Description
One of the most significant and promising spin-offs from research into the quantum properties of matter is spintronics, a field dedicated to the development of high-performance, low-power electronic devices capable of exploiting the magnetic orientation induced in a material as a result of the spin alignment of its electrons. A study conducted by a group of researchers at the Bose-Einstein Condensation Centre (BEC) in Trento and published in the journal Nature Physics now sheds light on some quantum mechanisms underlying this magnetic behaviour and their evolution over time.
To obtain the result, achieved thanks to the collaboration between the National Institute of Optics of the National Research Council (CNR-Ino), the Department of Physics of the University of Trento and the Trento Institute for Fundamental and Applied Physics of the National Institute of Nuclear Physics (Tifpa-Infn), as part of the Quantum at Trento (Q@TN) initiative, the researchers cooled a gas composed of sodium atoms to temperatures close to absolute zero, placing it in a quantum state capable of simulating the interface between two magnetic materials, the properties of which are characterised by a different spin orientation, a situation analogous to that found in memory devices, hard disks, in use today.
Cooling the gas down to almost absolute zero - the temperature at which atoms stop behaving like individual particles and form a single macroscopic quantum system known as a Bose-Einstein condensate - makes it possible to overcome the limitations associated with the nature of gases at room temperature. "Through the use of laser and microwave beams, atoms can be manipulated extremely precisely and prepared in a particular quantum state that can mimic the interface between two different magnetic materials. On one side of the interface the spins are all aligned along an intrinsic direction of the material, on the other side they rotate around the direction of the applied field,' state Gabriele Ferrari (Unitn) and Alessio Recati (CNR-Ino).
In standard magnetic materials, the electron spin usually orients itself along the direction of the applied magnetic field, while in materials characterised by strong magnetic anisotropy, it rapidly orients itself along a particular direction, even opposing the presence of an external magnetic field. The two different types of materials can be placed side by side, creating an interface that represents a clear discontinuity between the two different behaviours, and the system quickly reaches an equilibrium configuration. In the sample realised in the Trentino laboratory, by virtue of the intrinsic superfluid nature and the peculiar interatomic bonds that characterise Bose-Einstein condensates, the relaxation towards equilibrium takes place over a longer period of time, offering the opportunity to directly observe its evolution over time.
"This has made it possible to identify a new type of magnetic waves generated as a result of spin torsion, waves that propagate without friction within the cloud of atoms, destroying the interface from which they were generated," state Giacomo Lamporesi and Alessandro Zenesini of CNR-Ino. This observation, the result of a synergy between projects funded by the European Union, Infn and the Autonomous Province of Trento, crowns years of research by the Trento BEC Centre's laboratory in the field of out-of-equilibrium systems and opens the way to future research into the simulation of magnetic materials under conditions never observed before, useful for understanding frontier phenomena in 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.