Quantum spin coherence in halogen-modified ${\mathrm{Cr}}_7\text{Ni}$ molecular nanomagnets

Among the factors determining the quantum coherence of the spin in molecular magnets are the presence and the nature of nuclear spins in the molecule. We have explored modifying the nuclear-spin environment in ${\mathrm{Cr}}_7\mathrm{Ni}$-based molecular nanomagnets by replacing hydrogen atoms with deuterium or the halogen atoms, fluorine or chlorine. We find that the spin coherence, studied at low temperatures by pulsed electron-spin resonance, is modified by a range of factors, including nuclear spin and magnetic moment, changes in dynamics owing to nuclear mass, and molecular morphology changes.

Figure 1

Structures of the ${\mathrm{Cr}}_7\mathrm{Ni}$ molecules. (a) Structure of $\mathrm{Cs[}{\mathrm{Cr}}_7{\mathrm{NiF}}_8{\mathrm{Ac}}_{16}\text{]}$. The colored balls represent either different atom types—Cr (light green), Ni (dark green), and F (yellow)—or different interchangeable substituents—a central templating cation (blue) and carboxylate bridging ligand (red). Hydrogen atoms have been omitted for clarity. (b) Appropriately color coded chemical structures of some possible variants with abbreviated names.

Figure 2

Magnetic susceptibility ${\chi }_{\mathrm{m}}$ as a function of temperature $T$ for compounds templated around a ${\mathrm{Pr}}_2{\mathrm{NH}}_2^{+}$ cation.

Figure 3

Echo decay curves (black points) with the relevant fits (red line), for the $h$-Ben compound templated around a ${\mathrm{Pr}}_2{\mathrm{NH}}_2^{+}$ cation, at temperature $T=4$ K.

Figure 4

Phase memory time $T_{\mathrm{m}}$ and stretch parameter $x$ for compounds templated around a ${\mathrm{Pr}}_2{\mathrm{NH}}_2^{+}$ cation. Error bars from the fit are omitted as these were on the order of the marker size.

Figure 5

Phase memory time $T_{\mathrm{m}}$ and stretch parameter $x$ for compounds templated around a ${\mathrm{Cs}}^{+}$ cation. Error bars from the fit are omitted as these were on the order of the marker size.