Pressure-induced amorphization and collapse of magnetic order in the type-I clathrate Eu8Ga16Ge30

Autor(es)

Mardegan, J. R. L. ; Fabbris, G. ; Veiga, L. S. I. ; Adriano, C. ; Avila, M. A. ; Haskel, D. ; Giles, C.

• Tipo de documento: Artigo Científico
• Fonte: PHYSICAL REVIEW B; v. 88, n. 14, p. 8-pg., 2013-10-16.

Resumo

We investigate the low temperature structural and electronic properties of the type-I clathrate Eu8Ga16Ge30 under pressure using x-ray powder diffraction (XRD), x-ray absorption near-edge structure (XANES), and x-ray magnetic circular dichroism (XMCD) techniques. The XRD measurements reveal a transition to an amorphous phase above 18 GPa. Unlike previous reports on other clathrate compounds, no volume collapse is observed prior to the crystalline-amorphous phase transition which takes place when the unit cell volume is reduced to 81% of its ambient pressure value. Fits of the pressure-dependent relative volume to a Murnaghan equation of state yield a bulk modulus B-0 = 65 +/- 3 GPa and a pressure derivative B '(0) = 3.3 +/- 0.5. The Eu L2-edge XMCD data shows quenching of the magnetic order at a pressure coincident with the crystalline-amorphous phase transition. This information along with the persistence of an Eu2+ valence state observed in the XANES spectra up to the highest pressure point (22 GPa) indicates that the suppression of XMCD intensity is due to the loss of long range magnetic order. When compared with other clathrates, the results point to the importance of guest ion-cage interactions in determining the mechanical stability of the framework structure and the critical pressure for amorphization. Finally, the crystalline structure is not found to recover after pressure release, resulting in an amorphous material that is at least metastable at ambient pressure and temperature. (AU)

• Processo FAPESP: 12/17562-9 - Preparação de monocristais orientados para estudos de anisotropias eletrônicas, magnéticas e térmicas
• Beneficiário: Marcos de Abreu Avila
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 09/10264-0 - Estudo de compostos intermétalicos com aplicações termoelétricas por difração de raios x
• Beneficiário: José Renato Linares Mardegan
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 12/10675-2 - Estudo da dinâmica de magnetização do NiO por difração magnética resolvida no tempo
• Beneficiário: Carlos Manuel Giles Antunez de Mayolo
• Modalidade de apoio: Bolsas no Exterior - Pesquisa
• Processo FAPESP: 11/24166-0 - Estudo de compostos intermetálicos por espectroscopia de raios-X com utilização de radiação síncrotron
• Beneficiário: José Renato Linares Mardegan
• Modalidade de apoio: Bolsas no Exterior - Estágio de Pesquisa - Doutorado