• Journal of Magnetics
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• 제13권3호
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• pp.97-101
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• 2008

We investigated the exchange bias fields at the NiFe/FeMn and FeMn/CoFe interfaces in 18.9-nm NiFe/15.0-nm FeMn/17.6-nm CoFe trilayer thin films as the annealing temperature was varied from room temperature to $250^{\circ}C$ in a vacuum for 1 hour in a magnetic field of 150 Oe. Interestingly, magnetic hysteresis (M-H) measurements showed that NiFe/FeMn/CoFe trilayer thin films exhibited a completely contrasting variation of the exchange bias fields at both the NiFe/FeMn and FeMn/CoFe interfaces with annealing temperatures. High-angle X-ray diffraction (XRD) measurements indicated the absence of any discernible effect of thermal treatment on the NiFe(111) and FeMn(111) peaks. The compositional depth profile obtained from X-ray photoelectron spectroscopy (XPS) results presented the asymmetric compositional depth profiles of the Mn and Fe atoms throughout the FeMn layer. We contend that this asymmetric compositional depth profile and the preferential Mn diffusion into the NiFe layer, compared to that into the CoFe layer, are conclusive experimental evidence of the contrasting variation of the exchange bias fields at two interfaces having a common polycrystalline FeMn(111) layer.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2012년도 추계학술대회 논문집
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• pp.31-32
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• 2012

This paper presents a new design of magnetic bearing structure for application in Nuclear Power Plant (NPP). The proposed design includes so-called saturated coils which is used to generate the bias flux for bearing almost the whole mass of the rotor, and so-called linear auxiliary coil controlled to stabilize the suspension. The saturated coil is considered as an special electromagnet which is controlled to operate in the region of magnetic saturation in order to minimize the bias current as well as to enhance the magnetic flux density. This strategy will result in a very compact size of magnetic bearing as well as increasing the speed of the response of the current controller. The novel structure is expected to be applied to design very high power gas turbine generator of next generation of fast reactor in which the mass of rotor can reach 50 tons. The total power of the NPP can reach 2,000 MW. Moreover, the issue of arc occurrence between coils is also discussed and two solutions are proposed.

• Journal of Magnetics
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• 제15권3호
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• pp.132-137
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• 2010

Plasma etching of $SiO_2$ contact holes was statistically analyzed by a fractional factorial experimental design. The analysis revealed the dependence of the etch rate and DC self-bias voltage on the input factors of the magnetically enhanced reactive ion etching reactor, including gas pressure, magnetic field, and the gas flow rates of $CHF_3$, $CF_4$, and Ar. Empirical models of the DC self-bias voltage and etch rate were obtained. The DC self-bias voltage was found to be determined mainly by the operating pressure and the magnetic field, and the etch rate was related mainly to the pressure and the flow rates of Ar and $CHF_3$.

• Journal of Magnetics
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• 제14권4호
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• pp.147-149
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• 2009

We report the exchange bias in antiferromagnet/ferrimagnet $Cr_2O_3/Fe_3O_4$ core/shell nanoparticles. The magnetic field hysteresis curve for $Cr_2O_3/Fe_3O_4$ nanoparticles after field-cooling (FC) clearly showed both horizontal ($H_{EB}{\sim}$610 Oe) and vertical (${\Delta}M{\sim}$5.6 emu/g) shifts at 5 K. These shifts disappeared as the temperature increased toward the Neel temperature of $Cr_2O_3\;(T_N{\sim}$307 K). The $H_{EB}\;and\;{\Delta}M$ values were sharply decreased between the $1^{st}\;and\;the\;2^{nd}$ magnetic field cycles, and then slowly decreased with further cycling. These results are discussed in terms of the formation of single domains with pinned, uncompensated, antiferromagnetic spin and their evolution into multi-domains with cycling.

• 한국재료학회지
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• 제13권7호
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• pp.447-452
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• 2003

Effects of annealing and thickness of Co layer in Co/IrMn bilayers on the magnetic properties have been investigated. The highest interfacial exchange coupling energy($J_{K}$ = 0.12 erg/$\textrm{cm}^2$) was obtained for 10 nm Co layer thickness. Exchange bias field is inversely proportional to the magnetization, the thickness of the pinned layer, and the grain size of antiferromagnetic layer. Also it is related to the interfacial exchange energy difference, which is expected to depend on the surface roughness. These results almost agree with the random-field model of exchange anisotropy proposed by Malozemoff. Exchange bias field decreased slowly with increasing annealing temperature up to X$300^{\circ}C$. However, exchange bias field increased above $300^{\circ}C$.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 하계학술대회 논문집 C
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• pp.1379-1382
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• 1997

Diamond-like carbon(DLC) thin films are produced by using a filtered cathodic vacuum arc(FCVA) deposition system. Different magnetic components, namely steering, focusing, and filtering plasma-optic systems, are used to achieve a stable arc plasma and to prevent the macroparticles from incorporating into the deposited films. Effects of magnetic fields on plasma behavior and film deposition are examined. The carbon ion energy is found to be varied by applying a negative (accelerating) substrate bias voltage. The deposition rate of DLC films is dependent upon magnetic field as well as substrate bias voltage and at a nominal deposition condition is about $2{\AA}/s$. The structural properties of DLC films, such as internal stress, relative fraction of tetrahedral($sp^3$) bonds, and surface roughness have also been characterized as a function of substrate bias voltages and partial gas($N_2$) pressures.

• Journal of Magnetics
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• 제16권3호
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• pp.318-321
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• 2011

A new Fe-based amorphous compound powder was prepared from Fe-Si-B amorphous powder by crushing amorphous ribbons as the first magnetic component and Fe-Cr-Mo metallic glassy powder by water atomization as the second magnetic component. Subsequently by adding organic and inorganic binders to the compound powder and cold pressing, the new Fe-based amorphous compound powder cores were fabricated. This new Fe-based amorphous compound powder cores combine the superior DC-Bias properties and the excellent core loss. The core loss of 500 kW/$m^3$ at $B_m$ = 0.1T and f = 100 kHz was obtained When the mass ratio of FeSiB/FeCrMo equals 3:2, and meanwhile the DC-bias properties of the new Fe-based amorphous compound powder cores just decreased by 10% compared with that of the FeSiB powder cores. In addition, with the increasing of the content of the FeCrMo metallic glassy powder, the core loss tends to decrease.

• Journal of Magnetics
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• 제9권1호
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• pp.23-26
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• 2004

A magneto-current (MC) was investigated for magnetic tunnel transistor (MTT) with amorphous n-type Si film. A relative MC (more than 49.6%) was observed at an emitter-base bias voltage ($V_{EB}$) of 0.65 V at room temperature. Above a $V_{EB}$ of 0.70 V, however, a rapid decrease in MC was observed in the amorphous Si-based MTT. The collector current increasing and transfer ratio as emitter-base voltage were mainly due to the rapid creation electrons of conduction band states in the Si collector. This approach would make integration in various components and systems easier than a MTT grown on a semiconductor wafer.

• JSTS:Journal of Semiconductor Technology and Science
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• 제13권1호
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• pp.28-33
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• 2013

Spin-torque oscillators (STO) is a new device that can be used as a tunable microwave source in various wireless devices. Spin-transfer torque effect in magnetic multilayered nanostructure can induce precession of magnetization when bias current and external magnetic field are properly applied, and a microwave signal is generated from that precession. We proposed a semi-empirical circuit-level model of an STO in previous work. In this paper, we present a refined STO model which gives more accuracy by considering physical phenomena in the calculation of effective field. Characteristics of the STO are expressed as functions of external magnetic field and bias current in Verilog-A HDL such that they can be simulated with circuit-level simulators such as Hspice. The simulation results are in good agreement with the experimental data.

• 한국자기학회지
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• 제14권4호
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• pp.127-130
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• 2004

본 연구는 (pd/Co)$_{N}$FeMn 구조의 다층박막을 dc 마그네트론 스퍼터링 시스템으로 증착하여 교환결합된 수직이방성에 대한 자기적 특성과 열적안정성을 조사하였다. 반강자성 FeMn 두께를 0-2lnm에서 변화시키면서 측정한 결과 Ta(1.9 nm)/(Pd(0.8nm)/Co(0.8nm)$_{5}$Mn(15nm)/Ta(1.9nm)에서 127 Oe교환바이어스세기(exchange biasing field: H$_{ex}$)를 얻었다. 그리고 이 구조에서 열적 안정성을 조사하기 위하여 온도 변화에 따른 H$_{ex}$변화를 확인한 결과, 24$0^{\circ}C$까지는 H$_{ex}$가 115 Oe에서 195 Oe까지 증가하였고, 그 이후 33$0^{\circ}C$에서 교환 결합된 수직자기이방성 곡선이 사라지는 것을 관찰하였다.