Electron Spin-Lattice Relaxation of Fe³⁺ Ion in Rutile

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Detailed measurements of the electron spin-lattice relaxation time T₁ of Fe³⁺ ion in rutile were carried out from 1.7 K up to 30 K by the pulse saturation recovery method. It was found that below ∼15 K the relaxation was mainly due to the direct process, while above ∼15 K the Raman process dominated. The temperature dependence of the direct relaxation rate was found to be dependent on the kind of transition. At 4.2 K, the anisotropy of the direct relaxation rate was clearly observed. In order to explain these experimental results, computation of T₁ using magnetoelastic coupling tensor (G tensor), in which the elastic anisotropy of the lattice was taken into account, was carried out and the coupling of Fe³⁺ ion with lattice strain is discussed. For the Raman process, the relaxation rate was found to be proportional to T⁷ and the anisotropy of a factor of around 3 was observed.