Higher capacity data storage one step closer with new discovery
Worldwide, we keep producing more data every day. By 2020, digitally stored data is expected to reach 44 trillion gigabytes. The data storage capacities of conventional media, like magnetic tapes and hard drives, are reaching their limits. Heat-assisted magnetic recording might offer a way forward, though there are still some practical problems to overcome. One of the main issues is now partly solved. Researcher Carl Davies: “We have made an exciting discovery that opens the door to a more reliable form of heat-assisted magnetic recording.”
For more than half a century, magnetic metals have been used in hard disk-drives to store information in the form of bits. The newest development in magnetic data storage is heat-assisted magnetic recording. By temporarily heating the disk material with a focused laser beam during writing, it becomes much more receptive to magnetic effects, and allows writing to much smaller regions. Therefore, it can greatly increase the amount of data that can be stored on a magnetic device. A Big problem, however, is that the laser light nearly destroys the magnetism during each recording event, increasing the chance that recorded information can be irretrievably lost.
Faster, less energy and less risk
A consortium of researchers from the Netherlands, Russia and China have discovered a new route for heat-assisted magnetic recording that partly solves this problem. The magnetization is only gently heated so there is much less risk of destroying information. It is even possible that the speed and energy-efficiency of magnetic recording could be improved many times more via this new route.
Surprise
The researchers reveal that the key ingredient for this route is a difference in the thermal dependences of the magnetization and anisotropy. Interestingly, the discovery came as a total surprise. Davies: “we used iron garnet, which we expected to be the worst material possible for heat-assisted magnetic recording as it has a very small damping. All demonstrations so far have used metallic magnets with large magnetic damping. But while the damping in the iron garnet is inherently small, it becomes exceptionally large when the magnetization rotates over a large angle.”
By increasing the amplitude of the optical pulse, the switched magnetization takes on the form of “bullseye” domain patterns, as a result of the spatial symmetry of the delivered heat and the resulting precession (see inset for a schematic).
More research needed
“There is still much more physics to explore with this effect, and how it can be deployed in different materials,” Davies points out. One possibility involves using mid-infrared or far-infrared light as delivered by FELIX. Instead of heating the electronic system, which is inherently wasteful, one could rather target a resonance associated with the lattice, thus shrinking the anisotropy more efficiently. “Heat-assisted magnetic recording was initially seen as extremely difficult to achieve, and still has reliability problems. But with this discovery, a more reliable and efficient version is coming closer.”
Article
C.S. Davies, K.H. Prabhakara, M.D. Davydova, K.A. Zvezdin, T.B. Shapaeva, S. Wang, A.K. Zvezdin, A. Kirilyuk, Th. Rasing, and A.V. Kimel, “Anomalously damped heat-assisted route for precessional magnetization reversal in an iron garnet” Phys. Rev. Lett. (2019) 122, 027202
More information
Carl Davies, c.davies@ru.nl