Fe-implanted ZnO: Magnetic precipitates versus dilution

Abstract

Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors argue that the observed ferromagnetism stems from ferromagnetic precipitates or spinodal decomposition rather than from carrier mediated magnetic impurities, as required for a diluted magnetic semiconductor. In the present paper we answer this question for Fe-implanted ZnO single crystals comprehensively. Different implantation fluences and temperatures and post-implantation annealing temperatures have been chosen in order to evaluate the structural and magnetic properties over a wide range of parameters. Three different regimes with respect to the Fe concentration and the process temperature are found: 1) Disperse Fe${}^{2+}$ and Fe${}^{3+}$ at low Fe concentrations and low processing temperatures, 2) FeZn${}_2$O${}_4$ at very high processing temperatures and 3) an intermediate regime with a co-existence of metallic Fe (Fe${}^0$) and ionic Fe (Fe${}^{2+}$ and Fe${}^{3+}$). Ferromagnetism is only observed in the latter two cases, where inverted ZnFe${}_2$O${}_4$ and $\alpha$-Fe nanocrystals are the origin of the observed ferromagnetic behavior, respectively. The ionic Fe in the last case could contribute to a carrier mediated coupling. However, their separation is too large to couple ferromagnetically due to the lack of p-type carrier. For comparison investigations of Fe-implanted epitaxial ZnO thin films are presented.

14 pages, 17 figures

References in corpus (3)

• Crystalline Ni nanoparticles as the origin of ferromagnetism in Ni implanted ZnO crystals
• Crystallographically oriented magnetic ZnFe2O4 nanoparticles synthesized by Fe implantation into ZnO
• A Comment on "Memory Effects in an Interacting Magnetic Nanoparticle System"

Cited by in corpus (4)

• Crystallographically oriented Co and Ni nanocrystals inside ZnO formed by ion implantation and postannealing
• Non-DMS related ferromagnetism in transition metal doped zinc oxide
• Ferromagnetic transition metal implanted ZnO: a diluted magnetic semiconductor?
• Spinel ferrite nanocrystals embedded inside ZnO: magnetic, electronic and magneto-transport properties