Invited Paper MI+TF-ThA1
Magnetic Recording Sensor Materials and Technology Above 1 Tb/in²

Thursday, November 12, 2009, 2:00 pm, Room C1

Magnetic recording is constantly evolving to reach specific technology targets. Today’s hard disk drives can store information at >300 Gbit/in², and represent a striking example of nano-technology integrated into everyday life: data bits < 100nm x 20nm, read sensors with dimensions < 80nm, and read/write heads flying < 10nm above the disk. The specific challenge for the read sensor is to maintain adequate signal-to-noise ratio as its dimensions are reduced. For example, the development of recording head sensors for 1 Tb/in² and above requires sensors dimensions < 30nm. In this regime, all-metal current-perpendicular-to-the-plane (CPP) giant magnetoresistive (GMR) sensors are an attractive alternative to CPP tunnel-magnetoresistance (TMR) sensors. With typical resistance-area products in the range 0.03-0.10 Ω-µm², CPP-GMR sensors have the potential to deliver low sensor impedance at the smallest conceivable dimensions, and therefore lower noise and higher bandwidth performance. Among the challenges that CPP-GMR sensors face are low signal levels due to their low resistance, typically low DR/R when using thin magnetic layers, as well as current-induced noise and instability due to the spin-torque effect. I will review several paths that we have recently explored to increase signal and reduce spin-torque effects in CPP-GMR sensors. For increased signal, a key may be the synthesis and integration of new ferromagnetic thin-films alloys with high spin-polarization at the Fermi level (and therefore resulting in high magnetoresistance spin-valves), such as the predicted half-metallic Heusler alloys. For lower spin-torque effects we have demonstrated the effectiveness of dual spin-valves sensors, rare-earth cap layers for increased Gilbert damping, and synthetic-ferrimagnet free layers. I will present some of the physical concepts behind these approaches, and discuss recent data in the context of the specific technological requirements for magnetic recording around 1 Tb/in².