TY - JOUR

T1 - Magnetic field and stress induced martensite reorientation in NiMnGa ferromagnetic shape memory alloy single crystals

AU - Karaca, H. E.

AU - Karaman, I.

AU - Basaran, B.

AU - Chumlyakov, Y. I.

AU - Maier, H. J.

N1 - Funding Information: This work was supported by the U.S. Army Research Office, Contract No. DAAD 19-02-1-0261, the National Science Foundation – Division of Materials Research, Contract No. 0244126, the US Civilian Research and Development Foundation, Grant No. RE1-2525-TO-03, and the Deutsche Forschungsgemeinschaft.

PY - 2006/1

Y1 - 2006/1

N2 - Magnetic shape memory properties of a single crystal Ni2MnGa alloy were characterized through monitoring magnetic field induced strain (MFIS) as a function of compressive stress, and applied stress induced strain as a function of magnetic field. Compressive stress and magnetic field were applied perpendicular to each other along the [1 0 0] and [0 1 1] axes, respectively. The critical magnetic fields for variant reorientation, first cycle effect and cyclic evolution of MFIS are reported as a function of stress level. It was revealed that increasing constant magnetic field level significantly increases the stress required for the reorientation, i.e., magnetostress and leads to superelasticity in martensite. Possible microstructural mechanisms, considering the interplay between stress and magnetic field favored martensite variants, magnetic domains and magnetization rotation, are proposed. Moreover, it was observed that the MFIS evolution is field rate dependent as was evidenced by a rate dependent two-stage reorientation where the maximum MFIS magnitude increases as the field rate increases. This effect was attributed to the difference between the nucleation and propagation barrier strength for twin boundary motion in NiMnGa alloys. The magnetostress (5.7 MPa), blocking stress (5 MPa) and maximum MFIS (5.8%) combination observed in this study is the highest reported to date in NiMnGa alloys. The high blocking and magnetostresses are a consequence of the low test temperature (-95 °C) where the magnetocrystalline anisotropy energy is high and detwinning stress is low. Thus, for magnetic shape memory alloys, the selection of the operating temperature with respect to martensite start and Curie temperatures is critical in optimizing actuator performance since both magnetocrystalline anisotropy energy and detwinning stress are a strong function of temperature below the characteristic temperatures.

AB - Magnetic shape memory properties of a single crystal Ni2MnGa alloy were characterized through monitoring magnetic field induced strain (MFIS) as a function of compressive stress, and applied stress induced strain as a function of magnetic field. Compressive stress and magnetic field were applied perpendicular to each other along the [1 0 0] and [0 1 1] axes, respectively. The critical magnetic fields for variant reorientation, first cycle effect and cyclic evolution of MFIS are reported as a function of stress level. It was revealed that increasing constant magnetic field level significantly increases the stress required for the reorientation, i.e., magnetostress and leads to superelasticity in martensite. Possible microstructural mechanisms, considering the interplay between stress and magnetic field favored martensite variants, magnetic domains and magnetization rotation, are proposed. Moreover, it was observed that the MFIS evolution is field rate dependent as was evidenced by a rate dependent two-stage reorientation where the maximum MFIS magnitude increases as the field rate increases. This effect was attributed to the difference between the nucleation and propagation barrier strength for twin boundary motion in NiMnGa alloys. The magnetostress (5.7 MPa), blocking stress (5 MPa) and maximum MFIS (5.8%) combination observed in this study is the highest reported to date in NiMnGa alloys. The high blocking and magnetostresses are a consequence of the low test temperature (-95 °C) where the magnetocrystalline anisotropy energy is high and detwinning stress is low. Thus, for magnetic shape memory alloys, the selection of the operating temperature with respect to martensite start and Curie temperatures is critical in optimizing actuator performance since both magnetocrystalline anisotropy energy and detwinning stress are a strong function of temperature below the characteristic temperatures.

KW - Detwinning

KW - Ferromagnetic materials

KW - Ferromagnetic shape memory alloys

KW - Martensite reorientation

KW - Shape memory alloys

UR - http://www.scopus.com/inward/record.url?scp=27744461590&partnerID=8YFLogxK

U2 - 10.1016/j.actamat.2005.09.004

DO - 10.1016/j.actamat.2005.09.004

M3 - Article

AN - SCOPUS:27744461590

VL - 54

SP - 233

EP - 245

JO - Acta materialia

JF - Acta materialia

SN - 1359-6454

IS - 1

ER -