A hard drive surface as viewed using an electron microscope. Memory is stored magnetically in the pattern of dark and light patches.Image from Wikimedia Commons. / CC Attribution-Share Alike 3.0 Unported
The Spanish filmmaker Luis Buñuel once wrote, “You have to begin to lose your memory, if only in bits and pieces, to realize that memory is what makes our lives. Life without memory is no life at all.” The same might be said (albeit with less existential fanfare) of memory in the world of computers.
In the form of bigger hard drives, computer memory has revolutionized our ability to store everything from research articles, to Hollywood films, to cookbooks. Historically these devices have been enabled through the clever manipulation of magnetism. However, recent advances at UC Berkeley and elsewhere in the development of exciting materials known as multiferroics may be changing that recipe for success.
The inside of a modern hard drive works by almost exactly the same principles that kitchen magnets exploit when holding a wedding invitation to your fridge. A material with such magnetic (or more technically, ferromagnetic) properties such as a kitchen magnet is extremely useful because of its directionality. If you place two magnets together head-to-tail they attract, whereas if you flip the top magnet and repeat the process they push each other apart. A computer essentially writes and reads information by flipping little magnetic patches up or down and measuring what happens to another magnet placed on top of them.
There is a major difference, however, between the individual size of a magnet on your hard drive and a kitchen magnet. Each computerized bit on a hard drive may be 10 billion times smaller than the size of your thumbnail in area (see the figure above). It is precisely the smallness of these details that enable a computer to remember so much information.
In recent years, however, scientists have been playing around with more exotic forms of data storage. It turns out that some very specialized materials are not only like to be magnetically ordered, but are also naturally charged. That is to say, one side of the material likes to accumulate more electrons than the other side. Charging is a common enough effect in nature. When you rub a balloon against your hair you pull electrons from your hair onto the balloon. The subsequent tingling effect is a direct result of this charging. Thunderclouds exhibit charging when they accumulate massive amounts of electrons at their bases. When the energy is finally released it can result in spectacular shows of lightning.
When charging occurs naturally in a material, scientists say that the material is ferroelectric. A material that is both ferroelectric and ferromagnetic (or in cases, a variation called antiferromagnetic) is said to be multiferroic. If properly exploited, these extra properties may be quite useful in technology.
An experiment published last Sunday in the Nature Materials by researchers at UC Berkeley showed that electric voltages applied to the multiferroic bismuth ferrite could be used to directly manipulate a nearby material’s magnetic properties.
Stephen Wu, the paper’s lead author, explained that this could be an incredible step forward for technology. While people have been able to control magnetism using electricity before, never have they been able to do it in a way that requires no power, and never before have they been able to switch the direction of this magnetism so quickly. Such a development both saves energy and battery life, but also reduces the amount of heat within a system, thereby making it scalable. “You can make a lot of it, it’s static, and you can do it really fast,” said Wu, elaborating that if you could get such a system to work at room temperature, this magic combination of features could revolutionize the computing industry. In some of the most imaginative visions of the future, computers may not even be based on semiconductors or silicon at all, but rather on these new multiferroics and related compounds.
Silicon Valley may need to consider a name change.