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Effects of Mn and Gd incorporation on the electrical conductivity of Ga(1-x)M(x)As and Ga(1-x)M(x)N(m=Mn,Gd) films prepared by sputtering

Grant number: 06/01362-0
Support Opportunities:Scholarships in Brazil - Scientific Initiation
Effective date (Start): June 01, 2006
Effective date (End): May 31, 2009
Field of knowledge:Engineering - Electrical Engineering - Electrical, Magnetic and Electronic Measurements, Instrumentation
Principal Investigator:Jose Humberto Dias da Silva
Grantee:Marcel Henrique Arraya Aviles
Host Institution: Faculdade de Ciências (FC). Universidade Estadual Paulista (UNESP). Campus de Bauru. Bauru , SP, Brazil


The behavior of the direct current electrical conductivity and the electrical transport mechanisms in amorphous and nanocrystalline Ga(1-x)M(x)As and Ga(1-x)M(x)N films will be investigated. In these materials M represents Mn or Gd and x represents variable composition in the 0-0.1 range. The films will be prepared using the RF magnetron sputtering technique. Monocrystals with similar compositions, produced by MBE, are usually ferromagnetic, and are potential candidates to the development of electronic devices based on spin control, bringing considerable interest to the development of the related materials. One of our main aims is to analyze if the interactions between the magnetic moments of the M ions and the current carriers dominate the transport process, or if the structural disorder effects are dominant and inhibit the existence of ferromagnetic phases in the material. The electrical conductivity will be measured as a function of temperature (10K < T < 300K) for different x values, with and without the presence of a magnetic field (magneto-resistance). Special attention will be devoted to measurements near the Curie temperatures of the equivalent composition monocrystal. The measurements of the electrical conductivity variation with temperature will be used to evaluate the dominant transport regimes in different temperature intervals, and to determine the corresponding activation energies. Measurements of the current-voltage characteristics, and tests of Hall effect and thermo-electric potential, at room temperature, will be done for different concentrations (x) and different microstructures (dependent of deposition conditions). Modifications in the experimental setup will be made to allow the electrical characterization of the films. A cryostat, used in optical measurements, will be adapted for the electrical measurements. Simple experiments will be mounted for Hall effect thermo-electrical potential tests. The experiments will be controlled using a GPIB interface (IEEE-488). The programs for the interface control of the experiments and data acquisition will be made. The measured electrical characteristics of the films will be compared with magnetic, optical, compositional, and structural characterizations performed in the laboratory, and also with the literature data corresponding to the monocrystalline equivalent of these materials. In preliminary tests, made in the absence of magnetic field, we observed that an important increase of the resistivity appears in some of our Ga(1-x)Mn(x)As films in temperatures around 100K, which corresponds approximately to the Curie temperature of the monocrystalline Ga(1-x)Mn(x)As. This increase of the resistivity is observed in our films, although they have not presented ferromagnetic behavior up to 2K. This is an indication that, in spite of the absence of ferromagnetic order, the local interaction among the magnetic moments of the Mn ions with the conduction electrons in our samples can be similar to that observed in the ferromagnetic material. In the present work we will explore this behavior in more detail, using several compositions and different conditions of film deposition.

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