JinBae Kim

Characterization of as-synthesized FeCo magnetic nanoparticles by coprecipitation method

FeCo nanoparticles were synthesized by a coprecipitation method without any post treatments. The structure, morphology, and magnetic properties of the FeCo nanoparticles formed at different sodium borohydride reaction times (5, 10, 20, and 30 min) were examined. X-ray diffraction revealed the representative α-FeCo peaks in all samples. The mean crystalline sizes slightly decreased from 31 nm to 21 nm with increasing reducing agent reaction time. A maximum saturation magnetization of 204 emu/g at 300 K was obtained in the sample with a reaction time of 5 min.

Thickness-dependent magnetic domain change in epitaxial MnAs films on GaAs(001)

The authors report the change of the magnetic domain structure, dependent on the film thickness of MnAs films epitaxially grown on GaAs(001), investigated by magnetic force microscopy. Interestingly, as the film thickness decreases, the domain structure within the ferromagnetic α-MnAs stripes changes from a head-on domain structure to a simple 180° one around a thickness of 250nm. This result is understood by the change in the demagnetizing factor of the ferromagnetic stripes with the film thickness.

Observation of magnetic domain structures in epitaxial MnAs film on GaAs(001) with temperature hysteresis

The saturation magnetization of MnAs films epitaxially grown on GaAs(001) substrates exhibited temperature hysteresis in the temperature range of 10–45 °C. We investigated the cause of the temperature hysteresis using temperature- and field-controlled magnetic force microscopy (MFM). The MFM results showed that inside the ferromagnetic α-MnAs stripes of the film at 30 °C, 180° domains were formed during cooling but a single domain state was developed during heating. Despite the cooling procedure, a single domain state was found inside the α-MnAs stripes when a magnetic field of 800 Oe was applied. From these results, the spontaneous magnetization of the α-MnAs phase was ascribed to the temperature hysteresis.

Direct observation of the spin configurations of vertical Bloch line

We observed the spin configurations of Bloch lines in a ferromagnetic MnAs film on GaAs(001) by conventional magnetic force microscopy (MFM) and tilt-scanning (TS)-MFM. Due to the high lateral resolution of conventional MFM measurements, we were able to demonstrate the out-of-plane magnetic components within the Bloch line. Through vertical stray magnetic field mapping, the TS-MFM operation was shown to enable the detailed measurement and visualization of the spin configurations of the Bloch lines. This direct observation method of the spin configurations of vertical Bloch line structures allowed us to visualize antiparallel domain structure on the out-of-plane rotation of magnetization.

Control of Diffracted Magneto-Optical Enhancement in Ni Gratings

The so-called diffracted magneto-optical (MO) effects, in which the MO responses of diffracted beams are measured in the off-specular geometry, have been utilized to change the amplitude and the sign of MO signals. An enhancement of MO effect of the first-order diffraction was found. In this paper, the rigorous coupled-wave analysis implemented as Airy-like internal reflection series was developed to simulate the diffracted longitudinal MO Kerr effect. We demonstrate that the enhancement of the MO effect is controllable for a certain diffraction order by adjusting the geometrical parameters of Ni gratings. Furthermore, it is believed that the absolute magnitude and the MO enhancement can be more effectively tuned by designing the grating profile and carefully selecting the gyrotropic materials.

Microstructures and Corresponding Magnetic Properties of BaAl

We present the results of the magnetic domain structures of BaAl2Fe10O19 nanopowders prepared by a self-propagating combustion process. Amorphous precursors were calcined at 850 °C for 2 h with NaCl (Sample I) and without NaCl (Sample II). The transmission electron microscope and atomic force microscopy images evidently suggested that there was a topological difference between Sample I (plate- and rod-shaped nanopowders) and Sample II (rod-shaped nanoparticles). We observed a considerably enhanced coercivity in Sample II, compared to Sample I. This result can be understood by the change in the magnetic domain width due to the shape effect of the nanopowders, which was investigated by measuring the field-controlled magnetic force microscopy.

_{2}

Magnetic nanoparticles with a core/shell structure were fabricated by a sol-gel method and following hydrogen reduction process. The reduction process changed the crystal structure of synthesized nanoparticles from iron-oxide single phase to iron phase covered with an iron-aluminum oxide shell layer. These nanoparticles were dispersed by homogenizing and ultrasonication in order to form ferromagnetic ink. Using synthesized ink, patterns with soft magnetic properties were successfully printed on Si substrates by a direct printing method.

Fe

In this paper, we demonstrate the direct observation of closure-type domain structures in Ni magnetic grating by employing conventional magnetic force microscopy (MFM) and tilt-scanning (TS) MFM. Through sidewall scanning, the TS-MFM operation enabled the detailed analysis of the spin configurations of head-to-head and tail-to-tail domains. As a result, the domains had the surface domain configurations of the closure-type structures, which was in accord with micromagnetic simulated results.

_{10}

We present a systematic change of the magnetic domain structure with temperature in epitaxial ferromagnetic MnAs film on GaAs (001), observed in a wide temperature range of 15-45 degrees C by magnetic force microscopy. Interestingly, it is found that, as temperature increases, the domain structure within the ferromagnetic alpha-MnAs stripes shows a mixture of head-on and simple domains at 15 degrees C and then, takes a complete transition to simple ones above 15 degrees C. This change could be understood by change in the demagnetizing factor of the cross-section of the ferromagnetic stripes with temperature.

O

Nanoparticles were produced on polyimide (PI) film through oxidation of a Ni/sub 80/Fe/sub 20/ thin film on a PI precursor layer during its imidization reaction. Film properties were investigated through transmission electron microscopy, electron diffraction and X-ray photoemission spectroscopy. The size and shape of embedded and exposed particles were compared and it was verified that the exposed particles can be effectively used as a growth template for nano-sized structures.