ON THE MAXIMUM OF THE FIELD-DEPENDENT SUSCEPTIBILITY IN FERROMAGNETICMATERIALS

We propose two new methods to describe the ferromagnetic field-depende nt susceptibility within the mean-field theory. A parametric approach valid for any value of temperature, applied field, and spin quantum nu mber is developed; within this approach, the scaling functions for mag netization and susceptibility are determined for values of the reduced field, smaller than 10(-3). A simple analytic derivation of the scali ng functions is also given. As the susceptibility maximum is found to occur at a value of the relevant scaling variable which is of the orde r of unity, it cannot be accurately described by series expansions of the scaling function. A nonlocal parabolic approximant to the scaling function is constructed which reproduces its main features exactly. Th e methods of this paper are relevant to the study of the field-depende nt susceptibility of any ferromagnet in which long-range forces are kn own to dominate. It is suggested that the analysis be tested on the ex amples of the 'mean-field' ferromagnets HoRh4B4 and ZrZn2. The whole s cheme should be regarded as contributing to the elaboration of the adv antageous procedure for the determination of two independent critical exponents, which is based on general scaling analysis for the field-de pendent susceptibility and which avoids painstaking measurements of th e exact Curie temperature.