Finite size effect and dimensional crossover in antiferromagnetic epitaxial Cr2O3 thin films

We explore the finite size effect on the Néel temperature (TN) and the dimensional crossover in the antiferromagnetic epitaxial Cr2O3 thin films. TN and the critical exponent (β) were experimentally determined based on the temperature dependent anomalous Hall effect (AHE) emerging at the Pt/Cr2O3 interface. TN decreases with decreasing Cr2O3 thickness: ~285 K above 40 nm and ~240 K at 5.2 nm. The decrease of TN is prominent below 15 nm, and it is accompanied with the decrease of β Above 40 nm, β is about 0.325 (3D Ising model), and decreases about 0.25 around 15 nm, 0.125 (2D Ising model) below 10 nm. The thickness regime for the finite-size effects to emerge is higher than the reported cases of metallic ferromagnets probably because of the long-range exchange interactions between Cr³⁺ spins in Cr2O3.