Coexistence of magnetic states and metamagnetism in the Bi_2-xCr_xSe₃ topological insulators

The dichalcogenide Bi2Te3 and Bi2Se3 crystals belong to the 3D topological insulator family. Doping the crystals with magnetic ions can break the time-reversal symmetry and open an energy gap at surface Dirac points. This provides the opportunity of manipulating the surface transport and observing the anomalous quantum Hall effect. We studied magnetic properties of three single-crystalline Bi2-xCrxSe3 samples with x = 0.01, 0.03, and 0.06 within a temperature range from 2 to 300 K. The dc magnetization revealed the coexistence of antiferromagnetic and ferromagnetic ordering and paramagnetism. Their significance depends on the chromium content. The ferromagnetic phase transition was suppressed by high enough magnetic field. The antiferromagnetic transition near 80 K did not shift visibly up to 50 kOe. The Curie-Weiss law approximation gave the effective magnetic moment μ_eff close to 4.9 μB, which corresponds to divalent chromium ions. Metamagnetic phenomena were found for crystals with x = 0.03 and 0.06.