Periodic Reporting for period 1 - SPEC (Spin-Phonon interaction for Energy Conversion)
Reporting period: 2020-09-15 to 2022-09-14
Heat dissipation in microelectronic and information processing technologies is a fundamental problem that is increasingly aggravated by the reduction of the transistor dimensions, the increases in packing density and the amount of data. Therefore, fundamental breakthroughs beyond CMOS technologies and heat management strategies are important challenges that need to be faced for the sustainable development of a knowledge-based society.
The exploration of spin-based devices exploiting novel mechanisms has been identified as one of the possible routes to explore. In this context, the study of insulator spintronics has great potential. Since magnetic insulators can offer lower heat dissipation due to the absence of charge carriers and their associated heat losses, in this systems the information is carried by the excitations of the magnetic order (also known as magnons), which generate spin currents that propagate through the system. These spin currents can be exploited for thermoelectric conversion in the spin Seebeck effect (SSE). Moreover, magnetic insulators can offer a wide range of new functionalities due to the mutual interaction between several degrees of freedom: electronic, magnetic and lattice.
The overall objective of the project is to explore effects associated with the interaction of the spin and lattice excitations (i.e. magnon-phonon interaction) to investigate their potential for magnetic field control of heat currents as well as their contribution to thermoelectric conversion and possible enhancement of the SSE.
We have investigated the SSE in ferrimagnetic oxides with different degrees of magnetic compensation (i.e. total level of magnetization after summing up all the contributions from the different spin lattices of the ferrimagnet). By studying the effect of the magnon-phonon interaction on the SSE, we characterized the magnetic state of each investigated oxide (estimated the degree of magnetic compensation). We observed that the magnetic compensation has a significant impact on the magnetic field dependence of the SSE, possibly allowing for a magnetic field control of the thermoelectric conversion in these systems.
The exploration of spin-based devices exploiting novel mechanisms has been identified as one of the possible routes to explore. In this context, the study of insulator spintronics has great potential. Since magnetic insulators can offer lower heat dissipation due to the absence of charge carriers and their associated heat losses, in this systems the information is carried by the excitations of the magnetic order (also known as magnons), which generate spin currents that propagate through the system. These spin currents can be exploited for thermoelectric conversion in the spin Seebeck effect (SSE). Moreover, magnetic insulators can offer a wide range of new functionalities due to the mutual interaction between several degrees of freedom: electronic, magnetic and lattice.
The overall objective of the project is to explore effects associated with the interaction of the spin and lattice excitations (i.e. magnon-phonon interaction) to investigate their potential for magnetic field control of heat currents as well as their contribution to thermoelectric conversion and possible enhancement of the SSE.
We have investigated the SSE in ferrimagnetic oxides with different degrees of magnetic compensation (i.e. total level of magnetization after summing up all the contributions from the different spin lattices of the ferrimagnet). By studying the effect of the magnon-phonon interaction on the SSE, we characterized the magnetic state of each investigated oxide (estimated the degree of magnetic compensation). We observed that the magnetic compensation has a significant impact on the magnetic field dependence of the SSE, possibly allowing for a magnetic field control of the thermoelectric conversion in these systems.
We have grown both ferrimagnetic oxide layers with different degrees of magnetic compensation and also layers of antiferromagnetic oxides. To investigate their spin transport properties by the spin Seebeck effect (SSE), we built and optimized the measurement system.
We then performed the SSE measurements in the ferrimagnetic oxide layers and observed that the suppression of the SSE by the applied magnetic field in the different ferrimagnets is strongly affected by the degree of their magnetic compensation. We explore possible mechanisms that can explain the result. One possibility is that in the ferrimagnetic oxides with larger compensation, the strong SSE suppression is possibly due to the fact that the spin current is more affected by the magnetic field, possibly due to the opposite contribution from the two spin lattices of the ferrimagnet and an increase of the magnon scattering for the more compensated systems. A report on these results will be prepared for publication in a peer-reviewed journal.
We then performed the SSE measurements in the ferrimagnetic oxide layers and observed that the suppression of the SSE by the applied magnetic field in the different ferrimagnets is strongly affected by the degree of their magnetic compensation. We explore possible mechanisms that can explain the result. One possibility is that in the ferrimagnetic oxides with larger compensation, the strong SSE suppression is possibly due to the fact that the spin current is more affected by the magnetic field, possibly due to the opposite contribution from the two spin lattices of the ferrimagnet and an increase of the magnon scattering for the more compensated systems. A report on these results will be prepared for publication in a peer-reviewed journal.
We have observed that the spin Seebeck effect can be strongly affected by the application of magnetic fields in ferrimagnetic oxides with a large degree of magnetic compensation, advancing the knowledge on the mechanism for spin current generation in magnetic systems and having the potential for magnetic field control of thermoelectric conversion.
The possibility to tune the thermoelectric conversion by external means offers potential new type of functionalities which can have implications in heat management strategies. This can possibly contribute to the solution of the heat dissipation problem in current microelectronics and information processing industries, one of the main roadblocks for CMOS technology progress in the last 20 years.
The possibility to tune the thermoelectric conversion by external means offers potential new type of functionalities which can have implications in heat management strategies. This can possibly contribute to the solution of the heat dissipation problem in current microelectronics and information processing industries, one of the main roadblocks for CMOS technology progress in the last 20 years.