Co-doped ZnO System Research Articles

First Principles Study of Electronic and Optical Properties of Al-P Co-Doped ZnO in the Presence of Zn Vacancies.

The BP neural network optimized by the Adam algorithm was used to predict the defect formation energy of Al-P co-doped ZnO systems with different concentrations of P replacing O under the presence of different concentrations of VZn. It was found that the easily formed AlZnPo-1VZn, AlZnPO-2VZn, and AlZn2PO-1VZn systems. The first principles of density function were used to study the geometric, electronic, and optical properties of each system. The simulation results show that the bandgap values of the three systems have decreased relative to the intrinsic ZnO, among which AlZnPO-1VZn and AlZnPO-2VZn is still a p-type conductive system, AlZnPO-2VZn has the highest conductivity. From the analysis of reflectivity, absorption rate, and light transmittance, AlZn2PO-1VZn has the most relatively excellent optical properties, followed by AlznPo-2VZn.

Effect of Co Doping on the Physical Properties and Organic Pollutant Photodegradation Efficiency of ZnO Nanoparticles for Environmental Applications.

This paper presents a comprehensive investigation of the synthesis and characterization of Zn1-xCoxO (0 ≤ x ≤ 0.05) nanopowders using a chemical co-precipitation approach. The structural, morphological, and vibrational properties of the resulting ZnO nanostructures were assessed through X-ray diffraction, scanning electronic microscopy, and Raman spectroscopy to examine the influence of cobalt doping. Remarkably, a notable congruence between the experimental results and the density functional theory (DFT) calculations for the Co-doped ZnO system was achieved. Structural analysis revealed well-crystallized hexagonal wurtzite structures across all samples. The SEM images demonstrated the formation of spherical nanoparticles in all the samples. The vibrational properties confirmed the formation of a hexagonal wurtzite structure, with an additional Raman peak corresponding to the F2g vibrational mode characteristic of the secondary phase of ZnCo2O4 observed at a 5% cobalt doping concentration. Furthermore, a theoretical examination of cobalt doping's impact on the elastic properties of ZnO demonstrated enhanced mechanical behavior, which improves stability, recyclability, and photocatalytic activity. The photocatalytic study of the synthesized compositions for methylene blue (MB) dye degradation over 100 min of UV light irradiation demonstrated that Co doping significantly improves photocatalytic degradation. The material's prolonged lifetime, reduced rate of photogenerated charge carrier recombination, and increased surface area were identified as pivotal factors accelerating the degradation process. Notably, the photocatalyst with a Zn0.99Co0.01O composition exhibited exceptional efficiency compared to that reported in the literature. It demonstrated high removal activity, achieving an efficiency of about 97% in a shorter degradation time. This study underscores the structural and photocatalytic advancements in the ZnO system, particularly at lower cobalt doping concentrations (1%). The developed photocatalyst exhibits promise for environmental applications owing to its superior photocatalytic performance.

First-principles study on electronic structure and optical properties of N-Fe co-doped ZnO

In this paper, the electronic structure and photo-electric properties of N and Fe co-doped ZnO systems have been studied by using Density functional theory method. The results show that the formation energy of ZnO-N, ZnO-Fe, ZnO-N-Fe and ZnO-N-2Fe systems decreases in turn, the doping is easier to realize. Compared with the ZnO system, the activity of ZnO-Fe, ZnO-N-Fe and ZnO-N-2Fe systems increases in turn, the band gap of ZnO-N and ZnO-N-2Fe systems decreases, and the electron transition is easier in the doped system. The peak of the dielectric function shifts to the left, the absorption of the electron to the photon increases obviously, and the absorption spectrum appears red shift. It can be concluded that the electronic structure and optical properties of ZnO are greatly affected by the single and co-doping of N and Fe, which provides a theoretical basis for the further study.

Appealing stable room-temperature ferromagnetism by well-aligned 1D Co-doped zinc oxide nanowires

Certainly diluted magnetic semiconductor Zn1−xCoxO has been investigated over the years, yet the morphological aspects and the structural influence on the magnetic properties of Co-doped ZnO nanowires still needs a clear understanding. The 1D magnetic nanowires possess exceptional magnetic properties and potential candidate as magnetic devices, because ideal magnetic density of 1D NWs is 200,000-fold than the currently used magnetic disks. Herein, the Zn1−xCoxO (x = 2.5%, 5%, 10% and 15%) 1D nanowires with Curie temperature above the room temperature have been synthesized by a simple low-temperature (65 °C) hydrothermal method. The prepared samples have been investigated by various techniques that include field emission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, micro-Raman spectroscopy, X-ray photoelectron spectroscopy, UV–vis absorption, and superconducting quantum interference device. The experimental data was further confirmed by the density functional theory calculations to affirm our findings. Structural analysis indicated the wurtzite crystal structure of NWs with preferred growth in the (001) direction along the c-axis. XPS indicated presence of OH- groups on the surface of NWs, and as the Co content increases, there is a gradual change in the portion of Co++ ions into Co+++. Optical properties have shown decreased optical bandgap with increased doping and increased electronic concentration in the host ZnO and Raman analysis suggested fewer defects in the Co-doped ZnO NWs. By magnetic properties investigation, it was found that the Co ions substitute Zn ions in the wurtzite ZnO structure with no observation of metallic or oxide-rich phase. The magnetic moment per Co atoms of Co-doped ZnO NWs increased sigificantly compared to pure ZnO NWs. By density functional theory studies, the net magnetic moment of Co-doped ZnO NWS was recognized primarily by the exchange of spin-polarized Co-3d and adjacent electrons in the O-2p states. Henceforth, double-exchange in 3d electrons was dominant, and the Co-doped ZnO system turned out to be ferromagnetic which is consistent with our experimental findings.

Enhancement of optical, dielectric and transport properties of (Sm, V) co-doped ZnO system and structure-property correlations

In this work, V-doped and (Sm, V) co-doped ZnO samples have been synthesized using ball milling method followed by heat treatment. The dependence of structural, optical, electrical and dielectric properties of V:ZnO samples on the Sm doping concentration has been explored. The structural properties have been studied by means of X-ray diffraction (XRD) and Rietveld refinement. Oxidation states of the elements present in the samples are determined using X-ray photoelectron spectroscopy. Raman spectra of the samples further verified the observations obtained from XRD. The crystallite size and microstrain have been estimated from the Williamson-Hall analysis. Microstrain increases from 0.814 × 10−3 to 1.01 × 10−3 with increase in the Sm doping level. The morphology of the grains is significantly affected by the Sm doping. The enhancement of defect density with Sm doping is responsible for the observed red shift (3.29–3.19 eV) in the band gap. The frequency dependence of the dielectric properties has been studied at various fixed temperatures ranging from 25 to 350 °C. The increase in real dielectric constant with dopant content indicates the enhancement of energy storage capacity. The ac conductivity follows Jonscher's power law and it increases up to 1 mol% Sm concentration. Further increase in Sm extent leads to the decrease in ac conductivity. The impedance spectroscopy has been performed to understand electrical behavior of samples and Cole-Cole plots are fitted against the equivalent circuit model. The electrical activation energy values for conduction and relaxation vary in the range: 0.281–0.269 eV and 0.260–0.243 eV, respectively.

(S,C) co-doped ZnO properties and enhanced photocatalytic activity

(S,C) co-doped ZnO system was prepared by Sol-Gel method from a single source of dopant (thiourea). The X-Ray diffraction pattern was indexed in a wurtzite phase without secondary phases formation. The codoping was confirmed by the modification of the cell parameters and ZnC, ZnS, SC and CO bonds identification with XPS study. The electrical conductivity σe ~ 3 × 10−4(Ωm)−1 was improved at room temperature particularly for both compositions x = 0.05 and × = 0.1 which influenced positively the photo degradation of eosin under visible light. The proposed mechanism has led to a promising application of these materials as electrodes in the field of Dye Sensitized Solar Cells (DSSC). The optical constants were globally improved and impacted the photoactivity under UVA. The high performance of the catalyst (S,C)0.2ZnO which demonstrates electrical energy consumption per order of magnitude EE/O of 2.1 kWh m−3 was attributed to the lowest optical conductivity (σopt = 6.634 × 10+7), dissipation factor (tanδ = 2.75 × 10−7) and the highest relaxation time (τ = 1.242 × 10−15s). The prepared materials were stable under visible light and UVA irradiation even after five recycles. (S,C)0.2ZnO was found to remove eosin, Bisphenol A, Acetamiprid and 4-hydroxy benzoïc Acid efficiently under sunlight.

Study of the electronic structure and absorption spectrum of Co and H doped ZnO by first-principles

The redshift and blueshift of the absorption spectrum of Co-doped ZnO have been reported experimentally. The effects on the bandgap and absorption spectrum of Co doping and interstitial H coexisting in ZnO have not been fully elucidated. The electronic structures and absorption spectra of Co-doped ZnO, interstitial Co-doped ZnO, and supercell model with four different spacings of substitutional Co and interstitial H co-doped ZnO systems were calculated using first-principle analysis. Results indicated that the multibody effect of the doped systems is greater than Burstein–Moss effect. The bandgap of the doped systems is narrowed, and the absorption spectra are significant and presented in order as follows: ZnO < Zn0.9722Co0.0278O < Zn0.9583Co0.0417O < Zn0.9583Co0.0417Hi0.0417O < Zn0.9583Coi0.0417O.

Theoretical study of the effects of Mn: N ratios on electronic structure and magnetic properties of (Mn, N)-codoped ZnO

(Mn, N)-codope is an effective method to achieve both magnetism and p-type stability of ZnO system. In this paper, the magnetism and the p-type stability of (Mn, N)-codoped ZnO with the ratios of 1:1, 1:2 and 2:1 were analyzed through establishing a (2 × 2 × 2) ZnO supercell, in which Zn site was replaced by Mn atom and O site was replaced by N atom. The results of electronic structure analysis show that (Mn, N)-codope is easier to form stable p-type ZnO in comparison to N-mono dope. The p-d coupling between Mn 3d and N 2p states weakens the repulsive force between ions under (Mn, N)-codope condition and results in stable p-type. Especially, the (Mn, N)-codoped ZnO with 2:1 ratio has lower formation energy and higher p-type stability. Furthermore, the results of magnetic analysis also show that the (Mn, N)-codoped ZnO system with 2:1 ratio has higher total magnetic moment than 1:1 and 1:2. A significant ferromagnetic coupling raised by strong p-d interaction between Mn 3d and N 2p in the Mn-N-Mn complex is responsible for these results. However, high N doping ratio is not beneficial to the enhancement of ferromagnetism and p-type stability.

Room temperature ferromagnetism in Ni, Fe and Ag co-doped Cu–ZnO nanoparticles: an experimental and first-principles DFT study

We report an experimental and theoretical investigation on the room temperature ferromagnetism of Zn0.95Cu0.05O and Zn0.94Cu0.05M0.01O (M=Ni, Fe and Ag)Ni nanoparticles synthesized by sol–gel method. X-ray diffraction analysis reveals single hexagonal wurtzite; meanwhile the lattice parameters are found to be sensitive to the ionic radius of the doping elements and the crystallite size varies in the range 22–47 nm. Field emission scanning electron microscopy observations show particles with spherical shape for ZnO and semi-spherical shape for co-doped nanopowders. Magnetic measurements using SQUID reveal room temperature ferromagnetic ordering for doped and co-doped nanopowders with a lower saturation magnetization compared to Cu-doped ZnO. It is found that the co-doping has resulted in weakening the ferromagnetic phase at the expense of the paramagnetic. First-principles calculations indicate that only Cu and Fe codoped ZnO systems own ferromagnetism, which originated from the interaction between Fe-d and O-p electrons. However, all doped systems show positive formation energies indicating they are less stable than undoped ZnO.

Enhancement of room-temperature ferromagnetism and dielectric response in nanocrystalline ZnO co-doped with Co and Cu

Enhancement of ferromagnetic ordering and dielectric response in the nanoparticles of Co and Cu co-doped ZnO are the most important findings presented in this report. The co-doped nanoparticles of ZnO were prepared by hydrothermal method. Hydrothermal synthesis is an important preparation technique to establish one dimensional growth of the nanoparticles along the easy axis and this technique on the other hand improves the defect densities in the doped ZnO systems. XRD analysis of the undoped and co-doped ZnO nanoparticles confirms the presence of single phase hexagonal wurtzite lattice structure of ZnO without the signature of any impurity phases. Also, hydrothermally prepared rod like co-doped ZnO nanoparticles consist large number of defect centers at the surface and the presence of such defect centers were confirmed by the Raman and photoluminescence studies. The magnetic measurements of Co and Cu co-doped ZnO nanoparticles using SQUID magnetometer reveal the presence of magnetic ordering and the enhancement of the magnetization of the co-doped ZnO system at room temperature as compare to undoped/mono-doped ZnO nanoparticles. The presence of ferromagnetic ordering together with paramagnetic contribution in the Co and Cu co-doped ZnO sample was confirmed by the fitting of M-T curve using 3D spin wave model and Curie-Weiss law in the temperature range of ∼300 K down to ∼5 K. Our result suggests that the magnetic properties are strongly correlated to the structural defects and grain boundary defects. Also, the large dielectric response of the co-doped ZnO nanoparticles appears due to the trapping of the free charge carriers by the defect centers present at the surface of the rod like Co and Cu co-doped ZnO nanoparticles. These modulations as well as the enhancements of magnetic and dielectric response of the co-doped ZnO nanoparticles are very much useful for many magneto-dielectric device applications.

Effects on the magnetic and optical properties of Co-doped ZnO at different electronic states

Both blue and red shifts in the absorption spectrum of Co-doped ZnO have been reported at a similar concentration range of doped Co. Moreover, the sources of magnetism of Co-doped ZnO are controversial. To solve these problems, the geometry optimization and energy of different Co-doped ZnO systems were calculated at the states of electron spin polarization and nonspin polarization by adopting plane-wave ultra-soft pseudopotential technology based on density function theory. At the state of electron nonspin polarization, the total energies increased as the concentration of Co-doped increased. The doped systems also became unstable. The formation energies increased and doping became difficult. Furthermore, the band gaps widened and the absorption spectrum exhibited a blue shift. The band gaps were corrected by local-density approximation + [Formula: see text] at the state of electron spin polarization. The magnetic moments of the doped systems weakened as the concentration of doped Co increased. The magnetic moments were derived from the coupling effects of [Formula: see text]–[Formula: see text]. The band gaps narrowed and the absorption spectrum exhibited a red shift. The inconsistencies of the band gaps and absorption spectrum at the states of electron spin polarization and nonspin polarization were first discovered in this research, and the sources of Co-doped ZnO magnetism were also reinterpreted.

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.

Defect induced room-temperature ferromagnetism and enhanced dielectric property in nanocrystalline ZnO co-doped with Tb and Co

Microstructural, magnetic and dielectric properties of hydrothermally prepared dual ions doped (Tb and Co) zinc oxide (Tb0.05Co0.05Zn0.90O) nanoparticles are investigated in the present work. The polycrystalline single phase of undoped and doped ZnO nanoparticles with hexagonal wurtzite structure is confirmed by X-ray diffraction pattern. Raman and Photoluminescence spectroscopy studies are recorded at room temperature and the measurements ruled out the presence of any impurity phase in both undoped and Tb, Co co-doped ZnO samples. Also, the Photoluminescence emission spectra for the entire samples confirm the presence of various defect centers inside co-doped ZnO wurtzite nanostructure. Magnetic and dielectric properties of co-doped ZnO system are enhanced remarkably as compared to undoped as well as some mono-doped ZnO systems. The room temperature ferromagnetism with high coercive field and magnetization has been observed in the magnetic measurement and the outcome of the measurement will be fruitful for future spintronics device applications. The dielectric behavior has been explained on the basis of Maxwell-Wagner-Sillars polarization phenomenon. High value of dielectric constant was observed due to the presence of grain boundary defects and various others defect centers at the surface of the hexagonal rod like doped ZnO nanostructures.

Study on the effects of Ga-2N high co-doping and preferred orientation on the stability, bandgap and absorption spectrum of ZnO

Currently, the stability and visible light properties of Ga-2N co-doped ZnO systems have been studied extensively by experimental analysis and theoretical calculations. However, previous theoretical calculations arbitrarily assigned Ga- and 2N-doped sites in ZnO. In addition, the most stable and possible doping orientations of doped systems have not been fully and systematically considered. Therefore, in this paper, the electron structure and absorption spectra of the unit cells of doped and pure systems were calculated by first-principles plane-wave ultrasoft pseudopotential with the GGA[Formula: see text]U method. Calculations were performed for pure ZnO, Ga-2N supercells heavily co-doped with Zn[Formula: see text]Ga[Formula: see text]O[Formula: see text]N[Formula: see text] ([Formula: see text], [Formula: see text]) under different co-doping orientations and conditions, and the Zn[Formula: see text]GaN2O[Formula: see text] interstitial model. The results indicated that under different orientations and constant Ga-2N co-doping concentrations, the systems co-doped with Ga-N atoms vertically oriented to the [Formula: see text]-axis and with another N atom located in the nearest-neighboring site exhibited higher stability over the others, thus lowering formation energy and facilitating doping. Moreover, Ga-interstitial- and 2N-co-doped ZnO systems easily formed chemical compounds. Increasing co-doping concentration while the co-doping method remained constant decreased doped system volume and lowered formation energies. Meantime, co-doped systems were more stable and doping was facilitated. The bandgap was also narrower and red shifting of the absorption spectrum was more significant. These results agreed with previously reported experimental results. In addition, the absorption spectra of Ga-interstitial- and 2N-co-doped ZnO both blue shifted in the UV region compared with that of the pure ZnO system.

Growth of Co-Doped ZnO Ferromagnetic Nanoparticles by Sol-Gel Method

Co-doped ZnO nanoparticles have been synthesized by a simple sol-gel route using zinc acetate dihydrate and cobalt(II) acetate tetrahydrate as precursors. The X- ray diffraction and high-resolution transmission electron microscopy show that Co doping has a significant effect on the crystalline nature of ZnO nanoparticles. Thermal analysis indicates that the Co-doped ZnO system is well stable above 300 ∘C. Raman spectroscopy shows the prominent modes at 331, 434, and 579 cm−1 with 0–2 % doping, whereas additional modes at 490, 525, and 715 cm−1 corresponding to secondary phases have also been observed for 3–5 % of Co doping in ZnO nanoparticles. The M–H and M–T curves confirmed the ferromagnetic nature of Co-doped ZnO nanoparticles at room temperature.

Electron Spin Resonance Study of Co-doped ZnO System: Spin-Canted Magnetism and Sintering Effects

We report on the electron spin resonance (ESR) studies in the Mn:Ni and Mn:Gd co-doped ZnO system sintered at 500 and 800 °C. We found that sintering temperature has strong effect on the ESR line widths, with the Mn-Gd co-doped ZnO system showing the largest effect. Increasing sintering temperature has increased the line widths considerably, running into Kilo Oersted range. These large line widths indicate magnetic in-homogeneities and disorder and are consistent with the occurrence of secondary phases due to high-temperature sintering. Further analysing the asymmetry parameters, together with Δg/ g-values, we explain the weak ferromagnetism at low temperatures in 500°C sintered Mn:Gd-ZnO system to be due to spin canting which is the parasitic or the ‘spin-canted magnetism’. The ESR line intensity which is the spin susceptibility shows a paramagnetic behaviour in the range 300–100 K and shows a sharp rise and a peak around 40 K consistent with the magnetization data reported earlier. In the case of Mn:Ni–ZnO system, the Δg/ g and P asc parameters, which are proportional to spin canting and magneto-crystalline anisotropy, closely follow each other representing the classic picture of Moriya-Dzyaloshinsky.

Tailoring of room temperature ferromagnetism and electrical properties in ZnO by Co (3d) and Gd (4f) element co-doping

Nanoparticles of Co2+ and Gd3+ ions co-doped Zinc oxide were prepared by co-precipitation process followed by hydrothermal method. To obtain the desired crystallographic phase and also, to enhance the Oxygen vacancy, the as prepared sample was sintered at 400 °C in vaccum atmosphere. The presence of intrinsic defects and internal stress in the lattice structure of co-doped ZnO has been substantiated by the detail analysis of X-ray diffractograms. Different optical characterizations like Raman spectroscopy and photoluminescence (PL) spectra have been measured. The presence of defects/Oxygen vacancies are also critically analyzed by Raman and PL spectra of co-doped ZnO sample. Magnetic measurement such as magnetization as a function of magnetic field at different low temperatures (300-10 K) and magnetization as a function of temperature (field cooled and zero-field cooled) are measured by SQUID magnetometer. Interestingly, a very strong magnetic interaction and a large value of coercivity even at room temperature have been observed in the co-doped ZnO nanoparticles compared to the mono-doped ZnO nanoparticles. The presence of ferromagnetic ordering and large coercivity were successfully explained by the vacancy assisted bound-magnetic-polaron model and domain wall blowing theory. Negative exchange biased has been observed in our sample implies the formation and exchange interaction at the interface of FM/AFM bilayers. Dielectric measurement suggest that for both 5% Co2+ and Gd3+ ions co-doped ZnO system, the enhanced dielectric data is the contribution of large amount of space charge polarization and the intrinsic defects in the sample. Enhancement of the ac conductivity with the increase of temperature reveals the semiconducting nature of the co-doped ZnO systems.

Ab-initio study on electronic and magnetic properties of (Ga,Co) co-doped ZnO

Using first-principles calculations based on density functional theory within GGA formalism, we have studied the electronic structure and magnetic properties of (Ga,Co) co-doped ZnO system. The effect of impurity distances on ferromagnetic and antiferromagnetic ground state in Co0.056Zn0.944O has been studied. For the closest Co-Co distance, a ferromagnetic ground state with total magnetic moment of ∼⃒3.00μB per Co atom has been found. The electronic structure also displays a nearly halfmetallic order. Conversely, for the farthest Co-Co distance an antiferromagnetic ground state was found for Co0.056Zn0.944O. When Zn2+ ions are replaced by Ga ions in Co0.056Zn0.944O, the new (Ga,Co) co-doped ZnO system is more energetically stable. It has also been found that Ga-doping reduces the Co0.056Zn0.944O band gap due to the sp-d exchange interactions, which is in good agreement with the experimental data. Moreover, the Ga-doping changes the nearly halmetallic order of Co0.056Zn0944O to metallic. Results also show that Ga0.029Co0.056Zn0.915O is still ferromagnetic with a total magnetic moment of ∼⃒3.00μB per Co atom. It was also found that the ferromagnetic ground state in (Ga,Co) co-doped ZnO vanishes as Ga concentration increases.

Study of properties of (Mg, Al)-codoped ZnO with GGA and mBJ approximations

The physical properties of the codoped ZnO system Zn1−x−yMgxAlyO were studied using a Gaussian and plane waves basis set method implemented in CP2K code, combined to the modified Becke–Johnson potential approximation implemented in the Wien2k code. We have found that the magnesium doped ZnO enhances the optical properties and induces a blue shift in the optical band gap, but reduces its electrical properties. The incorporation of a low Mg concentration in Al doped ZnO achieves a good electrical conductivity and high transmittance. These results make this material a suitable candidate for electronic transparent devices.

Observation of low field microwave absorption in co-doped ZnO system

Abstract Room temperature low field microwave absorption (LFMA) in magnetic materials find application in microwave absorbers and low field sensors. However not all the magnetic materials show LFMA and the phenomenon is not fully understood. We report on the observation of low field microwave absorption (LFMA) or the non-resonant microwave absorption (NRMA) in the transition metal (TM) co-doped ZnO samples of the composition Zn 1− x (TM:TM) x O synthesized by solid state reaction technique. LFMA peaks and hysteresis matches very well with that of the magnetization hysteresis loop and the anisotropy fields at room temperature similar to the reports in the literature for other magnetic systems. However we show through our careful experiments that such a correlation between LFMA and the magnetization does not survive at low temperatures and particularly at 10 K the LFMA hysteresis collapses in our TM co-doped ZnO system; whereas the magnetization hysteresis loop becomes very big and anisotropy field becomes bigger in the range of kOe. We interpret the LFMA as field dependent surface impedance or eddy current losses, in terms of a possible role of anomalous hall resistivity that follows magnetization and the ordinary hall resistivity that only follows the applied field. We then argue that LFMA accordingly follows magnetization or applied field when AHE or OHE dominates respectively. Also we confirm the absence of LFMA signals in the rare earth co-doped ZnO system.