PHOENICS: PHOto-inducEd femtosecoNd magneto-electrIC Spin manipulation in antiferromagnets

• Applicant: Dr. Davide Bossini
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434259239

The digitisation of the world is predicted to continue growing so massively, that in 2025 the world data volume will be 5 times higher than in 2018. Data storage has recently shifted from local devices to the cloud. This change is dramatic: 49% of the world data will be stored in the cloud by 2025, which means in data-centres. The technology employed in these facilities relies on magnetic hard-disks and it cannot sustain the predicted growth rate of cloud storage for longer than 15 years. A technology for faster and more energy-efficient magnetic-recording devices needs to be developed. A promising novel approach is based on the idea that ultrashort laser pulses can be the writing and reading tool for femtosecond magnetic recording. Light has already demonstrated the potential to manipulate the magnetic order in solids on the femtosecond time-scale. It was also shown that such manipulation can even be extremely energy efficient in insulating materials. Recently it has been pointed out that magnetically ordered materials with no net magnetisation, i.e. antiferromagnets(AFs), are promising for spintronics. Moreover, AFs possess intrinsically faster spin dynamics in comparison with ferromagnets. Although some pioneer investigations have reported the ultrafast excitation and coherent (i.e. energy efficient) control of the oscillatory dynamics of the order parameter in dielectric AFs (L), the ultrafast switching of L is missing. In addition, the possibility to couple the femtosecond spin dynamics to charges has not been addressed yet, although it is necessary to integrate any novel magnetic recording concept with the charge-based present-day technology.
Our project aims at overcoming these limitations investigating a dielectric magnetoelectric AF, i.e. an AF in which both time-reversal and space-inversion symmetries are broken. This property generates a plethora of effects, on which our project relies. First, a combined action of DC magnetic and electric fields reverses L by 180 degrees. We will scale this concept to the ultrafast time-scale by employing the electric field of femtosecond laser pulses and thus demonstrate an energy efficient route to optically store information. Second, a magneto-optical effect linearly proportional to L is active, as already experimentally demonstrated. Such an effect, symmetry forbidden in conventional AFs, is necessary to disentangle the two states with reversed L generated by applying electric and magnetic fields. Third, it has been predicted that due to the magnetoelectricity the spin configuration in the AF affects the spectrum of the surface plasmon polariton (SPP) of a metallic layer deposited on top of the magnetic material. We will explore this scenario on the ultrafast time-scale, assessing whether spin dynamics in the AFs can change transiently the spectrum of the SPP. This concept carries the potential to transfer coherence from the photo-induced spin dynamics to charges on the femtosecond time-scale.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Mirko Cinchetti