Magnetocaloric materials have gained significant interest as an environment friendly
and efficient solid state refrigeration technology. We have been working on Heusler
alloys, primarily the non-stoichiometric Ni2MnGa system that rely on magnetic field induced first order structural transformation
(‘magnetostructural transformation’) for improved magnetocaloric effect (MCE). The
work was originally funded by the Army Research Laboratories. The magnetostructural
transformation temperature is sensitively dependent on composition, so that alloying
chemistry have to be optimized for martensitic transformation close to RT. In addition,
we have observed significant MCE increase (up to 80%) following stress assisted thermally
cycling of samples, and have demonstrated that one primary mechanism responsible for
the increased MCE is the development of preferred crystallographic orientation in
the martensite phase. The rationale for this approach derived from our previous work
on shape memory NiTi samples, where in situ neutron diffraction work LANL showed favorable texture when a sample was cooled from
the austenite to the martensite under low applied stress – an effect due to very low
shear modulus at the transformation temperature. That work was funded initially through
ARO and later through NSF.
In more recent work we have been studying the influence of elemental doping,
in order to bring the magnetostructural transformation from about 60 C to RT while
at the same time enhancing MCE.
M.V. McLeod, B.S. Majumdar, Z. Turgut. Magnetocaloric Improvements in Doped Heusler Alloys, MRS Advances 2 (2017) 3453-3458 (2017).
M.V. McLeod, A.K. Giri, B.A. Paterson, C.L. Dennis, L. Zhou, S-C. Vogel, B.S. Majumdar, et al. Magnetocaloric response of non-stoichiometric Ni2MnGa alloys and the influence of
crystallographic texture, Acta Mater; 97:245-56 (2015).
L. Zhou, A. Giri, K. Cho, H. Heinrich, B. Majumdar, Y. Sohn. Microstructural and Crystallographic Characterization of Ni2+x Mn1-x Ga Alloys (x =0.14,
0.16, 0.19, 0.22, and 0.24) by Transmission Electron Microscopy, Metallurgical and Materials Transactions E 1, 239-246 (2014).
A.K. Giri, B.A. Paterson, M.V. McLeod, C.L. Dennis, B.S. Majumdar, K.C. Cho, R.D. Shull. Effect of crystallographic alignment on the magnetocaloric effect in alloys near the
Ni2MnGa stoichiometry, Journal of Applied Physics 17A907 (2013).
B. Ye, B.S. Majumdar, I. Dutta. Texture development and strain hysteresis in a NiTi shape-memory alloy during thermal
cycling under load, Acta Mater. 57 (2009) 2403-2417.
B. Ye*, B.S. Majumdar, I. Dutta. Texture memory and strain-texture mapping in a NiTi shape memory alloy, Appl. Phys. Lett. 91 (2007) 061918.
Structural and Magnetic Properties of Magnetocaloric Ni-Mn-Ga Heusler Alloys as Influenced
by Elemental Doping and Processing - M.V. McLeod (2017).