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Nanoscale opto-magnetic recording becomes 3D

Date of news: 21 October 2019

Researchers from FELIX Laboratory and the Institute of Molecules and Materials (IMM) have demonstrated a proof-of-principle concept paving the way towards three-dimensional magnetic recording using light. Carl Davies and Andrei Kirilyuk from the FELIX Laboratory, together with Alexey Kimel from the IMM and collaborators from Japan and Russia, have unveiled an elegant solution to recording information in buried layers on a nanometre length-scale. Their results have been published in Nature Communications.

Ever since their invention, hard-disk drives have stored information inside a thin magnetic film, called a magnetic platter. Inside this platter, information is represented by magnetic domains, which can point up or down, corresponding to a 1 or 0 respectively. To write information i.e. switch a 1 to 0 or vice versa, a typical recording head flies just a few nanometres above the magnetic platter, selectively delivering a magnetic field. But, the density of information that can be stored in this way is now approaching fundamental limits, and scientists across the world are searching for ways to overcome these limits, as well as to make the recording process both faster and more energy-efficient.

Three-dimensional magnetic recording

The idea of stacking multiple magnetic platters to increase the information storage density is not new. However, it has always been assumed impossible to address a buried magnetic layer on its own, since the magnetic field delivered by the recording head will always be strongest at the nearest layer. In hard-disk drives nowadays, each platter is therefore accompanied by its own recording head, which is poor in terms of energy, space and complexity.

The trick

The researchers have developed a concept which allows for magnetic domains in buried layers to be switched in isolation, even with a layer-separation of just 80 nm. Instead of using magnetic fields to switch the domains, the idea involves femtosecond laser pulses that are single-handedly capable of switching magnetization due to ultrafast heating. Crucially, the laser pulses must be linearly-polarized, meaning the electric field of the light wave oscillates in one plane only.

When the laser pulse hits the top of the multi-layered stack, it would usually just reflect and deposit some energy in the top surface. If, however, the laser pulse is linearly-polarized in a particular way, it can excite a so-called surface-plasmon-polariton at certain interfaces inside the stack. Carl Davies explains: “Our trick for 3D magnetic recording relies on exciting plasmons at targeted interfaces, delivering ultrafast heat to well-defined nanolayers. By carefully designing the multilayers, we can choose which magnetic nanolayers we want to write information inside, simply by rotating the polarization-axis of the linearly-polarized laser light.”


By rotating the polarization-axis of the incident laser pulse, the magnetization in different nanolayers can be switched independently of each other.

Commercial applications

The researchers foresee many different ways to make the technique better for commercial applications. For example, in their demonstration the researchers used just two nanolayers which doubles the storage density. Davies: “The trick of using plasmons to write information should work for more nanolayers, since plasmons can be excited at different interfaces by changing the laser’s angle of incidence or wavelength.” Alternative materials could also be used, allowing infrared light to be used from FELIX to improve the efficiency of the process. Research in these directions could enable both the storage density and energy-efficiency to be increased multi-fold.


D. O. Ignatyeva, C. S. Davies, D. A. Sylgacheva, A. Tsukamoto, H. Yoshikawa, P. O. Kapralov, A. Kirilyuk, V. I. Belotelov and A. V. Kimel,Plasmonic layer-selective all-optical switching of magnetization with nanometer resolution, Nature Communications 10, 4786

More information

Carl Davies