Correlation between particle size/domain structure and magnetic properties of highly crystalline Fe3O4 nanoparticles

Abstract

Highly crystalline single-domain magnetite Fe3O4 nanoparticles (NPs) are important, not only for fundamental understanding of magnetic behaviour, but also for their considerable potential applications in biomedicine and industry. Fe3O4 NPs with sizes of 10–300 nm were systematically investigated to reveal the fundamental relationship between the crystal domain structure and the magnetic properties. The examined Fe3O4 NPs were prepared under well-controlled crystal growth conditions using a large-scale liquid precipitation method. The crystallite size of cube-like NPs estimated from X-ray diffraction pattern increased linearly as the particle size (estimated by transmission electron microscopy) increased from 10 to 64.7 nm, which indicates that the NPs have a single-domain structure. This was further confirmed by the uniform lattice fringes. The critical size of approximately 76 nm was obtained by correlating particle size with both crystallite size and magnetic coercivity; this was reported for the first time in this study. The coercivity of cube-like Fe3O4 NPs increased to a maximum of 190 Oe at the critical size, which suggests strong exchange interactions during spin alignment. Compared with cube-like NPs, sphere-like NPs have lower magnetic coercivity and remanence values, which is caused by the different orientations of their polycrystalline structure.

Approaching Ferrite-Based Exchange-Coupled Nanocomposites as Permanent Magnets

“…In fact, the H c measured for this sample (19.6(4) kA/m) is in the order of what is reported for pure Fe 3 O 4 nanoparticles. 54 Comparing the H c of the composites discussed here with previous literature is not straightforward. The range of values for composites with a comparable M s is rather wide, since the effect of size and elemental composition on H c is pronounced, yet poorly analyzed in the literature.…”

“…The H c values reported for CoFe 2 O 4 nanoparticles are always larger than those for γ-Fe 2 O 3 or Fe 3 O 4 nanoparticles of comparable size and morphology. 12,54 Consequently, the loss of Co in the spinel structure inevitably causes a softening of this phase and, in turn, of the magnetic composite as a whole. Thus, the H c is dramatically diminished for the 450 °C composite as a result of the high amount of soft phase (alloy = 40.03(9) wt %) and the pronounced Co deficiency in the hard phase, Co 0.23(7) Fe 2.77(7) O 4 .…”

Magnetic composites based on bovine serum albumin and poly(aspartic acid)

“…The Ms values for the MC were less than those of bare Fe 3 O 4 which proves that a nonmagnetic coating material surrounds the magnetic core. This decrease in magnetic properties of composites was reported by other researchers . Furthermore, this shows that the magnetic properties of these composites may be easily varied in a great extent by variation of concentration of magnetic filler.…”

Progress in the Preparation of Magnetite Nanoparticles through the Electrochemical Method

“…The effective surface area of 0.2 μm-magnetite particles is approximately 6 m 2 g -1 and increases considerably to 100 m 2 g -1 when the size is down to ~50 nm. The change in surface area due to the change in size does not change the crystal structure of magnetite (Li Q. et al, 2017). Nano-sized magnetite still exhibits black color, having a face-centered cubic unit cell of the same lattice parameter and unit cell volume, as shown in Table 2 (Cornell R.M.…”