Microwave Assisted Magnetic Recording

Current magnetic data storage is based on perpendicular recording technology which is expected to plateau soon. Ever-increasing demands on data storage require new technologies to maintain the growth of recording density. Microwave assisted magnetic recording (MAMR) is one of the most promising technologies that has the potential to support recording density up to 4-5 Tb/in2.

The project is to develop enabling technologies, with focus on microwave assisted magnetic recording, for recording density up to 4-5 Tb/in2. The project covers the key aspects of MAMR: i) development of MAMR media with high anisotropy energy, Ku, of 1.5-2×107erg/cc, grain size of 5-6 nm and small damping constant; ii) design and development of spin-torque oscillator (STO) with small driving current and large operation window for MAMR; and iii) MAMR media virtual design and demonstration of microwave assisted writing using high Ku magnetic media. The project is trying to address the critical points of STO for MAMR, including but not limited to i) being able to operate in an alternating head gap field of ±8000-10000 Oe with variable frequency, ii) the mechanism and approaches to reduce the driving current of STO and the integration approaches of STO with the current recording system to have least driving current; iii) the approaches to increase the operation/fabrication window of STO; iv) being able to generate microwave with large in-plane ac magnetic field tunable frequency up to 30-40GHz.

The team has the capability to fabricate flyable media using industry-grade sputter tool (Intervac Gen. II system). The team also has home-designed versatile sputter tools (ultra-high vacuum system and oblique sputtering system) for research and development. The team has all the necessary tools for magnetic (VSM, AGFM, SQUID, MOKE, etc) and microstructure (XRD, TEM, AFM/MFM, etc) characterization and electrical performance testing (spin-stand). Currently the team has achieved KU of 1.5×107erg/cc and grain size of 6-7 nm using CoPt thin films deposited at room temperature.

Cross-sectional TEM image of CoPt-X media (a) and its in-plane and perpendicular hysteresis loops (b).

The team is capable of designing, fabricating and testing of spin-torque oscillators (STO). The team has simulation package for STO design, necessary nano-fabrication tools and processes for STO fabrication and RF probe station for STO testing. Fig. 2 (a) depicts the simulated dynamics of STO with tilted reference layer. Fig. 2 (b) shows the optical and cross-sectional TEM images of fabricated STO devices with R-H (resistance versus applied field) transfer curve. Currently a patent on STO design with low driving current, large ac magnetic field and high microwave frequency has been filed.

Simulated dynamics of STO with tilted reference layer (a); optical and cross-sectional TEM images of fabricated STO devices with R-H transfer curve (b).

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