Researchers at the École polytechnique fédérale de Lausanne (EPFL) in Switzerland have discovered the first ever magnetic photoconductor, a modified perovskite material whose distinct properties could lead to the next generation of digital storage solutions.
The lab of László Forró at EPFL has synthesized a ferromagnetic photovoltaic material and found a quick (only quadrillionths of a second) and easy way to modify its magnetic properties, which can be very useful in magnetic data storage.
What is new about this perovskite
Postdoctoral student Bálint Náfrádi, who led the project at EPFL, describes the novel perovskite: “It is a 10–15% manganese-doped modification of the standard CH3NH3PbI3, where manganese partially replaces lead.”
The new perovskite material combines the advantages of ferromagnets and photoconductors, thus creating a new phenomenon: the “melting" of magnetization by photo-electrons. “It is a bulk ferromagnet below ~25K,” Náfrádi notes about the pioneering perovskite material. The magnetism can be switched off by visible light illumination. In the study, which could be basis for developing a new generation of magneto-optical data storage devices, a simple red LED was sufficient to disrupt the material’s magnetic order and generate a high density of traveling electrons, which can be tuned by changing the light’s intensity.
“Also, our strategy to replace lead instead of the halide atom to tailor the gap is new,” the researcher adds.
First ever magnetic photoconductor could lead to discovery of similar phenomena in known materials
Significantly, the team reports their discovery represents the first ever magnetic photoconductor. “Fundamentally, this is a synergy of two extended fields—research on photoconductors and on magnetic materials,” Náfrádi says. “The concept is rather simple, but the two communities are so separated that no one crossed the border before us.” Consequently, the team expects a rediscovery of many already known materials where similar phenomena are in play. “From a practical point of view, magnets are used in almost all aspects of the electronic ‘food chain,’ not only in IT but electricity production, engines, filters, radios, etc.,“ Náfrádi points out. “The new concept that light can be used to control the magnetic component could enrich all these engineering fields.”
Solving the heat problem and enabling a new generation of data storage
This newly discovered magnetic photoconductor could lead to new data storage solutions that were not feasible until now. “In magnetic data storage, the next generation HDDs are based on heat-assisted writing. Here, a strong laser heats up the magnetic media to facilitate data (re)write. The produced heat is a major issue in this technology, which continually delays its appearance since mid 2000s,” Náfrádi explains. “Our material offers the same functionality but without the heat and associated problems.”
Potential for more efficient solar cells
According to the research team, the new perovskite material could also have an impact on the advance of a new kind of solar cell that is “automatically” more efficient. “The optical band gap of ~830 nm of MAMn:PbI3 is significantly red-shifted by about 46 nm relative to that of the pristine MAPbI3 material (783 nm),” says Náfrádi. “If all other solar cell parameters are the same, this automatically increases the efficiency because a larger portion of the visible spectrum is covered.”
In the realm of fundamental science, Náfrádi and his colleagues are now fine-tuning their understanding of the new perovskite material’s magnetic and photo-magnetic properties. At the same time, they continue to development the material to achieve ferromagnetism above room temperature, which, according to Náfrádi, is a prerequisite for most of the applications.
The work is detailed in the article “Optically switched magnetism in photovoltaic perovskite CH3NH3(Mn:Pb)I3,” published in Nature Communications.
Written by Sandra Henderson, Research Editor, Novus Light Technologies Today