Hard disk drive structure

In contrast to the discussion above with amorphous barriers, it is possible to use first-principles electron-structure calculations to describe TMR with crystalline tunnel barriers. In the Julliere model the TMR is dependent only on the polarization of the electrodes, and not on the properties of the barrier. In contrast, theoretical work by Butler and coworkers showed that the transmission probability for the tunneling electrons depends on the symmetry of the barrier, which has a dramatic influence on the calculated TMR values [20]. In the case of Fe(100)/Mg0(100)/Fe (100) the majority of electrons in the Fe are spin-up. They are derived from a band of delta-symmetry. In 2004 these theoretical predictions were experimentally confirmed by Parkin et al. and Yusha et al. [21, 22]. Remarkably, by 2005 TMR read heads were introduced into commercial hard disk drives. 

So individually each Co layer is ferromagnetic, but the multilayer structure is actually antiferromagnetic. The extent of the interaction depends on the thickness of the nonferromagnetic layer and H. All current hard disk drives make use of this technology. 

Magnetic recording media, such as computer hard disk drives, rotate at high frequencies (5-15 kHz) and need lubricants to maintain opertation. Phosphazenes are of interest in this application due to their ability to form fluids with little to no volatility and, due to their phosphorus eontent, they do not support combustion. Two differing phosphazene fluid additives have been developed based on fluorine ehemistry." Structure (8) was an early... 

The biggest concern is disk space. A dataset of diffraction images can take more than 3 GB of disk space. This does not seem like an excessive amount, but with multiple datasets and refinement files, a single structure can very quickly require over 10 GB of disk space. Fortunately, 100-GB hard drives are not very expensive any more. 

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