United States

Current-induced spin-orbit torque (SOT) originating from the spin-Hall effect (SHE) has attracted attention due to their potential applications for SOT-MRAM, skyrmion and domain wall devices. For their applications, heavy metal with high spin Hall angle (|θSH|) and low resistivity (ρxx) is necessary for an efficient SOT operation. We have proposed Co/Pt/(Ir or Ru)/Pt/Co synthetic antiferromagnetic (AF) systems for SOT-MRAM (Fig. 1), and found that the Pt/Ir/Pt spacer layer exhibits AF interlayer exchange coupling (Jex) as well as large || and low ρxx [1, 2].
In this study, we study the current-induced SOT in perpendicularly magnetized Co/Pt/Ir/Pt/Co synthetic AF system which exhibits nearly compensated magnetization. The synthetic AF structures with various Pt, Ir and Co layer thicknesses were prepared by using UHV sputtering system. The stacks were patterned into Hall bar devices and magnitude of the was evaluated from the shift of the reversal magnetic field due to the SOT current. The results were compared with those of the ferromagnetic stack systems with Co/Pt and Co/[Pt/Ir]-multilayer structures.
Figures 2(a) and 2(b) show the typical current-induced SOT switching under various fixed external magnetic fields (Hy) in Sample A (Co/Pt structure) and Sample B (synthetic AF structure), respectively. The magnetizations of the two Co layers in the synthetic AF can be switched between two anti-parallel states simultaneously by SOT. The estimated values of current density () at Hy=0 mT for Samples A and B are 7.9×107 and 4.2×107 A/cm2, respectively [3]. The magnitude of in Sample B is about half that in Sample A. The magnitudes of estimated |θSH| for Samples A and B are 7.0% and 15.6%, respectively [3], which is consistent with SOT switching behavior (Fig. 2). In this presentation, we will also show the dependence of the magnitude of SHE on the strength of Jex in the synthetic AF system. This work was supported by the CIES Consortium, Spin-RNJ, RIEC, JST OPERA (JPMJOP1611), MEXT Next generation X-nics and JSPS KAKENHI (JP19H00844, JP21K18189).
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**References** [1] Y. Saito, N. Tezuka, S. Ikeda and T. Endoh, Phys. Rev. B 104,064439 (2021). [2] Y. Saito, S. Ikeda and T. Endoh, Appl. Phys. Lett. 119, 142401 (2021). [3] Y. Saito, S. Ikeda and T. Endoh, Phys. Rev. B 105, 054421 (2022). &lt;br&gt; &lt;br&gt;

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MMM 2022

Enhancement of current to spin current conversion efficiency in synthetic antiferromagnetic layer system

Current-induced spin-orbit torque (SOT) originating from the spin-Hall effect (SHE) has attracted attention due to their potential applications for SOT-MRAM, skyrmion and domain wall devices. For their applications, heavy metal with high spin Hall angle (|θSH|) and low resistivity (ρxx) is necessary for an efficient SOT operation. We have proposed Co/Pt/(Ir or Ru)/Pt/Co synthetic antiferromagnetic (AF) systems for SOT-MRAM (Fig. 1), and found that the Pt/Ir/Pt spacer layer exhibits AF interlayer exchange coupling (Jex) as well as large || and low ρxx [1, 2].
In this study, we study the current-induced SOT in perpendicularly magnetized Co/Pt/Ir/Pt/Co synthetic AF system which exhibits nearly compensated magnetization. The synthetic AF structures with various Pt, Ir and Co layer thicknesses were prepared by using UHV sputtering system. The stacks were patterned into Hall bar devices and magnitude of the was evaluated from the shift of the reversal magnetic field due to the SOT current. The results were compared with those of the ferromagnetic stack systems with Co/Pt and Co/[Pt/Ir]-multilayer structures.
Figures 2(a) and 2(b) show the typical current-induced SOT switching under various fixed external magnetic fields (Hy) in Sample A (Co/Pt structure) and Sample B (synthetic AF structure), respectively. The magnetizations of the two Co layers in the synthetic AF can be switched between two anti-parallel states simultaneously by SOT. The estimated values of current density () at Hy=0 mT for Samples A and B are 7.9×107 and 4.2×107 A/cm2, respectively [3]. The magnitude of in Sample B is about half that in Sample A. The magnitudes of estimated |θSH| for Samples A and B are 7.0% and 15.6%, respectively [3], which is consistent with SOT switching behavior (Fig. 2). In this presentation, we will also show the dependence of the magnitude of SHE on the strength of Jex in the synthetic AF system. This work was supported by the CIES Consortium, Spin-RNJ, RIEC, JST OPERA (JPMJOP1611), MEXT Next generation X-nics and JSPS KAKENHI (JP19H00844, JP21K18189).
 
**References** [1] Y. Saito, N. Tezuka, S. Ikeda and T. Endoh, Phys. Rev. B 104,064439 (2021). [2] Y. Saito, S. Ikeda and T. Endoh, Appl. Phys. Lett. 119, 142401 (2021). [3] Y. Saito, S. Ikeda and T. Endoh, Phys. Rev. B 105, 054421 (2022). 

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technical paper

#### Welcome to the 67th Annual Conference on Magnetism and Magnetic Materials, MMM 2022!

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Magnetic Tunnel junctions (MTJs) with Co2FeAl Heusler alloy electrode are expected to show giant TMR ratio at room temperature (RT) because of its half-metallicity. In previous work, although Co2FeAl/MgO/CoFe-MTJ showed a TMR ratio of 330% at RT [1], it is still smaller than those for MTJs with CoFeB electrodes. In order to realize a large TMR ratio at RT, it is necessary to fabricate high-quality Heusler alloy electrodes and to control the interface at the atomic level. Therefore, I focused on molecular beam epitaxy (MBE) technique, which enables the fabrication of highly ordered Heusler alloy thin films [2] and atomic level interfacial modification [3]. In this work, we prepared epitaxial Co2FeAl thin films by MBE technique and characterized their magnetic properties to identify the half-metallicity of the Co2FeAl films. In addition, TMR effect in Co2FeAl/MgO/CoFe-MTJs fabricated by MBE were investigated.
The films were deposited on MgO(001) substrate using MBE and sputtering methods. The stacking structure of the Co2FeAl films were Cr(20)/Co2FeAl(50)/MgO(5) (unit of nm). After the fabrication of Co2FeAl layers, the films were annealed at Ta=200~700°C. Structural and magnetic properties were measured by XRD, VSM and FMR. The stacking structure of MTJs was Cr(20)/Co2FeAl(30)/MgO(2.0)/CoFe(5)/IrMn(10)/Cr(5) (unit of nm). After the microfabrication, the MTJ devices were annealed at TMTJ=275~425°C under 1T magnetic fields. TMR effects were measured by DC 4-probe method.
The Co2FeAl film with Ta=600°C showed high B2 order parameter and high magnetization. In addition, as shown in Fig.1, it showed very small damping constant α of 1.8×10-3, indicating that the film has good half-metallicity. Fig.2 shows the magnetoresistance curves of the MTJs measured at RT. A relatively large TMR ratio of 125% at TMTJ=400°C was observed and the TMR ratio can be improved by insertion of ultrathin Mg or Al into the Co2FeAl/MgO interface due to suppression of the interfacial state and oxidation.
This work was supported by NEDO, JSPS, GP-Spin Program and JST SPRING, Grant Number JPMJS2114. 
**References** [1] W. Wang, H. Sukegawa and K. Inomata, Appl. Phys. Lett. 95, 182502 (2009)
[2] M. Oogane, A. P. McFadden and C. J. Palmstrøm, Appl. Phys. Lett. 112, 262407 (2018)
[3] K. Himi, K. Takahashi and S. Mitani, Appl. Phys. Lett. 78, 1436 (2001)
 
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Damping constant of Co2FeAl thin film deposited by molecular beam epitaxy and tunnel magnetoresistance effect using them

Metallic superlattices such as Co/Ir/Co exhibit the symmetric interlayer exchange coupling (IEC) (1). Recently, the antisymmetric interlayer exchange coupling (AIEC) was observed in a metallic superlattice when the in-plane spatial inversion symmetry was broken (2-5). However, the controllability and the applicability of AIEC have not been examined yet, and the systematic experiments exploiting well-controlled in-plane structural asymmetry are indispensable. This study systematically investigated the AIEC for the wedge-shaped Pt/Co/Ir/Co/Pt to clarify the nature of AIEC.
A double-wedged sample (DWS) of Ta (1)/Pt (2)/Co (tCo)/Ir (tIr)/Co (0.5)/Pt (2)/Ta (1) (thickness in nm) was deposited on a SiOx substrate using magnetron sputtering. The tCo and tIr were continuously varied from 0.6 to 1.6 nm and from 0 to 1.5 nm, respectively. The wedge direction of the Ir layer was orthogonal to that of the wedged bottom Co layer. DWS was patterned into Hall-bar-shaped devices, and the magnetic properties were investigated by exploiting the anomalous Hall effect (AHE). The IEC in Co/Ir/Co was confirmed from the periodic change of the saturation field (μ0Hs) against tIr. The AHE curves were largely shifted with an additional in-plane magnetic field (μ0Hip) of 50 mT (Fig. 1), indicating the existence of AIEC. The largest switching field shift (μ0ΔHsw) was 14.8 mT at tCo ~ 0.80 nm and tIr ~ 0.27 nm, which was an order of magnitude larger than the values reported previously (0.7~1.7 mT (3,5)). Similar to the tIr dependence of μ0Hs, μ0ΔHsw showed the oscillatory change against tIr with a local minimum at tIr ~ 0.87 nm, suggesting the correlation between the symmetric IEC and the AIEC. Furthermore, we developed the extended Stoner-Wohlfarth model and proposed the tunability of the AIEC effective field by the ratio of the AIEC energy and the antiferromagnetic coupling strength. Finally, we theoretically and experimentally demonstrated the perpendicular magnetization switching solely induced by μ0Hip for DWS. This study provides crucial information to manipulate the three-dimensional chiral magnetic structures (6). 

**References:** 
[1] M. D. Stiles, J. Magn. Magn. Mater., Vol. 200, p.322-337 (1999). 
[2] E. Y. Vedmedenko et al., Phys. Rev. Lett., Vol. 122, p.257202 (2019). 
[3] D.-S. Han et al., Nat. Mater., Vol. 18, p.703 (2019). 
[4] A. Fernández-Pacheco et al., Nat. Mater., Vol. 18, p.679 (2019). 
[5] K. Wang et al., Commun., Phys. Vol. 4, p.10 (2021). 
[6] H. Masuda et al., Phys. Rev. Appl., Vol. 17, p.054036 (2022). 

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Large antisymmetric interlayer exchange coupling enabling perpendicular magnetization switching by an in plane magnetic field

Ferrimagnetic Mn4N (Fig. 1) is a promising candidate for various spintronics devices thanks to their small magnetization (Ms ~ 100 kA/m) and clear perpendicular magnetic anisotropy (Ku = 0.1 MJ/m)[1]. Ni-[2,3] and Co-doped[4] Mn4N films have magnetic compensation (MC) points. Using Ni-doped Mn4N films at the vicinity of the MC composition, our group demonstrated ultrafast domain wall motion (vDW = 3,000 m/s[5]) driven only by spin-transfer torque at RT thanks to the compensation. Additionally, In-doped Mn4N[6] films show ferromagnetism. In this work, we focus on Sn-doped Mn4N (Mn4−xSnxN) film. Although the MC in Mn4−xSnxN bulks was reported at low temperature[7], no studies have been reported on MC of Mn4−xSnxN films. Therefore, we fabricated Mn4−xSnxN epitaxial films and evaluated their properties.
25-nm-thick Mn4−xSnxN epitaxial films (x = 0.0–1.0) were grown on the MgO(001) substrates by plasma-assisted molecular beam epitaxy. Both the longitudinal and transverse resistivities (ρxx & ρxy) were measured with van der Pauw method at RT. The ordinary Hall coefficient (RH) was calculated from the slope of the ρxy-μ0H loops at high field regime. The anomalous Hall resistivities ρAH were derived by excluding the component of ordinary Hall effect from ρxy.
Fig. 2 shows the ordinary Hall coefficient (RH) and the anomalous Hall angle (θAH (= ρAH/ρxx)) of Mn4−xSnxN films as a function of Sn composition, x. xcc is the composition where the sign of RH reversed. It suggests that the dominant career-type changed from electrons (RH < 0) to holes (RH > 0) with increasing x. Moreover, the sign reversal of θAH was observed twice at the composition except xcc, indicating it was not caused by change in the career-type. Although similar results were also obtained in Ni-[2], Co-[4] and In-[6] doped Mn4N, this was the first report that the multiple sign reversals of θAH were confirmed in Mn4N-based compounds. The origin seems to be the change of magnetic structures such as MC and ferrimagnetic-to-ferromagnetic transition. 
**References** [1] T. Hirose et al., AIP Adv. 10, 025117 (2020).
[2] T. Komori et al., J. Appl. Phys. 125, 213902 (2019).
[3] T. Komori et al., J. Appl. Phys. 127, 043903 (2020).
[4] H. Mitarai et al., Phys. Rev. Mater. 4, 094401 (2020).
[5] S. Ghosh et al., Nano Lett. 21, 2580 (2021).
[6] T. Yasuda et al., J. Phys. D. Appl. Phys. 55, 115003 (2022).
[7] M. Mekata, J. Phys. Soc. Japan 17, 796 (1962). 
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Epitaxial growth of Sn doped Mn4N films and their magneto

Spintronic nano-oscillators can provide energy efficient solution to realize neuromorphic applications. They have been shown to emulate biological neurons and perform
machine learning tasks with an accuracy similar to that of state-of-the-art neural networks [1]. Moreover, they can serve as synapses when operated as a spin diode [2]. In this context,
systems with compensated anisotropy could offer key advantages. For instance, an easy plane geometry achieved by compensating the anisotropy can produce spikes as an output, a
phenomenon, recently demonstrated via micromagnetic simulations for a spin Hall nano-oscillator (SHNO) geometry [3]. Moreover, an SHNO with a compensated or near zero effective
magnetization would require low operating current and exhibit extremely low phase noise, making it suitable to realize large chain of synchronized neurons [4]. A synapse or a spin diode
with a compensated anisotropy would also resonate at a relatively fixed frequency, which is an essential requirement for frequency multiplexing and transmitting data from the SHNO
based neurons. This motivates us to study spin Hall systems with compensated anisotropy. Here, Pt/CoFeB based thin films are used as the spin Hall system. The anisotropy has been tuned
by varying the thickness of the magnetic layer. The thin films have been fabricated into micro-strip waveguides and nano-constrictions to study the magnetization dynamics in these
systems which emulate the behaviour of an SHNO. Spin-torque ferromagnetic resonance (ST-FMR) technique is employed to evaluate the effective magnetization of the fabricated devices.
The measurements indicate the fabricated devices achieve compensation when the starting thin films have perpendicular anisotropy, implying the effects of post-fabrication anisotropy
reduction and shape anisotropy. Different nano-constriction geometries have been studied to evaluate the effect of shape on the compensation point. We also demonstrate frequency
tunability of the nano-synapses and thereby its weights by anisotropy modification. We then propose a non-volatile method to control the synaptic weights via electric fields which would
enable realization of compact and energy efficient neuromorphic chips. 
**References** [1] J. Torrejon et al., “Neuromorphic computing with nanoscale spintronic oscillators”, Nature 547, 428 (2017).
[2] N. Leroux et al., “Radio-Frequency Multiply-and-Accumulate Operations with Spintronic Synapses”, Phys. Rev. Appl. 15, 034067 (2021).
[3] D. Markovic et al., “Easy-plane spin Hall nano-oscillators as spiking neurons for neuromorphic computing”, Phys. Rev. B 105, 014411 (2022).
[4] A.A. Awad et al., “Long-range mutual synchronization of spin Hall nano-oscillators”, Nat. Phys. 13, 292 (2017).

Compensation of anisotropy in spin Hall systems for realizing neuromorphic applications

Spin-orbit-torque (SOT) based magnetic devices1 have gained considerable attention due to their non-volatility, speed, and energy efficiency. SOT-induced magnetization switching studies are limited by the rise-time and duration of available pulsed current sources 2,3. Recently, ultrafast SOT switching has been demonstrated using ~ps current pulses4,obtained from an optically excited photoconductive (Auston) switch4,5, although the switching dynamics have not yet been reported. Here, we report the ultrafast magnetization dynamics measured via the time-resolved polar magneto-optical Kerr effect (MOKE)5
in a ferromagnet (inset of Fig. 1), using the ultrafast SOT
effect due to a ~ 9 ps long current pulse generated from an Auston switch. The ~ps current pulse, without any in-plane magnetic field, introduces a demagnetization of ~30% and softens the magnet at an ultrafast timescale. In the presence of a 1600 Oe symmetry-breaking in-plane field, SOT tries to rotate the magnetic moments away from the saturation state, for a negative
current pulse (blue line in Fig. 1), which when combined with the ultrafast demagnetization, shows a reduced initial demagnetization coupled with SOT-oscillations at longer timescales.
However, for positive current, it induces a coherent rotation of the softened magnetic moments toward the negative saturation. Magnetization crosses zero in ~65 ps and switches fully after
about ~200 ps (red line in Fig. 1). Sub-ns current pulse-induced SOT dynamics are governed by domain-wall propagation with an additional incubation delay due to domain nucleation 6-8.
The absence of any incubation delay combined with the fast-switching time leads us to believe that the switching is probably governed by the coherent rotation of the softened magnetic
moment due to ultrafast heating by the ~ps current pulse excitation. A micromagnetic simulation coupled with 2-temperature ultrafast heating qualitatively agrees well with the observed dynamics (dotted lines in Fig. 1). Our work sheds significant insights on the mechanism of picosecond SOT-induced magnetization dynamics. 

**References** 1. D. Polley, A. Pattabi, J. Chatterjee, et al., Appl. Phys. Lett. 120, 140501 (2022). 
2. I.M. Miron, K. Garello, G. Gaudin, et al., Nature 476, 189 (2011). 
3. K. Garello, C.O. Avci, I.M. Miron, et al., Appl. Phys. Lett. 105, 212402 (2014). 
4. K. Jhuria, J. Hohlfeld, A. Pattabi, et al., Nat. Electron. 3, 680 (2020). 
5. Y. Yang, R.B. Wilson, J. Gorchon, et al., Sci. Adv. 3, e1603117 (2017). 
6. E. Grimaldi, V. Krizakova, G. Sala, et al., Nat. Nanotechnol. 15, 111 (2020). 
7. V. Krizakova, K. Garello, E. Grimaldi, et al., Appl. Phys. Lett. 116, 232406 (2020). 
8. G. Sala, V. Krizakova, E. Grimaldi, et al., Nat. Commun. 12, 656 (2021). 

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Fig. 1. Ultrafast magnetization dynamics with positive and negative ~ps current pulse direction. The theoretical analysis is shown in dotted lines.

Spin Orbit Torque Induced Ultrafast Magnetization Switching in a Ferromagnet

Skyrmion lattices are present in many different chiral magnetic systems and their existence derives from a number of competing interactions. In a recent work [1], we showed that Pt/FeCoB/Al2O3 multilayers can host skyrmion lattices over a range of applied perpendicular fields. A particular feature of this material system is the presence of a "high-frequency" mode (HFM) under transverse field pumping, in the range of 12-18 GHz, which involves the coherent precession of the skyrmion cores and results in the generation of spin waves that flow into the uniform background region between skyrmions. Here, we discuss the results of micromagnetics simulations with the MuMax3 code [2] where we examine the role of spin wave interactions with the skyrmion cores. As the applied field increases and skyrmions begin to annihilate, leaving vacancies in the hexagonal lattice, the excitation of the HFM can serve to "anneal" the lattice, resulting in a glassy state as shown in the Figure. The spin wave interactions are found to provide a dynamical repulsive force between the skyrmion cores, which result in a more homogeneous arrangement in terms of density, but at the expense of crystalline order. These results also shed new light on how dynamical excitations can influence phase transitions associated with the melting of skyrmion lattices [3]. 

**References** 
[1] T. Srivastava et al, arXiv:2111.11797 (2021).
[2] A. Vansteenkiste et al, AIP Advances, vol. 4, 107133 (2014).
[3] P. Huang et al, Nat. Nanotechnol., vol. 15, 761 (2020). 

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Simulated MFM images of skyrmion lattices under different applied fields, before and after the excitation of a high-frequency mode (HFM) that generates spin waves. The insets show
discrete Fourier transforms of the spatial order.

Annealing a skyrmion lattice with spin wave excitations

Sendust alloys (Fe73.7Al9.7Si16.6) [1] have high Δ1-band spin polarization and low magneto-crystalline anisotropy, and thus have great potential for use in the free layer of tunnel magnetoresistance (TMR) sensors [2]. The purpose of this study is to control the composition and atomic ordering of FeAlSi films for achieving excellent soft magnetic properties, and to clarify the mechanism of soft magnetic properties.
The stacking structure was MgO subs./MgO (20 nm)/FeAlSi (30 nm)/MgO (1.5 nm)/Ta (1 nm). FeAlSi films with various compositions were deposited and annealed at Ta = 300-600 °C after deposition. The magnetic domain of the samples were measured by magneto-optical Kerr effect (MOKE) microscopy. 
Figure 1 shows the experimental and simulated results for K1 at the film compositions where K1 ~ 0 was obtained. The results for the bulk are also shown. The simulated results, which use K1 of each ordered phase [3, 4] and degree of D03 order (SD03), show the same trend as the experimental results, with the K1 ~ 0 point shifting towards an Al-rich composition as the atomic order decreases. It was found that FeAlSi films with excellent soft magnetic properties can be obtained by controlling the volume ratio of D03-Fe3Al that is the unique phase with negative K1 in the ordered phases of FeAlSi films. Figure 2 shows the MOKE results for the Fe73.7Al9.7Si16.6 film annealed at Ta = 450 °C. The MOKE image shows a separation into easy axis-like areas (K1 < 0) and hard axis-like areas (K1 > 0). As a result of the phase separation, an overall K1 ~ 0 is realized. The separation into different K1 areas suggests that the composition and atomic ordering are not uniform in whole area of the FeAlSi films. This study indicates that the FeAlSi film is a promising material to significantly improve the performance of TMR sensors. This work was supported by JSPS Grants-in-Aid for Scientific Research, Tohoku University GP-Spin Program, NEDO Leading Research Project, Tohoku University CSIS, and Tohoku University CIES. 
Fig. 1. Experimental (plotted points) and simulation (solid lines) results of K1 dependence on Al concentration. 
Fig. 2 The comparison of MOKE and VSM results for the Fe73.7Al9.7Si16.6 film annealed at Ta = 450 °C. 
**References:** [1] H. Masumoto, T. Yamamoto, J. Jpn. Inst. Met. Vol. 1, p. 127 (1937) 
[2] S. Akamatsu, M. Oogane et al., AIP Adv. Vol. 11, p. 045027 (2021) 
[3] M. Takahashi et al., J. Jpn. Inst. Met. Vol. 10, p. 221 (1986) 
[4] T. Kamimori et al., J. Magn. Magn. Mater. Vol. 54, p. 927 (1986) 

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Figure 1 
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Figure 2

Systematic investigation of FeAlSi epitaxial films with excellent soft magnetic property

According to Clausiusâ€“Clapeyron relation Î”T/Î”H = Î”M/Î”S, a large field-induced transition temperature modulation Î”T can be expected for a phase transformation involving substantial change of the saturation magnetization Î”M [1]. Fig. 1(a) describes a strategy for obtaining large Î”M by exploiting the transition between a ferromagnetic martensite and a paramagnetic austenite [2]. The Curie temperature of the austenite TAC is far below the martensitic and reverse martensitic transition temperatures, denoted as TM and TA, respectively. Applying a magnetic field stabilizes the ferromagnetic phase, giving rise to increased TM and TA, without changing the thermal hysteresis TM - TA. We next consider a particular case where TM &lt; TAC &lt; TA (Fig. 1(b)). Since TM &lt; TAC, the martensitic transition now involves two ferromagnetic phases with much smaller Î”M. In contrast, the Î”M of the reverse martensitic transition is unaffected. Such an asymmetric thermomagnetic coupling controlled by the position of TAC provides a unique opportunity to tune the thermal hysteresis by external field. As a proof of concept, off-stoichiometric Fe48Mn24Ga28 Heulser alloy with TAC ~ 180 K satisfying the above conditions was chosen. The ingots were prepared by arc melting followed by annealing at 1273 K and then quenched in cold water. We used differential scanning calorimetry (DSC), thermomagnetic (M-T) curves, isothermal magnetization (M-H) loops and M-T minor loops [3] to characterize the dissimilar magnetic field effects on the martensitic and the reverse phase transformations. Figure 1(c) shows the experimental M-T curves with applied fields up to 8 T. TM clearly shows weaker field dependence than TA, leading to large field-controlled tunability of the thermal hysteresis. In the talk, we will also discuss the role of interface friction and magnetic entropy change in the phase transformation of this alloy.

Enhancing the hysteresis of phase transformation in Fe48Mn24Ga28 Heusler alloy via asymmetric thermomagnetic coupling

Co2-based full-Heusler compounds are among the most promising materials due to their exotic transport properties, high thermal stability, high Curie temperatures (Tc â‰ˆ 1100 K) for the bulk sample, high magnetic moment (~ 6 ÂµB/f.u.), low Gilbert damping constant (Î± = 0.004) and large anomalous Hall effect linked with their band structure [1-3]. The Taylor-Ulitovsky technique, known since 60-s and allows fast (up to a few hundred meters per minute) preparation quite long (up to few kilometers) and thin (typically 0.5 to 40 Âµm in diameter) metallic wires coated by flexible and insulating glass coating [4]. In addition, the existence of thin, flexible, insulating, and highly transparent glass coating, enhanced mechanical properties and fast and inexpensive fabrication method, glass coating can be useful for biomedical applications due to its biocompatibility [5]. We report on preparation and magnetic properties of Co2FeSi Heusler alloy glass-covered microwires with a metallic nucleus diameter of about 4,4 Âµm and total sample diameter of about 17,6 Î¼m. From the X-ray diffraction, XRD, analysis of the as-prepared Co2FeSi, it was shown that the structure consists of a mixture of nanocrystalline and amorphous phases. An increase in the average grain size, Dg, from 17.8 to 31.6 nm and content of nanocrystalline phase, C from 52 % to 97 % upon annealing at 873 K (1 h) is obtained from XRD analysis. Estimated from temperature dependence of magnetic moment Tc is between 1040 K and 1059 K. As illustrated in Fig. 1, the Co2-based Heusler glass-coated microwires present strong dependence of the magnetization and the structural properties on the annealing conditions. For annealing temperatures between 873 K and 973 K magnetic phase transition has been observed, as evidenced by sharp drop of the magnetic moment when we applied 50 Oe and 200 Oe external magnetic fields during FC and FH and change in hysteresis loops (see Fig.1).

Preparation and magnetic properties of Co2 based Heusler alloy glass

(1)National Physical Laboratory, Teddington, Middlesex, United Kingdom, (2)Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), Madrid, Spain, (3)Czech Metrology Institute, Brno,
Czechia, (4)Physikalisch-Technische Bundesanstalt, Braunschweig, Germany, (5)Instituto de Engenharia de Sistemas e Computadores (INESC-MN), Lisbon, Portugal, (6)University of Leeds,
Leeds, United Kingdom, (7)Istituto Nazionale di Ricerca Metrologica, Turin, Italy, (8)Sheffield Hallam University, Sheffield, United Kingdom 

**Abstract Body:** 

The interplay between thermal gradients and magnetic topological soliton systems represents an exciting frontier in the understanding of novel thermo-magnetic
interactions at the nanoscale [1,2]. Thermally driven non-equilibrium spin polarised charge currents and their interaction with the non-trivial topology of skyrmions is central in
understanding phenomena such as the topological Nernst effect in chiral magnetic systems within the context of spin caloritronics [3].
In this talk we will address aspects of scanning thermoelectric microscopy (SThEM), Fig 1 (a), where, we will present a novel thermal scanning probe technique that allows us to locally
investigate the thermoelectric response from the magnetic domain structure in YIG [4] to nanomagnetic topological solitons: domain-walls and skyrmions. By building up a localised
picture of the resulting spatially resolved electric field we can build an understanding of the underlying spin configuration.
We will discuss experimental and modelling results which elucidate to the local response from a pinned domain wall system in an ultra-thin magnetic layer, Fig 1(b). We demonstrate that
the domain-wall introduces an additional contribution to the total measured signal, Fig 1(c), which can only arise if we assume a Néel type domain-wall . We will also report on local
thermoelectric measurements of skyrmionic systems where we have investigated a set of device structures based on chiral magnetic multilayers, Fig 1(d). 

**Image Caption:** 

Fig. 1. (a) Schematic representation of the sThEM measurement setup used in this work showing the heated AFM probe used to apply the local thermal gradient. The electric field is probed
along the device ([endif]--> and the integrated response is mapped pixelwise. (b-c) sThEM micrographs for saturated and domain wall pinned configurations, respectively. (d) sThEM
micrograph of a skyrmion nucleated in a chiral magnetic multilayer. 

**References:** 

[1] Jakub Zázvorka, et al, Thermal skyrmion diffusion used in a reshuffler device Nature Nanotechnology, 14, 658–661 (2019). 
[2] Zidong Wang et al, Thermal generation, manipulation and thermoelectric detection of skyrmions, Nature Electronics, 3, 672–679 (2020). 
[3] Alexander Fernández Scarioni, Craig Barton, et al , Thermoelectric Signature of Individual Skyrmions, Phys. Rev. Lett. 126, 077202, (2021). 
[4] Alessandro Sola, Craig Barton, et al, Phys. Rev. Applied 14, 034056, (2020). 

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