Nonlinear magnetic susceptibility of molecular magnets: Tunneling of high-spin molecules

The magnetic susceptibility of high-spin molecules CrNi₆(S=15/2) and CrMn₆(S=27/2) has been measured at high frequency (680 MHz), in a magnetic field (up to 5 T), and at low temperature (down to 18 mK). A large decrease of the imaginary part of the susceptibility with increasing electromagnetic power is observed. This nonlinear effect is attributed to tunneling of the high-spin molecules between the two states |±S〉 of the ground doublet across the anisotropy-energy barrier.