Origin of ferromagnetism in Cu-doped ZnO

Abstract

It is widely reported during last decade on the observation of room temperature ferromagnetism (RTFM) in doped ZnO and other transition metal oxides. However, the origin of RTFM is not understood and highly debated. While investigating the origin of RTFM, magnetic ion doped oxides should be excluded because it is not yet settled whether RTFM is intrinsic or due to the magnetic ion cluster in ZnO. Hence, it is desirable to investigate the origin of RTFM in non-magnetic ion doped ZnO and Cu-doped ZnO will be most suitable for this purpose. The important features of ferromagnetism observed in doped ZnO are (i) observation of RTFM at a doping concentration much below than the percolation threshold of wurtzite ZnO, (ii) temperature independence of magnetization and (iii) almost anhysteretic magnetization curve. We show that all these features of ferromagnetism in ZnO are due to overlapping of bound magnetic polarons (BMPs) which are created by exchange interaction between the spin of Cu 2+ ion and spin of the localized hole due to zinc vacancy . Both the experimental and theoretical investigation show that the exchange interaction between Cu 2+ -Cu 2+ ions mediated by is responsible for RTFM in Cu-doped ZnO.

Magnetic Response Dependence of ZnO Based Thin Films on Ag Doping and Processing Architecture

“…Figure 6 shows the EPR measurements for the different films studied in this work. It can be observed a remarkable resonance peak at around , disclosing the Zn vacancy in the films [ 8 , 30 ]. The pure ZnO films show a low-intensity absorption peak, while the 10 at.% Ag-ZnO films show a larger absorption peak intensity, which increases considerably, independently of the annealing temperature.…”

“…The pure ZnO films show a low-intensity absorption peak, while the 10 at.% Ag-ZnO films show a larger absorption peak intensity, which increases considerably, independently of the annealing temperature. The spin concentration (N) can be estimated through the relation [8] N ∝ I(∆H pp ) 2 , where I is the intensity, and ∆H pp is the peak-to-peak width of the EPR spectrum. Figure 6d shows the EPR results of the samples showing a considerable enhancement in the spin concentration when Ag is inserted in the structure.…”

“…In addition, distinct authors related the RTFM properties with structural defects, in particular when metal dopants are employed [5,7]. However, some recent works have brought to light the RTFM in non-magnetic metal-doped ZnO, such as ZnO:Cu [8] and ZnO:Ag [9]. In these systems, the existence of the RTFM is associated with BMPs [5] and defects due to Zn or O vacancies.…”

“…However, some recent works have brought to light the RTFM in non-magnetic metal-doped ZnO, such as ZnO:Cu [ 8 ] and ZnO:Ag [ 9 ]. In these systems, the existence of the RTFM is associated with BMPs [ 5 ] and defects due to Zn or O vacancies.…”

“…In this context, the ZnO and metal-doped ZnO have been explored in distinct samples geometries. For nanoparticles (powder), the magnetic properties are studied in a wide range of temperatures, including room temperature [ 1 , 8 , 9 , 10 , 11 ]. On the other hand, considering the film geometry, the deposition technique, the deposition parameters and thicknesses of the films can be taken to advantage to change not just the structural properties of the ZnO and/or metal-doped ZnO, but also the magnetic properties, leading to interesting multifunctional materials for technological applications [ 7 , 12 , 13 ].…”