Superspin Glass Behavior of Interacting Ferromagnetic Nanoparticles in Discontinuous Magnetic Multilayers

Discontinuous magnetic multilayers [Co 80 Fe 20 ( t )/Al 2 O 3 (3 nm)] 10 with t = 0.9 and 1.0 nm are studied by Superconducting Quantum Interference Device (SQUID) magnetometry and ac susceptibility. Owing to dipolar interaction the superparamagnetic cluster systems undergo collective glass-like freezing upon cooling. While both samples exhibit very similar glass temperatures T g , 45 K and critical exponents z x , 10 and n , 1.4 as obtained from the temperature dependencies of the relaxation time, , and the nonlinear susceptibility, h 3 , dynamical scaling reveals different critical exponents, g (0.9 nm) , 1.0 and g (1.0 nm) , 0.6, respectively.