Orbital and spin moments of 5 to 11 nm Fe3O4 nanoparticles measured via x-ray magnetic circular dichroism

Abstract

The orbital and spin contributions to the magnetic moment of Fe in Fe3O4 nanoparticles were measured using X-ray magnetic circular dichroism (XMCD). Nanoparticles of different sizes, ranging from 5 to 11 nm, were fabricated via organic methods and their magnetic behavior was characterized by vibrating sample magnetometry (VSM). An XMCD signal was measured for three different samples at 300 K and 80 K. The extracted values for the orbital and spin contributions to the magnetic moment showed a quenching of the orbital moment and a large spin moment. The calculated spin moments appear somewhat reduced compared to the value expected for bulk Fe3O4. The spin moments measured at 80 K are larger than at 300 K for all the samples, revealing significant thermal fluctuations effects in the nanoparticle assemblies. The measured spin moment is reduced for the smallest nanoparticles, suggesting that the magnetic properties of Fe3O4 nanoparticles could be altered when their size reaches a few nanometers.

Surface Charge and Coating of CoFe2O4 Nanoparticles: Evidence of Preserved Magnetic and Electronic Properties

“…The calculated orbital and spin components indicate a m L close to zero for Fe cations (quenching of the orbital moment) in line with those reported in the literature for Co (1−x) Fe (2+x) O 4 48 and Fe 3 O 4 NPs, 48,68 while the values of m S are higher than the m S reported by Moyer 68 On the other hand, for Co ions the orbital and spin components are comparable (but slightly lower) to those reported in the literature for "bulk" CoFe 2 O 4 film. 48 The enhanced total magnetic moment of Fe in CoFe 2 O 4 NPs can be associated with a dominant concentration of Fe cations in the unit cell, as also observed by Moyer et al, 48 who showed an increase of Fe magnetic moments with increasing x in Co (1−x) Fe (2+x) O 4 structure.…”

Superparamagnetic dynamics and blocking transition in Fe$_3$O$_4$ nanoparticles probed by vibrating sample magnetometry and muon spin relaxation

“…Based on previous crystallographic studies of these samples [12], the cubic lattice parameter is 8.35 Å and the atomic density is about 13.7 Fe 3 O 4 units per nm 3 . Accounting for combined spins carried by the Fe 2+ and Fe 3+ ions in the spinel structure [18], the saturated magnetization density is about 55 µ B /nm 3 . Assuming a spherical NP shape with a radius of 2.6 nm, we have M s = 4000 µ B .…”

“…Among others, these behaviors include the precise manner in which the the blocking transition proceeds throughout the sample, and how this affects experimental data [11]; the influence of the structure and morphology across varying length scales [7,12]; and even the estimation of microscopic parameters such as the nanoparticle spin flip activation energy and fluctuation time [13]. There is increasing recognition that a more complete understanding is most likely to be obtained by attacking the problem with a variety of complementary techniques, such as magnetometry [9], Mössbauer spectroscopy [14], electronic microscopy [15] and holography [16], neutron scattering [17], x-ray magnetic spectroscopy [18], or x-ray magnetic scattering [19]. In this context, probes of local magnetism-i.e.…”

Unraveling Nanoscale Magnetic Ordering in Fe3O4 Nanoparticle Assemblies via X-rays

“…Fe3O4 carries a strong magnetization, supported by the spins of two ions, Fe 2+ and Fe 3+ , distributed ferrimagnetically throughout a spinel crystallographic structure [13,14]. Nano-sized Fe3O4 particles exhibit a strong bulk-like magnetic moment throughout the core of the particle with limited oxidation effects at the surface [15][16][17]. When their size is below about 100 nm, Fe3O4 particles are usually magnetically monodomain, thus forming a single giant magnetic moment, or "nanospin" [18,19].…”