In certain materials, spins create intricate magnetic patterns within the nanometer and micrometer range, with the magnetization direction twisting and curling along specific paths. Examples of these patterns include magnetic bubbles, skyrmions, and magnetic vortices. Spintronics seeks to utilize these small magnetic structures for data storage or logic operations with extremely low power usage, as opposed to current microelectronic components. However, the creation and stabilization of most of these magnetic textures is limited to a few materials and specific conditions (such as temperature and magnetic field). PPhysicists have recently examined a new method for generating and maintaining intricate spin textures, like radial vortices, in various compounds. In specific materials, spins create complex magnetic structures within the nanometer and micrometer scale, with the magnetization direction twisting and curving along specific paths. Examples of these structures include magnetic bubbles, skyrmions, and magnetic vortices. Spintronics seeks to utilize these small magnetic structures to store data or carry out logic operations with significantly lower power consumption than today’s dominant microelectronic components.A new technique has been explored by an international team led by HZB physicist Dr. Sergio Valencia to generate and stabilize complex spin textures, like radial vortices, in different materials. Radial vortices are characterized by the magnetization pointing towards or away from the center of the structure, which is typically unstable. This offers a new method to produce and maintain diverse magnetic textures in various compounds.Within this innovative method, radial vortices are generated using superconducting structures, and their stability is maintained through the presence of surface imperfections.
Superconducting YBCO-islands
The samples are comprised of micrometer-sized islands composed of the high-temperature superconductor YBCO onto which a ferromagnetic compound is applied. When the sample is cooled below 92 Kelvin (-181 °C), YBCO transitions into the superconducting phase. In this phase, an external magnetic field is applied and then promptly removed. This process allows for the penetration and pinning of magnetic flux quanta, resulting in the creation of a magnetic stray.The stray field in the YBCO layer creates new magnetic microstructures in the layer above it, with spins radiating out from the center in a radial vortex pattern. When YBCO transitions from superconducting to normal at higher temperatures, the stray field and the magnetic radial vortex should disappear. However, researchers have found that surface defects prevent this from happening, causing the radial vortices to partially retain their imprinted state even as the temperature approaches room temperature.
“Our method involves using the magnetic field produced by the superconducting structures to create specific magnetic domains on the ferromagnets positioned on them, and then using surface defects to maintain their stability. The resulting magnetic structures are similar to skyrmions and have potential applications in spintronics,” Valencia explains.
The Importance of Geometry
The smaller vortices created were approximately 2 micrometres in diameter, which is about ten times larger than typical skyrmions. The team conducted research on samples with circular and square geometries, and discovered that circular geometries enhanced the stability of the created magnetic radia.l vortices.”
According to Valencia, “This method is an innovative way to create and stabilize such structures and can be utilized in various ferromagnetic materials. These are promising new opportunities for the advancement of superconducting spintronics.”
Journal Reference:
- David Sanchez-Manzano, Gloria Orfila, Anke Sander, Lourdes Marcano, Fernando Gallego, Mohamad-Assaad Mawass, Francesco Grilli, Ashima Arora, Andrea Peralta, Fabian A. Cuellar, Jose A. Fernandez-Roldan, Nicolas Reyren, Florian Kronast, Carlos Leon, Alberto Rivera-Calzada, Javier E. Villegas, Jacobo Santamaria, SergiValencia. Radial Vortex Magnetic Textures Imprinted by Superconductor Stray Fields: Size-Dependence and High Temperature Stability. ACS Applied Materials & Interfaces, 2024; 16 (15): 19681 DOI: 10.1021/acsami.3c17671