AVS 59th Annual International Symposium and Exhibition
    Electronic Materials and Processing Thursday Sessions
       Session EM+MI-ThA

Invited Paper EM+MI-ThA8
Application of Magnetic Heusler Alloys to All-Metal Sensors for Ultrahigh-Density Magnetic Recording

Thursday, November 1, 2012, 4:20 pm, Room 009

Session: Semiconductor Heterostructures II + Heusler Alloys
Presenter: J.R. Childress, HGST San Jose Research Center
Correspondent: Click to Email
Magnetic Heusler alloys are attractive materials for a number of applications in spintronics due to their potential high spin-polarization at the Fermi level, advantageous for spin-injection experiments and magnetoresistive devices. In the magnetic recording heads used in today’s hard-disk drives (HDD’s), the magnetoresistive thin-film sensors are multilayer spin-valves which operate in the current-perpendicular-to-film-plane (CPP) geometry, and rely on the spin-filtering properties of ultrathin MgO tunnel barriers (junction resistance < 1 Ohm-micron2) to achieve large tunnel-magnetoresistance (TMR) values using standard CoFe and CoFeB magnetic alloys as electrodes. Sensors with lower resistance (and thus lower-noise) are continuously required as sensor dimensions are reduced to keep up with the increased areal density of recorded data (approaching 1 Tb/in2). Intrinsically, an all-metal sensor can operate similarly to TMR sensors and will be able to achieve much lower resistances (~ 0.05 Ohm-micron2) and lower noise, but also requires a relatively large giant magnetoresistance (GMR) ratio to achieve sufficiently large signal to noise ratios (SNR). A number of Co-based full-Heusler alloys have the required magnetization, high TCurie and a predicted half-metallic behavior at low temperatures, and are therefore of interest for this application. But while the high spin-polarization in these Heusler alloys can significantly increase the GMR signal, integrating these materials in recording head sensors is a challenge due to their complex crystalline structure which typically requires high-temperature processing, and strong sensitivity to compositional disorder. In addition, the high polarization and low magnetic damping observed in these materials results in a high sensitivity to spin-torque excitations which limits the maximum allowable bias voltage, and is also a source of noise which limits the signal to noise (SNR) ratio. The geometrical, thermal, and magnetic constraints which influence the integration of Heusler alloys in magnetic recording head sensors will be presented, along with some examples of materials characterization and multilayer stack optimization required to improve the properties and robustness of the devices. It is found that practical spin-valves with Heusler alloy-based magnetic layers can be fabricated with CPP-GMR ratios which can be increased to >10%, more than 2x larger than for conventional ferromagnetic alloys. The outlook for applicability of such sensors to magnetic recording at high densities > 1 Tb/in2 will be discussed.