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FERROMAGNETIC RESONANCE AT THE ATOMIC SCALE

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Single-atom spintronics measurements

Exploiting electron spin may make it possible to overcome current barriers to size reductions of electronic devices. Highly sensitive measurements of voltage correlated with spin properties have opened a window on mechanisms.

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Moore's law, a prediction made in 1965 that has largely held true, generally states that the number of transistors on an integrated circuit will double approximately every two years. As that law appears to be reaching its limit, the world is searching for ways to get more electronics with greater power into smaller devices, and spintronics is a promising candidate. Development of spintronics is already being pushed to a limit as well — the limit in our understanding of spin-dependent properties. Exceptional size reductions are expected by constrictions of atomic sizes. Scientists developed and exploited a highly sensitive experimental setup to explore the dynamical magnetic properties of a few atoms in a low-dimensional geometry. EU funding of the project 'Ferromagnetic resonance at the atomic scale' (ATOMICFMR) supported this effort. Scientists set out to study electrically detected ferromagnetic resonance (FMR) of nanostructures. FMR is the magnetisation precession (change in orientation of the total magnetic moment) induced by a radio frequency magnetic field. FMR interacts with spin currents. Further, it is now possible to measure FMR electrically due to its correlation with direct current (DC) transport. The team used their experimental tools that enable FMR detection in narrow nanoconstrictions or atomic contacts via a measurable DC voltage to study the resonance properties of a single atom. They combined experiments with simulations using the freely available code MuMax2 for micromagnetics simulations. Researchers demonstrated the ability to detect domain wall resonances (those at interfaces separating magnetic domains) in a nano-structured magnetic alloy (permalloy) with an electrical technique. Simulations fostered a full understanding of the relationship between measured voltages and the different resonances observed. The findings are a first and opened the door to a number of exciting experiments studying the relationship between magnetisation dynamics and electronic transport and the dynamical coupling of two nanostructures through a nanocontact. ATOMICFMR outcomes constitute a major contribution to the field of low-dimensional spintronics. They help lay the foundations for development of novel devices that overcome current size limitations and establish a position of EU leadership in an important emerging field for information technology.

Keywords

Spintronics, single atom, ferromagnetic resonance, atomic scale, permalloy

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