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 Cu2+ ion and spin of the localized hole due to zinc vacancy ({V}_{Zn}). Both the experimental and theoretical investigation show that the exchange interaction between Cu2+-Cu2+ ions mediated by {V}_{Zn} is responsible for RTFM in Cu-doped ZnO.
Highlights
Dilute magnetic oxides (DMOs) and dilute magnetic semiconductors (DMSs) are arguably the most interesting and intriguing magnetic materials and room temperature ferromagnetism (RTFM) in these materials is the most puzzling problem in contemporary solid state physics[1,2,3,4,5]
It is widely accepted that the ferromagnetic order depends on the presence of defect and this leads to results based on local probes like x-ray magnetic circular dichroism and x-ray absorption near edge spectroscopy doubtful[6,21,22,23,24]
(4) The ubiquitous feature like temperature independent magnetization has been observed in many reports, but no explanation has been provided till date and this raises a doubt whether the proposed exchange mechanism is relevant[30,31]
Summary
Dilute magnetic oxides (DMOs) and dilute magnetic semiconductors (DMSs) are arguably the most interesting and intriguing magnetic materials and room temperature ferromagnetism (RTFM) in these materials is the most puzzling problem in contemporary solid state physics[1,2,3,4,5]. The original idea of obtaining DMOs was to dope with only magnetic ions such as Mn, Fe, Co, Ni similar in line with studies on magnetic ions doped III–V and II–VI semiconductors[13,14,15,16] This idea was seriously challenged by raising a doubt in different experimental observations whether the RTFM is at all intrinsic[17,18,19,20]. (4) The ubiquitous feature like temperature independent magnetization has been observed in many reports, but no explanation has been provided till date and this raises a doubt whether the proposed exchange mechanism is relevant.
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