N.S. Negi

Multiferroic and magnetoelectric properties of CoFe2O4/Pb1−xSrxTiO3 composite films

To realize multiferroic and magnetoelectric properties, bi-layered nanocomposite films consisting of CoFe2O4 (CFO)/Pb1−xSrxTiO3 (PST) phases (x = 0.1, 0.2, and 0.3) have been deposited on Pt/TiO2/SiO2/Si substrate by using a metallo-organic decomposition process. Both the PST perovskite and the CFO spinel phases are confirmed from X-ray diffraction patterns and Raman spectra of the composite films. The composite films exhibit room temperature multiferroic properties. The values of saturation magnetization (Ms), remanent magnetization (Mr), and coercive field (Hc) of the composite films are in the range of 108–119 kA/m, 42–51 kA/m, and 44.5–64.1 kA/m, respectively. In addition, the saturation polarization (Ps), remanent polarization (Pr), and electrical coercive field (Ec) are observed in the range of 11.3–14.4 μC/cm2, 2.9–4.8 μC/cm2, and 56–59.5 kV/cm, respectively. The dielectric response in the presence of applied magnetic field, Hdc ∼ 238.6 kA/m shows a high magnetocapacitance value ∼385% at frequency ...

Structural and multiferroic properties of Bi1−xInxFeO3 (0 ≤ x ≤ 0.20) nanoparticles

Indium (In)-doped BiFeO3 (BFO) nanoparticles were prepared by an ethylene glycol based sol-gel method using the concept of aging for the formation of pure phase crystal structure. The x-ray diffraction patterns reveal the single phase rhombohedral structure for BFO and In-doped BFO nanoparticles and In substitution (0%-20%) at the Bi site does not transform the crystal structure of BiFeO3. The appearance of metal-oxide absorption bands at 555 cm−1 and 439 cm−1 in FTIR spectra confirms the formation of perovskite structure. The doping of In at Bi-site improves the particles surface morphology and reduces the average particles size to around 30 nm which markedly affect the magnetic and electrical properties of these nanoparticles. Saturation magnetization increases from 0.40 emu/gm for BFO nanoparticles to 3.20 emu/gm for 20% In-doped BFO (BFO2) nanoparticles. The coercivity reduces to 78 Oe for BFO2 due to decrease in magnetocrystalline anisotropy. In-doping at Bi-site improves the dielectric properties of...

Superparamagnetic La doped Mn–Zn nano ferrites: dependence on dopant content and crystallite size

Magnetic nanoparticles are found to exhibit exciting and substantially distinct magnetic properties due to high surface-to-volume ratio and several crystal structures in comparison to those discovered in their bulk counterparts. The properties of nanoparticles also largely depend on the route of their synthesis. In the present work, we report the synthesis of superparamagnetic nanoparticles of Mn0.5Zn0.5La x Fe2−x O4 (x = 0, 0.025, 0.050, 0.075, 0.1) ferrites by co-precipitation method. Structural, morphological and elemental study has been performed using x-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), FESEM and EDS. Different structural parameters (crystallite size, interplanar spacing and lattice constant) have been calculated from XRD. Formation of cubical spinel structure has been confirmed from XRD and FTIR. Cation distribution for all the samples has been proposed and used for calculation of various theoretical parameters. Magnetic properties have been investigated using vibrating sample magnetometer at room temperature and show transition between paramagnetic and superparamagnetic behavior. Maximum saturation magnetization and magnetic moment have been obtained at x = 0.050. The results are attributed to the solubility of La in Mn–Zn ferrite and the size of nanoparticles. The samples have also been analyzed for dielectric, electric and optical properties. For x ≤ 0.050, a blue shift in absorbance and photoluminescence measurements has been observed due to quantum confinement.

Multifunctional behaviour of nanostructured Pb0.7Sr0.3 (Fe0.012Ti0.988)O3 thin film

Structural, magnetic, electrical and optical properties of the Pb0.7Sr0.3(Fe0.012Ti0.988)O3 (PSFT) thin film have been studied. The PSFT solution was prepared by the sol–gel combined metallo-organic decomposition method and deposited on Si, Pt/Ti/SiO2/Si and fused quartz substrates by the spin-coating technique. The superparamagnetic relaxation between bulk nanoparticles and film nanograins has been done. The insulating gaps between the PSFT nanograins made symmetrically coupled plasmon modes and explored their potential in magneto-optic data storage, light generation, microscopy and bio-photonics.

METALLO-ORGANIC DECOMPOSITION SYNTHESIS AND CHARACTERIZATION OF FERROELECTRIC (PB1 −XCAX)TIO3 Thin Films

ABSTRACT Synthesis of ferroelectric (Pb1−xCax)TiO3 (PCT) thin films over Pt/Ti/SiO2/Si substrates by metallo-organic decomposition (MOD) technique using a new chemical precursor route is described. The Ca composition dependent changes in the structural, dielectric and ferroelectric properties of the PCT films have been investigated. Typical tetragonal structure of the PCT films is evidenced with Ca ≤ 40% and at higher Ca concentration ∼50% a transformation to a pseudocubic structure is observed. Dependence of the ferroelectric properties on the Ca substitution is related to the combined effect of reduction in internal stress in the films, decrease in the grain size and dielectric anisotropy.

Synthesis and characterization of nanostructured (Pb1− x Sr x )TiO3 thin films by a modified chemical route

The coating solutions of nanostructured (Pb1– x Sr x )TiO3 (PST) thin films have been prepared by the sol–gel combined metallo-organic decomposition method. The coating solutions were deposited on Pt/Ti/SiO2/Si substrates using a spin-coating technique with spinning speed of 4300 rpm and annealed at 650°C. The effect of Sr content in reducing the grain size and tetragonal distortion of PST films has been studied. The optimum conditions for crystalline phase formation in the films have been analyzed by thermogravimetric, differential thermal analysis and Fourier transform infrared spectroscopy. The phase and microstructure of the films were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The XRD pattern shows that the PST thin films are crystallized into tetragonal structures without any impurity phase and the distortion ratio reduces with increasing Sr concentration. The AFM results indicate an increase in grain size with increasing annealing temperature of the film and reduction in grain size with increasing Sr concentration.

Multiferroic and magnetoelectric properties of MnFe2O4/(Pb0.8Sr0.2)TiO3 composite films

Abstract MnFe2O4/(Pb0.8Sr0.2)TiO3 (MFO/PST20) heterostructured composite films with three different structures have been grown on Pt/TiO2/SiO2/Si substrates by metal–organic decomposition processing via spin coating technique. The structural analysis revealed that the crystal axes of the MnFe2O4 are aligned with those of the PST20 ferroelectric matrix with obvious interfaces and no diffusions exist in all the three composite films. These composite films exhibit simultaneously multiferroic and magnetoelectric responses at room temperature. The growth structure of MFO and PST20 layers has an effect on multiferroic and magnetoelectric coupling behaviours of the composite films. The bi- and four-layered MFO/PST20 composite films exhibit superior ferroelectric properties compared to the tri-layered film. The increasing MFO and PST20 layers in the composite films enhance ferromagnetic properties and are closely related to the strain release in MnFe2O4 phase. The MFO/PST20 bi-layered composite film shows a high magnetoelectric voltage co-efficient αE ~ 194 mVcm−1Oe−1 at a dc magnetic field Hdc ~ 2.5 kOe. A significant decrease in αE value has been observed for tri- and four- layered composite films. A close correlation between phase selective residual stress and magnetoelectric properties has been emerged. The results are reasonably encouraging for employing MnFe2O4 for growing multiferroic–magnetoelectric composite films.

Induced magnetoelectric coupling and photoluminescence response in solution-processed CoFe2O4/Pb0.6Sr0.4TiO3 multiferroic composite film

ABSTRACT CoFe2O4/(Pb0.6Sr0.4)TiO3 bi-layered composite film exhibits ferromagnetic and ferroelectric responses (Ms ∼ 162 emu/cm3, Hc ∼ 1.8 kOe, 2Pr ∼ 8.6 µC/cm2 and 2Ec ∼ 634 kV/cm) at room temperature. The temperature dependent dielectric anomaly near magnetic phase transition temperature suggests magnetoelectric coupling effect in the composite film. The maximum MD effect can reach as high as ∼49% at 3 kOe applied DC magnetic field. The composite film exhibits magnetoelectric voltage co-efficient αME ∼ 67 mVcm−1Oe−1. The photoluminescence emission bands of the composite film have a significant blue shift as compared to those reported for CFO and PST nanostructures.

Strain-induced structural, magnetic and ferroelectric properties of heterostructure BST–NZFO nanocomposite thin film at room temperature

Heterostructure