Enhanced Room Temperature Ferromagnetism Research Articles

Enhanced Room Temperature Ferromagnetism in Cobalt-Doped Copper Oxide Nanoparticles: Synthesis and Characterization

Enhanced Room Temperature Ferromagnetism in Cobalt-Doped Copper Oxide Nanoparticles: Synthesis and Characterization

Interface-induced enhanced room temperature ferromagnetism in hybrid transition metal dichalcogenides

Magnetic semiconductors with both electron charge and spin features exhibit tremendous potential in spintronics. Although defective transition-metal dichalcogenides are promising with induced room temperature (RT) magnetic moments, impacts of the defect type and underlying mechanisms remain unclear. Herein, two strategies involving elemental substitution and epitaxial growth have been explored to synthesize alloyed and hybrid MoSe2-xSx with lattice distortion and artificial interfaces respectively. Both experimental measurements and first-principle calculations demonstrate induced magnetism in the resultant MoSe2-xSx with the magnetization intensity closely associated to the atomic structure. The alloyed MoSe2-xSx exhibits satisfactory structural stability and atomic magnetic moments due to the Mo 4d orbital splitting induced by lattice distortion. Nevertheless, both enhanced RT ferromagnetism and thermomagnetic stability can be achieved for the hybrid MoSe2-xSx resulted from stronger localized spin polarization at the MoSe2/MoS2 interfaces. As such the work not only sheds light on the mechanisms underlying defect-induced ferromagnetism in transition-metal dichalcogenides, but also proposes an interface engineering strategy to induce significant ferromagnetism for multi-fields including spintronics, multiferroics and valleytronics.

Synthesis and characterization of niobium doped titanium oxide for spintronics applications

Spintronics is a promising field that involves vast applications exploiting both the intrinsic spin of the electron and its charge. Transition metal doped oxide based dilute magnetic semiconductors (DMS) are suitable for these purposes. This work reports undoped and niobium-doped titanium oxide (XNb=0.00, 0.5% and 1 wt%) nanoparticles, synthesized by a modified hydrothermal method. The structural properties were studied using X-ray diffraction, (XRD), which has depicted that the dopant niobium is well incorporated in the anatase titanium oxide lattices. The surface morphology of the freshly synthesized nanoparticles indicates the formation of spherical nanoparticles without any irregular structures, with good agreement of the particle sizes to the XRD results. Fourier-transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV) studies confirm the purity and the expected phases of the Nb doped TiO2. Vibrating sample magnetometer (VSM) studies show evidence of enhanced room temperature ferromagnetism in Nb doped TiO2. The optical properties of freshly synthesized Nb doped TiO2 reveal a band gap energy of around 3.12 eV. These results authenticate a good reason for considering a dilute magnetic semiconductor exhibiting room temperature ferromagnetism for spintronics applications.

Enhanced Room Temperature Ferromagnetism in Highly Strained 2D Semiconductor Cr2Ge2Te6

Emergent magnetism in van der Waals materials offers exciting opportunities in fabricating atomically thin spintronic devices. One pertinent obstacle has been the low transition temperatures (Tc) inherent to these materials, precluding room temperature applications. Here, we show that large structural gradients found in highly strained nanoscale wrinkles in Cr2Ge2Te6 (CGT) lead to significant increases of Tc. Magnetic force microscopy was utilized in characterizing multiple strained CGT nanostructures leading to experimental evidence of elevated Tc, depending on the strain percentage estimated from finite element analysis. Our findings are further supported by ab initio and DFT studies of the strained material, which indicates that strain directly augments the ferromagnetic coupling between Cr atoms in CGT, influenced by superexchange interaction; this provides strong insight into the mechanism of the enhanced magnetism and Tc.

Colossal permittivity, electrical conductivity and ferromagnetic properties of pure TiO2: Mono and binary doping

Advanced doping and binary doping techniques can open pathways to enabling rapid manufacture of high desired materials and structures. Herein, enhanced room temperature ferromagnetism with colossal dielectric constant were detected in pure, Fe doped, (Fe, Mn) and (Fe, Ni) codoped TiO2. High purity TiO2, Ti0.98Fe0.02O2, Ti0.96Fe0.02Mn0.02O2 and Ti0.96Fe0.02Ni0.02O2 compositions were synthesized by means of coprecipitation method. The XRD crystallographic planes of TiO2 compositions showed that mixed phases of rutile and anatase TiO2 were formed with absence of any impurities phases related to Fe, Mn or Ni oxides. Wide visible light band gap energy until 497 nm was achieved in TiO2 due to incorporation of (Fe, Mn) ions. Parallel relation between doping, codoping and particles size reduction was observed which reflects the strong influence of dopants on the grains growth of TiO2. Interestingly, Ti0.98Fe0.02O2, Ti0.96Fe0.02Mn0.02O2 and Ti0.96Fe0.02Ni0.02O2 compositions exhibit room temperature ferromagnetic behavior with constructive retentivity and coercivity values. Colossal dielectric permittivity (> 103) of 2335, 2327, 1857 and 1746 was detected for TiO2, Ti0.98Fe0.02O2, Ti0.96Fe0.02Mn0.02O2 and Ti0.96Fe0.02Ni0.02O2 structures, respectively. All TiO2 compositions reveal semiconducting-temperature performance and the electrical conductivity was enhanced due to (Fe, Mn) and (Fe, Ni) codoping. At low frequencies, the room temperature electrical conductivity of Ti0.96Fe0.02Mn0.02O2 and Ti0.96Fe0.02Ni0.02O2 is higher than that of TiO2 and Ti0.98Fe0.02O2. It seems that the defects chemistry and the charge carriers concentration of the pure TiO2 sample were affected by (Fe, Mn) and (Fe, Ni) codoping.

Unveiling Semiconductor Nanostructured Based Holmium-Doped ZnO: Structural, Luminescent and Room Temperature Ferromagnetic Properties.

This research work describes the synthesis of ZnO nanostructures doped with Ho3+ ions using a conventional sol–gel synthesis method. The nanostructured produced exhibited a wurtzite hexagonal structure in both ZnO and ZnO:Ho3+ (0.25, 0.5, 0.75 mol%) samples. The change in morphology with addition of Ho3+ dopants was observed, which was assigned to Ostwald ripening effect occurring during the nanoparticles’ growth. The photoluminescence emission properties of the doped samples revealed that Ho3+ was emitting through its electronic transitions. Moreover, reduced surface defects were observed in the Holmium doped samples whose analysis was undertaken using an X-ray Photoelectron Spectroscopy (XPS) technique. Finally, enhanced room temperature ferromagnetism (RT-FM) for Ho3+-doped ZnO (0.5 mol%) samples with a peak-to-peak line width of 452 G was detected and found to be highly correlated to the UV–VIS transmittance results.

Hydrothermal synthesis of Ce/Zr co-substituted BiFeO3: R3c-to-P4mm phase transition and enhanced room temperature ferromagnetism

A facile hydrothermal method was used for fabricating phase-pure Bi1−xCexFe1−xZrxO3 (x = 0.00, 0.03, 0.06) multiferroic ferrites, and the dependence of structural, optical, and magnetic properties on the composition have been investigated. The samples were investigated by X-ray diffraction, Raman and Fourier transform infrared spectroscopies, scanning electron microscopy, UV–Vis spectroscopy, and vibrating sample magnetometer at room temperature. Structural results show that the structure of Bi1−xCexFe1−xZrxO3 ferrites is indexed to a rhombohedral structure with the R3c space group. However, the weakening in the intensity, the expansion of the line-width of all bands, and some band shifts observed in Raman spectra indicate a structural transition from rhombohedral (R3c) to pseudo-tetragonal (P4mm) phase as the content of Ce/Zr increases. Also, a significantly enhanced intensity of the A1–2 mode in Raman spectra means that there is a novel behavior of magnetic anisotropy in the Ce/Zr co-substituted samples. A significant increase in optical bandgap with increasing of the Ce/Zr co-substitution suggests that the materials are suitable for technological applications. Magnetic properties of the samples show a magnetic transition from antiferromagnetic to ferromagnetic phase due to the presence of the rhombohedral to the tetragonal phase transition, and exchange interaction between the 4f orbitals of the Ce3+/Ce4+ and the 3d orbitals of the Fe3+/Fe2+.

Oxygen vacancy enhanced room temperature ferromagnetism in Ar+ ion irradiated WO3 films

Room-temperature ferromagnetism in WO3 films was enhanced by 130 keV Ar+ ion irradiation. The X-ray diffraction (XRD) and Raman measurements not only confirmed the monoclinic phase of the irradiated WO3 films, but also showed that oxygen vacancy (VO) defects were formed. The analysis of photoluminescence spectra strongly reconfirmed the presence of oxygen vacancy. X-ray photoelectron spectroscopy (XPS) measurements revealed that the contents of VO and induced W5+ ions increase with increasing irradiation fluence and rich W5+-VO defect complexes in the irradiated WO3 films were formed. Further, the magnetic measurements exhibited a 2-fold enhancement in the saturation magnetization at the largest fluence of 3 × 1016 ions/cm2. At lower irradiation fluence, a bound magnetic polaron model was proposed to reveal the ferromagnetic exchange coupling resulting from overlapping of VO+ and VO++ defect states, and 5d1 states of W5+. At high irradiation fluence, the carrier concentration reaches 1.02 × 1020/cm3 and carrier-mediated exchange interactions result in the film's ferromagnetism.

Enhanced room temperature ferromagnetism in Cr and Fe co-doped SnO2 nanoparticles synthesized by sol-gel method

The Cr and Fe atoms incorporated into SnO2 matrix by sol-gel method have been studied for enhancement in ferromagnetism and emission properties at room temperature. X-ray diffraction studies confirms the enrichment in crystallinity and pure rutile type tetragonal structure of SnO2 with co-doping of (Cr, Fe). Crystallite size from XRD analysis of co-doped SnO2 nanoparticles was found to decrease from 15 nm for pure SnO2 to 8 nm for (Cr, Fe) co-doped SnO2 nanoparticles. The particle size of prepared nanoparticles was exposed by transmission electron microscopy images and found to be in the range of 5–10 nm. A sharp photoluminescence peak marked at 425 nm with change in peak intensity was observed for all the compositions. Further, room temperature magnetic investigation for pure and modified SnO2 samples was done using Vibrating Sample Magnetometer. The value of saturation magnetization was found to increase from 4 × 10 −3emu/g for Cr doped SnO2 to 6 × 10 −2emu/g for (Cr, Fe) co-doped SnO2 which might be due to presence of oxygen vacancies in the system.

Enhanced room temperature ferromagnetism in MoS2 by N plasma treatment

The introduction of ferromagnetism in MoS2 is important for its applications in semiconductor spintronics. MoS2 powders were synthesized by hydrothermal method, followed by the N plasma treatment at room temperature. Weak ferromagnetism with saturated ferromagnetic magnetization of 0.64 memu/g has been observed in the as-synthesized MoS2 at room temperature, which is significant enhanced to 3.67 memu/g after the N plasma treatment for the proper duration. X-ray photoelectron spectroscopy demonstrates the adsorption of N, and higher valence state of Mo than +4 due to the bonding with N after the N plasma treatment. First principle calculation has been performed to disclose the possible origin of ferromagnetism. One chemical adsorbed N ion on S ion may form conjugated π bonds with adjacent two Mo ions to have a total magnetic moment of 0.75 μB, contributing to the enhanced ferromagnetism.

Electronic structure, optical and ferromagnetic properties of ZnO co-doped with Ag and Co according to first-principles calculations

First-principle calculations were performed to investigate the electronic structure, optical, and ferromagnetic properties of Ag/Co single- and co-doped ZnO. We found that both ZnO single-doped Ag and co-doped Ag/Co exhibit room-temperature ferromagnetism, whereas ZnO single-doped Co shows anti-ferromagnetism. Strongly enhanced room temperature ferromagnetism with saturate magnetization of 10.45 μB has been obtained in ZnO co-doped with Ag/Co, making it a promising room temperature ferromagnetic material. The magnetic moments of Ag/Co co-doped ZnO are mainly derived from the double-exchange effect between Co-3d state and O-2p state, which is consistent with Ruderman–Kittel–Kasuya–Yosida double exchange mechanism theory. In addition, Ag-doped ZnO undergoes a transition from magnetic to non-magnetic with the Ag doping concentration increasing from 2.77 mol% to 5.55 mol%. Ag/Co single- and co-doping can remarkly enhance absorption in the visible range. However, Ag single-doped ZnO has a long carrier lifetime and is conducive to the experimental design and preparation of new photocatalysts. Further research found that the interstitial hydrogen can induce the generation of magnetic order, reduce the magnetic moments and enhance the photocatalytic ability.

Role of simultaneous substitution of Cu2+ and Mn2+ in ZnS thin films: Defects-induced enhanced room temperature ferromagnetism and photoluminescence

In this study, we have synthesized Mn2+ and Cu2+ co-substituted ZnS thin films by chemical solution process. The role of the Cu2+ substitution levels (1, 3, 5 and 10%) on the structural, optical, photoluminescence and magnetic properties of Zn0.95Mn0.05S thin films has been investigated. The results show a ZnS-like hexagonal wurtzite structure without any secondary phases is successfully obtained. A relatively dense, homogeneous film surfaces with increased grain size by increment of Cu2+ substitution level are observed. The presence of Zn2+, Cu2+, Mn2+, S2− and incorporation of the Mn2+, Cu2+ within host ZnS are evidenced. With increasing the Cu2+ substitution level, the optical band gap energy has reduced. Near band (347–369 nm), blue (418–422 nm), green (525–545 nm) and yellow-orange (590–609) emissions have been detected. The origin of enhancement in room temperature ferromagnetism are attributed to the combined effect of the defects and super exchange mechanism. It is expected that the synthesized films will find a wide applications in fabrication of spintronic, magnetic, optoelectronic and phosphor nano devices.

ZnO nanorods decorated with nanocrystalline (nc) Au Particles:Electronic structure and magnetic behaviours

Electronic structures and magnetic behaviours of zinc oxide nanorods (ZnO-NRs) decorated with nanocrystalline “Au”-particles (nc-Au) have been studied using different spectroscopies, superconducting quantum interference device-type magnetometer and plane wave pseudopotential density functional theory calculations. The presence of intrinsic defects viz. zinc interstitials (Zni) and/or oxygen vacancies (VO) are established using different spectroscopies measurements. Ultraviolet photoelectron spectroscopy and valence band photoemission spectroscopy suggests that the valence band density of states of O 2p - Zn 4sp hybridized states of nc-Au/ZnO-NRs is higher than pure ZnO-NRs that could be correlated with its higher ferromagnetic behaviour. An enhanced room temperature ferromagnetism has been observed when nanocrystalline (nc) gold (Au) particles are decorated on the surface of ZnO-nanorods (ZnO-NRs). This enhanced magnetic moment in nc-Au/ZnO-NRs comes from the metallic electrons of nc-Au that induces large orbital magnetic moment at the nc-Au/ZnO-NR interface. Theoretical calculations shows the enhancement of the density of states at the valence band region of ZnO with a decoration of optimum content nc-Au particles along with the increase of oxygen vacancies in nc-Au/ZnO-NRs; that further confirms the enhancement of magnetization.

Enhanced room temperature ferromagnetism and green photoluminescence in Cu doped ZnO thin film synthesised by neutral beam sputtering

The Cu (3 to 15 at%) is incorporated into ZnO thin film by atomic beam co-sputtering has been investigated for enhancement in room temperature ferromagnetism and green photo-luminance. These Cu-ZnO thin films examined with Raman spectroscopy, X-Ray Diffraction (XRD), UV-Visible spectroscopy, Hall measurement, magnetic force microscopy (MFM) and magnetic hysteresis. Raman spectroscopy, XRD confirms wurtzite structure and improvement in the crystallinity of ZnO upto 7% Cu. Further increase in Cu concentration results in growth in Cu nanoparticles. On increasing Cu concentration, there is decrement in transparency and increase in band gap with increase in n-type carrier concentration as confirmed from UV-Visible and Hall measurement studies. Magnetic measurement exhibited unique feature of room temperature ferromagnetic ordering in undoped and doped sample upto 3% Cu. The enhancement in magnetic moment as well as green emission in photoluminescence response with increase in Cu doping indicates that generation of large defects in ZnO by Cu doping, which can be attributed to combined effect of the presence of oxygen vacancies and/or structural inhomogeneity as well as formation of bound magnetic polarons. Importantly, synthesised Cu doped ZnO thin films can be used as spin LEDs and switchable spin-laser diodes.

Magnetic and optical properties of two-dimensional SnS2 nanosheets doped with Ho ions

Ferromagnetic two-dimensional (2D) layered chalcogenide semiconductors have been considered as a promising candidate for the next-generation spintronic devices and photodevices. A major challenge is to prepare the stable ferromagnetic chalcogenide semiconductors materials with high Curie temperature. Herein, we introduce a facile approach to synthesize the two-dimensional SnS2 nanosheets with varying Ho dopant concentrations of 0 at.%, 0.71 at.%, 1.10 at.%, 1.43 at.%, 1.59 at.%, then we investigate the optical and magnetic properties of the-synthesized samples. The variable optical band gap and enhanced luminescence provide the evidences for the tune of the optical characteristics by changeable Ho doping concentration. Magnetic measurement results show that the enhanced room temperature ferromagnetism of the Ho doped two-dimensional SnS2 nanosheets with a maximum ferromagnetic response of 0.072 emu/g. Further first-principle calculations results address that the ferromagnetism of Ho-doped SnS2 is mainly derived from Sn vacancies and Ho substitution. This work suggests that the two-dimensional SnS2 nanosheets doped with rare earth atoms have potential applications in spintronics and optoeletronics.

Carbon doping of Ti0.91Co0.03La0.06O2 nanoparticles for enhancing room-temperature ferromagnetism using carboxymethyl cellulose as carbon source

The enhanced room temperature ferromagnetism (RTFM) as well as its mechanism in the C-doped Ti0.91Co0.03La0.06O2 nanoparticles using carboxymethyl cellulose (CMC) as the C source are reported. The samples were synthesized by a two-step sol-gel route and characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, and magnetic measurement techniques, respectively. The results support the uniform incorporation of C atoms into the anatase Ti0.91Co0.03La0.06O2 lattice and the associated remarkable RTFM as a result of C doping. Both interstitial C (Ci) and the substitutional C for Ti sites (CTi) in the C-doped samples were identified based on the XPS results. The variation tendency of saturation magnetization (Ms) is in accordance with that of the concentration of CTi i.e. the C˭O units content in the Ti0.91Co0.03La0.06O2 lattice. Furthermore, the RTFM is enhanced by the superposition effect of the ferromagnetic exchange coupling between Co2+ ions in the host and the ferromagnetic p-p coupling interactions between C 2p and O 2p states of the C˭O units in the C-doped Ti0.91Co0.03La0.06O2 nanoparticles.

Enhanced room temperature ferromagnetism in Cr-doped ZnO nanoparticles prepared by auto-combustion method * * Project supported by the Office of Research, Innovation, and Commercialization (ORIC), MUST Mirpur (AJK).

Zn1−xCrxO (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.09) nanoparticles were synthesized, by an auto-combustion method. Structural, optical, and magnetic characteristics of Cr-doped ZnO samples calcined at 600 °C have been analyzed by using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), UV–Vis spectroscopy and vibrating sample magnetometer (VSM). The XRD data confirmed the hexagonal wurtzite structure of pure and Cr-doped ZnO nanoparticles. The calculated values of grain size using Scherrer's formula are in the range of 30.7–9.2 nm. The morphology of nanopowders has been observed by FESEM, and EDS results confirmed a systematic increase of Cr content in the samples and clearly indicate with no impurity element. The band gaps, computed by UV–Vis spectroscopy, are in the range of 2.83–2.35 eV for different doping concentrations. By analyzing VSM data, significantly enhanced room temperature ferromagnetism is identified in Cr-doped ZnO samples. The value of magnetization is a 12 times increased of the value reported by Daunet al. (2010). Room temperature ferromagnetism of the nanoparticles is of vital prominence for spintronics applications.

Tuning of the electronic structure and magnetic properties of xenon ion implanted zinc oxide

A correlation between the electronic structure and magnetic properties of ZnO single crystals (ZnO SCs) and 300 keV xenon ion (Xe3+) implanted ZnO SCs has been studied using x-ray absorption near edge structure (XANES) spectroscopy, valence band photoemission spectroscopy (VB-PES), x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and a superconducting quantum interference device-type magnetometer. The XANES studies revealed that the number of unoccupied p-states in the implanted ZnO SCs is higher than in the pristine ZnO SCs. In the implanted ZnO SCs, the binding energy of the Zn 2p3/2 core level peak shifted to higher energy which further confirmed the increase in the valence band maximum (VBM) energy level. The VBM of the xenon ion (Xe3+) implanted ZnO SCs increased from 3.17–3.49 eV, obtained from UPS (He-I) measurements. A VB-PES study revealed that the number of electrons in the valence band of the O 2p–Zn 4sp hybridized states of the implanted ZnO SCs is higher than in the pristine ZnO SCs. The magnetic M–H loops demonstrated enhanced room temperature ferromagnetism in the Xe implanted ZnO SCs, attributable to the increasing number of surface defects and native defect sites in oxygen vacancies and zinc interstitials.

Physical properties of solution processable n-type Fe and Al co-doped ZnO nanostructured thin films: Role of Al doping levels and annealing

The role of annealing temperature and Fe and Al co-doping on structural, optical, electrical and magnetic properties of solution processable ZnO thin films were investigated. ZnO:Fe thin films fixed with 2% of typical ferrous component were obtained to examine the role of 1–10% Al doping. X-ray diffraction analyses clearly indicates that the films to be polycrystalline and preferentially oriented along the c-axis of the hexagonal wurtzite structure. The film thickness, homogeneous distribution and decreasing/increasing of grain size dependence on Al content/annealing temperature (TA) were assessed by scanning electron microscopy. X-ray photoelectron spectroscopy revealed that Al3+ and Fe2+ ions to substitute for Zn2+ without changing the wurtzite structure. A slight decrease in the optical band gap of ZnO at fixed Fe dopant and a considerable increase of the optical band gap with increased Al doping concentrations and TA were observed. The refractive index increases with the fixed Fe dopant level and then decreases by Al doping levels, whereas the extinction coefficient clearly increases depended on both of Fe and Al concentrations. The refractive index and extinction coefficient both decrease with TA. Hall measurements show n-type conductivity and the increase of charge carrier concentration by Al doping levels and TA. Magnetic studies indicate room temperature ferromagnetism in Al and Fe co-doped ZnO thin films, whereas no room temperature ferromagnetism for the Fe-doped ZnO thin films was observed. An enhanced room temperature ferromagnetism in Al and Fe co-doped ZnO thin films was observed to depend on TA.

Enhanced room temperature ferromagnetism in Ni doped SnO2 nanoparticles: A comprehensive study

We emphasized on a detailed investigation of the structural, optical, and magnetic properties of pure and Ni-doped SnO2 nanoparticles (NPs) synthesized by a sol-gel process. An extensive structural study has been carried out using various characterization techniques. The X-ray Diffraction (XRD) spectra show the formation of the single phase tetragonal structure of pure and Ni-doped SnO2 NPs without any noticeable impurity phase such as NiO. XRD results indicate that the crystallite size of SnO2 is found to be decreased with Ni doping, which has also been confirmed by the Field Emission Scanning Electron Microscopy study. X-ray Photoelectron Spectroscopy (XPS) measurements displayed a clear sign for Ni2+ ions occupying the lattice sites of Sn4+ in the SnO2 host which also gives clear evidence for the formation of single phase Sn1-xNixO2 NPs. The optical analysis shows a significant decrease in the energy gap of SnO2, i.e., (from 3.71 eV to 3.28 eV) as Ni concentration increases which may be correlated with the core level valence band XPS analysis. Photoluminescence studies show that Ni doping creates oxygen vacancies due to dissimilar ionic radii of Ni2+ and Sn4+. Superconducting quantum interference device measurements revealed that the Ni doped SnO2 NPs exhibit strong ferromagnetic behavior at room temperature and this analysis has been well fitted with a simple relationship to find out magnetic parameters proposed by Stearns and Cheng et al. Hence, our results demonstrate that Ni-doping has strong impact on the structural, optical, and magnetic properties.