Origin and control of high-temperature ferromagnetism in semiconductors

TL;DR

This paper reveals that high-temperature ferromagnetism in certain semiconductors arises from Cr-rich nanocrystals whose formation can be controlled during epitaxy, offering new insights and fabrication methods for magnetic semiconductor systems.

Contribution

It demonstrates that ferromagnetism in (Zn,Cr)Te is due to controllable nanocrystal formation influenced by the charge state of Cr ions during growth.

Findings

Ferromagnetism is dominated by Cr-rich nanocrystals.

Nanocrystal formation can be manipulated via charge state control.

Provides a bottom-up method for nanostructure fabrication.

Abstract

The extensive experimental and computational search for multifunctional materials has resulted in the development of semiconductor and oxide systems, such as (Ga,Mn)N, (Zn,Cr)Te, and HfO2, which exhibit surprisingly stable ferromagnetic signatures despite having a small or nominally zero concentration of magnetic elements. Here, we show that the ferromagnetism of (Zn,Cr)Te, and the associated magnetooptical and magnetotransport functionalities, are dominated by the formation of Cr-rich (Zn,Cr)Te metallic nanocrystals embedded in the Cr-poor (Zn,Cr)Te matrix. Importantly, the formation of these nanocrystals can be controlled by manipulating the charge state of Cr ions during the epitaxy. The findings provide insight into the origin of ferromagnetism in a broad range of semiconductors and oxides, and indicate possible functionalities of these composite systems. Furthermore, they demonstrate a bottom-up method for self-organized nanostructure fabrication that is applicable to any system in which the charge state of a constituent depends on the Fermi-level position in the host semiconductor.