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

We explore the finite size effect on the Néel temperature (T N ) and the dimensional crossover in the antiferromagnetic epitaxial Cr 2 O 3 thin films. T N and the critical exponent (β) were experimentally determined based on the temperature dependent anomalous Hall effect (AHE) emerging at the Pt/Cr 2 O 3 interface. T N decreases with decreasing Cr 2 O 3 thickness: ~285 K above 40 nm and ~240 K at 5.2 nm. The decrease of T N 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 Cr ³⁺ spins in Cr 2 O 3 .