Dynamic magnetic crossover at the origin of the hidden-order in van der Waals antiferromagnet CrSBr.

López-Paz, Sara A; Guguchia, Zurab; Pomjakushin, Vladimir Y; Witteveen, Catherine; Cervellino, Antonio; Luetkens, Hubertus; Casati, Nicola; Morpurgo, Alberto F et al. · Nat Commun · 2022

basic_science · Level V

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Abstract

The van-der-Waals material CrSBr stands out as a promising two-dimensional magnet. Here, we report on its detailed magnetic and structural characteristics. We evidence that it undergoes a transition to an A-type antiferromagnetic state below TN ≈ 140 K with a pronounced two-dimensional character, preceded by ferromagnetic correlations within the monolayers. Furthermore, we unravel the low-temperature hidden-order within the long-range magnetically-ordered state. We find that it is associated to a slowing down of the magnetic fluctuations, accompanied by a continuous reorientation of the internal field. These take place upon cooling below Ts ≈ 100 K, until a spin freezing process occurs at T* ≈ 40 K. We argue this complex behavior to reflect a crossover driven by the in-plane uniaxial anisotropy, which is ultimately caused by its mixed-anion character. Our findings reinforce CrSBr as an important candidate for devices in the emergent field of two-dimensional magnetic materials.