Specialized x-ray lasers reveal the inner workings of magnets, a discovery that could lead to smarter, faster computers. Using a light source that creates x-ray pulses one quadrillionth of a second in duration, a team of scientists from the University of Colorado at Boulder and the National Institute of Standards and Technology observed how magnetism works in iron and nickel atoms. They found that the metals behave differently. “The discovery that iron and nickel are fundamentally different in their interaction with light at ultrafast timescales suggests that the magnetic alloys in hard drives could be engineered to enhance the delivery of the optical energy to the spin system,” said NIST scientist Tom Silva. The next generation of computer disk drives will use optically assisted magnetic recording to achieve much higher drive capacities, Silva said. Now the question is: How do you optimize the delivery of optical energy to the magnetic system for maximum drive performance? The solution could help researchers find answers to some of their questions. Magnetism exists because all of a magnet’s “spins” — similar to tiny bar magnets with a north and south — are lined up to point in the same direction. Using laser pulses, the scientists scrambled the magnetic spins of the metal, causing the magnetization to rapidly disappear within 50-quadrillionths of a second in a process called ultrafast demagnetization. Although ultrafast demagnetization was discovered in 1996, the CU and NIST researchers saw for the first time that different kinds of spins in metal scramble on different timescales. Until now, it was assumed that all the spins in a metal alloy behaved the same because of the powerful quantum mechanical effect known as the exchange interaction, which lines up all the individual spins in the same direction. “What we have seen for the first time is that the iron spins and the nickel spins react to light in different ways, with the iron spins being mixed up by light much more readily than the nickel spins,” Silva said. “In the end, the exchange interaction still pulls the two spin systems back into synchronization after a few quadrillionths of a second. Seeing such a difference was only possible by taking advantage of the extremely fast x-ray technology.” The findings were published online in the Proceedings of the National Academy of Sciences. For more information, visit: www.colorado.edu