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Materials with Anomalous Magnetoresistance

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Optical and Microwave Properties of Materials with the Colossal Magnetoresistance and of Related Composites

Tech Area / Field

  • INS-DET/Detection Devices/Instrumentation
  • MAT-CER/Ceramics/Materials
  • MAT-COM/Composites/Materials
  • PHY-SSP/Solid State Physics/Physics

Статус
3 Approved without Funding

Дата регистрации
29.05.2000

Ведущий институт
Joint Institute for High Temperatures RAS / Scientific Center for Applied Problems in Electrodynamics, Russia, Moscow

Соавторы

  • CNRS / Institut Universitaire des Systemes Thermiques Industriels, France, Marseille\nTU Delft / National Center for HREM, The Netherlands, Delft\nInstitute for Applied Magnetism / Salvador Velayos Laboratory, Spain, Madrid\nFEM, Germany, Schwabisch Gmund

Краткое описание проекта

Objectives: (1) The comprehensive study of microwave, optical, and magnetoresistive properties of manganites and manganite-based composites in order to find out the materials most sensitive to microwave, optical, and ionizing radiation; (2) The development of prototypes for magnetic field controlled microwave and optical devices, as well as ionizing radiation sensors.

Attaining the Project Objectives includes the following tasks.

1. The development of novel manufacturing techniques for manganite-based materials (ceramics, films, and composites). Manufacturing of thin-film samples by the MOCVD technique and composite films by the ion-beam epitaxy. Improvement of preparation methods and heat treatment of the ceramic samples to obtain the reproducible homogeneous and single-phase materials. The manufacturing of artificial nanocomposites. The optimization of composition and heat treatment regimes in order to attain the maximum sensitivity to electromagnetic or/and ionizing radiation.

2. The diagnostics of the sample microstructure. Characterization of thin-film and ceramic samples by x-ray and neutron diffraction and high-resolution electron microscopy. The revealing of formation mechanisms for superstructures, regularly strained, and inhomogeneous states. The ESR study of local magnetic characteristics of the samples.

3. Magnetic and transport properties. The measurements of current-voltage characteristics, electrical resistivity, Hall effect, DC magnetization, and hysteresis loops in the wide temperature range (4.2 - 500 K), the analysis of the magnetic susceptibility and resistivity measurements for manganites and manganite based composites in the megagauss magnetic fields in order to find out the interrelation between transport and magnetic characteristics.

4. The optical and microwave measurements. Performing of the high-resolution magneto-optical studies to visualize the spatial distribution and time evolution of the magnetic order under the temperature and magnetic field variation. The studies of changes in the optical characteristics of manganite films under effect of magnetic field. The measurements of the surface impedance of the samples in the microwave range. The analysis of DC magnetic field effect on the microwave properties. The investigations of the photoinduced changes in conductivity and magnetic order. The ESR-based evaluation of the exchange interaction parameters and electron-phonon coupling constants.

5. The effect of ionizing radiation. Investigations and the analysis of the data on the variation of structure, transport, magnetic, microwave, and optical properties of the samples under effect of ionizing radiation (x-rays, gamma rays, neutrons, protons).

6. Theoretical studies. The theoretical studies of the systems with the interplay of different order parameters. The analysis of types and mechanisms underlying the formation of inhomogeneous states and phase separation in manganites. The analysis and numerical simulation of macroscopic magnetization distributions in systems with the phase separation and composites. The investigation of the DC magnetic field effect on electromagnetic and optical characteristics of the materials under study.

7. The search of the most efficient applications of the manganite-based materials in the magnetic field controlled microwave and optical devices and sensors. The choice of the optimum schematic designs. The manufacturing of laboratory prototypes.

Background information

Beginning from 1994, there is the worldwide upsurge of interest to the study of La1-xCaxMnO3 manganites, where a more than thousandfold drop of the electrical resistance was observed at magnetic field 6 T at 77 К. This effect is referred to as ‘colossal magnetoresistance’ (CMR). The interest to the systems with CMR stems from their promising applications for magnetic recording, magnetic field sensors, and other devices of the so called ‘spin electronics’.

The manganites are characterized by a complicated form of the phase diagram, involving the regions differing in the conductivity type, in the value of magnetoresistance, as well as in crystal and magnetic structure. The most promising materials from the viewpoint both of pure physics and possible applications are the those where the transition points corresponding to different types of ordering are close to each other. In these substances, small composition changes and relatively weak applied fields can produce rather pronounced effects, such as be switching from insulator to metallic state under pressure, magnetic and electric fields, and even x-ray irradiation

The persity of the charge transfer mechanisms and the charge carrier types in manganites should directly manifest itself in their optical and microwave properties. Moreover, the optical and microwave studies provide an important tool for revealing the dynamics of electron states and relaxation processes in the spin and electron subsystems. It is of special interest to investigate by these methods the inhomogeneous states (droplets and stripes) in manganites. The magneto-optical studies provide an opportunity to find out the spatial distributions and the evolution of magnetic order with the variation of temperature and magnetic field. The microwave studies allow one to determine reliably the spatial scale of inhomogeneities and their relation to microstructure of the systems. The optical and microwave irradiation can cause the additional effects such as photoinduced changes in the type of conductivity and magnetic order. The optical and microwave spectra of manganites turn out to be rather sensitive to the effect of applied electric and magnetic fields, especially in the presence of the inhomogeneous states and in the vicinity of the phase transition points. In particular, the manganites can exhibit the photochromic and electrochromic effects. Owing to the sensitivity to the external disturbances and nonlinearity of the response, the manganite-based materials are promising for the application in the microwave and optical devices. In spite of the importance of optical and microwave studies both for physics and applications of manganites, this field is rather poorly investigated.

Electrical, magnetic, and optical properties of manganites are strongly affected by their microstructure. In this connection, it is natural to suppose that any ionizing radiation giving rise to the local structural changes can significantly affect the characteristics of manganites. This effect can be implemented in detectors of radiation dose. The use of different kinds of radiation allows one to create controlled structural changes, which is important for providing a deeper insight into the physics of manganites and for the progress in technology. Actually, this range of problems was not studied yet.

The most promising materials for the microwave and optical studies, as well as for applications, can be regarded as natural composites. Therefore, it is natural to extend the possibilities of the CMR materials applications by the developing of artificial composite systems.

Small variation in technology can cause significant changes in the properties of manganites. Therefore, technological developments and the studies of transport and other physical properties should be supplemented by the detailed analysis of crystal and magnetic structure. The most detailed information can be provided here by neutron, x-ray, and magneto-optical techniques.

Previous experience the Project participants

In ITAE, the fundamental theoretical work was performed, which provided a unified approach to the analysis of the interplay between electron, magnetic, and crystal structure in manganites. In DC-MSU, the manufacturing technologies for the advanced manganite-based materials; there is also a long-term experience in the persified study of their composition and microstructure. Using the samples manufactured in DC-MSU, the participants from MIPT performed a comprehensive set of physical investigations including the measurements of electrical resistivity, magnetoresistance, and AC magnetic susceptibility. The studies of LaPrCaMnO samples allowed revealing the low-temperature transition from the antiferromagnetic insulating to the ferromagnetic metallic state, as well as the metal insulator transition induced by the isotope substitution of 16O by 18O. The theoretical analysis of these results was performed in ITAE. The MIPT group has also much experience in the ESR studies of metal oxides. The participants from JINR have a good experience in the neutron diffraction studies of crystal and magnetic structure of manganites, using, in particular, the high-resolution Fourier diffractometer. The DP-MSU studied of DC, low- and high-frequency, optical, and magneto-optical properties of magnetic materials. The pioneering investigations in the magneto-optics of manganites were performed. In ITAE, the electromagnetic characteristics of composites (DC, microwave, and optical) were widely studied, including composites of metal-insulator and metal-semiconductor type, and magnetic composite materials, in particular manganite-based composites. In ITAE, there was also created a unique set of technological facilities and the corresponding set of diagnostic equipment providing an opportunity to produce the nanocomposite materials and nanocomposite-based film structures. The participants from Russian Federal Nuclear Center "All-Russia Research Institute of Experimental Physics", Sarov (IEP) have a vast experience in the studies of materials under effect of high and ultrahigh magnetic fields up to 500 T. Under such conditions, the studies of magnetic susceptibility and conductivity were performed, in particular, for manganites and manganite-based materials. In IEP, there are also available, unique experimental facilities to study the properties of materials under effect of ionizing radiation. In Troitsk Institute of Innovation and Thermonuclear Research, Troitsk (TRINITI), there is a long-term experience in the theoretical analysis and numerical simulation of nonuniform distributions of magnetization. The participants from All-Russia Research Institute of Pulse Technology (VNII IT) have a long-term experience in the circuit design and in the development and implementation in industry of different electronic devices, including the magnetoresistive sensors.

Expected Results

1. The improved laboratory techniques will be elaborated for the synthesis of the manganite-based solid solutions. Several series of the thin-film and ceramic materials with the controlled microstructure and oxygen stoichiometry, which are the most promising for development of the devices sensitive to applied fields and other external factors, will be produced.

2. The laboratory technique of the manufacturing of manganite-based metal-insulator composites will be developed. Such materials should significantly enhance the possibilities for applications of the systems with colossal magnetoresistance.

3. Model nanocomposites with manganite nanoparticles embedded into the insulating oxide film will be manufactured. They should provide an opportunity to implement in full measure the effects of structure inhomogeneity, which can be hardly controlled in natural composites.

4. Based on measurements of transport properties, magnetic structure, high-frequency, and optical characteristics, the materials most sensitive to applied magnetic and electric fields will be found. As a result, it will be possible to choose generic materials promising for production of controlled microwave and optical elements.

5. The materials with the highest sensitivity to the effect of ionizing radiation will be found and the necessary recommendations concerning the design of radiation dose sensors will be elaborated.

6. The theoretical approach for the description of the systems with different order parameters will be developed, the possible types of non-uniform distributions of magnetization in manganites will be determined, and the effect of the inhomogeneous states on the microwave and optical properties of manganites will be analyzed.

7. The optimum schematic designs will be proposed and the laboratory prototypes of magnetic field controlled microwave and optical manganite-based devices and sensors will be manufactured.

Meeting ISTC Goals and Objectives

The activities of the most part of Project participants from Russia dealt with the developments of weapon systems and related military technologies. The knowledge and skills accumulated in this field are valuable for the developments of high technologies and their applications. Therefore, the participation in this project provides an opportunity to redirect the activities of high-class specialists from the weapons of mass destruction to peaceful purposes. The ISTC support of the studies in the framework of this Project will stimulate basic and applied research and technology development for peaceful purposes. This Project will promote the design of competitive instrumentation and equipment reinforcing the transition of the leading Russian R&D centers to the international market of civil technologies.

Scope of Activities

1. Development of the preparation technique of the manganite materials (ceramics, films, composites). preparation of the thin-film samples (La1-xRx)0.7Ca0.3MnO3, (La1-xRx)1-ySryMnO3, (La1-xRx)1-yCayMnO3, R1-yCeyMnO3, (La1-xRx)1-yNayMnO3 (R = Pr, Nd) by chemical vapor deposition technique on different substrates. Preparation of the ceramic Mn-based samples. The manufacturing of the composite films by the ion-beam technique.

2. Microstructure diagnostics of the samples by means of x-ray (EXAFS, EDX) methods, by high-resolution electron microscopy (SEM, HREM, TEM), and by the Raman spectroscopy. Derermination of the ion composition by the chemical analysis. The study of crystal and magnetic structure, phase composition, and stoichiometry of the samples by neutron scattering technique. The ESR studies of the local magnetic properties.

3. Magnetic and transport properties. The measurements of the resistivity, voltage-current characteristics, Hall-effect, DC magnetization, and AC magnetic susceptibility. The study of metal-insulator transitions in magnetic fields up to the megagauss range. The measurements of the local voltage-current characteristics of the thin-films by the scanning tunnel microscopy.

4. Optical and microwave measurements. Magneto-optical measurements for revealing spatial distribution and evolution of the magnetic order. The measurements of optical characteristics for the films under effect of magnetic field. The study of surface impedance in the microwave range. The investigation of DC magnetic field effect on the microwave properties. The ESR analysis of the parameter characterizing exchange and electron-phonon interactions.

5. Selection of the materials having the highest sensitivity to the ionizing radiation. and preparation of the irradiated samples for the detailed structural, transport, microwave, and optical studies.

6. Theoretical studies of the systems with the interaction of different order parameters. Analysis of the types and nature of inhomogeneous states and phase separation in manganites. Computer simulation of the macroscopic static distributions of magnetization. The study of magnetic field effect on microwave and optical properties.

7. The search for the most promising applications of manganite-based materials. The choice of materials most sensitive to the microwave and optical radiation. Manufacturing of the model devices and the study of their characteristics. Development of optimum design solutions.

Role of Foreign Collaborators

The cooperative research with the expected foreign Collaborators is already taking place in the fields related to the present Project. We suppose to continue and extend this cooperation. It is also expected that the informative parts of the quarter, annual, and final reports of the ISTC Project will be send to Collaborators. In accordance the Technical Schedule it is supposed to carry out collaborative studies using simultaneously the equipment and the samples prepared by Russian participants and foreign Collaborators. It is also planned to organize several Workshops and scientific seminars with the participation of the foreign Collaborators.


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