Study of the structural, electric and magnetic properties of Mn-doped Bi2Te3 single crystals

Breaking the time reversal symmetry of a topological insulator, for example by the presence of magnetic ions, is a prerequisite for spin-based electronic applications in the future. In this regard Mn-doped Bi2Te3 is a prototypical example that merits a systematic investigation of its magnetic properties. Unfortunately, Mn doping is challenging in many host materials-resulting in structural or chemical inhomogeneities affecting the magnetic properties. Here, we present a systematic study of the structural, magnetic and magnetotransport properties of Mn-doped Bi2Te3 single crystals using complimentary experimental techniques. These materials exhibit a ferromagnetic phase that is very sensitive to the structural details, with T-C varying between 9 and 13K (bulk values) and a saturation moment that reaches 4.4(5) mu(B) per Mn in the ordered phase. Muon spin rotation suggests that the magnetism is homogeneous throughout the sample. Furthermore, torque measurements in fields up to 33 T reveal an easy axis magnetic anisotropy perpendicular to the ab-plane. The electrical transport data show an anomaly around T-C that is easily suppressed by an applied magnetic field, and also anisotropic behavior due to the spin-dependent scattering in relation to the alignment of the Mn magnetic moment. Hall measurements on different crystals established that these systems are n-doped with carrier concentrations of similar to 0.5-3.0 x 10(20) cm(-3). X-ray magnetic circular dichroism (XMCD) at the Mn L-2,L-3 edge at 1.8K reveals a large spin magnetic moment of 4.3(3) mu(B)/Mn, and a small orbital magnetic moment of 0.18(2) mu(B)/Mn. The results also indicate a ground state of mixed d(4)-d(5)-d(6) character of a localized electronic nature, similar to the diluted ferromagnetic semiconductor Ga1-xMnxAs. XMCD measurements in a field of 6 T give a transition point at T approximate to 16 K, which is ascribed to short range magnetic order induced by the magnetic field. In the ferromagnetic state the easy direction of magnetization is along the c-axis, in agreement with bulk magnetization measurements. This could lead to gap opening at the Dirac point, providing a means to control the surface electric transport, which is of great importance for applications.