Saqlain A. Shah

Effect of doping concentration on absorbance, structural, and magnetic properties of cobalt-doped ZnO nano-crystallites

Controlled conduction of magnetic spins is desired for data processing in modern spintronic devices. Transition metal-doped ZnO is a potential candidate for this purpose. We studied the effects of cobalt doping on structural, absorbance, and magnetic properties of ZnO nano-particles. Different compositions (Zn0.99Co0.1O, Zn0.97Co0.3O, and Zn0.95Co0.5O) of cobalt-doped ZnO were fabricated using metallic chlorides by co-precipitation method. XRD revealed standard ZnO wurtzite crystal structure without lattice distortion due to impurities but showed presence of additional phases at higher doping ratios. Fourier transformed infrared spectroscopy also confirmed the standard ZnO profiles at lower doping ratios but additional phases at higher doping. Vibrating sample magnetometer showed soft ferromagnetic behavior for low impurity samples and harder ferromagnetic behavior for higher doping at room temperature. A simultaneous differential scanning calorimetry/thermo gravimetric analysis was performed to study the phase variations during crystallization.

Slew-rate dependence of tracer magnetization response in magnetic particle imaging

Magnetic Particle Imaging (MPI) is a new biomedical imaging technique that produces real-time, high-resolution tomographic images of superparamagnetic iron oxide nanoparticle tracers. Currently, 25 kHz and 20 mT/μ0 excitation fields are common in MPI, but lower field amplitudes may be necessary for patient safety in future designs. Here, we address fundamental questions about MPI tracer magnetization dynamics and predict tracer performance in future scanners that employ new combinations of excitation field amplitude (Ho ) and frequency (ω). Using an optimized, monodisperse MPI tracer, we studied how several combinations of drive field frequencies and amplitudes affect the tracers response, using Magnetic Particle Spectrometry and AC hysteresis, for drive field conditions at 15.5, 26, and 40.2 kHz, with field amplitudes ranging from 7 to 52 mT/μ0. For both fluid and immobilized nanoparticle samples, we determined that magnetic response was dominated by Néel reversal. Furthermore, we observed that the peak slew-rate (ωHo) determined the tracer magnetic response. Smaller amplitudes provided correspondingly smaller field of view, sometimes resulting in excitation of minor hysteresis loops. Changing the drive field conditions but keeping the peak slew-rate constant kept the tracer response almost the same. Higher peak slew-rates led to reduced maximum signal intensity and greater coercivity in the tracer response. Our experimental results were in reasonable agreement with Stoner-Wohlfarth model based theories.

Room temperature p-type conductivity and coexistence of ferroelectric order in ferromagnetic Li doped ZnO nanoparticles

Memory and switching devices acquired new materials which exhibit ferroelectric and ferromagnetic order simultaneously. We reported multiferroic behavior in Zn1−yLiyO(0.00≤y≤0.10) nanoparticles. The analysis of transmission electron micrographs confirmed the hexagonal morphology and wurtzite crystalline structure. We investigated p-type conductivity in doped samples and measured hole carriers in range 2.4 × 1017/cc to 7.3 × 1017/cc for different Li contents. We found that hole carriers are responsible for long range order ferromagnetic coupling in Li doped samples. Room temperature ferroelectric hysteresis loops were observed in 8% and 10% Li doped samples. We demonstrated ferroelectric coercivity (remnant polarization) 2.5 kV/cm (0.11 μC/cm2) and 2.8 kV/cm (0.15 μC/cm2) for y = 0.08 and y = 0.10 samples. We propose that the mechanism of Li induced ferroelectricity in ZnO is due to indirect dipole interaction via hole carriers. We investigated that if the sample has hole carriers ≥5.3 × 1017/cc, they can ...

Doxorubicin-loaded photosensitive magnetic liposomes for multi-modal cancer therapy

Multifunctional magnetic nanosystems have attracted an enormous attention of researchers for their potential applications in cancer diagnostics and therapy. The localized nanotherapies triggered by the external stimuli, like magnetic fields and visible light, are significant in clinical applications. We report a liposomal system that aims to treat cancer by magnetic hyperthermia, photodynamic therapy and chemotherapy simultaneously. The liposomes enclose clinically used photosensitizer m-THPC (Foscan) and anti-cancer drug doxorubicin, in its hydrophobic lipid bilayers, and contains magnetite nanoparticles in hydrophilic core. Three different sizes of magnetic nanoparticles (10, 22 and 30nm) and liposomes (40, 70 and 110nm) were used in this study. Magnetite single domain nanoparticles forming the magnetic core were superparamagnetic but liposomes expressed slight coercivity and hysteresis due to the clustering of nanoparticles in the core. This enhanced the heating efficiency (specific power loss) of the liposomes under an AC field (375kHz, 170Oe). Cell viability and toxicity were studied on HeLa cells using MTT assay and proteomic analysis. Confocal and fluorescence microscopy were used to study the photosensitizers profile and cells response to combined therapy. It revealed that combined therapy almost completely eliminated the cancer cells as opposed to the separate treatments. Magnetic hyperthermia and photodynamic therapies were almost equally effective whereas chemotherapy showed the least effect.

Raman scattering and interstitial Li defects induced polarization in co-doped multiferroic Zn0.96-yCo0.04LiyO (0.00 ≤ y ≤ 0.10) nanoparticles

Structural and Raman analysis confirmed a single phase wurtzite hexagonal crystalline structure of Li co-doped ZnO nanoparticles. In the Raman backscattering spectra, ELow2and EHigh2 modes corresponded to zinc and oxygen lattice vibrations. No extra vibration modes of secondary or metallic phases of Co or Li were observed. The intensity of Raman modes decreased with increasing Li content. High resolution X-ray photoelectron spectroscopy (XPS) of Zn and Co confirmed the +2 oxidation state. The deconvolution of high resolution XPS spectra of Li showed the presence of interstitial and substitutional Li defects. The room temperature polarization lay in the range of 0.155–0.225 μC cm−2 for different compositions. We observed an interesting result in the co-doped system, that even the low Li concentration sample, e.g., Zn0.94Co0.04Li0.02O, showed a P–E hysteresis loop of polarization at ∼0.20 μC cm−2. There was higher polarization for y = 0.10, due to more interstitial Li defects, and lower polarization for y = 0.06, due to more substitutional Li defects. We suggest that polarization might have appeared and been enhanced due to the net interaction of dipoles, formed by Li off-center impurities (interstitial Li defects).

Effective uniaxial anisotropy in optimized magnetite MPI tracers probed by freezing in a magnetic field

Magnetic particle imaging (MPI) relies on the specific non-linear magnetization response of superparamagnetic nanoparticle tracers for signal generation. Tracers should be tuned for optimal size distributions and magnetization responses under alternating magnetic field. Therefore, comprehensive understanding of the nanoparticle magnetization dynamics is necessary for producing efficient MPI tracers. In this study, we evaluated the dynamics of magnetization reversal of an optimized MPI tracer [1] after restricting the particles motion by freezing the solvent. Furthermore, we used an aligning field during freezing to introduce a preferred magnetization direction. The results indicate that the tracer magnetization response can be approximated by an effective uniaxial anisotropy despite the particles cubic point group symmetry.