Vergara Platero, José
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Vergara Platero
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José
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Ciencias
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InaMat2. Instituto de Investigación en Materiales Avanzados y Matemáticas
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Publication Open Access Thermal hysteresis in the structural, magnetic and transport properties of hard magnetic MnBi films(Elsevier, 2024-10-15) Vergara Platero, José; Favieres Ruiz, Cristina; Madurga Pérez, Vicente; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Universidad Pública de Navarra / Nafarroako Unibertsitate PublikoaIn this work, the magnetic and transport properties associated with structural changes in MnBi hard magnetic films, with different Bi concentrations, were detailed. Two particular temperature regimes were studied. In the first place, at temperatures close to and below 260 °C (melting temperature of Bi in the samples) the resistance of the MnBi films underwent strong changes, showing thermal hysteresis, and depending on the amount of Bi in the samples. Thus, these resistance changes were attributed to the presence of unalloyed Bi in the samples. The maximum value of the relative change of resistance, ΔRI/R(T2) (where ΔRI=R(T1)-R(T2) being T1 and T2 the temperatures just immediately below and above the structural transition) was around 180 % for the sample with the highest Bi concentration. Second, at temperatures above 260 °C, both the magnetic moment and the resistance of the samples also showed significant changes around the transition from the Low Temperature (α-MnBi) to the High Temperature (β-MnBi) phase. These changes, which were attributed to this structural transition, also presented thermal hysteresis and also depended on the Bi concentration of the samples. However, contrary to the previous situation, the samples with the lowest amount of unalloyed Bi, and consequently with the highest value of the MnBi volume fraction presented a maximum value of the ΔRII/R(T4) ratio, (where ΔRII=R(T3)-R(T4) being T3 and T4 the temperatures immediately above and below the structural transition from the β to the α MnBi phase) this magnitude reaching a maximum value of 25 % for the sample with the lowest Bi content.Publication Open Access Influence of bi content on the temperature of the formation of the hard magnetic MnBi phase: simultaneous irreversible drop of resistance(MDPI, 2022) Vergara Platero, José; Favieres Ruiz, Cristina; Madurga Pérez, Vicente; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; CienciasPulsed laser-deposited (PLD) MnBi films were fabricated by alternating deposition of Mn and Bi layers. In order to obtain the ferromagnetic MnBi phase, heat treatments were performed on the samples. Simultaneously, the resistance of the samples was monitored as a function of the temperature. Thus, on increasing the temperature, a steep decrease in the resistance of the films was observed, simultaneous to the onset of the formation of the MnBi phase. At room-temperature, these annealed samples showed a ferromagnetic behavior, as well as the presence of the characteristic LT-MnBi phase diffraction peaks in the X-ray diffraction patterns. The temperature of the generation of the MnBi phase depended on the relative concentration of Mn and Bi in the different samples: on increasing the Bi atomic concentration, the temperature of the generation of the MnBi phase decreased.