Nonlinear effects in the ac magnetic susceptibility of selected magnetic materials

In the present work, a brief description of the nonlinear magnetic susceptibility is given together with selected results outlining the relevance of this technique in the analysis of complex magnetic structures. In particular, details are provided concerning the ferromagnetic transition as observed through the third order magnetic susceptibility in two intermetallic compounds: Y2Fe17 and Gd5Si2.1Ge1.9. Moreover, results concerning the nonlinear behavior of a rutheno-cuprate compound, namely RuSr2GdCu2O8, are also reported with a discussion outlining the coexistence in this compound of ferromagnetic clusters exhibiting superparamagnetic behavior dispersed in an antiferromagnetic matrix.