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Pérez de Landazábal Berganzo, José Ignacio

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https://academica-e.unavarra.es/handle/2454/49767

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Pérez de Landazábal Berganzo

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José Ignacio

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InaMat2. Instituto de Investigación en Materiales Avanzados y Matemáticas

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0000-0003-1172-6141

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Author: Recarte Callado, Vicente × Author: Plazaola, Fernando × Subject: Defects ×

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    PublicationOpen 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.
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    PublicationOpen 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.