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Ni2 MnGa that possesses a Heusler L 21 structure undergoes a martensitic transformation from the parent cubic (austenitic) phase to a low temperature complex tetragonal structure at TM =202 K and has a Curie temperature of TC =376 K. Some research groups have observed an intermartensitic transformation at a temperature TI < TM, in Ni2 MnGa single crystals. In this work detailed studies on the influence of substitution in the Mn subsystem by magnetic Co on the intermartensitic transformation properties of Ni2 Mn1-x Cox Ga compounds have been done by magnetization (5- 400 K) and thermal expansion (80- 300 K) measurements. The samples Ni2 Mn0.92 Co.08 Ga, Ni2 Mn0.91 Co.09 Ga, and Ni2 Mn0.90 Co.10 Ga were studied. The intermartensitic transformation is observed in all of these alloys. As the Co concentration increases, the transformation becomes more pronounced and the temperature range for which the alloys stay in the intermartensitic state decreases as Co concentration increases. Similarities were observed between the magnetization and thermal expansion curves. The results are discussed in terms of the internal stress produced as a result of the Co substitution. © 2006 American Institute of Physics.

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Journal of Applied Physics