• Proceedings of the Korean Magnestics Society Conference
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• 1999.10a
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• pp.104-105
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• 1999

• Journal of the Korean Magnetics Society
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• v.21 no.6
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• pp.193-197
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• 2011

The thickness dependence of the magnetic switching volumes in electrodeposited CoPt films was investigated from the magnetization reversal and the magnetic interaction behavior. As the sample thickness is increased, the field difference between the wall pinning field ($H_{DW}$) and the nucleation field ($H_N$) as well as the absolute value of ${\Delta}$area are increased. Therefore, the decrement tendency of the switching diameter with increasing sample thickness can be well explained by the domain wall motion controlled by the domain wall pinning and the strength of dipolar interaction.

• Progress in Superconductivity and Cryogenics
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• v.5 no.3
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• pp.6-10
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• 2003

Silver nano-powder was added to Ma $B_2$ to make (Ag)$_{(x)wt.%}$(Mg $B_2$)$_{(l00-x)wt.%}$ (A $g_{x}$-Mg $B_2$) (10 $\leq$ x $\leq$ 50) composite superconductors to investigate the effect of the Ag nano-powder on the vortex pinning. Pellets made out of the mixed powder were put inside stainless steel tubes, which were sintered at 85$0^{\circ}C$ in Ar atmosphere. No impurity phase was identified for as-rolled samples. However, both the Mg $B_2$ and the A $g_{x}$-Mg $B_2$ composite pellets, when sintered, contain small amount of Mg $B_4$ and MgAg impurity phases. From the magnetization study, it was found that the flux pinning was improved in the high magnetic field region (> 3 T) only when 10w/o Ag was added to Mg $B_2$. The "two step" structures in ZFC M(T) curve gradually increased as the amount of Ag added increased. Pinning centers can be created by adding a suitable amount of Ag nano-powder which is not too large to increase the decoupling between the Mg $B_2$ grains.crease the decoupling between the Mg $B_2$ grains.

• 한국초전도학회:학술대회논문집
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• 2008.08a
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• pp.34-34
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• 2008

• Journal of the Korean Magnetics Society
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• v.26 no.6
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• pp.196-200
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• 2016

In this study the mechanisms of magnetization reversal and magnetic interaction effects on activation volumes for Sr-ferrite with different particle sizes are investigated. The activation volumes of C2 sample are larger than those of C3 sample in the range of low magnetic fields. But the fields above the coercivity of sample C2, the activation volumes of both samples are decreased linearly with increasing the applied magnetic field. These phenomena can be explained by the strengths of two critical fields representing the reverse domain nucleation field and the domain wall pinning field as well as the strength of dipolar interaction.

• Journal of Magnetics
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• v.16 no.2
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• pp.83-87
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• 2011

The vortex-driven magnetization process of micron-sized, exchange-coupled square elements with composition of $Ni_{80}Fe_{20}$ (12 nm)/$Ir_{20}Mn_{80}$ (5 nm) is investigated. The exchange-bias is introduced by field-cooling through the blocking temperature (TB) of the system, whereby Landau-shaped vortex states of the $Ni_{80}Fe_{20}$ layer are imprinted into the $Ir_{20}Mn_{80}$. In the case of zero-field cooling, the exchange-coupling at the ferromagnetic/antiferromagnetic interface significantly enhances the vortex stability by increasing the nucleation and annihilation fields, while reducing coercivity and remanence. For the field-cooled elements, the hysteresis loops are shifted along the cooling field axis. The loop shift is attributed to the imprinting of displaced vortex state of $Ni_{80}Fe_{20}$ into $Ir_{20}Mn_{80}$, which leads to asymmetric effective local pinning fields at the interface. The asymmetry of the hysteresis loop and the strength of the exchange-bias field can be tuned by varying the strength of cooling field. Micromagnetic modeling reproduces the experimentally observed vortex-driven magnetization process if the local pinning fields induced by exchange-coupling of the ferromagnetic and antiferromagnetic layers are taken into account.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.9
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• pp.752-757
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• 1998

Rotational Magnetization-vector measurements have been performed on a polycrystalline $Y_1Ba_2Cu_3O_{7-\delta}$ sample in field-cooled condition at 4.2 K. The experimental results show that vortex flux density(B) consists of 3 groups :(1) a weak pinning part ($B_w$) which stays at a fixed angle relative to the magnetic field f(H) ; (2) a strong pining part($B_s$) which rotates rigidly with the sample and has same magnitude with the sample rotation, and(3) and intermediated pining part ($B_i$) which rotates rigidly with the sample, but whose magnitude changes with the sample rotation Our results have been explained in terms of a distribution in the strength of the vortex pinning torque and a repulsive intervortex torque.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.1-5
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• 1999

The critical currents I$_c$ of the YBCO grain boundaries of 90-degree [100] symmetric tilt showed a hysteretic behavior depending on how the external magnetic fields were applied. Near 77K for fields less than ${\sim}$1 T, the field-cooled I$_c$ of grain boundaries was larger than the zero-field-cooled I$_c$. This result is consistent with the model in which the grain-boundary vortices can be pinned by neighboring Abrikosov vortices in the nearby grains.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.15-21
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• 1991

The magnetic properties of the $Y_{1}Ba_{2}Cu_{3-x}Sn_{x}O_{7-y}$ superconductor were studied as a function of Sn concentration by utilizing both the vibrating sample magnetometer (VSM) and torque magnetometer. Unlike the cases where Fe and Co were substituted for Cu, the superconducting transition temperature was maintained above 90 K until x reached the value of 0.36. The lower critical field $H_{c1}(T)$ and upper critical field $H_{c2}(T)$ are measured as a function of temperature and external magnetic field, respectively. By aid of these results, $H_{c1}(0)$.($H_{c2}(0)$), the coherence length ${\varepsilon}_{0}$, the penetration depth ${\lambda}_{0}$, and the Ginzburg-Landau parameter k were oqtained. Flux pinning was also observed in the sample.

• Journal of Magnetics
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• v.5 no.2
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• pp.50-54
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• 2000

NiMn-pinned spin valve films consisting of a layered glass/NiFe/Co/Cu/Co/NiFe/NiMn/Ta stack were made by do magnetron sputtering. After deposition, the structure was annealed in a series of cycles each including three hours at $220^\circ C, 2\times10^{-6}$ Torr, in a field of 350 Oe, to create an ordered antiferromagnetic structure in the NiMn layer and produce a strong unidirectional pinning field in the pinned magnetic layer, Optimum spin valve properties were obtained after seven annealing cycles, or 21 hours at $220^\circ C$, and were : MR ratio 1%, exchange coupling field 620 Oe, and coercivity of pinned layer 250 Oe. The exchange coupling field remained constant up to an operating temperature of $175^\circ C$, and the blocking temperature was about $380^\circ C$.