Magnetoelectric coupling of multiferroic chromium doped barium titanate thin film probed by magneto-impedance spectroscopy

Thin film of BaTiO3 doped with 0.1 at.% Cr (Cr:BTO) has been prepared by pulsed laser deposition technique. Film was deposited on Pt/SrTiO3 substrate at 500 degrees C in 50 mTorr Oxygen gas pressure using KrF (298 nm) laser. Polycrystalline growth of single phase Cr: BTO thin film has been confirmed by grazing angle X-ray diffraction. Cr: BTO film exhibited remnant polarization 6.4 mu C/cm(2) and 0.79 MV/cm coercivity. Magnetization measurement of Cr: BTO film showed magnetic moment 12 emu/cc. Formation of weakly magnetic domains has been captured by magnetic force microscopy. Theoretical impedance equation fitted to experimental data in Cole-Cole plot for thin film in presence of transverse magnetic field resolved the increase in grain capacitance from 4.58 x 10(-12) to 5.4 x 10(-11) F. Film exhibited high value 137 mV/cm-Oe magneto-electric (ME) coupling coefficient at room temperature. The high value of ME coupling obtained can reduce the typical processing steps involved in multilayer deposition to obtain multiferrocity in thin film. Barium titanate being best ferroelectric material has been tailored to be multiferroic by non ferromagnetic element, Cr, doping in thin film form opens an avenue for more stable and reliable spintronic material for low power magnetoelectric random excess memory applications

Single Frequency Impedance Analysis on Reduced Graphene Oxide Screen-Printed Electrode for Biomolecular Detection

A biofunctionalized reduced graphene oxide (rGO)-modified screen-printed carbon electrode (SPCE) was constructed as an immunosensor for C-reactive protein (CRP) detection, a biomarker released in early stage acute myocardial infarction. A different approach of single frequency analysis (SFA) study was utilized for the biomolecular sensing, by monitoring the response in phase angle changes obtained at an optimized frequency resulting from antigen-antibody interactions. A set of measurements were carried out to optimize a frequency where a maximum change in phase angle was observed, and in this case, we found it at around 10 Hz. The bioelectrode was characterized by contact angle measurements, scanning electron microscopy, and electrochemical techniques. A concentration-dependent response of immunosensor to CRP with the change in phase angle, at a fixed frequency of 10 Hz, was found to be in the range of 10 ng mL(-1) to 10 mu g mL(-1) in PBS and was fit quantitative well with the Hill-Langmuir equation. Based on the concentration-response data, the dissociation constant (K (d)) was found to be 3.5 nM (with a Hill coefficient n = 0.57), which indicated a negative cooperativity with high anti-CRP (antibody)-CRP (antigen) binding at the electrode surface. A low-frequency analysis of sensing with an ease of measurement on a disposable electroactive rGO-modified electrode with high selectivity and sensitivity makes it a potential tool for biological sensors

Induced magnetism and magnetoelectric coupling in ferroelectric BaTiO3 by Cr-doping synthesized by a facile chemical route

Pure phase barium titanate (BTO) and Cr doped BTO have been synthesized by a facile single step metal-organic decomposition (MOD) method. Thermal gravimetric analysis (TGA) is performed on the processed sample to analyse the thermal stability of the compound. A tetragonal to distorted cubic phase transformation of BTO by Cr doping has been confirmed by X-ray diffraction and Raman spectroscopy. Cr doping in BTO reduced the ferroelectric transition temperature from 122 degrees C to 108 degrees C. A ferroelectric polarization value of 14.5 mu C cm(-2) for pure BTO was obtained, which decreased to 3.7 mu C cm(-2) by 1.5 Cr doping. The diamagnetism of BTO partially transformed into ferromagnetic behaviour by Cr-doping at the expense of a decrease in polarization. The magnetoelectric coefficient has been measured by the dynamic MEB method which was recorded as 13 mV cm(-1) Oe(-1) for 1.5 Cr : BTO at room temperature. Induced electric polarization has been obtained by applying an external magnetic field due to the local interaction of d electron spins with disordered electric dipoles via oxygen vacancies created by the Cr doping in BaTiO3. Such materials possess immense potential in low energy consumption for miniaturized device applications in the area of spintronics, sensors and transducers and multistage memory

A Novel Approach to Improve Properties of BiFeO3 Nanomultiferroics

In this study we report the synthesis of Bi1-xInxFe1-yTiyO3 (0x0.1, 0y0.05) nanoparticles by a simple cost effective solution combustion method. Pure BFO samples shows distorted rhombohedral perovskite structure with space group R3c which is also supported by Fourier transform infrared spectra study. The codoping of In and Ti at A-B sites of BFO (BIFTO) partially distorts the crystal structure, increases the lattice strain, reduces the average particle size (14nm), and increases the Fe3+/Fe2+ ratio which significantly affect the observed results. The saturation magnetization increases significantly upon codoping (4.60emu/gm) by about 12 times than that of pure BFO (0.4emu/gm). The improved ferromagnetic properties upon codoping is further manifestated in large value of linear magnetoelectric coupling coefficient (4.8mV/cmOe) which further provides an indirect evidence for the collapse of space modulated spin structure. The activation energy increases with codoping (0.68eV), although less than 1eV which indicates that the conduction is still dominated by charged defect

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

CoFe2O4/(Pb0.6Sr0.4)TiO3 bi-layered composite film exhibits ferromagnetic and ferroelectric responses (M-s similar to 162 emu/cm(3), H-c similar to 1.8 kOe, 2P(r) similar to 8.6 mu C/cm(2) and 2E(c) similar to 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 similar to 49% at 3 kOe applied DC magnetic field. The composite film exhibits magnetoelectric voltage co-efficient alpha(ME) similar to 67 mV cm(-1) Oe(-1). The photoluminescence emission bands of the composite film have a significant blue shift as compared to those reported for CFO and PST nanostructures

High performance dendrimer functionalized single-walled carbon nanotubes field effect transistor biosensor for protein detection

We report a single-walled carbon nanotube (SWNT) field-effect transistor (FET) functionalized with Polyamidoamine (PAMAM) dendrimer with 128 carboxyl groups as anchors for site specific biomolecular immobilization of protein antibody for C-reactive protein (CRP) detection. The FET device was characterized by scanning electron microscopy and current-gate voltage (I-V-g) characteristic studies. A concentration-dependent decrease in the source-drain current was observed in the regime of clinical significance, with a detection limit of similar to 85 pM and a high sensitivity of 20% change in current (Delta I/I) per decade CRP concentration, showing SWNT being locally gated by the binding of CRP to antibody (anti-CRP) on the FET device. The low value of the dissociation constant (K-d = 0.31 +/- 0.13 mu g ml(-1)) indicated a high affinity of the device towards CRP analyte arising due to high anti-CRP loading with a better probe orientation on the 3-dimensional PAMAM structure

Magnetic, X-ray and Mossbauer studies on magnetite/maghemite core-shell nanostructures fabricated through an aqueous route

Uniform 6-13 nm sized 0D superparamagnetic Fe3O4 nanocrystals were synthesized by an aqueous 'co-precipitation method' under a N-2 atmosphere as a function of temperature to understand the growth kinetics. The crystal phases, surface charge, size, morphology and magnetic characteristics of as-synthesized nanocrystals were characterized by XRD, Raman spectroscopy, FTIR, TG-DTA, BET surface area, dynamic light scattering along with zeta potential, HR-TEM, EDAX, vibrating sample magnetometry and Mossbauer spectroscopy. TEM investigation revealed highly crystalline spherical magnetite particles in the 8.2-12.5 nm size range. The kinetically controlled as-grown nanoparticles were found to possess a preferential (311) orientation of the cubic phase, with a highest magnetic susceptibility of similar to 57 emu g(-1). The Williamson-Hall technique was employed to evaluate the mean crystallite size and microstrain involved in the as-synthesized nanocrystals from the X-ray peak broadening. In addition to FTIR and Raman spectra, Rietveld structural refinement of XRD confirms the magnetite phase with 5-20% maghemite in the sample. VSM and Mossbauer spectral data allowed us to fit the magnetite/maghemite content to a core-shell model where the shell is 0.2-0.3 nm thick maghemite over a magnetite core. The activation energy of <10 kJ mol(-1) calculated from an Arrhenius plot for the complex process of nucleation and growth by diffusion during synthesis shows the significance of the precipitation temperature in the size controlled fabrication processes of nanocrystals. Brunauer-Emmett-Teller (BET) results reveal a mesoporous structure and a large surface area of 124 m(2) g(-1). Magnetic measurement shows that the particles are ferromagnetic at room temperature with zero remanence and zero coercivity. This method produced highly crystalline and dispersed 0D magnetite nanocrystals suitable for biological applications in imaging and drug delivery

Magnetoelectric coupling-induced anisotropy in multiferroic nanocomposite (1-x)BiFeO3-xBaTiO(3)

Nanocomposite (1 - x)BiFeO3-xBaTiO(3) for x = 0.1, 0.2 and 0.3 compositions were prepared by sol-gel technique. X-ray diffractograms confirmed the formation of desired crystallographic phase of the composite. The average particle size was determined 75, 128 and 150 nm for x = 0.1, 0.2 and 0.3 samples by HRTEM measurement. Magnetic, dielectric and magnetoelectric response has been investigated to find out the magnetoelectric (ME) coupling at atomic scale mixing of the two phases. For effective ME coupling nanoscale synthesis provided large surface area and subsequently induced magnetic anisotropy in the sample. The computed value of magnetic anisotropy constant 4.8 x 10(3) erg/cm(3) was found to be maximum for x = 0.1 composition. It is believed that the anisotropy is being induced by ME coupling which changes with the composition. Correlated magnetic and dielectric transition temperatures were determined as an evidence of ME coupling in the material. To confirm the ME coupling room-temperature ME coupling coefficient (alpha) was calculated using dynamic method which was observed to have a maximum value of 2.74 mV/cmOe for x = 0.1 confirming the presence of room-temperature ME coupling in the nanocomposite. Spin flipping behaviour has been confirmed by ZFC-FC measurements at low temperature while the coercivity was found to be almost constant. Significantly, controlled coercivity behaviour has been correlated to the presence of ME coupling in the composite material, which can be very useful in memory device and spintronic application

Graphene functionalized with 3-mercatopropionic acid capped zinc peroxide nanoparticles: A potential ferromagnetic material at room-temperature

The literature reveals that ferromagnetism in zinc peroxide (ZnO2) is due to the exchange interaction between localized electron spin moments resulting from oxygen vacancies at the surface of nanoparticles, while in graphene may be due to existence of various defects. However ZnO2 show paramagnetic behaviour, whereas graphene exhibits very low magnetic intensity (0.0004 emu g(-1)). To enhance magnetization, graphene was treated with 3-mercatopropionic acid followed by coating with polyvinylpyrrolidone (PVP) capped ZnO2 nanoparticles. Interestingly coating of graphene over ZnO2 does not enhance magnetization, whereas coating of 15-20% ZnO2 nanoparticles over graphene enhances magnetization more than 30 times, which gradually decreases on increasing concentration of ZnO2 nanoparticles. Such coated graphene shows highest saturation of magnetization at room temperature ever reported in graphene (130 memu g(-1)). The Magnetic measurements studies of ZnO2 nanoparticles coated graphene indicates excellent room temperature ferromagnetic behaviour, which has been further confirmed by Electron Paramagnetic Resonance and Magnetic Force Microscopy studies. A comparative study was also done with ZnO nanoparticles with graphene and only 60 memu g(-1) magnetization has been observed. It has been concluded that higher magnetization in graphene coated with ZnO2 than ZnO is due to more oxygen vacancies in ZnO2 nanoparticles