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Multiscale origin of the magnetocaloric effect in Ni-Mn-Ga shape-memory alloys

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We have analyzed magnetization measurements in a series of composition-related Ni-Mn-Ga shape-memory
alloys. It is shown that the magnetocaloric effect in the vicinity of the martensitic transition mainly originates
from two different contributions: ~i! magnetostructural coupling on the mesoscopic scale between the magnetic
moments and the martensitic variants, which is also responsible for the magnetic shape-memory effect and ~ii! the microscopic spin-phonon coupling which gives rise to the shift of the transition temperature with the
applied magnetic field. The relative importance of these two contributions has been shown to vary with
composition, which is suitably expressed through the average number of valence electrons per atom e/a. In
alloys with a large difference between the Curie and martensitic transition temperatures (e/a.7.5), mesoscopic
coupling is dominant and a negative giant magnetocaloric effect ~increase of temperature by adiabatic demagnetization! is induced at moderate applied fields. In contrast, in alloys when these temperatures are very close to one another (e/a.7.7), the microscopic coupling is the most relevant contribution and gives rise to a positive giant effect.

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Reproducció digital del document publicat en format paper, proporcionada per PROLA i http://dx.doi.org/10.1103/PhysRevB.68.094401

# metadata.dc.source[].value
Articles publicats en revistes (Física Quàntica i Astrofísica)

# metadata.dc.title[].value
Multiscale origin of the magnetocaloric effect in Ni-Mn-Ga shape-memory alloys