Hard drives of the future

Data on a hard drive is stored by flipping small magnetic domains. Researchers from the Paul Scherrer Institute PSI and ETH Zurich have altered the magnetic arrangement in much faster than is possible with today’s hard drives.

Researchers used a new technique where an electric field triggers these changes, in contrast to the magnetic fields commonly used in consumer devices. This method uses a new kind of material where the magnetic and electric properties are coupled. Applied in future devices, this kind of strong interaction between magnetic and electric properties can have numerous advantages.

For instance, an electrical field can be generated more easily in a device than a magnetic one. In the experiment, the changes in magnetic arrangement took place within a picosecond (a trillionth of a second) and could be observed with X-ray flashes at the American X-ray laser LCLS. The flashes are so short that you can virtually see how the magnetisation changes from one image to the next - similar to how we are able to capture the movement of an athlete with a normal camera in a series of images with a short exposure time. In future, such experiments should also be possible at PSI’s new research facility, the X-ray laser SwissFEL.

One common method of data storage uses materials in which different magnetic domains can be oriented in different directions. In other words, the tiny elementary magnets inside the material are aligned along two possible directions, which enables one bit to be saved in the material. A bit is the smallest unit of information, for which there are two possibilities, often referred to as 0 and 1. In the storage device, these correspond to the two different magnetic directions. In a real hard drive, which must store a large amount of information, there are many small areas that correspond to single bits. To change the information on the hard drive, the direction of the magnetism in one domain must be flipped. In modern consumer devices this is achieved using a small magnetic field.

An electric field can be generated in a small space more easily than a magnetic field, which means that, in principle, smaller storage devices can be constructed if magnetism is switched by electric fields. A strong connection between magnetic and electric properties is exhibited by so-called multiferroic materials, which have been one of the hottest topics in materials research for a number of years.

Researchers from the Paul Scherrer Institute PSI and ETH Zurich have now studied the material TbMnO₃ and demonstrated that its magnetic arrangement can be changed by an electric field in a matter of picoseconds (10-12 s = one trillionth of a second), which is considerably shorter than the time it takes for today’s hard drives to be switched. “This shows that multiferroic materials can be switched quickly enough electrically for them to be used in magnetic storage devices,” explains Urs Staub, a research group leader at PSI and one of the research project supervisors. “Electric switching could have numerous advantages. In order to generate a magnetic field, you need a coil through which a current flows. An electric field can be generated without current.

“The material we studied can’t be used in technical devices - you need very low temperatures and strong electrical fields to observe the relevant phenomena. However, the basic result probably also applies for materials that are more suitable for applications and will presumably consist of a combination of thin layers of different materials.”