Nanoparticles of γ-Fe 2 O 3 have been prepared by the levitational gas condensation (LGC) method, and their structural and magnetic properties were studied by XRD, TEM and Mössbauer spectroscopy. Fe clusters evaporated from a surface of the levitated liquid Fe droplet and then condensed into nanoparticles of γ-Fe 2 O 3 with particle sizes of 14 to 30 nm in a chamber filled with mixtures of Ar and O 2 gases. From the main peak intensities of XRD and analyses of Mössbauer spectra, the amount of γ-Fe 2 O 3 and α-Fe in the sample is composed of about 93% and 7%, respectively. Mössbauer spectra consist of two sets of six Lorentzian lines corresponding to γ-Fe 2 O 3 and α-Fe. It was found that the phase transition from both γ- Fe 2 O 3 and α-Fe to Fe 3 O 4 , which was evaluated from the results of Mössbauer spectra, strongly depended on the O 2 flow rate. As a result, γ-Fe 2 O 3 was synthesized under the O 2 flow rate of 0.05 ≤ 2 O V (l/min) ≤ 0.15, whereas Fe 3 O 4 was synthesized under the O 2 flow rate of 0.15 ≤ 2 O V (l/min) ≤ 0.2.
Nanoparticles of Fe2O3 with a mean particle size of 4–50 nm have been prepared by the pulsed wire evaporation method, and its structural and magnetic properties were studied. From the main peak intensity of x-ray diffraction the amount of v̥-Fe2O3 and ɑ-Fe2O3 in sample is composed about 70% and 30%, respectively. The coercivity (53 Oe) and the saturation magnetization (14 emu/g) are about 20% of those of the bulk v̥-Fe2O3. A quadrupole line on the center of Mössbauer spectrum represents the superparamagnetic phase of v̥-Fe2O3 with a mean particle size of 7 nm or below.
The magnetic alloys of Cu-Fe (Cu 50 Fe 50 , Cu 80 Fe 20 and Cu 90 Fe 10 ) were prepared by a mechanical alloying method and their structural and magnetic behaviors were examined by X-ray diffraction and Mössbauer spectra. The magnetization curves did not distinctly show the saturation at 70 kOe for the concentrated alloys of Cu 80 Fe 20 and Cu 90 Fe 10 . The Mössbauer spectrum of Cu 80 Fe 20 at room temperature shows one Lorentzian line of the paramagnetic phase, whereas the Mössbauer spectrum of Cu 90 Fe 10 consists of a sextet Lorentzian line at room temperature and a centered doublet line. The Mössbauer spectra of Cu 90 Fe 10 measured in the temperature ranges from 13 to 295 K, implies that Cu 90 Fe 10 consists of two magnetic phases. One superimposed sextet corresponds to the ferromagnetic iron in Cu matrix and the other one indicates the superparamagnetic iron rich phase.
The effects of ion irradiation on a giant magnetoimpedance (GMI) have been investigated for a Co-based amorphous ribbon with various kinds of ions such as Xe, Ar, and N. The GMI ratio and M-H loop parameters were used to characterize the samples before and after the ion irradiation. The GMI ratio increased considerably in the ion irradiated samples and the GMI response showed a strong dependence on the irradiated ion species and driving frequencies. It was shown that the ion irradiations lead to a substantial modification of the magnetic properties including a large coercivity and shearing of the in-plane magnetization loops, thus suggesting the reduction of an exchange coupling.
Fe-Cr alloys are one of the important structural materials for fusion reactor applications, and often used as a model alloys for studying the basic mechanisms governing their behavior under an irradiation. In this study, Fe ions are irradiated on to Fe-Cr alloys with 9% of Cr contents. The magnetic Barkhausen Noise (BN) and Ferro Magnetic Resonance (FMR) experiments are conducted to investigate the changes of their magnetic properties under an ion irradiation. The BN and FMR resonance fields are increased with an increasing ion dosage. The directional ordering by irradiation induced defects seems to be responsible for the changes in the magnetic properties.
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