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Dynamics of the phase-change material GeTe across the structural phase transition

Frontiers of physics 2019年第2期14卷 65-71页

作者： T. Chatterji S. Rols U. D. Wdowik Institut Laue-Langevin 71 avenue des Martyres38000 GrenobleFrance Institut of Technology Pedagogical UniversityPodchorazych 2PL-30-084 KrakowPoland

Results of inelastic neutron scattering experinients and ab initio molecular dynamics simulations for GeTe 一 the parent compound of phase-change materials are reported. The inelastic neutron spectra of GeTe powder samples have been determined in the temperature range extending from 300 to 700 K. The phonon peaks undergo thermal shifts resulting from anharmonic effects being weaker for acoustic than optic modes. A small concentration of free charge carries arising from the presence of Ge-vacancies was found not to affect significantly the neutron weighted phonon densities of states of GeTe. The spectral pattern changes qualitatively across the structural phase transition, but the local structure of GeTe remains hardly affected, as confirmed by the analysis of temperature dependence of the pairdistribution function obtained from ab initio molecular dynamics investigations. The present theoretical studies support in a wide extent our experimental observations and also those provided by local probe methods.

关键词： phase-change mat erials inelastic neutron scattering ab initio molecular dynamics

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Physical prope rties of qua ternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals

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Frontiers of physics 2019年第2期14卷 59-64页

作者： Kaijian Huang Yuanshuai Sun Shanshan Sun Xiao Zhang Hechang Lei College of Civil Engineering Nanjing Forestry UniversityNanjing 210037China Department of Physics and Beijing Key Laboratory of Opto-electronic Functional Materials & Micro-nano Devices Renmin University of ChinaBeijing 100872China State Key Laboratory of Information Photonics and Optical Communications & School of Science Beijing University of Posts and TelecommunicationsBeijing 100876China

We have synthesized and investigated physical properties of two new quaternary compounds Gd2CoAl4T2 (T = Si, Ge) single crystals, which are isostructural to Tb2NiAl4Ge2 and Er2CoAl4Ge2. The most important structural feature of these materials is the anti-CaF2-type CoAl4T2 slabs. These materials show metallic behavior below 300 K and there is a long-range antiferromagnetic (AFM) transition appearing at 20 and 27 K for GdCoAl4Ge2 and Gd2CoAl4Si2, respectively. Resistivity and heat capacity measurements also confirm these bulk AFM transitions. Further analysis indicates that this long-range antiferromagnetism should result from the magnetic interaction between local moments of Gd^3+ ions.

关键词： magnetic mat erials rare earth compounds single crystal growth

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