Anomalous relaxation in a quasi-one-dimensional fractal cluster glass

The low-temperature spin glass state of the quasi-1D organic-based magnet [MnTPP]+[TCNE]- .x(1,3-C6H4Cl2) has unusually long relaxation times due to frustration induced by dipole-dipole interactions between fractal spin clusters. This long relaxation is investigated with in-field relaxation measurements. The extremely long relaxation process enables probing of time-dependent phenomena using conventional magnetic measurements, including sweep rate-dependent hysteresis curves, even for temperatures well above the spin glass transition temperature (Tg). For a temperature of (-)1.3Tg, the coercive field increased by 170% for differing sweep rates, while below Tg the change was less than 5%. A study of the temperature dependence of the coercive field reveals detailed information on the behavior of fractal spin clusters within the system. For temperatures above Tg, the largely single-chain spin clusters act independently during magnetic reversal. As the spin clusters branch out below Tg, magnetic reversal is more cooperative, reflecting an enhancement of the magnetic interaction in the interpenetrating fractal cluster system.