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• W75589637 abstract "The interaction between magnetic nanoparticles and high frequencies, such as microwaves or terahertz waves, is one of the most active field of research, with interesting applications in the screening of electromagnetic waves in electronic circuits, or medical applications such as the magnetic hyperthermia, or contrast in Nuclear Magnetic Imaging. Finite size effects are important in this field because they modify the basic properties of magnetic nanoparticles, for example, the blocking and the Curie temperature. In this thesis is shown new phenomena on nanomagnetism such as the colossal reduction of the Curie temperature in CoFe2O4 nanoparticles, the interaction between magnetic nanoparticles with microwave waves, the magnetic behavior of gold nanoparticles modified by different capping molecules, and new technological applications using terahertz radiation, such as the characterization of the drug diffusion into artificial membranes and human skin. In the colossal reduction of the Curie temperature in CoFe2O4 nanoparticles due to size effects, it was observed a distortion in the crystallographic structure for these ferrite nanoparticles with mean diameter below 3 nm, and thus, the exchange interaction among the atoms that form the nanoparticles also varies. Consequently, the Curie temperature, which is round 700 K for bulk CoFe2O4, reduces until 10 K for nanoparticles with a size below 3 nm. That reduction was observed measuring the stable and metastable curves ZFC-FC, the isothermal magnetization in the temperature range between 2 and 300 K, and the ac-magnetic susceptibility in the frequency range belong 1 Hz to 1kHz. Furthermore, the magnetic relaxation curves at zero field showed a blocking temperature in the proximity of the reduced Curie temperature, it being the first time where the blocking temperature and the Curie temperature for a system of magnetic nanoparticles have a similar value. All these properties can be studied measuring the microwave absorption of the magnetic nanoparticles, between 1 and 20 GHz. Using this experimental technique, the basic properties and the magnetization dynamics of magnetic nanoparticles is characterized in a fast way, and in addition, it open new technological applications in electronics and medicine. The surface modification as well as the magnetic properties of gold nanoparticles, using different capping molecules, have also been studied during this thesis. The type of bond at the surface of the nanoparticle stablished by the capping molecule generates a ferromagnetic shell that envelopes a diamagnetic core. This effect is due to the localization of surface charges in the proximity of the bond surface atom. In addition, it turns out that finire size effects in the gold nanoparticle affects to the size of the ferromagnetic domains, and hence, it is a crucial parameter that valance the interaction between the diamagnetic core and the ferromagnetic shell. Finally, in this work it is exposed new technological applications performed by terahertz radiation, which is compressed between 0.3 and 3THz, for example in the study of layered materials, the creation of terahertz tagging using resonance phenomenon at these frequencies, the detection of biomolecules by their characteristic resonances, and the study of the dffusion of topic drugs into artificial membranes and abdominal human skin. The principle advantages that represent terahertz waves in front of other radiations are that they are non-ionizating, non-invasive, contactless and their spatial resolution. As principal application, it is presented how the permeation process of topic drugs can be studied by terahertz waves.This work was performed studying the time ight of the T-ray between the emitter/receptor and the drop that contains the topic formulation, previously pipetted onto an artificial membrane or human skin. Using this technique was possible to obtain a rate of mass transfer of the topic drug that fully characterized the permeation process. This technique can complement other currently techniques such as skin striping but it carry out by a non-invasive and contactless method." @default.
• W75589637 created "2016-06-24" @default.
• W75589637 creator A5043516948 @default.
• W75589637 date "2014-06-11" @default.
• W75589637 modified "2023-09-27" @default.
• W75589637 title "Nanomagnetism and high frequency experiments. Basic science and technological applications" @default.
• W75589637 hasPublicationYear "2014" @default.
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