Magnetic relaxation in organic-based magnets

Spin glasses are magnetic systems with random, frustrated magnetic interactions. The result of this frustration is that these materials possess no true long range order, but rather have a “freezing transition” to a state which appears ordered on observable time scales. This frustration induces many complicated magnetic phenomena, including frequency dependence of the ac susceptibility and dc magnetic relaxation on an experimentally observable time scale.; This dissertation addresses the nature of magnetic relaxation observed in the organic-based magnet [MnTPP]+[TCNE]−· y(solvent). This material forms linear chains of alternating electron donor ([MnTPP]) and acceptor ([TCNE]) pairs with large interchain spacing. The low dimension of the structure enables this system to serve as an experimental platform for testing spin glass theory.; Relaxation and spin glass behavior was investigated in [MnTPP] +[TCNE]−·2(1,3-C₆H₄Cl ₂) by incorporating both ac and do magnetic measurements. A scaling analysis of the ac susceptibility reveals a spin glass transition at 4.1 K. The thermoremanent magnetization exhibits long time relaxation above this temperature. The effects of relaxation on magnetic reversal were examined via time dependent magnetic measurements.; The results of these measurements were analyzed using a fractal cluster model for spin glasses. This model provided a method for obtaining a physical interpretation of the results of the relaxation data. Through an extension of this model, the fractal dimension of the spin clusters was obtained. The value for the spin cluster dimension ranged from ∼0.8 to over 1.5 as the glass transition temperature is approached. These results suggest a picture of anisotropic spin clusters as the mechanism for magnetic ordering in [MnTPP] +[TCNE]−·y(solvent).