Magnetic Field Dependence of Spin Glass Free Energy Barriers

We measure the field dependence of spin glass free energy barriers in a thin amorphous Ge:Mn film through the time dependence of the magnetization. After the correlation length $\xi(t, T)$ has reached the film thickness $\mathcal {L}=155$~\AA~so that the dynamics are activated, we change the initial magnetic field by $\delta H$. In agreement with the scaling behavior exhibited in a companion Letter [Janus collaboration: M. Baity-Jesi {\it et al.}, Phys. Rev. Lett. {\bf 118}, 157202 (2017)], we find the activation energy is increased when $\delta H < 0$. The change is proportional to $(\delta H)^2$ with the addition of a small $(\delta H)^4$ term. The magnitude of the change of the spin glass free energy barriers is in near quantitative agreement with the prediction of a barrier model.