Isao Sakamoto

Fe Ion-induced phase transformation in 17/7 stainless steel

CEMS observation has showed the large difference in the fraction of the induced alpha phase between56Fe ion and57ion irradiation. In case of57Fe ion irradiation, the projectile57Fe probe atom observes the phase transformation which may be induced by itself. It is most probable that CEMS in57Fe ion irradiation reflects the phase transformation due to compositional changes and alloying effects.

ION-BEAM-INDUCED REACTIONS IN IRON-SILICON SYSTEM

The ion beam induced reactions at the Fe−Si interface are studied by using the technique of conversion electron Mössbauer spectroscopy. It is shown that after ion irradiation the formations of iron silicides occur significantly at the interface region between deposited films and substrates. It has also been shown that in the case of multilayered Fe−Si films an effective mixing is induced and a ferromagnetic amorphous layer is formed.

Iron Clustering and the Magnetic Properties in α-Al2O3 Crystals after Iron Implantation to High Doses

Magnetization and magnetoresistance were studied in iron-ion-implanted aluminum oxide crystals. The implantation was done up to a total dose of 3.5 x 1017 ions/cm2 into Al2O3 substrates with projectile energy of 100 keV. Using conversion electron Mössbauer spectroscopy, it is shown that most of the implanted ions precipitate as α-Fe clusters and that the nano-size clusters exhibit a transition from superparamagnetic to ferromagnetic state at the dose range of (1.5–2.0) x 1017 ions/cm2. A maximum magnetoresistance ratio of 7.5% was observed around a dose of 1.5 x 1017 ions/cm2 at a field of H=1.2 T.

Time dependence of filtered resonance radiation of57Fe

Abstract The time dependence of resonantly filtered 14.4 keV57Fe γ-rays was measured by means of delayed-coincidence techniques. Excellent agreement between theoretical and experimental decay curves has been obtained. The agreement indicates a possibility of measuring the recoilles fraction of 14.4 keV γ-rays emitted from the source.

Mössbauer study of martensitic transformation in Xe ion-irradiated type 304 austenitic stainless steel

Foil specimens of type 304 stainless steel have been irradiated with Xe+ ions in the range of 100–400 keV and 1×1020−1×1021 ions/m2 to elucidate the dynamics of the ion-induced martensitic phase transformation in stainless steel. It has been clearly shown by depth selective conversion electron Mössbauer spectroscopy (DCEMS) that the ion-induced martensitic phase in type 304 stainless steel has grown from the surface to a depth dependent both on the ion energy and the fluence of the Xe+ ions. Especially, we observed by means of DCEMS that the extension of the martensitic phase into the interior of stainless steel has been induced with increasing ion energy. It is concluded from these results that the depth distribution of the ion-induced martensitic phase is stress-induced by the formation of the highly pressurized Xe+ inclusion in type 304 stainless steel.

Study of martensitic transformation in stainless steel by CEMS and RBS channeling

Abstract The effect of Xe ion irradiation in a single crystal of 17/13 stainless steel has been studied, using RBS channeling techniques and conversion electron Mossbauer spectroscopy (CEMS). 300 keV Xe ions were used to induce martensitic transformation in the austenitic steel. A dynamic behavior of the transformation was observed as functions of the fluence and depth dependence. The martensite appears abruptly at a critical fluence, in contrast with polycrystalline 17/7 stainless steel.

The effect of Xe ion irradiation in 1713 single-crystalline austenitic stainless steel

Abstract The dynamics of the irradiation-induced martensitic transformation in a single crystal of 17 13 austenitic stainless steel has been studied using the RBS channelling technique, conversion electron Mossbauer spectroscopy (CEMS), and glancing incidence X-ray diffraction (GXRD). 300 keV xenon ions were used to induce the martensitic α phase in the austenitic steel. It is shown that in the single-crystalline steel the martensitic phase occurs abruptly and covers almost all, i.e. the region near the surface of the specimen in a very short fluence increase, i.e. from 4 × 1016 to 5 × 1016ions/cm2, which suggest an introduction of a critical transition, in contrast with the fluence dependence in polycrystalline 17 7 steel specimens; in the latter case the induced phase increases gradually to a saturated amount around a fluence of (5–7) × 1016ions/cm2.

Effect of He+ and B+ ion irradiation of amorphous alloy Fe100 − x Bx

Abstract The effect of irradiation of amorphous Fe100 −x Bx alloys (x = 15, 20 and 25) was studied by means of conversion electron Mossbauer spectroscopy and glancing angle X-ray diffraction. The amorphous and annealed ribbons were bombarded with 40 keV He+ and 30 keV B+ ions to fluence ranges of (1 – 10) × 1017 ions/cm2. He+ irradiation is observed to induce destabilization of the as-quenched FeB amorphous structure, i.e. precipitation of crystalline α-iron in the remaining amorphous state. B+ irradiation of crystallized alloys, on the other hand, effectively leads to reamorphization. It is suggested from these results that an amorphous structure with a composition near to Fe75 B25 stabilize defect structures induced by ion irradiation.

Structural and Magnetic Properties of Fe and Au Ion-Implanted Al2O3 Single Crystals

Au ion implantation in Fe ion-implanted Al2O3 (Fe/Al2O3) has been performed in order to tailor the structural, magnetic and optical properties of Fe granules in Al2O3 matrix. After Au ion implantation, Rutherford backscattering (RBS) measurements indicate the decrease and the redistribution of retained Fe atoms with the inclusion of Au atoms, and the patterns of X-ray diffraction (XRD) show the formation of Au granules in the Fe/Al2O3. Besides, the magnetization curves of the Fe/Al2O3 after Au ion implantation show still the superparamagnetic characteristics and the decrease of saturation magnetization, and the optical absorption measurements indicate the formation of Au granules in the Fe/Al2O3 in accordance with the XRD result. In addition, we investigated a behavior of Fe granules in Al2O3 matrix by conversion electron Mossbauer spectroscopy (CEMS), which indicates the decrease of superparamagnetic state as a function of Au ion dose. As a result, it is suggested that Au ion implantation has potentialities to tailor the physical properties of Fe granules in Al2O3 matrix.

Structural and magnetic properties of Fe-Al2O3 films prepared by helicon plasma sputtering

Fe-Al2O3 films have been prepared by on-off deposition of Fe with continuous Al2O3 deposition, and also subsequently irradiated by 400 keV Ar ions for controlling of the structural and magnetic properties of the films. CEM spectra of the as-deposited films show the decrease in the average hyperfine fields (Hhfs) with decreasing Fe/ Fe-Al2O3 volume ratio with keeping the Hhfs orientation parallel to the film plane. The decrease in Hhfs indicates the decrease of the Fe particle size and the in-plane orientation of Hhfs implies the non spherical shape of Fe particles in the film. On the other hand, 400 keV Ar ion irradiation induces the change from the superparamagnetic characteristics to the ferromagnetic one; the ferromagnetic peaks showing the random orientation of Hhfs appear and indicate the spherical growth of Fe particles in Al2O3 matrix.