Altermagnetic bulk and topological surface magnetizations for CrSb single crystals

We experimentally investigate the angle dependence of magnetization $M(α)$ for single crystals of CrSb. CrSb belongs to a new class of altermagnetic materials, the small net magnetization is accompanied by alternating spin splitting in the k-space. In addition, CrSb reveals also topological features with Weyl surface states originating from bulk band topology. We observe, that $M(α)$ oscillates around zero value, so magnetization is positive for $M(α)$ maxima and it is negative for $M(α)$ minima. The magnetization reversal curves $M(H)$ are non-linear with low-field hysteresis, but with almost linear high-field branches. The slope of the linear branches well correlates with $M(α)$ oscillations, so it is positive for $M(α)$ maxima and negative for $M(α)$ minima. We demonstrate, that the interplay between the positive and the negative $M(H)$ slopes originates from several magnetic phases in CrSb. In particular, current-carrying topological surface states are responsible for the diamagnetic-like $M(H)$ negative slope, which dominates for the directions of full spin compensation in the bulk CrSb altermagnetic spectrum. Due to the spin-momentum locking, topological surface states are spin-polarized, which is responsible for the low-field hysteresis. Thus, we experimentally demonstrate both the altermagnetic bulk and the topological surface magnetizations for the altermagnetic candidate CrSb.

💡 Research Summary

This research provides a definitive experimental demonstration of the coexistence and interplay between altermagnetic bulk properties and topological surface magnetizations in CrSb single crystals. Altermagnetism represents a newly identified class of magnetism where, despite a negligible net magnetization, a significant spin splitting occurs in k-space due to broken spin-rotation symmetry. The study focuses on characterizing how these intrinsic bulk properties interact with the topological features, specifically the Weyl surface states, which emerge from the bulk band topology of CrSb.

The experimental investigation primarily examines the angular dependence of magnetization, $M(\alpha)$. The researchers observed that the magnetization oscillates around a zero value, exhibiting positive values at $M(\alpha)$ maxima and negative values at $M(\alpha)$ minima. This periodic oscillation is a direct consequence of the alternating spin-splitting characteristic of altermagnetic materials. Furthermore, the study delves into the magnetization-field curves, $M(H)$, revealing a complex non-linear behavior. While the low-field regime exhibits hysteresis, the high-field branches transition into an almost linear regime. Crucially, the slope of these linear branches correlates precisely with the $M(\alpha)$ oscillations: the slope is positive during $M(\alpha)$ maxima and negative during $M(\alpha)$ minima.

The core of the scientific contribution lies in identifying the physical origin of these varying $M(H)$ slopes. The researchers demonstrated that the interplay between positive and negative slopes arises from distinct magnetic phases within the crystal. Specifically, the negative, diamagnetic-like slope in the $M(H)$ curves is attributed to the contribution of current-carrying topological surface states. This effect becomes particularly dominant in directions where the bulk altermagnetic spectrum achieves full spin compensation. Additionally, the low-field hysteresis is explained by the spin-momentum locking inherent in the topological surface states, which induces spin polarization in these states.

In conclusion, this work successfully validates CrSb as a prime candidate for studying altermagnetism. By proving that the magnetic response is a composite of the altermagnetic bulk and the topological surface, the study opens new avenues for the development of advanced spintronic devices that can leverage both the spin-splitting of altermagnets and the spin-polarized nature of topological surface states for high-efficiency information processing.