present a microscopic model for nanoparticles, of the maghemite (γ their magnetic properties. On account of Mössbauer spectroscopy and high-field magnetisation results, we consider a particle as composed of a core and a surface shell of constant thickness. The magnetic state in the particle is described by the anisotropic classical Dirac-Heisenberg model including exchange and dipolar interactions and bulk and surface anisotropy. We consider the case of ellipsoidal (or spherical) particles with free boundaries at the surface. Using a surface shell of constant thickness (∼ 0.35 nm) we vary the particle size and study the effect of surface magnetic disorder on the thermal and spatial behaviors of the net magnetisation of the particle. We study the shift in the surface "critical region" for different surface-to-core ratios of the exchange coupling constants. It is also shown that the profile of the local magnetisation exhibits strong temperature dependence, and that surfac...
We investigate the effect of surface anisotropy in a spherical many-spin magnetic nanoparticle. B... more We investigate the effect of surface anisotropy in a spherical many-spin magnetic nanoparticle. By computing minor loops, two-dimensional (2D) and 3D energyscape, and by investigating the behavior of the net magnetization, we show that in the case of not too strong surface anisotropy the behavior of the many-spin particle may be modeled by that of a macrospin with an effective energy containing uniaxial and cubic anisotropy terms. This holds for both the transverse and N\'eel's surface anisotropy models.
We regard the manifold f defined by the equations of motion (EM) of the gauge and ghost fields w.... more We regard the manifold f defined by the equations of motion (EM) of the gauge and ghost fields w.r.t. the gauge-fixed action as a fiber bundle over the manifold F defined by the EM of the gauge fields only w.r.t. the classical action. Accordingly, the BRST operator is interpreted as the nilpotent exterior derivative on F ; the ghost field appears as the differential 1-form. This fiber bundle setup allows us to prove that any gauge condition on f is equivalent to another one on the base manifold F and does not break the BRST symmetry of the quantized theory. MIRAMARE TRIESTE July 1992 Permanent address: Laboratoire de Physique Theorique, Universite Bordeaux I, 19 Rue du Solarium, F 33 175 Gradignan Cedex, France. Unite Associee au CNRS, U.A. 764. Permanent address: Laboratoire de Physique Theorique, Departement de Physique Faculte des Sciences, Universite MV, Av. Ibn Battota, B.P. 1014, Rabat, Morocco.
Abstract The study of ferromagnetic nanoparticles is of broad scientific interest, crossing the t... more Abstract The study of ferromagnetic nanoparticles is of broad scientific interest, crossing the traditional boundaries between physics, chemistry, and biology. Indeed, recent research can be found on magnetic nanoparticle assemblies in all of these fields. While we do not aim to provide an exhaustive study on the science of magnetic nanoparticles, we will aim to give a brief introduction to the physics of this class of material. In particular, we will outline some of the recent scientific research on these systems including both theoretical and experimental aspects. After providing a broad and general overview to theoretical aspects to the study of magnetic nanoparticle assemblies, including both equilibrium and dynamical considerations, we will discuss some of the principal experimental techniques which have been employed in the study of their collective magnetic properties. We pay particular attention to the interplay between the intrinsic properties of the material and the size, shape, temperature, and dipolar interactions, which define the global state of the nanoparticle array. We further introduce and discuss experimental methods used to characterize magnetic nanoparticle assemblies, providing a brief overview of the methodology and select some representative results to demonstrate the type of information that can be obtained with each technique under varying experimental conditions.
We present a microscopic model for nanoparticles, of the maghemite (γ their magnetic properties. ... more We present a microscopic model for nanoparticles, of the maghemite (γ their magnetic properties. On account of Mössbauer spectroscopy and high-field magnetisation results, we consider a particle as composed of a core and a surface shell of constant thickness. The magnetic state in the particle is described by the anisotropic classical Dirac-Heisenberg model including exchange and dipolar interactions and bulk and surface anisotropy. We consider the case of ellipsoidal (or spherical) particles with free boundaries at the surface. Using a surface shell of constant thickness (∼ 0.35 nm) we vary the particle size and study the effect of surface magnetic disorder on the thermal and spatial behaviors of the net magnetisation of the particle. We study the shift in the surface "critical region" for different surface-to-core ratios of the exchange coupling constants. It is also shown that the profile of the local magnetisation exhibits strong temperature dependence, and that surfac...
We investigate the effect of surface anisotropy in a spherical many-spin magnetic nanoparticle. B... more We investigate the effect of surface anisotropy in a spherical many-spin magnetic nanoparticle. By computing minor loops, two-dimensional (2D) and 3D energyscape, and by investigating the behavior of the net magnetization, we show that in the case of not too strong surface anisotropy the behavior of the many-spin particle may be modeled by that of a macrospin with an effective energy containing uniaxial and cubic anisotropy terms. This holds for both the transverse and N\'eel's surface anisotropy models.
We regard the manifold f defined by the equations of motion (EM) of the gauge and ghost fields w.... more We regard the manifold f defined by the equations of motion (EM) of the gauge and ghost fields w.r.t. the gauge-fixed action as a fiber bundle over the manifold F defined by the EM of the gauge fields only w.r.t. the classical action. Accordingly, the BRST operator is interpreted as the nilpotent exterior derivative on F ; the ghost field appears as the differential 1-form. This fiber bundle setup allows us to prove that any gauge condition on f is equivalent to another one on the base manifold F and does not break the BRST symmetry of the quantized theory. MIRAMARE TRIESTE July 1992 Permanent address: Laboratoire de Physique Theorique, Universite Bordeaux I, 19 Rue du Solarium, F 33 175 Gradignan Cedex, France. Unite Associee au CNRS, U.A. 764. Permanent address: Laboratoire de Physique Theorique, Departement de Physique Faculte des Sciences, Universite MV, Av. Ibn Battota, B.P. 1014, Rabat, Morocco.
Uploads
Papers by H. Kachkachi