A new 2D magnet brings together future devices

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We all know the image of electrons slipping around the nucleus of an atom and forming chemical bonds in molecules and materials. But what is less known is that the electrons have an additional unique property: the spin. It is difficult to make an analogy, but one could roughly describe the spin of electrons as a spinning spinning around its axis. But what is even more interesting is that when electron spins align in a material, it leads to the well-known phenomenon of magnetism.

One of the most advanced areas of technology is spintronics, a still experimental attempt to design and build devices, such as computers and memories, that operate on the spin of electrons rather than just the movement of charges ( what is called electric current). . But such applications require new magnetic materials with new properties. For example, it would be extremely advantageous for magnetism to occur in an extremely thin layer of material, referred to as two-dimensional (2D) materials, including graphene, which is essentially a thick graphite layer of atoms.

However, finding 2D magnetic materials is difficult. Chromium iodide (CrI₃) has recently revealed many interesting properties, but it is rapidly degrading under ambient conditions and its insulating nature promises few applications in spintronics, most requiring magnetic materials metal and air-stable.

At present, the groups of Andras Kis and Oleg Yazyev at EPFL have discovered a new two-dimensional metal magnet that is stable in air: platinum diselenide (PtSe).₂). The discovery was made by Ahmet Avsar, a postdoctoral fellow at Kis Lab, who was searching for something completely.

Explain the discovery of magnetism in PtSe₂, the researchers first used calculations based on functional density theory, a method that models and studies the structure of complex systems with many electrons, such as materials and nanostructures. Theoretical analysis has shown that the magnetism of PtSe₂ is caused by so-called "defects" on its surface, which are irregularities in the arrangement of atoms. "More than a decade ago, we found a somewhat similar scenario for graphene defects, but PtSe₂ It was a total surprise for us, "says Oleg Yazyev.

The researchers confirmed the presence of magnetism in the material with a powerful magnetoresistance measurement technique. Magnetism was surprising because PtSe perfectly crystalline₂ is supposed to be non-magnetic. "This is the first time that a magnetism induced by defects is observed in this type of two-dimensional materials," says Andras Kis. "It expands the range of 2D ferromagnetic magnets into materials that would otherwise be overlooked by massive database mining techniques."

Remove or add a layer of PtSe₂ is enough to change the way spins talk between layers. And what makes it even more promising is the fact that its magnetism, even within the same layer, can be further manipulated by strategically placing flaws on its surface – a process called electron beams or protons.

"Such ultra-thin metal magnets could be incorporated into the next generation of Transfer Transfer Torque Magnetic Random Access Memory (STT MRAM) devices," says Ahmet Avsar. "2D magnets could reduce the critical current required to change magnetic polarity and help us continue miniaturization – these are the main challenges that companies hope to solve."