Static, dynamic, and tunneling fingerprints of antiferromagnetism in layered NiCl 2

The recent surge of interest in magnetism in van der Waals (vdW) crystals has opened opportunities for exploring antiferromagnetic order and spin dynamics in the two-dimensional limit. Here, we present a comprehensive study of the layered antiferromagnetic NiCl2, combining static magnetization, broadband microwave absorption spectroscopy, and tunneling transport measurements. Despite early studies of bulk NiCl2, our systematic approach provides a modern reexamination of its magnetic properties with several new insights. We find nearly identical in-plane and out-of-plane saturation fields once demagnetization corrections are applied, as well as a pronounced spin-flop transition at low fields. The Néel transition temperature (N) shows minimal anisotropy at low fields but undergoes a distinct crossover between in-plane and out-of-plane field orientations at high fields. Spin resonance experiments reveal strongly anisotropic behavior: robust in-plane antiferromagnetic resonance modes are observed over a broad gigahertz frequency and temperature range, while out-of-plane measurements show suppressed response near N. This enables the extraction of the effective factor across a wide temperature window. Furthermore, tunneling magnetoconductance through a thin NiCl2 flake barrier exhibits field-enhanced transmission with clear signatures of the spin-flop and saturation fields. Our findings establish NiCl2 as a model vdW antiferromagnet for studying the interplay of static order, spin dynamics, and tunneling transport, highlighting its potential for future applications in two-dimensional spintronics. © 2026 American Physical Society