The magnetic properties, crystal and magnetic structures of Nd5 SixGe4-x were investigated by ac susceptibility and high resolution neutron powder diffraction. The magnetic and crystalline phase diagrams were derived. Four distinct structures exist in the Nd 5SixGe4-x system: Gd5Ge 4-type [O(II)], Gd5Si2Ge2-type (M), Gd5Si4-type [O(I)], and Zr5Si4-type (T). The refinements of the neutron powder diffraction patterns revealed that the Nd5SixGe4-x compounds exhibit mixed ferro-antiferromagnetic structures. The ac susceptibility measurements showed that the magnetic ordering temperature of Nd5SixGe 4-x increases slightly with increasing silicon content, except that it increases by a factor of 2 in the orthorhombic Gd5Si 4-type [O(I)] phase region. The abrupt change of the magnetic ordering temperature between x = 2.25 and x = 2.5, where the monoclinic Gd5Si 2Ge2-type (M) structure changes to the orthorhombic Gd 5Si4-type [O(I)] structure, suggested that a first order magnetostructural transition likely takes place in this narrow composition range (2.25 < x < 2.5). The investigation of Nd5Si2.335 Ge1.665 revealed that Nd5Si2.335Ge 1.665 adopts the Gd5Si2Ge2-type (M) structure and undergoes a first order magnetostructural transition from the paramagnetic-monoclinic Gd5Si2Ge2-type (M) structure to the orthorhombic Gd5Si4-type [O(I)] structure upon cooling. The T1-T1 bonds increases by ∼1 A when the the Gd 5Si4-type [O(I)] structure (10 K) transforms to the Gd 5Si2Ge2-type (M) structure (140 K). The giant magnetocaloric effect is not observed in Nd5Si2.335Ge 1.665 probably due to the co-existence of the M phase and the O(I) phase. The maximum magnetic entropy change in Nd5Si2.335Ge 1.665 is 7.3 J/kg K for magnetic field change from 0 to 7 Tesla, which is similar to that obtained in Nd5Si1.5Ge2.5, the neighboring phase O(I).
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.101661 |
| Date | January 2007 |
| Creators | Wang, Huabin, 1969- |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Master of Science (Department of Physics.) |
| Rights | © Huabin Wang, 2007 |
| Relation | alephsysno: 002613102, proquestno: AAIMR32798, Theses scanned by UMI/ProQuest. |
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