New options for spintronic devices: Switching between 1 and 0 with low voltage
A thin magnetic FeRh film is grown onto a ferroelastic BTO substrate with two different crystal domains a and c. At 0 Volt ferromagnetic domains (red-blue pattern) are observed above BTO a-domains, whereas above c-domains the net magnetization is zero. At 50 Volt all BTO domains are converted into c-domains, which switches off ferromagnetic domains in FeRh. © HZB
Scientists from Paris and Helmholtz-Zentrum Berlin have been able to switch ferromagnetic domains on and off with low voltage in a structure made of two different ferroic materials. The switching works slightly above room temperature. Their results, which are published online in Scientific Reports, might inspire future applications in low-power spintronics, for instance for fast and efficient data storage.
Their sample consisted of two different ferroic layers: on a ferroelastic BaTiO3 (BTO) substrate a thin film of ferromagnetic FeRh was grown. Last year, they observed already that a small voltage across the BTO could change magnetic order in the ferromagnetic FeRh film via a strong magnetoelectric coupling between both layers.
Now, they could see much larger effects. “We could switch ferromagnetic states in the FeRh film completely on and off with a low voltage applied to the underlaying BTO”, reports Sergio Valencia, the HZB scientist who led the study. With XPEEM imaging at BESSY II they observed the transition between different magnetic orders in the FeRh layer, driven by an electrical field applied across the BTO substrate.
Electric fields, strain, magnetic order and temperature
It works because a low voltage on the BTO substrate deforms its crystal structure via a ferroelastic effect, creating a strain. This strain is transferred to the FeRh film grown on top of the BTO and influences its magnetic order. As physicist Valencia puts it: “By the strain on the BTO substrate we can increase the transition temperature of FeRh, a characteristic temperature which separates antiferromagnetic order from ferromagnetic order. Below this temperature, FeRh is antiferromagnetic (net magnetic moment is zero), above it becomes ferromagnetic. Normally this transition temperature for FeRh is around 90°C, but under strain (through the voltage applied to the BTO substrate) it is shown to rise to ca. 120 °C. To demonstrate this effect, the experiment was conducted at 115 °C, a temperature at which in absence of strain FeRh was observed to be ferromagnetic. When the voltage was applied to the BTO substrate, the strain transferred from BTO to the FeRh increased the temperature needed to have a ferromagnetic order and the FeRh became antiferromagnetic.
Switiching near room temperature
“This is quite relevant. Here we have a structure showing switching effects between two different magnetic states close to room temperature. This is precisely what you need in order to develop room temperature working devices. Moreover, to switch between these two states we use electric fields instead of magnetic fields which consumes less energy. In the near future we aim at doping the FeRh film with palladium to get effects even closer to room temperature.” Valencia says.
To the article: Scientific Reports doi:10.1038/srep10026
Local electrical control of magnetic order and orientation by ferroelastic domain arrangements just above room temperature, L. C. Phillips, R. O. Cherifi, V. Ivanovskaya, A. Zobelli, I. C. Infante, E. Jacquet, N. Guiblin, A. A. Ünal, F. Kronast, B. Dkhil, A. Barthélémy, M. Bibes and S. Valencia
- Ernst Eckhard Koch Prize and Innovation Award on Synchrotron Radiation 2025At the 27th BESSY@HZB User Meeting, the Friends of HZB honoured the dissertation of Dr Enggar Pramanto Wibowo (Friedrich-Alexander University Erlangen-Nuremberg). The Innovation Award on Synchrotron Radiation 2025 went to Prof. Tim Salditt (Georg-August-University Göttingen) and Professors Danny D. Jonigk and Maximilian Ackermann (both, University Hospital of RWTH Aachen University).
- Bright prospects for tin perovskite solar cellsPerovskite solar cells are widely regarded as the next generation photovoltaic technology. However, they are not yet stable enough in the long term for widespread commercial use. One reason for this is migrating ions, which cause degradation of the semiconducting material over time. A team from HZB and the University of Potsdam has now investigated the ion density in four different, widely used perovskite compounds and discovered significant differences. Tin perovskite semiconductors produced with an alternative solvent had a particular low ion density — only one tenth that of lead perovskite semiconductors. This suggests that tin-based perovskites could be used to make solar cells that are not only really environmentally friendly but also very stable.
- Synchrotron radiation sources: toolboxes for quantum technologiesSynchrotron radiation sources generate highly brilliant light pulses, ranging from infrared to hard X-rays, which can be used to gain deep insights into complex materials. An international team has now published an overview on synchrotron methods for the further development of quantum materials and technologies in the journal Advanced Functional Materials: Using concrete examples, they show how these unique tools can help to unlock the potential of quantum technologies such as quantum computing, overcome production barriers and pave the way for future breakthroughs.