Limits for extending the coherence lifetime in force detected NMR spectroscopy are explored using time suspension pulse sequences based on the “magic echo.” Two micron-sized single crystals of $\mathrm{K}\mathrm{P}{\mathrm{F}}_6$ and ${\left(\mathrm{N}{\mathrm{H}}_4\right)}_2\mathrm{S}{\mathrm{O}}_4$ were used for demonstration, where a typical experiment measured signals of $\sim {10}^{14}$ spins from a $\sim 0.8\mu \mathrm{m}$ wide imaging slice. By studying the decay of the dipolar echo maximum it is demonstrated that spectral linewidths of $1.1\mathrm{kHz}$ collected from a $100\mathrm{kHz}$ wide frequency slice can be obtained, extending the coherence lifetime for both samples by an order of magnitude.

• Received 22 May 2006

DOI:https://doi.org/10.1103/PhysRevB.74.104414