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. Results: The nanoparticles were applied in planta using two different application methods, injection and spraying, and magnets were used to retain the particles in movement in specific areas of the plant. The main experimental approach, using correlative light and electron microscopy provided evidence of intracellular localization of nanoparticles and their displacement from the application point. Long range movement of the particles through the plant body was also detected, particles having been found near the magnets used to immobilize and concentrate them. Furthermore, cell response to the nanoparticle presence was detected. Conclusion: Nanoparticles were capable of penetrating living plant tissues and migrating to different regions of the plant, although movements over short distances seemed to be favoured. These findings show that the use of carbon coated magnetic particles for directed delivery of substances into plant cells is a feasible application.

A systematic study of the effect of oxygen content on the structural, magnetotransport, and magnetic properties has been undertaken on a series of ${\mathrm{LaMnO}}_{3+\mathrm{\delta }}$ samples, with $\delta =0,$ 0.025, 0.07, 0.1, and 0.15. Measurements of the ac initial magnetic susceptibility, magnetization, magnetoresistance, and neutron diffraction, including small-angle neutron scattering (SANS), were performed in the temperature range 1–320 K using high magnetic fields up to 12 T. The antiferromagnetic order found in ${\mathrm{LaMnO}}_3$ evolves towards a ferromagnetic order as δ increases. This behavior is accompanied by a drastic reduction of the static Jahn-Teller distortion of the ${\mathrm{MnO}}_6$ octahedra. The ferromagnetic coupling weakens for $\delta >~\mathrm{0.1.}$ The magnetic behavior is interpreted by taking into account two effects caused by the increase in δ: cation vacancies and ${\mathrm{Mn}}^{4+}{/\mathrm{M}\mathrm{n}}^{3+}$ ratio enhancement. The orthorhombic crystallographic structure becomes unstable at room temperature for $\delta >~\mathrm{0.1.}$ The sample $\delta =0.1\mathrm{}$ shows a structural transition from rhombohedral to orthorhombic below $T_S\approx 300\mathrm{K}$ with a huge change in the cell volume. All the studied compounds were found to be insulating at low temperatures with no appreciable magnetoresistance, except for $\delta =0.15,$ in which we observed a large value for the magnetoresistance. The SANS results indicate that magnetic clustering effects are important below $T_C$ for $\delta >~0.07,$ which could explain the intriguing ferromagnetic insulator state. In the $\delta =0.07\mathrm{}$ and $\delta =0.10\mathrm{}$ samples we found at temperatures below $T_C$ magnetic and structural anomalies that are characteristic of charge ordering.

The great potential of using nanodevices as delivery systems to specific targets in living organisms was first explored for medical uses. In plants, the same principles can be applied for a broad range of uses, in particular to tackle infections. Nanoparticles tagged to agrochemicals or other substances could reduce the damage to other plant tissues and the amount of chemicals released into the environment. To explore the benefits of applying nanotechnology to agriculture, the first stage is to work out the correct penetration and transport of the nanoparticles into plants. This research is aimed (a) to put forward a number of tools for the detection and analysis of core-shell magnetic nanoparticles introduced into plants and (b) to assess the use of such magnetic nanoparticles for their concentration in selected plant tissues by magnetic field gradients. plants were cultivated in vitro and treated with carbon-coated Fe nanoparticles. Different microscopy techniques were used for the detection and analysis of these magnetic nanoparticles, ranging from conventional light microscopy to confocal and electron microscopy. Penetration and translocation of magnetic nanoparticles in whole living plants and into plant cells were determined. The magnetic character allowed nanoparticles to be positioned in the desired plant tissue by applying a magnetic field gradient there; also the graphitic shell made good visualization possible using different microscopy techniques. 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.

Ac initial magnetic susceptibility, thermal expansion, and magnetostriction measurements were performed on a polycrystal of ${\mathrm{La}}_{0.60}{\mathrm{Y}}_{0.07}{\mathrm{Ca}}_{0.33}{\mathrm{MnO}}_3$ manganese oxide. We observed a spontaneous volume magnetic contribution ( $\cong 1\times {10}^{-3\mathrm{}}$ at $T_C=160\mathrm{}\pm 5\mathrm{K}$). This extra contribution sharply decreases at $T_C$ as a consequence of the metal ( $M$)–insulator ( $I$) transition, and is suppressed under an applied magnetic field. This shows that the transition to the $M$ state is induced by the field in the $I$ regime, producing strong magnetoelastic effects. The present results demonstrate the close relationship between magnetoelastic and magnetotransport properties in this compound.

The effects of magnetic field and pressure on the unusual spontaneous behavior of ${\mathrm{La}}_{2/3}$ ${\mathrm{Ca}}_{1/3}$ ${\mathrm{MnO}}_3$ 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 ${\mathit{T}}_{\mathit{c}}$ 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 ${\mathit{T}}_{\mathit{c}}$. At ${\mathit{T}}_{\mathit{c}}$ the compound undergoes a paramagnetic-ferromagnetic transition accompanied by an insulator-metal-like transition with anomalies in the electrical and volume properties. Above ${\mathit{T}}_{\mathit{c}}$ the magnetic field and the pressure favor electrical conduction by enhancing the double-exchange interaction. Below ${\mathit{T}}_{\mathit{c}}$ the metallic state is favored by the magnetic field and the pressure in a different way. © 1996 The American Physical Society.