76 research outputs found
Phase composition of iron oxide nanoparticles studied using hard X-ray absorption spectroscopy
At the surface of iron oxide nanoparticles, an oxidized or disordered layer is often found. Due to the large surface-to-volume ratio of nanomaterials, such a surface layer plays an important role in the overall magnetic properties of the particles. Consequently, it is important to characterize the surface layer if applications of iron oxide nanoparticles, e.g., for magnetic hyperthermia, magnetic particle imaging, or ferrofluidics, are envisaged. In this work, we tuned the phase of the surface layer of 14 nm iron oxide nanoparticles via annealing procedures. The phase composition of the particles is systematically studied using hard X-ray absorption spectroscopy
Synthesis of iron oxide nanoparticles by decomposition of iron-oleate: influence of the heating rate on the particle size
Reduced thermal expansion by surface-mounted nanoparticles in a pillared-layered metal-organic framework
Control of thermal expansion (TE) is important to improve material longevity in applications with repeated temperature changes or fluctuations. The TE behavior of metal-organic frameworks (MOFs) is increasingly well understood, while the impact of surface-mounted nanoparticles (NPs) on the TE properties of MOFs remains unexplored despite large promises of NP@MOF composites in catalysis and adsorbate diffusion control. Here we study the influence of surface-mounted platinum nanoparticles on the TE properties of Pt@MOF (Pt@Zn2(DP-bdc)2dabco; DP-bdc2-=2,5-dipropoxy-1,4-benzenedicarboxylate, dabco=1,4-diazabicyclo[2.2.2]octane). We show that TE is largely retained at low platinum loadings, while high loading results in significantly reduced TE at higher temperatures compared to the pure MOF. These findings support the chemical intuition that surface-mounted particles restrict deformation of the MOF support and suggest that composite materials exhibit superior TE properties thereby excluding thermal stress as limiting factor for their potential application in temperature swing processes or catalysis
Phase composition and magnetic properties of post-annealed asymmetric Pt/Fe/Pt/Au/Fe thin films
Controlling Magnonic Spin Current through Magnetic Anisotropy and Gilbert Damping
The magnon propagation length, (MPL) of a ferro/ferrimagnet (FM) is one of
the key factors that controls the generation and propagation of
thermally-driven spin current in FM/heavy metal (HM) bilayer based
spincaloritronic devices. Theory predicts that for the FM layer, MPL is
inversely proportional to the Gilbert damping (alpha) and the square root of
the effective magnetic anisotropy constant (K_eff). However, direct
experimental evidence of this relationship is lacking. To experimentally
confirm this prediction, we employ a combination of longitudinal spin Seebeck
effect (LSSE), transverse susceptibility, and ferromagnetic resonance
experiments to investigate the temperature evolution of MPL and establish its
correlation with the effective magnetic anisotropy field, H_K^eff (proportional
to K_eff) and alpha in Tm3Fe5O12 (TmIG)/Pt bilayers. We observe concurrent
drops in the LSSE voltage and MPL below 200 K in TmIG/Pt bilayers regardless of
TmIG film thickness and substrate choice and attribute it to the noticeable
increases in H_K^eff and alpha that occur within the same temperature range.
This study not only highlights the ability to manipulate MPL by controlling
H_K^eff and alpha in FM/HM based spincaloritronic nanodevices, but also shows
that the tuning of alpha is more effective than H_K^eff in controlling MPL and,
hence, the spincaloritronic efficiency.Comment: 5 main text figure
PrÀparation von Eisenoxid-, Manganoxid- und Kompositnanopartikeln und deren mikroskopische Charakterisierung
Selective growth of MFU-4l single crystals on microstructured plasma polymer coatings
Crystals of the metalâorganic framework Ulm-4l(arge) grow site selectively and with ă1 0 0ă orientation on microtextured plasma polymer coatings.</p
Structure and magnetic properties of ferrimagnetic [Gd/Fe]n multilayer and GdxFe100âx thin films
The structural and magnetic properties of two series of [Gd(2, 4 nm)/Fe(t)]n multilayer films with varying Fe thickness were investigated and compared to those of amorphous ferrimagnetic GdFe alloys of the same corresponding composition. Transmission electron microscopy studies confirmed the high interface quality of both multilayer series. Furthermore, the microstructure was analyzed, revealing polycrystallinity in both Gd and Fe layers with strong (101Ì0)-oriented textured growth of Gd particularly for the multilayer series with 2 nm Gd. Magnetic measurements confirm an out-of-plane magnetic easy axis in the alloy samples and an in-plane magnetic easy axis in all multilayer samples. Twisted spin states in samples with a low remanent magnetization were identified. Magnetic compensation points of both multilayer series are compared to those of the alloy samples. It was found that the dependence of the magnetic compensation point on effective Gd concentration in the series with 2 nm Gd closely resembles the strong dependence observed in the alloy counterparts. In contrast, a weaker dependence is revealed for the multilayer series with 4 nm Gd, which makes this system more robust against variations in composition required for applications
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