The Co-substitution for Ni in the Mn-rich NiMnGa Heusler alloys changes substantially their structural and magnetic ordering. The results will be discussed within the basic thermodynamic relations

Albertini, Franca

Arnold, Zdenek

Cavallari, Chiara

Fabbrici, Simone

Kamarad, Jiri

Paoluzi, Antonio

Solzi, Massimo

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Abstract Submitted to the
The International Conference on Magnetism - ICM 2009
in Karlsruhe, Germany
July 26-31, 2009
Direct and indirect measurement of magnetocaloric effect in
NiCoMnGa alloys∗
Jiri Kamara´d1, Simone Fabbrici2, Chiara Cavallari3, Massimo Solzi3, Franca Albertini2,
Zdenek Arnold1, Antonio Paoluzi2
1 Institute of Physics AS CR, v.v.i., Prague, Czech Republic
2 Istituto dei Materiali per l’Elettronica ed il Magnetismo, IMEM-CNR, Parma, Italy
3 Universita degli Studi di Parma, Parma, Italy
The Co-substitution for Ni in the Mn-rich NiMnGa Heusler alloys changes substantially
their structural and magnetic ordering. Temperature of martensitic transitions TM decreases
and difference between magnetization of their martensitic and austenitic phases increases
with increasing Co-content [1]. These results stimulated us to study magnetocaloric effects
(MCE) in the Ni50−xCoxMn25+yGa25−y alloys (x=0;5;7) by the direct adiabatic measure-
ment of dT induced by field 1T and by the indirect determination of MCE from magnetiza-
tion measurements in fields up to 5T using the Maxwell relation. In comparison with pure
stoichiometric alloy Ni2MnGa , dS(TM) = -2.2 J/Kkg, the substantially higher and positive
values of dS(TM) were determined for the Co-doped alloys, dS(TM) = +6.7 J/Kkg for x=5
and +9.9 J/Kkg for x=7. The adiabatic dT measurement was used to estimate specific heat
of the alloys. The results will be discussed within the basic thermodynamic relations.
[1] S.Y. Yu et al., Appl. Phys. Lett. 91, 102507 (2007)
∗This work was supported by Grant Agency of CR, Project No.202/09/1027


Direct and indirect measurement of magnetocaloric effect in NiCoMnGa alloys

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Direct and indirect measurement of magnetocaloric effect in NiCoMnGa alloys

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