Page 58 - ILLS Annual Report 2018

MATERIALS SCIENCE
J.I. Pérez-Landazábal. Spanish
Public University of Navarra and Institute for Advanced Materials – INAMAT
‘I received a PhD. degree in solid-state physics from the Basque Country University in 1995.
My research interests include ferromagnetic shape memory alloys and magnetic nanoparticles for
medical applications. Nowadays, my activity is mainly focused on miscrostructural and magnetic characterisation, phase transformations and defects in solids. I have authored more than 140 scientific articles SCI.’
Low-temperature, giant magnetocaloric effect in an out-of-equilibrium arrested phase
High-intensity two-axis diffractometer with variable resolution D20
Generally, a magnetic material can be cooled or heated by the application
of a magnetic field: the so-called magnetocaloric effect [1]. In particular,
in metamagnetic shape memory alloys, the magnetic field can also induce a drastic structural transition—the martensitic transformation (from a high-temperature phase—austenite—to a low-temperature phase—martensite)—which can lead to a giant magnetocaloric effect [2]. In some of these alloys, the austenite phase can be retained at low temperatures [3], and its ‘anomalous’ transition to martensite
on heating promotes a peculiar ‘giant’ and ‘direct’ magnetocaloric effect.
AUTHORS
J.I. Pérez-Landazábal, V. Recarte, V. Sánchez-Alarcos,
J.J. Beato-López and C. Gómez-Polo (Public University of Navarra
and Institute for Advanced Materials – INAMAT – Pamplona, Spain) J.A. Rodríguez-Velamazán (ILL)
J. Sánchez-Marcos (Universidad Autónoma de Madrid, Spain)
E. Cesari (University of the Balearic Islands, Palma de Mallorca, Spain)
ARTICLE FROM
Sci. Rep. (2017)—doi: 10.1038/s41598-017-13856-5
REFERENCES
[1] V.K. Pecharsky, K.A. Gschneidner Jr., A.O. Pecharsky and A.M. Tishin, Phys. Rev. B 64 (2001) 144406.
[2] T. Krenke, E. Duman, M. Acet, E.F. Wassermann, X. Moya, Ll. Mañosa and A. Planes, Nat. Mat. 4 (2005) 450
[3] V.K. Sharma, M.K. Chattopadhyay and S.B. Roy, Phys. Rev. B 76 (2007) 140401.
The magnetocaloric effect is usually evaluated in isothermal conditions through the magnetic field-induced entropy change. In the present case, at low temperature we observe a direct magnetocaloric effect (with positive entropy change after field removing) associated with an ‘anomalous’ forward martensitic transformation, as opposed to the inverse
effect (with negative entropy change after field removing) observed in a conventional forward transformation. The magnitude of this magnetocaloric effect is such that large adiabatic temperature changes under moderate applied fields can be induced—almost twice the values obtained in the conventional forward transformation under higher applied fields and among the largest values obtained in magnetic shape memory alloys.
Neutron thermo-diffraction measurements in figure 1 show direct evidence of both the austenite retention at 10 K
after 50 kOe magnetic field cooling and the subsequent phase evolution upon heating in a Ni45Mn36.7In13.3Co5 alloy. The sample shows a mixture of austenite
and martensite at 10 K. The anomalous martensitic transformation from retained austenite to martensite on heating is evidenced by the reduction in intensity of the (200)A austenitic reflection at 2θ = 47.5 o (λ = 2.41 Å) and the corresponding increase in the martenstic one at around 52 o. The austenitic peak intensity does not cancel out due to the concurrence of martensitic and austenitic reflections at the same angle. Conversely, as expected the conventional reverse transformation from martensite
to austenite takes place on heating above 200 K, where the austenitic peak intensity starts increasing (and the martensite peak intensity starts decreasing). Therefore, the same forward austenite-to-martensite transformation can be produced by heating and by cooling.
ANNUAL REPORT 2018