Speaker
Mr
Solomon Akaraka Owerre
(University of Montreal)
Description
We study the phase transition of the escape rate of exchange-coupled dimer
of single-molecule magnets which are coupled either ferromagnetically or antiferromagnetically in a staggered magnetic field and an easy $z$-axis anisotropy. The Hamiltonian for this system has been used to study dimeric molecular nanomagnet [Mn$_4$]$_2$ which is comprised of two single molecule magnets coupled antiferromagnetically. We generalize the method of mapping a single-molecule magnetic spin problem onto a quantum-mechanical particle to dimeric molecular nanomagnets. The problem is mapped to a single particle quantum-mechanical
Hamiltonian in terms of the relative coordinate and a coordinate dependent reduced mass. It is shown that the presence of the external staggered magnetic field creates a phase boundary separating the first- from the second-order transition. With the set of parameters used by R. Tiron, $\textit{et al}$ , \prl {\bf 91}, 227203 (2003), and S. Hill, $\textit{et al}$ science {\bf 302}, 1015 (2003) to fit experimental data for [Mn$_{4}$]$_2$ dimer we find that the critical temperature at the phase boundary is $T^{(c)}_0 =0.29K$. Therefore, thermally activated transitions should occur for temperatures greater than $T^{(c)}_0$.
Author
Mr
Solomon Akaraka Owerre
(University of Montreal)
Co-author
Manu Paranjape
(Université de Montréal)
