Slow spin relaxation induced by magnetic field in [NdCo(bpdo)(H₂O)₄(CN)₆].3H₂O

We report on a comprehensive investigation of the magnetic properties of [NdCo(bpdo)(Hsub₂O)₄(CN)₆] . 3H₂O (bpdo = 4, 4´-bipyridine-N,N´-dioxide) by use of electron paramagnetic resonance, magnetization, specific heat and susceptibility measurements. The studied material was identified as a magnet with an effective spin S D 1=2 and a weak exchange interaction J/k_B = 25 mK. The ac susceptibility studies conducted at audio frequencies and at temperatures from 1.8 to 9 K revealed that the application of a static magnetic field induces a slow spin relaxation. It is suggested that the relaxation in the magnetic field appears due to an Orbach-like process between the two lowest doublet energy states of the magnetic Nd³⁺ ion. The appearance of the slow relaxation in a magnetic field cannot be associated with a resonant phonon trapping. The obtained results suggest that the relaxation is influenced by nuclear spin driven quantum tunnelling which is suppressed by external magnetic field.