Symmetry Modulation and Enhanced Multiferroic Characteristics in Bi_1‐xNd_xFeO₃ Ceramics

Abstract

BiFeO 3 is recognized as the most important room temperature single phase multiferroic material. However, the weak magnetoelectric (ME) coupling remains as a key issue, which obstructs its applications. Since the magnetoelectric coupling in BiFeO 3 is essentially hindered by the cycloidal spin structure, here efforts to improve the magnetoelectric coupling by destroying the cycloidal state and switching to the weak ferromagnetic state through symmetry modulation are reported. The structure is tuned from polar R3c to polar Pna2 1 , and finally to nonpolar Pbnm by forming Bi 1-x Nd x FeO 3 solid solutions, where two morphotropic phase boundaries (MPBs) are detected. Greatly enhanced ferroelectric polarization is obtained together with the desired weak ferromagnetic characteristics in Bi 1-x Nd x FeO 3 ceramics at the compositions near MPBs. The change of magnetic state from antiferromagnetic (cycloidal state) to ferromagnetic (canted antiferromagnetic) is confirmed by the observation of magnetic domains using magnetic force microscopy. More interestingly, combining experiments and first-principles-based simulations, an electric field-induced structural and magnetic transition from Pna2 1 back to R3c is demonstrated, providing a great opportunity for electric fieldcontrolled magnetism, and this transition is shown to be reversible with additional thermal treatment.

Multiferroic Properties and Magnetoelectric Coupling of Fe‐Doped (Ba0.7Ca0.3)TiO3‐Ba(Zr0.2Ti0.8)O3 Ceramics

“…However, there are few natural single‐phase magnetoelectric materials as conventional ferroelectricity requires closed‐shell d 0 or s 2 cations, whereas ferromagnetism needs open‐shell d n configurations with unpaired electrons . To avoid such natural exclusion between magnetism and ferroelectricity, considerable effort has focused on the introduction of magnetism (ferroelectricity) in ferroelectrics (ferromagnetics) and the search for type‐II multiferroics, where ferroelectricity is caused by special magnetic orders rather than the intrinsic noncentrosymmetric crystal structure …”

A magnetic phase diagram for nanoscale epitaxial BiFeO3 films

“…The magnetic order of BFO, particularly the existence of the cycloid, can be altered by external stimuli such as strain, 4,18 magnetic 19,20 and electric 21 fields, and chemical doping/substitution. 22,23 Presently BFO research is heavily focused on the electric-field control of magnetism. In this endeavor, the most common approaches include using the exchange coupling to a ferromagnetic overlayer, 24,25 controlling the weak ferromagnetic moment, 26 or switching the cycloid plane with the electric field.…”

Designing polar textures with ultrafast neuromorphic features from atomistic simulations

“…Such strategy of combining items (i)-(iii) may be used to design (and understand) novel neuromorphic materials. For instance, one may wonder if the solid solutions (Bi,R)FeO 3 , where R is a rare-earth ion, can also present neuromorphic features since they can have different phases: a strong ferroelectric rhombohedral R3c state with a polarization oriented along [111], the 'typical' tilted, non-polar Pnma phase, but also unusual complex states with different polarization values and anomalous tilting patterns [7,[47][48][49][50][51][52][53].…”