Characterizing Magnetism in Magnetically Doped Topological Insulators

Topological insulators are materials with non-trivial topological order, which behave as conductors on the surface but insulators in their interiors. Some previous studies on magnetically doped topological insulators have observes ferromagnetic behavior while others have observed superparamagnetic behavior. This study was conducted to characterize the magnetic behavior of V-(Bi,Sb)₂Te₃ and V-Sb₂Te₃ and determine how this varies with thickness, method of doping, and the addition of bismuth. A superconducting quantum interference device magnetometer was used to measure the magnetic moment of V-(Bi,Sb)₂Te₃ and V-Sb₂Te₃ as a function of temperature and field. From the temperature-dependent data, the samples of V-(Bi,Sb)₂Te₃ had lower Curie temperatures than those of V-Sb₂Te₃, with the thin samples of V-(Bi,Sb)₂Te₃ also having somewhat lower Curie temperatures than the thicker samples of V-(Bi,Sb)₂Te₃. From the field-dependent data, two-phase switching behavior was observed below the Curie temperatures of the samples of V-Sb₂Te₃ and delta-doped V-(Bi,Sb)₂Te₃. It is apparent that there are multiple factors that influence the magnetic behavior of topological insulators.