United States

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 (&gt; 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.&lt;br&gt;

**References:**&lt;br&gt;

M. Sagawa, S. Fujimura, N. Togawa, Journal of Applied Physics, Vol. 55, p. 2083 (1984)&lt;br&gt;
D. P. Arnold, N. Wang, Journal of microelectromechanical systems, Vol. 18, p.1255 (2009)&lt;br&gt;

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MMM 2022

Integration of hard magnetic layer in MEMS process

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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technical paper

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

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We present results obtained within the density functional theory framework with the focus on understanding magnetic properties of Sm7Pd3 compound. The binary Sm7Pd3 compound crystallizes in the Th7Fe3-type structure, space group in P63mc, in which the samarium atoms occupy three independent sites two 6(c) and one 2(b), and the palladium atoms occupy a single 6(c) site. To get the correct effect of the localized Sm 4f states and account for the strong correlations between f, d and p states of constituent elements, we used the full potential linearized augmented plane wave (FP-LAPW) method as implemented in WIEN2k, along with the localized treatment of 4f states using the Hubbard U approach. Theoretically derived magnetic anisotropy confirms experimental observations, where the c-axis represents the easy magnetization direction. By evaluating possible magnetic states, including ferromagnetic, ferrimagnetic and partial antiferromagnetic arrangements of the magnetic moments, we find that assuming ferrimagnetic Sm7Pd3 leads to the best match between the calculated and experimentally observed molar magnetic moments. We also analyze and discuss how f, d, and p electrons contribute to the emergence of rather unusual magnetic phenomena observed experimentally in the magnetically hard Sm7Pd3 magnet. Acknowledgment: This work was performed at Ames National Laboratory and supported by the Division of Materials Science and Engineering of the Office of Basic Energy Sciences, Office of Science of the U. S. Department of Energy (DOE). Ames National Laboratory is operated for the U.S. DOE by Iowa State University of Science and Technology under Contract No. DE-AC02-07CH11358.

Competing magnetic states in Sm7Pd3

Single phase polycrystalline samples of (Ho(1-x)Ndx)2CoMnO6 (x = 0.0 â€“ 0.2)(HNCMO) double perovskite were prepared by using conventional solid state reaction route and their structural and dielectric properties were analyzed. These compounds are of monoclinic structure having space group P21/n. From the plots of XRD it is seen that the most intensed peaks are shifting towards lower Bragg angle, which reveals an increase in lattice parameters with increase in Nd doping. The grain size decreases with increase in Nd concentration which is seen from the FESEM images. The average grain size of HNCMO (x = 0.0, 0.05, 0.1, 0.2) are found to be 416Î¼m, 347Î¼m, 337Î¼m, 300Î¼m respectively. Room temperature frequency variation of real and imaginary parts of dielectric constant show a drop in their value with increase in frequency. Moreover, a dispersion in the low frequency region is observed and is attributed to the contribution of space charge polarization. At the same time, we have observed a decrease in the value of dielectric loss with Nd substitution. The frequency dependence of both real and imaginary components of impedance data show charge carriersâ€™ relaxation across grains and grain boundaries. The complex impedance data were modelled using an equivalent circuit having constant phase element and resistance. The observed impedance data deviate from the standard Debye model. 

**References** 1. K. Pushpanjali Patra and S. Ravi, “Magnetic Properties and Exchange Bias Behavior in Nanocrystalline (Ho1-xSmx)2CoMnO6 (x = 0 – 0.5) Double Perovskite,” Journal of Magnetism and Magnetic Materials, vol. 540, (2021). 
2. I. N. Bhatti, I. N. Bhatti, R. N. Mahato, and M. A. H. Ahsan, “Physical properties in nano-crystalline Ho2CoMnO6,” Ceramics International, vol. 46, no. 1, pp. 46–55, (2020). 
3. Aakansha and S. Ravi, “Structural, magnetic and dielectric properties of Cr substituted yttrium iron garnets,” Journal of the American Ceramic Society, vol. 101, no. 11, pp. 5046–5060, (2018). 

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Structural and Dielectric Behavior of (Ho(1 x)Ndx)2CoMnO6 (x = 0.0 – 0.2) Double Perovskite

Phase changing materials have long been a central theme in condensed matter physics. A representative example is an iron-rhodium (FeRh) which undergoes a first-order phase transition from antiferromagnetic to ferromagnetic phase near room temperature. Along with the change of magnetic ordering, the phase transition also accompanies a significant change of electrical conductivity of about 40% [1] as well as a small expansion of the unit cell of about 1% [2]. Furthermore, the transition is modulated not only by temperature but also by magnetic field or doping [3], which makes FeRh-based materials very attractive for future applications, such as heat-mediated antiferromagnetic memory [4], magnetic refrigeration [5], and magnetic sensors [6]. Despite the intensive researches, however, our understanding of phase transition of FeRh is still far from satisfactory. The crux of this transition is a large change in the electrical conductivity, but its origin is still under debate. Such large resistance change cannot be understood solely by the change in magnetization, i.e., magnetic scattering mechanism between antiferromagnetic and ferromagnetic spin alignments. Recently, we obtained a high-quality FeRh films with a sharp phase transition, which shows no residual magnetic moment in the antiferromagnetic phase. In this study, we investigate the fundamental electrical transport of FeRh by using terahertz time-domain-spectroscopy (THz-TDS). Based on Drude model, the extrinsic (momentum scattering time, Ï„) and the intrinsic (charge density/effective mass, n/m*) contributions of electrical conductivity was quantified independently. We found that, only n/m* changes abruptly during the phase transition, contrary to monotonic decrease of Ï„ with increasing temperature. Therefore, our result strongly supports that the origin of the currently controversial FeRh phase transition is a change in band structure. Our work could be an important piece for the complete understanding of magnetic phase transition of FeRh. 

**References** [1] I. Sujuki et al. J. Appl. Phys. 109, 07C717 (2011) 
[2] M. Ibarra et al. Phys. Rev. B 50, 4196 (1994) 
[3] R. Barua et al. Appl. Phys. Lett. 103, 102407 (2013) 
[4] X. Marti et al. Nat. Mater. 13, 367 (2014), T. Moriyama et al. Appl. Phys. Lett. 107, 122403 (2015) 
[5] M. P. Annaorazov et al. J. Appl. Phys. 79, 1689 (1996), V. K. Pecharsky et al. Phys. Rev. B 64, 144406 (2001) 
[6] J. Van Driel et al. J. Appl. Phys. 85, 1026 (1999), V. K. Pecharsk et al. J. Magn. Magn. Mater. 321, 3541 (2009) 

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Intrinsic origin of phase transition in FeRh

The R2T2X (R = rare-earth, T = transition and X = s and p block element) series of compounds are interesting owing to their fascinating structural and physical properties. In this present work, we have studied the magnetic and physical properties of Pr2Pd2In and its new isostructural Pr2Pd2Sn polycrystalline compounds. The samples were synthesized by arc-melting method and confirmed to crystallize in the Mo2B2Fe-type tetragonal structure with space group P4/mbm where atoms are arranged in the layered Shastry-Sutherland lattice. This structure is an intrinsically frustrated system due to the triangular arrangement of the rare-earth atoms. The dcâ€“ and acâ€“magnetic susceptibility, specific heat, and electrical resistivity measurements indicate an unstable antiferromagnetic transition below at T = 5 K and T = 2.5 K for Pr2Pd2In and Pr2Pd2Sn, respectively. The antiferromagnetic order is unstable in applied magnetic fields, becoming ferromagnetic beyond a field value of 1.5 T and 1.3 T for Pr2Pd2In and Pr2Pd2Sn, respectively. The field dependent magnetization shows a metamagnetic behavior in both compounds with the critical field of 1.5 T and 1.3 K at 2 K for Pr2Pd2In and Pr2Pd2Sn, respectively. The electronic specific heat coefficient values of 235 mJ/molPr K2 for Pr2Pd2In and 311 mJ/molPr K2 for Pr2Pd2Sn estimated from CP (T) data indicated that the compounds belong to the heavy fermion family. The metallic behavior is identified from electrical resistivity of both compounds with a characteristic of electron-phonon scattering in the paramagnetic region. The variety of magnetic properties such as para-, ferro- and antiferromagnetic behavior including metamagnetic transition is observed due to the magnetic frustration from distorted triangles of Pr-atoms in Pr2Pd2In and Pr2Pd2Sn. The existence of frustrated moments due to the triangular arrangements of Pr atoms is discussed in both compounds.

Antiferromagnetic Behavior in the Frustrated Intermetallic Compounds Pr2Pd2X (X = In, Sn)

This study investigates the structural and magnetic properties of Î±â€“CoV2O6 and Cr doped Î±â€“CoV2O6 samples synthesized through a wet chemical method [1]. X-ray diffraction (XRD) revealed that Î±â€“CoV2O6 form a monoclinic crystal structure [2], with lattice parameters a = 9.25 Ã…, b = 3.50 Ã…, c = 6.63 Ã…, Î² = 111.44Â°, and Î± = Î³ = 90Â°. The crystal is made of linear chains of Co2+ ions along the bâ€“axis, demonstrating the one-dimensional nature of the compound [3]. Cr doping resulted in small changes in the lattice parameters and an increase of microstrain in the form of peak broadening [4], accompanied by changes in the crystallite size of the samples. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements show that the particles are aggregated with nonuniform shapes and sizes, with average particle sizes of 141 Â± 19 nm, 79 Â± 24 nm, and 58 Â± 10 nm for Î±â€“CoV2O6, Î±â€“Co(V0.97Cr0.03)2O6 and Î±â€“Co(V0.95Cr0.05)2O2 respectively. The presence of Cr in the doped samples was confirmed through energy dispersive spectroscopy (EDS). Vibrating sample magnetometry (VSM) was used to investigate the magnetic properties of the samples by measuring the temperature dependence of magnetization, M(T) at 0.1 T, 2.5 T, and 5 T, under zero-field-cooled (ZFC) and field-cooled (FC) protocols. The field dependence of magnetization, M(Î¼0H) and time dependence of magnetization, M(t) were measured. M(T) curves revealed antiferromagnetic (AFM) behavior at 0.1 T with AFM to paramagnetic (PM) transitions increasing from 15 Â± 0.2 K for Î±â€“CoV2O6 to 15.5 Â± 0.2 K for Î±â€“Co(V0.95Cr0.05)2O6. M(T) curves measured at 2.5 T reveals a ferrimagnetic (FI) like behavior with spin-glass like irreversibility between ZFC and FC. Ferrimagnetic to paramagnetic transition increase from 13 Â± 0.2 K to 13.4 Â± 0.2 K with increasing Cr concentration. M(T) at 5 T reveals a ferromagnetic (FM) behavior with a ferromagnetic to paramagnetic transition increasing from 14.4 Â± 0.2 K to 15.1 Â± 0.2 K. Field-induced metamagnetic transitions were observed in M(Î¼0H) curves below 15 K for all samples with an increase of saturation magnetization with increasing Cr concentration. M(t) curves at fields between 1.5 and 5 T suggest a spin-glass-like freezing. 

**References** [1] Wang Y et al., ACS Appl. Mater. Interfaces, 8, (2016) 27291–7. 
[2] Shu H et al., J. Magn. Magn. Mater., 407, (2016) 129–34. 
[3] He Z et al., J. Am. Chem. Soc., 131, (2009) 7554–5. 
[4] Khorsand Zak A et al., Solid State Sci., 13, (2011) 251–6.

Structural and Magnetic properties of α–CoV2O6 and Cr doped α–CoV2O6

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

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

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

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

Magnetic fields are thought to govern the dynamics of protoplanetary disks by mediating inward gas accretion and, possibly, setting up turbulent concentrations of dust to form the first planetary building blocks. A subset of these building blocks then accretes to form rocky planets, which may host a magnetic core dynamo. In the case of Earth, the crust also became partitioned into a system of mobile tectonic plates that gave rise to a biosphere.

Characterizing ancient magnetic fields using rocks surviving from these early times can provide information about protoplanetary disk and dynamo physics while tracking the motion of the first continents. I will present how recent advances in paleomagnetic instrumentation based on the nitrogen vacancy color center have enabled access to complex meteorites and early Earth rocks that record magnetic fields in the protoplanetary disk and document the development of dynamos and plate tectonics on the Earth and Mars. These new techniques hold promise for challenging problems in broad areas of geomagnetism.

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