J.R. Rhee

Exchange biasing field of NiFe/[IrMn–Mn]/CoFe multilayers depending on Mn content

Exchange bias by inserting a submonolayer of Mn between two neighboring IrMn layers in NiFe/[IrMn–Mn]/CoFe multilayers was investigated. As-deposited CoFe pinned layers with an [IrMn–Mn] layer resulted in larger exchange biasing field (Hex) and blocking temperature (Tb) than when pure Ir22Mn78 was used. Hex and Tb improved with content of 76.8–78.1 vol % Mn, but Hex and Tb of NiFe/IrMn/CoFe dropped considerably with addition of more than 0.6 vol % Mn. The Hex obtained for as-grown two multilayer samples with 77.5 and 78.7 vol % Mn, were 259 and 150 Oe, respectively. In the case of IrMn with 77.5 vol % Mn, Hex increased to 475 Oe at 350 °C but decreased to 200 Oe at 450 °C. The magnetic properties and thermal stabilities of the NiFe/[IrMn–Mn]/CoFe multilayer were enhanced by suitable additions of Mn. In applications where higher Hex and Tb were required, the proper contents of Mn could be used.

Effects of crystal texture on exchange anisotropy in NiO spin valves

The effects of crystal texture on magnetoresistance, exchange anisotropy field Hex and coercive field Hc in the NiO350 A/NiFe50 A/Cu20 A/NiFe50 A spin valve films deposited on Corning glass, MgO(100), MgO(110), and MgO(111) by rf and dc magnetron sputtering techniques were investigated. The Hex and Hc of the NiO350 A/NiFe50 A bilayers grown on MgO(111) and Corning glass were almost the same 90–93 Oe and 56–60 Oe, respectively. The Hex of the bilayer film on MgO(100) decreased to 68 Oe, however, the Hc of that increased to 114 Oe. The steplike magnetoresistance curve of the spin valve film on MgO(110) disappeared. The x-ray scan of the NiO film deposited on Corning glass shows weakly preferred crystal orientation of NiO(200), (111) and (220) texture, and the NiO films on the MgO single crystals have been grown (100), (110), and (111) epitaxial textures. These results show that there is no clear trend of increasing Hex for films with greater (111) texture. The large Hc of the bilayer on MgO(100) is probably...

Detection of Magnetic Nanoparticles and Fe-hemoglobin inside Red Blood Cells by Using a Highly Sensitive Spin Valve Device

A highly sensitive, giant magnetoresistance-spin valve (GMR-SV) biosensing device with high linearity and very low hysteresis was fabricated by photolithography. The detection of magnetic nanoparticles and Fe-hemoglobin inside red blood cells using the GMR-SV biosensing device was investigated. When a sensing current of 1 ㎃ was applied to the current electrode in the patterned active devices with an area of 2×6 ㎛², the output signals were about 13.35 ㎷. The signal from even one drop of human blood and nanoparticles in distilled water was sufficient for their detection and analysis.

Mn diffusion effect in the exchange biased NiFe/FeMn/NiFe trilayers

We have fabricated NiFe/Mn/FeMn/Mn/NiFe multilayers using ultrahigh vacuum ion-beam deposition system to study the diffusion effect of the inserted Mn on exchange biasing. As the thickness of the Mn layer was changed from 0 to 1.5 nm, the exchange biasing field Hex(top) at the top interface of FeMn/Mn/NiFe was decreased from 258 Oe to 24 Oe. On the other hand, the Hex(bottom) was slightly decreased 103 Oe to 78 Oe without a change in the coercive field Hc. Above 1.2 nm, a reverse phenomena of Hex was observed. After annealing at 200 °C, the Hex(top) was increased by almost a factor of 2; however, the Hex(bottom) did not change. The analyses of x-ray patterns and Auger spectroscopy showed that the abnormal tendency of Hex(bottom) originated from the diffusion of Mn atoms at bottom interface into the FeMn layer during film growth, and that the Mn was concentrated at the interface by annealing.

Comparison of Soft magnetic Properties of Permalloy and Conetic Thin Films

The soft magnetic property for the Corning glass/Ta(5 nm)/[Conetic, Permalloy)/Ta(3 nm) prepared by the ion beam deposition sputtering was investigated. The coercivity and saturation magnetic field of conetic (NiFeCuMo) and permalloy (NiFe) layer with easy and hard direction along to the applying magnetic field during deposition was compared with each other. The surface resistance of conetic film with a thickness of 10 nm was 2 times lower than one of permalloy film. The coercivity and the magnetic susceptibility of conetic film decreased and increased 3 times to one of permalloy film, respectively. These results suggest that a highly sensitive GMR-SV or MTJ using conetic film can be possible to develop the bio-device.

Pt Thickness Dependence of Oscillatory Interlayer Exchange Coupling in [CoFe / Pt / CoFe] / IrMn Multilayers with Perpendicular Anisotropy

The interlayer exchange coupling (IEC) in glass/[Buffer:NiO/Pt]/Co/sub 90/Fe/sub 10//Pt/Co/sub 90/Fe/sub 10//Ir/sub 22/Mn/sub 78/ multilayers within an out-of-plane easy axis is studied. The observed oscillatory behavior of the IEC as a function of the nonmagnetic metallic layer (Pt) is thought to be related to the antiferromagnetic ordering induced by the antiferromagnetic IrMn layer.

A Pulse-type Hysteresis Loop Tracer For Rare Earth Based Permanent Magnets

Introduction Much work is currently under way on rare earth permanent magnets (NdFeB and SmCo based magnets) which exhibit large values of remanent magnetization, coercivity and energy product, compared to conventional magnets such as ferrites and AlNiCo [1]-[4]. With their excellent permanent magnetic properties particularly large coercivity, it is required to apply magnetic fields as large as 50 kOe for a full saturation; in this regards, the measurements of magnetic properties of rare earth based magnets have been a problem in the circles of research community by using conventional electromagnets which normally can generate maximum magnetic fields up to 20 kOe. The main aim of the present work is to generate pulse magnetic fields with bi-polarity and measure the whole hysteresis loop of a permanent magnet from a single measurement. The pulsed high magnetic fields with bi-polarity are generated by approaching the damping ratio of current amplitude to 1 when a large Capacitance charge is discharged into a solenoid. The generated bi-polar magnetic fields permit m measure minor loops as well as maior loous, and also to demametize the samples. ExDerimental A. The Basic Construction .,

Fabrication and Characterization of a Wrist Wearable Cuffless Pulsimeter by Using the Hall Effect Device

A wrist wearable cuffless pulsimeter with a portable and small size apparatus using Hall effect is fabricated. The analysis of the pulse wave measured by the testing product of pulsimeter is done to measure the pulse rate and blood pressure. The blood pressure obtained by the puslimeter is compared with the practical values measured by electronic or mercury liquid blood pressure meters. The detail analysis of a pulse wave measured by a wrist wearable cuffless pulsimeter detecting the changes of the magnetic field can be used to develop a new diagnostic algorithm of blood pressure applying for oriental medical apparatus.

Field sensitivity in spin-valve sandwiches with antiferromagnetic NiO films

We have investigated the MR ratios and the field sensitivities in Ni/sub 81/Fe/sub 15//Cu/Ni/sub 81/Fe/sub 19/ spin-valve sandwiches grown on antiferromagnetic NiO films as a function of the NiO thickness and the uniaxial deposition field. The MR ratio has a maximum value of 4.5% at 420 /spl Aring/ of NiO and 180 Oe of uniaxial deposition field, and a field sensitivity of 0.6%/Oe. In order to obtain a higher MR ratio and field sensitivity, we have studied the effects of adding a Co layer between the interfaces of NiFe and Cu and also the effects of a NiO film on top or at bottom on the spin-valve sandwiches. The MR sandwiches with the Co layer increases to 8.2%, however, the sensitivity decreases to 0.37%/Oe due to the high coercivity of Co. The Co inserted structure with the NiO film on top has a low MR ratio of 5.7% and a high sensitivity of 5.8%/Oe. The thermal stability of the sandwiches with the NiO film on top is superior to that of the NiO film at bottom.

[Ni/Mn] superlattice-based spin-valves with high thermal stabilities

Ni/Mn superlattice-based spin-valve films were fabricated by dc sputtering method. Coercivity (H/sub c/) of the pinned layer and exchange coupling field (H/sub ex/) between the pinned layer and pinning Ni/Mn superlattice with an antiferromagnetic phase were investigated in order to optimize the deposition conditions and annealing process. The thickness of each layer was controlled by deposition time. The H/sub ex/ and H/sub c/ of Ni/Mn superlattice-based spin-valves increased gradually with the number of annealing cycles and number of bilayers. At the Ni composition of 38 at.% for the annealing time of 12 hours, the largest H/sub ex/ and H/sub c/ of glass/[Ni/Mn]/sub 50//NiFe(60 /spl Aring/)/Cu(30 /spl Aring/)/NiFe(60 /spl Aring/) spin-valves are 305 Oe and 245 Oe, respectively. However, the magnetoresistance (MR) ratio is small, due to the shunting effect of Ni/Mn superlattice and the interdiffusion between NiFe and Cu.