Magnetic shape memory alloys

← back to Main Page

Introduction

Magnetic shape memory (MSM) alloys have the capability to produce large magnetic field-induced strain of several percent. The large strain can either be caused by a magnetic field-induced structural reorientation (usually by twin boundary motion) or by a magnetic field-induced phase transformation (usually a martensitic phase transformation). The former is mostly referred to as MSM-effect, magnetoplasticity or more precisely as magnetically induced reorientation (MIR). The magnetic field-induced phase transformation is correctly referred to as MSM effect or as magnetically induced martensite/austenite (MIM/MIA). During MIR, twin boundaries move in order to allow those twin variants having a smaller angle between easy magnetization axis and applied field direction to grow, at the expense of unfavourably oriented twin variants.

Structural reorientation gives rise to strain (a), which usually occurs by twin boundary motion, either by an external stress or magnetic field (b).

The most investigated MSM-material so far is the Heusler alloy Ni₂MnGa, but also other MSM-alloys and MSM-polymer-composites have been under scrutiny in order to overcome some of the disadvantages of (bulk) Ni₂MnGa, e.g. brittleness, difficult preparation and cost. The magnetic field and the stress induced movement of twin boundaries can be exploited for actuators, sensors and, as it is an energy dissipating process, also for vibration damping devices. Our group is working mainly on different, bulk MSM-alloys and MSM-polymer-composites.

Ni-Mn-Ga	Ni-Mn-In-Co	Ni-Fe-Ga-Co	MSM-polymer-composites

Selected publications

• J. Liu, N. Scheerbaum, D. Hinz, O. Gutfleisch: Martensitic transformation and magnetic properties in NiFeGaCo magnetic shape memory alloys, Acta Materialia 56 (2008) 3177-3186.

• N. Scheerbaum, O. Heczko, J. Liu, D. Hinz, L. Schultz, O. Gutfleisch: Magnetic field-induced twin boundary motion in polycrystalline NiMnGa fibres, New Journal of Physics 10 (2008) 73002/1-8.

• J. Liu, N. Scheerbaum, J. Lyubina, O. Gutfleisch: Reversibility of magnetostructural transition and associated magnetocaloric effect in NiMnInCo, Applied Physics Letters 93 (2008) 102512/1-3.

• N. Scheerbaum, D. Hinz, O. Gutfleisch, K.-H. Müller, L. Schultz: Textured polymer bonded composites with Ni–Mn–Ga magnetic shape memory particles, Acta Materialia 55 (2007) 2707-2713.