Electrodeposition of Ferromagnetic Nanostructures

The fabrication of one-dimensional ferromagnetic nanostructured materials such as nanowires and nanotubes by the electrodeposition technique is discussed. The size, shape and structural properties of nanostructures are analysed by controlling the deposition parameters such as precursors used, deposition potential, pH, etc. The growth of nanostructures and various characterization techniques are studied to support their one-dimensionality. A comparative study of ferromagnetic nanowires and nanotubes is made using angular-dependent ferromagnetic resonance technique

High-frequency characterization of Permalloy nanosized strips using network analyzer ferromagnetic resonance

We report on the dynamic properties of Permalloy nanostrips at gagahertz frequencies. The thickness of the strips is 100 nm, strip width is 300 nm, strip spacing is 1 μm, and length is 0.3–100 μm; aspect ratios are 1:1, 1:2, 1:3, 1:5, 1:10, and 1:333. The dynamic behavior was studied by network analyzer ferromagnetic resonance (FMR) using Permalloy strips on a coplanar waveguide in flip-chip geometry. The FMR mode frequencies (fr) can be controlled by the aspect ratio as well as by the applied magnetic field (H). In longer strips (1:10 and 1:333), the excitation frequencies show a soft mode behavior (Heff = 990 Oe) when the field is along the hard axis. However, along the easy axis (along the strip length), fr increases with applied field. At a field of 3 kOe, fr values are almost independent of aspect ratio along the easy axis except for the 1:1 strip. Along the hard axis, the frequencies are strongly dependent upon the aspect ratio. We also observed that the frequency linewidths of the strips are dependent on the aspect rati

Spin dynamics of room temperature van der Waals (vdW) ferromagnets and their usage in microwave devices

Quasi-two-dimensional van der Waals (vdW) materials exhibiting room-temperature (RT) long-range ferromagnetic nature have emerged as a significant research field to explore fundamental condensed matter physics due to their intriguing physical properties. These vdW materials enable a futuristic platform for implementing novel spintronics devices. Here, we examined the spin dynamics of polycrystalline Fe5GeTe2 and Fe4.8Co0.2GeTe2 vdW materials using ferromagnetic resonance (FMR) spectroscopy. Vibrating Sample Magnetometer (VSM) study reveals that both materials have a soft ferromagnetic character at room temperature. From room temperature FMR measurements, the effective magnetization of Fe5GeTe2 and Fe4.8Co0.2GeTe2 derived ∼0.54 ± 0.056 and 0.50 ± 0.017 kOe, respectively. These results are consistent with reported VSM data. Fe5GeTe2 and Fe4.8Co0.2GeTe2 exhibit broad FMR linewidths of 0.697 ± 0.036 and 0.748 ± 0.056 kOe, respectively, which can be due to inhomogeneous line broadening. Besides its intrinsic contribution to linewidth, it is also affected by extrinsic Gilbert damping (αext). The value of αext is influenced by conflicting intra-band and inter-band electronic transitions, according to Modified Kambersky's theory. Furthermore, the effective Gilbert damping constant (α) obtained is 0.0513 ± 0.0046 for Fe5GeTe2 and 0.0526 ± 0.0031 for Fe4.8Co0.2GeTe2 at RT. Additionally, we developed microwave signal processing devices using these materials and evaluated their functionality both as a microwave band-reject filter and an adjustable phase shifter. The stop-band response was studied across the 5 to 25 GHz frequency range under an applied magnetic field as high as 7 kOe. For these flip-chip-based devices, attenuation is −5 dB/cm for the Fe5GeTe2-based filter and −3.2 dB/cm on sample Fe4.8Co0.2GeTe2 at 6.95 and 5.37 kOe, respectively. The same micro-strip filter was used as a tunable phase shifter in the off-resonance region. The optimal differential phase shift studied for Fe5GeTe2 and Fe4.8Co0.2GeTe2-based phase shifters in the high-frequency region (22 GHz for Fe5GeTe2 and 18 GHz for Fe4.8Co0.2GeTe2) is 23°/cm and 14°/cm, respectively, at high magnetic fields. These versatile devices find integration across a wide spectrum of applications, such as phased-array antennas, radar systems, and wireless communication systems, offering their benefits to diverse fields

Fabrication of compact circular ring antenna loaded with Gd-YIG ferrites: Photon–magnon interaction

In telecommunications technology, transmitting and receiving signals is not possible without an integrated antenna. Recently, novel approaches of transmitting and receiving signals using advancement in quantum technology as “information coherent transfer” have been emphasized which overcomes the limitations of superconducting qubits. In the present investigation, a compact-sized circular-ring antenna was designed for a 12 GHz centre frequency. The antenna was topped with Gd(x)-doped YIG (x = 0.0, 0.1, 0.2, 0.3) thin disks to investigate its tunable operation over the tri-band (C to Ku) frequencies due to the photon–magnon coupling, which enables coherent qubit information transmission from an electromagnetic (EM) carrier to the magnons. The proposed prototype of the antenna is validated using HFSS simulation. To characterize the frequency tunability of the designed antenna, we measured the return loss (S11) via a vector network analyzer as a function of dc magnetic field. Different concentrations of Gd-doped YIG ferrites (Gdx-YIG) have been loaded on ring antennas to observe strong anti-crossing phenomena with the application of an external magnetic field. The designed antenna has a tunability of around 300% for a small applied magnetic field up to 3.7 kOe. The maximum gain of dual resonance antenna is 1.4 for higher magnetic field of 3.7 kOe. The highest efficiency and lowest bandwidth of 30% and 14% respectively, for Gd0.1-YIG disk are observed. The measured normal mode splitting spectrum as a function of bias magnetic field that gives the maximum coupling strength is 153 MHz for a Gd concentration of 0.1. For practical applications, such antennas are suitable for use in tunable tri-band or multi-band applications (C to Ku)

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

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

Effect of Ta buffer layer on the structural and magnetic properties of stoichiometric intermetallic FeAl alloy

The magnetostructural phase transition in Fe50Al50 alloy with chemically ordered paramagnetic B2 and disordered ferromagnetic (FM) A2 phase has applications in spintronics such as phase-change magnetic memory and magnonic devices. We first conducted a systematic first-principles density functional theory study of the A2 and B2 phases in the Fe50Al50 alloy. A theoretical understanding of this equiatomic alloy’s electronic and spin-dynamical properties leads us to the experimental exploration of the FM A2 phase. Therefore, we deposit the 50 nm Fe50Al50 alloy thin film using sputtering and investigate the influence of the Ta buffer layer on its structural and magnetic properties. Our results reveal that the film with a buffer layer exhibits the A2 phase with appreciably higher saturation magnetization (848 emu/cc) than the film without a buffer layer (576 emu/cc). However, the surface roughness and Gilbert damping (α) slightly increase with the presence of the buffer layer from 0.41 to 0.56 nm and 4.35 × 10−3–4.94 × 10−3, respectively. The enhancement in α is due to extrinsic contributions induced by surface inhomogeneities

Microstrip-tunable band-pass filter using ferrite (Nanoparticles) coupled lines

In this paper, we designed, fabricated, and characterized a novel band-pass filter using ferrite nanoparticles as the active element in microstrip geometry. Two 50-ω Cu transmitting/receiving antennas (one side fed and the other side shorted) were fabricated by photolithography on top of a thick layer of ferrites (Fe3O4) nanoparticles. The filter is based on ferromagnetic resonance. It is very compact and has very wide frequency tunability. Linear dependence is obtained between the resonance frequency and the applied dc magnetic field. The bandwidth and Q-factor of the filter are observed to be almost constant over the field range studied. Theoretical calculations have been performed considering the ferrite nanoparticles as an effective medium with effective demagnetization. The frequency for different applied fields was calculated for different volume fractions, and it is shown theoretically that the control of band-pass frequency can also be achieved by varying the volume fraction of the nanoparticles in the effective medium. © 2009 IEEE

Size dependent microwave properties of ferrite nanoparticles: Application to microwave devices

We studied the magnetic field dependence of the resonance frequency (fr) and frequency linewidth (Δf) of iron oxide nanoparticles (Fe3 O4) with different particle sizes spin-coated on a coplanar waveguide. Using a vector network analyzer, we find that the resonance frequency increases with an increase in applied field for all particle sizes, while Δf decreases with the increase in the particle size. We have also carried out a theoretical study using the power absorbed by the different regions of the coplanar waveguide and found that the results are in accordance with the experiment. © 2009 American Institute of Physics