Katsumi Hoshino

Magnetoresistance and preferred orientation in Fe-Mn/Ni-Fe/Cu/Ni-Fe sandwiches with various buffer layer materials

Magnetoresistance effects and film structures have been investigated in [Fe–Mn/Ni–Fe/Cu/Ni–Fe/buffer layer/Si] sandwiches with various buffer layer materials. The sandwich with Nb, Ta, Ti, Zr or Hf buffer layer has strong (111) texture. Cu, Ag, Au and Cr buffer layers do not cause strong (111) texture. When the sandwich has strong (111) texture, the Ni–Fe layer neighboring the Fe–Mn antiferromagnetic layer is strongly exchange-biased by the Fe–Mn layer, and thus the sandwich shows a high magnetoresistance ratio.

Exchange coupling between antiferromagnetic Mn-Ir and ferromagnetic Ni-Fe layers

Exchange couplings between antiferromagnetic Mn–Ir and ferromagnetic Ni–Fe layers have been investigated while varying the Mn–Ir composition. These exchange couplings appeared at room temperature at Ir compositions between 20 and 46 at.%. The maximum exchange coupling field of 3.2 kA/m was obtained for Mn–20 at.%Ir(59 nm)/Ni–Fe(20 nm)/Zr(10 nm). Dependence of the exchange coupling fields on each layer thickness was also investigated. The Mn–Ir/Ni–Fe bilayers maintained high exchange coupling fields at Mn–Ir layer thicknesses above 10 nm.

CPP–GMR Heads With a Current Screen Layer for 300

Current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) heads with a current screen layer were fabricated, and the recording performance was measured. An output voltage of 1.9 mV and head-amp signal-to-noise ratio (SNR) of about 30 dB were obtained from a 50-nm-wide head with an operating voltage of 120 mV. The MR ratio was 4%-5%, shield gap was 36 nm and resistance was 72 Omega. With using the thermal fly-height control (TFC), the fabricated head showed a potential to yield a 382 Gb/in2 recording (1252 kBPI times 305 kTPI). The current screen structure reduced the spin torque noise since just a low sensing current of 1-2 mA was required for obtaining a high output. Newly developed CPP-GMR films with a current screen layer showed the MR ratio of 18%-19% with the RA product of 0.2-0.3 Omega ldr mum2. Calculation showed that this film allows us to achieve 30 dB or more in the head-amp SNR when the sensor width was 40 nm or larger. The current screen CPP-GMR head is thus an attractive candidate that has a high potential suitable for an areal density of 500 Gb/in2 or more. Below 40 nm, an all metal CPP-GMR head with the MR ratio of 10% or more would be the best candidate.

{\hbox{Gb/in}}^{2}

A current-perpendicular-to-the-plane spin-valve (CPP-SV) structure having half-metal materials laminated between CoFe layers was investigated. A CPP-SV film having a CoMnGe free layer had a resistance-change-area product ΔRA of 0.9 mΩ μm2, almost the same as that of a CPP-SV film having a simple CoFe free layer. But the ΔRA of a CPP-SV film with a CoFe/CoMnGe/CoFe sandwiched free layer was 1.6 mΩ μm2. CPP-SV films having CoFe/iron-added-magnetite/CoFe sandwiched layers were also investigated and found to have a ΔRA of ≈2 mΩ μm2. We found that a CoFe/half-metal/CoFe sandwiched layer was a stronger source of spin-dependent scattering than a CoFe layer and simple half-metal layer.

Recording

Magnetoresistance effects and interlayer exchange coupling between magnetic layers have been investigated in [Hf/Fe–Mn/Ni–Fe–Co/Cu/Ni–Fe–Co/Hf] multilayers by varying the thicknesses of the Ni–Fe–Co, Fe–Mn, and Cu layers. When the Fe–Mn layer is thicker than 5.0 nm, it applies a strong exchange-bias field to the neighboring Ni–Fe–Co layer. The multilayers show high magnetoresistance ratios at Cu-layer thicknesses between 2.0 and 3.0 nm, because the interlayer exchange coupling is weak. The interlayer exchange coupling between the two Ni–Fe–Co layers is always ferromagnetic at Cu-layer thicknesses between 0.5 and 5.0 nm.

Current-perpendicular-to-the-plane giant magnetoresistance in structures with half-metal materials laminated between CoFe layers

We investigated the influence of the ferromagnetic current screen layer on a current perpendicular to the plane-giant magnetoresistance (CPP-GMR). We prepared a bottom-type synthetic-pinned spin-valve film with a ferromagnetic current screen layer of naturally oxidized CoFe, which was separated magnetically from the free and pinned layers. When the CoFe layer thickness increased to above 1.0nm before oxidation, we observed a magnetic moment corresponding to the unoxidized CoFe. We also found that the MR ratio abruptly increased from 1.6% to 7.2% with the increase in the CoFe layer thickness from 1.0to3.7nm before oxidation, which was the same tendency observed in the magnetic moment. The MR ratio seemed to be strongly dependent on the magnetic moment of the current screen layer. The MR curve with the high MR ratio had two peaks near the zero magnetic fields. Based on the analysis of the magnetization configuration of the free, pinned, and current screen layers, we found that the ferromagnetic properties o...

Magnetoresistance and Interlayer Exchange Coupling between Magnetic Layers in Fe–Mn/Ni–Fe–Co/Cu/Ni–Fe–Co Multilayers

A current-perpendicular-to-the-plane (CPP)-spin-valve sensor with iron-added magnetite layers (IMLs) was investigated. We prepared bottom synthetic-pin spin-valve films with CoFe∕IML∕CoFe sandwiched layers as both free layers and pinned layers. The slope of resistance-change-area product (ΔRA) versus IML thickness is around 0.5–0.6Ωμm2∕nm, and this indicates that using IMLs results in large bulk scattering. Magnetite and iron grains were observed in transmission electron microscopy images even in a 2-nm-thick IML in a CPP giant magnetoresistance structure. As a result, ΔRA up to 2–2.5mΩμm2 and MR ratio of 2.0%–2.6% at RA of 0.08–0.1Ωμm2 were obtained by using IML in CPP-spin-valve films.

Influence of ferromagnetic current screen layer on current perpendicular to the plane-giant magnetoresistance

Shielded GMR heads with an in-stack bias layer were designed, fabricated, and their read performance was measured. Since the bias layer and the free layer antiferromagnetically couple at the edge of the sensor, a closed magnetic flux structure (CFS) is formed. The results of micromagnetic simulation revealed that when an MnIr antiferromagnetic layer is used to pin the magnetization of the bias layer, the Ms⋅t of the bias layer normalized by that of the free layer should be between 1.2 and 1.5. Here Ms and t are the saturation magnetization and the thickness of the layer. The read waveform of the fabricated head was noise free and well biased. The obtained read sensitivity of the CFS head was four times higher than that of a conventional abutted junction head. Calculation revealed that the read sensitivity of the CFS head was almost five times higher than that of conventional heads when the magnetic track width was reduced to 100 nm. Thus, CFS heads show potential for high track density recording.Shielded GMR heads with an in-stack bias layer were designed, fabricated, and their read performance was measured. Since the bias layer and the free layer antiferromagnetically couple at the edge of the sensor, a closed magnetic flux structure (CFS) is formed. The results of micromagnetic simulation revealed that when an MnIr antiferromagnetic layer is used to pin the magnetization of the bias layer, the Ms⋅t of the bias layer normalized by that of the free layer should be between 1.2 and 1.5. Here Ms and t are the saturation magnetization and the thickness of the layer. The read waveform of the fabricated head was noise free and well biased. The obtained read sensitivity of the CFS head was four times higher than that of a conventional abutted junction head. Calculation revealed that the read sensitivity of the CFS head was almost five times higher than that of conventional heads when the magnetic track width was reduced to 100 nm. Thus, CFS heads show potential for high track density recording.

Current-perpendicular-to-the-plane spin-valve films with iron-added magnetite layers

We investigated exchange couplings between magnetic layers and antiferromagnetic layers in (Mn-Ir, Fe-Mn)/Ni-Fe-Co and Ni-Fe-Co/(Mn-Ir, Fe-Mn) films formed by ion beam sputtering. We changed a stacking order between the magnetic layers and antiferromagnetic layers, and the thickness of the antiferromagnetic layers. In both the Fe-Mn/Ni-Fe-Co and the Ni-Fe-Co/Fe-Mn films, high exchange bias fields applied to the Ni-Fe-Co layers were observed, when the thickness of the Fe-Mn layer was 10-20 nm. When the Mn-Ir layers were formed on the Ni-Fe layers, the high exchange bias fields were also observed. However, the exchange bias fields were very low when the Mn-Ir layers were formed under the Ni-Fe layers. The decrease of the exchange bias field was caused by the deterioration of the (111) texture near the top surface which faces the Ni-Fe layer in the Mn-Ir layer.

Read performance of GMR heads with in-stack longitudinal bias layer

Abstract We investigated saturation fields and film textures of NiFeCo/Cu giant magnetoresistive multilayers with weak (1 0 0), weak (1 1 1) and strong (1 1 1) textures. The texture was changed by using various buffer layer materials. For 1 nm thick Cu layers, the saturation field of the multilayers was more than 100 kA/m, and not significantly changed by the texture of the multilayers. While for 2.3 nm thick Cu layers, the saturation field was changed by the texture of the multilayers. The saturation fields were 13.7 kA/m and about 2–3 kA/m for (1 0 0) and (1 1 1) texture, respectively.