MAGNETIC SUSCEPTIBILITY OF SPIN SYSTEMS WITH SEVERAL TIME DEPENDENT TEMPERATURES

The longitudinal susceptibility of a spin system in contact with a lattice is calculated from quantum statistics in the high temperature approximation. The method is based on the concept of time dependent temperatures describing the relaxation of several partial energies 〈{thorn}v〉(t). The result for χ∥ (Ω) is a sum of Debye functions. Explicit formulas for the relaxation times and the coefficients of the Debye functions are given in terms of the Hamiltonians. Three cases are especially discussed: 1. A part of the spin system is strongly coupled to the Zeeman system. 2. The lattice is weakly coupled to the total spin system. It is shown that on certain conditions the total spin systems may be treated as isolated from the lattice. 3. A part of the spin system dependent on the static magnetic field is isolated from the rest. An example is discussed which explains recent measurements obtained in CeCl3 · 7H2O. © 1968 Springer-Verlag.