Presence Of Magnetoelectric Coupling Research Articles

Orientation dependent magnetocapacitance tuning in epitaxial (La,Sr)MnO3/(K,Na)NbO3-based heterostructures

We fabricated multiferroic heterostructures composed of La0.67Sr0.33MnO3 (LSMO) and (K0.48Na0.48Li0.04) (Nb0.81Ta0.15Sb0.04)O3 (KNN-LTS) on (001)-, (110)-, and (111)-oriented SrTiO3 substrates using pulsed laser deposition technique. X-ray diffraction confirmed the coherent growth of LSMO layers, while KNN-LTS layers exhibited partial relaxation in the heterostructures, with relaxation increasing from (001) to (111) orientations. Notably, the (111)-oriented LSMO, which displayed the highest out-of-plane lattice relaxation, exhibited superior magnetic properties. On the other hand, (001)-oriented sample showcased the maximum ferroelectric and piezoelectric properties due to its high elastic deformation, whereas (111)-oriented sample, characterized by higher intrinsic lattice deformation, demonstrated better dielectric properties. Our elemental analysis confirmed interface charge transfer, indicating the presence of magnetoelectric coupling within the heterostructures. Then, the magnetocapacitance effect was attributed to a combination of interface magnetoelectric coupling and magnetoresistance in LSMO. The (111)-oriented sample displayed a remarkable MC value of approximately 62% near the transition temperature (around 352 K) of LSMO, while the (110)-oriented sample reached the highest MC of approximately 65% at 300 K. These findings suggest that engineered ferroelectric/ferromagnetic heterostructures hold promise for high MC performance at room temperature and offer opportunities for modulation with crystallographic orientation, making them potentially valuable for applications in multiferroic devices.

Neutron Diffraction Magnetic and Mossbauer Spectroscopic Studies of Pb0.8Bi0.2Fe0.728W0.264O3 and Pb0.7Bi0.3Fe0.762W0.231O3 Ceramics

We report on high-temperature crystallographic structure, magnetic and physical properties of chemically B-site disordered lead-bismuth iron tungstate, (PFW)1−x(BFO)x (which can be written as Pb0.8Bi0.2Fe0.728W0.264O3 (0.8PFW–0.2BFO) for x = 0.2 and Pb0.7Bi0.3Fe0.762W0.231O3 (0.7PFW–0.3BFO) for x = 0.3) or PBFW), solid solutions through neutron diffraction (ND), magnetization, electron paramagnetic resonance, and Mössbauer spectroscopic studies. From the high temperature magnetic susceptibility measurement, it is observed that increase antiferromagnetic to paramagnetic phase transition around TN = 435 K (Pb0.8Bi0.2Fe0.728W0.264O3) and 504 K (Pb0.7Bi0.3Fe0.762W0.231O3), compared to pure PFW. Room-temperature crystallographic study confirms the formation of pseudo cubic structure with Pm-3m space group, whereas the magnetic structure is commensurate G-type antiferromagnetic ordering. The obtained temperature dependent structural parameters from the ND, evidenced to existence of strong spin-lattice coupling around TN for both the compounds. The discontinuity in the Pb/Bi–O bond length around ferroelectric transition (TC) indicates the presence of magnetoelectric coupling. Interestingly, microscopic 1:1 B-site ordered nanoclusters of PBFW exhibits the ferrimagnetic clusters along with antiferromagnetic order and it observed through the opening of M vs H hysteresis curves in the lower field regime. The EPR and Mössbauer spectroscopic studies well support the magnetic property and also reveal the Fe+3 state, and the weak signal in EPR and broader linewidth in the Mössbauer spectra exhibit the B-site disorderliness.

Doping induced modification in magnetism and magnetoelectric coupling at room temperature in Fe2Te(1-x)NbxO6

The polycrystalline Fe2TeO6 (FTO) and Fe2Te(1-x)NbxO6 [x = 0.5 (FTON5), x = 0.10 (FTON10)] is prepared via solid state reaction route. Comparative structural study is done by the Rietveld refinement of the powder X-ray diffraction data of all the prepared samples. We observe the presence of ferroelectricity in FTO via remanent polarization versus electric field (PE) hysteresis loop measurement with remanent polarization ∼4.85 nC/cm2. On application of 1.2 T external magnetic field, this observed remanent polarization changes 60% which confirms the presence of magnetoelectric (ME) coupling in the material. The magnetic field dependent PE loops also confirms the presence of ME coupling in both FTON5 and FTON10. In case of FTON10 the remanent polarization changes by 80% on application 1.2 T. The presence ME coupling is also observed through the nonlinear magnetoelectric voltage response on application of modulated DC magnetic field in both FTO and FTON5. This nonlinear voltage response changes to linear behavior for FTON10 due to Nb doping.

Magnetic properties and magnetoelectric coupling enhancement in Bi5Ti3FeO15 ceramics

Abstract In this study, pure and single-phase Bi 5 Ti 3 FeO 15 (BTFO) ceramics were prepared by the standard solid-state sintering method. Magnetic and Mossbauer spectroscopy measurements revealed the paramagnetic behaviour of the material down to 3.7 K. However, the measurements of the magnetoelectric (ME) effect proved the existence of a strong ME coupling in the samples. It was shown that the optimisation of BTFO production process and applying additional electrical poling to the material at elevated temperature allowed a significant increase in the strength of ME coupling. Mossbauer spectroscopy measurements revealed a distribution of the quadruple splitting values because of the location of iron ions in different, symmetrically non-equivalent positions in the crystalline lattice. It is assumed that the presence of ME coupling in the paramagnetic-like BTFO compound is caused by the clustering of Fe 3+ ions in the perovskite-like lattice.

Highly resistive fast-sintered BiFeO3 ceramics

ABSTRACTThis contribution presents an alternative synthesis route to produce highly resistive BiFeO3 multiferroic samples. The use of a fast sintering process followed by quenching to room temperature resulted in ceramic bulks with a resistance higher than 1012 Ohm.m at room temperature. In addition, anomalies found in the dielectric and resistivity characterization indicated the presence of magnetoelectric coupling in the synthesized BiFeO3 sample.

Enhanced magneto-electric property and Raman spectroscopy of nanocrystalline AlxGa(1−x)FeO3 (x=0.05, 0.10 and 0.20)

To enhance the magnetoelectric property of GaFeO3 (GFO), Al3+ doped samples (AlxGa(1−x)FeO3, x=0.05, 0.10 and 0.20) are prepared by the sol-gel technique. Crystallographic phases of the samples are confirmed by X-ray diffractograms. Morphology, average size of nanoparticles including the distribution of sizes are obtained from the results of field emission scanning electron microscopy and high-resolution transmission electron microscopy. Distribution of blocking temperatures and magnetocrystalline anisotropy are determined from the analyses of the observed magnetic hysteresis loops and thermal variation of magnetization curve under zero field cooled and field cooled conditions. Variations of dielectric constant and dielectric loss with frequency show the dispersion in the low frequency region. Ferroelectric orderings have been improved in the doped samples compared to that of GFO. Polarization vs. electric field loops recorded at room temperature indicate that. Magnetic field dependent dielectric constant and negative magneto-capacitance co-efficient of the samples measured at room temperature confirmed that all the samples are multiferroic. Raman spectra and their analyses provide a greater insight into the phase purity and physical properties of the samples. Simultaneous enhancement in magnetic and electric polarizations together with the presence of magneto-electric coupling in the doped samples may enhance the quality of applications in devices.

Enhanced dielectric, ferroelectric and magnetodielectric properties in three phase 0.45Bi0.9La0.1FeO3–0.55Co0.5Ni0.5Fe2O4–BaTiO3 composite

The piezomagnetic–piezoelectric composites of (1 − x) (0.45Bi0.9La0.1FeO3–0.55Co0.5Ni0.5Fe2O4)–(x) BaTiO3, with the compositions x = 0, 0.10, 0.15, 0.20 and 1.0, equivalently denoted as (0.45BLFO–0.55CNFO)/BT, were prepared by solid state reaction method. The presence of constituent phases, spinel phase of Co0.5Ni0.5Fe2O4, orthorhombic phase of Bi0.9La0.1FeO3 and perovskite phase of BaTiO3, were confirmed by X-ray diffraction analysis. FESEM micrographs show grain size variations from 530 to 670 nm. The temperature-dependent dielectric constant at various frequencies (50, 100, and 500 kHz, and 1 MHz) has been studied, and the dielectric study reveals the increase of dielectric constant and decrease of dielectric loss of composites with incorporation of BT content. Magnetic hysteresis loop was measured at low temperature (5 K) using superconducting quantum interference device and the variation of magnetization with temperature indicates the presence of spin glass behavior in the composite. The values of remnant polarization (2Pr) and the coercive field (2Ec) increase monotonously with an increase in BT content. The highest values of 2Pr (1.4 µC/cm2) and 2Ec (11.9 kV/cm) were obtained for 20 mol% BT addition. The presence of magnetocapacitance depicts the magnetoelectric coupling at room temperature. The highest value of the magnetocapacitance (3.4 %) has been observed for 20 mol% addition of BT. The value of magnetoelectric (ME) voltage coefficient (α) for composition x = 0.10 was found to be 2.3 mV/cm-Oe at 4000 Gauss, indicating the presence of ME coupling in the composites.

Mössbauer Spectroscopy and Magnetoelectric Effect Studies of Multiferroic Ceramics Based on BiFeO<sub>3</sub>

In this work the results of investigations for (BiFeO3)x(BaTiO3)1-xand Bi1-xNdxFeO3solid solutions are described. Samples were prepared by the conventional solid-state sintering method. X-ray diffraction,57Fe Mössbauer spectroscopy, and magnetoelectric effect measurements were applied as complementary methods to determine the structure and magnetic properties of materials. For (BiFeO3)x(BaTiO3)1-xsolid solutions Mössbauer spectroscopy revealed the relationship between the content of BiFeO3and the magnetic properties of the samples. Moreover, the presence of magnetoelectric coupling in (BiFeO3)x(BaTiO3)1-xsolid solutions was registered at room temperature for the materials sintered at various temperatures. The maximum value of magnetoelectric voltage coefficient was achieved for 0.7(BiFeO3)0.3(BaTiO3) sintered at 1153K. Structure of Bi1-xNdxFeO3solid solutions was investigated in the whole range of concentration. Hyperfine interactions parameters were determined for the first time for these solid solutions.

Study of (1−x) BaTiO3–x Ni0.5Zn0.5Fe2O4 (x = 5, 10 and 15%) magneto-electric ceramic composites

Structural, magnetic, ferroelectric and magneto-electric studies of BaTiO3 (BTO)–x Ni0.5Zn0.5Fe2O4 (NZFO) ceramic composites are reported. The fraction of NZFO, i.e., ferrite phase is varied from 0% to 15%. The prepared ceramics are studied using X-ray diffraction, Raman spectroscopy, magnetization and ferroelectric measurements. Using X-ray diffraction and Raman spectroscopy measurements, the bi-phase formation of the composites is confirmed. From the high temperature magnetization measurements, anomaly in the magnetization is observed at ferroelectric transition temperature of BTO phase indicating the presence of magneto-electric coupling. Positive Up Negative Down (PUND) measurements are employed to capture the true ferroelectric polarization, i.e., true switched charge density (QS). The strength of ME coupling is studied by measuring the QS before and after magnetic poling and it is observed that for x = 10% composition the ME coupling is maximum for the studied compositions.

Magnetoelectric coupling-induced anisotropy in multiferroic nanocomposite (1 − x)BiFeO3–xBaTiO3

Nanocomposite (1 − x)BiFeO3–xBaTiO3 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 × 103 erg/cm3 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 (α) 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.

Enhanced dielectric and ferroelectric properties of Ba and Ti co-doped BiFeO3 multiferroic ceramics

Multiferroic ceramics Bi0.8Ba0.2Fe1−xTixO3 with x = 0, 0.1 and 0.2 were prepared by using the conventional solid state reaction method. The structural, dielectric, ferroelectric and magnetic properties were investigated. The structure phase transition from rhombohedral to tetragonal with increasing the Ti substitution concentration was confirmed using X-ray diffraction. The reduction of low frequency dispersion in the dielectric constant and loss with an increase in the Ti content was observed. The ferroelectric measurements revealed that the leakage current is significantly suppressed with Ti substitution. Magnetic hysteresis loops showed a continuous decrease in magnetization with Ti substitution, which can be attributed to the collinear antiferromagnetic spin structure in tetragonal structure. In addition, a remarkable change in the polarization and ferroelectric loop area after poling the samples in the dc magnetic field indicates the presence of magnetoelectric coupling at room temperature.

Stabilization of dielectric anomaly near the magnetic phase transition in Ca2+ doped BiFeO3 multifunctional ceramics

Stabilization of a prominent peak in the variation of dielectric constant in Ca2+ doped BiFeO3 ceramics near the antiferromagnetic to paramagnetic phase transition is reported. Temperature dependent dielectric data also shows perceptible frequency dispersion starting from temperatures well below the Neel temperature. This observation has been explained in terms of “skin effect”. Clear signature of magneto-electric coupling is shown using the P–E loops measurement of magnetically poled samples. The presence of magneto-electric coupling is explained in terms of the modulation of canted spin structure. Using Rietveld refinement of X-ray and neutron data, it is shown that the rhombohedral distortion decreases with increasing Ca2+ content. Analysis of SQUID–VSM magnetic hysteresis data proves the occurrence of structure induced anti-ferromagnetic to weak ferromagnetic transition. Significance of these observations for future applications of divalent doped BiFeO3 ceramics is also discussed.