Disk chopper time-of-flight spectrometer

Molecular spin cluster V15 under magnetic field

The molecular spin cluster V15 is a polyoxovanadate with 15 one half spins but total spin ground state S=1/2 due to strong antiferromagnetic (AFM) interactions. Below 1K, the relaxation of the magnetisation exhibits a very peculiar behaviour called ˝butterfly˝ hysteresis and the ground state is composed of two non-degenerate S=1/2 Kramers doublets with a gap 2Δ0 ≈ 30 µeV.
The experiment, performed on the upgraded IN5 multi-chopper spectrometer using a dilution fridge (T = 45 mK) and a cryomagnet with magnetic fields up to 1 Tesla, allowed us to completely elucidate the mechanism leading to this zero-field split ground state (see Fig.).

Ref.: Mechanism of ground state selection in the frustrated molecular spin cluster V15,
G. Chaboussant, S. T. Ochsenbein, A. Sieber, H. U. Güdel, H. Mutka, A. Müller and B. Barbara, Europhys. Lett., 66 (3), pp. 423–429 (2004)