Low temperature noncollinear behavior in FePt nanogranular thin film system

We report the low temperature noncollinear magnetic behavior of direct current (DC) sputtered FePt thin films investigated by performing DC magnetization, thermoremanence, magnetic relaxation, and electrical transport measurements down to 1.8 K. The obtained results, interestingly, indicate a transition from ferromagnetic state to a low temperature disordered state where a collective frozen magnetic state with grain moments oriented randomly occurs. The magnetic relaxation and electrical resistivity measurements at low temperature support the spin-glass like phase, which diminishes and finally disappears with an applied field of moderate strength. We interpret the observed low temperature noncollinear magnetic behavior to be due to random freezing of grain moments.