Session PP05: V: General Magnetism II

Towards the geometrical control of the energy landscape of domain walls in Complex 3D nanostructures

Three-dimensional nanomagnetic systems, featuring novel and unconventional spin textures, offer an exciting platform to explore new magnetic phenomena, and also offer possibilities for the development of more efficient, capable and multifunctional technologies [1]. The three-dimensional geometry is predicted to have a significant influence on the dynamics of magnetic domain walls [2], soliton-like textures that form the basis of many spintronics devices proposed in recent years. Specifically, the introduction of curvature and torsion in these three-dimensional structures allows for direct control over properties such as anisotropy and chirality [3,4]. This way, new physics and functionalities can be realised, from three-dimensional chiral spin states [5] to ultrafast domain wall dynamics [6].

In this work, we demonstrate the capacity to engineer the energy landscape of Bloch point domain walls via the introduction of curvature in a 3D nanostructure. By a careful design of the geometry of the nanostructures, grown using focused electron beam induced deposition (FEBID) [7], we are able to stabilize Bloch point domain walls and introduce well defined pinning positions. To map the energy landscape of these domain walls, we employ soft X-ray magnetic microscopy and analyze XMCD-images after applying magnetic fields. This enables us to showcase our capability to control the strength of pinning by adjusting the curvature of the nanostructure. This insight into the control of the magnetic behaviour via complex geometries will help pave the way to the next generation of 3D spintronic devices.   

Magneto-crystaline composite topological defects and half-Hopfions

We consider a new class of topological defects in B20 magnetic materials such as FeGe and MnSi. These are combined topological defects in the form of twin boundaries in crystaline order and skyrmions in magnetic order, that allow stable configurations that can be viewed as stable Half-Hopfions   

High pressure magnetic diffraction studies on CePtSi2

CePtSi₂ shows pressure induced superconductivity with a maximum transition temperature of 0.14 K between 1.4 and 2.1 GPa. Here we present high pressure magnetic neutron diffraction studies on CePtSi₂ using polycrystalline and single-crystal samples. We determined magnetic structure at ambient pressure to be a spin-density-wave structure with magnetic propagation vector of (0.32,0,0.11) and averaged ordered moment of 0.45(5)µ_B. Using high pressure neutron diffraction, we investigated pressure dependence of the magnetic propagation vector and the moment. Our results provide insight on the primary role in the superconducting pairing mechanism of CePtSi_2.   

Behavior of the Magnetic Vortex and Antivortex under Parity and Topological Charge Conjugation Symmetries

Basing on the novel definition of topological charge conjugation operation, it is proved that a discrete spatial symmetry, the parity transformation  acting on the n=2 magnetic vortex (magnetic antivortex) with n the "spin" dimension, is equivalent to a topological charge conjugation operation which switches the magnetic vortex (magnetic antivortex) into the corresponding magnetic antivortex (magnetic vortex) marking the complete equivalence between physics and topology. It is also shown that the out-of-plane magnetization vector forming in a n=3 magnetic vortex in the "curling" configuration is decoupled from the linked Amperian current density vector under the parity transformation but the spatial symmetry is conserved. These results indicate that topological magnetic solitons and anti-solitons in the form of magnetic vortexes and antivortexes, respectively behave differently from other images of classical vortexes in nature.   

Magnetic Properties of Tb0.3Dy0.7Fe2

Nanometric thin films of Tb_0.3Dy_0.7Fe₂ (TFD) were synthesized using RF magnetron sputtering using a single target. Films were synthesized at five different thicknesses from 50 to 250 nm and on several substrates, including carbon fiber reinforced polymer (CFRP), SiO₂, Al₂O₃, and mica. The magnetic properties were studied using a vibration sample magnetron (VSM) at several angles, magnetic field, and field plane orientations. TFD particles, known as magnetostrictive, were integrated into CFRP and have been shown to enhance magnetic response, which is desirable for designing an ultra-sensitive sensor for prognostics and diagnostics of early onset structural damage monitoring. [1] The nanometric films will effectively be integrated as an ultra-sensitive sensor in composites.   

Data Imaging and XRD analyses for characterization of magnetic nanoparticles and nanostructures

Ferromagnetic Fe, Co, and Ni core-shell nanoparticles embedded in varies carbon-based matrixes have attracted huge interest as a rapidly growing class of materials for many applications. Different experimental, theoretical techniques and algorithms have been developed to characterize the size, crystal structure, elemental composition, and a variety of chemical and physical properties of synthesized magnetic nanoparticles. We unveil groundbreaking advancements towards an innovative algorithm designed to process SEM, HR-STEM images and seamlessly map these with PXRD elemental analysis. This intricate process of pattern recognition harnesses the power of traditional filtration techniques, from Fourier transforms to mathematical tools and the cutting-edge reconnection algorithm. Our primary objective is to categorize the morphology nanostructures based on size parameters - length for nanotubes or nanosheets and radius of nanoparticles. We describe the main characteristics of the techniques by providing various examples of their use for analysis delves deep into characterization the degree of porosity, layer sizes, and their subsequent influence on magnetic properties and insights into the role of graphitization and amorphism. A diverse range of layered nanostructures, nanoparticles, including metal and metal-free phthalocyanine and porphyrin, to name a few, synthesized by pyrolysis and annealing and tested under the PPMS to ascertain their magnetic attributes to bridge the correlation between observed magnetic properties of core-shell and layered structures of synthesized nanostructures.   

Detection of Hysteretic Magnetism of Manganese Phthalocyanine in a Vertical Tunnel Heterojunction

We have studied the magnetism of manganese phthalocyanine (MnPc) in EGaIn/MnPc/Pt heterojunctions where sublimated crystalline MnPc films as thin as 1 nm are sandwiched between non-magnetic bottom-layer Pt and top-layer soft-landing eutectic GaIn (EGaIn) electrodes. Using tunneling magnetoresistance measurements under external magnetic field sweeps, we observed resistance peaks at the temperature-dependent coercive fields of MnPc. The hysteretic behavior indicates a ferromagnetic coupling between MnPc molecules with a magnetic easy axis perpendicular to the substrate surface. As the temperature is decreased to 2K, well below Tc, the superconductivity transition temperature of the EGaIn electrode, the magnetoresistance shows pronounced features that are consistent with the appearance of laminar and tubular topology associated with the intermediate state of the superconducting EGaIn [1]. A similar behavior was observed in TbPc₂ molecules deposited on superconducting Pb(111) surfaces [2]. Our work illustrates the interaction of crystalline magnetic molecules (MnPc) with the superconducting phases of adjacent electrodes and promises spintronic or spin qubit device applications.

[1] Prozorov, R. Equilibrium topology of the intermediate state in type-I superconductors of different shapes. Phys. Rev. Lett. 98, 257001 (2007).

[2] Serrano, G., Poggini, L., Cucinotta, G. et al. Magnetic molecules as local sensors of topological hysteresis of superconductors. Nat. Commun. 13, 3838 (2022).   

Elliptical skyrmion-antiskyrmion interaction in a magnetic film

Two different experimental papers [1] and [2] have demonstrated that elliptical skyrmions can exist in a magnetic material which typically host antiskyrmions. These are Bloch-type skyrmions which elongate in two distinct directions for clockwise and counterclockwise chiralities. It has been theoretically demonstrated [3] that isolated elliptical skyrmions can be nucleated in thes same material with a magnetic force microscope tip. In addition, elliptical skyrmions and antiskyrmions can exist simulataneously in the same material [1]. Therefore, it is important to study their interaction. We determine the spin vector field of the elliptical skyrmion-antiskyrmion state by using the Belavin-Polyakov (BP) formalism for the two-dimensional, three-component model with the nearest-neighbor Heisenberg exchange interaction. Theoretical calculations indicate that the interaction is dictated by the chirality of the elliptical skyrmion due to the rotation of the spins. Then, we use this spin field as the initial state in a numerical model with the real material parameters from [1] to compare the interaction to theoretical predictions. 

[1] Jena J., Göbel B., Ma T., Kumar V., Saha R., Mertig I., Felser C., Parkin S.S.P., Elliptical Bloch skyrmion chiral twins in an antiskyrmion system, Nat. Comms., 11 (2020), p. 1115.

[2] Peng L., Takagi R., Koshibae W., Shibata K., Nakajima K., Arima T., Nagaosa N., Seki S., Yu X., Tokura Y., Controlled transformation of skyrmions and antiskyrmions in a non-centrosymmetric magnet, Nature Nanotechnol., 15 (2020), pp. 181-186.

[3] D. Capic, Elliptical skyrmions: Theory and nucleation by a magnetic tip in an antiskyrmion-hosting material, Journal of Magnetism and Magnetic Materials,  563, (2022),169866.