Controlled spin-to-charge conversion in noncollinear antiferromagnet-based Py/Mn$_{3}$Pt heterostructure

TL;DR

This study demonstrates efficient spin-to-charge conversion in Py/Mn₃Pt heterostructures, highlighting noncollinear antiferromagnets as promising materials for ultrafast spintronic devices through broadband ferromagnetic resonance measurements.

Contribution

It provides the first systematic investigation of magnetization dynamics and spin pumping in Py/Mn₃Pt bilayers, establishing their potential for high-performance spintronic applications.

Findings

Enhanced damping indicates efficient spin pumping into Mn₃Pt

Effective spin-mixing conductance comparable to other antiferromagnetic heterostructures

Gilbert damping remains predominantly Gilbert type across frequencies

Abstract

Noncollinear antiferromagnets (NCAFs) have recently emerged as promising candidates for future spintronic technologies, offering ultrafast switching, negligible stray fields allowing dense packing, and robustness against external magnetic perturbations. When interfaced with ferromagnets (FMs), they can strongly influence interfacial exchange and spin-torque mechanisms that enable manipulating magnetic order and realizing functionalities beyond conventional heavy metals (HMs) based FM/HM heterostructures. Here, we perform a broadband ferromagnetic resonance (FMR) study to systematically investigate the magnetization dynamics and spin-to-charge conversion in permalloy (Py) and Mn$_3$Pt bilayers. High-quality Py films provide a well-defined FMR spectra with a low Gilbert damping parameter ( $\alpha_{\mathrm{eff}} \approx 9.8 \times 10^{-3}$). We observe a pronounced enhancement of damping with intrinsic value $\alpha_{\mathrm{int}} \approx 3.1 \times 10^{-2}$ in the Py/Mn$_3$Pt bilayer, indicating efficient spin pumping into the NCAF layer. Frequency dependent linewidth analysis shows a predominantly Gilbert type damping in the bilayers and the corresponding effective spin-mixing conductance ( $g^{\uparrow\downarrow}_{\mathrm{eff}} \approx 4.8 \times 10^{18}$m$^{-2}$) is comparable to that of other high-performance antiferromagnetic heterostructures. These results are significant for establishing NCAFs as a candidate material for spin generation and highlights the potential of Py/Mn$_3$Pt bilayers for efficient and ultrafast spintronic applications.

Equations

$$\frac{dP}{dH}=$$

$$+A_{\text{Asym}}\frac{(\Delta H{)}^2-4(H-H_{\text{r}}{)}^2}{{\left[4(H-H_{\text{r}}{)}^2+(\Delta H{)}^2\right]}^2}$$

$$f=\frac{\gamma {\mu }_0}{2\pi }\sqrt{(H_r+H_K)(H_r+4\pi M_{eff}+H_K)}$$

$$\Delta H=\Delta H_0+\frac{2\pi {\alpha }_{\text{eff}}\hslash }{\gamma }f$$

$$M_{\text{eff}}=M_S-\frac{2K_S}{{\mu }_0{M}_S}\times t_{\mathrm{Py}}^{-1},$$

$${\alpha }_{\text{eff}}={\alpha }_{\text{int}}+g_{\text{eff}}^{\uparrow \downarrow }\frac{\gamma \hslash }{4\pi M_S}\times t_{\mathrm{py}}^{-1}$$

$$g_{\text{eff}}^{\uparrow \downarrow }=\frac{M_{\text{eff}}{t}_{{\text{Ni}}_{80}{\text{Fe}}_{20}}}{g{\mu }_B}\left({\alpha }_{{\text{Ni}}_{80}{\text{Fe}}_{20}/{\text{Mn}}_3\text{Pt}}-{\alpha }_{{\text{Ni}}_{80}{\text{Fe}}_{20}}\right)$$

Full text

††preprint: APS/123-QED

1 Introduction

Antiferromagnetic materials (AFs) have emerged as promising candidates for next-generation spintronics devices due to their ultrafast spin dynamics, robustness against external magnetic fields, and potential for low-power operations Han et al. (2018); Mangin et al. (2006); Chowdhury et al. (2023); Bai et al. (2022). Their integration enables novel spin transport phenomena such as the spin Hall effect, domain wall motion, and spin wave propagation, offering enhanced scalability and energy efficiency for future spin based technologies Shiino et al. (2016); Wu et al. (2024). In recent experimental advancements, noncollinear antiferromagnets (NCAFs) with a triangular spin structure have revealed robust optical and magnetotransport responses such as the anomalous Hall effect (AHE) Nakatsuji et al. (2015), anomalous Nernst effect Ikhlas et al. (2017); Pandey et al. (2024), Kerr effect Higo et al. (2018), and magnetic spin Hall effect (MSHE) Yang et al. (2017); Busch et al. (2021); Wu et al. (2020). This unexpected charge and spin transports in NCAFs are driven by the magnetic symmetries, leading to a nonzero Berry curvature in the momentum space Nayak et al. (2016); Zuniga-Cespedes et al. (2023); Li et al. (2023).

The family of manganese based NCAFs Mn3X (X= Ga, Ge, Sn, Pt) have gained further prominence as they combine the properties of conventional ferromagnets (large optical and magneto-transport responses) with the advantages of AFs (non-volatility, negligible stray fields and ultrafast dynamics) Nagaosa et al. (2010); Nayak et al. (2016); Fukami et al. (2016); Yang et al. (2017); Poelchen et al. (2023); Pal et al. (2022). These compounds are highly regarded as spin Hall materials, as the transverse spin currents possess unconventional components rather than the orthogonal relations observed in the conventional spin Hall effect. The strength of spin polarization and spin Hall angle is strongly influenced by the crystallographic orientations Cao et al. (2023), as demonstrated experimentally in Mn3Pt Bai et al. (2021); Cao et al. (2023) and Mn3Ir/Ni80Fe20 films Holanda et al. (2020); Zhang et al. (2016). The Berry-curvature driven electrical and magneto-optical responses, which can be used as a read-out signal, are suppressed in the cubic members of the Mn3X family (X = Pt, Ir) owing to their large magnetocrystalline anisotropy and the presence of degenerate non-topological spin configurations Panda et al. (2025); Xie et al. (2022); Yoon et al. (2025); Rimmler et al. (2025). Mn3Pt, for instance, exhibits two distinct spin configurations, a non-topological T2 spin structure, characterized by a helical spin configuration Bai et al. (2021); Gurung et al. (2019) and a topological phase T1, in which the Mn spins lie in the (111) plane and point toward the centers of the surrounding triangles (Fig. 1(a)) Kota et al. (2008). Although both the spin states are energetically favorable during growth, one can tune the growth parameters to obtain the non-trivial T1 state, as discussed in our previous work Sinha et al. (2025a). While the previous studies focused on the trivial T2 state Bai et al. (2021); Gurung et al. (2019), the T1 state is more interesting, as it can exhibit spontaneous anomalous Hall effect persisting beyond 300 K.

In this work, we investigate the magnetization dynamics and spin-to-charge conversion efficiency in billayers consisting of permalloy (Py) and Mn3Pt with the triangular T1 AF spin order. Magnetic and transport measurements confirm the antiferromagnetic ground state with pronounced AHE response directly originating from Berry-curvature-driven effects. The spin-sinking in Mn3Pt is probed through thickness-dependent FMR studies and its effect on the magnetic parameters of the Py layer. The efficiency of Mn3Pt as a spin sink also depends on its epitaxial integration with Py. To gain insight into this aspect, scanning tunneling microscopy (STM) is employed to investigate the surface morphology of different terminations. In addition, we report the STM investigation of the thickness-dependent evolution of the Py surface for the first time. Our findings aim to establish Mn3Pt based bilayers as viable candidates for efficient spin-to-charge conversion, paving the way for next-generation antiferromagnetic spintronic devices.

2 Experimental Methods

Mn3Pt and Py(Ni80Fe20)/Mn3Pt thin films were grown in an ultrahigh vacuum sputtering chamber (Hind High Vacuum, India) with a base pressure of 2 × 10*-8* mbar. Mn3Pt (20 nm) films were deposited on Si via co-sputtering of Mn (99.9%) and Pt (99.999%) targets powered by direct current (DC) and radio frequency (RF) sources, respectively. During growth, the working pressure is maintained at 7.2 x 10*-3* mbar. The sputtering powers for Pt and Mn targets were set at 25 W and 60 W respectively. In order to remove surface contaminants, silicon substrates were ultrasonically cleaned in sequence with acetone and isopropyl alcohol. The substrates were further degassed by a series of cyclic annealing up to 700°C. The growth temperature was maintained at 600°C, and the samples were subsequently post-annealed for one hour to improve their crystallinity. Ultrathin films of Py with thicknesses (t = 10, 11, 14, 16 nm) are grown on 20 nm thick Mn3Pt films at 400 °C. An optimized growth rate of 0.4 Ås*-1*, confirmed by x-ray reflectivity (XRR) measurements, was employed to precisely control the thickness of the Py layers. Structural characterization was performed using X-ray diffraction (XRD) with a PANalytical X’Pert diffractometer with Cu-K$\alpha$ source ($\lambda=1.5418\,\text{\AA }$). The surface morphology was analyzed using atomic force microscopy (AFM) (Oxford Instruments Asylum Research, MFP-3D system). All scanning tunneling microscopy (STM) measurements were carried out at room temperature using Quazar STM equipped with a home-built active vibration cancellation system Sinha et al. (2025b, c). The STM tips were prepared from polycrystalline PtIr and W wires, which were chemically etched and subsequently annealed at high temperature. The magnetization properties were measured using Quantum Design magnetic property measurement system (MPMS3). Magnetotransport measurements are performed in a standard four-probe geometry using a Quantum Design PPMS. The magnetization dynamics were investigated using vector network analyser (VNA-Keysight, USA) based broadband FMR spectroscopy through a coplanar waveguide (CPW) placed between the poles of DC magnet transmission mode. The CPWs effectively transmit microwave signals from a radio frequency (RF) source across a wide range of frequencies. A microwave RF field ($H_{RF}$) near the CPW excites the magnetic sample at resonance with suitable DC magnetic field and frequency. The sample was placed upside down on the signal line of the “S”-shaped CPW, ensuring that the RF magnetic field ($h_{rf}$) to be perpendicular to the external DC magnetic field. The fixed frequency FMR spectra was acquired by sweeping the direct current (DC) magnetic field in the field sweep mode.

3 Results and discussion

3.1 Growth and structural characterization

X-ray diffraction (XRD) patterns of the Mn3Pt and Py/Mn3Pt films show a strong preferential orientation along the (111) crystallographic direction (Fig. 1(b))Liu et al. (2018). The thicknesses of the Py(t)/Mn3Pt bilayers, as accurately determined by XRR measurements indicate a fixed Mn3Pt layer thickness of approximately 20 nm. To gain insight into the chemical depth distribution of the bilayers, time-of-flight secondary ion mass spectrometry (TOF-SIMS) is used to investigate the depth profiling in a Py(16 nm)/Mn3Pt(20 nm)/Si film, as shown in Fig. 1(c). The profile reveals a well-defined multilayer stack, where successive layers of Py, Mn3Pt and Si substrate can be clearly identified from signals arising from Ni*+, Fe+, Mn+, Pt+* and Si*+* respectively. The gradual transitions between these elemental profiles indicate well-defined interfaces and minimal inter-diffusion across the layers. The Mn and Pt signals are spatially confined within the intermediate region, consistent with the expected stoichiometry of Mn3Pt. The presence of Ni and Fe signals diminishes before the onset of Mn and Pt, confirming the discrete layering. The Si*+* signal rises abruptly following the Mn3Pt layer, further validating the successful fabrication of the heterostructure on the Si substrate. The interfacial roughness evaluated from XRR oscillations simulations (Fig. 1d), is found to be less than a nanometer. This shows high-quality contact at the interface, which is crucial for efficient spin pumping across the interface.

The surface morphology of Mn3Pt and Py/Mn3Pt films are further investigated using AFM. Topographic images presented in Fig. 1(e-h) reveal a smooth and homogeneous surface morphology for all samples, demonstrating topographical uniformity, which is critical to ensure reliable interface quality in heterostructures. Quantitative analysis of the root mean square (RMS) surface roughness shows values of 0.27 nm for Mn3Pt (20 nm) and 0.47 nm, 0.78 nm & 0.97 nm for Py(10 nm, 11 nm, 16 nm)/Mn3Pt (20 nm) respectively. The low roughness of Py deposited on Mn3Pt, consistent with XRR measurements, suggests a high degree of interfacial compatibility between layers, which is essential for spintronics applications.

These measurements are complemented by the highly resolved STM topography ($30\times 30$ nm2) scans (Fig. 2). Mn3Pt (111) surface shows an atomically flat termination, consistent with the large area AFM scans. Atomically resolved image acquired over $3.5\times 3.5$ nm2 area shows the hexagonal arrangement of the Mn3Pt (111) surface (Fig. 2b). The periodic atomic contrast modulation arises from variations in the local density of states at different atomic sites on the (111) termination. In the superimposed Kagome ball model shown in the inset, the bright atomic sites represent the Mn triangular sublattice, whereas the dark regions correspond to Pt atoms. The estimated distance between two dark sites is approximately 0.542 nm. Theoretically, the distance between two adjacent Pt atoms in the (111) plane is given by $\sqrt{2}a$, where $a$ is the lattice constant of Mn3Pt. From this relation, the estimated in-plane lattice constant is found to be 0.384 nm. Such atomically flat termination is crucial for lattice-matched growth and efficient spin pumping.

High-resolution STM images ($30\times 30$ nm2) acquired on Py (10 nm)/Mn3Pt (Fig. 2(c)) reveal the formation of clusters on a flat, well terminated surface. The top layers Py clusters are uniformly spatially distributed on the surface. The lateral dimension of the clusters vary between 1-3 nm. This granular morphology is attributed to the relatively low growth temperature of 400 ∘C. Higher deposition temperature can stimulate the migration of grain boundaries and aids the coalescence of more and more grains which in turn increases surface roughness Kumar et al. (2024). However, the STM topography obtained on Py(16 nm)/Mn3Pt ((Fig. 2(d)) shows coalescence of the grains, which leads to the formation of some large agglomerates. This has been previously observed in Py thin films grown on Si(100) substrate Kharmouche and Cherrad (2024).

3.2 Large magneto-transport effects in NCAF films

The M-H loop in Fig. 3(a) confirms the antiferromagnetic behavior of the Mn3Pt thin films. The observed saturation magnetization of $\sim$ 10 emu/cm3 is two orders smaller compared to that of the ferromagnetic Py films (Fig. 3(c)). This weak magnetism arises from the small out-of-plane projection of the Mn spins. Owing to the strong spin–orbit coupling of the Pt atoms, the three Mn moments canted by approximately $0.1^{\circ}$ out of the Kagome (111) plane Chen et al. (2014). The small hysteresis is due to the negligible domain reorientation in cubic compounds. The magnetic anisotropy in cubic compounds is almost an order higher than the hexagonal compounds, as the triangular spin configuration point along the three equivalent directions Zuniga-Cespedes et al. (2023); Sinha et al. (2025a). This is also evident in the reversible M-T curves shown in Fig. 3(b).

Hexagonal members of the family show large bifurcation in the ZFC-FC curves due to negligible magnetic anisotropy in the Kagome plane Sinha et al. (2025c). Despite a negligibly small net moment, Mn3Pt film shows large anomalous Hall resistivity ($\rho_{xy}^{AHE}$) between 2-300 K, as shown in Fig. 3(d). AHE effect in cubic compounds has both intrinsic and extrinsic contributions. The intrinsic contribution to the anomalous Hall effect (AHE) can be described by the vector spin chirality $\bm{\epsilon}=\mathbf{S}_{1}\times\mathbf{S}_{2}+\mathbf{S}_{2}\times\mathbf{S}_{3}+\mathbf{S}_{3}\times\mathbf{S}_{1}$, whereas the extrinsic contribution arises from the scalar spin chirality $\chi=\mathbf{S}_{1}\cdot(\mathbf{S}_{2}\times\mathbf{S}_{3})$. As observed in previous studies, the intrinsic contribution to the AHE is governed by vector spin chirality, which dominates the scattering process Xu et al. (2024); Sinha et al. (2025a). In cubic compounds, a combination of time-reversal operation and mirror symmetry constitutes a good symmetry. The anomalous Hall effect (AHE) arises as a combined consequence of mirror-symmetry breaking induced by spin canting and the application of a magnetic field. A sizable AHE response has been estimated through Brillouin-zone integration of the Berry curvature component along (111) direction Gurung et al. (2019); Chen et al. (2014). AHE based hysteresis loop indicates a coercivity of $\approx 100{mT}$ (inset of Fig. 3(d)). The extraction of $\rho_{xy}^{AHE}$ from $\rho_{xy}$ is discussed in the supplementary section Fig.(S2) zzS . The NCAFs with a small coercivity are ideal for the spintronic application, as they allow easy manipulation of the magnetic ordering and also provide a strong readout signal and negligible stray field that enables dense packing.

3.3 Optimization of Py films for FMR

To investigate the influence of deposition temperature on magnetic properties, M-H measurements were conducted on Py (10 nm) thin films deposited at four representative substrate temperatures: 27 ∘C, 200 ∘C, 300 ∘C, and 400 ∘C. The measurement was carried out with a field applied parallel to the surface of the films deposited at four different temperatures, as illustrated in Fig. 3(c). M–H loops reveal that the saturation magnetization ($M_{\mathrm{s}}$) of Py thin films increases with the growth temperature, reaching a peak at 300  ∘C. The maximum $M_{\mathrm{s}}$ value of 844 $\pm$ 11 emu/cm3 is obtained at 300  ∘C, beyond which $M_{\mathrm{s}}$ doesn’t show any significant change with temperature. The initial enhancement in $M_{\mathrm{s}}$ with temperature is attributed to the crystallization of Py from its amorphous state Dong et al. (2021).

The FMR spectra acquired on Py thin films grown at different temperatures are shown in Fig. 4(b). The transmission spectra measured at frequency 10 GHz for the four representative growth temperatures. The red lines are best fit to the symmetric and antisymmetric Lorentzian functions Dürrenfeld et al. (2015) shown in Eq. (1),

[TABLE]

where $A_{\text{Sym}}$ and $A_{\text{Asym}}$ represent the symmetric and antisymmetric absorption coefficients of the Lorentzian function, respectively. H, $H_{r}$, and $\Delta H$ represent the in-plane external DC magnetic field, resonance field and resonance linewidth (full width at half maximum), respectively. Py films exhibit a clear trend of reduced ferromagnetic resonance (FMR) linewidth broadening ($\Delta H$) and resonance field ($H_{r}$) with increasing growth temperature, which can be seen in Fig. 4(b). The decrease in $H_{r}$ from 2100 Oe (27  ∘C) to 1000 Oe (400  ∘C) is consistent with the enhancement in $M_{\mathrm{s}}$ with growth temperature.

This behavior suggests an improvement in the magnetic damping and overall film crystallinity at higher growth temperature (i.e., 400 ${}^{\circ}\text{C}$). Fig. 4(c) shows FMR spectra of Py film grown at 400 ${}^{\circ}\text{C}$. The measured $H_{r}$ versus frequency is fitted to the Kittel equation as show in Fig. 4(d) Jungfleisch et al. (2015):

[TABLE]

where $H_{K}$, $\mu_{0}$ and $\gamma$ are surface anisotropy, permeability of free space, and gyromagnetic ratio, respectively. The effective magnetization $M_{eff}$ obtained from the fitting is close to 740 $emu/cm^{3}$. The slight variation from squid measurement could be driven by surface anisotropy.

FMR linewidth obtained from lorentzian fitting of the measured FMR spectra are plotted as a function of the applied frequency in Fig. 4(e). From the linear fit of the $\Delta H$-f data using the Landau–Lifshitz–Gilbert (LLG) formalism, the effective Gilbert damping parameter ($\alpha_{\mathrm{eff}}$) is extracted from the slope, according to the equation Sun et al. (2020):

[TABLE]

where $\Delta H_{0}$ represents the inhomogeneous broadening in FMR linewidth likely arising from the magnetic inhomogeneity due to defects in the sample. Gilbert damping constant ($\alpha_{eff}$) decreased with increasing growth temperature and has the lowest value of 0.00978 in Py films grown at 400∘C (shown in Fig. 4(f)), which is comparable to previously reported values Nibarger et al. (2003); Hazra et al. (2019); Inaba et al. (2006).

Between 300 *∘*C and 400 *∘*C, the effective damping ($\alpha_{\text{eff}}$) tends to saturate, which is consistent with previous reports on the influence of thermal annealing on Gilbert damping. Beyond a certain threshold temperature (400 *∘*C), structural distortions arise due to perturbations in the atomic distribution of the Py layer. This may drive interdiffusion across the interface, as Ni and Fe atoms migrate in opposite directions Schulz et al. (2021). The depth profiles obtained from TOF-SIMS reveal no detectable signatures of Ni and Fe ion migration across the interface at 400 *∘*C. Additionally $\Delta H_{0}$ is found to decrease with growth temperature. This originated from the inhomogeneities caused by irregular grain boundaries at low-temperature growth. These effects arise due to the local variation of the anisotropy fields in inhomogeneous thin films with discontinous grains. Given these findings, we have chosen Py films grown at 400 ∘C for integration into magnetic heterostructures with Mn3Pt films for efficient response of spin transport in antiferromagnetic-ferromagnetic systems Manschot et al. (2004).

3.4 Spin pumping in Py/Mn3Pt heterostructure

FMR spectra measured on Py(11 nm)/Mn3Pt(20 nm) bilayers are shown in Fig. 5(a). The field sweeps are measured with an interval of 1 GHz , between 6–12 GHz. The red lines represent the best fit to the data using symmetric and antisymmetric Lorentzian functions, as described by Eq. (1). The variation of f is plotted as a function of ($H_{r}$) in Fig. 5(b) for all Py thicknesses, and then fitted to the Kittel equation.

Using these fits, we extract the uniaxial anisotropy field ($H_{k}$) and effective saturation magnetization ($M_{eff}$) of the ferromagnet. The average value of $H_{k}$ measured on the four different thicknesses is around 140 Oe. The value of the uniaxial magnetic anisotropy constant ($K_{u}$) estimated using the relation $K_{u}=\frac{1}{2}H_{K}M_{s}$, is around $5.27\times 10^{4}\ \text{erg/cm}^{3}$. In Fig. 5(d) , the variation of $M_{eff}$ is plotted as a function of thickness and fitted with the equation:

[TABLE]

Where $\mu_{0}$ is the permeability of free space, and $M_{\mathrm{s}}$ and $K_{S}$ are the saturation magnetization and surface anisotropy constant, respectively. Based on the fitting, $M_{\mathrm{s}}$ and $K_{S}$ are evaluated to be 1089 emu/cm3 and 0.42 erg/cm2. The obtained saturation magnetization ($M_{\mathrm{s}}$) values show good agreement between the SQUID data and the FMR measurements.

The variation of $\Delta H$ with frequency for all thicknesses is shown in Fig. 5(c) and fitted using the Landau-Lifshitz-Gilbert (LLG) equation [Eq. (3)]. The linear dependence of $\Delta$H with frequency indicates that the damping in this system is driven by Gilbert type damping.

The estimated values of ($\alpha_{eff}$) show a monotonic increase with t*-1* as shown in Fig. 5(e). Interfacing Mn3Pt with Py enhances the Gilbert damping parameter ($\alpha_{eff}$) by one order higher compared to the reference Py films. The enhanced Gilbert damping observed in Py(111)/Mn3Pt(111) is due to spin pumping into the antiferromagnetic Mn3Pt layer, where the injected spin current is absorbed through multiple mechanisms. The uncompensated interfacial spins pinned by antiferromagnetic domains within Mn3Pt, provide a channel for angular momentum transfer from the ferromagnet. Second, strong bulk spin–orbit coupling in Mn3Pt relaxes the pumped spin angular momentum, acting as a facet-independent mechanism that contributes to damping. Third, the noncollinear magnetic structure of Mn3Pt allows for the emergence of the magnetic spin Hall effect (MSHE), which can further mediate spin current absorption depending on current and field orientation Holanda et al. (2020); Lund et al. (2021); Frangou et al. (2016); Pal et al. (2024). The noncollinear magnetic order of Mn3Pt provides spin channels for transverse spin absorption, enhancing the damping and leading to larger linewidth broadening in FMR.

$\alpha_{eff}$ is linearly fitted to the inverse of thickness $t_{py}^{-1}$ using the following expression Khan et al. (2024):

[TABLE]

where $\alpha_{\text{int}}$ represents the intrinsic Gilbert damping constant and $g_{\text{eff}}^{\uparrow\downarrow}$ denotes the effective spin mixing conductance of Py/Mn3Pt heterostructures. The gyromagnetic motion of the spins in the Py layer exerts a momentum across the interface that is explained by the parameter called the spin-mixing conductance ($g_{\text{eff}}^{\uparrow\downarrow}$) Ding et al. (2024). Based on the fitting parameters, the values of $\alpha_{\text{in}}$ and $g_{\text{eff}}^{\uparrow\downarrow}$ are $3.1\times 10^{-2}$ and $4.8\times 10^{18}\,\mathrm{m}^{-2}$, respectively, the order of which is comparable to other Py/Mn3X/Pt heterostructures Holanda et al. (2020); Mosendz et al. (2010); Kimata et al. (2019); Hayashi et al. (2021). The increase in damping parameter as a consequence of enhanced spin pumping is related to the effective spin mixing conductance (g${}^{\uparrow\downarrow}_{eff}$) and thickness of the Py film ($t_{Ni_{80}Fe_{20}}$), which is given by the following expression Wang et al. (2014):

[TABLE]

In this equation, $\left(\alpha_{\text{Ni}_{80}\text{Fe}_{20}/\text{Mn}_{3}\text{Pt}}-\alpha_{\text{Ni}_{80}\text{Fe}_{20}}\right)$ is the damping enhancement by spin pumping. The real part of the effective spin-mixing conductance, g${}^{\uparrow\downarrow}_{eff}$, governs spin angular momentum transfer across the interface, while the imaginary part is typically negligible.

The plot of g${}^{\uparrow\downarrow}_{eff}$ with thickness of Py layer shows a non-monotonic behavior, which increases up to $\sim$ 11 nm, then decreases or saturates. The behavior of g${}^{\uparrow\downarrow}_{eff}$ with Py thickness reflects the dynamic balance between efficient spin transfer and loss mechanisms like spin backflow and interface scattering Kumar et al. (2025); Sharma et al. (2022). The peak indicates an optimal thickness for maximizing spin pumping efficiency at the interface. These results together provide strong evidence for spin pumping across the Py/Mn3Pt interface. This work shows that chiral antiferromagnetic systems, such as Mn3Pt can offer an alternative gateway to manifest spin to charge degrees of freedom through the magnetic inverse spin Hall effect.

4 Conclusion

In this work, we establish Mn3Pt, a noncollinear antiferromagnet with strong Berry-curvature, as an efficient spin sink in Py/Mn3Pt heterostructures. Chemical and structural analyses down to atomic scale resolution confirm atomically sharp and low-roughness interfaces. While the optimized Py layers with intrinsically low damping provide a robust platform for precise ferromagnetic resonance (FMR) studies, Mn3Pt thin films exhibit a pronounced anomalous Hall effect (AHE) with a low coercivity, reflecting the Berry-curvature-driven transport response associated with the nontrivial topology of their band structure. When interfaced with Py, the FMR spectra display a significant linewidth broadening compared to reference Py films. This enhanced damping originates from spin pumping across the interface, where precessing spins in Py efficiently transfer angular momentum into the Mn3Pt layer. The noncollinear magnetic order of Mn3Pt acts as an effective spin-absorption channel, suppressing backflow and reinforcing interfacial spin transparency. The combination of a strong AHE response and broadened FMR spectra demonstrates the dual role of Mn3Pt, as a topological material enabling robust charge-spin conversion and as a highly efficient sink for transverse spin currents. These findings highlight Mn3Pt based bilayers as a promising platform for next-generation antiferromagnetic spintronic devices, offering tunable damping, high spin-mixing conductance, and low-power operation.

5 ACKNOWLEDGMENTS

This work was suppoerted by ANRF Core Research Grant (CRG/2023/008193), Government of India. IS and SM acknowledge partial support from the DST-funded project ’CONCEPT’ under the National Programme on Nano Science and Technology (DST/NM/QM-10/2019), Government of India. We acknowledge the Department of Physics at IIT Delhi for XRD, PPMS, and MPMS measurements facility. The authors also thank the Central Research Facility (IIT Delhi) for TOF-SIMS depth profiling measurements.

The authors declare no competing financial interests.