Multiferroics Research Papers - Academia.edu (original) (raw)

- by
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- Physics, Multiferroics, Physical sciences, CHEMICAL SCIENCES
- by Alison Hale
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- Engineering, Mathematics, Physics, Electromagnetism
- by Shouguo Wang
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- Materials Engineering, Condensed Matter Physics, Nanotechnology, Multiferroics

The iron potassium fluorides with the general formula Kx FeII x FeIII 5−x F15 (2 􏰕 x 􏰕 3) are interesting multiferroic materials, for which the coexistence of all the three ferroic orders (elastic, electric, and magnetic) is simultaneously observed below the magnetic transition. Although the phase diagram has been previously defined, in particular for the potassium-rich K3Fe5F15 phase, its complex magnetic behavior has not been completely understood. In this paper, the information obtained by magnetization measurements carried out on an oriented single crystal, revealing high anisotropy with coercive field reaching 14 kOe on the easy axis, are combined with Mo ̈ssbauer spectroscopy and powder neutron diffraction data to define the magnetic structure. The ferrimagnetic behavior of K3Fe5F15 arises from an antiferromagnetic triangular spin system, determined by neutron diffraction, frustrated by the difference in the magnetic contributions of adjacent structural layers, originated by F...

- by Massimo Solzi
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- Physics, Materials Science, Chemistry, Nanotechnology
- by Chemistry International
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- Inorganic synthesis, Multiferroics, BiFeO3

In the present work, it was reported for the first time the new synthesis of Sm 2 NiMnO 6 double perovskite oxides by solegel auto-combustion method. The Rietveld analysis of the X-ray ceramics diffraction pattern recorded at room temperature for Sm 2 NiMnO 6 ceramics sintered at 1000 C/5 min from powders obtained at 700 C/7 h confirm the formation of the double perovskite with a monoclinic structure and the space group P2 1 /n. The HRTEM analysis shows clear lattice fringes that confirm a high crystallinity level of the material corresponding to the monoclinic structure. The non-linear dielectric character was checked for the first time in Sm 2 NiMnO 6 double perovskite and the results reveals a strong nonlinearity and a small hysteretic behaviour. The present structural, magnetic and dielectric data make the Sm 2 NiMnO 6 system due to its multiferroic character a promising candidate to different modern electronic devices applications.

- by Felicia Gheorghiu
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- Multiferroics, double perovskite, Sm2NiMnO6 ceramics, HRTEM analyse
- by James Scott
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- Engineering, Spintronics, Advanced Materials, Multiferroics
- by Heng-Hui Wu
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- Materials Engineering, Multiferroics

The effects of milling energy induced during intermediate mechanical activation of precursors on the synthesis of nano-structured BiFeO3 powders have been systematically investigated. X-ray diffractometer, laser particles size analyzer, field emission scanning electron microscope, vibrating sample magnetometer and electrical evaluation techniques were used to study phase composition, particles size distribution, morphology, magnetic properties and ferroelectric properties of the products, respectively. Applying a total energy of 171.18kJ/g during milling led to formation of an amorphous structure which resulted in decreasing the formation temperature of bismuth ferrite phase by about 100˚C, although small amounts of secondary phases were detected. This sample shows the mean particles size of 170nm and the mean crystallite size of 40nm, when calcined at 750˚C. Saturation magnetization (MS) increased from 0.054 to 0.071A.m2/kg and coercive field (HC) decreased from 32.63 to 6.37kA/m by increasing the milling energy from 13.48 to 171.18kJ/g. In addition, electrical hysteresis loops demonstrated a decrease in the current leakage by increasing the milling energy and lowering the calcination temperature.

- by sunil patil
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- Engineering, Materials Engineering, Materials Chemistry, Multiferroics

The rare earth orthochromites are extremely interesting due to the richness of their optical, dielectric, and magnetic properties as well as due to their multiferroic properties which make them suitable materials to study in the nanoregime. However, the wet-chemical synthesis of these materials in nanosize is nontrivial. Here, we report for the first time, the detailed Raman spectra as well as magnetic and dielectric properties of chemically synthesized GdCrO3 nanoparticles of size ranging from 40 to 60 nm. The magnetic properties are dictated by competing Cr3+–Cr3+, Gd3+–Cr3+, and Gd3+–Gd3+ superexchange interactions in different temperature regions, resulting into an antiferromagnetic ordering at 167 K due to the Cr3+–Cr3+ followed by weak ferromagnetic ordering due to the onset of Cr3+–Gd3+ interactions. At lower temperature, it shows weak antiferromagnetic ordering due to Gd3+–Gd3+ interaction. Below 95 K, GdCrO3 nanoparticles showed the presence of negative magnetization due to Gd3+ and Cr3+ interactions resulting into weak ferromagnetic coupling. The Raman spectroscopy shows the characteristic Raman shifts indicating that below 450 cm−1, Gd3+ ions play a dominant role in determining the phonon frequencies of GdCrO3, and above 450 cm−1, the Cr+3 ions dominate. We also present for the first time the low temperature dielectric constant and loss tangent data for GdCrO3 in a broad temperature and frequency range. The dielectric constant shows a decrease in comparison to the bulk values due to the size dependent effects. It also shows a peak centered at around 320 K above which it shows a sharp decrease. The dielectric loss value in GdCrO3 nanoparticles is quite small and shows an interesting frequency dependent anomaly at lower temperature which might be due to the coupling between magnetic and dielectric order parameters.

We report the temperature-dependent Raman and dielectric spectroscopy of chemically synthesized BiFeO3 nanoparticles (average size 50−60 nm). The Raman spectra (90−700 K) show two sets of transitions in the lowest Raman E mode, associated with Bi−O bond motion situated in close proximity to the spin reorientation transitions reported for BiFeO3, thereby indicating the existence of possible coupling between magnons and phonons for particle size below the helical order parameter (62 nm). These transitions are slightly shifted in temperature in comparison to the bulk single crystals. We also observe a step-like behavior in Raman peak position around the Neel temperature, suggesting that the phonons are influenced by the magnetic ordering in nanosized BiFeO3. The heat-flow measurements show two sharp endothermic peaks at 1094 and 1223 K representing rhombohedral to orthorhombic or monoclinic transition followed by transition into the cubic phase above 1200 K. The low temperature (20−325 K), frequency-dependent (1−106 Hz) dielectric constant and loss tangent measurements show that the loss tangent (10−3) and ac conductivity values (10−8 Ohm−1-cm−1) are orders of magnitude lower than the reported values for BiFeO3 ceramics, indicating high levels of ionic purity of our samples. The real part of the permittivity shows a slight reduction in its value (30) in comparison to the bulk single crystals. Similar to the Stokes Raman shift, its temperature-dependent dielectric constant also shows four weak anomalies at 85, 168, 205, and 230 K situated in close proximity to the spin reorientation transitions, indicating magnetoelectric coupling.

- by Tuhin Subhra Maity
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- Raman Spectroscopy, Nanoparticles, Dielectric Physics, Multiferroics
- by Nicholas C Bristowe
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- Multiferroics, Magnetism, Mathematical Sciences, DFT
- by Christos Takoudis
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- Inorganic Chemistry, Multiferroics, MOCVD, Csd

In the present attempt, we report modified features of structural, dielectric, magnetic and ferroelectric behaviour of BiFeO 3 (BFO) by perovskite-spinel composite approach. ZnFe 2 O 4 (ZFO) is used as spinel phase. The structural measurement of composite show anisotropically compression in the BiFeO 3 lattice with ZFO compositions and stimulates the variation in bond length, bond angle, tilting angle, electron density and resultant polarization. This affects on magnetic and dielectric behaviour of BFO. Room temperature magnetic measurement revealed enhancement of magnetization of BFO in composite, attributed to spin restructuring due to change in magnetic anisotropy, exchange energy and stress energy at interface with ZFO composition. There is around 7 times enhancement in magnetization as compared to pure BFO phase. Dielectric profile of composites shows decrease in dielectric constant as well as dielectric loss as compared to single phase BFO. P-E loop exhibits leaky ferroelectric behaviour of composite system with drop down in leakage current by 2 order of magnitude than pure BFO phase. Magnetic contributions of individual phases in composite are determined by Vegard Law while dielectric contributions are modelled by Maxwell-Garnett (MG) equation. The present work demonstrates that BFO-ZFO: perovskite-spinel composite approach to modify magnetic, dielectric and ferroelectric behaviour and to facilitate BFO as room temperature multiferroic system.

- by VISHWAJIT M GAIKWAD
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- Composites, Magnetic Materials, Multiferroics, Ferroelectrics
- by Munees Waran
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- Multiferroics

The effect of Nd doping on Bi1−xNdxFeO3 (x = 0.0, 0.175, 0.20) multiferroics synthesized by chemical co-precipitation method has been investigated by Rietveld analysis of X-ray powder diffraction (XRD) data. The formations of the single-phase compounds were confirmed by XRD. X-ray diffraction along with the Rietveld-refinement showed a gradual change in crystal structure from rhombohedral to triclinic with increasing Nd doping concentration. The bond distances along with bond angles between atoms for all the compounds were calculated which supports the structural results. Raman spectroscopy also recommends a structural change and is accompanied by the weakening of long-range ferroelectric order with increasing doping concentration (x). The results of Raman spectra for BiFeO3 (BFO) match well with the earlier reported bulk ceramic and epitaxially grown thin film of BFO. The ferroelectric-paraelectric transition in 20% Nd BFO substituted was explained according to the change of Bi–O covalent bond as a result of decline of stereochemical activity of Bi lone pair electron and is further confirmed through ferroelectric polarization (P–E) hysteresis loop.

- by Ashwini Kumar
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- Multiferroics

Polycrystalline Bi1−xBaxFe1−yMyO3 (M = Co and Mn; x = 0.1, y = 0.1) were synthesized by solid-state route method to study the compositional driven structural transformations in multiferroics. Room temperature X-ray diffraction patterns confirmed the formation of perovskite structure. Rietveld-refined crystal structure parameters revealed the existence of rhombohedral R3c symmetry for both the samples. The samples were found to be nearly free from any other secondary phases. Raman analysis reveals that Ba atom substitutes Bi site and Mn and Co atom substitutes Fe site into the BiFeO3 with the shifting of phonon modes. The red shift is attributed to Co or Mn doping where as blue shift occurs from Ba doping. The differential scanning calorimetry reveals the corresponding Neel temperature 370 °C and 326 °C for Co and Mn doped samples. Ba and Co substitution with x = 0.1 and y = 0.1 has not affected the Neel temperature of the parent BiFeO3 as well of Ba and Mn substitution. The variation of frequency dispersion in permittivity and loss pattern due to A-site and B-site substitution in BiFeO3 was observed in the dielectric response curve.

- by Ashwini Kumar
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- Multiferroics, Multiferroic, BiFeO3

Multiferroic xBa0.95Sr0.05TiO3-(1‒x)BiFe0.9Gd0.1O3 [xBST-(1‒x)BFGO], where x=0.00-0.40, have been synthesized by the conventional solid-state reaction method. The crystalline phase, microstructure, relaxor behavior, ac conductivity, impedance spectroscopy, dc magnetic properties, complex initial permeability and magnetoelectric coefficient of these solid solutions have been investigated. The crystal structure is found to change from rhombohedral in BFGO rich compositions to cubic when x≥0.30. Room temperature dielectric properties are investigated within the frequency range of 1 kHz -1 MHz and found to increase with BST content. The frequency dependence of high temperature dielectric measurements indicated that the composites with x≥ 0.20, exhibit relaxor ferroelectric behavior. The ac conductivity obeys the Jonscher’s universal power law and BST helps to enhance the electrical conductivity of the composites. Studies of impedance spectroscopy suggest that only grains have the contribution to the conductivity mechanism in this material. Magnetizations as a function of applied magnetic field measurements show weak ferromagnetism for
0.10≤x≤ 0.30 composites. The maximum value of remnant magnetization is found to be 0.565×103 A/m (=0.08 emu/g) for x =0.25 which is better than previously reported BaTiO3 - BiFeO3 systems. The complex initial permeability is found to improve with the increase in BST concentration due to the reduction of oxygen vacancies. In addition, an enhanced magnetoelectric (ME) coupling is also observed and determined by the ME coefficient. The maximum value of ME coefficient is found to be 21.71×10-4 V/A (=1.67 mV/cm Oe) for the x =0.25 composition. The BST-BFGO solid solutions show high-performance multiferroic properties and can be selected for further investigation.

- by Julhash Miah
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- Nanomaterials, Nanotechnology, Multiferroics
- by Munees Waran
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- Magnetic Materials, Multiferroics

Nickel ferrite nanoparticles were synthesized by wet chemical co-precipitation method and the corresponding
temperature dependent structural, magnetic and optical properties of these nanoparticles have
been investigated. X-ray diffraction patterns show the single phase cubic spinal crystal structure belonging
to the space group Fd3m. The average crystallite size varies in the range 8–20 nm with varying
sintering temperature. Raman spectroscopy exhibits a doublet-like peak behaviour which indicates the
presence of mixed spinel structure. The saturation magnetization, coercivity and remanence increase
with increasing sintering temperature from 250 to 550 C. The non-saturation and low values of magnetization
at high fields indicate the strong surface effects to magnetization in NiFe2O4 nanoparticles. The
g-value calculated from electron spin resonance spectrum indicates the transfer of divalent metallic ion
from octahedral to tetrahedral site (i.e. mixed spinel structure). The dielectric permittivity, loss tangent
and ac conductivity measurements show strong temperature dependence at all frequencies. The observed
ac conductivity response suggests that the conduction in ferrite nanoparticles is due to feeble polaron
hopping between Fe3+/Fe2+ ions. Room temperature UV–vis diffuse spectra indicate that NiFe2O4 is an
indirect band gap material with band gap ranges from 1.27 to 1.47 eV with varying sintering temperature.
The photoluminescence study clearly indicates that the Ni2+ ions occupy both octahedral and
tetrahedral sites confirming mixed spinel structure.

- by Dr. Mukesh Jewariya and +2
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- Multiferroics

Barium (Ba) doping at Bismuth (Bi) site is reported to enhance magnetic properties of Bismuth Ferrite (BiFeO 3) while Yttrium (Y) doping at the same is found to improve ferroelectric and dielectric properties. To investigate the combined effect of Ba and Y co-doping, Ba 0.1 Bi 0.9-x Y x FeO 3 (x ¼ 0.0, 0.1 and 0.2) are synthesized using chemical synthesis route and their magnetoelectric and dielectric properties are studied in detail. The X-Ray Diffraction study confirms the single phase nature of the synthesized samples. The ferroelectric property is enhanced for x ¼ 0.1 while the magnetic studies show enhanced magnetisation for both co-doped samples with highest enhancement in x ¼ 0.1. The doped samples exhibit a first order field induced metamagnetic transition. The dielectric constant also increases with reduced tangent loss and conductivity for x ¼ 0.1. Therefore, co-doping with Ba and Y improves the magnetoelectric and dielectric property of BiFeO 3 .

- by Swarnali Hait
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- Multiferroics, Magnetoelectrics, Ferroelectrics, Ferroelectric materials
- by Dilsom Sanchez
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- Applied Physics, Multiferroics, Multiferroic as a photovoltic, AIP

The effect of Sr2+ doping on Bi1-xSrxFeO3 (x = 0.0, 0.15, 0.175, 0.25) multiferroic ceramics synthesized by citrate sol-gel method has been investigated by Rietveld analysis of X-ray powder diffraction data, Raman spectroscopy and dielectric measurement. X-ray diffraction along with the Rietveld–refinement showed a gradual change in crystal structure from rhombohedral (R3c) to pseudotetragonal (P4/mmm) with enhanced divalent Sr2+ ion concentration. All the 13 Raman modes predicted by group theory (ΓR3c = 4 A1 + 9 E) for R3c structure of Bi1-xSrxFeO3 (x = 0.0, 0.15, 0.175, 0.25) were observed in the present study. The A1-2 and E-4 modes are completely suppressed, while to that A1-3, E-8 mode in Bi1-xSrxFeO3 (x = 0.175, 0.25) and E-2, E-5, and E-8 modes (x = 0.25) disappear completely as compared to parent BFO. The structural phase transition and weakening of long-range ferroelectric order with increasing doping concentration are thus further confirmed from Raman scattering spectra. The dielectric anomaly has been occurred in dielectric constant and dielectric loss near 325 °C, 305 °C, 270 °C and 250 °C (f = 10 kHz) in BiFeO3, Bi0.85Sr0.15FeO3, Bi0.825Sr0.175FeO3 and Bi0.75Sr0.25FeO3, respectively.

- by Ashwini Kumar
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- Condensed Matter Physics, Multiferroics
- by Ashwini Kumar
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- Rietveld refinement, Structural Analysis, Multiferroics, Spinel Ferrite

The structural, vibrational, magnetic and dielectric properties of polycrystalline BiFeO3 and Bi0.95Pr0.05FeO3 are investigated by combining X-ray diffraction, Raman scattering spectra, magnetometry and dielectric measurements. Structural symmetry with rhombohedral R3c phase is revealed for both parent and 5% Pr substitution at Bi site, serving no chemical pressure and causes no structural transition from R3c to any other phase is identified from x-ray diffraction patterns and Raman scattering spectra. The shifting of phonon modes towards higher frequency side is attributed to lower atomic mass of Pr ion as compared to Bi ion. The magnetic measurements at room temperature indicate that Pr substitution induces ferromagnetism and discerns large and non-zero remnant magnetization as compare to pristine BiFeO3. Both dielectric permittivity and loss factor of Bi0.95Pr0.05FeO3 strongly decreases with increased frequency. Significant role of hopping of oxygen ion vacancies in Bi0.95Pr0.05FeO3 is inferred from modulus spectra and ac conductivity analysis.

Bi 1-x La x FeO 3 single-phase solid solution with 0 x 0.3 was obtained by mechanochemical synthesis and characterized by X-ray diffraction, FT NIR Raman spectroscopy and magnetic studies. The nanocrystalline powders of rhombohedrally distorted perovskite structure R3c were studied 'as synthesized' by mechanosynthesis and after annealing at 500 C for 1 h. The annealing, which resulted in recrystallization of the amorphous shell of the nanograins, was found to modify the external lattice modes of Bi 1-x La x FeO 3 and resulted in changes in the temperature variation of the magnetization.

- by Izabela Szafraniak-Wiza and +1
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- Magnetic Materials, Raman Spectroscopy, Multiferroics, X-ray Diffraction

A 0.9BiFeO3–0.1Ba0.8Sr0.2TiO3 ceramic is synthesized by conventional solid-state reaction method and investigated by structural, dielectric, thermal, Raman spectra and magnetization properties. The 0.9BiFeO3–0.1Ba0.8Sr0.2TiO3 is crystallized in rhombohedral distorted perovskite structure with space group R3c. The dielectric loss is investigated over wide range of temperature at 100 kHz. During its evolution, an anomaly is observed at 300 C which corresponds to TN (antiferromagnetic transition temperature). Besides, it is confirmed by DSC measurement. A magnetic property is confirmed by the temperature dependence of magnetization (M–T) under an applied magnetic field of 0.05 T. That revealed an antiferromagnetic transition of 0.9BiFeO3–0.1Ba0.8Sr0.2TiO3 ceramic. The latter confirms which was
previously mentioned. Furthermore, these results reveal considerable spectral changes in the vicinity of the Neel temperature TN. Finally, this shift is discussed through structural, dielectric, thermal, vibrational and magnetic combination near the TN phase.

- by Khelifi Hedi
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- Multiferroics, BiFeO3
- by Pawan Kumar
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- Engineering, Crystallography, Multiferroics, Smart Materials and Structures

The Z ferrite Sr3Co2Fe24O41, produced from a stoichiometric aqueous inorganic sol-gel precursor, is reported and its magnetic hysteresis loop characterized for the first time. The precursor was an iron(III)hydroxide sol stabilised with NO3 - counterions and doped with stoichiometric nitrate salts, which had a particle size similar to halide stabilised Ba3Co2Fe24O41 Z ferrite precursor sols investigated previously. When fired the amorphous gel formed a mixture of α-Fe2O3, BaM and CoFe2O4 from 600°C, but these products then converted directly to the pure Z phase at 1200°C, without first forming the Y ferrite (Ba2Co2Fe12O22) phase always observed prior to Z ferrite crystallization in Ba3Co2Fe24O41 systems. The resulting material was a very soft ferrite, with a very low coercivity of 5.6 kA m-1 and a magnetisation of 48.5 emu g-1 at an applied field of 5 T.

- by Robert C Pullar
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- Magnetic Materials, Multiferroics, Ferrite, Sol Gel Process

BFO (Bismuth ferrite) or BiFeO3 multiferroics Nano-powders were synthesized by a Sol–gel Auto-combustion and Xerogel methods at 400°C to 800°C temperature range. The Sol-gel technique is a wet-chemical method used for synthesis of solid materials like glassy and ceramic from small molecules. Here, the sol or solution evolves gradually towards the formation of a gel, convert from liquid state to solid state. The sol was transparent and homogenous, the pH (potential of hydrogen) ranges 1 to 2 were controlled by the help of Ammonia Solution (NH4OH). Ethylene Glycol was the chelating agent of Fe3+ and Bi3+ cations. We were measured by various characterization techniques like X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and UV Spectrum measurements. BFO Nano-powders with different size in nm are synthesized. In this paper, we exertion to explain, two types of sol–gel techniques and finally shown that one of them is a better Sol–gel process to synthesis a pure BFO.

- by Mohammad Nazmul Hossain
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- Multiferroics

Single-phase BiFeO3, Bi0.825Pb0.175FeO3 and Bi0.725La0.1Pb0.175FeO3 ceramic samples were prepared via solid state reaction route to study the effects of co-doping (La/Pb) on their crystal structure and ferroelectromagnetic behavior. X-ray diffraction data accompanied by Rietveld refinement showed that BiFeO3 crystallize in rhombohedral distorted perovskite structure (space group-R3c) while to that BPFO and BLPFO crystallize in tetragonal (P4/mmm) symmetry. Presence of E (TO9) and E (LO9) modes in Raman scattering spectra for BiFeO3 and Bi0.725La0.1Pb0.175FeO3 infers ferroelectric nature. However, absence of both modes in Bi0.875Pb0.175FeO3 indicates the paraelectric nature. The room temperature dielectric constant (10 Hz–1 MHz) of BiFeO3, Bi0.825Pb0.175FeO3 and Bi0.725La0.1Pb0.175FeO3 is about 100, 60, and 200. Ferroelectromagnetic measurements revealed the existence of ferroelectricity with remnant polarization of 0.24 μC/cm2 in Bi0.725La0.1Pb0.175FeO3, paraelectricity in Bi0.875Pb0.175FeO3, and weak (strong) ferromagnetism with remnant magnetizations of 0.25 (1.57) emu/g in Bi0.725La0.1Pb0.175FeO3 (Bi0.825Pb0.175FeO3).

- by Poorva sharma
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- Multiferroics

Synthesis of the precursors, using research grade materials and locally available facilities, is optimized in order to obtain a suitable sol for BiFeO 3. The optimally synthesized BiFeO 3 sol is then spun onto Cu and glass substrates to obtain films of thickness 100-300nm. Films are studied with the help of XRD, VSM, SEM, and Spectroscopic Ellipsometry. X-ray diffraction results show the formation of BiFeO 3 even in the as-deposited samples. However, some secondary phases were also present with high intensity. After annealing at 300 o C, secondary phases became less intense but could not be completely eliminated. Another BiFeO 3 sol was prepared by changing the solvents and by controlled addition of sodium oleate as ligand. Thin films, prepared using this sol, are single phased even in the as-deposited form. (110) preferred orientation of these BiFeO 3 thin films is achieved after annealing at 300 o C. Ferroelectric switching with a phase angle of 180 o is observed as a function of externally applied electric field. Ferromagnetic properties are also observed in these BiFeO 3 thin films. Dense nanostructure with uniformly distributed grains ~ 100 nm is observed by scanning electron microscope. Optical results show absorption in the blue and green region with a band gap ~ 2.7 eV. Dielectric constants of the films show dispersion in the range of 100Hz-1MHz. These results demonstrate that careful use of solvents and ligands can result in pure BiFeO 3 sol and then thin films; a promising candidate for memory and photovoltaic applications.

- by Shahzad Naseem
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- Multiferroics

Nano-structured Bi1−xBaxFeO3(x = 0, 0.2) were synthesized by solid-state reaction.Ferromagnetic, ferroelectric and dielectric properties enhanced with Ba doping.The best properties obtained in calcined doped sample at 850 °C.20wt.% Ba-dopant change the structure of BFO from rhombohedral to pseudo-cubic.Bi1−xBaxFeO3(x = 0, 0.2) compounds were synthesized by conventional solid-state reaction method. Structural, morphological, magnetic and ferroelectric properties of the products were investigated systematically by employing X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer as well as electrical evaluation techniques, respectively. The XRD results demonstrated distorted rhombohedral BiFeO3 crystal structure with the space group of R3c. However, 20wt% Ba doped sample underwent a structural phase transition from rhombohedral to distorted pseudo-cubic structure. FESEM images of the BiFeO3 sample calcined at 850 °C showed agglomerated nano-particles with a mean particle size of 60 nm, while Bi0.8Ba0.2FeO3 sample showed uniform cubic particles with a mean particle size of 220 nm. For Bi0.8Ba0.2FeO3 sample calcined at 850 °C, an anomaly in permittivity was observed in the vicinity of 370 °C which is around the Neel temperature of bismuth ferrite and is in agreement with the recent reports.

- by Ebrahim Mostafavi and +1
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- Synthesis of nanoparticles, Nanotechnology, Electrical and Magnetic Properties of Composites, Nanostructured materials

Being coexistence of at least two stable, simultaneous different orders (generally ferroelectricity and ferromagnetism and/or antiferromagnetism) in a single material due to the interaction between the two order parameters – namely, magnetization and electric polarization multiferroicity occurs. Those materials which show multiferroicity are known as Multiferroic magnetoelectric materials, which have received a considerable attention to the scientists and research community in recent years owing to their versatility and multi-functionality of these materials in various novel multifunctional devices as well as the understanding of fascinating fundamental physics due to the coupling of the two order parameters (i.e., magnetization and polarization).
Single phase ferroelectric nanomaterials, pure Barium Titanate (BaTiO3) (BTO), Cr-doped BTO (BaTi1−xCrxO3), Nd-doped BTO (Ba1−xNdxTiO3) are synthesized by solid state reaction process. The detailed microstructural analysis has been performed using XRHRD, FESEM, FTIR techniques. The Rietveld Refinement of the XRD data reveals the crystallinity of the samples. This divulges that the well crystallized samples are formed with tetragonal structure having ‘P4mm’ symmetry and the lattice parameter ‘a’ tended to decrease, while the lattice parameter ‘c’ tended to increase. A large value of the dielectric constant (~8000) and tan (δ) loss (0.124) are observed for pure BaTiO3 at room temperature at 100 Hz. We have found the transition temperature for pure BTO 403 K (130℃) which is 404 K (131℃) for BTCrO.

- by Arindam Samanta and +1
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- Synthesis of nanoparticles, FTIR spectroscopy, Nanoparticles, Multiferroics
- by Tahir Murtaza
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- Multiferroics

Multiferroic bulk YMnO3 sample was prepared
through the solid state reaction method. After characterizing
the sample structurally, a systematic investigation of
magnetization and specific heat has been undertaken over a
temperature range 2–300 K under different magnetic fields.
Based on these studies, it has been found that the sample
exhibited a paramagnetic to ferrimagnetic phase transition
of spin glass type at *42 K that could be attributed to spin
cantering. The magnetic transition peak seen in the magnetic
entropy change versus temperature curves became
broader with increasing magnetic field. A large magnetic
entropy change of *1 J mol-1 K-1 was obtained under a
magnetic field change of 0–10 T.

- by Manish Gupta
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- Multiferroics
- by Kota Venkata Siva Kumar
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- Multiferroics

In the present study, the electrical properties of BiFeO 3 ceramic specimens prepared by solid-state sin-tering method by using two thermal treatment strategies are comparatively investigated. The room temperature XRD pattern shows perovskite single-phase, in the limit of XRD accuracy, for BiFeO 3 ceramic prepared by single-step method. For two-step sintering method sample small amounts of secondary Bi 2 Fe 4 O 9 phases were identified. The ceramics show a non-homogeneous microstructure, consisting of ceramic grains with irregular morphology and interconnected porosity mainly in the grain boundary regions in the case of two-step sintering sample. The most interesting feature is the conduction anomaly observed on the conductivity in the low-frequency range close to dc-conductivity. The Arrhenius plot of the dc-conductivity determined at the lowest frequency vs. 1/T shows two distinct linear regions separated by the mentioned temperature range of (189e244) K, for which the dc conductivity could not be determined from the present impedance spectroscopy data only. It is clear that in the mentioned temperature range (for both samples), a conduction anomaly takes place.

- by Felicia Gheorghiu and +1
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- Multiferroics, BiFeO3 ceramics, Conductivity anomaly

Single phase Bi0.80La0.15A0.05FeO3-δ (A = Ca, Sr,Ba) dense ceramics were synthesized via solid
state reaction method. Structural studies through X-ray diffraction shows that all prepared ceramics
crystallized in a rhombohedrally (R3C) distorted BiFeO3 structure with compressive lattice distortion
induced by the rare earth (La3+) ion and divalent co-doping at the Bi-site for the Raman study. Scanning
electron micrograph of the compounds showed the uniform distribution of grains on the sample surface
with high density. A large ferromagnetic hysteresis loop is observed for La/Ba co-doped BiFeO3 as
compared with BiFeO3 prepared under similar conditions, with saturation magnetization of 6.85 emu/g
and remnant magnetization of 2.72 emu/g at 300K. Clear ferromagnetic ground state was observed in
Bi0.80La0.15Ba0.05FeO3 and weak ferromagnetism in BLCFO and BLSFO samples. Dielectric constant and
dielectric loss were found to decrease with increase in frequency for all the compounds. These improved
properties of La/Ba co-doped BFO demonstrate the possibility of enhancing the magnetic applicability
and makes very promising for industrial applications such as new devices in information storage.

- by abdul gaffoor
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- Spintronics, Nanoparticles, Multiferroics, Pulsed Laser Deposition

As the limit of Moore’s law is reached, an alternative to conventional CMOS
technology must be soon realized. The field of Spintronics presents a possibility
of logic computation by switching of magnetic spins. However, the realization of
spintronic devices faces a major challenge with the lack of a scalable and energyefficient
transducer. A promising path for low-power and controlled magnetization
switching is by using the Magnetoelectric effect, which couples the electric field to
the intrinsic magnetization. The magnetoelectric transducer consists of a bi-layer of
piezoelectric-magnetostrictive thin-film materials, in which the coupling between the
electric and the spin domain occurs via strain. The strain induced in the piezoelectric
layer by the applied electric field is transferred to the magnetostrictive film that in
turn switches the intrinsic magnetization. For the application of these magnetoelectric
transducers in spintronic devices, a detailed understanding of the coupling mechanism
between the bi-layer as well as voltage-controlled strain generation must be developed
in order to improve the efficiency of these devices. This thesis aims to study
this magnetoelectric coupling in CoFeB/PZT composite multiferroic system using
Anisotropic Magnetoresistance. A change in magnetization is caused via strain by
applying a voltage to the gate electrode of the device. The switching of magnetization
affects the resistance of the waveguide along the direction of magnetization, which is
used to quantify the change in the magnetoelastic field per unit applied voltage. The
materials used in this work are feasible for fabricating in integrated devices and are
compatible for generating spin waves in coplanar waveguides. To this end, various
devices are developed at the nanometre scale that have different gating configurations
and device parameters. The objective is to identify the effect of non-uniform strain
on the coupling coefficient and study the gatability for different device configurations.
Magnetoelectric switching was observed in many devices and a strong coupling
coefficient was found in case of non-uniform strain configuration. This gives a proof
of concept for resistance based magnetoelectric characterization and motivates the use
of these materials in magnetoelectric transducer for spin wave generation. Although
the values of coupling coefficients were lower than those reported previously, at the
nanometre scale, less voltage is needed for switching of magnetization. This paves
way for low-power spintronic devices for scalable circuits. Finally, the detection of
magnetization switching is attempted by reversing the magnetoelectric transduction
and measuring the generated voltage. The thesis is concluded by addressing various
fabrication related challenges and delineates the goals for future work.

- by Achintya Paradkar
- •
- Spintronics, Multiferroics, Magnetoelectrics, Nanomagnetism and spintronics

In the present work, low pressure synthesis of BiMnO 3 (BMO) nanoparticles (NPs) by hydrothermal method is reported. Temperature-driven structural transitions of BMO are studied by X-ray diffraction (XRD) and exhibited that as-synthesized BMO is stabilized in monoclinic phase with C2 symmetry. However at 473 K, XRD pattern reveals abrupt changes in the intensity of peaks and lattice parameters. The origin of temperature-dependent symmetry transition is understood by sphenoid to prismatic transition by curtail of crystalline growth along (110) direction. The monoclinic structure with C2/c symmetry is found till 723 K. However, at 773 K and above XRD patterns are matched with Bi 2 Mn 4 O 10 and Bi 2 O 3 phases. The temperature profile of magnetic study exhibits antifer-romagnetic behaviour. M–H curve provides evidence of weak ferromagnetism. The present results suggest that NPs of BMO exhibit coexistence of antiferro-magnetism–ferromagnetism, however bulk BMO is ferromagnetic. X-ray pho-toelectron spectroscopy study reveals the presence of Mn in both ?3 and ?4 states in BMO NPs. Superexchange interaction between Mn 4? –O–Mn 3? induces AFM along with weak FM in BMO. This study signifies the low pressure synthesis of BMO and its anomalous structural and magnetic behaviour.

- by VISHWAJIT M GAIKWAD
- •
- Magnetic Materials, Nanoparticles, Multiferroics, Hydrothermal Synthesis
- by Emo Chiellini and +1
- •
- ZnO, Multiferroics, Polyethylene, Ion Beam Modifications
- by Ismat Bibi
- •
- Mechanical Engineering, Condensed Matter Physics, Nanoparticle, Multiferroics

Multiferroic BaTiO3–CoFe2O4–BaTiO3thin films were synthesized by spin coating of Co(NO3)2–Fe(NO3)3and Ba(OAc)2–Ti(i-OPr)4dissolved in a mixture of acetic acid and dimethylformamide. Stepwise thermaltreatment at 200, 400 and 800◦C led to the desired phases. The phase formation process was monitoredby thermoanalytic, XRD, IR and Raman measurements. SEM was used to characterize the structure andthickness of each layer. Two samples with different thicknesses of perovskite and spinel layers are dis-cussed. Sample 1 consists of 120 nm CoFe2O4between two 70 nm BaTiO3layers. For sample 2, the 90 nmBaTiO3top and bottom layers are enclosing 220 nm CoFe2O4. The surface qualities were determined byAFM indicating rms roughness values of about 4 nm. Magnetic investigations reveal slightly anisotropicbehavior. Polarization measurements show hysteresis loops (PS(max)= 29 µC cm−2; PR(max)= 17 µC cm−2)with switching peaks at the corresponding coercive fields

- by Roberto Köferstein
- •
- Decomposition, Raman Spectroscopy, Nanomaterials, Nanoparticles

Multiferroic materials like Bismuth Iron Oxide (BiFeO3), YMnO3, BiMnO3, TbMnO3 has attracted worldwide attraction due its wide range of applications in data storage devices, spintronic devices, sensors and multiple stage memories. Among these materials BiFeO3 is a promising candidate as it exhibit room temperature antiferromagnetic and ferroelectric properties. However, BiFeO3 suffers from some drawbacks including large leakage current, inhomogeneity in spin structure and volatile nature of Bi2O3. In order to overcome these problems we here report Lanthanum (La)
doped Bi1-xLaxFeO3 (where, x=0.0-0.5) thin films prepared by sol-gel method. The effect of La substitution on structural, optical, magnetic and dielectric properties has been studied. Undoped BiFeO3 thin films show the presence of impurity phase of Bi2Fe4O9 however it is seen that La doping hinders the formation of secondary phases and gives pure rhombohedrally distorted perovskite structure. Moreover, with increasing La content transition from rhombohedral to orthorhombic symmetry is also observed. XRD peaks shift to low angles arises due to slight difference in ionic radii of La+3 (1.06Å ) and Bi+3 (1.03Å ). Band gap of undoped BiFeO3 is low as compared to La doped for x=0.1
due to the presence of impurity phase and with increase in La content the band gap decreases from 2.7-2.6eV. La+3 doping also affect the dielectric properties as dielectric constant increases with x. Ferromagnetic behavior, as opposed to antiferromagnetic, in
undoped and doped BiFeO3 is due to suppression of spiral spin structure. An enhancement in magnetization is observed with increasing La content.

- by Shahzad Naseem
- •
- Thin Films and Coatings, Multiferroics