Magnetism in small amounts of hydrogen: Research team develops new ideas to improve properties of ultra-thin materials

Magnetic two-dimensional materials consisting of one or a few atomic layers were only recently known and promise interesting applications such as future electronics. Until now, however, the magnetic state of these materials has not been well controlled.

A German-American research team led by the Helmholtz Zentrum Dresden Rosendorf (HZDR) and the Technical University of Dresden (TUD) reports in the journal nanolettersthis is an innovative idea that can overcome this shortcoming – by allowing the two-dimensional layer to react with hydrogen.

Two-dimensional materials are ultrathin and in some cases consist of a single atomic layer. Due to its special properties, this still young material offers exciting prospects for spintronics and data storage. In 2017, experts discovered a new variant—magnetic two-dimensional materials. Until now, however, it has been difficult for these systems to switch back and forth between two magnetic states through targeted chemical influence, a prerequisite for building novel electronic components.

To overcome this problem, research groups at HZDR and TUD, led by Junior Research Group Leader Rico Friedrich, turned their attention to a special group of two-dimensional materials: layers obtained from crystals in which relatively strong chemical bonds exist: so-called Non-Van Dehua 2D materials.

Twenty years ago, future Nobel Prize winners in physics Konstantin Novoselov and Andre Geim were able to produce targeted two-dimensional materials for the first time. They used tape to peel off a thin layer from a graphite crystal, thereby isolating a single layer of carbon, known as graphene. This simple trick works because the individual layers of graphite are only loosely chemically bonded. By the way, this is exactly why you can draw lines on paper with a pencil.

“Only in recent years has it been possible to separate the individual layers from the crystal using liquid-based processes, where the bonding forces between the layers are stronger than those in graphite,” says the head of the junior research group Dresden Concept Rico Friedrich explains.

“The resulting two-dimensional material is more chemically active than graphene, for example.” The reason: The surfaces of these layers have unsaturated chemical bonds, making them easy to combine with other substances.

Turn 35 into 4

Friedrich and his team came up with the idea that if the reactive surfaces of these two-dimensional materials react with hydrogen, it should be possible to specifically influence the magnetic properties of the thin layers. However, it is unclear which 2D systems are particularly suitable for this.

To answer this question, the experts compiled a library of 35 previously developed new 2D materials and performed detailed and extensive calculations using density functional theory.

The challenge is to ensure the energetic, dynamic and thermal stability of the hydrogen passivation system and to determine the correct magnetic state – a task that can only be accomplished with the support of multiple high-performance computing centers.

When the hard work was done, four promising 2D materials were left. The group took a closer look at these again. “Ultimately, we were able to identify three candidates that can be magnetically activated through hydrogen passivation,” Friedrich reports. Cadmium titanate (CdTiO₃) proved to be particularly remarkable – through the influence of hydrogen it became ferromagnetic, i.e. a permanent magnet.

Three candidate materials treated with hydrogen should be easy to control magnetically, making them suitable for new electronic components. Because the layers are so thin, they can be easily integrated into flat device components—an important aspect for potential applications.

Experiments are already underway

“The next step is to confirm our theoretical findings experimentally,” says Rico Friedrich. “Some research groups are already trying to do this, such as the University of Kassel and the Leibniz Institute for Solid State and Materials Research in Dresden.” But at HZDR and TUD, research into 2D materials continues: Beyond this , Friedrich and his team are investigating new 2D materials that may be relevant for long-term energy conversion and storage.

One focus is on the possible decomposition of water into oxygen and hydrogen. Green hydrogen obtained in this way can be used as an energy storage medium when solar and wind energy are too little.