Recently theoretical works predict that some semiconductors (e.g. ZnO) doped with magnetic ions are diluted magnetic semiconductors (DMS). In DMS magnetic ions substitute cation sites of the host semiconductor and are coupled by free carriers resulting in ferromagnetism. One of the main obstacles in creating DMS materials is the formation of secondary phases because of the solid-solubility limit of magnetic ions in semiconductor host. In our study transition metal ions were implanted into ZnO single crystals with the peak concentrations of 0.5-10 at.%. We established a correlation between structural and magnetic properties. By synchrotron radiation X-ray diffraction (XRD) secondary phases (Fe, Ni, Co and ferrite nanocrystals) were observed and have been identified as the source for ferromagnetism. Due to their different crystallographic orientation with respect to the host crystal these nanocrystals in some cases are very difficult to be detected by a simple Bragg-Brentano scan. This results in the pitfall of using XRD to exclude secondary phase formation in DMS materials. For comparison, the solubility of Co diluted in ZnO films ranges between 10 and 40 at.% using different growth conditions pulsed laser deposition. Such diluted, Co-doped ZnO films show paramagnetic behaviour. However, only the magnetoresistance of Co-doped ZnO films reveals possible s-d exchange interaction as compared to Co-implanted ZnO single crystals.
We report the structural and magnetic properties of ZnO single crystals implanted at 623 K with up to 10 at. % of Ni. As revealed by X-ray diffraction, crystalline fcc-Ni nanoparticles were formed inside ZnO. The magnetic behavior (magnetization with field reversal and with different temperature protocol) of all samples is well explained by a magnetic Ni-nanoparticle system. Although the formation of Ni:ZnO based diluted magnetic semiconductor cannot be ruled out, the major contribution to the magnetic properties stems from crystalline nanoparticles synthesized under these implantation conditi…
The magneto-transport properties of single proton-implanted ZnO and of Li(7\%)-doped ZnO microwires have been studied. The as-grown microwires were highly insulating and not magnetic. After proton implantation the Li(7\%) doped ZnO microwires showed a non monotonous behavior of the negative magneto-resistance (MR) at temperature above 150 K. This is in contrast to the monotonous NMR observed below 50 K for proton-implanted ZnO. The observed difference in the transport properties of the wires is related to the amount of stable Zn vacancies created at the near surface region by the proton implan…
Unwanted secondary phases are one of the major problems in diluted magnetic semiconductor creation. Here, the authors show possibilities to avoid such phases in Fe implanted and postannealed ZnO(0001) single crystals. While -Fe nanoparticles are formed after such doping in as-polished crystals, high temperature (1273 K) annealing in O2 or high vacuum before implantation suppresses these phases. Thus, the residual saturation magnetization in the preannealed ZnO single crystals is about 20 times lower than for the as-polished ones and assigned to indirect coupling between isolated Fe ions rather…
We present superparamagnetic clusters of structurally highly disordered Co-Zn-O created by high fluence Co ion implantation into ZnO (0001) single crystals at low temperatures. This secondary phase cannot be detected by common x-ray diffraction but is observed by high-resolution transmission electron microscopy. In contrast to many other secondary phases in a ZnO matrix it induces low-field anomalous Hall effect and thus is a candidate for magneto-electronics applications.
Unexpected ferromagnetism has been observed in carbon doped ZnO films grown by pulsed laser deposition [Phys. Rev. Lett. 99, 127201 (2007)]. In this letter, we introduce carbon into ZnO films by ion implantation. Room temperature ferromagnetism has been observed. Our analysis demonstrates that (1) C-doped ferromagnetic ZnO can be achieved by an alternative method, i.e. ion implantation, and (2) the chemical involvement of carbon in the ferromagnetism is indirectly proven.
Room-temperature ferromagnetism has been induced within ZnO single crystals by implant-doping with Fe ions. For an implantation temperature of 620 K and an ion fluence of 4x10^16 cm^-2, very tiny Fe particles, formed inside the host matrix, are responsible for the ferromagnetic properties. They were identified using synchrotron X-ray diffraction and Moessbauer spectroscopy. On the other hand, Fe ions implanted at a temperature of 253 K and an ion fluence of 4x10^15 cm^-2 are incorporated into the host matrix and develop a room temperature diluted magnetic semiconductor (DMS).
We investigated ZnO(0001) single crystals annealed in high vacuum with respect to their magnetic properties and cluster formation tendency after implant-doping with Fe. While metallic Fe cluster formation is suppressed, no evidence for the relevance of the Fe magnetic moment for the observed ferromagnetism was found. The latter along with the cluster suppression is discussed with respect to defects in the ZnO host matrix, since the crystalline quality of the substrates was lowered due to the preparation as observed by x-ray diffraction.
Magneto-optical properties of ZnO:Co and ZnO:Ni films were measured. Magnetization measurements show that some of the films are paramagnetic and others are ferromagnetic. Magnetic circular dichroism clarified that Zn1-xCoxO and Zn1-xNixO included in samples are paramagnetic diluted magnetic semiconductors. Ferromagnetic precipitations seem to be responsible for the observed ferromagnetic behaviors. Criteria to judge the ferromagnetic DMS are also discussed.
The structural and magnetic properties of V doped ZnO are presented. V ions were introduced into hydrothermal ZnO single crystals by ion implantation with fluences of 1.2*10^16 to 6*10^16 cm^-2. Post-implantation annealing was performed in high vacuum from 823 K to 1023 K. The ZnO host material still partly remains in a crystalline state after irradiation, and is partly recovered by annealing. The V ions show a thermal mobility as revealed by depth profile Auger electron spectroscopy. Synchrotron radiation x-ray diffraction revealed no secondary phase formation which indicates the substitution…
We simulated and experimentally investigated the sputter yield of ZnO and GaAs nanowires, which were implanted with energetic Mn ions at room temperature. The resulting thinning of the nanowires and the dopant concentration with increasing Mn ion fluency were measured by accurate scanning electron microscopy (SEM) and nano-X-Ray Fluorescence (nanoXRF) quantification, respectively. We observed a clear enhanced sputter yield for the irradiated nanowires compared to bulk, which is also corroborated by iradina simulations. These show a maximum if the ion range matches the nanowire diameter. As a c…
A close link between the charge transfer electronic structures and polarity dependent high-TC ferromagnetism of TM2+:ZnO DMSs (TM2+ = 3d ions) is demonstrated. Trends in ferromagnetism across the 3d series of TM2+:ZnO DMSs predicted from their charge transfer energies reproduce experimental trends well. These results provide a unified basis for understanding both n- and p-type ferromagnetic oxide DMSs.
Ion implantation is an interesting method to dope semiconducting materials such as zinc oxide provided that the implantation-induced defects can be subsequently removed. Nitrogen implantation followed by anneals under O2 were carried out on zinc oxide nanowires in the same conditions as in a previous study on bulk ZnO [J. Appl.Phys. 109, 023513 (2011)], allowing a direct comparison of the defect recovery mechanisms. Transmission electron microscopy and cathodoluminescence were carried out to assess the effects of nitrogen implantation and of subsequent anneals on the structural and optical pro…
Magnetic anisotropies of Co-implanted ZnO (0001) films grown on single-crystalline Al2O3 (11-20) substrates have been studied by ferromagnetic resonance (FMR) technique for different cobalt implantation doses. The FMR data show that the easy and hard axes have a periodicity of 60 degrees in the film plane, in agreement with the hexagonal structure of the ZnO films. This six-fold in-plane magnetic anisotropy, which is observed for the first time in ZnO-based diluted magnetic semiconductors, is attributed to the substitution of cobalt on Zn sites in the ZnO structure, and a clear indication for …
We have studied the structural, magnetic and electronic properties of Co-implanted ZnO (0001) films grown on Al2O3 (1120) substrates for different implantation doses and over a wide temperature range. Strong room temperature ferromagnetism is observed with magnetic parameters depending on the cobalt implantation dose. A detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted ZnO films. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the ZnO layer, th…
Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors argue that the observed ferromagnetism stems from ferromagnetic precipitates or spinodal decomposition rather than from carrier mediated magnetic impurities, as required for a diluted magnetic semiconductor. In the present paper we answer this question for Fe-implanted ZnO single crystals comprehensively. Different implantation fluences and temperatures and post-implantation annealing temperatures have been chosen in order to evaluate the structural and magnetic properties over a w…
We report on the stability and magnetic state of ion implanted $^8$Li in single crystals of the semiconductor ZnO using $β$-detected nuclear magnetic resonance. At ultradilute concentrations, the spectra reveal distinct Li sites from 7.6 to 400 K. Ionized shallow donor interstitial Li is stable across the entire temperature range, confirming its ability to self-compensate the acceptor character of its (Zn) substitutional counterpart. Above 300 K, spin-lattice relaxation indicates the onset of correlated local motion of interacting defects, and the spectra show a site change transition from dis…
We have studied the influence of intrinsic and extrinsic defects in the magnetic and electrical transport properties of Co-doped ZnO thin films. X ray absorption measurements show that Co substitute Zn in the ZnO structure and it is in the 2+ oxidation state. Magnetization (M) measurements show that doped samples are mainly paramagnetic. From M vs. H loops measured at 5 K we found that the values of the orbital L and spin S numbers are between 1 and 1.3 for L and S = 3/2, in agreement with the representative values for isolated Co 2+. The obtained negative values of the Curie-Weiss temperature…
We report on the structural and magnetic properties of a cobalt-implanted ZnO film grown on a sapphire substrate. X-ray diffraction and transmission electron microscopy reveal the presence of a (10-10)-oriented hexagonal Co phase in the Al2O3 sapphire substrate, but not in the ZnO film. Co clusters, with a diameter of is about 5-6 nm, form a Co rich layer in the substrate close to the ZnO/Al2O3 interface. Magnetization measurements indicate that there exist two different magnetic phases in the implanted region. One originates from the Co clusters in Al2O3, the other one belongs to a homogeneou…
Although zinc oxide is a promising material for the fabrication of short wavelength optoelectronic devices, p-type doping is a step that remains challenging for the realization of diodes. Out of equilibrium methods such as ion implantation are expected to dope ZnO successfully provided that the non-radiative defects introduced by implantation can be annealed out. In this study, ZnO substrates are implanted with nitrogen ions, and the extended defects induced by implantation are studied by transmission electron microscopy and X-ray diffraction (XRD), before and after annealing at 900^{\circ}C. …
In the last decade, transition-metal-doped ZnO has been intensively investigated as a route to room-temperature diluted magnetic semiconductors (DMSs). However, the origin for the reported ferromagnetism in ZnO-based DMS remains questionable. Possible options are diluted magnetic semiconductors, spinodal decomposition, or secondary phases. In order to clarify this question, we have performed a thorough characterization of the structural and magnetic properties of Co- and Ni-implanted ZnO single crystals. Our measurements reveal that Co or Ni nanocrystals (NCs) are the major contribution of the…
We report room temperature ferromagnetism in as-implanted Eu doped ZnO (ZnO:Eu). To address the origin of ferromagnetism ab initio calculations of ZnO:Eu system are performed. Results show that the ferromagnetism is induced by ZnO point defects as Eu ions in perfect ZnO tend to align antiferromagnetically.
The results of XPS core-level and valence band measurements, photoluminescence spectra of a-SiO2 implanted by Zn-ions (E=30 keV, D=1*1017 cm^-2) and Density Functional Theory calculations of electronic structure as well as formation energies of structural defects in silica glass induced by Zn-ion implantation are presented. Both theory and experiment show that it is energetically more favorable for implanted zinc ions to occupy the interstitial positions instead of cation substitution. As a result, the Zn-ions embedded to interstitials, form chemical bonds with the surrounding oxygen atoms, fo…
Diluted Magnetic Semiconductors (DMS) doped with a small concentration of magnetic impurities inducing ferromagnetic DMSs have attracted a lot of attention in the few last years. In particular, DMS based on III-V and II-VI semiconductors doped with transition metal are deeply investigated by both theoretical and experimental scientists for their promoting applications in spintronics. In this work, we present the magnetic properties of doped Mn ions in semi-conductor for different carrier's concentration. For the case of Zn1-xMnxO, the results of our calculations, dealt within Monte Carlo study…
Recently the point defect responsible for the intra-3$d$ luminescence of cobalt in doped ZnO samples has been indentified\,\cite{pssb2019}. In this work we further extend our investigation to other point defects in Co-doped ZnO. We use density-functional theory and GW calculations to determined the orbital-resolved band structure of cobalt doped zinc oxide (ZnO). We show that mainly O-p and Co-d orbitals take part in the process and confirm that an oxygen interstitial nearby a cobalt atom is a likely defect to occur in Co-implanted ZnO samples. We also rule out that other common point defects …
In this paper, a correlation between structural and magnetic properties of Fe implanted ZnO is presented. High fluence Fe^+ implantation into ZnO leads to the formation of superparamagnetic alpha-Fe nanoparticles. High vacuum annealing at 823 K results in the growth of alpha-Fe particles, but the annealing at 1073 K oxidized the majority of the Fe nanoparticles. After a long term annealing at 1073 K, crystallographically oriented ZnFe2O4 nanoparticles were formed inside ZnO with the orientation relationship of ZnFe2O4(111)[110]//ZnO(0001)[1120]. These ZnFe2O4 nanoparticles show a hysteretic be…
We have investigated electronic structures and magnetic properties of potential ZnO based diluted magnetic semiconductors: (Fe, Co) and (Fe, Cu) codoped ZnO. The origins of ferromagnetism are shown to be different between two. (Fe, Co) codoped ZnO does not have a tendency of Fe-O-Co ferromagnetic cluster formation, and so the double exchange mechanism will not be effective. In contrast, (Fe, Cu) codoped ZnO has a tendency of the Fe-O-Cu ferromagnetic cluster formation with the charge transfer between Fe and Cu, which would lead to the ferromagnetism through the double-exchange mechanism. The f…
The discovery of reversible 300 K ferromagnetic ordering in a diluted magnetic semiconductor is reported. Switching of room-temperature ferromagnetism between "on" and "off" states is achieved in Co2+:ZnO by lattice incorporation and removal of the native n-type defect, interstitial Zn. Spectroscopic and magnetic data implicate a double-exchange mechanism for ferromagnetism. These results demonstrate for the first time reversible room-temperature ferromagnetic ordering in a diluted magnetic semiconductor, and present new opportunities for integrating magnetism and conductivity in semiconductor…
Pure metals (Cu, Ti, Zr, V, Pd) and diluted Pd-alloys (Pd-Ag, Pd-Pt, Pd-Ru, Pd-Rh) were implanted by 25 keV deuterium ions at fluences in the range (1.2÷2.3)x1022 D+/m2. The post-treatment depth distributions of deuterium ions were measured 10 days and three months after the implantation using Elastic Recoil Detection Analysis (ERDA) and Rutherford Backscattering (RBS). Comparison of the obtained results allowed to make conclusions about relative stability of deuterium and hydrogen gases in pure metals and diluted Pd alloys. Very high diffusion rates of implanted deuterium ions from V and Pd p…
We report on the structural and magnetic characterization of Co0.1Zn0.9O and Mn0.1Zn0.9O nanopowders obtained by a soft chemistry route. We show that those samples fired at low temperatures display a ferromagnetic interaction that can not be attributed to the presence of impurities. A magnetic aging mechanism is observed, reflecting the key role played by defects in the stabilization of ferromagnetism in this kind of diluted magnetic semiconductors.
The origin of room temperature (RT) ferromagneticlike behavior in ZnO-based diluted magnetic semiconductors is still an unclear topic. The present work concentrates on the appearance of RT magnetic moments in just mixed ZnO/Co3O4 mixtures without thermal treatment. In this study, it is shown that the magnetism seems to be related to surface reduction of the Co3O4 nanoparticles, in which, an antiferromagnetic Co3O4 nanoparticle (core) is surrounded by a CoO-like shell. This singular superficial magnetism has also been found in other mixtures with semiconductors such as TiO2 and insulators such …
We have studied the electronic structure of Zn$_{0.9}$Fe$_{0.1}$O nano-particles, which have been reported to show ferromagnetism at room temperature, by x-ray photoemission spectroscopy (XPS), resonant photoemission spectroscopy (RPES), x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe$^{3+}$ ionic state with mixture of a small amount of Fe$^{2+}$ and that Fe$^{3+}$ ions are dominant in the surface region of the nano-particles. It is shown that the roo…
We have studied the structural, electronic and magnetic properties of spinel $\rm Co_3O_4$(111) surfaces and their interfaces with ZnO (0001) using density functional theory (DFT) within the Generalized Gradient Approximation with on-site Coulomb repulsion term (GGA+U). Two possible forms of spinel surface, containing $\rm Co^{2+} $ and $\rm Co^{3+} $ ions and terminated with either cobalt or oxygen ions were considered, as well as their interface with zinc oxide. Our calculations demonstrate that $\rm Co^{3+} $ ions attain non-zero magnetic moments at the surface and interface, in contrast to…
Cobalt and silver co-doping has been undertaken in ZnO thin films grown by pulsed laser deposition in order to investigate the ferromagnetic properties in ZnO-based diluted magnetic materials and to understand the eventual relation between ferromagnetism and charge carriers. Hall transport measurements reveal that Ag doping up to 5% leads to a progressive compensation of the native n-type carriers. The magnetization curves show ferromagnetic contributions for all samples at both 5 K and room temperature, decreasing with increasing the Ag concentration. First principles modeling of the possible…
The existence of semiconductors exhibiting long-range ferromagnetic ordering at room temperature still is controversial. One particularly important issue is the presence of secondary magnetic phases such as clusters, segregations, etc... These are often tedious to detect, leading to contradictory interpretations. We show that in our cobalt doped ZnO films grown homoepitaxially on single crystalline ZnO substrates the magnetism unambiguously stems from metallic cobalt nano-inclusions. The magnetic behavior was investigated by SQUID magnetometry, x-ray magnetic circular dichroism, and AC suscept…
Structural and magnetic properties have been studied for polycrystalline Zn_{1-x}TM_xO, where TM (transition metal ions) = Mn, Fe, and Co. No bulk ferromagnetism was observed for single-phase materials, contrary to the existing theories. Single-phase samples demonstrate paramagnetic Curie-Weiss behavior with antiferromagnetic interactions, similar to other diluted magnetic semiconductors. Non-optimal synthesis conditions lead to formation of second phases that are responsible for spin-glass behavior (ZnMnO_3 impurity for Zn_{1-x}Mn_xO (S. Kolesnik et al., J. Supercond.: Incorp. Novel Magn. 15,…
We have investigated the magnetic properties of Mn and Cu substituted SrZnO2 single crystals (SrZn0.99Mn0.01O2 and SrZn0.99Cu0.01O2). We observed signatures of weak ferromagnetism as a sharp increase of magnetic susceptibility below 5 K even in the low percentage (x= 0.01) of Mn substituted single crystals. Magnetic susceptibility data measured parallel or perpendicular to the ab plane yield anisotropic behavior with Curie Weiss temperature of about -320 K and -410 K, respectively, suggesting the presence of strong antiferromagnetic couplings among Mn atoms at high temperatures, similar to the…
We report on the results of x-ray absorption (XAS), x-ray magnetic circular dichroism (XMCD), and photoemission experiments on {\it n}-type Zn$_{1-x}$Co$_x$O ($x=0.05$) thin film, which shows ferromagnetism at room temperature. The XMCD spectra show a multiplet structure, characteristic of the Co$^{2+}$ ion tetrahedrally coordinated by oxygen, suggesting that the ferromagnetism comes from Co ions substituting the Zn site in ZnO. The magnetic field and temperature dependences of the XMCD spectra imply that the non-ferromagnetic Co ions are strongly coupled antiferromagnetically with each other.
We have calculated the chemical trend of magnetic exchange parameters ($J_{dd}$, $N α$, and $N β$) of Zn-based II-VI semiconductors ZnA (A=O, S, Se, and Te) doped with Co or Mn. We show that a proper treatment of electron correlations by the LSDA+$U$ method leads to good agreement between experimental and theoretical values of the nearest-neighbor exchange coupling $J_{dd}$ between localized 3$d$ spins in contrast to the LSDA method. The exchange couplings between localized spins and doped electrons in the conduction band $N α$ are in good agreement with experiment as well. But the values for …
The magnetic properties of Mn-doped ZnO semi-conductor have been investigated using the Monte Carlo method within the Ising model. The temperature dependences of the spontaneous magnetization, specific heat and magnetic susceptibility have been constructed for different concentrations of magnetic dopant Mn and different carrier concentrations. The exact values of Mn concentration and carrier concentration at which high temperature transition occurs are determined. An alternative for the explanation of some controversies concerning the existence and the nature of magnetism in Mn diluted in ZnO …
We review pitfalls in recent efforts to make a conventional semiconductor, namely ZnO, ferromagnetic by means of doping with transition metal ions. Since the solubility of those elements is rather low, formation of secondary phases and the creation of defects upon low temperature processing can lead to unwanted magnetic effects. Among others, ion implantation is a method of doping, which is highly suited for the investigation of those effects. By focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that there are manifold sources for ferromagnetism in this material which can …
Puzzling disagreement between photoemission and optical findings in magnetically doped GaN and ZnO is explained within a generalized alloy theory. The obtained results show that the strong coupling between valence-band holes and localized spins gives rise to a mid-gap Zhang-Rice-like state, to a sign reversal of the apparent p-d exchange integral, and to an increase of the band-gap with the magnetic ion concentration.
Spin polarized current is the main ingredient of diluted magnetic oxides due to its potential manipulation in spintronic devices. However, most research has focused on ferromagnetic properties rather than polarization of electric current, because direct measurements were difficult and the origin of spin polarized currents has yet to be fully understood. The method to increase the spin polarized current percentage is beyond practical consideration at the present status. To target this problem, we focus on the role of oxygen vacancies and nano grain size on the spin polarized current, which are …
Recently, diluted Magnetic Semiconductors (DMS) doped with a small concentration of magnetic impurities, especially DMS doped with transition metal, inducing ferromagnetic DMSs have attracted a great interest. Using the Monte Carlo method within the Ising model,we study the magnetic properties of doped Mn ions in semi-conductor for different carrier's concentration. For the case of Zn1-xMnxO, the results of our calculations show the effect of carriers in understanding the existence and the control of the magnetic order. We give also the exact values of carriers' concentration that should be ad…
We report on the magnetic and structural properties of Ar and Mn implanted InAs epitaxial films grown on GaAs (100) by Molecular Beam Epitaxy (MBE) and the effect of Rapid Thermal Annealing (RTA) for 30 seconds at 750C. Channeling Particle Induced X- ray Emission (PIXE) experiments reveal that after Mn implantation almost all Mn atoms are subsbtitutional in the In-site of the InAs lattice, like in a diluted magnetic semiconductor (DMS). All of these samples show diamagnetic behavior. But, after RTA treatment the Mn-InAs films exhibit room-temperature magnetism. According to PIXE measurements t…
In the past decade, room temperature ferromagnetism was often observed in transition metal doped semiconductors, which were claimed as diluted magnetic semiconductors (DMS). Nowadays intensive activities are devoted to clarify wether the observed ferromagnetism stems from carrier mediated magnetic impurities, ferromagnetic precipitates, or spinodal decomposition. In this paper, we have correlated the structural and magnetic properties of transition metal doped ZnO, TiO2, and Si, prepared by ion implantation. Crystalline precipitates, i.e., transition metal (Co, Ni) and Mn-silicide nanocrystals…
We study the possibility of d0 ferromagnetism in the compound MgO doped with nitrogen (N). The Haldane-Anderson impurity model is formulated within the tight-binding approximation for determining the host band-structure and the impurity-host hybridization. Using the quantum Monte Carlo technique, we observe a finite local moment for an N impurity, and long-range ferromagnetic correlations between two N impurities. The ferromagnetic correlations are strongly influenced by the impurity bound state. When the ferromagnetic correlation between a pair of impurities is mapped onto the isotropic Heise…
The magnetic properties of Zn$_{1-x}$Co$_x$O ($x=0.07$ and 0.10) thin films, which were homo-epitaxially grown on a ZnO(0001) substrates with varying relatively high oxygen pressure, have been investigated using x-ray magnetic circular dichroism (XMCD) at Co $2p$ core-level absorption edge. The line shapes of the absorption spectra are the same in all the films and indicate that the Co$^{2+}$ ions substitute for the Zn sites. The magnetic-field and temperature dependences of the XMCD intensity are consistent with the magnetization measurements, indicating that except for Co there are no additi…
