Affiliations: [a] Precision and Intelligence Laboratory, Tokyo Institute
of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan | [b] Division of Materials Science and Engineering,
Graduate School of Engineering, Hokkaido University, Sapporo 060-8628,
Japan | [c] Institute of Materials Science, University of Tsukuba,
Tsukuba, Ibaraki 305-8573, Japan
Abstract: Martensitic and magnetic transformation temperatures were
investigated for Ni_2MnGa alloys as a function of the degree
of long-range order (LRO) associated with L2_1 structure.
The degree of order was changed by changing the heat treatment temperature.
Besides, thermal properties such as thermal expansion (CTE), specific heat
(C_P) and thermal conductivity (\lambda)
were measured up to 1273 K. It was found that with increasing the heat
treatment temperature, the degree of second neighbor ordering lowered, but that
the degree of first neighbor ordering did not show good correlations with the
heat treatment temperatures. Martensitic transformation temperature
(M_s) and Curie temperature (T_C) vary
with the square of the degree of LRO.C_P and
\lambda at room temperature are 29.5
Jmol^{-1}K^{-1} and 23.2
Wm^{-1}K^{-1}. CTE is ranged between 15
\times 10^{-6}K^{-1}
and 34 \times
10^{-6}K^{-1}. Temperature dependence of
these thermal properties is described.
Keywords: Ni[TeX:] _2MnGa, long range order, L2[TeX:] _1 structure, Curie temperature, martensitic transformation temperature, thermal expansion, specific heat, heat treatment
