Giant Magnetoresistance Materials
Development and Investigation of Materials with Giant Magnetoresistance as Basis for Sensors and Devices Controlled by Magnetic Field
Tech Area / Field
- MAT-SYN/Materials Synthesis and Processing/Materials
8 Project completed
Senior Project Manager
Karabashev S G
MISIS (Steel and Alloys), Russia, Moscow
- Universiteit Leiden / Kamerlingh Onnes Laboratory, The Netherlands, Leiden\nTechnical University of Vienna / Institute for Experimental Physics, Austria, Vienna\nUniversity of Maryland at College Park / Department of Physics, USA, MD, College Park\nDepartment of the Navy / Naval Research Laboratory, USA, DC, Washington
Project summaryThe 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 1T at low temperatures (4.2-20K).
After the discovery of a negative Giant Magnetoresistance (GMR) effect in Lanthanum manganites, considerable interest was paid to investigation of these materials and their properties. Chemical composition of these compounds can be expressed as La1-xAxMnO3+y, where A - alkali earth elements, Pb or Cd. They have perovskite like crystal lattice with the valence of Mn being mixed between 3+ and 4+. It should be pointed out that the GMR effect was detected only in crystallographically perfect single crystals (both bulk and thin film). In addition, the value of GMR was eextremely sensitive to the prehistory 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 LaAlO3 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 GMR effect is observed (up to room temperature) as well.
La1-xAxMnO3+y are rather well known and their properties are thoroughly investigated. The GMR effect, however, was detected in these materials only some 3 years ago. The reason is that earlier these compounds were studied mostly using polycrystal samples, transport properties of which are determined mostly by grain boundaries, but the compound itself.
As for the single crystals of these compounds, they were grown by spontaneous crystallization from the Pb-containing melt. The problem, however, was that due to high solubility of Pb the crystals composition was La1-x(Pb,A)xMnO3+y. Possibly because of Pb contamination they have shown no GMR effect. Recently, using Floating Zone Melting with radiation heating single crystals of La1-xSrxMnO3+y with a significant GMR effect were prepared. This method seems to be the promising one for the growth of GMR La1-xAxMnO3+y crystals, because it causes no contamination of the growing crystal.
The main objectives of this work are:
- development of the technological procedure for preparation of both bulk and thin film single crystals of La1-xAxMnO3+y compounds with the high values of magnetoresistance in the temperature intervals needed for technical applications;
- investigation of properties of these crystals as well as the feasibility of using them as sensors in magnetic recording and registration devices.
Technical and scientific approach suggested in this project ensures the achievement of these goals. The participants of the project are skilful scientists having a lot of experience in preparation and investigation of single crystals, thin films and ceramic products of different metal and metal oxide materials. Earlier they were engaged in development of materials for weapon systems.
It should be pointed out that the project participants have already obtained some preliminary results on the project topic:
- Single crystal thin films of La1-xAxMnO3+y (A=Ca, Sr) X=0.2, 0.3. The films were deposited on SrTiO3 (100) single crystal substrates by magnetron sputtering. In comparison with the films obtained by laser ablation method they reveal higher values of GMR effect R(H) (up to 46% in magnetic field of 1kG at 115K for La0.7Ca0.3MnO3+y).
Bulk single crystals of La0.7Sr0.3MnO3+y and La0.7Ca0.3MnO3+y having R(H) as high as 5% in magnetic field at 1kG.