United States

A near field transducer (NFT) is a key component for heat-assisted magnetic recording (HAMR). The lollipop design and its variations have had success in HAMR recording systems employed in hard disk drives [1][2]. The designed mode resonance, or mode beating, results in excellent coupling between optical light and the excitation of plasmonic current in the NFT. However, the resonant plasmonic oscillation also yields substantial heating, bringing reliability challenges. In addition, such a resonant design can make the plasmonic excitation of media grains highly dependent on the spacing between the NFT recording peg and the grains in the media. In this paper, we present a design analysis for a novel NFT using a nanocomposite structure to create distributed optical feedback (DFB) for maintaining plasmonic resonance. Figure 1 shows a schematic view of the design. The NFT is made of an array of Au rectangular rods, each separated by a constant gap, &lt;i&gt;G&lt;/i&gt;, of nanometer dimension and the Au rods are embedded in a dielectric material. The insert in the figure shows the 2D COMSOL simulation results of the optical field intensity at the peg end of the NFT with W=660nm and G=5nm. For this structure, the optimal free-space optical wavelength λ=710nm. The 2μm long DFB Au nanocomposite has an optical coupling efficiency of 30% with very little field intensity decay at the peg end. Figure 2 shows the calculated electric field intensity in the dielectric gap before the last rod as a function of the width of the Au rods for different gap spacing. In conclusion, the DFB Au nanocomposite NFT design enables enhanced material stability, hence, enhancing the NFT reliability. Plasmonic excitation of medium grains by the NFT has also been modeled and the analysis of its sensitivity to the spacing between the NFT and medium grain will be presented.&lt;br&gt;
**References** &lt;br&gt;
[1] W.A. Challener, et al, Nature Photonics, 3 (4), 220-224 (2009). [2] K. Shimazawa, W. Xu, K. Fujil, US11,315,591B1, Headway Technologies, (2022)&lt;br&gt;
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/a8c7f55237937414983d1c74a4ee8e37.png)&lt;br&gt;
Fig.1 Schematic view of the distributed feedback Au nanocomposite NFT design. The insert shows the simulation results of optical field intensity inside the dielectric gaps along the 2μm
long NFT. The optical wavelength is optimal at λ=710 nm.&lt;br&gt;
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/83b4073ee2d5e0467ecdc5f198abf0d6.png)&lt;br&gt;
Fig.2. Optimization of the DFB Au nanocomposite NFT for Different Au rod width and dielectric gap. The electric field is measured at the end of 2μm long NFT.

MMM 2022

Plasmonic Near Field Transducer of Nanocomposite with Distributed Feedback

A near field transducer (NFT) is a key component for heat-assisted magnetic recording (HAMR). The lollipop design and its variations have had success in HAMR recording systems employed in hard disk drives [1][2]. The designed mode resonance, or mode beating, results in excellent coupling between optical light and the excitation of plasmonic current in the NFT. However, the resonant plasmonic oscillation also yields substantial heating, bringing reliability challenges. In addition, such a resonant design can make the plasmonic excitation of media grains highly dependent on the spacing between the NFT recording peg and the grains in the media. In this paper, we present a design analysis for a novel NFT using a nanocomposite structure to create distributed optical feedback (DFB) for maintaining plasmonic resonance. Figure 1 shows a schematic view of the design. The NFT is made of an array of Au rectangular rods, each separated by a constant gap, G, of nanometer dimension and the Au rods are embedded in a dielectric material. The insert in the figure shows the 2D COMSOL simulation results of the optical field intensity at the peg end of the NFT with W=660nm and G=5nm. For this structure, the optimal free-space optical wavelength λ=710nm. The 2μm long DFB Au nanocomposite has an optical coupling efficiency of 30% with very little field intensity decay at the peg end. Figure 2 shows the calculated electric field intensity in the dielectric gap before the last rod as a function of the width of the Au rods for different gap spacing. In conclusion, the DFB Au nanocomposite NFT design enables enhanced material stability, hence, enhancing the NFT reliability. Plasmonic excitation of medium grains by the NFT has also been modeled and the analysis of its sensitivity to the spacing between the NFT and medium grain will be presented. 
**References** 
[1] W.A. Challener, et al, Nature Photonics, 3 (4), 220-224 (2009). [2] K. Shimazawa, W. Xu, K. Fujil, US11,315,591B1, Headway Technologies, (2022) 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/a8c7f55237937414983d1c74a4ee8e37.png) 
Fig.1 Schematic view of the distributed feedback Au nanocomposite NFT design. The insert shows the simulation results of optical field intensity inside the dielectric gaps along the 2μm
long NFT. The optical wavelength is optimal at λ=710 nm. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/83b4073ee2d5e0467ecdc5f198abf0d6.png) 
Fig.2. Optimization of the DFB Au nanocomposite NFT for Different Au rod width and dielectric gap. The electric field is measured at the end of 2μm long NFT.

technical paper

#### 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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Energy-assisted magnetic recording (EAMR) is thought to solve the trilemma by improving writability and enhancing areal recording density [1, 2]. On the other hand, servo signal writing time, which takes a few days per one drive on manufacturing process, is one of serious problems for high areal recording density in hard disks. Magnetic printing is a strong candidate for servo track writing with extremely high speed and low cost. A new master structure, herein called double magnet master (DMM) medium, was recently proposed for magnetic printing to improve printing characteristics onto EAMR media [3, 4]. However, the detailed combination of double magnets to further improve printing characteristics, has not been clarified yet. In this study, the micromagnetic simulation has been carried out in order to reveal an appropriate combination of magnets in DMM. 
The conventional single magnet master media were proposed by our previous reports [5, 6]. The magnetic pattern in the conventional master media is a soft single magnet (SSM) of FeCo or a single hard magnet (HSM) of CoPt. Thus, the DMM can be expected to utilize two kinds of magnet combinations such as soft-hard double magnet (SDM) and (semi-)hard-hard double magnet (HDM). The recording field distribution and the printed magnetization were calculated by utilizing micromagnetic simulation [3]. The recording media consists of hexagonal grain with diameter of 4.6 nm and has the coercivity of 10kOe. The magnetizations printed by 4 kinds of master were shown in Fig. 1. The printed magnetic pattern is L/S with the same pattern width of 10nm corresponding to the bit length. The upper panels of each magnetization distribution of Fig. 1 schematically shows 4 kinds of combinations of magnets. SDM and HDM can clearly print the L/S pattern better than SSM and HSM. Moreover, the SDM has better printing characteristics than that of HDM. The SDM has the FeCo pattern with large magnetization to enhance the recording field, which is larger than that of CoPt in HDM during the application of printing field more than about 8kOe. Therefore, the SDM master is more adequate for magnetic printing onto EAMR media. 
**References:** [1] M. H. Kryder et al., "Heat assisted magnetic recording", Proc. IEEE, vol. 96, no. 11, pp. 1810-1835 (2008). 
[2] J.-G. Zhu, X. Zhu and Y. Tang, "Microwave assisted magnetic recording", IEEE Trans. Magn., vol. 44, no. 1, pp. 125-131 (2008). 
[3] T. Komine, "Master structure dependence of double magnet master on performance of magnetic printing onto energy-assisted magnetic recording media", IEEE Trans. Magn. (2022) Early access. DOI: 10.1109/TMAG.2022.3147910 
[4] T. Komine, "Double magnet master media for magnetic printing onto energy-assisted magnetic recording media", IEEE Trans. Magn. Vol. 58, 3200105 (2021). 
[5] T. Komine, T. Murata, Y. Sakaguchi and R. Sugita, " Feasibility of perpendicular magnetic printing at 1Tb/in2 ", IEEE Trans. Magn., vol. 44, no. 11, pp. 3416-3418 (2008). 
[6] N. Sheeda, M. Nakazawa, H. Konishi, T. Komine and R. Sugita, "Perpendicular anisotropy master medium in magnetic printing for writing high-density servo signal", IEEE Trans. Magn., vol. 45, no. 10, pp. 3676-3678 (2009). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/adef29e0870d9bb032f5269bd8d806ce.png) 
Fig.1 Magnetization distribution of printed by 4 kinds of master media.

Combination dependence of printing characteristics in double magnet master media for energy assisted magnetic recording

The L10 typed FePt granular film with moderate Curie temperature (TC) is a promising candidate as a next-generation technology material for HAMR [1]. In HAMR, since laser heat was utilized for decreasing switching field (Hsw) during recording, controlling the temperature dependence of Hsw and its distribution is required. The temperature where Hsw = 0 without and with taking into account of thermal fluctuation are TC and blocking temperature (TB), respectively. Therefore, TB/ TC and ΔTB/ TC show thermal fluctuation indexes.
In this presentation we propose a method to evaluate TB and its distribution by measuring thermal hysteresis of remanent magnetization (Mr) for FePt granular films. Fig. 1 shows a schematic diagram of TB evaluation method and its distribution. First, the magnetization of all the magnetic grains in a granular film is aligned in the same direction. As the temperature rises, the number of blocking grains increases, and the magnetization of those grains is frozen in the opposite direction due to dipole field from the surrounding grains. Here the Mr during temperature rise and fall are defined as Mrfor and Mrback, the percentage of blocking grains is expressed as (Mrfor - Mrback) / 2Mrfor, and its temperature dependence corresponds to the cumulative distribution of thermally demagnetized grains. The derivative of the cumulative distribution curve gives the frequency distribution of blocking grains, which corresponds to the TB distribution. 
Fig. 2 shows the ratio of the average value of TB (TBave) to TC (TBave / TC) versus ΔTB for FePt granular films with various GBMs, where the minimum and maximum values of the TB variance are defined as TBmin and TBmax, respectively, and ΔTB = TBmax - TBmin. For each temperature, ΔTB varied from 86.4 to 182.7 K, depending on the GBM, and showed negative correlation with TBave/ TC with the present measurement time condition (τ) of thermal hysteresis of 60 s. Based on this result, the ΔTB at τ = 2 × 10-7 s, which corresponds to the recording time of HDD, was calculated to be ΔTB = 18.8- 53.9 K (ΔTB/ TC = 4.49× 10-2- 7.32 × 10-2). 
**References:** [1] D. Weller et al., Phys. Status Solidi A, 210, 1245 (2013). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/9f679886064d89da0d37e72ba469526b.png) 
Fig. 1 Evaluation method of blocking temperature. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ec30a175f22e7bdec473617c8f51cc5c.png) 
Fig. 2 TBave / TC versus ΔTB for FePt granular films with various GBM.

Evaluation of blocking temperature and its distribution for L10 typed FePt granular films

Voltage-controlled magnetic anisotropy (VCMA) effect in ferromagnetic ultrathin films is an emerging technology that enables energy-efficient magnetization switching [1,2]. Besides, microwave assisted magnetization switching (MAS) technology has also attracted interests as an energy assisted magnetization switching method [3]. On the other hand, microwave voltage applied to a VCMA gate on an ultrathin ferromagnetic nanowire results the parametric excitation of magnetization precession and propagating spin wave [4]. In this study, we numerically demonstrated AC voltage-induced magnetization switching, which showed magnetization switching was well assisted. 
Fig. 1(a) shows the schematic illustrations for the ferromagnetic nanodot covered by a dielectric layer. DC bias magnetic field (Hb) was applied at θ with respect to the anisotropy axis. The voltage-induced modulation of the anisotropy was numerically modeled by the local sinusoidal ΔHk-change with the amplitude of 0.1Hk. The dependence of the precession amplitude on the excitation frequency fexc when Hb close to the switching field at various incident angles is plotted in Fig. 1(b). Two resonance peaks are observed, which represent the ferromagnetic resonance (fexc = fprecession ) and the parametric resonance (fexc = 2fprecession). The parametric resonance presents a typical spectrum that the precession amplitude abruptly increases with frequency. Fig. 1(c) presents the dependence of switching fields on the excitation frequency as a parameter of the field incident angle. When the field applied non-parallel to the anisotropy axis, the switching field shows two local minima, which are due to the resonances in Fig. 1(b). 
The comparison of the switching fields among the 3 different switching methods is shown at Fig. 2. The switching field with AC voltage-induced method is 35% smaller than magnetic field only, demonstrated that the AC voltage-induced method assist magnetization switching well. 
**References:** [1] T. Yamamoto, et al., Phys. Rev. Appl., Vol. 13, p.014045 (2020). 
[2] J. Liu, et al., J. Magn. Magn. Mater., Vol. 513, p.167105 (2020). 
[3] J. Zhu, et al., IEEE Trans. Magn., Vol. 44-1, p.125-130 (2008). 
[4] R. Verba, et al., Sci. Rep., Vol. 6, p.25018 (2016). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/50647de04bbaf23bf2ce231e22165a52.png) 
Fig. 1 (a) The schematic illustrations for the ferromagnetic nanodot covered by dielectric layer. Dependence of the precession amplitude (b) and the switching field (c) on the excitation frequency. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/96f332d8343db93b84ea45f414692c11.png) 
Fig. 2 Comparison of the switching field among 3 different methods.

Numerical analysis of magnetization switching assisted by AC voltage controlled magnetic anisotropy effect

Microwave-assisted magnetic recording (MAMR) [1] has attracted much attention as one of the recording techniques for the ultra-high-density recording. Theoretical analysis of microwave-assisted magnetization switching (MAS) was studied in the case when DC field was applied parallel to the anisotropy direction [2, 3], which indicated that the effect of microwave assistance was explained by the equivalent magnetic field applied along anisotropy axis given by ω/γHk. However, the analysis of MAS is quite complex when DC field is applied non-parallel to the anisotropy axis. This study proposes an approximated estimation method when DC field is applied non-parallel to the anisotropy axis. 
Fig. 1 shows the schematic drawing of the normalized equivalent field, ω/γHk due to magnetization dynamics. Normalized DC field (hDC) is applied at θ with respect to the anisotropy axis. Circular polarized normalized field (hAC) is applied in the x-y plane. Here, the angle of the precession axis φ is approximated by the average of φ1 and φ2 which stand for the angles between the anisotropy axis and the magnetization directions at the maximum mx and the minimum mx, respectively. The direction of the equivalent field is defined to be anti-parallel to the precession axis in this study. In our previous study, we confirmed the in-plane and z components of the normalized effective fields were approximated by Eqs. (1). These equations well explained micromagnetic calculation and the resultant switching fields (hSW) well agreed with the asteroid curve Eq. (2). 
hxy =hDCsinθ - ω/γHksinφ +hAC , hxy =hDCcosθ - ω/γHkcosφ Eqs. (1)
hxy2/3 + hz2/3 = 1 Eq. (2)
Hence, hSW is given by φ. φ1 and φ2 are obtained from the equilibrium condition (∂E/∂φ1,2 =0) of the magnetic energy defined by Zeeman and anisotropy energy. Fig. 2 compares the approximation and micromagnetic calculation for various θ when hAC is 0.05. hSW are plotted as a function of the microwave frequency lower than critical frequency. The error between the approximation and micromagnetic simulation is less than 2% which is quite small. 
**References:** [1] Jian-Gang Zhu, et al., IEEE Trans. Magn., Vol. 44, pp.125-131 (2008). 
[2] G. Bertotti, et al., Phys. Rev. Lett., Vol. 86-4, pp. 724-727 (2001). 
[3] S. Okamoto, et al., J. Appl. Phys., Vol. 107, 123914 (2010). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/652a7caba2a1ed49c23b8e677fb18bea.png) 
Fig. 1 Schematic illustrations for the equivalent field. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/d06a5261306c56ba63e749dc8e99a678.png) 
Fig. 2 Comparison between approximation and micromagnetic simulations.

Approximation of microwave assisted magnetization switching field applied with incident angle

In bit patterned media recording (BPMR), the areal density is increased by reducing the distance between the magnetic islands. Thus, the BPMR faces a two-dimensional (2D) interference problem. To solve the 2D interference, the output of the BPMR channel is passed through the equalizer to convert it into the desired signal, which has the known coefficient interference. However, mapping between the output of the BPMR channel and the desired signal is a nonlinear problem. Therefore, the nonlinear equalizer based on neural network structure is proposed in [1]. However, because the training process is too complicated, the equalizer based on the neural network is used to estimate the 1D generalized partial response (GPR) target. To improve the equalizer based on the neural network, we introduce the neural network equalizer and method to train the neural network equalizer with a 2D GPR target. In the proposed model (Fig. 1), firstly, we use the method in [2] to estimate the parameters of the serial target (step 0). These target coefficients are kept to create the desired signal d[j,k] as the label for the training process of the neural network. To train the neural network, we use the received signal y[j,k] as the input and the signal d[j,k] as the label (step 1). Next, we re-train the target’s coefficients by using the trained neural network to create the y[j,k] as the label and the modulated signal a[j,k] as the input (step 2). Finally, the neural network is re-trained using the target coefficients from step 2 and remaking step 1 (step 3). Therefore, the GPR target is optimized by the nonlinear equalizer of the multi-layer perceptron (MLP). The results from the simulations (Fig. 2) show that our proposed model improves the bit error ratio (BER) performance compared to the previous studies [1] and [2] after re-training the neural network at step 3. 
**References:** [1] J. Shen and N. Nangare, “Nonlinear Equalization for TDMR Channels Using Neural Networks,” 2020 54th Annual Conference on Information Sciences and Systems (CISS), 2020, pp. 1-6. 
[2] T. A. Nguyen and J. Lee, “Effective Generalized Partial Response Target and Serial Detector for Two-Dimensional Bit-Patterned Media Recording Channel Including Track Mis-Registration,” Appl. Sci., 2020. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/bf15037962ee025e380d807b5f6395aa.png) 
Fig.1. Diagram of the proposed model. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/9b33f7e3908bb35d4ee040eeea1c3a92.png) 
Fig. 2. BER performance of the proposed model.

Optimization of Two Dimensional Generalized Partial Response Target Using Multi

Transcranial magnetic stimulation (TMS) is a safe, effective and non-invasive treatment for several psychiatric and neurological disorders. TMS is FDA approved treatment for depression and obsessive-compulsive disorders [1]–[3]. Lately, there has been a research surge in utilizing this novel technology in treating other neurological and psychiatric ailments. The application of TMS on other several neurological disorders requires the magnetic flux density and electrical field to be focal and targeted to a small region in the brain [4]. Multiple coil designs have been introduced in the literature to improve the focality of TMS coils, whereas, slight few numbers of these designs have adapted soft magnetic materials as coil cores to focus the magnetic flux. In this study, several soft magnetic materials will be investigated as TMS coil cores both in Finite Element Simulations and experimentally on rat head model. 
Finite element analysis of the rat head model will be done using Sim4life while investigating variations associated with changing the coil core material. In addition to investigate the effect of adding a V- shape tip to the core with 2 different angels 60 and 120 degrees [5]. Materials proposed for the analysis in this study include but not limited to Iron Cobalt Vanadium alloy (FeCoV), AISI 1010 Carbon Steel and Manganese Zinc ferrites (MnZn). Magnetic Properties of these materials will be characterized using Physical Property Measurement System (PPMS) to ensure using accurate magnetic properties in our simulations. 
Simulation results are presented below in (Fig. 2), indicating significant E-Field distribution variation when introducing a ferromagnetic core in TMS coil, concentrating the E-Field to the targeted region in rat head model without stimulating adjacent regions. It was observed that the relative permeability of the core material affects the focality of the stimulation significantly.
Acknowledgment: Authors acknowledge Commonwealth Cyber Initiative Central Virginia Node Grant # FP00010500. 
**References:** [1] M. S. George et al. Arch. Gen. Psychiatry, vol. 67, no. 5, pp. 507–516, May 2010 
[2] D. W. Dodick, C. T. Schembri, M. Helmuth, and S. K. Aurora Headache J. Head Face Pain, vol. 50, no. 7, pp. 1153–1163, Jul. 2010 
[3] O. of the Commissioner, FDA, Mar. 24, 2020. 
[4] J. Selvaraj, P. Rastogi, N. Prabhu Gaunkar, R. L. Hadimani, and M. Mina IEEE Trans. Magn., vol. 54, no. 11, pp. 1–5, Nov. 2018 
[5] I. C. Carmona, D. Kumbhare, M. S. Baron, and R. L. Hadimani, AIP Adv., vol. 11, no. 2, p. 025210, Feb. 2021 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/8a38a4c9fe12b20ed6b90103013ae0a7.png) 
Figure 1: TMS coil postion on rat head model. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/9b577978fc0d1fa99cbbb8ec148c2c0c.png) 
Figure 2: E-Field distribution simulation results. Left: E-Field distribution without ferromagnetic core. Right: E-Field distribution including a ferromagnetic core.

Investigation of Soft Magnetic Material Cores in Transcranial Magnetic Stimulation Coils and the Effect of Changing Core Shapes on the Induced Electrical Field in Small Animals

In the last years, the railway industry has been one of the leading sectors in the research of alternatives to reduce the costs associated with maintenance. The components of railway tracks suffer huge amounts of pressure that could compromise railway safety and must be revised, repaired and renew frequently according to strict criteria. In the case of the sleeper, the maximum stress allowed by the different authorities is in the order of ∼100 MPa [1] before substitution. Currently, the main testing procedures are based on visual inspection or in situ measurements, making maintenance procedures economically inefficient. 

With the development of industry 4.0, researchers have been studying the fabrication of smart-sleepers capable of monitoring the sleeper structural stress in real-time [2]. Current technology makes extensive use of expensive optical fiber based instruments [2,3]. Thus, making it difficult to extend its use to big extensions of railway lines. 

Magnetic microwires fabricated by the Taylor-Ulitovsky technique appear in this context as an alternative for smart-sleeper technology. The microwires obtained using this technique are characterized by their small cross section (d =0 .5-40 µm), environment insulation thanks to the glass-coating and high sensitivity to external stimuli [4]. These properties, along with their cheap fabrication costs has motivated the study of this microwires for structural measurements in concrete structures similar to concrete sleepers [5]. 

In this work we show the possibility of glass coated magnetic microwires of working as railway monitorization devices. This is done by measuring the effect of longitudinal stress on the hysteresis loops of several Co- and Fe-rich microwires with different compositions. By analyzing the hysteresis loops, as shown in Fig 1 and Fig 2, we are able to obtain a calibration function that relates the coercitive field, Hc, with the applied stress over a wide applied stresses range. 
**References:** [1] Parvez A., Foster, S. J., Engineering Structures, Vol 141, p 241-250, (2017). 
[2] Jing G. et al., Construction and Building Materials, Vol 271, 121533, (2021). 
[3] Butler et al., Structural Health Monitoring, Vol 17(3), p 635-653, (2018). 
[4] Corte-Leon P. et al, Journal of Alloys and Compounds, Vol 789, p 201-208. (2019) 
[5] Olivera, J., et al (2019. Sensors, Vol 19(21), 4685 (2019) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/b422981d4496bf381544640a70e25c48.png) 
Figure 1: Response of wire Fe4.39 Co65.12 Si6.79 Cr8.88 Mo0.15 to stress a) Hysteresis loop evolution. b) Microwire calibration function. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/f2b3344c1519bfc3cd9db189fd16b7ef.png) 
Figure 2: Response of wire Fe66.99 Si6.45 Nb5.79 Ni1.13 upon to stress a) Hysteresis loop evolution. b) Microwire calibration function.

Effect of Applied Stresses on Magnetic Properties of Co and Fe rich Glass

Amorphous ferromagnetic glass-coated microwires are known for their excellent magnetic properties, such as magnetic softness, ultrafast magnetization switching and the giant magnetoimpedance (GMI) effect. Said properties, as well as the hysteresis loop shape and domain structure of as-prepared microwires are strongly affected by the magnetostriction constant [1]. However, these properties are prone to change after submitting the microwires to different annealing processes and/or external stimulus, and are dependent on the sample’s geometry [1,2]. The combination and manipulation of these parameters are widely studied to adapt magnetic microwires to new technological applications. 

Fe-rich microwires commonly exhibit bistable magnetic behaviour and poor GMI values. Past experiments on thin Fe microwires have shown an enhancement on their GMI effect after current annealing of samples, with hints to a change in their magnetic domain structure [3]. However, while thin microwires are promising materials for development of microsensors, thicker ones are suitable for different applications, such as stress monitoring and tuneable composite materials. Thus, a study of Fe-rich, thick microwires is carried out. 

A Fe71.8B13.27Si11.02Nb2.99Ni0.92 glass-coated microwire was produced, with metallic nucleus and total diameters d=47.9µm and D=63.2µm (ρ=d/D≈0.8). While short (12cm, same lenght as the pick-up coil used for measurement) samples show regular squared hysteresis loops, common for Fe microwires, asymmetric hysteresis loops are observed in 24cm long samples (Figure 1.a). Current annealing results in coercivity, Hc, increasing in both samples, being most noticeable for the long one (Figure 1.b). 

On the other hand, GMI measurement yields an unexpected result, as, while its current annealing results in a proportionally smaller GMI ratio, ΔZ/Z, enhancement than that obtained on thin ones, the as-prepared microwire shows much higher ΔZ/Z -values and a double peak structure, usually denoting a different domain structure (Figure 2). 
**References:** [1]: V. Zhukova, M. Churyukanova, A. Talaat, et al. Effect of stress-induced anisotropy on high frequency magnetoimpedance effect of Fe and Co-rich glass-coated microwires. J. Alloys Compound, Vol. 735, p.1818-1825 (2018). https://doi.org/10.1016/j.jallcom.2017.11.235 
[2]: V. Zhukova, J.J. del Val, L. Gonzalez-Legarreta, et al. Optimization of Soft Magnetic Properties in Nanocrystalline Fe-Rich Glass-Coated Microwires. JOM, Vol. 67, p.2108–2116 (2015). https://doi.org/10.1007/s11837-015-1546-x 
[3]: A. Gonzalez, M. Ipatov, P. Corte-Leon, et al. Effect of Joule heating on GMI and magnetic properties of Fe-rich glass-coated microwires, AIP Advances, Vol. 12, p.035021 (2022). https://doi.org/10.1063/9.0000290 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/be63c179803fbf03b88c5b5a57095d67.png) 
Fig.1: a) hysteresis loops of annealed samples and b) coercive field dependence on annealing times. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ec67e59dbb9667cd72f643c47aff7de0.png) 
Fig.2: GMI ratios of as-prepared and annealed a) thin and b) thick microwires.

Current Annealing Dependence of Magnetic Properties of Thick Fe rich Glass

Rapidly solidified submicronic amorphous glass-coated wires have been extensively investigated recently due to their unique combination of reduced diameters (100 to 900 nm), very long sample length (10-2 to 103 m), and bistable magnetic behavior, suitable for both sensing and magnetic logic applications [1].
Here we report on the interaction between domain walls that propagate inside amorphous (Co0.94Fe0.06)72.5Si12.5B15 glass-coated submicronic wires with nearly zero magnetostriction (λ = -1 × 10-7). 
The experimental set-up relies on six pick-up coils (C2 through C7) distributed evenly along the wire and two nucleation coils (C1 and C8) placed at its ends, the entire system being in a long magnetizing solenoid. If there is no signal in the nucleation coils, the sample magnetization reverses from one end (C1) to the other (C8), with only one propagating domain wall being detected successively by the pick-up coils: C2 → C3 → C4 → C5 → C6 → C7.
By applying synchronized rectangular nucleation signals in C1 and C8, magnetization reversal starts at both wire ends. Through the signal amplitudes, we adjusted the time interval between the generation of the two domain walls moving towards each other, and, in this way, the location on the wire axis where the two domain walls would collide. The collision results in a double amplitude peak within one of the pick-up coils, as compared to the peak that corresponds to a single domain wall passing through such a coil. By keeping the nucleation signal constant in C1 at 0.5 mA and varying the signal in C8 between 0.1 and 0.9 mA, one can relocate the domain wall interaction point in any pick-up coil. Fig. 1 shows the displacement of the collision point for an amorphous sample with 750 nm in diameter. 
The results show that the interaction of domain walls in such small diameter cylindrical amorphous wires is fully controllable, which is vital for magnetic logic applications.
Work supported by the Romanian Executive Unit for Financing Higher Education, Research, Development and Innovation (UEFISCDI) through project PN-III-P4-ID-PCE-2020-1856 MaDWallS (contract PCE1/2021). 
**References:** [1] S. Corodeanu, C. Hlenschi, C. Rotarescu, H. Chiriac, N. Lupu, T.-A. Óvári, J. Alloy. Compd., Vol. 905, 164260 (2022). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/d355a9fe62bc2e2b132951458fee1cbe.png) 
Fig. 1. Displacement of domain walls interaction point for an amorphous submicronic wire with 750 nm in diameter.

Controlled Domain Wall Interactions in Nearly Zero Magnetostrictive Amorphous Submicronic Wires

Studies of amorphous magnetic wires have become a traditional topic of applied magnetism owing to excellent magnetic properties and the development of prospective applications [1,2]. Taylor-Ulitovsky fabrication technique provides the broadest microwires diameters range together with improved corrosion, mechanical properties and biocompatibility related to the presence of the glass-coating [2,3]. However, the latter is a source of additional magnetoelastic anisotropy, Kme, which is one of the most important factors determining the magnetic properties of the amorphous materials. 
One effective method for evaluation of magnetic anisotropy in magnetic wires is the ferromagnetic resonance, FMR [2]. Additionally, FMR allows the evaluation of several material properties as saturation magnetization, g-factor, damping parameter, etc. [2,4].
We report experimental results of FMR and magnetic properties of various Fe and Co-based glass-coated microwires. We observed that the coercivity, Hc, of Co-Fe-rich microwires depends on the chemical composition: the highest Hc is observed for the microwire with highest Fe content. Such dependence must be attributed to Fe content influence on the magnetostriction coefficient, λs [3]. 
FMR spectra presents considerable dependence on resonance field, Hr, frequency, f (Fig.1) and Kme [4]. In all studied microwires Hr increases with f. Hr is also affected by the microwire diameter: the FMR spectra for microwires with similar chemical composition, but diameter almost an order of magnitude different are shown in Fig.2. On the other hand, even for the same λs (mostly determined by the chemical composition), Kme is affected by the value of the internal stresses, σi, that it is mostly determined by the ratio ρ, between metallic nucleus diameter, d, and total microwire diameter, D [3,4]. Therefore, the difference observed in FMR spectra must be attributed not only to different d, but also to the difference in σi. Additionally, in thin enough microwires the interface layer between the glass-coating and metallic nucleus can affect the FMR behavior [3]. 
**References:** [1] M. Knobel, M. Vázquez, L. Kraus, Giant Magnetoimpedance, in Handbook of Magnetic Materials, Elsevier, Vol. 15, p497 (2003). 
[2] K. Mohri, et al., IEEE Trans. Magn., Mag-26, p.1789 (1990). 
[3] A. Zhukov et al., J. Alloys Compd., Vol. 814, p. 152225 (2020), doi:10.1016/j.jallcom.2019.1522250925-8388. 
[4] L. Kraus, Ferromagnetic resonance in individual wires: From micro- to nanowires, in Magnetic Nano- and Microwires (ed. M. Vázquez), Elsevier, ch. 15 (2015). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/2a10fd15ef0f2efe3407501f33976e66.png) 
Fig.1. FMR spectra of Fe79B8Si10C3 microwire (d=19.2 μm). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/3569f4ed375587f77086b525a888aecc.png) 
Fig.2. FMR spectra of Fe74B13Si11C2 (d=19.2 μm) and Co2.25Fe72.75Si15B10 (d=2 μm) microwires.

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