(a) TEM image of the as-prepared nanocubes. It shows a 2D ordered array of the nanocubes with an average side of about 6 nm. (b) HRTEM image shows the lattice fringes of the sample, with the corresponding SAED shown in the inset.
FC and ZFC measurements recorded in a field of 90 Oe. (a) and curves for sample C. The inset shows an enlarged image from 25 to 55 K. The blocking temperature is . The bifurcation point is defined as . (b) and curves for samples A, B, and C. The inset shows an enlarged image from 25 to 50 K. The blocking temperature for sample A is .
(a) calculated from the and curves of sample C presented in Fig. 2(a). The Curie points are determined as, . (b) calculated from the curves of samples A, B, and C. The Curie point determined for sample A is 37.9 K, reduced from 39.0 K for sample C.
Selective curves for (a) sample A, (b) sample B, and (c) sample C.
Temperature dependent coercivity, , for samples A, B, and C. For sample C, a small coercivity is observed even in the temperature range, .
FC and ZFC loops measured at . The sample is cooled from 80 K down to 5 K in the applied field of 0 Oe (ZFC) and 50 kOe (FC). The inset is an enlarged view of the low field region.
Saturation magnetization, , for sample C. It is determined from the loops by linearly extrapolating the high field PM behavior to the axis of . The inset is for the reduced function, , normalized to the value determined at .
of sample C. The fitting analysis by Eq. (4) is represented by the solid curve and the fitting analysis by the Néel–Brown equation, with , is represented by the dashed-dotted curve.
of sample B partially diluted in distilled water and fitting analysis by the Néel–Brown equation, with .
Zeeman energy density, , vs the thermal energy, , at the nucleation field, . The magnitude of 1/slope gives the switching volume, .
Curie temperature, and blocking temperature, , for samples A, B, and C. is determined from the maximum of and is determined from the peak position of the curve. The uncertainty reflect one half of the step size in the measurements around the temperature of interests.
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