Computers use different kinds of memory technologies to store data. Long-term memory — typically a hard disk or flash drive — needs to be dense in order to store as much data as possible. But the central processing unit (CPU) — the hardware that enables computers to compute — requires its own memory for short-term storage of information while operations are executed. Random Access Memory (RAM) is one example of such short-term memory.
Reading and writing data to RAM needs to be extremely fast in order to keep up with the CPU’s calculations. Most current RAM technologies are based on charge (electron) retention, and can be written at rates of billions of bits per second (or bits/nanosecond). The downside of these charge-based technologies is that they are volatile, requiring constant power or else they will lose the data.
In recent years, magnetic alternatives to RAM, known as Magnetic Random Access Memory (MRAM), have reached the market. The advantage of magnets is that they retain information even when memory and CPU are powered off, allowing for energy savings. But that efficiency comes at the expense of speed. A major challenge for MRAM has been to speed up the writing of a single bit of information to less than 10 nanoseconds.
Based on experiments in the Netherlands on ultrafast magnetic switching using short laser pulses, special circuits were developed to study how magnetic metals respond to electrical pulses as short as a few trillionths of a second, or picoseconds. It was found that in a magnetic alloy made up of gadolinium and iron, the fast electrical pulses can switch the direction of the magnetism in less than 10 picoseconds — orders of magnitude faster than any other MRAM technology.
The electrical pulse temporarily increases the energy of the iron atom’s electrons; increasing energy causes the magnetism in the iron and gadolinium atoms to exert torque on one another, and eventually leads to a reorientation of the metal’s magnetic poles.
Researchers sought ways to expand the method to a broader class of magnetic materials. When stacking a single-element magnetic metal such as cobalt on top of the gadolinium-iron alloy, the interaction between the two layers allows them to manipulate the magnetism of the cobalt on unprecedented time-scales as well.