If you are curious just how Heat Assisted Magnetic Recording is able to increase the storage densities of your HDDs then this post at Nanotechweb and the linked article will make a great read.  They deal with how plasmonic near-field transducers, which will oscillate in time with the frequency of a light source, as long as the light source's frequency is equal to or less than the plasma frequency.  This causes heat but nowhere near as much as if the light was used directly and so avoids potentially damaging hotspots.  They also delve into the materials which are being tested to provide more efficient heat transmission; it is not light reading but it is very informative for those curious about HAMR's development and future.

"Heat-assisted magnetic recording (HAMR) is a leading technology for advancing hard-disk-drive areal density beyond 1 Tb/in2. To reduce the magnetic coercivity, near-field transducers (NFTs) made of plasmonic nanostructures are used."

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