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Tunneling States in Pt2C60 Assigned by Magnetic Relaxation Measurements

Marcelo H. Herbst,Nelson M. Pinhal,N.V. Vugman,Cláudio José Magon,A. J. C. Filho-2007-01-01
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TL;DRAbstract

Electron spin-lattice relaxation times for Pt2C60, an amorphous solid showing paramagnetic centers distributed randomly over ca. 1% of fullerene molecules, were measured in the 7 – 100K temperature range. Attempts to fit the whole data to a Raman process were unsuccessful. We therefore invoke a more general frequency dependence in the form of a power law, where Raman rate varies with T as 1/T1Raman ∝ T . This affords α = 0.60 for the low temperature data. Above 75K we found an exponential factor of 3.9 ± 0.5. From the experimental exponents it is clear that, for sufficiently low temperatures, 1/T1 ∝ T , which supports a model where an ensemble of two-level systems (TLS) with a continuous distribution of energy splittings and potential barriers between the two levels, is responsible for the spin-lattice relaxation. On the other hand, at temperatures above ~ 75K the experimental data show a curvature. The spin-lattice relaxation rate increases quite sharply, suggesting activation of new

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Electron spin-lattice relaxation times for Pt2C60, an amorphous solid showing paramagnetic centers distributed randomly over ca. 1% of fullerene molecules, were measured in the 7 – 100K temperature range. Attempts to fit the whole data to a Raman process were unsuccessful. We therefore invoke a more general frequency dependence in the form of a power law, where Raman rate varies with T as 1/T1Raman ∝ T . This affords α = 0.60 for the low temperature data. Above 75K we found an exponential factor of 3.9 ± 0.5. From the experimental exponents it is clear that, for sufficiently low temperatures, 1/T1 ∝ T , which supports a model where an ensemble of two-level systems (TLS) with a continuous distribution of energy splittings and potential barriers between the two levels, is responsible for the spin-lattice relaxation. On the other hand, at temperatures above ~ 75K the experimental data show a curvature. The spin-lattice relaxation rate increases quite sharply, suggesting activation of new

Keywords

Amorphous solidCondensed matter physicsRelaxation (psychology)Raman spectroscopyAtmospheric temperature rangeLattice (music)Activation energyParamagnetism

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