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MA: Magnetismus

MA 27: Spinstrukturen und magnetische Phasenüberg
änge

MA 27.10: Vortrag

Donnerstag, 27. März 2003, 17:30–17:45, HSZ/405

Effect of cooling rate on the phase relationship and magnetic entropy change in Gd₅(Si,Ge)₄ — •Aru Yan, Axel Handstein, Oliver Gutfleisch, Konstantin Nenkov, Wei Zhang, and Karl-Hartmut Müller — Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden, PO Box 270116, D-01171 Dresden, Germany

The effects of cooling rate on the phase relationship and magnetic entropy change of Gd₅(Si, Ge)₄ were investigated. A large magnetic entropy change was observed in Gd₅(Si,Ge)₄ sample quenched from 1000^∘C, which was attributed to a magnetic field-induced martensitic phase transition around 284 K. The value of the entropy change is 9.5 J/kg K under a magnetic field of 5 T at phase transition temperature. However, the magnetic field-induced martensitic phase transition could not be detected in the slowly cooled sample (1000^∘C /1 K/min) and the magnetic ordering occurs via a second order paramagnetic-ferromagnetic transition at 300 K, accompanied by a lower magnetic entropy change. This behaviour could be confirmed by heat capacity measurements. XRD results have shown that the sample subjected to quenching consists mainly of monoclinic Gd₅(Si₂Ge₂)-type phase (with a small amount of orthorhombic Gd₅Si₂-type phase), while slow cooling is favourable for developing the orthorhombic phase with Gd₅Si₂-type structure. Further analysis revealed that the monoclinic Gd₅(Si₂Ge₂)-type phase, which is responsible for the giant magnetocaloric effect in Gd₅(Si, Ge)₄, is actually a metastable phase at room temperature.