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To reach densities in excess of 1 Tbit/in2  we propose to develop three axes: a) self-assembled coercive nanoparticles, b) exchange spring media and percolated media, and c) bit-patterned media (nanoscale patterning). This entails resolving several conflicting requirements with regard to: 1) Signal to Noise Ratio (SNR), 2) Writability, and 3) The thermal stability. Modelling throughout is very crucial for the best selection and performance evaluation. The key issues to be addressed, and the basic problems raised, and the approaches proposed are outlined below.

L10-Fe(Co)Pt granular and nanoparticle materials

The L10-ordered, face-centred tetragonal (fct) is thermodynamically stable, but the low-anisotropy, chemically disordered face-centred cubic (fcc) phase is kinetically favoured. Prolonged high-temperature annealing is currently needed to achieve the phase transformation. Then, the particles tend to coalesce and to form multi-twinned nanocrystals, with a subsequent decrease in the coercive field (Hc).  In order to overcome this problem, the project proposes the following methods:
  • An industrially compatible media production process with a new method able to achieve the structural fcc/fct  conversion without grain growth (Flash annealing by Xenon) and orienting grains under an external magnetic field. 
  • Large-area arrays of nanoparticles confined in the pores of robust ultra-thin nanostructured oxide membranes, allowing to achieve the fcc/fct conversion in situ.
  • Large-scale production of fct-FePt nanoparticles (d  ≤  6  nm) by one-step chemical synthesis based on a high- temperature  reflux method.

Media Writability

The use of high coercive materials in ultra-high-density magnetorecording, , raises the problem of media writability, which is limited by  the write field of the head. To overcome this problem, maintaining high bit thermal stability, the project proposes to manufacture:  

  • Exchange Spring Media (ESM) and  Percolated Media (PM) with controlled hard layer coercivity (5<10 kOe) and thermal stability (60kBT300K).

Large-area nanoscale patterning 

Patterned and self-assembled nanoparticle media have been proposed as most favourable approach  for storage densities in the Tbit/in² regime.  However, no cheap and mass-production-compatible manufacturing methods exist up to now. The net production cost of the hard disk needs to be less than $ 5 per disk to compete in the magnetic storage market.  A breakthrough in nanopatterning production techniques is needed to decrease the costs.  In addition to developments in sophisticated nanolithographic techniques (EBL, FIB), to be used for fundamental studies, the project proposes new nanopatterning techniques, compatible with mass production:

  • Temperature- or radiation (UV)-assisted nanoimprit lithography (NIL) (25 nm dot size and uniformity better than 5%) 
  • Nanoparticle media patterning by filling ultrathin nanohole membranes by electrodeposition (UPMC patent) or chemical nano-engineering.

Modelling of patterned media

In patterned media, the capability of a given head/media combination to address the targeted islands depends on the switching dynamics of both the head and field and switching dynamics of the media.  The reversal of the targeted island is possible if the write field switches within a certain window. Its permitted size depends on various factors including the switching field distribution of the islands, the interaction  field with the surrounding islands, and the fluctuations in the position of the islands on the media side. It also depends on the write field profile, write field gradient, and write field dynamics. To deal with all these aspects, the project proposes to carry out:  
  • Multi-scale recording simulations to solve the dynamic magnetization processes simultaneously for the head and patterned media.

Magnetization reversal

Since the key physical phenomenon in magnetic recording is the reversal of magnetization, the project proposes to:  

  • Better understand the dependence of the magnetization process and reversal mechanisms in nanostructured media on particle anisotropy, domain configuration, Bloch wall pinning, interparticle interactions and switching field distribution. Due to the rapid access times required emphasis will be given in the magnetization dynamics in the nsec timescale which lies in the  limits of the conventional Néel-Brown-Arrhenius model of thermal decay and the gyromagnetic switching.

Modelling and readback signal processing  

To test the feasibility of the high-density storage device and to verify the storage capacity, the project  proposes to perform :
  • Characterization of the readback signal, evaluation/projection of the operational target SNR for a standard sequence detector and estimation of the raw information error rate achievable.  

Magnetic recording media: design and testing of a prototype media with an areal density higher than 1 Tbit/in2

In order to make an industrial size prototype HD , the project proposes to:   

  • Design media by micromagnetic simulation and signal modelling, and to evaluate the recording performance (W/R, SNR) of industrial size prototype media, with an areal density higher than 1 Tbit/in2, by both a static (magnetoresistive scanning microscope) and a dynamic (spinstand) tester.
Last Updated on Friday, 21 November 2008 14:16