Superparamagnetic Co36C64 granular film

Nanocomposite Co-C thin films of about 15 nm thick were prepared by pulsed filtered vacuum arc deposition. The films were characterized by X-ray photoelectron spectroscopy, non-Rutherford backscattering spectrometry, X-ray diffraction, and magnetic force microscopy. The as-deposited films were amorphous. After annealing at 350 deg. C for 1 h in vacuum (<10-3 Pa), the films were found to consist of nanocrystalline Co grains encapsulated in carbon. The superparamagnetism of the annealed Co36C64 film was demonstrated by the measurement of DC susceptibility and magnetic hysteresis using a SQUID magnetometer. The superparamagnetic relaxation blocking temperature was marked to be about 12 K by the peak of the zero-field-cooled magnetization under a field of 100 Oe. The magnetic properties of these annealed granular Co-C films transform from superparamagnetism to ferromagnetism when the Co concentration increases