United States

Soft magnetic composites(SMCs) consist of ferromagnetic particles, in the micrometer-range which are embedded in an electrically insulating material, in order to reduce the eddy-currents in the high-frequency regime. We want to utilize numerical simulations in order to optimize such materials in terms of power-loss and permeability. The problem one faces is that the samples have macroscopic sizes, however if one would want to resolve these materials on the micro-scale, it would limit the total simulation size to a few micrometers. Introducing a truncated geometry or cut-off would also not solve this problem as demagnetization effects would come into play for any finite sized sample. However due to the torus-like shape of the sample, the magnetic flux closure reduces the strayfield to zero. To overcome these issues we developed and implemented our own method for calculating the micromagnetic strayfield with periodic boundary conditions(PBCs)[1]. PBCs allow us to simulate an infinite sample and therefore avoid the demagnetization effects. A complete magnetic simulation framework including PBCs will be presented with which the spatially- and time-resolved magnetization response to an external field is simulated. &lt;br&gt; The model will be validated among other things by reproducing experimental setups that have successfully reduced the power-loss of SMCs. Suetsuna et al.[2] have shown that the power-loss reduces by roughly half when the sample is exposed to a magnetic field during annealing, because an aligned anisotropy direction is induced. This was replicated in the simulation and as can be seen in figure 1 the simulated power-loss P&lt;sub&gt;m&lt;/sub&gt; decreases by half when an aligned anisotropy is applied, without altering the relative permeability mu&lt;sub&gt;r&lt;/sub&gt;.&lt;br&gt;

**References** &lt;br&gt;
[1] Bruckner, Florian, et al. &quot;Strayfield calculation for micromagnetic simulations using true periodic boundary conditions.&quot; Scientific Reports 11.1 (2021): 1-8.
[2] Suetsuna, Tomohiro, et al. &quot;Soft magnetic composite containing magnetic flakes with in-plane uniaxial magnetic anisotropy.&quot; Journal of Magnetism and Magnetic Materials 473 (2019):
416-421.&lt;br&gt;

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1c066203e20a987f28c178a793a3e69b.png)&lt;br&gt;

Fig. 1 Powerloss P&lt;sub&gt;m&lt;/sub&gt; and permeability mu&lt;sub&gt;r&lt;/sub&gt; were calculated from hysteresis simulations utilizing the SMC model with aligned and random anisotropy.

MMM 2022

Simulation of Soft Magnetic Composites with Periodic Strayfield Calculation

Soft magnetic composites(SMCs) consist of ferromagnetic particles, in the micrometer-range which are embedded in an electrically insulating material, in order to reduce the eddy-currents in the high-frequency regime. We want to utilize numerical simulations in order to optimize such materials in terms of power-loss and permeability. The problem one faces is that the samples have macroscopic sizes, however if one would want to resolve these materials on the micro-scale, it would limit the total simulation size to a few micrometers. Introducing a truncated geometry or cut-off would also not solve this problem as demagnetization effects would come into play for any finite sized sample. However due to the torus-like shape of the sample, the magnetic flux closure reduces the strayfield to zero. To overcome these issues we developed and implemented our own method for calculating the micromagnetic strayfield with periodic boundary conditions(PBCs)[1]. PBCs allow us to simulate an infinite sample and therefore avoid the demagnetization effects. A complete magnetic simulation framework including PBCs will be presented with which the spatially- and time-resolved magnetization response to an external field is simulated. The model will be validated among other things by reproducing experimental setups that have successfully reduced the power-loss of SMCs. Suetsuna et al.[2] have shown that the power-loss reduces by roughly half when the sample is exposed to a magnetic field during annealing, because an aligned anisotropy direction is induced. This was replicated in the simulation and as can be seen in figure 1 the simulated power-loss Pm decreases by half when an aligned anisotropy is applied, without altering the relative permeability mur. 

**References** 
[1] Bruckner, Florian, et al. "Strayfield calculation for micromagnetic simulations using true periodic boundary conditions." Scientific Reports 11.1 (2021): 1-8.
[2] Suetsuna, Tomohiro, et al. "Soft magnetic composite containing magnetic flakes with in-plane uniaxial magnetic anisotropy." Journal of Magnetism and Magnetic Materials 473 (2019):
416-421. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1c066203e20a987f28c178a793a3e69b.png) 

Fig. 1 Powerloss Pm and permeability mur were calculated from hysteresis simulations utilizing the SMC model with aligned and random anisotropy.

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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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.

The Co-based tetragonal compounds ACo2As2 (A = Ca, Sr, Ba & K) crystallize in ThCr2Si2-type structure and exhibit properties that delicately depend upon the interlayer As-As distance dAs-As which regulates the oxidation state of Co-ions by controlling the extent of the interlayer As-As bonds. As a result, it indirectly controls the magnetic ground state of these materials. BaCo2As2, which has a large value of dAs-As = 3.78 Ã…, shows a nonmagnetic ground state [1]. On the other hand, CaCo2As2 with dAs-As = 2.73 Ã… exhibits an A-type collinear antiferromagnetic (AFM) ordering below its NÃ¨el temperature [2]. SrCo2As2 with dAs-As = 3.33 Ã…, intermediate to those of its Ca and Ba analogs, shows no evidence of long-range magnetic ordering but develops stripe-type AFM as well as ferromagnetic spin fluctuations [3,4]. Another recently explored compound KCo2As2, where the dAs-As = 4.08 Ã… is largest among this series, exhibits a suppressed non-magnetic ground state [5]. These observations collectively suggest that increasing the interlayer Co-ion distance reduces the magnetic character within the ACo2As2 system. In this work, we explore the combined effect of the change of electron count as well as the increase in dAs-As introduced through the partial substitution of Sr-ions with K-ions in the Sr1-xKxCo2As2 system. We report on the magnetic characteristics and electron transport properties of this hole-doped system and explore the interdependency of structural parameters, charge density and many-body interactions within the material.

Optimization of electronic correlations and magnetism in SrCo2As2 via hole doping

The bonding strength between adsorbates and substrate is related to the degree of anti-bonding sates filling during the adsorbates-substrate interaction, which is an important descriptor of electrochemical performance.[1,2] Based on first-principles calculations, the Gibbs free energy (ΔGH) of transition metal doped WSe2 (TM-WSe2, TM=Ti, Mn, Fe, Co, Ni and Cu) are decreased, especially for the Ni-WSe2 and Cu-WSe2 which are -0.20 and 0.06 eV, respectively. By analyzing the partial density of states (PDOS) and integrated-crystal orbital Hamilton population (ICOHP), the decreased ICOHPspin up values of TM-WSe2 improve the interaction of Se-H, thereby the H atom is easier to be adsorbed on the Se active site. While ICOHPspin down values of TM-WSe2 are increased, this indicates the weak interaction of Se-H, which promotes desorption of H2 molecule (i.e. Tafel/Heyrovsky reaction step). Therefore, the synergistic effect of spin up and spin down anti-bonding states filling makes TM-WSe2 possess an enhanced HER performance.
This work was supported by the National Natural Science Foundation of China (22161142002). 

**References** [1] M. D. Hossain, Z. Liu, M. Zhuang, et al. Adv. Energy Mater. 9, 1803689 (2019).
[2] X. Ai, X. Zou, H. Chen, et al. Angew. Chem. Int. Edit. 59, 3961-3965 (2020). 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ca6db3176d27aa10f7c9cdaaa4ad3d03.png)

Role of Spin resolved Anti

Electrical manipulation of spin textures inside antiferromagnets represents a new opportunity for developing spintronics with superior speed and high device density. Injecting spin currents into antiferromagnets and realizing efficient spin-orbit-torque-induced switching is however still challenging. Because of the diminishing magnetic susceptibility, the nature and the magnitude of current-induced magnetic dynamics remain poorly characterized in antiferromagnets, whereas spurious effects further complicate experimental interpretations (1-4). In this work (5), by growing a thin film antiferromagnetic insulator, α-Fe2O3, along its non-basal plane orientation, we realize a configuration where an injected spin current can robustly rotate the Néel vector within the tilted easy plane, with an efficiency comparable to that of classical ferromagnets. The spin-orbit torque effect stands out among other competing mechanisms and leads to clear switching dynamics. Thanks to this new mechanism, in contrast to the usually employed orthogonal switching geometry, we achieve bipolar antiferromagnetic switching by applying positive and negative currents along the same channel, a geometry that is more practical for device applications. By enabling efficient spin-orbit torque control on the antiferromagnetic ordering, the tilted easy plane geometry introduces a new platform for quantitatively understanding switching and oscillation dynamics in antiferromagnets. 

**References:** 
(1) P. Zhang, J. Finley, T. Safi, et al., Phys. Rev. Lett. Vol. 123, p. 247206 (2019). 
(2) Y. Cheng, S. Yu, M. Zhu, et al., Phys. Rev. Lett. Vol. 124, p. 027202 (2020). 
(3) C. C. Chiang, S. Y. Huang, D. Qu, et al., Phys. Rev. Lett. Vol. 123, p. 227203 (2019). 
(4) H. Meer, F. Schreiber, C. Schmitt, et al., Nano Lett. Vol. 21, p. 114 (2021). 
(5) P. Zhang, C.-T. Chou, H. Yun, et al., arXiv:2201.04732 (2022), accepted by Phys. Rev. Lett.. 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/a90d62d1e45b790c41f59d4e912618cc.png)

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/ada364ba0fb517bf5dc098221db9333b.png)

Control of Néel Vector with Spin Orbit Torques in an Antiferromagnetic Insulator with Tilted Easy Plane

We study the spin Hall effect (SHE) and the orbital Hall effect (OHE) in magnetic materials using automatic high-throughput calculation scheme. The SHE is a phenomenon in which an applied electric field induces a spin current. This effect plays a key role in various spintronics devices. Although the SHE has been researched mainly in nonmagnetic materials, SHE in magnetic materials has gained a considerable attention recently as they can exhibit a large SHE[1]. The OHE, a phenomenon in which electric field generates a flow of orbital angular momentum, has also been attracting attention as a new driving mechanism of devices [2]. For future application, exploring materials with large SHE or OHE is demanded.

In this study, we perform a systematic evaluation of the spin Hall conductivity (SHC) and the orbital Hall conductivity (OHC) of select materials from MAGNDATA[3], a database of magnetic materials. We target collinear materials both ferromagnets and antiferromagnets, and evaluate their intrinsic contributions of SHC and OHC based on Kubo-formula.

Figure 1 shows the results of SHC and OHC of 84 materials. The OHCs in most materials are nearly ten times larger than the SHCs. Interestingly, the Mn3Pt has a colossal OHC reaching about 14000 (hbar/e)S/cm, which is higher than either OHC of Mn (~10000) and Pt (~2000) [4], suggesting the importance of the material structure. Further analysis of both theoretical aspect and data science will be presented at the conference. 
**References** [1] C. Qin, et al., Phys. Rev. B 96, 134418 (2017); Y. Zhang et al., New J. Phys. 20, 7 (2018).
[2] H. Kontani, et al., J. Phys. Soc. Jpn., 76, 103702 (2007).
[3] S.V. Gallego et al., J. Appl. Crystallogr. 49, 1750 (2016).
[4] D. Jo, D. Go, and H-W. Lee, Phys. Rev. B 98, 214405 (2018).
 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/cbe43c182795ae5e425fe406cfe50027.png)

High throughput study of spin and orbital transport in magnetic materials

Within this talk we show the importance of accurate implementations of the RKKY interactions for antiferromagnetically coupled ferromagnetic layers with thicknesses exceeding the exchange length. In order to evaluate the performance of different implementations of RKKY interaction, we develop a benchmark problem by deriving the analytical formula for the saturation field of two infinitely thick magnetic layers that are antiparallelly coupled (Fig. 1). Without external field, the magnetization in the layers is parallel to the easy axis (y-direction) in the +y and -y direction. When a field in the x-direction is applied, a partial domain wall is formed (Fig. 1). We find that there exists a critical field that fully saturates the structure in the x-direction which is given by, Hx,crit = 2 K1/Js [1+Jrkky2/(AK1)], where Jrkky is the RKKY coupling strength, K1 the anisotropy constant and A exchange constant [1]. This benchmark problem shows that state-of-the-art implementations in commonly used finite-difference codes lead to errors of the saturation field that amount to more than 20% for mesh sizes of 2 nm which is well below the exchange length of the material. In order to improve the accuracy, we develop higher order cell based (see Fig. 2 - paper, cell O1 and O2) and nodal based finite-difference codes (see Fig. 2 - paper, node) that significantly reduce the error compared to state-of-the-art implementations (see Fig. 2 - mumax) [2]. For the second order cell based and first order nodal based finite element approach, the error of the saturation field is reduced by about a factor of 10 (2% error) for the same mesh size of 2 nm. 

**References** 
[1] D. Suess, S. Koraltan, F. Slanovc, F. Bruckner, C. Abert, "Accurate finite-difference micromagnetics of magnets including RKKY interaction -- analytical solution and
comparison to standard micromagnetic codes", https://arxiv.org/abs/2206.11063 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/5b0630c6640f4a9ee05ac6fd7125be33.png) 

Fig. 1: Analytic benchmark problem of two infinitely extended layers, that are antiferromagentically coupled via Jrkky.

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/5afd4b7f7745e1b47296276e4f0a8a2e.png) 

Fig. 2: Convergence towards the analytic solution of Hx =5 x 2 K1/Js for different micromagnetic codes as function of discretization length dz. It is shown that standard finite difference
codes (e.g. mumax) that uses zero order methods for the RKKY interaction show significant errors. The developed method (paper,cell O2) shows significantly better convergence.

Accurate finite difference micromagnetics of magnets including RKKY interaction

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

Development of Dy µ disks for coherent imaging of helimagnetic domains

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

Imaging thermally induced Ising

LaFe13-x-yMxSiyN3 compounds (M = Mn) were synthesized by flowing ammonia over intermetallic precursors at 623 K for 4 hours. The nitrides were characterized by room temperature powder X-ray diffraction, magnetic thermogravimetry (mTGA), differential scanning calorimetry (DSC), and magnetization measurements. The nitrides derived from Si-poor (y â‰¤ 3) cubic intermetallics retain the NaZn13-type crystal structure and the lattice parameters, a, of the synthesized trinitrides increase by ~3 % compared to the precursors. The nitrogenation increases ferromagnetic ordering temperature by approximately 200 K when compared with the corresponding nitrogen-free NaZn13-type phases, but unlike those of the latter, TCs of the nitrides are independent of the Fe/Si ratio. Partial substitution of Fe with Mn lowers TC of the trinitride similarly to the non-nitrogenated precursors. The magnetic ordering transitions in the nitrides are broad, resulting in rather weak magnetocaloric effects peaking at -2.0 J/Kg K for a 0 to 5 T magnetic field change. The nitrides are stable below 750 K, but they begin to lose nitrogen above this temperature, fully decomposing above 1050 K. Ames Laboratory is operated for the U.S. Department of Energy (DOE) by Iowa State University under Contract No. DE-AC02-07CH11358. This work was supported by the Division of Materials Science and Engineering of the Office of Basic Energy Sciences of the U.S. DOE.

Synthesis and magnetic properties of LaFe13 x

There has been a need for rapid screening of people infected virus including with COVID-19 or influenza. Virus detection methods using magnetic harmonics of magnetic nanoparticles (MNPs) with superparamagnetism has been reported [1, 2]. In this study, we report the detection of influenza virus based on magnetic second harmonic signals [3], and the detection sensitivity was 100 pg/mL. Figure 1 shows the developed system for virus detection. The excitation coil generated AC magnetic fields of amplitude of 6.6 mT with 1 kHz and the detection coil detect the second harmonic signals of MNPs under DC magnetic field of 6.6 mT. The measurement of the magnetization response of MNPs completed in one minute. The samples contained MNPs (Nanomag-D, average diameter 20 nm, 5 mg/mL, 9.24Ã—1012 particles) coated with protein-A, with which antibodies (Nucleoprotein InA245). Antigens (Influenza A virus) bound to the antibodies by antigen-antibody reaction. Figure 2 shows the relation between the second harmonic signal normalized by the fundamental signal R2/R0 and the third harmonic signal normalized by the fundamental signal R3/R0 with five different antigen concentrations (0, 103, 105, 107, 109 antigens). R2/R0 was about 2.3 times larger than R3/R0. This result indicates that the detection of viruses using the second harmonic signal has a larger detectable range of the number of antigens. In addition, the value of R2/R0 significantly reduce at 104 antigens (Fig. 2(a)). This result indicate that we can detect 104 antigens (100 pg/mL). In the future, we aim to achieve detection sensitivity of the PCR method (1 pg/mL) by investigating the optimal detection coil shape, excitation frequency, and concentration of MNPs for virus detection.

Rapid Virus Detection using Magnetic Second Harmonics of Superparamagnetic Iron Oxide Nanoparticles

The proximity-coupling of a chiral non-collinear antiferromagnet (AFM) (1,2) with a singlet superconductor allows spin-unpolarized singlet Cooper pairs to be converted
into spin-polarized triplet pairs (3,4) thereby enabling non-dissipative, long-range spin
correlations (3,4). The mechanism of this conversion derives from fictitious magnetic
fields that are created by a non-zero Berry phase (5) in AFMs with non-collinear
atomic-scale spin arrangements (1,2). In this invited talk, I will describe our recent achievement of long-ranged lateral Josephson supercurrents through an epitaxial thin
film of the triangular chiral AFM Mn3Ge (6). The Josephson supercurrents in this
chiral AFM decay by approximately 1–2 orders of magnitude slower than would be
expected for singlet pair correlations (3,4) and their response to an external magnetic field reflects a clear spatial quantum interference. Given the long-range supercurrents
present in both single- and mixed-phase Mn3Ge, but absent in a collinear AFM IrMn, our results pave away for the topological generation of spin-polarized triplet pairs (3,4) via Berry phase engineering (5) of the chiral AFMs.

If time permits, I will also present our experimental realization of spin-triplet supercurrent spin-valves (SVs) (7,8) in chiral antiferromagnetic Josephson junctions (JJs) and a direct current superconducting quantum interference device (dc SQUID), the latter of which reveals an intriguing 0-to-π phase transition (8) on top of the SV response to out-of-Kagome plane magnetic fields. 

**References:** 
(1) Nakatsuji, S. et al. Nature 527, 212 (2015), 
(2) Nayak, A. K. et al. Sci. Adv. 2, e1501870 (2016), 
(3) Linder, J. & Robinson, J. W. A. Nat. Phys. 11, 307 (2015), 
(4) Eschrig, M. Rep. Prog. Phys. 78, 104501 (2015), 
(5) Xiao, D., Chang, M.-C. & Niu, Q. Rev. Mod. Phys. 82, 1959 (2010), 
(6) Jeon, K.-R. et al, Nat. Mater. 20, 1358 (2021), 
(7) Banerjee, N. et al. Nat. Comm. 5, 4771 (2014), 
(8) Glick, J. A. et al. Sci. Adv. 4, eaat9457 (2018).

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Simulation of Soft Magnetic Composites with Periodic Strayfield Calculation

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