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Background: In recent years, the application of nanotechnology in several fields of bioscience and biomedicine has been studied. The use of nanoparticles for the targeted delivery of substances has been given special attention and is of particular interest in the treatment of plant diseases. In this work both the penetration and the movement of iron-carbon nanoparticles in plant cells have been analyzed in living plants of Cucurbita pepo.

The results open a wide range of possibilities for using magnetic nanoparticles in general plant research and agronomy. The nanoparticles can be charged with different substances, introduced within the plants and, if necessary, concentrated into localized areas by using magnets. Also simple or more complex microscopical techniques can be used in localization studies.

The effect of the substitution for Mn with Al in the magnetoresistive perovskite La 2/3 Ca 1/3 MnO 3 has been studied by preparing the series La 2/3 Ca 1/3 Mn 1Ϫx Al x O 3 (xр0.2). A careful study of the magnetic, structural, and transport properties has been carried out by means of electrical resistance, magnetoresistance, ac magnetic susceptibility, x-ray-diffraction, and neutron-diffraction techniques. Up to xϭ0.05 the Curie temperature ͑and the associated metal-insulator transition͒ decreases drastically with Al doping and the magnetoresistive properties do not change very much. For xу0.1 the lattice spontaneously begins to lose oxygen atoms and for xϭ0.2, 3% of oxygen vacancies are present. This fact along with the random distribution of the Al atoms makes these compounds rather disordered from a structural and magnetic point of view. However, the magnetoresistance is enhanced, reaching colossal values of 10 7 % at Hϭ12 T at low temperatures for xϭ0.2.

The effects of magnetic field and pressure on the unusual spontaneous behavior of La 2/3 Ca 1/3 MnO 3 have been thoroughly investigated. Resistivity and volume thermal expansion, both under magnetic field and pressure, ac susceptibility under pressure, magnetostriction, magnetoresistance, and neutron diffraction measurements, have allowed us to determine the relevant underlying mechanisms in this system. Above T c the neutron measurements reveal short-range ferromagnetic correlations and the anomalous volume thermal expansion indicates that local distortions are present. Both experiments support the formation of magnetic polarons above T c . At T c the compound undergoes a paramagnetic-ferromagnetic transition accompanied by an insulatormetal-like transition with anomalies in the electrical and volume properties. Above T c the magnetic field and the pressure favor electrical conduction by enhancing the double-exchange interaction. Below T c the metallic state is favored by the magnetic field and the pressure in a different way.

We present a study on the magnetic properties of naked and silica-coated Fe 3 O 4 nanoparticles with sizes between 5 and 110 nm. Their efficiency as heating agents was assessed through specific power absorption (SPA) measurements as a function of particle size and shape. The results show a strong dependence of the SPA with the particle size, with a maximum around 30 nm, as expected for a Néel relaxation mechanism in single-domain particles. The SiO 2 shell thickness was found to play an important role in the SPA mechanism by hindering the heat outflow, thus decreasing the heating efficiency. It is concluded that a compromise between good heating efficiency and surface functionality for biomedical purposes can be attained by making the SiO 2 functional coating as thin as possible. 81.16.Be, 75.50.+a PACS: