On the Driving Forces of Magnetically Induced Martensitic Transformation in Directionally Solidified Polycrystalline Ni-
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A. Possible Available Driving Forces for the Magnetically Induced Martensitic Transformation
RECENT reports have shown that Ni-Mn-Z (Z = In, Sn, Sb) systems as a new class of metamagnetic shape memory alloys (MSMAs)[1,2] are based on a magnetically induced martensitic transformation
QIAODAN HU is with the Shanghai Key Laboratory of Materials Laser Processing and Modification, Shanghai Jiao Tong University, Shanghai 200240, P.R. China, and also with the School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] ZHENNI ZHOU, LIANG YANG, YUJIN HUANG, and JIANGUO LI are with the School of Materials Science and Engineering, Shanghai Jiao Tong University. JUN LI is with the School of Materials Science and Engineering, Shanghai Jiao Tong University, and also with the Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai Jiao Tong University, Shanghai 200240, P.R. China. Contact e-mail: [email protected] Manuscript submitted June 6, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS A
(MIMT) from ferromagnetic (FM) austenite to antiferromagnetic (AFM) martensite.[3,4] The unique MIMT results in an unprecedented variety of physical properties, such as large magnetic field induced strain (MFIS),[1,5] inverse magnetocaloric effect (MCE),[3,6] baro-caloric effect,[7] giant magneto-resistance effect,[8] and high magneto-thermal conductivity.[9] Moreover, this peculiar transformation is observed not only in single crystals, but also in polycrystalline specimens. Thus, their diverse properties are of great potential for many applications in high-performance actuators,[10] environment-friendly magnetic refrigerators,[3,6,7] and energy harvesting,[11] etc. These excellent properties have attracted much attention over the last decade. As for these MSMAs, the application of the magnetic field leads to an evident negative shift in the transformation equilibrium temperatures due to a large magnetization difference between the martensite and the austenite, as shown in Figure 1(a). In other words, if the sample is at a constant temperature (T0) close to Mf, when increasing the magnetic field, the MIMT from AFM martensite to FM austenite will occur due to the changes in chemical free energy. Therefore, one
Fig. 1—Schematics of (a) the magnetization vs temperature (M–T) curves affected by the magnetic fields and (b) the possible available driving forces of the magnetically induced phase transformation, including the magnetic anisotropy energy (MAE), and the Zeeman energy difference between austenite and martensite. Forward and reverse transformation start and finish at Ms, As and Mf, Af, respectively. Ms: saturation magnetization.
considers that the driving forces of the MSMAs are the Zeeman energy from the difference in the saturation magnetizations of transforming phases (Figure 1(b)). In contrast, the MIMT in the ferromagnetic shape memory alloys (FSMAs)[12] is hardly triggered by the Zeeman energy because of a small magnetization jump
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