Controlling Phase Assemblage in a Complex Multi‐Cation System: Phase‐Pure Room Temperature Multiferroic (1−x)BiTi_(1−y)/2Fe_yMg_(1−y)/2O_3–xCaTiO₃

Abstract

order parameters would lead to switching of the electrical polarization ( P ) by the magnetic fi eld H , or the magnetization ( M ) by the electric fi eld E , which has been proposed as a possible candidate to replace the presently used volatile random access memories (RAM). [ 3,4 ] A magnetoelectric multiferroic memory would benefi t from nonvolatility and nondestructive reading of magnetic RAM and the lowpower, high-speed features of ferroelectric RAM. [ 3,4 ] Bulk BiFeO 3 exhibits both ferroelectric and long-range magnetic order at room temperature, however it is a pure antiferromagnet because the cycloidal magnetic ordering leads to cancellation of the Dzyaloshinsky-Moriya interactionmediated canted moments, and also prevents any linear magnetoelectric effect. [5][6][7][8] The cycloidal ordering can be destabilized in strained and nanostructured fi lms of BiFeO 3 leading to fi nite magnetization. [ 9,10 ] Electric fi eld-induced switching of the magnetization of a ferromagnetic layer coupled to BiFeO 3 has been demonstrated in thin fi lm devices. [ 10,11 ] Powder neutron diffraction (PND) and Möss-bauer studies show that PbFe 0.5 Ta 0.5 O 3 , PbFe 0 .5 Ta 0.5 O 3 -PbTiO 3 solid solution, and the Aurivillius phases Bi n +1 Fe n −3 Ti 3 O 3 n +3 (3.5 ≤ n ≤ 7) are not long-range magnetically ordered at room temperature: [12][13][14][15] ( n = 5) at room temperature. [ 16,17 ] Recently, we have reported a generic design route for room temperature multiferroic materials that integrates a percolating network of magnetic ions to produce long-range magnetic order with enhanced ferroelectric switching properties at the morphotropic phase boundary (MPB) between two polar phases with different polarization directions. This was exemplifi ed in the perovskite oxide (1− x )BiTi (1− y )/2 Fe y Mg (1− y )/2 O 3 -x CaTiO 3 (BTFM-CTO) system, using techniques that defi nitively proved the coexistence and switchability of both orders within the perovskite structure. [ 18 ] The order parameters are not only switchable at room temperature but are also coupled as demonstrated by the linear magnetoelectric effect. [ 18 ] The structure of the perovskite at the MPB is complex and has been the subject of detailed studies over Controlling Phase Assemblage in a Complex

Room Temperature Magnetically Ordered Polar Corundum GaFeO3 Displaying Magnetoelectric Coupling

“…The observation of linear magnetoelectric coupling is consistent with the symmetry of the magnetic structure: above the Morin transition, α-Fe 2 O 3 adopts 2/m magnetic point symmetry (which is centrosymmetric, permitting weak ferromagnetism but not linear magnetoelectric coupling), but the cation ordering in polar corundum GaFeO 3 eliminates the inversion center, thus lowering the magnetic point symmetry to m , which permits both weak ferromagnetism and linear magnetoelectric coupling . The observed magnitude of α is similar to that observed in other Fe-based polar magnetoelectrics that are ordered magnetically above room temperature. ,, Demonstration of switchable electrical polarization (i.e., ferroelectricity and multiferroicity) was not possible in these samples due to the high dielectric loss.…”

“…The observed magnitude of α is similar to that observed in other Fe-based polar magnetoelectrics that are ordered magnetically above room temperature. 10,12,51 Attempts to measure electrical polarization loops were hampered by the high dielectric loss at room temperature, whilst measurements at 100 K were possible at applied fields of up to 120 kVcm -1 but did not achieve ferroelectric switching.…”

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

“…Similar results were also obtained in magnetic ion‐doped PbTiO 3 , Bi 4 Ti 3 O 12 , K 0.45 Na 0.49 Li 0.06 NbO 3 , and SrTiO 3 . Recently, Mandal et al designed a room temperature magnetoelectric material by constructing a percolating network of magnetic units with strong superexchange interaction in morphotropic phase boundary (MPB) 0.85BiTi 0.1 Fe 0.8 Mg 0.1 O 3 –0.15CaTiO 3 ceramics, and the canting of the antiferromagnetic structure contributes to the ferromagnetism . Such a result undoubtedly promotes the progress of multiferroics.…”

The Polar/Antipolar Phase Boundary of BiMnO3–BiFeO3–PbTiO3: Interplay among Crystal Structure, Point Defects, and Multiferroism

“…Among different approaches under investigation for enhancing the phase stability of Bi‐containing perovskites while improving their multiferroic properties, the preparation of solid solutions stands out as a very promising route . It can lead to the appearance of morphotropic phase boundaries (MPBs) at which property enhancement takes place and phase‐change functional responses can be obtained .…”