Electron spin coherence in antiferromagnetically coupled binuclear Mn complexes

We report a pulse electron spin resonance study of binuclear Mn molecular complexes whose magnetic properties are controlled by the ligand substitution. An electron spin echo in these complexes in the solid phase and also diluted in a frozen solution matrix was detected, and the spin decoherence time $T_2$ of Mn spins at different temperatures was determined. We observe a simple exponential $T_2$ relaxation in the latter samples and a nonexponential relaxation process in the former ones. The data analysis establishes the hyperfine coupling to the protons as an important source of the electron spin decoherence. Furthermore, the data clearly suggest an important role of the intermolecular spin-spin coupling for the $T_2$ relaxation. The influence of both mechanisms should be considered as limiting factors for coherent spin manipulation in molecular magnets with regard to their possible application for quantum computing.

Figure 1

Unit cell of the binuclear Mn complex 1. The substituted peripheral ligand L is encircled by the dashed oval.

Figure 2

The intensity of the primary electron spin echo $V\left(\tau \right)$ vs the delay time $\tau$ measured on the powder samples at $T=6$ K, symbols, and fits to the nonexponential decay function, lines (see the text). The presentation of $V\left(\tau \right)$ on the $\log$-scale vs $\sqrt{\tau }$ for complex 2 at 6 and 80 K is shown in the inset.

Figure 3

The intensity of the primary electron spin echo vs the time delay $\tau$ observed in the frozen solutions of the complexes 1 – 3 at $T=6$ and 80 K. Inset: The presentation on the $\log$-scale visualizes a single characteristic decay time $T_2$.

Figure 4

The electron spin echo envelope modulation (ESEEM) observed on complex 1 in the powder form and in a frozen solution at $T=6$ K using the primary echo sequence. The period of the modulation corresponds to the proton Larmor frequency ${\nu }_{{}^1\mathrm{H}}$ (see text).