• The Bulletin of The Korean Astronomical Society
• /
• v.44 no.2
• /
• pp.55.2-55.2
• /
• 2019

The firehose instability is driven by a pressure anisotropy in a magnetized plasma when the temperature along the magnetic field is higher than the perpendicular temperature. Such condition occurs commonly in astrophysical and space environments, for instance, when there are beams aligned with the background magnetic field. Recently, it was argued that, in weak quasi-perpendicular shocks in the high-β intracluster medium (ICM), shock-reflected electrons propagating upstream cause the temperature anisotropy. This electron temperature anisotropy can trigger the electron firehose instability (EFI), which excites oblique waves in the shock foot. Scattering of electrons by these waves enables multiple cycles of shock drift acceleration (SDA) in the preshock region, leading to the electron injection to diffusive shock acceleration (DSA). In the study, the kinetic properties of the EFI are examined by the linear stability analysis based on the kinetic Vlasov-Maxwell theory and then further investigated by 2D Particle-in-Cell (PIC) simulations, especially focusing on those in high-β (β~100) plasmas. We then discuss the basic properties of the firehose instability, and the implication of our work on electron acceleration in ICM shock.

• Journal of the Korean Magnetics Society
• /
• v.10 no.6
• /
• pp.280-294
• /
• 2000

[(300nm)Ta/(500nm)NdFeB/(300nm)Ta] thin films were deposited at 5 mTorr Ag gas pressure by RF-DC magnetron sputtering, and their magnetic properties were investigated. The [Ta/NdFeB/Ta] films deposited on heated Si substrates showed high perpendicular anisotropy and excellent hard magnetic properties. The films sputtered at tile substrate temperature of T$\sub$s/=650$^{\circ}C$ and 700$^{\circ}C$ showed (BH)$\sub$max/=20 MGOe and $\sub$i/H$\sub$c/= 18.9 kOe along the perpendicular direction to the film plane, respectively.

• Journal of the Korean Magnetics Society
• /
• v.16 no.3
• /
• pp.173-177
• /
• 2006

We have investigated the magnetoresistance (MR) effect of the spin valve structures composed of perpendicularly magnetized Pd/Co multilayers, with changing the space layer (Pd or Cu) thickness, the stacking number of the Pd/Co multilayers, and the Co insertion-layer thickness. The Cu space layer showed larger MR ratio than the Pd space layer. The Co insertion-layer between Cu layer and pinned layer enhanced the MR ratio about three times. The maximum MR ratio of 7.4 % was established in the sample with the Co insertion-layer thickness of 0.62 and 1.01 nm.

• Journal of the Korean Ceramic Society
• /
• v.37 no.4
• /
• pp.320-326
• /
• 2000

Development of texture in SiC materials by hot-pressing and subsequent annealing was studied. Crystallographic texture type was characterized by measuring X-ray pole figures on the perpendicular plane to the hot-pressing direction. Observed all pole figures were nearly axially symmetric (fiber texture). In case of ${\beta}$-SiC materials, the pole density of basal plane (0004) increased as annealing time increased, in contrast, other planes (hkil) of ${\beta}$-SiC materials and all planes of ${\alpha}$-SiC materials nearly remained unchanged. In the case of ${\beta}$-SiC materials, therefore, a weak texture of (0001) plane at the normal direction took place in the 8h annealed samples, resulting from grian growth. The fracture toughness values of ${\alpha}$-SiC materials measured in both planes parallel and perpendicular to the hot-pressing direction were very similar. However, the fracture toughness of ${\beta}$-SiC materials measured parallel to the hot-pressing direction were higher than that measured perpendicular to the hot-pressing derection, relatively, because of the texture and the microstructure anisotropy.

• Journal of the Korean Magnetics Society
• /
• v.17 no.6
• /
• pp.221-225
• /
• 2007

The effects of $Ga^+$ ion irradiation on the magnetic properties of the $Co_{73}Pt_{27}-TiO_2$ perpendicular magnetic recording media were investigated. As $Ga^+$ ion dose increased from $1\times10^{15}ions/cm^2\;to\;30\times10^{15}ions/cm^2$, the perpendicular magnetic anisotropy was degraded and no longer observed above $20\times10^{15}ions/cm^2$ dose. The deterioration of the perpendicular magnetic anisotropy and ferromagnetic properties can be attributed to the concentration profile change due to Ga+ ion implantation. The magnetic islands of $70\times70nm^2\;and\;100\times100nm^2$ size were successfully fabricated with $Ga^+$ ion irradiation.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2003.12a
• /
• pp.61-61
• /
• 2003

• Proceedings of the Korean Magnestics Society Conference
• /
• 2007.05a
• /
• pp.182.2-182.2
• /
• 2007

• Proceedings of the Korean Magnestics Society Conference
• /
• 2009.05a
• /
• pp.145-145
• /
• 2009

• Proceedings of the Korean Magnestics Society Conference
• /
• 2009.12a
• /
• pp.82-83
• /
• 2009

• Proceedings of the Korean Vacuum Society Conference
• /
• 2003.08a
• /
• pp.140-140
• /
• 2003