Rearrangement of variants in Ni2MnGa under magnetic field
Rearrangement of variants in Ni2MnGa under magnetic field
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DOI：
10.1016/j.stam.2003.10.028
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发表时间：
2004-01
影响因子：
5.5
通讯作者：
N. Okamoto;T. Fukuda;T. Kakeshita;T. Takeuchi;K. Kishio
中科院分区：
文献类型：
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作者：
N. Okamoto;T. Fukuda;T. Kakeshita;T. Takeuchi;K. Kishio
研究了在202k温度下马氏体相变的Ni2MnGa单晶中与变异体重排相关的磁场诱导应变。随着温度的降低，马氏体相的四方性略有降低，在77 K时其值约为0.940。当在零磁场下冷却至77 K后，沿[001]P（“P”为母相）方向施加磁场时，试样沿该方向收缩。随着这种收缩，c轴（易磁化轴）沿磁场方向的变异体的比例增加，达到100%左右。当沿[001]P方向施加3.2 MA/m的磁场冷却试样时，在202 K马氏体相变温度下，该分数达到100%。磁场重排引起的能量耗散与应力-应变曲线的耗散基本一致。根据单轴磁晶各向异性常数（310kj /m3, 77k）计算得出，磁场作用在孪晶面上的最大剪切应力约为2.5 MPa。这是一个适当的值，因为它大于压缩试验获得的变体重排所需的剪切应力（1.2-2.2 MPa）。
Magnetic field-induced strain which appears in association with rearrangement of variants in a stoichiometric Ni2MnGa single crystal exhibiting a martensitic transformation at 202 K has been investigated. The tetragonality of the martensite phase decreases slightly as temperature decreases and its value at 77 K is about 0.940. When the field is applied along the [001]P(‘P’ stands for the parent phase) direction after cooling down to 77 K under zero magnetic field, the specimen contracts along this direction. In association with this contraction, the fraction of the variant whose c axis (easy axis of magnetization) lies along the field direction increases and reaches about 100%. When the specimen is cooled under magnetic field of 3.2 MA/m applied along [001]P, this fraction reaches 100% at the martensitic transformation temperature of 202 K. The energy dissipated due to rearrangement of variants by magnetic field is nearly the same as that obtained from its Stress–strain curve. The maximum shear stress by the magnetic field acting on the twinning plane is evaluated to be about 2.5 MPa from its uniaxial magnetocrystalline anisotropy constant (310 kJ/m3at 77 K). This is an adequate value because it is larger than the shear stress required for the rearrangement of variants (1.2–2.2 MPa) obtained by compressive tests.