Novel magneto-electric multiferroics from first-principles calculations

Abstract

Interest in first-principles calculations within the multiferroic community has been rapidly on the rise over the last decade. Initially considered as a powerful support to explain experimentally observed behaviours, the trend has evolved and, nowadays, density functional theory calculations has become also an essential predicting tool for identifying original rules to achieve multiferroism and design new magneto-electric compounds. This chapter aims to highlight the key advances in the field of multiferroics for which first-principles methods have contributed significantly. The essential theoretical developments that made this search possible are also briefly presented.To cite this article: J. Varignon, N. C. Bristowe, E. Bousquet and Ph. Ghosez, C. R. Physique # (2014). RésuméNouveaux matériaux multiferroïques à partir de calculs de premiers principes.L'intérêt pour les calculs ab initio dans la communauté des multiferroïques n'a cessé de croître au cours de la dernière décennie. Initialement considérés comme un support efficace pour expliquer les comportements observés expérimentalement, la tendance a évolué et, actuellement, les calculs réalisés dans le cadre de la théorie de la fonctionnelle de la densité apparaissent aussi comme un outil prédictif incontournable permettant d'identifier de nouvelles voies pour parvenir au multiferroïsme et créer de nouveaux matériaux magnéto-électriques. Ce chapitre vise à présenter quelques avancées clefs dans le domaine des multiferroïques, auxquelles les méthodes ab initio ont conbribué de manière significative. Les développements théoriques essentiels ayant permis ces avancées sont aussi brièvement discutés.

Coupling and electrical control of structural, orbital and magnetic orders in perovskites

“…Magneto-electric multiferroics are widely studied due to their intriguing coupling between ferroelectricity and magnetism (electric field control of magnetism and conversely), and are proposed as promising candidates for lower energy consumption spintronic devices 7 9 . However, materials combining both ferroelectric and (anti)-ferromagnetic order parameters are elusive in nature and the identification of new single phase multiferroics remains a challenge for modern day research 54 .…”

“…The first observation is that the symmetry breaking due to the A cation layering turns the X antipolar modes to polar modes, i.e. in-plane (110) P xy and out-of-plane (001) P z 10 12 54 56 57 . The first and fourth trilinear couplings of Eq.…”

Electric Field Control of Jahn-Teller Distortions in Bulk Perovskites

“…Unfortunately, these AFD distortions are known to often prevent 9 the appearance of the polarization in the material. The use of anharmonic lattice mode couplings between polar and non-polar lattice distortions is a promising pathway to engineer "improper" ferroelectricity in layered perovskite derivatives [10][11][12][13] , and furthermore to achieve novel functional possibilities via these couplings [14][15][16][17][18][19][20] . Interesting anharmonic couplings do not only exist in layered perovskites, but can also appear in bulk ABO 3 perovskites 19,21,22,[25][26][27][28] Following this spirit, achieving an electric field control of Jahn-Teller distortions necessarily requires the identification of a material exhibiting a relevant coupling be- tween the polarization and the Jahn-Teller distortion, which to the best of our knowledge has not yet been discovered in bulk perovskites 23 .…”

“…Recently, the concept of "hybrid improper ferroelectricity" has emerged within the community of oxide perovskites [8][9][10][11]. This concept is related to an unusual coupling of lattice modes, giving rise in the free energy expansion to a trilinear term −λPR 1 R 2 linking the polar motion P to two independent nonpolar distortions R 1 and R 2 .…”

“…Strain engineering, through thin film epitaxy, for example, can provide a powerful tool to unlock a polar mode in perovskites [10,[27][28][29][30][31][32]. This is the case for BiFeO 3 which was recently proposed to adopt an unusual Pb2 1 m symmetry under large epitaxial tensile strain [18,[33][34][35]].…”