Spins in molecular magnets can experience both anisotropic exchange interactions and on-site magnetic anisotropy. In this paper, we study the effect of exchange anisotropy on the molecular magnetic anisotropy both with and without on-site anisotropy. When both the anisotropies are small, we find that the axial anisotropy parameter $D_M$ in the effective spin Hamiltonian is the sum of the individual contributions due to exchange and on-site anisotropies. We find that even for axial anisotropy of about $15\%$, the low-energy spectrum does not correspond to a single-parent spin manifold but has intruder states arising from other parent spins. In this case, the low-energy spectrum cannot be described by multiplet states arising from a single approximate total spin state. We study the magnetic susceptibility, specific heat as a function of temperature, and magnetization as a function of applied field to characterize the system in this limit. We find that there is synergy between the two anisotropies, particularly for large systems with higher site spins.

• Received 18 June 2018
• Revised 6 November 2018

DOI:https://doi.org/10.1103/PhysRevB.98.214409