Enhancement Of Ferromagnetic Properties Research Articles

Defect engineered enhancement of ferromagnetic properties in samarium doped Bi4Ti3O12 – BiFeO3 ceramics

The near future will bring lots of changes for computer memories, because mainstream silicon-based technology can no longer increase data throughput. A magnetoelectric memory would boost PC storage performance and at the same time increase energy efficiency as these memory cells do not need external power. In this work, we examined the recently reported possibility of developing a novel class of multiferroic materials on the basis of the rare-earth ions embedded in ferroelectric structures of the Aurivillius-family. For the first time powders of Bi6.3Sm0.7Fe3Ti3O21 were prepared by a sol gel method and then successfully sintered to dense polycrystalline materials.

Effect of molar concentration on structural, magnetic domain and optical properties of BiFeO3 thin films

Pure crystalline bismuth ferrite BiFeO3 (BFO) thin films have been deposited on the cleaned glass substrate by sol–gel spin-coating technique with different molar concentrations (from 0.1 to 0.5 M) of the precursor solution. The influence of molar concentrations on the structural, magnetic and optical properties has been investigated by different advanced techniques. The X-ray diffraction patterns of BFO films revealed that the increase of the molar concentration from 0.1 to 0.5 M induced the structural transformation from distorted orthorhombic to single orthorhombic phase. The average crystallite size of BFO thin films was calculated using Scherrer formula and found to be in the range of 15–28 nm. The elemental composition of Bi, Fe and O was confirmed using energy-dispersive spectroscopy of X-rays. The atomic force microscopic images revealed that shape of particles are changing from ellipsoid to nanorods with increasing the molar concentration from 0.3 to 0.5 M. The root means square roughness of BFO films was also varying from 6.34 to 29.88 nm. The stripe-like structure of domain was explored through magnetic force microscopy. The films prepared from the precursor of molar concentration of 0.5 M revealed the microscopic remnant magnetization of 0.19 emu/cm3 and coercivity of 443.06 Oe from the M–H measurements. This enhancement of ferromagnetic properties may be due to the formation of nanorods resulted by destroying the cycloid spin structure. The optical bandgaps were also tuned from 2.58 to 2.49 eV due to increase of the crystallite size from 15 to 28 nm.

Enhancement of ferromagnetic properties in (Fe, Ni) co-doped ZnO flowers by pulsed magnetic field processing

In this study, Zn0.97Fe0.01Ni0.02O diluted magnetic semiconductor (DMS) flowers were fabricated through hydrothermal method with 4 T (Tesla) pulsed magnetic field (PMF). Rietveld refinement of X-ray diffraction (XRD) patterns and Raman analysis indicated that the synthesized samples have the hexagonal wurtzite structure without any other secondary (impurity) phases. The O1s X-ray photoelectron spectroscopy (XPS) and Raman measurements of the synthesized samples showed the existence of oxygen vacancy (VO). The results indicated that PMF could increase the contents of VO and doped ions. The magnetic measurement showed that the room temperature ferromagnetic (RTFM) property of (Fe, Ni) co-doped ZnO is enhanced by PMF. The enhancement of RTFM is attributed to the intrinsic interaction of magnetic ions (Fe3+, Ni2+) via VO created by pulsed magnetic field processing.

Enhancement of ferromagnetic properties in composites of BaSnO3 and CoFe2O4

In this paper, we report structural and magnetic properties of BaSnO3(BSO)(1−x)–CoFe2O4 (CFO)(x) composite (with x = 0%, 1% (C1), 2% (C2) and 5% (C3) in molar ratio) synthesized using nitrate precursor method. The X-ray diffraction (XRD) pattern of the composite powder confirmed presence of both BaSnO3 with the cubic perovskite structure and CoFe2O4 with the cubic spinel structure. No signature of any other phases in pure BaSnO3, CoFe2O4 and composites have been detected either in XRD or energy dispersive X-ray (EDS) analysis. The temperature dependent zero field cooled (ZFC) & field cooled (FC) magnetization and magnetic field dependence magnetization measurements have been carried at room temperature of the pure BaSnO3. We observe a weak ferromagnetic (FM) behavior at room temperature in pure BaSnO3 even though it is non-magnetic in nature. The room temperature Raman spectroscopy and electron spin resonance measurements of the sample confirm the presence of oxygen vacancy and formation of F-center, which is responsible for the FM behavior. The oxidation state and elemental analysis have been carried out using X-ray photoelectron spectroscopy (XPS). The magnetic field dependence of magnetization of the composite samples reveal increase of saturation magnetization (Ms), remanence magnetization (Mr) and coercivity (Hc) with increase in ferrite content in the composite. Significant enhancement in FM components is observed with lowering of temperature.

Effect of Annealing on Room Temperature Multiferroics of BiFe<sub>1-x</sub>Co<sub>x</sub>O<sub>3</sub>

We studied the effect of annealing and Co ion doping on the structure, leakage current, ferroelectric polarization and magnetism of BiFeO3 samples. X-ray diffraction patterns demonstrate that an appropriate Co doping concentration is favor of suppressing the secondary phase but annealing treatment is apt to the growth of both the main and the secondary phases. The current density as a function of an electric field indicates that Co doping increases the leakage current density as samples before annealing but suppresses it after annealing. Annealing treatment improves the leakage for Co-doped sample and reduces it for the undoped sample. Ferroelectric hysteresis loops reflect that Co ions doping is liable to increase the ferroelectric polarization, while the sample is annealed it will do opposite effect. However the annealing treatment do improve the ferroelectricity for pure BiFeO3 sample. The magnetic hysteresis at room temperature shows the obvious enhancement of ferromagnetic properties with the sample after annealing.

Magnetic and ferroelectric characteristics of Gd 3 + and Ti 4 + co-doped BiFeO 3 ceramics

Polycrystalline BiFeO $_{\mathrm {\mathbf {3}}}$ and Bi $_{\mathrm {\mathbf {0.9}}}$ Gd $_{\mathrm {\mathbf {0.1}}}$ Fe $_{\boldsymbol {1-}\boldsymbol {{x}}}$ Ti x O 3 (x = 0, 0.01, 0.05 and 0.1) samples were synthesized by solid-state reaction route. Structural, magnetic and ferroelectric properties of these samples were investigated. X-ray powder diffraction (XRD) results confirmed the presence of a significant amount of Bi $_{\mathrm {\mathbf {2}}}$ Fe $_{\mathrm {\mathbf {4}}}\textit {O}_{\mathrm {\mathbf {9}}}$ impurity phase in the undoped BiFeO $_{\mathrm {\mathbf {3}}}$ sample. Mössbauer spectroscopy studies corroborated the XRD studies to confirm the presence of impurity phase. We have observed that gadolinium (Gd $^{\boldsymbol {3+}}$ ) and titanium (Ti $^{\boldsymbol {4+}}$ ) doping, respectively, on Bi $^{\boldsymbol {3+}}$ and Fe $^{\boldsymbol {3+}}$ sites facilitated a significant reduction in the impurity phase formation in BiFeO $_{\mathrm {\mathbf {3}}}$ . Interestingly, Gd $^{\boldsymbol {3+}}$ -doping significantly reduced the impurity phase formation as compared to the undoped BiFeO $_{\mathrm {\mathbf {3}}}$ sample. This impurity phase formation was further overcome by doping higher (x $\boldsymbol {\ge } $ 0.05) amounts of Ti in BiFeO $_{\mathrm {\mathbf {3}}}$ . The crystallographic site occupancies of Gd and Ti were confirmed by Rietveld refinement of XRD data, Mössbauer spectroscopy and magnetization measurements. An enhancement in ferromagnetic properties along with moderate ferroelectric properties have been observed after co-doping. There was an increasing trend in remnant polarization (P $_{\mathrm {\mathbf {r}}}$ ) with the increase in Ti concentration besides an improvement in the characteristic saturation magnetization. Our results demonstrate that Gd $^{\boldsymbol {3+}}$ and Ti $^{\boldsymbol {4+}}$ doping could be used to enhance multifunctional properties of BiFeO $_{\mathrm {\mathbf {3}}}$ ceramics to enable them as potential material for various devices.

Structural, Photocatalytic and Enhanced Magnetic Properties of Bi1-xHoxFeO3 Nanoparticles Synthesized Via Sol-Gel Method

Bi1-xHoxFeO3 (BHFO, x = 0, 0.05, 0.10, 0.15, 0.20) nanoparticles were successfully synthesized via a simple double solvents based sol-gel route. X-ray diffraction analysis shows the BHFO samples with x = 0-0.10 are pure-phased perovskite structure. Scanning electron microscopy images reveal that the BHFO particles are in nano scale. UV-Vis measurement was taken to determine the band gap of BHFO samples, suggesting the band gap of BHFO samples can be modulated by Ho doping. The absorption spectra of RhB solution show that the BHFO nanoparticles have photocatalytic effect of degrading RhB organic dye which reaches a maximum of 42% for x = 0.10. Well-shaped M–H hysteresis loops of BHFO nanoparticles were observed at 300 K. The magnetism at room temperature is obviously enhanced by Ho doping. For x = 0.10, the BHFO sample performed the strongest ferromagnetism (Ms = 5.3 emu/g, Mr = 1.5 emu/g). The result confirms the contribution of Ho3+ towards enhancement of ferromagnetic properties of BiFeO3.

Enhancement of ferromagnetic properties in Zn0.98Cu0.02O by additional Co doping

Abstract Zn 0.98 Cu 0.02 O and Zn 0.95 Cu 0.02 Co 0.03 O powders were synthesized by sol–gel method, and the effects of Co codoping on the structure, optical and magnetic properties of the Zn 0.98 Cu 0.02 O powders were studied in detail. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurement shows the Zn 0.98 Cu 0.02 O and Zn 0.95 Cu 0.02 Co 0.03 O powders were single phase with the ZnO wurtzite structure, and there was no ferromagnetic-related secondary phase in these powders. Moreover, these powders exhibited ferromagnetism at the room temperature investigated by the magnetic measurement, and the ferromagnetism of the Zn 0.98 Cu 0.02 O and Zn 0.95 Cu 0.02 Co 0.03 O samples were originated from the fact that the Cu ions and Co, Cu ions doped into the ZnO lattices, respectively. In addition, the saturation magnetization (Ms) was significantly increased with Co codoping due to the increased density of oxygen vacancies.

Giant enhancement in ferromagnetic properties of Pd nanoparticle induced by intentionally created defects

The important central question related to origin of ferromagnetic properties in the non-magnetic materials at nano-dimensions has been investigated by a novel approach of studying the evolution of magnetic properties by intentionally creating defects. The ferromagnetic response of Pd is found to increase by 20 times for nanoparticle (NP) dispersed in carbon matrix and increase by about 3.5 times in case of Pd nanoparticles dispersed in SiO2 matrix on exposure to swift heavy ion irradiation. Ferromagnetic response is found to increase by about 9.3 times on subjecting the Pd nanoparticles to hydrogen loading-deloading cycle. Ferromagnetic properties of Pd nanoparticles dispersed in carbon and SiO2 matrices, despite having same size and concentration, are observed to be vastly different due to matrix effect. These changes in ferromagnetic properties are correlated to the change in the electronic structure due to matrix, nanoparticle size, and creation of defects in the nanoparticle core and at NP-matrix interface during post deposition treatments. Giant enhancement in the magnetic properties and change in electronic properties point toward a core and surface magnetic structure in metal nanoparticle.

Enhancement of ferromagnetic properties in Zn0.95Co0.05O nanoparticles by indium codoping: An experimental and theoretical study

Nanoparticles of Zn0.95−xCo0.05InxO (x=0.0 to 0.07) were synthesized by the pyrolitic reaction of sol-gels obtained from respective metal precursors. X-ray diffraction and high-resolution transmission electron microscopy studies confirm the formation of impurity-free wurtzite type ZnO structure for all the compositions. While pristine ZnO is diamagnetic, Zn0.95Co0.05O nanoparticles show weak paramagnetic behavior at room temperature. When “In.” is codoped with Co with x=0.0 to 0.07 in Zn0.95−xCo0.05InxO, a systematic increase in magnetic moment is observed up to x=0.07. First-principles modeling supports that the ferromagnetic phase become more favorable at higher indium doping concentrations.

Growth of Epitaxial ZnO:Mn/ZnO:V Heterostructures and Ferroelectric-ferromagnetic Characterization

AbstractThe wide band gap semiconductor ZnO is well known for its multifunctionality in the form of ferromagnetism (FM), piezoelectricity, and magneto optics. ZnO has been found to grow with intrinsic oxygen deficiencies which in turn are believed to give ferromagnetism and high conductivity in this material. Doping Zn2+ sites by V5+ ions creates a mixed valency as well as strain in the original ZnO hexagonal structure because of the reduced ionic size of vanadium. The mixed valency creates charge polarity between Zn-O and V-O bonds. This charge polarity and the rotation of the nonlinear V-O bonds with respect to Zn-O bonds under electric field have been shown to produce ferroelectricity. Furthermore, Mn doping of ZnO has also shown enhancement in ferromagnetic properties in ZnO. For this material to be a viable ferromagnetic material the magnetic properties should not be from segregated phases. In the present study we have grown undoped, Mn, and V doped ZnO thin films using pulsed laser deposition (PLD). ZnO target with 2% atomic Mn doping and a target with 0.5% atomic V doping were prepared by solid state reactions and sintering. Films were grown both epitaxially on sapphire substrates and in polycrystalline form on silicon substrates. Magnetization measurements by the PPMS showed M vs. H hysteresis loops with saturation for all ZnO: Mn films. V doped films showed high saturation polarization for film deposited at high pressures. We have also fabricated epitaxial bilayers of ZnO:V/ZnO:Mn on sapphire substrates. Ferroelectric and ferromagnetic properties of these heterostructures are presented.

Enhancement of ferromagnetic properties in In 1.99Co 0.01O 3 by additional Cu doping

This paper reports room-temperature ferromagnetism in Co- and Cu-doped In 2 O 3 samples synthesized by a solid-state reaction method. Structure and composition analyses revealed that Co and Cu were incorporated into the In 2 O 3 lattices. Photoluminescence measurement revealed an additional emission at 520 nm from these doped samples. The magnetic measurement showed that additional Cu doping greatly enhanced the ferromagnetism of In 1.99 Co 0.01 O 3 bulk samples. The implication of the effects of additional Cu doping is also discussed.

Enhancement of ferromagnetic properties in BiFeO3 polycrystalline ceramic by La doping

The authors present the structure transformation and magnetic properties of Bi1−xLaxFeO3 (x=0.0–0.15) ceramics prepared by a conventional solid-state reaction processing. Magnetic measurements reveal that remnant magnetization of 15% La-doped BiFeO3 has enhanced about 20 times as compared to pure BiFeO3. It is the structural phase transition (R3c–C222) near x=0.15 that destructs the spin cycloid, and thus enhances the ferromagnetic properties significantly. In these Bi1−xLaxFeO3 ceramic samples, besides the known antiferromagnetic Néel temperature TN1∼615K, another Néel temperature TN2∼260K can be observed due to the trace impurity phase of Bi2Fe4O9 in these ceramic samples.

Enhancement of magnetic properties in (Ga,Mn)N nanowires due to N2 plasma treatment

The local structure of Mn impurities in ferromagnetic (Ga,Mn)N nanowires was investigated using extended x-ray absorption fine structure (EXAFS). By N2 plasma treatment, the nitrogen concentration increased and the ferromagnetic signal also increased. The EXAFS results showed that the Mn concentration occupying Ga sites increased and interstitially doped Mn atoms significantly decreased due to the plasma treatment. As a result, the N vacancies reduced and crystalline quality improved, resulting in the enhancement of ferromagnetic properties.

Effects of Implanted Nitrogen on the Microstructural, Optical, and Magnetic Properties of Mn-Implanted GaN

The effects of implanted nitrogen on microstructural, magnetic, and optical properties of Mn-implanted GaN were studied. N and Mn ions were coimplanted into -GaN and subsequently annealed at 973-1173 K. Compared with Mn-implanted samples, the Curie temperature and magnetic moment significantly increased. From high-resolution transmission electron microscopy, Mn nitrides such as and drastically decreased, and the concentration of N vacancies was reduced by the N implantation. This led to the increase of Mn concentration occupying Ga lattice sites, evident by the shift of Raman mode at to higher energy by about . The photoluminescence peak at 2.92 eV shifted to 2.86 eV and became strong with N implantation, indicating an increase in effective hole concentration increased due to an enhanced activation of Mn impurities in -GaN. Consequently, the enhancement of ferromagnetic property by coimplantation of Mn and N ions originated from the increase of hole concentration via the increase of Mn concentration in GaN, due to the suppression of production of Mn-N compounds.

Enhancement of ferromagnetic properties in Zn1−xCoxO by additional Cu doping

The high-temperature ferromagnetism in Co-doped ZnO samples fabricated by the standard solid-state reaction method is reported. Additional Cu doping into bulk Zn0.98Co0.02O is essential to achieve room-temperature ferromagnetism. Structure and composition analyses revealed that cobalt is incorporated into the lattice structure, forming a solid solution instead of precipitates. In the case of Zn0.97Cu0.01Co0.02O, the coercive field measured by a vibrating sample magnetometer at room temperature is 60Oe. The implication of the effect of Cu doping in bulk Zn0.98Co0.02O is also discussed.

Enhancement of magnetic properties by nitrogen implantation to Mn-implanted p-type GaN

N and Mn ions were co-implanted into p-type GaN and subsequently annealed at 700–900 °C. Compared with Mn-implanted sample, the (Mn+N)-implanted sample revealed a larger ferromagnetic signal. This was attributed to the increase of Ga–Mn magnetic phases. Mn–N compounds, such as Mn6N2.58 and Mn3N2, decreased and the resistivity significantly increased, meaning a reduction of N vacancies. It is suggested that enhancement in ferromagnetic properties in the (Mn+N)-implanted GaN originated from the reduction of N vacancies and the increase of Ga–Mn magnetic phases.

Evidence of Mn Occupation of Ga Site in Ferromagnetic (Ga, Mn)N Semiconductor Observed by EXAFS

The local structure of Mn impurities in a ferromagnetic (Ga, Mn)N semiconductor was investigated using extended X-ray absorption fine structure (EXAFS). The ferromagnetic signal increased and maintained up to room temperature as N ions were implanted into Mn-implanted GaN. The X-ray results showed that Mn ions occupied Ga sites to form (Ga, Mn)N semiconductor. The Mn concentration occupying Ga sites increased from 2.5 to 3.8% and the formation of Mn-N compounds such as Mn 6 N 2 . 5 8 and Mn 3 N 2 was prohibited by implanting N atoms. As a result, the N-vacancies reduced and net hole concentration increased, resulting in the enhancement of ferromagnetic property.