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Ferromagnetic hysteresis and aftereffect in polycrystalline TDAE-C60

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5 Author(s)
Dunsch, L. ; Institut für Festkörper-und Werkstofforschung Dresden, 01171 Dresden, Germany ; Eckert, D. ; Frohner, J. ; Bartl, A.
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The microscopic origin of ferromagnetic ordering as well as the existence of hysteresis in TDAE-C60 are contradictorily discussed in the literature. At 1.7 K the zero-field magnetization, M(0), extrapolated from the demagnetization curve of a TDAE-C60 powder, is only a small fraction of the saturation magnetization Ms≈1.2 A m2/kg (or emu/g) measured at a field of 4 MA/m. The small value of M(0)/Ms may be due to (i) a large amount of small superparamagnetic particles and/or (ii) alignment of a canted magnetic structure at high field. After leaving TDAE-C60 powder in a sealed quartz tube with He for eight weeks this ratio increased from about 8% to 65% but Ms remained unchanged. This observation points to agglomeration of superparamagnetic clusters increasing the contribution to the ferromagnetic behavior. Typical extrinsic magnetic quantities describing a ferromagnetic material, such as remanence Mr, coercivity JHc and viscosity S, have also been measured. For temperatures 10, 5, and 1.7 K typical values of Mr and JHc are 30, 90, 200 μT, and 50, 110, and 200 A/m, respectively. The values of coercivity have the order of magnitude of those of low-carbon steel (at room temperature). After leaving a pressed TDAE-C60 sample in a sealed quartz tube with He for six weeks Mr increased and JHc decreased, both by about 30%. The samples show a logarithmic time-dependence of magnetization ΔM=-S ln(1+t/t0) with large values of the viscosity S. In the remanent state (at H=0) the measured values of S/Mr are 0.025, 0- .021, and 0.019 for T=10, 5, and 2.5 K, respectively. © 1997 American Institute of Physics.

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Journal of Applied Physics  (Volume:81 ,  Issue: 8 )