J. Bartolomé

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

We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.2 nm (25\char21{}7000 atoms) prepared by sequential sputtering of Co and

Magnetotransport through the spin-reorientation transition in Tm2Fe14B

{\mathrm{Al}}_{2}{\mathrm{O}}_{3}.

Magnetic nanoparticles with bulklike properties (invited)

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

Size-dependent properties of magnetoferritin.

{K}_{\mathrm{eff}}.

Neutron powder diffraction study of the desorption of deuterium in Nd2Fe17Dx≈5

We find that

Structural and magnetic properties of R/sub 2/Fe/sub 14/BH/sub x/

{K}_{\mathrm{eff}}

Magnetic and thermal properties of 4 f − 3 d ladder-type molecular compounds

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).

Low-temperature specific heat of NdMO3(M=Co, Fe, Cr, Ni): Magnetic ordering of Nd

The electrical resistivity and Hall effect for a single crystal of Tm2Fe14B have been measured over the range of temperature (T) from 4 to 600 K in magnetic fields of up to 5 T. The resistivity exhibits a small step-like rise at the spin-reorientation temperature Ts, which is 311 K, and a broad minimum at 535 K. In addition, the Hall coefficient shows an anomaly at Ts, and drops sharply as T approaches the Curie temperature (549 K) from below. The lower-temperature anomalies, both in the resistivity and in the Hall coefficient, show that the spin-reorientation transition in Tm2Fe14B is of first order. The high-temperature Hall anomaly is probably produced by critical spin fluctuations near the Curie point. Dominant scattering mechanisms that underlie the Hall effect and magnetoresistance in Tm2Fe14B are inferred.

YBa2Cu3O7−δ low field diamagnetic properties: A multiharmonic analysis

The magnetic behavior of Fe3� xO4 nanoparticles synthesized by either high-temperature decomposition of an organic iron precursor or low-temperature coprecipitation in aqueous conditions is compared. Transmission electron microscopy, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and magnetization measurements show that nanoparticles synthesized by thermal decomposition display high crystal quality and bulklike magnetic and electronic properties, while nanoparticles synthesized by coprecipitation show much poorer crystallinity and particlelike phenomenology, including reduced magnetization, high closure fields, and shifted hysteresis loops. The key role of the crystal quality is thus suggested, because particlelike behavior for particles larger than about 5 nm is observed only when the particles are structurally defective. These conclusions are supported by Monte Carlo simulations. It is also shown that thermal decomposition is capable of producing nanoparticles that, after further stabilization in physiological conditions, are suitable for biomedical applications such as magnetic resonance imaging or biodistribution studies. V C 2011 American Institute of Physics. [doi:10.1063/1.3559504]

Thermophysical properties of the intermetallic Mn3MN perovskites II. Heat capacity of manganese zinc nitride: Mn3ZnN and manganese gallium nitride: Mn3GaN

We report a detailed experimental study of maghemite nanoparticles, with sizes ranging from 1.6 to 6 nm, synthesized inside a biological mould of apoferritin. The structural characterization of the inorganic cores, using TEM and x-ray diffraction, reveals a low degree of crystalline order, possibly arising from the nucleation and growth of multiple domains inside each molecule. We have also investigated the molecular structure by means of atomic force microscopy in liquid. We find that the synthesis of nanoparticles inside apoferritin leads to a small, but measurable, decrease in the external diameter of the protein, probably associated with conformational changes. The magnetic response of the maghemite cores has been studied by a combination of techniques, including ac susceptibility, dc magnetization and Mössbauer spectroscopy. From the equilibrium magnetic response, we have determined the distribution of magnetic moments per molecule. The results show highly reduced magnetic moments. This effect cannot be ascribed solely to the canting of spins located at the particle surface but, instead, it suggests that magnetoferritin cores have a highly disordered magnetic structure in which the contributions of different domains compensate each other. Finally, we have also determined, for each sample, the distribution of the activation energies required for the magnetization reversal and, from this, the size-dependent magnetic anisotropy constant K. We find that K is enormously enhanced with respect to the maghemite bulk value and that it increases with decreasing size. The Mössbauer spectra suggest that low-symmetry atomic sites, probably located at the particle surface and at the interfaces between different crystalline domains, are the likely source of the enhanced magnetic anisotropy.