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Growth and transport properties of thin Co-based Heusler films; Wachstum und Transporteigenschaften duenner Co-basierter Heusler-Filme

Abstract

During this work, thin films of Co-based Heusler compounds were deposited under optimized conditions, and their structural, magnetic, and transport properties were investigated. The growth of the thin film samples was accomplished by two different methods. At first Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al and Co{sub 2}FeSi were deposited by sputter deposition from stoichiometric targets. This is considered the standard technique for the preparation of thin Heusler films. Also for the compounds investigated here it resulted in samples with a high degree of L2{sub 1} ordering. An excess of Fe atoms on Si sites was discovered by a detailed X-ray analysis in conjunction with NMR spectroscopy. The choice of different substrates allowed the adjustment of the growth direction. On the other hand, bulk magnetometry revealed that these sputter deposited films exhibit only a reduced magnetic moment, which is an indication of a reduced spin asymmetry at the Fermi level. One source of this problem seems to be a high residual gas pressure, which leads to an increased sample contamination. To improve this situation, a pulsed laser deposition system was constructed and put into operation. The resulting film growth under ultra-high vacuum conditions led to a further improvement of the short-range crystallographic ordering  More>>
Authors:
Publication Date:
Jul 01, 2010
Product Type:
Thesis/Dissertation
Report Number:
ETDE-DE-2424
Resource Relation:
Other Information: TH: Diss. (Dr.rer.nat.)
Subject:
36 MATERIALS SCIENCE; BAND THEORY; CHARGE TRANSPORT; CHROMIUM ALLOYS; COBALT BASE ALLOYS; COBALT SILICIDES; CRYSTAL GROWTH; DEPOSITION; ELECTRON SPECTRA; ELECTRONIC STRUCTURE; EMISSION SPECTRA; ENERGY-LEVEL DENSITY; FERMI LEVEL; HALL EFFECT; HEUSLER ALLOYS; IRON ALLOYS; IRON SILICIDES; KERR EFFECT; LASER BEAM MACHINING; LASER RADIATION; MAGNETIC CIRCULAR DICHROISM; MAGNETIC DIPOLE MOMENTS; MAGNETIC PROPERTIES; MAGNETIZATION; MAGNETORESISTANCE; MANGANESE SILICIDES; NMR SPECTRA; NUCLEAR MAGNETIC RESONANCE; PHOTOELECTRIC EMISSION; PULSED IRRADIATION; QUATERNARY ALLOY SYSTEMS; SPECTRAL SHIFT; SPUTTERING; TEMPERATURE DEPENDENCE; THIN FILMS; X-RAY DIFFRACTION
OSTI ID:
21423520
Research Organizations:
Mainz Univ. (Germany). Fachbereich 08: Physik, Mathematik und Informatik
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
TRN: DE11G5274
Availability:
Commercial reproduction prohibited; OSTI as DE21423520
Submitting Site:
DE
Size:
157 pages
Announcement Date:
May 14, 2011

Citation Formats

Schneider, Horst. Growth and transport properties of thin Co-based Heusler films; Wachstum und Transporteigenschaften duenner Co-basierter Heusler-Filme. Germany: N. p., 2010. Web.
Schneider, Horst. Growth and transport properties of thin Co-based Heusler films; Wachstum und Transporteigenschaften duenner Co-basierter Heusler-Filme. Germany.
Schneider, Horst. 2010. "Growth and transport properties of thin Co-based Heusler films; Wachstum und Transporteigenschaften duenner Co-basierter Heusler-Filme." Germany.
@misc{etde_21423520,
title = {Growth and transport properties of thin Co-based Heusler films; Wachstum und Transporteigenschaften duenner Co-basierter Heusler-Filme}
author = {Schneider, Horst}
abstractNote = {During this work, thin films of Co-based Heusler compounds were deposited under optimized conditions, and their structural, magnetic, and transport properties were investigated. The growth of the thin film samples was accomplished by two different methods. At first Co{sub 2}Cr{sub 0.6}Fe{sub 0.4}Al and Co{sub 2}FeSi were deposited by sputter deposition from stoichiometric targets. This is considered the standard technique for the preparation of thin Heusler films. Also for the compounds investigated here it resulted in samples with a high degree of L2{sub 1} ordering. An excess of Fe atoms on Si sites was discovered by a detailed X-ray analysis in conjunction with NMR spectroscopy. The choice of different substrates allowed the adjustment of the growth direction. On the other hand, bulk magnetometry revealed that these sputter deposited films exhibit only a reduced magnetic moment, which is an indication of a reduced spin asymmetry at the Fermi level. One source of this problem seems to be a high residual gas pressure, which leads to an increased sample contamination. To improve this situation, a pulsed laser deposition system was constructed and put into operation. The resulting film growth under ultra-high vacuum conditions led to a further improvement of the short-range crystallographic ordering and a clear enhancement of the magnetic properties. The additional use of a metallic buffer layer resulted in samples with a smooth surface. This opens the door for a number of further analytical experiments, such as tunneling spectroscopy or Brillouin light scattering. After this successful demonstration of this growth technique, an additional method for the flexible variation of the film stoichiometry was implemented. In this work, this method was successfully applied in the deposition of Co{sub 2}Mn{sub 1-x}Fe{sub x}Si films. All samples in this series show a high degree of atomic ordering. Their magnetization values are compatible with the Slater-Pauling rule for half-metallic Heusler compounds. The availableness of these high quality quaternary alloy films allowed the systematic investigation of their electronic properties. Band structure calculations predict that the substitution of Mn by Fe leads to a shift of the Fermi energy over the minority energy gap, whereas the density of states remains nearly unchanged. The corresponding changes in the topology of the Fermi surface could be tested by electronic transport measurements. This is particularly obvious in the normal Hall effect. Here a transition from a hole-like charge transport in Co{sub 2}MnSi to an electron-like transport in Co{sub 2}FeSi could be demonstrated. This is in accordance with the corresponding band structure calculations. Additionally, with these samples comparative XMCD experiments were performed. The densities of states reconstructed from these spectra show the expected shift of the Fermi energy as well. Furthermore, the behavior of the anomalous Hall effect was studied. Here it could be seen that the effect is influenced by two mechanisms: On the one hand an intrinsic contribution, caused by the topology of the Fermi surface and on the other hand by temperature dependent impurity scattering. These two effects have an opposing influence on the anomalous Hall effect. This can lead to an observable sign reversal of the anomalous contribution. This behavior has been predicted just recently and was in this work systematically investigated for the first time for Heusler compounds. (orig.)}
place = {Germany}
year = {2010}
month = {Jul}
}