The effects of annealing on structural and magnetic properties of [Mn/Bi] multilayered thin films

• Main Authors: Yi-Lun Huang, 黃一倫
• Other Authors: Ko-Wei Lin
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/jj3uz3

碩士 === 國立中興大學 === 材料科學與工程學系所 === 106 === In this study, we preparing a series of Mn/Bi multilayer thin films were deposited on a SiO2 substrate using a dual ion sputtering system and it divided into two parts: (1)Ag/[Mn/Bi]10/SiO2 multilayer films and with 70V low-energy ion beam assisted deposition [Mn/Bi]. (2) manipulate the number of layers of MnBi thin films, such as Ta/Mn/Bi/SiO2, Ta/Bi/Mn/Bi/SiO2, followed by rapid thermal annealing process. By controlling the annealing temperature and annealing time, the influence of the microstructure and magnetic properties of the Mn/Bi multilayer film was investigated. In the Ag/[Mn/Bi]10 system, the XRD results show that the as-deposited Mn/Bi thin film is mainly composed of unreacted Bi and Mn. The MnBi thin film was not reacted, and only a less of the h.c.p. structure of MnBi was bombarded on the substrate with the End Hall ion source. After annealing at 550°C for 30 minutes, Bi and Mn react to form different structures of MnBi and Mn oxides (eg, MnO, Mn3O4). From the AFM results, the roughness of the MnBi thin film after bombardment with the ion beam was smaller, and the roughness of the MnBi thin film increased after annealing. The results of magnetic properties have shown that the coercivity(Hc) of [Mn/Bi]10 multilayer measured at room temperature is about 540 Oe, and the saturation magnetization(Ms) is about 180 emu/cm3. The ESCA results show that after the 150 day exposure to air, the oxygen further diffused into the inner area where more MnBi content would exist.Considering the electron configuration of Mn (3d5) ~ Bi (6p3) bonding, Mn in MnBi can be easily oxidized due to the unpaired electrons in 3d orbits. In the second part of the Ta/Mn/Bi system, the XRD and TEM results show that during the annealing process for the trilayer film, Mn bidirectionally diffuses into c-axis textured Bi-seed layers which makes the MnBi(102) diffraction peak stronger than the bilayer film. However, the melting point of manganese is too high to the presence of unreacted Mn in the film after annealing, includes the oxides from manganese. The hysteresis loops results show that the MnBi thin film annealed at 350°C for 1 hour are paramagnetism. On the other hand, the MnBi thin film with a trilayer structure can formed more LTP-MnBi due to the reaction, thus the saturation magnetization(Ms) is higher than bilayer.