Ho-Wan Joo

Enhancement of magnetoresistance in [Pd∕Co]N∕Cu∕Co∕[Pd∕Co]N∕FeMn spin valves

The dependences of the stack number and Co and Cu thicknesses on magnetoresistance, and perpendicular exchange biasing in the [Pd∕Co]×N1∕Cu∕Co∕[Pd∕Co]×N2∕FeMn spin valves, were investigated. The magnetoresistance ratio of the spin valves with N1=4 and N2=2 was above 5% for the Cu between 1.5 and 2.5nm, and the exchange-biasing field (Hex) was increased to 600Oe. When the Co thickness over the Cu layer was increased from 0.48to1.28nm, the ratio likewise rose to 7.4% due to the strengthened spin-dependent scattering effect. Moreover, the Co thickness below the Cu layer rose to 9.1%. The maximum ratio of 10.2% was obtained in the structure of the [Pd0.8∕Co0.32]×2∕Pd0.8∕CoFe0.48∕Cu2.25∕CoFe0.6∕[Pd0.8∕Co0.48]×2∕FeMn15 (nanometer) multilayer with Hex=450Oe.

Enhancement of giant magnetoresistance properties of NiO spin valves with an oxidized free layer naturally in the air

The effect of specular electron scattering on the natural oxidation of a free layer in NiO spin valves has been investigated. The magnetoresistance ratio and the exchange biasing field (Hex) of NiO(600 A)/Ni81Fe19(50 A)/Co(7 A)/Cu(20 A)/Ni81Fe19(70 A) spin valves were increased from 4.9% to 7.3%, and 110 to 170 Oe after the natural oxidation in the atmosphere for 80 days, respectively. The sheet resistance ρ decreased from 28 to 17 μΩ m, but Δρ did almost not change after the oxidation. The spin valves enhanced by the specular electron scattering in the naturally oxidized Co/NiFe/NiFeOx free layer were confirmed from the depth profiles using Auger electron spectroscopy.

Magnetoresistive Properties of Array IrMn Spin Valves Devices

To develop array magnetic sensors, specular-type giant magnetoresistive- spin valve (GMR-SV) film of Glass/Ta(5)MiFe(7)/IrMn(10)NiFe(5)//CoFe(5)/Cu(2.6)/CoFe(5)//NiFe(7)/Ta(5)(nm) was deposited by using a high-vacuum sputtering system. One of 15 way sensors in the area of was Patterned a size of in multilayer sample by Photo-lithography. All of 15 sensors with Cu electrodes were measured a uniform magnetic properties by 2-probe method. The highest magnetic sensitivity of MR and output voltage measured nearby an external magnetic field of 5 Oe were MS

Laser annealing in exchanged-biased films with out-of-plane and in-plane magnetic anisotropy

The local magnetization reversal of an exchange-biased in-plane FeMn/NiFe bilayers and out-of plane [Pd/Co]5/FeMn multilayers as a function of exposed region is investigated. The multilayer films are deposited using ion-beam and dc magnetron sputtering method. Laser annealing using a diode pumped solid state (Nd:YAG) laser is then utilized to locally reverse the unidirectional anisotropy in the films. The hysteresis loops for the exchange biased films are also analyzed by the magnetic optical Kerr effect and the extraordinary Hall effect.

Post-annealing Effect of Giant Magnetoresistance-Spin Valve Device for Sensor

In order to detect of the magnetic property in the cell unit, we studied the GMR-SV (giant magnetoresistance-spin valves) biosensor, which was depended on the micro patterned features according to two easy directions of longitudinal and transversal axes. Here, the multi layer structure was glass/NiO/NiFe/CoFe/Cu/CoFe/NiFe. The uniaxial anisotropy direction was applied to the patterned biosensor during the deposition and vacuum post-annealing at under the magnitude of 300 Oe, respectively. Considering the magnetic shape anisotropy effect, the size of micro patterned biosensor was a after the photo lithography process. By our experimental results, we confirmed that the best condition of GMR-SV biosensor should be the same direction of the axis sensing current and the easy axis of pinned NiO/NiFe/CoFe triple layer oriented to the width direction of device, and the direction of the easy axis of free CoFe/NiFe bilayer was according to the longitudinal direction of device.

Thickness and annealing temperature dependence of perpendicular exchange biasing in [Pd/Co]/FeMn multilayers

The thickness of Pd, Co, FeMn, and buffer (Ta, Pd) layers and annealing temperature dependences on perpendicular exchange biasing field (H/sub ex/) and coercivity field (H/sub c/) in Ta(Pd)/[Pd/Co]/sub n//FeMn/Ta(Pd) multilayers are investigated. Hysteresis loops with perpendicular magnetization curves were measured using extraordinary Hall effect. Increase in the thickness of buffer Ta layer lead to the enhancement of both H/sub ex/ and H/sub c/. The H/sub ex/ of 0.1 nm Pd sample increased slightly from 125 Oe to 145 Oe, and vanished at 0.5 nm Pd. As the Co thickness decreases, the H/sub ex/ and H/sub c/ increased up to 360 Oe and 633 Oe in 0.48 nm and 0.32 nm Co sample, respectively. H/sub ex/ increased up to 130 Oe as the FeMn thickness increases to 12 nm, and decreased to 90 Oe at 21 nm FeMn thickness. H/sub ex/ is also observed to increase as the annealing temperature increases. At 330 /spl deg/C, the perpendicular anisotropy disappeared.

Magnetoresistance Effect of Ta/NiFe/Cu/Co Pseudo Spin Valve Structure

The dependence of sensitivity, MR ratio, coercivity (Hc) and switching fields as a function of thickness of each magnetic layers(Co, NiFe and Cu) were investigated in pseudo spin valves with a structure of Ta/NiFe/Cu/Co. As measured results dependence of the thickness of each magnetic layer, we obtained MR ratio of 7.26% for Ta(4 nm)/NiFe(7.5 nm)/Cu(3 nm)/Co(5 nm) pseudo spin valves. Also, we could control properties of magnetoresistance for independent magnetization courses of each magnetic layer. Especially, we found that we could control coercivity as constant MR ratio dependence of Co thickness.

Exchange Bias Perpendicular Magnetic Anisotropy and Thermal Stability of (Pd/Co) N /FeMn Multilayer

Magnetic properties and thermal stability by exchange biased perpendicular magnetic anisotropy in (Pd/Co)FeMn multilayer deposited by do magnetron sputtering system are investigated. We measured the perpendicular magnetization curves of (Pd(0.8nm)/Co(0.8nm)FeMn multilayer as function of FeMn thickness and annealing temperature. As FeMn thickness increases from 0 to 21nm, the perpendicular exchange bias(Hex) obtained 127 Oe at FeMn thickness 15nm. As the annealing temperature increases to 24, the E increased from 115 Oe to 190 Oe and disappeared exchange biased perpendicular magnetic anisotropy effect at 33.EX>..

Study on the Specular Effect in NiO spin-valve Thin Films

Magnetic properties are investigated for top- and bottom-type spin valves of Si/SiO/NiO(60nm)/Co(2.5nm)/Cu(1.95nm)/Co(4.5nm)/NOL(t nm; Nano Oxide layer). The MR ratios of the bottom-type spin valves with NOL are larger than those of the top-type spin valves. However, the enhancement of the former is lower than the latter. Both of spin-valves also showed almost constant Ap and smaller p. Enhanced MR ratios of spin valves with NOL result mainly from small values of with constant Ap which due to specular diffusive electron scattering at NOL(NiO)/metal interfaces.