Ky-Am Lee

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...

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.

Soft Magnetoresistive Properties of Conetic Thin Film Depending on Ta Buffer Layer

The property of soft magnetism for the Corning glass/non-buffer or buffer Ta/Conetic(NiFeCuMo)/Ta prepared by the ion beam deposition sputtering was studied. The effect of crystal property and post annealing treatment depending on the thickness of Conetic thin films was investigated. The coercivities of Conetic thin films with easy and hard direction along to the applying magnetic field during deposition were compared with each other. The coercivity and magnetic susceptibility of Ta(5 nm)/Conetic(50 nm) thin film were 0.12 Oe and 1.2 , respectively. From these results, firstly, the Conetic thin film was more soft magnetism thin film than other one such as permalloy NiFe. Secondly, the usage of soft magnetism Conetic thin film for GMR-SV (giant magneoresistance-spin valve) or MTJ (Megnetic Tunnel Junction) structure in a low magnetic field can be possible.

Dependence of Coercivity and Exchange Bias as Surface Magnetic Anisotropy in [Pd/Ferromagnet] Multilayer with Out-of-plane Magnetic Anisotropy

Dependence of the exchange bias and coercivity as surface magnetic anisotropy and ferromagnet materials for and /FeMn multilayers with perpendicular magnetic anisotropy were investigated. The coercivity was proportionally increased to 670 Oe by increasing stack number N in Ta(2.1 nm)/[Pd(3.1/N)//Ta(2.1) multilayers with perpendicular magnetic anisotropy. Also, the coercivity in exchange biased multilayer was tend to increased by increasing stack number N. But coercivity of each materials have been in order of Co (600 Oe), (520 Oe) and (320 Oe) as function of the ferromagnet materials. The other side, exchange force of each materials is 300 Oe when the reiteration layer number N is 3. In over number of reiteration layer 3, they maintained coercivity between 200 Oe and 300 Oe.

Magnetoresistance Effect of [Pd/Co] Spin-valve with Perpendicular Anisotropy

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.

Local Magnetization Reversal of FeMn/NiFe Films Using Laser Annealing

We have studied local magnetization reversal and magnetic properties induced by Laser annealing method in the strip-patterned Ta/NiFe/FeMn/Ta and Ta/NiFe/FeMn/NiFe/Ta multilayers fabricated by ion-beam deposition. The films were exposed to the emission of the DPSS (Diode Pumped Solid State, Nd:YAG) laser under 600 G. The laser beam intensity increased up to 440 mW. When the laser illuminated the patterned film with the power of above 200 m W, the intensity of MR peak located in +87 Oe shrunk. A new MR peak was generated at -63 Oe. When the laser power is 400 mW, the location of positive MR peak(Hex/) was changed slightly from +87 Oe to +76 Oe, and the MR ratio was decreased from 0.9% to 0.1 %. On the other hand, the new (negative) MR peak shifted from -63 Oe to -80 Oe, with the MR ratio increased up to 0.3%. As the illuminated area expanded, the intensity of opposite MR peak increased and it of negative MR peak decreased. This proved that the local reversal of exchange biasing should be realized by laser annealing.

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.