TY - JOUR
T1 - PHASE STABILITY of L21 PHASE in Co-BASED HEUSLER ALLOYS
AU - Umetsu, Rie Y.
AU - Okubo, Akinari
AU - Nagasako, Makoto
AU - Ohtsuka, Makoto
AU - Kainuma, Ryosuke
AU - Ishida, Kiyohito
N1 - Funding Information:
The authors would like to express sincere thanks to Professor K. Ishikawa of Kanazawa University, Dr. K. Kobayashi of Tohoku University and emeritus Professor T. Kanomata of Tohoku-Gakuin University for their help in the experimental work and their valuable discussions. The powder ND experiments were carried out under the cooperative research work with emeritus Professor Y. Yamaguchi of Tohoku University. A part of this work was supported by a grant-in-aid from the Japan Science and Technology Agency, a grant for Scientific Research from the Japan Society for the Promotion of Science, and by a Global COE project grant.
Funding Information:
The authors would like to express sincere thanks to Professor K. Ishikawa of Kanazawa University, Dr. K. Kobayashi of Tohoku University and emeritus Professor T. Kanomata of Tohoku-Gakuin University for their help in the experimental work and their valuable discussions. The powder ND experiments were carried out under the cooperative research work with emeritus Professor Y. Yamaguchi of Tohoku University. A part of this work was supported by a grant-in-aid from the Japan Science and Technology Agency, a grant for Scienti¯c Research from the Japan Society for the Promotion of Science, and by a Global COE project grant.
Publisher Copyright:
© 2014 World Scientific Publishing Company.
PY - 2014/12/1
Y1 - 2014/12/1
N2 - Order-disorder phase transition temperature from L21 to B2 phase, TtL21=B2, in Co-based Heusler alloys was systematically investigated based on the Braggs-Williams-Gorsky (BWG) approximation. Because height of TtL21=B2 closely correlates to phase stability of the L21 phase, confirmation of TtL21=B2 would be a key to obtain a highly ordered L21 phase. From modification with the BWG approximation it was shown that the degree of order indicated temperature dependence, namely, the degree of order decreased above around 0.6 TtL21=B2 and reached zero at TtL21=B2. Therefore, it should be better to select the Co-based Heusler alloys with a higher value of TtL21=B2 if the higher degree of order in the L21 phase is desired by thermal annealing at as low temperature as possible. From powder neutron diffraction (ND) studies of Co2Y Ga (Y = Ti, V, Cr, Mn and Fe) alloys it was actually confirmed that materials with higher value of TtL21=B2 indicated higher degree of order even in the same annealing temperature. Studies for the phase state in Co-Ti-Fe-Ga films also showed that a height of TtL21=B2 concretely correlated to the phase stability of the L21 phases, that is, the specimen with higher value of TtL21=B2 was easy to obtain with a higher degree of order.
AB - Order-disorder phase transition temperature from L21 to B2 phase, TtL21=B2, in Co-based Heusler alloys was systematically investigated based on the Braggs-Williams-Gorsky (BWG) approximation. Because height of TtL21=B2 closely correlates to phase stability of the L21 phase, confirmation of TtL21=B2 would be a key to obtain a highly ordered L21 phase. From modification with the BWG approximation it was shown that the degree of order indicated temperature dependence, namely, the degree of order decreased above around 0.6 TtL21=B2 and reached zero at TtL21=B2. Therefore, it should be better to select the Co-based Heusler alloys with a higher value of TtL21=B2 if the higher degree of order in the L21 phase is desired by thermal annealing at as low temperature as possible. From powder neutron diffraction (ND) studies of Co2Y Ga (Y = Ti, V, Cr, Mn and Fe) alloys it was actually confirmed that materials with higher value of TtL21=B2 indicated higher degree of order even in the same annealing temperature. Studies for the phase state in Co-Ti-Fe-Ga films also showed that a height of TtL21=B2 concretely correlated to the phase stability of the L21 phases, that is, the specimen with higher value of TtL21=B2 was easy to obtain with a higher degree of order.
KW - Braggs-Williams-Gorsky approximation
KW - degree of order
KW - Order-disorder phase transition temperature
KW - phase stability
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U2 - 10.1142/S2010324714400189
DO - 10.1142/S2010324714400189
M3 - Article
AN - SCOPUS:85039434735
SN - 2010-3247
VL - 4
JO - SPIN
JF - SPIN
IS - 4
M1 - 1440018
ER -