| Titre : | Prédiction théorique des propriétés magnéto- électroniques de nouveaux composés pérovskite |
| Auteurs : | HAMLAT Mama, Auteur ; AMARA Kadda, Directeur de thèse |
| Type de document : | texte manuscrit |
| Editeur : | Université de Saida– Dr. Moulay Tahar Faculté des sciences |
| Format : | 103ص |
| Accompagnement : | CD |
| Langues: | Français |
| Index. décimale : | BUC-D 000097 |
| Catégories : |
DOCTORATE LMD diploma (3rd Cycle) Specialty: physics Option: materials physics |
| Mots-clés: | : perovskite, p-type half metallic ferromagnetism, mechanical stability, magnetic phase transition, thermodynamic properties. : البيروفسكايت ، مغناطيسية حديدية نصف معدنية من النوع p ، الاستقرار الميكانيكي ، انتقال الطور المغناطيسي ، الخواص الديناميكية الحرارية. : pérovskite, ferromagnétisme demi-métallique type-p , stabilité mécanique, transition de phase magnétique, propriétés thermodynamiques |
| Résumé : |
Abstract :
By using first principal calculation, some physical properties of LiBeO3, KBeO3 and KMgO3 compounds are investigated under the GGA and TB-mBJ approximations using FP-LAPW method. The structural optimization shows that they are most stable in their ferromagnetic states. The computed elastic constants and formation energy elucidate that they are mechanically stable and can be synthesizable. Further, their spin-polarized electronic structure calculations display the half-metallic feature. On the other hand, the net magnetic moment for each compound has the integer value of (3μB), where the ferromagnetism is primarily due to O-p orbital. The Curie temperature is estimated to be 660.88K, 639K and 626K for LiBeO3, KBeO3 and KMgO3, respectively. الملخص: باستخدام الحساب الأساسي الأول ، يتم فحص بعض الخصائص الفيزيائية لمركبات LiBeO3 و KBeO3 و KMgO3 وفقًا لتقديرات GGA و TB-mBJ باستخدام طريقة FP-LAPW. يُظهر التحسين الهيكلي أنها أكثر استقرارًا في حالاتها المغناطيسية. توضح الثوابت المرنة المحسوبة وطاقة التكوين أنها مستقرة ميكانيكيًا ويمكن تصنيعها. علاوة على ذلك ، تعرض حسابات الهيكل الإلكتروني ذات الاستقطاب الدوراني ميزة النصف معدنية. من ناحية أخرى، فإن العزم المغناطيسي الكلي لكل مركب له قيمة عددية صحيحة تبلغ (3μB) ، حيث يرجع السبب الرئيسي للمغناطيسية الحديدية إلى مدار O-p ، وتقدر درجة حرارة Curie بـ 660.88 K و 639 K و 626 K لـ LiBeO3 و KBeO3 و KMgO3 ، على التوالي. Résume : En utilisant le calcul de premiers principes, certaines propriétés physiques des composés LiBeO3, KBeO3 et KMgO3 sont étudiées dans les approximations GGA et TB-mBJ en utilisant la méthode FP-LAPW. L'optimisation structurelle montre qu'ils sont plus stables dans leurs états ferromagnétiques. Les constantes élastiques et l'énergie de formation calculées montrent qu'ils sont mécaniquement stables et peuvent être synthétisées. De plus, les calculs de leurs structures électroniques polarisées en spin affichent le caractère demi-métallique. D'autre part, le moment magnétique total pour chaque composé a la valeur entière de (3μB), où le ferromagnétisme est dû principalement à l'orbital O-p. La température de Curie est estimée à 661K, 639K et 626K pour LiBeO3, KBeO3 et KMgO3, respectivement. |
| Note de contenu : |
Introduction:
In the last few years, there has been a growing interest in the so called half-metallic ferromagnetic materials due to their outstanding physical, chemical, mechanical, optical, and magnetic properties [1], which are potentially promising in spintronic devices [2]. In a half metal, the electrons of one spin channel are metallic while those of the other are insulating, the spin polarization at Fermi level is complete (100%), and the magnetic moment is an integer. It is worth noting that the first prediction of a half metallic material was published in 1983 by De Groot et al in half- Heusler compound NiMnSb [3]. Later, numerous materials with different structures were also predicted with half-metallic ferromagnetism such as: the study of Japanese research groups on Co2MnZ compounds, where Z match to Si and Ge [4], the quaternary Heusler CoFeCrAl by Iltaf Muhammad [5], The oxide compounds CrO2 [6], TiO2, and VO2 [7] have been predicted as half-metallic ferromagnets, the double perovskites X2FeMoO6 (X = Ba, Ca, Sr) are reported to be HMs with 100% spin polarization [8] . Bouadjemi et al. [9] found that the cubic perovskite oxide PrMnO3 presents a half-metallic behavior. The same character appears in Dilute magnetic semiconductors (DMSs), e.g. Cu-doped ZnO [10]. As above-mentioned, much effort has been spent to comprehend, forecast and grow new half metallic material. During the last decades, the HMF used in spintronics technology was based exclusively on transition metals. The latter have an electronic filling up to the d or f orbital [11]; and it is precisely these electrons which are at the origin of the magnetism and of the HMF in the materials based on these elements. In contrast, recent research, theoretical and experimental, has revealed the existence of magnetism in materials involving light elements such as alkali and alkaline earth metals [12-14]. Used with carbon, nitrogen or oxygen, these materials have been predicted to be excellent HMF, the origin of which is no longer linked to d or f electrons as in transition metals, but to s and p electrons of these three elements. In this case the simple perovskite, not including transition elements are very promising candidates. General introduction 2 This is what motivated us to suggest a study of IA-IIA-O3 materials as LiBeO3, KBeO3 and KMgO3 in the cubic phase, using ab-initio simulation studies [15], within the framework of the DFT according to the wien2k code [16] with a systematic study of the structural, elastic, magnetic, electronic and thermodynamic properties. This thesis is organized as follows: In chapter 1, we try to provide a general overview on perovskite and ferromagnetic materials; also we consider the various possible applications. In chapter 2, we described the employed method. Discussion of the results obtained in the present work will be presented in chapter 3. Finally, we will end this study with a general conclusion and our perspectives. |
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