Magnetic blocking from exchange interactions: slow relaxation of the magnetization and hysteresis loop observed in a dysprosium-nitronyl nitroxide chain compound with an antiferromagnetic ground state.

2013 
The combination of the ani- sotropic Dy III ion and organic radicals as spin carriers results in discrete and one-dimensional lanthanide-radical magnetic materials, namely, (Dy- A3(NITThienPh)2 )( 1) and (Dy2- A6(NITThienPh)2)n (2; hfac = hexa- fluoroacetylacetonate, NITThienPh = 2- (5-phenyl-2-thienyl)-4,4,5,5-tetrameth- yl-imidazoline-1-oxyl-3-oxide). Linking monomeric 1 with the Dy III ion leads to the formation of polymeric 2, and the transformation between them is chemically controllable and reversible. The characterization of both static and dynamic magnetic properties shows that the dominant intrachain exchange interaction is important to observe magnetic bistability in 2 rather than that in 1. Monomeric 1 exhibits para- magnetic behavior, whereas polymeric 2 shows the unusual coexistence of su- perparamagnetic and two-step field-in- duced metamagnetic behaviors. The antiferromagnetic ground state of 2 does not prevent the dynamic relaxa- tion of the magnetization with the finite-sized effect in the lanthanide- radical system. Energy barriers to ther- mally activated relaxation for 2 are 53 and 98 K in the low- and high-tempera- ture regimes, respectively. A hysteresis loop is observed with the coercive field of 99 Oe at 2 K.
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