J. Stankiewicz

University of Zaragoza, Caesaraugusta, Aragon, Spain

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Publications (6)10.73 Total impact

  • J Stankiewicz, F Luis, A Camon, M Kroll, J Bartolome, W Blau
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    ABSTRACT: The average switching fields H-c of Fe nanowires with diameter D approximate to 12.5 nm prepared in porous alumina membranes have been measured down to 300 mK, using SQUID and micro-Hall magnetometry. On cooling from T = 300 to 5 K, H-c increases monotonically as predicted for thermally-activated magnetization-reversal models. Both the zero-temperature limit of H-c and the activation energy obtained are much smaller than those predicted for rotation at unison. Below 5 K, H-c shows a maximum, which we attribute to a crossover to a different reversal mechanism. (C) 2003 Elsevier B.V. All rights reserved.
    Journal of Magnetism and Magnetic Materials 01/2004; 272(Part 3, SI):1637-1639. · 2.00 Impact Factor
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    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).
    Physical Review B 02/2002; 65(9). · 3.66 Impact Factor
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    Acta Physica Polonica Series a 01/2002; 101(2):289. · 0.53 Impact Factor
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    ABSTRACT: We study the magnetic properties of Co clusters with diameters between 0.8 and 3nm prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data. Comparing this to the distribution of activation energies, obtained from the AC susceptibility, we have determined accurately the effective anisotropy constant Keff. We find that Keff is enhanced with respect to the bulk value and it increases as the average particle size decreases.
    Journal of Magnetism and Magnetic Materials 01/2002; 242:575-577. · 2.00 Impact Factor
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    ABSTRACT: Nd2Fe14-xSixB (x=0.25, 0.5, 0.75, 1.0, 1.5, 2.0) intermetallic compounds were investigated by magnetometry, 57Fe Mössbauer effect, electric resistivity, and differential scanning calorimetry mainly in the vicinity of the spin reorientation temperature, TSR. The Curie temperature, TC, and TSR were determined for different compositions and the spin phase diagram was constructed. 57Fe Mössbauer spectra showed noticeable changes in the reorientation region. For temperatures above the transition, the spectra were analysed using 6 Zeeman patterns associated with 6 inequivalent crystal sites in Nd2Fe14B according to site occupations (16k1:16k2:8j1:8j2:4c:4e). In the transition region, 12 subspectra had to be incorporated in the analysis. Electric resistivity measurements showed a typical metallic behaviour with no anomalies in the magnetic transition region. Differential scanning calorimetry measurements revealed broad endothermic two stage peaks around TSR.
    Acta Physica Polonica Series a 02/1999; · 0.53 Impact Factor
  • J. Bartolomé, J. Stankiewicz
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    ABSTRACT: The electrical resistivity of R2Fe14C (R = Lanthanide series) polycrystalline samples was measured over the temperature range of 4–700 K. At low temperatures the scattering of electrons is caused by spin-wave modes involving all spins. In the paramagnetic region, T > Tc, the magnetic resistivity saturates. Finally, the total resistivity increases linearly with temperature due to phonon scattering.
    Journal of Magnetism and Magnetic Materials 01/1999; 196:776-778. · 2.00 Impact Factor