Size-Dependent Magnetic Properties of Single-Crystalline Multiferroic BiFeO₃ Nanoparticles

Abstract

As-prepared, single-crystalline bismuth ferrite nanoparticles show strong size-dependent magnetic properties that correlate with: (a) increased suppression of the known spiral spin structure (period length of approximately 62 nm) with decreasing nanoparticle size and (b) uncompensated spins and strain anisotropies at the surface. Zero-field-cooled and field-cooled magnetization curves exhibit spin-glass freezing behavior due to a complex interplay between finite size effects, interparticle interactions, and a random distribution of anisotropy axes in our nanoparticle assemblies.

Simple top-down preparation of magnetic Bi0.9Gd0.1Fe1−xTixO3nanoparticles by ultrasonication of multiferroic bulk material

“…The coercivity was found to be reduced for these nanoparticles compared to that of bulk ceramic samples as was also observed for the reduced size single crystalline BiFeO 3 nanoparticles [18]. This indicates that the magnetic properties of these nanoparticles are related with their reduced size and crystallinity as was also determined in similar nanostructures [18,20,44]. Compared to the bulk ceramics, the coercive fields of the synthesized nanoparticles are much smaller and almost negligible for Bi 0.9 Gd 0.1 Fe 1−x Ti x O 3 (x= 0.20) nanoparticles (Table 1).…”

“…Furthermore, the M-H hysteresis loops of the synthesized nanoparticles exhibit a single-phase-like magnetization behaviour compared to the linear curve of the bulk, and this ultimately indicate qualitatively that a large fraction of the ultrasonicated specimen was converted into nanoparticles from bulk powders. Our results can be compared to a recent study where single crystalline BiFeO 3 nanoparticles were synthesized using facile sol-gel methodology based on the glycol gel reaction [18]. The highest M s for BiFeO 3 nanoparticles was 1.55 emu/g at 50 kOe with an average particle size of 14 nm [18].…”

“…Notably, in this present investigation, the M s for Bi 0.9 Gd 0.1 FeO 3 nanoprticles is 2.50 emu/g at 20 kOe for an average particle size of 11 ± 2 nm and this is much higher compared to the values observed in Refs. [18] and [20]. The large value of magnetization may be associated with their reduced particle size as was observed in Ref.…”

“…As was mentioned earlier, the magnetic ordering of BiFeO 3 -based multiferroic ceramics is antiferromagnetic with a spiral modulated spin structure [12,14,42] and an incommensurate long-wavelength period of 62 nm. The en-hanced magnetic properties in these nanoparticles could be explained as : i) due to the modification of the long range spiral-modulated spin structure of BiFeO 3 the ferromagnetic properties were enhanced for the synthesized nanoparticles with sizes much smaller than 62 nm [18] ii) the ionic radius of Gd 3+ (0.938Å) ion is much smaller than that of Bi 3+ (1.17Å) ion which may also lead to large distortion in lattice structure thereby leading to reduction of spiral spin modulation in BiFeO 3 [20] ; and iii) Gd 3+ is magnetically active (effective magnetic moment is 8.0 Bohr Magnetron) and the ferromagnetic coupling between Gd 3+ and Fe 3+ ions may contribute significantly to enhance the magnetization [20].…”

Effects of Magnetoelectric Ordering Due to Interfacial Symmetry Breaking

“…Magnetoelectric coupling can be found in a variety of materials including bulk structures, thin-film heterostructures, and nanoparticles [10][11][12][13][14]. The various mechanisms and symmetries involved in magnetoelectric materials are often competing and producing magnetic and lattice frustration [6].…”