Tuning the effective anisotropy in a voltage-susceptible exchange bias heterosystem*

Voltage and temperature tuned ferromagnetic hysteresis is investigated by SQUID and Kerr-magnetometry in a thin film heterostructure of a perpendicular anisotropic Co/Pd ferromagnet exchange coupled to the magnetoelectric antiferromagnet $Cr_{2}O_{3}$. An abrupt disappearance of exchange bias with a simultaneous more than two-fold increase in coercivity is observed and interpreted as a competition between the effective anisotropy of $Cr_{2}O_{3}$ and the exchange coupling energy between boundary magnetization and the adjacent ferromagnet. The effective anisotropy energy is given by the intrinsic anisotropy energy density multiplied by the effective volume separated from the bulk through a horizontal antiferromagnetic domain boundary. Kerr measurements show that the anisotropy of the interfacial $Cr_{2}O_{3}$ can be tuned, isothermally, and in the absence of an external magnetic field, by application of an electric field. A generalized Meiklejohn-Bean model accounts for the change in exchange bias and coercivity as well as the asymmetric evolution of the hysteresis loop. In support of this model, the reversal of the boundary magnetization is experimentally confirmed as a contribution to the magnetic hysteresis loop.