Phthalocyanines with iron (orange) and manganese (violet) centers co-assemble on a gold surface to form a checkerboard pattern. The magnetism of iron and manganese differs in strength and points in opposite directions (red and blue arrows), fulfilling the prerequisites for atomically-thin ferrimagnets. Image: University of Basel, Department of Physics.Two-dimensional (2D) magnetic structures are regarded as a promising material for new types of data storage, as they would allow the magnetic properties of individual molecular building blocks to be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute (PSI) in Switzerland, together with colleagues in Sweden and India, report their findings in a paper in Nature Communications.
Ferrimagnets are composed of two centers that are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets would be suitable for use as sensors, data storage devices or in a quantum computer, since the two-dimensional arrangement allows the magnetic state of individual atoms or molecules to be manipulated. For mathematical and geometrical reasons, however, it has so far not been possible to produce 2D ferrimagnets.
The scientists in Thomas Jung’s research groups at the PSI and the Department of Physics at the University of Basel have now found a method for making such a 2D ferrimagnet.
The researchers first produce ‘phthalocyanines’ – hydrocarbon compounds with different magnetic centers composed of iron and manganese. When these phthalocyanines are applied to a gold surface, they arrange themselves into a checkerboard pattern consisting of alternating iron and manganese centers. The researchers were able to prove that the surface is now magnetic, and that the magnetism of the iron and manganese is of different strengths and points in opposing directions – all characteristics of a ferrimagnet.
“The decisive factor of this discovery is the electrically-conductive gold substrate, which mediates the magnetic order,” explains Jan Girovsky from the PSI, lead author of the study. “Without the gold substrate, the magnetic atoms would not sense each other and the material would not be magnetic.”
The decisive influence of the conducting electrons in the gold substrate is confirmed by a physical effect detected in each magnetic atom using scanning tunneling spectroscopy. These experiments were conducted at various temperatures and thus provide evidence of the strength of the magnetic coupling in the new magnetic material. Model calculations confirmed the experimentally-observed effect and indicated that special electrons attached to the surface of the gold substrate are responsible for this type of magnetism.
“The work shows that a clever combination of materials and a particular nanoarchitecture can be used to produce new materials that otherwise would be impossible,” says Nirmalya Ballav of the Indian Institute of Science Education and Research in Pune, who has been studying the properties of molecular nano-checkerboard architectures for several years with Jung. These magnetic molecules have great potential for a number of applications, as their magnetism can be individually investigated and modified using scanning tunneling spectroscopy.
This story is adapted from material from the University of Basel, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.