• Title/Summary/Keyword: JKMS

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Coersivity Alteration of Free Layer in the [Co/Pd] Spin-valves with Perpendicular Magnetic Anisotropy ([Pd/Co] 다층박막을 이용한 수직스핀밸브 구조에서 비자성층에 인접한 강자성 물질과 그 두께에 따른 자유층의 보자력 변화)

  • Heo, Jang;Choi, Hyong-Rok;Lee, Ky-Am
    • Journal of the Korean Magnetics Society
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    • v.20 no.3
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    • pp.89-93
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    • 2010
  • We study the giant magneto-resistance (GMR), coercivity and their dependence on the ferromagnetic layers adjacent to the nonmagnetic layer in a spin-valve structure, [Pd/ferromagnetic] multilayers with perpendicular anisotropy. We fabricated a basic spinvalve structure of $[Pd/Co]_2$/ferro-magnetic layer/nonmagnet/ferro-magnetic layer/$[Pd/Co]_2$/FeMn and investigated the dependence of its GMR and magnetic properties such ad coercivity on the ferromagnetic material to reduce the coercivity of the free layer. We try to reduce the freelayer coercivity by controlled the anisotropy, we insert the material NiFe, $Co_8Fe_2$, $Co_9Fe_1$ to ferromagnetic layers adjacent to the Cu layer. Then, we have been able to reduce the coercivity as low as 100 Oe, and also achieved 6.7% of magneto-resistance ratio when the ferromagnetic layer thickness was 0,7 nm.

Superparamagnetic Properties of γ-Fe2O3 Nanoparticles (초미세 나노분말 γ-Fe2O3의 초상자성 특성연구)

  • Lee, Seung-Wha;Lee, Jae-Gwang;Chae, Kwang-Pyo;An, Sung-Yong
    • Journal of the Korean Magnetics Society
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    • v.20 no.5
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    • pp.196-200
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    • 2010
  • $\gamma-Fe_2O_3$ nanoparticles have been prepared by a sol-gel method. The structural and magnetic properties have been investigated by XRD, VSM and Mossbauer spectroscopy. $\gamma-Fe_2O_3$ powder annealed at $150^{\circ}C$ has a spinel structure and superparamagnetical behavior. The estimated size of superparammagnetic $\gamma-Fe_2O_3$ nanoparticle is around 7 nm. The hyperfine fields at $-261^{\circ}C$ for the A and B patterns were found to be 503 and 485 kOe, respectively. The blocking temperature ($T_B$) of superparammagnetic $\gamma-Fe_2O_3$ nanoparticle is about $-183^{\circ}C$. The magnetic anisotropy constant of $\gamma-Fe_2O_3$ nanoparticle was calculated to be $1.6{\times}10^6ergs/cm^3$. $\gamma-Fe_2O_3$ nanoparticle annealed at $150^{\circ}C$ can be a candidate for biomedicine applications as magnetic carriers.

Second Harmonic Rotational Anisotropy of Polycrystalline Fe Films on Glass Substrates (유리 위에 증착된 다결정 Fe 자성박막의 이차조화파 회전 이방성)

  • Lee, Feel;Jeong, Jae-Woo;Lee, Hun-Sung;Lee, Kyung-Dong;Kim, Ji-Wan;Shin, Sung-Chul
    • Journal of the Korean Magnetics Society
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    • v.19 no.2
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    • pp.47-51
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    • 2009
  • The surface structure of polycrystalline Fe films of various thicknesses on glass substrates have been studied using a Ti: Sapphire laser at 780 nm. We found that the surface structure possesses C$_s$ crystal structure close to $C_{2v}$ through symmetry consideration. We present one-fold intensity profile with one mirror plane in second harmonic (SH) intensity as a proof of $C_s$ symmetry. $C_s$ and $C_{2v}$ surface symmetries usually appear at the (110) surface of a cubic diamond single crystal [1]. Therefore this surface symmetry would be related to bcc (110) growth orientation coinciding with XRD measurement. Further we treated surface normalized SH asymmetry with various thicknesses. The SH asymmetry increases with increasing of film thickness. From these results, it is observed that the surface structure of thin polycrystalline Fe film below 5 nm is almost isotropic, while in the case of the thicker Fe films, surface structure have $C_s$ symmetry structure close to $C_{2v}$.

Effect of the Removal of an Initial Oxide Layer and the Anodization Time on the Growth of the Porous Alumina Layer (초기 산화피막 제거와 양극산화 시간에 따른 다공성 알루미나 막의 성장)

  • Kim, Dae-Hwan;Lue, Sang-Hee;Lee, Hyo-Jin;Park, Young-Ok;Lee, Eun-Joong;Kouh, Tae-Joon
    • Journal of the Korean Magnetics Society
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    • v.20 no.5
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    • pp.191-195
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    • 2010
  • We have investigated the effect of the removal of an initial oxide layer and the anodization time on the growth of the porous alumina layer. The porous alumina layer was fabricated by two-step anodization process with phosphoric acid. We have observed the changes in the uniformity of the pore structure by varying the removing time of the initial oxide layer after the first anodization with phosphoric acid and chromic acid, and noted that its uniformity improves with the removing time. We have also determined the thickness of the alumina layer after the final anodization process and found that the thickness increases linearly with the anodization time. Under 150 V of anodization voltage with phosphoric acid, the growth rate of the porous alumina layer is determined to be 22.5 nm/min.

The Multiferroic Properties Study of YMn2-xFexO5 (x=0.00, 0.01) by Neutron Diffraction (고 분해능 중성자 회절 실험에 의한 YMn2-xFexO5 (x = 0.00, 0.01)의 다강체 특성 연구)

  • Kim, Dong-Hyun;Kim, Chul-Sung
    • Journal of the Korean Magnetics Society
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    • v.17 no.5
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    • pp.183-187
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    • 2007
  • Compounds of multiferroic materials $YMn_{2-x}Fe_xO_5$ (x = 0.00, 0.01) were prepared using the sol-gel method. The crystallographic, magnetic and electric properties are studied using x-ray diffraction (XRD), neutron diffraction, vibrating sample magnetometer (VSM) and physical property measurement system (PPMS). The crystalline structure of $YMn_2O_5$ was found to be orthorhombic (Pbam) at room temperature. The lattice constants of $YMn_2O_5$ were determined to be $a_0=7.275\;{\AA},\;b_0=8.487\;{\AA},\;c_0=5.674\;{\AA}$. The lattice constants not changed with Fe concentrations. Our data demonstrate the correlation of magnetic and electric properties in $YMn_2O_5$ materials.

Magnetization Reversal Behavior of Submicron-sized Magnetic Films in Response to Sub-ns Longitudinal Field Pulses Along the Easy Axis (1 ns 이하의 자화 용이축 펄스 자기장에 의한 자성박막의 자화 반전 거동)

  • Lee, Jin-Won;Han, Yoon-Sung;Lee, Sang-Ho;Hong, Jong-Ill
    • Journal of the Korean Magnetics Society
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    • v.17 no.5
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    • pp.188-193
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    • 2007
  • We simulated the magnetization reversal behavior of submicron-thickness magnetic films by applying pulses of sub-ns-long durations and amplitudes along the easy axis. The films were rectangular and elliptical $Ni_{80}Fe_{20}$, and their thickness was 2 nm and 4 nm. We observed different behaviors depending upon the shape and thickness of the films and found a normal non-switching in regions in which we expected complete switching after relaxation. In the elliptical film, the non-switching regions were found to be random and to be widely distributed throughout the switching map. The strong demagnetization field along the z-axis, the film thickness direction, is likely responsible for this abnormal behavior. In the rectangular film, the abnormal non-switching regions were less distributed than they were in the elliptical film due to edge domains resulting from the small $M_z$ or demagnetization field during the switching. Our simulation confirms that large demagnetization is detrimental to the ultra-fast magnetization reversal of magnetic ultra-thin films.

Effects of Annealing Temperature on Electromagnetic Wave Absorption Characteristics in FeCuNbSiB Alloy Flakes/Polymer Composite Sheets (FeCuNbSiB 합금 박편/폴리머 복합 시트의 전자파 흡수 특성에 미치는 자성분말 어닐링 온도의 영향)

  • Noh, Tae-Hwan;Lee, Tae-Gyu
    • Journal of the Korean Magnetics Society
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    • v.17 no.5
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    • pp.198-204
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    • 2007
  • The effects of annealing temperature on electromagnetic wave absorption characteristics in $Fe_{73.5}Cu_1Nb_3Si_{15.5}B_7$ (at%) alloy flakes/polymer composite sheets available for quasi-microwave band have been investigated. The composite sheet including the magnetic flakes annealed at $425{\sim}475^{\circ}C$ for 1 h exhibited highest power loss in the GHz frequency range as compared with the sheets composed of the alloy flakes annealed at higher temperature than $475^{\circ}C$ or in as-milled state. Moreover the imaginary part of complex permeability had largest value in the GHz frequency range for the sheets including the flakes annealed at $425{\sim}475^{\circ}C$. The large value of power loss of the sheets including the magnetic flakes annealed at $425{\sim}475^{\circ}C$ was attributed to the high imaginary part of the complex permeability. However, because of its large transmission parameter $S_{21}$, the composite sheet having the magnetic flakes annealed at $525^{\circ}C$ showed low power loss.

The Electronic Structure and Magnetism of Superlattices Consisted of Heuslerand Zinc-blende Structured Half-metals (Heusler 화합물과 Zinc-blende 구조를 가지는 반쪽금속으로 이루어진 초격자의 전자구조와 자성)

  • Cho, Lee-Hyun;Bialek, B.;Lee, Jae-Il
    • Journal of the Korean Magnetics Society
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    • v.18 no.5
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    • pp.163-167
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    • 2008
  • The electronic structure and magnetism of superlattice systems consisted of Heusler compound $Co_2MnSi$ (CMS) and zinc-blende MnAs (MA) are investigated by means of the all-electron full potential linearized augmented plane wave method within the generalized gradient approximation. Four superlattice systems are considered, that is CMS(m)/MA(n), where m and n, being either 2 or 4, denote the number of alternatingly arrayed layers of the compounds in a superlattice along [001] direction. From the calculated total magnetic moments as well as the total density of states, it is found that neither of the four systems is half-metallic. It is also found that the Mn atoms are antiferromagnetically coupled in the systems of CMS2/MA2 and CMS2/MA4. The total and atom-resolved density of states of the four superlattices are compared with those of the bulk $Co_2MnSi$ and MnAs, and the influences of the change in the systems symmetry on the magnetism and half-metallicity are discussed.

Dependence of Coercivity and Exchange Bias by Thickness and Materials of Inserted Layer in [Pd/Co]5/X/FeMn Multilayer with Out-of-plane Magnetic Anisotropy (수직자기이방성을 갖는 [Pd/Co]5/X/FeMn 다층박막에서 삽입층 물질과 두께에 따른 교환바이어스와 보자력의 의존성)

  • Heo, Jang;Park, Dong-Hun;Kang, Wang-Son;Ji, Sang-Hun;Lee, Ky-Am
    • Journal of the Korean Magnetics Society
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    • v.18 no.5
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    • pp.185-189
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    • 2008
  • We observe the change of coercivity and exchange bias, depending on inserting material and thickness in a [Pd(0.6 nm)/$Co(0.2)]_5$/ FeMn(10) multilayer structure with perpendicular anisotropy. When 0.78 and 1.28 nm thick NiFe substitutes for Co in a $[Pd(0.6 nm)Co(0.2)]_4$/Pd(0.6)/NiFe(t)/FeMn(10) structure, we obtain the exchange bias of 360 Oe. In addition, when $Co_8Fe_2$ and $Co_9Fe_1$ are inserted for Co/FeMn interface, we obtain the exchange bias of 380 nm for a 0.68 nm thick $Co_8Fe_2$ and 580 Oe for a 0.52 nm thick $Co_9Fe_1$.

Characteristics of Mineral Mg Dissolving Sensor in Edible Water using GMR-SV Device (거대자기저항 스핀밸브 소자를 이용한 음용수 미네랄 Mg 용해센서 특성 연구)

  • Lee, Ju-Hee;Kim, Da-Woon;Kim, Min-Ji;Park, Kwang-Seo;Kang, Joon-Ho;Lee, Sang-Suk
    • Journal of the Korean Magnetics Society
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    • v.18 no.5
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    • pp.174-179
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    • 2008
  • The measurement dissolution sensor system using GMR-SV device with magnetic sensitivity of 0.8 %/Oe and Mg-film thick of 200 nm and Mg-foil thick of 50 mm was fabricated and characterized. During the water dissolving process of Mg-film and Mg-foil, the subtle variation of magnetic field by the decrease of current in solenoid was detected by the GMR-SV sensor. The variations of Mg bubble number and ORP as a function of time for three different kinds of edible, tap, and distilled water, are measured and compared. A After 45 min, the speed of fast dissolving Mg was shown the order of edible > tap > DI water. The variation of output magnetoresistance as a function of dissolved time of Mg-film and Mg-foil for edible water, which is composed of mineral content of $0.8{\sim}5.4\;mg/l$ was investigated. The response times for the dissolution in edible water were 5 min and 20 min, respectively. From the measurement of dissolving time and speed for Mg-film and Mg-foil using GMR-SV device, the mineral Mg sensor system in edible water can be possible to develop.