Absence of ferromagnetic order in high quality bulk Co-doped ZnO samples

Abstract

Bulk Zn1−xCoxO samples were synthesized via standard solid-state reaction route with different Co molar concentrations up to 21%. A detailed microstructural analysis was carried out to investigate alternative sources of ferromagnetism, such as secondary phases and nanocrystals embedded in the bulk material. Conjugating different techniques we confirmed the Zn replacement by Co ions in the wurtzite ZnO structure, which retains, however, a high crystalline quality. No segregated secondary phases neither Co-rich nanocrystals were detected. Superconducting quantum interference device magnetometry demonstrates a paramagnetic Curie–Weiss behavior with antiferromagnetic interactions. We discuss the observed room temperature paramagnetism of our samples considering the current models for the magnetic properties of diluted magnetic semiconductors.

Enhancement in the structure quality of ZnO nanorods by diluted Co dopants: Analyses via optical second harmonic generation

“…There are three peaks corresponding to ZnO: a strong E 2 (H) (high) mode at 438 cm À1 associated with A 1 (TO) mode at 380 cm À1 , and E 2H -E 2L second order mode at 330 cm À1 . 28,31 These are all characteristic signatures of ZnO. There is also a broad band from 500 cm À1 to 600 cm À1 having two distinct peaks at 550 cm À1 and 580 cm À1 corresponding to AM (additional mode and cannot be attributed to ZnO mode) and A 1 (LO) 31 mode, respectively.…”

“…28,31 These are all characteristic signatures of ZnO. There is also a broad band from 500 cm À1 to 600 cm À1 having two distinct peaks at 550 cm À1 and 580 cm À1 corresponding to AM (additional mode and cannot be attributed to ZnO mode) and A 1 (LO) 31 mode, respectively. The presence of an excess concentration of Co either inside the ZnO lattice in the form of doping or in the growth solution introduce disorder in the ZnO crystal and subsequently generate strain in the ZnO lattice.…”

“…Although there are several published reports related to Co doped ZnO, 21-32 the research is limited to the study of magnetic property, [29][30][31][32] such as ferromagnetism at room temperature. Effect of Co doping on the surface properties and crystalline quality of ZnO have rarely been addressed.…”

CoO doping effects on the ZnO films through EBPDV technique

“…It is important to note that the temperature used in this work to obtain the ZnO phase is low compared with conventional ZnO powders, where phase formation and sintering of the particles occurs above 1400 • C [21]. The powders are crystalline at ZnO hexagonal form, indexed by JCPDS card No.…”

“…Much attention has been directed to ZnO doped with transition-metal ions, such as Co ions [21]. This diluted magnetic semiconductor has proposed as an alternative…”