Heterostructures for exploring altermagnetic and superconducting spintronics – HEXAS

Altermagnetism describes a symmetry class of compensated magnets in which the spin symmetry group to which they belong allows for alternating spin polarizations both in the crystal space and in the momentum space of the non-relativistic electronic structure. Altermagnets combine merits of ferromagnets, such as magnetoresistance and spin torque effects, and merits of antiferromagnets, such as zero net magnetization and THz dynamics, that were regarded as principally incompatible. In addition, they have merits unparalleled in either of the above-mentioned two traditional basic magnetic phases: for example, the unconventional spin splitter effect and the ability to host spin-polarized triplet-superconductivity.
The actual development of a new avenue in spintronics, using altermagnetism, now calls for the more direct demonstration and detailed understanding of more core spin-physics effects, and in more materials. So far, four altermagnets have been experimentally demonstrated: RuO2, MnTe, Mn5Si3, and CrSb. Not only is the choice of altermagnetic material relevant, but the choice of other materials and optimization of the interfaces that make up heterostructures are essential to take advantage of the spin polarization of altermagnets.
This project will demonstrate core spin-physics associated with the ability of altermagnets to display no net magnetization and yet spin polarization. A key focus hereby will be on the experimental observation of the tunnel magnetoresistance and spin transfer torque effects, as well as spin polarized triplet-superconductivity, and their theoretical modelling in actual heterostructures. We will use Mn-based materials such as Mn5Si3, and MnTe as model material systems, embedded in ad hoc heterostructures. The major advantage of our consortium lies in the fact that we are the only ones to date to have mastered the growth of altermagnetic Mn5Si3, and subsequently demonstrated and manipulated its altermagnetic character. Building on this breakthrough is a key drive of the present proposal, as it now allows us to further explore spin polarization for altermagnetic spintronics, using ad hoc heterostructures.
The partnership between two German (IFW and JGU) and two French laboratories (SPINTEC and CINaM) brings along a unique combination of know-how and experimental capabilities to study dedicated samples with different approaches – high quality thin film deposition, nanofabrication, superconductivity, magneto-transport based on tunnel magnetoresistance and spin torque manipulation, and different material-specific theoretical modelling methodology.