Defect Induced Room Temperature Ferromagnetism Research Articles

Probing defect induced room temperature ferromagnetism in Chemical Vapor Deposition grown MoO3 flakes: A correlation with electronic structure and first principle-based calculations

The pure α-MoO3 microflakes grown by the Chemical Vapor Deposition (CVD) technique are annealed at various temperatures (150 °C, 250 °C, and 350 °C) in a hydrogen (H2) atmosphere to induce ferromagnetism. All the samples exhibit ferromagnetism at room temperature, and the 250 °C annealed sample shows the highest magnetization of 0.087 emu/g. The presence of oxygen vacancies, verified through the analysis of X-ray photoelectron spectroscopy (XPS) and the Electron Probe Microanalyzer (EPMA) data, was found to be the main cause of the origin of ferromagnetism. A one-to-one correspondence is found between the concentration of oxygen vacancies and the magnetic moment, which is corroborated by first-principle-based calculations. The study suggests that the incorporation of H in the MoO3 matrix and the formation of HxMoO3 and MoO2, are other factors that influence ferromagnetism.

The size dependence and defect induced room temperature ferromagnetism of ZnO and Zn 1-x-y AlxZyO (Z=Mg/Ni) nanocomposites

In the current research, Al-Mg-ZnO and Al-Ni-ZnO nanocomposites were synthesized by using simple soft chemical route. Prepared nanocomposites of Al-Mg-ZnO and Al-Ni-ZnO with capsule shape distributed magnetite nanostructured were carried out under the calcinated at 120 C for 12 h in furnace. The structural morphology and characterization analysis of as prepared nanocomposites was analyzed by XRD, UV–vis. FTIR, PL, TEM, VSM studies. XRD analysis confirmed the highly pure crystallized cubic phases. The XRD peaks show that the crystalline sizes are of the order of 22 nm, 19 nm, and 11nm. Magnetic property of the prepared nanocomposites was discussed in room temperature using VSM measurement. In spite of a number of researchers reporting the effect of codoping ZnO nanoparticles (NPs) with two different metals was modify the properties of the entire system such as enrich in room-temperature ferromagnetism. In this research we tried to by experimentally observed the magnetic properties of a series of soft chemical synthesized Zn1-x-yAlxZyO (Z=Mg/Ni) nanocomposites. Interestingly, it was found that in comparison to un-doped ZnO NPs and co-doped with two different metals. The ferromagnetic signal changes in a co-doped system in which one of the Mg/Ni ions increases the concentration of defects mechanism when Mg/Ni ions exhibited only one oxidation state. The potential role of charge transfer ferromagnetism is involving Mg2+ and Ni2+ ions substituted into ZnO lattice, The origin of magnetism in the nanocomposites is due to exchange interaction between local spin polarized electrons and the conduction electrons. The potential role of charge transfer ferromagnetism involving mixed valence ions and effects defect mechanism was used to explain the room temperature ferromagnetism.

Defect induced room temperature ferromagnetism in undoped ZnO and Zn1−x-yAlxZyO (Z=Mg/Ni) Nanocomposites

Defect induced room temperature ferromagnetism in undoped ZnO and Zn1−x-yAlxZyO (Z=Mg/Ni) Nanocomposites

Influence of La doping on structural, photo-luminescence and magnetic properties of SnO2 nanostructures co-doped with Gd

In this paper, we report the existence of defect induced room temperature ferromagnetism (RTFM) in (La, Gd) co-doped SnO2 nanostructures prepared by sol-gel method. The single phase rutile tetragonal structure (P42/mnm) of SnO2 was found to remain intact with doping as confirmed by X-Ray Diffraction (XRD) patterns with the average crystallite size in the range of 14–10 nm. Diffuse reflectance UV–vis reveals an increase in band gap energy of SnO2 on La and Gd doping. Further, all the SnO2 samples shows visible Photoluminescence (PL) emission in the region 424–525 nm associated with vacancies/defects. Further, the observed RTFM in doped SnO2 nanostructures is mainly due to presence of oxygen vacancies which is also supported by PL measurements.

Prediction and observation of defect-induced room-temperature ferromagnetism in halide perovskites

The possibility to induce a macroscopic magnetic moment in lead halide perovskites (LHPs), combined with their excellent optoelectronic properties, is of fundamental interest and has promising spintronic applications. However, these possibilities remain an open question in both theory and experiment. Here, theoretical and experimental studies are performed to explore ferromagnetic states in LHPs originated from lattice defects. First-principle calculations reveal that shallow-level Br vacancies in defective CsPbBr3 can produce spin-splitting states and the coupling between them leads to a ferromagnetic ground state. Experimentally, ferromagnetism at 300 K is observed in room-temperature synthesized CsPbBr3 nanocrystals, but is not observed in hot-injection prepared CsPbBr3 quantum dots and in CsPbBr3 single crystals, highlighting the significance played by vacancy defects. Furthermore, the ferromagnetism in the CsPbBr3 nanocrystals can be enhanced fourfold with Ni2+ ion dopants, due to enhancement of the exchange coupling between magnetic polarons. Room-temperature ferromagnetism is also observed in other LHPs, which suggests that vacancy-induced ferromagnetism may be a universal feature of solution-processed LHPs, which is useful for future spintronic devices.

Defect induced room temperature ferromagnetism in high quality Co-doped ZnO bulk samples

The nature of the often reported room temperature ferromagnetism in transition metal doped oxides is still a matter of huge debate. Herein we report on room temperature ferromagnetism in high quality Co-doped ZnO (Zn1−xCoxO) bulk samples synthesized via standard solid-state reaction route. Reference paramagnetic Co-doped ZnO samples with low level of structural defects are subjected to heat treatments in a reductive atmosphere in order to introduce defects in the samples in a controlled way. A detailed structural analysis is carried out in order to characterize the induced defects and their concentration. The magnetometry revealed the coexistence of a paramagnetic and a ferromagnetic phase at room temperature in straight correlation with the structural properties. The saturation magnetization is found to increase with the intensification of the heat treatment, and, therefore, with the increase of the density of induced defects. The magnetic behavior is fully explained in terms of the bound magnetic polaron model. Based on the experimental findings, supported by theoretical calculations, we attribute the origin of the observed defect-induced-ferromagnetism to the ferromagnetic coupling between the Co ions mediated by magnetic polarons due to zinc interstitial defects.

Boosting of Power Conversion Efficiency of 2D ZnO Nanostructures-Based DSSC by the Lorentz Force with Chitosan Polymer Electrolyte

Power conversion efficiency (PCE) of dye-sensitized solar cells (DSSCs) fabricated from titanium tetra-isopropoxide (TTIP) treated Li doped two dimensional (2D) ZnO nanostructures based photoelectrode with chitosan polymer electrolyte is reported here. The defect induced room temperature ferromagnetism (RTFM) is observed and has been established from the bound magnetic polaron mechanism (BMP) for an optimum concentration of Li doped ZnO (ZnO:Li) nanostructures. Also, the incorporation of Li in the 2D ZnO nanostructure (2DZL) reduces the charge transfer resistance and hence an enhanced PCE of 5.58% (which is about two and half times superior to that of pristine ZnO). As the fabricated 2DZL exhibits RTFM, a field of 200 Oe when applied to this DSSC showed an improved PCE of 5.83%. The mechanism of such an enhancement is explained from the effect of Lorentz force and the results are discussed.

Defect induced room temperature ferromagnetism in methylammonium lead iodide perovskite

The meteoric rise in the photovoltaic performance of organic-inorganic hybrid perovskite is a conspicuous reflection of its defect tolerance nature. The presence of lattice defect in organo lead halide perovskite can manipulate or even gives rise to some exceptional properties which otherwise would have remained unseen. One of such properties reported in this article is the experimental observation of defect mediated room temperature ferromagnetism in methylammonium lead halide perovskite for the very first time, ably supported by ab-initio calculations. Theoretical analysis predicts that the ferromagnetism principally arises from the iodine vacancies in the orthorhombic and cubic crystal phases but not in the tetragonal phase. The low temperature (100 K) ferromagnetic hysteresis loop was stable even at a high temperature of 380 K, substantiating the fact that the origin of magnetism embedded in its defective nature.

Defect induced room temperature ferromagnetism and optical properties of (Co, Y) co-doped ZnO nanoparticles

Abstract In this work, pristine zinc oxide (ZnO), Co2+ doped zinc oxide (ZCO) and Co-Y co-doped zinc oxides (ZCYO) are synthesized by sol-gel method. To increase the oxygen vacancy, the as-prepared samples are annealed in vacuum furnace. Refinement of the recorded X-ray diffractograms (XRD) shows that all the samples have grown in single hexagonal phase with space group P63mc and the nanocrystallites are grown with average sizes lie in the nanometer regime (10–29 nm). Fourier-transform infrared spectroscopy (FTIR) and photoluminescence (PL) spectroscopy could not detect any secondary phase except the desired one. Interestingly, room temperature ferromagnetism (RTFM) is observed in Co-Y co-doped sample where maximum magnetization is quite high (∼0.34 emu/g) compared with undoped ZnO. Absence of any metal cluster in ZCYO by XRD and optical analyses ruled out the ordering due to clustering. Thus origin of RTFM in ZCYO is intrinsic in nature. The defect mediated RTFM observed in ZCYO nanoparticles due to exchange interaction between dopants ions is explained by the oxygen vacancy together with the presence of the increase of surface defects due to co-doping of Co ion and non-magnetic Y ion.

X-ray absorption, photoemission and electron spin resonance studies of Ar+ ion implanted ZnO

Defect induced room temperature ferromagnetism (RT-FM) in Ar+ implanted ZnO single crystal (ZnO-SC) is observe from the electron Spin Resonance (ESR) spectra and is correlated with their electronic structure studies using synchrotron radiation based X-ray absorption near edge structure (XANES) spectroscopy and valence band photoemission spectroscopy (VB-PES). Enhancement of absorption intensity at the edge of XANES spectra of Ar+ implanted ZnO indicates the increase of local density of states (DOS); which arises from the surface defects and/or dangling bonds in ZnO. VB-PES spectra change upon Ar+ implantation, becoming broader, implying the induced surface defects in ZnO-SC. X-ray photoelectron spectroscopy studies confirm that the Zn 2p3/2 core level peak shifts in lower energy side in Ar+ implanted ZnO-SC that is associated with the formation of oxygen vacancies/defects in ZnO-SC which is responsible for the RT-FM.

Defect-induced room temperature ferromagnetism in silicon carbide nanosheets

Silicon carbide (SiC) nanosheets with different sizes and thickness were synthesized by a liquid exfoliation method by varying the exfoliating time in the N, N-dimethylformamide organic solvent. During the exfoliating time increasing from 4 to 16 h, the size of the SiC nanosheets decreases gradually from 500 to 200 nm, and the thickness decreases from 9 to 3.5 nm. Results showed that all prepared SiC nanosheets show intrinsic room temperature ferromagnetism, which is greatly different to the diamagnetism nature of virgin bulk SiC. Moreover, the saturation magnetization of the SiC nanosheets increases monotonously from 0.005 to 0.018 emu/g as the size and thickness decrease. Further studies via transmission electron microscopy, superconducting quantum interference device, and electron spin resonance revealed that the origin of the ferromagnetism in SiC nanosheets might be attributed to the defects with carbon dangling bond on the surface of nanosheets.

Defect-induced room-temperature ferromagnetism in single-walled carbon nanotubes

Room-temperature ferromagnetism in single-walled carbon nanotubes (SWNTs) was observed and investigated in this work. Sizeable magnetization was observed in SWNTs aged in air, further increasing by hydrothermal treatment. The magnetic moment appears to arise from a spin-1 species in the pristine sample and from a spin-3/2 species in the hydrothermally treated samples. The spin-1 state may be attributed to the carbon vacancies, whereas the spin-3/2 state may be attributed to hydrogen adsorbed to the carbon vacancies by the hydrothermal treatment.

Defect induced room temperature ferromagnetism in single crystal, poly-crystal, and nanorod ZnO: A comparative study

A comparative study has been made for the defect induced room temperature ferromagnetism of single crystal, poly-crystal, and nanorod zinc oxide (ZnO), based on the magnetic properties and electronic properties by means of X-ray absorption near edge structure spectroscopy (XANES), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), valence band photoemission spectroscopy (VB-PES), and SQUID-type magnetometry. Magnetic measurement demonstrates the defect-induced ferromagnetic nature at room temperature in different ZnO films and a strong correlation between their electronic properties and magnetic responses. The higher ferromagnetic behaviour in polycrystalline ZnO is attributed to the increasing number of surface defects and native defect sites (oxygen vacancies and zinc interstitials) present in ZnO. XANES studies reveal that the number of unoccupied p states in polycrystalline ZnO is higher than single crystal ZnO as well as nanorod ZnO. The more amount of oxygen vacancy causes the highest intensity the O 1 s peak to appear in the XANES spectra of polycrystalline ZnO. In polycrystalline ZnO, the binding energy of the Zn 2p3/2 core level peak shifted to lower energy that further confirms the increase of the valence band maximum (VBM) position. The VBM of single crystal, poly-crystal, and nanorod-ZnO is 3.64 eV, 3.99 eV, and 3.71 eV, respectively, obtained from UPS (He-I) measurements. VB-PES studies confirm that the number of electrons in the valence band of O 2p - Zn 4sp hybridized states of poly-crystal ZnO is higher than single crystal and nanorod-ZnO.

Defect induced room temperature ferromagnetism in lead-free ferroelectric Bi0.5K0.5TiO3 materials

Development the multiferroic materials based on the lead-free ferroelectric materials is the new possible channel to create the next generation devices. The pure Bi0.5K0.5TiO3 and Mn-doped Bi0.5K0.5TiO3 materials were synthesized using sol-gel method. While the substitution of Mn for Ti site reduces the optical band gap in Bi0.5K0.5TiO3, the room temperature ferromagnetism is obtained in both un-doped and Mn-doped Bi0.5K0.5TiO3 materials. By means of the first-principles calculations, the ferromagnetism in Mn-doped Bi0.5K0.5TiO3 materials can be explained by the mixed valence states of Mn ions through the crystal field mechanism and that in un-doped Bi0.5K0.5TiO3 materials is ascribed to the formation of O or Ti vacancies during the sample growth.

Joint effect of ferromagnetic and non-ferromagnetic cations for adjusting room temperature ferromagnetism of highly luminescent CuNiInS quaternary nanocrystals

In this work, highly luminescent quaternary CuNiInS nanocrystals (NCs) are put forward as a good prototype for investigating defect-induced room temperature ferromagnetism. A ferromagnetic Ni cation can preserve the strong luminescence of NCs without introducing intermediate energy levels in the center of the forbidden band. The strong luminescence of NCs is used as an indicator for monitoring the concentration of vacancy defects inside them, facilitating the investigation of the origin of room temperature ferromagnetism in CuNiInS NCs. Our results reveal that the patching of Cu vacancies with Ni will result in bound magnetic polarons composed of both and a substitution of Cu by Ni giving rise to the room temperature ferromagnetism of CuNiInS NCs. Either the ferromagnetic Ni or the non-ferromagnetic Cu cation can tune the magnetism of CuNiInS NCs because of the change of bound magnetic polaron concentration at the altered concentration ratio of and .

Defect-induced room temperature ferromagnetism in mechanically milled nanocrystalline In2O3 powder

Although bulk In2O3 is diamagnetic, recent studies reported that In2O3 nanowires and thin films how ferromagnetic behavior at room temperature due to the defects induced during the preparation. This research work shows that mechanical milling is an effective approach to induce defects in ground materials. Structural, optical and magnetic properties of as-received and milled In2O3 powders have been studied. Magnetic characterization showed that milled In2O3 for 40h became totally ferromagnetic with a hysteresis loop at room temperature; having a saturation magnetization of 0.05emu/g due to intrinsic defects induced during milling process. XRD analysis confirms the absence of any impurities or secondary phases which can induce ferromagnetism ordering.

Zn interstitial defects induced room temperature ferromagnetism in Na+ ions codoped Zn0.95Co0.05O powders

Sodium co-doped Zn0.95Co0.05O nanoparticles (0.01 ≤ X ≤ 0.05) were synthesized using simple wet chemical (co-precipitation) method. The structural, surface morphology and the optical properties of the prepared samples were investigated by X-ray diffraction (XRD), scanning electron microscope, UV-diffuse reflectance spectroscopy (UV-DRS) and Photoluminescence (PL) spectra measurements. The magnetic measurements of the prepared samples with vibrating sample magnetometer exhibited room temperature ferromagnetism. The results obtained from the above studies shows no trend following on Na co-doping concentrations, within our arbitrary selection limit of Na ion. However, the XRD pattern confirms the single phase of Na co-doped samples without any secondary phases. The behaviors associated with intrinsic defects are explored by UV-DRS and PL emission spectra. Further, the origin of observed ferromagnetism and its lack of dependence on Na ion doping was analysed and reported.

Defects-Induced Room Temperature Ferromagnetism in ZnO Nanorods Grown from ε-Zn(OH)2

This paper reports the zinc interstitial-induced room temperature ferromagnetism (RT-FM) in undoped ZnO nanorods synthesized by aging e-Zn(OH)2 precursor in 0–2 mol·L–1 NaOH at 80 °C for 10.0 h. The variations of the defect states and ferromagnetism of the ZnO nanorods with NaOH concentration were investigated by X-ray diffraction, Raman scattering, photoluminescence, electron spin resonance, X-ray photoelectron spectroscopy, and superconducting quantum interference device so as to identify the origin of RT-FM. The experimental results revealed that the increase of the NaOH concentration led to the increase of the oxygen-related defects but the decrease of the zinc interstitials in association with the magnetization value. A direct correlation between the ferromagnetism and the relative concentration of the zinc interstitials was established, which indicated that the zinc interstitials may play an important role in mediating the RT-FM in the undoped ZnO nanorods.

Correlating defect induced ferromagnetism and gas sensing properties of undoped tin oxide sensors

A correlation between gas sensing properties and defect induced Room Temperature Ferromagnetism (RTFM) is demonstrated in non-stoichiometric SnO2 prepared by solution combustion method. The presence of oxygen vacancies (VO), confirmed by RTFM is identified as the primary factor for enhanced gas sensing effect. The as-prepared SnO2 shows high saturation magnetization of ∼0.018 emu/g as compared to ∼0.002 and ∼0.0005 emu/g in annealed samples and SnO2 prepared by precipitation respectively. The SnO2 prepared by precipitation which is an equilibrium method of synthesis shows lesser defects compared to the combustion product and hence exhibits lesser sensitivity in spite of smaller crystallite size. The study utilizes RTFM as a potential tool to characterize metal oxide gas sensors and recognizes the significance of oxygen vacancies in sensing mechanism over the microstructure.

Defects Induced Room Temperature Ferromagnetism in ZnO Thin Films

Polycrystalline ZnO thin films are prepared by the co-sputtering method under different oxygen partial pressures. Films deposited in pure argon gas exhibit ferromagnetism, whereas other films deposited under different oxygen partial pressures are diamagnetism. XPS results show the presence of Zn interstitial and oxygen vacancy in all of samples. Further analysis indicates that Zn interstitial may play an important role in triggering magnetic order on the undoped ZnO thin films by inducing an alteration of electronic configuration.