Structural Transitions and Magnetic Properties of Ni 50 Mn 36.7 In 13.3 Particles with Amorphous-Like Phase
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THE Ni-Mn-Ga/Ni-Mn-In ferromagnetic shape memory alloys (FSMAs) have attracted much interest due to the colossal magnetic-field-induced strain (MFIS). The MFIS can be achieved through the reorientation of martensitic variants (e.g., Ni-Mn-Ga[1–3]) or reverse martensitic phase transformation (e.g., Ni-Mn-In[4–8]) while a magnetic field is applied. Besides the colossal MFIS, the Ni-Mn-In FSMAs also exhibit the giant magnetoresistance and large inverse magnetocaloric effect.[7–11] The phase transformation behaviors and structural characteristics of the Ni-Mn-Ga/Ni-Mn-In FSMAs have been well documented.[1–11] The previous studies focused mainly on bulk polycrystalline materials and single crystals. However, the intrinsic brittleness of bulk polycrystalline alloys and high cost of single crystals have significantly hindered their practical applications. To overcome this problem, and driven by the motivation to design new types of functional materials used as D.M. LIU, Graduate Student, is with the Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819, P.R. China. Z.H. NIE, Lecturer, and Y.D. WANG, Professor, are with the School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, P.R. China. Contact e-mail: [email protected] Y. REN, Senior Research Scientist, is with the X-ray Science Division, Argonne National Laboratory, Argonne, IL 60439. J. PEARSON, Engineer, is with the Materials Science Division, Argonne National Laboratory. P.K. LIAW, Professor, is with the Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996. D.E. BROWN, Associate Professor, is with the Department of Physics, Northern Illinois University, DeKalb, IL 60115. Manuscript submitted April 21, 2010. Article published online May 19, 2011 3062—VOLUME 42A, OCTOBER 2011
nanoscale actuators, Wang and co-workers[12,13] have prepared Ni-Mn-Ga nanoparticles through the highenergy ball-milling method. It is found that the Ni-MnGa nanoparticles prepared by ball milling showed a disordered face-centered-cubic structure, which transformed back to the ordered Heusler structure upon annealing. The annealed Ni-Mn-Ga nanoparticles undergo new sequences of martensitic structural transitions, different from their coarse-grained counterparts.[12,13] Actually, high-energy ball milling provides an effective routine in synthesizing a variety of alloy phases with the equilibrium or nonequilibrium state. For different intermetallic compounds with a variety of ordered atomic arrangements, the ball-milling process can induce amorphous particles, nanostructured particles, metastable crystalline, quasi-crystalline particles, etc.[12–22] Zhou and Bakker[18,19] reported that both ordered Co2Ge and GdAl2 are ferromagnets at lower temperatures. After ball milling, Co2Ge eventually transforms to the amorphous state,[18] while GdAl2 disorders atomically but remains crystalline.[19] The milling intensities can also affect the nature of the pa
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