Magnetic moment fluctuation temperature

Fig. 5.28 The 4/ shell of each Gd atom carries a local magnetic moment which remains constant with temperature. The relative axes of these magnetic moments fluctuate with rising temperature. This behavior can be modeled by spin waves being characterized by the angle a between nearest neighbors. From [127], copyright 1998, reproduced with permission from World Scientific Publishing Co. Pte. Ltd...

SF magnetic spin fluctuation temperature A exp experimental magnetic moment... 

At temperatures much higher than T,t, the temporal fluctuations of the magnetic moment are slow compared to thermal fluctuations, and the susceptibility is expected to be strongly temperature dependent, behaving like a Curie-Weiss law with a Curie-Weiss temperature of the order of Tsf. At temperatures much lower than Tsf, the intrinsic magnetic moment fluctuations are rapid compared to thermal fluctuations, and the resultant dynamical magnetic moment averages to zero over the timescale of interest so that the susceptibility approaches a constant value in the limit T- 0. In this model, anomalies in other... 

With the decrease in temperature, the SPR spectra of the sol-gel silica glasses undergo a shift towards lower magnetic fields with a marked broadening. Such behaviour is well described in the framework of a theoretical model based on the Landau-Lifshitz damped precession equation and an appropriate linewidth expression taking into account low-temperature freezing of the fluctuations of orientations of the magnetic moments. 

Two possibilities are considered for the discrepancy in the amount of the magnetic moment. One is as follows since the observing time of the NMR signal is longer than that of the neutron diffraction, it is considered that rapid spin fluctuations do not contribute to the static moment in NMR experiment. The other possibility is ascribed to a field induced phase transition. In ref. [4] it is reported from the ESR experiment that a phase transition occurs around the applied field of 0.05 T in the temperature region between Tn and T. Since the NMR experiment was performed in an applied field of 0.5 T, the magnetic phase is different from that of the neutron diffraction experiment that was carried at zero magnetic field. 

At this point we want to stress that the heavy fermion systems (22) are related to a very large spin enhanced susceptibility or localized magnetic moments, very narrow bands of elementary excitations at the Fermi level, and a new type of pairing, in the case where they become superconducting, at low temperatures even if they were spin fluctuators above the critical superconducting transition temperature Tg. 

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