• Journal of the Mineralogical Society of Korea
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• v.24 no.1
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• pp.37-42
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• 2011

Magnetic properties at low-temperatures can diagnose the presence of certain magnetic minerals in rocks. At the Verwey transition temperature ($T_v$, ~105~120 K), magnetite transforms from monoclinic to cubic structure as the temperature increases. At the isotropic point ($T_i$, ~135 K), magnetocrystalline anisotropic constant of magnetite passes through zero (from negative to positive) as the temperature decreases so that its optimal remanence acquisition axis changes from [111] to [001]. A sharp remanence drop was observed at $T_v$ during warming of LTSIRM (low-temperature saturation isothermal remanent magnetization). For cooling of RTSIRM (room-temperature saturation isothermal remanent magnetization), the remanence decreased on passing $T_i$ and $T_v$. On warming of RTSIRM, remanence recovery becomes more prominent as the average grain size of magnetite increases. In summary, the SIRM memory decreases with increasing grain size of magnetite. A similar, but rather gradual, remanence transition occurs for natural samples due to contribution of cations other than Fe. As a non-destructive tool, low-temperature magnetic behavior is sensitive to unravel the magnetic remanence carriers in terrestrial rocks or meteorites.

• Journal of the Mineralogical Society of Korea
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• v.26 no.1
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• pp.19-25
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• 2013

Recent progress in Martian exploration identified hematite as the major candidate for the strong magnetic anomalies observed in Martian lithosphere. In the present study, grain-size dependence of thermoremanent magnetization and low-temperature stability of room-temperature saturation isothermal remanent magnetization (RTSIRM) were monitored using synthetic hematites. For hematite, the antiferromagnetic spin configuration is re-arranged from being perpendicular to the c-axis to be parallel to the c-axis below the Morin transition ($=T_M$). A large fraction of RTSIRM is demagnetized at $T_M$ (= 260 K) during zero-field cooling from 300 K to 10 K. About 37% of the initial RTSIRM is recovered on warming from 10 K to 300 K. Shallow Martian subsurface at 1~2 km depth would experience low-temperature cooling-warming of $T_M$ because average Martian surficial temperature is about 220 K. However in most Martian lithosphere whose temperatures are higher than 260 K, the very stable magnetic memory of hematite could be a contributor to Martian magnetic anomalies.

• Journal of the Mineralogical Society of Korea
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• v.24 no.1
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• pp.31-36
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• 2011

Meteorites are extraterrestrial solid rock fragments that fell from the outer space. Investigating mineral magnetic properties of the Meteorites is essential in understanding the evolution of planets and asteroids in the Solar System. In particular, magnetic characterization of magnetic mineral can provide constraints on the progress of differentiation in ancient planetary bodies. In the present study, ratio of thermoremanent magnetization (TRM) over saturation isothermal remanent magnetization (SIRM) was applied to diagnose the magnetic minerals in meteorites and igneous rocks. Distinctive classification of TRM/SIRM suggests that kamacite, tetrataenite, magnetite, and (Cr,Ti)-rich iron oxide are responsible for the magnetization of H5 Richardton, LL6 St. Severin, ALH84001, and DaG476, respectively. The TRM/SIRM ratio could be an efficient tool in identifying magnetic minerals especially when rocks or meteorites contain unstable material under heating.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.179-179
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• 2016

희토류계 영구자석은 높은 보자력과 잔류 자화을 가지고 있어 자기기록저장매체, MEMS(엑츄에이터), 센서 등의 응용 분야에 적용시키기 위해 다양한 연구들이 진행되고 있다. 하지만 희토류계 원소의 수급 및 가격의 문제점으로 친환경자석으로의 전환 및 희토류나 중희토류를 사용하지 않는 비희토류계 영구자석을 개발하는 연구에 대한 필요성이 대두되고 있다. 이 중 Fe-N 계 자성 물질인 $Fe_{16}N_2$는 포화 자화 값이 현재까지의 자성물질 중 가장 높은 값(240emu/g)을 나타내며 상대적으로 높은 결정자기이방성 상수를 가지고 있어 비희토류계 영구자석 물질 중 하나로 주목받고 있다. 본 연구에서는 $Fe_{16}N_2$ 박막을 얻기 위해 DC Magnetron Sputtering 방법을 이용하여 Si wafer 위에 박막을 증착하고 증착공정 조건 중 질소 유량 및 Sputtering Power를 변수로 따른 박막의 성장, 조직변화, 자성 특성을 관찰을 통해 최적의 공정 조건을 찾고자 하였다. $N_2$ 가스 유량 변화에 따른 박막의 성장 속도는 거의 변화가 없었으며 $N_2$ 가스 유량의 증가에 따라 박막 내 Fe의 함유량은 감소하였다. 모든 공정 조건에서 $Fe_3N$, $Fe_4N$, $Fe_{16}N_2$ 상들이 섞여 성장하였으며 XRD를 통한 상분석과 더불어 VSM을 통한 자성 특성을 분석해본 결과 $Fe_{16}N_2$의 분율이 가장 높게 성장된 공정 조건은 Power는 200W, $N_2$ 가스 유량은 20sccm이었으며 이 조건에서 2.45T의 포화 자화 값과 1.4T의 잔류 자화 값을 얻을 수 있었다.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.389-393
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• 2000

Effects of Co addition and heat treatment on the magnetic properties of Fe-Si-B thin films were investigated. The compositions of metalloids, i.e, B and Si, in the alloys were kept 10 at.% each. Heat treatments were carried out in the temperature range from 100 to $300^{\circ}C$ for up to 60 min. Amorphous thin films of FeCoSiB were deposited on the water-cooled substrates by dc magnetron sputtering. The composition of thin films was controlled by placing proper number of pellets of alloying elements and analyzed by ICP, resulting in $Fe_{80-X}Co_ XB_{10}Si_{10}$ (X=8~18 at.%). Saturation magnetization of the alloys increased as Co concentration increased up to 10 at.% and then decreased with further increase of Co concentration. However, coercive force of the films decreased with the increase of Co concentration. Furthermore, the coercive force was also reduced by the annealing due to the residual stress relief.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.22-35
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• 1995

In this study, crystal structures and magnetic properties of as-ast, annealed and rapidly solidified Mn-A1-M( M=Cu, Fe) alloys have been investigated. In $Mn_{0.56}Al_{0.44}$ alloys, the largest fraction of $\tau$ phase and values of magnetic properties was obtained in Mnl, i6Alo or alloy. And this alloy was used as the basic composition. In $Mn_{0.56-X}M_{X}Al_{0.44}$ alloys, when annealed, $\tau$- and $\beta$-Mn phase appeared at x< 0.08, $\tau$- and $\kappa$ phase at 0.10 $\leq x \leq$ 0.12 and $\kappa$- phase only at 0.15 $\leq x \leq$0.20 . When rapidly solidified, specimens showed similar phases as when annealed except that $\varepsilon$ phase appeared at x=0.04. In Mnu FexAlo 44 alloys, asyast specimens showed $\tau$-, $\beta$-Mn and $\gamma_2$- phase at x<0.08 and K and $\beta$-Mn phase at x>0.10. When rapidly solidified, Mn-Fe-Al specimens showed $\varepsilon$-, $\gamma_2$- and small amount of $\tau$- and $\kappa$ phase at x<0.08 and $\kappa$- phase only at 0.$\leq x \leq$0.20. All the alloys investigated were ferromagnetic. The Curie temperature of annealed specimens and rapidly solidified of Mno 5sAlu 44 alloy were -650K and -644K. Spontaneous magnetization( UII of annealed and rapidly solidified specimens were 40-45 (emu/g) and 50-52(emu/g), respectively. Remanent (M,) to saturation magnetization( Ms) ratio was -0.7. M, of rapidly solidified specimen was about 48(emu/g). Magnetic properties of $Mn_{0.56}Al_{0.44}$ alloys were found to be determined by the relative fraction of ferromagnetic r- and K- phase. When M= Cu and x=0.15, maximum as($\sigma_{0.0}$) was obtained by about 64.3 emu/g), and when M=Fe and x=0.15, 66.4( emu/g). The Curie temperature decreased as x increased.

• Journal of the Korean Magnetics Society
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• v.14 no.3
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• pp.105-108
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• 2004

Array of magnetic Ni nanostructures has been fabricated on Si substrate by using nanoporous alumina film as a mask during deposition. The nanostructures are truncated cone-shape and the lateral sizes are comparable to height. While the continuous film shows well-defined in-plane magnetization, the nanostructure shows perpendicular component of magnetization at remanence. The hysterectic behavior of nanostructures is dominated by the demagnetizing field instead of interaction among them.

• Journal of the Microelectronics and Packaging Society
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• v.22 no.3
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• pp.45-50
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• 2015

The goal of this research is the create novel magnets with no rare-earth contents, with larger energy product by comparison with currently used ferrites. For this purpose we developed nano-sized hard-type/soft-type composite ferrite in which high remanent magnetization (Mr) and high coercivity (Hc). Nano-sized Ba-ferrite, Ni-Zn ferrite and $BaFe_{12}O_{19}/Ni_{0.5}Zn_{0.5}Fe_2O_4$ composite ferrites were prepared by sol-gel combustion method by use of glicine-nitrate and citric acid. Nanocomposite ferrites were calcined at temperature range $700-900^{\circ}C$ for 1h. According to the X-ray diffraction patterns and FT-IR spectra, single phase of NiZn-ferrite and Ba-ferrite were detected and hard/soft nanocomposite ferrite was indicated to the coexistence of the magnetoplumbite-structural $BaFe_{12}O_{19}$ and spinel-structural $Ni_{0.5}Zn_{0.5}Fe_2O_4$ that agreed with the standard JCPDS 10-0325 data. The particle size of nanocomposite turn out to be less than 120 nm. The nanocomposite ferrite shows a single-phase magnetization behavior, implying that the hard magnetic phase and soft magnetic phase were well exchange-coupled. The specific saturation magnetization ($M_s$) of the nanocomposite ferrite is located between hard ($BaFe_{12}O_{19}$) and soft ferrite($Ni_{0.5}Zn_{0.5}Fe_2O_4$). The remanence (Mr) of nanocomposite ferrite is much higher than that of the individual $BaFe_{12}O_{19}$ and $Ni_{0.5}Zn_{0.5}Fe_2O_4$ ferrite, and $(BH)_{max}$ is increased slightly.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.161.2-161.2
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• 2017

희토류계 영구자석은 대부분의 전기, 전자 제품의 핵심부품이며 높은 보자력, $BH_{max}$를 가지고 있어 자기기록저장매체, MEMS(엑츄에이터), 소형센서, 소형모터 등의 응용 분야에 적용시키기 위해 다양한 연구들이 진행되고 있다. 그러나 영구자석에 들어가는 희토류계 원소의 수급의 어려움 및 가격의 문제점으로 친환경 자석으로의 전환 및 희토류나 중희토류를 사용하지 않는 비희토류계 영구자석을 제조 및 개발하는데 많은 연구가 이루어지고 있다. 이 중 Fe-N 계 자성물질인 $Fe_{16}N_2$는 포화 자화 값이 현재까지의 비희토류계 자성물질 중 가장 높은 값(240emu/g)을 나타내며 상대적으로 높은 결정자기이방성 상수를 가지고 있어 비희토류계 영구자석 물질 중 하나로 주목받으며 연구되어지고 있다. 본 연구에서는 $Fe_{16}N_2$ 박막을 얻기 위해 DC Magnetron Sputtering 방법을 이용하여 Si wafer 위에 박막을 증착하고 증착시간에 따라 두께를 제어하여 제조한 후 박막의 미세구조, 상 분석, 자성 특성을 관찰을 통해 최적의 공정 조건을 찾고자 하였다. 증착 시간에 따른 박막의 성장 속도는 일정하게 증가하였으며, 증착 시간의 증가에 따라 박막 내 $Fe_{16}N_2$의 상대적인 분율은 감소하였다. 모든 공정 조건에서 $Fe_3N$, $Fe_4N$, $Fe_{16}N_2$ 상들이 섞여 성장하였으며 XRD를 통한 상분석과 더불어 VSM을 통한 자성 특성을 분석해본 결과 $Fe_{16}N_2$의 분율을 가장 높게 성장된 공정 조건은 증착 시간이 10분이며 박막의 두께가 ${\sim}1{\mu}m$ 일 때, 최적의 조건을 얻을 수 있었으며, 이 때의 자성 특성을 분석한 결과 ~2.45T의 포화 자화 값과 ~1.41T의 잔류 자화 값을 얻을 수 있었다.

• Journal of the Korean Magnetics Society
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• v.10 no.5
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• pp.225-231
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• 2000

The crystallographic and magnetic properties of the sample F $e_{0.8}$ $Co_{0.18}$(BN)$_{0.02}$ synthesized by microwave arc-melting with the maximum power of 3.5 kW have been studied by the methods of an X-ray diffraction and the measurement of the magnetic hysteresis using the vibrating sample magnetometer at room temperature. The samples were prepared in a form of pellet pressed under the pressure of 9,000 N/c $m^2$, rolled coldly, and treated with the different temperatures. The X-ray diffraction pattern of pelleted sample shows that the crystal structure of the sample is bcc as same as that of Fe with a good uniformity. The X-ray diffraction pattern shows that a residual stress, which exists in the sample, is eliminated by final 90$0^{\circ}C$ annealing. As rolling rate and heat treatment temperature increases, the saturation magnetization and the remanence of the samples increase whereas the coercivity of the samples shows decrease. Also the saturation magnetization and the remanence of the samples were affected by rolling rate and rolling direction than heat treatment temperature, but the coercivity of the samples was affected by rolling rate and direction as well as heat treatment temperature. This means that a domain wall motion is easy due to elimination of a residual stress and an inclusion which exists in the sample by rolling and heat treatment and a local induced-magnetization easy axis was also formed to parallel to the rolling direction due to creation of the like-atom pairs across the slip plane by rolling......