The remaining portions of the crystal appear to be composed of a yet unidentified phase of Fe2O3 in addition to Wüstite phases, as we would expect for diiron(III)oxide, although with space groups and values being similar, the oxidation state is difficult to determine with absolute certainty. a Magnetic characterization A typical feature in magnetic nanoparticles is their irreversible ferromagnetic behavior below the blocking temperature TB and reversible magnetization above it caused by superparamagnetic behavior of the nanoparticles. The blocking temperature can be found experimentally by measuring magnetization under field-cooling (FC) and zero-field cooling (ZFC) conditions. Below TB, the Neel relaxation time N is larger than the measurement time m (typically 100 s), and magnetization depends strongly on the field history. Above TB, magnetization is strongly affected by thermal fluctuations (m > N), making FC and ZFC curves coincide. In other words, for a given measurement time hysteretic behavior observed below TB would not be observed above m, TB. We measured temperature dependence of magnetization for the Fe3O4 nanocyrstal samples under ZFC and FC conditions. The dc (m = 100 s) magnetization of the ferrofluid samples was measured with a dc field of 100 Oe in the temperature range between 9 K and 350 K. Zero-field cooled (circle symbols) and field cooled (square symbols) magnetization vs. Figure 5. temperature for polymorphous Fe3O4 nanoparticles. Magnetization measured with a dc field of 100 Oe. m = 100 s. In the entire temperature range up to 350 K, the Fe3O4 nanoparticle samples demonstrated strong ferromagnetic behavior as evidenced by the gap between the ZFC and FC curves persisting even at 350 K (Figure 5). From the ZFC curve, we can loosely estimate TB to be ~ 175 K, but even above that temperature equilibrium magnetization of the nanoparticle sample was not reached, and superparamagnetic behavior of the nanoparticles was not observed. Strong ferromagnetic behavior of the Fe3O4 nanoparticle samples was confirmed in magnetic hysteresis measurements. Consistent with the results of dc magnetization measurements, magnetic
The remaining portions of the crystal appear to be composed of a yet unidentified phase of Fe2O3 in addition to Wüstite phases, as we would expect for diiron(III)oxide, although with space groups and a values being similar, the oxidation state is difficult to determine with absolute certainty. Magnetic characterization A typical feature in magnetic nanoparticles is their irreversible ferromagnetic behavior below the blocking temperature TB and reversible magnetization above it caused by superparamagnetic behavior of the nanoparticles. The blocking temperature can be found experimentally by measuring magnetization under field-cooling (FC) and zero-field cooling (ZFC) conditions. Below TB, the Neel relaxation time N is larger than the measurement time m (typically 100 s), and magnetization depends strongly on the field history. Above TB, magnetization is strongly affected by thermal fluctuations (m > N), making FC and ZFC curves coincide. In other words, for a given measurement time m, hysteretic behavior observed below TB would not be observed above TB. We measured temperature dependence of magnetization for the Fe3O4 nanocyrstal samples under ZFC and FC conditions. The dc (m = 100 s) magnetization of the ferrofluid samples was measured with a dc field of 100 Oe in the temperature range between 9 K and 350 K. Figure 5. Zero-field cooled (circle symbols) and field cooled (square symbols) magnetization vs. temperature for polymorphous Fe3O4 nanoparticles. Magnetization measured with a dc field of 100 Oe. m = 100 s. In the entire temperature range up to 350 K, the Fe3O4 nanoparticle samples demonstrated strong ferromagnetic behavior as evidenced by the gap between the ZFC and FC curves persisting even at 350 K (Figure 5). From the ZFC curve, we can loosely estimate TB to be ~ 175 K, but even above that temperature equilibrium magnetization of the nanoparticle sample was not reached, and superparamagnetic behavior of the nanoparticles was not observed. Strong ferromagnetic behavior of the Fe3O4 nanoparticle samples was confirmed in magnetic hysteresis measurements. Consistent with the results of dc magnetization measurements, magnetic