Yasuhiro Kawawake

Large MR ratios in spin valves bounded with insulating antiferromagnets

Abstract MR properties of spin valves composed of AF/Co/Cu/Co(/Cu/Co/AF′) layers were studied using insulating antiferromagnets, α-Fe2O3, Nio as the bottom AF and top AF′ layer. Spin valves using IrMn as the top AF′ layer were also prepared for comparison. The MR ratios of α-Fe2O3/Co/Cu/Co/Cu/Co/AF′ spin valves using Ir Mn and α-Fe2O3 as the top AF’ layers were about 21% and 28%, respectively. The experimental data are compared with numerical results using the Barnas’ model. The large MR ratios in the spin valves bounded with insulating anti-ferromagnets such as α-Fe2O3 may be attributed to the specular scattering effect at the interface of Co and α-Fe2O3.

Giant Magnetoresistanc of Dual Spin-Valves Using Antiferromagnetic .ALPHA.-Fe2O3 as a Pinning Layer.

We report the large magnetoresitance (MR) ratio of a dual spin-valve structure in α-Fe2O3(50 nm)/Co/Cu/Co/Cu/Co/α-Fe2O3(50 nm) films using the insulating antiferromagnetic α-Fe2O3 as a pinning layer. The MR ratio of a dual spin-valve is obtained as 27.8%, the highest value ever reported. This large MR ratio may indicate that the specular reflection of the conduction electrons occurs at the metal/insulator (Co/α-Fe2O3) interfaces.

Spin-Valve Memory Elements Using [{Co-Pt/Cu/Ni-Fe-Co}/Cu] Multilayers

A new type of magnetoresistive memory using spin-valve multilayers composed of semi-hard magnetic layers and soft magnetic layers separated with nonmagnetic layers was developed. The fabricated memory element was composed of a word line of Au film and a magnetoresistive sense line of [{CoPt/Cu/NiFeCo}/Cu]N multilayers. This spin-valve memory has nonvolatile and nondestructive readout properties.

Magnetoresistance in CoMnB/Co(Fe)/Cu/Co(Fe) spin-valves

Abstract Magnetoresistance in AM/M′/Cu/M spin-valves was studied, where AM = CoMnB or CoNbZr and M′,M = Co or CoFe. M′ is a thin magnetic layer interposed between an AM and a Cu layer to enhance the MR ratio, and M is a magnetic layer having a larger H c than the AM layer. A considerably large MR ratio, 7.6%, with small switching field was obtained for the spin-valves with AM = CoMnB and M′(=M) = Co. Surface oxidation of the M layer was effective in increasing the saturation field of the spin-valves. These spin-valves are very thin (≤10 nm) and are advantageous for MR heads having narrow shield gaps.

Thermal stability of PtMn based synthetic spin valves using thin oxide layer

Thermal stability of PtMn based synthetic spin valves with a thin oxide layers (OL) in pinned and/or free layers has been studied. Temperature dependence of the magnetoresistance(MR) curves and thermal treatment in the magnetic field show that the OL do not deteriorate thermal stability of the spin valves. PtMn based synthetic spin valves with Ta/NiFeCr seedlayer exhibit a stronger (111) orientation and better MR properties than those with a Ta seedlayer. Furthermore, PtMn based synthetic spin valves on a Ta/NiFeCr seedlayer with and without thin OL in the pinned layer show good thermal stability. An aniferromagnetic coupling of CoFe/Ru/CoFe in these spin valves with a Ta/NiFeCr seedlayer, even though the Ru interlayer was oxidized, is more thermally stable than that in the spin valves with a Ta seedlayer at more than 400 °C.

Enhanced gmr in PtMn based spin-valves with specular reflective thin oxide layers

PtMn based Spin-valves with or without specular reflective thin oxide layers, OL, were prepared by sputtering. The MR ratios and /spl Delta/Rs of the spin-valves without OL were about 8% and 1.2 /spl Omega/. The values were increased up to 12-15% and /spl supe/2.6 /spl Omega/ by inserting an OL into the pinned and free layers. PtMn based spin-valves with synthetic AF and OL as the pinning layers were also studied. The MR ratio and /spl Delta/Rs were about 11% and 2.9 /spl Omega/. These PtMn based spin-valves showed better thermal stability than IrMn based spin-valves.

Spin valves with a thin pinning layer of α-Fe2O3 or α-Fe2O3/NiO

Magnetoresistive (MR) properties of spin valves pinned by a thin α-Fe2O3 layer were investigated. In spin valves consisting of α-Fe2O3/Ni–Fe(2 nm)/Co(1 nm)/Cu(2 nm)/Co(1 nm)/Ni–Fe(5 nm), the MR ratio remained nearly constant at about 12%, when the α-Fe2O3 layer thickness was reduced from 50 to 10 nm, while the exchange anisotropy field Hex decreased from 22 to 6 kA/m. The spin valves with a thinner α-Fe2O3 layer showed higher sensitivity to magnetic field than the ones with a thicker α-Fe2O3 layer. The measurement of MR ratio after annealing at 573 K in the α-Fe2O3/Co/Cu/Co spin valves revealed that the spin valve with a 30-nm-thick α-Fe2O3 layer was more stable against heat treatment than the one with a 50-nm-thick α-Fe2O3 layer. Heat treatment increased Hex in spin valves with both thick and thin α-Fe2O3 layers. Spin valves with NiO(10 nm)/α-Fe2O3(10 nm) as a pinning layer showed larger Hex than spin valves with either α-Fe2O3(10 nm) or NiO(10 nm) pinning layers.

Vacuum deposition of Co-Cr perpendicular anisotropy films on polymer substrates treated with ion beam

The author investigated the effect of ion-beam treatment of polymer substrate surfaces on magnetic properties, microstructure, adhesive force, and recording performances of vacuum-deposited Co-Cr films. Films which are deposited on the ion-beam-treated substrates have higher H/sub c perpendicular to / than that of the films on untreated substrates without the treatment and have H/sub keff/ values high enough for perpendicular magnetic recording applications. With ion-beam treatment the adhesive force of the Co-Cr films is considerably improved, becoming of practical strength. The films deposited on the treated substrates reproduced voltage as high as that of Co-Cr films with Ti underlayer. Ion-beam treatment of the polymer substrates therefore makes both glow discharge treatment and the use of a Ti underlayer unnecessary and promises high manufacturing productivity. >

Temperature dependence of giant magneto-resistance in PtMn-and Fe2O3-based specular spin valves

Temperature dependence of the giant magneto-resistance (MR) was measured for spin valves with and without nano-oxide layer (NOL). In spin valves with NOL, the MR ratio increased more remarkably on lowering the temperature than in those without NOL. The temperature dependence of MR ratio and that of the resistivity were explained by using two-current model. The MR ratio enhanced with NOL is attributed to the increase of the mean free path of up-spin electrons.

Thermal stability of α-Fe2O3/CoFe/Ru/CoFe-based spin valves

Magnetoresistive (MR) properties of α-Fe2O3-based spin valves with and without a CoFe/Ru/CoFe synthetic antiferromagnet (SAF) were studied at elevated temperatures and after the annealing in different conditions. The pinning field of the spin valve consisting of α-Fe2O3(20 nm)/CoFe(2 nm)/Ru(0.7 nm)/CoFe(2 nm)/Cu(2 nm)/ CoFe(1 nm)/NiFe(5 nm)/Ta(3 nm)was larger than 300 Oe at 200 °C, which was about five times as much as that of the spin valve consisting of α-Fe2O3(20 nm)/CoFe(2 nm)/Cu(2 nm)/CoFe(1 nm)/NiFe(5 nm)/ Ta(3 nm). The MR ratio and sheet resistance change in the α-Fe2O3(20 nm)/CoFe(2 nm)/Ru(0.7 nm)/CoFe(2 nm)/Cu(2 nm)/ CoFe(0.5 nm)/NiFe(3 nm)/Ta(3 nm)film were 9.8% and 2.6 Ω/□, respectively, after annealing at 270 °C for 3 h. The simple spin-valve structure with the same composition also showed good thermal stability of MR properties against annealing at 200 °C without an applied magnetic field.