Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: Influence of the surface and of interparticle interactions

Physical Review B (Impact Factor: 3.66). 02/2002; 65(9). DOI: 10.1103/PhysRevB.65.094409
Source: arXiv

ABSTRACT We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.2 nm (25–7000 atoms) prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared with previous structural characterizations. The distribution of activation energies has been independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant Keff. We find that Keff is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal process is shown to proceed classically down to the lowest temperature investigated (1.8 K).

  • [Show abstract] [Hide abstract]
    ABSTRACT: A Reply to the Comment by Mikkel F. Hansen and Steen Mørup.
    Physical Review Letters 02/2003; 90(5). · 7.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: (FexNi1−x)4N (0.5 ≤ x ≤ 0.8) compounds were prepared by combining a simple reduction route with nitridation process under flowing ammonia gas at various temperatures. The microstructure as well as magnetic and microwave absorbing properties of as-prepared products was investigated. The reflection loss of (FexNi1−x)4N-paraffin composites with a filler mass fraction of 50% was calculated from permittivity and permeability, and the magnetization hysteresis loops of the composites were measured at 300 K. It has been found that the saturation magnetization value of as-prepared products increases as x rises from 0.50 to 0.80. Particularly, the reflection loss of (Fe0.67Ni0.33)4N-paraffin composite (x = 0.67) with a matching thickness of 2 mm is −17.5 dB at 12.0 GHz, lower than that of the composites with x = 0.50, 0.75, and 0.80. Moreover, (Fe0.67Ni0.33)4N-paraffin composite with a matching thickness of 2 mm has the reflection loss exceeding −10 dB in a maximum frequency range of 10.5–14.0 GHz, which is ascribed to its proper match of electromagnetic parameters and large magnetic loss. In one word, (Fe0.67Ni0.33)4N has great potential as a thin broadband microwave absorbent.
    Journal of Applied Physics 03/2013; 113(11). · 2.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Due to finite size effects, such as the high surface-to-volume ratio and different crystal structures, magnetic nanoparticles are found to exhibit interesting and considerably different magnetic properties than those found in their corresponding bulk materials. These nanoparticles can be synthesized in several ways (e.g., chemical and physical) with controllable sizes enabling their comparison to biological organisms from cells (10-100 μm), viruses, genes, down to proteins (3-50 nm). The optimization of the nanoparticles' size, size distribution, agglomeration, coating, and shapes along with their unique magnetic properties prompted the application of nanoparticles of this type in diverse fields. Biomedicine is one of these fields where intensive research is currently being conducted. In this review, we will discuss the magnetic properties of nanoparticles which are directly related to their applications in biomedicine. We will focus mainly on surface effects and ferrite nanoparticles, and on one diagnostic application of magnetic nanoparticles as magnetic resonance imaging contrast agents.
    International Journal of Molecular Sciences 01/2013; 14(11):21266-21305. · 2.46 Impact Factor

Full-text (2 Sources)

Available from
Jun 4, 2014

Similar Publications