• Title/Summary/Keyword: pinning field

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Magnetization Reversal and Magnetic Switching Volume in Electrodeposited CoPt Magnetic Films with Different Thickness (전기도금법으로 제작한 두께가 다른 CoPt 자성막의 자화역전과 자기역전 부피)

  • Kim, Hyeon-Soo;Jeong, Soon-Young;Lee, Chang-Hyeong;Suh, Su-Jeong
    • 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.

Influence of Ag nano-powder additions on the superconducting properties of Mg $B_2$ materials

  • K. J. Song;Park, S. J.;Kim, S. W.;Park, C.;J. H. Joo;Kim, H. J.;J. K. Chung;R. K. Ko;H. S. Ha
    • 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.

Magnetic Field Dependence of the Activation Volume for Sr-ferrite Particles (Sr-페라이트 자성 입자의 활성화 부피의 자기장 의존성)

  • Kim, Hyeon Soo;Jeong, Soon Young;Kim, Kyung Min;Kwon, Hae-Woong
    • 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.

Magnetization Process in Vortex-imprinted Ni80Fe20/Ir20Mn80 Square Elements

  • Xu, H.;Kolthammer, J.;Rudge, J.;Girgis, E.;Choi, B.C.;Hong, Y.K.;Abo, G.;Speliotis, Th.;Niarchos, D.
    • 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.

Behavior of the Vortex Flux in a Polycrystalline $Y_1Ba_2Cu_3O_{7-\delta}$Superconductor in a Rotational Experiment (회전실험에서의 다결성 $Y_1Ba_2Cu_3O_{7-\delta}$ 초전도체내의 vorterx flux의 거동)

  • 박성재;김용석;김채옥
    • 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.

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Possible pinning of grain-boundary vortices by neighboring Abrikosov vortices in the nearby grains (Abrikosov 볼텍스에 의한 결정입계 볼텍스의 속박 현상)

  • Kim, Dong-Ho
    • 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.

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Magnetic Properties of the $Y_{1}Ba_{2}Cu_{3-x}Sn_{x}O_{7-y}$ $High-T_{C}$ Superconductor (고온 초전도체 $Y_{1}Ba_{2}Cu_{3-x}Sn_{x}O_{7-y}$의 자기적 특성 연구)

  • 이성규;이주일;김문석;유성초;임우영;백종성
    • 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.

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High Exchange Coupling Field and Thermal Stability of Antiferromagnetic Alloy NiMn Spin Valve Films

  • Lee, N. I.;J. H. Yi;Lee, G. Y.;Kim, M. Y.;J. R. Rhee;Lee, S. S.;D. G. Hwang;Park, C. M.
    • 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 $380^\circ C$.

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