• Journal of the Korean Magnetics Society
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• 제8권4호
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• pp.231-240
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• 1998

We investigated that the fabrication and reproducing signal characteristics of tri-layered magnetoresistance (MR) element for the high density magnetic thin film heads and sensors. Magnetoresistance curve of tri-layered MR element predicted by computer modeling was saturated above external field of -15 Oe~+22 Oe, and it was shifted to linearized region as large as 4 Oe. In the case of fabricated real device, magnetoresistance curve was saturated above external field of $\pm$15 Oe, and it was shifted to linearized region as large as 4 Oe. As shown in real device, MR response curve was in good agreement with the simulation results. As a result of experimental data of reproducing output signal in real device, it retained normal sinusoidal waveforms in 1~4 Oe external magnetic field. In this magnetic field region, the fabricated heads with tri-layered MR element can be operated with good reproduced characteristics. This will be beneficial to the use of efficient processes of manufacturing elements and the vacuum deposition techniques which control thin film properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제15권4호
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• pp.373-379
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• 2002

We investigated the evolution of magnetoresistance and magnetic property of tunneling magnetoresistive(TMR) device with microstructure and plasma oxidation time. TMR devices have potential applications for non volatile MRAM and high density HDD reading head. We prepared the tunnel magnetoresistance(TMR) devices of Ta($50{\AA}$)/NiFe($50{\AA}$)/IrMn($150{\AA}$)/CoFe($50{\AA}$)/Al($13{\AA}$)-O/CoFe($40{\AA}$)/FiFe($400{\AA}$)/Ta(($50{\AA}$) structure which have $100{\times}100\mu\textrm{m}^2$ junction area on $2.5{\times}2.5\textrm{cm}^2$ Si/$SiO_2$(($1000{\AA}$) substrates by an inductively coupled plasma(ICP) magnetron sputter. We fabricated the insulating layer using an ICP plasma oxidation method by with various oxidation time from 30 sec to 360 sec, and measured resistances and magnetoresistance(MR) ratios of TMR devices. We found that the oxidized sample for oxidation time of 80 sec showed the highest MR radio of 30.31 %, while the calculated value regarding inhomogeneous current effect indicated 25.18 %. We used transmission electron microscope(TEM) to investigate microstructural evolution of insulating layer. Comparing the cross-sectional TEM images at oxidation time of 150 sec and 360 sec, we found that the thickness and thickness variation of 360 sec-oxidized insulating layer became 30% and 40% larger than those of 150 sec-oxidized layer, repectively. Therefore, our results imply that increase of thickness variation with oxidation time may be one of the major treasons of the MR decrease.

• Journal of Magnetics
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• 제9권1호
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• pp.9-12
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• 2004

We have investigated sintering effects on Fe/Mo ordering and magnetoresistance (MR) in double perovskite-reflection lines due to $Sr_2FeMoO_6$ (SFMO). Polycrystalline samples have been prepared by the conventional solid-state reaction by sintering in a stream of 5% $H_2/Ar$ gas. All samples are single phase and exhibit a series of superstructurecation ordering at Fe and Mo sites. As sintering temperature increases from 900 to $1300^{\circ}C$, the degree of Fe/Mo ordering increases from 82 to 92%, magnetization (15 K, 7 kOe) increases from 1.6 to 2.7 ${\mu}_B/f.u.,$ and Curie temperature increases at a rate of 4.3 K/% with the increase of Fe/Mo ordering ratio. The magnitude of MR measured at 5 K is 19% for sample prepared at $1000^{\circ}C$ with magnetic fields of 7 kOe. The observed MR is proportional to the square of magnetization indicating that the MR feature in SFMO is explained by the spin-polarized tunneling at grain boundaries.

• Journal of the Korean Magnetics Society
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• 제3권1호
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• pp.29-33
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• 1993

Magnetoresistance was studied for the ferromagnetic tunneling junction in $Permalloy/Al_{2}O_{3}/Co$ prepared by evaporation in a vacuum of $1{\times}10^{-6}$Torr. We measured voltage-current characteristic and magnetic valve effect of prepared ferromagnetic tunneling junction sample. We investigated field-dependency of tunnel resistance by Wheat-stone bridge method and measured magnetic hysteresis curve by vibrating sample magnetometer. The tunneling is confirmed by measuring voltage-current characteristic. The hysteresis curve of magnetoresistance corresponds well with that of magnetization. The magnetoresistance ratio ${\Delta}R/R$ is 0.6% at room temperature.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.60-60
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• 2011

Giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), and magnetic random-access memory (MRAM) are currently active research areas in spintronics. The high magnetoresistance and the high spin polarization (P) of electrons in the ferromagnetic electrodes of tunnel junction or intermediate layers are required. Magnetite, Fe3O4, is predicted to possess as half-metallic nature, P ~ 100% spin polarization, and has a high Curie temperature (TC~850 K). Experiments demonstrated that the P~($80{\pm}5$)%, ~($60{\pm}5$)%, and ~40-55% for epitaxial (111), (110) and (001)-oriented Fe3O4 thin films, respectively. Epitaxial Fe3O4 films may enable us to investigate the effects of half metals on the spin transport without grain-boundary scattering.In addition, it has been reported that the Verwey transition (TV, a first order metal-insulator transition) of 120 K in bulk Fe3O4 is strongly affected by many parameters such as stoichiometry and stress, etc. Here we report that the growth modes, magnetism and transport properties of Fe3O4 thin films were strongly dependent on the oxygen pressure during film growth. The average roughness decreases from 1.021 to 0.263 nm for the oxygen pressure increase from $2.3{\times}10-7$ to $8.2{\times}10^{-6}$ Torr, respectively. The 120 K Verwey transition in Fe3O4 was disappeared for the sample grown under high oxygen pressure.

• Journal of the Korean Magnetics Society
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• 제11권5호
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• pp.196-201
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• 2001

The dependence of CoFe interfacial layer thickness and plasma oxidation condition on tunneling magnetoresistance (TMR) in Ta/NiFe/FeMn/NiFe/Al$_2$O$_3$/NiFe/Ta tunnel junctions was investigated. As the CoFe layer thickness increases, TMR ratio rapidly increases to 13.7 % and decreases with further increase of the CoFe layer thickness. The increase of TMR with the CoFe thickness up to 25 was thought to be due mails to the high spin-polarization of CoFe. The maximum MR of 15.3% was obtained in the Si(100)/Ta(50 )/NiFe(60 )/FeMn(250 )/NiFe(70 )/Al$_2$O$_3$/NiFe(150 )/Ta(50 ) magnetic tunnel junction with a 16 Al oxidized for 40 sec using a Ar/O$_2$ (1:4) mixture gas.

• Journal of Magnetics
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• 제16권2호
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• pp.169-172
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• 2011

This study reports an alternative method for measuring the magnetoresistance of unpatterned magnetic tunnel junctions similar to the current-in-plane tunneling (CIPT) method. Instead of using microprobes, a series of point contacts with different spacings are coated on the top surface of the junctions and R-H loops at various spacings are then measured by the usual four-point probe method. The values of magnetoresistance and resistance-area products can be obtained by fitting the measured data to the CIPT theoretical model. The test results of two types of junctions were highly similar to those obtained from standard CIPT tools. The proposed method may help to accelerate the process for evaluating the quality of magnetic tunnel junctions when commercial CIPT tools are not accessible.

• Progress in Superconductivity and Cryogenics
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• 제21권4호
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• pp.48-52
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• 2019

Recently, many studies have been reported on the magnetoresistance and Hall effect of REBCO thin films and bulk. The voltage interferes quench detection of high-temperature superconducting magnet and generates leakage current in no insulation high-temperature superconducting coil. Therefore, in this paper, experiments on magnetoresistance and Hall effect of commercial YBCO and GdBCO tapes have been carried out. As a result, anomalous voltages expected for the magnetoresistance and Hall effect of REBCO tapes were observed and analyzed. In addition, the voltage characteristics of REBCO have been identified, and the Hall coefficient are calculated for use in high magnetic field magnet applications.

• Journal of the Korean Magnetics Society
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• 제16권6호
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• pp.271-275
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• 2006

We investigated the magnetoresistance of perpendicularly magnetized magnetic tunnel junction composed of Co/Pd multilayers. The magnetoresistance was maximized with Co electrodes of about 5 nm thickness, which evidenced the important role of the interface in tunneling process. Both the change in perpendicular magnetic anisotropy and improvement of junction resistance were observed with changing Co sublayers, while the spin scattering became dominant with increasing Pd sublayers.

• Journal of Magnetics
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• 제8권2호
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• pp.89-92
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• 2003

The tunneling magnetoresistance (TMR) of a ramp-edge type junction with SrTiO$_3$barrier layer has been stud-ied. The samples with a structure of glass/NiO(600${\AA}$)/Co(100${\AA}$)/SrTiO$_3$(400 ${\AA}$)/SrTiO$_3$(20-100${\AA}$)/NiFe(100${\AA}$) were prepared by the sputtering and etched by the electron cyclotron (ECR) argon ion milling. Nonlinear I-V characteristics were obtained from a ramp-type tunneling junctions, having the dominant difference between two different external magnetic fields (${\pm}$100 Oe) perpendicular to the junction edge line. In the SrTiO$_3$ barrier thickness of 40${\AA}$, the TMR was 52.7% at a bias voltage of -50 mV The bias voltage dependence of resistance and TMR in a ramp-type tunneling junction was similar with those of the layered TMR junction.