This research aims to make a substantial contribution to the field of photonics by synergistically exploring the utilization of innovative multiferroic materials while pushing the boundaries of photonic device design. Drawing upon a robust foundation of preliminary data from prior modeling endeavors, this research seeks to realize a practical optical switch through the intricate interplay between multiferroic materials and both electric and magnetic fields. The proposed Anisotropic Photonic Crystal Slab promises to achieve complete photonic band gaps across all polarizations, unlocking a realm of extraordinary phenomena including self-collimation, negative refraction, and zero-index refraction. 

The architecture of the photonic device is designed using the CrystalWave numerical simulation suite, which empowers calculations employing the 3D Finite-Difference Time-Domain (FDTD) method across both spatial and frequency domains, alongside the Plane Wave Expansion method. Advanced equipment such as the Direct Laser Writer and E-Beam Lithography will be employed to manufacture prototypes. 

The current phase of the investigation has yielded several promising photonic structures, with a select few demonstrating favorable attributes. In collaboration with students from the Department of Material Science and Engineering, various types of multiferroic nanoparticles suitable for this project have been fabricated. Presently, ongoing efforts involve the exploration of the alteration of dielectric constants within diverse polymer-multiferroic nanoparticle blends under the influence of electromagnetic fields. 

The proposed research stands poised to drive substantial progress in the realm of Photonics, delivering noteworthy contributions to the evolution of pioneering devices for optical computing while potentially extending its sphere of influence to other scientific domains. These include the advancement of sophisticated photonic solar sails and biosensors.

Exploring the synergy of light and matter interactions: Multiferroic photonic crystals for novel photonics applications

Silicon Carbide (SiC) is a wide bandgap semiconductor, which has been widely applied to power electronics due to its excellent properties of wide band gap, high break down voltage and thermal stability. However, defects, such as threading edge dislocations (TEDs), threading screw dislocations (TSDs) and basal plane dislocations (BPDs), can limit the performance of the devices [1,2], so characterization of those defects becomes a critical aspect to improve the quality of 4H-SiC wafers. Synchrotron monochromatic beam X-ray topography (SMBXT) is a powerful technique to characterize the defects with the advantages of large field of view and clear contrast of the defects. SMBXT in 11-28 reflection has been widely used, however, the penetration depth, around 17um [3], appears to be shallow to characterize device with deep PN junction. Therefore, a new reflection with deeper X-ray penetration depth and clear contrast on the defects has been sought for. 22-4 16 reflection, the harmonic reflection of 11-28, shows better contrast on the defects, higher strain sensitivity and deeper X-ray penetration. Contrasts from the same defect of 4H-SiC with 24 um epilayer in 11-28 and 22-4 16 reflections are compared as shown in Fig. 1. From 11-28 SMBXT, BPD segments near the surface of the wafer can be observed, as shown in the blue arrows in Fig 1(a), but contrasts of the segments lying deeper in the crystal are blurred as shown in the green boxes. On the other hand, in 22-4 16 SMBXT (Fig 1(b)), the contrasts of the full BPDs can be clearly seen and the contrasts of BPD segments lying deeper in the crystal are highlighted in green boxes to compare with contrasts in 11-28 reflection. This result also proves that the penetration depth of 22-4 16 SMBXT is deeper than that of 11-28 SMBXT. Previously we have simulated images of defects in 11-28, 0008 and 000 12 using the principle of ray tracing, showing good correlation with the topograph[4,5]. In this paper, we apply the ray tracing principle to simulate defect images in the 22-4 16 topograph and compare and discuss the contrast for the different defect types. Reference: [1] K. Konishi, R. Fujita, Y. Mori and A. Shima, Semiconductor Science and Technology 2018 Vol. 33 Issue 12 [2] W. Gao, G. Yang, Y. Qian, X. Han, C. Cui, Xi. Pi, D. Yang and R. Wang, Frontiers in Materials, Jan 2023, DOI:10.3389/fmats.2023.1022878 [3] Q. Cheng, H. Peng, S. Hu, Z. Chen, Y. Liu, B. Raghothamachar and M. Dudley, Materials Science Forum 1062, 366-370 [4] H. Peng, Z. Chen, Y. Liu, B. Raghothamachar, X. Huang, L. Assoufid and M. Dudley, J. Appl. Crystallogr. 55 (2022) 544-550. [5] H. Peng, Z. Chen, Y. Liu, Q. Cheng, S. Hu, X. Huang, L. Assoufid, B. Raghothamachar and M. Dudley

Ray Tracing Simulation of Defects of 4H-SiC in 22-4 16 Reflection of Synchrotron Monochromatic Beam X-Ray Topography in Grazing Incident Geometry

Ferrite-based junction circulators [1,2] are microwave devices made of at least three ports that have been widely used in emission/reception applications ensuring an
isolation between the incoming and outgoing signals. They are especially useful in single antenna applications where signals are being transmitted and received simultaneously.
Conventional circulators are based on a ferrite disk, magnetized to saturation, placed under the central conductor ensuring electromagnetic waves to propagate in a non-reciprocal manner.
The external magnetic field allowing this saturation is provided by a permanent magnet positioned right above of the central conductor.
Due to the size, weight, cost of these systems and the fact that high frequency applications are recently the main concern, the miniaturization of the circulator is inevitable. This can be
achieved using self-biased hexagonal ferrite materials [3,4] which eliminates the use of a permanent magnet. These self-polarized materials, suitable for high frequency applications, are
pellets made out of hexaferrite powder pressed and sintered. During pressing, the orientation of the particles should be achieved in the remanence state using an external magnetic field. In
order to avoid the application of a magnetic field during pressing, and thus to minimize the cost of manufacturing circulators, we propose to design and manufacture circulators based on
hexaferrite particles in the form of platelets. It has been shown that this platelet shape, as shown in Fig. 1, induces a self-alignment of the crystals with the particles orienting themselves
spontaneously, therefore dropping the application of an external magnetic field in any way. This material will be then characterized using a coaxial cell capable of determining its dielectric
and magnetic properties such as the permittivity and the permeability [5]. The values obtained will then be used in the simulation of a coplanar circulator [6,7], that operates in the 5G band
especially around 28 GHz, using HFSS simulator. 

**References ** 
1. H. Bosma, IEEE Transactions on Microwave Theory and Techniques, Vol 12(1), p. 61-72 (1964). 
2. Y. S. Wu and F. J. Rosenbaum. IEEE Transactions on Microwave Theory and Techniques Vol 22(10), p. 849-856 (1974). 
3. N. Zeina, H. How, C. Vittoria, In 1992 IEEE International Magnetics Conference (INTERMAG), pp. 458-458 (1992). 
4. N. Noutehou, C. Patris, D. Névo, Circulateur planaire ultra-compact en bande Q." In JNM (2019). 
5. F. Costa, M. Borgese, M. Degiorgi, In Electronics, Vol 6(4), p. 95 (2017). 
6. O. Zahwe,H. Harb and H. Nasrallah, Int. Arab J. Inf. Technol., Vol 16(3A), p.600-608 (2019). 
7. R. El Bouslemti,F. Salah-Belkhodja and Y. H. A. Fekhar, Revue Méditerranéenne des Télécommunications, Vol 4(1) (2014). 

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Development of an Auto Oriented Circulator Based on Hexaferrite Materials in the 5G Frequency Band

One of the most important parts of a fluxgate sensor is the magnetic core. This work is dedicated to the study of fluxgate sensors based on the nanocrystalline wire as a core
and comparing them to the performance of amorphous wire with chemical composition (Co94Fe6)75Si15B10 [1]. Both wires were manufactured by the Institute of Technical Physics, Iasi,
Romania. Compared to the previous studies on nanocrystalline materials, we demonstrate that proper processing of nanocrystalline alloys can bring sensors with properties comparable to
the traditionally used amorphous alloys, but with better stability at elevated temperatures.
The amorphous Fe73,5Si13,5B9Cu1Nb3 master alloy wires 0.5m in length, and 0.12 mm in diameter were annealed by DC pulse to achieve the nanocrystalline structure. Contrary to other
researchers we found problems with surface oxidation in air, so our annealing was performed in Argon. During the annealing and cooling, we applied mechanical stress to achieve
transverse anisotropy. The character of changing Hc varies depending on tension as shown in Fig.1. Higher tension increases anisotropy and reduces the longitudinal permeability (Fig. 2).
Best results were shown by wires annealed under tension 9 g and 13 g with the current in the range 485 mA up to 510 mA. In these cases, coercivity was in the range of 7 A/m up to 17
A/m at 1 kHz. Annealed wires were used as a core for fluxgate sensors of the Förster and Vacquier types and with ring core.
As an example, Förster type sensor with amorphous (Hc = 20 A/m) wire as a core had max. sensitivity of 0.88 V/mT and min. the noise of 164pT/√Hz at 1 Hz.
By using nanocrystalline wire with Hc = 17A/m we achieved lower sensitivity (0.7 V/mT) but lower noise (111 pT/√Hz). The nanocrystalline core with lower Hc (9 A/m) had higher
sensitivity (1.1 V/mT) but higher noise (204 pT/√Hz) compared to the amorphous core. And the core with Hc = 13A/m had almost the same results as the amorphous wire.
This study was supported by the Grant Agency of the Czech Republic within the Nanofluxgate project (GACR GA20-27150S). 

**References:** 

[1] P. Ripka, D. Hrakova, “Multiwire Parallel Fluxgate Sensors”, IEEE Transactions on Magnetics. 2022, 58(2), 1-5. ISSN 0018-9464. DOI 10.1109/TMAG.2021.3093017 
[2] Y.-F. Li, M. Vazquez, D.-X. Chen, “Circular magnetization process of nanocrystalline wires as deduced from impedance measurements”, Journal of Applied Physics 97, 124311 (2005) 

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Creep induced Magnetic Anisotropy of Nanocrystalline Wire as a Core of Fluxgate Sensor

Susceptibility measurement of magnetic nanoparticles (MNPs) in radio frequency (RF) has been widely studied. However, most of the studies only examined frequencies
up to 20 GHz [1]. In addtion, applying two axial DC fields to increase resonance in specific frequency range and magnetic susceptibility has hardly been done before, since applying a
single static DC field is more common [2-3]. The MNPs can be used for magnetic hyperthermia and biological substances detection [4-6]. In this study, we proposed a novel method for
measuring magnetic susceptibility by a broadband microstrip line type probe up to 67 GHz [7]. Fig. 1 shows the basic principle of the experimental setup. The microtube with MNPs
(SVM-025-5H, 200 nmf, about 300 ml) was put on the microstrip line type probe, which is connected with a network analyzer (N5227A) to generate a magnetic field in a range of 10 MHz
to 67 GHz. The MNPs were put between two electromagnets connected with power supplies to generate a changeable DC field up to 1000 Oe and another orthogonal about 35 Oe DC field.
When the two orthogonal DC fields are around equal, the magnetic susceptibility of MNPs should maximize because of the magnetic switching theory [8], which results in enhancing the
signal to noise ratio. By applying the bias magnetic field, we measured the transmission coefficient, S21, of the microstrip line type probe and obtained magnetic susceptibility [7]. Fig. 2
shows the magnetic susceptibility when the DC field ranges from 0 Oe to 1000 Oe. In the DC field around 0 Oe, the magnetic susceptibility was very low because the MNPs were relaxed.
However, in the DC field of 25 Oe-75 Oe, we observed clear magnetic resonances in 20 - 40 GHz. The resonance frequency increased as the DC field increased. In this case, both fixed and
changeable DC fields are around 35 Oe, which means the magnetic susceptibility is biggest at this condition and the orthogonal DC field enhance the signal to noise ratio to detect magnetic
nanoparticle. The clear magnetic resonance of MNPs has hardly been observed in this broad bandwidth up to 67 GHz before. 


**References:** 

[1] B. K. Kuanr, V. Veerakumar and K. Lingam, Journal of Applied Physics, Vol. 105 (2009). 
[2] M. Jadav, S. P. Bhatnagar, IEEE Transactions on Magnetics, Vol. 56, p. 1-8 (2020). 
[3] P. C. Fannin, I. Malaescu and C. N. Marin, The European Physical Journal E, Vol. 27, p. 145-148 (2008). 
[4] A. Shikano, L. Tonthat, Transaction of the Magnetics Society of Japan Special Issues, Vol. 6, p. 100-104 (2022). 
[5] S. Yabukami, T. Murayama and S. Takahashi, IEEE Transactions on Magnetics, Vol. 58, 6100305 (2022, in press). 
[6] T. Yoneyama, A. Kuwahata and T. Murayama, IEEE Transactions on Magnetics, Vol. 58 (2022, in press). 
[7] S. Yabukami, C. Iwasaki and K. Nozawa, IEEE Transactions on Magnetics, Vol. 58, No. 2, p. 1-5 (2022) 

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Method for Measuring Magnetic Susceptibility of Magnetic Nanoparticles up to Millimeter Wave Frequency Range

The usage of antibody selective biding for the detection of biomolecules provides a fast and low-cost testing platform. The most common type of antibody selective biding
bio-detection tags the bio-molecule of interest with a visual marker. An example of this type of bio-detection is the lateral flow immunoassays like the pregnancy or rapid COVID tests [1].
These visual nanotags are a valid solution for binary detection in high concentrated samples. To have a quantifiable and high sensitivity bio-sensing we use magnetic nanoparticles. The
measurements of this type of magnetic nanotags require expensive laboratory equipment. A novel method using the self-resonant frequency (SRF) of inductors allows high sensitivity with
low-cost and portable systems.
Using the equivalent impedance calculation [2] and the Lichtenecker’s mixing formulas [3] we extracted an analytic simplification to describe the relation between masses of nanomaterial
in the sensing area to variations of the SRF of the inductor. The model correlates variations of the refraction index of the nanotag making the technique able to quantify not only magnetic
nanotags but other types of nanomaterials like gold or latex.
The mathematical model and its simplifications are tested against electromagnetic simulations and experimental measurements. These verifications demonstrate the validity of the model,
the value of magnetic nanoparticles as nanotags for precise quantification, and the advantages of the SRF measuring method for low-cost, high-sensitivity systems. 

**References:** 

1] Moyano, A. et al., 2020. Magnetic Lateral Flow Immunoassays. Diagnostics. 
[2] Qin Yu. et al., 2002. RF Equivalent Circuit Modeling of Ferrite-Core Inductors and Characterization of Core Materials. 
[3] A.V. Goncharenko. et al., 1999. Lichtenecker’s equation: applicability and limitations. 

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Self resonant frequency of inductors for quantification of magnetic nanoparticles

Permanents magnets, or hard ferromagnets, provide a “free” source of magnetic field, with no need of external power. Considering the integration with microsystems,
permanent micromagnets are critical components for the fabrication of microscale motors, generators, switches, pumps, acoustic speakers and energy harvester. Even though the
understanding of magnetism and magnetic materials has led to advancements in their magnetic properties [1], the application of permanent magnets in microsystems is still limited. The
reasons for that are: i) the methods for magnet fabrication at the macroscale (casting and powder processing) are fundamentally different to thin-film microfabrication approaches (physical
vapor deposition, chemical vapor deposition, electrochemical deposition); ii) even if microfabrication approaches are exploited, difficulties remain in depositing thick magnetic films (> 1
μm) and issues due to process compatibility [2].
In this work, we present a process to integrate MEMS (MicroElectroMechanical Systems) and thick permanent magnets. We have designed test structures (Fig. 1) and optimized a process
to fabricate the devices. The optimizations concern: i) deposition of a micron-thick layer of a magnetic material; ii) thermal treatment to enhance the magnetic characteristics of the
material; iii) patterning technique employed to obtain micromagnets; iv) introduction of a passivation layer to protect the material from the subsequent process steps. An image of the final
fabricated device is shown in Fig.2. Examples of application of said process to devices for energy harvesting and magnetic sensing will be discussed. 

**References:** 

M. Sagawa, S. Fujimura, N. Togawa, Journal of Applied Physics, Vol. 55, p. 2083 (1984) 
D. P. Arnold, N. Wang, Journal of microelectromechanical systems, Vol. 18, p.1255 (2009) 

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Integration of hard magnetic layer in MEMS process

Amorphous alloys have excellent low loss characteristics and are suitable for high-performance motor cores [1]. Due to the limitation of the thickness of extremely thin soft magnetic materials, stamping is not suitable for processing. At present, the most commonly used processing method is EDM [2], but this method will generate high temperature at the edge of the material, thereby changing the internal structure of the edge of the material, making iron loss worsens. 
In this paper, a ring-like experiment method was used to explore the effect of EDM on the deterioration of iron loss. The first part of the paper analyzes the research situation of the scholars on the deterioration of the iron loss at the edge of the soft magnetic material core; The second part introduces the basic principles and specific methods of the ring-like experiment（The sample and principle are shown in Fig. 1）, and explores the relationship between the ratio of the area affected by cutting to the total area and the deterioration of iron loss. Taking 0.05mm ultra-thin silicon steel as a control（Some experimental results are shown in Fig. 2）, comparing the degree of iron loss deterioration of the two materials, and analyzing the iron loss deterioration law of ultra-thin soft magnetic materials; The third part analyzes the metallographic diagram of the material, observing the crystallization of amorphous alloys at the edge after EDM cutting and the behavior of 0.05mm ultra-thin silicon steel grains, and explains the reasons for the difference in the degree of deterioration of the two materials from a microscopic point of view; Finally, summarize the relevant conclusions. 
To sum up, this paper compares the iron loss deterioration of amorphous alloys and other ultra-thin soft magnetic materials, and explores the iron loss deterioration law of amorphous alloys with different proportions of the area affected by cutting from the perspective of experimental data and microstructure. In the follow-up work, according to this law, the exact value of the iron loss deterioration at the cutting edge of the material is deduced to provide guidance for the application of amorphous alloys. 
**References:** [1] Li T , Zhang Y , Liang Y , et al. Multiphysics Analysis of an Axial-Flux In-Wheel Motor With an Amorphous Alloy Stator[J]. IEEE Access, 2020, 8:1-1. 
[2] Chai F , Li Z , Chen L , et al. Effect of Cutting and Slot Opening on Amorphous Alloy Core for High-Speed Switched Reluctance Motor[J]. IEEE Transactions on Magnetics, 2020, PP(99):1-1. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/d02ef63c98d1b3b945fec492fdd4a75a.png) 
Fig. 1 Test ring samples and principle 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/696424145d13f052da5f61f4252674b7.png) 
Fig. 2 Part of the experimental data

Study on Deterioration of Iron Loss of Amorphous Alloy by Wire Electrical Discharge Machining

Studies of Giant Magnetoimpedance (GMI) effect have attracted considerable attention considering various technological applications [1,2]. Up to now, most attention has been paid to the achievement of the highest GMI as well as to tailoring of the magnetic field dependence of GMI effect through the modification of the magnetic anisotropy of the magnetic materials. Generally, the magnetic anisotropy of amorphous materials can be controlled by the magnetostriction coefficient (that to great extend is linked to the chemical composition of material) or by special thermal treatment (including magnetic field or stress-annealing) [2,3]. Most of studies of GMI effect are performed in different families of magnetic wires [1-3]. 
Recently, a new approach allowing to tune the magnetic anisotropy of magnetic wires by depositing of magnetic and non-magnetic layers onto the glass-coating [4].
Accordingly, the purpose of this paper is to study the GMI effect in amorphous Co-rich microwires with Co- layers deposited onto glass-coating. 
Studies of magnetic properties and GMI effect of as-prepared amorphous Fe3.6Co69.2Ni1B12.5Si11Mo1.5C1.2 and of the same microwires with deposited Co-layer microwires reveals that both samples present soft magnetic properties and high GMI effect. Low field hysteresis loops of both samples are rather similar, while the contribution of Co-layer is observed in hysteresis loop measured at higher magnetic field (see Figs 1a,b). Such character of hysteresis loop is similar to those observed in microwires with mixed amorphous- crystalline structure [5]. However, the GMI ratio, ΔZ/Z and magnetic field, H, dependences of GMI effect are affected by the Co-layer (see Fig.2). In particularly, higher GMI ratio and sharper peaks on ΔZ/Z (H) dependencies. 
We discussed observed experimental dependences considering both change of the internal stresses originated by the Co-layer as well as the magnetostatic interaction between the amorphous ferromagnetic nucleus and deposited Co Layer. 
**References:** 
[1] T. Uchiyama, K. Mohri, and Sh. Nakayama, IEEE Trans. Magn., 47, No 10 (2011) pp. 3070-3073 
[2] F.Qin, H.-X. Peng, Prog.Mater. Sci,58 (2013) 183–259 
[3] A. Zhukov, et.al. J. Alloys Compound 814 (2020) 152225, 
[4] K.R. Pirota, M. Hernandez-Velez, D. Navas, A. Zhukov and M. Vázquez, Adv. Funct. Mater. 14 No 3 (2004) 266-268. 
[5] V. Zhukova, et.al. , Chemosensors, 9 (2021) 100, doi: https://doi.org/10.3390/ chemosensors9050100 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/fcd16c5915024c52cc375c38ac9ea4a7.png) 
Fig.1 Low field (a) and high field hysteresis loops of studied microwires 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1b1cb1408a5636b26250156f0a2b3a1b.png) 
Fig.2. ΔZ/Z (H) dependencies of microwire without Co-layer (a) and with Co-layer deposited onto glass-coating (b)

Magnetic properties and giant magnetoimpedance effect in multilayered microwires

Recently, multifunctional composite materials with magnetic wire inclusions for non-destructive and non-contact stress and temperature monitoring have been proposed [1]. Therefore, studies of temperature dependence of the Giant magnetoimpedance, GMI, effect become essentially relevant. There are only very few studies on temperature dependence of GMI and most of them were performed in thick amorphous wires without glass coating and in very limited temperature range [2,3,4]. Although usually the highest GMI effect is observed in Co-rich magnetic wires, GMI effect of Fe-rich glass-coated microwires can be substantially improved by stress-annealing induced magnetic anisotropy [5]. 
GMI effect and magnetic properties under temperature influence of as-prepared and stress annealed (annealing temperature Tann= 325 oC, stress applied during the annealing σ= 190MPa) thin amorphous Fe75B9Si12C4 glass-coated microwires produced by the Taylor Ulitovsky technique are analyzed. Remarkable change in the hysteresis loops and GMI effect is observed for both samples upon heating. For as-prepared FeBSiC microwire a beneficial influence of temperature on the GMI ratio is observed and hysteresis loops change of character from almost rectangular shape to inclined one (Fig.1). On the other hand, although GMI ratio improvement after stress-annealing decreases with the temperature increasing (Fig.2), temperature dependence can be tuned by the stress annealing conditions. Additionally, almost complete reversibility of the changes induced by the temperature is observed. 
Temperature dependence of the hysteresis loops and GMI effect of studied microwires is explained considering the heating effect on the internal stresses relaxation, the modification of the thermal expansion coefficients of the metallic nucleus and the glass coating and in terms of the Hopkinson effect. 
**References:** [1] A. Allue et al., Compos. Part A Appl. Sci. and Manuf., Vol. 120, p.12 (2019). 
[2] J. Nabias, A. Asfour and J. Yonnet, IEEE Trans. Magn., Vol. 53(4), p.4001005 (2017). 
[3] J.D. Santos, R. Varga, B. Hernando and A. Zhukov, J. Magn. Magn. Mater. 321, p.3875 (2009). 
[4] M. Kurniawan et al., J. Electron. Mater., Vol. 43, p.4576 (2014). 
[5] V. Zhukova et al., Scr. Mater., Vol. 142, p.10 (2018). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/4bac301404213f54c4bb4adca5d0984b.png) 
Fig.1. Hysteresis loops (a) and GMI ratio at f= 50 MHz (b) of as-prepared sample, measured at different temperature. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/2cf9acf5640bce6a1403026372c49c55.png) 
Fig.2. Hysteresis loops (a) and GMI ratio at f= 50 MHz (b) of stress annealed sample at 325 oC during 15 min (applied stress σ= 190 MPa), measured at different temperature.

Effect of temperature on magnetic properties and magnetoimpedance effect in Fe rich microwires

Soft magnetic material with high magnetic flux density (B), high permeability (µ), and high resistivity (ρ) is the key for miniaturized high frequency (>10 MHz) passive devices. The popularity of ferrites wane beyond 10 MHz owing to their prohibitively large magnetic losses (Pm), similarly, the spherical ferromagnetic alloys are too lossy due to eddy current losses (Pe). Of late, composites of electrically insulated magnetic particles attracted much attention. However, the trade-offs between µ, ρ, Pm and Pe, etc. demand judicious design of materials to stem eddy-current losses and skin effect by optimizing the thickness and properties of the insulation layer surrounding the magnetic body [1,2]. 
Here we demonstrate magnetically-aligned FeSiB-based soft magnetic flakes (SMFs; 63-106 µm, t:2-5 µm) coated with optimally thick (~10 nm) SiO2 as the potential magnetic core for power inductors operating beyond 10 MHz. The SMFs with such a high aspect ratio was fabricated by combination of mechanical ball milling of ribbons and then electrically insulted by an optimized sol-gel procedure in presence of silane coupling agent (APTES). Milling helped to reduce ribbon thickness below its skin depth to eliminated Pe at high frequencies. The effect of milling (duration, RPM, BPR) and coating conditions on the properties of the SMFs were thoroughly investigated. An optimally-tiny fraction of the milled flakes is allowed to become nanocrystalline (Fig. 1c) that augments B and µ without incurring losses. XPS and magnetization measurement results indicate that the thin but robust insulation layer is preserved through the post-annealing process which is necessary for removal of stress. B-H loop shows post-processing, coercivity is reduced significantly (from ~57 to ~6 Oe), but magnetic flux remains same. 
**References:** [1] T. Suzukia, P. Sharmaa, A. Makino, J. Magn. Magn. Mater. 491 (2019) 165641 
[2] F. Luo, X. Fana, Z. Luoa, W. Hua, J. Wangd, Z. Wu, G. Li, Y. Li and X. Liu, J. Magn. Magn. Mater. 498 (2020) 166084 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/080b991caad833ef058948eeb3dc2146.png) 
Fig 1: (a) Schematic representation of the SMFs core. (b) SEM image of the FeSiB-based as-milled flakes. (c) XRD patterns and (d) hysteresis loops of the as-milled and of SiO2 coated flakes (~63-106 µm) before and after annealing at 425oC in an inert atmosphere.

Fabrication and soft magnetic properties of FeSiB based flakes with insulating surface layer

Ultra-rapid annealing (URA) is an effective method to induce nano-crystallization in Fe-B based melt-spun amorphous precursors. The grain size after nano-crystallization depends on the heating rate employed for URA and thus, samples with a range of mean grain sizes can be prepared without altering the chemical composition. Such nanocrystalline samples are ideal for investigating the effect of mean grain size (D) on the core loss. In this study, we prepared a series of nanocrystalline Fe86B13Cu1 samples with grain sizes of 14.5, 21.7, 31.9 and 40.6 nm by varying heating rate between 10 and 104 K s-1. The core loss was measured on an Epstein frame in a frequency range between 10 Hz and 30 kHz. The measured core loss was separated into 3 parts, i.e. the hysteresis loss (Ph), classical eddy current loss (Pc) and the residual part, often referred to as the anomalous loss (Pa). Figure 1(a) shows an example of the relationship between Pa and the product of frequency (f) and the maximum polarization (Jm). The anomalous loss at Jm between 0.6 and 1.0 T is described universally by a simple power dependence with an exponent of about 1.4 over a wide frequency range between 10 Hz to 30 kHz. The grain size dependence of the coercivity (Hc) and the loss per cycle is shown in Fig. 1(b). Hc follows roughly a D3 dependence, suggesting that the samples contain large induced anisotropies. The hysteresis loss per cycle (Ph/f) reflects this steep D dependence while the anomalous loss at low frequencies appears almost independent of the grain size. Thus, the grain size effect on the total loss at low frequencies is attributable to the change in the hysteresis loss which reflects the static coercivity. However, the anomalous loss at 30 kHz shows a clear increase with an increase in D, indicating that the anomalous loss also becomes influential to the grain size dependence of the total core loss at high frequencies. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/60af3f772649b19f2c862fbc70aeea50.png) 
Fig. 1. (a) Anomalous loss versus Jm*f for a mean grain size (D) = 14.5 nm, and (b) changes in the coercivity and core loss per cycle as a function of D for nanocrystalline Fe86B13Cu1.

Underline digital video library

Exploring the synergy of light and matter interactions: Multiferroic photonic crystals for novel photonics applications

Ray Tracing Simulation of Defects of 4H-SiC in 22-4 16 Reflection of Synchrotron Monochromatic Beam X-Ray Topography in Grazing Incident Geometry

Development of an Auto Oriented Circulator Based on Hexaferrite Materials in the 5G Frequency Band

Creep induced Magnetic Anisotropy of Nanocrystalline Wire as a Core of Fluxgate Sensor

Method for Measuring Magnetic Susceptibility of Magnetic Nanoparticles up to Millimeter Wave Frequency Range

Self resonant frequency of inductors for quantification of magnetic nanoparticles

Integration of hard magnetic layer in MEMS process

Study on Deterioration of Iron Loss of Amorphous Alloy by Wire Electrical Discharge Machining

Magnetic properties and giant magnetoimpedance effect in multilayered microwires

Effect of temperature on magnetic properties and magnetoimpedance effect in Fe rich microwires

Fabrication and soft magnetic properties of FeSiB based flakes with insulating surface layer

Effect of grain size on the core loss of nanocrystalline Fe86B13Cu1 prepared by ultra rapid annealing

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