Flexomagnetism and vertically graded Néel temperature of antiferromagnetic Cr2O3 thin films

Abstract

Antiferromagnetic insulators are a prospective materials platform for magnonics, spin superfluidity, THz spintronics, and non-volatile data storage. A magnetomechanical coupling in antiferromagnets offers vast advantages in the control and manipulation of the primary order parameter yet remains largely unexplored. Here, we discover a new member in the family of flexoeffects in thin films of Cr₂O₃. We demonstrate that a gradient of mechanical strain can impact the magnetic phase transition resulting in the distribution of the Néel temperature along the thickness of a 50-nm-thick film. The inhomogeneous reduction of the antiferromagnetic order parameter induces a flexomagnetic coefficient of about 15 μ_B nm^-2. The antiferromagnetic ordering in the inhomogeneously strained films can persist up to 100 °C, rendering Cr₂O₃ relevant for industrial electronics applications. Strain gradient in Cr₂O₃ thin films enables fundamental research on magnetomechanics and thermodynamics of antiferromagnetic solitons, spin waves and artificial spin ice systems in magnetic materials with continuously graded parameters.