Slow Magnetic Relaxation in Weak Easy-Plane Anisotropy: the Case of a Combined Magnetic and HFEPR Study.

Two pseudotetrahedral cobalt(II) complexes exhibiting slow magnetic relaxation under an applied direct-current field are investigated. The weak easy-plane anisotropy is accurately determined by high-field/high-frequency electron paramagnetic resonance spectroscopy as D = 2.57 cm-1 and E = 0.82 cm-1 for 1 and D = 5.56 cm-1 and E = 1.05 cm-1 for 2. In addition, hysteresis loops are observed for the two compounds at very low temperatures.