Magnetic and Magnetoelectric Properties of AurivilliusThree- and Four-Layered Intergrowth Ceramics

Abstract

In this work, we have prepared intergrowth of multiferroic compounds namely Bi4RTi3Fe0.7Co0.3O15-Bi3RTi2Fe0.7Co0.3O12−δ (BRTFCO15-BRTFCO12) (rare earth (R) = Dy, Sm, La) by solid-state reaction method. From the X-ray diffraction Rietveld refinement, the structure of the intergrowths was found to be orthorhombic in which satisfactory fittings establish the existence of three-layered (space group: b 2 c b) and four-layered compounds (space group: A21am). Analysis of magnetic measurements confirmed a larger magnetization for theSm-modified intergrowth compound (BSTFCO15-BSTFCO12) compared to Dy- and La-doped ones. The emergence of higher magnetic properties can be due to distortion in the unit cell when some Bi3+ ions are replaced with the Sm3+, bonding of Fe3+-O-Co3+ as well as a possible mixture of FexCoy-type nanoparticles that are formed generally in the synthesis of intergrowths. The changes in the magnetic state of the Aurivillius intergrowths have been reflected in the magnetoelectric (ME) coupling: higher ME coefficient (~30 mV/Cm-Oe) at lower magnetic fields and is constant up to 3 kOe. The results were corroborated by Raman spectroscopy and variation of temperature with magnetization data. The results revealed that the RE-modified intergrowth route is an effective preparative method for higher-layer Aurivillius multiferroic ceramics.

Magnetoelectric Properties of Aurivillius-Layered Perovskites

“…The Sm 3+ -doped REBTFC sample showed a higher value of magnetization. The results are consistent with our recent work on rare-earth modified Aurivillius intergrowths whose magnetization follows the similar rare-earth dependence [57]. The magnetic moment per formula unit (µ f .u. )…”

“…However, further studies are needed to establish the plausible reason for obtaining a high ME coefficient. As it is reported, the impurity phases of Co/Fe compositions influence the ME nature in Aurivillius compounds [57]. The presence of circled regions of SEM micrograph dots (nanoregions) represents a Co/Fe-rich magnetic phase.…”

“…The refining analysis revealed that all samples consisted mainly of a single-phase structure with an admixture of another phase of Bi 12 Fe 0.5 Ti 0.5 O 20 belonging to the I23 space group. From the XRD studies, it could be concluded that the pyrochlore (Bi 12 FeO 20 ) formation was mainly due to the substitution of heterovalent elements (Ti 4+ , Fe 3+ , and Co 2+ ) in the B-site of the ABO 3 perovskites of the Aurivillius phases [55,57]. The reliability parameters (R p , R wp , and R exp ) and goodness of fit (χ 2 ) were within the specified range and well-matched between theoretical and experimental diffraction patterns.…”

“…Raman scattering spectra of the prepared ceramics are shown in Figure 4a-c to investigate lattice vibrational modes, lattice distortion, and occupancy of doped ions at the specified A-and B-sites. All observed modes of the prepared samples showed similar characteristic modes of the orthorhombic structure of three-layered Aurivillius compounds [57,62,63]. The overlapped peaks were de-convoluted using Lorentzian peak fittings, for…”

“…In addition, the polarization of Aurivillius phase compounds depended on factors such as crystal symmetry, strain effects, phase transitions, and the competition of dopants. The Aurivillius phase compounds caused lattice distortion in the BO 6 octahedron, which affected the electric dipole moments [57]. The asymmetric and unsaturated ferroelectric hysteresis (P-E) loops illustrated the leaky nature or accounted for the presence of a greater number of oxygen vacancies or defective charge carriers.…”