Evidence for high-Tcferromagnetism inZnx(ZnO)

Abstract

Zn x ͑ZnO͒ 1−x granular films with nominal atomic concentration of x =0ϳ 1 were prepared by magnetron cosputtering method. Ferromagnetism is observed in films with 0.04Յ x Ͻ 0.60. The room-temperature saturated magnetization increases with increasing x and reaches its maximum value of about 3.34 emu/cc at x = 0.31. The temperature-dependent magnetization curve could be fitted within the framework of Stoner model in a large temperature range from 50 to 800 K. The obtained Curie temperature is higher than 500°C. It is found that the main point defects in ZnO are Zn interstatial and oxygen vacancy. Room-temperature photoluminescence analysis and high-temperature x-ray diffraction measurement show conclusive evidence that the native point defect of Zn interstitial plays a crucial role in the observed magnetic behaviors. By implicating the shallow donor related carriers and/or extending the charge-transfer mechanism to metal/semiconductor heterostructure, the result could be qualitatively explained based on the Stoner theory of band magnetism. These findings may help to get further insight into the ferromagnetic origin in nonmagnetic ion doped ZnO systems.

Structural, optical, XPS and magnetic properties of Zn particles capped by ZnO nanoparticles

“…It is worth pointing out that the maximum magnetization of the nanoparticles is obviously independent from their average particle size and ZnO content. The highest room temperature saturation magnetization obtained in this study was 0.27 emu/g (Z17), which was found to be a higher value in comparison to the literature one (from 6 × 10 -4 to 6 × 10 -3 emu/g) for non-doped ZnO nanoparticles of various sizes in the range of 4-500 nm [19,22,26,39,45,[73][74][75]. Higher values of up to 0.62 emu/g were reported for the ZnO nanofilms, but significant error was obviously possible in the thin films masses determination.…”

“…The existance of RFTM in the undoped ZnO stimulated discussion about the role of intrinsic defects in this phenomenon. For the Zn-O system, also known as a pristine oxide, it was shown that defects, such as Zn and O vacancies [16][17][18][19][20][21], Zn interstitials [22], grain boundaries [23] and lattice distortions [24], might contribute to the development of RTFM. If all these defects are indeed responsible for the ferromagnetism in thin films and nanoparticles, they should be thermodynamically stable at least to room temperature, and magnetic exchange interaction between them should be strong enough for the existence of ferromagnetism to be feasible [25].…”

Carbon doped ZnO: Synthesis, characterization and interpretation

“…This shows how subtle the search for magnetism in these materials can be and the role of intrinsic or extrinsic defects, if any, has not been thoroughly established. Added to this, there are other claims of RT ferromagnetism in pure ZnO induced from intrinsic defects [16][17][18][19][20][21]. So it is essential that one pays special care for characterizing the samples in order to avoid any biased conclusions.…”

Synchrotron photoemission study of (Zn,Co)O films with uniform Co distribution

“…Diluted magnetic semiconductors (DMS) have been recently intensively studied for spintronic applications (Bonanni and Dietl, 2010;Ueda et al, 2001) and ZnCoO focuses a great part of attention here (Khare et al, 2006;Assadi et al, 2009;De Carvalho et al, 2010;Zhang et al, 2009;Gilliland et al, 2010). This is possible because high cobalt concentration in ZnO is expected due to the nearly identical Co 2 þ and Zn 2 þ ionic radii.…”