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Electrical Resistivity and Demagnetization Characteristics of Salt-added Nd-Fe-B-type Magnet
M. S. Kang,K. M. Kim,H. W. Kwon,D. Wu,M. Yue,M. C. Kang,C. W. Yang,D. H. Kim,J. G. Lee,J. H. Yu 한국자기학회 2019 Journal of Magnetics Vol.24 No.3
Nd-Fe-B-type die-upset magnet with high electrical resistivity was fabricated by hot-deforming the mixture of melt-spun Nd-Fe-B-type flakes (MQU-F: Nd13.6Fe73.6Co6.6Ga0.6B5.6) and Dy-containing salts: eutectic (DyF₃–LiF) salt mixture and DyF₃ single salt. Profound electrical resistivity enhancement was feasible in the Nd-Fe-B-type die-upset magnet by adding Dy-containing salts. More profound electrical resistivity enhancement was achieved in the magnet added with dielectric eutectic (DyF₃–LiF) salt mixture with respect to the magnet added with single DyF₃ salt. This was attributed to better electrical insulation between the flakes by forming more continuous coverage of the flake interface with the easily melted dielectric salt. Coercivity of the die-upset magnet was also profoundly enhanced by optimal addition of Dy-containing salts, and this was attributed to substitution of some Nd in the Nd₂Fe14B-type grains near flake surface by Dy atoms from the added salt. Kerr microscopy revealed that for both the magnets with or without salt addition, formation of reverse domain initiated mostly inside the flake. Reversed domain started to form at higher reverse field for the magnet added with Dy-containing salt than for the magnet without salt addition. Practical demagnetization occurred largely by formation of new reverse domains at random places rather than enlargement of previously formed reverse domain for both the magnets with or without salt addition.
Optical Characterization of ZnMnO Thin Films on c-Al2O3
H. J. LIN,D. Y. Lin,J. S. Wu,W. C. CHOU,C. S. YANG,J. S. WANG,W. H. Lo 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1
Various optical measurement technologies have ben used to characterize ZnMnO thin filmswith different Mn compositions grown by molecular beam epitaxy(MBE) on c-Al2O3 substrates. Thelat- tice constant and the crystalization quality have ben evaluated by using X-ray diraction (XRD). Photoluminescence (PL) has ben used to reveal the neutral-donor-bound exciton (D0X) and to checkthelm'squality. Defect-relatedabsorptionsignatures,inadditiontonear-band-edgeabsorp- tion, due to the zinc vacancy and the donor-aceptor pair (DAP) have ben found in the surface photovoltagespectra(SPS).Freexcitonictransitionsandtheirphonon-asistedreplicashaveben observed in the re ectance spectra. Our experimental results not only unveil specic optical tran- sitionenergies but also indicate arapid materiald deterioration whenMn incorporation goes beyond a certain amount to cause manganese segregation. Various optical measurement technologies have ben used to characterize ZnMnO thin filmswith different Mn compositions grown by molecular beam epitaxy(MBE) on c-Al2O3 substrates. Thelat- tice constant and the crystalization quality have ben evaluated by using X-ray diraction (XRD). Photoluminescence (PL) has ben used to reveal the neutral-donor-bound exciton (D0X) and to checkthelm'squality. Defect-relatedabsorptionsignatures,inadditiontonear-band-edgeabsorp- tion, due to the zinc vacancy and the donor-aceptor pair (DAP) have ben found in the surface photovoltagespectra(SPS).Freexcitonictransitionsandtheirphonon-asistedreplicashaveben observed in the re ectance spectra. Our experimental results not only unveil specic optical tran- sitionenergies but also indicate arapid materiald deterioration whenMn incorporation goes beyond a certain amount to cause manganese segregation.
The multiple merger assembly of a hyperluminous obscured quasar at redshift 4.6
Dí,az-Santos, T.,Assef, R. J.,Blain, A. W.,Aravena, M.,Stern, D.,Tsai, C.-W.,Eisenhardt, P.,Wu, J.,Jun, H. D.,Dibert, K.,Inami, H.,Lansbury, G.,Leclercq, F. American Association for the Advancement of Scienc 2018 Science Vol.362 No.6418
<P><B>Mergers drive a powerful dusty quasar</B></P><P>Massive galaxies in the early Universe host supermassive black holes at their centers. When material falls toward the black hole, it releases energy and is observed as a quasar. Astronomers found a population of powerful distant quasars that are obscured by dust, but it has been unclear how they are formed. Díaz-Santos <I>et al.</I> observed the dust-obscured quasar WISE J224607.56-052634.9 at submillimeter wavelengths, finding three small companion galaxies connected to the quasar by bridges of gas and dust. They inferred that galaxy mergers can provide both the raw material to power a quasar and large quantities of dust to obscure it.</P><P><I>Science</I>, this issue p. 1034</P><P>Galaxy mergers and gas accretion from the cosmic web drove the growth of galaxies and their central black holes at early epochs. We report spectroscopic imaging of a multiple merger event in the most luminous known galaxy, WISE J224607.56−052634.9 (W2246−0526), a dust-obscured quasar at redshift 4.6, 1.3 billion years after the Big Bang. Far-infrared dust continuum observations show three galaxy companions around W2246−0526 with disturbed morphologies, connected by streams of dust likely produced by the dynamical interaction. The detection of tidal dusty bridges shows that W2246−0526 is accreting its neighbors, suggesting that merger activity may be a dominant mechanism through which the most luminous galaxies simultaneously obscure and feed their central supermassive black holes.</P>
Influence of Hydrostatic Pressure on FLDs for AZ31B Sheets
H. Wang,Y. Wu,P.D. Wu,K.W. Neale 한국소성가공학회 2011 기타자료 Vol.2011 No.8
Sheet metal formability in terms of the Forming Limit Diagram (FLD) for magnesium alloy AZ31B sheets is studied by using the recently developed Elastic Visco-Plastic Self-Consistent (EVPSC) model, in conjunction with the classical M-K approach. The effect of superimposed hydrostatic pressure on FLDs is numerically assessed. It is found that the superimposed pressure delays the initiation of necking for any strain path. The increment of formability becomes significant when the pressure is larger than about half the initial tensile yield stress of the sheet metal. The difference in predicted FLDs between that with a superimposed hydrostatic pressure and that with a stress component normal to the sheet plane is also discussed.