United States

Magnetic random access memories (MRAM) store information on magnetization direction instead of electric charge. All optical switching (AOS) of a magnetic tunnel junction provides an efficient way to enable writing at speeds orders of magnitude faster than electrical alternatives based on spin torque methods, allowing for write operations at THz frequencies. The [Tb/Co] multilayer is particularly interesting, since its large perpendicular magnetic anisotropy would allow data retention at small sizes and could be integrated into a magnetic tunnel junction [1-2]. This work reports magnetization reversal driven by femtosecond light pulses on a [Tb/Co] based perpendicular magnetic tunnel junction patterned to sub-100nm lateral dimensions. This optical switchable electrode was integrated into an MgO based MTJ having synthetic anti-ferrimagnet reference layer element, where the AOS magnetization direction can be read directly from the resistance state of the junction. The optically switchable electrodes are [Tb/Co]&lt;sub&gt;x5&lt;/sub&gt; multilayers coupled to a 1.4nm FeCoB layer through a 0.2nm W insertion layer. Patterned AOS-MTJ nanopillars fabricated with diameters down to 80 nm showed TMR ratios up to 74% and a resistance area product of 112 Ω μm&lt;sup&gt;2&lt;/sup&gt;. Figure 1) shows the hysteresis loop for a [Tb 0.6nm/ Co 1.4nm]&lt;sub&gt;x5 &lt;/sub&gt;multilayer. It was possible to observe a toggle switching between low and high resistance states, corresponding to parallel and anti-parallel alignment of the two electrodes, after each 50 fs long laser pulse applied on the device. A systematic study on the switching probability will be compared to existing results of AOS experiments on continuous films. There it was possible to demonstrate that reliable and robust toggle switching can be achieved for specific Tb and Co thickness in the range of 0.6-0.9 nm of Tb and 1.3-1.5 nm of Co. The magnetization reversal is reliable after a 150.000 pulse sequence. Single shot AOS is achievable using laser pulse durations from 50 fs up to 10 ps and fluences 3-6.5 mJ/cm&lt;sup&gt;2&lt;/sup&gt;. These results pave the way towards an AOS ultra-fast and energy-efficient memory.&lt;br&gt;
**References** &lt;br&gt;
[1] A. Olivier et al., Nanotechnology 31, 425302 (2020).&lt;br&gt;
[2] L. Avilés-Félix et al., Scientific Reports 10, 1 (2020).&lt;br&gt;
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/dca0d23bf1cc210d5479056d84ef1c36.png)&lt;br&gt;
Figure 1 a) AOS-MTJ stack illustration b) R-H loop in perpendicular field c) AOS field-free toggle switching between P and AP states.

MMM 2022

Field free all optical switching in Tb/Co multilayer magnetic tunnel junction

Magnetic random access memories (MRAM) store information on magnetization direction instead of electric charge. All optical switching (AOS) of a magnetic tunnel junction provides an efficient way to enable writing at speeds orders of magnitude faster than electrical alternatives based on spin torque methods, allowing for write operations at THz frequencies. The [Tb/Co] multilayer is particularly interesting, since its large perpendicular magnetic anisotropy would allow data retention at small sizes and could be integrated into a magnetic tunnel junction [1-2]. This work reports magnetization reversal driven by femtosecond light pulses on a [Tb/Co] based perpendicular magnetic tunnel junction patterned to sub-100nm lateral dimensions. This optical switchable electrode was integrated into an MgO based MTJ having synthetic anti-ferrimagnet reference layer element, where the AOS magnetization direction can be read directly from the resistance state of the junction. The optically switchable electrodes are [Tb/Co]x5 multilayers coupled to a 1.4nm FeCoB layer through a 0.2nm W insertion layer. Patterned AOS-MTJ nanopillars fabricated with diameters down to 80 nm showed TMR ratios up to 74% and a resistance area product of 112 Ω μm2. Figure 1) shows the hysteresis loop for a [Tb 0.6nm/ Co 1.4nm]x5 multilayer. It was possible to observe a toggle switching between low and high resistance states, corresponding to parallel and anti-parallel alignment of the two electrodes, after each 50 fs long laser pulse applied on the device. A systematic study on the switching probability will be compared to existing results of AOS experiments on continuous films. There it was possible to demonstrate that reliable and robust toggle switching can be achieved for specific Tb and Co thickness in the range of 0.6-0.9 nm of Tb and 1.3-1.5 nm of Co. The magnetization reversal is reliable after a 150.000 pulse sequence. Single shot AOS is achievable using laser pulse durations from 50 fs up to 10 ps and fluences 3-6.5 mJ/cm2. These results pave the way towards an AOS ultra-fast and energy-efficient memory. 
**References** 
[1] A. Olivier et al., Nanotechnology 31, 425302 (2020). 
[2] L. Avilés-Félix et al., Scientific Reports 10, 1 (2020). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/dca0d23bf1cc210d5479056d84ef1c36.png) 
Figure 1 a) AOS-MTJ stack illustration b) R-H loop in perpendicular field c) AOS field-free toggle switching between P and AP states.

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.

<iframe width="560" height="315" src="https://s3.amazonaws.com/pf-user-files-01/u-59356/uploads/2022-11-02/un13zp7/MMM%20Welcome%20Video%20v5.mp4" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

For tickets to the event, please register at the following link: https://magnetism.org/registration

Please register for the MMM 2022 conference to join the event.

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

Quantum computation and cryogenic electronics have gained considerable importance in this last decade. Currently, a bottleneck for advancing it further is the power consumption of conventional electronic components, which is not adapted to the needs of cryogenic circuits. Perpendicular Spin-Transfer-Torque Magnetic Random Access Memory (p-STT-MRAM) has potential to comply with cryo-electronics requirements of low power. Previous works done on cryogenic temperature switching of STT-MRAM have assessed its characteristics and the Write Error Rate for different device diameters [1]. The conditions to write an STT-MRAM are promising (0.7V at 9K with 200ns pulses, corresponding to a writing energy of 11.2 pJ) [2]. However, the full integration of MRAMs into quantum processors demands a much lower operating voltage (below 0.1V).Therefore, we focused our research on engineering MTJs for low anisotropy to reduce the critical switching voltage VC and consequentially the write energy per bit Ebit. Our approach consists in changing the interface of the storage layer by adding an insertion layer as in Mg+Ox/X/FeCoB/W/Y/W, where X can be wedges of Mg, FeCoB and Y is permalloy (Py). This type of device can show high thermal stability at cryogenic temperatures (i.e.4K), while having no retention at 300K. This strategy allows the reduction of the storage layer anisotropy by at least one order of magnitude.
Figure 1 shows a current pulse phase diagram of a junction with Mg insertion. Upon changing the operation temperature the write current density JC for junctions with different insertion layers is varying as reported in Figure 2. Device diameter, composition and thickness play an important role in modulating the anisotropy. Tuning these parameters it is possible to bring the switching currents close to 20µA for a 30nm diameter device at 10K (red curve), corresponding to Ebit=1.2pJ. This can be further improved by modulating the required current density with composition as shown in the figure 2. 
**References** [1] L. Rehm, G. Wolf, B. Kardasz, M. Pinarbasi, and A. D. Kent, "Sub-nanosecond spin-torque switching of perpendicular magnetic tunnel junction nanopillars at cryogenic temperatures", Appl. Phys. Lett. Vol. 115, p.182404 (2019).
[2] Lili Lang, Yujie Jiang, Fei Lu, Cailu Wang, et al, "A low temperature functioning CoFeB/MgO-based perpendicular magnetic tunnel junction for cryogenic nonvolatile random access memory", Appl. Phys. Lett. Vol. 116, p.022409 (2020) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/7104e850bea9e89cf9c614e4c15db138.png)

Control of Interface Anisotropy for Spin Transfer Torque in Perpendicular Magnetic Tunnel Junctions for Cryogenic Temperature Operation

Magnetic skyrmions are recently attracting attention from the viewpoint of application to next-generation spintronics devices such as ultra-low-power Brownian computers. Skyrmions are expected to function as information carriers in those devices because of their unique features such as Brownian motion at near room temperature, small size, easy detection and easy control (1-4). In order to realize such devices, electrical gating and amplification of the skyrmion signal are indispensable. The primary mechanism of the voltage control technique for skyrmions is the voltage-controlled-magnetic-anisotropy effect (VCMA effect) (5-6). In the previous studies using the VCMA effect, for example, modulation of the diffusion coefficient (2) and creation/annihilation of the skyrmions (3) have been demonstrated. However, “skyrmion gates/transistors” have not been realized experimentally yet. Obstacles might be that the conditions creating skyrmions are easily affected by the local stress introduced from the gate fabrication. Furthermore, a non-negligible energy barrier that appears at the edge of the gate electrode, traps the skyrmions there. In this talk, we will present our attempts to realize a device in which skyrmions are not trapped at the edge of the gate electrode.
A skyrmion film consisting of Ta|Co16Fe64B20|Ta|MgO|SiO2 was deposited on a thermally oxidized silicon substrate by the magnetron sputtering. In order to apply voltage to the magnetic layer, thin Ru gate electrodes with a thickness of 2 [nm] were deposited onto this film, and the MOKE microscope observed the motion of skyrmions. Narrow gate electrodes trapped skyrmion at the edge of the electrodes even though no voltage was applied. The wider Ru electrode enables a free passage of the skyrmions through the edge. The result is one of the fundamentals of realizing the skyrmion transistors. 

Acknowledgement: The authors acknowledge to Ono laboratory in Kyoto Univ. This research and development work was supported by ULVAC, Inc., JST CREST Grant number JPMJCR20C1, Japan and JSPS KAKENHI Grant Number JP20H05666. 

**References:** 
(1) J. Zázvorka et al., Nat. Nanotechnol., 14, 658–661 (2019), 
(2) T. Nozaki et al., Appl. Phys. Lett., 114, 012402 (2019), 
(3) M. Schott et al., Nano Letters., 17, 3006-3012 (2017), 
(4) B. W. Walker et al., Appl. Phys. Lett., 118, 192404 (2021), 
(5) M. Weisheit et al., Science 315, 349 (2007), 
(6) T. Maruyama et al., Nature Nanotech., 4, 158 (2009), 
(7) Y. Jibiki et al., Appl. Phys. Lett., 117, 082402 (2020)

Control of the skyrmion passage by a gate electrode

FeRh is an archetypal system for the investigation of ultrafast behaviour in coupled transitions due to its meta-magnetic phase transition occurring around 380 K [1]. In this coupled phase transition, the electronic structure transforms lowering the resistivity by ≈ 33%, the lattice expands isotropically with a volumetric expansion of ≈ 1%, and the magnetic order changes from a G-type antiferromagnet (AF) to a ferromagnet (FM) [1], [2]. Previous x-ray diffraction (XRD) studies have indicated that the lattice expands with first-order dynamics within 10-30 ps [3], with long-range AF order throughout the transition [4]. The sub-ps capabilities of the SACLA free-electron laser allowed for investigation of the ultrafast behaviour of the FeRh lattice upon laser excitation. This shows new dynamics at high fluences which were compared to the quasi-static behaviour of the Bragg peaks as measured using heated XRD. We describe the lattice temperature (see Fig. 1a) and expansion as a function of pump-probe delay. We have observed a perturbation to the expected dynamics above fluences of 5 mJ cm-2 where the lattice initially contracts before finally expanding as predicted. We demonstrate that a model (see Fig. 1b) using a transient lattice state [5] can explain the observed behaviour. Our model suggests that the transient state is paramagnetic, reached by a subset of the phonon bands which are preferentially coupled to the electronic system [6]. A complete description of the FeRh structural dynamics requires consideration of coupling strength variation across the phonon frequencies. 
**References** [1] J. S. Kouvel and C. C. Hartelius, J. Appl. Phys., 33, 1343, (1962).
[2] J. S. Kouvel, J. Appl. Phys., 37, 1257–1258, (1966).
[3] S. O. Mariager, F. Pressacco, G. Ingold, et al., Phys. Rev. Lett., 108, 087201, (2012).
[4] M. Grimes, N. Gurung, H. Ueda, et al., AIP Adv., 12, 035048, (2022).
[5] B. Mansart, M. J. G. Cottet, G. F. Mancini, et al., Phys. Rev. B, 88, 054507, (2013).
[6] M. Grimes, H. Ueda, D. Ozerov, et al., Sci. Rep., 12, 8584 (2022) 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/35b9247688f80a37d426011d0dfbd8b5.png)

Determination of sub ps lattice dynamics in FeRh thin films.

Experimental and computational studies on the stress-dependent magnetic property of silicon steel are on-going. A physical magnetization model, an energy-based
multiscale magnetization model called multi-domain particle model (MDPM) [1], was developed, which successfully predicted the stress-dependent properties of silicon steel without using
measured stress-dependent data.
To avoid measurement under arbitrary combination of stress and magnetization directions, several stress models have been developed. This study examines two of them by comparing with
the MDPM. One is the equivalent stress (ES) theory [2] and the other is the stress decomposition (SD) method [3]. The latter assumes that the stress effect can be decomposed into its
principal directions.
A rotational single sheet tester applied a compressive stress to a non-oriented silicon steel sheet in the rolling direction (RD, φ=0). A magnetic field was applied along φ = 0 or π/4. Fig. 1
shows the measured stress dependence of hysteresis loss wx
in the RD when the amplitude of Bx
is 0.5, 0.7 and 1.0 T, where By has only a small effect on the stress dependence of wx
. It
supports the assumption of stress decomposition.
BH loops under the excitation angle of π/4 were simulated using the MDPM, where the directions of stress and applied magnetic field are denoted by φσ
and φH. Fig. 2 shows BH loops as
below: [reference, blue lines] φH=π/4 and φσ=0 with σ = −40, −80 MPa, [ES theory, green lines] φH=φσ=π/4 with σ = −10, −20 MPa based on the ES theory, [SD, brown lines] synthesized
loops of φH=φσ=0 with σ = −40, −80 MPa and φH=φσ=π/2 with σ = 0, and [modified SD, red lines] synthesized loops of φH=φσ=0 with σ = −40, −80 MPa and φH=φσ=π/2 with σ = +40,
+80 MPa. The ES theory roughly predicts the stress dependent loops along φ = π/4, but fails to predict decomposed loops along φ = 0, π/2. The SD fails to reconstruct loops along φ=π/2
because a compressive stress along φ=0 acts as a tensile stress along φ=π/2. The modified SD roughly predicts the stress dependent loops in all the directions by giving tensile stresses
along φ=π/2. 
**References** [1] T. Matsuo, Y. Takahashi, K. Fujiwara, J. Magn. Magn. Mater., vol. 499, 166303, 2020.
[2] M. Rekik, L. Daniel, O. Hubert, IEEE Trans. Magn., vol. 50, 2001604, 2014.
[3] M. Nakano, et. al, IEEJ Trans. Ind. Appl., vol. 129, pp. 1060–1067, 2009. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/e1f0bcd2c0c40783e8767d4d94ed46a2.png) 

Comparison of measured loss increase Δwx with φH = 0, π/4 and φσ = 0.
 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/021523014ab029406572a4271db10186.png) 

Simulated BH loops along (a) φ = π/4, (b) φ = 0, and (c) φ = π/2.

Computational Validation of Method for Decomposition of Mechanical Stress Effect on Magnetic Property of Silicon Steel Sheet

As microwave-assisted magnetic recording (MAMR) is being employed in commercial hard disk drives, technology challenges remain [1][2]. A key one of them is the need for relatively strong ac field amplitude. Here, we present a novel scheme to substantially enhance the efficiency of the ac field. For a single domain magnetic particle of uniaxial anisotropy, the anisotropy energy is Ean=Ksin2θ where θ is the angle between the magnetic moment of the particle and the easy axis and K is the anisotropy energy density. The effective magnetic field due to this anisotropy is Han=HkcosΘ where Hk = 2K/Ms . Since the anisotropy field is a cosine function of the magnetization angle, the resonance frequency varies during a magnetization reversal. Hence, if the applied ac field frequency can match this resonance frequency variation during a magnetization reversal, the efficiency of the ac field should be significantly enhanced. Figure 1 shows the calculation for a single domain particle of Hk=30kOe. A magnetic field with a 2o angle w.r.t. the easy axis and duration of 1ns is applied opposite to the initial magnetization The ac field is a rotating perpendicular to the easy axis with a during of 1ns. The ac field frequency is either a constant (black), linearly decreases to zero, or follows the function of ω0cos(0.86t/τ) where τ=1ns. The horizontal axis is the initial ac field frequency. The ac field amplitude is set as 1% of the anisotropy field at 300 Oe. In the case of the cosine-varying frequency ac field, the switching field reduction is more than 75% Hk, at 6kOe. The substantially enhanced switching field reduction shows the efficiency gain by having ac field frequency following the resonance frequency reduction during the magnetization reversal. Figure 2 shows the switching field of a particle of Hk=25kOe and the ac field frequency is the cosine-varying case. When the ac field amplitude exceeds 350 Oe, the switching can be achieved without the reversal field applied. 
**References** 
[1] J.-G. Zhu, X. Zhu, and Y. Tang, “Microwave assisted magnetic recording,” IEEE Trans. Magn., vol. 44, no. 1, pp. 125–131, Jan. 2008. 
[2] Akihiko Takeo, et al, "Extended Concept of MAMR and its Performance and Reliability," Paper C1, TMRC 2020, August 2020. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/e05b39ad4289c136f43aa718eda6f9c9.png) 
Fig. 1. Switching field vs the initial frequency of ac fields with the frequency being constant (black), linearly decreasing (blue), or cosine-varying (red). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ab59ce146174a0a2902158a7d364dcb7.png) 
Fig. 2. Switching field vs initial ac field frequency for a cosine-varying frequency rotating ac field.

Efficiency Enhanced Magnetic Resonance Switching of Single Domain Particle with Uniaxial Anisotropy

The application of Nd-Fe-B magnet with substitution of Nd by cheap and abundant Ce elements is seriously limited due to the intrinsically inferior magnetic properties of Ce-Fe-B [1-3]. Recently, dual-main-phase (DMP) sintered magnet was successfully developed [4], which allowed special distribution of heterogeneous main phases (Ce-rich and Nd-rich R2Fe14B main phases), contributing remarkably to balance the utilization of high-abundance rare earths and the performance. This work demonstrated a novel design of quasi-trivalent DMP Ce magnets using the strategy of two main phases with giant magnetic anisotropy energy gap (MAEG). The maximum energy product of DMP Ce magnet with 40% weight percentage of Ce over total rare earth is optimized to be 40.57 MGOe, as shown in Fig. 1, which is the energy-product record. The superior magnetic properties are closely corelated to the average valence of Ce. The average valence of Ce in the DMP magnets was quasi-trivalent, proved by XPS spectroscopy, as shown in Fig. 2, which was lower than that in the single-main-phase magnets.
Furthermore, with an isostructural heterogenous configuration in the DMP magnets could manipulate electron migration and induce magnetic Ce3+ in the main phase, thereby improving the remanence. It was possible to control the Ce valence for the design of high-performance Ce magnets using main phases with diversity of MAEG. This would undoubtedly provide ideas for researching and developing new rare earth materials with a synergistic composition and structure. Compared with Nd-Fe-B magnets, the new quasi-trivalent DMP Ce magnets would save 30-40% Nd and remarkably reduce the production cost of magnets with much higher Ce content. 
**References:** [1] J. F. Herbst, Rev. Mod. Phys. 63, 819 (1991). 
[2] D. Li, Y. Bogatin, J. Appl. Phys. 69, 5515 (1991). 
[3] S. X. Zhou, Y. G. Wang, R. Høier, J. Appl. Phys. 75, 6268, (1994). 
[4] M.G. Zhu, W. Li, Y.K. Fang, et al. J. Appl. Phys. 109, 07A706 (2011). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/820e12846854022ea880456a41a440c1.png) 
Fig. 1 Demagnetization curve of the DMP-Ce-0.4 magnet at room temperatures. The energy-product record of 40.57 MGOe is reported for DMP-Ce-0.4 magnet. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/570ea6fc6a5760005e128776d2926bec.png) 
Fig. 2 Semi-quantitative fitting of the Ce 3d core-level spectra for the DMP-Ce-0.4 magnet using the ordinary least squares approach, where the standard XPS spectra of Ce3+ and Ce4+ were sourced from the Avantage software database.

Novel Quasi trivalent Dual

We are studying the effect that illumination by coherent resonant x-rays may have on magnetic domain memory (MDM) in a [Co/Pd] / IrMn multilayers [1-3]. MDM is the
ability of the magnetic domains to retrieve their exact same domain topology upon field cycling. In the case of [Co/Pd] / IrMn multilayers, MDM is induced by exchange couplings
between the Co/Pd ferromagnetic layer and the IrMn antiferromagnetic layer. We found that under high dose of x-ray illumination, the material may lose its existing MDM. To investigate
this potential effect, we have used both x-ray resonant magnetic scattering (XRMS) along with magneto-transport measurements [4,5] to track the exchange bias while the sample is
illuminated with x-rays, as illustrated in Figure 1. Magneto-transport is here used to measure the hysteresis loop of the multilayered material and observe exchange bias. A loss of exchange
bias would indicate that the x-rays illumination dose may alter the strength of the exchange couplings and ultimately the amount of MDM. Knowing if a loss of exchange bias has occurred
requires collecting magneto-transport data as well as XRMS data and correlating the observed changes under various dose of x-ray illumination. The data has been collected at different
angles, different configurations, and different temperatures. These configurations consist of Hall effect measurements as well as magnetoresistance measurements. Also, data was collected
using various sets of electrical contacts: a set of inner contacts around the x-ray transmission window and as set of outer contacts for reference. The outer contacts were located at a distance
of ~1 cm whereas the spacing between inner contacts was ~100 microns. These measurements have been carried at BYU in order to better understand the shape of the data observed in-situ
at the APS 

**References:** 

[1] K. Chesnel, A. Safsten, M. Rytting, and E.E. Fullerton, Nature Communications 7, (2016). 
[2] K. Chesnel, B. Wilcken, M. Rytting, S.D. Kevan, and E.E. Fullerton, New Journal of Physics 15, 023016(2013). 
[3] K. Chesnel, J. Nelson, B. Wilcken, and S.D. Kevan, Journal of Synchrotron Radiation 19, 293 (2012). 
[4] C. Hurd, Hall Effect in Metals and Alloys (Springer, 2012). 
[5] L.J. van der Pauw, A Method of Measuring Specific Resistivity and Hall Effect of Discs of Arbitrary Shape (1958). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/4b50c3a1949acb220aa816766ae3c2d9.png)

The effect of x ray illumination on magnetic domain memory in [Co/Pd] / IrMn multilayers

Arrays of magnetic nanowires (NWs) are an attractive platform with tremendous potential for developing novel magnetic applications, e.g., next-generation information technologies or sensors [1]. The synthesis of NWs by electrochemistry shows multiple degrees of freedom allowing for tailoring the composition, crystallographic structure and, consequently, magnetic properties [2,3]. Herein, FeNi NWs were grown by electrodeposition into anodized aluminum oxide (AAO) membranes (Fig. 1a). The broad range of electrolytes and voltages used, allowed us to study the anomalous FeNi co-deposition by a compositional analysis, being explained within a modified Bocris-Drazic-Despic (BDD) model [4]. X-ray diffraction patterns showed a change from bcc crystallographic structure for Fe-rich NWs to fcc structure at mid and low Fe content, with biphasic bcc-fcc phase for equiatomic NWs. Tuning the synthesis conditions led to FeNi NWs with a range of magnetic hardness, observing an increase in coercivity (from 0.2 kOe to 1 kOe) for a decreased Fe content (Fig. 1b). Coercivity angular measurements showed that the magnetization reversal is dominated by transverse domain wall reversal and indicated a decrease in magnetostatic interactions among NWs as the source of the coercivity rise. First-order reversal curves (FORCs) highlighted the limited role of the magnetic interactions in the arrays, except for Fe0.80Ni0.20 NWs which showed a FORC diagram for magnetically interacting NWs (Fig. 1c). This study shows how the magnetic properties of the NWs can be tailored through an optimized control of the synthesis conditions and adapted to the requirements of the final application. Fig. 1: (a) SEM image of NWs grown inside the AAO template, (b) Hysteresis loops for FeNi NWs with different compositions, and (c) FORC diagram for Fe0.80Ni0.20 NWs. Acknowledgements Authors acknowledge support from EU M-ERA.NET and MICINN through COSMAG (PCI2020-112143) and NEXUS (PID2020-11521RB-C21). A.J.C.-H. and E.M.P. acknowledge support from "La Caixaâ€ Foundation (ID 100010434) through the Doctoral INPhINIT Incoming program (LCF/BQ/DI20/1178002) and AEI (JdC-I program, IJC2020-043011-I/MCIN/AEI/10.13039/501100011033) and EU by NextGenerationEU/PRTR, respectively.

Analysis of the Magnetic Interactions in FeNi Nanowire Arrays through FORC and Angular Coercivity Measurements

Magnetic skyrmions [1] are topologically stabilized, magnetic quasi-particles, which exhibit interesting physical phenomena and are also potential candidates for efficient neuromorphic computation schemes. On the micro-meter scale, they are detectable with Kerr-microscopy, using the magneto-optical Kerr-effect. However, depending on the material stack, temperature, the growth procedure and other influences, those measurement might suffer from noise, low-contrast, intensity gradients or defects, therefore manual data treatment is normally necessary to generate data that can be evaluated easily.
Our approach is to use a convolutional neural network, based on the U-Net [2], to detect the position and shape of the skyrmions in our measurement data. This work was motivated by reports that machine learning has been successfully applied to (micro-)magnetic problems [3]. We are tuning the U-Net with various techniques to optimize the predictions and identify skyrmions and defects fast and with high reliability. A well-trained neural network is shown to minimize manual treatment of data. The approach is also easily extendable to other magnetic structures. 

**References:** 

[1] Everschor-Sitte et al., Journal of Applied Physics 124, 240901 (2018) 
[2] Ronneberger et al., MICCAI 2015. Lecture Notes in Computer Science, vol 9351. Springer, Cham. (2015) 
[3] Alexander Kovacs et al., Journal of Magnetism and Magnetic Materials 491, 165548 (2019) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/b905ba9abf4990b3c3c3e3a184f5069f.png)

Skyrmion detection with U Net

The frustrated interactions in nanomagnetic arrays can lead to the emergence of complex behaviour. Here we consider nanomagnets with dimensions on the crossover from single ferromagnetic domain (macrospin) and vortex states [1-3], in both ordered and disordered array geometries. Magnetic force microscopy reveals that there is a ratchet-like transformation of macrospins into vortices, during minor loop magnetic reversals. Simulations show that interactions with neighbouring magnets play an important role, giving cooperative growth of macrospin and vortex chains. This gradual evolution of linkages is neuromorphic in character, and interesting for both neurally-inspired computation [1] and self-assembly of magnonic circuits[3]. 

**References:** 

[1]Gartside, Jack C., et al. "Reconfigurable Training and Reservoir Computing via Spin-Wave Fingerprinting in an Artificial Spin-Vortex Ice." Nature Nanotechnology (2022)
[2]Gartside, Jack C., et al. "Reconfigurable magnonic mode-hybridisation and spectral control in a bicomponent artificial spin ice." Nature Communications 12.1 (2021): 1-9.
[3]Stenning, Kilian D., et al. "Magnonic bending, phase shifting and interferometry in a 2d reconfigurable nanodisk crystal." ACS nano 15.1 (2020): 674-685.

Premium content

Field free all optical switching in Tb/Co multilayer magnetic tunnel junction

Downloads

Next from MMM 2022

Control of Interface Anisotropy for Spin Transfer Torque in Perpendicular Magnetic Tunnel Junctions for Cryogenic Temperature Operation

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES