Spin echo measurements at an avoided crossing in the molecular nanomagnet Cr₇Mn

We report spin echo measurements of spin relaxation times in dilute samples of the spin S = 1 molecular nanomagnet [(CH₃)₂NH₂][C₇MnF₈((CH₃)₃CCOO)₁₆] ("Cr₇Mn") in the vicinity of an avoided crossing. Our samples are diluted by co-crystallizing Cr₇Mn with Ga₇Zn, a diamagnetic isostructural analogue. By coupling samples to a loop-gap resonator (LGR), we use a custom FPGA-based pulsed electron-spin resonance (ESR) spectrometer to perform parallel-mode spin echo experiments. With the resonant frequency of the LGR tuned to the tunnel splitting of Cr₇Mn, ~4 GHz, we observe a clear spin echo signal near zero field, which decreases at higher fields. From this signal, we measure both T₁ and T₂, finding that T₁ ~ 300 μs and T₂ ~ 180 ns for a 0.5% sample at zero field. Surpisingly, our measured T₂ values do not depend strongly on dilution. We will also present data on the field dependence of relaxation times.