Weak Room Temperature Research Articles

Tailoring the optoelectronic and spintronics properties of Cr-doped ZnS nanostructure thin films

This paper discusses the tailoring of the optoelectronic and spintronic of Cr3+-doped ZnS nanostructured electron beam evaporated thin films. The XRD measurements confirm the zinc blende cubic structure for the films with a preferred orientation along the (111) direction. The nanostructured features of the films were verified from the XRD and AFM results. The EDXS and XPS data show the stoichiometric chemical and electronic states of the films. Spectrophotometry measurements for the films show that the energy gap decreases from 3.67 eV to 3.43 eV as the Cr3+ increases from 0 at. % to 8.0 at.%. Such reduction of the Eg of the Cr3+-doped ZnS is attributed to the sp-d coupling. The strong PL asymmetric peak of the Cr3+-doped ZnS is observed, which is quenched and red shifted with increasing Cr doping level. Furthermore, the magnetic measurements show the occurrence of weak room temperature ferromagnetic behavior. On the other hand, the results further show that the magnetization increases with the increase of the Cr3+ dopants up to x = 0.05, then decreases with increasing the Cr doping above x = 0.05. This can be attributed to the development of the antiferromagnetic ordering.

Ag(I), Au(I) and Au(I)-Ag(I) clusters based on tris[(6-methylpyridin-2-yl)methyl]phosphine

Three novel clusters, [Ag3L2][BF4]3, [Au2L2][BF4]2 and [Au2Ag2L2(MeCN)2][BF4]4 have been assembled on the platform of tris[(6-methylpyridin-2-yl)methyl]phosphine (L). The obtained clusters feature the pronounced Ag∙∙∙Ag and Au∙∙∙Au metallophilic interactions (dM–M = 2.90–3.06 Å) proved by both crystallographic data and QTAIM analysis. Moreover, the clusters {Au2} and {Au2Ag2} appear to emit a weak solid-state room temperature phosphorescence with λmax = 435 and 530 nm, respectively.

Structural, optical, dielectric and magnetic behaviour of Cu1-xCoxO (x = 0.2-0.10) nano-composites and their applications in efficient removal of Cr (VI) ion from water

Hexavalent Chromium (VI) is one of the main pollutants coming from industrial waste, dyes, paints, and plastics. It is one of the major concerns due to the adverse effects associated with Cr (VI) including respiratory cancer, skin irritation, kidney damage, liver damage and perforated eardrums. Many physico-chemical techniques used for the removal of Cr (VI) are not environment-friendly and cost-effective because of the large number of chemicals used. In the present study polyvinylpyrrolidone (PVP) capped Pure and Cu1−xCoxO (x = 2, 4, 6, 8 and 10) nanocomposites synthesized by the chemical co-precipitation method were investigated for their structural, optical, magnetic, and dielectric and for the effective removal of Cr (VI) ions from contaminated water. The monoclinic structure of synthesized materials was confirmed from detailed X-ray powder diffraction (XRD) analysis and Fourier transfer infrared (FTIR) measurements. High-resolution transmission electron microscope (HRTEM) analysis confirmed the synthesis of elongated nanoparticles with an average crystalline size of ∼12–30 nm. The optical properties were determined from the analysis of diffused reflectance spectroscopy (DRS) and results showed a decreasing trend in bandgap values from 2.56 to 2.03 eV with an increase in Co2+ ion content. The presence of Cr (III) ions resulting from reduction of Cr (VI) to Cr (III) was confirmed by high-resolution X-ray photoelectron spectroscopy (XPS) analysis. The vibrating sample magnetometer (VSM) measurements revealed weak room temperature ferromagnetism in all synthesized nanocomposites tailored by Co2+ ion substitutions. The dielectric constants and dielectric losses of synthesized nanocomposites exhibit significant variation with frequency (∼1 kHz–5 MHz) and temperature (∼25 °C–300 °C) due to inter-granular activities and grain boundary effects. The adsorption capacity of the synthesized materials for the removal of Cr (VI) ions was evaluated for different initial Cr (VI) ion concentrations and adsorbent doses at room temperature. The fitted adsorption data were found to be in good agreement with the Langmuir isotherm model relative to the Freundlich and Temkin models.

Room temperature polar and weak-ferromagnetic oxide with low dielectric loss

Single-phase materials that are simultaneously ferroelectric and ferromagnetic at room temperature are promising for devices such as non-volatile random-access memory. Perovskite BiFeO3 which crystallizes in the polar rhombohedral structure (R3c) is ferroelectric and antiferromagnetic at room temperature. Here, we report a family of perovskite oxides in the BiFeO3 – Bi2/3TiO3 – ATiO3 (where A2+ is divalent alkaline earth metal ions e.g., Ca2+, Sr2+, Ba2+) ternary phase diagram that is polar as well as weak ferromagnetic above room temperature. The composition (Bi0.9167A0.075)(Fe0.9Ti0.1)O3 crystallizes in the polar rhombohedral structure space group R3c as corroborated by powder X-ray and neutron diffraction analysis. The nearly pure A-site perovskite possesses a long-range magnetic ordering above room temperature. These perovskites show a low dielectric loss, and the electrical response is dominated by grain contributions below 723 K.

Physical characterizations of Sn1-xZn2xCr2O5 nanocomposites and their adsorption performance towards methylene blue

Herein, the structure, thermal stability, optical, magnetic characteristics, and adsorption performance towards methylene blue (MB) of Sn1-xZn2xCr2O5 nanocomposites (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1), prepared by the hydrothermal method, were investigated. The crystal structures, elemental chemical compositions and surface morphology were conducted using XRD, TEM, EDX, and SEM techniques. The structural parameters significantly depend on the elemental composition. For example, a tetragonal SnO2 phase was formed at x = 0, and 0.2, while a spinel-structured ZnCr2O4 was formed at x ≥ 0.4 beside the orthorhombic CrO3 phases. The mass magnetic susceptibility and magnetization of the Sn1-xZn2xCr2O5 nanocomposites displayed a weak room temperature ferromagnetism behavior. The maximum surface area (100.89 m2/g), evaluated via the Brunauer-Emmett-Teller method, was achieved for Sn0.6Zn0.8Cr2O5 nanocomposite. The optical band gap and Urbach energy show opposite trends and are slightly influenced by Zn content. Moreover, the impact of the Zn2+ ratio on the structure, optical, thermal stability, and magnetic characteristics was correlated. The adsorption performance of the Sn1-xZn2xCr2O5 nanocomposite (0 ≤ x ≤ 0.6) revealed an excellent removal efficiency (max ∼87.64%) towards MB dye with apparent rate kinetic constant of 44.9 × 10–2 min–1.

Probing the Magnetic Properties of Boron-Doped Graphenic-Based Carbon Materials

Graphenic carbon (GC) has been successfully synthesized from biomass (coconut shell charcoal) using the liquid phase exfoliation method. The dopants, in the form of light atoms such as boron (B-GC), were introduced with the aim of improving their magnetic properties. X-ray diffraction was used to identify the GC and B-GC, and the results show broad peaks around 24° and 43°, indicating the presence of graphene-like carbon structure. The bonding structure was also analyzed using X-ray photoelectron (XPS). It reveals the main bonds in GC consist of sp2, sp3, and C=O. While the B-GC sample shows an additional bond, namely the B-C bond, as an indicator of the successful doping process of B into the GC structure. Both GC and B-GC show weak room temperature ferromagnetism. Furthermore, these findings show that introducing boron atoms into the graphenic structure can improve magnetization.

Structural, Optical, Magnetic and Electrochemical Properties of CeXO2 (X: Fe, and Mn) Nanoparticles

CeXO2 (X: Fe, Mn) nanoparticles, synthesized using the coprecipitation route, were investigated for their structural, morphological, magnetic, and electrochemical properties using X-ray diffraction (XRD), field emission transmission electron microscopy (FE-TEM), dc magnetization, and cyclic voltammetry methods. The single-phase formation of CeO2 nanoparticles with FCC fluorite structure was confirmed by the Rietveld refinement, indicating the successful incorporation of Fe and Mn in the CeO2 matrix with the reduced dimensions and band gap values. The Raman analysis supported the lowest band gap of Fe-doped CeO2 on account of oxygen non-stoichiometry. The samples exhibited weak room temperature ferromagnetism, which was found to be enhanced in the Fe doped CeO2. The NEXAFS analysis supported the results by revealing the oxidation state of Fe to be Fe2+/Fe3+ in Fe-doped CeO2 nanoparticles. Further, the room temperature electrochemical performance of CeXO2 (X: Fe, Mn) nanoparticles was measured with a scan rate of 10 mV s-1 using 1 M KCL electrolyte, which showed that the Ce0.95Fe0.05O2 electrode revealed excellent performance with a specific capacitance of 945 Fּ·g-1 for the application in energy storage devices.

Photophysics and solar cell application of a benzodithiophene conjugated polymer containing cyclometalated platinum units

Cyclometalated platinum(II) chromophores were combined with benzodithiophene (BDT) units to form a conjugated molecule and polymer in order to ascertain their photophysical and electrochemical properties, as well as their potential for use in bulk heterojunction organic solar cells. Weak fluorescence and room temperature phosphorescence were observed for both the small molecule model complex and polymer, leading to the assumption that the presence of platinum metal centers serves to enhance intersystem crossing (ISC). Nanosecond and picosecond transient absorption spectroscopy were employed to study the excited state dynamics which revealed ISC rates of the polymers (3 × 1012 s−1) is faster than that of the model (2.5 × 1011 s−1). These fast ISC rates ensure a high population of triplet excited states, which was confirmed by singlet oxygen sensitization measurements. A laser power dependence of the triplet yield was observed to be more pronounced for the polymer, likely due to triplet-triplet annihilation within single polymer chains. Unfortunately, energy level estimations from electrochemistry and emission spectra placed the triplet state at or below the energy of the charge transfer state to PCB71M acceptor. Organic solar cells were constructed using the model or polymer as donor in conjunction with PC71BM as acceptor. The polymer donor provided the higher photocurrent efficiency at just over 1% in a non-optimized device.

Observation of magnetoelectric effect in CuO-doped SrBi4Ti4O15 ceramics

Room temperature magnetoelectric coupling effect was observed in CuO-doped SrBi4Ti4O15 lead-free ferroelectric ceramics. Interstitial doping of CuO resulted in the formation of secondary phases at lower angles, which was confirmed from X-ray diffraction studies. Due to the strong magnetic superexchange interactions of CuO, weak room temperature ferromagnetic hysteresis curve was observed. The highest saturation magnetization of 1.61 memu/g and remnant polarization of 6.21 µC/cm2 was achieved for x = 1 mol% of CuO-doped ceramic. Further, the existence of weak magnetoelectric effect (χE = 0.1352 mVcm-1Oe-1) was also achieved. The obtained weak magnetoelectric effect is due to the presence of spontaneous magnetization and oxygen deficiency in the prepared samples.

Microstructure, phase relationships and microhardness of Fe60Al40–n Hf n alloys (n = 1, 3, and 5 at.%)

Abstract The microstructural evolution, solidification behavior, phase relationships, microhardness and room temperature magnetic properties of the hypoeutectic Fe60Al40-n Hf n (n = 1, 3, and 5 at.%) compositions are investigated in detail. The micro-structure of the studied alloys is composed of Fe–Al based dendrites and eutectic mixture. The components of the eutectic are B2 Fe–Al based and HfFe6Al6 τ1 phases. With increasing Hf fraction, the amounts of eutectic and τ1 phases increase continuously which results in significant strengthening. Based on the differential scanning calorimetry results, the eutectic reaction temperature is measured as 1251 °C. Fe60Al40-n Hf n alloys show weak room temperature ferromagnetism and their magnetization values also increase with increasing Hf content.

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.

Room temperature ferromagnetism in multiferroic BaCoF[formula omitted] thin films due to surface, substrate and ion doping effects

Using a microscopic model and the Green’s function technique we have studied the influence of different surface, size and substrate effects on the magnetic properties of BaCoF4 thin films. The magnetization and the magnetic phase transition temperature increase for a compressible substrate Al2O3, whereas they decrease for a tensile substrate such as MgO. The film thickness influences also the magnetic properties. We have discussed a competition, a concurrence between the surface and substrate effects. Doping of bulk BaCoF4 with Al ions leads to weak room temperature ferromagnetism. Due to the magnetoelectric coupling is obtained that the polarization increases with increasing external magnetic field.

Effect of pressure on the elemental composition and magnetic properties of lithium-doped ZnO thin films

The paper presents the results of a study of the effect of pressure in a vacuum chamber on magnetic characteristics of Zn1-xLixOy thin films obtained by pulsed laser deposition on sapphire substrates as well as the results of elemental analysis across thickness of the samples. Secondary ion mass spectrometry demonstrated that the method of pulsed laser deposition allows for the synthesis of zinc oxide based thin films characterized by a high uniformity of elemental composition across thickness. It was established that different pressure in the vacuum chamber affects the number of oxygen vacancies in thin films, but not the distribution of elements across thin film thickness. Weak room temperature ferromagnetism was observed in Zn1-xLixOy thin films synthesized at a pressure of 3.15·10−5 Torr; it increases upon the increase in lithium concentration. Interstitial lithium atoms are considered to play a important role in its occurrence. The results of the study allow for expansion of the body of knowledge about the nature of room temperature ferromagnetism in zinc oxide based thin film structures as well as for developing technologies for high-quality thin film materials for recording and storing information.

Structural and Magnetic Properties of Nitrogen Acceptor Co-doped (Zn,Fe)Te Thin Films Grown in Zn-Rich Condition by Molecular Beam Epitaxy (MBE)

We have investigated the structural and magnetic properties of (Zn,Fe)Te:N thin films grown under Zn-rich condition with Fe composition fixed at 1.4% and N concentrations varying in the range [N] = 1.8 × 1018–5.1 × 1019 cm−3. Structural analysis by x-ray diffraction (XRD) detects some additional extrinsic diffraction peaks possibly from Fe-N compounds in the N-doped film with [N] = 5.1 × 1019 cm−3 only. Accordingly, x-ray absorption fine structure (XAFS) analysis reveals the shifting of Fe atoms from substitutional position for N-doped films with high N concentrations, [N] ≥ 1.8 × 1019 cm−3, whereas N-doped films with intermediate N concentrations [N] ≤ 4.3 × 1018 cm−3 are composed of pure diluted phase with substitutional Fe atoms in the valence state deviating from Fe2+. Magnetization measurement using SQUID confirms drastic change of magnetic properties; the linear dependence of magnetization on magnetic field, typical of van Vleck-type paramagnetism in the film without N-doping changes into room temperature ferromagnetic behaviors with hysteretic magnetization curves for N-doped films. The observed weak room temperature ferromagnetic behavior of the N-doped films with [N] ≤ 4.3 × 1018 cm−3 may reflect the deviation of substitutional Fe valence state from Fe2+ to Fe2+/3+ mixed states. On the other hand, the robust room temperature ferromagnetic behavior exhibited by N-doped films with [N] ≥ 1.8 × 1019 cm−3 may originate from precipitates of Fe-N compounds with Fe being in Fe2+/3+ or other valence state.

Investigation on electronic structure and magnetic properties of Co and Mn incorporated nanoscale SnO2

The effect of Co and Mn co-doping and annealing on electronic structure and magnetic properties of nanoscale SnO2 were investigated using complementary experimental techniques. The high resolution transmission electron microscope (HRTEM) image showed spherical-like morphology and signalled the nanoscale regime of investigated samples. The results of X-ray photoelectron spectroscopy (XPS) analysis indicated the oxidation state of Co and Mn mostly as 2+. Moreover, XPS and Raman analysis corroborated the formation of oxygen vacancies as result of substitution tetravalent Sn with divalent Co and Mn. The XPS valence band spectra unveiled the formation of occupied states above the top of the valence band in as-synthesized Co and Mn co-doped SnO2 samples. Magnetic measurements disclosed the paramagnetic nature for the as-synthesized Co and Mn co-doped SnO2 samples and also demonstrated the dominating antiferromagnetic exchange interactions between the magnetic moments of Co and Mn. Interestingly, the annealed samples (Sn0.96Co0.02Mn0.02O2, Sn0.94Co0.02Mn0.04O2 and Sn0.94Co0.04Mn0.02O2) exhibited weak room temperature ferromagnetism (RTFM). The observed RTFM was explained based on the bound magnetic polaron (BMP) model. The comprehensive experimental investigations provide an interesting insight into the magnetic behaviour within the co-doped system.

Room temperature multiferroism in BaCoF4 films prepared by pulsed laser deposition

The much lower magnetic ordering temperature of multiferroic fluorides strongly limits their practical applications [J. F. Scott and R. Blinc, J. Phys. 23, 113202 (2011)]. In this paper, (010) oriented BaCoF4 films have been prepared on (0001) Al2O3 substrates by pulsed laser deposition. The clear observation of amplitude and phase hysteresis loops by piezoresponse force microscopy confirms the ferroelectricity at room temperature. In contrast to the antiferromagnetism in bulk BaCoF4 with a much lower Néel temperature of 69.6 K [Eibschütz et al., Phys. Rev. B 6, 2677 (1972)], clear magnetic hysteresis loops are observed in BaCoF4 films, indicating the weak room temperature ferromagnetism. The nearly unchanged saturated ferromagnetic magnetization of about 30 emu/cm3 between 5 K and 300 K suggests that the Curie temperature of BaCoF4 films is much higher than room temperature. Exchange bias is clearly observed, with a blocking temperature of 250 K. Magnetoelectric coupling is demonstrated by the observed magnetocapacitance effect at room temperature.

Ag8+ ion irradiation modulated structural, microstructural, defect, and magnetization in ZnO thin films

The irradiation effect of high energy silver ion (Ag8+) has been investigated on ZnO thin films to understand their impact on structural, microstructural, optical, electronic and magnetic properties. The RF sputtered pristine ZnO/Si thin films are polycrystalline and highly textured along (0 0 2) plane. The irradiated ZnO/Si samples showed enhanced structural and microstructural defects with irradiation time. The lattice parameters have reduced for irradiated ZnO thin films, suggesting structural deformation. The irradiation has resulted into enhanced defect density and strain in these thin films. A weak room temperature ferromagnetic moment (3.24 × 10−4 emu cm−2) has been observed, which has reduced drastically for Ag8+ irradiated samples up to 1.05 × 10−4 emu cm−2. The observed reduction in saturation magnetization has been attributed to the enhanced microstructural defects, lowering the free charge carriers and increasing the recombination centers simultaneously.

Ferromagnetic Enhancement in ZnTiO3 films induced by Co doping

Abstract ZnTiO3 is a promising wide band gap semiconductor material due to its actual and potential applications in catalysts, nonlinear optics, luminescent materials, microwave dielectrics, gas sensors, and solar cells. In this report, Co-doped ZnTiO3 nanocrystal films were prepared on Si wafers using chemical solutions, and their structural, optical, and magnetic properties were investigated. Co2+ ion in the films was confirmed via X-ray photoelectron spectroscopy. X-ray diffraction demonstrated that Co-doped ZnTiO3 films are a hexagonal space group (No. 148), and the lattice constant a increases but c decreases with the increasing Co content. All of the films show weak room temperature ferromagnetic order, and their saturated magnetizations increase slowly with increasing Co composition, which may be related to bound magnetic polarons. The average radius of bound magnetic polaron is approximately 15 A. The optical parameters of the films were extracted via spectroscopy ellipsometry. At 532 nm, n, defined as the refractive index of the films, gradually increases as the Co increases. With Co content x from 0.00 to 0.10, EOBG (the optical band gap of the Co-doped ZnTiO3) decreases from 4.37 to 4.10 eV, S0 (the average oscillator strength) decreases from 7.90 × 10−5 to 6.33 × 10−5 nm−2, and λ0 (the average oscillator wavelength) decreases from 0.0156 to 0.0134 nm, but E0/S0 (the electro-optical parameter) of the samples increases from 1.01 × 10−14 to 1.46 × 10−13 eVm2. The present report will be constructive for possible applications of ZnTiO3 in magnetic-optical devices.

Impact of iron on the room temperature luminescence efficiency of oxygen-containing precipitates in silicon

Oxygen precipitation in silicon has been associated with a weak room temperature sub-bandgap luminescence emission at around 1600 nm. We show that the additional presence of iron impurities enhances this emission by an order of magnitude and results in a red shift of the peak luminescence by approximately 45 nm. We not only observe an increase in the luminescence emission with iron contamination level but also with the density and size of the oxide precipitates. Moreover, we provide evidence that the sub-bandgap luminescence emission increases proportionally with the concentration of iron segregated to oxide precipitates after high temperature (>700 °C) annealing and thus allows evaluation of the gettering efficiency of oxygen-containing precipitates. Annealing of iron-contaminated samples at low temperatures (550 °C) results in a considerable reduction in the interstitial iron concentration without changing the sub-bandgap luminescence, indicating that the sink to which iron diffuses depends upon temperature.

Effect of indium doping on magnetic properties of cerium oxide nanoparticles

Ce1-xInxO2 (x = 0.0, 0.02, 0.04, 0.06, 0.10 and 0.15) nanoparticles have been successfully synthesized by sol gel method using citric acid as a gelling agent. The gel obtained was characterised using DG-DTA analysis. The XRD confirmed the fluorite phase formation and purity of the compounds. Morphological studies revealed the flaky and porous nature as seen from SEM images. TEM showed that the average particle size obtained is less than 20 nm. The existence of Ce3+/Ce+4 oxidation states is confirmed from XPS data which in turn results in the oxygen deficiency in the system. The Electrical studies displayed the typical semiconductor nature of the nano-particles. The dilute magnetic property has been studied using VSM where the existence of very weak room temperature ferromagnetism is seen in pristine sample which is found to be enhanced on indium doping where for Ce0.85In0.15O2 composition showed a super-paramagnetic nature with negligible coercivity (Hc), in magnetisation v/s field studies. The saturation magnetisation (Ms) and coercivity (Hc) are further found to be enhanced at 50 K. When compared with the bulk sample the magnetism here was found to be lowered or reduced. This suggests that the oxygen vacancies and defects in the nanostructure are responsible for the observed magnetic behaviour in the prepared compounds.