Defect-induced magnetism in SiC: Interplay between ferromagnetism and paramagnetism

TL;DR

This study investigates defect-induced magnetism in SiC, revealing that while defects cause a large paramagnetic response, the ferromagnetic signal remains weak and is primarily a local effect, explaining previous controversies.

Contribution

The paper combines experimental neutron irradiation and first-principles calculations to clarify the nature and limitations of defect-induced ferromagnetism in SiC.

Findings

Large paramagnetic component scales with defect concentration

Weak ferromagnetic signal appears only at low fluence or after annealing

Defects favor spin polarization but hinder magnetic interaction

Abstract

Defect-induced ferromagnetism has triggered a lot of investigations and controversies. The major issue is that the induced ferromagnetic signal is so weak that it can sufficiently be accounted for by trace contamination. To resolve this issue, we studied the variation of the magnetic properties of SiC after neutron irradiation with fluence covering four orders of magnitude. A large paramagnetic component has been induced and scales up with defect concentration, which can be well accounted for by uncoupled divacancies. However, the ferromagnetic contribution is still weak and only appears in the low fluence range of neutrons or after annealing treatments. First-principles calculations hint towards a mutually exclusive role of the concentration of defects: Defects favor spin polarization at the expense of magnetic interaction. Combining both experimental and first-principles calculation results, the defect-induced ferromagnetism can be understood as a local effect which cannot be scaled up with the volume. Therefore, our investigation answers the long-standing question why the defect-induced ferromagnetic signal is weak.