High-frequency magnetic spectroscopy on the molecular magnetic cluster V15

A novel type of high-frequency magnetic resonance spectroscopy was used to investigate magnetic excitations of the molecular magnetic cluster V15 in the frequency range from 1.5 cm−1 to 10 cm−1, at low temperatures, between 2.5 K and 30 K. In the optical transmission spectra, we observed absorption lines over a wide range of magnetic fields up to 6.5 T, which correspond to the Zeeman splitting of the low-lying spin states. Our frequency-domain technique, and advanced data analysis allow accurate determination of the principal values of the anisotropic g tensor, and other mode parameters, even for powder samples. The g values were obtained as g∥c = 1.981 ± 0.003 and g⊥c = 1.953 ± 0.003, while the intrinsic linewidth was found to be Δν = 0.02–0.035 cm−1 (210–370 Oe). The temperature dependence of Δμ, the mode contribution to the magnetic permeability, is in good agreement with theory.