Appearance Of Weak Ferromagnetism Research Articles

Effect of rare earth orthoferrite GdFeO3 on the band gap modulation and magnetic switching in Bi0.5Na0.5TiO3 ceramics

ABSTRACT This manuscript illustrates the structural, dielectric, optical and magnetic behaviour of [((Bi0.5Na0.5)1-xGdx)(Ti1-xFex)O3] O3 [BNTGF], x = 0.0,0.1, 0.2, 0.3, 0.4 and 0.5 prepared by mixed-oxide technique. The structural and phase identification is confirmed by X-ray diffraction, Scanning electron microscopy, Fourier transform infrared Spectroscopy and Raman analysis. The dielectric constants of the GdFeO3 modified ceramics are less than the reported values of the parent materials. Inverse variation of ferroelectric properties such as remnant polarization (Pr ) and coercive field (Ec) with GdFeO3 doping is clear from room temperature hysteresis loops. Appearance of weak ferromagnetism in the samples is established from the room temperature magnetic hysteresis loops due to the carrier-mediated exchange interactions with smaller values of magnetic parameters. The energy gap of the materials obtained from UV-vis spectra shows a drastic decrease compared to that of pure Bi0.5Na0.5TiO3.

Structural and magnetic properties of Ba and Sn co-substituted bismuth ferrite

BiFeO3(BFO) and Bi0.90Ba0.10Fe1-xSnxO3(x = 0, 0.01 and x = 0.03) compounds were synthesized by conventional solid-state route. X-ray diffraction (XRD) patterns demonstrated that the compounds crystalized in rhombohedral structure with R3c (IUCr No. 161) space group. The XRD patterns and Fourier transformation infrared spectra evidenced that the crystal structure was distorted due to the substitutions. The magnetic properties of the compounds were greatly influenced by the substitution of Ba and Sn elements at their respective sites. The appearance of weak ferromagnetism with significant remnant magnetization and improved coercive field compared to that of BFO could be ascribed to suppression of spiral modulated spin structure. Higher breakdown voltages were observed in the substituted compounds from the polarization measurements.

Strain-controlled ferromagnetism in BiFeO3 nanoparticles

Multiferroic materials are at the core of voltage-controlled spintronic devices. Therefore, an understanding of the underlying electronic correlations and their effects associated with their complex energy landscape is an important and ongoing task. One key parameter in oxide-based perovskite multiferroics is their sensitivity to strain effects under confinement. Here, we report on the ferromagnetism induced by strain-engineering at the nanoscale on BiFeO3 (BFO) nanoparticles. By controlling synthesis parameters, we were able to modify the BFO lattice parameters up to 0.15% and as a consequence, induce ferromagnetism in otherwise antiferromagnetic bulk BFO. In order to understand the driving mechanisms behind such an effect, we performed density functional theory calculations (DFT) using the BFO parameters obtained from the experiment. We found that small distortions of the structural lattice parameters of the order of 0.01% are sufficient to induce a significant spin imbalance close to the Fermi energy at the Fe sites. This may explain the appearance of weak ferromagnetism in strained BFO thin films reported earlier and offers a new route to novel voltage-controlled spintronic devices based on multiferroic materials.

Significance of isostructural distortion and strong magnetoelastic coupling in the weak ferromagnet YFe0.9Cr0.1O3

We report the appearance of weak ferromagnetism above the long-range canted antiferromagnetic order TN = 553 K at which the Fe-Cr interactions become dominant in YFe0.9Cr0.1O3. The weak ferromagnetic order above TN appears due to the increasing magnetic interactions in Fe-sublattices resulting in a canted antiferromagnetic transition at TFe-Fe = 620 K. Electrical hysteresis loop studies and Positive-Up Negative-Down protocol measurements reveal spontaneous but weak ferroelectricity in the system. Dielectric measurements as a function of temperature and frequency reveal a relaxorlike dielectric anomaly within a temperature interval of 400–500 K and anomalous signatures at and temperatures above TN. Synchrotron x-ray diffraction studies over a broad temperature range, 298–873 K, illustrate a significant magnetoelastic coupling at TN and around TFe-Fe. Isostructural distortions are further revealed over the temperature range of 400–500 K from the x-ray diffraction studies. Analyses of the diffraction patterns reveal the delicate interplay between the in-plane and out-of-plane exchange interactions over TN and in isostructural distortion regions. We strongly argue that the ferroelectricity in YFe0.9Cr0.1O3 results from the magnetostriction and Dzyaloshinskii-Moriya interaction manifested through a significant magnetoelastic coupling at TN and TFe-Fe.

Annealing control of hydrothermally grown hematite nanorods: Implication of structural changes and Cl concentration on weak ferromagnetism

In-situ X-ray diffraction coupled with thermogravimetry and differential scanning calorimetry were used to elucidate the crystal phase transition from akaganeite to hematite nanorods. The results indicate that though complete phase transformation occurs at ∼663 K, residual chlorines from the hydrothermal synthesis conditions strongly affect spin moment. The high temperature (>1023 K) shock-annealing reduced the chlorine concentration and consequent suppress most of surface defects on the rods. High temperature annealed hematite nanorods were then studied in terms of magnetic properties under different applied hydrostatic pressures and exhibited a shift of TM to higher values, from 261 to 282 K with initial rate (∂TM/∂P coefficient) of 46 K GPa−1. Such positive dependence of TM with hydrostatic applied pressure is consistent with several works reported in the literature investigating different morphologies in bulk and at nanoscale. In fact, gradual reduction of Cl species increases the spin mobility allowing the appearance of weak-ferromagnetism at room temperature. The crossover results strongly support the hypothesis that Cl dominates spin mobility.

Structural and multiferroic properties of Bi 0.885 Sm 0.115 FeO 3

Abstract The structural, vibrational, ferroelectric, and magnetic properties of monophasic and highly crystalline pure BiFeO 3 and Bi 0.885 Sm 0.115 FeO 3 solids as prepared by standard solid-state reaction route were reported. X-ray diffraction (XRD) patterns confirmed the rhombohedral R 3 c structure of both BiFeO 3 and Bi 0.885 Sm 0.115 FeO 3 ceramics. Rietveld refinements of XRD data revealed that the doping ions lead to unit cell contraction in three directions due to lower ionic radii of Sm 3+ ion (0.96 A) substituted at higher ionic radii Bi 3+ ion (1.03 A). The room temperature ferroelectric and magnetic hysteresis loops present the coexistence of magnetism and ferroelectricity in a single phase. The ferroelectric hysteresis loops exhibit an unsaturated behavior and represent a partial reversal of polarization at room temperature. Besides, this the room temperature magnetization measurement leads to an appearance of weak ferromagnetism.

Unusual enhancement of multiferroicity in YMn2−xTixO5 due to ferroelectrically active TiO6 oxygen octahedral units

Polycrystalline YMn2−xTixO5 (x = 0.00–0.05) samples with partial substitution of Mn by Ti are prepared in order to modulate the multiferroicity of YMn2O5. It is revealed that the substituting Ti ions are in the Ti4+ valence state and prefer to occupy the Mn4+ sites. The lattice structure has slight volume expansion upon the Ti substitution, although the symmetry remains unchanged. A proper Ti4+ substitution surprisingly allows significant enhancement of ferroelectric polarization and appearance of weak ferromagnetism. It is suggested that the substitution induced Ti4+O6 octahedra and modulated exchange-striction are possibly responsible for the enhanced ferroelectricity and improved ferromagnetism.

Enhanced magnetization and improved insulating character in Eu substituted BiFeO3

The polycrystalline Bi1−xEuxFeO3 (x = 0, 0.05, and 0.1) ceramics were synthesized by conventional solid-state route. X-ray diffraction studies and Raman measurements revealed that the compounds crystallized in rhombohedral structure with R3c space group. In addition, a nominal percentage of orthorhombic phase was observed in 10 mol. % Eu substituted BiFeO3. Appearance of weak ferromagnetism and significant increase in Néel temperature TN in the substituted compounds were discussed on the basis of structural distortions. Enhanced remnant magnetization of 75 memu/g and large coercive field of 6.4 kÖe were observed in 10 mol. % Eu substituted BiFeO3. Equivalent circuit model was employed to estimate the grain and grain boundary contributions towards the electrical parameters such as resistance and conductivity. Non-Debye type of relaxation was confirmed from impedance and electric modulus studies. The obtained frequency variation of ac conductivity at different temperature obeys Jonscher's power law and is consistent with the correlated barrier hopping model. Temperature variations of ac conductivity explained that electronic hopping, oxygen vacancies movement, and/or creation of defects contribute to conduction in all the compounds.

Multiferroic properties in Zn and Ni co-doped BiFeO3 ceramics by solution combustion method (SCM)

In present paper, we synthesize the multiferroic Bi1−xZnxFe1−yNiyO3 (x=y=0.025, 0.05, 0.075 and 0.1) ceramics by using solution combustion method (SCM). The room temperature ferroelectric and magnetic hysteresis loops present the co-existence of magnetism and ferroelectricity in a single phase. This ferroelectric hysteresis loops exhibit an unsaturated behavior and represents a partial reversal of polarization at room temperature. Beside, this it was found that the room temperature magnetization measurement is giving rise to the appearance of weak ferromagnetism. The Bi0.975Zn0.025Fe0.975Ni0.025O3 and Bi0.9Zn0.1Fe0.9Ni0.1O3 ceramics display the clear evidence of dielectric anomaly around 300 and 325°C which corresponds to antiferromagnetic to paramagnetic phase transition of BiFeO3 ceramics. The structural study shows the Bi1−xZnxFe1−yNiyO3 (x=y=0.025, 0.05, 0.075 and 0.1) ceramics have rhombhohedral perovskite structure. The surface morphology of the samples was examined by SEM.

Composition- and temperature-driven structural transitions in Bi1−xCaxFeO3 multiferroics: a neutron diffraction study

Neutron powder diffraction and magnetization measurements of the Bi1−xCaxFeO3 (0.05 ≤ x ≤ 0.14) compounds were carried out to follow the effect of the heterovalent A-site doping on the long-range structure and magnetic properties of the BiFeO3 multiferroic. Ca substitution induces the appearance of weak ferromagnetism in the initial ferroelectric R3c phase, but modifies the picture of polar displacements, so the average PbZrO3-like antiferroelectric structure is stabilized at x = 0.11. Further increase of the Ca content leads to transformation of the antipolar ionic shifts to give rise to the Pbam → Imma transition near x = 0.14. A structural study performed for the x = 0.05 compound at high temperature revealed the R3c → Pnma phase transition at 950 K. For x = 0.1 samples, an intermediate heating-induced structure separating the R3c and Pnma phases was found.

Weak ferromagnetic polar phase in the BiFe1−xTixO3 multiferroics

Neutron powder diffraction and magnetization measurements of selected samples of the BiFe1−xTixO3 series were performed. Ti4+ substitution was shown to induce the appearance of weak ferromagnetism in the initial polar R3c phase stable at x ≤ 0.1. In the concentration range 0 ≤ x ≤ 0.1, room-temperature residual magnetization increases from 0 to 0.25 emu/g (the latter is characteristic of the field-induced weak ferromagnetic state in pure BiFeO3). The calculated ferroelectric polarization decreases from ~70 μC/cm2 (x = 0) to ~60 μC/cm2 (x = 0.1) at room temperature. Magnetic ordering coexists with the large spontaneous polarization in a broad temperature range to make the BiFe1−xTixO3 (x → 0.1) perovskites promising for multiferroic applications.

Metallicity and Ferromagnetism in Nanosystem of Charge Ordered Nd0.5Sr0.5MnO3

The fascinating phenomenon of destabilization of charge/orbital order in Nd0.5Sr0.5MnO3 with the reduction of grain size is critically investigated. Based on our magnetic and transport experiments followed by a theoretical analysis, we analyze various possible mechanisms and try to delineate a universal scenario behind this phenomenon. We revisit this issue carefully and discuss various evidences from experiments in nano and bulk manganites on the absence of correlation between size reduction and pressure effects on manganites. We propose a phenomenological model based on enhanced surface disorder to explain the appearance of weak ferromagnetism and metallicity in nanosize Nd0.5Sr0.5MnO3 system. All evidence seems to suggest that the transport is mediated through the surface via enhanced density of states in the nanometric grains. We provide theoretical support for this by performing an ab-initio electronic structure calculation as well as from a recent numerical simulation and argue that the mechanism is likely to be general in all nanosize charge ordered manganites.

Electronic structure of RuSr2EuCu2O8studied by x-ray absorption and photoemission spectroscopies

Local electronic structures of ruthenocuprate RuSr${}_{2}$EuCu${}_{2}$O${}_{8}$ (RuEu-1212) were investigated by using x-ray absorption near-edge structure (XANES) and valence-band photoemission (VB-PES) measurements at room temperature, 80 K, and 25 K. The XANES results indicate that when RuEu-1212 is below Curie temperature, ${T}_{\mathrm{M}}$, electrons are transferred not only from Cu 3$d$ states, but also from Ru 4$\phantom{\rule{0.16em}{0ex}}d$ states, to O 2$p$ orbitals. Additionally, the partial spectral weight distributions derived from VB-PES measurements provide evidence of a weak overlapping between Ru 4$\phantom{\rule{0.16em}{0ex}}d$ states and strongly Cu 3$d\ensuremath{-}$O 2$p$ hybridized states below the Fermi level, which results in a weak coupling between the CuO${}_{2}$ and RuO${}_{2}$ layers. The analysis of extended x-ray absorption fine structure shows that the appearance of weak ferromagnetism and superconductivity is accompanied by a significant decrease of dynamic local lattice distortions of high-shell Cu-Sr and Ru-Sr bonding in RuEu-1212.

Structural and magnetic characterization of Bi_{0.9}Ca_{0.1}Fe_{0.98}X_{0.02}O_3 (X = Mg, Al, Ti, V) polycrystalline multiferroic compounds

The multiferroic compounds Bi_{0.9}Ca_{0.1}Fe_{0.98}X_{0.02}O_3, X = Mg, Al, Ti, V, were prepared by the solid state reaction method and were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and differential scanning calorimetry. The compounds were found to have the rhombohedral perovskite-like structure, accompanied by the existence of small amounts of the usual impurity phases Bi_2Fe_4O_{9} and Bi_{25}FeO_{40}. The appearance of weak ferromagnetism is due to partial destruction of the spiral spin structure due to lattice distortion and suppression of oxygen vacancies. The magnetic transition temperatures of the compounds are 342, 346, 349, and 345 °C, respectively.

Multiferroic properties in BiFe1−xZnxO3 (x = 0.1–0.2) ceramics by solution combustion method (SCM)

Multiferroic BiFe1−xZnxO3 (x=0, 0.1, 0.15, and 0.2) ceramics were prepared by solution combustion method (SCM). The room temperature ferroelectric and magnetic hysteresis loops shows coexistence of magnetism and ferroelectricity. It was found that room temperature magnetization measurement gives rise to the appearance of weak ferromagnetism and exhibits a superparamagnetic nature at 5K in BiFe1−xZnxO3 (x=0.1–0.2) ceramics. The ferroelectric hysteresis loops measured at room temperature. It shows the unsaturated behavior which indicates the partial reversal of polarization. A dielectric constant with temperature measurement in BiFe0.9Zn0.1O3 and BiFe0.85Zn0.15O3 samples exhibits an apparent dielectric anomaly around 350 and 300°C and demonstrates an antiferromagnetic to paramagnetic phase transition (TN) of BiFeO3. The structural study was carried out using X-ray diffraction (XRD) pattern and showed that BiFe1−xZnxO3 (x=0.1–0.2) ceramics have rhombhohedral perovskite structure and surface morphology of the samples were examined by scanning electron microscope (SEM).

Surface spin glass and exchange bias effect in Sm0.5Ca0.5MnO3 manganites nano particles

In this letter, we report that the charge/orbital order state of bulk antiferromagnetic Sm0.5Ca0.5MnO3 is suppressed and confirms the appearance of weak ferromagnetism below 65 K followed by a low temperature spin glass like transition at 41 K in its nano metric counterpart. Exchange anisotropy effect has been observed in the nano manganites and can be tuned by the strength of the cooling magnetic field (Hcool). The values of exchange fields (HE), coercivity (HC), remanence asymmetry (ME) and magnetic coercivity (MC) are found to strongly depend on cooling magnetic field and temperature. HE increases with increasing Hcool but for larger Hcool, HE tends to decrease due to the growth of ferromagnetic cluster size. Magnetic training effect has also been observed and it has been analyzed thoroughly using spin relaxation model. A proposed phenomenological core-shell type model is attributed to an exchange coupling between the spin-glass like shell (surrounding) and antiferromagnetic core of Sm0.5Ca0.5MnO3 nano manganites mainly on the basis of uncompensated surface spins. Results suggest that the intrinsic phase inhomogeneity due to the surface effects of the nanostructured manganites may cause exchange anisotropy, which is of special interests for potential application in multifunctional spintronic devices.

Magnetic and magnetotransport behavior of overdoped nanocrystalline Nd 1– xSr xMnO 3 (0.50≤ x≤0.63)

The nanocrystalline samples of Nd 1– x Sr x MnO 3 (NSMO) ( x=0.5, 0.55, 0.60, 0.63) were synthesized by sol-gel based polymeric precursor route. Structural, magnetic and magnetotransport properties were studied systematically. It was found that in the composition range ( x=0.50–0.63), Nd 1– x Sr x MnO 3 showed paramagnetic to ferromagnetic (PM-FM) transition in the vicinity of T C∼270 K but the FM phase was weakened as the Sr concentration increased. The appearance of weak ferromagnetism was explained in terms of the core-shell model. Moreover, for x=0.63 sample, a second transition is observed below T C at T=185 K, which is possibly due to the appearance of A-AFM/C-AFM or a mixture of both the phases. Resistivity vs temperature ( ρ-T) curve showed that the resistivity of all the samples was much larger than the single crystals of corresponding compositions due to large contribution of the grain boundaries in the present nanocrystalline samples. In all samples, extrinsic kind of MR behavior dominated because of nanocrystalline nature of the samples, which was nearly of the same order (∼10%) in all samples. However, the intrinsic kind of MR behavior was also significant in x=0.50 sample, because of the strongest FM feature in this sample.

Preparation and characterization of Bi0.9M0.05N0.05FeO3(M = Sm, Gd; N = Sr, Y) polycrystalline multiferroic compounds

AbstractThe multiferroic compounds Bi0.9Gd0.05Sr0.05FeO3, Bi0.9Sm0.05Sr0.05FeO3, Bi0.9Gd0.05Y0.05FeO3, and Bi0.9Sm0.05Y0.05FeO3 were prepared by the conventional ceramic method and were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and differential scanning calorimetry. The compounds were found to have the rhombohedral perovskite‐like structure, accompanied by the existence of small amounts of Bi2Fe4O9 and Bi25FeO40 impurity phases. The appearance of weak ferromagnetism in Bi0.9Gd0.05Sr0.05FeO3 and Bi0.9Sm0.05Sr0.05FeO3 is due to partial destruction of the spiral spin structure due to lattice distortion and oxygen vacancies. The magnetic transition temperatures of the compounds are 360 °C and 355 °C, respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhanced multiferroic properties in Ti-doped Bi2Fe4O9 ceramics

Structural, magnetic, and ferroelectric properties have been investigated for Bi2Fe4(1−x)Ti4xO9 (0≤x≤0.2) bulk ceramics, which were synthesized by a modified Pechini method. X-ray diffraction reveals that all samples are single phase with no impurities detected. Compared with antiferromagnetic Bi2Fe4O9 compound, doping with Ti ions induces the appearance of weak ferromagnetism at room temperature, which is discussed in terms of the collapse of the frustrated antiferromagnetic spin structure. Moreover, appropriate Ti doping also significantly reduces electric leakage and leads to the enhancement of electrical polarization. Among all samples, the optimal multiferroics with Mr∼0.0188 emu/g and Pr∼0.262 μC/cm2 at room temperature is found for x=0.15 ceramics. It is thus shown that Ti-doped Bi2Fe4O9 is a promising candidate for preparing multiferroic materials.

Temperature dependence of magnetic properties and change of specific heat in perovskite ErCrO3 chromites

In this paper, the temperature dependence of magnetic properties and specific heat are systematically investigated for perovskite ErCrO3 chromites. The results show that there exists a strong temperature dependence of magnetic ordering and phase coexistence in the region of low temperature. Specifically, ErCrO3 possesses the long-range antiferromagnetic ordering and the appearance of weak ferromagnetism, occurring at T N =133 K. In the range of higher temperature, above 133.0 K, the reciprocal of magnetic susceptibility χ −1 behaves linearly, indicating a typical Curie–Weiss behavior fitted. The effective magnetic moment μ eff=10.57μ B and asymptotic paramagnetic Curie temperature T cw=−30 K, which suggests the predominance of antiferromagnetic interactions in ErCrO3 chromites. Around T SR≈22 K, ErCrO3 undergoes a spin reorientation from $\varGamma _{4}(G_{x},A_{y},F_{z};F^{R}_{z})$ to $\varGamma _{1}(A_{x},G_{y},C_{z};C^{R}_{z})$ or Γ 1(0). Also, the stability of the ferromagnetic Γ 4 phase increases with increasing applied field. Furthermore, the ac susceptibilities exhibit frequency-independent anomalies near 133 K and the coexistence of the magnetic configuration $\varGamma _{2}(F_{x},G_{y},C_{z};F^{R}_{x},C^{R}_{y})$ and Γ 4. Combining the magnetic properties and the specific-heat measurements, this current magnetization can be interpreted from the interaction between Cr3+–Cr3+, Cr3+–Er3+ and Er3+–Er3+.