Both the authors contributed equally to this work.
Key Properties of NiMnGa Based Single Crystals Grown with the SLARE Technique†
Article first published online: 23 JUL 2012
Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Advanced Engineering Materials
Volume 14, Issue 8, pages 614–635, August 2012
How to Cite
Rolfs, K., Chmielus, M., Guldbakke, J. M., Wimpory, R. C., Raatz, A., Petry, W., Müllner, P. and Schneider, R. (2012), Key Properties of NiMnGa Based Single Crystals Grown with the SLARE Technique. Adv. Eng. Mater., 14: 614–635. doi: 10.1002/adem.201200065
The support of this work by Deutsche Forschungsgemeinschaft (SPP1239, grant No. Schn 1106 and No. Ra 1736) is gratefully acknowledged. P. M. acknowledges partial financial support of the Department of Energy Office of Basic Energy Sciences (DOE BES) through contract DEFG-02-07ER46396 for performing the experiments with the rotating magnetic field and the magnetization measurements. PM is thankful to ETH Zürich, Switzerland, for donating the DMMT and SMMT.
- Issue published online: 6 AUG 2012
- Article first published online: 23 JUL 2012
- Manuscript Accepted: 18 JUN 2012
- Manuscript Received: 15 FEB 2012
- Department of Energy Office of Basic Energy Sciences (DOE BES)
Magnetic shape memory alloys (MSMAs), exhibit large strains and hence are materials, which could substitute giant magnetostrictive and piezoelectrical materials in actuating devices. The actuation stress needed to induce the strain is much lower than in other actuator materials. Since the strain can be induced without phase transformation by a magnetic field, the development of actuators with high working frequencies is possible. However, for reasonable applications, large strains have to be induced with small magnetic fields. Up to now repeatable magnetically induced strains of 5–10% in magnetic fields of less than 500 mT have been achieved only in single crystals. The production of NiMnGa based single crystals is difficult and time consuming. The crystal quality is affected by porosity and impurities. With the Bridgeman based method called Slag Remelting and Encapsulation (SLARE) single crystalline ingots of NiMnGa, NiMnGaFe, and NiMnGaCo of high quality were grown and characterized. The results show that MSMA properties depend on the position within the single crystalline rods due to a composition gradient. The influence of surface treatment demonstrates that the decrease of surface roughness leads to a decrease of twinning stress. MSMAs with twinning stresses above 1 MPa show a magnetic field induced strain (MFIS) when tilting is not restricted by constraints. Softer samples can adapt to constraints much better and show large MFIS. Substituting Ni by Fe and Co, shifted the phase transitions successfully to higher temperatures. NiMnGa alloyed with up to 6 at.% Co showed three different martensite structures: a non-modulated tetragonal structure, a modulated tetragonal structure, showing the same behavior as NiMnGa with identical structures and a non-modulated orthorhombic structure with a stress–strain-behavior explainable by the double twinning mechanism.