Structural and magnetic properties of ZnO:TM (TM: Co,Mn) nanopowders

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...

We report here on the magnetic properties of ZnO:Mn and ZnO:Co doped nanoparticles. We have found that the ferromagnetism of ZnO:Mn can be switched on and off by consecutive low-temperature annealings in O2 and N2 respectively, while the opposite phenomenology was observed for ZnO:Co. These results suggest that different defects (presumably n-type for ZnO:Co and p-type for ZnO:Mn) are required to induce a ferromagnetic coupling in each case. We will argue that ferromagnetism ...

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 si...

We synthesized pure and Co-doped (6.25 12.5 at.) ZrO$_2$ nanopowders in order to study their magnetic properties.We analyzed magnetic behavior as a function of the amount of Co and the oxygenation, which was controlled by low pressure thermal treatments. As prepared pure and Co-doped samples are diamagnetic and paramagnetic respectively. Ferromagnetism can be induced by performing low pressure thermal treatments, which becomes stronger as the dwell time of the thermal treatme...

ZnO nanoparticles with Wurtzite structure were prepared by chemical methods at low temperature in aqueous solution. Nanoparticles are in the range from about 10 to 30 nm. Ferromagnetic properties were observed from 2 K to room temperature and above. Magnetization vs temperature, M(T) and isothermal measurements M(H) were determined. The coercive field clearly shows ferromagnetism above room temperature. The chemical synthesis, structural defects in the bulk related to oxygen ...

This letter reports on the magnetic properties of Ti1-xCoxO2 anatase phase nanopowders with different Co contents. It is shown that oxygen vacancies play a fundamental role in promoting the long-range ferromagnetic order in the material studied, in addition to the transition-metal doping. Furthermore, the results allow ruling out the premise of a strict connection between Co clustering and the ferromagnetism observed in the Co:TiO2 anatase system.

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 ...

Zn doped Mn ferrites nanoparticles were fabricated by using Co-precipitation. Variation in structure, magnetic and optical properties of MnZn ferrites has been discussed. First of all, samples were synthesized, annealed at different temperatures and then characterized. The as-synthesized and annealed samples were investigated by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive spectroscopy (EDX), Ultra Violet visible spectrometry (Uv-Vis spectrom...

The nature of the often reported room temperature ferromagnetism in transition metal doped oxides is still a matter of huge debate. Herein we report on room temperature ferromagnetism in high quality Co-doped ZnO (Zn1-xCoxO) bulk samples synthesized via standard solid-state reaction route. Reference paramagnetic Co-doped ZnO samples with low level of structural defects are subjected to heat treatments in a reductive atmosphere in order to introduce defects in the samples in a...

We discuss the properties of semiconducting bulk ZnO when substituted with the magnetic transition metal ions Mn and Co, with substituent fraction ranging from $x$ = 0.02 to $x$ = 0.15. The magnetic properties were measured as a function of magnetic field and temperature and we find no evidence for magnetic ordering in these systems down to $T$ = 2 K. The magnetization can be fit by the sum of a Curie-Weiss term with a Weiss temperature of $\Theta\gg$100 K and a Curie term. W...