Magnetic properties of Fe3C nanograins embedded in carbon matrix

Abstract

Magnetron dc cosputtering of a composite target of graphite disk plus iron rods was used in manufacturing carbon films with Fe 3 C nanograin inclusions. Both temperature-and field-dependent magnetizations, M (T) and M (H), were measured for samples of various carbon concentrations ͑from 37% to 85%͒. M (T) were measured in both conditions of zero-field cooling and a field cooling at Hϭ100 Oe. Experimental results of (T), obtained from M (T), of zero-field cooling, were theoretically fitted by using Wolhfarth's model of noninteracting particles with log-normal distribution function of particle size.

Ferromagnetism dependence on hole carriers in polycrystalline silicon films co-doped with Mn and B

“…It shows a distinct splitting between the ZFC and FC curves in all the films below 230 K. In the case of diluted magnetic semiconductors, the FC and ZFC curves begin to split at a temperature below the Curie temperature, then change monotonously with further decrease of temperature [22][23][24]. While in the magnetic nano-particle system, the FC and ZFC curves only overlap in high-temperature range and in ZFC curve, a peak at a ''blocking'' temperature could be observed, which was caused by the competition between the thermal energy and the magnetic anisotropy energy of nano-particles [25][26][27]. In Fig.…”

Structure and magnetic properties of FePt nanograins embedded in amorphous carbon films

“…By assuming a lognormal function for the grain-size distribution, we used the Wolfarth model [8] which assumed no magnetic interactions between the neighboring grains to calculate the wðTÞ of ZFC curves. The method of calculation can be found in our previous work [9]. The results of calculation for the asdeposited films are shown as a solid line in Fig.…”

“…According to Bitoh et al [8], the contribution to the susceptibility at each temperature contains two parts. One part is from the unblocked grains with volume V oV m ; the other part is from the blocked grains with V > V m : The critical volume V m is temperature-dependent and is determined from [8,9] with k B the Boltzman constant, K a the anisotropic constant, f 0 the relaxation frequency around 10 À9 -10 À11 s À1 , and t 0 the usual measuring time taken as 100 s. The discrepancy between the results of the experiment and the calculation with smaller experimental values drops a hint that in the as-deposited films the fractions of the grain diameter larger than D m (T=60 K) (BV m 1/3 ) of around 12 nm are less than those of calculation. Our TEM images, referring to Fig.…”

Resistance and magnetoresistance of annealed amorphous carbon films containing Fe3C nanograins

“…Grain-size, and thus saturation magnetization, is increasing with T a : But only T a ¼ 250 C and 350 C show magnetoresistances at low temperatures. The largest magnetoresistance ratio (MR) of 23% at T ¼ 2 K is observed in the film annealed at T a ¼ 350 C.Carbon films (100 nm in thickness) containing pure Fe 3 C nanograins were deposited on SiO 2 substrates by using DC magnetron co-sputtering technique [3,4]. Electrical resistance has been measured from T ¼ 52300 K in a conventional four-terminal geometry with an in-plane current.…”

“…Carbon films (100 nm in thickness) containing pure Fe 3 C nanograins were deposited on SiO 2 substrates by using DC magnetron co-sputtering technique [3,4]. Electrical resistance has been measured from T ¼ 52300 K in a conventional four-terminal geometry with an in-plane current.…”