United States

In recent years, magnetic nanoparticles have attracted attention and been actively discussed for biomedical applications. Mg-Zn ferrite nanoparticles embedded in amorphous SiO2 were synthesized using the wet chemical method, and their magnetic properties and transverse relaxation for application as a medium for magnetic resonance imaging (MRI) were examined. We previously found that these Mg-Zn ferrite nanoparticles exhibited significant hyperthermia effect for human breast cancer cells [1]. Namely, if this material shows function as a contrast agent for MRI, it is expected to be useful for both diagnosis and treatment as theranostics [2].&lt;br&gt;
Image contrast in MRI is caused by the difference in MR signal due to the magnetic moment of the protons, which are hydrogen nuclei. That contrast depends on the proton density, T1 relaxation time, and T2 relaxation time. In this study, magnetic relaxation phenomena were analyzed by magnetization measurements and AC magnetic susceptibilities. The AC magnetic susceptibilities for various particle sizes of the Mg0.8Zn0.2Fe2O4 nanoparticles were measured in the range of 150–350 K under an AC magnetic field of 1 Oe, 100 Hz. The temperature corresponding to the peak of χ” shifted to higher values as the particle size increased. Relaxation phenomena were evaluated using Cole-Cole plot analysis, and these samples were found to follow the Debye single-relaxation phenomenon.&lt;br&gt;
Spin-echo magnetic resonance measurements for Mg0.8Zn0.2Fe2O4 nanoparticles with particle sizes between 8 and 20 nm were performed using a 0.3-T MRI system. The particles exhibited a significant T2 shortening effect compared with that of agarose as a background control. All particles exhibited effective relaxivity, R2, which was five times higher than that of the intrinsic core of conventional iron oxide agents of ferucarbotrans.
The results show that Mg-Zn ferrite nanoparticles embedded in amorphous SiO2 have the potential for theranostics applications.&lt;br&gt;
**References:**&lt;br&gt;[1] Hamada, S., Aoki, K., Kodama, K., Nashimoto, and Ichiyanagi, Y., 2022. AC magnetic susceptibility and heat dissipation of Zn-doped Mg-ferrite nanoparticles. J. Magn. Magn. Mater. 559 p.169539.&lt;br&gt;
[2] S.S. Kelkar, T.M. Reineke, 2011. Theranostics: Combining imaging and therapy, Bioconjug. Chem. 22 (10) Pp.1879–1903.&lt;br&gt;

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1667cc929141399df168a77f67560e1a.png)&lt;br&gt;
Fig1. Imaginary parts of the AC magnetic susceptibilities of Mg0.8Zn0.2Fe2O4 for various particle sizes.&lt;br&gt;
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/0285b23e318e4d0a34a5a0604d96d8aa.png)&lt;br&gt;
Fig.2 T2 relaxation curves of Mg0.8Zn0.2Fe2O4 nanoparticles nanoparticles. Iron oxides and agarose samples are shown for comparison.&lt;br&gt;


MMM 2022

Magnetic Relaxation and Magnetic Resonance Effect of Mg Zn Ferrite Nanoparticles

In recent years, magnetic nanoparticles have attracted attention and been actively discussed for biomedical applications. Mg-Zn ferrite nanoparticles embedded in amorphous SiO2 were synthesized using the wet chemical method, and their magnetic properties and transverse relaxation for application as a medium for magnetic resonance imaging (MRI) were examined. We previously found that these Mg-Zn ferrite nanoparticles exhibited significant hyperthermia effect for human breast cancer cells [1]. Namely, if this material shows function as a contrast agent for MRI, it is expected to be useful for both diagnosis and treatment as theranostics [2]. 
Image contrast in MRI is caused by the difference in MR signal due to the magnetic moment of the protons, which are hydrogen nuclei. That contrast depends on the proton density, T1 relaxation time, and T2 relaxation time. In this study, magnetic relaxation phenomena were analyzed by magnetization measurements and AC magnetic susceptibilities. The AC magnetic susceptibilities for various particle sizes of the Mg0.8Zn0.2Fe2O4 nanoparticles were measured in the range of 150–350 K under an AC magnetic field of 1 Oe, 100 Hz. The temperature corresponding to the peak of χ” shifted to higher values as the particle size increased. Relaxation phenomena were evaluated using Cole-Cole plot analysis, and these samples were found to follow the Debye single-relaxation phenomenon. 
Spin-echo magnetic resonance measurements for Mg0.8Zn0.2Fe2O4 nanoparticles with particle sizes between 8 and 20 nm were performed using a 0.3-T MRI system. The particles exhibited a significant T2 shortening effect compared with that of agarose as a background control. All particles exhibited effective relaxivity, R2, which was five times higher than that of the intrinsic core of conventional iron oxide agents of ferucarbotrans.
The results show that Mg-Zn ferrite nanoparticles embedded in amorphous SiO2 have the potential for theranostics applications. 
**References:** [1] Hamada, S., Aoki, K., Kodama, K., Nashimoto, and Ichiyanagi, Y., 2022. AC magnetic susceptibility and heat dissipation of Zn-doped Mg-ferrite nanoparticles. J. Magn. Magn. Mater. 559 p.169539. 
[2] S.S. Kelkar, T.M. Reineke, 2011. Theranostics: Combining imaging and therapy, Bioconjug. Chem. 22 (10) Pp.1879–1903. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1667cc929141399df168a77f67560e1a.png) 
Fig1. Imaginary parts of the AC magnetic susceptibilities of Mg0.8Zn0.2Fe2O4 for various particle sizes. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/0285b23e318e4d0a34a5a0604d96d8aa.png) 
Fig.2 T2 relaxation curves of Mg0.8Zn0.2Fe2O4 nanoparticles nanoparticles. Iron oxides and agarose samples are shown for comparison.

poster

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

The Conference was held from October 31 to November 4 and offers both in-person and on-demand content.

MMM 2022 is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a tutorial, and several special sessions. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

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Along the advances of wide-bandgap power devices, the electrical equipment is developing toward higher switching frequencies and more complex switching modes in recent years [1]. Accurate prediction of the core loss of magnetic components has been a challenge for electrical equipment as the excitation varies depending on the operating mode of switched-mode power supplies [2]. However, few studies provide systems with variable-characteristic-parameters excitations [3]. It is not clear how the core loss of soft magnetic materials was affected by the characteristic parameters of complex non-sinusoidal excitations.
Therefore, this paper presents the results of an extensive core loss study performed on nanocrystalline alloy (FT-3KL), amorphous alloy (1K101) and ultra-thin oriented silicon steel (GT-50). Firstly, an automatic experimental setup for core loss measurement of soft magnetic materials fed by a SiC MOSFET full-bridge inverter is built, as shown in Fig 1. This setup can provide real-time voltage waveforms adjustment, data visualization and automatic post-processing, which makes the measurement more rapid and accurate. 
Then, the effect of characteristic parameters of square waveforms, rectangular waveforms contained zero-voltage, pulse-width-modulation (PWM) waveforms and sinusoidal-pulse-width-modulation (SPWM) waveforms on core loss are analyzed comparatively. For square and rectangular excitations, the core loss shows regular distributions with duty cycles and phase shift ratios. For SPWM excitations, the effect of the modulation ratios on the core loss is greater than that of the carrier ratios. Meanwhile, the SPWM excitation with bipolar modulation will produce greater loss than that with unipolar modulation. The results are partly shown in Fig 2. In addition, the regular distributions will be interfered by the severe switching oscillations from the inverter, which makes the prediction of core loss more complicated. This paper can provide reference for the performance optimization of high-frequency electrical equipment. 
**References:** [1] J. Wang, N. Rasekh and X. Yuan, IEEE Transactions on Industry Applications., vol. 57, p.650-663 (2021) 
[2] E. Stenglein and T. Dürbaum, IEEE Transactions on Magnetics., vol. 57, p.1-10 (2021) 
[3] I. Sirotić, M. Kovačić and S. Stipetić, IEEE Transactions on Industry Applications., vol. 57, p.4796-4804 (2021) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/954026ca597848d2dc8b4d2c13ddb3e7.png) 
Fig 1: Schematic diagram of the experimental setup for core loss measurement. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/e614256947851fc07967396dceaae020.png) 
Fig 2: Core loss of FT-3KL under SPWM excitations with variable modulation ratios.

Core Loss Measurement and Analysis for Soft Magnetic Materials Under Complex Non Sinusoidal Excitations

High-frequency transformer operates under high temperature and non-sinusoidal excitation. The magnetic properties and loss of soft magnetic materials under these conditions are complicated, which are quite different from those under normal temperature and sinusoidal excitation[1-2]. At present, most of the relevant researches separate the temperature dependence of magnetic properties from non-sinusoidal excitation, which not sufficient to characterize the magnetic properties of soft magnetic materials[3-4]. 
This paper carried out magnetic property measurement and analysis under various temperatures (25~120°C) of high-frequency magnetic materials ferrite (N87) and nanocrystalline (FT-3KL) with multi-frequency (1~20kHz), different non-sinusoidal waveform excitation (square and rectangular wave), and multiple excitation states (Duty ratio 0.1~0.9). As shown in Fig.1(a), the temperature dependence of ferrite is significant, and its loss is less affected by the excitation state, while nanocrystalline is more sensitive to the excitation waveform. As shown in fig.1(b), the loss of nanocrystalline appears to be a minimal when the duty ratio is 0.5 and exhibits a symmetrical distribution. 
As shown in Fig.2, Based on experimental data, we consider the effect of temperature in the modeling of loss prediction and improve the model which based on the Steinmetz formula. By comparing the measured results and the predicted values, the accuracy of the new loss model is within 15%, which is greatly improved compared to other existing loss models under the influence of temperature. 
This work can provide a theoretical basis for the micro-magnetization mechanism of magnetic materials under complex operating conditions. The complete analysis of the magnetic properties and new loss model of the above materials will be shown in the full-text version. 
**References:** [1] J. Chen, D. Wang and Y. Jiang, IEEE Transactions on Magnetics, vol. 54, no. 11, pp. 1-7, Nov. 2018 
[2] S. Li, B. Sarlioglu and S. Jurkovic, IEEE Transactions on Industry Applications, vol. 53, no. 5, pp. 4923-4933, Sept.-Oct. 2017 
[3] Shaoshen Xue et al., IET Science, Measurement & Technology, 2016, 10(8) : 846-854. 
[4] S. Barg, K. Ammous and H. Mejbri, IEEE Transactions on Power Electronics, vol. 32, no. 3, pp. 2146-2154, March 2017** 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/38f0d336091a642737231dc0f54c604a.png) 
Fig. 1 (a) Duty ratio and loss curve of N87 excited by 20KHz square wave, B=0.15T (b) Duty ratio and loss curve of FT-3Kl excited by 20KHz square wave, B=0.9T 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/33ec72cef353530a202f016ba75def43.png) 
Fig. 2 Comparison of N87 loss prediction and measurement results

Magnetic property measurement and analysis of high frequency transformer core material under non

With the development of high-speed motors, how to reduce the iron loss of the motor has become the focus of attention in academia and industry. Amorphous alloys have been gradually applied to high-speed motors due to their high frequency and low iron loss characteristics. However, due to their low saturation flux density, As a result, the motor torque is greatly limited. 
When the amorphous alloy is formed, a large internal stress is generated in the material due to the rapid temperature change[1]. Usually, annealing treatment is required to eliminate the influence of internal stress on magnetic properties. During the annealing treatment of amorphous transformer cores, a magnetic field is usually applied in the direction of the magnetic circuit to improve the state of the magnetic domain, increase the saturation magnetic flux density in this direction and reduce the iron loss[2]. However, the magnetic field annealing technology has not been applied to the field of motors. In this paper, the amorphous material processed by this process is made into the shape of stator teeth, and the stator yoke is spliced with non-magnetic field annealing to form a complete stator core, as shown in Figure 1. Show. Since the magnetic field of the tooth is a pulsed magnetic field, this technology can effectively reduce the iron loss of this part and increase the motor torque to a certain extent. 
In order to reduce the difficulty of motor processing and the loss caused by many splicing positions, the motor structure is further optimized. As shown in Figure 2, the motor stator is composed of four parts with the same structure, and the teeth of each part are approximately parallel to the magnetization direction. However, due to the fact that the magnetic field of the yoke part is not always consistent with the direction of the magnetic field treatment in the actual motor operation, the iron loss of the stator yoke part of this structure is slightly larger than that of the stator structure without magnetic field treatment. The structure of the ratio realizes the optimal distribution of iron loss and performance improvement. 
**References:** [1]Sato, T., & Todaka, T. (2018). Effect of magnetic annealing on magnetic characteristic of amorphous wound core. IEEE Transactions on Magnetics, 54(11), 1-4. 
[2]Gao Jie, He Chengxu, Song Wenle, Yang Fuyao, Liu Yang. Effects of Longitudinal Magnetic Annealing Treatment and Tensile Stress on Magnetization Characteristics and Loss of 1K101 Amorphous Alloy Ribbon [J]. Metal Heat Treatment, 2022,47(03):39-43 . 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1b002bb090f1b41bdc71043674d3936d.png) 
Fig.1 Four splicing schemes and stator punching 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/bc1e5af15229c379cd341a6bb7ef583b.png) 
Fig.2 Magnetic properties test samples of amorphous alloys

Loss Analysis of Magnetized Annealed Amorphous Alloy Applied to Stator Teeth

We studied the spin-Hall magnetotransport across an epitaxial and nonmagnetic Y3Al5O12 (YAG) insertion layer in the Pt/Tb3Fe5O12 (TbIG) system. YAG (tYAG nm) /TbIG (30 nm) bilayers were grown on Ga3Gd5O12 (GGG) (111) substrates by pulsed laser deposition, before 5 nm of Pt was sputtered on the sample and patterned into Hall bars. tYAG dependences of anomalous Hall resistance (RAHE, with linear background contribution subtracted) were measured. At low tYAG values, a hysteretic RAHE loop is observed at low fields but with reducing effect with rising tYAG. At high fields RAHE behaviour is present, with magnitudes comparable with Pt/TbIG sample. The temperature dependence of low- and high-field RAHE were investigated, with the goal of identifying the origin of such discrepancies and further guidance for interfacial design of spintronics devices.
**References:** 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/eec1a66c80c2b9462946e09a927f7697.png) 
Fig. 1. Field dependence of RAHE of Pt/YAG/TbIG samples at 10 K (a) and 300 K (b).

Low and High

Ferrimagnetic rare earth iron garnets (X3Fe5O12, where X denotes a rare earth element) are promising materials for various applications, such as magneto-optical (MO) isolators, spintronic and spin wave devices. The three types of cation sites (dodecahedral, octahedral and tetrahedral) can be occupied by a wide range of ions resulting in a large variation of the physical properties of the garnet. This can be utilized to tailor its MO response or magnetic properties. 

To determine the contribution of each sublattice to the MO response and therefore to characterize sublattice magnetism, an analysis of spectrally dependent MO hysteresis loops can be used [1]. For this purpose, we measured field dependent polar MO Kerr effect (MOKE) spectra in the range from 1.4 eV to 4.5 eV of various ferrimagnetic garnet thin films, such as terbium iron garnet (TbIG) or yttrium iron garnet (YIG), prepared by pulsed laser deposition on GGG substrates. This allowed us to extract MOKE hysteresis loops with very high spectral resolution. The resulting hysteresis loops exhibited spectrally dependent shapes and were modelled as a sum of two hysteresis loops, shown for 300 nm thick epitaxial TbIG in Fig. 1. Moreover, their contributions to the MOKE spectra were separated as shown in Fig. 2. These results suggest that rather than sublattice contributions this analysis led to the identification of components with two different magnetic anisotropies within this particular film. The TbIG has a strain-induced perpendicular magnetic anisotropy when grown on GGG. This anisotropy, however, may not be retained for thicker samples [2] due to strain relaxation leading to an evolution of magnetic anisotropy across the layer. These results can be compared with those on YIG films, where the spectral response of the octahedral and tetrahedral Fe sublattices can be separated. This work demonstrates field dependent MOKE spectra as an effective tool to separate not only sublattice contributions but also an evolution of magnetic anisotropy across the film. 
**References:** [1] M Deb, E Popova, A Fouchet and N Keller, J. Phys. D: Appl. Phys. 45 455001 (2012) 
[2] V. H. Oritz, M. Aldosary, J. Li, et al. APL Materials 6, 121113 (2018) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/8e25eafd35dbf5ee3c5905bdddbb2577.png) 
Fig. 1 Separation of MOKE hysteresis loop of 300 nm thick TbIG film on GGG 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/0a79af8640ed78fe22f84f65879730ca.png) 
Fig. 2 Individual loop contributions to the MOKE spectra of 300 nm TbIG on GGG

Field Dependent Magneto Optical Spectra of Ferrimagnetic Garnets to Identify Magnetic Contributions

This paper conducted a study on the reduction of the number of split Magnetization and the prevention of irreversible demagnetization using the I-Core of a double spoke type motor. Recently, as interest in spoke-type motors using ferrite permanent magnets has increased, the need for research on magnetization and irreversible demagnetization in double spoke-type rotor shapes has emerged. However, in the existing spoke-type rotor shape, the magnet was deeply embedded in the rotor, making it difficult to magnetization. As it is important to use permanent magnets excluding rare earths in the future, the use of spoke-type motors becomes important, and design to consider magnetization and prevent irreversible demagnetization accordingly is important. Therefore, this paper proposed a magnetization yoke shape design in consideration of magnetization and irreversible demagnetization on using I-Core of Double Spoke type PMSM to solve this problem. 
Currently, the price of rare earth materials is soaring to the highest level due to the rapid increase in demand for rare earth materials worldwide. Against this background, permanent magnet motors (PMSM) using existing rare earths are increasing in manufacturing costs and the electric motor used to solve this problem is a spoke type permanent magnet synchronous motor (PMSM) using a ferrite permanent magnet. However, the general spoke type PMSM does not have much difference in inductance between the d-axis and the q-axis, so the use of the reluctance torque is small. However, this shape is a conventional magnetization model, and there is a disadvantage that it does not become a magnet when magnetization proceeds. Since there is an increase in the number of magnetization and inconvenience in a irreversible demagnetization during division and magnetization, a magnetization yoke shape is proposed to solve this problem. This study investigated the method for reducing the number of magnetization in the existing split magnetization method using I-Core of Double spoke type PMSM and the magnetization yoke shape to prevent irreversible demagnetization. 
**References:** H. S. Seol, T. C. Jeong, H. W. Jun, J. Lee, D. W. Kang, “Design of 3-Times Magnetizer and Rotor of Spoke-Type PMSM Considering Post-Assembly Magnetization”, IEEE Transactions on Magnetics, vol. 53, no 11, pp. 1-5, (2017) 
H. W. Kim, K. T. Kim, Y. S. Jo, and J. Hur,“Optimization methods of torque density for developing theneodymium free spoke-type BLDC motor,” IEEE Trans.Magn., vol. 49, no. 5, pp. 2173–2176, (2013) 
D. -W. Nam, K. -B. Lee, and W. -H. Kim, “A study onCore Skew considering manufacturability of double-layerspoke-type PMSM,” Energies 2021, 14, 610, (2021) 
S. I. Kim, S. Park, T. Park, J. Cho, W. Kim, and S. Lim,“Investigation and Experimental Verification of a NovelSpoke-Type Ferrite-Magnet Motor for Electric-VehicleTraction Drive Applications”, IEEE Trans. Ind. Electron., vol.61, no. 10, pp. 5763-5770, (2014) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ba303488889a1efd0182aaa8bd6e5d8f.png) 
Fig. 1 It is a rotor shape using I-Core. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/7fd033a4d0f615289039e9d75b0358a4.png) 
Fig. 2 It is the magnetization result of a double spoke type rotor.

Design of Magnetization Yoke to Reduce the Number of Double Spoke Type PMSM Magnetization using I Core

In this study, we observe the effect of doping Nickel in Fe3O4 lattice coated with oleic acid. Fe3O4 particles agglomerate and lost their nanoparticle regime hence the addition of Nickel decreases the magnet moment slightly to get a good monodisperse particle and better stability in the nano region (10-12nm). In the present study, Ni Doped Fe3O4 MNPs were synthesized through the coprecipitation method and the single-phase has been confirmed via XRD, and coating is confirmed by FTIR. The magnetic variation is explained as Ni2+ ions (3μB) have a lesser magnetic moment than Fe2+ (4μB) and Fe3+ (5μB) ions. As a result, M = MB-MA gives the net magnetization. The saturation magnetization of the bulk magnetite (Fe3O4) is found to be lower i.e. (0.5 emu/g for x=0.7) as compared to the Ms value for the synthesized Fe3O4 nanoparticles (3 emu/g). Due to the presence of vacancy at the octahedral site of Fe/Ni, the magnetization value of x=0.1 decreases abnormally (fig.1). The suppression of saturation magnetization (Ms) as the concentration of Ni2+ ions rises might be because of the reduced magnetic field contribution by Ni2+ ions compared to Fe2+ and Fe3+ ions as shown in insert fig.1. To investigate the spin dynamics in NixFe3-xO4 electron paramagnetic resonance (EPR) measurements have been performed as shown in the power adsorption derivatives (PAD) (fig 2). The resonance field (Hres) also lies in the range from 3.25 kOe to 3.75 kOe while increasing the Ni concentration of NixFe3-xO4 (0 ≤ x ≤ 0.7) nanoparticles in corroboration with field-dependent magnetic behavior where Ni suppresses the moment and resulted in the random orientation of the spins. The decrease in peak-to-peak line width (ΔHPP) is attributed to the weak magnetic interactions (super-exchange) between Ni-O-Fe with the increase in doping Ni concentration from x = 0.1 to x = 0.7. The detailed structural and electron paramagnetic resonance measurements on oleic acid-coated NixFe3-xO4 (0 ≤ x ≤ 0.7) provide a tunable spin dynamic and improve the saturation magnetization, which is a key parameter for spintronics, magneto-optoelectronics, EMI shielding, and supercapacitor applications. 
**References:** 1. K. Usadel Phys. Rev. B. 73 (2006). 
2. E. De Biasi, E. Lima, C.A. Ramos, A. Butera, R.D. Zysler, J. Magn. Magn. Mater. 326 (2013) 138–146. 
3. A. Sukhov, K.D. Usadel, U. Nowak, J. Magn. Magn. Mater. 320 (2008) 31–35. 
4. C.A. Ramos, E. De Biasi, R.D. Zysler, E. Vassallo Brigneti, M. Vázquez, J. Magn. Magn. Mater. 316 (2007) e63–e66. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/307a932614aaa0f8118f8c02d6235dc8.png) 
Figure 1 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/117eb6578f12d7908df3cd5564cfc603.png) 
Figure 2

Magnetic and spin resonance studies of NixFe3 xO4 (0 ≤ x ≤ 0.7) magnetic nano particles

As 5G technology moves higher into the microwave frequency regime, the risk of coupling EM energy into susceptible electronic circuits grows. Minimizing this interference is driving the need for compact, lightweight broadband absorbers to protect sensitive and high precision electronics. Manganese zinc ferrite (Mn1-xZnxFe2O4) microparticles have previously been demonstrated to be magnetically lossy up to 10 GHz, the desired frequency regime, and have the potential to meet the energy density and attenuation performance needs [1, 2]. However, optimizing the shielding effectiveness requires improved understanding of Mn1-xZnx stoichiometry and the dominant dielectric and magnetic absorption mechanisms for each stoichiometry. This presentation discusses results, up to 20 GHz, from experimentally investigating the shielding effectiveness and quality factor attenuation of Mn1-xZnxFe2O4 with a mean particle size of 30 microns, loaded to 50 volume percent in epoxy, and variation in x values from 0 to 1 in intervals of 0.1. Complex permeability and permittivity measurements were conducted to identify the absorption mechanism. An increase in absorption was observed in Mn1-xZnxFe2O4 for x=0.3 and 0.4 compared with other stoichiometries. A likely explanation of the observed increase is provided [3]. 
**References:** [1] T. Tsutaoka, Journal of Applied Physics 93, 2789 (2003); https://doi.org/10.1063/1.1542651 
[2] R. Dosoudil, M. Usakova, J. Franek, J. Slama and A. Gruskova, "Particle Size and Concentration Effect on Permeability and EM-Wave Absorption Properties of Hybrid Ferrite Polymer Composites," in IEEE Transactions on Magnetics, vol. 46, no. 2, pp. 436-439, Feb. 2010, doi: 10.1109/TMAG.2009.2033347. 
[3] This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy?s National Nuclear Security Administration under contract DE-NA0003525.

The Role of Stoichiometry in Mn1 xZnx Ferrite Microwave Absorbers

In the present work, the effect of crystallite size on the magnetic properties of nanocrystalline FeCo2O4, synthesized by co-precipitation technique, has been studied. The as synthesized sample has been annealed at 500 , 900 & 1000 to vary the crystallite size. The XRD results confirm the presence of single cubic phase in all the annealed samples and increase in the crystallite size with the increasing annealing temperature. FESEM images show the spherical morphology of prepared nanoparticles which become irregular in shape as temperature increases and particle size also increases with increasing annealing temperature. XPS analysis confirms the mixed oxidation states of Fe with Fe+2 and Fe+3, Co with Co+2 and Co+3. The temperature dependence magnetization (M-T curves) and field dependence magnetization (M-H curves) at different temperatures have been measured using Quantum design MPMS3 SQUID magnetometer. The low temperature M-H curves show the presence of metamagnetic phase transition in the samples annealed at 900 oC and 1000 oC. This possibly occurs due to the co-existence of ferromagnetic and antiferromagnetic phases in the synthesized samples. The coexistence of AFM and FM phases may be attributed to spin canting/surface spin disorder in nanocrystalline magnetic nanoparticles. Furthermore, the samples annealed at higher temperature show strong ferromagnetism, higher saturation magnetization, higher coercivity and remanence. Moreover, the M-H curves, measured below 100 K, of the samples annealed at 500 oC and 900 oC show jumps in the magnetization value at certain magnetic fields (see Fig. 1). The detail correlation between structural and observed magnetic properties will be described and discussed in this paper. 
**References:** 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/64409106aa92a732b7e0764df9ed8838.png)

Study of crystallite size on magnetic properties of nanocrystalline FeCo2O4

With 10 million deaths in 2020 cancer remains one of the most challenging diseases in contemporary medicine. Chemotherapy, surgery, and radiation therapy are commonly used to treat cancer. These treatments severely harm healthy tissues and succeed rarely in advance stages of disease. Recent studies indicate that magnetic hyperthermia, which involves targeted delivery of magnetic nanoparticles to tumor cells followed by localised remote heating of cancer tissues could revolutionise clinical practice in the treatment of cancer, either as standalone intervention or adjunct to radiotherapy and chemotherapy. Water dispersible magnetic nanoparticles (MNPs) of ferrites (AFe2O4; A=Fe, Mn, Co) are the promising candidates for magnetic hyperthermia due to their high chemical stability, biocompatibility, moderate magnetization and high specific absorption rates (SAR). In this article, we have evaluated magnetic hyperthermia efficiency of water based magnetic fluids of AFe2O4 nanoparticles. AFe2O4 nanoparticles were synthesized by chemical co-precipitation method. Nanoparticles were coated with a bilayer of oleic acid and dispersed in water. MNPs concentrations in magnetic fluids were 70 mg/mL for Fe3O4, 200 mg/mL for MnFe2O4 and 60 mg/mL for CoFe2O4. Structural and magnetic properties of MNPs were investigated by X-Ray diffraction (XRD) and vibrating sample magnetometer (VSM), respectively. XRD study revealed that AFe2O4 NPs exhibits cubic inverse spinel structure. Fe3O4 (Ms = 48 emu/g, Mr = 2.60 emu/g, Hc = 49 Oe), MnFe2O4 (Ms = 40 emu/g, Mr = 2.60 emu/g, Hc = 35 Oe) and CoFe2O4 (44 emu/g, Mr = 10.10 emu/g, Hc =440 Oe) NPs exhibits soft ferromagnetic behaviour. Magnetic hyperthermia measurements were performed as a function of magnetic field strength (2-10 mT) and field frequency (162-935.6 kHz) for 10 minutes. MNPs exhibits highest SAR values for 10 mT field strength at 935.6 kHz. Amongst the tested MNPs, Fe3O4 has the highest SAR value (27.35 W/g), followed by MnFe2O4 (1.91 W/g) and CoFe2O4 (0.94 W/g). Considering this, it is concluded that amongst the inverse spinel ferrite nanostructures AFe2O4 (A=Fe, Mn, Co), Fe3O4 nanoparticles are most suitable for magnetic fluid hyperthermia applications. 
**References:** 

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