Multifunctional testing instrument helps improve production of laser-heated hard disk drives with enhanced storage capacities

 

November 8, 2014

The Agency for Science, Technology and Research (A*STAR)

Today''s hard disk drives can hold terabytes of digital data, but manufacturers are having trouble squeezing more storage capacity into these devices using conventional procedures. Now, a new technique that promises to solve this impasse -- heat-assisted magnetic recording (HAMR) -- can be integrated more efficiently into future hard drives thanks to an analytical tool.

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Today's hard disk drives can hold terabytes of digital data, but manufacturers are having trouble squeezing more storage capacity into these devices using conventional procedures. Now, a new technique that promises to solve this impasse -- heat-assisted magnetic recording (HAMR) -- can be integrated more efficiently into future hard drives thanks to an analytical tool developed by A*STAR researchers.

Data-storing 'bits' inside hard disk drives have to be turned on and off with magnetic fields. But as bit sizes diminish to improve storage density, the recording heads need stronger and stronger fields to resolve individual magnetic grains. Eventually, impractically large fields are required to read and write data.

The HAMR approach uses a small laser mounted on the disk recording head to heat up the magnetic material before writing to it. The increase in temperature reduces the magnetic field intensity necessary for data storage and consequently, smaller bit sizes can be used. Rapid cooling of the magnetic grains ensures the stability of the freshly recorded data.

Researchers are confident that the HAMR technique can lead to 20-terabyte hard drives within a few years if some specific challenges can be overcome. One current problem is that accurately testing the temperature-dependent recording in localized regions is difficult. Typical analytical methods have to heat up relatively large sample volumes, a time-consuming process that can irreversibly damage HAMR media.

Hongzhi Yang, with a team from the A*STAR Data Storage Institute and the National University of Singapore designed an improved 'pump-probe' laser device to scrutinize HAMR devices. The instrument uses an initial intense beam to heat up a localized region of the magnetic disk. Then, a weaker laser probes the heated region for the micro-magneto-optic Kerr effect (μ-MOKE), a phenomenon that can gauge a material's magnetization state. By repeating these measurements with different heating beam conditions, the researchers obtained detailed data on HAMR writing, reading and magnetic states from specific microscopic spots on the hard drive surface -- information currently unavailable through other techniques.

"The challenge in developing this testing instrument was integrating the complex optical and mechanical components to achieve good signal-to-noise ratios and uniform temperature distribution in the media during heating," says Yang. "But compared to traditional bulk-heating techniques, our method is much faster, allows full disk measurement and avoids annealing effects."

The team is confident that this instrument can be incorporated into disk drive manufacturing plants as HAMR captures a larger share of magnetic recording technology.

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Story Source:

The above story is based on materials provided by The Agency for Science, Technology and Research (A*STAR). Note: Materials may be edited for content and length.

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Journal Reference:

1. H. Z. Yang, Y. J. Chen, S. H. Leong, C. W. An, K. D. Ye, M. J. Yin, J. F. Hu. A multi-functional testing instrument for heat assisted magnetic recording mediaa). Journal of Applied Physics, 2014; 115 (17): 17B726 DOI: 10.1063/1.4865969

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New family of materials for energy-efficient information storage and processing

 

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A schematic illustration of the crystal structure of h-RFeO3. The arrows on the Fe sites indicate the atomic magnetic moments. The coexisting spontaneous electric polarization (P) and magnetic polarization (M) are both along the same crystal direction.

Switching the polarity of a magnet using an electric field (magnetoelectric memory [MEM] effect), can be a working principle of the next-generation technology for information processing and storage. Multiferroic materials are promising candidates for the MEM effect, due to the coexistence of electric and magnetic orders. On the other hand, the coexistence of spontaneous electric and magnetic polarizations is rare in known materials, which hinders the application potential of the MEM effect.

This article briefly reviews a new family of multiferroic materials -- hexagonal rare earth ferrites -- that have been demonstrated ferroelectric and ferromagnetic simultaneously by experiments. Both the ferroeletricity and ferromagnetism in hexagonal ferrites originate indirectly from structural distortions, resulting in so-called improper ferroelectric and ferromagnetic orders. Naturally, structural distortions may mediate the coupling between the electric and magnetic polarizations in hexagonal rare earth ferrites, causing the MEM effect, as predicted by theory.

The possible MEM effect in rare earth hexagonal ferrites is particularly useful for information storage and processing because the non-volatile nature of the magnetic polarization avoids the energy cost of constant memory refreshing and a constant flow of current. The polarity of magnets are used to store information, for example, in the hard disk of computers. The information is modified by "writing" the polarity using a magnetic field, which requires a flow of current that costs significant amount of energy. If the polarity can be switched using an electric field (the MEM effect), the energy-efficiency will be greatly improved, because the generation of the electric field intrinsically needs less power than for generating a magnetic field. The fact that the electric field can be easily localized also suggests application in miniaturized devices.

This research was supported in part by Nebraska EPSCoR.

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Story Source:

The above story is based on materials provided by World Scientific. Note: Materials may be edited for content and length.

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Journal Reference:

1. Xiaoshan Xu, Wenbin Wang. Multiferroic hexagonal ferrites (h-RFeO3,R=Y,Dy-Lu): a brief experimental review. Modern Physics Letters B, 2014; 28 (21): 1430008 DOI: 10.1142/S0217984914300087