Molecular magnets – the multifunctional materials of the future

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Unique materials combining magnetism with other properties, such as optical activity, porosity, sorption capacity or sensitivity to light, may revolutionize future technologies.

Magnets used currently are metal alloys and oxides. They are gray, heavy and hard, as anybody who has ever played with magnetic blocks knows. They may be covered with plastic to make them colorful and pleasant to touch, but it does not influence their weight in any way. How about imagining light, colorful or transparent magnets that glow in the dark? If we were to succeed in creating such materials, their application would not be limited to toys. Magnets are necessary for the functioning of many indispensable devices from electric engines to complicated electronic memory storage media. Materials that combine the functions currently performed by individual elements of complex systems at the molecular level (magnetism, conductivity, photoactivity, light emission capacity) would enable the construction of smaller, cheaper and more effective devices. Creation of such multifunctional materials of the future is the aim of the work of the scientists from the Inorganic Molecular Materials Group at the Jagiellonian University. Members of the team include not only experienced, renowned scientists, but also young, promising adepts at chemistry with a track record of such achievements as the Diamond Grant or a gold medal in the International Chemistry Olympiad.

Magnetic attraction

The magnetic force of attraction has been stimulating the human imagination and thirst for knowledge for centuries. Although the compass – the first magnetic device – was created over two thousand years ago, magnetic phenomena are still protecting many secrets and scientists continue to discover new aspects of the mystery.

Most substances that surround us are diamagnetic, which means they are only weakly influenced by the magnetic field. A stronger effect, although still difficult to observe in everyday life, is characteristic for paramagnets. It is connected with the presence of the so-called "paramagnetic centers" – metal ions or radicals containing unpaired electrons. Substances that are strongly attracted by magnets are usually ferromagnets, in which the paramagnetic centers are close enough to interact with each other. Each ferromagnet becomes paramagnetic above a certain temperature called the Curie temperature. At this point, its paramagnetic centers become independent and chaotically arranged. They may align in parallel only in a strong magnetic field. Below the Curie temperature, paramagnetic centers start to notice each other and act in a synchronized way. Some ferromagnets can be permanently magnetized and maintain an aligned arrangement of paramagnetic centers even when they are removed from the magnetic field.

Squeezing the magnetic sponge

Magnetic molecular materials studied by the scientists from the Faculty of Chemistry of the Jagiellonian University are created by combining simple organic and inorganic molecules and ions into extended architectures. The design of such structures resembles building with Lego blocks. Using modern crystal engineering methods, from an infinite number of elements called "building blocks," scientists select those that offer the best chance to create a substance with the desired functions. It is not a simple task, as the properties of the newly created materials depend on the nature of the building blocks used as well as their relative arrangement.

One of the interesting properties offered by molecular materials is the possibility to switch between magnetic states under the influence of external factors: light, temperature, pressure or humidity. Scientists from the Jagiellonian University succeeded in obtaining magnetic sponges, in which the removal of water causes a reversible rearrangement of structure associated with a change in magnetic properties. They also constructed porous magnets sensitive to the presence of water and other small molecules of gases or solvents. Another achievement is the discovery of exceptionally interesting compounds characterized by bistability, which may occur in two different magnetic states, e.g., paramagnetic and ferromagnetic, in identical conditions. Systems of this kind "remember their history," which means that they "know", for example, whether they were previously cooled or heated. Another possibility offered by molecular materials is the combination of magnetism with interesting optical properties. The research team at the Jagiellonian University managed to create photomagnets switched by the light and luminescent magnets that emit light in the visible range.

Crystals of molecular magnetic material

Beyond known physics

The combination of properties that have never coexisted in one substance before sometimes leads to the discovery of unknown physical phenomena. An important example is chiral magnets, which, similar to natural sugars or amino acids, show optical activity. When exposed to irradiation, some chiral compounds emit light of the wavelength they are exposed to, decreased by half (e.g., they emit blue light when exposed to red light), which is used in laser technology. If such substances are also ferromagnets, their emission capacity grows significantly in a magnetic field. This phenomenon is called the "magnetically enhanced, second-harmonic generation." On the other hand, the creation of microscopic magnets consisting of single molecules has resulted in the discovery of quantum magnetic effects.

The main problem in the practical application of molecular magnetic materials is their low Curie temperatures, which are in most cases far below 0OC. However, there are certain systems that become magnets at room temperature, which proves that this problem can be overcome. "Intelligent materials that can recognize the presence of other substances and respond simultaneously to numerous factors in the form of light, pressure or magnetic or electric fields may, in the future, change the methods of data processing, storage of gases or detection and neutralization of harmful substances," says Beata Nowicka, PhD, a member of the research team.

Research team: Professor Barbara Sieklucka; Robert Podgajny, PhD; Beata Nowicka, PhD; Tomasz Korzeniak, PhD; Dawid Pinkowicz, PhD; Szymon Chorąży, MSc; Olaf Stefańczyk, MSc; Bernard Czarnecki, MSc; Mateusz Reczyński; Alexandra Halemba; Anna Hoczek; Ireneusz Szewczyk; Tomasz Dańko; Mirosław Arczyński; Wojciech Nogaś; Marcin Foryś; Justyna Rakoczy; Michał Magott

Collaborating team:Institute of Nuclear Physics, Polish Academy of Sciences: Professor Maria Bałanda; Professor Tadeusz Wasiutyński; Robert Pełka, PhD; Magdalena Fitta, PhD; Jagiellonian University: Michał Rams, PhD; University of Science and Technology (AGH): Professor Czesław Kapusta