Ph'D defense Youcef KARAR

M Youcef KARAR will present his thesis "Electrodeposition of bismuth-manganese thin films in Deep Eutectic Solvents for the development of the LTP-BiMn magnetic phase".
Abstract :
Due to the economic crisis regarding rare earth elements, the synthesis of rare earth-free permanent magnets has attracted great interest from the scientific community. Manganese-based hard intermetallic magnetic phases such as BiMn are promising candidates. This thesis focused on the electrochemical elaboration of the low temperature BiMn phase (LTP-BiMn) using Deep Eutectic Solvents (DES) as electrolytes. The latter have physicochemical properties close to those of ionic liquids and have the advantage of being inexpensive and environmentally friendly. First, bismuth and manganese were studied separately in order to understand their electrochemical behavior. Bismuth was studied in reline which is a mixture of choline chloride and urea with a molar ratio of 0.5 which proved to be a good environment to obtain high quality bismuth deposits. As for manganese, the deposits obtained in the reline were not adherent, in addition to a low faradic yield. Therefore, another DES was used (ethaline) where urea was replaced by ethylene glycol. In this case, the quality of the manganese thin films was significantly improved since ethaline has a higher conductivity and a lower viscosity than reline. Secondly, Bi-Mn codeposits were prepared in ethaline using different precursor salts as sources of Bi(III) and Mn(II) ions. It was found that the equimolar composition for the alloy was only approached for the bath with bismuth nitrate and manganese sulfate. The low temperature phase is formed by a peritectic reaction mechanism above 262 °C, therefore the thin films were annealed under secondary vacuum at 300 °C in order to induce interdiffusion between the two elements. Magnetic measurements revealed the presence of a ferromagnetic signal with a coercivity of 4.1 kOe confirming the presence of magnetic grains and thus the formation of the BiMn alloy. To the best of our knowledge, this coercivity value is the highest ever achieved for electrochemically grown thin films.

Supervisors : Éric CHAINET and Nassima BENBRAHIM

Jury members :
Prof. Yves WOUTERS
Université de Grenoble Alpes, Examinateur
Prof. Amor AZIZI
Université Ferhat Abbas Sétif 1, Rapporteur
Dr. Mireille TURMINE
Maître de Conférences, Sorbonne Université, Rapporteur
Maître de Conférences, Université Mouloud Mammeri de Tizi Ouzou, Examinateur
Dr. Laurent CAGNON
Chargé de recherche CNRS, Université Grenoble Alpes, Invité
Maître de Conférences, Université Mouloud Mammeri de Tizi Ouzou, Invité
Prof. Nassima BENBRAHIM
Université Mouloud Mammeri de Tizi Ouzou, Co-directrice de thèse, Invitée
Directeur de recherche CNRS, Université Grenoble Alpes, Directeur de thèse


Date infos
Defense 10 May 2022 at  9H30
Address  of the defense : Bâtiment ENSIMAG, salle E407, 681 rue de la passerelle, 38400, Saint Martin d’Hères