Ferromagnetism on a paramagnetic host background in cobalt-doped Bi₂Se₃ topological insulator

Cobalt-doped Bi₂Se₃ topological insulators have been grown though melt-grown reaction. The Bi₂Se₃ matrix is diamagnetic and doped sample is a superposition of ferromagnetism (FM) and paramagnetism (PM) behavior at low temperature. The values of M_Smol, H_c, and M_r increase as the Co concentration increases. Two possible explanations have been proposed for the origin of ferromagnetism in Co-doped Bi₂Se₃. One is the magnetic ordering from nanoclusters of Co-Se compound in the crystals, and the other is Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between magnetic impurities.