Thermal stability of holmium single atom magnets in a magnetic field*

The size of a stable magnetic bit has recently reached the atomic limit, which raised questions about the thermal stability and the means to control magnetic information. Using the example of holmium single atom magnets on magnesium oxide (MgO), we show magnetic bistability up to 35 K and reveal a coercive field of more than 8 T at that temperature. Our scanning tunneling microscopy study finds a spontaneous magnetization reversal at about 45 K and 8 T. We estimate the transverse magnetic anisotropy energy from magnetic field and bias voltage dependent switching of Ho atoms at 4.3 K and constrain the Ho/MgO ground state to either J_z = 7 or 8, both compatible with magnetic bistability at magnetic fields larger than 10 mT.