Koichi Mizushima

Energy Levels of Iron Group Impurities in TiO2

By changing the location of Fermi level of TiO 2 by lithium doping, ESR signals of some transition metal impurities in this crystal were pursued. The conclusions are: the Cr 3+ , Mn 4+ and Fe 3+ levels are near or overlapped with the valence band, the V 3+ , Mn 2+ and Fe 2+ levels are near the conduction band, the Cr 2+ level is above the bottom of the conduction band, the Mn 3+ and V 4+ levels are near the center of the band gap, and consequently the energy level separation between Mn 2+ and Mn 3+ and that of V 3+ and V 4+ are small ( i. e. less than 2 eV). The calculated level structures with the aid of these experimental results are related to the metallic and insulative nature of magnetic oxides, in general.

Dielectric Properties of the Low Temperature Phase of Fe3O4 at a Microwave Frequency

Conductivities and dielectric constants of the low temperature phase of Fe 3 O 4 at a microwave frequency were measured by a cavity perturbation method. The conductivity in the c direction is about three times as large as that in the a and b directions. From the result it is expected that for an ion on B site the nearest neighbour ions of the same valency are in the [±1, 0, 1], [0, ±1, 1] directions which have components along the c direction.

Effective In-Plane Anisotropy Field in αFe2O3

From measurement of magnetic resonance under forced strain, two magnetoelastic coupling constants of αFe 2 O 3 were obtained separately. The trigonal magnetoelastic coupling constant B 15 is dominant and it explains quantitatively the in-plane anisotropy field in the (111) plane observed in resonance experiment, confirming the theory of the coupling proposed by Iida and Tasaki formerly.

Temperature Dependence of EPR of Mn4+ and Cr3+ in Rutile

The spin lattice relaxation time and the EPR parameters g , D and E of Mn 4+ and Cr 3+ in rutile have been measured from 78 K up to 470 K. They show a stronger temperature dependence for Mn 4+ than for Cr 3+ , being against the conventional theoretical predictions. We presume that it comes from the difference in the bonding character of these ions. It is expected that the closer location of the energy levels of the empty orbitals of Mn 4+ is favorable for the force constant between Mn 4+ and O 2- to become smaller than that between Cr 3+ and O 2- .

Electron Spin-Lattice Relaxation of Fe3+ Ion in Rutile

Detailed measurements of the electron spin-lattice relaxation time T 1 of Fe 3+ 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 T 1 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 Fe 3+ ion with lattice strain is discussed. For the Raman process, the relaxation rate was found to be proportional to T 7 and the anisotropy of a factor of around 3 was observed.

Electron Spin-Lattice Relaxation of Mn4+ and Cr3+ Ions in Rutile

The electron spin-lattice relaxation time T 1 of isoelectronic Mn 4+ and Cr 3+ ions in rutile was measured from 1.7 K up to 35 K by the pulse saturation recovery method. It was found that, in the low temperature region, where relaxation was mainly due to the direct process, the relaxation rates of both Mn 4+ and Cr 3+ ions were in the same order of magnitude. On the other hand, above 15 ∼20 K where relaxation was mainly due to the Raman process, the relaxation rate of Mn 4+ ion was found to increase more rapidly than that of Cr 3+ ion.