Lorentz electron microscopy methods for measuring nontrivial topological spin texture phenomena in real space

The transmission electron microscope (TEM) is a powerful tool to directly observe a material's atomic structure and electromagnetic properties. Lorentz TEM (LTEM) provides a field-free imaging mode and it was in this way that the first real space images of topological magnetic skyrmions and their antiparticles, antiskyrmions, were acquired [1,2]. Combining LTEM with external stimuli such as magnetic fields, heat, and electric/thermal currents allows the direct observation of a spin texture’s in-situ response. The ability to drive controlled transformations between different magnetic states including magnetic (anti)skyrmions is at the heart of many spintronics applications. Of these, controlled thermal current-driven transformations are especially desirable, as they enable the recycled use of heat lost in modern industrial energy cycles. Here, we review field-free TEM methods [3], demonstrate a thermal current-driven topological transformation between magnetic textures in the recently discovered antiskyrmion-host magnet (Fe_0.63Ni_0.3Pd_0.07)₃P and reveal that the antiskyrmions intrinsic to (Fe_0.63Ni_0.3Pd_0.07)₃P are hybrid topological strings composed of skyrmions on the surfaces and an antiskyrmion in the bulk using vector field electron tomography. Such topological complexity necessitates the existence of a Bloch point quadrupole, which we present in high resolution for the first time.

[1] X. Z. Yu, et al., Nature 465, 901 (2010).

[2] A. K. Nayak, et al., Nature 548, 561 (2017).

[3] D. V. Christensen et al., J. Phys. Mater. 7, 032501 (2024).