One of the most significant and promising results of research on the quantum properties of matter is spintronics, a sector dedicated to the development of high performance and low energy consumption devices capable of exploiting the magnetic orientation that is created in a material when the spin of its electrons aligns.
A study conducted by the group of researchers of the Bose-Einstein Condensation Center (BEC) in Trento and published in the October issue of Nature Physics now sheds light on a number of quantum mechanisms that are responsible for this magnetic behavior and their evolution over time.
The study involved the National Institute of Optics of the National Research Council (Cnr-Ino), the Physics Department of the University of Trento and the Trento Institute for Fundamental Physics and Applications (Tifpa) of the Infn (National Institute for Nuclear Physics), within the Q@TN Initiative. To achieve this result, the researchers cooled a sodium atoms gas to temperatures close to absolute zero, which put it in a quantum state that simulates the interface between two magnetic materials with a different spin orientation, a situation that is similar to that present in memory devices, as hard disks, in use today. When gases are cooled to almost absolute zero - the temperature at which atoms stop behaving as individual particles and form a single macroscopic quantum system called the Bose-Einstein condensate - they overcome the limits associated with the nature of gases at room temperature. "Atoms can be manipulated with precision using laser and microwave beams, and can be prepared in a particular quantum state that mimics the interface between two different magnetic materials. On one side of the interface all the spins are aligned along an intrinsic direction of the material, on the other they rotate in the direction of the magnetic field", Gabriele Ferrari (UniTrento) and Alessio Recati (Cnr-Ino) said.
In standard magnetic materials, the electron spin is usually orientated in the direction of the applied magnetic field, while in materials characterized by strong magnetic anisotropy, it quickly orientates in a particular direction, even opposite an external magnetic field.
The two different types of materials can be put side by side by creating an interface that represents a break between the two different behaviors, and the system quickly reaches a configuration of equilibrium. In the experiment that we made in the laboratory, by virtue of the intrinsic superfluidity and the peculiar interatomic bonds that characterize Bose-Einstein condensates, relaxation towards equilibrium occurs over a longer period, in a way that makes it possible to directly observe its evolution over time. "This made it possible to identify a new type of magnetic waves generated as a result of the spin torque, waves that propagate without friction inside the cloud of atoms, destroying the interface from which they were generated", Giacomo Lamporesi (Cnr-Ino) and Alessandro Zenesini (Cnr-Ino) explained. This observation, which is the result of the synergy between projects financed by the European Union, the Infn and the Autonomous Province of Trento, crowns years of research by the laboratory of the BEC Center of Trento in the field of far-from-equilibrium systems and opens the way for future research in simulation of magnetic materials in conditions never observed before, which are useful to understand many phenomena of spintronics. Thanks to the universality of these mechanisms, which extend beyond the world of magnetic materials, this result also represents a first step towards the simulation of phenomena that are usually studied in subnuclear physics and astrophysics.