Using x-ray diffraction to identify precipitates in transition metal doped semiconductors

TL;DR

This paper uses x-ray diffraction to identify crystalline precipitates in transition metal doped semiconductors, revealing limitations of XRD in detecting certain nanocrystals responsible for ferromagnetism.

Contribution

It correlates structural and magnetic properties in doped semiconductors and highlights the challenge of detecting nanocrystals with conventional XRD.

Findings

Crystalline precipitates cause ferromagnetism in doped semiconductors.

Orientation of nanocrystals can prevent detection by XRD.

XRD limitations can lead to misinterpretation of magnetic origins.

Abstract

In the past decade, room temperature ferromagnetism was often observed in transition metal doped semiconductors, which were claimed as diluted magnetic semiconductors (DMS). Nowadays intensive activities are devoted to clarify wether the observed ferromagnetism stems from carrier mediated magnetic impurities, ferromagnetic precipitates, or spinodal decomposition. In this paper, we have correlated the structural and magnetic properties of transition metal doped ZnO, TiO2, and Si, prepared by ion implantation. Crystalline precipitates, i.e., transition metal (Co, Ni) and Mn-silicide nanocrystals, are responsible for the magnetism. Additionally due to their orientation nature with respect to the host, these nanocrystals in some cases are not detectable by conventional x-ray diffraction (XRD). This nature results in the pitfall of using XRD to exclude magnetic precipitates in DMS materials.