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Breakthrough in Ultrafast Magnetism Research at Max Planck Institute
Researchers at the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) have pioneered a cutting-edge technique to explore ultrafast magnetism in various materials. Their work showcases the generation and application of magnetic field steps that can switch on in mere picoseconds.
Magnetic fields play a crucial role in the manipulation of material magnetization. Under steady or gradually fluctuating conditions, materials tend to align their magnetization akin to a compass needle responding to the Earth’s magnetic field. However, when magnetic fields are altered on ultrafast timescales—faster than the material can react—new dynamics of magnetization arise. These rapid changes are vital for fundamental studies of non-equilibrium matter states and hold promise for the development of advanced magnetic memory technologies, which require quicker writing speeds.
To tackle this complex issue, the research team engineered an innovative superconducting device designed to generate ultrafast, unipolar magnetic field steps. These steps feature instantaneous magnetic changes with rise times on the picosecond scale and decay times in the super-nanosecond range. “Our objective is to create a universal, ultrafast stimulus that can transition any magnetic sample between stable magnetic states,” explains lead author Giovanni De Vecchi. “This achievement has the potential to spur advancements across both scientific investigation and technological development.”
Utilizing Superconductors for Rapid Magnetic Changes
Under the leadership of Andrea Cavalleri, the team successfully initiated this process by rapidly quenching supercurrents flowing in a thin disc of superconducting YBaâ‚‚Cu₃O₇ subjected to an external magnetic field. Supercurrents are generated to repel magnetic fields from superconductors. “By abruptly disrupting these currents with ultrashort laser pulses, we were able to create ultrafast magnetic field steps, with rise times of about one picosecond,” states co-author Gregor Jotzu.
A significant challenge for the researchers was to monitor these magnetic transients in real time. By positioning a spectator crystal adjacent to the superconducting sample, they could track the evolution of the magnetic field. The optical characteristics of this crystal are influenced by the local magnetic field, enabling the team to follow magnetic field changes via the polarization rotation of a femtosecond laser pulse. “With this method, we reached sub-picosecond resolution and unprecedented sensitivity,” adds co-author Sebastian Fava.
Advancing to Ultrafast Magnetic Switching
Although the current work does not yet achieve full magnetization switching, the researchers are optimistic that refining the device’s geometry could increase both the intensity and rapidity of the magnetic field transients. “With appropriate enhancements, we foresee a range of applications from controlling phase transitions to fully switching magnetic order parameters,” remarks Andrea Cavalleri.
This research was supported by the Deutsche Forschungsgemeinschaft through the Cluster of Excellence CUI: Advanced Imaging of Matter. The MPSD is part of the Center for Free-Electron Laser Science (CFEL), a collaborative endeavor with DESY and the University of Hamburg. The study was conducted in partnership with Alexey Kimel, a professor at Radboud University.
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