Tunable Magnonic Crystal Induced by Superconducting Strips for Spin Wave Control

Core Concepts

A periodic arrangement of superconducting strips can induce a tunable magnonic crystal in a nearby magnetic film, enabling dynamic control over spin wave propagation and band structure.

Abstract

Bibliographic Information:

Kharlan, J., Szulc, K., Kłos, J. W., & Centała, G. (2024). Tunable magnonic crystal in a hybrid superconductor–ferrimagnet nanostructure. arXiv preprint arXiv:2408.01240v2.

Research Objective:

This study investigates the feasibility of inducing and controlling a magnonic crystal (MC) within a uniform magnetic layer using the stray magnetic field generated by a periodic array of superconducting (SC) strips.

Methodology:

The researchers employed a two-step semi-analytical approach, validated by finite-element method (FEM) simulations in COMSOL Multiphysics. First, they determined the stray field generated by the SC strips by solving the London equation. Subsequently, they calculated the spin wave (SW) spectrum within this field by solving the Landau-Lifshitz equation using the plane-wave method.

Key Findings:

• The stray field produced by the SC strips creates a periodic potential landscape within the magnetic layer, effectively inducing an MC.
• The depth of this potential landscape, and consequently the strength of the MC effect, can be tuned linearly by adjusting the external magnetic field applied to the system.
• Varying the spacing and width of the SC strips allows for further tailoring of the stray field profile and, therefore, the SW spectrum.
• Even with very narrow gaps between the SC strips, distinct band gaps in the SW spectrum are maintained, a feature not typically observed in conventional MCs.

Main Conclusions:

This research demonstrates a novel method for on-demand induction and control of MCs in thin magnetic films using a relatively simple and tunable setup. This approach offers significant advantages over conventional MC fabrication techniques, enabling dynamic manipulation of SW propagation and band structure.

Significance:

This study contributes significantly to the field of magnonics by introducing a new paradigm for reconfigurable MCs. The ability to dynamically control SW properties using external stimuli opens up exciting possibilities for developing novel magnonic devices for information processing and beyond.

Limitations and Future Research:

The study primarily focuses on a specific geometry and material system. Further research could explore the applicability of this approach to other magnetic materials and SC patterns, potentially leading to even more versatile and efficient magnonic devices. Additionally, investigating the impact of temperature variations on the MC properties would be beneficial for practical applications.

Stats

The FM film is 20 nm thick.
The SC strips are 400 nm wide and 100 nm thick.
The London penetration depth of the SC material is 50 nm.
The external magnetic field used is up to 50 mT.
The distance between adjacent SC strips (d) is varied, with examples of 25 nm, 100 nm, 300 nm, and 400 nm.

Quotes

Key Insights Distilled From

Tunable magnonic crystal in a hybrid superconductor--ferrimagnet nanostructure

by Juli... at arxiv.org 11-04-2024

https://arxiv.org/pdf/2408.01240.pdf

Deeper Inquiries

How might the integration of this tunable magnonic crystal with other spintronic components lead to the development of novel devices?

Integrating this tunable magnonic crystal with other spintronic components presents exciting opportunities for developing novel devices with enhanced functionalities and performance. Here are some potential avenues:

Reconfigurable magnonic logic gates: By combining the tunable magnonic crystal with spin-wave logic elements, such as spin-wave interferometers or spin-wave majority gates, one could create reconfigurable logic circuits. The ability to dynamically control the magnonic crystal's band structure allows for on-demand activation or deactivation of specific spin-wave propagation paths, enabling the realization of logic functions that can be modified in real-time.

Multiplexed spin-wave communication channels: The frequency-dependent spin-wave transmission properties of the magnonic crystal can be exploited for multiplexing applications. By tuning the external magnetic field or the superconducting strip separation, one can selectively route spin waves of different frequencies through distinct magnonic bands, enabling the creation of multiple communication channels within a single device. This could significantly enhance the bandwidth and data transfer rates in spin-wave-based communication systems.

Tunable spin-wave filters and resonators: The magnonic crystal's ability to selectively transmit or reflect spin waves based on their frequency makes it a promising candidate for developing tunable spin-wave filters and resonators. By adjusting the crystal's properties, one can precisely control the passband or resonant frequency, enabling the development of highly selective and adaptable filtering and resonant elements for spin-wave-based signal processing applications.

Enhanced spin-wave detection sensitivity: Integrating the magnonic crystal with spin-wave detectors, such as spin valves or magnetic tunnel junctions, could lead to enhanced detection sensitivity. By tuning the crystal to confine spin waves within the active region of the detector, one can increase the interaction time between the spin waves and the detector, resulting in a stronger output signal and improved sensitivity.

Hybrid superconducting-magnonic quantum devices: The proximity of the superconducting strips to the magnetic layer opens up possibilities for exploring hybrid superconducting-magnonic quantum phenomena. The interaction between spin waves (magnons) and superconducting quasiparticles could lead to the development of novel quantum devices, such as magnon-mediated superconducting qubits or highly sensitive magnonic detectors for superconducting quantum circuits.
These are just a few examples, and further research into the integration of this tunable magnonic crystal with other spintronic components is likely to uncover even more innovative device concepts with the potential to revolutionize fields such as information processing, communication, and sensing.

Could the presence of defects or imperfections in the superconducting strips significantly impact the performance and tunability of the magnonic crystal?

Yes, the presence of defects or imperfections in the superconducting strips can significantly impact the performance and tunability of the magnonic crystal. Here's why:

Distortion of the stray magnetic field: Defects in the superconducting strips, such as variations in width, thickness, or edge roughness, can distort the uniformity of the Meissner currents flowing within them. This, in turn, leads to a non-ideal, inhomogeneous stray magnetic field profile in the magnetic layer, deviating from the desired periodic potential landscape.

Scattering and localization of spin waves: The distorted stray field acts as scattering centers for spin waves propagating through the magnonic crystal. This scattering disrupts the coherent propagation of spin waves, leading to increased damping, reduced group velocity, and potentially even localization of spin waves around the defects.

Modification of the magnonic band structure: The presence of defects can modify the magnonic band structure, shifting the frequencies of band edges and gaps, and even introducing localized modes within the bandgaps. This can significantly alter the intended filtering, resonant, or waveguiding properties of the magnonic crystal.

Impact on tunability: Defects can also affect the tunability of the magnonic crystal. The non-uniform stray field may respond differently to changes in the external magnetic field or temperature, leading to unpredictable shifts in the magnonic band structure and hindering the ability to precisely control the spin-wave propagation characteristics.
The severity of these impacts depends on the type, size, and distribution of defects. For instance, small, isolated defects might only introduce minor perturbations, while large-scale inhomogeneities or a high density of defects can severely degrade the performance and tunability of the magnonic crystal.
Therefore, ensuring high quality and uniformity in the fabrication of the superconducting strips is crucial for realizing the full potential of this tunable magnonic crystal platform. Advanced fabrication techniques and thorough characterization methods are essential for minimizing defects and achieving the desired performance in practical devices.

What are the potential implications of this research for advancing our understanding of wave phenomena in condensed matter physics?

This research on tunable magnonic crystals induced by superconducting patterns holds significant potential for advancing our understanding of wave phenomena in condensed matter physics, particularly in the realm of:

Hybrid quantum systems: This work provides a platform for studying the interaction between spin waves (magnons) and superconducting phenomena. The interplay of these excitations in a precisely controlled environment could reveal new insights into hybrid quantum systems and potentially lead to the discovery of novel quantum states or phases.

Artificial gauge fields for spin waves: The spatially varying magnetic field generated by the superconducting strips acts as an effective vector potential for spin waves, mimicking the effect of an artificial gauge field. This opens up avenues for exploring spin-wave transport phenomena in the presence of artificial gauge fields, analogous to the study of electrons in magnetic fields, but within a completely different energy and length scale.

Band structure engineering in magnonic systems: This research demonstrates a novel approach to engineering magnonic band structures using the stray field of superconducting patterns. This method offers a high degree of control and tunability, potentially enabling the realization of complex magnonic band structures, such as magnonic topological insulators or Dirac cones for spin waves, with unique transport properties.

Nonlinear dynamics in magnonic crystals: The tunability of this system allows for exploring nonlinear spin-wave dynamics in magnonic crystals. By driving the system with strong excitations or modulating the external field, one can investigate phenomena like soliton formation, Bose-Einstein condensation of magnons, or other nonlinear wave phenomena in a highly controllable setting.

Magnon-phonon coupling: The presence of the superconducting strips can also influence the lattice vibrations (phonons) in the magnetic layer. This opens up possibilities for studying magnon-phonon coupling in a system where both the magnonic and phononic properties can be tuned, potentially leading to new insights into energy transfer mechanisms and dissipation processes in hybrid systems.
Overall, this research provides a versatile platform for investigating a wide range of fundamental wave phenomena in condensed matter physics. The ability to precisely control and manipulate both the spin-wave and superconducting properties in a single device offers exciting opportunities for advancing our understanding of hybrid quantum systems, artificial gauge fields, and nonlinear dynamics in magnonic systems, with potential implications for future technological advancements in spintronics and quantum information processing.