Open Access
Giant direct and inverse magnetocaloric effect linked to the same forward martensitic transformation
(Springer Nature, 2017) Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Sánchez-Alarcos Gómez, Vicente; Beato López, Juan Jesús; Rodríguez Velamazán, José Alberto; Sánchez Marcos, J.; Gómez Polo, Cristina; Cesari, Eduard; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física
Metamagnetic shape memory alloys have aroused considerable attraction as potential magnetic refrigerants due to the large inverse magnetocaloric effect associated to the magnetic-field-induction of a reverse martensitic transformation (martensite to austenite). In some of these alloys, the austenite phase can be retained on cooling under high magnetic fields, being the retained phase metastable after field removing. Here, we report a giant direct magnetocaloric effect linked to the anomalous forward martensitic transformation (austenite to martensite) that the retained austenite undergoes on heating. Under moderate fields of 10 kOe, an estimated adiabatic temperature change of 9 K has been obtained, which is (in absolute value) almost twice that obtained in the conventional transformation under higher applied fields. The observation of a different sign on the temperature change associated to the same austenite to martensite transformation depending on whether it occurs on heating (retained) or on cooling is attributed to the predominance of the magnetic or the vibrational entropy terms, respectively.
Open Access
Long-range atomic order and entropy change at the martensitic transformation in a Ni-Mn-In-Co metamagnetic shape memory alloy
(MDPI, 2014) Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Cesari, Eduard; Rodríguez Velamazán, José Alberto; Física; Fisika
The influence of the atomic order on the martensitic transformation entropy change has been studied in a Ni-Mn-In-Co metamagnetic shape memory alloy through the evolution of the transformation temperatures under high-temperature quenching and post-quench annealing thermal treatments. It is confirmed that the entropy change evolves as a consequence of the variations on the degree of L21 atomic order brought by thermal treatments, though, contrary to what occurs in ternary Ni-Mn-In, post-quench aging appears to be the most effective way to modify the transformation entropy in Ni-Mn-In-Co. It is also shown that any entropy change value between around 40 and 5 J/kgK can be achieved in a controllable way for a single alloy under the appropriate aging treatment, thus bringing out the possibility of properly tune the magnetocaloric effect.
Open Access
Experimental observation of vacancy-assisted martensitic transformation shift in Ni-Fe-Ga alloys
(American Physical Society, 2019) Unzueta, Iraultza; Alonso de Robador Lorente, Daniel; Cesari, Eduard; Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; García, José Ángel; Plazaola, Fernando; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
Positron annihilation lifetime spectroscopy is used to experimentally demonstrate the direct relationship between vacancies and the shift of the martensitic transformation temperature in a Ni55Fel7Ga28 alloy. The evolution of vacancies assisting the ordering enables shifts of the martensitic transformation up to 50 K. Our results confirm the role that both vacancy concentration and different vacancy dynamics play in samples quenched from the L2(1) and B2 phases, which dictate the martensitic transformation temperature and its subsequent evolution. Finally, by electron-positron density functional calculations V-Ni is identified as the most probable vacancy present in Ni55Fe17Ga28. This work evidences the capability of vacancies for the fine-tuning of the martensitic transformation temperature, paving the way for defect engineering of multifunctional properties.
Open Access
Influence of defects on the irreversible phase transition in the Fe-Pd doped with Co and Mn
(Rede Latino-Americana de Materiais, 2018) Bonifacich, Federico Guillermo; Lambri, Osvaldo Agustín; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Sánchez-Alarcos Gómez, Vicente; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The appearance of BCT martensite in Fe-Pd-based ferromagnetic shape memory alloys, which develops at lower temperatures than the thermoelastic martensitic transition, deteriorates the shape memory properties. In a previous work performed in Fe70Pd30, it was shown that a reduction in defects density reduces the non thermoelastic FCT-BCT transformation temperature. In the present work, the influence of quenched-in-defects upon the intensity and temperature of the thermoelastic martensitic (FCC-FCT) and the non thermoelastic (FCT-BCT) transitions in Fe-Pd doped with Co and Mn is studied. Differential scanning calorimetric and mechanical spectroscopy studies demonstrate that a reduction in the dislocation density the stability range of the FCC-FCT reversible transformation in Fe67Pd30Co3 and Fe66.8Pd30.7Mn2.5 ferromagnetic shape memory alloys.
Open Access
Magnetocaloric effect enhancement driven by intrinsic defects in a Ni45Co5Mn35Sn15 alloy
(Elsevier, 2019) Sánchez-Alarcos Gómez, Vicente; López García, Javier; Unzueta, Iraultza; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Beato López, Juan Jesús; García, José Ángel; Plazaola, Fernando; Rodríguez Velamazán, José Alberto; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física
The influence of mechanically-induced defects on the magnetostructural properties is analyzed in a Ni-Co-Mn-Sn alloy subjected to soft milling and subsequent annealing treatments. It is found that, opposite to what occurs in Ni-Mn-Sn ternary alloys, the annealing treatment affects the magnetic properties in a different way in martensite and in austenite. In particular, the saturation magnetization significantly increases in martensite after annealing whereas just a very slight variation is observed in austenite. This leads to the interesting fact that the presence of microstructural defects, far for worsening, makes the magnetocaloric effect to be higher in the as-milled state than after annealing. This behavior is explained as the result of the combination of the effect of defects on the Mn-Mn distance, the effect of Co on the magnetic exchange coupling between Mn atoms, and the effect of defects on the vibrational entropy change at the martensitic transformation.
Open Access
Study of the martensitic transition in Ni-Mn-Sn-Ti ferromagnetic shape memory alloys
(Rede Latino-Americana de Materiais, 2018) Bonifacich, Federico Guillermo; Lambri, Osvaldo Agustín; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Sánchez-Alarcos Gómez, Vicente; Fisika; Institute for Advanced Materials and Mathematics - INAMAT2; Física; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In the present work, mechanical spectroscopy measurements as a function of temperature and strain have been performed in (at.%) Ni50Mn37Sn13-xTix (x=0, 0.5 and 2) ferromagnetic shape memory alloys in order both to study martensitic transition phenomenon and also to determine its temperature of appearance. For mechanical spectroscopy measurements, a five elements piezoelectric device recently developed has been used. In addition, other characterization techniques as, differential thermal analysis and superconducting quantum interference magnetic spectroscopy, were also used. Besides, relaxation processes near the martensitic transition temperature have been also observed.
Open Access
Entropy change caused by martensitic transformations of ferromagnetic shape memory alloys
(MDPI, 2017) L'vov, Victor A.; Cesari, Eduard; Kosogor, Anna; Torrens Serra, Joan; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Física; Fisika
In this paper, our most recent findings on the influence of magnetic order on the main transformational caloric and elastic properties of shape memory alloys (SMAs) are reviewed. It is argued that ferromagnetic order has a strong influence on the temperature interval of martensitic transformation (MT), the characteristics of stress-induced MT, and the shear elastic modulus of SMA. The problem of separation of the magnetic contributions to the entropy change ΔS and heat Q exchanged in the course of martensitic transformation (MT) of SMA is considered in general terms, and theoretical formulas enabling the solution of the problem are presented. As an example, the ΔS and Q values, which were experimentally determined for Ni-Mn-Ga and Ni-Fe-Ga alloys with different Curie temperatures TC and MT temperatures TM, are theoretically analyzed. It is shown that for Ni-Mn-Ga martensites with TM < TC, the ratio of elastic and magnetic contributions to the entropy change may be greater or smaller than unity, depending on the temperature difference TC – TM.
Open Access
Changes in the crystalline degree in neutron irradiated EPDM viewed through infrared spectroscopy and inelastic neutron scattering
(Rede Latino-Americana de Materiais, 2018) Lambri, Osvaldo Agustín; Giordano, E. D.; Bonifacich, Federico Guillermo; Pérez de Landazábal Berganzo, José Ignacio; Recarte Callado, Vicente; Física; Fisika; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The changes in the degree of crystallinity in commercial Ethylene Propylene Diene rubber-type M (EPDM) irradiated with neutrons at different doses has been studied by means of inelastic neutron scattering and infrared absorption spectroscopy experiments. EPDM samples were taken from the housing of non-ceramic electrical insulators which are used in outdoor transmission lines of 66 kV. Inelastic neutron scattering spectra were recorded at 5 K with an accessible energy-transfer range between 180 - 3500 cm-1. Infrared studies were performed at room temperature with an energy transfer between 4000 - 400 cm-1. Controlled neutron irradiation allows to obtain different volume fraction and size of crystalline zones in EPDM. The obtained results are discussed and correlated with studies of differential scanning calorimetry, dynamic mechanical analysis and positron annihilation lifetime spectroscopy from where the changes in crystallinity in EPDM were indirectly studied. Inelastic neutron scattering studies were not appropriate for determining the changes in the crystallinity degree in neutron irradiated commercial EPDM. In contrast, from infrared absorption spectroscopy the changes in crystallinity could be determined successfully.
Open Access
Routes for enhanced magnetism in Ni-Mn-In metamagnetic shape memory alloys
(Elsevier, 2019) López García, Javier; Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Fabelo, O.; Cesari, Eduard; Rodríguez Velamazán, José Alberto; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
The authors provide in-depth physical insight into the enhancement of the magnetic properties of metamagnetic shape memory alloys produced by thermal treatment and cobalt doping. They use neutron scattering to study the atomic order and magnetic structures in the austenitic phases of Ni50Mn34In16 and Ni45Co5Mn37In13 alloys in two different states induced by thermal treatments. The increase of the magnetization in the austenite phase, particularly by cobalt doping, is explained by the enhanced ferromagnetic coupling between the magnetic moments located in octahedral sites. The spin density maps obtained from polarized neutron diffraction reveal the magnetic interaction pathways responsible for this coupling scheme.
Open Access
Identification of a Ni-vacancy defect in Ni-Mn-Z (Z = Ga, Sn, In): an experimental and DFT positron-annihilation study
(American Physical Society, 2019) Unzueta, Iraultza; Sánchez-Alarcos Gómez, Vicente; Recarte Callado, Vicente; Pérez de Landazábal Berganzo, José Ignacio; Zabala, Nerea; García, José Ángel; Plazaola, Fernando; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
By means of experimental positron-annihilation-lifetime measurements and theoretical density functional theory (DFT) positron-lifetime calculations, vacancy-type defects in Ni50Mn50−xSnx (x = 25, 20, 15, 13, 10) and Ni50Mn50−xInx (x = 25, 20, 16, 13) systems are systematically studied. The study is extended to Ni-Mn-Ga systems as well. Experimental results are complemented with electron-positron DFT calculations carried out within the local density approximation and generalized gradient approximation, where five different parametrizations accounting for the γ (r) enhancement factor are analyzed. Theoretical results indicate that the Boronski-Nieminen parametrization of γ (r) is the one that best predicts the experimental results, which ultimately enables us to identify VNi as the vacancy present in the studied samples. The characteristic positron lifetime related to VNi ranges between 181 and 191 ps in Ni-Mn-Sn/In systems. Positron-annihilation-lifetime spectroscopy results in these two systems delimit the lower bound of the achievable vacancy concentration, which is much larger compared with the reported values in Ni-Mn-Ga systems. The present work, along with setting the basis for positron simulations in Ni-Mn based Heusler alloys, delimits the effect that the variation of vacancies has in the martensitic transformation in Ni-Mn-Sn systems.