The femtoflip of the spin
Julian Hintermayr defended his PhD thesis at the Department of Applied Physics and Science 果冻传媒 on February 20th.
Electron spin is the key factor influencing their magnetic behavior. In our world addicted to data production and storage, most information is stored in magnetic drives where the orientation of spin (whether up or down) represents the 1s and 0s that represent your emails, photos, and videos. To change 1s to 0s, and vice versa, involves the application of a magnetic field to change spin direction. However, this process is slow, particularly considering the amount of data that we create and access daily. For his PhD research, Julian Hintermayr created new ultrathin layered materials with strong magnetic interactions and alternating magnetization directions to speed up this data writing process.
The key property of electrons governing magnetic behavior is their spin, which can be imagined as a tiny compass needle pointing either up or down. Recently, researchers have discovered that light鈥攕pecifically, ultrafast laser pulses with a twisted polarization lasting less than a trillionth of a second鈥攃an generate spin currents and make magnetic materials "dance" in new and exciting ways.
In modern data centers, most information is stored in magnetic hard drives, where the direction of magnetization determines whether a bit represents a 鈥�0鈥� or a 鈥�1.鈥�
Writing a bit involves applying a magnetic field to orient the magnetization in the desired direction. During this process, the magnetization vector rotates around the field at frequencies like those used by WiFi before settling into its final state.
While this might seem fast by everyday standards, it remains a relatively slow storage technology, leaving ample room for improvement.
For his PhD research, and his colleagues developed new ultrathin layered materials with strong magnetic interactions and alternating magnetization directions.
These materials allow magnetic oscillation frequencies to be boosted into the terahertz range 鈥� a thousand times faster than those of conventional ferromagnetic materials.
Making Spins Dance
To drive these ultrafast oscillations, known as resonances, Hintermayr employed two innovative techniques that use laser pulses to generate spin currents.
The first method involves placing a second magnetic layer adjacent to the oscillating layer. When a laser pulse strikes this second layer, it generates a spin current that "kicks" the first layer into ultrafast precession. By systematically varying the thickness of the materials, Hintermayr was able to uncover new insights into the excitation mechanism and the underlying physics of this process.
The second method utilizes light with a specially rotating polarization to excite spins in heavy elements such as platinum. By introducing a second laser pulse and carefully tuning the time delay and polarization states between the two pulses, it was even possible to amplify or suppress the oscillations. This approach provides an unprecedented level of control over ultrafast magnetic dynamics.
Exciting possibilities
Hintermayr鈥檚 findings open up exciting possibilities for controlling magnetism using light alone, paving the way for faster, more energy-efficient technologies.
The ability to manipulate spins with such precision could lead to breakthroughs in data storage and computation, replacing traditional methods with ultrafast, light-driven solutions.
Hintermayr鈥檚 research not only deepens our understanding of spin dynamics but also lays the foundation for the next generation of magnetic devices.
Title of PhD thesis: . Supervisors: Bert Koopmans and Reinoud Lavrijsen.