Yasunari Sugita

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.

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.

Thermally stable exchange-biased magnetic tunnel junctions over 400 °C

Exchange-biased magnetic tunnel junctions (MTJs) with interposed Fe1−xPtx metal alloy layers between the Al oxide barrier and the ferromagnetic electrodes maintain large tunneling magnetoresistance (TMR) after thermal treatment in excess of 400 °C, owing to an improved barrier interface. After 400 °C annealing, TMRs of MTJs with Fe1−xPtx (x=0.1–0.2) exhibit over 40% and retain 30% TMR after 420 °C annealing. The tunnel barrier height derived from the current–voltage curve fitted to the Simmons equation increases with richer Pt content. Secondary ion mass spectroscopy depth profiles and cross-section transmission electron micrographs of MTJs with Fe0.85Pt0.15 show a clear interface around the Al oxide barrier even after annealing at 400 °C.

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.

/spl alpha/-Fe/sub 2/O/sub 3/ spin-valve using Co/Ru/Co synthetic antiferromagnet

This paper reports the enlargement of pinning field, H/sub p/, in spin-valves with /spl alpha/-Fe/sub 2/O/sub 3/ as a pinning layer utilizing a Co/Ru/Co synthetic antiferromagnet as the pinned layer. H/sub p/ of /spl alpha/-Fe/sub 2/O/sub 3//Co is only 18 kA/m with a 20-nm-thick /spl alpha/-Fe/sub 2/O/sub 3/ layer. On the other hand, H/sub p/ is improved over 40 kA/m by replacing the pinned layer with Co/Ru/Co synthetic antiferromagnet. We studied the dependence of H/sub p/ in /spl alpha/-Fe/sub 2/O/sub 3/ spin-valves with the Co/Ru/Co on Ru and /spl alpha/-Fe/sub 2/O/sub 3/ layer thickness.

Enhancement of Giant Magnetoresistance in NiCoFe/Cu/Co with a Ag Capping Layer Prepared by Sputtering

Enhancement of giant magnetoresistance (GMR) in NiCoFe/Cu/Co with the addition of Cu/Ag capping layers prepared by sputtering on Si(001) single crystal substrates with Cu buffer layer was observed. This enhancement of magnetoresistance (MR) ratio may be attributed to the specular scattering of conduction electrons at the surface of the Ag capping layer. The dependence of the MR ratio on the Ag capping layer thickness was visible in the broad peaks at around t(Ag)=2 nm.

Thermal stability of exchange-biased magnetic tunnel junctions with stabilizing layer

Summary form only given. The applications of magnetic tunnel junctions (MTJs) for devices with CMOS such as MRAM need a high tunneling magnetoresistance ratio (TMR) and good thermal stability over 400/spl deg/C. Exchange-biased MTJs with CoFe and Mn-X antiferromagnetic layer show large TMR but annealing over 350/spl deg/C degrades the TMR due to diffusing Mn. Exchange-biased MTJs with a magnetic stabilizing layer (MS-layer) of magnetic metal alloy, with structures of PtMn/CoFe/Ru/CoFe/(MS-layer)/AlOx/(MS-layer)/CoFe, were investigated and showed good thermal stability up to 400/spl deg/C. The samples were prepared by magnetron sputtering and the tunnel barrier formed in situ.