Qualitative comparison of the thermodynamics of Mn12-ac and Fe8 molecule magnets for dβ ~ 0.031

Abstract

The magnetization and the specific heat of two single molecule magnets (SMM) with spin-10, Mn12-ac and Fe8, are compared for Dβ ~ 0.031. The rhombic term in the Fe8 molecule makes the x-component of its magnetization to be larger than that of the Mn12-ac molecule. The axial symmetry of the Mn12-ac favors the z-component of its magnetization, in comparison to the Fe8 molecule. For T ≳ 18 K, the specific heat of the Mn12-ac is large (80%, at most) than that of the Fe8, at the same temperature. The corrections from the S = 9 excited states of these SMM's do not invalidate our results. An unexpected result occurs when the angle between the easy-axis and the external magnetic field equals π/4: the aforementioned percentage difference of the specific heat reaches 3% for D β ≲ 0.025 and h/k ∈[1.93, 2.04], when they are compared at distinct temperatures . This small percentage difference also happens for the average specific heat of both SMM's at those temperatures and h/DMn ∈ [1.97, 2.1].