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

Hybrid anisotropy heterostructures consist of two exchange coupled magnetic layers with in-plane and out-of-plane magnetic anisotropy where the exchange coupling is controlled by a non-magnetic spacer layer [1,2], Fig.1. Previous studies have investigated the quasi-static magnetic properties of these structures using magnetometry and polarised neutron reflectivity (PNR) to determine the magnitude and extent of the coupling in these layer [3]. In this work we extend the study of hybrid anisotropy thin films to include the dynamic properties of these structures. We undertake angle dependent FMR measurements using VNA-FMR where the angle of the applied magnetic field can be varied whilst keeping the waveguide in a fixed position. The experimental details of our measurement are identical to those report in [4] except that we replace the Picoprobe waveguide with a NanOsc Coplanar Waveguide v4. Our results demonstrate that the angle dependence of the resonance frequency depends on the degree of coupling between the two magnetic layers. In systems with significant exchange coupling (e.g.: Pd spacer thickness of 1.2 & 2 nm) we observe a dominant â€˜acousticâ€™ mode which shows a maximum frequency for an applied field angle of approximately 40o to the sample plane, Fig.2. The increase in frequency is ~25% for an applied field of 6 kOe. To further understand this effect, we have conducted micro-magnetic simulations using MuMax3 [5] which are able to reproduce the key features of the experimental results which will be presented in the full paper for spacer thicknesses of 0, 1.2, 2, 4, 6 and 100 nm). This shows that the angle of the applied field may be used to tune the resonance response of these materials over a significant frequency range.

Frequency Tunability with Field Angle in Hybrid

Self-spin-orbit torque (SOT) that arises from within the ferromagnetic layer itself, such as FePt [1] and CoPt [2] systems, offers new design possibilities for the SOT devices. Unlike FePtâ€™s self-SOT that relies on chemical ordering and apparent global symmetry breaking, CoPt was found to possess rather robust self-SOT with A1-disorder phase. This kind of bulk-SOT which does not rely on the apparent symmetry-breaking attracted our attention. A question arises as to whether the bulk-SOT generated by the structural disorder is comparable to that generated by apparent symmetry-breaking such as composition gradient and interface cutting? This study investigates the microstructural ordering effects on the CoPtâ€™s self-SOT phenomena using orientation-resolved synchrotron x-ray diffraction. Three samples, (i)Ta/CoPt (20nm)/Ta (denoted as baseline-CuPt); (ii) Ta/[Co(0.5nm)/Pt(0.5nm)]20/Ta (denoted as superlattice-CoPt); (iii) Ta/Cu(2nm)/CoPt(20nm)/Cu(2nm)/Ta (denoted as Cu-CoPt), were investigated. All three samples were determined to possess the A1 phase with close Ïxx (â‰ˆ 55 Î¼Î©â—cm) under the Hall device structure. The baseline-sample possessed a (111)-textured A1-phase microstructure, and it yielded a damping-like torque efficiency ÎµDT=0.174Â±0.037. This value is close to that reported in the representative literature of CoPt self-SOT [2]. A similar microstructure, while with an enhanced ÎµDT=0.636Â±0.0333, was obtained in the superlattice sample due to the multi-interface symmetry-breaking effects. However, we found that the microstructure appeared to contain randomly-oriented grains in the Cu-CoPt sample, and this resulted in ÎµDT=0.502Â±0.089. The results imply that the short-range symmetry-breaking could contribute to the SOT in a level close to that achieved by the apparent symmetry-breaking.

Strong Bulk Spin orbit Torque Effect Enabled by Microstructural Disordering

Interlayer DMI (IL-DMI) has been recently predicted and observed in multilayer thin film heterostructures1-3, coupling two neighboring magnetic films via a non-magnetic interlayer in a chiral fashion. IL-DMI could be utilized to obtain complex chiral magnetic states in one layer, controlled by the magnetic configuration of a neighboring layer, of great interest to spintronic applications. Previous work using magnetometry techniques indicates the existence of non-zero IL-DMI in Synthetic Antiferromagnetic (SAF) bilayers with highly asymmetric properties; one layer close to the spin reorientation transition, and the other fully out-of-plane. In these systems, IL-DMI is manifested as a chiral exchange bias under in-plane magnetic fields. In this contribution, we further investigate these systems via a combination of X-ray magnetic scattering and imaging techniques, revealing the presence of periodic chiral magnetic structures. In particular, X-ray Magnetic Circular Dichroism Photo Electron Emission Microscopy (XMCD-PEEM) measurements evidence the formation of ring-like structures of sizes after applying a field cycling protocol (Fig. 1). In order to understand more in detail the magnetic configuration of these textures, we reconstruct the spatially resolved magnetization vector by combining different relative sample-beam XMCD projections, yielding the presence of 360 degree domain walls separating the outer and inner domains. During the presentation, we will discuss in detail the role that IL-DMI and other magnetic interactions play in the formation and shape of these rings.

Tunable in plane chirality via Interlayer DMI interactions in Synthetic Anti

Magnetic multilayers constitute a rich class of material systems with a number of precisely tunable parameters (e.g., layer thickness and repeat number) that determine both their magnetic and electronic properties [1]. We present a comprehensive characterization of structural and magnetic properties of the novel system Pt/Co/Mn, which extends the group of Pt/Co/X (X = metal) multilayers that have been investigated thus far. The structural properties of the sputter-deposited Pt/Co/Mn stacks were determined from X-ray reflectometry and scanning transmission electron microscopy experiments. Subsequently, we performed magnetometry measurements in order to study hysteresis loops as a function of varying layer thickness values. We demonstrate that an increasing Co layer thickness changes the magnetic anisotropy from out of plane to in plane, whereas the deposition of thicker Mn layers leads to a decrease in the saturation magnetization, see Fig. 1. Temperature-dependent magnetometry measurements reinforce the hypothesis of antiferromagnetic coupling at the Co/Mn interfaces being responsible for the observed Mn thickness dependence of the magnetization reversal. Moreover, magneto-optical imaging experiments indicate systematic changes in magnetic domain patterns as a function of the Co and Mn layer thickness and suggest the existence of bubblelike domainsâ€”potentially even magnetic skyrmionsâ€”in the case of sufficiently thick Mn layers, which are expected to contribute to a sizable Dzyaloshinskii-Moriya interaction in the multilayer stacks. We identify Pt/Co/Mn as a highly complex multilayer system with strong potential for further fundamental studies and possible applications [2]. This work is supported by the Deutsche Forschungsgemeinschaft (DFG) through the research fellowship LO 2584/1-1, the NSF through I-MRSEC Grant No. DMR-1720633 and US DOE, Office of Science, MSED under Contract No. DE-SC002260.

Structural and Magnetic Properties of Pt/Co/Mn Multilayers

Artificial spin ices (ASIs) are arrays of Ising-like magnetic nanoislands that are of interest for investigating fundamental physics as well as designing information processing devices. Recent efforts have pushed ASIs beyond the Ising model by using systems capable of possessing both Ising and complex spin textures (CSTs) such as vortices, which alters the nature of dipolar coupling and gives rise to exotic physics in existing ASI lattices [1-3]. CST-Ising studies in metal-based ASIs have primarily focused on field-dependent properties, as temperature-dependent experiments present challenges for metal-based systems. However, we have found that ASIs fabricated from the epitaxial complex oxide La0.7Sr0.3MnO3 (LSMO) can facilitate studies of CST-Ising formations in thermally active ASIs. CST-Ising formations in thermalized LSMO ASIs occurs through a careful balance of inter- and intra-island energetics enabled by the LSMO magnetic parameters [1]. Using x-ray photoemission electron microscopy (XPEEM) to perform magnetic domain imaging, we studied the thermal evolution of ex situ magnetized LSMO-based brickwork ASIs using a series of short (~5 min) annealing steps at 350 K (near LSMO bulk Tc ~ 370 K). We observed that the spin texture evolution can be tuned through the ASI lattice parameter, a. While ASIs with a = 600 nm formed only Ising states and experienced a few spin flips (~1 % of nanoislands) between annealing steps, ~20% of initially Ising nanoislands transformed into CSTs after the first annealing step for ASIs with a = 638 nm. Furthermore, we observed that thermal fluctuations in nanoisland domain states can occur through several different routes including Ising spin flips and transformations in magnetization topology (i.e., Ising-to-CST, CST-to-Ising, and CST-to-CST states). These results suggest the potential to introduce exotic kinetics in existing ASI lattices and would provide further insights into designing magnetically-reconfigurable computing architectures.

Imaging thermally induced Ising

Non-collinear antiferromagnetic orders are of strong interest in the fields of spintronic, topological magnetism and multiferroicity [1]. However, the magnetic imaging of these materials is particularly challenging due to their zero net magnetization. The main goal of this work is to achieve the fully vectorial reconstruction of a non-collinear magnetic order, by the combination of Resonant X-ray Magnetic Scattering (RXMS) [2] and Coherent Diffraction Imaging (CDI) [3] . Dy epitaxial films exhibiting an antiferromagnetic helical phase and strong X-ray magnetic scattering at the Dy L3 edge [4] are interesting candidates. The micro-patterning of Dy nanofilms (top-down approach) is required to synthetize model micro-objects and to efficiently implement this technique. We present the results of the microfabrication process and the full structural and magnetic characterization of the Dy Âµ-disks. The high crystalline quality of the Dy(0001) epitaxial films is maintained after the optical lithography and Ion Beam Etching. X-ray diffraction (Fig.1) indicates moderate decrease in the coherence length (10%) and increase in mosaÃ¯city (17%) in 2mm diameter disks compared with continuous films. A fcc phase however tends to form, most likely due to hydrogenation during the patterning process . SQUID measurements and Resonant X-Ray Magnetic Scattering (BM28-ESRF) confirm the occurrence of the helical phase in the Dy Âµ-disks, with similar NÃ©el and Curie temperatures as in continuous films. (002-t) magnetic satellites reveal that helical turn angles in the patterned samples do not differ significantly from those observed in epitaxial films [5] (Fig. 2). The role of the buffer layer (Nb or Nb/Y) on the crystal quality and the presence of crystalline defects is also carefully investigated, since structural speckles in CDI have to be avoided for measurements and proper analysis of the magnetic contributions.

Development of Dy µ disks for coherent imaging of helimagnetic domains

Artificial spin ice lattices consist of extended arrays of dipole coupled nanomagnets. This relatively simple system has seen a striking amount of applications, such as mimicking spin frustration, reconfigurable magnonic crystals, and in the last years it displayed potential for novel forms of computation. We have recently investigated the effects of the internal texture of these nanomagnets, specifically the thermal behavior, and found the excitation of magnons, and additional fluctuations at the ends of the nanomagnet. These effects offer a different view of the effect of temperature on the magnetism than the traditional flipping of the Ising spin. Here, we present measurements using AC susceptibility and temperature dependent MOKE of artificial spin ice structures, which indicate the presence of these additional texture fluctuations. It is shown that, even though they exist on a different length scale than the binary switch of the internal magnetization, both types of fluctuations can be tuned through the interaction strength of the mesospins. In addition, we present a detailed simulation study that shows the effects of coupling of these texture fluctuations across a gap, both in a double magnet configuration and an ASI vertex, and capture these fluctuations in energy landscapes. We determine the energy barriers, eigenmodes, and curvatures of the energy landscapes at the metastable minima and relate them to the attempt frequencies of the system. These investigations of the internal texture could lead to a rethinking of the artificial spin ice lattice, in which case the internal textures could be used to mimic magnetic effects on different length scales.

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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

Frequency Tunability with Field Angle in Hybrid

Strong Bulk Spin orbit Torque Effect Enabled by Microstructural Disordering

Tunable in plane chirality via Interlayer DMI interactions in Synthetic Anti

Structural and Magnetic Properties of Pt/Co/Mn Multilayers

Imaging thermally induced Ising

Development of Dy µ disks for coherent imaging of helimagnetic domains

Effects of thermal fluctuations within and among the magnetic textures in artificial spin ice

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