Teruo Teranishi

Crystal Distortion in Copper Ferrite-Chromite Series

The cation distributions in copper ferrite-chromite series and the copper ferrite quenched from high temperatures are measured by X-ray diffraction method. The lattice parameters are also measured as a function of chromium ion content and of temperature. The critical fractions of copper ions on 16d and 8a sites for the occurrence of bulk crystal distortion from cubic to tetragonal symmetry are determined. The critical temperature for the distortion of copper ferrite is 360°C. This crystal distortion depends only upon the copper ion distribution. The abrupt appearance of distortion and coexistence of two phases, cubic and tetragonal, near the critical fraction and the critical temperature suggest that this distortion is of the first order as predicted by the statistical theory. From the aging of the distortion, the activation energy for copper ion to migrate from 16d site to 8a site is obtained. From the comparison of the critical fraction of copper ion in this series with those in other mixed spinels, the...

Optical Properties of a Magnetic Semiconductor: Chalcopyrite CuFeS2.: I. Absorption Spectra of CuFeS2 and Fe-Doped CuAlS2 and CuGaS2

Optical absorptions have been measured in chalcopyrite, CuFeS 2 , and Fe-doped CuAlS 2 and CuGaS 2 . An extra absorption band with two peaks is observed at the low energy region of the absorption edge for Fe-doped CuAlS 2 and CuGaS 2 .Energy positions of two absorption peaks are 1.3 eV and 2.0 eV for CuAlS 2 and 1.2 eV and 1.9 eV for CuGaS 2 , respectively. The intensity of this absorption band increases with the increase of doped Fe ions and grows into the absorption edge of CuFeS 2 . Its oscillator strength comes up to 7·10 -2 . In chalcopyrite photoconductivity is observed and its maximum is just at the same energy region of the absorption edge. By comparing our results with those of absorption measurements for Cu- or Fe-doped ZnS it is concluded that this absorption band originates from the charge transfer transitions relating to 3d electron of Fe ions and the absorption edge of CuFeS 2 rises from the band-to-band transition corresponding to this charge transfer transition.

Magnetic and Electric Properties of Chalcopyrite

The torque of a natural single crystal of chalcopyrite in a uniform magnetic field is measured. At room temperature and liquid nitrogen temperature the torque of a disc parallel to (110)-plane shows two-fold symmetry and the easy direction is [1\bar10]. The temperature dependence of the torque is also measured. The torque vanishes at 550°C. Two principal susceptibilities parallel and perpendicular to c-axis, χ // and χ ⊥ , are calculated from the torque and the powder susceptibility. The conductivity, the Hall coefficient and their temperature dependences and the thermoelectric power are also measured. Their behaviours are those of typical semiconductors. Hall mobility and thermoelectric power are rather large, although chalcopyrite contains transition element, Fe, in its chemical foumula. The crystal structure, the electronic states of constituent elements, magnetic and electric properties are considered together, and it is concluded that the 3d-shell in this material is independent of the valence bond w...

Magnetic Properties of FeS2 and CoS2

Magnetic properties of FeS2 and CoS2 having pyrites structure are studied. Magnetic susceptibility of a good natural pyrites (FeS2) crystal is almost temperature‐independent down to 4.2°K. The constant susceptibility is explained by the Van Vleck paramagnetic term and diamagnetic one of the core. This suggests iron in pyrites is in divalent and low‐spin state contrary to the assumption of L. R. Walker et al. that iron in pyrites is in a trivalent state from the Mossbauer isomer‐shift data. CoS2 is a ferromagnet of a Curie temperature of 130°K. The spontaneous magnetization σ and the Curie constant Cmol are measured on a synthetic crystal of CoS2. We obtained the values, σ=44.4 emu/g and Cmol=0.37 emu·deg. The values are compatible when we assume Co is in divalent and low‐spin state. This fact accords with the result of magnetic measurement of FeS2.

Amorphous GdCo disk for thermomagnetic recording

Thermomagnetic recording was carried out on 150‐mm‐diam amorphous GdCo disks rotated at a speed of 1800 rpm. GdCo films showing good uniformity were deposited on glass disks by rf sputtering technique. Bits as small as 1 μm in width were recorded, making use of compensation temperature with a laser power of 5.6 mW and were read out with a laser power of about 2 mW. Thermal stability and dependence of the Kerr rotation angle on wavelength were also measured. It was confirmed that GdCo film is a most promising material for thermomagnetic recording.

Vacuum Ultraviolet Reflectance Spectra and Band Structures of Pyrites (FeS 2 , CoS 2 and NiS 2 ) and NiO Measured with Synchrotron Radiation

Reflectance spectra of FeS 2 , CoS 2 and NiS 2 pyrites have been measured in the photon energy region from 4 to 30 eV with synchrotron radiation and compared with the results of NiO and related compounds. Dielectric constants, optical constants, effective electron numbers as well as energy-loss functions are evaluated by means of the Kramers-Kronig analysis. Fine structures of the reflectance spectra are qualitatively interpreted providing information on band structures. Characteristic features of band structures related to the 3 d electrons in the low-spin state are experimentally elucidated.

Optical Reflectivity Spectrum of a CuFeS2 Single Crystal

Critical reflectivity spectra have been measured at room temperature on a single crystal of CuFeS 2 between 0.025 and 6 eV. The experimental results have been used to calculate the optical constants, the dielectric constant and the absorption coefficient. There have been found an absorption band with peaks at 1.0 and 2.1 eV and an absorption edge at approximately 3.2 eV. The band can be assigned to the charge-transfer transition from the valence band to the empty 3d states of Fe, and the edge can be attributed to the commencement of the band to band transition. A schematical energy level diagram for CuFeS 2 is given from the result.

Infrared Luminescence of Fe3+ in CuGaS2 and CuAlS2

A sharp luminescence line due to the crystal-field transition ( 4 T 1 – 6 A 1 ) of Fe 3+ in the tetrahedral symmetry is observed for the first time in iron-doped I-III-VI 2 chalcopyrite type compounds, CuGaS 2 and CuAlS 2 . The peak energy is 4,942 cm -1 and 5,804 cm -1 respectively. These values are rather small as compared to those in many ferric oxides in which the excitation energy of 4 T 1 in octahedral symmetry is observed around 10,000 cm -1 . The Zeeman effect is also observed and is explained quantitatively by the use of the ligand field theory: We find that g ⊥ of the lowest excited state is zero and the spin-orbit parameter 18 cm -1 .

Relaxation of Amorphous Gd-Co Films through Electrical Resistivity Measurement

Irreversible decrease of electrical resistivity in an amorphous Gd-Co alloy film has been observed and is analyzed assuming a simple relaxation process. An apparent activation energy of 0.5 eV is obtained.

Amorphous Thin Film Disk For Magneto-Optical Memory

Amorphous rare earth-transition metal films as media of magneto-optical memory are described. Improvements of amorphous GdCo film in stabilizing recorded bits and in making uniform film were performed. High speed recording and reading experiment were carried out on GdCo disk of 150 mm in diameter, and excellent stability of recorded bits, considerable uniformity, and high sensitivity for recording were confirmed. Thermal stability and spectra of Kerr rotation angle of GdCo film were also measured. It is shown that GdCo film is very promising material for magneto-optical memory.