Spin-flip temperature

Figure 7 Relative change of electrical resistivity during isothermal aging condition with falling and rising temperatures obtained by PPM calculations [25, 33] without (a) and with (b) incorporating thermal activation process in the spin flip probability 6. The assumed temperature dependency of 6 is indicated in figure c.

For paramagnetic spin systems, there are two major processes of relaxation (55). One relaxation mode involves spin-flipping accompanied by lattice phonon creation and/or annihilation (spin-lattice relaxation), and the other mode is due to the mutual flipping of neighboring spins such that equilibrium between the spins is maintained (spin-spin relaxation). For the former mode of relaxation, th decreases with increasing temperature, and the latter relaxation mode, while in certain cases temperature dependent, becomes more important (th decreases) as the concentration of spins increases. 

The physical role of the ua terms is clear at low temperatures they forbid processes in which charge is ultimately transferred from one large dot to another. Spin flip events — e.g. when an electron hops onto the small dot and then an electron with opposite spin hops off the small dot to the same large dot — remain possible and under appropriate conditions lead to a MCK fixed point. 

Fig. 31. Decrease of energy during simulated annealing. The temperature is exponentially lowered from kT=l to 0. The insert shows a cross section through the energy landscape as a function of the number of stochastic 1-spin-flips...

Tu. In our study of these materials we have found some evidence that this temperature could be related to a spin flip scattering mechanism which is also responsible for the Kondo resistivity observed in these materials. 

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