Dynamic Magnetic Crossover at the Origin of the Hidden-Order in van der Waals Antiferromagnet CrSBr

Abstract

The van der Waals material CrSBr stands out as a promising two-dimensional magnet. Especially, its high magnetic ordering temperature and versatile magneto-transport properties make CrSBr an important candidate for new devices in the emergent field of two-dimensional magnetic materials. To date, the magnetic and structural properties of CrSBr have not been fully elucidated. Here, we report on the detailed temperature-dependent magnetic and structural properties of this material, by comprehensively combining neutron scattering, muon spin relaxation spectroscopy, synchrotron X-ray diffraction, and magnetization measurements. We evidence that this material undergoes a transition to an A-type antiferromagnetic state below T N ≈ 140 K, with a pronounced two-dimensional character as deduced from the determined critical exponent of β ≈ 0.18. In our analysis of the field-induced metamagnetic transition, we find that the ferromagnetic correlations within the monolayers persist clearly above the Néel temperature in this material. Furthermore, we unravel the low-temperature (i.e. T < T N ) magnetic 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 magnetic field. These take place upon cooling below T s ≈ 100 K, until a spin freezing process occurs at T * ≈ 40 K. We argue this complex dynamic behavior to reflect a magnetic crossover driven by the in-plane uniaxial anisotropy, which is ultimately caused by the mixed-anion character of the material. Our findings indicate that the magnetic and structural properties of CrSBr widen its potential application as a component for spin-based electronic devices.

Spin Waves and Magnetic Exchange Hamiltonian in CrSBr

“…Thus we conclude, as did ref. [7], that the 30 K discontinuity is not associated with a change in the spatially-averaged 2 ) Bragg peak (which is smeared out in Q ⊥ due to crystal twinning) is shown. Above and near the phase transition, a streak of scattering along ℓ appears, signaling two-dimensional (2D) magnetic correlations.…”

“…The single crystal neutron diffraction is shown in Figure 2 and confirms the ground state magnetic order in ref. [7]: below a transition temperature of 132.3(6) K, new Bragg peaks appear at half-integer ℓ positions in accord with (00 1 2 ) magnetic order. In the Supporting Information, we refine the Bragg intensities and show they indicate A-type antiferromagnetism in Figure 1.…”

“…CrSBr forms in 2D layers of magnetic Cr 3 + ions forming a rectangular lattice, as shown in Figure 1. In bulk, it orders magnetically at T N = 132 K [5][6][7] with A-type antiferromagnetism: ferromagnetic planes DOI: 10.1002/advs.202202467 polarized along the b-axis, alternating in orientation for an overall antiferromagnetic (AFM) order, and becoming ferromagnetic (FM) in the monolayer limit. [8] This material is air-stable and has a semiconducting gap low enough to gate with realistic electric fields.…”