PROPERTIES OF MAGNETIC SOLIDS

Author: AGUDO MADURGA PEDRO ANTONIO.
Year: 2004.
University: COMPLUTENSE DE MADRID [www.ucm.es].
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: INSTITUTO DE MAGNETISMO APLICADO "SALVADOR VELAYOS".

Summary: The amendment, by adding small amounts of different elements, both the structure and the mechanical and magnetic properties of magnetic amorphous alloys and nanocristalinas of FeSiBNbCu traditionally used in applications that require a material magnetically sweet, has been targeted fundamental study of different research groups over the last few years. With a view to contributing to this study were produced using ultra-cooling technique, composition of amorphous tapes nominal NixFe73.5-xSi13.5B9Nb3Cu (x = O, 5, 10, 15.20 Y25) YCrxFe73.5-xSi135B9Nb3Cu (x = O, 2, 4 Y6). In the case of the tapes that were not incorporated, after checking through difractometria X-ray the amorficidad of them were subjected to various heat treatments one-hour between 623 and 973 K Yse the marked structural and magnetically. For structural characterization was used, in addition to the difractometria X-ray, differential scanning calorimetry and spectroscopy M6ssbauer at room temperature, found that in addition to destabilize heat, the appearance of a crystalline phase rich in Ni-magnetically hardens prematurely the material. For characterization using a magnetometer magnetic induction and a vibrant magnetometer sample, we found that the values of coercive field increase significantly for alloys with larger amount of Ni (20 Y25% at.), Even when the material retains its structure nanocristalina . For measures imanación with temperature used a balance termomagnética Check the Curie temperature of the amorphous phase decreases from 603 to 543 K depending on the amount of increases Neither of the samples. In the case of samples which are incorporated Cr, after checking through difractometria X-ray the amorficidad of them were subjected to heat treatment for one-hour of 813 and 973 K Yse the characterized both structurally and magnetically . Here are subjected, for a period of up to 28 days, to the action of two different means aggressive, corrosive atmosphere simulating industrial and marine. Regularly extracted samples for electrochemical characterization, gravimetric and magnetic, and for the study of the corrosion products, we found that shows that he had not been incorporated Cr deteriorating completely, both structurally and magnetically, in the course of the first week of the trial. The shows that better behavior, both as an anticorrosive magnetic show, is that it has incorporated a 4% at. Cr thus formed on the surface a passive protective layer that prevents the degradation of the material and allows you to continue to be magnetically sweet.

Author: GONZÁLEZ LÓPEZ DEL CASTILLO IVÁN.
Year: 2004.
University: SANTIAGO DE COMPOSTELA [www.usc.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FÍSICA.

Summary: The phenomenon of magnetorresistencia colossal (WRC) attracted the attention of the scientific community in the mid-nineties. It consists of a large drop (in the order of a factor 10000-77K) of the electrical resistivity of certain materials to apply a magnetic field outside relatively small (approximately 6 W). The phenomenon has important technological applications. Typical compounds with WRC are perovskitas manganese RE_ (1-x) AE_xMnO3, where RE is a rare earth and AE a alcalinotérreo. The x allows for the preparation of compounds doped with different numbers of electrons in the conduction band without changing the crystalline structure of the material. The dynamics of electrons driving, which determine the magnetic and electrical properties of the material, stems from rivalry between a term of kinetic energy, which tends to relocate electrons, and a term of electrostatic interaction, which tends to locate (model dual exchange, DE). When the kinetic energy dominates, the ground state is ferromagnetic metallic and order (FM). When the electrostatic interaction dominates, the ground state is insulated and orderly antiferromagnético (AF). This is known as phase separation electronics. The size of the regions is of the order of nanometers. The thesis discusses various aspects of the phase separation in the model were included. Our fundamental concern is the competition between the phases FM and AF. The results of the thesis is as follows. In the first chapter, we show that in the separate states all cargo carriers are in the regions FM. In the second, we calculate the phase diagram at the TH in the field approximation means to different values of doped. We demonstrate that the phase diagram is insulating regions with separate states, separate states drivers and homogeneous states, and studying transitions between them. Subsequently we present several findings pertaining to a system of magnetic polarones in the model were included. We use a simplified model consisting of a chain AF Doped dadoras non-magnetic impurities. In the third chapter, we study the retroactive effect in the matrix AF electron conduction linked to its impurity giver. Show that appears a region with distortions spin widespread in the AF structure, similar to a domain wall and which stabilizes the magnetic polarón. In the fourth, we discuss the effect of these distortions prevalent spin in a system doped with a finite density of impurities dadoras. We demonstrate that a certain critical density, the order of winter the size of the region of distortion, you get a non-trivial dependence of the energy system as a function of the density of impurities dadoras, which can be interpreted as an attractive interaction between polarones magnetic. We found also that the state consisting of distortions polarones with magnetic spin extendías is unstable above a certain critical density, which leads to the system to a state order without AF long-range, even below the density percolation system polarones magnetic. In the fifth chapter, we analyze the evolution of the chain with temperature. We demonstrate that the state of magnetic polarón remains stable until temperatures much higher than the temperature of Néel of c 8 adena if 294 No dopar.

Author: Gich Garcia Martí.
Year: 2005.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: Inst.de Cièn.dels Mat.de Barc. C.S.I.C.
Place of preparation: Inst.de Cièn.dels Mat.de Barc. C.S.I.C.

Summary: We have studied different approaches to synthesize composites consisting of nanoparticles magnèticas Matrix silica type Airgel or xerogel. We have obtained materials with very different properties both in terms of their magnetism (soft or hard materials), its optical properties (transparent, opaque, anisótropos) or its density and have studied some of its possible applications magnetoopticas. Arrays of silicon in the form of xerogel have also been used to stabilize a polymorphic metastable oxide Fe (III), very little known, epsilon-Fe2O3. It has become a characterization of the magnetic properties of the material and has been its Curie temperature is 510 K and at room temperature which is a ferrimagneto colinear with a magnetization moderate (20 emu / Ga saturation) and a magnetic high that make anisotropia his coercitividad is unusually large for an oxide Fe (20 kOe). Between 150 i 80 K the epsilon-Fe2O3 is a transitional phase magnetic and structural second order resulting in a structure magnetic incomensurable type "wave quadrada. It has been shown that in conjunction with this transition phase of the material presents a acoblamiento magnetoeléctrico.

Author: DELGADO TRUJILLO FERNANDO SALVADOR.
Year: 2005.
University: LA LAGUNA [www.ull.es].
Place of defense: FACULTAD DE FÍSICA.
Place of preparation: FACULTAD DE FÍSICA.

Summary: This paper presents a detailed study of the molecular characterization magneto-estructural of magnetic materials based on ion malonate: synthesis of hybrid materials or metalo-orgánicos, growth and development of monocrystals species studied, structural characterization using X-ray diffraction characterization magnetic through interpretation of the actions of magnetic susceptibility. Within the field of Magnestimos Molecular, Supramolecular Chemistry and coordination along with the Engineering Cristalina play a very important role in the design of new materials. An understanding of the forces that govern the packaging crystalline (covalent links, hydrogen bond, weak interactions, etc.) is of vital importance in the rational design of new functional magnetic materials. Acid malónico is presented as a ligand very fruitful in the development and design of new molecular magnetic materials in the light of the results obtained. A wide variety of crystalline structures, from monomers to polymers coordination structure mono-, bi-and three-dimensional presented in this work. The characterization magneto-estructural of these compounds has led to an investigation of the factors that control the packaging of crystalline complexes malonate and the resultant magnetic properties of these compounds. The study magneto-estructural is organized response center used paramagnetic and dimensionality of the network crystalline. The paramagnetic centers used in the preparation of malonate as new species have been characterized as follows: Transition metal in the first installment [Cu (II), Co (II), Ni (II) and Mn (II)], lantánidos [ Ce (III), Sm (III) and Ho (III)], Mn (III) and Cr (III). The magnetic properties of the new species is explained taking into account the spatial distribution of paramagnetic centers, the nature of its magnetic and orbital geometry ligand acting as a bridge. Different strategies developed in the design delas species presented in this paper, allow control over the dimensionality of the crystal lattices of malonate resulting in compounds with interesting magnetic properties.

Author: TORRES BRUNA JOSE MARIA.
Year: 2005.
University: ZARAGOZA [www.unizar.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: THIS WORK VERSA ON CHANGE FACED THE MATERIALS MAGNETIC TO HAPPEN DETAMAÑOS MACROSC6PICOS A MICROSCOPICOS And NANOSCOPICOS. STRUCTURED HAS BEEN IN TWO PARTES.EN PART IS STUDYING SYSTEMS NANOPARTICULAS MAGNETICAS OF COBALT, CONTAMAÑOS THE ORDER OF NANOMETRO, ON WHICH HAVE BEEN ESTUDIADO EFFECT OF REDUCCIÓNDEL SIZE OF PARTICULATE MATTER ON THE CONSTANT ANISOTROPIA. ALSO HAS BEEN ESTUDIADO LAINTERACCION BETWEEN ELLAS.SE HAS COMPROBADO HOW TO REDUCE THE SIZE OF PARTICULATE MATTER, THE ANISOTROPIA OF ESTASAUMENTA IN MORE OF AN ORDER OF MAGNITUDE OVER THE ANISOTROPIA OF COBALT MASIVO.TAMBIEN HAS DEVELOPED A MODEL-BASED INTERACTIONS DIPOLARES THAT PERMITEREPRODUCIR THE PILOT THAT RESULT OF ENERGY INCREASES THE BARRIER TO ENHANCE LAINTERACCION AMONG PARTICULAS.EN THE SECOND PART IS ESTUDIADO NETWORKS HAVE HOLES LITOGRAFIADAS IN LAMINAS DELGADASDE IRON. HAVE THE HOLES ON THE ORDER OF SIZES MICRA. RESULTS EXPERIMENTALESMUESTRAN THAT CAN CONTROL THE FIELD COERCITIVO OF THE AREA LITOGRAFIADA THROUGH LOSPARAMETROS OF THE NETWORK: SIZE OF HOLES AND SEPARATION BETWEEN ELLOS.TAMBIÉN HAS DEVELOPED A PROGRAM TO MAKE SIMULATIONS MICROMAGNETICAS SOBREESTOS SYSTEMS TO REPRODUCE CUALITATIVAMENTE RESULTS EXPERIMENTAL AND THAT ADEMASPERMITEN SIMULAR NETWORKS WITH GEOMETRIA WISH TO BE.

Author: SERRATE DONOSO DAVID.
Year: 2005.
University: ZARAGOZA [www.unizar.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: INSTITUTO DE CIENCIA DE MATERIALES DE ARAGON.

Summary: The dissertation deals with the phenomena of spin-dependent transport properties on media in highly polarized spin. The work combines the empirical analysis of the results with a more general and theoretical. This ambitious goal is addressed from three complementary perspectives: the optimization and research materials with potential applicability, a phenomenological approach to the theory underlying physics, and finally implemented in real devices. The materials studied, as well as devices manufactured with them, meet the qualities of high spin polarization of the carriers and Curie temperature above ambient temperature, so that possess properties magnetorresistivas even at room temperature, making them of great interest to the new technology sector based on Espintrónica. These materials and devices are: double perovskitas ordered, Heusler alloys, magnetite, manganita, unions and planar magnetic tunnel spin valves. Due to the variety of scientific problems treated in the thesis has been used a lot of experimental techniques with high performances: powder diffraction of X-rays, electrons and thermal neutrons, sample preparation by solid state reaction and the method download arc microscopias electronic scanning and transmission, high magnetic fields continuous (12 Tesla) and pulsed (60 Tesla), dc resistivity and ac method by four points, magnetoestricción and thermal expansion by the method of gauges extensiométricas, magnetometry SQUID, MOKE and VSM and finally techniques growth of thin films (spraying cathodic deposition by ion beams, perfilometría). The first deals with the optimization of the Curie temperature (Tc) and magnetorresistencia doubles perovskitas in policristalina. It estucian several key points in this field. The most important is the analysis of the physical parameters which influence the intensity of the ferromagnetic interaction, which in turn determines the value of Tc. Combining the information gathered on the magnetic properties and crystal structure has been established the unit with Tc doping electronic and structural parameters. By the theory elaborated, explaining the phase diagrams of the series of double perovskitas A2FeMoO6, A2FeReO6 and Sr2Fe1-xCrxReO6. Specifically, the structural effects will mean that Tc depends linearly on the matrix elements of the term of hamiltoniano atomic kinetic, which combines state t2g of atoms Fe-Mo, Fe-Re and Cr-Re with orbital O2p intermediate. No less important is the detailed structural study of the series Sr2Fe0.75T0.25MoO6 (T = Sc, Ti, V, Cr, Mn, Fe and Co), which reveals the linear dependence between the relationship of voómenes of octaedros [Fe-T] O6 and MoO6 and structural disorder between sites Fe and Mo. The prevention of such a structural disorder is triggered a loss of the spin polarization of doubles perovskitas. A model based on a theory of treating disturbances to the first order of the interaction espín-órbita in atom Re provides a credible explanation for the magnetic hardness and acoplo magnetoestructural observed in the double perovskitas based Re. It also explains a number of anomalies detected in these compounds: magnetostriction anisótropa giant, the behavior of insulating compounds monoclinical and magnetorresistencia anisótropa in Ca2FeReO6. The following is an effort towards better understanding of the phenomenon of magnetorresistencia intergranular in materials listed in the second paragraph. It first shows the effect of tunnel electronic artificial joints Co. electrodes separated by a sweep 8-of alú 6be mine. The equations of transport through individual insulating barriers are widespread in the case of granular materials, where the artificial barrier is replaced by grain boundaries. This development is used to study the nature of the grain boundary in the materials mentioned above. This study provides a valuable tool to extract physical parameters of importance in effect magnetorresistivo, as are the magnetic nature of the surface, the spin polarization of effective mechanisms or driving across the border grain. Finally, the last chapter of the thesis is devoted to the development of sensors based on spin valves for testing immune recognition. This gives a specific application of the transport properties studied in the thesis. The method presented in the production of nanoparticles of Fe-coated C, and ending with the manufacture of a chip capable of detecting them in their role as accounts magnetic attached to a laptop nitrocellulose membrane.

Author: HERRERO ALBILLOS JULIA.
Year: 2006.
University: ZARAGOZA [www.unizar.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: We have characterized the ordinance magnetic transitions' compounds RCo2 with R = Pr, Nd, Tb, Dy, Ho and Er measures by differential scanning calorimetry (DSC) and measures imanación depending on the magnetic field and temperature. The study of the compounds NdCo2 and PrCo2 establishes beyond doubt the nature of their second-order transitions ferromagnéticas. The characterization of the effect magnetocalórico in compounds with first-order transitions has shown that the latent heat is maintained constant over the whole range, and therefore ordered the state transitions in this family are dominated by structural effects. Measures have been made magnetic circular dichroism (XMCD) on the threshold of absorption L2, 3 and K of C and M4, 5 Er and neutron diffraction low angle (SANS) as a function of temperature and magnetic field in the composite ErCo2. Measures have also been made susceptibility paramagnética depending on the temperature and frequency excitation. The measures XMCD have allowed us to study whether the magnetic moments of Er and Co.. Analysis of the spectra has shown the existence of a new phase within the area paramagnética diagram of phases in which the net magnetic moment of the subnet cobalt is antiparalelo the direction of the magnetic field applied. SANS measures demonstrate the existence of short-range correlations in phase paramagnética of ErCo2 with correlation length of approximately 0.7 - 0.8 nm. The measures susceptibility paramagnética show that the aggregate present at the stage paramagnética consist solely of Co atoms. Moreover, the joint analysis of the measures of susceptibility paramagnética depending on the temperature and frequency excitation, XMCD and SANS demonstrate the existence of magnetic moment of Co himself at the stage paramagnética of ErCo2. The application of the rules endorsed measures XMCD on the threshold L2, 3 Co have shown that the moments of spin and orbital Co. spend their own direction with regard to the magnetic field applied to different temperatures. Therefore, there is a range of temperatures at which not met the acoplo predicted by the third Hund rule for the moments of spin and orbital Co.. This is because the fields of trade interatómicos acting on the band 3d Co dominate against the acoplo espín-órbita infra-atómico.

Author: RODRIGUEZ VELAMAZAN JOSE ALBERTO.
Year: 2006.
University: ZARAGOZA [www.unizar.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: This thesis has dealt with the study of certain compounds transition from spin Fe (II) in around two main axes: (i) eldesarrollo a new facility fotocalorimetría and its application to the study calorimétrico of phenomena fotoinducidosque of these compounds at low temperature, and (ii) the study magnetic fotomagnético, structural and calorimétrico of dosfamilias compounds that continue to encourage the approximation polymer interactions intermoleculares .- It has developed a facility calorimetry (AC and relaxation techniques) modulation resistive allowing fotoexcitar abaja temperature samples in the order of 1 mg. We have designed and obtained substrates heaters suitable for modulaciónresistiva .- We have made the first steps calorimetric state metaestable fotoinducido two compounds SCO: [Fe (PM? BiA) 2 (NCS) 2], representing the approximate molecular and Faith (pmd) 2 [Cu (CN) 2] 2, representing the approximate polymeric .- abnormalities detected reflect relaxation of the state of the AS BS, and agree with the characterization magnetic .- The results show the compaction of the samples to form powder pellets produces unamodificación the properties of the same, which has sought to understand through a full characterization contécnicas various .- We have studied the family of two-dimensional polymeric compounds Fe (L) 2 [Ag (CN) 2] 2 (L = py; 3-mepy; 4-mepy; 3,4-dimepy; 3-Clpy), which has been characterized by magnetic techniques, fotómagnéticas, calorimetric, spectroscopy Mdssbauer and ray diffraction X. ? '. ; Y- The compound Fe (py) 2 [Ag (CN) 2] 2 is a transitional spin in two steps, where the state is attributed intermediate-partirde the results of experiments magnetism and difrácción X-ray powder-a mixture of species in high bajoespín without long-range order. They are counted similar cases described in the literature - The replacement of one or two of the hidrógenos pyridine ring methyl groups or by Cl-ions produced important changes inthe structures (different from each other and different from the compound with L = py ) and the magnetic behavior of the compounds, while prevail transitions in two steps .- In the compound with L = 4-mepy transition in two steps has been revealed only through the actions decalorimetría, which shows the importance the combination of different techniques in the study of these compounds .- Except compound with L = 3-mepy, non transition from spin, the rest of the compounds are fotomagnéticamenteactivos. The characteristic of the transition in two stages is also observed in the fotomagnetismo of these systems, both in lasrelajaciones isotherm state metaestable fotoinducido, as in the relaxation of this rule to increase the temperature. Estecomportamiento is also rare .- cooperatividad in this family is generally low, and the relationship between T (LIESST) Tc and follows the same trend as in other compounds based networks metalocianato. Temperatures T (LIESST), are comparatively low in relation to lasde other systems, no more than 72 K. - has been studied family of two-dimensional polymeric compounds Fe (L) 2 [Ni (CN) 4] (L = py; 3-mepy; 3-Clpy), which has sidocaracterizada using magnetic techniques, fotomagnéticas and calorimetric .- The activity fotomagnética in the family Fe (L) 2 [Ni (CN) 41 is smaller than in the family Fe (L) 2 [ Ag (CN) 2] 2, with lower rates defotoexcitación and values of T (LIESST) to 63 K-cooperatividad of these systems is, on the contrary, higher than in the family silver, but it has been observed 8 do the 3b2 behavior magnetic a major influence on a number of factors such as the method of preparation, the pH of the disoluciónprecursora or even manipulation of the sample prior to the action, which were associated with the grain size in the polvopolicristalino and with the existence the impurities and defects.

Author: ABAD MUÑOZ LIBERTAD.
Year: 2006.
University: AUTÓNOMA DE BARCELONA [www.uab.es].
Place of defense: ICMABCSIC SALA DE ACTOS DE MATGAS.
Place of preparation: instituto de ciencia de materiales de barcelona.

Summary: In recent years, the complex oxides have attracted the interest of the scientific community because of the wide range of physical properties and technological possibilities they offer, such as ferroelectricidad, ferromagnetism and superconductivity in high-temperature criticizes. Moreover, improved techniques for preparation of thin layers and advances in the processes of microfabricacion have enabled the development of devices magnetoelectrónicos such as spin valves or joints magnetic tunnel [1.2]. This has led to the birth of the promising field of the call espintrónica in which the use of the spin degrees of freedom mail is expected to enable the development and manufacture of new devices that improve performance and provide new functionality to existing devices [ 3]. The development of these new devices spin requires the existence of sources with electron spin polarization total. In nature there are certain materials that present this property of total polarization of electrons driving. These materials are called semimetales and among them are oxides of manganese structure perovskita such as La2/3Ca1/3MnO3 (LCMO) or La2/3Sr1/3MnO3 [4,5,6,7,8]. This paper will look at properties of ferromagnetic oxide semimetálico and made La2/3Ca1/3MnO3 grown on substrates monocrystalline of SrTiO3 (STO) and LaAlO3 (LAO) at the Institute of Material Science Barcelona (ICMAB-CSIC) by the technique spray cathodic radiofrequency (RF- sputtering). These materials derived compound LaMnO3, which is insulated and antiferromagnético, can become conductors and ferromagnetic by replacing a certain fraction of trivalent cation (The) on the other divalent as Ca, Sr, Ba… gaining prolific family of calls commonly manganitas valence mixed [9,10,11]. The manganitas have general formula R1-xDxMnO3 and crystalline structure type perovskita where R is a trivalent cation (eg La, Pr or Nd) and D is a divalent cation. To maintain the neutrality of burden of this compound doped, the manganitas present a mixed valence state with a fraction nominal 1-x of Mn3 + with a configuration electronic 3d4 (t2g (3) eg (1)) and a fraction, also rated x-Mn4 + with a configuration electronic 3d4 (t2g (3) eg (0)). At the level of doping x ~ 0.33, manganita Calcium is ferromagnetic metal and because of the interaction of electrons roving eg through the mechanism of dual exchange (DE) mediated by oxígenos the structure [12.13]. Moreover, it is the composition of higher Curie temperature, TC, hence we have chosen as a subject of study this theory [14]. The La2/3Ca1/3MnO3 shows a rich phase diagram magnetic depending on the level of doping and temperature with an intimate relationship between the state and the magnetic conductivity [15.16]. In particular for x ~ 0.33 is obtained by the state in league with the ferromagnetic metal at low temperatures and a paramagnetic state and high temperature insulation that promotes call magnetorresistencia colossal (WRC), which presents the manganitas [17]. The manufacture and quality control structure and morphology of the surface layers is an essential and unavoidable step for the use of these materials in the implementation of devices magnetoelectrónicos such as magnetic tunnel joints (MTJ) [18,19,20,21, 22,23,23]. Excessive surface roughness can lead to a multitude of problems related to the coupling between electrodes or training shorts off through the barrier isolator unions magnetic tunnel [24.25]. Therefore, an important part of this thesis is devoted to analysis 8 and contr 1ff8 ol process growth of thin layers of LCMO on monocrystalline substrates of SrTiO3 (STO) or LaAlO3 (LAO). It will show in layers LCMO / STO and in the early stages of its growth mode of growth prevailing in our layers, layer is a layer (layer by layer mode), giving rise to a morphology terraces and stairs and thus getting extremely flat layers. [26,27,28,29,30,31]. Instead, we will see how the system LCMO / LAO shows a three-dimensional growth from the beginning what will be reflected in roughness higher than those obtained in the system LCMO / STO. In this thesis show some of the problems and challenges that appear in the manufacture of thin layers and heterostructures based manganitas and have effect on the degradation of important physical parameters such as temperature Curie or saturation magnetization. Specifically present results obtained on thin layers grown on STO monocrystals and LAO. In the case of system LCMO / STO try to find out what is the origin of this degradation of property and other problems associated with the microstructure. Advertiremos as these problems may be solved in part thanks to thermal treatments of the thin layers in the presence of air and high temperatures and will discuss whether the structural reconstruction, the structural tension, the oxygen content or segregation of cargo in order zones load may be the cause. [32,33,34,35,36,37,38,39]. Moreover, a crucial aspect for the implementation of devices based on oxides is the surface resistance and the intercaras [40]. In this study the contact resistance between the manganita and noble metals with the help of the atomic force microscopy working mode sensitivity current (current sensing) [41,42,43]. It detects the presence of a magnetically dead layer which can be reduced to an order of magnitude with high temperature heat treatment in the presence of air [44,45,46,47]. 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Author: JUNQUERA PEREZ ALEJANDRO.
Year: 2006.
University: OVIEDO [www.uniovi.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTAD DE CIENCIAS.

Summary: In developing this thesis to qualify for the title of Doctor of Physics, have been prepared networks ranked nanopozos, diluted regime, embedded in a thin layer of Cox Si1-xo in a thin layer of CoxZr1-xy have been analyzed processes investment of the imanación taking place. Each of these magnetic amorphous alloys is with a well-defined uniaxial anisotropy and exhibit magnetic properties very similar to analyze. For the manufacture of nanostructures has been necessary to develop a team of electron beam lithography and a team of litografia optics, both newly acquired and have also launched an experimental system pickling ion, which was carrying over into disuse 20 years, which has been modified in order to carry out attacks by ion bombardment. Once manufactured nanostructures, we studied changes in coercitividad and anisotropy depending on the depth of the wells, the geometry of each network inclusions (networks rectangular or square), the symmetry of the wells (circular or elliptical reasons) , and the direction of the applied magnetic field, which presents the hysteresis cycle of the parallel component of the imanación and combining these cycles with those obtained for the perpendicular component of the imanación, we obtained values of the countryside and the angle form the imanación with the direction of the field applied at the time of investment. All this has studied the investment processes of imanación, comparing the results with investment patterns are well known as rotation or consistent investment by displacement of a domain wall of 180 °. We will see how effectively nanostructures alter the behavior of the continuous sheet emerging as key parameter depth of the nanopozos, distinguishing between nanopozos deep depth equal to or less than the thickness of the magnetic foil in which they are embedded and how this opens the possibility of modeling problems of basic character. We will also see that happens to foil naoestructurada if fill the naopozos with polycrystalline Co., or with more complex materials as an alloy CoxGd1-x, and whether these modifications to the system heading further help control the magnetic properties. We conclude our work trying to design a system that allows us to anchor the walls of a magnetic thin layer of CoxSi1-x so asymmetrical, and thus obtain what is called effect ratchet magnetic. To do this we will use a network Symmetric nanopozos like those described above, but instead of symmetrical grounds now will be a network of reasons skewed so if the investment process of imanación is produced by nucleation and movement of a domain wall it is an anchor most effective when moving in a direction that if it did so in the opposite direction and therefore increase the coercive field more in one direction than another. Such asymmetric effects are of great importance in the technological development of sensors or adjusting signal but can also find in nature because they are the basis of operation of biological motors.