EPFL researchers have revealed layer-dependent magnetism in platinum diselenide-based devices. Image: Alberto Ciarrocchi/EPFL 2019.One of the most cutting-edge fields in technology is spintronics, a still-experimental effort to design and build devices – such as computers and memories – that run on a property of electrons known as spin, rather than the movement of charges (which we know as electrical current). When the spins of electrons align together in a material, this leads to the well-known phenomenon of magnetism.
Such applications demand new magnetic materials with new properties. For example, it would be a huge advantage if magnetism could occur in so-called two-dimensional (2D) materials such as graphene, which is basically an atom-thick layer of graphite.
However, finding 2D magnetic materials is challenging. Chromium iodide (CrI3) recently revealed many potentially interesting properties, but it degrades rapidly under ambient conditions and its insulating nature doesn't promise much in the way of spintronics applications, most of which require metallic and air-stable magnetic materials.
Now, the groups of Andras Kis and Oleg Yazyev at the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have found a new metallic and air-stable 2D magnet: platinum diselenide (PtSe2). This discovery was made by Ahmet Avsar, a postdoc in Kis's lab, who was actually looking into something else entirely, and is reported in a paper in Nature Nanotechnology.
To explain the discovery of magnetism in PtSe2, the researchers first used calculations based on density functional theory, a method that models and studies the structure of complex systems with many electrons, such as materials and nanostructures. This theoretical analysis showed 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 defects in graphene, but PtSe2 was a total surprise for us," says Oleg Yazyev.
The researchers confirmed the presence of magnetism in the material using a powerful magneto-resistance measurement technique. The magnetism was surprising, since perfectly crystalline PtSe2 is supposed to be non-magnetic. "This is the first time that defect-induced magnetism in this type of 2D materials is observed," says Kis. "It expands the range of 2D ferromagnets into materials that would otherwise be overlooked by massive database-mining techniques."
Removing or adding one layer of PtSe2 is enough to change the way the electron spins talk to each other across layers. And what makes the material even more promising is the fact that its magnetism, even within the same layer, can be further manipulated by strategically placing defects across its surface. This is known as ‘defect engineering’ and can be accomplished by irradiating the material's surface with electron or proton beams.
"Such ultra-thin metallic magnets could be integrated into the next generation spin-transfer torque magnetic random-access memory [STT MRAM] devices," says Avsar. "2D magnets could reduce the critical current required to change magnetic polarity, and help us with further miniaturization. These are the major challenges that companies are hoping to solve."
This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.