Absence of ferromagnetism in bulk polycrystallineZn0.9Co0.1O

Abstract

The atomic structure and the magnetic properties of 5 and 10 at. % Co-doped ZnO samples prepared by a high-pressure and high-temperature method have been investigated by various techniques, including x-ray diffraction with Rietveld refinements, scanning electron microscopy, high-resolution transmission electron microscopy, nanometer-sized element mapping, x-ray photoelectron spectroscopy, near-edge x-ray absorption fine structure, and extended x-ray absorption fine structure and magnetization measurements. It is found that Co ions with a valence of 2+ substitute Zn ions in the wurtzite ZnO structure. No metallic or oxidic Co-rich clusters were detected in the samples. If Co 2+ ions substitute Zn 2+ ions, no intrinsic ferromagnetism is observed in ZnO at doping levels up to 10 at. % Co even down to 5 K. A paramagnetic behavior with partially antiferromagnetic interactions is observed. Thus, in bulk Co-doped ZnO system any observation of ferromagnetism is probably due to small clusters of second phase materials. However, in thin films the situation might be more complex, since other extrinsic influences, such as strain or proximity effects, may modify the electronic and magnetic properties.

Intense violet–blue emission and paramagnetism of nanocrystalline Gd3+ doped ZnO ceramics

“…Paramagnetism is expected to arise from the exchange interaction of magnetic moments mediated by the defects in doped nanoceramics. Similar paramagnetic behavior was reported for transition metal doped ZnO and SnO 2 [29][30][31][32][33]. Adhikari et al [34] observed the absence of ferromagnetic and antiferromagnetic ordering in Gd doped SnO 2 nanoparticles.…”

Cobalt substituted ZnO thin films: a potential candidate for spintronics

“…In one case, giant magnetic moment of 6.1 l B /Co has been reported in the insulating ZnO:Co thin films [6], whereas in some other cases, RTFM is either claimed to be carrier mediated [7,8] or attributed to the presence of Co clusters [13][14][15]. Contrary to the above, ZnO:Co films are reported to be paramagnetic [16][17][18].…”

“…The RTFM observed in these oxide semiconductors has opened a new window for potential application of these materials in realization of spintronic devices. However, the experimental findings on the room temperature ferromagnetic ordering in transition metal doped oxide semiconductors reported so far are at large variance and the nature (i.e., extrinsic or intrinsic) and origin of room temperature ferromagnetism is yet far from being clearly understood [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. In our earlier study on chemically synthesized nanocrystalline ZnO:Co powder samples [3][4][5], we have established the presence of RTFM in these samples as an intrinsic effect.…”

Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory

“…12 A wide range of contradictory experimental results, debating the success [13][14][15][16][17][18] versus failure [19][20][21][22][23] of obtaining a T c above room temperature based on such dilute magnetic oxide systems, have injected much excitement about the origin of ferromagnetism in these systems. Among all these systems, ZnO belongs to the list of the most suitable candidates for spintronics application due to its abundance and environment-friendly nature and also due to its potential as a suitable optoelectronic material with a wide band gap ͑ϳ3.3 eV͒ and high exciton binding energy of 60 meV.…”