International researchers found that magnetostriction significantly influences muon localization in particular materials, overturning previous presumptions in muon spectroscopy. This advancement, accomplished through innovative simulations, sheds light on the magnetic stage transitions in manganese oxide and has implications for studying comparable materials.Muon spectroscopy works as an essential experimental approach for exploring the magnetic characteristics of products. This technique involves embedding a spin-polarized muon within the crystal lattice and observing the effect of the surrounding environment on its habits. It operates on the concept that the muon will settle into a particular place primarily affected by electrostatic forces, a position that can be determined through the computation of the materials electronic structure.But a brand-new research study led by scientists in Italy, Switzerland, UK, and Germany has actually discovered that, a minimum of for some materials, that is not completion of the story: the muon website can change due to a well-known but formerly disregarded impact, magnetostriction.Pietro Bonfà from the University of Parma, lead author of the research study simply published in Physical Review Letters, describes that his group and their coworkers at the University of Oxford (UK) have been using density-functional theory (DFT) simulations for a minimum of a decade to discover muon sites.”We started with challenging cases, such as europium oxide and manganese oxide, and in both cases, we could not find an affordable way to fix up DFT forecasts and the experiments,” he says. “We then checked simpler systems and we had numerous effective predictions, but those two cases were truly bothering us. These compounds should be easy but rather turned out to be extremely complicated and we did not comprehend what was happening. Manganese oxide is a textbook case of an antiferromagnetic system, and we might not explain muon spectroscopy results for it, which was a bit embarrassing.”The issue, he explains, was the contradiction in between the expectation to find the muon in a high proportion position, and its well-known propensity to make bonds with oxygen atoms. The antiferromagnetic order of the material lowers the proportion, and the position near to the oxygen atoms ends up being incompatible with experiments.Challenges and Solutions in DFT SimulationsBonfà suspected that the description might be connected to the product undergoing a magnetic phase shift and started trying to recreate the phenomenon in simulations of manganese oxide. “Because it is a complicated system, you need to include some corrections to DFT, such as the Hubbard U criterion,” he states. “But we were picking its worth empirically, and when you do that, you have a great deal of unpredictability, and the outcomes can change considerably depending on the worth you select.”Still, Bonfàs initial simulations suggested that the muon positions might be driven by magnetostriction, a phenomenon that triggers a material to change its shape and dimensions during magnetization. To show it beyond doubt, he coordinated with the MARVEL laboratories at EPFL and PSI of Nicola Marzari and Giovanni Pizzi.”We used a state-of-the-art technique called DFT+U+V, which was very important to make simulations more precise,” explains Iurii Timrov, a researcher in the Laboratory for Materials Simulations at PSI and co-author of the research study. This approach can be utilized with onsite U and intersite V Hubbard criteria that are computed from very first concepts rather of being selected empirically, thanks to the usage of density-functional perturbation theory for DFT+U+V that was developed within MARVEL and executed in the Quantum ESPRESSO bundle. “Although we had actually already figured out that magnetostriction was at play, having the correct info on the foundation of the simulation was extremely essential, and that came from Iuriis work,” includes Bonfà.In the end, the option of the puzzle was fairly basic: magnetostriction, which is the interplay between flexible and magnetic degrees of liberty in the product, causes a magnetic stage shift in MnO at 118K, at which the muon site switches. Above that temperature, the muon ends up being delocalized around a network of equivalent sites– which describes the unusual habits observed in experiments at high temperatures.The researchers anticipate that the same may hold true also for lots of other rocksalt-structured magnetic oxides. In the future, Timrov describes, the group desires to keep studying the same product likewise consisting of temperature level effects, utilizing another advanced strategy developed in MARVEL and called stochastic self-consistent harmonic approximation. In addition, and in cooperation with Giovanni Pizzis group at the Paul Scherrer Institute, this method will be provided to the neighborhood through the AiiDAlab user interface, so that all experimentalists can use it for their own studies.Reference: “Magnetostriction-Driven Muon Localization in an Antiferromagnetic Oxide” by Pietro Bonfà, Ifeanyi John Onuorah, Franz Lang, Iurii Timrov, Lorenzo Monacelli, Chennan Wang, Xiao Sun, Oleg Petracic, Giovanni Pizzi, Nicola Marzari, Stephen J. Blundell and Roberto De Renzi, 24 January 2024, Physical Review Letters.DOI: 10.1103/ PhysRevLett.132.046701 The study was funded by the Swiss National Science Foundation.
International researchers discovered that magnetostriction considerably affects muon localization in certain materials, reversing previous assumptions in muon spectroscopy. It runs on the concept that the muon will settle into a specific location primarily influenced by electrostatic forces, a position that can be identified through the computation of the products electronic structure.But a new study led by scientists in Italy, Switzerland, UK, and Germany has actually found that, at least for some products, that is not the end of the story: the muon website can change due to a widely known but previously disregarded impact, magnetostriction.Pietro Bonfà from the University of Parma, lead author of the research study just published in Physical Review Letters, describes that his group and their colleagues at the University of Oxford (UK) have been utilizing density-functional theory (DFT) simulations for at least a decade to discover muon sites. “Although we had actually currently figured out that magnetostriction was at play, having the right information on the structure blocks of the simulation was very essential, and that came from Iuriis work,” includes Bonfà.In the end, the service of the puzzle was relatively simple: magnetostriction, which is the interplay in between flexible and magnetic degrees of liberty in the material, causes a magnetic stage shift in MnO at 118K, at which the muon website switches.
