Magnetic Sensors Based on CMR Effect
Design and Fabrication of Magnetic Field Sensors and Devices Controlled by Magnetic Field on the Base of Colossal Magnetoresistance Materials
Tech Area / Field
- PHY-SSP/Solid State Physics/Physics
8 Project completed
Senior Project Manager
Mitina L M
MISIS (Steel and Alloys), Russia, Moscow
- Leiden University / Leiden Institute of Physics, The Netherlands, Leiden\nCentre National de la Recherche Scientifique, France, Saclay\nInstitut de Ciencia de Materials de Barcelona, Spain, Bellaterra
The search for the new materials with the high value of magnetoresistance (MR), which can be used as active elements in systems for recording, detection and transformation of magnetic field, is till now an actual scientific task. Metal - Ferromagnetic Metal layered composites were traditionally used for these purposes. The objects can have the value of MR as high as 15% in the field of IT at low temperatures (4.2-20K). After the discovery of negative Colossal Magnetoresistance (CMR) effect in Lantan manganites, considerable interest was paid to investigation of these materials and their properties. Chemical composition of these compounds can be expressed as Lai.xAxMnO3+y, where A - alkali earth elements. They have perovskite like crystal lattice with the valence of Mn being mixed between 3+ and 4+. The value of CMR was extremely sensitive to the prehistory of samples preparation.
The record high value of MR (R(H) - R(H))/R(H), where R(H) is the resistance in magnetic field H, was observed on the La0.67Ca0.33MnO3+y thin film, which was obtained by laser ablation method on the LaAlOs single crystal substrate. It was as high as 127000% at 77K in the magnetic field of 6T. So, La1 –xAxMnO3+y compounds have not only five orders of magnitude higher magnetoresistance than the metal layered structures, but higher temperatures where CMR effect is observed (up to room temperature), as well. It should be pointed out that in addition to the technical applications mentioned above these materials can be used in some other areas. First, they are supposed to be used for development of a so-called spin transistor (a transistor controlled by magnetic field). Preliminary results have shown that in comparison with the transistors prepared on the basis of Co/Cu layered structure the Lai.xAxMnOs+y ones are characterised by much lower value of leakage current. Second, single crystal thin films of these compounds reveal magnetooptical Faraday effect, which is of the same order of magnitude as in the ferroyttrium garnet. This feature of Lai-xAxMnO3+y thin films can be used for preparation of digital circuits with the magnetooptical converters.
The basic compound LaMnO3+d has orthorhombic or monoclinic crystal lattice depending on oxygen contain. It is characterised by semiconducting type of electrical conductivity. Upon cooling from the melting temperature this compound undergoes the magnetic transition from the paramagnetic into ferromagnetic state. Substitution of La by A - element leads to remarkable changes in the material properties and characteristics:
- an increase of Mn4+ ion concentration;
- the lattice symmetry increase and in certain interval of A-element concentration becomes cubic;
- paramagnetic-antiferromagnetic transition transforms into paramagnetic-ferromagnetic one;
- at the temperatures below T Curie electrical conductivity changes to the metallic type.
It should be pointed out that both Neel and Curie temperatures of these compounds depend on A-elements concentration and oxygen stoichiometry as well. CMR effect is observed in the temperature region of Ferromagnetic transition. Earlier a model of double exchange was proposed for the description of the influence of ferromagnetic state on electrical conductivity. The semiconductor - metal transition, which accompanied the magnetic transition, was explained in the framework of zone model. The exchange interaction between Mn ions occurs due to the double exchange through the oxygen ions. Mn^-Mn^ interaction is of antiferromagnetic type, whereas Mn^-Mn^ and Mn^-Mn^ ones are ferromagnetic. The mechanism of conductivity in these compounds at low temperatures is of jumping type with the exchange of carriers between Mn^ and Mn^ ions proceeding without spin turnover.
The main objectives of the work are:
- Development of the technological procedure for preparation of both single crystals and thin films of La1-xAxBO3+y compounds with the high values of magnetoresistance in the temperature intervals needed for technical applications;
- Investigation of properties of these samples as well as the feasibility of using them as magnetic field sensors and magnetic field controlled devices;
- Theoretical consideration of the colossal magnetoresistance effect in La1-xAxBO3+y compounds.
- development of technology for preparation of bulk and thin film single crystals of La1-xAxBO3+y compounds, where A = Ca, Sr, Ba; B = Mn, Ni, Co.
- experimental data base on electrical and crystallographic properties of La1-xAxBO3+y bulk and thin film single crystals in the connection with preparation conditions; data on correlation between heat treatment, oxygen content, and electrical properties in La1-xAxBO3+y single crystals;
- fabrication and testing of complex structures of CMR and HTSC films on different substrates, using as a substrate CMR single crystals;
- bulk and thin film single crystal samples La1-xAxBO3+y producing for investigations;
- scientific papers on La1-xAxBO3+y investigations.
Technical Approach and Methodology.
In order to achieve the objectives of this project it supposed to use the following methodology:
- theoretical approach of the correlated magnetic and structure transformations in compounds having a perovskite like crystal structure with the mixed valence of elements;
- calculation of the theoretical predictions for the concentration and temperature dependencies of the magnetoresistance close to the phase transition boundaries in the phase diagram of the system in the weak magnetic fields;
- synthesis and processing of the ceramic products of RE1-xAxBO3+y compounds by a standard ceramic route;
- growth of bulk single crystals by Floating Zone Melting with radiation heating in air, inert gas and oxygen ambient;
- thin film deposition by magnetron sputtering method on SrTiO3, LaAlO3, NdGaO3, MgO, ZrO2 and Si single crystal substrates;
- preparation of layered and planar GMR structures by means of magnetron sputtering, photolitho-graphy and ion plasma etching;
- determination of phase composition, atomic and crystallographic structure by means of XRD analysis, electronography, Rutherford backscattering,
- electron spectroscopy in temperature intervals, which includes the temperatures of magnetic and phase transitions;
- neutron scattering investigations to determine the charge/polaron ordering, spin dynamics, and lattice dynamics;
- measurements of magnetoresistance and Hall effect in 77K-400 K temperature interval at 0-1.5 T magnetic field by 4-probe method;
- measurements of magnetic susceptibility and magnetisation in 77K-400K temperature interval by means of modulation method;
- determination of valence of cations in crystal lattice of single crystals obtained and analysis of electron structure by means of photoelectric as well as Auger spectroscopy.
Collaborators and their input into the project
The University of Maryland, MD, USA (Center for Superconductivity Research, Materials Science and Technological Engineering Center, Condensed Matter Physics Dept.) will give an opportunity to use the University facilities for testing the samples quality by RBS, conducting low temperature investigations (< 77 K), studying high frequency properties by ferromagnetic resonance method. Also the University of Maryland will support the project by giving an opportunity to use some technologi-cal and measuring equipment, suppliers and materials, by supporting visits of the MISIS team members for joint investigation to the University and conferences in the USA – 1 person-months/year.
The Naval Research Laboratory, Washington, DC, USA will give an opportunity to use the Laboratory facilities for conducting electronic paramagnetic resonance, heat capacity and tunnel investigations. Also NRL will support the project by giving an opportunity to use some technological and measuring equipment, suppliers and materials, by supporting visits of the MISIS team members for joint investigation at the NRL and conferences in the USA - 1 person-months/year.
The National Institute of Standards and Technology (NIST), MD, USA will use the facilities at the Center for Neutron Research to carry out neutron scattering investigations. Also NIST will support the project by supporting visits of the MISIS team members for joint investigation at the NIST and conferences in the USA - 1 person-months/year.
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