Paul Kolbo

“All-Heusler alloy” current-perpendicular-to-plane giant magnetoresistance

A materials system of ternary full Heusler alloys exhibiting substantial current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) has been theoretically proposed and experimentally realized. Observed trends in magnetoresistance are broadly consistent with the modeling results. A CPP-GMR of 6.7% and ΔRA of 4 mΩ μm2 have been demonstrated in the bottom spin-valve configuration. The spin-stand testing of narrow-track recording heads confirmed compatibility of these materials with hard disk drive reader technology.

Demonstrating a tunneling magneto-resistive read head

We demonstrate the feasibility of a read head using a high-resistance spin-dependent tunneling (SDT) junction. The head consists of a 1.5 /spl mu/m or 1.7 /spl mu/m wide flux guide on top of the junction. The junction is about 0.8 /spl mu/m wide and varies in height, There is a pinned layer at the bottom of the stack. The tunnel barrier is made by plasma oxidation of about 10 /spl Aring/ of aluminum. The barrier has resistance of about 3.7 k/spl Omega/ /spl mu/m/sup 2/, leading to a typical head resistance of a few k/spl Omega/. The heads are lapped to the edge of the junction, and show 5% to 8% TMR during transfer curve measurement. Isolated pulses during the spin stand test shows large signal up to 5.7 mV. We find a voltage sensing preamp is a better choice over a current sensing one.

2

We review the 2 Tbit/in2 reader design landscape based on existing knowledge and projection. We found that the reader signal-to-noise ratio (SNR) requirement will be highly challenging due to the rapid increase in noise and the additional requirements from assisted writing. An acceptable level of channel bit density can be achieved in spite of a slow head-to-media spacing (HMS) reduction provided that both the shield-to-shield (SS) spacing and the ¿a¿ parameter scale with the bit length. We expect the side reading control for high ktpi to be difficult, and potentially a reader side shield will be required. The reader will likely use a higher quality MgO tunneling giant magnetoresistance (TGMR) stack with improved permanent-magnet coercivity. Certain new structures such as the differential reader or the trilayer will likely be part of the solution.

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

The current-in-plane giant magnetoresistive (GMR) trilayer readback sensor (CIP-3L), where only one permanent magnet at the back edge of the GMR stack is used to stabilize and bias a dual free layer system, is reviewed. Micromagnetic modeling is employed to show that the design has improved efficiency over abutted junction (ABJ) tunneling magnetoresistive (TMR) head designs. An experimental evaluation of how permanent magnet thickness (PM Th), interlayer exchange coupling (J), and stripe height impact the signal-to-noise ratio, symmetry, and stability of prototype CIP-3L heads is conducted. The study indicates that PM Th >400 nm, J<-0.8 erg/cm2, and a read width to SH aspect ratio of 1:1 to 0.75:1, gives optimal transfer curve performance. A head gimbal assembly spinstand comparison on perpendicular recording media with best-in-class TMR readers shows that although the amplitude of the CIP-3L heads is lower (believed to be process related), the symmetry, stability, and most important, bit-error rate normalized to electrical write width and read width, are comparable. In addition, the CIP-3L design shows better linearity and low-frequency noise performance than TMR heads. The areal density performance of the best CIP-3L heads shows 195 Gb/in2 recording capability and linear densities of 1100 kbpi

Reader Design Outlook

Narrow-track current-perpendicular-to-the-plane giant magnetoresistive heads containing Heusler alloy layer have been fabricated utilizing an abutted junction hard bias design. The head performance has been tested quasistatically and dynamically under high density recording conditions using a perpendicular magnetic recording media.

Current-in-Plane GMR Trilayer Head Design for Hard-Disk Drives: Characterization and Extendibility

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/.

Heusler alloy based current-perpendicular-to-the-plane giant magnetoresistance heads for high density magnetic recording

A sloped write pole design is assessed for perpendicular magnetic recording at high areal densities. Modeling shows that there is a significant increase in magnetic field from the sloped pole design over the conventional pole design at a fixed write width. Spin stand measurements were carried out in order to investigate the recording benefits of the sloped pole design. Writing improvements from this writer were best observed at high media coercivity.