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1.
ACS Appl Mater Interfaces ; 14(45): 51496-51509, 2022 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-36318544

RESUMO

Synthetic antiferromagnets with perpendicular magnetic anisotropy (PMA-SAFs) have gained growing attention for both conventional and next-generation spin-based technologies. While the progress of PMA-SAF spintronic devices on rigid substrates has been remarkable, only few examples of flexible thin-film heterostructures are reported in the literature, all containing platinum group metals (PGMs). Systems based on Co/Ni may offer additional advantages with respect to devices containing PGMs, i.e., low damping and high spin polarization. Moreover, limiting the use of PGMs may relieve the demand for critical raw materials and reduce the environmental impact of related technologies, thus contributing to the transition toward a more sustainable future. Here, we discuss for the first time the realization of Co/Ni-based PMA-SAFs on polymer tapes and exploit it to obtain flexible giant magneto-resistive spin valves (GMR-SVs) with perpendicular magnetic anisotropy. Several combinations of buffer and capping layers (i.e., Pt, Pd, and Cu/Ta) are also investigated. High-quality flexible SAFs with a fully compensated antiferromagnetic region and SVs with a sizable GMR ratio (up to 4.4%), in line with the values reported in the literature for similar systems on rigid substrates, were obtained in all cases. However, we demonstrate that PGMs allows achieving the best results when used as a buffer layer, while Cu is the best choice as a capping layer to optimize the properties of the stacks. We justify the role of buffer and capping layers in terms of different interdiffusion mechanisms occurring at the interface between the metallic layers. These results, along with the high robustness of the samples' properties against bending (up to 180°), indicate that complex and bendable Co/Ni-based heterostructures with reduced content of PGMs can be obtained on flexible tapes, allowing for the development of novel flexible and sustainable spintronic devices for applications in many fields including wearable electronics, soft robotics, and biomedicine.

2.
Commun Chem ; 5(1): 177, 2022 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-36697751

RESUMO

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.

3.
ACS Appl Mater Interfaces ; 13(31): 37483-37493, 2021 Aug 11.
Artigo em Inglês | MEDLINE | ID: mdl-34328310

RESUMO

The electronic properties of semiconducting inorganic lead sulfide (PbS) nanocrystals (NCs) and organic linker molecules are dependent on the size of NCs as well as the used ligands. Here, we demonstrate that a weakly binding ligand can be successfully attached to PbS NCs to form a coupled organic-inorganic nanostructure (COIN) by mixing with a strong binding partner. We use the weakly binding zinc ß-tetraaminophthalocyanine (Zn4APc) in combination with the strongly binding 1,2-ethanedithiol (EDT) as a mixed ligand system and compare its structural, electronic, and (photo-)electrical properties with both single-ligand COINs. It is found that binding of Zn4APc is assisted by the presence of EDT leading to improved film homogeneity, lower trap density, and enhanced photocurrent of the derived devices. Thus, the mixing of ligands is a versatile tool to achieve COINs with improved performance.

4.
Nat Commun ; 12(1): 2611, 2021 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-33972515

RESUMO

Skyrmions and antiskyrmions are topologically protected spin structures with opposite vorticities. Particularly in coexisting phases, these two types of magnetic quasi-particles may show fascinating physics and potential for spintronic devices. While skyrmions are observed in a wide range of materials, until now antiskyrmions were exclusive to materials with D2d symmetry. In this work, we show first and second-order antiskyrmions stabilized by magnetic dipole-dipole interaction in Fe/Gd-based multilayers. We modify the magnetic properties of the multilayers by Ir insertion layers. Using Lorentz transmission electron microscopy imaging, we observe coexisting antiskyrmions, Bloch skyrmions, and type-2 bubbles and determine the range of material properties and magnetic fields where the different spin objects form and dissipate. We perform micromagnetic simulations to obtain more insight into the studied system and conclude that the reduction of saturation magnetization and uniaxial magnetic anisotropy leads to the existence of this zoo of different spin objects and that they are primarily stabilized by dipolar interaction.

5.
Chemistry ; 27(22): 6804-6814, 2021 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-33586233

RESUMO

Defect engineering and metal encapsulation are considered as valuable approaches to fine-tune the reactivity of metal-organic frameworks. In this work, various MOF-808 (Zr) samples are synthesized and characterized with the final aim to understand how defects and/or platinum nanoparticle encapsulation act on the intrinsic and reactive properties of these MOFs. The reactivity of the pristine, defective and Pt encapsulated MOF-808 is quantified with water adsorption and CO2 adsorption calorimetry. The results reveal strong competitive effects between crystal morphology and missing linker defects which in turn affect the crystal morphology, porosity, stability, and reactivity. In spite of leading to a loss in porosity, the introduction of defects (missing linkers or Pt nanoparticles) is beneficial to the stability of the MOF-808 towards water and could also be advantageously used to tune adsorption properties of this MOF family.

6.
Sci Rep ; 9(1): 19264, 2019 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-31848357

RESUMO

We have investigated the structure and chemical composition of nanoparticles synthesized by thermal decomposition of a mixture of iron oleate and manganese oleate in a high-boiling solvent in the presence of Na-oleate and oleic acid as surfactants by analytical transmission electron microscopy (TEM). The particles appear core-shell like in bright field TEM images. Higher spatial resolution TEM (HRTEM) analysis reveals a FeO/MnO like structure in the core and a spinel like structure in the shell. With high-resolution analytical methods like energy dispersive x-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS), the distribution of the metals Mn and Fe was investigated. Differences in the oxidation state of these metals were found between the core and the shell region. The presence of sodium from the used surfactant (Na-oleate) on the surface of the particles has been proved.

7.
Beilstein J Nanotechnol ; 7: 957-69, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27547613

RESUMO

BACKGROUND: In nanoscale layered S/F1/N/F2/AF heterostructures, the generation of a long-range, odd-in-frequency spin-projection one triplet component of superconductivity, arising at non-collinear alignment of the magnetizations of F1 and F2, exhausts the singlet state. This yields the possibility of a global minimum of the superconducting transition temperature T c, i.e., a superconducting triplet spin-valve effect, around mutually perpendicular alignment. RESULTS: The superconducting triplet spin valve is realized with S = Nb a singlet superconductor, F1 = Cu41Ni59 and F2 = Co ferromagnetic metals, AF = CoO x an antiferromagnetic oxide, and N = nc-Nb a normal conducting (nc) non-magnetic metal, which serves to decouple F1 and F2. The non-collinear alignment of the magnetizations is obtained by applying an external magnetic field parallel to the layers of the heterostructure and exploiting the intrinsic perpendicular easy-axis of the magnetization of the Cu41Ni59 thin film in conjunction with the exchange bias between CoO x and Co. The magnetic configurations are confirmed by superconducting quantum interference device (SQUID) magnetic moment measurements. The triplet spin-valve effect has been investigated for different layer thicknesses, d F1, of F1 and was found to decay with increasing d F1. The data is described by an empirical model and, moreover, by calculations using the microscopic theory. CONCLUSION: The long-range triplet component of superconducting pairing is generated from the singlet component mainly at the N/F2 interface, where the amplitude of the singlet component is suppressed exponentially with increasing distance d F1. The decay length of the empirical model is found to be comparable to twice the electron mean free path of F1 and, thus, to the decay length of the singlet component in F1. Moreover, the obtained data is in qualitative agreement with the microscopic theory, which, however, predicts a (not investigated) breakdown of the triplet spin-valve effect for d F1 smaller than 0.3 to 0.4 times the magnetic coherence length, ξF1.

8.
Water Res ; 100: 98-104, 2016 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-27179596

RESUMO

In this study we present a new, environmental friendly and economic method, called Lt-delafossite process to treat industrial wastewater (initial Cu(2+)-concentrations of 1-15.6 g/l) by subsequent synthesis of nano-crystalline (doped) delafossite (CuFeO2) solely by precipitation and ageing at temperatures between 50 °C and 90 °C. The reached water purification rates are exclusively ≥99.99% for both wastewater models and wastewaters from electroplating industry. We succeeded to synthesize a mixture of 3R and 2H delafossite at 50 °C after 90 h and ≥70 °C after 16 h of ageing directly from industrial wastewater without any additional phases. In all cases green rust (GR), a Fe(II-III) layered double hydroxysulphate, Cu2O (cuprite) and Fe10O14(OH)2 (ferrihydrite) precipitates first. During ageing of the residues the metastable phases transform to delafossite. The residues are characterized by XRD, FTIR, SEM, TEM, VFTB and Mößbauer measurements.


Assuntos
Galvanoplastia , /química , Resíduos Industriais , Metais Pesados/química , Eliminação de Resíduos Líquidos , Poluentes Químicos da Água/química , Purificação da Água
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