• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.3
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• pp.238-246
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• 2003

We have performed the simulation of ferromagnetic resonance spectra on the exchange coupled bilayer thin films at perpendicular configuration. Variables considered in spectrum calculation were the interfacial exchange constants per unit area, the layer thickness, and the surface anisotropy constants. In case of antiferromagnetic coupling, variation of exchange constant gave a great effect to the absorption spectra of the low and the high magnetization layer. Variation of thickness in low magnetization layer did nt nearly influenced the resonated field of the high magnetization layer. Also, the increase of negative surface anisotropy increased the resonance field of the low and the high magnetization layer.

• Journal of the Korean Magnetics Society
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• v.21 no.1
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• pp.10-14
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• 2011

We have measured the ferromagnetic resonance (FMR) signal in as deposited and $400^{\circ}C$ annealed CoFeB/MgO thin film to investigate the annealing effect on magnetic anisotropies and FMR linewidth (${\Delta}H_{PP}$). The uniaxial anisotropy field ($H_{K1}$) was only observed in the as deposited sample. Whereas, in the $400^{\circ}C$ annealed sample, the biaxial anisotropy field ($H_{K2}$) was additionally observed in accompany with uniaxial anisotropy field ($H_{K1}$). The appearance of biaxial anisotropy fields was originated from the crystalline growth of bcc CoFeB(001) from the MgO(001) interface and by the B diffusion during thermal annealing. Also, the ${\Delta}H_{PP}$ of $400^{\circ}C$ annealed sample was increased compared with that of as deposited sample, which was due to the broad distribution of the magnetization axis by the biaxial anisotropy.

• Journal of the Korean Magnetics Society
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• v.7 no.3
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• pp.129-133
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• 1997

To investigate the influence of the Hf concentration and the annealing effect in $Co_{1-x}Hf_x$(X=0.16, 0.24 at.%) systems, ferromagnetic resonance experiments have been carried out. Spin wave resonance spectra for all samples consist of several volume modes and one (or two) surface mode. It is suggested that both surfaces of the film have a perpendicular hard axis to the film plane (negative surface anisotropy). The surface anisotropy $K_{s2}$ at substrate-film interface is varied slowly from -0.07 to -0.32 erg/$\textrm{cm}^2$ and the surface anisotropy $K_{s1}$ at film-air interface is varied from 0.18 to -0.47 erg/ $\textrm{cm}^2$ with increasing annealing temperature in the amorphous $Co_{84}Hf_{16}$ thin films. Also, the surface anisotropy $K_{s2}$ is varied slowly from -0.31 to -0.41 erg/$\textrm{cm}^2$ and the surface anisotropy $K_{s1}$is varied from -0.19 to -0.60 erg/$\textrm{cm}^2$ with increasing annealing temperature in the amporphous $Co_{84}Hf_{16}$ thin films. We conjecture that the variation of surface anisotropy $K_{s1}$ is due to the increase of Co concentration resulted from Hf oxidation for low temperature annealing(150~175 $^{\circ}C$) and the diffusion of Co atoms near the film surfaces for high temperature annealing (200~225 $^{\circ}C$).

• Journal of the Korean Magnetics Society
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• v.2 no.3
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• pp.251-256
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• 1992

Artificial superlattices of Co/Pd were prepared by RF magnetron sputtering Multilayered structure and compositional modulation were analyzed with a side angle x-ray diffractometer. It has been found that expansion of Co lattice occured in this artificial superlattice due to the lattice mismatch between Co and Pd. Perpendicular magnetic anisotropy could be observed when the Co layer thickness became less than 8${\AA}$ and maximum coercivity of 2350 Oe could be obtained in [Co(2.5 ${\AA}$)/Pd(9.3 ${\AA})]_{50}$/Pd$(200\;{\AA})$ with a perfect squareness of magnetic hysteresis loop. Characteristic of perpendicular magnetic anisotropy in Co/Pd superlattices could be related to the expansion of Co lattice caused by Pd layer and it turned out that as the thickness of Pd layer increased, perpendicular magnetic anisotropy increased. The interface anisotropy energy and volume anisotropy energy were calculated to be 0.29 ergs/$cm^2$ and -$6.9{\times}10^6$ ergs/$cm^3$ respectively, which are consistent with the values reported elsewhere.

• Journal of the Korean Geotechnical Society
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• v.38 no.2
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• pp.29-38
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• 2022

The friction anisotropy of shear resistance can be selectively used in geo-structures. For example, larger axially loaded deep foundation, soil nails, and tiebacks increase load carrying capacity due to induced large shear resistance while pile penetration and soil sampling produce minimal shear resistance. Previous studies confirmed direction-dependent shear resistance induced by interface between soil and surface asperity of plate inspired by geometrical shape of snake scale. The aim of this paper is to quantitatively evaluate interface friction angle with different surface asperities. Using the modified direct shear test, a total of 51 cases, which sand are prepared at the relative density of 40%, are conduced including 9 plates, two shear direction (shearing direction against the height of surface asperity is increased or decreased during shearing test), and three initial vertical stress (100 kPa, 200 kPa, 300 kPa). Experimental results show that shear stress is increased with higher height of surface asperity, shorter length of surface asperity, and the shearing direction that the height of surface asperity increases. Also, interface friction angle is decreased with larger surface asperity ratio, and shearing direction with increasing height of surface asperity produces larger interface friction angle regardless of the surface asperity ratio.

• Proceedings of the Korean Magnestics Society Conference
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• 1991.05a
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• pp.103-104
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• 1991

• Proceedings of the Korean Magnestics Society Conference
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• 1999.04a
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• pp.30-31
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• 1999

• Proceedings of the Korean Magnestics Society Conference
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• 2013.05a
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• pp.55-56
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• 2013

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.169-169
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• 1999

We studied magnetic properties of co thin films deposited on Pd (111) surface, which attracted much attention recently due to the perpendicular magnetic anisotropy, using magnetic circular dichroism(MCD). Special attention was paid on the effect of Pd capping and interface roughness on the direction of magnetic easy axis, and for that purpose MCD signals for all Co thicknesses were measured with two different ways : in-plane and out-of-plane geometry. In case of bare Co films deposited on smooth Pd(111) surface, no MCD signal was observed under 4$\AA$ co thickness. At 4$\AA$ Co thickness, MCD signal at the out-of-plane geometry was observed, and for thicker Co films, only in-plane MCD signal was measured. This type of magnetic easy axis transition has been reported for other cases like Co/Pt system. The effect of 5$\AA$ Pd capping on these bare Co films made an remarkable change on the transition of magnetic easy axis. Out-of-plane MCD signals exists up to 20$\AA$ Co thickness, and disappears at 24$\AA$ Co thickness. In-plane MCD signals first appears at 10$\AA$ Co thickness and gradually increases up to 24$\AA$ Co thickness. Between 10$\AA$ and 20$\AA$ Co thickness, in-plane and out-of-plane MCD signal coexist. The formation of multi-domain structure or the existence of tilted magnetic easy axis is an possible scenario for such an interesting coexistence. The effect of interface roughness was also tested by measuring MCD signal on Co films deposited on un-annealed Pd(111) surface. Out-of-plane MCD signal was observed up to 8$\AA$ Co thickness and the anisotropy of MCD signal at 4$\AA$ Co thickness was very large with respect to that of Co film deposited on the smooth substrate. Above 8$\AA$ thickness, there exists only in-plane MCD signal. From above results, it was concluded that both Pd capping and interface roughness induce and reenforce the perpendicular magnetic anisotropy. The large perpendicular magnetic anisotropy of Co/Pd multilayer system made by sputtering method can be well understood from our results.

• Journal of the Korean Magnetics Society
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• v.9 no.5
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• pp.251-255
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• 1999

NiFe(60 $\AA$)/Co(0$\AA$$\leq$x$\AA$$\leq$15$\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valve thin films were prepared on 4$^{\circ}$ tilt-cut Si(111) substrates with a 50 $\AA$ thick Cu underlayer without applying any external magnetic field during the deposition, and the effects of inserted ultrathin Co layer on magnetic anisotropy and GMR properties of the NiFe(60 $\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valves were investigated. As the ultrathin Co layer was inserted into the NiFe/Cu interface of the spin valves, GMR ratio was increased from about 1.5% to 3.5%, and the easy axis of NiFe(60 $\AA$) layer was rotated by 90$^{\circ}$. Accordingly, it was aligned along the same direction with the easy axis of Co(30 $\AA$)layer. Therefore, squared R-H curves was obtained in the spin valves, which is favorable properties for the digital GMR devices such as MRAM. In order to investigate the change of magnetic anisotropy of NiFe layer of the spin valves in more details,XRD measurement was performed using NiFe(500 $\AA$) and NiFe(500 $\AA$)/Co(10 $\AA$) thin films on the same templates. Strong (220) NiFe peak was observed in both films regardless of the inserted Co layer, so it was thought that the variation of magnetic anisotropy of NiFe layer is from the interface effect, the change of interface from NiFe/Cu to NiFe/Co, rather than the volume effect such as the change of magnetocrystalline effect.