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We investigated the Gilbert damping in La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) and La$_{0.7}$Sr$_{0.3}$MnO$_3$/Pt (LSMO/Pt) heterostructures using first-principles calculations and Wannier interpolation techniques. Our work is motivated by recent experimental observations showing smaller Gilbert damping in LSMO/Pt films compared to their reference single-layer LSMO films, despite expectations of enhanced spin-pumping effects in the former. We analyze the electronic structures and transport behaviors, finding that LSMO thin films have a high spin Hall angle ($|{\theta_{\mathrm{SH}}}|$). However, in LSMO/Pt, the presence of platinum significantly increases longitudinal conductivity, reducing $|\theta_{\mathrm{SH}}|$. Despite the lower $|\theta_{\mathrm{SH}}|$, LSMO/Pt shows a notable anti-damping contribution to Gilbert damping due to a larger spin diffusion length. In contrast, pure LSMO films with large $|\theta_{\mathrm{SH}}|$ exhibit higher damping due to efficient spin-to-charge conversion via a self-induced inverse spin Hall effect (ISHE), as reported in a recent experiment. Finally, this work demonstrates that by fine-tuning the ratio of spin Hall conductivity to longitudinal charge conductivity, it is possible to engineer heterostructures with desired spin-to-charge or charge-to-spin conversion efficiencies even with weaker spin-orbit couplings.

This article reports dependence of exchange bias (EB) effect on interparticle interactions in nanocrystalline Co/CoO core/shell structures, synthesized using conventional sol-gel technique. Analysis via powder X-Ray diffraction (PXRD) studies and transmission electron microscope (TEM) images confirm absence of crystalline phases other than core-shell Co-CoO with average particle size $\approx$18 nm. Volume fraction ($\varphi$) is varied (from 20\% to 1\%) by introduction of stoichiometric amount of non-magnetic amorphous silica matrix (SiO$_2$) which leads to a change in interparticle separation/interaction. The influence of exchange and dipolar interactions on the EB effect, caused by the variation in interparticle interaction/separation is studied for a series of Co/CoO core/shell nanoparticle systems. Studies of thermal variation of magnetization ($M- T$) and magnetic hysteresis loops ($M- H$) for the series point towards strong dependence of magnetic properties on dipolar interaction in concentrated assemblies whereas individual nanoparticle response is dominant in isolated nanoparticle systems. The analysis of the EB effect reveals a monotonic increase of coercivity ($H_C$) and EB field ($H_E$) with increasing volume fraction. When the nanoparticles are close enough and the interparticle interaction is significant, collective behavior leads to an increase in the effective antiferromagnetic (AFM) CoO shell thickness which results in high $H_C$, $H_E$. Moreover, in concentrated assemblies, the dipolar field superposes to the local exchange field and enhances the EB effect contributing as an additional source of unidirectional anisotropy., Comment: 14 pages, 7 figures

Spin pumping has significant implications for spintronics, providing a mechanism to manipulate and transport spins for information processing. Understanding and harnessing spin currents through spin pumping is critical for the development of efficient spintronic devices. The use of a magnetic insulator with low damping, enhances the signal-to-noise ratio in crucial experiments such as spin-torque ferromagnetic resonance (FMR) and spin pumping. A magnetic insulator coupled with a heavy metal or quantum material offers a more straight forward model system, especially when investigating spin-charge interconversion processes to greater accuracy. This simplicity arises from the absence of unwanted effects caused by conduction electrons unlike in ferromagnetic metals. Here, we investigate the spin pumping in coupled ferrimagnetic (FiM) Y3Fe5O12 (YIG)/Tm3Fe5O12 (TmIG) bilayers combined with heavy-metal (Pt) using the inverse spin Hall effect (ISHE). It is observed that magnon transmission occurs at both of the FiMs FMR positions. The enhancement of spin pumping voltage (Vsp) in the FiM garnet heterostructures is attributed to the strong interfacial exchange coupling between FiMs. The modulation of Vsp is achieved by tuning the bilayer structure. Further, the spin mixing conductance for these coupled systems is found to be 10^18 m^-2. Our findings describe a novel coupled FiM system for the investigation of magnon coupling providing new prospects for magnonic devices.

The efficient generation of spin currents and spin torques via spin-orbit coupling is an important goal of spintronics research. One crucial metric for spin current generation is the spin Hall angle, which is the ratio of the spin Hall current to the transversely flowing charge current. A typical approach to measure the spin Hall angle in nonmagnetic materials is to generate spin currents via spin pumping in an adjacent ferromagnetic layer and measure the transverse voltage from the inverse spin Hall effect in the nonmagnetic layer. However, given that the spin Hall effect also occurs in ferromagnets, single ferromagnetic layers could generate a self-induced transverse voltage during spin pumping as well. Here we show that manganite based La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) films deposited by pulsed laser deposition exhibit a significant self-induced inverse spin Hall voltage while undergoing spin pumping. We observe efficient spin to charge conversion in the LSMO films via the inverse spin Hall effect. A spin pumping voltage of 1.86 $\mu$V is observed in the LSMO (12 nm) film. Using density functional theory and the Kubo formalism, we calculate the intrinsic spin current conductivities of these films and show that they are in reasonable agreement with the experimental measurements.

High spin to charge conversion efficiency is the requirement for the spintronics devices which is governed by spin pumping and inverse spin Hall effect (ISHE). In last one decade, ISHE and spin pumping are heavily investigated in ferromagnet/ heavy metal (HM) heterostructures. Recently antiferromagnetic (AFM) materials are found to be good replacement of HMs because AFMs exhibit terahertz spin dynamics, high spin-orbit coupling, and absence of stray field. In this context we have performed the ISHE in CoFeB/ IrMn heterostructures. Spin pumping study is carried out for $Co_{40}Fe_{40}B_{20} (12\ nm)/ Cu (3\ nm)/ Ir_{50}Mn_{50} (t\ nm)/ AlO_{x} (3\ nm)$ samples where \textit{t} value varies from 0 to 10 nm. Damping of all the samples are higher than the single layer CoFeB which indicates that spin pumping due to IrMn is the underneath mechanism. Further the spin pumping in the samples are confirmed by angle dependent ISHE measurements. We have also disentangled other spin rectifications effects and found that the spin pumping is dominant in all the samples. From the ISHE analysis the real part of spin mixing conductance (\textit{$g_{r}^{\uparrow \downarrow}$}) is found to be 0.704 $\pm$ 0.003 $\times$ $10^{18}$ $m^{-2}$.

Large charge-to-spin conversion (spin Hall angle) and spin Hall conductivity are prerequisites for development of next generation power efficient spintronic devices. In this context, heavy metals (e.g. Pt, W etc.), topological insulators, antiferromagnets are usually considered because they exhibit high spin-orbit coupling (SOC). In addition to the above materials, 5d transition metal oxide e.g. Iridium Oxide (IrO 2 ) is a potential candidate which exhibits high SOC strength. Here we report a study of spin pumping and inverse spin Hall effect (ISHE), via ferromagnetic resonance (FMR), in IrO 2 /CoFeB system. We identify the individual contribution of spin pumping and other spin rectification effects in the magnetic layer, by investigating the in-plane angular dependence of ISHE signal. Our analysis shows significant contribution of spin pumping effect to the ISHE signal. We show that polycrystalline IrO 2 thin film exhibits high spin Hall conductivity and spin Hall angle which are comparable to the values of Pt., Comment: 5 pages, 5 figures

Manganites have shown potential in spintronics because they exhibit high spin polarization. Here, by ferromagnetic resonance we have studied the damping properties of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$/Pt bilayers which are prepared by oxide molecular beam epitaxy. The damping coefficient ($\alpha$) of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) single layer is found to be 0.0104. However the LSMO/Pt bilayers exhibit decrease in $\alpha$ with increase in Pt thickness. This decrease in the value of $\alpha$ is probably due to high anti-damping like torque. Further, we have investigated the angle dependent inverse spin Hall effect (ISHE) to quantify the spin pumping voltage from other spin rectification effects such as anomalous Hall effect and anisotropic magnetoresistance. We have observed high spin pumping voltage ($\sim$~20 $ \mu V$). The results indicate that both anti-damping and spin pumping phenomena are occuring simultaneously., Comment: 5 figure

Ferromagnetic materials exhibiting low magnetic damping ($\alpha$) and moderately high saturation magnetization are required from the viewpoints of generation, transmission and detection of spin wave. Since spin-to-charge conversion efficiency is another important parameter, high spin mixing conductance ($g_{r}^{\uparrow \downarrow}$) is the key for efficient spin-to-charge conversion. Full Heusler alloys e.g. $Co_2Fe_{0.4}Mn_{0.6}Si$ (CFMS), which are predicted to be 100$\%$ spin polarized, possess low $\alpha$. However, the $g_{r}^{\uparrow \downarrow}$ at the interface between CFMS and a paramagnet has not fully been understood. Here, we report the investigations of spin pumping and inverse spin Hall effect in $CFMS/Pt$ bilayers. Damping analysis indicates the presence of significant spin pumping at the interface of CFMS and Pt, which is also confirmed by the detection of inverse spin Hall voltage. We show that in CFMS/Pt the $g_{r}^{\uparrow \downarrow}$ (1.77$\times$10$^{20}$m$^{-2}$) and interface transparency (84$\%$) are higher compared to values reported for other ferromagnet/heavy metal systems.