Spintronics at BESSY II: Domain walls in magnetic nanowires
Magnetic sensitive PEEM images obtained at HZB: a) XAS image of the crossed nanowires. X-ray beam and magnetic field are aligned along the nanowire(vertical) direction (green arrow). b-f) XMCD images of the cross for different applied fields. © HZB
Magnetic domains walls are known to be a source of electrical resistance due to the difficulty for transport electron spins to follow their magnetic texture. This phenomenon holds potential for utilization in spintronic devices, where the electrical resistance can vary based on the presence or absence of a domain wall. A particularly intriguing class of materials are half metals such as La2/3Sr1/3MnO3 (LSMO) which present full spin polarization, allowing their exploitation in spintronic devices. Still the resistance of a single domain wall in half metals remained unknown. Now a team from Spain, France and Germany has generated a single domain wall on a LSMO nanowire and measured resistance changes 20 times larger than for a normal ferromagnet such as Cobalt.
The magnetic domain texture inherent to magnetic domain walls holds potential for spintronic applications. The electrical resistance in ferromagnets depends on whether domain walls are or not present. This binary effect (known as domain wall magnetoresistance) could be used to encode information in spintronic memory devices. Yet, their exploitation is hindered due to the small changes in resistance observed for normal ferromagnets. A particularly interesting class of materials are manganite perovskites such as La2/3Sr1/3MnO3 (LSMO). These compounds present only one type of spin (full spin polarization) which could potentially lead to domain wall magnetoresistance effects large enough to be exploited in a new generation of spintronic sensors and injectors.
Despite this promising perspective, there exist large discrepancies in the reported values of the domain wall magnetoresistance for this system. The scientists from Spain, France and Germany have fabricated nanowire-based devices enabling the nucleation of individual magnetic domain walls. Magneto transport measurements in these devices show that the presence of a domain wall leads to an increase of the electrical resistance of up to 12%. In absolute terms, the observed resistance change is 20 times larger than that reported for Cobalt.
This work is the result of a longstanding collaboration which involves film growth and nanofabrication, transport measurements, contact microscopy (MFM) imaging, theoretical simulations and the use of advanced characterization techniques such as X-ray photoemission electron microscopy. The combination of a wide variety of different techniques provides a comprehensive multi-facet view of a complex problem which has allowed to reach new insights into a highly debated open question.
- Magnetic field during catalyst synthesis triples ammonia yieldApplying an external magnetic field during the synthesis of CoFe₂O₄ electrocatalysts triples the ammonia yield during electrocatalytic conversion. The magnetic field alters the surface states of the spinel oxide thin films, making catalytically active sites more accessible. In the journal 'Advanced Functional Materials', a team led by Marcel Risch at HZB and Sanjay Mathur at University of Cologne demonstrates a scalable strategy for developing next-generation electrocatalysts for efficient and sustainable chemical production.
- Materials chemistry shapes the future of catalysisThe synthesis of materials can serve as a tool for developing smart, adaptive electrocatalysts. This rapidly evolving field of research involves in-situ analytics, data-driven discoveries and autonomous robotics. These new approaches could accelerate the discovery of long-lasting and efficient catalysts for future energy conversion and the decarbonisation of the chemical industry. A recent article by Dr Prashanth Menezes and his team in the renowned journal Angewandte Chemie provides an overview of this research.
- Imaging Ellipsometry for Process Control of Thin-Film DevicesA German–Israeli research team led by Dr. Andreas Furchner has demonstrated how imaging ellipsometry enables non-destructive characterisation and quality control of microstructured MXene thin films during device fabrication. The authors used two complementary ellipsometry approaches for precise, multi-scale access to key material properties. The work positions imaging ellipsometry as a powerful platform for monitoring thin-film uniformity, device integrity, and functionality throughout processing, including critical lithographic steps. The study was published in Applied Physics Letters and selected as an Editor’s Pick.