Mohammed Shariat Ullah Patwari

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/.

Simulation of Erase After Write on 2.4 T FeCo Solid Pole Writer

We have developed a multiscale fast Fourier transform (FFT) based micromagnetic model to simulate erase after write (EAW) for a 2.4 T FeCo solid pole writer. The simulated remnant state of the writer showed vortices at the pole tip, break and paddle regions that qualitatively match an experimental MFM image. Dynamic responses show that EAW worsens with a longer breakpoint. Sensitivity of EAW with breakpoint is in good agreement with experimental data. We also find that cross track anisotropy reduced EAW risks; however, perpendicular anisotropy is detrimental to EAW. Simulations indicate that EAW risks may be substantially reduced if a demagnetization pulse of polarity opposite to that of the last write is applied to the writer.

FePt as Read Sensor Hard Bias Material

A low temperature chemical ordering approach was presented for L10 phase FePt alloys application in read sensor hard bias. We show that platinum seed and cap layers together can help the iron-rich FePt layer to achieve A1 to L10 phase transformation at temperatures as low as 300 °C. For platinum-rich FePt alloy iron seed and cap layers are effective in promoting its phase transformation. Element cap and seed together are more effective to obtain high coercivity than either of them alone. In order to implement FePt permanent magnet in transducer product, new thermal processes and sequences are needed.

Modeling of 1/f noise due to thermally induced magnetic switches of anti-ferromagnetic grains in magnetic tunneling readers

Magnetic 1/f noise is one of the major noise sources in state-of-the-art magnetic tunneling read heads for hard disk drive applications. The 1/f noise can be induced by thermally activated magnetic switching of antiferromagnetic (AFM) grains in the reader stack. This noise mechanism is studied here by micro-magnetic modeling. The modeling shows that the 1/f like noise power spectrum can come from the addition of several Lorentzian type noise spectra corresponding to the switching of individual AFM moments that are most likely located near the edges of the AFM layer. Additionally, the modeling shows that magnetic glitches can be generated by the switching of the reference layer edge curling state at the top or bottom edge of the layer, which is induced by the switching of one or more AFM moments in those areas.