United States

In-depth investigation of structural and magnetic property correlation in technologically important heavy metal/ferromagnet/oxide heterostructures are crucial for the development of spintronics based devices [1]. In recent times, in Ta/CoFeB/TaO&lt;sub&gt;x&lt;/sub&gt; heterostructures, zero-field magnetization switching, reasonably large Dzyaloshinskii-Moriya interaction, and stabilization of skyrmions have been reported [2-4]. Here, we study the change in magnetic and structural properties of sputter deposited (1 nm) Ta/(1.5 nm) CoFeB/(0.5 nm) TaO&lt;sub&gt;x&lt;/sub&gt; heterostructures induced by post-deposition annealing at 300 °C. Both as-deposited and annealed film stacks possess in-plane magnetic anisotropy and we observe nearly two times increase in the saturation magnetization (M&lt;sub&gt;s&lt;/sub&gt;) of annealed film stack (~ 800 emu/cc) in comparison to the as-deposited one (~ 400 emu/cc). The surface topography study suggests reduced surface roughness for the annealed film stack as compared to the as-deposited stack. Using, x-ray photoelectron spectroscopy we analyze the B 1s, Ta 4f and Fe 2p spectra for both as-deposited and annealed heterostructures. Interestingly, the analysis of Ta spectra revealed that B has intermixed with Ta layers in the annealed stack, thus forming new chemical states such as TaB and TaOB (cf. Fig.1). Boron 1s peak analysis suggests that the annealing causes B diffusion out of the CoFeB layer and subsequent exposure to the atmosphere results in the formation of BO&lt;sub&gt;x&lt;/sub&gt;. Analysis of Fe 2p spectra in the annealed stack shows an additional signature of metallic Fe&lt;sup&gt;0&lt;/sup&gt; 2p&lt;sub&gt;1/2 &lt;/sub&gt;peak, which likely plays a critical role in enhancing the M&lt;sub&gt;s&lt;/sub&gt; (cf. Fig.2). These XPS results are crucial in thorough understanding of the mechanism that governs M&lt;sub&gt;s&lt;/sub&gt; and ultimately, spin-orbit coupling induced effects in ferromagnetic thin film heterostructures.

![](https://assets.underline.io/uploads/markdown_image/1/image/a5c66219d056c0e02fc86687536ed4ca.jpg)

Fig. 1. XPS spectra of Ta 4f core levels of as-deposited and annealed films. The binding energy shift in the annealed spectra are due to formation of new chemical state such as TaB.


![](https://assets.underline.io/uploads/markdown_image/1/image/92c1c60f482d4ee564ad597e655c00b7.jpg)

Fig. 2. XPS spectra of Fe 2p core levels of as-deposited and annealed films. An additional peak Fe0 2p1/2 is observed in the annealed film stack.

2022 Joint MMM-INTERMAG

Study of As-deposited and Annealed Ta/CoFeB/TaOx Heterostructures Using X-Ray Photoelectron Spectroscopy

The 15th Joint MMM-INTERMAG Conference (2022 Joint) 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 plenary session, and an evening session, with about 1500 presentations overall. 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 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

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

Please register for the Joint MMM-Intermag 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.

In-depth investigation of structural and magnetic property correlation in technologically important heavy metal/ferromagnet/oxide heterostructures are crucial for the development of spintronics based devices [1]. In recent times, in Ta/CoFeB/TaOx heterostructures, zero-field magnetization switching, reasonably large Dzyaloshinskii-Moriya interaction, and stabilization of skyrmions have been reported [2-4]. Here, we study the change in magnetic and structural properties of sputter deposited (1 nm) Ta/(1.5 nm) CoFeB/(0.5 nm) TaOx heterostructures induced by post-deposition annealing at 300 °C. Both as-deposited and annealed film stacks possess in-plane magnetic anisotropy and we observe nearly two times increase in the saturation magnetization (Ms) of annealed film stack (~ 800 emu/cc) in comparison to the as-deposited one (~ 400 emu/cc). The surface topography study suggests reduced surface roughness for the annealed film stack as compared to the as-deposited stack. Using, x-ray photoelectron spectroscopy we analyze the B 1s, Ta 4f and Fe 2p spectra for both as-deposited and annealed heterostructures. Interestingly, the analysis of Ta spectra revealed that B has intermixed with Ta layers in the annealed stack, thus forming new chemical states such as TaB and TaOB (cf. Fig.1). Boron 1s peak analysis suggests that the annealing causes B diffusion out of the CoFeB layer and subsequent exposure to the atmosphere results in the formation of BOx. Analysis of Fe 2p spectra in the annealed stack shows an additional signature of metallic Fe0 2p1/2 peak, which likely plays a critical role in enhancing the Ms (cf. Fig.2). These XPS results are crucial in thorough understanding of the mechanism that governs Ms and ultimately, spin-orbit coupling induced effects in ferromagnetic thin film heterostructures.

![](https://assets.underline.io/uploads/markdown_image/1/image/a5c66219d056c0e02fc86687536ed4ca.jpg)

Fig. 1. XPS spectra of Ta 4f core levels of as-deposited and annealed films. The binding energy shift in the annealed spectra are due to formation of new chemical state such as TaB.


![](https://assets.underline.io/uploads/markdown_image/1/image/92c1c60f482d4ee564ad597e655c00b7.jpg)

Fig. 2. XPS spectra of Fe 2p core levels of as-deposited and annealed films. An additional peak Fe0 2p1/2 is observed in the annealed film stack.

technical paper

The interface driven exchange bias effect (EB) is a well-studied phenomenon observed in ferromagnetic (FM)/antiferromagnetic (AFM) thin film systems resulting from the interfacial exchange coupling between the F and AF spins [1]. In numerous studies, asymmetrically shaped hysteresis loops have been reported mainly described by coherent rotation of the magnetic domains on the one hysteresis branch and rapid nucleation and domain wall propagation on the other one [2, 3]. Romanens et al. were able to correlate these asymmetries in perpendicular magnetized thin film systems to higher domain nucleation densities when the applied field is aligned antiparallel to the EB field compared to the parallel orientation [4]. Here the statistics of magnetic domain nucleation during the magnetization reversal process in exchange-biased magnetic nano-stripes is investigated by high-resolution optical Kerr microscopy. In such structures the magnetization dynamics are governed by the exchange bias field, the shape anisotropy and stray field interactions between the stripes. The dependency of the nucleation on these parameters is investigated systematically by variation of the lateral dimensions of the stripes and the orientation of the exchange bias fields relative to the stripe axis. Understanding the nucleation behavior of magnetic domains in nanostructures is an important step in the development of spintronic devices.

![](https://assets.underline.io/uploads/markdown_image/1/image/edc0ef18b758f66d641af727d520c25e.jpg)

Investigation of magnetic domain nucleation in exchange-biased nanostructures

Investigation of magnetic domain nucleation in exchange-biased nanostructures

Micrometer diameter bilayers of 20 nm Permalloy/20 nm Cobalt Oxide deposited on nanomechanical resonators were used to investigate exchange bias effects. The mechanical compliances of two resonator axes were enhanced by severing one torsion arm, Figure 1, resulting in a unique three-axis resonator that responds resonantly to torques generated by a three-axis RF field [1]. Our technique permits simultaneous measurement of three orthogonal torque components. Measurements of the anisotropies associated with exchange bias effects have been made. First, at cryogenic temperatures, observations of shifted linear hysteresis loops confirm the presence of a positive exchange bias at the Py/CoO interface. A rotating DC bias field was used to probe in-plane anisotropies through the out-of-plane torque, as shown in Figure 2 (open circles). Training effects in both the linear and rotating hysteresis data were observed and show that most of the training occurs during the first half of the first loop, consistent with an athermal training mechanism [2]. The data from the rotating hysteresis loops were fit with parameters from a macrospin solution to the Landau-Lifshitz-Gilbert equation. In order to reproduce our observations standard anisotropy terms, a spin-flop coupling term [3], and a rotatable anisotropy axis [3,4] are introduced to the model. Each parameter of the exchange bias model accounts for specific features of the rotational loop. A unidirectional anisotropy asymmeterizes the extrema magnitudes. The orientation of the rotatable anisotropy axis with respect to the ferromagnetic magnetization introduces a one-fold rotational symmetry that would otherwise be at least two-fold. The spin-flop term influences the angular positions of the peaks in the torque curve.

![](https://assets.underline.io/uploads/markdown_image/1/image/904fce60d2079057eb98db71f95841b7.jpg)

Figure 1: Electron micrograph of a micromechanical device used for demonstration of the three-axis torque measurement technique. The arrows indicate the three orthogonal torsional displacements.

![](https://assets.underline.io/uploads/markdown_image/1/image/a6f1c83647a790b3299d22bf142cc7ae.jpg)

Figure 2: Thermomechanically calibrated experimental data of the z torque component (resonator at liquid nitrogen temperature). Data were recorded during a rotational hysteresis loop. Fits from macrospin solutions to the LLG equation are shown.



Three-axis torque investigation of exchange bias in a micromagnetic disk

Thin ferromagnetic films with perpendicular anisotropy exhibit nano-sized magnetic domains forming various patterns. When an external magnetic field is applied and cycled, the domains pattern is usually lost. However, if the ferromagnetic layer is coupled with an underlying antiferromagnetic layer, it may show magnetic domain memory (MDM). [1-3] MDM is the ability of the magnetic domains to retain their exact same domain topology upon field cycling. We are studying the effect that illumination by coherent resonant x-rays may have on MDM in a [Co / Pd] / IrMn multilayers. Our x-ray resonant magnetic scattering (XRMS) data suggests that under high dose of x-ray illumination, the material may lose its existing MDM. To investigate this possible effect we have used magneto-transport measurements [4,5] to track the exchange bias while the sample is illuminated by x-rays, using synchrotron radiation (see Fig.1a). Magneto-transport is here used to measure the magnetization loop from which we can extract a bias field. 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 (Fig.1b) as well as XRMS data (Fig.1c) and correlating the observed changes under various dose of x-ray illumination.These measurements include Hall effect signal and as well as magnetoresistance signal, collected both on inner contacts and on outer contacts. For the outer contacts, the spacing between wire bonds is ~1cm, whereas for the inner contacts, the spacing between wire bonds is ~100 . These measurements help us understand the shape of the magneto-transport data collected under x-ray illumination and determine if x-ray illumination has an effect on exchange couplings, and ultimately MDM.

![](https://assets.underline.io/uploads/markdown_image/1/image/766a2108304b1d8f9a1fe3c41b68e2d2.jpg)

a) Instrument used for our x-ray resonant magnetic scattering (XRMS) experiment at the APS, showing the vacuum scattering chamber and the octupolar magnet to apply a field in any direction. b) Magneto-transport measurement taken while [Co/Pd] / IrMn multilayers was illuminated with x-rays. c) XRMS speckle pattern from the [Co/Pd] / IrMn film, measured at the Co L3 edge.

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

Advances in synthesis and characterization of magnetic nanoparticles (NPs) have yielded great gains in the understanding of their complex magnetic behaviour, with implications for numerous applications. Recent work using Ni NPs as a model soft ferromagnetic (FM) system achieved quantitative understanding of the superparamagnetic blocking temperature-particle diameter relationship1. This hinged, however, on the assumption of an FM NP volume lower than the chemical volume due to a non-FM surface dead shell, indirectly deduced from magnetometry. Here, we completely determine both the chemical and magnetic internal structure of such Ni NPs, via unpolarized, half-polarized, and fully-polarized small-angle neutron scattering (SANS) measurements and analyses, coupled with X-ray diffraction and magnetometry. The postulated magnetic dead shell is not only detected but conclusively identified as a Ni phosphide, derived from the trioctylphosphine commonly used in hot-injection syntheses. The shell thickness (t*) can be controlled by synthesis temperature (Ts), falling to as little as 0.5 nm at 170 °C (Fig. 1). Polarized SANS further reveals bulk-like ferromagnetism in the Ni core, the magnetic scattering length density (SLD) being in ideal agreement with magnetometry (Fig. 2), quantitatively supporting prior modeling of superparamagnetism. These findings advance the understanding of synthesis-structure-property relationships in metallic magnetic NPs, point to a route to ligand-free stabilization, and highlight the power of polarized SANS measurement and analysis capabilities for magnetic NP science and technology. Work supported by the UMN DOE Center for Quantum Materials.

![](https://assets.underline.io/uploads/markdown_image/1/image/d1fcb57216327d31778b53fae71eebc0.jpg)

Fig. 2. Ni core magnetic SLD vs. T (circles) from half-polarized SANS for the NPs at Ts = 170 °C, superimposed on magnetometry field-cooled (FC) (solid line) and zero field-cooled (ZFC) (dashed line) data measured at 50 Oe.


![](https://assets.underline.io/uploads/markdown_image/1/image/9a9b611d4e7684db8891288e9cd064ae.jpg)

Fig. 2. Ni core magnetic SLD vs. T (circles) from half-polarized SANS for the NPs at Ts = 170 °C, superimposed on magnetometry field-cooled (FC) (solid line) and zero field-cooled (ZFC) (dashed line) data measured at 50 Oe.

Chemically-induced Magnetic Dead Shells in Superparamagnetic Ni Nanoparticles from Polarized Small-Angle Neutron Scattering

Cobalt ferrite nanoparticles (NP) are competitive systems in technological and biomedical applications due to a suitable combination of excellent chemical and magnetic characteristics, such as a high chemical stability, surface active sites, and ease of synthesis and functionalization, together with a high anisotropy constant, a high coercivity, and a moderate saturation magnetization. However, in order to control the functional response of Co-ferrite NP, one of the biggest challenges is to quantitatively disentangle the dependence of the overall magnetic response on the composition, structure, or surface chemistry. In this work, we address the key role of the structural defects on the magnetic properties of Co-ferrite NP investigated by element- and site-specific X-ray magnetic circular dichroism (XMCD) combined with high-resolution transmission electron microscopy of individual NP [1]. We studied a series of samples of monodisperse 8 nm NP, prepared by chemical routes [2,3], with similar stoichiometry and cation distribution but with a tunable number of structural defects. Element- specific XAS and XMCD spectra and hysteresis loops reveal that the collinear alignment of Co2+ (Oh) cations is much more affected by the structural disorder than that of the Fe3+ cations. This is because structural defects give rise to effective local anisotropy axes, causing a prevalent Co2+ spin canting through the spin−orbit coupling due to the relatively large value of the partially unquenched moment of these cations. As the structural disorder is further increased, the rest of the cations in the two sublattices are progressively dragged off the ferromagnetic alignment, being Fe3+(Td) cations the least sensitive to defects due to the smaller number of next-nearest neighbors in the Td-sublattice. Our work highlights the importance of combining advanced synthesis with the use of complementary local probes with element, valence, site, and structural sensitivity to enhance the performance of nanoscale magnetic materials.

![](https://assets.underline.io/uploads/markdown_image/1/image/a5aa5eb0e8a24261183ee2e55ee59892.jpg)

HRTEM images for Co-ferriteNP with increasing crystalline quality. Bottom panel: XMCD hysteresis loops measured at 2 K for Co2+ cations in Oh sites for highly-defective (left) and highly-crystalline (right) NP.

Disentangling Atom- and Site- Selective Spin Canting in Co-ferrite Nanoparticles with Tunable Structural Disorder

Developments in the design and fabrication of the high saturation magnetization nanoparticles in the single-domain size regime are highly desirable due to their extensive applications in biomedicine, magnetic resonance imaging, microelectromechanical systems, radio frequency electronics, and soft robotics. In this work, we present for the first time an in-depth investigation of different-sized iron cobalt (Fe65Co35) nanoparticles covering magnetization configurations from flower to vortex to multi-domain states. A finite element micromagnetic model was used to predict magnetic properties of Fe65Co35 nanoparticles ranging in size from 10 to 100 nm. The simulation results reveal that the flower-to-vortex transition of the Fe65Co35 nanoparticles occurs at around 20 nm, corresponding to the particle size with the highest coercivity. A decrease in remanence is expected for larger particle sizes, where simulations showed the most dramatic drop for particles between 40 and 60 nm. Furthermore, the simulated behaviors were verified experimentally. By systematically varying the reaction parameters, Fe65Co35 nanocubes with tunable edge lengths were synthesized. Scanning electron microscope (SEM) images of as-synthesized samples indicate a narrow size distribution. The measured hysteresis loops confirmed the maximum coercive field for cubes of size 17 nm and the sudden decrease in remanence for samples within the range of 40–60 nm. By combining chemical synthesis and micromagnetic calculations, we have experimentally unveiled the size-dependent spin configurations in Fe65Co35 nanoparticles. These results open the door to a more accurate design and control of spin texture, remanence, and coercivity in high magnetization nanoparticles which are vital building blocks of new biomedical and electronic materials.

![](https://assets.underline.io/uploads/markdown_image/1/image/53e8432506b4365fa494f1cd89ca89bd.jpg)

Fig. 1 SEM images of Fe65Co35 nanocubes with various edge lengths, (a) 17 nm, (b) 34 nm, (c) 40 nm, (d) 62 nm, (e) 77 nm, (f) 92 nm, and (g) 97 nm. The scale bars are 200 nm.

![](https://assets.underline.io/uploads/markdown_image/1/image/fe1f235133cb8a4f69fbfa4a62a75798.jpg)

Fig. 2 (a) The simulated spin configuration for a cube of each respective size. (b) Simulated hysteresis loops of a 5×5×5 sphere array with different sizes. (c) Measured hysteresis loops of as-synthesized Fe65Co35 nanocubes at 300 K.

Exploring the Single Domain Limit of High Magnetization Nanoparticles: A Combined Theoretical and Experimental Study

Anthrax is a fatal disease caused by bacteria called bacillus anthracis. The bacteria can be used as a bioterror agent due to its high toxicity and resistance to the external environment of its spore. Dipicolinic acid (DPA) is released when the spore germinates; therefore, sensitively detecting DPA as a biomarker of the spores is focused on by many researchers [1]. Among them, nano-sensors including trivalent lanthanide ions have been used to detect DPA sensitively and promptly because the trivalent lanthanide ion such as europium (Eu3+) and terbium (Tb3+) shows unique fluorescent properties originated from their energy levels, and the intensity can be enhanced by chelating with DPA called antenna effect [2]. However, nanomaterials such as polymers or inorganic nanoparticles containing fluorescent substances usually quench the fluorescence by absorbing the excitation and emission light concurrently [3]. Therefore it is necessary to separate the fluorescent signal from the nanomaterials to improve its sensitivity. Herein, we develop terbium ion-coordinated iron oxide (Fe3O4-Tb) nanoparticles and detect DPA via measuring fluorescent signals from the Tb-DPA complexes [4]. The Fe3O4-Tb nanoparticles have a magnetite (Fe3O4) core and the surface is enveloped by Tb3+ that is coordinated with polyacrylate. Because of the small crystallite size of the Fe3O4-Tb nanoparticle, it has a trivial coercivity; therefore, Fe3O4-Tb nanoparticles do not agglomerate each other and reacts DPA with high reproducibility [5]. When the Fe3O4-Tb nanoparticles contact with DPA, Tb3+ is disassociated from the nanoparticle surface and chelated with DPA. The formed Tb-DPA complexes have a green fluorescence under certain ultraviolet (UV) wavelengths. We separate the iron oxide core via a permanent magnet to prevent quenching of the nanoparticles, then the clear signal shows a lower detection limit (5.1 nM) than the infectious dosage of anthrax (60 μM) [6]. The detecting method also has a high selectivity when compared with other aromatic carboxylic acids, which have a molecular structure similar to DPA.

![](https://assets.underline.io/uploads/markdown_image/1/image/14a2f16e4463e6542107f235846a8f38.jpg)

Fig.1. Detection mechanism for DPA with Fe3O4-Tb nanoparticles and the fluorescent intensity dependent on the concentration of DPA.

Fluorescent detection of dipicolinic acid as a biomarker for anthrax using Tb ion-coordinated Fe3O4 nanoparticles

Ensemble magnetization of magnetic nanoparticles (NPs) has a sensitive dependence on the structural arrangement of particles. To better understand the correlation between spatial positions of NPs and ensemble magnetization, an experimental system is needed where particle position can be adjusted while simultaneously probing nanoscale magnetization. Here, we describe experiments using polarization analyzed small angle neutron scattering (PASANS) to study the change in magnetic correlations of ~7 nm iron oxide (Fe3O4) NPs embedded in stretched silicone rubber. PASANS is a powerful tool for mapping both the inter- and intra- particle magnetization of NPs on length scales ranging from 0.1 – 100 nm. The magnetic NP polymer gel, or magnetogel, can be stretched on the neutron beamline during an experiment. The macroscopic stretching is accompanied by nanoscale deformations, where polymer chains move to accommodate a new equilibrium configuration. NPs embedded in the gel change their configuration as a function of applied stress, providing a method to adjust the average center-to-center spacing between particles. The scattering data from the unstretched gel in a 1 T applied magnetic field can be modelled by 7.4 nm iron oxide NPs assembled in a hard sphere packing with 30% volume fraction. When the sample is stretched 3x its original size in a direction parallel to the applied field, the morphology changes dramatically. Specifically, the data can be described using a cluster model where NP dimers have emerged (Figures 1a and 1b). Stretching causes the particles to morph from semi-close packed, but individual, 7.4 nm diameter NPs into dimer-like clusters that are 15 nm long, as viewed perpendicular to the applied field (Figures 2a and 2b). These PASANS experiments clearly demonstrate that stretching the magnetogel modulates the structural characteristics of magnetic NPs in a pronounced, controllable manner.

![](https://assets.underline.io/uploads/markdown_image/1/image/39e948b29d4a9faea0cd8a27867ee2bb.jpg)

Fig. 1: Magnetic scattering from (a) unstretched and (b) 3x stretched gel in a 1 T field. The data set in (a) is fit to a hard sphere-like packing and (b) is fit to a model containing dimers

![](https://assets.underline.io/uploads/markdown_image/1/image/5b350fa63e4727cecd3c135d0fb252f5.jpg)

Fig. 2: Schematic showing rearrangement of NPs in (a) unstretched and (b) 3x stretched configurations.

Magnetic Correlations of Iron Oxide Nanoparticles as Probed by PASANS in Stretched Magnetogel Composites

The utilization of magnetic torques at the nano and microscale induced via an externally applied magnetic field is of particular interest for applications such as micromixing [1] and mechanical cancer cell destruction [2]. Over the past several years, synthetic antiferromagnetic (SAF) nanoplatelets with perpendicular magnetic anisotropy (PMA) have been identified as one of the most promising vehicles due to their high tunability, easy-axis/hard-plane PMA efficiently transferring the full magnetic torque to their environment [3]. However, the fabrication of these nanoplatelets, especially in the submicron regime with a high yield is still a challenge and efficient characterization methods of the magnetic properties and mechanical behavior in a fluid environment are still lacking. In this work, we present a novel fabrication method based on substrate conformal imprint lithography (SCIL) [4] and discuss the size effect on the magnetic properties. The basic thin film stack is shown in the insert of Fig. 1. Platelets with 1.89 ± 0.02 µm dimeter (Fig. 1) and 102 ± 1 nm diameter were successfully produced with a yield of ~108 and ~ 1010 particles per 2 inch wafer. MOKE and SQUID were used to measure the hysteresis loop. A dramatically increase of the coercivity (Hc) after patterning is observed (see Fig. 2) rendering the particles ferromagnetic at zero applied field destroying their favorable properties. To define where the increase comes from, a systematic size study is conducted on PMA-SAF nanoplatelets fabricated through electron beam lithography (EBL). We find that Hc and its distribution increase with decreasing size (see Fig. 2). A model based on local anisotropy distribution and thermal activation was established to fit the data [5]. The fit can accurately describe the Hc behavior giving insight on how to engineer the particles. In this talk we will discuss the physics, our current methods to circumvent the Hc issue and give an outlook on single-platelet mechanical behavior characterization methods [6].

![](https://assets.underline.io/uploads/markdown_image/1/image/1f533b6fc3b9014d316dd90edc92ea86.jpg)

![](https://assets.underline.io/uploads/markdown_image/1/image/cd16737989cc4310aba5cad6a49c1556.jpg)

Substrate Conformal Imprint Lithography Defined Synthetic Antiferromagnetic Nanoplatelets for Torque Related Applications

Substrate Conformal Imprint Lithography Defined Synthetic Antiferromagnetic Nanoplatelets for Torque Related Applications

The structural inversion symmetry plays an important role in low-dimensional nanomagnets, due to its strong influence on magnetic and electrical properties. It can lead to the appearance of chiral effects, such as the topological Hall effect [1], or to the formation of chiral noncollinear magnetic textures, as skyrmions [2] and chiral domain walls (DWs) [3]. These chiral structures are envisioned to be the key components for realizing novel concepts for magnonics [4], antiferromagnetic spintronics [5], spin-orbitronics [6], and oxitronics [7]. The main magnetic interaction being responsible for the stabilization of chiral magnetic textures is the intrinsic Dzyaloshinskii-Moriya interaction (DMI) [8,9]. It originate in certain magnetic crystals in which the unit cell lacks inversion symmetry, such as the gyrotropic magnetic crystals, or appear typically in ultrathin films or bilayers due to the inversion symmetry breaking on the film interface [3]. At present, tailoring of DMI is done by optimizing materials, either doping a bulk single crystal or adjusting interface properties of thin films and multilayers. A viable alternative to the conventional material screening approach can be the exploration of the interplay between geometry and topology. This interplay is of fundamental interest throughout many disciplines in condensed matter physics, including thin layers of superconductors [10] and superfluids [11], nematic liquid crystals [12], cell membranes [13], semiconductors [14]. In the emergent field of curvilinear magnetism chiral effects are associated to the geometrically broken inversion symmetries [15]. Those appear in curvilinear architectures of even conventional materials. There are numerous exciting theoretical predictions of exchange- and magnetostatically-driven curvature effects, which do not rely on any specific modification of the intrinsic magnetic properties, but allow to create non-collinear magnetic textures in a controlled manner by tailoring local curvatures and shapes [16,17]. Until now the predicted chiral effects due to curvatures remained a neat theoretical abstraction. Recently, we provided the very first experimental confirmation of the existence of the curvature-induced chiral interaction with exchange origin in a conventional soft ferromagnetic material. It is experimentally explored the theoretical predictions, that the magnetisation reversal of flat parabolic stripes shows a two step process [18,19]. At the first switching event, a domain wall pinned by the curvature induced exchange-driven DMI is expelled leading to a magnetisation state homogeneous along the parabola's long axis. Measuring the depinning field enables to quantify the effective exchange-driven DMI interaction constant. The magnitude of the effect can be tuned by the parabola's curvature. It is found that the strength of the exchange-induced DMI interaction for the experimentally realised geometries is remarkably strong, namely ~0.4 mJ/m2, compared the surface induced DMI. The presented study legitimates the predictive power of full-scale micromagnetic simulations to design the properties of ferromagnets through their geometry, thus stabilising chiral textures. We explore these curvilinear magnetic thin films for the realization of novel artificial magnetoelectric materials based on curvilinear helimagnets embedded in piezoelectric matrix [20], to enable the geometrical tuning of the magnetochirality in curvilinear 1D architectures [21], tailoring of magnetic states in flat nanospirals [22] and as components of shapeable magnetoelectronics for interactive wearables [23].

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