Magnetism in thin layers: one electron makes the difference
Researchers at the Paul Scherrer Institute PSI can selectively manipulate magnetism at the interfaces between thin layers. This is an important step on the way to novel types of computer memory
Graphene was a milestone. When Andre Geim and Konstantin Novoselov produced the first single-atom thick layer of carbon in 2004, they had no idea they were establishing a completely new field of research. Previously, though, ultra-thin layers just a few atoms thick – so-called two-dimensional crystalline materials – had already revealed astonishing optical, electronic, magnetic, and even superconducting properties. In this area, Thorsten Schmitt’s team is among the top research leaders internationally.
The researchers in the Spectroscopy of Quantum Materials group at the PSI Center for Photon Science specialise in the production and spectroscopic investigation of thin atomic layers made up of different chemical compounds, which they stack on top of each other alternately – like a sandwich. They keep finding interesting phenomena in these hybrid materials – most recently in a superlattice in which layers of lanthanum nickelate (LaNiO3) and lanthanum titanate (LaTiO3) alternate. Lanthanum nickelate is non-magnetic (paramagnetic), and lanthanum titanate is antiferromagnetic (see box below: «Magnetism briefly explained»). When the two materials are stacked on top of each other, electrons – negatively charged elementary particles – jump from the titanate to the nickelate, and thus the magnetism changes: Lanthanum nickelate becomes antiferromagnetic, while lanthanum titanate is now non-magnetic.
A sensation in physics
To someone outside the field, this exchange may sound like a useless sleight-of-hand trick. For researchers in physics, however, it is recognised as an important step, because in this way they can tailor materials to enable novel applications, for example, for magnetic memories of the future. Lanthanum titanate is not well suited for this purpose, since as an insulator, it does not conduct electrical current. Lanthanum nickelate, on the other hand, is a good conductor and, in combination with the new magnetic property, a promising starting material for the building blocks of so-called spintronic computers. In these, the classical ferromagnetism of a computer hard drive is replaced by antiferromagnetic memory cells based on the spins of electrons. For such components, the properties on the surface or at interfaces are crucial. «Our research is not oriented towards developing such memories ourselves, but rather towards understanding fundamental properties that define the functional principle for future applications – we are doing basic research,» Schmitt emphasises. This is urgently needed, because many phenomena in two-dimensional materials are not yet understood, and researchers are constantly making surprising discoveries.
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