Piezomagnetism in Epitaxial Cr$_{2}$O$_{3}$ Thin Films

Recently, the magnetoelectric material Cr$_{2}$O$_{3}$ attracted renewed interest due to its potential for future spintronics applications which can be realized by novel magnetic thin film heterostructures [1]. Here we study thin films of Cr$_{2}$O$_{3}$ (111) on c-Al$_{2}$O$_{3}$ (111) substrate which are grown by thermal evaporation of Cr metal in an O$_{2}$ atmosphere. X-ray diffraction data reveal stoichiometric epitaxially grown Cr$_{2}$O$_{3}$ (111) films. Owing to a lattice mismatch of $\sim $4{\%} at the interface between the Al$_{2}$O$_{3 }$substrate and the film we observe a strong stress induced piezomagnetic moment in the Cr$_{2}$O$_{3}$ film. We measure the temperature dependence of this piezomoment by Superconducting Quantum Interference Device (SQUID) magnetometry and Kerr rotation. The presence of high inherent stress, a significant piezomagnetic moment and the possibility to realize high electric fields makes our Cr$_{2}$O$_{3}$ thin films ideal candidates for the challenging quest of the symmetry allowed but hitherto undiscovered piezomagnetoelectric effect. [1] Ch. Binek, B. Doudin, J. Phys. Condens. Matter\textbf{ 17}, L39 (2005). \newline