Structural imperfections and attendant localized/itinerant ferromagnetism in ZnO nanoparticles

Abstract

Using synchrotron-based x-ray magnetic spectroscopy, we report a study focusing on the local symmetry of Cu-dopant and resultant structural imperfections in mediating Cu-doped ZnO nanoparticles' ferromagnetism (FM). Prepared by an antisolvent method, Cu appeared to preferably populate on the basal plane of ZnO with a local symmetry of [CuO 4 ]. This unique symmetry was antiferromagnetic in nature, while electronically and structurally coupled to surrounded oxygen vacancies (V o) that yielded a localized FM, because of a strong dependency on the number/location of the [CuO 4 ] symmetry. Surprisingly, the FM of undoped but oxygen-deficient ZnO appeared to be more itinerant and long-range, where V o percolated the FM effectively and isotropically through oxygen's delocalized orbital. By adopting the approach of structural imperfection, this study clearly identifies V o 's (defect's) true characters in mediating the FM of magnetic semiconductors which has been thought of as a long-standing debate, and thus provides a different thinking about the traditional extrinsic ferromagnetic-tuning in the semiconductors. It even illuminates recent research concerning the intrinsic FM of low-dimensional systems that contain defects but non-magnetic elements.

Electronic structure and magnetic behaviors of exfoliated MoS2 nanosheets

“…The peaks 'a 1 ' and 'a 2 ' are attributed to the absorption of 'S-atoms' in the −2 oxidation state (S 2 − ) and the weak peak 'b' is assigned to 'S-atoms' in the +6 oxidation state (negligible) [50] appearing at approximately ~9 eV higher energy. A double structure shoulder peak, at the position (~2468.4 eV and ~2466.3 eV) just below peak 'a 1 ', imply fingerprints the presence of sulphur vacancy (V S ) that may play as an electron donor in the MoS 2 electrical properties [51,52] similar to oxygen defects [53]. Sulphur vacancy at the edge of nanosheets gives rise to magnetic edge moment this is due to edge spins at the nanosheets [5] that responsible for the RT-FM observed in a few layered MoS 2 nanosheets.…”

Significant room-temperature ferromagnetism in porous ZnO films: The role of oxygen vacancies

“…These findings challenged the understanding of magnetism, and led researchers to discuss the role of defects in controlling the magnetism of semiconducting and insulating oxides. Many experiments have shown that there is a connection between room-temperature magnetic order and various defects such as oxygen vacancies [2,4,[11][12][13], cation vacancies [14,15], cation interstitial ions [16], or minor hydrogen contamination [17], even in the absence of magnetic dopants [18]. Although there is a consensus that the ferromagnetism is related to native defects, considerable controversy still exists regarding the origin of the magnetism.…”

“…As an example, Liu et al [24] showed that ab initio calculations yield a net moment of 0.98 B per single oxygen vacancy. However, the saturation moment at room temperature in doped ZnO is only a few emu/cm 3 , too small to be of practical use [10][11][12][24][25][26]. Therefore, it remains an interesting question as to how defects induce the RTFM of undoped ZnO films and how to devise ways to manipulate this RTFM.…”

Lattice Defects Induce Multiferroic Responses in Ce, La‐Substituted BaFe0.01Ti0.99O3 Nanostructures

“…An upward curvature observed in the M – T curve suggests a Curie–Weiss like behavior. It is a phenomenon which is attributed to a short‐range ferromagnetism, or a spin‐cluster character within a matrix of spin disorder . This type of behavior exists due to an increase in competition between AFM and ferromagnetic state .…”