Kimihito Tagaya

ESR Study of X-Irradiated Ba(NO3)2

Single crystals of Ba(NO3)2 were irradiated with X-rays at room temperature, and ESR measurements were performed over the temperature range from 85 K to 373 K. It was concluded that F, O2-, O3- and NO2 centers were produced. The sites and orientations of O2- and NO2 centers in a Ba(NO3)2 crystal were determined from the principal directions of the g or hyperfine tensor. The superhyperfine interactions of F and O2- centers with adjacent 135Ba, 137Ba and 14N nuclei were investigated. Optical absorption measurements were also performed, and it was concluded that the absorption band at 335 mµ was due to the F-center.

Magnetic Properties of β-FeSi2 Semiconductor

High-quality crystals of β-FeSi2 are ion-beam synthesized on the surface of a floating-zone(FZ)-grown Si wafer, and superconducting quantum interference device (SQUID) and ESR measurements are performed. β-FeSi2 semiconductors exhibit paramagnetic properties, and the Weiss temperature is positive near room temperature. The magnetic susceptibility changes anomalously with temperature.

FMR Study of Nickel Oxide with Spinel-Type Defect Structure in Thin Films

Ferromagnetic resonance measurements are performed on precipitates with a spinel-type defect structure formed in thin films of NiO. The g value and the cubic magnetic anisotropy constants K1 and K2 of the ferrimagnetic precipitates are determined. The temperature dependences of the g value and magnetic anisotropy fields of the precipitates are measured over the range from room temperature to 90 K. The anomalous shift in the resonance field of protrusive precipitates is also studied.

ESR of AgNO3

A broad ESR absorption was observed for a single crystal of AgNO3 at room temperature. The absorption intensity increased suddenly with decreasing temperature from 120 K, and became maximum at 81 K. Then, the g-value approached 2.0. The absorption intensity at 81 K was about twenty times as strong as that at room temperature. The spin number was nearly equal to the molecule number of AgNO3 at 81 K. A possible interpretation for the results is discussed in terms of an electron transfer from the NO3- ion to the Ag+ ion.

ESR study of X-irradiated NaNO3

Single crystals of KNO3 were irradiated with X-rays at room temperature, and ESR measurements were performed over the temperature range from 85 K to 400 K. The g and hyperfine tensors of some paramagnetic centers were determined, and it was concluded that F, O2-, O3- and NO2 centers were produced. The sites and orientations of O2-, O3- and NO2 molecules in a KNO3 crystal were also determined. The superhyperfine interactions of F and O2- centers with adjacent 14N and 39K nuclei were investigated, and the superhyperfine components were determined. Further, isothermal annealing measurements were performed for the F and O3- centers.

ESR Study of Irradiated Pb(NO3)2

Single crystals of Pb(NO3)2 were irradiated with X or γ-rays at room temperature, and ESR measurements were performed over the temperature range from 85 K to room temperature. It was concluded that besides O2- , O3- and NO2 centers, F-centers were produced, in which an electron was trapped by an NO3- vacancy. The orientations of F and NO2 centers in a Pb (NO3)2 crystal were determined from the principal directions of the g or hyperfine tensor. The superhyperfine interactions of F and O2- centers with adjacent 207Pb and 14N nuclei were also investigated, and the spin-density distributions on these atoms were estimated.

Exchange Anisotropy of Ferrimagnetic Precipitates of Nickel Oxide in NiO Matrix

When the spins of small ferrimagnetic precipitates of nickel oxide with a spinel-type defect structure are coupled with the spins of the antiferromagnetic NiO matrix by exchange interaction across the interface, an exchange anisotropy is produced in each ferrimagnetic precipitate. Ferromagnetic resonance and electron micrographical examinations were performed on such precipitates of nickel oxide. The exchange anisotropy of the precipitates was studied, and the value of exchange anisotropy energy per cm 2 of interface between ferrimagnetic nickel oxide and antiferromagnetic NiO was estimated.

Exchange Anisotropy of Ni-Ferrite Precipitates in Fe-Doped NiO

When the spins of Ni-ferrite precipitates in a single crystal of Fe-doped NiO are coupled with the spins of the antiferromagnetic NiO matrix by exchange interaction across the interface, an exchange anisotropy is produced in each Ni-ferrite precipitate. FMR and magnetization measurements were performed together with electron micrographical examinations on the Ni-ferrite precipitates. The exchange anisotropy energy related to the coupling of spins between Ni-ferrite and NiO across the (111) interface was determined to be 0.9±0.1 erg/cm 2 .