Bijoy K. Kuanr

Synthesis and characterization of yttrium iron garnet (YIG) nanoparticles - Microwave material

Magnetic Yttrium Iron Garnet (YIG) nanoparticles (NPs) were prepared by sol–gel (SG) and solid-state (SS) reaction methods to elucidate the nanoscale size on the magnetic behavior of NPs. It is found that YIG prepared by these two methods are different in many ways. The average NP sizes prepared by SG and SS methods were calculated by Scherrer formula from XRD data. SEM images show the change in grain size for both types of NPs. The sintering temperature required to form pure garnet phase is 750°C for SG and 1000°C for SS NPs. The saturation magnetizations (Ms) were 1070 Oe for SG and 1125 Oe for SS NPs, respectively. The coercivity (Hc) of SS NPs are twice larger than SG NPs. This is due to the larger crystal sizes of the SS NPs, hence more crystal boundaries. Dynamic properties were studied by ferromagnetic resonance (FMR) technique in field-sweep and frequency-sweep mode at different fixed frequencies and at different fixed magnetic fields, respectively. Resonance field (Hr) observed to increase linear...

Relation Between Static and Dynamic Magnetization Effects and Resonance Behavior in Ni Nanowire Arrays

The dynamic properties of arrays of 1-D nickel nanowires (NWs) with high aspect ratio have been studied by ferromagnetic resonance technique using a flip-chip method in the frequency domain. The fundamental magnetic parameters such as spontaneous magnetization, gyromagnetic ratio (y), Gilbert damping (α), and magnetic anisotropies of the NWs of various lengths were determined from resonance frequency - field [ f_res(H₀)] and frequency linewidth - field [Δf_res(H₀)] data. The effective fields of the NW system were observed to decrease slightly with the increasing length of NWs. The value of gyromagnetic ratio (y) increases from shorter length NWs and then saturates above 16 μm length NWs. From the Δf_res(H₀) data, we quantitatively determined Gilbert damping (α). The value of α first increases for smaller lengths and then saturates for higher lengths >30 μm, which may be attributed to intrinsic and extrinsic relaxation contributions to linewidth. We observed the dc current (I_DC) effects on RF properties [ f_res(I_DC) and Δf_res (I_DC) data] of coplanar waveguide (CPW)-based NW structures. Resonance frequency as well as frequency linewidth decreased with increase in I_DC. We conclude that the Joule heating effect causes increase in temperature, which decreases saturation magnetization and anisotropy field (H_ani), and hence there is a decrease of f_res and Δf_res with the increase of I_DC.

One dimensional FexCo1-x nanowires; ferromagnetic resonance and magnetization dynamics

Soft magnetic nanowires (NWs) are widely used for microwave and mm-wave components. The investigation of magnetization damping behavior of NWs have attracted great interest due to large influence of loss to the device, like integrated microwave device, magnetic sensors, and magnetic random access memory. With increasing operational frequency and degree of integration, the requirements to characterize 1-dimensional NWs become increasingly high. The purpose of this work is to study the magnetization dynamics in FexCo1-x NWs. A series of FexCo1-x (x=0, 0.25, 0.5, 0.75, 1) NWs were grown by controlled electro-deposition. By adjusting FexCo1-x concentration (x=0 to 1), the saturation magnetization, increased more than 20%. Ferromagnetic resonance (FMR) both in field and frequency sweep mode are employed to characterize the NWs in flip-chip geometry. It is observed that FMR field (Hr) increases with increase in applied frequency. At a fixed frequency, Fe NWs resonate at a lower field than the Co substituted NWs...

Synthesis and characterization of iron oxide nanoparticles (IONPs) and their cytotoxicity effects on lung epithelial carcinoma cells

From last decade, iron oxide nanoparticles (IONPs) have been extensively used in a wide variety of biological and medical applications such as contrast agent in magnetic resonance imaging (MRI), in magnetic hyperthermia to cure cancer, drug delivery, cell labeling and so on. However, studies related to their cytotoxicity effects on human cells are still limited. Here, we have synthesized IONPs (Fe3O4) by electrochemical method and surface modified with several polymers such as polyethylene glycol (PEG), dextran. The size, structure, morphology and magnetic properties were characterized using various techniques such as XRD, TEM, VSM and surface modification was characterized using FTIR. The XRD results revealed that IONPs were Fe3O4 with a core diameter of 30u2005nm. Further, in order to investigate the cytotoxic effect of bare Fe3O4 IONPs (Fe-NPs), human lung cancer cells were exposed to 10-100u2005µg/ml bare Fe-NPs for 24 or 48 hrs. We found that bare Fe-NPs did not significantly affect the viability of lung cancer cells within first 24u2005hr of exposure. In contrast, after 48u2005hr exposure to bare Fe-NPs, the cell viability was decreased in a concentration-dependent manner. So, these data indicate that in order to use Fe-NPs for biomedical applications, long term effects on human cells must be thoroughly investigated.From last decade, iron oxide nanoparticles (IONPs) have been extensively used in a wide variety of biological and medical applications such as contrast agent in magnetic resonance imaging (MRI), in magnetic hyperthermia to cure cancer, drug delivery, cell labeling and so on. However, studies related to their cytotoxicity effects on human cells are still limited. Here, we have synthesized IONPs (Fe3O4) by electrochemical method and surface modified with several polymers such as polyethylene glycol (PEG), dextran. The size, structure, morphology and magnetic properties were characterized using various techniques such as XRD, TEM, VSM and surface modification was characterized using FTIR. The XRD results revealed that IONPs were Fe3O4 with a core diameter of 30u2005nm. Further, in order to investigate the cytotoxic effect of bare Fe3O4 IONPs (Fe-NPs), human lung cancer cells were exposed to 10-100u2005µg/ml bare Fe-NPs for 24 or 48 hrs. We found that bare Fe-NPs did not significantly affect the viability of lung can...

BaM/YIG nano-composites: A microwave material for C to U band application

Hexaferrites have become important candidates for a variety of microwave and millimeter wave devices due to their large uniaxial magneto-crystalline anisotropy and high saturation magnetization. The goal of the present investigation is to synthesize Barium hexaferrite/Yttrium Iron Garnet (BaFe12O19/Y3Fe5O12): (BaM/YIG) Nano-Composites (NCs) to be used in broad band microwave frequency range applications, especially as microwave absorber. X-ray diffractometry, Vibrating Sample Magnetometer (VSM), and ferromagnetic resonance (FMR) techniques were used to characterize these NCs. Using a Cu coplanar wave guide and a Vector Network Analyzer, broadband (C to U) microwave absorption were investigated by placing the bulk sample in flip chip mode. Various mathematical models were employed to fit the experimental data to yield intrinsic and extrinsic damping parameters.

Magnetization Dynamics and Reversal Mechanisms in Ni Nanowire and Nanotube Arrays

Highly ordered arrays of Ni nanowires (NWs) and nanotubes (NTs) were electrodeposited into porous anodic alumina templates with 200 nm pore diameter. The geometrical parameters of the NW/NT arrays were tuned by the deposition conditions. The fabricated NWs and NTs had various lengths depending upon deposition time and NTs had a wall thickness of ~40 nm. Morphological characterizations were performed using a scanning electron microscope and transmission electron microscope yields the topology of NWs and NTs, structural properties were determined using X-ray diffraction, and magnetic characterization was done using SQUID. Dynamic properties have been studied by ferromagnetic resonance technique in frequency sweep mode. A comparative study of the magnetization reversal processes was also performed by analyzing the angular variation of resonance frequency of NWs/NTs. The resonance frequency increases linearly with magnetic field for studied arrays. In NWs the magnetization reversal mode is curling mode, whereas for NTs it is coherent rotation mode.

Localized cancer treatment by radio-frequency hyperthermia using magnetic nanoparticles immobilized on graphene oxide: from novel synthesis to in vitro studies

We have produced an innovative, theranostic hybrid nanocomposite of graphene oxide and iron oxide (GO-Fe3O4) for radio-frequency hyperthermia therapy. A new electrochemical synthesis route for the GO-Fe3O4 nanocomposite is employed. Superparamagnetic nanoparticles used for magnetic hyperthermia for biomedical application face longstanding obstacles, including the large number of nanoparticles required to achieve the desired therapeutic temperature, poor colloidal stability in aqueous suspension or physiological media, poor biocompatibility and, most importantly, low specific absorption rate (SAR). To limit the dosage of nanoparticles for therapeutic use, efforts are being made to increase the heating efficiency of nanoparticles. We have introduced an alternative way to increase the SAR value by improving the colloidal stability of magnetic nanoparticles. It is necessary to immobilize these nanoparticles on a support to prevent their agglomeration and precipitation in aqueous suspension. To address these issues, we report a reproducible electrochemical synthesis route for the GO-Fe3O4 nanocomposite. Our nanocomposite demonstrated good colloidal stability and low cytotoxicity in vitro. Due to its good colloidal stability, the nanocomposite had a high SAR of 543 W g-1 and corresponding intrinsic loss power of 5.98 nH m2 kg-1, which is 46% better than the best commercial equivalents. In vitro cytotoxicity studies demonstrated almost 70% cell viability at 200 μg mL-1 GO-Fe3O4 nanocomposite, a comparable concentration for clinical use according to FDA standards. We also showed the therapeutic potential of the nanocomposite using magnetic hyperthermia. We observed cancer cell (A549 human lung epithelial adenocarcinoma) ablation at 41, 42 and 43 °C for 30, 45, and 60 min. A maximum cancer cell death rate of 80.5% was observed at 43 °C for 60 min under alternating magnetic field exposure. Thus, the nanocomposites could be used in the efficient treatment of cancer.

Microwave monolithic filter and phase shifter using magnetic nanostructures

Monolithic Microwave Integrated Circuit (MMIC) have major impact on the development of microwave communication technology. Transition metal based ferromagnetic nano-wired (FMNWs) substrate are of special interest in order to fabricate these MMIC devices. Their saturation magnetization is comparatively higher than ferrites which makes them suitable for high frequency (>10 ∼ 40 GHz) operation at zero or a small applied magnetic field. The CoFeB nanowires in anodic alumina templates were synthesized using three-electrode electro-deposition system. After electro-deposition, 1μm thick Cu layer was sputtered on the top surface of FMNW substrate and lithography was done to design microstrip lines. These microstrip transmission lines were tested for band-stop filters and phase shifters based on ferromagnetic resonance (FMR) over a wide applied magnetic field (H) range. It was observed that attenuation and frequency increase with the increase of magnetic field (upto 5.3 kOe). For phase shifter, the influence of magnetic material was studied for two frequency regions: (i) below FMR and (ii) above FMR. These two frequency regions were suitable for many practical device applications as the insertion loss was very less in these regions in comparison to resonance frequency regions. In the high frequency region (at 35 GHz), the optimal differential phase shift increased significantly to ∼ 250 deg/cm and around low frequency region (at 24 GHz), the optimal differential phase shift is ∼175 deg/cm at the highest field (H) value.

Rare earth doped M-type hexaferrites; ferromagnetic resonance and magnetization dynamics

M-type hexagonal barium ferrites come in the category of magnetic material that plays a key role in electromagnetic wave propagation in various microwave devices. Due to their large magnetic anisotropy and large magnetization, their operating frequency exceeds above 50 GHz. Doping is a way to vary its magnetic properties to such an extent that its ferromagnetic resonance (FMR) response can be tuned over a broad frequency band. We have done a complete FMR study of rare earth elements neodymium (Nd) and samarium (Sm), with cobalt (Co) as base, doped hexaferrite nanoparticles (NPs). X-ray diffractometry, vibrating sample magnetometer (VSM), and ferromagnetic resonance (FMR) techniques were used to characterize the microstructure and magnetic properties of doped hexaferrite nanoparticles. Using proper theoretical electromagnetic models, various parameters are extracted from FMR data which play important role in designing and fabricating high-frequency microwave devices.

Fabrication of Magnetically Tunable Schottky Diode Using Bismuth Ferrite Thin Film on Gold

Gold (50 nm)/bismuth ferrite (BFO) (100 nm) metal–semiconductor Schottky junction is fabricated using pulsed laser deposition (PLD) method on a Si substrate. BFO (BiFeO₃) target for PLD deposition was made using BFO nanoparticles synthesized through sol-gel method. The forward- and reverse-bias current–voltage (<inline-formula> <tex-math notation=LaTeX>