Hitoshi Kanai

Spin-valve heads in the current-perpendicular-to-plane mode for ultrahigh-density. recording

We have investigated the magnetoresistance properties of spin valves in the current-perpendicular-to-plane (CPP) mode. Conventional single spin-valve (SV) film shows resistance area product RA=81 m/spl Omega//spl mu/m/sup 2/, and resistance change area product /spl Delta/RA=0.35 m/spl Omega//spl mu/m/sup 2/. For a CPP element of a single SV with oxide layers, /spl Delta/RA dramatically increased to 9.0 m/spl Omega//spl mu/m/sup 2/. Micromagnetics simulation revealed that the readback performance of the CPP head with low-impedance conventional SV film was much affected by sense current. On the other hand, the medium impedance CPP head, such as the SV film with oxide layers, shows several advantages compared with the low impedance head, such as higher output voltage, less influence by magnetic field of the sense current, and narrower core width.

Spin-valve read heads with NiFe/Co/sub 90/Fe/sub 10/ layers for 5 Gbit/in/sup 2/ density recording

Successful use of a NiFe/Co/sub 90/Fe/sub 10/ bilayer as a soft magnetic free layer in spin-valve films with a GMR enhanced structure comprised of NiFe/Co/sub 90/Fe/sub 10//Cu/Co/sub 90/Fe/sub 10//FeMn is outlined. The GMR ratio of the spin-valve film with Co/sub 90/Fe/sub 10/ is over 7% and the coercivity of the free NiFe/Co/sub 90/Fe/sub 10/ bilayers is less than 5 Oe. A merged inductive/spin-valve head was fabricated with a read track-width of 1.3 /spl mu/m and a read gap-length of 0.26 /spl mu/m using spin-valve film with a Ta(50 /spl Aring/)/NiFe(45 /spl Aring/)/Co/sub 90/Fe/sub 10/(30 /spl Aring/)/Cu(32 /spl Aring/)/Fe/sub 10/(22 /spl Aring/)/FeMn(100 /spl Aring/)/Ta(100 /spl Aring/) structure and 260 /spl Aring/ thick domain control Co/sub 78/Cr/sub 10/Pt/sub 12/ magnet layers. Its read/write performance was tested on a low noise CoCr/sub 17/Pt/sub 5/Ta/sub 4/ thin film disk with an Mr/spl middot/t of 0.41 memu/cm/sup 2/ and a coercivity of 2500 Oe. There is no Barkhausen noise in the readback waveform. The result of the microtrack sensitivity profiles reveals an effective read track-width of 0.8 /spl mu/m. A normalized output for a track-width of 880 /spl mu/Vpp//spl mu/m and D/sub 50/ of 166 kFCI was obtained. Using a PRML channel, a bit error rate of less than 10/sup -8/ was obtained without error correction at a data rate of 3.3 MB/s and at a linear density of 217 kBPI on a thin film disk with an Mr/spl middot/t of 0.72 memu/cm/sup 2/. Thus, 5 Gbit/in/sup 2/ density recording with a linear density of 217 kBPI and a track density of 23 kTPI is possible.

Spin-valve sensors with domain control hard magnet layers

We have fabricated unshielded narrow-track NiFe/Cu/NiFe/FeMn spin-valve sensors with a height of 2 /spl mu/m and a track-width of less than 2 /spl mu/m using CoCrPt hard magnets (4/spl pi/Mr=5500 G, Hc=1000 Oe) as a domain control layer. Barkhausen noise was completely suppressed by a longitudinal biasing field from the CoCrPt layers. The bias state was improved by applying a strong ferromagnetic exchange coupling field of 30 Oe between the free and pinned NiFe layers through a 14 /spl Aring/-thick Cu interlayer. We have also fabricated shielded CoCrPt magnet-biased spin-valve read heads with a track-width of 1.7 /spl mu/m. The heads had no Barkhausen noise and very low crosstalk noise.

Spin-valve head with specularly reflective oxide layers for over 100 Gb/in/sup 2/

We have developed spin valves with thin oxide reflective layers, which exhibit a greatly improved magnetoresistance (MR) performance while keeping other good properties, such as an exchange bias field of over 1000 Oe and a coercivity and an interlayer coupling field of less than 10 Oe. The giant magnetoresistance (GMR) values reached over 12% for the spin valve with a single specular layer and over 15% for the spin valve with double specular layers. The oxide reflective layers helped improve MR performance due to enhanced specularity at the oxide interfaces. Evidence of enhanced specularity was provided by the observed reduced sheet resistance and oscillatory interlayer exchange coupling between the free layer and the spacer in the spin valve. The observation of the oscillation was possible due to amplified Ruderman-Kittel-Kasuya-Yoshida (RKKY) coupling, as seen in a multilayered superlattice composed of ferromagnetic layers with nonmagnetic spacers. We successfully fabricated read heads by incorporating such spin valves. In particular, very narrow read track width was achieved in the head with double reflective layers. The read track width was estimated to be less than 0.14 /spl mu/m. The head was tested on a low noise CoCrPt-based alloy disk with a coercivity of 3170 Oe and an areal moment of 0.36 memu/cm/sup 2/. The head showed a normalized output of 8.6 mV//spl mu/m with an asymmetry of 0.5% at 2 mA sense current, a /spl sim/40% increase over that of the head with a single reflective layer that was used in the demonstration of 56.1 Gb/in/sup 2/. We have therefore demonstrated that our head with the specular layers can be used for an areal density of over 100 Gb/in/sup 2/ in magnetic recording with the help of advanced media and integration techniques.

Top, bottom, and dual spin valve recording heads with PdPtMn antiferromagnets

We fabricated top-type (Substrate/free layer/Cu/pinned layer/antiferromagnetic layer) and bottom-type (Sub./antiferro/pinned/Cu/free) spin valve heads using PdPtMn antiferromagnets. Bottom type spin valve head with a buffer layer of Ta/NiFe showed similar exchange bias field and MR ratio as top-type spin valve head. Dual spin valve (DSV) films with two pinning layers of PdPtMn had an enhanced MR ratio by 40% compared to the top-type spin valve. Patterned DSV elements with 3 /spl mu/m MR height showed relatively large deviation from the optimum bias state. In order to adjust the bias point, asymmetric DSV elements with Cu layers of different thicknesses were investigated. Asymmetric DSV with the structure of Ta/NiFe/PdPtMn/CoFe/Cu(t/sub 1/)/CoFe/NiPe/CoFe/Cu(t/sub 2/)/CoFe/PdPtMn (t/sub 1//spl ne/t/sub 2/) showed an improvement for just bias using sense current magnetic field. The possibility of reducing the PdPtMn critical thickness for exchange coupling was investigated using ultra high vacuum (UHV) deposition environment. UHV technique is significantly useful to obtain exchange bias field (H/sub ua/) of PdPtMn(t)/ferro at t 500 Oe), large sheet resistance change (/spl Delta//spl rho///sub total/=1.6 /spl Omega/), and good thermal stability up to 300/spl deg/C. The total thickness of DSV was also reduced from 80 to 53 nm. Single and dual spin valves with thin PdPtMn pinning layer are very promising sensors for ultra high density recording applications.

NiFe/CoFeB Spin-valve Heads For Over 5 Gbit/in/sub 2/ Density Recording

This paper outlines the successful use of NiFe/(Co/sub 90/Fe/sub 10/)/sub 100-x/Bx (x=5, 10%) for soft magnetic, thermally stabilized spin-valves. The GMR effect in the NiFe/CoFeB spinvalve increases after annealing. The annealing effect of CoFeB on CoFeB/Cu interfaces is investigated by high resolution TEM-EDX analysis. Merged inductive NiFe/CoFeB spin-valve heads with a read gap length of 0.18 /spl mu/m and a write gap length of 0.28 /spl mu/m having NiO(400 /spl Aring/)/NiFe(10 /spl Aring/)/CoFeB/sub 5/(10 /spl Aring/)/Cu(32 /spl Aring/)/CoFeB/sub 5/(20 /spl Aring/)/Ta(100 /spl Aring/) spin-valve film and high Bs laminated FeZrN/NiFe top poles were fabricated. Their read/write performance were tested on a low noise CoCr/sub 19/Pt/sub 5/Ta/sub 2/Nb/sub 2/ thin-film disk with an Mrt of 0.6 memu/cm/sup 2/ and a coercivity of 2600 Oe. A normalized output per track-width of 1000 /spl mu/Vpp//spl mu/m and a 50% rolloff linear density (D/sub 50/) of 182 kFCI is obtained. This performance well exceeds the performance of 5 Gbit/in/sup 2/ spin-valve heads. The measured S/N was 26.8 dB for a spin-valve head with with a narrow read track-width of 0.68 /spl mu/m, and the feasibility of 8 G bit/in/sup 2/ recording density is studied using a 1/7 code Narrow Band PRML channel.

Effect of thin oxide capping on interlayer coupling in spin valves

We controlled interlayer coupling from ferromagnetic to antiferromagnetic by appropriately capping spin valves with thin oxides. The interlayer coupling field was -16.6 Oe at a Cu-spacer thickness of 30 /spl Aring/. The sign of coupling changed at a Cu-spacer thickness of 20 /spl Aring/. The antiferromagnetic coupling achieved in this way allowed a reduction of thickness of the Cu spacer down to 20 /spl Aring/ without loss of good magnetic and electrical properties, and this led to a significant improvement in the MR response of the spin valves. The interlayer coupling field was only +8.6 Oe even at a Cu-spacer thickness of 20 /spl Aring/. We attribute the improvement in MR response to less current shunting through the most conductive Cu layer and to enhanced specular scattering at the interface between the free and the oxide capping layer.

Magnetic and electrical properties of spin valve with single and double specular oxide layers

Appropriate oxide capping on a spin valve significantly improved electrical and magnetic properties. The interlayer exchange coupling oscillated in the thickness range of a Cu spacer (between 20 and 30 A). The coupling was antiferromagnetic and it allowed us to reduce the Cu spacer down to 20 A without sacrificing the good properties of the spin valve. The improvement is due to enhanced specular reflection at the interface between the magnetic and the oxide layer and to less current shunting through the Cu spacer. In particular, the Cu in the capping acts as a filter controlling the diffusion of oxygen, which has led to the soft magnetic properties. Embedding an additional thin oxide layer into the pinned layer further improved the magnetoresistance response of the spin valve. Confinement of electrons between two oxides helps increase the occurrence of spin-dependent scattering. As a result, high giant magnetoresistance values resulted. The coupling oscillated from ferromagnetic to antiferromagnetic as a ...

Analysis of thermal magnetic noise in spin-valve GMR heads by using micromagnetic simulation

The size of the sensor in spin-valve GMR heads has been reduced to increase the areal magnetic recording density. Thermal magnetic noise, which arises from thermal fluctuation, becomes the main source of head noise and a limitation on recording density. Insufficient abutted permanent magnetic biasing yields an asymmetrical waveform both for signal output and thermal magnetic noise. This is due to the same mechanism as that of Barkhausen noise. In contrast, it has been found that small Hex, which is the exchange coupling strength between the bottom pinned layer (Pin1) and the antiferromagnetic biasing layer, emphasizes thermal magnetic noise without affecting signal output. In a head with small Hex, the magnetization near the air bearing surface and the top of the Pin2 layer tilts in the direction of the track width and randomly flips in the opposite direction. In synthetic ferrimagnetic heads, thermal magnetic noise chiefly depends on Hex rather than unidirectional anisotropy, Hua. The value of Hua does n...

Very large giant magnetoresistance of spin valves with specularly reflective oxide layers

We developed a spin valve with oxide specular layers that shows a giant magnetoresistance value of 20%. The spin valve also showed an exchange bias field of over 1000 Oe. The giant magnetoresistance was mainly due to an increase in the sheet resistance change and resulted from additional specular reflection at the interface of the free layer. The method we used was to modify specularly reflective oxide layers of the free and the capping layers.