Pat J. Ryan

Commercial TMR heads for hard disk drives: characterization and extendibility at 300 gbit/in/sup 2/

Tunneling magnetoresistive (TMR) reading heads at an areal density of 80-100 Gbit/in/sup 2/ in a longitudinal magnetic recording mode have for the first time been commercialized for both laptop and desktop Seagate hard disk drive products. The first generation TMR products utilized a bottom TMR stack and an abutted hard bias design. These TMR heads have demonstrated three times the amplitude of comparable giant magnetoresistive (GMR) devices, resulting in a 0.6 decade bit error rate gain over GMR. This has enabled high component and drive yields. Due to the improved thermal dissipation of current-perpendicular-to-plane geometry, TMR runs cooler and has better lifetime performance, and has demonstrated the similar electrical static discharge robustness as GMR. TMR has demonstrated equivalent or better process and wafer yields compared to GMR. The TMR heads is proven to be a mature and capable reader technology. Using the same TMR head design in conjunction with perpendicular recording, 274 Gbit/in/sup 2/ has been demonstrated. Advanced design can reach 311 Gbit/in/sup 2/.

Tunneling magnetoresistive heads beyond 150 Gb/in/sup 2/

Tunneling magnetoresistive (TMR) readers capable of 150 Gb/in/sup 2/ of areal density magnetic recording for hard disk drive were demonstrated with bit-error-rate performance. The head design used is basically a bottom type stack of Ta/PtMn/CoFe/Ru/CoFe/oxide barrier/CoFe/NiFe/Ta cap with abutted hard bias stabilization. The electrical reader width is about 4 /spl mu/ to reach a very high track density and shield-to-shield spacing is about 700 /spl Aring/ for high linear density. On-track bit error floor is better than 10/sup -5/ at a linear density of 900 KBPI and the recording system noise is dominated by the media. The best areal density achieved (using -4 OTC reference level) is 143 Gb/in/sup 2/ using symmetric squeeze and 152 Gb/in/sup 2/ using asymmetric squeeze method, respectively. It was found that the TMR head has several decibels more signal-to-noise ratio gain over spin valve readers at 150 Gb/in/sup 2/ and beyond. The TMR head is also suitable for perpendicular recording application.

Spin tunneling heads above 20 Gb/in/sup 2/

Spin tunneling recording heads above 20 Gb/in/sup 2/ have been fabricated using a bottom tunneling junction stack. The spin tunneling stack is made of Ta/PtMn/CoFe/Ru/CoFe/AlO/NiFe/Ta and stabilized by a permanent magnet abutted junction. The effective junction width is about 0.4 /spl mu/m wide and lapped to the junction with an optimum stripe height. The barrier has resistance area product of 15-20 /spl Omega//spl mu/m/sup 2/, leading to a typical head resistance of around 50 /spl Omega/. Isolated pulses during the spin-stand test shows large signal up to 10 mV. On track error rate floor is better than 10/sup -9/ and the head signal-to-noise ratio is also better than that of. a conventional spin valve GMR head. The areal density estimated (using BER of 10/sup -5/) is above 20 Gb/in/sup 2/.

Spinwave propagation and coupling in magnonic waveguides

In this study, we start with the Landau-Lifshitz-Gilbert equation to describe the spinwaves in magnetic medium using the linearization approach. First, the reflection and refraction behaviors of spinwaves on an interface of a nonuniform magnetic medium is investigated. The study is then extended to spinwave propagation in lossless planar magnonic waveguides. Spinwave modes have been characterized based on the magnetic properties of the waveguides. Coupling between spinwaves in the structure of double magnonic waveguides is found to be possible due to the dipole interaction of the spinwaves. The spinwave coupling and power transfer associated with it is totally dependent on the waveguide structure and properties and the spinwave modes.

Spinwave propagation in lossless cylindrical magnonic waveguides

Spinwave propagation in clad cylindrical magnonic waveguides is investigated under linear approximation. With the assumption of no magnetic damping, characteristic equation to determine the bound spinwave modes has been obtained based on the structural and magnetic properties of the waveguides. The study is then applied to homogenous magnetic nanowires with no cladding. Spinwave characteristics and properties, such as the dispersion relationship and group velocity, can be described analytically.

A study on pinned layer magnetization processes in different antiferromagnetic coupling systems of spin-valves

In this paper we report on magnetization reversal processes of pinned layers in different ferromagnetic and anti-ferromagnetic bilayer and spin-valve structures by observing hysteresis, switching field distribution (SFD), and time-dependent effects. The fact that time-dependent coercivity Hc tendency is more pronounced in ordered AF materials than that of disordered AF materials implies a spin reversal of some AF grains with locally low pinning field and low blocking temperature. We propose a simple qualitative model to explain our results in terms of a distribution of the pinning reversal field and temperature in AF layer, which may be due to a grain size distribution in the AF layer and an incomplete and inhomogeneous phase transformation in some ordered AF materials. High resolution electron microscopy (HREM) results reveal that lattice spacing does change from place to place in AF region of some ordered AF materials. The evidence indicates an incomplete and inhomogeneous phase transformation in the or...

Variation of magnetoresistive sensitivity maps of patterned giant magnetoresistance sensors

A scanning probe microscope which combines probe contacts for the supply of current with a magnetic force microscope (MFM) for fully automated imaging of electrically active, patterned sensor-like devices across a wafer was developed. This was used for magnetoresistive sensitivity mapping (MSM) of giant magnetoresistive sensors with different stabilization schemes. Multiple measurements of sensors showed that the MSM images were very repeatable. The complex image patterns varied significantly from sensor to sensor across a wafer. With MFM tips magnetized perpendicular to the ferromagnetic films in the sensor, MSM signals at the top and bottom of the sensor were significantly more intense than signals at the sensor interior. Results from micromagnetic calculations were found to be consistent with the experimental observations.

Characterization of exchange coupling at NiFe-CoPt interface

NiFe/CoPt bilayer films were deposited onto Si wafers and the exchange coupling at the NiFe-CoPt interface was quantified by measuring the magnetization curve of the soft layer. By using CoPt layers of different thicknesses, different sputter etching times between CoPt and NiFe deposition steps and different annealing times of the bilayer, the exchange coupling field at the NiFe-CoPt interface was successfully altered. The preliminary data reported here might be seen as an initial step toward controlling and optimizing the interfacial exchange field that provides longitudinal bias for magnetoresistive heads with overlaid structures.

Ordering of magnetic nanoparticles in bilayer structures

In this study, we predict crystalline ordering of magnetic nanoparticles in a bilayer structure where only magnetic dipole interaction is taken into account. Estimates show that the two-dimensional lattice structure can be observed in the liquid nitrogen temperature regime. The results can be extended to magnetic nanoparticle multilayers. In addition, the study implies an order?disorder phase transition of the magnetic nanoparticle ensemble induced by external perpendicular magnetic fields.

Thin soft sendust laminated CoPt hard films

The C-axis of the Co-based permanent magnet films tends to grow gradually toward perpendicular direction as the film thickness increases. Reported here is a novel way to solve this problem. That is to laminate the Co-based hard magnet films with thin soft magnetic films. The effects of soft film underlayer and lamination, on the magnetic properties of CoPt films has been studied and reported here. Three types of soft magnetic material NiFe, NiFeRe and FeAlSi were chosen to conduct the experiments. Amorphous thin soft sendust film was found to meet the goal. It is found that there was a dramatic improvement of the in-plane loop squareness by inserting a 100 /spl Aring/ amorphous FeAlSi film into the 1200 /spl Aring/ CoPt film. The squareness (S) and the remnant magnetization thickness product (MrT) of the CoPt film (1200 /spl Aring/) without soft FeAlSi film lamination are 0.27 and 3.0 memu/cm/sup 2/, respectively, while the S and the MrT of the CoPt film (1200 /spl Aring/) with soft FeAlSi lamination are 0.60 and 6.32 memu/cm/sup 2/, respectively. Multi-lamination is possible if thick CoPt film is required in applications.