United States

Spintronics is a prime candidate for information storage and logic devices due to its significant advantages over traditional CMOS technology, such as low-power consumption, non-volatility, and high endurance. Recently, spin-gapless semiconductors (SGSs) have been introduced for modern spintronics-based applications and are promising candidates for designing quantum computing, data storage, coding, and decoding. In SGSs, spin-polarized charge carriers or spin current are the primary functions of these magnetic materials [1]. SGS materials such as CoFeMnSi Heusler Alloy offer high spin polarization (64%), high Curie temperature (620 K), and low damping constant (0.0046) are all intriguing properties that can be used in room-temperature spintronic device applications [2]. SGS has unique features such as almost temperature-independent carrier concentration, and quantum linear magnetoresistance in a low-temperature range [3].
In this abstract, the effect of changing the sputtering power from 30W to 50W and 90W on an RF sputtered thin film of CoFeMnSi (CFMS) Heusler alloy with a nominal thickness of 30 nm with temperature-dependent electrical and magneto-transport properties has been studied. Fig. 1(a) shows Hall resistivity as a function of applied magnetic field for CFMS 90W (30nm) thin-film recorded at 10K, 50K, 100K, 200K, 250K, and 300K. Fig. 1(b) demonstrates the SGS behavior of the material in nearly temperature-independent carriers&#39; concentrations with the same order up to 300K. Fig. 1(c) depicts magnetoresistance (MR) curves of 90W (30nm) CFMS thin film within the temperature range of 10K to 200K. The MR curves exhibit a linear field-dependent trend. In this temperature range, the observed MR is negative. The peak presence at zero magnetic fields signifies the localization and as we increase the field, the path contributing to localization is go out of the phase.&lt;br&gt;&lt;br&gt;
**References**&lt;br&gt; [1]. D. Rani, L, Bainsla, A. Alam, and K. G. Suresh, “Spin-gapless semiconductors: Fundamental and applied aspects”, Journal of Applied Physics, vol. 128, no. 22, 2020.
[2]. L. Bainsla, A. I. Mallick, M. Raja, A. K. Nigam, B. Varaprasad, Y. Takahashi, A. Alam, K. G. Suresh, and K. Hono “Spin gapless semiconducting behavior in equiatomic quaternary CoFeMnSi Heusler alloy”, Physical Review B, vol. 91, 2015.
[3]. X. L. Wang, “Proposal for a new class of materials: spin gapless semiconductors”, Physical review letters, vol. 100, 2008.&lt;br&gt;&lt;br&gt;
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MMM 2022

Study of Cobalt Based Spin Gapless Semiconducting Heusler Alloy Thin Film

Spintronics is a prime candidate for information storage and logic devices due to its significant advantages over traditional CMOS technology, such as low-power consumption, non-volatility, and high endurance. Recently, spin-gapless semiconductors (SGSs) have been introduced for modern spintronics-based applications and are promising candidates for designing quantum computing, data storage, coding, and decoding. In SGSs, spin-polarized charge carriers or spin current are the primary functions of these magnetic materials [1]. SGS materials such as CoFeMnSi Heusler Alloy offer high spin polarization (64%), high Curie temperature (620 K), and low damping constant (0.0046) are all intriguing properties that can be used in room-temperature spintronic device applications [2]. SGS has unique features such as almost temperature-independent carrier concentration, and quantum linear magnetoresistance in a low-temperature range [3].
In this abstract, the effect of changing the sputtering power from 30W to 50W and 90W on an RF sputtered thin film of CoFeMnSi (CFMS) Heusler alloy with a nominal thickness of 30 nm with temperature-dependent electrical and magneto-transport properties has been studied. Fig. 1(a) shows Hall resistivity as a function of applied magnetic field for CFMS 90W (30nm) thin-film recorded at 10K, 50K, 100K, 200K, 250K, and 300K. Fig. 1(b) demonstrates the SGS behavior of the material in nearly temperature-independent carriers' concentrations with the same order up to 300K. Fig. 1(c) depicts magnetoresistance (MR) curves of 90W (30nm) CFMS thin film within the temperature range of 10K to 200K. The MR curves exhibit a linear field-dependent trend. In this temperature range, the observed MR is negative. The peak presence at zero magnetic fields signifies the localization and as we increase the field, the path contributing to localization is go out of the phase. 
**References** [1]. D. Rani, L, Bainsla, A. Alam, and K. G. Suresh, “Spin-gapless semiconductors: Fundamental and applied aspects”, Journal of Applied Physics, vol. 128, no. 22, 2020.
[2]. L. Bainsla, A. I. Mallick, M. Raja, A. K. Nigam, B. Varaprasad, Y. Takahashi, A. Alam, K. G. Suresh, and K. Hono “Spin gapless semiconducting behavior in equiatomic quaternary CoFeMnSi Heusler alloy”, Physical Review B, vol. 91, 2015.
[3]. X. L. Wang, “Proposal for a new class of materials: spin gapless semiconductors”, Physical review letters, vol. 100, 2008. 
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poster

#### 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.

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We report a large spin-current generation from the interface of the Ti/Pt bilayer. By doing the spin-torque ferromagnetic resonance (ST-FMR)1 in Ti(5)/Pt(1.5)/Py(5)/Pt(1.5) heterostructure, we observe a large enhancement of the damping-like torque that cannot be explained by the spin Hall effect (SHE) of Pt due to the cancellation of the spin-current generated from the symmetrically placed Pt layers on either side of the ferromagnet. We observe that the sign of damping-like torque generated in Ti/Pt/Py/Ti heterostructure is opposite as compared to Pt/Py bilayers which rule out the possibility of the conversion of orbital-current generated by Ti into the spin-current using the spin-orbit coupling of Pt2–5. This effect is reproduced for different thicknesses of Py (4 -8 nm). We confirm that this effect disappears when Pt is substituted by Cu. All these pieces of evidence together suggest a possible formation of the Rashba surface at the Ti/Pt interface due to their work function difference (approximately 1.3 eV). This could be a way to boost up the generated spin-current by exploiting the interfacial Rashba-Edelstein effect and bulk spin hall effect together for practical applications. 
**References** 1 L. Liu, T. Moriyama, D.C. Ralph, and R.A. Buhrman, Phys. Rev. Lett. 106, 1 (2011).
2 D. Go, F. Freimuth, J.P. Hanke, F. Xue, O. Gomonay, K.J. Lee, S. Blügel, P.M. Haney, H.W. Lee, and Y. Mokrousov, Phys. Rev. Res. 2, 1 (2020).
3 Y. Choi, D. Jo, K. Ko, D. Go, and H. Lee, ArXiv:2109.14847v1 1 (2021).
4 S. Lee, M.G. Kang, D. Go, D. Kim, J.H. Kang, T. Lee, G.H. Lee, J. Kang, N.J. Lee, Y. Mokrousov, S. Kim, K.J. Kim, K.J. Lee, and B.G. Park, Commun. Phys. 4, 3 (2021).
5 S. Ding, A. Ross, D. Go, L. Baldrati, Z. Ren, F. Freimuth, S. Becker, F. Kammerbauer, J. Yang, G. Jakob, Y. Mokrousov, and M. Kläui, Phys. Rev. Lett. 125, (2020). 
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Large spin current generation from the Rashba surface at Ti/Pt interface

Transition metal dichalcogenides (TMDs) are potential materials for exerting efficient spin-orbit torque (SOT) on the adjacent ferromagnetic (FM) layer due to their high spin-orbit coupling (SOC) and broken inversion symmetry at the interface [1]. An unconventional SOT is recently observed in WTe2/NiFe heterostructures due to low symmetry in WTe2 [2]. PtSe2 is one of the TMDs having high SOC [3]. In this work, we measured the effective spin Hall efficiency (SHE) in PtSe2/NiFe/Pt heterostructure using spin-torque ferromagnetic resonance (STFMR). PtSe2 was synthesized by salinization of a sputtered Pt (3 nm) film. The growth of PtSe2 was confirmed using Raman measurements, which shows two peaks at 176 cm-1 (Eg) and 206 cm-1 (A1g). Subsequently, a 6 nm thick NiFe (Py) layer followed by Pt (3 nm) capping layer was deposited on PtSe2 using magnetron sputtering. For STFMR measurements, RF current of frequency varying from 3 GHz to 7 GHz was applied to the device in the presence of an external magnetic field (H). The mixing voltage (Vmix) across the device was measured and the symmetric & anti-symmetric components (VS, VA) of Vmix, linewidth (ΔH), and resonance field (Hr) were extracted (Fig.1) from the fitting of STFMR spectra. Effective SHE was calculated using the ratio of VS and VA and found to be increased 33% for PtSe2/Py/Pt compared to reference (Py/Pt). This change in SHE is due to the presence of PtSe2, which was further confirmed by making a stack with Pt/Py/Pt structure. STFMR signal of all three stacks has been compared in Fig. 1 (a). No clear signal was observed for Pt/Py/Pt which confirms the presence of SOT due to PtSe2. Damping parameter was extracted by the fitting of linewidth (ΔH) vs. frequency (f) curve (Fig. 2) and was found to be enhanced by 131% in the case of PtSe2/Py/Pt compared to its reference Py/Pt. Large enhancement in damping parameter indicates large spin pumping into PtSe2. These results indicate the suitability of using PtSe2 as a potential material for spin-orbit torque. 
**References** [1] Q. Shao et al., Nano Letter 16, 7514-7520 (2016)
[2] D. MacNeill et. al., Nature Physics, 13, 300-305 (2017)
[3] Marcin Kurpas and Jaroslav Fabian, Physical Review B, 103, 125409 (2017)
 
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Study of Spin Orbit Torque in PtSe2/NiFe/Pt Heterostructure

Microwave resonant (FMR) and Inverse Spin Hall effect (ISHE) in ferromagnetic materials have attracted high interest due to its significant contribution in spintronic devices [1]. Co-planar waveguide ferromagnetic resonance (CPW-FMR) technique is versatile tool to study the spin dynamics and its related parameters- saturation magnetization (Ms), spin mixing conductance (g↑↓), anisotropy field (Hk), geomagnetic ration (γ), Gilbert damping (α) and role of inhomogeneity (ΔH0) in magnetic thin films. In the present study, high frequency (5 GHz - 40 GHz) dependent FMR and FMR induced spin current (ISHE) measurement has been performed on DC magnetron sputtered Ni80Fe20 (10 nm) and Ni80Fe20 (10 nm) /Pt (5 nm) thin film stacking via CPW - FMR set up. RT field swept microwave absorption spectra of Ni80Fe20 thin films fig. 1(a) and FMR induced voltage spectra (ISHE) fig.1 (b) of thin films were recorded. The spin dynamics parameters such as α, (ΔH0 ), (g↑↓) are 7.61 x 10 -3 , 4.12 Oe and ~ 1.04 x 1020 m-2 respectively extracted via line shape analysis as shown in inset of fig.1(a). Other parameters- Meff, γ, Hk are deduced from the above detailed CPW- FMR studies using Kittle fit eq. [2] in f vs Hres curve as shown in inset of fig.1(a) are ~ 1.047 T, 1.61 x 10 11 s-1T-1 , 88.38 Oe respectively. The ability to pump the spins from Py layer to Pt layer interface has induced by one order from ~ 1019 m-2 to 1020 m-2 in our studies as compare to previous reported literatures [3-4], which is attributed to the highly homogeneity and low magnetic interfacial anisotropy present in Py/Pt thin film stacking. Frequency dependent induced voltage (VISHE) is symmetric in nature inactive of the detection of pure spin current and magnitude is higher (VISHE2GHz ~ 120 µV) which is in corroboration with damping and spin mixing conductance of Py/Pt thin film. The ISHE results are in agreement with the literature [5-6]. The thickness dependent study is under progress for the tuneable detection of pure spin current. 
**References** 1.I. Zutic , J. Fabian, and S. D. Sarma, Reviews of modern physics, 76(2), 323 (2004).
2.C. Kittel, Physical Review, 71(4), 270. (1947).
3.O. Mosendz et al, Physical Review B, 82(21), 214403 (2010).
4.S. Mizukami, Journal of magnetism and magnetic materials, 226, 1640-1642 (2001)
5.R. Iguchi e al, Japanese journal of applied physics, 51(10R), 103004 (2012).
6.S. Martín-Rio, Journal of Magnetism and Magnetic Materials, 500, 166319 (2020). 
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High Frequency (5 GHz – 40 GHz) Microwave Resonant Absorption and Inverse Spin Hall Effect in Py/Pt Thin Film stacking

Non-reciprocal (NR) microwave components providing a unidirectional flow of energy are essential for signal processing. Spin waves (SWs) possess attractive
characteristics that make them commonly harnessed to design NR components. However these components are presently mainly ferrite-based and bulky; more compact and integrable
systems are desirable. Synthetic antiferromagnet (SAF) films with strong dipole-dipole interactions have been proposed [1] as a versatile platform on which strongly NR behaviors could be
obtained at micron-scale physical dimensions in the frequency range of their eigen excitations. We have studied the NR behavior of SWs in Co40Fe40B20 (17 nm) /Ru (0.7 nm)/CoFeB (17 nm) SAFs using inductive propagative spin wave spectroscopy, analytical modeling and
numerical micromagnetics using the mumax3 solftware. The films were patterned in 20 micron-wide stripes used as SW conduits. Two inductive antenna separated by a variable distance
[2-8 microns, Fig. 1(a)] are used to generate and collect the spin waves by means of a 2-port vector network analyzer. We determine the forward and backward transmission parameters for
variable applied fields and variable field-to-wavevector orientations. When the SAF is in the scissors state, all directions show substantial frequency and amplitude non-reciprocities (Fig.
1), except when the wavevector is perpendicular to the applied field, where only NR amplitude is observed. We model this behavior by computing the dispersion relation of the acoustical
and optical spin waves of the SAF and their sensitivity to the radio frequency (RF) fields of the antenna, as well the inductive transduction back to the electrical domain. We will show how
the dispersion relations and the symmetries of the susceptibility tensor can be used to design optimally NR transmission parameters. 
**References** [1] Mio Ishibashi et al., Science Advances, 6, eaaz6931 (2020). 
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Fig. 1: (a) Device and geometrical conventions; (b) Reflection parameter of antenna 1, used to identify the frequencies of the acoustical and optical modes at k=0 (blue lines). (c) and (d)
forward and backward transmission parameters.

Electrical Evidence and Modeling of the Giant Non Reciprocity of Spin

The field of magnonics is emerging at blistering pace due to its promising room-temperature applications in logic-based devices at low-power consumption. In view of this,
the exploration of suitable ferromagnetic (FM) La0.67Sr0.33MnO3
(LSMO) and ferroelectric (FE) Pb(Mg0.33Nb0.67)O3-PbTiO3(PMN-PT) magnetoelectric (ME) heterostructures is of
prime interest due to their intimate interface contact [1].
In the present work, a 50-nm-thick LSMO was grown on PMN-PT(001) and PMN-PT(111) single crystals by using pulsed laser deposition. The epitaxial nature of LSMO is confirmed by
x-ray diffraction data. The static and dynamic magnetic response of LSMO/PMN-PT is studied by performing magnetization (M) and ferromagnetic resonance (FMR) measurements. Due
to strong ME coupling at the interface, the LSMO/PMN-PT(001) shows four-fold symmetry of magnetic anisotropy (MA) whereas LSMO/PMN-PT(111) shows isotropic behaviour (see
Fig. 1). The observation can be interpreted on the basis of coupling between the resultant polarisations of PMN-PT and the net M vector of LSMO [2]. To know the effect of ME-induced
MA on the magneto-dynamic response of LSMO, FMR measurements were carried. The FMR data are fitted with the Kittel’s equation and obtained the Gilbert damping constant (α),
which is a key parameter for spin-wave (SW) dynamics, is in the order of 10-2. As the LSMO/PMN-PT(001) is anisotropic in nature, α is found to be smaller along the hard axis than the
easy direction. On the other hand, the LSMO/PMN-PT(111) is isotropic in nature, so that the α remains same in all directions. In order to explore the electric (E-) field effect on the spin
dynamics, FMR data are collected for the LSMO/PMN-PT poled (E = ±10 kV/cm) samples, where a significant reduction in α values is seen. From these combined results, we conclude
that α depends strongly on MA of the films other than its surface roughness, defects, etc. [3]. Although more investigations are required, this particular work hints that it becomes possible
to realize E-field controlled SWs in FM/FEs to develop futuristic magnonic devices. 
**References** 
[1] D. Pesquera, E. Khestanova, M. Ghidini, S. Zhang, A. P. Rooney, F. Maccherozzi, P. Riego, S. Farokhipoor, J. Kim, X. Moya, M. E. Vickers, N. A. Stelmashenko, S. J. 
Haigh, S. S. Dhesi, and N. D. Mathur, Nat. Commun. 11, 3190 (2020). 
[2] G. Venkataiah, Y. Shirahata, M. Itoh, and T. Taniyama, Appl. Phys. Lett. 99, 102506 (2011).
[3] K. Yamada, K. Kogiso, Y. Shiota, M. Yamamoto, A. Yamaguchi, T. Moriyama, T. Ono, and M. Shima, J. Magn. Magn. Mater. 513, 167253 (2020). 

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Fig.1. The polar plots of normalized remanent magnetization (Mr/Ms) of (a) LSMO/PMN-PT(001) and (b) LSMO/PMN-PT(111) heterostructures.

Variation of Gilbert damping constant via interface induced magnetic anisotropy in LSMO/PMN PT heterostructures

Understanding the interaction between magnons and phonons is the key for magnonic applications. In this work, we develop an optical reflectometry to investigate the population of magnons and phonons. Unlike the Brillouin light scattering (BLS) spectroscopy [1, 2], where the sophisticated tandem Fabry-Perot interferometer and single frequency laser with sharp line width are necessary, we use a simple laser-based reflectometry to measure the Kerr rotation and reflectance which are sensitive to the magnon and phonon, respectively.
Using this optical technique, we study the spatial distribution of magnons and phonons in a thulium iron garnet (TmIG) under the temperature gradient generated by current induced Joule
heating. Both the magnon and phonon populations are decaying exponentially as a function of distance from the electrical heating line. We find that the characteristic decay length of the
population of magnons and phonons are different, indicating the non-equilibrium between magnons and phonons in TmIG. Moreover, the characteristic length of magnon population
decreases as increasing the heating power or decreasing the magnetic field, while that of phonon population is almost constant. The different characteristic length of magnon and phonon
population is attributed to the enhanced non-linear magnon scattering processes at high magnon population regime. Our work revealing the magnon-phonon non-equilibrium in TmIG will
motivate the magnonic researches where the role of the magnon-phonon interaction is crucial [3]. 
**References** [1] M. Agrawal., et al., Phys. Rev. Lett. 111, 107204 (2013).
[2] K. An., et al., Phys. Rev. Lett. 117, 107202 (2016).
[3] G.-H. Lee., et al., Appl. Phys. Lett. 119, 152406 (2021).

Probing magnon phonon non

Long-distance transmission of spin angular momentum in antiferromagnetic insulators has attracted much attention [1]. In our previous study, we investigated the spin
transmission in NiO by the enhancement of the damping constant due to the spin pumping effect in NiO tNiO nm/FeNi multilayer films. The results imply that the spin transmission length
could be much greater than 100 nm [2]. In order to accurately determine the transmission length, the structure used in those measurements requires the NiO thickness tNiO >> 100 nm
because the pumped spin current diffuses in the film thickness direction. However, depositing such a thick NiO layer while maintaining the film quality is not practical.In this study, we
devise a structure having the spin transmission in the lateral direction of the NiO layer as shown in Fig. 1 and characterize the damping constant enhancement with respect to the lateral
length lNiO.
Multilayers of NiO 10 nm/FeNi 5 nm/Au 5 nm were fabricated on a single crystalline MgO substrate by magnetron sputtering. The epitaxial growth of the NiO was confirmed by the
RHEED images. We performed the homodyne ferromagnetic resonance measurements for various lNiO. From the lNiO dependence of the damping constant obtained from the measurements, we attempted to derive the in-plane spin transmission length in the NiO. 
**References** 
[1] R. Lebrun et al., Nature 561, 222 (2018)
[2] T. Ikebuchi et al., Appl. Phys. Exp. 14, 123001 (2021) 
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Fig. 1 Schematic illustration of the lateral device and measurement configuration

Characterization of long distance spin transport in antiferromagnetic NiO

In this work, we report the design of a spin torque nano-oscillator (STNO) combined with magnetic flux concentrators (MFCs) to improve the sensitivity of detecting magnetic fields, where the STNO consists of two out-of-plane (OP) ferromagnetic layers separated by a MgO insulating layer (see Fig. 1(a)) and the MFCs placed next to STNO are permalloy. We carried out micromagnetic simulations on the spin-transfer torque (STT) induced magnetic dynamics in the free layer of STNO. Based on the Landau-Lifshitz-Gilbert (LLG)
equation with STT term, the time evolved magnetization precession of the free layer is plotted in Fig. 1(b). First, we show that the ferromagnetic resonance frequency (FMR) of the free
layer magnetization precession can be tuned by the charge current density and external magnetic fields. In addition, the FMR as a function of external magnetic field strength is also studied
on STNO with and without MFCs, see Fig. 1(c). We observed a general suppression of the resonance frequency due to the damping effect of the magnetization induced by MFCs placed at
different distances to the STNO (see Fig. 1(d)). The FMR shift of the STNO free layer magnetization as function of external magnetic field is summarized in Fig 1. (e). By placing MFCs
next to STNO, the lowest detectable magnetic field strength is enhanced from 10 μT to 10 nT. It is concluded that MFCs improve the sensitivity of STNO to external fields due to the
distortion caused by the magnetization damping. The results presented in this work could inspire the optimal design of STNO and MFC-based ultra-low magnetic field sensors. 
![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/300448a262a8a122d2d995834592eccc.png) 
Fig. 1. (a) Schematic view of STNO with a diameter of 80 nm. Charge current is defined as +J and applied in the positive direction. (b) Evolution of the free layer magnetization resonating
in-plane from the initial condition x,y,z> = (0, 0, 1). (c) Schematic view of MFCs placed next to STNO. (d) The distance between MFCs and STNO affects the resonance frequency. J=5e10 A/m2. (e) FMR shift of the magnetization induced by an external magnetic field for an STNO with and without MFCs, where LOD stands for limit of detection. J=5e10 A/m2, MFCs are placed at 70 nm to the STNO.

Magnetic Field Detection Using Spin Torque Nano Oscillator Combined with Magnetic Flux Concentrators

Recent experimental and theoretical work has focused new interest on how magnons can influence the transport properties of metallic ferromagnets (FM). Here we demonstrate the influence the Gilbert damping parameter, αGD, has on both the electron and magnon populations available for transport in two distinctly different CoxFe1-x alloys. The absolute Seebeck coefficient, αabs, is measured for each of the films [1], and we compare to our calculated total thermopower, αtot. To calculate the electronic and magnonic components,
we employ a semi-classical approach; the classical free-electron model estimates the diffusive thermopower component, αMott [2], while we compute the relativistic magnon-drag component, αmd, based on the spin transfer mechanism [3,4]. From these results, we obtain quantitatively comparable measured Seebeck coefficients for both alloys, subsequently showing αmd dominates the low-damping sample, while the alloy with normal damping follows αMott well over our temperature regime. We further present anisotropic magnetoresistance (AMR) [5] and magnetothermopower (MTP) [6] measurements over the temperature range of interest from 125 to 250 K, where we previously reported a significant non-electronic thermal conductivity [7]. AMR measurements align with expected FM metal behavior, while MTP shows a field-dependence as H ∥ ▽T in the low-damping FM metal. We estimate the magnitude of this behavior using the relationship between α(H,⊥) and the inverse resistance, R -1, and calculated the expected α(H,∥) [6]. This argues for an additional field-direction dependent
contribution to thermopower, which could be a novel form of magnon-drag. 
**References** 1. S. J. Mason, A. Hojem, and D. J. Wesenberg, Journ. of Appl. Phys. 127 (2020). 
2. M. Jonson and D. Mahan, Phys. Rev. B 21 (1980). 
3. M. E. Lucassen, C. H. Wong, and R. A. Duine, Appl. Phys. Let. 99 (2011). 
4. B. Flebus, R. A. Duine, and Y. Tserkovnyak, EPL 115 (2016). 
5. J. Shi, S. S. Parkin, and L. Xing, Journ. Of Mag. and Mag. Mater. 125, (1993). 
6. A. D. Avery, M. R. Pufall, and B. L. Zink, Phys. Rev. B – Cond. Mat. and Mater. Phys. 86,(2012). 
7. M. R. Natale, D. J. Wesenberg, and E. R. Edwards, Phys. Rev. Mater. 5, (2021). 
8. M. R. Natale, D. J. Wesenberg, and E. R. Edwards, in preparation 

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Fig. 1: Temperature dependence of absolute thermopower for Co25Fe75 alloy. Calculated diffusive, αMott, (green), magnon-drag, αmd, (orange), and total thermopower, αtot, (marron)overlayed with experimental measurements, αmeas
, from 125-250K.

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Fig. 2: MTP measurement for Co25Fe75 at 200K. αabs(H) is measured in-plane for Hext ⊥ ▽T and Hext ∥ ▽T. Curved arrows indicate the field sweep direction and are color coordinated to distinguish between field-orientation. Dotted lines are expected values.

Magnon drag observed via field

Skyrmions are of great interest in spintronic devices because their small size and the high-speed motion when driven by a current or a spin-wave (SW). Skyrmion motion
along a narrow track is important for racetrack-type spintronic devices, since a skyrmion moving along the propagation direction of an injected electrical or SW current (forward) is the
means by which data are moving[1]. To design the devices, knowing how to adjust the skyrmion motion becomes important.
We carried out simulations of SW driven skyrmion motion using OOMMF [2], with fixed parameters D = 1.5 mJ/m2, MS = 1004 kA/m, A = 3.6 pJ/m, and Ku = 1 MJ/m3. We found that for tracks narrower than 50 nm the skyrmion always moves forwards. For wider tracks, the skyrmion will initially move both backward and close to the track edge, before moving forward at longer times once the track edge is reached, as shown in Fig 1. We attribute this to an additional repulsive force on the skyrmion from the track edge. For samples with Gilbert damping
constant α > 0.06, the skyrmion will move forward without retrograde motion.
The Thiele equation is a widely-used way to analyse skyrmion motion. The SW driving force on a skyrmion is usually the SW scattering force [3], but the strength of the scattering and the
energy change associated with changes in skyrmion size owing to absorbed SWs are hard to extract from magnetization data. Thus, we use the SW transmission T and reflection
coefficients R to make an estimate of the forces involved. We can obtain T from the ratio of the SW amplitude downstream of the skyrmion and without skyrmion at same position.
Similarly, we obtain R from the difference between magnetization data upstream of the skyrmion and without skyrmion.
As an example, we consider the data from a simulation with track width w = 100 nm and α = 0.03. By Analysing T and R, the decrease in T after ~30 ns, shown in Fig.2, will reduce the
effort that leads to the skyrmion moving backward. Meanwhile the increasing force from the sample edge also helps the skyrmion overcome the Spin-Ttansfer Torque between transmitted
SW and skyrmion[4], allowing it to move forwards. 
**References** 
1. Sampaio, J., Cros, V. et al. Nature Nanotech 8, 839–844 (2013) 
2. Donahue, M., Porter D. et al, National Institute of Standards and Technology(1999) 
3. Zhang, X. et al New J. Phys. 19, 065001 (2017) 
4. Yan, X., S. Wang et al. Phys. Rev. Lett. 107, 177207 (2011) 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/d19058f8a75b91bfae124e6b897fb99c.png) 
The snapshots of w = 40 nm, 90 nm tracks 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/1486ee39a892911ac9e318a9a335f631.png) 
Time-dependent SW T, R, A and skyrmion acceleration data

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