• Proceedings of the Korean Magnestics Society Conference
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• 2013.12a
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• pp.29-29
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• 2013

We predict agigantic perpendicular magnetocrystalline anisotropy (MCA) in Fe (001) capped by 5d transition metal (TM) overlayers by using first principles calculations. Analysis of atom-by-atom contribution to MCA reveals that gigantic MCA as large as 11 meV/TM originates not from Fe atoms but from the 5d TMs through the strong spin-orbit coupling. More specifically, it is the hybridization between TM and Fe d orbitals that also induces non-negligible magnetic moments in TM. Furthermore, spin-channel decompositions of MCA matrix with and without the presence of Fe substrate identify the electronic origin of the perpendicular MCA that the down-down channel contribution plays the most crucial role for the sign changes of MCA of TM overlayers upon the hybridization with Fe-3d.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.492-495
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• 2000

In order to develop an ultra-thin CoCr perpendicular magnetic recording layer, we prepared CoCrTa/Ti double layer for perpendicular magnetic recording media by new facing targets sputtering system, Crystallgraphics and magnetic characteristics of CoCrTa on underlayer substrate temperature have been investigated. Crystallgraphic and magnetic characteristic of thin films were evaluated by X-ray diffractometry(XRD), vibrating sample magnetometer(VSM) and atomic force microscopy(AFM). The coercivity and anisotropy field was increased by increasing under layer substrate temperature, c-axis orientation of CoCrTa magnetic recording layer was improved 8$^{\circ}$ to 5.6$^{\circ}$when under layer substrate temperature was 250[$^{\circ}C$]. Also, through annealing effect for CoCrTa/Ti double layer, it was certain that crystallgraphics and magnetic characteristics was improved.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.208-211
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• 2000

We prepared Co-Cr-Ta and Co-Cr-Ta/Ti thin film for perpendicular magnetic recording media by facing targets sputtering system (FTS system). Ti underlayer effects on crystallographic and magnetic characteristics of Co-Cr-Ta perpendicular magnetic recording media have been investigated. Crystallgraphic and magnetic characteristic of prepared thin films were evaluated by x-ray diffractometry(XRD), vibrating sample magnetometer(VSM) and kerr hysteresis loop measurement. The coercivity and anisotropy field increase by introduced Ti underlayer when substrate temperature is higher than 150$^{\circ}C$. The c-axis dispersion angle and grain size of Co-Cr-Ta/Ti thin film is decrease than Co-Cr-Ta when substrate temperature is higher than 100$^{\circ}C$. Consequently, the use of a Ti underlayer highly orientated can be improved crystallographic and magnetic characteristics of Co-Cr -Ta perpendicular media layer.

• Journal of the Korean Magnetics Society
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• v.22 no.1
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• pp.1-5
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• 2012

We investigate the exchange bias effect in $[Pd/Co]_5$ superlattice structures which are representative system of the perpendicular magnetic anisotropy. We fabricate Si/$[Pd/Co]_5$/FeMn structures, and study the exchange bias variations by measuring hysteresis loop variations with thickness of FeMn layer. In order to optimize the perpendicular magnetic anisotropy, we fix the thickness of Pd with 1.1 nm and investigate the dependence of the perpendicular magnetic anisotropy on the ferromagnetic Co layer thickness. As results, we find that the biggest coercivity in 0.3 nm of Co layer without FeMn layer. The biggest exchange bias field is found for 0.3 nm of Co layer when we change the Co thickness with fixed FeMn thickness. When we vary thickness of FeMn layer, the biggest coercivity is found for 5 nm of FeMn layer. No exchange bias is observed when the FeMn layer is thinner than 3 nm, and the exchange bias field increases with FeMn layer thickness continuously up to 15 nm.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.17-22
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• 2000

A quaternary alloy film of $CoCr_{16.2}Pt_{10.8}Ta_4$was investigated for its magnetic properties and c-axis orientation with and without Ti underlayer. Additional elements such as Ta, Pt have been frequently introduced in CoCr alloy film for perpendicular recording as a means of improving magnetic performance. It has been reported that the addition of Pt and Ta in CoCr increase the coercivity and the magnetic isolation of columnar grains, respectively. However, CoCrPtTa perpendicular magnetic layer should be more increased its perpendicular magnetic anisotropy than at present for the application of ultrahigh recording density. The improvement of underlayers and substrate materials is one of the promised schemes to intensify the perpendicular magnetic anisotropy. In this study, the insertion of Ti underlayer shows the remarkable improvement of c-axis orientation compare with the direct deposition on the bare glass. The mechanism about this effect of Ti underlayer on CoCrPtTa is not to be clarified yet. Meanwhile, it is found that the magnetic domain of CoCrPtTa on 20 nm Ti underlayer has the continuous stripe pattern but the one of CoCrPtTa on 90 nm Ti underlayer shows the discrete mass type from the results of MFM investigation. This phenomenon is to be a distinct evidence that the improvement of perpendicular anisotropy by the adoption of Ti underlayer is originated from the reinforcement of the grain boundary segregation in CoCrPtTa alloy. Moreover, the transition of the M-H hysteresis pattern with the thickness of Ti underlayer indicates that the major contribution of Ti underlayer is not the magnetocrystalline anisotropy but the shape anisotropy due to the formation of uniform columnar grains by the nonmagnetic alloy segregation.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.52.2-52.2
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• 2020

At quasi-perpendicular shocks in the high-�� (��=Pgas/Pmag~100) intracluster medium (ICM), various microinstabilities occur by the temperature anisotropies and/or drift motions of plasma. In the downstream, the Alfvén ion cyclotron instability (AIC) due to the ion temperature anisotropy (Ti⊥>Ti║) is triggered by shock-reflected ions, the whistler instability (WI) is driven by the electron temperature anisotropy (Te⊥>Te║) as a consequence of the shock compression of magnetic fields, and the mirror instability is generated due to the ion and/or electron temperature anisotropy. At the shock foot, the modified two stream instability (MTSI) is possibly excited by the cross-field drift between ions and electrons. In the upstream, electron firehose instability (EFI) is driven by the electron temperature anisotropy or the relative drift between incoming and reflected electrons. These microinstabilities play important roles in the particle acceleration in ICM shocks, so understanding of the microinstabilities and the resultant plasma waves is essential. In this study, based on a linear stability analysis, the basic properties of the microinstabilities in ICM shocks and the ion/electron scale fluctuations are described. We then discuss the implication of our work on the electron pre-acceleration in ICM shocks.

• Current Applied Physics
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• v.18 no.11
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• pp.1212-1217
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• 2018

The electric field-induced modifications of magnetic anisotropy in CoFeB/MgO systems are studied using X-ray resonant magnetic scattering and magneto-optical Kerr effect. Voltage dependent changes of the magnetic anisotropy of -12.7 fJ/Vm and -8.32 fJ/Vm are observed for Ta/CoFeB/MgO and Hf/CoFeB/MgO systems, respectively. This implies that the interfacial perpendicular magnetic anisotropy is reduced (enhanced) when electron density is increased (decreased). X-ray resonant magnetic scattering measurements reveal that the small in-plane magnetic component of the remanent state of CoFeB/MgO systems with weak magnetic anisotropy changes depending on the applied voltage leading to modification of the magnetic anisotropy at the CoFeB/MgO interface.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.94-97
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• 2008

We investigated how the magnetic anisotropy in $[Co(2\;{\AA})/Ni(8\;{\AA})]{\times}N$ multilayers varied with the type and thickness of an underlayer. The magnetic measurements clearly showed that the perpendicular magnetic anisotropy could be developed in the Co/Ni multilayer by adopting an underlayer with [111] texture. The coercivity of the Co/Ni multilayer increased from 99 Oe to 430 Oe as the thickness of an Au underlayer increased from $50\;{\AA}$ to $500\;{\AA}$. The increase in coercivity is ascribed to the development of the stronger [111] texture in the Co/Ni multilayer as an Au underlayer gets thicker.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.200.2-200.2
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• 2007

• Proceedings of the Korean Magnestics Society Conference
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• 2002.04a
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• pp.150-151
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• 2002