• Journal of Powder Materials
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• v.12 no.5 s.52
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• pp.362-368
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• 2005

The structural and magnetic properties of nanostructued Fe-20 ;wt.%Si alloy powders were investigated. Commercial Fe-20 wt.%Si alloy powders (Hoeganaes Co., USA) with 99.9% purities were used to fabricate the nanostructure Fe-Si alloy powders through a high-energy ball milling process. The alloy powders were fabricated at 400 rpm for 50 h, resulting in an average grain size of 16 nm. The nanostructured powder was characterized by fcc $Fe_{3}Si$ and hcp $Fe_{5}Si_3$ phases and exhibited a minimum coercivity of approximately 50 Oe.

• Proceedings of the Korean Magnestics Society Conference
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• 2005.12a
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• pp.154-155
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• 2005

Multi-layer film of $MgO/(FePt-B)_{50nm}/ MgO$ was deposited on Si(100) substrates by RF magnetron sputtering. The boron chips were uniformly placed oil tile FePt target. The boron content of thin film was found to be about 5, 10, 15, 25 and $33 at\%$ by using a CAMECA SX-51 wavelength dispersive spectroscopy (WDX). It is observed that X-ray diffraction patterns of FePt-B film by post-annealing exhibited a transformation from disordered fcc structure to ordered $Ll_0$ phase with fct structure from around $400^{\circ}C$. By adding B, annealing temperature for ordering is about $200^{\circ}C$ lower than that of pure FePt. This remarkable decrease of the annealing temperature is closely related to the high diffusivities of Fe and Pt associated with the defects caused by movements of B atoms. The maximum coercivity(Hc) for FePt films was found to be ${\~}$13 kOe after annealing at $600^{\circ}C$ for 1hr.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.411-414
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• 2005

It is reported that $\varepsilon$ (HCP) and $\gamma$ (FCC) phases of a Fe-17Mn alloy transform to $\alpha'$ phase, which has BCC structure, under a deformation condition. In this study, we investigated the effect of strain-induced-transformed $\alpha'$ phase on sliding wear of the Fe-17Mn alloy that originally had e and y phases. Wear tests of the materials were carried out using a pin-on-disk wear tester at various loads of 0.5N-50N under a constant sliding speed condition of 0.38m/s against glass $(83\%\;SiO_2)$ beads. The sliding distance and radius were loom and 9 mm, respectively. Wear rate of the Fe-17Mn alloy was calculated by dividing the weight loss, measured to the accuracy of $10^{-5}g$ by the measured specific gravity and sliding distance. Worn surface and wear debris of the specimens were examined using an SEM and XRD. During the wear, $\alpha'$ phase of BCC structure was formed by strain-induced transformation when the applied wear load exceeded critical values. The $\alpha'$ phase formed by the strain induced transformation increased the wear rate of the Fe-17Mn alloy.

• Journal of the Korean Vacuum Society
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• v.4 no.1
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• pp.67-76
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• 1995

자기저항헤드용 Ni-Fe-Co/Cu/Ni-Fe-Co/Fe-Mn 다층박막에서 자기적 성질과 전기적 성질에 관하여 조사하였다. 저 포화자계에서 고 자기저항을 나타내는 스핀 밸브형 다층박막을 제작하기 위하여 Borond이 도핑된 p-type Si(100)기판위에 Ni-Fe-Co 단층박막과 Si/Ni-Fe-Co/Cu/Ni-FeCo, Si/Ni-Fe-Co/Fe-Mn 구조의 다층막을 제작하여 자기적 특성을 조사하였다. Ni-Fe-Co 단층박막의 자기적 특성은 고정된 아르곤 분압에서 박막의 두께 등에 의존성이 있는 것으로 나타났다. 또한 Si/Ni-Fe-Co($70AA$)/Fe-Mn 구조에서 Ni-Fe-Co와 Fe-Mn 계면에서의 두 자성층의 이방성 차이에 의해서 발생되어지는 교환자기이방성이 존재하였으며, 교환자기이방성자계값은 Fe-Mn 두께가 $150\AA$일 때 가장 큰 값을 나타내었다. Ni-Fe-Co texture와 교환자기이방성자계값은 Fe-Mn 두께가 $150\AA$일 때 가장 큰 값을 나타내었다. Ni-Fe-Co texture와 교환자기이방성자계값의 의존성을 알아보기 위하여 Ti, Cu를 바닥층으로 사용하였다. Ti을 바닥층으로 사용하였을 경우, 교환자기이방성자계값은 23.5 Oe 정도의 가장 큰 값을 나타내었다. XRD 분석결과, Ti 바닥층이 Cu 바닥층이나, 바닥층이 없는 경우와 비교하여 성막된 Ni-Fe-Co 자성층의 강한 fcc(111) texture를 형성하는 것으로 나타났다. 각각의 단층박막과 다층박막에서의 자기적 특성을 측정한 후, Si/Ti($50\AA$)/Ni-Fe-Co($70\AA$)/Cu($23\AA$)/Ni-Fe-Co($70\AA$)/Fe-Mn(150$\AA$)/Cu(50$\AA$)의 스핀밸브구조를 갖는 다층박막을 제작하였으며, 11 Oe의 낮은 포화자계값에서 4.1%의 고 자기저항값을 얻을 수 있었다.

• Korean Journal of Materials Research
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• v.28 no.10
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• pp.595-600
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• 2018

This study investigates the microstructural properties of CoCrFeMnNi high entropy alloy (HEA) oxynitride thin film. The HEA oxynitride thin film is grown by the magnetron sputtering method using nitrogen and oxygen gases. The grown CoCrFeMnNi HEA film shows a microstructure with nanocrystalline regions of 5~20 nm in the amorphous region, which is confirmed by high-resolution transmission electron microscopy (HR-TEM). From the TEM electron diffraction pattern analysis crystal structure is determined to be a face centered cubic (FCC) structure with a lattice constant of 0.491 nm, which is larger than that of CoCrFeMnNi HEA. The HEA oxynitride film shows a single phase in which constituting elements are distributed homogeneously as confirmed by element mapping using a Cs-corrected scanning TEM (STEM). Mechanical properties of the CoCrFeMnNi HEA oxynitride thin film are addressed by a nano indentation method, and a hardness of 8.13 GPa and a Young's modulus of 157.3 GPa are obtained. The observed high hardness value is thought to be the result of hardening due to the nanocrystalline microstructure.

• Journal of Powder Materials
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• v.31 no.1
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• pp.8-15
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• 2024

The emergence of ferrous-medium entropy alloys (FeMEAs) with excellent tensile properties represents a potential direction for designing alloys based on metastable engineering. In this study, an FeMEA is successfully fabricated using laser powder bed fusion (LPBF), a metal additive manufacturing technology. Tensile tests are conducted on the LPBF-processed FeMEA at room temperature and cryogenic temperatures (77 K). At 77 K, the LPBF-processed FeMEA exhibits high yield strength and excellent ultimate tensile strength through active deformation-induced martensitic transformation. Furthermore, due to the low stability of the face-centered cubic (FCC) phase of the LPBF-processed FeMEA based on nano-scale solute heterogeneity, stress-induced martensitic transformation occurs, accompanied by the appearance of a yield point phenomenon during cryogenic tensile deformation. This study elucidates the origin of the yield point phenomenon and deformation behavior of the FeMEA at 77 K.

• Journal of the Korean Magnetics Society
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• v.13 no.2
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• pp.53-58
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• 2003

Annealing effects of exchange bias fields ($H_{2ex}$(top), $H_{lex}$ (bottom)) on composite type NiFe/[FeMn/Mn]$_{80}$/NiFe multilayers have been studied. Three samples with ultra-thin Mn inserted layers on glass/Ta(50 $\AA$)/NiFe(150 $\AA$)/[F $e_{53}$M $n_{47}$(1.25 $\AA$)/Mn(0 $\AA$, 0.11 $\AA$, 0.3 $\AA$)]$_{80}$/NiFe(90 $\AA$)/Ta(50 $\AA$) were prepared by ion beam sputtering. The average x-ray diffraction peak ratios NiFe(111) of FeMn (111) fcc textures for the Mn inserted total thicknesses of 0 $\AA$, 9 $\AA$, and 24 $\AA$ were about 0.65, 0.90, and 1.5, respectively. For the sample without Mn inserted layer, the $H_{2ex}$ of 260 Oe up to 300 $^{\circ}C$ disappeared at 350 $^{\circ}C$. For two multilayer samples with ultra-thin Mn layers of 0.11 $\AA$ and 0.3 $\AA$, the $H_{2exs}$ of 310 Oe and 180 Oe up to 300 $^{\circ}C$ endured of 215 Oe and 180 Oe at 350 $^{\circ}C$, respectively. The $H_{ex}$ (bottom)s of three samples decreased from 100 Oe to 70 Oe up to 250 $^{\circ}C$, while these values increased beyond 300 $^{\circ}C$. This observation can be attributed to less diffusive path of Mn atoms in bottom NiFe than top NiFe layer. The top and bottom coercive fields slightly varied about 5 Oe∼10 Oe. From these results, we could obtain the enhancement of exchange coupling intensity and thermal stability by an ultra-thin Mn inserted layer on NiFe/[FeMn/Mn]$_{80}$/NiFe Multilayers.

• Journal of the Korean Magnetics Society
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• v.17 no.3
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• pp.120-123
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• 2007

The typical double-barrier magnetic tunnel junction (DMTJ) structure examined in this paper consists of a Ta 45/Ru 9.5/IrMn 10/CoFe7/$AlO_x$/free layer/AlO/CoFe 7/IrMn 10/Ru 60 (nm). The free layer consists of an $Ni_{16}Fe_{62}Si_8B_{14}$ 7 nm, $Co_{90}Fe_{10}$ (fcc) 7 nm, or CoFe $t_1$/NiFeSiB $t_2$/CoFe $t_1$ layer in which the thicknesses $t_1$ and $t_2$ are varied. The DMTJ with an NiFeSiB-free layer had a tunneling magnetoresistance (TMR) of 28%, an area-resistance product (RA) of $86\;k{\Omega}{\mu}m^2$, a coercivity ($H_c$) of 11 Oe, and an interlayer coupling field ($H_i$) of 20 Oe. To improve the TMR ratio and RA, a DMTJ comprising an amorphous NiFeSiB layer that could partially substitute for the CoFe free layer was investigated. This hybrid DMTJ had a TMR of 30%, an RA of $68\;k{\Omega}{\mu}m^2$, and a of 11 Oe, but an increased of 37 Oe. We confirmed by atomic force microscopy and transmission electron microscopy that increased as the thickness of NiFeSiB decreased. When the amorphous NiFeSiB layer was thick, it was effective in retarding the columnar growth which usually induces a wavy interface. However, if the NiFeSiB layer was thin, the roughness was increased and became large because of the magnetostatic $N{\acute{e}}el$ coupling.

• Journal of the Korean Magnetics Society
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• v.11 no.2
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• pp.72-77
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• 2001

Top spin valve films with PtMn antiferromagnetic layers were deposited using a multi-target dc magnetron sputtering in (100)Si substrates overcoated with 500 $\AA$ of Al$_2$O$_3$. Firstly, the post-deposition annealing was performed at 270$\^{C}$ in a unidirectional magnetic field of 3 kOe to induce the crystallographic transformation of the PtMn layer from a fcc (111) to a fct (111) structure. Secondly, the spin valve films were annealed without magnetic fields and magnetic properties were measured. In Si/A1$_2$O$_3$ (500$\AA$)/Ta(50$\AA$)NiFe(40$\AA$)/CoFe(17$\AA$)/Cu(28$\AA$)/CoFe (30$\AA$)PtMn(200$\AA$)Ta(50$\AA$) top spin valve samples, the MR ratio decreased slowly with increasing annealing temperature up to 325$\^{C}$. But above 325$\^{C}$, the MR ratio decreased rapidly to 1%, due to a collapse of the exchange coupling between a antiferromagnetic layer and a pinned layer with increasing annealing temperature. Also above 325$\^{C}$, the exchange biased field rapidly decreased and the interlayer coupling field rapidly increased with increasing annealing temperature. A change in the interlayer coupling field was resulted from the increase in interface roughness due to Mn-interdiffusion through the grain boundaries. We confirmed the temperature in changing magnetic properties agreed well with the blocking temperature of PtMn based spin valve structure.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.82-83
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• 2002

Y-Mn 계열 반강자성체를 갖는 스핀 밸브의 경우에 씨앗층의 영향을 크게 받게 된다. 특히, (111) texture의 발달이 없는 경우에는 큰 교환결합자계를 얻을 수 없고 또한 공정후 열처리의 조건에 매우 크게 영향을 받음을 알 수 있다. Bottom형 교환 결합형 스핀밸브의 경우에 (111) texture의 향상을 위해 Cu 또는 NiFe와 같은 fcc 재료를 씨앗층으로 사용한다. (중략)