Finite-Size Scaling Effects in Chromia thin films

Controlling magnetism by electrical means remains a key challenge in the area of spintronics. The use of magnetoelectrically active materials is one of the most promising approaches to this problem. Utilizing Cr$_2$O$_3$ as the magnetoelectric pinning layer in a magnetic heterostructure both temperature assisted and isothermal electrical control of exchange bias have been achieved [1,2]. Interestingly, this ME switching of exchange bias has only been achieved using bulk Cr$_2$O$_3$ crystals, isothermal switching of exchange bias using thin film chromia remains elusive. We investigate the origin of unusually pronounced finite-size scaling effects on the properties of Cr$_2$O$_3$ grown by Molecular Beam Epitaxy; in particular we focus on the different temperature dependencies of the magnetic susceptibility of bulk vs. thin film chromia, the change in N\`{e}el temperatures, and the implications for the magneto electric properties of chromia thin films. \\[4pt] [1] P. Borisov et al., Phys. Rev. Lett. 94, 117203 (2005).\\[0pt] [2] X. He et al., Nature Mater. 9, 579 (2010).