Hyperfine Structure and g-Tensor Anisotropy of the Paramagnetic Resonances of Manganese in TiO2

Several characteristic resonances of the paramagnetic spectrum of a manganese‐doped TiO₂ single crystal in its rutile structure were measured with high precision in order to improve the accuracy of the spin Hamiltonian parameters. The measurements were performed at room temperature and at X‐band frequencies. Especially, the anisotropy of the g tensor and that of the A tensor were evaluated using the resonance data measured at orientations of the magnetic field parallel to the three magnetic axes of the rutile crystal. The hyperfine structure patterns of the manganese resonances are discussed qualitatively for various crystal orientations; two properly selected |Δm_I|=1 transitions were used to estimate the upper limit of the quadrupole‐term parameters of the spin Hamiltonian. The paramagnetic resonances of manganese in rutile were also investigated at liquid nitrogen temperature and at X‐band frequencies. Aside from a spectrum that is very similar to the spectrum already observed at room temperature and assigned to tetravalent manganese atoms, having a spin value of $\mathrm{S=}\frac{3}{2}$ , additional manganese resonances of strong intensity were observed. Though it is very likely that these resonances can be attributed to manganese atoms of a different valence state, the paramagnetic data at X‐band frequencies are insufficient to determine the origin of these resonances unambiguously.