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Room temperature quantized double layer charging was observed in 2 nm Cu2ZnSnS4 (CZTS) quantum dots. In addition to this we observed a distinct non-linearity in the quantized double ...layer charging arising from UV light modulation of double layer. UV light irradiation resulted in a 26% increase in the integral capacitance at the semiconductor-dielectric (CZTS-oleylamine) interface of the quantum dot without any change in its core size suggesting that the cause be photocapacitive. The increasing charge separation at the semiconductor-dielectric interface due to highly stable and mobile photogenerated carriers cause larger electrostatic forces between the quantum dot and electrolyte leading to an enhanced double layer. This idea was supported by a decrease in the differential capacitance possible due to an enhanced double layer. Furthermore the UV illumination enhanced double layer gives us an AC excitation dependent differential double layer capacitance which confirms that the charging process is non-linear. This ultimately illustrates the utility of a colloidal quantum dot-electrolyte interface as a non-linear photocapacitor.
The exchange-bias field (HEB) and its angular dependence are systematically investigated in Co/CoO core-shell nanowire assemblies (∼15 nm in diameter and ∼200 nm in length) consisting of ...single-crystalline Co core and polycrystalline CoO shell. Giant exchange-bias field (HEB) up to 2.4 kOe is observed below a blocking temperature (TEB ∼150 K) in the aligned Co/CoO nanowire assemblies. It is also found that there is an angular dependence between the HEB and the applied magnetization direction. The HEB showed a peak at 30° between the applied field and the nanowire aligned direction, which may be attributed to the noncollinear spin orientations at the interface between the ferromagnetic core and the antiferromagnetic shell. This behavior is quantitatively supported by an analytical calculation based on Stoner–Wohlfarth model. This study underlines the importance of the competing magnetic anisotropies at the interface of Co/CoO core-shell nanowires.
•Giant exchange bias is observed in oriented Co/CoO core-shell nanowire assemblies.•Study of angular and temperature dependence of the exchange bias effect.•Competing magnetic anisotropies at the interface of Co/CoO core-shell nanowires.•Effect of misaligned spins in FM/AFM interface on angular dependence of exchange bias.•We explain the analytical model that accounts for experimental results.
•Significance of structural modifications in Gd3Fe5-xScxO12 for magnetic refrigeration applications.•XRD, DFT, Mossbauer spectral analysis, and magnetic data consistently support preferred Sc3+ ...substitution at the octahedral site (x < 1.0).•Enhanced magnetocaloric properties: High magnetic entropy change (-ΔSm) of 3.82 J/(kg·K) at 37.5 K, H = 5 T.•High relative cooling power (RCP) of 408 J/kg at H = 5 T for × = 0.25.•Potential practical applications as a magnetocaloric material.
This paper presents the tunable magnetic and magnetocaloric properties of Scandium-doped gadolinium iron garnets, Gd3 Fe5-xScxO12 (x = 0.0 to 0.25) compounds prepared by a facile auto-combustion method. The sample analyzed has a dominant cubic crystal structure (space group: Ia3¯d)) with a small fraction of an orthorhombic secondary phase, as determined by Rietveld analysis of X-ray diffraction patterns. The structural, magnetic, Mössbauer spectroscopy and first-principles density functional theory (DFT) studies show a preferential substitution of Sc3+ at the octahedral site of Fe3+ions. The ferrimagnetic (FIM) transition is present in all samples, with the transition temperature decreasing from 560 K for × = 0.0 to 521 K for × = 0.25. The Sc3+dopedGd3Fe4.75Sc0.25O12exhibits an improved magnetocaloric effect (MCE) with a maximum magnetic entropy change (-ΔSMmax)3.82 J kg-1K−1, and a higher relative cooling power (RCP) value of 408 J kg−1, which is ∼ 7 % higher than the Gd3Fe5O12(380 J kg−1) sample. These findings suggest that by incorporating Sc3+, the magnetic and magnetocaloric properties of Gd3Fe5-xScxO12 can be tailored for potential applications in low-temperature magnetic refrigeration.
A simple cation exchange reaction has been adapted to produce the CoxFe3−xO4 nanorods with different concentration of Co. The substitution of Fe2+ with Co2+ ions increase the magnetocrystalline ...anisotropy and coercivity of pristine superparamagnetic Fe3O4 nanorods. Atomic concentration of 5–11% of Co2+ in Fe3O4 nanorods renders coercivity of 300–460 Oe at room temperature and 2200–4050 Oe at 10 K. Hydrocarbon long‐chain amine (oleylamine) functionalized nanorod assemblies form a multiple tunnel junction, where organic amine monolayers act as insulating tunnel barriers. CoxFe3−xO4 nanorods show a magnetoresistance switching behavior at room temperature and the switching field is consistent with the magnetic coercivity. A 14–15% TMR is recorded at room temperature in CoxFe3−xO4 nanorod assemblies, which increases to 23–26% at 150 K at a magnetic field of ±2 T. The calculated spin polarization for Co0.33Fe2.67O4 nanorods at room temperature is 52%. A similar spin polarization and TMR as Fe3O4 in Co‐doped Fe3O4 nanorod assemblies is obtained. Thus, controlled doping of Co ions engineers the coercivity and remanence of the “super‐paramagnetic” Fe3O4 without hindering their TMR performances, which could be very useful for memory devices.
Monodisperse CoxFe3‐xO4 nanorods are synthesized using a cation exchange reaction with Fe3O4. Magnetic and tunneling magnetoresistance (TMR) properties are engineered via different doping concentration of Co in the nanorods. CoxFe3‐xO4 nanorod assemblies show 15% TMR at room temperature with a switching behavior. Controlled magnetic coercivity with high spin polarization of nanorod assemblies would have enormous potential in magnetic memory and data storage.
Drug Release Technology
In article number 2306940, Jian Tian, Shengqian Ma, and co‐workers developed a novel magnetothermally‐triggered drug release carrier. Created using a controlled encapsulation ...method, this carrier fully fixes and confines iron oxide nanoparticles (IONPs) within metal‐organic frameworks (MOFs), preserving the MOF's morphology and porosity and effectively segregating IONPs. It enhances heating efficiency and shows promise for magneto‐thermally modulated drug dosing at tumor sites, offering potential advancements in cancer treatment.
•Iron carbide (Fe5C2) nanoparticles show ferromagnetic properties with high saturation magnetization.•Fe5C2 nanoparticles reveal an extended optical absorption property.•We have demonstrated Fe5C2 ...nanoparticles as a hyperthermia heat probe with dual magneto-photo-thermal therapeutic features.•Fe5C2 nanoparticles suspension displays enhanced SAR values relative to that of Fe3O4 nanoparticles.
Localized heat generation using nanoparticles is a promising supplementary technique to the well-established cancer treatments, such as chemotherapy and radiotherapy. Here, we demonstrate that iron carbide (Fe5C2) nanoparticles with a thin carbon shell have the collective magnetothermal and photothermal effects based on the ferromagnetic and photonic properties. When the Fe5C2 nanoparticle suspension is irradiated with a NIR laser (808 nm), it yields unprecedented heating effects. Further, owing to the observed high magnetization and coercivity, the Fe5C2 nanoparticle suspension on exposure to an alternating magnetic field (ACMF) exhibits an enhanced specific absorption rate (SAR) as compared to Fe3O4 nanoparticles of the same size. This significant improvement in the SAR arises from the cooperative contribution from the hysteresis and susceptibility losses. This work also gives quantitative information about the ACMF effects on heating ability as well as provides some guidelines for obtaining enhanced heating activity in nanoparticle suspensions of a given magnetic material.
Abstract
The development of external stimuli‐controlled payload systems has been sought after with increasing interest toward magnetothermally‐triggered drug release (MTDR) carriers due to their ...non‐invasive features. However, current MTDR carriers present several limitations, such as poor heating efficiency caused by the aggregation of iron oxide nanoparticles (IONPs) or the presence of antiferromagnetic phases which affect their efficiency. Herein, a novel MTDR carrier is developed using a controlled encapsulation method that fully fixes and confines IONPs of various sizes within the metal–organic frameworks (MOFs). This novel carrier preserves the MOF's morphology, porosity, and IONP segregation, while enhances heating efficiency through the oxidation of antiferromagnetic phases in IONPs during encapsulation. It also features a magnetothermally‐responsive nanobrush that is stimulated by an alternating magnetic field to enable on‐demand drug release. The novel carrier shows improved heating, which has potential applications as contrast agents and for combined chemo and magnetic hyperthermia therapy. It holds a great promise for magneto‐thermally modulated drug dosing at tumor sites, making it an exciting avenue for cancer treatment.
Superparamagnetic iron oxide nanoparticles (SPIONs) are widely investigated and utilized as magnetic resonance imaging (MRI) contrast and therapy agents due to their large magnetic moments. Local ...field inhomogeneities caused by these high magnetic moments are used to generate T
contrast in clinical high-field MRI, resulting in signal loss (darker contrast). Here we present strong T
contrast enhancement (brighter contrast) from SPIONs (diameters from 11 nm to 22 nm) as observed in the ultra-low field (ULF) MRI at 0.13 mT. We have achieved a high longitudinal relaxivity for 18 nm SPION solutions, r
= 615 s
mM
, which is two orders of magnitude larger than typical commercial Gd-based T
contrast agents operating at high fields (1.5 T and 3 T). The significantly enhanced r
value at ultra-low fields is attributed to the coupling of proton spins with SPION magnetic fluctuations (Brownian and Néel) associated with a low frequency peak in the imaginary part of AC susceptibility (χ"). SPION-based T
-weighted ULF MRI has the advantages of enhanced signal, shorter imaging times, and iron-oxide-based nontoxic biocompatible agents. This approach shows promise to become a functional imaging technique, similar to PET, where low spatial resolution is compensated for by important functional information.
It has been possible to incorporate cadmium ions in ZnS quantum dots (QDs). It is studied how the substitution of Cd2+ ions by zinc ions affects the structural, morphological, and optical properties ...of ZnS QDs. Zn1-xCdxS QDs are prepared by a simple beaker chemistry approach and characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy, and UV-visible and photoluminescence (PL) spectroscopies. XRD studies confirmed that all the prepared samples are in zinc-blende phase. With the increase of cadmium content, the diffraction peaks shifted towards lower diffraction angles and the lattice constant increased linearly. Optical studies revealed that the strong absorption edge also shifted towards the higher wavelength region with the increase of Cd content. Hence, the optical bandgap of the QDs decreases with the increase of Cd content. Due to the quantum confinement of the carriers in the QDs, the bandgap energy is higher than that of the corresponding bulk material. The PL spectrum of the undoped ZnS QDs contains five peaks (centered at 365, 400, 420, 450, and 470 nm) which are attributed to the recombination of the defect states of ZnS.
It has been possible to incorporate cadmium ions in ZnS quantum dots (QDs). It is studied how the substitution of Cd super(2+) ions by zinc ions affects the structural, morphological, and optical ...properties of ZnS QDs. Zn sub(1-x) Cd sub(x) S QDs are prepared by a simple beaker chemistry approach and characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy, and UV-visible and photoluminescence (PL) spectroscopies. XRD studies confirmed that all the prepared samples are in zinc-blende phase. With the increase of cadmium content, the diffraction peaks shifted towards lower diffraction angles and the lattice constant increased linearly. Optical studies revealed that the strong absorption edge also shifted towards the higher wavelength region with the increase of Cd content. Hence, the optical bandgap of the QDs decreases with the increase of Cd content. Due to the quantum confinement of the carriers in the QDs, the bandgap energy is higher than that of the corresponding bulk material. The PL spectrum of the undoped ZnS QDs contains five peaks (centered at 365, 400, 420, 450, and 470 nm) which are attributed to the recombination of the defect states of ZnS.
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