Florin Zavaliche

Charge-based scanning probe readback of nanometer-scale ferroelectric domain patterns at megahertz rates

We present a method for data storage in continuous ferroelectric (FE) media, applicable to storage systems based on one or more scanning probes. Written FE domains are read back in a destructive fashion by applying a constant voltage of magnitude greater than the coercive voltage, as is done in FE random access memory (FeRAM). The resulting flow of screening charges through the readback amplifier provides sufficient signal to allow readback of domains of minimum dimension of the order of 10 nm at MHz rates, orders of magnitude faster than previously demonstrated techniques for readback of domains in continuous FE media.

Head–Disk Lubricant Transfer and Deposition During Heat-Assisted Magnetic Recording Write Operations

Lubricant accumulation was found on the media surface the instant when the laser is turned OFF during heat-assisted magnetic recording write operations. By changing the write cycles, laser ON/OFF duration, media, and head temperatures, we find that this lubricant accumulation is related to the change in head-media temperatures. The observed lubricant deposition process is restricted to a short time window (1-2 μs) after the laser is turned OFF. An equilibrium model of thermal displacement due to evaporation and condensation processes is presented and used to discuss the effect of the head-media temperature changes on the lubricant accumulation. Possible solutions to minimize the lubricant transfer and deposition are discussed.

Write-Induced Head Contamination in Heat-Assisted Magnetic Recording

One detrimental by-product of heat-assisted magnetic recording writing is the creation of head contamination. Here, we present the current understanding of the driving forces, growth mechanisms, and growth rates of write-induced head contamination. The combination of an evaporation and condensation model with shear forces suggests a flow of lubricant on the head may precipitate contamination. The contamination is observed to grow in the head–media gap until it contacts the media surface, at which point an additional material pickup mechanism can be activated. Evidence of contact-induced transfer and a chemical reaction of the contamination is presented, and the impacts of contamination on head temperatures and thermal gradient is presented. Depending on the contamination properties, head temperatures may be increased substantially, leading to increased reliability risk. Consistent with previous analyses, we find that contamination may increase media thermal gradient.

Head-disk lubricant transfer and reposition during heat assisted write and read operations

Heat Assisted Magnetic Recording (HAMR) is the most important of the next generation storage technologies that are currently competing to supplant perpendicular magnetic recording (PMR). Recently, HAMR has demonstrated one terabit per square inch (1 Tb/in2) recording density and extensibility of this new technology well beyond this density seems practical [1]. HAMR technology enhances the magnetic writing process by the inclusion of a strong optical field that propagates from the read-write head and instantaneously heats the magnetic recording layer to above its Curie temperature, thus allowing magnetic recording on media with ultrahigh magnetic anisotropy that otherwise could not be written with conventional writers. During HAMR writing, the HAMR media will experience ultra-rapid heating, reaching a peak temperature in excess of 500 C. These conditions will thermally stress the lubricant film on the media which, along with the carbon overcoat, protects the magnetic storage layer from environmental, thermal and tribological degradations. The cumulative effect of these repetitive heating cycles on the redistribution of the lubricant film of the media is a significant concern, due to the need to maintain a functioning lubricant film on the media and the negative effect on the head flyability with lubricant accumulation on its surface. The effect of these high temperature transients on the distribution of lubricant on both the media surface and the head are probed and specific rates of its accumulation and deposition are determined by varying the number of write cycles, laser-on durations, the head flying height (FH), and the peak surface temperature.