MAGNETOCALORIC RESPONSE OF NON-STOICHIOMETRIC Ni2MnGa ALLOYS AND THE INFLUENCE OF CRYSTALLOGRAPHIC TEXTURE.
Currently, there is significant interest in magnetocaloric materials for solid state refrigeration. In this work, polycrystalline Heusler alloys belonging to the Ni2+xMn1-xGa family, with x between 0.08 and 0.24, were evaluated for the purpose of finding composition(s) with an enhanced magnetocaloric effect (MCE) close to room temperature. Differential scanning calorimetry (DSC) was successfully used to screen alloy composition for simultaneous magnetic and structural phase transformations; this coupling needed for a giant MCE. The alloy with x = 0.16 showed an excellent match of transformation temperatures and exhibited the highest magnetic entropy change, ΔSM, in the as-annealed state. Furthermore, the MCE increased by up to 84 % with a 2 Tesla (T) field change when the samples were thermally cycled through the martensite to austenite transformation temperature while held under a constant mechanical load. The highest ΔSMmeasured for our x = 0.16 alloy for a 2 T magnetic field change was -18 J/kg-K. Texture measurements suggest that preferential orientation of martensite variants contributed to the enhanced MCE in the stress-assisted thermally cycled state.
New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.
M V
MV
McLeod
TKC Global, Herndon, VA 20171, USA.
A K
AK
Giri
National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
B A
BA
Paterson
National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
C L
CL
Dennis
University of Central Florida, Orlando, FL 32816, USA.
L
L
Zhou
Los Alamos National Laboratory, Lujan Neutron Science Center, Los Alamos, NM 87545, USA.
S C
SC
Vogel
Los Alamos National Laboratory, Lujan Neutron Science Center, Los Alamos, NM 87545, USA.
O
O
Gourdon
Los Alamos National Laboratory, Lujan Neutron Science Center, Los Alamos, NM 87545, USA.
H M
HM
Reiche
US Army Research Laboratory, Aberdeen Proving Ground, MD 21005 USA.
K C
KC
Cho
University of Central Florida, Orlando, FL 32816, USA.
Y H
YH
Sohn
National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
R D
RD
Shull
New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.
B S
BS
Majumdar
NiMnGa alloy; magnetocaloric; polycrystalline; preferred orientation; twinning