The invincible IRON-TALC: 2D magnetic layers

Isolated single layers from layered crystals are called two dimensional (2D) materials. In one direction the layers within these materials are held together only by weak so called van der Waals (vdW) forces. This allows us to isolate only a single layer without destroying its structure. One could imagine layered crystals as stacked sheets of paper. In this analogue to vdW forces, gravity holds the individual sheets together in a pile, but we do not need much force to overcome it and take one sheet. In 2004, graphene was isolated as the first 2D material, a single layer of graphite. In the following years many different 2D materials were reported, bringing new and unexpected properties, and opening many potential applications in future electronics and sensors. If we think about the sheets of paper as analogues to layers of 2D materials, what would happen if the paper material was magnetic? Do atomically thin magnetic sheets even exist? If so, would the added magnetic interaction keep the sheets strongly together, or would it maybe rip them apart? From 1960s a theor em called Merming Wagner theorem states that 2D magnets are not possible to exist above absolute zero temperature (-273.15 degrees Celsius). This would mean that in our paper analogue, sheet of magnetic paper would have internal forces that want to either cancel magnetism or rip the individual sheets apart. In other words, 2D magnets should not exist. This well-known fact in the fields of physics and materials science did not help in motivating the researchers to look for 2D magnets. Almost two decades after the discovery of the first 2D material (graphene) and after countless non-magnetic 2D materials were found, the first reports on 2D magnetism appeared. However, these very rare crystals also happen to be very unstable. Being made out of reactive elements as chlorine or tellurium they cannot be exposed to ambient air. Our project aims at finding air-stable 2D magnets. While many people are familiarized with talc, maybe as baby-powder, or additive in cosmetics, or the powder that you put on your hands for rock climbing, most people do not know that talc is 2D material. Another issue which commonly happens in talc is that iron atoms can be integrated into its layers rather easily. This frequently happens in nature. Our project will show that unique structure of talc gives iron trapped in talc an atomically thin protection from the environment, that this trapped iron in talc is magnetic, and that finally this system is truly an air-stable 2D magnet.

The START project "The invincible IRON-TALC: 2D magnetic layers" was led by Priv.-Doz. Aleksandar Matkovic, and realized at Montanuniversität Leoben. The goal of the project was to investigate a field of two-dimensional (2D) magnetic phyllosilicates. These are naturally occurring layered minerals, and they are used extensively in many industries as food, cosmetics, and pharmaceuticals. However, the use in electronic and in nanotechnologies is marginal. The discrepancy comes mostly from the needed properties in the different applications, mainly their crystallinity. Currently, these sheet clays are used as high purity powders, commonly with sub micron crystalline grains. To reach their potential in nanotechnologies, we need single crystals and well defined thin films. This project altered the scientific community to the new class of 2D insulators. We have shown that these materials are magnetic when they are prepared as only few nanometer thin crystalline layers. These materials are fully stable in air even when in a monolayer form (about one nanometer thin). This is a major advantage over other 2D magnets, that face immediate degradation in air. The project has employed a total of ten team members over its four-year duration, and resulted in over twenty research articles. We have observed for the first time that phyllosilicates have magnetic response in mono layers and that they are fully ambiently stable in 2D form. We have further imaged magnetic domains in this material class, providing the first direct observation of layered anti ferromagnetism and domain formation. We have also made a connection between their crystal structure and magnetic response, opening a path to tune magnetic properties. Atomically thin magnetic insulators are needed for the next generation of magnetic memories. These would allow to integrate magnetic memory bits directly in the logic units of our computers. Such integration would enable ultra fast memory processing units, which presents a novel processor architecture where memory elements and logic are blended into one. Our project has opened a pathway to realizing these advanced computing technologies based on abundant, bio compatible and bio degradable materials, therefore reducing the need for rare earth elements, electronic waste footprint, and opening potential bio sensing applications.