The field dependence of the ac susceptibility of a concentrated frozen ferrofluid containing ultrafine Fe-C particles of monodisperse nature has been analyzed using static scaling. For the first time, a divergent behavior of the nonlinear susceptibility of a dipole-dipole interacting system is demonstrated. From the analysis, the critical exponents gamma = 4.0 +/- 0.2 and beta = 1.2 +/- 0.1 were extracted. The results support the existence of a low temperature spin-glass-like phase in interacting magnetic nanoparticle systems. [S0031-9007(98)07527-9].
Bibliographical noteCopyright (1998) by the American Physical Society.