Nitrogen and vacancy clusters in ZnO

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Understanding the interaction of group V impurities with intrinsic defects in ZnO is important for developing p-type material. We have studied N-doped ZnO thin films and N-doped bulk ZnO crystals, with positron annihilation spectroscopy, in contrast to earlier studies that have concentrated on N-implanted ZnO crystals. We show that the introduction of N impurities into ZnO, irrespective of whether it is done during the growth of thin films or bulk crystals or through implantation and subsequent thermal treatments, leads to the formation of stable vacancy clusters and negative ion-type defects. Interestingly, the stability of these vacancy clusters is found almost exclusively for N introduction, whereas single Zn vacancy defects or easily removable vacancy clusters are more typically found for ZnO doped with other impurities.DFG, SFB 787, Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Pressure control of magnetic clusters in strongly inhomogeneous ferromagnetic chalcopyrites

Room-temperature ferromagnetism in Mn-doped chalcopyrites is a desire aspect when applying those materials to spin electronics. However, dominance of high Curie-temperatures due to cluster formation or inhomogeneities limited their consideration. Here we report how an external perturbation such as applied hydrostatic pressure in CdGeP2:Mn induces a two serial magnetic transitions from ferromagnet to non-magnet state at room temperature. This effect is related to the unconventional properties of created MnP magnetic clusters within the host material. Such behavior is also discussed in connection with ab initio density functional calculations, where the structural properties of MnP indicate magnetic transitions as function of pressure as observed experimentally. Our results point out new ways to obtain controlled response of embedded magnetic clusters

The influence of the starch coating on the magnetic properties of nanosized cobalt ferrites obtained by different synthetic methods

To investigate the magnetic behavior of starch-coated cobalt ferrites, well-established synthetic methods, i.e., coprecipitation, mechanochemical, ultrasonically assisted coprecipitation, microemulsion, and microwave-assisted hydrothermal syntheses were chosen for their preparation. The obtained materials had pure single-phase spinel structures. Scanning and transmission electron microscopy analyses revealed that the morphology of the samples is not uniform, and particle aggregation is a dominant process. Fourier transform infrared spectra and thermogravimetric analysis confirmed the presence of starch in all–coated samples. The unusually higher saturation magnetization of starch-coated samples than their as-prepared analogs, obtained by coprecipitation, ultrasonically assisted coprecipitation, and microwave-assisted hydrothermal methods, might be explained by the Ostwald ripening mechanism induced by the coating process. A decrease in magnetization was noticed for the starch-functionalized nanomaterials synthesized by mechanochemical and microemulsion methods, in comparison to their as-prepared analogs, i.e., the size distribution of such nanoparticles is narrow, and the average diameter of the grains is near critical for the Ostwald ripening process.Preprint:[https://doi.org/10.21203/rs.3.rs-27272/v1]Peer-reviewed manuscript: [http://aspace.agrif.bg.ac.rs/handle/123456789/5759