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.
The non-trivial topology of electronic bands in Weyl semimetals originates from band inversion due to strong spin–orbit coupling. The Weyl semimetals have pairs of Weyl gap-less nodes in the bulk Brillouin zone. The tungsten ditelluride WTe2 likely belongs to type II Weyl semimetals. Doping WTe2 with magnetic ions could induce magnetic ordering in this crystal, which provides prospects for practical applications. We studied the magnetic properties of the iron-doped single crystals Fe0.03W0.97Te2, annealed and unannealed, in comparison with the undoped WTe2. Measurements of the dc magnetization were carried out from 1.8 to 400 K. We revealed pronounced ferromagnetic ordering that was affected by annealing. Anomalies associated with antiferromagnetism and paramagnetism were also found. The magnetic order was suppressed by a field of 60 kOe. The rise in susceptibility with increasing temperature was observed at high temperatures in all samples and was treated using a model developed for Weyl semimetals. The Curie–Weiss law fit at 60 kOe showed that the effective magnetic moment was close to that of Fe2+. Metamagnetism was demonstrated for the unannealed doped WTe2 crystal. The data for the heat capacity of the iron-doped sample agreed with results for the undoped WTe2.
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