Dilute Magnetic Oxides Research Articles

Structural, magnetic, and optoelectronic properties of rock salt MgO co-doped with Eu-TM (TM = Cu, Ag, and Au) for spintronic and UV detector applications: SP-DFT investigations

This study analyzes how adding europium and transition metals (Cu, Ag, and Au) at a 12.5% concentration to magnesium oxide (MgO) affects its physical characteristics and potential uses. To do so, the full potential linearized augmented plane wave (FP-LAPW) method, based on spin-polarized density functional theory (SP-DFT), is used to derive the results. Wu and Cohen’s generalized gradient approximation (GGA-WC) described the exchange-correlation potential. The modified Becke-Johnson exchange potential (TB-mBJ) was also used to improve the findings of optoelectronic properties. When Eu and TM (Cu, Ag, and Au) impurities are co-doped into the nonmagnetic (NM) semiconductor MgO, the structural optimization results show that the lattice constants increase, and the bulk modulus decreases with increasing the atomic number of transition metals. The resulting dilute magnetic oxides (DMOs) are stable in the spin-polarized ferromagnetic (FM) phase, and the formation energy values confirm their stability in the [Formula: see text] cubic structure, with the lowest value belonging to Eu[Formula: see text]TM[Formula: see text]Mg[Formula: see text]O. Similarly, calculations of electronic properties using the WC-mBJ functional demonstrate that all compounds have an indirect half-metallic bandgap at L-[Formula: see text] equal to 2.53, 2.49, and 1.39 eV for Eu[Formula: see text]Cu[Formula: see text]Mg[Formula: see text]O, Eu[Formula: see text]Ag[Formula: see text]Mg[Formula: see text]O, and Eu[Formula: see text]Au[Formula: see text]Mg[Formula: see text]O, respectively. They have an integer magnetic moment of 6 [Formula: see text]. The density of states shows that at the Fermi level, the 4f-Eu, d-TM, and p-O states give rise to new energy levels. This indicates that the f–p–d hybridization provides this system with its FM properties. Also, these compounds’ dielectric function and absorption spectra are calculated and analyzed to learn more about their optical properties. The results provide insight into the optical behavior of the materials. It is observed that the co-doped compounds exhibit greater optical absorbance than their un-doped MgO counterparts do. This theoretical investigation opens the way to preparing high magnetic moment DMOs using TM and rare earth as dopants suitable for spintronic and UV devices.

Novel Single-Crystalline HfTiO2 1D Nanostructures with Room-temperature Ferromagnetism

Dilute magnetic semiconductor oxides (DMSOs) hold great promise in bridging spintronics with semiconductor electronics, offering the potential for highly compact, high data-processing devices with reduced power consumption. HfO2 stands out...

Synthesis and characterization of transition metals (Mn, Fe, Co, Ni) doped tin oxide for magnetic and antimicrobial studies

Dilute magnetic semiconductor oxides (DMSOs) are attractive prospects for improved charge and spin degrees of freedom control. The current research presents an overview of the structural analysis and magnetic characteristics of DMSOs based on binary metal oxide nanomaterials with various ferromagnetic or paramagnetic dopants, such as Mn, Fe, Co, and Ni, which display increased ferromagnetic behaviour at ambient temperature. The co-precipitation approach was used to create nanoparticle samples of pure SnO2, Sn0.97Mn0.03O2, Sn0.97Fe0.03O2, Sn0.97Co0.03O2, and Sn0.97Ni0.03O2. The emission spectra for the high, wide emission band are 366 nm and 655 nm. Room temperature magnetic hysteresis loops for Mn, Fe, and Ni-doped SnO2 indicate ferromagnetic behaviour when compared to pure and Co-doped SnO2, with Sn0.97Mn0.03O2, Sn0.97Fe0.07O2, and Sn0.97Ni0.03O2 samples exhibiting increased coercivity and retentivity. The antibacterial activity of pure SnO2, Sn0.97Mn0.03O2, Sn0.97Fe0.03O2, Sn0.97Co0.03O2, and Sn0.97Ni0.03O2 nanoparticles was determined.

Magnetic field control and swift heavy ion beam assisted tuning of resistive switching properties of BSFO/CFO/LNO heterostructures

Resistive switching (RS) behavior in mixed oxide insulators has shown a great promise as memristors or non-volatile resistive random-access memory (RRAM) applications. For dilute magnetic oxide multilayers, a novel approach of controlled defects induced and the magnetic field control of RS behavior is proposed. Resistive switching in Bi0.6Sr0.4FeO3 /CoFe2O4 /LaNiO3 (BSFO/CFO/LNO) multilayer heterostructures has been investigated as a case study. All oxide junctions consisting of conducting LaNiO3 (LNO) bottom electrode and BSFO-CFO active layers were fabricated by using chemical solution deposition. A set of samples were irradiated with 150 MeV Ag11+ ions for three different ion fluence of ∼1 × 10+11 ions cm−2, 1 × 10+12 ions cm−2 and 5 × 10+12 ions cm−2. Polycrystalline phase pure films with smooth, crack free surfaces were observed for pristine and irradiated samples. Optical spectroscopy revealed a decrease in the transmittance upon increasing ion fluence due to increase in the light scattering centres. The optical band gap showed a systematic decrease from 2.09 eV to 1.65 eV with increasing ion fluence. Room temperature I-V characteristics showed consistent and pronounced bipolar switching for all samples below ± 5 V. Upon applied magnetic fields of 0.58 T, the resistive switching ratios were found to increase significantly and were further tuned by 150 MeV Ag11+ ion beam irradiations. The magnetic field control of electrical transport properties in the controlled defect assisted oxide heterojunctions offers new insights to the existing understanding of oxide-based RS mechanism.

Chemical-substitution dependence of magnetization strength in room- temperature ferromagnetism of dilute magnetic oxides: Valence and spin state of slightly doped cobalt in (In,Al)2O3

This study investigates the valence and spin states of cobalt ions and the magnitude of room-temperature ferromagnetic magnetization in In1.9−xAlxCo0.1O3 (0≤x≤0.3) prepared by a chemical solution method. According to X-ray photoelectron spectroscopy, the Co ions in the Al-free sample (x=0) existed in a mixed state of trivalent Co3+ and divalent Co2+. The abundance ratio of Co2+ increased with Al content, and only divalent ions were present at x=0.3. A magnetic susceptibility analysis showed that both the spin and orbital degrees of freedom were magnetized in Co2+, whereas Co3+ was in a low-spin state. Co3+ was converted to Co2+ by vacuum annealing. The higher the conversion ratio of Co3+ to Co2+, the stronger was the room-temperature ferromagnetism.

Electronic Structure, Optical and Magnetic Properties of Oxygen-Deficient Gray TiO2–δ(B)

The gray-colored oxygen-deficient TiO2–δ(B) nanobelts have been synthesized through a combination of the hydrothermal method followed by an ion exchange process and vacuum annealing. Electron paramagnetic resonance reveals an existence of F-centers in the form of electron-trapped oxygen vacancies within the anionic sublattice of the gray bronze TiO2 that induces its colouration. The diffuse reflectance spectroscopy showed that the formation of oxygen vacancies into TiO2(B) significantly increases its absorption intensity in both visible and near infrared ranges. The band gap of TiO2(B) with anionic defects is equal to 3.03 eV (against 3.24 eV for white TiO2(B) treated in air). Room temperature ferromagnetism associated with the defects was detected in gray TiO2–δ(B), thus indicating it belongs it to the class of dilute magnetic oxide semiconductors. It was found that in the low-temperature range (4 K), the magnetic properties of vacuum annealed TiO2(B) do not differ from those for TiO2(B) treated in air. We hope that the findings are defined here make a contribution to further progress in fabrication and manufacturing of defective TiO2-based nanomaterials for catalysis, magnetic applications, batteries, etc.

Chemical-Substitution Dependence of Magnetization Strength in Room- Temperature Ferromagnetism of Dilute Magnetic Oxides: Valence and Spin State of Slightly Doped Cobalt in (In,Al)2o3

Chemical-Substitution Dependence of Magnetization Strength in Room- Temperature Ferromagnetism of Dilute Magnetic Oxides: Valence and Spin State of Slightly Doped Cobalt in (In,Al)2o3

Structural, optical and magnetic characterization of Ni2+ ions doped chromium oxide (Cr2O3) nanoparticles

In this present investigation, we have performed a systematic study to determine the suitability of chromium oxide (Cr2O3) as diluted magnetic oxide (DMO). Pristine Cr2O3 and Ni2+ ion-doped nanoparticles synthesized via a cost-effective, simple co-precipitation method. XRD studies with Raman and FT-IR confirm that Cr2O3 nanoparticles with Ni2+ ions doping exhibiting rhombohedral structure without the presence of any secondary phase. The TEM micrographs confirm the formation of highly crystalline pristine and Ni2+ ions doped Cr2O3 nanoparticles, whereas SAED and HRTEM confirm the rhombohedral structure of pristine and Ni2+ ions doped Cr2O3 nanoparticles in accordance with XRD results. X-ray Photoelectron Spectroscopy (XPS) confirms Ni2+ ions are successfully doped in Cr2O3 lattice structure and also reveals the presence of oxygen defects. UV–Vis absorption and tauc's plot illustrates marginal red shift in the optical bandgap from 2.85 eV (Pristine Cr2O3) to 2.75 eV (x = 0.07) with Ni doping. Magnetic measurement of pristine and Ni doped Cr2O3 nanoparticles carried out at room temperature depicts the presence of weak room temperature ferromagnetism (RTFM). Magnetic behavior in pristine Cr2O3 nanoparticles is attributed to mixed-valence state and surface effect. With the Ni doping, Cr2O3 nanoparticles, magnetic behavior is associated with induced exchange interaction with oxygen defects. Bound Magnetic Polarons (BMP) model was employed to calculate the defect's density and to explain magnetic behaviors in the doped powder samples.

Novel magnetic polyaniline nanocomposites based on as-synthesized and surface modified Co-doped ZnO diluted magnetic oxide (DMO) nanoparticles

Novel room temperature ferromagnetic (RTFM) polyanline (PANI) nancomposites (NCs) based on diluted magnetic oxide (DMO) nanoparticles (NPs) were successfully achieved. PANI-NCs were fabricated by chemical oxidation method of aniline in situ of Co-doped ZnO as DMO-NPs. The Co-doped ZnO-NPs were synthesized using sol–gel technique. PANI-NCs that loaded with NPs before and after treatment with oleic acid (OA) were investigated in this work. All the investigated samples showed excellent RTFM behaviors. XRD, FTIR and UV–Vis results are indicating occurrence of the substitution for Zn position by Co ions in ZnO matrix. The morphological examination of PANI-NCs confirmed the role of the surface treatment of DMO-NPs using OA on enhancing the dispersibility of NPs throughout the polymer matrix. Such effect plays a significant role in increasing the interfacial regions between NPs and polymer as well as the morphology of PANI, which reflected on their RTFM characteristic parameters and the electrical DC conductivity.

Structural, electronic and magnetic properties of Mn doped CeO2: An ab-initio study

Onwards the ab-initio approach, we investigate the electronic structure of the Mn doped CeO2 Ceria Fluorite-like. We have studied the stability of the Diluted Magnetic Oxides (DMO)-compounds as function of the impurity. A stable half-metallic ferromagnetic phase is revealed after introducing Mn impurities in the non-magnetic semi-conductor intrinsic CeO2. The total moments of the doped system vary from 0.234 to 0.744 μB for 8% and 25% of Mn. The interaction responsible for magnetism is also determined. Finally, the variation of the Curie temperature, which has reached about 840 (K) for 25% of Mn impurity in instead of 340 (K) for 8% is also determined.

Lithium Niobate Single Crystals and Powders Reviewed—Part II

A review on lithium niobate single crystals and polycrystals has been prepared. Both the classical and recent literature on this topic is revisited. It is composed of two parts with several sections. The current part discusses the available defect models (intrinsic), the trends found in ion-doped crystals and polycrystals (extrinsic defects), the fundamentals on dilute magnetic oxides, and their connection to ferromagnetic behavior in lithium niobate.

Nano-Structured Dilute Magnetic Semiconductors for Efficient Spintronics at Room Temperature

In recent years, many efforts have been made to develop advanced metal oxide semiconductor nanomaterials with exotic magnetic properties for modern applications w.r.t traditional analogues. Dilute magnetic semiconductor oxides (DMSOs) are promising candidates for superior control over the charge and spin degrees of freedom. DMSOs are transparent, wide band gap materials with induced ferromagnetism in doping, with a minor percentage of magnetic 3d cation to create a long-range antiferromagnetic order. Although significant efforts have been carried out to achieve DMSO with ferromagnetic properties above room temperature, it is a great challenge that still exists. However, TiO2, SnO2, ZnO and In2O3 with wide band gaps of 3.2, 3.6, 3.2 and 2.92 eV, respectively, can host a broad range of dopants to generate various compositions. Interestingly, a reduction in the size of these binary oxides can induce ferromagnetism, even at room temperature, due to the grain boundary, presence of defects and oxygen vacancies. The present review provides a panorama of the structural analysis and magnetic properties of DMSOs based on binary metal oxides nanomaterials with various ferromagnetic or paramagnetic dopants, e.g., Co, V, Fe and Ni, which exhibit enhanced ferromagnetic behaviors at room temperature.

Grain growth kinetics and magnetic properties of a V-doped ZnO dilute magnetic oxide

Zn0.95V0.05O ceramics, elaborated from milled ZnO and V2O5 nanopowders, were sintered at 900, 1000 and 1100 °C for 1, 2, 4, 6, 10 and 14 h. The growth kinetics was studied identifying the grain growth exponent, the activation energy and the pre-exponential factor. The high V2O5 concentration allowed a rapid grain growth at 900 °C only at the very first stages (t < 1 h). Meanwhile, at temperatures of 1000 and 1100 °C, the grain growth was extremely fast with a growth exponent of 0.72. The magnetic properties of the samples indicate that ferromagnetism exist in all samples in different magnitudes depending on the sintering conditions. In particular, the maximum magnetization was obtained on the sample sintered at 1100 °C for 14 h, despite the reduction of V concentration. Additionally, secondary paramagnetic phases were detected in the samples sintered at lower temperatures and shorter sintering times.

Activation and Enhancement of Room-Temperature Ferromagnetic Exchange in (Cu,N)-codoped In2O3 Dilute Magnetic Nanowires

Spin manipulation in dilute magnetic oxide nanowires is an important topic for achieving nanometer-sized spin-based magnetic devices. In this study, single-crystalline Cu-doped and (Cu,N)-codoped I...

Role of Ce4fhybridization in the origin of magnetism in nanoceria

Nanoscale CeO2 (nanoceria) is a prototypical system that presents d0 ferromagnetism. Using a combination of x-ray absorption spectroscopy, x-ray magnetic circular dichroism and modelling, we show that nanostructure, defects and disorder, and non-stoichiometry create magnetically polarized Ce 4f and O 2p hybridized states captured by the vacancy orbitals (Vorb) that are vital to ferromagnetism. Further, we demonstrate that foreign ions (Fe and Co) enhance the moment at Ce 4f sites while the number of Vorb is unchanged, pointing clearly to the mechanism of orbital hybridization being key missing ingredient to understanding the unexpected ferromagnetism in many nanoscale dilute magnetic oxides and semiconductors.

First-principles investigations on extrinsic acceptor defects in alkaline-earth metal and N doped CuAlO2

First-principles calculations based on density functional theory were performed to investigate the behavior of alkaline-earth metal (Be, Mg, Ca) and/or N in CuAlO2. It was found that MgAl acceptor is easier to be formed than either of BeAl and CaAl due to its lowest formation energy in CuAlO2. An O-rich condition in the growth process of CuAlO2 may facilitate the formation of extrinsic acceptor defects. The nitrogen prefers to substitute O site rather than to occupy the interstitial site in CuAlO2 but the p-type conductivity of CuAlO2 can hardly be enhanced by N doping due to the high formation energy of NO defect. In addition, the alkaline-earth metal and N co-doping in CuAlO2 is not feasible to form dual-acceptor complex since the incorporation of MAl (M = Be, Mg, Ca) with NO is unstable. The substitution of alkaline-earth metal for Al sites in CuAlO2 may cause the photon absorption in the visible light and thus degrades the transmittance of CuAlO2, which agrees well with some experimental results. Based on spin polarized electronic structure and total energy calculations, it is predicted that room temperature ferromagnetism can be observed in alkaline-earth doped CuAlO2 and therefore it is a promising p-type dilute magnetic oxide.

Magnetic properties of iron doped zirconia as a function of Fe concentration: From ab initio simulations to the growth of thin films by atomic layer deposition and their characterization by synchrotron radiation

The authors investigated the magnetic properties of Fe-doped zirconia, ZrO2:Fe, grown by atomic layer deposition, for different concentrations of Fe dopant, a substitutional impurity to Zr. Their growth recipe allows the deposition of films in which the percentage of Fe, x, ranges from diluted (x ∼ 1–2 at. %) up to high (x ∼ 25 at. %) concentrations. By x-ray magnetic circular dichroism, the authors carefully analyzed the magnetic moments of these dilute magnetic oxides at low temperature (T = 5 K), determining the best dopant range maximizing the magnetic signal. In particular, the authors found that the magnetic signal decreases as the Fe concentration increases. By comparison with ab initio simulations, the authors enlighten the microscopic mechanisms responsible for this peculiar behavior.

Effect of additional Zn2+ dopant on the ferromagnetic properties of Co-doped CeO2 nanoparticles prepared by sol–gel method

Effect of additional Zn2+ dopant on the ferromagnetism (FM) of Co doped CeO2 nanoparticles was studied. The Zn and Co co-doped CeO2 nanoparticles (Ce0.97−xZn x Co0.03O2: where x = 0, 0.01, 0.03, 0.05) were prepared by sol–gel technique. The crystal structure, morphology, and magnetic properties were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy (Raman) and physical property measurement system (PPMS). XRD and Raman studied showed that certain amount of Zn2+ can readily be incorporated into the lattice of Co doped CeO2 with single-phase of CeO2 original cubic fluorite crystal structure, and no ferromagnetic secondary phase was observed. SEM images show Zn and Co co-doped CeO2 nanoparticles were spherical and uniform size. The PPMS studied indicate that the room-temperature FM of Co doped CeO2 nanoparticles increase with additional Zn2+ dopant. This result is helpful in understanding the origin of FM in diluted magnetic oxides (DMO) as well as improving the magnetic property of DMO.

Investigation of room temperature ferromagnetic behaviour in dilute magnetic oxides

ABSTRACTManipulating the ferromagnetic interactions on the introduction of 3d and 4f orbital ions in semiconducting host material is essential for the growth of new generation spin based electronic devices. In this article we discuss about electronics which is based on the spin degree of freedom of the electron. In last few years there is tremendous work on introduction of magnetism in semiconducting devices. In this article we discussed the effect of doping and the cause of origin of magnetism in the dilute magnetic oxides.

Effect of Co and O defects on ferromagnetism in Co-doped ZnO: An X-ray absorption spectroscopic investigation

Understanding of origin of ferromagnetism in dilute magnetic oxides (DMO's) has become one of the most challenging research problems in condensed matter physics. Here we are reporting a detailed study of magnetic properties and electronic structure of two 5% Co-doped ZnO samples (the as-prepared sample Zn0.95Co0.05O and the hydrogenated sample Zn0.95Co0.05O:H). The as-prepared sample is found to be paramagnetic while through hydrogenation, we observed inducement of remarkable ferromagnetism in it. The H-mediated magnetic transition is accompanied by electronic structure modifications with no structural deviations. To get in-depth information into electronic structure correlations of the observed ferromagnetism, we have investigated their electronic properties in detail. For this purpose, we have employed the site-selective and element-sensitive X-ray-absorption spectroscopy (XAS) in the vicinity of the Cobalt L2,3 edge, the oxygen K edge, and the Zinc L3 edge using synchrotron radiation. The Co L2,3 edge spectra clearly show that Co dopants reside at the Zn sites for both these samples and that they are tetrahedrally coordinated with the ligand O atoms. Very minor changes are observed in the Zn L3 edge spectra. However, the O 1s edge spectra display dominant additional components in the ferromagnetic hydrogenated sample Zn0.95Co0.05O:H, not observed in the as-prepared non-magnetic sample Zn0.95Co0.05O. We conclude that the observed spectral features can be attributed to the presence of O vacancies and the hybridization of Co 3d states with O 2p vacancy states. These two factors together are likely to play important role in inducement of ferromagnetic ordering in this Co-doped ZnO system. However, which of these two weighs more in this mechanism, cannot be pinpointed and more studies are required in this regard.