Bad neighbour, good neighbour: how magnetic dipole interactions between soft and hard ferrimagnetic nanoparticles affect macroscopic magnetic properties in ferrofluids

Abstract

Hard ferrimagnetic CoFe2O4 nanoparticles become softer in the presence of neighbouring soft ferrimagnetic MnFe2O4 nanoparticles.

Selective magnetometry of superparamagnetic iron oxide nanoparticles in liquids

“…Sensitivity of RIXS-MCD spectra to different elements and crystal sites provides a straightforward way to disentangle individual contributions to magnetization, which has been recently used for the selective determination of magnetic anisotropy in core/shell and mixed ferrite nanoparticle systems. 45,48,57 Here we verify whether it can be applied to separate magnetization profiles of SPION from that of the carrier liquid. Results of the measurements performed at room temperature on Zn 0.53 Fe 2.47 O 4 nanoparticles suspended in water are shown in Fig.…”

“…[31][32][33][34] Spectroscopic methods, which are capable of probing individual magnetic components by taking advantage of their element and site selectivity, are indispensable to unravel the response of particles from that of the carrier liquid. 57 Fe Mössbauer spectroscopy (MS), magnetic particle spectroscopy (MPS) and X-ray magnetic circular dichroism (XMCD) are often used for characterization of iron oxide nanoparticles. 9,16,23,[35][36][37][38][39][40][41] Although the XMCD spectra has a lower energy resolution and the experimental setup is more involved than that of MS and MPS, XMCD has the advantage that it can be applied to any magnetic element.…”

Manipulating Dispersions of Magnetic Nanoparticles

“…Dipolar attractions between stronger, homogeneous "nanomagnets" take effect preferentially (Figure 1b). Daffe et al 18 constructed a 1:1 binary FF composite, composed of ∼6 nm diameter of "hard" CoFe 2 O 4 and "soft" MnFe 2 O 4 ferrimagnetic nanospheres, and froze the dispersion to capture the binary ferrofluid structure at low temperature (10−45 K). The measured hysteresis loops showed the long-range magnetic dipole interactions within small particle clusters.…”

New reflections on hard X-ray photon-in/photon-out spectroscopy

“…The bulk sensitivity has been recently exploited in the RIXS-MCD characterization of various nanosized materials where it was needed to access the entire volume: from buried thin films of a few tens of nm 92 to bimagnetic core-shell NPs in powder 93 and liquid phase 94 or even binary ferrofluids composed of two magnetically different types of NPs. 95 The magneto-spectroscopy RIXS-MCD is indeed very well suited for investigating magnetic colloidal NPs in the liquid phase. The in situ characterization is an important aspect as the physico-chemical properties of the NPs may change in the powder form.…”

“…The measurements were performed on the frozen phase of the samples (below the freezing temperature of the carrier liquid, heptane) in a He-flow cryostat using a dedicated cryo-liquid cell. 95 They were kept in magnetic saturation using an electromagnet that provided a field up to ±1.5 Tesla. A strong dichroic signal ascribed to the contribution of tetrahedral Mn 2+ ions was found in the Mn RIXS-MCD map (see Figure 12(a)), while a weak signal with opposite sign was obtained in the Co RIXS-MCD map (see Figure 12(b)) in agreement with the presence of octahedral Co 2+ ions.…”