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MA: Fachverband Magnetismus

MA 26: Magnetic Shape Memory Alloys II

MA 26.5: Vortrag

Mittwoch, 25. März 2009, 15:45–16:00, HSZ 103

Reversibility of magnetostructural transition in Ni-Mn-In-Co magnetic shape memory alloys — •Jian Liu, Julia Lyubina, Nils Scheerbaum, and Oliver Gutfleisch — IFW Dresden, Institute for Metallic Materials, P.O. Box 270116, D-01171 Dresden, Germany

For Ni-Mn-based Heusler alloys showing a magnetic-field induced martensitic transition, the reversibility of the magnetostructural transition is of crucial importance for magnetic-shape-memory actuator materials. It is desirable that the austenite induced by the magnetic field is able to transform back to the initial martensite when the magnetic field is removed. A complete recovery of the initial martensite state may bring about magneto-elasticity (two-way shape memory effect), while the irreversible magnetostructural transition would result in magneto-plasticity (one-way shape memory effect). Here, by analyzing isothermal magnetization curves under magnetic field cycling, the reversibility of the magnetostructural transition was investigated in Ni45Mn37In13Co5 in form of bulk sample and melt-spun ribbons. Hysteresis in the thermally and magnetically induced martensitic transformation plays an important role in the reversibility of the magnetostructural transition. In ribbons with a large hysteresis of 18 K, a residual field-induced austenite is present after removing the magnetic field, while, in the bulk sample, the magnetostructural transition is reversible at moderate temperatures due to a relatively smaller hysteresis of 8 K. Additionally, the magnetocaloric effect strongly depends on the sample history due to the occurrence of the irreversible magnetostructural transition, especially for the ribbons.