Magnetic Properties at Finite Temperatures Spin-Fluctuation Effects

3 Magnetic Properties at Finite Temperatures Spin-Fluctuation Effects 

The study of spin fluctuations in clusters and the resulting temperature dependence of the magnetic properties is a subject of considerable current interest. In this section we discuss results derived from the spin-fluctuation theory described in Section 6.2.2 which takes into account both the fluctuations of the magnetic moments and the itinerant character of the d electron states. 

In order to discuss the temperature-induced spin-fluctuations in small Feyv and Niyv clusters we consider the low-temperature limit of the local free-energy F/( ) (Eq. (16)). For these clusters one always obtains AF/( ) = Fy( ) — F/( = /jl ) 0, which indicates, as expected, that the ferromagnetic order is stable at low temperatures. Comparing the behavior of AF/( ) for different atoms i within the ferromagnetic cluster provides useful information concerning the stability of the local magnetizations and its environmental dependence. 

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