Jigang Wang (center) and his team, Tianqi Li (left) and Aaron Patz (right), specialize in ultrafast spectroscopy, which helps scientists understand changes in materials in very short time scales. Photo: Ames LaboratoryResearchers at the U.S. Department of Energy (DOE)’s Ames Laboratory, Iowa State University, and the University of Crete in Greece have found a new way to switch magnetism that is at least 1000 times faster than currently used in magnetic memory technologies. Magnetic switching is used to encode information in hard drives, magnetic random access memory, and other computing devices. The discovery, reported in Nature, potentially opens the door to terahertz (1012 hertz) and faster memory speeds.


“The challenge facing magnetic writing, reading, storing, and computing is speed, and we showed that we can meet the challenge to make the magnetic switches think ultrafast in the femtosecond range—one quadrillionth of a second—by using quantum ‘tricks’ with ultrashort laser pulses ” says Wang, who is also an assistant professor of physics and astronomy at Iowa State University.


“But the speed of such thermal magnetic switching is limited by how long it takes to vibrate the atoms, and by how fast a magnetic field can reverse magnetic regions,” says Wang. “And it is very difficult to exceed the gigahertz (109 hertz) switching speed limit of today’s magnetic writing/reading technology.”



Wang’s team specializes in using ultrafast spectroscopy, which Wang likens to high-speed strobe photography, because both use an external pump of energy to trigger a quick snapshot that can be then re-played afterwards. In ultrafast laser spectroscopy, a short pulse of laser light is used to excite a material and trigger a measurement all on the order of femtoseconds.

“In one CMR manganite material, the magnetic order is switched during the 100-femtosecond-long laser pulse. This means that switching occurs by manipulating spin and charge quantum mechanically,” says Wang. “In the experiments, the second laser pulse ‘saw’ a huge photo-induced magnetization with an excitation threshold behavior developing immediately after the first pump pulse.”



Source: Ames Laboratory