Novel way of transferring magnetic information
25 May 2016. NUS physicists discovered a new way of transferring magnetic information across an insulator, paving the way for the development of devices that operate in the teraherz frequency range.
In the field of spintronics, coupling between magnetic layers which form a sandwich with a barrier in between is essential for a variety of devices. Traditionally, when two magnetic layers are stacked close to each other, they couple together to exchange electrons with each other. The electrons carry across their spin, and the directions of magnetisation of the two layers are aligned. This coupling is broken if the two magnetic layers are separated by an insulating spacer that is more than a few atoms thick. The insulator is almost impenetrable for free electrons.
A team led by Prof ARIANDO from the Department of Physics in NUS found that the use of a polar oxide insulator enables the range of the magnetic coupling to jump from about one to 10 nanometres, and its strength varies up and down with spacer thickness. This discovery is startling as no electrons could ever make their way across such an impenetrable layer. In addition, the range achieved would previously have required a metallic system to transmit the electrons across the magnetic layers.
While many people are used to downloading data from the Cloud onto mobile devices, most do not know where the data comes from. Digital information is stored in minute magnetic dots written in layers that are only a few nanometers thick that cover the surface of millions of saucer-sized spinning disks. These hard disks are stacked by the thousands in server farms worldwide. A bottleneck that stifles the progress of this emerging field lies in the demand for faster data transmission rates. The recent discovery by the team paves the way for the development of devices that operate in the terahertz frequency range, which makes encoding and transmission of data many times faster. Unlike the time of French physicist Louis NÉEL whose discovery of anti-ferromagnetism found an application 60 years later, nowadays, it should not take 60 years to find an application for new discoveries in magnetism.
Now that the research team has provided the recipe for the insulator that allows the magnetic effect to occur, they intend to further investigate the effect to fully understand the mechanism, and to utilise their discovery to develop a new generation of magneto optical devices in the terahertz frequency range as well as to enable electromagnetic tuning of magnetic information.
Figure shows the spin information is conveyed across a polar insulator through orbital excitation. [Image credit: Ariando]
Lu, WM. Long-range magnetic coupling across a polar insulating layer. Nature Comm. 7 (2016) 11015.