Search Results (168)

One-dimensional (1D) multiferroic composite nanofibers are known to exhibit enhanced magnetoelectric (ME) coupling compared to their thin-film and bulk counterparts with similar compositions. While measuring their local ME coupling at the nanoscale is essential for understanding multiferroic interactions, it remains challenging due to their complex structure. In this work, multiferroic Pb(Zr_0.52Ti_0.48)O₃-CoFe₂O₄ (PZT-CFO) Janus-type nanofibers were synthesized by electrospinning. This unique structure is expected to provide a more compact and continuous interface between the ferroelectric and ferromagnetic phases compared to core–shell configurations. X-ray diffraction confirmed the coexistence of the perovskite PZT and spinel CFO phases without detectable impurities. The Janus configuration was directly verified by scanning electron microscopy and Kelvin probe force microscopy, which revealed a distinct surface potential contrast between the two halves of a single nanofiber. Magnetic hysteresis loops demonstrated the macroscopic ferromagnetic behavior of the nanofiber assembly. Local magnetoelectric coupling was probed using piezoresponse force microscopy under an applied magnetic field. An enhancement of the intrinsic piezoresponse from 15 pm to 19 pm. was observed upon applying an 8000 Oe magnetic field, providing direct evidence of strain-mediated ME coupling at the nanoscale. Although no ferroelectric domain switching was observed, likely due to the substrate clamping effect, the observed piezoresponse modulation confirms the functional ME interaction. These findings suggest that the Janus nanofibers hold promise for applications in one-dimensional multiferroic devices. Full article

A-site-ordered quadruple perovskite manganites, AMn₇O₁₂, show many interesting physical phenomena, including orbital and spin modulations, spin-induced multiferroic properties, and competitions between different magnetic ground states. Doping with Cu²⁺ can result in colossal magnetoresistance properties, ferrimagnetism, and additional structural modulations producing electric–dipole helicoidal textures. Many previous works have focused on large-concentration doping, reaching ACu₃Mn₄O₁₂ compositions. Small-concentration doping has been investigated in a limited number of systems, e.g., in BiCu_xMn_7−xO₁₂. In this work, we investigated solid solutions of NdCu_xMn_7−xO₁₂ with x = 0.1, 0.2, and 0.3, prepared at 6 GPa and 1500 K. Specific heat measurements detected three magnetic transitions at x = 0 (at T_N3 = 9 K, T_N2 = 12 K, and T_N1 = 84 K) and two transitions at x = 0.1 (at T_N2 = 10 K and T_N1 = 78 K), while only one transition was found at x = 0.2 (T_N1 = 72 K) and x = 0.3 (T_N1 = 65 K). Differential scanning calorimetry (DSC) measurements showed sharp and strong peaks near T_OO = 664 K at x = 0, corresponding to an orbital-order (OO) structural transition from I2/m to Im-3 symmetry. DSC anomalies were significantly broadened and their intensities were significantly reduced at x = 0.1–0.3, and structural transitions were observed near T_OO = 630 K at x = 0.1, T_OO = 600 K at x = 0.2, and T_OO = 570 K at x = 0.3. The x = 0.1 sample clearly showed double-peak features on the DSC curves near T_OO because of the presence of two close phases. High-resolution synchrotron powder X-ray diffraction studies gave strong evidence that phase separation phenomena took place in the x = 0.1–0.3 samples, where two I2/m phases with an approximate ratio of 1:1 were present (e.g., a = 7.47143 Å, b = 7.36828 Å, c = 7.46210 Å, and β = 90.9929° for one phase and a = 7.46596 Å, b = 7.37257 Å, c = 7.45756 Å, and β = 90.9328° for the second phase at x = 0.3). The Curie–Weiss temperature changed from negative (for x = 0, 0.1, and 0.2) to positive (for x = 0.3). T_OO, T_N1, the Curie–Weiss temperature, and magnetization (at 5 K and 70 kOe) changed almost linearly with x. Full article

Double perovskites are represented by the formula A₂BB’O₆ and AA’BB’O₆. These materials have been synthesized using the solid-state reaction, sol–gel, Pechini, and hydrothermal methods. X-ray fluorescence, X-ray diffraction, magnetic measurements, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction, synchrotron X-ray diffraction, neutron powder diffraction, extended X-ray absorption fine structure, and Raman spectroscopy have been used for the characterization of double perovskites. X-ray diffraction, synchrotron X-ray diffraction, and neutron powder diffraction coupled with the Rietveld method determine the crystal structure of a sample. These materials present various properties and applications. The present review aims (i) to report a process to determine the symmetry, apparent size, and apparent strain using the Rietveld method; (ii) show how experimental characterization techniques complement each other in the investigation of double perovskites; (iii) describe how the synthesis method can help in the uncovering of double perovskites with improved properties; and (iv) exemplify some of the main applications of double perovskites. Full article

We experimentally investigate the structural, magnetic, transport, and electronic properties of two d⁵ iridate double perovskite materials La₂BIrO₆ (B = Mg, Zn). Notably, despite similar crystallographic structure, the two compounds show distinctly different magnetic behaviors. The M = Mg compound shows an antiferromagnetic-like linear field-dependent isothermal magnetization below its transition temperature, whereas the M = Zn counterpart displays a clear hysteresis loop followed by a noticeable coercive field, indicative of ferromagnetic components arising from a non-collinear Ir spin arrangement. The local structure studies authenticate perceptible M/Ir antisite disorder in both systems, which complicates the magnetic exchange interaction scenario by introducing Ir-O-Ir superexchange pathways in addition to the nominal Ir-O-B-O-Ir super-superexchange interactions expected for an ideally ordered structure. While spin–orbit coupling (SOC) plays a crucial role in establishing insulating behavior for both these compounds, the rotational and tilting distortions of the IrO₆ (and MO₆) octahedral units further lift the ideal cubic symmetry. Finally, by measuring the Ir-L₃ edge resonant inelastic X-ray scattering (RIXS) spectra for both the compounds, giving evidence of spin–orbit-derived low-energy inter-J-state (intra t_2g) transitions (below ~1 eV), the charge transfer (O 2p → Ir 5d), and the crystal field (Ir t_2g → e_g) excitations, we put forward a qualitative argument for the interplay among effective SOC, non-cubic crystal field, and intersite hopping in these two compounds. Full article

Rare-earth transition metal-based double perovskite ceramics E₂TMO₆ (where E = rare-earth metals, T = transition metals, and M = metal) have received impressive attention lately for cryogenic applications as a result of their intrinsic physical features such as multiferroicity, dielectric features, and adjustable magnetic transition temperature. However, determination and enhancement of magnetic transition temperature of E₂TMO₆ ceramic are subject to experimental procedures and processes with a significant degree of difficulties and cumbersomeness. This work proposes an extreme learning machine (ELM)-based intelligent method of determining magnetic transition temperature of E₂TMO₆ ceramics with activation function sigmoid (SM) and sine (SE) at varying magnetic field. The outcomes of the SE-ELM and SM-ELM models were compared with genetically optimized support vector regression (GEN-SVR) predictive models using RMSE, CC, and MAE metrics. Using the testing samples of E₂TMO₆ ceramics, SE-ELM predictive model outperforms GEN-SVR with a superiority of 6.3% (using RMSE metric) and 15.7% (using MAE metric). The SE-ELM predictive model further outperforms the SM-ELM model, with an improvement of 5.3%, using CC computed with training ceramic samples. The simplicity of the employed descriptors, coupled with the outstanding performance of the developed predictive models, would potentially strengthen E₂TMO₆ ceramics exploration for low-temperature cryogenic applications and circumvent energy challenges in different sectors. Full article

The appearance of spin-induced ferroelectric polarization in the so-called type-II multiferroic materials has received a lot of attention. The nature and mechanisms of such polarization were intensively studied using perovskite rare-earth manganites, RMnO₃, as model systems. Later, multiferroic properties were discovered in some RFeO₃ perovskites and possibly in some RCrO₃ perovskites. However, R₂NiMnO₆ double perovskites have ferromagnetic structures that do not break the inversion symmetry. It was found recently that more complex magnetic structures are realized in A-site-ordered quadruple perovskites, RMn₃Ni₂Mn₂O₁₂. Therefore, they have the potential to be multiferroics. In this work, dielectric properties in magnetic fields up to 9 T were investigated for such perovskites as RMn₃Ni₂Mn₂O₁₂ with R = Ce to Ho and for BiMn₃Ni₂Mn₂O₁₂. The samples with R = Bi, Ce, and Nd showed no dielectric anomalies at all magnetic fields, and the dielectric constant decreases with decreasing temperature. The samples with R = Sm to Ho showed qualitatively different behavior when the dielectric constant started increasing with decreasing temperature below certain temperatures close to the magnetic ordering temperatures, T_N. This difference could suggest different magnetic ground states. The samples with R = Eu, Dy, and Ho still showed no anomalies on the dielectric constant. On the other hand, peaks emerged at T_N on the dielectric constant in the R = Sm sample from about 2 T up to the maximum available field of 9 T. The Gd sample showed peaks on dielectric constant at T_N between about 1 T and 7 T. Transition temperatures increase with increasing magnetic fields for R = Sm and decrease for R = Gd. These findings suggest the presence of magnetic-field-induced multiferroic states in the R = Sm and Gd samples with intermediate ionic radii. Dielectric properties at different magnetic fields are also reported for Lu₂NiMnO₆ for comparison. Full article

A novel, eco-friendly perovskite solar cell design is investigated using numerical simulations based on the finite-difference time-domain (FDTD) method. The proposed structure incorporates a two-dimensional (2D) photonic crystal (PhC) architecture featuring a titanium dioxide (TiO₂) cylindrical electron extraction layer. To reduce fabrication complexity and overall production costs, a hole-transport-layer-free (HTL-free) configuration is employed. Simulation results reveal a significant enhancement in photovoltaic performance compared to conventional planar structures, achieving an ultimate efficiency of 42.3%, compared to 36.6% for the traditional design—an improvement of over 16%. Electromagnetic field distributions are analyzed to elucidate the physical mechanisms behind the enhanced absorption. The improved optical performance is attributed to strong coupling between photonic modes and surface plasmon polaritons (SPPs), which enhances light–matter interaction. Furthermore, the device exhibits polarization-insensitive and angle-independent absorption characteristics, maintaining high performance for both transverse magnetic (TM) and transverse electric (TE) polarizations at incidence angles up to 60°. These findings highlight a promising pathway toward the development of cost-effective, lead-free perovskite solar cells with high efficiency and simplified fabrication processes. Full article

We have conducted a first-time investigation into the multiferroic properties and band gap behavior of ${\mathrm{CuFeO}}_2$ doped with Al, Ga, and In ions at the Fe site, employing a microscopic model and Green’s function formalism. The tunability of the band gap across a broad energy spectrum highlights the potential of perovskite materials for advanced applications, including photovoltaics, photodetectors, lasers, light-emitting diodes, and high-energy particle sensors. The disparity in ionic radii between the dopant and host ions introduces local lattice distortions, leading to modifications in the exchange interaction parameters. As a result, the influence of ion doping on various properties of ${\mathrm{CuFeO}}_2$ has been elucidated at microscopic level. Our findings indicate that Al doping enhances magnetization and reduces the band gap energy. In contrast, doping with Ga or In results in a decrease in magnetization and an increase in band gap energy. Additionally, it is demonstrated that ferroelectric polarization can be induced either via external magnetic fields or by Al substitution at the Fe site. The theoretical results show good qualitative agreement with experimental data, confirming the validity of the proposed model and method. Full article

Using the s-d model and Green’s function theory, we investigated for the first time the electron and hole doping effects on the magnetic and optical properties of the double perovskites ${\mathrm{Ba}}_2{\mathrm{FeMoO}}_6$ (BFMO) and ${\mathrm{Sr}}_2{\mathrm{FeMoO}}_6$ (SFMO). Our aim was to find the doping ions that lead to an increase in Curie temperature $T_C$. On the basis of a competition mechanism between spin exchange and s-d interactions, we explain at a microscopic level the decrease in magnetization M and band gap energy $E_g$, as well as the increase in $T_C$ of BFMO and SFMO through substitution with rare earth ions at the Ba(Sr) sites. The influence of doping with K at the Ba(Sr) and Co at the Fe sites on the magnetic properties and the band gap is also discussed. A very good qualitative coincidence with the existing experimental data was observed. Moreover, we found that both M and $T_C$ decrease with decreasing the size of BFMO and SFMO nanoparticles. Full article

The poor magnetic and magneto-optical properties of BiFeO₃, along with its significant lattice mismatch with silicon, have limited its application in silicon-based integrated magneto-optical devices. In this study, co-doping with Sr²⁺ and Ti⁴⁺ ions effectively transformed the trigonal structure of BiFeO₃ into a cubic phase, thereby reducing the lattice mismatch with silicon to 2.8%. High-quality, highly oriented, silicon-based cubic Sr,Ti:BiFeO₃ thin films were successfully fabricated using radio frequency magnetron sputtering. Due to the induced lattice distortion, the characteristic periodic spiral spin antiferromagnetic structure of BiFeO₃ was suppressed, resulting in a significant enhancement of the saturation magnetization of cubic Bi_0.5Sr_0.5Fe_0.5Ti_0.5O₃ (48.0 emu/cm³), compared to that of pristine BiFeO₃ (5.0 emu/cm³). Furthermore, the incorporation of Sr²⁺ and Ti⁴⁺ ions eliminated the birefringence effect inherent in trigonal BiFeO₃, thereby inducing a pronounced magneto-optical effect in the cubic Sr,Ti:BiFeO₃ thin film. The magnetic circular dichroic ellipticity (ψ_F) of Bi_0.5Sr_0.5Fe_0.5Ti_0.5O₃ reached an impressive 2300 degrees/cm. Full article

This study systematically investigates the magnetic ordering and magnetocaloric properties of a series of polycrystalline compounds, Gd_1-xDy_xScO₃ (x = 0, 0.1, 0.2 and 1). X-ray powder diffraction (XRD) analysis confirms that all samples exhibit an orthorhombic perovskite structure with a space group of Pbnm. The zero-field cooling and field cooling magnetization curves demonstrate a transition from antiferromagnetic to paramagnetic phases, with Néel temperatures of about 3 K for GdScO₃ and 4 K for DyScO₃. The doping of Dy³⁺ weakened long-range antiferromagnetic order and enhanced short-range magnetic disorder in GdScO₃, leading to vanished antiferromagnetic transition between 2 and 100 K for the sample of x = 0.2. Using the Arrott–Noakes equation, we constructed Arrott plots to analyze the system’s critical behavior. Both the compounds with x = 0.1 and x = 0.2 conform to the 3D-Heisenberg model. These results indicate the weakened long-range antiferromagnetic order induced by Dy³⁺ doping. Significant maximal magnetic entropy change (−Δ$S_{\mathrm{M}}^{\mathrm{M}\mathrm{a}\mathrm{x}}$) of 36.03 J/kg K at 3 K for the sample Gd_0.9Dy_0.1ScO₃ is achieved as the magnetic field changes from 0 to 50 kOe, which is higher than that of GdScO₃ (−Δ$S_{\mathrm{M}}^{\mathrm{M}\mathrm{a}\mathrm{x}}$ = 34.32 J/kg K) and DyScO₃ (−Δ$S_{\mathrm{M}}^{\mathrm{M}\mathrm{a}\mathrm{x}}$ = 15.63 J/kg K). The considerable magnetocaloric effects (MCEs) suggest that these compounds can be used in the development of low-temperature magnetic refrigeration materials. Full article

In this study, BiBaO₃ perovskite was successfully synthesized via the sol–gel method and thoroughly characterized to evaluate its structural, microstructural, dielectric, electrical, and magnetic properties. X-ray diffraction (XRD) confirmed the formation of a single-phase perovskite structure with high crystallinity. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) revealed a uniform grain morphology and elemental composition consistent with the intended stoichiometry. Dielectric measurements exhibited strong frequency-dependent behavior, suggesting potential for capacitive applications. The electrical conductivity displayed thermally activated behavior, indicative of semiconducting characteristics. Magnetic measurements showed weak ferromagnetic behavior at room temperature, an unusual observation for undoped BaBiO₃-based systems. This magnetism may stem from subtle structural distortions or compositional variations introduced during synthesis. Comparison with previously reported studies underscores the significant influence of the synthesis route and microstructural features on the multifunctional properties of BiBaO₃. Overall, the results highlight the promise of sol–gel-derived BiBaO₃ as a candidate for multifunctional electronic and magnetic applications. Full article

Intense circularly polarized luminescence is crucial for high-performance electroluminescent, optoelectronic, and photonic devices. This study investigates the magneto-chiral characteristics of two achiral soluble diamagnetic perovskite-type PbQDs. Magnetic fields of 158 and 198 mT are applied using an electromagnet in a toluene solution at 25 °C. Both PbQDs show a magnetic circularly polarized luminescence magnitude of approximately 10⁻³ within the (480 to 580) nm wavelength range. The strength of the magnetic circularly polarized luminescence increases with the intensity of the applied magnetic field. Furthermore, the study demonstrates rapid and reversible switching of the rotation direction of the magnetic circularly polarized luminescence when the magnetic poles are rapidly changed. These results suggest that the direction (right- and left-rotating light) and circular polarization of circularly polarized luminescence (CPL) from circularly polarized perovskites can be alternately and freely controlled by applying an external magnetic field with an appropriate direction and strength. Full article

The Curie temperature (Tc) of LaMnO₃-based perovskites is one of the most important properties associated with their magnetic and spintronic applications. The search for new perovskites with even higher Tc is a challenging problem in material design. Through the systematic optimization of support vector regression (SVR) architecture, we establish a predictive framework for determining the Curie temperature (Tc) of doped LaMnO₃ perovskites, leveraging fundamental atomic descriptors. The correlation coefficient (R) between the predicted and experimental Curie temperatures demonstrated high values of 0.9111 when evaluated through the leave-one-out cross-validation (LOOCV) approach, while maintaining a robust correlation of 0.8385 on the independent test set. The subsequent high-throughput screening of perovskite compounds exhibiting higher Curie temperatures was implemented via our online computation platform for materials data mining (OCPMDM), enabling the rapid identification of candidate materials through systematic screening protocols. The findings demonstrate that machine learning exhibits significant efficacy and cost-effectiveness in identifying lanthanum manganite perovskites with elevated Tc, as validated through comparative computational and empirical analyses. Furthermore, a web-based computational infrastructure is implemented for the global dissemination of the predictive framework, enabling the open-access deployment of the validated machine learning model. Full article

The use of perovskite manganite nanoparticles in magnetic hyperthermia has attracted significant attention due to their tunable magnetic properties and high specific absorption rate (SAR). In this work, we present a combined experimental and theoretical investigation of the frequency- and amplitude-dependent magnetic heating behavior of La_0.51Sr_0.49MnO₃ (LSMO) and Dy-doped La_0.51Dy_0.045Sr_0.445MnO₃ (DLSMO) nanoparticles. The nanoparticles were synthesized via the sol–gel method and characterized by XRD and SEM, while SAR values were experimentally evaluated under varying magnetic field strengths (60–120 Oe) and frequencies (150–300 kHz). In parallel, theoretical modeling based on Néel and Brownian relaxation mechanisms was employed to predict SAR behavior as a function of particle size, magnetic anisotropy, and fluid viscosity. The results reveal that Dy doping enhances magnetic anisotropy, which modifies the relaxation dynamics and leads to a reduction in SAR. The model identifies the optimal nanoparticle size (~18–20 nm) and ferrofluid viscosity to maximize heating efficiency. This combined approach provides a comprehensive framework for designing and optimizing perovskite-based nanoparticles for magnetic hyperthermia applications. Full article