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Tuning Ferroelectric, Dielectric, and Magnetic Properties of BiFeO <sub/>3</sub> Ceramics by Ca and Pb Co-Doping
摘要： Effects of Ca/Pb co-doping on structure, ferroelectric, dielectric, and magnetic properties of BiFeO3 ceramics are investigated. A structure transition from a rhombohedral phase (space group R3c) to a cubic phase (space group Pm3m) with the increment of Ca/Pb concentration is revealed by X-ray diffraction and Raman spectra. In order to compensate the valence change caused by Ca2+ dopant, Pb ions present tetravalent state under the existence of Ca ions. The room-temperature ferroelectric behavior depends upon Ca/Pb co-doping and the structural transition in BiFeO3 ceramics. Meanwhile, the variation of the dielectric loss tangent in the frequency range of 102–107 Hz and the leakage current at room temperature illustrate that Ca/Pb co-doping increases resistivity and reduces leakage current. Compared with that of Sr/Pb co-doping, the co-doping of Ca/Pb has improved the leakage current by two orders of magnitude, besides further increasing the ferroelectric polarization and dielectric properties under the same co-doping concentration. In addition, enhanced ferromagnetism is observed with the increase of Ca/Pb content, which can be attributed to the effective suppression of spiral cycloidal spin structure and spin canting resulting from the structural transition.
关键词： BiFeO3,ferroelectricity,co-doping,dielectricity,ceramics,magnetism
更新于2025-09-23 15:23:52
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Fundamental and Practical Limits of Achieving Artificial Magnetism and Effective Optical Medium by Using Self-Assembly of Metallic Colloidal Clusters
摘要： The self-assembly of metallic colloidal clusters (so called plasmonic metamolecules) has been viewed as a versatile, but highly effective approach for the materialization of the metamaterials exhibiting artificial magnetism at optical frequencies (including visible and near infrared (NIR) regimes). Indeed, several proofs of concepts of plasmonic metamolecules have been successfully demonstrated in both theoretical and experimental ways. Nevertheless, this self-assembly strategy has barely been used and still remains an underutilized method. For example, the self-assembly and optical utilization of the plasmonic metamolecules have been limited to the discrete unit of the structure; the materialization of effective optical medium made of plasmonic metamolecules is highly challenging. In this work, we theoretically exploited the practical limits of self-assembly technology for the fabrication of optical magnetic metamaterials.
关键词： colloids,magnetism,self-assembly,plasmonic metamolecules
更新于2025-09-23 15:23:52
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Single spin localization and manipulation in graphene open-shell nanostructures
摘要： Turning graphene magnetic is a promising challenge to make it an active material for spintronics. Predictions state that graphene structures with specific shapes can spontaneously develop magnetism driven by Coulomb repulsion of π-electrons, but its experimental verification is demanding. Here, we report on the observation and manipulation of individual magnetic moments in graphene open-shell nanostructures on a gold surface. Using scanning tunneling spectroscopy, we detect the presence of single electron spins localized around certain zigzag sites of the carbon backbone via the Kondo effect. We find near-by spins coupled into a singlet ground state and quantify their exchange interaction via singlet-triplet inelastic electron excitations. Theoretical simulations picture how electron correlations result in spin-polarized radical states with the experimentally observed spatial distributions. Extra hydrogen atoms bound to radical sites quench their magnetic moment and switch the spin of the nanostructure in half-integer amounts. Our work demonstrates the intrinsic π-paramagnetism of graphene nanostructures.
关键词： scanning tunneling spectroscopy,graphene,Kondo effect,magnetism,spintronics
更新于2025-09-23 15:23:52
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-electron materials: Sn monolayer on a SiC(0001) surface
摘要： Materials with sp magnetism demonstrate strongly nonlocal Coulomb interactions, which opens a way to probe correlations in the regimes not achievable in transition metal compounds. By the example of Sn monolayer on a SiC(0001) surface, we show that such systems exhibit unusual but intriguing magnetic properties at the nanoscale. Physically, this is attributed to the presence of a significant ferromagnetic coupling, the so-called direct exchange, which fully compensates ubiquitous antiferromagnetic interactions of the superexchange origin. Having a nonlocal nature, the direct exchange was previously ignored because it cannot be captured within the conventional density functional methods and significantly challenges ground state models earlier proposed for Sn/SiC(0001). Furthermore, heavy adatoms induce strong spin-orbit coupling, which leads to a highly anisotropic form of the spin Hamiltonian, in which the Dzyaloshinskii-Moriya interaction (DMI) is dominant. The latter is suggested to be responsible for the formation of a nanoskyrmion state at realistic magnetic fields and temperatures.
关键词： Dzyaloshinskii-Moriya interaction,SiC(0001) surface,direct exchange,nonlocal Coulomb interactions,nanoskyrmion state,sp magnetism,Sn monolayer
更新于2025-09-23 15:21:21
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Effects of carbon doping and vacancy defect on the magnetism of anatase TiO2
摘要： The magnetism origin and mechanism of anatase TiO2 with C doping and vacancy remain controversial. In this study, the effects of C doping and vacancy defect on the magnetism of TiO2 were investigated by generalized gradient approximation and Hubbard U method based on density functional theory. Systems with coexisting interstitial C and O vacancies achieved half-metallic ferromagnetism, and the Curie temperature was above the room temperature. The system used as electron injection source reached 100% electron spin polarization. The Ti32CO2O62 system exhibited ferromagnetism, and the Curie temperature was above the room temperature. The magnetism source of Ti16CiO31 and Ti32CO2O62 demonstrated strong hybrid coupling electron exchange effects among Ti-3d, O-2p, and C-2p orbits which is consistent with the RKKY model of d-p orbital electron exchange.
关键词： Carbon doping and vacancy defect,Magnetism,Anatase TiO2,First-principles
更新于2025-09-23 15:21:21
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Green Synthesis Approach for Nano sized CoFe2O4 through Aloe Vera Mediated Sol-gel Auto Combustion Method for High Frequency Devices
摘要： Nanosized CoFe2O4 was synthesized by Aloe vera-mediated sol-gel auto-combustion method. The yielded nanoparticles were characterised by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) to investigate the phase formation and morphology of the obtained powders. FTIR, XRD and Raman spectra revealed the formation of single phase CoFe2O4. FESEM micrographs showed the formation of some bud like structure and the particle size obtained is around 50-65?nm. Investigation of magnetic properties viz. saturation magnetization (Ms), remenant magnetization (Mr) and coercivity (Hc) were studied from the M-H loop and were found to be 72.23 emu/gm, 31.29 emu/gm, 1519 Oe respectively. In addition, the massive dielectric constant, low dielectric loss, and AC conductivity of the CoFe2O4 nanoparticles were dependent on the frequency (100 Hz-1 MHz), method of preparation and grain size. Room temperature ferroelectric measurement reveals a partially unsaturated P-E loop due to the high coercive field and influence of leakage current.
关键词： Aloe vera plant extract,magnetism,nanostructured materials,Dielectric properties,sol-gel auto combustion
更新于2025-09-23 15:21:21
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Effects of Nd, Al Doping on the Structure and Properties of BiFeO3
摘要： The BiFeO3(BFO) and Bi0.95Nd0.05Fe1-xAlxO3 (x = 0, 0.03, 0.05, 0.075, 0.1) powders were prepared at 200 °C for 24 h by hydrothermal method. The effects of Al doping content on the structure, morphology, magnetic, and photocatalytic properties were studied. X-ray diffraction (XRD) and Fourier transform infrared spectrometer (FTIR) demonstrated the compounds are distorted rhombohedral perovskite structure without any other heterogeneity and structural transition. Field emission scanning electron microscope (FESEM) reflected surface of compounds is a dense, agglomerated sphere. As the concentration of Al3+ increases, a small part of the spherical crystallites eventually becomes cauliflower shape. Energy-dispersive X-ray (EDS) showed the Bi0.95Nd0.05Fe0.95Al0.05O3 sample mainly consists of five elements (Bi, Fe, O, Nd, Al) and atom radio matched well with the formula. Vibrating sample magnetometer (VSM) integrated in a physical property measurement system (PPMS-9) illustrated introducing Nd3+ ions into BFO will enhance its magnetism at room temperature. However, with the increase of non-magnetic ion Al3+ concentration in Bi0.95Nd0.05Fe1-xAlxO3 (x = 0, 0.03, 0.05, 0.075, 0.1), the network structure of Fe-O-Fe was destroyed, which led to the decrease of its net magnetization, so that the hysteresis loop shows paramagnetism. The photocatalytic performance of BFO increased initially and decreased afterwards as Al3+ concentration increased, and the best catalytic performance was achieved at x = 0.05.
关键词： Hydrothermal method,Magnetism,Nd, Al doping,BiFeO3
更新于2025-09-23 15:21:21
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Whirling spins with a ferroelectric
摘要： Ferroelectric polarization enables the emergence and control of magnetic skyrmions at an oxide interface. Controlling magnetism with an electric field is a burgeoning scientific challenge with significant technological implications. The reduced power required to electrically manipulate magnetization opens up exciting prospects for functional devices with unprecedented performance. Ferroelectric materials are especially suitable because they possess spontaneous electric polarization, switchable by an applied electric field. A ferroelectric interfaced with a thin-film ferromagnet has already been shown to modify the electronic structure of the ferromagnet near the interface, allowing control of properties such as the interfacial magnetization and magnetic order via ferroelectric polarization. Now, writing in Nature Materials, Lingfei Wang and colleagues put a new spin on ferroelectric-controlled nanoscale magnetism. They demonstrate a strategy for creating and manipulating magnetic nanoscale vortices, so-called skyrmions, using intrinsic ferroelectric polarization at oxide interfaces.
关键词： oxide interface,ferroelectric polarization,skyrmions,nanoscale magnetism,Dzyaloshinskii–Moriya interaction
更新于2025-09-23 15:21:01
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Light-induced magnetism in plasmonic gold nanoparticles
摘要： Strategies for the ultrafast optical control of magnetism have been a topic of intense research for several decades because of the potential impact in technologies such as magnetic memory, spintronics and quantum computation, as well as the opportunities for nonlinear optical control and modulation in applications such as optical isolation and non-reciprocity. Here we report experimental quantification of optically induced magnetization in plasmonic gold nanoparticles due to the inverse Faraday effect. The induced magnetic moment is large under typical ultrafast pulse excitation (<1014?W?m?2 peak intensity), with magnetization and demagnetization kinetics that are instantaneous within the subpicosecond time resolution of our study. Our results support a mechanism of coherent transfer of angular momentum from the optical field to the electron gas, and open the door to all-optical sub-wavelength strategies for optical isolation that do not require externally applied magnetic fields.
关键词： ultrafast optical control,quantum computation,inverse Faraday effect,spintronics,magnetic memory,plasmonic gold nanoparticles,light-induced magnetism
更新于2025-09-23 15:19:57
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Unraveling Origins of EPR Spectrum in Graphene Oxide Quantum Dots
摘要： Carbon nanostructures are utilized in a plethora of applications ranging from biomedicine to electronics. Particularly interesting are carbon nanostructured quantum dots that can be simultaneously used for bimodal therapies with both targeting and imaging capabilities. Here, magnetic and optical properties of graphene oxide quantum dots (GOQDs) prepared by the top-down technique from graphene oxide and obtained using the Hummers’ method were studied. Graphene oxide was ultra-sonicated, boiled in HNO3, ultra-centrifuged, and finally filtrated, reaching a mean flake size of ~30 nm with quantum dot properties. Flake size distributions were obtained from scanning electron microscopy (SEM) images after consecutive preparation steps. Energy-dispersive X-ray (EDX) confirmed that GOQDs were still oxidized after the fabrication procedure. Magnetic and photoluminescence measurements performed on the obtained GOQDs revealed their paramagnetic behavior and broad range optical photoluminescence around 500 nm, with magnetic moments of 2.41 μB. Finally, electron paramagnetic resonance (EPR) was used to separate the unforeseen contributions and typically not taken into account metal contaminations, and radicals from carbon defects. This study contributes to a better understanding of magnetic properties of carbon nanostructures, which could in the future be used for the design of multimodal imaging agents.
关键词： magnetism,graphene oxide,photoluminescence,EPR,quantum dots
更新于2025-09-23 15:19:57