Bismuth ferrite (BF) exhibits excellent multiferroic properties at room temperature, making it a promising candidate for energy storage devices. Over the past few years, bismuth ferrite nanoparticles (BFNP) have gained significant attention due to their potential applications. The main goal of this study is to make pure, single-phase PbTiO3 (PT)-doped BiFeO3 (BF-xPT, x = 0.2 and 0.4) powders using the sol-gel method (with sizes ranging from 40 nm to 1.6 mu m). PbTiO3 doping helps to reduce the crystallographic defects in BiFeO3, leading to its improved structural stability and better control over particle size. The structural, morphological, and optical properties of the BFNP were investigated using high-resolution x-ray diffraction (HR-XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy dispersive x-ray (EDX) analysis, UV-visible spectroscopy, and photoluminescence (PL) spectroscopy. A significant change in the crystallographic structure from tetragonal to monoclinic was observed. The particle size distribution was quantified using TEM, revealing average nanoparticle sizes of 110 +/- 35 nm for BF-0.2PT and 79 +/- 15 nm for BF-0.4PT. The bulk samples of BF-0.2PT and BF-0.4PT measure around 1.6 mu m and 350 nm, respectively. Additionally, the optical band gaps (OBG) of these nanoparticles were found to be tunable between 2.18 and 2.62 eV, depending on the particle size and doping concentration. The tunability of the OBG in BF-xPT nanoparticles makes them promising candidates for solar cell applications, energy storage devices such as supercapacitors, and many more. The broader impact of this work lies in its potential to advance the development of efficient, sustainable materials, contributing to the progress of clean energy technologies and paving the way for more effective solutions in renewable energy, energy conversion, and optoelectronic industries.

Nano-Crystalline powder of 0.6BiFeO3−0.4PbTiO3 solid solution was synthesized by sol-gel method. It is already being reported that bismuth ferrite (BiFeO3) is one of the most favourable multiferroic materials which show Curie temperature and Néel temperature, both are well above the room temperature. This raise the possibility of developing new kinds of devices based on coupling of magneto-electric at room temperature. The magneto-electric coupling is an interesting phenomenon where cross-coupling exists between electric and magnetic interactions. This kind of coupling is very important from the applications point of view for developing new generation multifunctional sensor, actuator and data storage devices. The synthesis has been successfully achieved by using maleic acid as chelating agent. The calcinations of gel at 550 °C yielded pure BF-0.4PT powders, with average particle size of 40 nm as determined using scanning electron microscopy (SEM). Rietveld analysis of room temperature x-ray diffraction data of BF-0.4PT shows that the system has two tetragonal phases with tetragonality of 8.82% and 1.18%. Room temperature M-H measurement reveals exchange bias of ~100 Oe, which confirms core-shell type structure present in nano BF-0.4PT powder.

The role of size reduction on the structural parameters, antiferromagnetic transition temperature (TN), and spin reorientation transition temperature of BiFeO3-0.25PbTiO3 (BF-0.25PT) has been studied. Rietveld analysis using high resolution synchrotron x-ray powder diffraction data confirms that the space group of BF-0.25PT solid solutions is monoclinic Cc and not rhombohedral R3c for both bulk and nanocrystalline powders. This settles a longstanding controversy about the structure of these solid solutions toward the BiFeO3 rich end of the morphotropic phase boundary in the BiFeO3-xPbTiO3 system. Using magnetization and neutron powder diffraction data, we show that the Néel transition temperature (TN) of BF-0.25PT increases from 445 K for bulk to 480 K for 150 nm particle size. This is in marked contrast to the scaling theories of phase transitions in finite size systems. We also show that the spin reorientation transition occurring below TN in bulk monoclinic compositions like BF-0.25PT is suppressed in the nanocrystalline samples of ∼150 nm particle size. Based on Rietveld refined structural parameters, we show that the asymmetry and non-linearity of the Fe-O-Fe superexchange pathways grow with decreasing particle size and that they exhibit a strong correlation with TN. We believe that the substantially enhanced Dzyaloshinskii-Moriya interaction with decreasing particle size as a result of asymmetric and non-collinear Fe-O-Fe superexchange pathways may be the key factor in raising the TN on decreasing the particle size. These observations present a new facet of type-I multiferroic materials, where superexchange pathways are intimately dependent on the ferroelectric distortion.

Geometrically frustrated Dy2Ti2O7 spin ice is known for robust magnetic behavior where structural and dielectric properties are coupled with its magnetism. Herein, effects of Fe substitution, at the magnetic Dy site (0 <= x <= 0.15) in Dy2Ti2O7 compound have been systematically examined in terms of structural distortions and magnetic perturbations through structural, dielectric, optical and magnetic studies. The experimental findings suggest that Fe substitution does not change the crystal electric field acting on the rare earth ion, though it produces significant structural distortions. These findings suggest that spin dynamics non-monotonically depends on the nature and dynamics of neighboring magnetic ion's spin (Fe spin in this case), because of existing strong spin correlations. This dependency provides a new possibility to tune or modify the spin dynamics of the correlated magnetic states in these materials via magnetic perturbations, which can be controlled by the externally applied magnetic field.

Nanoparticles of multiferroic BiFeO3-xPbTiO(3) (BF-0.2PT) was synthesized using sol-gel process in the size range of 50-160 nm. The optimization procedure for the preparation pure single phase was carefully investigated and structural effects are addressed. The Rietveld refinement shows similar to 14.6% tetragonal phase is present in bismuth rich compostion, whose tetragonality is around 20.4%. The results indicate that the size and morphology of sample changes with sintering temperature.

Bioactive glass-based composite (45S5–HA–Fe2O3–CoO) were prepared through controlled crystallization of respective biocomposites through sintering process. The crystalline phases in bioactive glass composites were identified by using X-ray diffraction (XRD) analysis. Nucleation and crystal growth temperatures were found by thermogravimetric analysis (TGA)/differential thermal analysis (DTA) technique. These biocomposite were immersed in simulated body fluid (SBF) for different time periods, i.e. 1, 3, 7, 14 and 21 days. Hydroxyapatite was formed on these samples and was confirmed by FTIR, SEM, and pH measurements. The magnetic properties of these samples were evaluated by vibrating sample magnetometer (VSM).The density and compressive strength were enhanced with an increase in Fe2O3 and CoO content in the base bioglass powder. This study will help the researcher to know the bioactivity and magnetic properties of the implant material like bone and teeth.

The Néel temperature (TN) in conventional antiferromagnets (AFM) decreases with decreasing particle size. In contrast, we present here evidence for an exotic facet of multiferroicity, whereby one can raise the TN by more than 200 K by decreasing the particle size. We illustrate this by taking the example of a tetragonal composition with x = 0.5 in the solid solutions of (1 − x)BiFeO3-xPbTiO3 (BF-xPT). We attribute it to the increase in the strength of the superexchange interaction via a decrease in the ferroelectric distortion in nanocrystalline powder of BF-0.5PT. The BF-0.5PT nanoparticles also exhibit exchange bias effect due to AFM core-FM shell type magnetic nanostructure.

The coexistence and coupling of magnetic and ferroelectric orderings in single phase multiferroics has evinced enormous scientific interest as it involves breaking of time reversal and space inversion symmetries in the same material. The mutual controllability of the two diverse orderings in multiferroics has potential for developing new generation multifunctional sensor, actuator and data storage devices. We present here evidence for a new exotic facet of multiferroicity, whereby one can raise the strength of antiferromagnetic (AFM) superexchange interaction and hence tune the Néel temperature (TN) from ~120K in bulk to ~350K in 18nm size particles by tuning the ferroelectric distortion in the tetragonal phase of multiferroic (1-x)BiFeO3 -xPbTiO3 solid solutions . This observation is unique to multiferroics only as the TN in non-multiferroic AFM oxides decreases with particle size. Our results provide a scientific basis for designing room temperature single phase multiferroics, useful for making multifunctional device operating at room temperature.