Magnetic skyrmions have gained significant attention in the field of spintronics due to their topological protection and potential applications. These nanoscale magnetic structures, which possess particle-like properties, have shown promise in spintronic storage devices because of their unique features, small size, and lower energy consumption compared to conventional alternatives. However, the limited stability and low density of magnetic skyrmions have restricted their wide-scale applicability, as they typically require an external magnetic field to exist and operate effectively.
A New Approach
In a recent report published in Science Advances, Yuzhu Song and a team of researchers present a novel approach to address the limitations of magnetic skyrmions. They successfully formed high-density, spontaneous magnetic biskyrmions without the need for an external magnetic field in ferrimagnets using the thermal expansion of the lattice. By investigating the negative thermal expansion of a lattice, the team discovered a strong connection between the atomic-scale ferrimagnetic structure and the nanoscale magnetic domains in a ferrimagnet compound composed of a holmium-cobalt system.
The research team characterized the positive and negative thermal expansion of the compound. They utilized neutron powder diffraction measurements and Lorentz transmission electron microscopy to examine the ferrimagnetic structure and magnetic domains. Through variable-temperature dependent neutron-powder diffraction measurements, the team obtained crystal and magnetic structures of the compound, revealing distinct variations in profile intensity across different temperature ranges and complex magnetic structural changes.
By determining the crystal structure and exploring the magnetic moments of holmium and cobalt, the researchers were able to observe the temperature-dependent evolution of the magnetic and structural parameters of the ferrimagnet across the entire temperature range. With increased temperature, the unit cell of the magnetic compound expanded due to anharmonic lattice vibrations. Additional neutron powder diffraction studies allowed the team to calculate the magnetic components and total magnetic moments of the holmium and cobalt atoms.
The team proposed that the negative thermal expansion of the lattice plays a critical role in generating high-density, spontaneous magnetic biskyrmions within the ferrimagnet compound. They compared the outcomes with another compound containing iron that exhibits positive thermal expansion. Interestingly, they did not observe any skyrmions in the iron-containing compound, highlighting the correlation between lattice expansion and the presence of stable biskyrmions in the holmium-cobalt system.
The researchers confirmed the existence of stable biskyrmions across a wide temperature range without the application of a magnetic field. By characterizing the lattice negative thermal expansion and comparing it with positive thermal expansion in a different compound, they verified the correlation between negative thermal expansion and the gradual increase of biskyrmions with decreasing temperatures. This observation further supports the hypothesis that negative thermal expansion enables the stabilization of high-density biskyrmions in the rare earth magnet.
This ground-breaking research opens up new possibilities for the generation and stabilization of spontaneous biskyrmions in ferrimagnet compounds. As these biskyrmions exhibit high densities and remain stable throughout a wide temperature range, they hold great potential for applications in spintronics. The ability to form biskyrmions without the need for external magnetic fields expands the practicality and versatility of these topologically protected quasiparticles.
Yuzhu Song and their team’s investigation into the negative thermal expansion of a lattice has led to exciting developments in the field of spintronics. By exploring the behavior of a rare earth magnet compound, they successfully generated high-density, spontaneous magnetic biskyrmions across a wide temperature range. This breakthrough has the potential to revolutionize the design and functionality of spintronic storage devices, paving the way for more efficient and compact systems. As researchers continue to explore the unique properties of magnetic skyrmions, further advancements are likely to emerge, opening up new opportunities for a wide range of applications in the future.
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