Resolving the spin polarization and magnetic domain wall width of (Nd,Dy)2_{2}Fe14_{14}B with spin-polarized scanning tunneling microscopy

The electronic structure and the domain wall width of industrial (Nd,Dy)$_{2}$Fe$_{14}$B hard magnets were investigated using low-temperature, spin-polarized scanning tunneling microscopy (STM) in ultra-high vacuum. In a first step, atomically clean and flat surfaces were prepared. The flat terraces were separated by monatomic steps. Surface termination was identified as the Fe c layer from atomically resolved STM imaging. The electronic density of states and its spin polarization agree well with ab initio predictions of the Fe c layer. High-resolution spin-polarized STM images allowed to finally resolve the domain wall width w of only 3.2 ± 0.4 nm

Crustal structure derived from seismic refractions and wide-angle reflections in the Mizuho Plateau, East Antarctica

Large seismic explosion experiments were conducted on the traverse route from Syowa to Mizuho Stations by the 41st Japanese Antarctic Research Expedition (JARE-41) in 1999-2000 and JARE-21 in 1980-1981. The P-wave velocity structure of the ice sheet, the crust and the uppermost mantle in the Mizuho Plateau, East Antarctica, is deduced from travel-time analysis of the combined data of refractions and wide-angle reflections. The ice sheet has a surface layer 60-100 m in thickness with P-wave velocity of 2.34 - 3.01 km/s, while the deeper part has a P-wave velocity of 3.80 - 3.85 km/s. There is a v-shaped valley with a drop of 600 m in the basement topography at the middle of the profile line; this is consistent with the variations of the ice-sheet flow. The uppermost crust has a P-wave velocity of 6.17 - 6.20 km/s on the coastal side, 6.08 km/s under the above mentioned v-shaped valley and 6.21 - 6.26 km/s on the inland side. The middle and the lower crustal P-wave velocities are 6.45 and 6.56 km/s, and their thicknesses are about 10 and 20 km, respectively. The Moho boundary is almost 40km deep with a gentle dip toward the inland direction with a Pn velocity of 8.03 km/s. The Vp/Vs value of 1.70 for the entire crust is derived from S-wave travel-time analysis. Moreover, calculated gravity anomalies, based on the obtained velocity structure and a density-velocity relation obtained in the laboratory experiments, coincide well with observed anomalies, but there are some misfits at the v-shaped valley of the basement rock and around the S-1 and S-6 shot points at both ends of the profile. Compared with the results from high pressure laboratory measurements of velocities for metamorphic rocks, it is implied that felsic gneiss is possibly dominant in the uppermost crust along the Mizuho traverse route and that the basement layer with a P-wave velocity of 4.69 km/s near the coast and the v-shaped valley may be a mixture of ice with sand or stone

The Foresight in Seismological Research in Antarctica

第3回極域科学シンポジウム/第32回極域地学シンポジウム 11月29日（木） 統計数理研究所 ３階セミナー

Seismic refraction and wide-angle reflection exploration by JARE-43 on Mizuho Plateau, East Antarctica

The 43rd Japanese Antarctic Research Expedition (JARE-43) carried out seismic exploration experiments on Mizuho Plateau,East Antarctica,in the austral summer season of ,2001-2002. The exploration was composed of seven large explosions and 161seismic stations distributed along the 151 km-long seismic line.The first arrival time data are analyzed by a refraction method.It is found that the ice sheet is composed of two layers:the upper layer with P wave velocity of 2.7-2.9 km/s has thickness of 35-45 m,and the lower layer with P wave velocity of 3.7-3.9 km/s continues to the bedrock.Lateral velocity variation in the upper-most crust is revealed:P wave velocity for the upper-most crust in the southern and central parts is 6.1-6.2 km/s and that in the northern part is5.9 km/s. This result implies that the geological boundary observed along the coast in the Lu tzow-Holm Bay and Prince Olav Coast regions possibly continues to the inland area.The S wave velocity is also obtained to be roughly 3.5km/s for the whole upper-most crust.Travel time analysis of two distinct reflection phases shows two horizontal reflecting planes located at 19 and 40km depth; the latter corresponds to the Moho discontinuity