We present a detailed investigation of the magnetic and structural properties of magnetically doped 3D topological insulator Bi2Se3. From muon spin relaxation measurements in zero magnetic field, we find that even 5% Fe doping on the Bi site turns th
e full volume of the sample magnetic at temperatures as high as ~250 K. This is also confirmed by magnetization measurements. Two magnetic phases are identified; the first is observed between ~10-250 K while the second appears below ~10 K. These cannot be attributed to impurity phases in the samples. We discuss the nature and details of the observed magnetism and its dependence on doping level.
Inelastic neutron scattering was employed to study the magnetic excitations of Mn3+ dimers in LaMn0.1Ga0.9O3. The nearest-neighbor interaction of Mn3+ ions is ferromagnetic in the basal (a,b)-plane, but antiferromagnetic along the c-direction, thus t
wo different types of dimer excitations are simultaneously present in the experiments. From the observed energy spectra we derive Heisenberg-type exchange interactions Jab=0.210(4) meV and Jc=-0.285(5) meV as well as an axial anisotropy parameter D=0.036(6) meV. These parameters considerably differ from those derived for the isostructural parent compound LaMnO3 due to structural effects.
