Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Q54: Skyrmion Lattice and Magnetization TexturesFocus Recordings Available

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Sponsoring Units: GMAG Chair: John Singleton, NHMFL/ LANL; Marcelo Jaime, Los Alamos Natl Lab Room: McCormick Place W476 
Wednesday, March 16, 2022 3:00PM  3:12PM 
Q54.00001: Skyrmion tilting by a transport current selffield Morten R Eskildsen, Allan Leishman, Nathan S Chalus, Grace M Longbons, Eric D Bauer, Marc Janoschek, Ulrich Welp, WaiKwong Kwok, Robert Cubitt, Jonathan S White Skyrmions are known to be weakly coupled to the crystalline directions in the host material and in particular they will closely follow the direction of the applied magnetic field. Here we report on smallangle neutron scattering (SANS) studies of the skyrmion lattice (SkL) in circular MnSi crystal in the presence of a radial electric current. Here, the magnetic selffield generated by the current is perpendicular to both the current direction and the applied magnetic field. Despite being orders of magnitude smaller than the applied field, the selffield causes a tilting of the SkL which can be observed by SANS. In my talk I will discuss these effects and provide a quantitative comparison between the selffield and SkL tilting angle. 
Wednesday, March 16, 2022 3:12PM  3:24PM 
Q54.00002: Skyrmion Lattice Manipulation with Electric and Thermal Currents Nathan S Chalus, Allan Leishman, Grace M Longbons, Eric D Bauer, Marc Janoschek, Ulrich Welp, WaiKwong Kwok, Robert Cubitt, Jonathan S White, Morten R Eskildsen Understanding how to manipulate a Skyrmion lattice (SkL) is necessary to create new technologies that make use of them. Here we report on smallangle neutron scattering (SANS) studies of the SkL in MnSi under the influence of radial electric and thermal currents. Using a semicircular sample, the currents have a 1/r dependence. Applying an electric current through the sample causes the SkL to rotate. Interestingly, the rotation angle shows a nonmonotonic current dependence and eventually changes sign at high currents. This is likely due to competing effects from electrical and thermal currents, which go as I and I^{2} respectively. In my talk, I will discuss the interplay between these two competing effects. 
Wednesday, March 16, 2022 3:24PM  3:36PM 
Q54.00003: skyrmionic material mediated by RKKY interactions sarah a schwarz We grew a skyrmionic material mediated by RKKY interactions with a low temperature phase transition. We will discuss the growth process as well as characterization in the RUS with specialized transport devices. We will also discuss how the skyrmion density and structure impacts the characteristics of the material. 
Wednesday, March 16, 2022 3:36PM  4:12PM 
Q54.00004: Interplay between magnetic frustration, magnetocrystalline anisotropy and DzyaloshinskiiMoriya interaction in chiral CoZnMn alloys Invited Speaker: Victor Ukleev The competition between the magnetic interactions in noncentrosymmetric compounds results in complex phase diagrams. The interplay between symmetric exchange, antisymmetric DzyaloshinskiiMoriya interaction and crystal anisotropy stabilizes longrange modulated magnetic phases hosting topological skyrmion lattice (SkL). In chiral cubic helimagnets, SkLs are usually stabilized by thermal fluctuations over a narrow region below the magnetic ordering temperature T_{c} [1]. Recently a new class of chiral alloys CoZnMn with βMn structure was found to be SkLhosting in the large temperature range, even above room temperature [2]. Moreover, an additional lowtemperature disordered equilibrium skyrmion phase (LTSk) has been recently found in Co_{7}Zn_{7}Mn_{6} [3]. Here, by using multiple quantum beam probes, we unveil a direct correlation between the stability of the LTSk – stable far from T_{c}, and a concomitant enhancement of an underlying magnetic fluctuation rate that is driven by geometric magnetic frustration. The influences of other leading skyrmion stability mechanisms, such as those derived from thermal fluctuations [1] and low T cubic anisotropies [4], are shown to be weak in this system. We therefore advance the existing of a fundamental mechanism for stabilizing topological phase in Co_{7}Zn_{7}Mn_{6} that draws upon magnetic frustration as the key ingredient [6]. The elaboration of a such a stability mechanism could find general relevance in the ongoing research topological magnetic textures amongst the multifarious frustrated magnets. 
Wednesday, March 16, 2022 4:12PM  4:24PM 
Q54.00005: Hopfions in Anisotropic Heisenberg Magnets Avadh B Saxena, Radha Balakrishnan, Rossen Dandoloff We find exact static soliton solutions for the unit spin vector field of an inhomogeneous, anisotropic threedimensional (3D) Heisenberg ferromagnet. Using Whitehead's integral expression, we calculate the corresponding Hopf invariant H analytically and obtain an integer, showing that these solitons are Hopfions. H is a product of two integers, the first being the usual winding number of a baby Skyrmion in two dimensions, while the second encodes the periodicity in the third dimension. We study the underlying geometry of H, by mapping the 3D unit vector field to tangent vectors of three appropriately defined space curves. Our analysis shows that a certain intrinsic twist is necessary to yield a nontrivial topological invariant. We illustrate our results using the invariant H of the exact Hopfions we have found. 
Wednesday, March 16, 2022 4:24PM  4:36PM 
Q54.00006: Neutron Diffraction Study of Complex Helical Magnetic Ordering in Eu(Co_{1‑x}Ni_{x})_{2‑y}As_{2} Single Crystals Tianxiong Han, Santanu Pakhira, Yan Wu, Simon Riberolles, David C Johnston, Robert J McQueeney, Benjamin G Ueland, Sangeetha N.S EuCo_{2y}As_{2} crystallizes in the uncollapsedtetragonal ThCr_{2}Si_{2}type structure and exhibits caxis helical antiferromagnetic (AF) ordering of the Eu below T_{N}=47 K with an AF propagation vector of t=(0,0,0.73(7)). EuNi_{2y}As_{2} is the electrondoped analogue which has the collapsedtetragonal structure and shows caxis helicalAF ordering below T_{N}=15 K with t=(0,0,0.92). Here, we present results from neutron diffraction measurements on singlecrystal samples that reveal changes to the magnetic ordering of Eu(Co_{1x}Ni_{x})_{2y}As_{2} across the doping series. We find good agreement with the magnetic phase diagram derived from previous thermodynamic and transport measurements. For x=0.1, we find a caxis helical structure with the Eu ferromagnetically aligned within the ab plane and the planes AF stacked along c consistent with t~(0,0,0.67). With more Ni doping, upon cooling, ferromagnetic ordering of the Co/Ni sets in prior to AF ordering of the Eu. This creates a complex groundstate magnetic structure with a superposition of the inplane helix structure and caxis ferromagnetism. t changes with increasing x, reaching ~(0, 0, 0.85) at x=0.8. 
Wednesday, March 16, 2022 4:36PM  4:48PM 
Q54.00007: Magnetic Structures and Interactions of the Candidate Skyrmion Material Gd_{2}PdSi_{3} Joseph Paddison, Binod K Rai, Andrew F May, Stuart Calder, Matthew B Stone, Matthias D Frontzek, Cristian Batista, Andrew Christianson The centrosymmetric material Gd_{2}PdSi_{3} may host a skyrmion phase under applied magnetic field [1,2]. Unusually, this proposed state is stabilized by frustrated interactions within triangular Gd^{3+ }planes, rather than by antisymmetric interactions. However, neither the zerofield magnetic structure nor the underlying spin Hamiltonian of Gd_{2}PdSi_{3} has been conclusively determined [3,4]. Here, we present neutron diffraction and spectroscopy measurements on an isotopicallyenriched polycrystalline Gd_{2}PdSi_{3 }sample. Our analysis of magnetic diffuse and inelastic scattering data indicates substantial ferromagnetic interplanar coupling, and spatiallyextended interactions in triangular planes, likely consistent with an RKKY mechanism [5]. Our Rietveld refinements show that the ordered magnetic moments lie perpendicular to the magnetic propagation vector, k ~ (0.15,0,0), and constrain candidate magnetic structures. We discuss our neutron data in the context of theoretical and experimental studies of candidate spintexture materials. 
Wednesday, March 16, 2022 4:48PM  5:00PM 
Q54.00008: Fermisurface origin of helical single Qstate and skyrmion lattice in centrosymmetric Gd compounds Juba Bouaziz, Eduardo MendiveTapia, Stefan Blügel, Julie Staunton We show from first principles that cylindrical structures within the Fermi surface are the origin of the singleQ helical state in the GdRu$_2$Si$_2$ and Gd$_2$PdSi$_3$ intermetallic compounds. The geometry of the Fermi surface nesting describes the strength and sign of the underlying pairwise RudermanKittelKasuyaYosida interactions between the Gd moments as the main mechanism. These interactions are quasitwodimensional, isotropic within the Gd layers, and provide a transition temperature and helix period in very good agreement with experiment. Using atomistic spindynamical simulations, we investigate the effects of magnetic anisotropy and construct a general magnetic phase diagram that explains the stabilization of the 2Q skyrmion lattice observed in experiment with applied magnetic fields. 
Wednesday, March 16, 2022 5:00PM  5:12PM 
Q54.00009: Helimagnetic and skyrmionic correlations close to the Quantum Critical Points of MnSi under pressure and of Mn_{1x}Fe_{x}Si. Catherine Pappas, Andrey O Leonov, Lars J Bannenberg, Ravil Sadykov, Rob Dalgliesh, Chris Goodway, Deborah L. Schlagel, Thomas A. Lograsso, Eddy LelièvreBerna, Peter Falus, Peter Fouquet, Thomas Wolf, Frank Weber MnSi is home to chiral skyrmions but also to phenomena arising from the interplay between localised and itinerant magnetism. Under mechanical or chemical pressure in the form of Fe doping in Mn_{1x}Fe_{x}Si, a nonFermi liquid behavior setsin which has been attributed to a chiral spin liquid and quantum fluctuations. Here we present a comprehensive investigation of these phenomena by combining small angle neutron scattering and neutron spin echo spectroscopy. 
Wednesday, March 16, 2022 5:12PM  5:24PM 
Q54.00010: Room temperature emergent electromagnetic induction of YMn_{6}Sn_{6} Aki Kitaori, Naoya Kanazawa, Tomoyuki Yokouchi, Fumitaka Kagawa, Naoto Nagaosa, Yoshinori Tokura Emergent electromagnetic induction based on electrodynamics of noncollinear spin states [12] may enable dramatic miniaturization of inductor elements widely used in electric circuits, yet many issues are to be solved toward application. One such problem is how to increase working temperature. We report the large emergent electromagnetic induction achieved around and above room temperature based on shortperiod (≤ 3 nm) spinspiral states of a metallic helimagnet YMn_{6}Sn_{6} [34]. The observed inductance value L and its sign are observed to vary to a large extent, depending not only on the spin helix structure controlled by temperature and magnetic field but also on the current density. The present finding on roomtemperature operation and possible sign control of L may provide a new step toward realizing microscale quantum inductors. 
Wednesday, March 16, 2022 5:24PM  5:36PM 
Q54.00011: Geometryinduced motion of magnetic skyrmions in curved ferro and antiferromagnetic films Kostiantyn Yershov, Attila Kákay, Volodymyr Kravchuk Here, we present the effect of the spontaneous drift of a magnetic skyrmion in curved films under the action of the curvature gradients without any external stimuli. The strength of the curvatureinduced driving is determined by the type of DzyaloshinskiiMoriya interaction, while the trajectory is determined by the type of magnetic ordering. Using rigid particlelike assumption, we show that for the case of Neel skyrmions the driving force is linear with respect to the gradient of the curvature, while for Bloch skyrmions the driving is proportional to the product of the mean curvature and its gradient. During the motion along the surface, the skyrmion experiences deformation which depends on the skyrmion type. The equations of motion for Neel and Bloch magnetic skyrmions in curved ferromagnetic and antiferromagnetic materials are obtained in terms of collective variables. All analytical predictions are confirmed by numerical simulations. 
Wednesday, March 16, 2022 5:36PM  5:48PM 
Q54.00012: Magnetic Properties of Thin Film Copper Selenate David King, Jinke Tang, John Ackerman Cu_{2}OSeO_{3} is a chiral ferrimagnetic insulator. It is also a cubic helimagnet that hosts a magnetic skyrmion lattice. Previous magnetic studies of Cu_{2}OSeO_{3} have used single crystals or thin layers of milled down single crystal Cu_{2}OSeO_{3}. We present data showing the magnetic properties of thin film Cu_{2}OSeO_{3}, focusing on the AC magnetic susceptibility. These data are used to develop a magnetic phase diagram of thin film Cu_{2}OSeO_{3} that we compare with the phase diagram developed from single crystal data. 
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