Increase in Néel temperature in chromium oxide Cr2O3 subjected to severe shear stress

The effects of severe shear strain on the magneto-structure correlations of chromium oxide Cr2O3 were investigated. Shear stress was applied through high-pressure torsion (HPT) processing at a pressure of PHPT = 6 GPa. Through ac magnetization measurements, a maximum increase in the Néel temperature TN of Cr2O3 of approximately 30 K was observed in the HPT-processed sample for a revolution number of N = 1/2. This demonstrates the potential of HPT to expand the temperature stability range of antiferromagnetic order in Cr2O3. Analysis of the x-ray diffraction patterns of HPT-processed Cr2O3 revealed a special state of lattice expansion induced by shear strain within the unit cell. Direct exchange interactions originating from the overlapping of the Cr3+ ion orbitals and superexchange interactions involving the O2− ligands were examined using the variations in atomic distances and bonding angles. The increase in TN at a small N is attributed to enhanced antiferromagnetic interactions resulting from the decrease in the distance between the closest neighboring Cr3+ ions. By contrast, the reduction in TN observed at a higher N is explained by the modifications of the interchain interactions.