Proceedings of the Korean Magnestics Society Conference (한국자기학회:학술대회 개요집)
The Korean Magnetics Society (KMS)
- Semi Annual
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- 2233-9485(pISSN)
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- 2233-9574(eISSN)
Domain
- Physics > Particle Physics/Field Theory
2011.12a
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Although yttrium iron garnet (YIG) has provided a great vehicle for the study of spin waves in the past, associated difficulties in film deposition and device fabrication using YIG had limited the applicability of spin waves to practical devices. However, microfabrication techniques have made it possible to characterize both the resonant as well as the travelling characteristics of spin waves in permalloy (Py). A variety of methods have been used for measuring spin waves, including Brillouin light scattering (BLS), magneto-optic Kerr effect (MOKE), vector network analyzer ferromagnetic resonance (VNA-FMR), and pulse inductive microwave magnetometry (PIMM). PIMM is one of the most preferred methodologies of measuring travelling spin waves. In this method, an electrical impulse is applied at one of two coplanar waveguides patterned on top of oxide-insulated Py, producing a local disturbance in the magnetization of the Py. The resulting disturbance travels down the Py in the form of waves, and is inductively picked up by the other coplanar waveguide. We investigate the effect of the pulse width of excitation pulses on the generated spin wave packets using both experimental results and micromagnetic simulations. We show that spin wave packets generated from electrical pulses are a superposition of two separate spin wave packets, one generated from the rising edge and the other from the falling edge, which interfere either constructively or destructively with one another, depending upon the magnitude and direction of the field bias conditions. A method of spin wave amplitude modulation is also presented by the linear superposition of spin waves. We use interfering spin waves resulting from two closely spaced voltage impulses for the modulation of the magnitude of the resultant spin wave packets.
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We have prepared FePtCu L10 bit patterned media, of which magnetic properties and microstructural details are obtained by direct measurement and observations. The patterning process on the continuous film induced a drastic changes in the coercivity, SFD, and angular dependencies. The origin of the changes are explained by micromagnetic simulations with the finite element models including the details of the microstructures.
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Limited understanding of the surface properties of
$Pt_3Ni$ for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) has motivated the study of magnetic properties and electronic structures of Pt segregated$Pt_3Ni$ (111) surface during adsorption of oxygen molecule on it. The first principle method based on density functional theory (DFT) is carried out. Nonmagnetic Pt has induced magnetic moment due to strong hybridization between Ni 3d and Pt 5d. It is found that an oxygen molecule prefers bridge site with Pt rich subsurface environment for adsorption on the surface of Pt segregated$Pt_3Ni$ (111). It is seen that there is very small charge transfer from$O_2$ to Pt. The curve of energy versus magnetic moment of the oxygen explains the magnetic moments in transition states. We found the dissociation barrier of 1.07eV significantly higher than dissociation barrier 0.77eV on Pt (111) suggesting that the dissociation is more difficult on Pt segregated$Pt_3Ni$ (111) surface. The spin polarized densities of states are presented in order to understand electronic structures of Pt and$O_2$ during the adsorption in detail. -
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Kim, Ji-Hyun;Lukashev, Avel;Wang, Serl-Un;Kim, Jae-Sung;Chen, Xumin;Rojas, Geoffrey;Sessi, Violetta;Honolka, Jan;Skomski, Ralph;Sabirianov, Renat F.;Enders, Axel 19
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We have demonstrated the fabrication of sub 30 nm MTJ pillars with PMA characteristics. The multi-step IBE process performed at
$45^{\circ}$ and$30^{\circ}$ , using NER resulted in almost vertical side profiles. There deposition on the sidewalls of the NER prevented lateral etching of the resist hard mask allowing vertical MTJ side profile formation without any reduction in the lithographically defined resist lateral dimensions. For the 28nm STT-MTJ pillars, the measured TMR ratio was 13 % with resistance of 1$k{\Omega}$ , which was due to remaining redeposition layers less than 0.1 nm thick. With further optimization in multi-step IBE conditions, it will be possible to fabricate fully operating sub 30 nm perpendicular STT-MTJ structures for application to future non-volatile memories. -
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In this study, the magnetism and the elastic properties of Fe-Si alloys have been investigated using the all-electron FLAPW method based on the GGA. The local magnetic moment of Fe atoms decreases gradually. From the Pugh's relation and
$C_P$ , in the ordered$D0_3$ $Fe_3Si$ , we predict that it presents intrinsic ductility. -
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Yun, Ha-Yeong;U, Jun-Hwa;Min, Ji-Hyeon;Lee, Ji-Seong;Kim, Seung-Hyeon;Kim, Ji-Seok;Kim, Yeong-Geun 50
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Kweon, Jin-Jung;Lee, Kyu-Won;Park, Jun-Kue;Jeon, Gi-Wan;Kim, Hyo-Jung;Lee, Cheol-Eui;Noh, S.J.;Kim, H.S. 55
We have carried out spectroscopic studies on the physical properties of graphite tiles modified by electron and proton irradiation. While increase in local order was observed in the electron-irradiated sample, structural disorder and amorphization were revealed in the proton-irradiated sample, with considerably decreased electrical conductivity. Besides, C-OH bond with a sp3 configuration was identified in the proton-irradiated sample, apparently giving rise to a narrow ESR peak ascribed to localized spins. -
We have carried out magnetic and spectroscopic studies on the physical properties of hydrothermally-treated PCBM samples. Strong ferromagnetic ordering was observed depending on the treatment time, and was studied in relation to the atomic bonding configurations.
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Lee, Yeon-Sub;Min, Byoung-Chul;Park, Seung-Young;Langer, Jurgen;Ocker, Berthold;Maass, Wolfram;Kim, Young-Keun;Shin, Kyung-Ho 74
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Lee, Heon-Seong;Ryu, Gwang-Su;Yu, Cheon-Yeol;Song, Hyeon-Seok;Jeon, Geon-Rok;Yang, Se-Hun;Parkin, Stuart S.P.;Sin, Seong-Cheol 90
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Song, Hyon-Seok;Yang, See-Hun;Lee, Kyeong-Dong;Sohn, Jeong-Woo;Parkin, Stuart;You, Chun-Yeol;Shin, Sung-Chul 91
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The analogy between spin configurations in spin ice materials like
$Ho_2Ti_2O_7$ and proton configurations in water ice,$H_2O$ , has been appreciated for many years (see Bramwell and Gingras, Science, 294, 1495, 2001). However it is only in the last few years that this equivalence has been extended into the realm of electrodynamics. In this talk I shall describe our recent experimental work that identifies magnetic charges ("monopoles"), transient magnetic currents ("magnetricity") and the universal properties expected of an ideal magnetic Coulomb gas (magnetic electrolyte - "magnetolyte"). These universal properties include the Onsager-Wien effect, "corresponding states" behaviour, Debye-Huckel screening and Bjerrum pairing. I will describe experimental results for both traditional spin ice materials ($Ho_2Ti_2O_7$ ,$Dy_2Ti_2O_7$ ) and a recently discovered system ($Dy_2Ge_2O_7$ ). -
Chun, Sae-Hwan;Chai, Yi-Sheng;Oh, Yoon-Seok;Kim, In-Gyu;Jeon, Byung-Gu;Kim, Han-Bit;Jeon, Byeong-Jo;Haam, S.Y.;Chung, Jae-Ho;Park, Jae-Hoon;Kim, Kee-Hoon 101
The control of magnetization by an electric field at room temperature remains as one of great challenges in materials science. Multiferroics, in which magnetism and ferroelectricity coexist and couple to each other, could be the most plausible candidate to realize this long-sought capability. While recent intensive research on the multiferroics has made significant progress in sensitive, magnetic control of electric polarization, the electrical control of magnetization, the converse effect, has been observed only in a limited range far below room temperature. Here we demonstrate at room temperature the control of both electric polarization by a magnetic field and magnetization by an electric field in a multiferroic hexaferrite. The electric polarization rapidly increases in a magnetic field as low as 5 mT and the magnetoelectric susceptibility reaches up to 3200 ps/m, the highest value in single phase materials. The magnetization is also modulated up to 0.34 mB per formula unit in an electric field of 1.14 MV/m. Furthermore, this compound allows nonvolatile, magnetoelectric reading- and writing-operations entirely at room temperature. Four different magnetic/electric field writing conditions generate repeatable, distinct M versus E curves without dissipation, offering an unprecedented opportunity for a multi-bit memory or a spintronic device applications. -
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Park, Ho-Yeong;Kim, Tae-Ho;Lee, Jong-Uk;Kim, Yu-Chan;Seok, Hyeon-Gwang;Searson, Peter;Hyeon, Taek-Hwan;Lee, Gwan-Hui 121
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Lee, Jong-Uk;Kim, Tae-Ho;Kim, Yu-Chan;Seok, Hyeon-Gwang;Maitra, Anirban;Hyeon, Taek-Hwan;Lee, Gwan-Hui 122
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Seo, Ju-Yeon;Kim, Jae-Hyeon;Kim, Yeong-Jin;Kim, Seong-Hyeon;Lee, Jin-Yong;Hwang, Do-Geun;Lee, Hyeon-Suk 184
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