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Originally posted by: klaviernista
Originally posted by: darfur
Originally posted by: darfur
Neat and all, but I thought that one problem with increasing the density of modern hard drives is that the magnetic fields created by all the little bits start to interfere with one another.
How is this any different at 10 times the density (well 10 times smaller anway)?
Anyone?
I examine patent applications for magentic media at the patent and trademark office. The problem you are describing has been around for a long time, as has so called "nanodot" media. This problem is called "intergranular exchange coupling" and contributes to increased noise in high density magentic media.
This problem arose as a result of the industry striving towards increased recording density. One way to get increased recording density is to reduce the size of the grains in magnetic layer (Basically, 1 grain=1 bit, so more grains =more bits per square inch). The problem with this is that as you reduce grain size, the coercivity (basically the strength by which a magnetic domain is held in a fixed direction) decreases. In other words, the orientation of each domain in each bit becomes more susceptible to being influenced by external magentic fields. Well, as each grain is magnetic and the coercivity of each grain is low at small grain sizes, the magnetic field of each grain impacts the orientation of the domain in each surrounding grain. As a result, the noise of the media is increased.
Industry has come up with a variety of ways to combat this problem. the most common way to prevent or reduce this type of coupling is to introduce Cr into the magnetic layer. Cr only has a certain solubilty in the crystalline lattice of a Co alloy (Co is the most common element used for the magentic layers in magentic media). When the CoCr magnetic layer is formed, it is first deposited (via sputtering or cvd) and then annealed. As a result of the annealing step, excess Cr segregates from within the crystalline grain into the area between adjacent grains (called the grain boundary). By controlling the amount of Cr which segregates, the spacing between grains is controlled. As you probably know, magnetic field intensity decreases as the distance from its origin increases. Thus, the influence of each grains magnetic field on surrounding grains is substantially reduced by the introduction of Cr into the grain boundary. In addition, non-magentic oxides such as SiO2 and TiO2 have also been used to segregate grains.
So, with nanodot media and quantum dot media, it is likely that some form of segregant will be utilized to separate each dot, or the dots themselves will be spaced apart when they are dposited so as to minimize this type of grain coupling. Many quantum dot media are formed by self assembly methods, so control over spacing between each dot can usually be controlled realtively easily.
Hope that helps. Probably more info then you wanted, but if you have more questions about magentic media let me know.
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Just to make sure I understand this...
The smaller the grain the harder it is to keep the magnetic charge of the grain affected other grains... and is also more vunarable to external interruptions....
How is Cr stuff put onto a disc? As I understand it, it goes inbetween the layers of the grains and seperates them from each other and makes each grain less suspectable too changing each others charge...
We would also have to figure out how to make a read/write head that would be able to read and write onto something so small and would have to make very preciese readings...
Am I understanding this?