Layer- and Field-Dependent Magnetic Order in 2D CrSBr Revealed by Pulsed Nanocalorimetry
Understanding the evolution of magnetic order in the two-dimensional limit remains a central challenge in van der Waals magnets, where thermodynamic measurements are constrained by the femtogram-scale mass of exfoliated flakes. Here, microsecond pulse-heating nanocalorimetry is used to measure the heat capacity and magnetic entropy of CrSBr flakes down to the monolayer limit. The measurements reveal the entropy landscape associated with magnetic ordering, uncovering a decreasing interlayer transition temperature toward the monolayer limit and an entropy-derived effective moment per layer that increases with thickness toward the expected spin-only scale. Thermodynamic anomalies capture a crossover from bulk-like interlayer antiferromagnetism to a regime dominated by intralayer ferromagnetic correlations. A pronounced layer-parity effect further emerges, with odd-layer samples displaying an additional high-temperature contribution associated with uncompensated magnetic layers. Under in-plane magnetic fields applied along the easy axis, antiferromagnetic order is progressively suppressed, allowing extraction of a thickness-dependent characteristic suppression field reflecting weakened interlayer exchange coupling. Entropy analysis further reveals an extended regime of magnetic fluctuations persisting well above the interlayer ordering transition. Together, these results establish nanocalorimetry as a powerful thermodynamic probe of low-dimensional magnetism, providing direct access to magnetic entropy, exchange interactions, and dimensional crossover in atomically thin van der Waals magnets.