The field sweep rate $(v=dH/dt)$ and temperature $(T)$ dependence of the magnetization reversal of a single-chain magnet is studied at low temperatures. As expected for a thermally activated process, the nucleation field ($H_{\mathrm{n}}$) increases with decreasing $T$ and increasing $v$. The set of $H_{\mathrm{n}}(T,v)$ data is analyzed with a model of thermally activated nucleation of magnetization reversal. Below 1 K, $H_{\mathrm{n}}$ becomes temperature independent but remains strongly sweep rate dependent. In this temperature range, the reversal of the magnetization is induced by a quantum nucleation of a domain wall that then propagates due to the applied field.

• Received 12 September 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.237203