Electrophoretic deposition of polymers and proteins for biomedical applications.

Theoretical results for the magnetization dynamics of a magnonic crystal formed by grooves on the surface of a ferromagnetic film, called a surface-modulated magnonic crystal, are presented. For such a system, the role of the periodic dipolar field induced by the geometrical modulation is addressed by using the plane-wave method. The results reveal that, under the increasing of the depth of the grooves, zones with magnetizing and demagnetizing fields act on the system in such a way that magnonic band gaps are observed in both Damon-Eshbach and backward volume geometries. Particularly, in the backward volume configuration, high-frequency band gaps and low-frequency flat modes are obtained. By taking into account the properties of the internal field induced by the grooves, the flattening of the modes and their shift towards low frequencies are discussed and explained. To test the validity of the model, the theoretical results of this work are confirmed by micromagnetic simulations, and good agreement between both methods is achieved. The theoretical model allows for a detailed understanding of the physics underlying these kinds of systems, thereby providing an outlook for potential applications on magnonic devices.

/pdf/dipolar-interaction-induced-band-gaps-and-flat-modes-in-2tls5ciu5o.pdf

Dipolar interaction induced band gaps and flat modes in surface-modulated magnonic crystals

Standing spin waves in thin films with a tiny periodic surface modulation are quantized in such a way that a multiple of their wavelength fits into one modulation period. This paper tackles the question how these film modes evolve into modes in a one-dimensional magnonic crystal consisting of periodic individual wire structures. By sequentially increasing the surface modulation and subsequent dynamic characterization of the same sample, simple transition rules are found connecting the modes of both systems with one another.

/pdf/spin-wave-modes-in-transition-from-a-thin-film-to-a-full-206ezapy5i.pdf

Spin-wave modes in transition from a thin film to a full magnonic crystal

The effects of the electric and magnetic field variation on multiferroic heterostructure were studied in this work. Thin films of polycrystalline Fe50Pt50 (FePt) were grown by dc-sputtering on top of the commercial slabs of lead magnesium niobate-lead titanate (PMN-PT). The sample was a (011)-cut single crystal and had one side polished. In this condition, the PMN-PT/FePt operates in the L-T (longitudinal magnetized-transverse polarized) mode. A FePt thin film of 20 nm was used in this study to avoid the characteristic broad microwave absorption line associated with these films above thicknesses of 40 nm. For the in-plane easy magnetization axis (01-1), a microwave magnetoelectric (ME) coupling of 28 Oe cm kV −1 was estimated, whereas a value of 42 Oe cm kV −1 was obtained through the hard magnetization axis (100). Insight into the effects of the in-plane strain anisotropy on the ME coupling is obtained from the dc-magnetization loops. It was observed that the trend was opposite along the easy and hard magnetic directions. In particular, along the easy-magnetic axis (01-1), a square and narrow loop with a factor of Mr /MS of 0.96 was measured at 10 kV/cm. Along the hard-magnetic axis, a factor of 0.16 at 10 kV/cm was obtained. Using electric tuning via microwave absorption at X-band (9.78 GHz), we observe completely different trends along the easy and hard magnetic directions; Multiple absorption lines along the latter axis compared to a single and narrower absorption line along the former. In spite of its intrinsic complexity, we propose a model which gives good agreement both for static and microwave properties. These observations are of fundamental interest for future ME microwave components, such as filters, phase-shifters, and resonators.

In-plane anisotropic effect of magnetoelectric coupled PMN-PT/FePt multiferroic heterostructure: Static and microwave properties

The growing number of nanoparticle applications in science and industry is leading to increasingly complex nanostructures that fulfill certain tasks in a specific environment. Nickel nanorods already possess promising properties due to their magnetic behavior and their elongated shape. The relevance of this kind of nanorod in a complex measurement setting can be further improved by suitable surface modification and functionalization procedures, so that customized nanostructures for a specific application become available. In this review, we focus on nickel nanorods that are synthesized by electrodeposition into porous templates, as this is the most common type of nickel nanorod fabrication method. Moreover, it is a facile synthesis approach that can be easily established in a laboratory environment. Firstly, we will discuss possible applications of nickel nanorods ranging from data storage to catalysis, biosensing and cancer treatment. Secondly, we will focus on nickel nanorod surface modification strategies, which represent a crucial step for the successful application of nanorods in all medical and biological settings. Here, the immobilization of antibodies or peptides onto the nanorod surface adds another functionality in order to yield highly promising nanostructures.

https://www.mdpi.com/1996-1944/11/1/45/pdf

Applications, Surface Modification and Functionalization of Nickel Nanorods.

Exchange bias properties of [FeNi/IrMn]n multilayer films with variable thickness of the ferromagnetic layers and different repetitions n were determined by using static and dynamic measurement techniques. The static magnetic properties were revealed through magnetometry measurements at room temperature following major hysteresis loops and first-order reversal curves protocols. Room temperature x-band ferromagnetic resonance (FMR) and vector network analyser (VNA)-FMR experiments were used to determine dynamically the exchange anisotropy in the FeNi/IrMn multilayers. From the static measurements the exchange anisotropy was determined while dynamic measurements allowed the determination of additional parameters including anisotropy field, saturation magnetization and rotatable anisotropy. The differences between the values of the exchange biased obtained from each technique are discussed.

Exchange bias in (FeNi/IrMn)n multilayer films evaluated by static and dynamic techniques

Dynamic ferromagnetic resonance (FMR, X-band 9.8 GHz) and static first-order reversal curve (FORC) techniques are combined to study the intrinsic exchange-bias distribution via measurements of in-plane angular variation in (FeNi/IrMn)n multilayers. The angular dependence of the exchange bias field was qualitatively and quantitatively investigated using both methods, which are sensitive to different couplings between the ferromagnetic layers. We have used the analysis of the angular dependence of first-order reversal curve (AFORC) data, extracted from FORC curves measured from up to in steps. In addition, its counterpart angular dependence of FMR (AFMR) measurements were carried out and correlated with the AFORC results. The AFORC proved to be useful for simultaneously studying the magnetization reversal processes and magnetic interactions between the layers of the (FeNi/IrMn)n. These interactions are related to the structure and interfaces in the (FeNi/IrMn), and the results obtained by AFMR and AFORC are contrasted with a modified theoretical model for domain-wall formation.

https://iopscience.iop.org/article/10.1088/1361-6463/aa5613/pdf

Angular dependent FORC and FMR of exchange-biased NiFe multilayer films

In this paper, we present a systematic study of a series of 1-D magnonic crystals defined as periodic arrays of grooves in a Permalloy thin film. Thin films of Ni80Fe20 with dimensions $350~\mu \text{m}$ by $10~\mu \text{m}$ and thickness 40 nm were prepared on the top of signal line of coplanar waveguides by a combination of photolithography, e-beam lithography and lift-off processing. Starting from thin films, stripe-type periodic structures (grooves) with a depth of 4 nm were created in a controlled manner by focused ion beam. By changing the dimensions of the distance between the grooves, it was possible to systematically tune single, double, triple, and quadruple ferromagnetic resonance (FMR) absorption modes. Broadband FMR experiments were carried out to collect the frequency and field-dependent FMR spectra. The experimental results are corroborated with micromagnetic simulations.

Splitting of Ferromagnetic Resonance Spectra in Periodically Modulated 1-D Magnonic Crystal

We explored a series of highly uniform magnetic nanoparticles (MNPs) with a core-shell nanoarchitecture prepared by an efficient solvothermal approach. In our study, we focused on the water dispersion of MNPs based on two different CoFe2O4 core sizes and the chemical nature of the shell (MnFe2O4 and spinel iron oxide). We performed an uncommon systematic investigation of the time and temperature evolution of the adiabatic heat release at different frequencies of the alternating magnetic field (AMF). Our systematic study elucidates the nontrivial variations in the heating efficiency of core-shell MNPs concerning their structural, magnetic, and morphological properties. In addition, we identified anomalies in the temperature and frequency dependencies of the specific power absorption (SPA). We conclude that after the initial heating phase, the heat release is governed by the competition of the Brown and Neel mechanism. In addition, we demonstrated that a rational parameter sufficiently mirroring the heating ability is the mean magnetic moment per MNP. Our study, thus, paves the road to fine control of the AMF-induced heating by MNPs with fine-tuned structural, chemical, and magnetic parameters. Importantly, we claim that the nontrivial variations of the SPA with the temperature must be considered, e.g., in the emerging concept of MF-assisted catalysis, where the temperature profile influences the undergoing chemical reactions.

/pdf/self-limitations-of-heat-release-in-coupled-core-shell-2fcy2l6hvz.pdf

Self-Limitations of Heat Release in Coupled Core-Shell Spinel Ferrite Nanoparticles: Frequency, Time, and Temperature Dependencies

In this paper, we present a systematic study of a series of 1-D magnonic crystals defined as periodic arrays of grooves in a Permalloy thin film. Thin films of Ni<sub>80</sub>Fe<sub>20</sub> with dimensions <inline-formula> <tex-math notation=\"LaTeX\">$350~\\mu \\text{m}$ </tex-math></inline-formula> by <inline-formula> <tex-math notation=\"LaTeX\">$10~\\mu \\text{m}$ </tex-math></inline-formula> and thickness 40 nm were prepared on the top of signal line of coplanar waveguides by a combination of photolithography, e-beam lithography and lift-off processing. Starting from thin films, stripe-type periodic structures (grooves) with a depth of 4 nm were created in a controlled manner by focused ion beam. By changing the dimensions of the distance between the grooves, it was possible to systematically tune single, double, triple, and quadruple ferromagnetic resonance (FMR) absorption modes. Broadband FMR experiments were carried out to collect the frequency and field-dependent FMR spectra. The experimental results are corroborated with micromagnetic simulations.

Shankar Khanal

Papers

Exchange bias in (FeNi/IrMn)n multilayer films evaluated by static and dynamic techniques

Angular dependent FORC and FMR of exchange-biased NiFe multilayer films

Splitting of Ferromagnetic Resonance Spectra in Periodically Modulated 1-D Magnonic Crystal

Self-Limitations of Heat Release in Coupled Core-Shell Spinel Ferrite Nanoparticles: Frequency, Time, and Temperature Dependencies

Splitting of Ferromagnetic Resonance Spectra in Periodically Modulated 1-D Magnonic Crystal (II)