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Title: Electron spin resonance and magnetic characterization of the Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}

Abstract

Electron spin resonance was applied on samples of Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}. The results are discussed under the scope of magnetization measurements, optical metallography, and wavelength dispersive spectroscopy. Polycrystalline arc-melted samples submitted to different heat treatments were investigated. The correlation of the electron spin resonance and magnetization results permitted a characterization of the present phases and their transitions. Two coexisting phases in the temperature range between two phase transitions have been identified and associated to distinct crystallographic phases. Additionally, the magnetic moment at high temperatures has been estimated from the measured effective g factor. A peak value of 21.5 J/kg K for the magnetocaloric effect was obtained for a sample heat treated at 1500 deg. C for 16 h.

Authors:
; ; ; ; ;  [1]
  1. Instituto de Fisica Gleb Wataghin, Universidade Estadual de Campinas, Unicamp, Cx. P. 6165, 13083-970, Campinas, Sao Paulo (Brazil)
Publication Date:
OSTI Identifier:
20787759
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 72; Journal Issue: 22; Other Information: DOI: 10.1103/PhysRevB.72.224435; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CORRELATIONS; ELECTRON SPIN RESONANCE; GADOLINIUM ALLOYS; GERMANIUM ALLOYS; HEAT TREATMENTS; LANDE FACTOR; MAGNETIC MOMENTS; MAGNETIZATION; PARAMAGNETISM; PHASE TRANSFORMATIONS; POLYCRYSTALS; SILICON ALLOYS; SPECTROSCOPY; WAVELENGTHS

Citation Formats

Pires, M.J.M., Carvalho, A. Magnus G., Gama, S., Silva, E.C. da, Coelho, A.A., and Mansanares, A.M. Electron spin resonance and magnetic characterization of the Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}. United States: N. p., 2005. Web. doi:10.1103/PHYSREVB.72.2.
Pires, M.J.M., Carvalho, A. Magnus G., Gama, S., Silva, E.C. da, Coelho, A.A., & Mansanares, A.M. Electron spin resonance and magnetic characterization of the Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}. United States. doi:10.1103/PHYSREVB.72.2.
Pires, M.J.M., Carvalho, A. Magnus G., Gama, S., Silva, E.C. da, Coelho, A.A., and Mansanares, A.M. Thu . "Electron spin resonance and magnetic characterization of the Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}". United States. doi:10.1103/PHYSREVB.72.2.
@article{osti_20787759,
title = {Electron spin resonance and magnetic characterization of the Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}},
author = {Pires, M.J.M. and Carvalho, A. Magnus G. and Gama, S. and Silva, E.C. da and Coelho, A.A. and Mansanares, A.M.},
abstractNote = {Electron spin resonance was applied on samples of Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}. The results are discussed under the scope of magnetization measurements, optical metallography, and wavelength dispersive spectroscopy. Polycrystalline arc-melted samples submitted to different heat treatments were investigated. The correlation of the electron spin resonance and magnetization results permitted a characterization of the present phases and their transitions. Two coexisting phases in the temperature range between two phase transitions have been identified and associated to distinct crystallographic phases. Additionally, the magnetic moment at high temperatures has been estimated from the measured effective g factor. A peak value of 21.5 J/kg K for the magnetocaloric effect was obtained for a sample heat treated at 1500 deg. C for 16 h.},
doi = {10.1103/PHYSREVB.72.2},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 22,
volume = 72,
place = {United States},
year = {Thu Dec 01 00:00:00 EST 2005},
month = {Thu Dec 01 00:00:00 EST 2005}
}
  • Gd{sub 5}Si{sub 4}, Gd{sub 5}Ge{sub 4}, and Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88} compounds were studied by electron spin resonance. The arc-melted samples were initially characterized by optical metallography, x-ray diffraction, and static magnetization measurements. The electron spin resonance results show a negative paramagnetic g shift for Gd{sub 5}Si{sub 4} and Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}, and a smaller positive one for Gd{sub 5}Ge{sub 4}. The values of the exchange parameter (j) between the localized Gd-4f spins and the conduction electrons are obtained from the g shifts. These values are positive and of the same order of magnitude for Gd{sub 5}Si{sub 4} andmore » Gd{sub 5.09}Ge{sub 2.03}Si{sub 1.88}, and negative one order of magnitude smaller for Gd{sub 5}Ge{sub 4}. The electron spin resonance data were interpreted considering the strongly bottlenecked solution of the coupled Bloch-Hasegawa equations.« less
  • The Si{sub 2}{sup +} and Ge{sub 2}{sup +} cation radicals were generated by pulsed laser vaporization and isolated in rare-gas matrices at 4 K for electron spin resonance (ESR) investigations. The electronic ground states were established as X{sup 4}{Sigma} for both cations with the three unpaired electrons occupying predominantly valence p-type orbitals. In the case of {sup 29}Si{sub 2}{sup +}, the observed nuclear hyperfine interaction (A tensor) was compared with that computed in an ab initio configuration interaction type calculation. The dependence of the hyperfine parameters on internuclear distance was also investigated. For comparison purposes, all diatomic and triatomic cationsmore » studied in the gas phase and in rare-gas matrices at sufficiently high resolution to observe nuclear hyperfine interaction are listed. For {sup 29}Si{sub 2}{sup +} in neon, g{sub {perpendicular}} = 1.993 (1), {vert bar}A{sub {perpendicular}}{vert bar} = 52.4 (5) MHz, and D = 27.6 (8) GHz; for {sup 73}Ge{sub 2}{sup +}, g{sub {perpendicular}} = 1.939 (1) and {vert bar}A{sub {perpendicular}}{vert bar} = 10 (3) MHz.« less
  • The coexistence of ferromagnetic and paramagnetic phases in the 4f-electron systems Gd{sub 5}(Si{sub 1.5}Ge{sub 2.5}) and Gd{sub 5}(Si{sub 2}Ge{sub 2}) during the magnetic-martensitic phase transition have been observed. A dc magnetic field reversibly changes both the magnetic and crystal structures of the alloys above their respective Curie temperatures. A negative imaginary component of the ac magnetic susceptibility for both alloys has been observed in the ferromagnetic state. The results are discussed in terms of indirect Ruderman-Kittel-Kasuya-Yosida and direct superexchange interactions, and anomalies of the relaxation process.
  • The electron spin resonance (ESR) at phosphorus dopants in the P-doped Si{sub 1-x}Ge{sub x} alloys (0 < x < 0.057) with the concentration of phosphorus in the range 10{sup 15}-10{sup 16} cm{sup -3} is studied at temperatures from 3 to 30 K. The ESR spectra of the alloys (x > 0) are compared to the ESR spectra of similar silicon samples (x = 0). It is found that, from the smallest Ge content x = 0.008, the ESR spectra contain two additional lines. It is assumed that these lines are due to phosphorus dopants located in clusters with higher Gemore » content. It is found that an increase in the Ge content in the alloys up to x = 0.024 yields only an increase in the concentration of such clusters. At x {>=} 0.024, the Ge content increases with x both inside and outside the clusters.« less
  • Gd 5(Si xGe 1–x) 4 has mixed phases in the composition range 0.32 < x < 0.41, which have not been widely studied. In this paper, we have synthesized and indexed single crystal samples of Gd 5Si 1.3Ge 2.7 and Gd 5Si 1.4Ge 2.6. In this study, we have investigated the first order and second order phase transition temperatures of these samples using magnetic moment vs. temperature and magnetic moment vs. magnetic field at different temperatures. We have used a modified Arrott plot technique that was developed and reported by us previously to determine the “hidden” second order phase transitionmore » temperature of the orthorhombic II phase.« less