• Journal of the Korean Magnetics Society
• /
• v.16 no.3
• /
• pp.173-177
• /
• 2006

We have investigated the magnetoresistance (MR) effect of the spin valve structures composed of perpendicularly magnetized Pd/Co multilayers, with changing the space layer (Pd or Cu) thickness, the stacking number of the Pd/Co multilayers, and the Co insertion-layer thickness. The Cu space layer showed larger MR ratio than the Pd space layer. The Co insertion-layer between Cu layer and pinned layer enhanced the MR ratio about three times. The maximum MR ratio of 7.4 % was established in the sample with the Co insertion-layer thickness of 0.62 and 1.01 nm.

• Journal of Magnetics
• /
• v.9 no.1
• /
• pp.9-12
• /
• 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
• /
• v.3 no.1
• /
• pp.29-33
• /
• 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.

• Journal of the Korean Magnetics Society
• /
• v.11 no.5
• /
• pp.196-201
• /
• 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.

• Korean Journal of Materials Research
• /
• v.14 no.2
• /
• pp.94-100
• /
• 2004

We have investigated the magnetic domain structure and the thermal stability of magnetotransport properties of IrMn biased spin-valves containing Co, CoFe and NiFe. The magnetic domain structures were imaged using a magneto-optical indicator film(MOIF) technique. To investigate the thermal stability, magnetoresistance(MR) was measured at annealing temperature(TANN) and room temperature($T_{RT}$) followed by the annealing. Domain imaging reveal that the increase of annealing temperature led to changes in the exchange coupling between the two ferromagnet(FM) layers through nonmagnetic layer rather than between FM and antiferromagnet. unlike the NiFe biased IrMn spin valve with large domains, MOIF pictures of Co and CoFe biased IrMn spin valve structures show the formation of many small microdomains. The magnetic structure, as revealed by the domain images, appeared unchanged while the MR dropped dramatically. From the combined giant magnetoresistance(GMR) and MOIF results, it was apparent that the decrease of MR ratio was not related to the spin valve magnetic structure up to about $350^{\circ}C$($T_{RT}$ ).

• Journal of Magnetics
• /
• v.5 no.1
• /
• pp.19-22
• /
• 2000

The effects of a hard-biased Held on the magnetic and magnetoresistive properties of a crossed spin-valve head are investigated by computer simulation with particular emphasis on the asymmetry of the output signal. The spin-valve considered in this work is NiMn (25 nm)/NiFe (2.5 m)/Cu (3 nm)/NiFe (5.5 m), with a length of 1500 m and a width of 600 nm. A simple model is used where each magnetic layer consists of a single domain, and the magnetoresistance is a function of the angle between the magnetization directions of the two magnetic layers. The ideal crossed spin-valve structure is not realized with the present model and magnetic parameters, but the deviation from ideality is decreased by the hard-biased field. This results in the improvement of the linearity of the output signal with the use of the bias field. The magnetoresistance ratio and magnetoresistive sensitivity, however are reduced. The magnetic properties including the magnetoresistance are found to be strongly affected by magnetostatic interactions, particularly the inter-layer magnetostatic field.

• Journal of the Korean Magnetics Society
• /
• v.12 no.6
• /
• pp.201-205
• /
• 2002

The tunneling magnetoresistance (TMR) of a ramp-edge type junction has been studied. The samples with a structure of NiO(60)/Co(10)/NiO(60)/Si$_3$N$_4$(2-6)/NiFe(10) (nm) were prepared by the sputtering and etched by the electron cyclotron (ECR) argon ion milling. Nonlinear I-V characteristics was obtained from a ramp-type tunneling junctions having the dominant difference between zero and ＋90 Oe perpendicular to the junction edge line. The voltage dependence of TMR was stable up to a bias volt of $\pm$10 V with a TMR ratio of about -10%, which may be very peculiar magnetic tunneling properties with asymmetric tunneling process between wedge Co pinned layer and NiFe free layer.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.2
• /
• pp.120-125
• /
• 2006

By employing a rapid solidification method and atmospheric annealing at $450^{\circ}C-1hr$, we were able to manufacture inexpensively granular CuCo alloy ribbons with thickness of $20{\mu}m$ showing giant magnetoresistance (GMR) ratio of more than 5% at a high magnetic field of 0.5T. To verify maximum MR effect, the MR ratio, saturation magnetization, and microstructure change were investigated with Co contents between 5 and 30 at%. It was possible to obtain GMR ratios of 5.2% at 1.2T, and 3% at 0.5T, which implies an appropriate MR for industrial purpose at a Co content of $8{\sim}l4%$. MR ratio was reduced rapidly at a Co content below 5% due to superparamagnetic effect and at a Co content above 20% due to agglomeration of Co clusters. Surface oxidation during rapid solidification and atmospheric annealing did not have much affect on MR ratio. Our result implies that our economic CuCo granular alloy ribbons may be appropriate for high magnetic field sensor applications with wide content range of $8{\sim}14$ at%Co.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2000.09a
• /
• pp.299-300
• /
• 2000

• Journal of the Korean Magnetics Society
• /
• v.10 no.5
• /
• pp.210-219
• /
• 2000

The magnetoresistance characteristics of FeN/Co/Cu/Co and FeN/Co/Cu/Co/Cu/Co/FeN multilayers using ferromagnetic iron-nitrides (FeN) has been studied. The microstructure of FeN film is the mixed ${\alpha}$-Fe and $\varepsilon$-Fe$_3$N phase on the condition that the flow rate of N$_2$ gas is over 0.4 sccm. The magnetoresistance effect is observed because of shape magnetic anisotropy induced by needle-shaped $\varepsilon$-Fe$_3$N phase. This magnetoresistance effect changes, because the degree that the shape magnetic anisotropy adheres to the adjacent Co pinned layer is varied according to the flow rate of N$_2$ gas and the thickness of FeN film. The best magnetoresistance effect is obtained on the condition that the thickness of Co free layer is 70 ${\AA}$ and the maximum MR ratio(%) value of 3.2% shows in the FeN(250 ${\AA}$)/Co(70 ${\AA}$)/Cu(25 ${\AA}$)/Co(70 ${\AA}$)/Cu(25 ${\AA}$)/Co(70 ${\AA}$)/FeN(250 ${\AA}$) mutilayer film which is fabricated at the N, gas flow rate of 0.5 sccm and the FeN film thickness of 250 ${\AA}$. Four steps are observed in the magnetoresistance curve owing to this difference of coercive force, because respective magnetic layers in the multilayer possess different coercive forces. These effects observed in these mutilayer films can be expected to application to the memory device the same MRAM as can carry out simultaneously four signals.