F. D’Orazio

Surface effects in noninteracting and interacting γ-Fe2O3 nanoparticles

Abstract From AC susceptibility, magnetization and Mossbauer spectroscopy measurements, we show the dominant role of the surface properties and surface-to-core exchange coupling on the static and dynamic properties of γ-Fe 2 O 3 particles (2.7, 4.6 and 8.7xa0nm) dispersed in a polymer or powdered. Measurements of the switching field of individual particles are presented, demonstrating basic surface effects.

Magnetic properties of maghemite nanoparticle systems: surface anisotropy and interparticle interaction effects

Abstract The static and dynamic magnetic properties of powders of maghemite nanoparticles with average diameter D =2.7, 4.6 and 8.7xa0nm have been investigated by magnetisation, AC susceptibility at variable frequency (5 ν 4 xa0Hz) and Mossbauer spectroscopy measurements. The results provide an insight into the correlation between intra-particle and inter-particle effects.

Magnetic and structural properties of Fe/Al multilayers

Abstract Static and dynamic magnetic properties of Fe/Al multilayers, grown by RF magnetron sputtering on Si(1xa00xa00), are investigated. Magneto-Optical Kerr Effect shows in-plane uniaxial anisotropy and very soft behavior on six samples characterized by different number of bilayers. The coercive fields range between 2 and 8xa0Oe. Brillouin light scattering reveals spin-wave surface modes that depend on the number of Fe/Al repetitions and are attributed to the total multilayer stack and to individual layers.

Spin freezing in maghemite nanoparticle systems

Abstract The static and dynamical properties of two powder samples of γ -Fe 2 O 3 nanoparticles, with average diameter D =2.7 and 4.6xa0nm have been investigated by AC and DC susceptibility measurements. The results provide evidence of a collective dynamical freezing due to dipole interactions, at a size-dependent temperature ( T =95xa0K for D =2.7xa0nm; 130xa0K for D =4.6xa0nm ). Between 50 and 60xa0K, a change of magnetic regime occurs for both samples induced by increasing surface effects with decreasing temperature.

Dynamic studies of γ-Fe2O3 nanoparticle systems

Abstract The dynamic properties of two series of samples of γ-Fe 2 O 3 nanoparticles (average diameter D =4.7 and 8.3xa0nm), dispersed in a polymer, were investigated by means of linear and non-linear AC susceptibility measurements over a large frequency range ( 5 4 Hz ). The temperature and frequency dependence of both linear and non-linear susceptibilities was analysed for different degrees of dispersion of particles in the polymer, i.e. for different strengths of inter-particle interactions.

Blocking temperature distribution in implanted Co–Ni nanoparticles obtained by magneto-optical measurements

Abstract Three samples of Co–Ni alloy nanoparticles with different compositions were prepared by sequential ion implantation in silica slides. Transmission electron microscopy (TEM) showed the presence of spherical nanoparticles dispersed in the matrix. Magneto-optical Kerr effect analysis identified two magnetic components attributed to superparamagnetic particles in unblocked and blocked states, respectively. Magnetic field loops were measured as a function of temperature. Blocking temperature distributions were obtained; and their comparison with the size distributions derived from TEM provided the average magnetic anisotropy of the particles.

Interface effects on the magnetic properties of exchange coupled Co/Fe multilayers studied by Brillouin light scattering

Abstract Exchange-coupled 5[Co ( x ) /Fe (3 x ) ]/Co ( x ) with x =5, 10, 15xa0nm multilayers were grown by UHV electron-beam evaporation. The influence of the interface magnetic anisotropy and interlayer exchange interaction on the magnetic properties was studied by means of Brillouin light scattering from thermally excited spin waves. Both the Damon–Eshbach surface mode of the total multilayer and bulk standing modes are present in the BLS spectra. A careful study of spin waves frequency dependence on the applied magnetic field allowed the determination of the magnetic parameters of the Co/Fe multilayers.

Magneto-optical characterization of MnxGe1- x alloys obtained by ion implantation

Magneto-optical Kerr effect hysteresis loops at various wavelengths in the visible/near-infrared range have been used to characterize the magnetic properties of alloys obtained by implanting Mn ions at fixed energy in a Ge matrix. The details of the hysteresis loops reveal the presence of multiple magnetic contributions. They may be attributed to the inhomogeneous distribution of the magnetic atoms and, in particular, to the known coexistence of diluted Mn in the Ge matrix and metallic Mn-rich nanoparticles embedded in it [Phys. Rev. B 73 (2006) 195207].